WO2008122085A1 - Nanocomposites - Google Patents

Nanocomposites Download PDF

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Publication number
WO2008122085A1
WO2008122085A1 PCT/AU2008/000493 AU2008000493W WO2008122085A1 WO 2008122085 A1 WO2008122085 A1 WO 2008122085A1 AU 2008000493 W AU2008000493 W AU 2008000493W WO 2008122085 A1 WO2008122085 A1 WO 2008122085A1
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WO
WIPO (PCT)
Prior art keywords
nanocomposite
filler
active substance
dispersant
polymer matrix
Prior art date
Application number
PCT/AU2008/000493
Other languages
French (fr)
Inventor
Laura Anne Poole-Warren
Rosslyn Anne Simmons
Katie Elizabeth Styan
Charles Mckenzie Williams
Nicole Fong
Brooke Farrugia
Original Assignee
Newsouth Innovations Pty Limited
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Publication date
Priority to AU2007901798A priority Critical patent/AU2007901798A0/en
Priority to AU2007901798 priority
Application filed by Newsouth Innovations Pty Limited filed Critical Newsouth Innovations Pty Limited
Publication of WO2008122085A1 publication Critical patent/WO2008122085A1/en

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00Nanotechnology for materials or surface science, e.g. nanocomposites
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08GMACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00Polymeric products of isocyanates or isothiocyanates
    • C08G18/06Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/40High-molecular-weight compounds
    • C08G18/48Polyethers
    • C08G18/4854Polyethers containing oxyalkylene groups having four carbon atoms in the alkylene group
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08GMACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00Polymeric products of isocyanates or isothiocyanates
    • C08G18/06Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/65Low-molecular-weight compounds having active hydrogen with high-molecular-weight compounds having active hydrogen
    • C08G18/66Compounds of groups C08G18/42, C08G18/48, or C08G18/52
    • C08G18/6666Compounds of group C08G18/48 or C08G18/52
    • C08G18/667Compounds of group C08G18/48 or C08G18/52 with compounds of group C08G18/32 or polyamines of C08G18/38
    • C08G18/6674Compounds of group C08G18/48 or C08G18/52 with compounds of group C08G18/32 or polyamines of C08G18/38 with compounds of group C08G18/3203
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G
    • C08J5/00Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/005Reinforced macromolecular compounds with nanosized materials, e.g. nanoparticles, nanofibres, nanotubes, nanowires, nanorods or nanolayered materials
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08LCOMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L75/00Compositions of polyureas or polyurethanes; Compositions of derivatives of such polymers
    • C08L75/04Polyurethanes
    • C08L75/08Polyurethanes from polyethers
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G
    • C08J2375/00Characterised by the use of polyureas or polyurethanes; Derivatives of such polymers
    • C08J2375/04Polyurethanes
    • C08J2375/08Polyurethanes from polyethers
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUSE OF INORGANIC OR NON-MACROMOLECULAR ORGANIC SUBSTANCES AS COMPOUNDING INGREDIENTS
    • C08K3/00Use of inorganic substances as compounding ingredients
    • C08K3/34Silicon-containing compounds

Abstract

The present invention discloses a nanocomposite comprising an active substance. The nanocomposite comprises a polymer matrix, a nanoparticulate filler dispersed through said polymer matrix, and a dispersant for aiding dispersion of the filler in the matrix. In the nanocomposite, the active substance is the dispersant and the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite, or the active substance is not the dispersant but is associated with the filler or with the dispersant or with both the filler and the dispersant and the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite, or the active substance is the filler and the polymer matrix is such that the active substance is releasable from the nanocomposite.

Description

Nanocomposϊtes Technical Field

The present invention relates to nanocomposites comprising actives.

Background of the Invention In 2004, the value of the global biomaterials market was estimated to be US$3.7 billion, with soft polymers representing a substantial proportion of this total. In terms of medical devices manufactured using these biomaterials, US sales of medical catheters exceeded US$13.1 billion in 2003 with the market expected to surpass US$23 billion by 2009. This industry is driven by innovation in design and materials and the market continues to grow at a significant rate due to scientific and technological advances in these areas. The worldwide market for biomedical polyurethanes (PU) alone is currently valued in excess of A$450 million and Australian research has been a significant contributor to the worldwide PU biomaterial market.

Polymer nanocomposites have the advantages over conventional polymers of improved mechanical properties, barrier properties and more recently they have shown potential for biological activity. Research on these types of composites began to appear in the biomedical literature as recently as 5 years ago however little information on their biological performance exists.

A key design criteria for biomedical materials is that they perform in a manner that is appropriate to the target application. Devices such as blood contacting catheters and similar percutaneous applications frequently fail due to infection and thrombosis, two surface-linked phenomena that are difficult to prevent. Other devices such as small diameter vascular grafts also have high failure rates due to thrombosis, and infection is hypothesised to be an initiating factor in many cases. As many as 45% of hospital infections are thought to be device related and it is estimated that there are approximately 1 million hospital acquired infections in the United States related to indwelling devices such as central venous catheters. The high cost of these infections of approximately $3000 per incident is a problem that impacts on health economics, however it is the patient morbidity and even mortality that is the greatest concern. The issue of devices acting as a nidus for infection remains a critical problem today and there is an unmet clinical need for new approaches to preventing and treating biofilm formation on medical devices.

Thrombosis itself is also a critical issue for many blood contacting devices and the occurrence of septic thrombosis is a critical clinical problem with longer term catheters. One of the most common recommended treatments for infected indwelling catheters is closing off the catheter after filling with heparin and antibiotics. The effectiveness of such management approaches is not high and methods for prevention of such complications are lacking. It is clear that infection and thrombosis are the leading causes of morbidity and mortality associated with catheterization and that there is a strong link between their pathogenesis. Currently there are no materials available that have a dual functionality in prevention of both bacterial adhesion and coagulation/platelet activation events. A major disadvantage of virtually all biomedical polymers, including PUs, is their inability to resist bacterial adhesion, and their induction of the deposition of blood clots and inflammation.

Polyurethane (PU) elastomers are versatile materials that have many biomedical applications. Their uses span longer term applications such as pumping bladders in heart assist devices through to shorter term indwelling catheters. Such catheters are used in applications from the urinary system through to the more critical blood contacting applications. Such indwelling catheters are typically TGA approved for use up to 30 days but in practice their use may extend well beyond this. In all of these applications, the excellent mechanical properties of PU are highly advantageous, allowing fabrication of thin walled devices with high strength and flexibility. Typical elastic moduli found in flexible grades of biomedical PU are up to 30 MPa with elongations in excess of 600%. The latter compares favourably with silicones which also have high elongations, but have significantly lower moduli of less than 1 MPa and poor abrasion resistance.

Object of the Invention

It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. Summary of the Invention

In a broad form of the invention there is provided a nanocomposite comprising an active substance, said nanocomposite comprising:

• a polymer matrix;

• a nanoparticulate filler dispersed through said polymer matrix; and • a dispersant for aiding dispersion of the filler in the matrix; wherein the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite.

The active substance may be a releasable active substance. It may be soluble in the polymer matrix. It may be compatible with the polymer matrix. It is located in the nanocomposite. It may be dispersed through the matrix, or it may be located in specific regions of the nanocomposite, for example on the surfaces of the particles of the nanoparticulate filler. The active substance may be the dispersant, i.e. the same substance may act as a dispersant and as an active substance which is releasable from the nanocomposite. Alternatively the active substance may not be the same as the dispersant, i.e. there may be a separate dispersant and active substance. In this case, the active substance may be located on or near the surface of the filler. It may be located on the surface of the filler. It may be adsorbed on the surface of the filler. It may be absorbed into the filler. It may be both adsorbed on the surface and absorbed into the filler. It may be associated with (e.g. coupled to, bonded to, mixed with, adsorbed onto or otherwise associated with) the dispersant. In the case where the active is absorbed into the filler, the nature of the filler and of the active substance is such that the active substance can diffuse out of the filler. The active substance may be the nanoparticulate filler, i.e. the same substance may act as a filler and as an active substance which is releasable from the nanocomposite. The filler may comprise the active substance. The active substance may have more than one activity, e.g. it may have antithrombotic activity and antibiotic activity. The nanocomposite may have more than one active substance. Each may have similar activity, or they may have different activity. For example the nanocomposite may comprise an antithrombotic substance and an antibiotic substance which are different. In some forms of the invention the polymer matrix is not a hydrogel. The polymer matrix may be hydrophobic. The polymer matrix may have a low water content, for example less than about 10% by weight, or less than about 5, 2 or 1% by weight.

In some forms of the invention the nanocomposite comprises more than one active substance that is releasable from the nanocomposite. In a first aspect of the invention there is provided a nanocomposite comprising an active substance, said nanocomposite comprising:

• a polymer matrix;

• a nanoparticulate filler dispersed through said polymer matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein:

• the active substance is the dispersant, and the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite, or

• the active substance is not the dispersant but is associated with the filler or with the dispersant or with both the filler and the dispersant, and the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite, or

• the active substance is the filler, and the polymer matrix is such that the active substance is releasable from the nanocomposite. In a second aspect of the invention there is provided a nanocomposite comprising at least two active substances, said nanocomposite comprising:

• a polymer matrix, wherein said matrix is not a hydrogel;

• a nanoparticulate filler dispersed through said polymer matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the polymer matrix and the filler are such that the active substances are releasable from the nanocomposite.

The polymer matrix may be a low water content polymer.

The dispersant may be a surfactant. Examples of surfactant dispersants are well- known in the art. The dispersant may be a surfactant having biological activity. It may be a quaternary ammonium salt. It may be a bis-quaternary ammonium salt or a quaternary phosphonium salt. It may be for example chlorhexidine or 1-aminoundecanoic acid or Ethoquad® O/12PG.

The polymer matrix may be an elastomer. It may be a thermoset polymer. It may be a thermoplastic polymer. It may be a partially crystalline polymer. It may be a polyurethane, for example a polyetherurethane, a polyester urethane, a polycarbonate urethane etc. It may be a silicone. It may be a polydimethylsiloxane elastomer. It may be polyisobutylene. It may be ρoly(styrene-b-isobutylene-b-styrene) (SIBS). It may be some other type of elastomer.

The nanoparticulate filler in the nanocomposite may be intercalated or partially intercalated. It may be exfoliated or partially exfoliated. The filler may be partially intercalated and partially exfoliated. The filler may comprise particles having an aspect ratio of at least about 100. It may have an aspect ratio of less than about 100, or less than about 10. It may be an inorganic filler. It may for example comprise montmorillonite. It may be an organic filler. It may be a fibrous organic filler. It may comprise for example nanotubes (single walled or multiwalled nanotubes, or a mixture of single walled and multiwalled nanotubes). The nanotubes may be carbon nanotubes, or boron nitride nanotubes or a mixture of these. The filler may be present in the nanocomposite at a level of between about 0.1 and about 30% by weight. The rate of release is commonly reduced in proportion (for example in direct proportion) to the loading of nanoparticulate filler. The inventors hypothesise that this is due to a barrier effect or similar mechanism. In this context, "barrier effect" refers to a decrease in release rate of an active substance due to the tortuous path created by exfoliated/intercalated particles of the filler and/or changes to the polymer surrounding the particles and/or interactions between the active substance and the nanoparticulate filler. The filler may cause a release inhibition of up to about 95%. The release inhibition is defined as:

[l-(Rnps/RcOnt)] x l00% where

Rnps is the rate of release of the active substance from the nanocomposite, and

Rcont is the rate of release of the active substance from a control substance that has the same composition as the nanocomposite but having no nanoparticulate filler.

The active substance may be a drug, or may be some other active substance. It may be an antibiotic, an antithrombotic agent or an anticancer drug. It may be present in the nanocomposite at a level of at least about 0.1%, or between about 0.1 and about 30% by weight. The active substance may be releasable from the nanocomposite over a period of at least one week.

In an embodiment of the invention there is provided a biofunctional nanocomposite including:

• a low water content polymer matrix;

• a particulate filler dispersed through said polymer matrix;

• a dispersant for aiding dispersion of the filler in the matrix; and

• at least one pharmacologically active substance; wherein the dispersant is the pharmacologically active substance or, if more than one pharmacologically active substance is present, one of the pharmacologically active substances. Thus the nanocomposite of this embodiment comprises:

• a low water content polymer matrix;

• a particulate filler dispersed through said polymer matrix; • a dispersant for aiding dispersion of the filler in the matrix, said dispersant being a pharmacologically active substance; and

• optionally at least one additional pharmacologically active substance.

In another embodiment of the invention there is provided a nanocomposite comprising an active substance, said nanocomposite comprising: • a low water content polymer matrix;

• a nanoparticulate filler dispersed through said polymer matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the polymer matrix and the filler are such that the active substance is releasable 5 from the nanocomposite.

In another embodiment there is provided a nanocomposite comprising an active substance, said nanocomposite comprising:

• a polyurethane matrix;

• a nanoparticulate inorganic filler having an aspect ratio of at least about 100, saidQ filler being dispersed through said polyurethane matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the polyurethane matrix and the filler are such that the active substance is releasable from the nanocomposite.

In another embodiment there is provided a nanocomposite comprising an actives substance, said nanocomposite comprising:

• a polyurethane matrix;

• nanoparticulate montmorillonite filler dispersed through said polyurethane matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; Q wherein the polyurethane matrix is such that the active substance is releasable from the nanocomposite.

In another embodiment there is provided a nanocomposite comprising:

• a polyurethane matrix;

• nanoparticulate montmorillonite filler dispersed through said polyurethane matrix;5 and

• dodecylamine as a dispersant for aiding dispersion of the filler in the matrix and as an active substance; wherein the polyurethane matrix is such that the dodecylamine is releasable from the nanocomposite. Q In another embodiment there is provided a nanocomposite comprising:

• a polyurethane matrix;

• about 1% by weight of nanoparticulate montmorillonite filler dispersed through said polyurethane matrix; and • dodecylamine as a dispersant for aiding dispersion of the filler in the matrix and as an active substance; wherein the polyurethane matrix is such that the dodecylamine is releasable from the nanocomposite. In another embodiment there is provided a nanocomposite, said nanocomposite comprising:

• a polymer matrix;

• a nanoparticulate filler dispersed through said polymer matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the dispersant is an active substance, and wherein the polymer matrix and the filler are such that the dispersant is releasable from the nanocomposite. The dispersant may be a quaternary ammonium compound. It may be a dispersant that is not a quaternary ammonium compound.

In another embodiment there is provided a nanocomposite, said nanocomposite comprising:

• a polyurethane matrix;

• an inorganic nanoparticulate filler having an aspect ratio of at least about 100, said filler being dispersed through said polyurethane matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the dispersant is an active substance, and wherein the polyurethane matrix and the filler are such that the dispersant is releasable from the nanocomposite over at least one week.

In another embodiment there is provided a nanocomposite, said nanocomposite comprising: • a polymer matrix;

• a nanoparticulate filler dispersed through said polymer matrix;

• an active substance; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite material.

In another embodiment there is provided a nanocomposite, said nanocomposite comprising:

• a polyurethane matrix; • an inorganic nanoparticulate filler having an aspect ratio of at least about 100, said filler being dispersed through said polymer matrix;

• an active substance; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite material over at least one week.

In another embodiment there is provided a nanocomposite comprising an active substance, said nanocomposite comprising:

• a polymer matrix; and • a nanoparticulate filler dispersed through said polymer matrix; wherein the active substance is a dispersant for aiding dispersion of the filler in the matrix, and wherein the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite.

In another embodiment there is provided a nanocomposite comprising an active substance, said nanocomposite comprising:

• a polymer matrix;

• a nanoparticulate filler dispersed through said polymer matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the active substance is not the dispersant but is associated with the filler or with the dispersant or with both the filler and the dispersant, and the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite. In another embodiment there is provided a nanocomposite comprising:

• a polymer matrix;

• a nanoparticulate filler dispersed through said polymer matrix; and • a dispersant for aiding dispersion of the filler in the matrix; wherein the nanoparticulate filler is an active substance and the polymer matrix is such that the active substance is releasable from the nanocomposite.

In a third aspect of the invention there is provided a process for making a nanocomposite comprising: (i) combining a solution comprising a polymer matrix in a solvent with a nanoparticulate filler and a dispersant; and

(ii) removing the solvent; wherein the solution comprises an active substance so that the nanocomposite is capable of releasing said active substance. The active substance may be additional to the nanoparticulate filler and the dispersant. The active substance may be the nanoparticulate filler. The active substance may be the dispersant. Both the nanoparticulate filler and the dispersant may be active substances. The solution may comprise more than one, e.g. 2, 3, 4 or 5 or more than 5, active substances. The polymer may be a low water content polymer. It may be a hydrophobic polymer. In some embodiments, the solvent is not water. In some embodiments the solvent is non-aqueous.

In some embodiments the active substance is the dispersant, and the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite. In other embodiments the active substance is the filler, and the polymer matrix is such that the active substance is releasable from the nanocomposite.

The dispersant may be located on the surface of the nanoparticulate filler prior to step (i). Thus the nanoparticulate filler may be a dispersant treated nanoparticulate filler. Step (i) may comprise combining the solution with a suspension comprising the nanoparticulate filler and the dispersant in a carrier. It may comprise combining the solution with the nanoparticulate filler having the dispersant on the surface thereof. The solvent may be a non-solvent for the nanoparticulate filler. It may be a poor solvent for the nanoparticulate filler. It may be a solvent for the dispersant. It may be a solvent for the polymer matrix.

The process may comprise the step of agitating the nanoparticulate filler and the dispersant in the carrier to form the suspension prior to step (i). The process may comprise the step of agitating the nanoparticulate filler and the dispersant in a carrier and then removing the carrier, in order to form the dispersant treated nanoparticulate filler. The dispersant treated filler may be a dry filler.

In cases in which the filler is agitated with the dispersant in a carrier, the agitation may be sufficient for the dispersant to intercalate and/or exfoliate the nanoparticulate filler. The agitation may be sufficient for the dispersant to at least partially exfoliate the nanoparticulate filler. It may be sufficient that the nanoparticulate filler in the nanocomposite is either intercalated or exfoliated. The step of removing the solvent may also comprise removing the carrier, if present.

In an embodiment of the invention there is provided a process for making a biofunctional nanocomposite including: (i) preparing a solution comprising a low water content polymer matrix, a particulate filler, a dispersant for aiding dispersion of the filler in the matrix, and at least one pharmacologically active substance in a solvent; and (ii) removing the solvent; wherein the dispersant may be the at least one pharmacologically active substance, to result in the formation of a biofunctional nanocomposite.

In another embodiment is provided a process for making a nanocomposite comprising:

(i) combining a solution comprising a polymer matrix in a solvent with a nanoparticulate filler and a dispersant; and

(ii) removing the solvent; wherein the nanoparticulate filler comprises an active substance so that the nanocomposite is capable of releasing said active substance.

In another embodiment there is provided a process for making a nanocomposite comprising:

(i) combining a solution comprising a polymer matrix in a solvent with a nanoparticulate filler and a dispersant; and

(ii) removing the solvent; wherein the dispersant is an active substance so that the nanocomposite is capable of releasing said active substance.

In another embodiment there is provided a process for making a nanocomposite comprising:

• agitating a nanoparticulate filler and a dispersant in a carrier sufficient that the nanoparticulate filler in the nanocomposite is either intercalated or exfoliated to form a suspension;

• combining a solution comprising a polymer matrix in a solvent with the suspension; and

• removing the solvent and the carrier; wherein either the solution or the suspension or both comprises an active substance so that the nanocomposite is capable of releasing said active substance.

In another embodiment there is provided a process for making a nanocomposite comprising:

(i) combining a solution comprising a polymer matrix in a solvent with a dispersant treated nanoparticulate filler; and (ii) removing the solvent; wherein either the solution comprises an active substance, or the dispersant treated nanoparticulate filler comprises an active substance, or both, so that the nanocomposite is capable of releasing said active substance. In another embodiment there is provided a process for making a nanocomposite comprising:

• agitating a nanoparticulate filler and a dispersant in a carrier;

• removing the carrier in order to form a dispersant treated nanoparticulate filler;

• combining a solution comprising a polymer matrix in a solvent with the dispersant treated nanoparticulate filler; and

• removing the solvent; wherein either the solution comprises an active substance, or the dispersant treated nanoparticulate filler comprises an active substance, or both, so that the nanocomposite is capable of releasing said active substance. The invention also provides nanocomposite made by the process of the third aspect.

In a fourth aspect of the invention there is provided an article for direct or indirect contact with body fluids and/or tissues, said article comprising a nanocomposite according to the first or second aspect, or a nanocomposite made by the process of the third aspect. The article may be an article for implantation into a patient. The active substance(s) may be soluble in the body fluids. They may be releasable into the body fluids or tissues.

The invention also provides the use of a nanocomposite according to the first or second aspect, or a nanocomposite made by the process of the third aspect, for the fabrication of an article for direct or indirect contact with body fluids and/or tissues. The article may be an article for implantation into a patient.

In a fifth aspect of the invention there is provided the use of an article according to the fourth aspect for a purpose selected from prevention of blood clotting, treatment of heart disease, treatment or prevention of an infection and treatment or prevention of cancer. In a sixth aspect of the invention there is provided a method of treating or preventing a condition in a patient comprising the step of implanting an article according to the fourth aspect into said patient, wherein the active substance is indicated for said treatment or prevention. In a seventh aspect of the invention there is provided a method of delivering an active substance comprising exposing an article comprising a nanocomposite according to the first or second aspect, or made by the process of the third aspect, to a medium capable of releasing the active substance therefrom. The medium may be a solvent for the active substance.

In an embodiment the active substance is an antifouling agent. In this case the nanocomposite may be in the form of an antifouling coating, for example on the hull of a boat. The medium would then be the water (e.g. seawater) in which the hull is at least partially immersed in use. The present invention also provides a nanocomposite according to the first aspect wherein the polymer matrix comprises a polyetherurethane and the active substance is an antimicrobial agent and the concentration of the active substance in the polymer matrix is such that the nanocomposite resists growth of microbes on the surface thereof for at least 2 days, or at least about 3, 4, 5, 6, 7, 14, 21 or 28 days. It may resist said growth after inoculation of the surface with the microbes. The active substance may be chlorhexidine or a salt thereof. The concentration of the active substance in the polymer matrix may be at least about 1% by weight or may be about 1 to about 5% by weight, e.g. about 1, 2, 3, 4 or 5% by weight. The invention also provides an article for implantation into a patient, said article comprising the nanocomposite described above. The article may be an artificial portion of a urinary tract. The patient may be a human patient, or may be a non- human patient.

The present invention also provides a nanocomposite according to the first aspect wherein the polymer matrix comprises a polyetherurethane and the active substance is a substance for reducing surface cell adhesion, and concentration of the active substance in the polymer matrix is such that the nanocomposite shows a reduction in fibroblast adhesion relative to a nanocomposite having the same composition except for the absence of the active substance. The reduction in surface cell adhesion may be at least about 10%, or at least about 20, 30, 40, 50, 60, 70, 80, 90, 95 or 99% after 72 hours. The active substance may be montmorillonite modified with an alkylamine having at least 12 carbon atoms, or having between 12 and 18 carbon atoms. The alkylamine may be C 12, C 14, Cl 6 or Cl 8 alkylamine. It may be dodecylamine. It may have no carboxylic acid functionality. The concentration of the active substance may be at least about 1% by weight, or about 1 to about 5% by weight, e.g. about 1, 2, 3, 4 or 5% by weight. The alkylamine may be substantially non-cytotoxic at the concentration used. The invention also provides an article for implantation into a patient comprising the nanocomposite described earlier in this paragaraph. The patient may be a human patient or may be a non- human patient.

Brief Description of the Drawings Preferred embodiments of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein:

Figure 1 is a schematic showing different structures of nanocomposites and of a microcomposite;

Figure 2 is a diagram showing structuring of organic modifiers on to clay surfaces; Figure 3 is a diagrammatic representation of a nanocomposite according to the present invention;

Figure 4a shows the structure of a polyetherurethane used in Embodiment A presented herein;

Figure 4b shows the structure of methyl tallow bis-2-hydroxyethyl ammonium chloride; Figure 5 shows transmission electron micrographs (TEMs) of PEU-QACMMT materials from Embodiment A at magnification 1000Ox (scale bar 2000nm): a) PEU/CV; b) PEU-

QACMMT-1/CV; c) PEU-QACMMT-7/CV d) PEU/PR; e) PEU-QACMMT-I /PR; f)

PEU-QACMMT-7/PR;

Figure 6 shows a graph of drug release 8OA Release of crystal violet and phenol red from PEU materials; a) 0 to 5 days, and b) 0 to 30 days (mean ± one standard deviation);

Figure 7 shows a graph illustrating the effect of QACMMT loading on the release of PR from PEU materials into pH6 water (mean ± one standard deviation);

Figure 8 shows a graph illustrating the effect of QACMMT loading on the release of CV from PEU materials into pH6 water (mean ± one standard deviation) Figure 9 is a graph showing the ratio of ultimate stress in test materials compared with

PEU control materials in Embodiment B;

Figure 10 is a graph showing the ratio of elastic modulus of test materials compared with control PEU materials in Embodiment B;

Figure 11 is a graph showing the ratio of bacterial growth on test materials compared with control materials at 24 hours in Embodiment B;

Figure 12 is a graph showing the ratio of mammalian cell numbers after exposure to test, compared with control, material extracts after 48 hours in Embodiment B;

Figure 13 is a graph showing fibroblast attachment onto terminal functional group test materials; Figure 14 is a graph showing fibroblast attachment onto carbon chain length group test materials;

Figure 15 is a graphs showing cell growth inhibition of terminal functional group test materials; and Figure 16 is a graph showing cell growth inhibition of carbon chain length group test materials.

Detailed Description of the Invention

In the context of the present invention the term nanocomposite refers to organic:inorganic composites where one phase, typically the inorganic phase, has dimensions on the nanoscale. Thus nanocomposites may be defined as composite materials in which at least one dimension of the filler exists on the nanoscale within a carrier matrix. A nanocomposite may be either intercalated, where there is polymer interspersed between particles, but particles are still stacked, or exfoliated where particles are randomly dispersed within the polymer matrix (see Figure 1). Where there is no polymer between particles, the composite is a microcomposite.

In this specification, where practicable, any option(s) presented herein may be combined with any other option(s) presented herein. In any of the aspects and embodiments described herein, the nanocomposite may be a bioactive nanocomposite.

Organic modification (OM), as described herein, functions by interacting with the nanoparticle surface and forcing apart the particles. The OM also compatibilises hydrophilic/polar particles with organic polymer (see Figure 2).

The present invention provides a nanocomposite comprising an active substance, said nanocomposite comprising:

• a polymer matrix; • a nanoparticulate filler dispersed through said polymer matrix; and

• a dispersant for aiding dispersion of the filler in the matrix; wherein the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite.

The active substance may be the dispersant or it may not be the same as the dispersant, i.e. there may be a separate dispersant and active substance.

The dispersant may be located on and/or near the surface of the filler. In some examples an excess of dispersant may be used, so that some of the dispersant may be located on and/or near the surface of the filler and some may be dispersed through the polymer matrix. The dispersant may be a surfactant. It may be an amphiphile. It may have a polar group with an affinity for the nanoparticulate filler and a non-polar group with an affinity for the polymer matrix. The dispersant may be neutral, anionic, cationic or zwitterionic. Suitable dispersants include quaternary ammonium salts having at least one long chain alkyl group, bis-quaternary ammonium salts having a long chain alkylene group, alkyl aryl ethoxylates, alkyl sulfonates, alkyl aryl sulfonates and other well known surfactants. The quaternary alkyl ammonium salts may be alkyltrimethyl ammonium salts (e.g. chlorides or bromides), where the alkyl group is between about C6 and C24. The alkyl group maybe between about C12 and C 16, C6 and C 12, C 12 and C 18, Cl 8 and C24, C6 and C18, C12 and C24 or C14 and C18 (e.g. C12, C13, C14, C15, C16, C17, C18, C19, C20, C21, C22, C23 or C24), or may be a mixture of different chain length alkyl groups. The dispersant may be an ammonium salt, hi this case, exposure of the filler to the dispersant may be conducted at a pH at which the amine of the dispersant is protonated. This pH may vary depending on the nature of the dispersant. It may be a pH below the isoelectric point of the dispersant. It may be less than about 4, or less than about 3.5, 3, 2.5 or 2, or between about 2 and 4, 3 and 4, 2 and 3, 2.5 and 4, 2.5 and 3.5 or 3.5 and 5, e.g. about 2, 2.5, 3, 3.5 or 4. The dispersant may be active. The process for making the nanocomposite in this case may comprise adjusting the pH to the above described pH. The adjusting may be by means of a buffer or by means of an acid, e.g. a mineral acid (such as hydrochloric, sulfuric, nitric, phosphoric or hydrobromic acid). The dispersant may be a biologically active dispersant. It may comprise a polar group and a biologically active group. It may be a biologically active surfactant. Suitable dispersants include chlorhexidine, octadecyltrimethylammonium chloride (or bromide), 11- aminoundecanoic acid, Ethoquad® O/ 12PG and methyl tallow bis-2-hydroxyethyl ammonium chloride. A list of suitable dispersants is set out below: chlorhexidine diacetate - dispersant and active substance polyhexamethylene biguanide - dispersant and active substance aminoundecanoic acid - dispersant octylamine - possible pharmacological activity dodecylaniine - dispersant, possibly with pharmacological activity tetradecylamine- dispersant, possibly with pharmacological activity hexadecylamine - dispersant, possibly with pharmacological activity octadecylamine - dispersant, possibly with pharmacological activity dodecylamine — dispersant, possibly with pharmacological activity aminododecanoic acid - dispersant poly(tetramethylene oxide) - dispersant octanol - dispersant dodecanol - dispersant octadecanol - dispersant s poly(acrylic acid) - dispersant

In some embodiments the active substance is not the dispersant but is located on the surface of the filler. It may be associated with the dispersant. Suitable examples of such actives include heparin, argatroban, methacryloyloxyethyl phosphorylcholine (MPC), polyhexamethylene biguanide (*PHMB*) and small cationic antibacterial peptides.o These are active substances that relate specifically to applications i.e. anticoagulants or antibacterials but it will be understood that other active substances, for example with other functionalities, may also be suitable. These materials may locate at or near the surface of the filler although may not function as a dispersant.

In some embodiments the active substance has an opposite electrical charge to as surface charge on the nanoparticulate filler. This may serve to couple the active substance to the filler due to an electrostatic interaction.

The dispersant may be present in the nanocomposite at between about 0.5 and about

5g/100g filler, or between about 0.5 and 2, 0.5 and 1, 1 and 5, 2 and 5 or 1 and 3g/100g filler, e.g. about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5g/100g filler. In some embodiments0 the filler has a net electrical charge. It may be a net negative charge or a net positive charge. If the filler has a net negative charge, the dispersant is preferably cationic. If the filler has a net positive charge, the dispersant is preferable anionic. If the filler has a net electrical charge, the dispersant may be present at between about 50 and about 200% of the ion exchange capacity of the filler, or between about 50 and 150, 50 and 100, 100 ands 200, 150 and 200 or 100 and 150%, e.g. about 50, 60, 10, 80, 90, 100, 110, 120, 130, 140,

150, 160, 170, 180, 190 or 200% of the ion exchange capacity of the filler.

In some embodiments more than one dispersant is used. There may be 1, 2, 3, 4 or 5 dispersants used. These may be present in any desired ratio. If two dispersants are used, the ratio between them, on a weight or mole basis, may be between about 1:5 and 5:1, oro between about 1:4 and 4:1, 1:3 and 3:1, 1:2 and 2:1, 1:5 and 1:1, 1:1 and 1:5, 1:3 and 3:1 or 1 :1.5 and 1.5:1, e.g. about 1:5, 1 :4, 1:3, 1:2, 1:1.5, 1:1.2, 1:1.1, 1:1, 1.1:1, 1.2:1, 1.5:1, 2:1, 3:1, 4:1 or 5:1. Each dispersant may, independently, be as described above.

In some embodiments the polymer matrix is not a hydrogel. The polymer matrix may be a low water content polymer matrix. The water content of the low water content polymer matrix may be for example less than about 10% by weight, or less than about 9, 8, 7, 6, 5, 4, 3, 2 or 1% by weight. It may be between about 0 and about 10% water by weight, or between about 0 and 5, 0 and 2, 0 and 1, 0 and 0.5, 0 and 0.2, 0 and 0.1, 0.1 and 10, 0.5 and 10, 1 and 10, 5 and 10, 1 and 5, 0.5 and 1, 0.1 and 1 or 0.1 and 0.5%, e.g. about 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10% by weight. The polymer matrix may be an elastomer. It may be a thermoset polymer. It may be a thermoplastic polymer. It may be a thermoplastic elastomer. It may be a soluble polymer. It may be soluble for example in dimethylformamide, dimethyl acetamide, propylene glycol, dimethylsulfoxide or some other suitable solvent. It may be a partially crystalline polymer. It may be a polyurethane, for example a polyetherurethane or a polyesterurethane or a polycarbonate urethane. A suitable polyurethane is 1,4- butanediol/dipherrylmethane diisocyanate (BD/MDI). The polymer matrix may be an ethylene-vinyl acetate (EVA) copolymer. It may be a partially hydrolysed EVA copolymer. It may be a silicone elastomer. It may be a biocompatible polymer matrix. It may be a non-biodegradable polymer matrix. The polymer matrix may comprise a copolymer. It may comprise a homopolymer. It may comprise a mixture or blend of polymers, e.g. a mixture or blend of elastomers. It may comprise an interpenetrating polymer network.

The nanoparticulate filler in the nanocomposite may be intercalated. It may be exfoliated. It may be partially intercalated and partially exfoliated. The nanoparticulate filler may be an inorganic filler. It may be a nanoparticulate filler. It may comprise nanoparticles that are in the form of platelets or rods or nanotubes, or some other form. The filler may comprise particles having an aspect ratio of at least about 100, or at least about 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900 or 1000, or between about 100 and about 2000, or between about 100 and 1000, 100 and 500, 100 and 250, 100 and 150, 200 and 500, 300 and 500, 500 and 2000, 1000 and 2000, 500 and 1000 or 200 and 300, e.g. about 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800 or 2000. In other embodiments, for example where the nanoparticulate filler is an active substance, the aspect ratio may be between about 1 and about 100, or between about 1 and 50, 1 and 10, 1 and 5, 1 and 2, 2 and 100, 10 and 100, 50 and 100, 2 and 20 or 2 and 10, e.g. about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100. In this context the aspect ratio maybe defined as the ratio of the largest dimension of the particle to the smallest dimension of the particle. It may be defined as the ratio of the length to the thickness of the particle. The particles of the filler may have a particle size, or a maximum dimension, of less than about 10 microns, or less than about 5, 2, 1, 0.5, 0.2 or 0.1 microns, or between about 0.1 and about 10 microns, or between about 0.1 and 5, 0.1 and 2, 0.1 and 1, 0.1 and 0.5, 0.5 and 10, 1 and 10, 5 and 10 or 1 and 5 microns, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 microns. The particles maybe less than lOOnm, or less than 50, 20 or lOnm, and may be between about 1 and about lOOnm, or between about 10 and 100, 50 and 100, 1 and 50, 1 and 20 or 10 and 50nm, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or lOOnm. The particle size in this context may be a mean particle diameter for the particles. It may be a mean hydrodynamic diameter. Alternatively it may be a maximum particle diameter for the particles, or may be a maximum hydrodynamic diameter.

The nanoparticulate filler may be an inorganic filler. It may be a silicate filler. It may be a naturally occurring filler. It may for example comprise montmorillonite. The filler may have ion exchange capacity. It may have cation exchange capacity. It may have anion exchange capacity. It may have an ion exchange capacity of between about 10 and about 200mEq/100g, or between about 10 and 150, 10 and 100, 10 and 50, 50 and 200, 100 and 200, 150 and 200, 50 and 150 or 50 and lOOmEq/lOOg, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 85, 90, 95, 100, 105, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200mEq/g. It may have no ion exchange capacity. The filler may be present in the nanocomposite at a level of between about 0.1 and about 30% by weight, or between about 0.1 and 20, 0.1 and 10, 0.1 and 5, 0.1 and 2, 0.1 and 1, 0.1 and 0.5, 0.5 and 30, 1 and 30, 5 and 30, 10 and 30, 20 and 30, 10 and 20, 0.5 and 10, 1 and 10, 2 and 10, 5 and 10, 1 and 5 or 1 and 3%, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 15, 20, 25 or 30% by weight. In some cases there may be more than one filler, e.g. 2, 3, 4 or 5 fillers. In this case, each filler, or the sum of all fillers, may be in present in the above concentrations. In some aspects the nanoparticulate filler is an organic filler. It may be the active substance or may comprise the active substance, or it may be some other type of organic filler. It may be a polymeric filler. The nanoparticulate filler may be a mixture of fillers. It may be a mixture of organic fillers (e.g. 2, 3, 4 or 5 thereof). It may be a mixture of inorganic fillers (e.g. 2, 3, 4 or 5 thereof). It may be a mixture of at least one (e.g. 1, 2, 3, 4 or 5) organic filler and at least one (e.g. I5 2, 3, 4 or 5) inorganic filler. Any one or more of the fillers may comprise the active substance. There may be one or more fillers comprising the active substance and one or more fillers not comprising the active substance. The filler may be a porous filler. It may be a nanoporous filler. It may be a microporous filler. It may be a non-porous filler. It may be absorbent filler. It may be a non-absorbent filler.

The nanoparticulate filler may cause a release inhibition of up to about 99%, where release inhibition is as defined previously. The release inhibition may be up to about 95, 90, 80, 70, 60 or 50%. It maybe between about 10 and 99%, or between about 10 and 95, 10 and 90, 10 and 75, 10 and 50, 30 and 95, 50 and 95, 75 and 95, 50 and 90 or 40 and 80%, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 85, 90, 91, 92, 93, 94, 96, 97, 98 or 99%. Thus the presence of the nanoparticulate filler may result in a reduction in the release rate of the active substance of the above percentage. The nanocomposite may be capable of perturbing the release of any releasables incorporated therein. The perturbation might affect the release rate, release change with time, and/or the release duration.

The release of the active substance may be at least partly by diffusion through the polymer matrix. The polymer matrix may be semi-crystalline. In cases where the polymer matrix is semi-crystalline, the diffusion may be primarily through the non-crystalline regions of the polymer matrix. In the case of a polyurethane polymer matrix, the diffusion may be primarily through the soft regions of the polyurethane. It will therefore be understood that by changing the crystallinity, or the nature or proportion of the soft regions, the diffusion (i.e. release of the active substance) may be changed correspondingly. Additionally, the presence of particles of filler in the polymer matrix (particularly in the non-crystalline regions or soft regions) may affect the diffusion (i.e. the release of the active substance) by increasing the effective path from a particular location to the outside of the nanocomposite. The presence of particles of filler in the polymer matrix may affect the diffusion by inhibiting diffusion of the active substance through the polymer matrix, e.g. due to an affinity between the particles of filler and the active substance. Thus an increase in loading of the filler may cause a reduction in the release rate of the active substance.

Release of the active substance may in some cases be at least partially by erosion or degradation of the nanocomposite. In this case, fillers or other components that reduce the rate of erosion or rate of degradation may reduce the rate of release of the active substance. The mechanism of this reduction may relate to an increase in hardness, resilience or some other physical property due to the filler or other component, or it may relate to a reduction in degradation, e.g. due to the presence of an antioxidant or to a microbicide which may reduce microbial degradation. Release of the active substance may be by a combination of diffusion of the active substance out of the nanocomposite and of erosion or degradation of the nanocomposite. It may be primarily by diffusion. It may be primarily by erosion or degradation.

In some embodiments the filler comprises the active substance. The filler may be a nanoparticulate active substance, e.g. a nanoparticulate drug. The filler may comprise the active substance adsorbed on and/or in a support. The support may be a nanoparticulate support. It may be a porous support. It may be a microporous support or a nanoporous support, or may be both microporous and nanoporous. It may be a porous nanoparticulate support. It may be a support that is capable of releasing the active substance into the polymer matrix.

The active substance may be a drug, or may be some other active substance. It may be an antibiotic, an antifungal, an antibacterial, an antithrombotic agent, a heart drug or an anticancer drug. It may be present in the nanocomposite at a level of at least about 0.1%, or at least about 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 15, 20, 25 or 30% by weight, or between about 0.1 and about 2%, or between about 0.1 and about 30, 0.1 and 20, 0.1 and 10, 10 and 20, 10 and 30, 15 and 30, 15 and 20, 0.1 and 5, 1 and 10, 5 and 10, 1 and 5, 0.5 and 2, 0.1 and 1, 0.1 and 0.5, 0.01 and 0.2, 0.2 and 2, 0.5 and 2, 1 and 2, 0.5 and 1, 0.5 and 1.5 or 0.2 and 0.5%, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25 or 30%. It may be present in the nanocomposite at a level sufficient to allow release thereof at a therapeutically effective dose for at least about 1 week when implanted into a patient. The active substance may be releasable from the nanocomposite over a period of at least one week, or at least about 2, 3 or 4 weeks or at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 months, or between about 1 week and about 24 months, or between about 1 week and 12 months, 1 week and 6 months, 1 week and 3 months, 1 week and 1 month, 1 and 24 months, 1 and 12 months, 1 and 6 months, 6 and 24 months, 12 and 24 months or 6 and 12 months, e.g. about 1, 2, 3 or 4 weeks or about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24 months, and may be releasable from the nanocomposite over the above periods at a therapeutically effective dose. It will be understood that the therapeutically effective dose may depend on the nature of the active substance. If the active substance is an antimicrobial substance, the active substance may be releasable over the above periods at a level sufficient to prevent growth of the microorganism against which the active substance is active on the surface of the nanocomposite. Again it will be clear that the actual rate will depend on the nature (particularly the potency, for example as measured by its minimum inhibitory concentration, or MIC, or by its LD50) of the active substance. Further, it will be understood that the therapeutically effective dose may depend on the nature of the therapeutic application of the nanocomposite. For instance, the therapeutically effective dose might be relevant to the local physiological environment, or it might be relevant to the systemic physiological environment. The biological activity of the active substance may include antibiotic activity, antifungal activity, antibacterial activity, antithrombotic activity, cardiac activity or antitumour activity, and may comprise more than one of these. The nanocomposite may comprise one active substance, or may comprise more than one active substance. It may for example comprise 2, 3, 4 or 5 active substances. In some embodiments at least one of the active substances is a nanoparticulate filler. In some embodiments at least one of the active substances is a dispersant.

Figure 3 illustrates an example of a nanocomposite according to the present invention. In Figure 3, nanocomposite 100 comprises an active substance, a molecule of which is shown in Fig. 3 as 110 located in matrix 120. It will be understood that, whereas only one molecule 110 is shown in Fig. 3, a large multitude of such molecules will be distributed throughout matrix 120. In some embodiments, molecule 10 is a dispersant molecule, which has a dual function: assisting in dispersion of filler particles in the nanocomposite and as a biologically active substance which can be released from the nanocomposite so as to perform its biological (e.g. pharmacological) function. Matrix 120 is a polymer, commonly a low water elastomer, such as a polyetherurethane or a silicone. The active substance is soluble in matrix 120. Nanocomposite 100 has a nanoparticulate filler dispersed through polymer matrix 120. Particles of the filler are shown as particles 130 and 135. Particles 130 are fully exfoliated, and exist separated from other filler particles 130. Some particles 135 are not fully exfoliated, however have matrix polymer 120 between the particles, i.e. they are intercalated. In the example of Fig. 3, the particles are high aspect ratio particles, for example montmorillonite, however low aspect ratio particles (e.g. spherical nanoparticles) may also be used. Nanocomposite 100 also comprises a dispersant for aiding dispersion of filler particles 130 and 135 in matrix 120. Some molecules of dispersant are shown in Fig. 3 as 140, however it will be understood that many more such molecules will be located on the surfaces of particles 130 and 135. Commonly these are amphiphilic molecules or surfactants, which serve to compatiblise filler particles 130 and 135 with matrix 120. They may in some instances be biologically active, and may be releasable from nanocomposite 100. Molecule 110 is capable of diffusing through matrix 120, so as to be released from matrix 120. If matrix 120 is a polyurethane, the diffusion is primarily through the soft segment domains thereof. The presence of filler particles 130 and 135 slows the release of the active substance from nanocomposite 100. In order to be released, molecule 110 must diffuse to surface 150, where it can pass into medium 160 (e.g. a bodily fluid to which surface 150 of nanocomposite 100 is exposed), in which is at least partially soluble. From Fig. 3 it can be seen that path 170 (solid line) is the shortest route for molecule 110 to exit nanocomposite 100, as it can not pass through particles 130 or 135. In the absence of particles 130 and 135, direct route 175 (dashed line) would be available to molecule 110. For this reason, the presence to particles 130 and 135 delays the release of molecule 110 from nanocomposite 100. Clearly the higher the concentration of particles 130 and 135, the greater the delay to release of molecule 110.

The invention also provides a process for making the nanocomposite. The process comprises:

(i) combining a solution comprising a polymer matrix in a solvent with a nanoparticulate filler and a dispersant; and

(ii) removing the solvent.

Step (ii) generates the nanocomposite. The solution comprises an active substance so that the nanocomposite is capable of releasing said active substance. The active substance may be the nanoparticulate filler, or may be the dispersant, or it may be neither or it may be both. In the event that the active substance is neither the dispersant nor the filler, it will also be present in the solution of (i). It may be present in said solution as a solute or in a non-dissolved form e.g. dispersed in the solution. It may optionally be preadsorbed onto or preabsorbed into the filler. It will therefore be understood that, whereas the active substance is present in the solution, it may not itself be in solution (i.e. dissolved), for example in the case where it is a nanoparticulate filler. Thus the solvent may be a solvent for the active substance or it may be a non-solvent for the active substance. It may be a poor solvent for the active substance. The solution may be a liquid solution. It may be a viscous liquid solution.

The dispersant may be located on the surface of the nanoparticulate filler prior to step (i). Thus the nanoparticulate filler may be a dispersant treated nanoparticulate filler. It may be an organically modified nanoparticulate filler. The organic modification may comprise treatment (e.g. ion exchange) with a dispersant e.g. a surfactant such as a quaternary ammonium surfactant. Step (i) may comprise combining the solution with a suspension comprising the nanoparticulate filler and the dispersant in a carrier. It may comprise combining the solution with the nanoparticulate filler having the dispersant on the surface thereof. The solution of the polymer may be in a volatile solvent. Suitable solvents include dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, propylene carbonate, toluene, xylene, chloroform or any other suitable volatile solvent that can dissolve the polymer. In the present context, "volatile" refers to a solvent that may be removed by evaporation. The solution may be between about 1 and about 10% polymer w/v, or about 1 to 5, 1 to 2, 2 to 10, 5 to 10 or 3 to 8% w/v, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10% w/v. The process may comprise the step of dissolving the polymer in the solvent to provide the solution. The dissolving may comprise at least partially immersing the polymer in the solvent. It may comprise swelling the polymer with the solvent. It may comprise heating the polymer in the solvent. It may comprise agitating (e.g. swirling, stirring, shaking) the solvent with the polymer. It may comprise mild agitating. It may comprise vigorous agitating. A suitable temperature and time for the dissolving will depend on the particular nature of the polymer and solvent and the desired concentration of the polymer in the solvent. Suitable temperatures are less than or equal to the boiling point of the solvent. They may for example be between about 20 and about 1000C, or about 20 to 80, 20 to 60, 20 to 40, 40 to 100, 60 to 100, 20 to 80 or 40 to 8O0C, e.g. about 20, 30, 40, 50, 60, 70, 80, 90 or 1000C, although other temperatures may be used on occasions. The time for dissolving may be up to about 14 days, or up to about 7, 3 or 1 days, or may be between about 0.1 to 14, 0.5 to 14, 1 to 14, 3 to 14, 7 to 14, 0.1 to 7, 0.1 to 2, 0.1 to 1, 0.1 to 0.5, 1 to 10, 1 to 7, 7 to 10 or 3 to 8 days, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 days.

The process may also comprise the step of forming the polymer. Such steps are well known and documented. In the case of a polyetherurethane, for example, this step comprises mixing a polyol (e.g. polytetramethylene oxide polyol) with a polyisocyanate or oligomer or prepolymer thereof (e.g. MDI, TDI, HMDI etc.), optionally with a chain extender such as 1,4-butanediol, in the presence of a catalyst such as dibutyltin dilaurate or diacetate. The polymer may be formed in the solvent of the solution in step (i) of the process, or it may be preformed and then dissolved in the solvent to generate the solution.

The process may comprise the step of agitating the nanoparticulate filler and the dispersant in the carrier to form the suspension prior to step (i). The process may comprise the step of agitating the nanoparticulate filler and the dispersant in a carrier and then removing the carrier, in order to form the dispersant treated nanoparticulate filler. The dispersant treated filler may be a dry filler. Suitable carriers include volatile solvents as described above or other suitable volatile solvents. The carrier may be a solvent for the dispersant. The step of removing the carrier may comprise evaporating the carrier. It may comprise filtering or decanting in order to remove part of the carrier, and evaporating to remove further carrier. The evaporating may comprise heating and/or applying a vacuum and/or passing a gas (e.g. air, nitrogen, carbon dioxide) over and/or through the dispersant treated nanoparticulate filler. In cases in which the filler is agitated with the dispersant in a carrier, the agitation may be sufficient for the dispersant to intercalate and/or exfoliate the nanoparticulate filler. The agitation may be sufficient for the dispersant to at least partially exfoliate the nanoparticulate filler. The above agitation steps may comprise one or more of shaking stirring, sonicating, ultrasonicating or otherwise vigorously stirring. It may be sufficient that the nanoparticulate filler in the nanocomposite is either intercalated or exfoliated. The step of removing the solvent may also comprise removing the carrier, if present. The step of removing the solvent may comprise evaporating the solvent. It may comprise filtering or decanting in order to remove part of the solvent, and evaporating to remove further solvent. The evaporating may comprise heating and/or applying a vacuum and/or passing a gas (e.g. air, nitrogen, carbon dioxide) over the nanocomposite. It may comprise allowing the nanocomposite and solvent to stand so as to allow the solvent to evaporate slowly.

The invention also provides an article for direct or indirect contact with body fluids and/or tissues, said article comprising a nanocomposite according to the present invention, or a nanocomposite made by the process of the present invention. The article may be for example a stent (e.g. a urinary stent), a vascular implant, a synthetic blood vessel, a catheter (e.g. a urinary catheter), some other externally communicating device, a subcutaneous implant for implantation in soft tissue etc.

The article maybe implanted into a patient in need of said article, or of the active substance contained therein. The patient may be a human. The patient may be a non- human. The patient may be a primate (e.g. a non-human primate), a mammal, a vertebrate or may be an invertebrate. The patient may be for example a marsupial or a reptile or a fish or a bird. The patient may be selected from the group consisting of human, non- human primate, equine, murine, bovine, leporine, ovine, caprine, feline and canine. The patient may be selected from a human, horse, cattle, sheep, dog, cat, goat, llama, rabbit and a camel, for example.

Also provided is a method of delivering an active substance to a medium. The method comprises exposing an article comprising a nanocomposite according to the invention to the medium. The medium may be any medium capable of releasing the active substance therefrom. It may be a solvent for the active substance. The active substance may be soluble in the medium. In some embodiments it is only sparingly soluble, which may further extend the release of the active substance into the medium. The medium may be a bodily fluid or a tissue of a patient, e.g. blood, stomach fluid or some other fluid, or it may be a non-biological medium, e.g. water (e.g. seawater), a reaction medium or some other suitable medium.

The present invention relates to polymer nanocomposites for producing materials with multiple functionalities. These nanocomposites (see Figure 1) are based on a low water content organic polymer matrix with an inorganic nanoparticle inclusion and an organic modifier to facilitate dispersion of nanoparticles. They are able to sustain release of low molecular weight active agents, e.g. drugs, over at least about 1 month. They may be contrasted with hydrogel (high water content) systems, which display different release profiles.

Optimal dispersion within the nanocomposites may be achieved with up to about 5% loading of particulate filler. The loading of filler in the nanocomposite may be dependent on the nature (chemical, physical) of the filler, the desired release rate of the active substance, the effect of the filler on physical properties of the nanocomposite (hardness, flexibility, degradation, abrasion resistance etc.) and other factors. Commonly the loading will be between about 0.1 and 10% by weight or volume. It may be between about 0.1 and 5, 0.1 and 2, 0.1 and 1, 0.1 and 0.5, 0.5 and 10, 1 and 10, 5 and 10, 0.5 and 5, 0.5 and 2 or 1 and 5%, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10%, or may be more than 10%. The active agent of the nanocomposite may remain active on release from the nanocomposite. To prevent disruption of the dispersive action of organic modifiers by the active agent, the dispersants with dual activities (i.e. ability to disperse and having desired activity) may be used. Combination of two or more active organic modifiers (co-modification) may be employed in order to allow multiple activities without disruption of dispersion.

The inventors have found that polymer nanocomposites have enhanced stability under physiological conditions. This is particularly important in improving biostability in materials such as polyurethanes and may also be applicable to modulating degradation in other degradable materials. The inventors hypothesise a mechanism involving protection of soft segments of the polymer, modulation of inflammatory response and barrier effect. Polyurethanes are segmented or block copolymers comprising alternating blocks of soft and hard segments. Polyurethanes are known to suffer from biodegradation (hydrolytic, oxidative and enzymatic) under biological conditions that provide an active chemical agent diffusing into the material and some level of stress in the material. It is primarily the soft segment that is susceptible to this phenomenon and many techniques have been used to protect this part of the material including the use of polyols in the soft segment that are more resistant to degradation, coating the surface of the polymer with a protective material and the incorporation of antioxidants into the material. The incorporation of fillers, e.g. nanoparticles in the polymer structure, as described herein, may protect the soft segment in a number of ways. The nanoparticles may be integrated into the structure of the material resulting in a more oxidatively stable soft segment structure. Alternatively or additionally, the particles may present themselves as stress concentrators in the material thereby alleviating stresses on the soft segment The nanoparticles may also provide a physical barrier to the diffusive molecules believed to cause the degradation. The barrier effect is the result of the tortuous path presented to the diffusive molecules by the nanoparticles dispersed throughout the polymer matrix and other factors as described earlier.

Polymer nanocomposite based on active drug particles or other active agents may be produced via supercritical fluid or other processing methods. Nanoparticles may act as active agent and also as a filler to enhance mechanical properties. Sample Applications 1. Antibacterial polymer - chlorhexidine (CHX) modified nanoparticles in polyetherurethane matrix. CHX binds strongly to silicate and causes dispersion (Scheme 1 in Figure 2). In the present specification the abbreviation "CHX" may be used to refer to chlorhexidine or to a salt, for example acetate, thereof. These may be used interchangeably, or else it will be apparent from the particular context the precise nature of the species referred to.

2. Antithrombotic polymer - alkyl chain modification from C8 to Cl 8.

3. Combined antithrombotic and antibacterial polymer - multi-walled carbon nanotube (MWNT) modified polymer with combined antibacterial modification (e.g. CHX). An antitibacterial material may be covalently bound onto MWNT or may be incorporated directly in dispersed MWNT systems. 4. Combined antithrombotic and antibacterial polymer.

The present work provides elastomeric nanocomposites with combined antibacterial and anti-thrombotic properties. This work was conducted to determine design criteria for the development of advanced biomaterials that are capable of producing multiple biological effects. It was designed to adapt earlier work on biomedical polyurethane nanocomposite systems to the design of new systems that combine antibacterial and antithrombotic properties. The present work provides a nanocomposite approach to designing advanced materials that are capable of producing a specific biological effect. In particular, materials with combined antibacterial and anti-thrombotic properties which could be exploited in blood contacting applications were investigated.

In some embodiments, the present disclosure provides nanocomposites in which the organic modifier acts as both a dispersant and as an active agent. Earlier work has shown that the approach of using an organic modifier with dual functionality may employ other antimicrobial compounds which are able to act as dispersing agents. For example, chlorhexidine diacetate (CHX) has been demonstrated to cause increased silicate basal spacing as well as producing partially exfoliated PU nanocomposites. These nanocomposites also displayed antibacterial activity against coagulase negative staphylococci, the most common microorganism associated with medical device infection.

It has also been found that an organic modifier complexed with a nanoparticle within a material may produce surface modification of the polymer. Nanocomposites incorporating dodecylamine appear to prevent cell adhesion and have potential to minimise platelet interactions. In addition, dodecylamine (DDA) and the related compound aminoundecanoic acid (AUA) facilitate nanocomposite exfoliation.

The present work therefore was aimed at exploiting the mechanisms underlying the dispersive function and biological activity of organic modifiers and using them to determine design criteria for elastomeric composites with dual functionality for use in medical devices.

Use of nanocomposites has many advantages over other polymer modification approaches. First, the nanocomposite approach is applicable to a broad range of existing polymeric materials currently used in medical devices. This may serve to minimize or lessen the regulatory hurdles for the new technologies. Second, significant levels of antimicrobial agent may be held by the polymer via association with the large surface area of the nanoparticles. Finally, the presence of the nanoparticle itself may affect barrier properties. It is thought that this may allow sustained release of antimicrobial from the polymer.

The present invention therefore relates to:

1. new methods for incorporating active agents within biomaterials and presenting active agents in vivo;

2. design criteria for systems that allow dual modification of biomaterials to allow multiple biological functions through use of the concept of organic co- modification of nanoparticles using two or more active agents;

3. new nanocomposite systems based on incorporating nanoparticulate active agents produced via supercritical fluid processing that act mechanically as a nanofiller and biologically as a "drug" depot; 4. elastomeric polymers with both antibacterial and antithrombotic properties produced by combinations of concepts from 2 and 3; and

5. methods of functionalising polymers with widespread applicability since the process of functionalisation of matrix polyurethanes by way of nanoparticle inclusion could be easily adapted to other processing methods and polymer systems.

Typically in medical applications, active agents are either released from bulk polymers or are coupled onto the polymer surface. While both of these methods have been demonstrated to produce biological effects, the persistence of activity is relatively short. This is due to rapid release of small molecules from most systems and surface fouling with proteins and other molecules that occurs in vivo resulting in masking of surface expressed active agents. The present nanocomposite system has been shown to release both positive and electronegative molecules for up to one month or more and, due to the high surface area of silicate particles, sequestration of high levels of active agent is possible. The gradual release that occurs from the nanocomposites is thought to continually refresh the surface expressed molecules and, if levels of release are optimised, minimal toxicity will occur. That this approach can be applied to almost any polymer system with slight modifications renders the approach an attractive one from a manufacturing and regulatory perspective. Previously reported nanocomposite systems have used organic modifier simply as a mechanism to optimise nanoparticulate dispersion. While this is important for improvements in mechanical properties, the scope for these organic modifiers to also act as bioactive agents is enormous and currently has not previously been exploited. The inventors have now found that biological function can be impacted by nanocomposites containing low particle loadings. In particular, it has been shown that a QAC (quaternary ammonium compound) may function efficiently as both OM and as an active agent (e.g. antibacterial agent). A disadvantage of this particular modifier was its relatively high cytotoxicity, a problem often seen with antimicrobials. This may be due to the fact that the mechanisms for killing bacteria often have similar effects on mammalian cells. Use of co-modification approaches have been shown to modulate antibacterial bioactivity while maintaining dispersion. The major hurdles related to this co-modification approach are in identification of appropriate organic modifiers with dual functions and in maintaining dispersion of nanoparticles within the polymer matrix. The present work addresses these problems by optimising existing approaches using CHX modifiers and also by modifying existing non-specific antimicrobials with selected alkyl chain lengths to optimise dispersion combined with antibacterial activity.

Drug loading of polyurethane nanocomposites (PUNCs) may disrupt nanoparticle dispersion when an active agent is loaded before casting the polymer. The inventors hypothesise that this is because active agents carrying a charge can interact with either the nanoparticle or the organic modifier and thereby prevent intercalation. The present work overcomes this problem using two novel processing techniques: drug loading of well dispersed PUNCs using supercriticial CO2, and formation of nanoscale drug particles using supercritical fluid processing. Supercitical fluids have previously been used for polymer synthesis and it appears that polymer properties are not compromised by such processing. By exposing pre-formed PUNCs to supercritical CO2, it is therefore possible incorporate drugs into the bulk polymer following fabrication of the nanocomposite. This novel approach allows loading of drugs into PUNCs without disruption of the nanocomposite morphology. Use of a non-toxic solvent such as CO2, minimises the toxicity of the resulting system. In a second approach, nanoparticles of varying sizes are manufactured from active agents and their impact on polymer mechanical properties and drug releasing properties were then investigated. It has been shown that nanoparticles in the nanometer to micron range can be formed from various drugs without loss of activity via this technique. Much research continues to be applied to the problem of developing biomedical materials that are either antibacterial or antithrombotic. Common approaches tend to focus on surface modification using antibiotics or anticoagulants. These approaches have been ineffective in the past with most commercial devices having limited success on the market. Earlier work has suggested that non-specific antimicrobials are more effective that specific antimicrobials and that the likelihood of developing resistant strains is lower.

Dual functionality against both clot (thrombus) formation and bacterial adhesion has been little studied. Specific molecules have been used as both antibacterials and antithrombotics, however these are typically based on heparin and similar polysaccharides as the anticoagulant and non-specific antimicrobials such as QACs as the antibacterial. While the QAC approach has been applied to the PUNC system, the inventors have found that this approach is not viable due to high cytotoxicity of the released molecule. In addition, the material modification approach proposed is typically based on the aforementioned surface modification approach which has several disadvantages as discussed earlier. The present work addresses this problem by combining a non-toxic OM with a long carbon chain with a non-specific antimicrobial in a co-modification system. The long carbon chain molecule can diffuse through the PU and modify the surface hydrophobicity, preventing activation of coagulation and platelet adhesion. It is thought that the mechanism for this is similar to that proposed for phospholipid surface modification. The smaller charged antimicrobial is capable of diffusing at a greater rate and may inhibit microbial adhesion and growth. Two methods were used in the present work for loading the antimicrobial agent: simple mixing into the polymer before casting; and post-fabrication using supercritical fluid processing.

Application of the above approaches to other polymeric systems is also possible. Most of the research has been conducted on solvent cast materials and although this is useful for a range of applications, the ability to thermally process nanocomposites would be advantageous. The present work illustrates the flexibility of the present approach to different processing methods. Dispersion and biological function are compared for solvent cast and compression moulded PUNC films, hi addition, a similar system is studied using a hydrogel base combined with silicate nanoparticles to demonstrate the flexibility of the approach.

The present work aimed to: • identify alternative organic modifiers that are capable of functioning both as dispersing agent and bioactives and determine the parameters for optimised dispersion of nanofillers within polyurethane matrices using these modifiers;

• incorporate non-dispersive, antibacterial active agents into nanocomposites post- processing and determine the impact on PUNC properties and on release profiles of the active agent;

• produce blood compatible nanocomposites based on MWNT combined with bioactive modifiers; and

• determine strategies for design of dual modifications of PUNCs for both antibacterial and antithrombotic properties

Suitable materials which may be used as the matrix in a nanocomposite according to the present invention include polyurethanes, in particular polyetherurethaπes. A typical poly(etherurethane) is based on lOOOg/mol poly(tetramethylene oxide) polyol (PTMO), 4,4' diphenylmethane diisocyanate (MDI), and 1,4 butanediol (BDO) as the chain extender was used as the polymer component. The soft segment comprises ~65w% PTMO with resulting Shore hardness of the order of 8OA. Suitable nanoparticles for use in the nanocomposites include the silicate based montrnorrilonite (MMT: Nao.33[(Ali.67Mgo.33)Si40IO(OH)2]»H20) and multi-walled carbon nanotubes (MWNT). The latter may be used either unmodified or COOH functionalised. The inventors have shown that biostability improves in a QAC nanocomposite as silicate loading increased. Although the mechanisms for this are not clear, they were hypothesised to be due to either a barrier effect due to the presence of the nanoparticles, an uptake effect where the nanoparticles absorbed molecules likely to encourage degradation or an effect relating to damping of the inflammatory response caused by release of QAC.

Aim 1. Identification of organic modifiers that function both as dispersing agent and bioactives

A requirement for these modifiers is a positively charged region combined with a hydrophobic region, e.g. a long alkyl chain, that will compatibilise the hydrophilic silicate with the organic polymer. Chlorhexidine (CHX) has two positively charged region at either end of the molecule with terminal chlorines for antibacterial activity. The central region of the molecule is a short alkyl chain that is hypothesised to interact with the polymer. CHX is an attractive choice given that it is less toxic that QACs and is an approved antibacterial drug. Polyhexamethylene biguanide (PHMB) is another antibacterial molecule chosen on the basis of it having terminal 3-carbon alkyl chains. This disinfectant also appears to have lower toxicity than most QACs however it is not an approved drug at this stage.

Possible dispersants that act as antithrombotic molecules include phosphorylcholine type molecules. These amphiphilic molecules that are similar to the components of lipid bilayer cell membranes, are naturally non-fouling and this may prevent both bacterial adhesion and adhesion and activation of platelets and the coagulation cascade. DDA is one such molecule that has been shown to cause a reduction in mammalian cell adhesion to PUNCs. Aim 2. Incorporation of antibacterial and antithrombotic active agents postprocessing using supercritical CO2

PUNCs based on MMT and PU may be fabricated using organic modifiers described above. These may either have bioactivity via use of a bioactive organic modifier or will be control PUNCs without bioactive function. Following fabrication of films via solvent casting and compression moulding, active agent may be loaded into the polymer using supercritical CO2. Preliminary studies conducted using crystal violet (CV) as a model active agent have determined the appropriate range of parameters for achieving loading. Conditions that caused no visual change in PUNC were temperatures up to 70°C combined with pressures of about 20MPa applied over up to 96 hours. Under these conditions, consistent loading of CV throughout nanocomposite films was demonstrated with subsequent release of CV still occurring after one week.

Suitable active agents that may be used in the above nanocomposite include the antibacterials CHX, PHMB, gendine (combined gentian violet and CHX) and furanones and antiplatelet drugs such as ticlopidine, dipyridamole and salicylic acid for f antithrombotic activity.

Aim 3. Combination of MWNT and bioactive modifiers for improved blood compatibility

PUNCs based on MWNT have been fabricated by the inventors and assessed for their electrically conductive properties. Dispersion in these nanocomposites can be problematic and various approaches to producing optimised dispersion within the polymer matrix have been studied. Covalent modification approaches using long carbon chain molecules have demonstrated significant improvements in mechanical properties, suggesting improved dispersion. Being based on carbon, the nanotubes themselves may confer antithrombotic activity on the resulting PUNCs. Improvements in mechanical performance by PUNCs based on covalently modified MWNT may be achieved. Also improvements in blood compatibility may be achieved based on surface expression of the long carbon chain molecules outlined above. Thus modified MWNT with a range of carbon chain lengths attached may be be mixed with PU to form composites. Aim 4. Determination of strategies for combined antibacterial and antithrombotic modification of PUNCs

PUNCs based on MWNT as described above may be loaded with antibacterial agents via either pre-fabrication or post-fabrication (supercritical fluid) drug loading, as described earlier. CHX may be used in order to conver antibacterial properties to the MWNT based nanocomposite. Alternatively, co-modification may be used to include both antibacterial and antithrombotic dispersants on the nanoparticle surface. In another approach drug nanoparticles may be produced via supercritical CO2 processing of active drug particles. These may be used as a nanofiller with the ability to slowly release drug into the polymer matrix and surrounding fluid. Detailed Description of the Preferred Embodiments

The inventors have developed several particular embodiments of the present invention.

Embodiment A: Modulation of Model Drug Release from Polyurethane Organosilicate Nanocomposites Development of bioactive materials that function to prevent or encourage specific biological events has been the topic of much research in the biomaterials field. While approaches using either simple loading of drug into the material matrix or more complex approaches of surface modification have been studied extensively, the ability of nanocomposites to sustain drug release has only been considered more recently. The present embodiment examines the release of model drugs from a polyurethane organosilicate nanocomposite, and specifically evaluates the impact of nanoparticulate loading and drug charge on release profiles. Nanocomposites were fabricated from a biomedical poly(ether)urethane with the natural layered silicate montmorillonite (MMT) as a nanoinclusion. MMT was organically modified with methyl tallow bis-2- hydroxyethyl ammonium chloride to facilitiate dispersion. Nanocomposites were loaded with model drugs crystal violet (CV) or phenol red (PR) prior to solvent casting and release evaluated spectrophotometrically over 30 days. Results for both nanocomposites loaded with positive or electronegative model drugs showed that drug release was prolonged and that there was slower initial release and lower total release after 30 days. As nanoparticle loading increased this effect was more pronounced and the CV model drug proved more interactive than the PR. The nanocomposite approach used in this study is highly feasible for extending release of low molecular weight drugs. 1. Introduction Nanocomposites containing nanoscale nanoparticulate inclusions have potential for both improving mechanical properties of base polymers as well as theoretically providing the large surface area of particle inclusions for sequestering molecules with potential for bioactivity. Nanocomposites are now well represented in the literature with diverse polymer/nanoparticle combinations having been investigated. Typically, enhancements are conferred by the nanoparticle to the host polymer's mechanical, thermal, and barrier properties.

Materials studied in the present work were nanocomposites prepared by the dispersion of layered silicates in a biomedical polyurethane (PU). Specifically, the PU used in this study was a biomedical poly(ether)urethane (PEU) typically used in cardiovascular applications such as pacemaker leads and in catheters for both blood and urinary contacting applications. Montmorillonite (MMT) is a commonly utilised natural layered silicate, and was employed as the nanoparticle in these studies. A typical MMT layer is 250nm in two dimensions and lnm in the other, giving an aspect ratio of 250 and total surface area of over 700m2/g. In order to generate a nanocomposite, these silicate layers need to be delaminated, a process which is hindered by the natural tendency of layered silicates to stack in groups of around 1000 units. Usually, organic modification (OM) of the silicate via utilisation of the cationic exchange capacity (CEC) is conducted in order to increase the compatibility of the inorganic silicate with the organic polymeric component. Also, while quaternary ammonium compounds (QAC) are the most frequently employed organic modifications (OM), it is theoretically possible that any positively charged species of appropriate geometry be capable of cationic exchange onto the MMT.

The present embodiment focussed on studying PU nanocomposites as drug releasing biomaterials. The incorporation into biomaterials of low molecular weight drugs such as those having anti-bacterial activity is of great interest. Subsequent release of loaded drugs would allow targeted activity at the site of the device as opposed to systemic therapy, thereby avoiding unwanted systemic side effects and providing a more temporally consistent dosage compared to oral ingestion or intravenous injection. Release of incorporated drugs from polymers is typically diffusion controlled, thus can be manipulated simply through modulation of the diffusivity of the biomaterial. Diffusivity is a factor of the chemistry and physical nature of both the incorporated drug and the polymer. Polyurethanes as a class have a broad range of physical and chemical properties, and therefore the release of drags can be highly variable. Hydrogel nanocomposite drug delivery systems have been explored previously.

Although these systems are mechanically and chemically dissimilar to the thermoplastic elastomeric PEU in the current study, the underlying mechanisms are comparable. A poly(ethylene-co-vinyl acetate) hydrogel nanocomposite drug delivery system has been explored utilising a series of silicates of similar chemistry but varying aspect ratio (Cloisite® 2OA, Somasif™ MAElOO, Somasif™ MAE300). The corticosteroid dexamethasone was loaded into the nanocomposites by simple mixing, and its release into phosphate buffered saline was in all cases decreased by the presence of the silicate and was dependent on the silicate loading.

In other previous work, a series of systematic studies was conducted on the release of model drags of varying charge from N-isopropylacrylamide and poly(acrylic acid-co- poly(ethylene glycol) methyl ether acrylate) hydrogel composites. In early studies, the layered silicate MMT, 3-acrylamidopropyl trimethylammonium chloride (TMAACI) MMT, Cloisite® 30B, or TMAACl bentonite was utilised. In subsequent work, a positively charged mineral hydrotalcite was used and modified with the negatively charged 2-acryloylamido-2-methyl propane sulfonic acid. A strong electrostatic interaction was proposed to exist between the model drug and the silicate; positive crystal violet release was decreased, and negative phenol red release increased, by addition of negative MMT. Organic modification of the silicate was seen to effectively 'shield' this electrostatic interaction. These hydrogel systems were expected to behave differently to the thermoplastic elastomer PEU system of the present work due to large differences in the material properties of the host polymers. The conflicting results in these hydrogel based studies suggest that a reduction in the model drag release with silicate loading could occur for the PEU in the present work. Alternatively, if there are variable interactions between drag, polymer and nanoparticle, an increase might also occur. The underlying hypothesis of the present work is that release of incorporated drag molecules can be modulated by incorporating nanoparticle inclusions. The proposed mechanism for this perturbation of release is based on reported barrier effect endowed by the presence of nanoparticles in the polymer matrix. As well as being able to tailor release rate without having to adjust polymer chemistry, this approach offers significant advantages over direct surface modification for improving performance of biomedical devices. The continual renewal via surface blooming of the incorporated drug will produce a surface environment similar to that of a surface modified polymer. A potential advantage to this approach is that the active drug molecules can be released from the surface and so their activity is not hindered by covalent attachment to the surface as they may be in the case of surface modification.

The specific aims of the present work were to i) assess the ability of various loadings of dispersed layered silicate inclusions to modulate the release of model drugs from PEU, and ii) examine the impact of drug charge on the degree of release modulation achievable from PEU.

2. Materials and Methods 2. 1 Polγ(ether)urethane

Polyether urethane (PEU) with chemical structure illustrated in Figure 4a was used in this study. The polymer was supplied by Urethane Compounds (Melbourne, Australia) and contained lOOOg/mol ρoly(tetramethylene oxide) polyol (PTMO), 4,4' diphenylmethane diisocyanate (MDI), and 1,4 butanediol (BDO) as the chain extender. The components were combined in the ratio 100 : 7.5 : 46.3 respectively, with 0.003 dibutyltin dilaurate added as catalyst, thus the PEU contained about 65w% PTMO (soft segment). 2.2 Nanoparticles

MMT of chemical formula Nao.33[(Al1.67Mgo.33)Si4θ1o(OH)220 sourced from Southern Clay Products (Texas, USA) was used as the base silicate, and had CEC (cation exchange capacity) of 92.6mEq/100g. An organically modified MMT named Cloisite® 3OB (referred to as "QACMMT" or the "nanoparticle") was also sourced from Southern Clay Products, and this organosilicate had the QAC methyl tallow bis-2-hydroxyethyl ammonium chloride as shown in Figure 4b as an OM. This QAC is derived from animal adipose tissue, with the tallow indicating an alkyl chain of varying carbon atoms in length: 5% Ci4, 30% C16, and 65% C18. 2.3 Model Drugs The model drugs used are shown in Table 1, and were chosen based on their chemical properties, MW and ease of detection. Crystal violet (CV, GURR Searle Diagnostic) and phenol red (PR5 Sigma) have similar MW, size, three-dimensional movement capability, and structure, but are cationic versus electronegative respectively. These factors combined with an absence or presence of hydrogen bonding capability respectively, allow qualitative examination of the effect of the drug compound's chemistry on release.

2 A Model Drug-Loaded Material Preparation

A 5w% solution of PEU in dimethylacetamide (DMAc, Sigma Aldrich) was prepared at 6O0C and allowed 1 week for complete dissolution. A 5w% suspension of QACMMT in toluene (Sigma Aldrich) was also prepared: QACMMT was dried at 6O0C for at least 3h, combined with toluene and vigorously mixed on a magnetic stirrer for 30min. As a polar activator, methanol (Univar) and distilled deionised water were then added at 30w% and 6w% of the QACMMT mass, respectively. The suspension was vigorously stirred for a further 30min, and then placed in an ultrasonic water bath for lOmin. To prepare a model drug-loaded composite, the PEU/DMAc solution was combined with the nanoparticle suspension in appropriate proportions to produce composites of 1 and 7g nanoparticle / lOOg PEU. Model drug was also added at an initial model drug loading (Mi) of lw% (g drug/10Og composite). This solution was then stirred on a magnetic stirrer for about 24h at about 5O0C.

Following stirring, mixtures were cast directly into specially manufactured drug release pour plates to be used for the drug release assay. Plates consisted of 48mm ID glass cylinders attached with silastic to glass sheets, providing consistent material thickness and equal material area exposure to the sink medium. DMAc was removed at 6O0C under a dry air atmosphere at partial vacuum of 400 to 500mbar in a laboratory vacuum oven (Binder VD) for 48h. An average material thickness of about 150μm was produced as measured using digital micrometers. Materials were designated as polymer- nanoparticle-nanoparticle loading-model drug, for example PEU-QACMMT-I -CV is a material containing Ig QACMMT/lOOg PEU and Ig CV/100g PEU-QACMMT composite. Materials were prepared with loadings as detailed in Table 2. 2.5 Model Drug Release Assay

At the commencement of the assay, 5OmL of the sink liquid (pH6 distilled deionised water) was added to the model drug-loaded sample in each well and a ImL sample immediately taken and replaced with ImL of fresh sink liquid. The plate was then covered with plastic to prevent evaporation and aluminium foil to prevent light degradation of the model drug(s), and placed in a 370C incubator on an orbital shaker. Further ImL samples were taken periodically as required and stored in 1.5mL Eppendorf microvials in the dark at room temperature until the end of the assay. The samples were diluted with the sink liquid as necessary and then assayed spectrophotometrically. Tests were ran for a period of 4 weeks. Each assay contained triplicates of each material, and the entire assay was repeated in triplicate for independent material batches. Plots of the mass released at time t (Mt)/ total mass loaded (Mi) versus time were prepared for visual observation of the release kinetics. Initial release rate was calculated from the slope of the initial linear region of this plot. To confirm the significance of the drug release results, some controls were run. First, potential for degradation of the model drugs at the processing temperatures used was assessed in water heated to 500C for 24h (replicating mixing process) and 6O0C for 48h (replicating casting process) was assessed. Second, the maintenance of pH in the PR sink pH was assessed at various times throughout the 4 week assay period. CV sink pH was not assessed due to the strong staining power of CV. 2.6 Transmission Electron Microscopy (TEM)

A sample of about 1 x about 4mm dimension was inserted into a holder and frozen in a sucrose solution using liquid nitrogen. TEM sections were then prepared using a Reichert Ultracut E cryo-ultramicrotome equipped with a diamond knife and operated at - 800C. Sections were placed on 400-mesh copper grids and analysed in a Hitachi H-7000 TEM operated with a beam current of lOOkeV. Several sections from the one sample were prepared and imaged to assess nanoparticle dispersion in drug loaded and unloaded samples. 3. Results

3. 1 Model Drug Release

Assay controls showed that degradation of the model drugs did not occur in water at the relevant processing temperatures. The pH of the PR sink water was observed to drop from pH6 pre-assay to pH4 post-assay likely due to the release of the weakly acidic PR, however this should not have affected the assay greatly since PR absorbance at 430nm changes between pH 6.6 - 8.0 and the effect of the sink pH on the release kinetics is likely to be minimal. The maintenance of a pH6 sink was not verified for the CV assay due to a desire to avoid pH meter contamination, however CV absorbance at 592nm changes between pH 0 - 2 and any sink pH changes should therefore be inconsequential. A comparison of the release of PR and CV from neat PEU is shown in Figures 6a

(over 5 days) and 6b (over 30 days). PR was released at a higher initial rate than CV, however the total release of PR at equilibrium was about 10% lower than that of CV. Further, equilibrium was reached more rapidly for PR than for CV, and even after 4 weeks the CV did not appear to have reached a stable plateau. Figure 7 shows the release profiles of PR from PEU and PEU-QACMMT composites into water over a period of one month. Immediately obvious is the reduction in the total PR released with increased QACMMT loading. A slight reduction was observed for the lw% QACMMT loading and a significant reduction of about 10% seen for a loading of 7w% QACMMT. Also noticeable is the reduction in the initial release rate when 7w% QACMMT was incorporated into the PEU. Figure 8 shows the release profiles of CV from PEU and PEU-QACMMT composites into water over a period of one month. The trends observed are similar to those of PR, however the magnitude is greater for CV. That is, QACMMT loadings of lw% and 7w% resulted in reductions in total CV release of about 15% and about 80%. That the initial release rate of CV was significantly perturbed is obvious for both QACMMT loadings, especially the 7w% QACMMT loading.

Burst effect, initial release rate and total % released were derived from the in vitro drug release data of Figure 7 and Figure 8, and are presented in Table 3. The burst effect, which refers to the amount of release at the zero time point owing to surface residence of the model drug after manufacture, was higher for the PR materials, and was decreased as the QACMMT loading increased. The trends in initial release rate and total release show that nanoparticle loading impacts on both parameters, with the effect being more pronounced for the positively charged CV. 3.1 Silicate Dispersion

TEM was conducted with representative images for CV and PR loaded PEU and PEU-QACMMT composites are presented in Figure 5 at a magnification of 1000Ox. (include TEM of PUNC with no drug at 1 and 7%). Materials containing either lw% CV or lw% PR displayed lower degrees of dispersion compared with the non-drug loaded nanocomposites. hi PEU-QACMMT-I -CV silicate existed as clumps on the order of about 1000 to about 2000nm, whereas in PEU-QACMMT-I -PR silicate existed as larger clumps on the order of ~4000nm which appeared to be agglomerations of smaller clumps. At the higher 7w% QACMMT loading the difference between the CV and PR loaded composites was less noticeable, however it appeared that PEU-QACMMT-7-PR was less honiogenously dispersed than PEU-QACMMT-7-CV. 4. Discussion

Enhancement of the barrier effect in nanocomposites is generally attributed to i) the change to the base polymer properties effected by the included organosilicate silicate layers, ii) physical disturbance to the path length of penetrating species, and iii) chemical interaction of the penetrating species with the included organosilicate layers. Examination of these processes experimentally is difficult. It is now generally acknowledged that composites in general likely contain two very different polymer types: the 'bulk polymer' having properties of the neat polymer, and the 'interfacial polymer' near to the organosilicate inclusion, which is supposed to have dramatically different properties, and is usually suggested to be more crystalline in nature. The effect of organosilicate on the segmented structure of PU has not been elucidated, with seemingly contradictory findings being reported in the literature ranging from less hydrogen bonding between hard domains, to more hard domain order, to no change in PU morphology. Typically, decreased permeability is attributed to the black box-like 'tortuous path' effect whereby the increased path length a penetrating species necessarily travels due to the impermeable silicate layers 'blocking' its route is solely responsible. Tortuous path models have been developed incorporating silicate layer length, loading, alignment, and degree of dispersion, however these models do not always fit experimental data well. This poor fit to experimental data is presumably due to the disregard of the effect the silicate may have on the polymer matrix itself and of chemical interactions between the drug and the polymer/nanoparticle/organic modifier. The opposing constrained polymer model, while based on the tortuous path models, also considers the changes to the base polymer properties. It allows input of diffusion coefficients and volume fractions for three polymer regions (base, interfacial, and the OM), however no experimental data is reported as evidence since measurement of the interfacial region is difficult.

The final contribution to barrier effect enhancement is the chemical interaction of components. The system of the present invention is made complex by the segmented structure of the PEU and the included nanoparticle that is essentially two component, silicate and QAC. The interaction of both model drugs with each component of the composite has been considered for the system studied and is summarised in Table 4, and further discussed in the following sections in light of the measured model drug release profiles from neat PEU and from nanocomposites. 4. 1 Comparison of Model Drug Release from Neat PEU The PEU of this study has soft segment ethers of negative polarity (C-O-C), while the hard segment has both positive amine (NH2) and negative carbonyl (C=O) polarity. Considering the model drugs, CV has positive cationic polarity (N+), while PR has both negative thionyl (S=O) and positive hydroxyl polarity (OH). Therefore, it is thought that CV would be attracted to the soft segment and PR repulsed. Consideration of the model drug interaction with the hard segment is more complex, with both attractive and repulsive forces present in each case. The N+ of CV is attracted to title hard segment C=O and repulsed by the adjacent NH2. One study in the literature using CV in a similar PU concluded that the CV was mainly dissolved in the hard segments, and that the phase separation of PU was unaffected by CV. The PR has S=O repulsed by the C=O and attracted to the NH2, as well as OH repulsed by the NHa and attracted to the C=O, of the hard segment. There appear to be no reported studies concerning PR incorporation in PEU, however it is hypothesised to be readily miscible, although not strongly interactive, with the hard segment. Overall, CV is likely to be dispersed throughout the PEU, and PR mainly located within the hard segments.

That the burst effect and initial release rate from PEU are significantly higher for the PR materials as seen in Table 3 and Figures 6a and 6b is not unexpected and supports the premise that a significantly lower attraction of the PR for the PEU exists than for CV and PEU. It was not expected however given the lower level of interaction and the faster initial release rate, that the total release of PR be lower than that of CV. It is unlikely that some change in the PEU diffusivity occurs after the initial few days, or that some error in the assay procedure existed, as the effect would also have been seen for CV. While the explanation has not been investigated, perhaps a proportion of the polar PR molecule (S=O at one end, OH at the other) associates into colloid-like agglomerations within the PEU as a response to the presence of predominantly repulsive forces, akin to surfactant behaviour. Thus, freely dispersed PR may release quickly relative to CV, while agglomerated PR may prefer to remain together. This proposition may account for the rapid initial rate and sharp plateau of PR release. 4.2 Model Drug Release from PEU-QACMMT Composites The interaction of the model drugs with the organosilicate in isolation from the nanocomposite is considered initially. The QACMMT is effectively an electrostatically neutral material as the silicate negative charge and QAC positive charge should be balanced, however hydroxyls are present on the silicate edges and on the QAC. PR is attracted only weakly to the silicate edge hydroxyls and QAC hydroxyls via hydrogen bonding and dipole-dipole attractions with its thionyl and hydroxyl groups. The burst effect of PR reported in Table 3 is reduced as silicate loading increases, also strongly supporting this attractive force. It is probable that this was the cause of the poor silicate dispersion seen in TEM images depicted in Figure 5. Thus in the composite material, PR was considered to be weakly associated mainly with the PEU hard segments, and was therefore considered primarily 'non-interactive'.

Considering CV interactions, CV N+ is likely more strongly positive than the N+ in the QAC organic modifier. Justification for this is a) the use of three of its five valence electrons in covalent bonds, and b) resonance delocalisation of the lone nitrogen electron pair into the aromatic benzene ring that is deficient an electron pair due to the double bond with the CV central carbon atom. CV is probably also attracted to the silicates edge hydroxyls. Evidence for this CV interaction with the silicate can be seen in the lowering of the burst effect as silicate loading increases. It was therefore hypothesised that CV at least partially displaces the QAC from the silicate during the mixing phase of material preparation and this could explain the poor silicate dispersion demonstrated by TEM for the PEU-QACMMT-CV materials in Figure 5. Thus in the composite material, CV was considered to be associated with the silicate particles primarily, and the PEU hard segments secondarily, and was therefore considered 'interactive'. The three factors thought to be involved in the enhanced barrier effect as detailed earlier are base PEU change, silicate barriers, and/or attractive interactions. For both PR and CV an increase in the QACMMT loading led to a decrease in both initial release rate and total release.

The release profiles measured suggest increased resistance to release due to some combination of the three factors, with all being hypothesised to be involved with the increased modulation observed when the silicate loading was increased. The effect observed for PR being significantly weaker than that seen for CV on the other hand, suggests that the difference between the two molecules' release profiles was due primarily to the interaction factor (since changes to the base PEU would be similar based on the similar degree of silicate dispersion). This also provides proof of principle that inclusion of layered silicate could be beneficial to achievement of an optimal local drug concentration to the release location given the right combination of material and surrounding conditions. 4.3 The impact of nanoparticle dispersion The degree of silicate dispersion present in the model drug-loaded composites of this study was observed to be low compared with that of non-loaded composites assessed in this and previous studies. Poor silicate dispersion is more likely due to preferential interactions between silicate and model drugs rather that that between silicate and PU, as discussed previously. While dramatic differences in silicate dispersion, and hence barrier effect, would negate valid comparison of materials, the differences observed in TEM images imply this is not likely to be a dominant factor between PEU-QACMMT-CV and PEU-QACMMT-PR composites. In fact, the similar levels of dispersion in the two systems combined with the dramatic differences in total release suggest that drug-silicate and drug-OM interactions may be dominant over simple physical disturbance to the path length of penetrating species in perturbation in release profile. 5. Conclusions

Polyurethane nanocomposites loaded with positive or electronegative model drugs were able to prolong drug release with a slower initial release and lower total release after 30 days. This effect was greater as nanoparticle loading increased and was more pronounced with the more interactive CV model drug. A critical observation made was that silicate dispersion was disrupted in all drug loaded nanocomposites, a phenomenon likely due to interactions between the silicate or the OM and the drugs. Regardless of the disruption in dispersion, the decreased rate of drug release observed in nanocomposites compared with neat PEU suggests that the nanocomposite approach is highly feasible for extending release of low molecular weight drugs.

Table 1 : Chemical structure and MW of model drugs.

Model Drug Crystal Violet Phenol Red

Chemical

Structure

Figure imgf000044_0001

MW 407.99 354.38

Charge 1 x Positive Negative 2

Hydrogen

Bonding no yes

Capability

Largest

1.38 1.03 Dimension (nm) !

Ring Rotation

2 2 (# capable)

Absorbance Peak 592 430

Figure imgf000045_0001

1 Using three-dimensional optimization module of ACD/Chemsketch Freeware.

2 Negatively charged through dipole forces as opposed to possession of free electron pairs.

Table 2

Material Loading CV Loading PR Loading

(g nanoparticle / 10Og PEU) (g / lOOg composite) (g / lOOg composite)

PEU-CV - 1 -

PEU-QACMMT-I -CV 1 1 -

PEU-QACMMT-7-CV 7 1 -

PEU-PR - - 1

PEU-QACMMT-I -PR 1 - 1

PEU-QACMMT-7-PR 7 1

Table 3

Burst Effect ] [nitial Release Rate Total Release

Material (% loaded ± s.d.) (mg/d ± sd) (% loaded ± sd)

PEU-PR 1.2 ±0.3 46.0 ±0.9 72.2 ±1.0

PEU-QACMMT-1-PR 1.4 ±0.4 44.4 ±1.2 69.3 ± 0.5

PEU-QACMMT-7-PR 0.7 ±0.3 26.1 ±1.3 59.5 ±1.4

PEU-CV 0.6 ±0.1 27.7 ±3.6 86.9 ±5.3

PEU-QACMMT-I -CV 0.7 ±0.1 24.0 ±1.3 68.4 ±5.1

PEU-QACMMT-7-CV 0.0 ±0.0 3.3 ±1.0 2.8 ±1.1

Table 4 : Assumed interaction of drugs with composite components (interacting species shown in brackets). A semi-quantitative ranking was attempted after consideration of the relative strengths of chemical interactions, which in ascending order have been assigned the rating in brackets: hydrogen bonding (1), dipole-dipole (1), ion-dipole (2), ion-ion (3).

Drug Soft segment Hard segment Silicate QAC

Figure imgf000045_0002

- (S=O-C-O-C) + (S=O -HN) + (OH- -OH) ++ (S=O-N+)

PR - (OH-C-O-C) + (OH- -O=C) + (S=O -HO) + (OH-OH) + (OH -NH) - - (S=O -MMT-) + (S=O -HO) - (S=O - O=C)

'+' designates attraction (strong +++, moderate ++, weak +). '-' designates repulsion (strong — , moderate - -, weak -).

Embodiment B: Antibacterial polyurethane organosilicate nanocomposites Thermoplastic polyurethanes are versatile polymers much used for biomedical applications due to their mechanical properties and biocompatibility. Like most implantable materials they are susceptible to bacterial colonization, particularly in applications at high risk of bacterial contamination such as percutaneous catheters. The objective of this work was to assess the antibacterial activity and the cell responses to a series of nanocomposite variants fabricated from a polyether polyurethane and organically modified silicates containing either antibacterial dispersing agents, non- antibacterial dispersing agents, or combinations of the two. The results suggest that co- modification is a promising approach for modulating both bacterial and mammalian cell responses to achieve appropriate antibacterial properties without cell inhibition. Infection of implantable and indwelling medical devices causes significant morbidity and mortality. Approximately half of the 2 million hospital acquired infections in the United States are related to indwelling devices such as central venous catheters. For relatively common implanted devices such as heart valves and vascular grafts, the infection rate is of the order of 4% of all devices implanted. The issue of devices acting as a nidus for infection remains a critical problem and there is an unmet clinical need for new approaches to preventing and treating biofilm formation on medical devices.

Formation of biofilm on substrates begins with surface conditioning, followed rapidly by reversible bacterial adsorption and then irreversible adhesion. Strategies for prevention of bacterial colonisation are key to preventing biofilm formation since removal of biofilm once formed is difficult. In the past such approaches have included surface and bulk modification using a range of specific antimicrobials such as rifampin and nonspecific antibacterial compounds such as chlorhexidine and silver. Success rate is variable and disadvantages with these methods range from development of antibiotic resistance, short term efficacy of active agent release and deterioration of material properties with modification.

There are several advantages of using nanocomposites as a base for antimicrobial materials. First, the antimicrobial can double as both a dispersing agent resulting in exfoliation of the particles and as a means of conferring antibacterial properties. Second, significant levels of antimicrobial agent can be held by the polymer via association with the large surface area of the nanoparticles. Finally, the presence of the nanoparticle has the potential advantage of impacting on barrier properties which is hypothesised to allow sustained release of antimicrobial from the polymer.

The major goal of this work was to formulate antibacterial polymers via a nanocomposite approach and to examine their impact on bacterial adhesion and growth and on mammalian cell growth. Experimental Methods Materials. Polymer nanocomposites were prepared using a polyether polyurethane (PEU) containing lOOOg/mol poly(tetrarnethylene oxide) polyol (PTMO)5 4,4' diphenylmethane diisocyanate (MDI), and 1,4 butanediol (BDO) as the chain extender. The PEU contained about 65w% PTMO soft segment. The nanoparticle used was a sodium montmorillonite (MMT) with the chemical formula Nao.33[(Al1.67Mgo.33)Si4010(OH)2]'H2θ with a cation exchange capacity (CEC) of 92.6mEq/100g. Two modifiers were used in these studies. Ethoquad® O/12PG is a synthetically produced quaternary ammonium compound with an 18 carbon alkyl chain. 1-aminoundecanoic acid (AUA) is a synthetic compound having amine and carboxyl functionality located at opposite ends of a ClO alkyl chain. When acidified to a pH below its isoelectric point (pi), AUA has a positively charged head structure to enable cation exchange with the silicate.

Silicate Modification. MMT was suspended in distilled, deionised Milli-Q water at lw% by vigorously stirring for 24h and organic modification (OM) was achieved by adding the modifier either directly to the solution (EQ) or to solution acidified using 1OM HCl to a pH just below 4 (AUA). Modifiers were added at 110% of the CEC. The MMT solution was stirred vigorously for 24h at about 6OC. For co-modification with EQ and AUA, both were added simultaneously at mass ratios of 1:0, 1:3, 1:1, 3:1 and 0:1. These were designated as %CEC theoretically occupied by the EQ. For example, the organosilicate EQ75MMT contained EQ at 75%CEC and AUA at 25%CEC. For all organosilicates, the product was isolated by lOmin of centrifugation at

3010Og at 15C, and then dried at 6OC overnight. Dried organosilicate was crushed in a glass mortar and pestle, sieved with a 325-mesh (45μm) sieve, and then dried again at 6OC for several hours before use. The modified MMT was analysed by thermal gravimetric analysis (TGA) to determine percent organic component and allow calculation of loadings.

Nanocomposite Preparation. Nanocomposites were prepared via solution casting by first suspending EQ modified MMT in toluene and then mixing overnight with a 5% solution of PEU in dimethylacetamide. Nanocomposites based on AUA modified MMT or co-modified MMT were prepared by adding dry organosilicate directly to the dissolved PEU solution to minimise material loss. Table 5 shows the types of materials fabricated and their MMT loadings. Loading was expressed as g silicate/10Og PEU and g OM/lOOg PEU based on results from TGA. Loadings of 1 w% and 3w% were prepared. Table 5. Materials and nanoparticle loadings studied

Material g silicate/lOOg g OM/100g

PEU PEU

PEU 0 0

PEU-EQOMMT-I* 0.8 0.2

PEU-EQ25MMT-1 0.8 0.2

PEU-EQ50MMT-1 0.8 0.2

PEU-EQ75MMT-1 0.8 0.2

PEU-EQ100MMT- 0.8 0.2

1 1

PEU-EQOMMT- 2.5 0.5

3**

PEU-EQ25MMT-3 2.5 0.5

PEU-EQ50MMT-3 2.5 0.5

PEU-EQ75MMT-3 2.4 0.6

PEU-EQ 100MMT- 2.5 0.5 3

* 1 % loading; * *3% loading PEU-EQOMMT was modified by AUA alone PEU-EQ IOOMMT was modified by EQ alone

Material Characterization. Samples were prepared for transmission electron microscopy (TEM) to assess nanocomposite formation by cryomicrotomy using a diamond knife. TEM images were taken for the lw% materials only. Tensile properties of materials were conducted based on ASTM D 882 using strips of 12mm width and an Instron tensiometer at a strain rate of 1 OOmm/min. Bacterial Adhesion Testing. A slime-producing radiolabeled variant of S. epidermidis (ATCC 35984) was used to assess bacterial adhesion and growth. A suspension was prepared by inoculating bacterial colonies into trypticase soy broth (TSB) supplemented with 0.25% glucose to increase slime production, and 80μCi (2.96 MBq) of tritiated thymidine (thy-H3+) for bacterial radiolabelling. Overnight cultures were washed and resuspended in media without radiolabel and diluted to an optical density (OD) at 660nm of 1 in media. Discs (1 lmm diameter) of test samples as specified in Table 5 were cleaned and sterilised. Each disc was placed in ImL of thy-H3+ containing medium and incubated in 24-well plates with bacteria or without bacteria. Bacterial inocula equivalent to an ODO.1 solution was used. After Ih incubation, samples were washed and incubated in fresh media with radiolabel for 24 hours and then washed and heated in 0.5mL of 0.2M sodium hydroxide (NaOH) for 3h at 80 C to destroy the bacterial membranes and enable even dispersion of the thy-H3+ throughout the NaOH and scintillation fluid prior to counting. Radioactivity associated with test samples was expressed as a ratio to counts from control PEU without nanoparticles.

Mammalian Cell Growth Inhibition Studies. Samples were washed and sterilized followed by extraction in complete media (Eagle's minimum essential media (EMEM, Sigma) + 10v% fetal calf serum (FCS, Gibco)) at a ratio of 4g/20 mL. A monolayer of L929 mouse fibroblasts (ATCC CCL-I) was prepared by seeding at 106 cells/mL in complete media and incubating for 1 day at 37C and 5% CO2. Extracts were applied to the cell monolayers and incubated a further 2 days. Null samples that were not exposed to extraction fluid were also included. After 2 days of incubation in extraction fluid, cell monolayers were washed with Dulbecco's phosphate buffered saline without calcium and magnesium (DPBS, Sigma), trypsinised (0.12% trypsin, 0.02% ethylene diamine tetra- acetic acid (EDTA), 0.04% glucose, JRH Biosciences), and assessed by flow cytometry. Fluorescent beads (Bangs Laboratories) were added at a about 1:10 ratio with cells to allow quantification of cell numbers. The cell / bead mixture was analysed by flow cytometry and results expressed as the ratio of cells exposed to test extracts over the number exposed to control (PEU only) extracts. Results and Discussion

Silicate dispersion observed in TEM images (not shown) was good in the EQ only and AUA only nanocomposites. In all nanocomposites based on co-modified silicate materials, larger silicate clumps of dimension 1 - 2 μm were observed for PEU- EQ25MMT and PEU-EQ75MMT, while for EQ50MMT clumps of 1 - 4μm in dimension were observed. It is likely that this silicate dispersion morphology would also be present for the more concentrated 3w% loadings. Ultimate mechanical properties were similar in all test materials compared with the PEU controls, although there was a trend for co- modified materials to have slightly lower strength than controls. Elastic modulus data suggests that while there was no significant difference between test and controls, a similar trend of lower modulus in the co-modified variants occurred (Figures 9 and 10).

Figure 11 shows the results of the antibacterial assay. It was observed that an increase in the EQ fraction caused an increase in antibacterial activity against S. epidermidis. The AUA only variant (EQO loading), showed no inhibition of bacterial growth compared with the PEU control (ratio of 1) suggesting that AUA had no antibacterial effect. No effect of increasing the load of particles from 1 to 3w% was observed. Figure 12 shows the results from the mammalian cell growth studies.

PEU-EQOMMT (AUA only) material extracts had no effect on mammalian cell growth, whereas the PEU-EQ IOOMMT (EQ only) material negatively affected cell growth, reducing cell growth to <60% of control PEU. The two mechanisms by which the

EQ loading was increased in the composite material were by increasing the nanoparticle loading and by increasing the fraction of EQ on each nanoparticle. As the EQ loading on the silicate increased from 0%CEC to 100%CEC in the composite or as the particle loading increased from lw% to 3w%, the cell growth tended to decrease compared with controls. For the lw% loadings, materials with EQ loading up to 75% CEC did not cause unacceptable levels of cell growth inhibition. For the 3w% loadings, materials with EQ loading up to 50% CEC did not cause unacceptable levels of cell growth inhibition.

Although the co-modified nanocomposites had lower dispersion than their singly modified counterparts, co-modification was shown to be a viable means of modulating bacterial and host response to a biomaterial. It is considered that other organic modifiers may be able to be used to achieve both dispersion and antibacterial activity. Conclusions

The results of this study demonstrate that silicate co-modification is a potential means of controlling the host response to biomaterials. Polymers with EQ loading of up to 75% CEC were shown to maintain antibacterial activity and have acceptable cell growth inhibition levels, suggesting that this approach is a promising one for producing a biocompatible, antibacterial material.

Embodiment C: Polyurethane organosilicate nanocomposites for antibacterial drug delivery in urinary tract biomaterials The urinary system maintains homeostasis by controlling blood composition and volume. In situations where obstruction of the ureter(s) or urethra is evident, stents or catheters are utilised as a temporary or permanent solution. Significant problems associated with the current use of these devices are biofilm formation and encrustation, as the polymers commonly used for urinary device manufacturing are prone to bacterial colonisation. It is therefore necessary to develop materials with improved antibacterial properties. The inventors have previously shown that antibacterial polyurethanes (PU) based on quaternary ammonium compounds can be produced via the nanocomposite route. The present work aims to achieve this through the use of PU nanocomposites loaded with the antimicrobials chlorhexidine diacetate and polyhexamethylene biguanide (PHMB). It is hypothesised that controlled and sustained release of these antimicrobials can be obtained by the barrier effect created by the presence of nanoparticles dispersed within the material. Materials and Methods: Montmorillonite (MMT) was organically modified with chlorhexidine diacetate or PHMB, and co-modified with the antimicrobials and aminoundecanoic acid (AUA), to facilitate silicate dispersion. Subsequently, nanocomposites of a polyether PU (Urethane Compounds, 80A) and the organically modified layered silicates (OMS) were prepared by solvent casting. X-Ray Diffraction (XRD) (Siemens D5000) was used to analyse the silicate spacing within the nanocomposites, and Thermogravimetric Analysis (TGA) and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectrometry were used to determine successful organic modification of the MMT. Antibacterial assays were conducted to determine interactions using Staphylococcus epidermidis. Results and Discussion: ATR-FTIR and TGA results showed successful organic modification of MMT. XRD results suggest that greater silicate spacing within the polyurethane nanocomposites were obtained when compared to the modified silicates themselves, suggesting that their interaction with polyurethane aids with dispersion. Silicates modified using chlorhexidine diacetate had the greatest average distance between silicate layers relative to those modified with PHMB and AUA. Both PHMB and chlorhexidine diacetate were shown to be effective against S. epidermidis when nanocomposites were tested on lawn plates. Given the superior dispersion and antibacterial activity observed with nanocomposites based on chlorhexidine diacetate modified MMT, further studies will be pursued to examine biofilm formation and encrustation under static and dynamic conditions. Embodiment D: Polyurethane Nanocomposite Biomaterials: Improvement of Dispersion and Preliminary Fibroblast and Platelet Interaction

The addition of organosilicate to polymer matrices over the past decade has received growing attention due the resulting improvement in the materials mechanical properties. While there is much research continuing to improve these and other material properties, there has been little research into the use of polymer nanocomposites (NCs) as biomaterials. The focus of the present work is improvement of silicate dispersion via use of organic modifiers with different chemistries and evaluation of the resulting blood compatibility of these organosilicate nanocomposites. Specifically, NCs based on poly(ether)urethane (PEU) and organically modified montmorillonite (MMT) have been studied. The specific aims of the research are to (A) determine the effect on silicate dispersion of using bifunctional organic modifiers (amine and acid terminal groups) versus organic modifiers with a single amine functional group and (B) to evaluate in vitro interactions of fibroblasts and platelets with the NCs prepared. NCs were prepared using PEU (Urethane Compounds, 80A), and two silicates organically modified (OMS) using either dodecylamine (MMTl 2CH3) or aminododecanoic acid (MMT12COOH). NCs were produced via solvent casting. OMS were analysed by thermogravimetric analysis (TGA) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). To determine the basal spacing of OMS and PEU/OMS NCs X-ray diffraction (XRD) was used. Preliminary fibroblast and platelet interaction studies were also conducted.

TGA and ATR-FTIR analysis showed that MMT was successfully modified. XRD determined that MMT12CH3 and MMT12COOH had basal spacings of 1.41 and 1.40nm respectively an increase from MMT basal spacing of 1.23nm. XRD analysis of the PEU/OMS NCs of various OMS loadings showed that PEU-MMTl 2CH3 NCs have increased basal spacing as compared to the PEU-MMT12COOH NCs. Preliminary results on fibroblast interaction with the NCs showed that there was a decrease in fibroblast attachment on PEU-MMTl 2CH3 as compared to fibroblast attachment on the control PEU5 whereas the PEU-MMTl 2COOH showed an increase in cell attachment compared to the control. Preliminary platelet attachment results showed a similar trend in platelet attachment to that found for fibroblast attachment. Given that cell growth inhibition studies have previously shown that similar molecules to 12COOH are non-cytotoxic, these results suggest that modulation of blood interactions without compromising cell viability will be possible with these new materials. Application experiments

1. In Vitro urinary Tract Model

The aim of this experiment was to determine the number of days that nanocomposite materials, loaded with various amounts of Chlorhexidine Diacetate (CHX), can remain free from infection and biofilm formation in the presence of S. Epidermidis (ATCC 35983) within an in vitro urinary tract (UT) model that was developed by Gaonkar et al. [Gaonkar TA, Sampath LA, Modak SM, 2003, "Evaluation of the Antimicrobial Efficacy or Urinary Catheters Impregnated with Antiseptics in an In Vitro Urinary Tract Model", Infection Control and Hospital Epidemiology, Vol. 24, No. 27, pp 506-13]. A further aim was to investigate the release of Chlorhexidine Diacetate (CHX) from nanocomposites.

The nanocomposite materials, initially cast as thin films, were formed into tubes (approx. 16F diameter, 60mm long) and positioned within the UT model, [hi the present context, "F" (in "16F") refers french gauge, which is a system that defines the external diameter of tubing. One FG = 0.33mm OD.] In particular, materials investigated in this experiment were loaded with lwt% and 5wt% nanoparticles of 110%CEC, 200%CEC and 300%CEC CHX-modifed MMT (CHXMMT), and lwt% and 5wt% 110%CEC CHXMMT materials with an additional lwt% and 2wt% of free-CHX. The UT model was constructed using two tubes. The base of the first tube was removed to form a cylinder representing the urethra, and the second tube was attached to the base of this cylinder as a collecting tube. Within the "urethra", sample materials were centrally positioned and a column of 6.5mL Modified Trypticase Soy Agar (TSA) was poured around the sample, leaving approximately lcm segments protruding from each end of the agar column. The upper part of the cylinder was then filled with 2.5mL artificial urine media (AUM) to represent the bladder, and the bottom surface of the agar column, representing the meatus, was inoculated with 20 μL of 107 CFU/ml of S. epidermidis. Each day, the "meatus" was re-inoculated and fresh AUM was used to refill the "bladder". To determine infection, the AUM was subculrured daily.

Spectrophotometer measurements taken at 254nm were used to determine the initial levels of CHX within the nanocomposite materials, as well as the remaining levels of CHX after infection of the AUM was detected in the in vitro urinary tract model. Daily levels were also assessed in a similar fashion for a period of 7 days. For the measurement of initial and final levels of CHX in the materials, lcm segments of 16F diameter tubes of the test materials were placed in test tubes, immersed in 2mL methylene chloride and vortexed every 5 minutes over 20 minutes. 2mL of 50% reagent alcohol was then added to the test tubes, and again vortexed every 5 minutes over 20 minutes. The final solution was centrifuged at 3400rmp for 7 minutes and the upper layer, containing the CHX, was used to spectrophotometrically determine the concentration of the antimicrobial. For the investigation of daily CHX release, the material segments were immersed in 2mL 0.9% saline and subsequently removed at the appropriate times for CHX measurement. The saline was then processed using a similar method as described for the determination of initial and final CHX levels.

Results from the UT model indicated that control materials of neat polyurethane and materials loaded with 1% and 5% MMT became infected within 2 days of inoculation with S. Epidermidis. Materials consisting of lower loadings of CHX - lwt% and 5wt% 110%CEC CHXMMT, lwt% 200%CEC CHXMMT and lwt% 300%CEC CHXMMT, showed bacterial growth in the AUM within 3 days. Materials with higher CHX loadings remained sterile for significantly longer periods of time: 5wt% 200%CEC CHXMMT materials were sterile for an average of 16.8 days, and the 5wt% 300%CEC CHXMMT materials were sterile for an average of 13.4 days. Nanocomposites including added free- CHX remained sterile for even longer periods, remaining uninfected for over 20 days for the lwt% free-CHX materials, and over 30 days for the 2wt% free-CHX materials. These results indicate that nanocomposites with CHX loadings greater than 5% 200%CEC CHXMMT, particularly those with added free-CHX, are effective in the prevention of infection within the in vitro UT model for up to, and over, 30 days.

Spectrophotometric measurements of the initial levels of CHX in the material samples showed comparable results to those obtained from TGA. Post-UT model materials indicated that up to 80% of the available CHX was released from the samples before infection of the AUM in the UT model was detected. 2. Cell adhesion tests

The following are results obtained from fibroblast interaction with the nanocomposite materials to assess cell adhesion to the test nanocomposite materials and cell growth inhibition due to exposure to the test nanocomposite material extracts. Along with results obtained from the fibroblast interaction, surface analysis of the nanocomposite materials suggests the resulting decrease cellular attachment is associated with surface expression of montmorillonite and modification compounds on certain nanocomposite materials. Fibroblast Attachment and Cell Growth Inhibition

The aim of this experiment was to assess the fibroblast interaction with the fabricated nanocomposite materials.

The nanocomposites were fabricated by solvent casting. Two separate groups of nanocomposites were fabricated and analysed by fibroblast attachment assay. The two groups contained the following materials:

1. Carbon Chain Length

The materials that were tested included the base polyurethane, polyurethane loaded with 1% un-modified montmorillonite and polyurethane loaded with 1% montmorillonite modified with the following compounds:

• Octylamine (8CH3)

• Dodecylamine (12CH3)

• Tetradecylamine (14CH3)

• Hexadecylamine (16CH3) • Octadecylamine (18CH3)

2. Terminal Functional Group

The materials that were tested included the base polyurethane, polyurethane loaded with 1% and 3% un-modified montmorillonite and polyurethane loaded with 1% and 3% montmorillonite modified with the following compounds: • Aminododecanoic Acid (12COOH)

• Dodecylamine (12CH3) Experimental Methods Fibroblast Attachment

Fibroblast interaction with the nanocomposite materials was investigated by seeding murine fibroblasts (NIH3T3) transfected with green fluorescent protein (GFP) onto the test materials. Cells were grown in Dulbecco's modified eagles medium (DMEM) which was supplemented with 10% foetal bovine serum (FBS) and 2% penicillin / streptomycin. Cells were seeded onto washed and EtO sterilised materials at a density of 50,000 cells/mL and incubated (5% CO2, 37°C) for 24 and 72 hour periods. Fibroblasts on the surface of materials were counted following imaging by fluorescent microscopy. Cell Growth Inhibition

Cell growth inhibition with the nanocomposite materials was investigated by exposing mouse fibroblasts (L929) to test material extracts. Test materials were placed into glass extraction vials to which eagle's minimum essential medium (EMEM, supplemented with 10% foetal bovine serum (FBS) and 2% penicillin / streptomycin) was added and incubated ((5% CO2, 37°C) for 24 hours. Cells were seeded onto tissue culture wells and after 24 hours the old media was aspirated off and replaced with media containing test material extracts, cells there then incubated for a further 48 hours. The number of cells exposed to media extracts was determined via the use of a coulter counter and cell growth inhibition as compared to the base polyurethane was determined. Results

Fibroblast adhesion results show when comparing the terminal functional group

(Fig. 13) there is not a significant difference in the number of fibroblasts that adhere to the base polyurethane and the nanocomposite materials that contain 1% and 3% of both unmodified niontmorillonite and montmorillonite modified with aminododecanoic acid.

There was a significant reduction in the number of fibroblasts adhering to the nanocomposite materials that contained 1% and 3% loading of montmorillonite modified with dodecylamine. The results showed when comparing the length of the carbon chain (Fig. 14), base polyurethane, and the nanocomposite materials containing unmodified montmorillonite and montmorillonite modified with octylamine showed no significant difference in the number of fibroblasts that adhered to the materials. The remaining nanocomposite materials, that contained montmorillonite modified with modification compounds with a carbon chain length of twelve units or more, showed a significant decrease in the number of fibroblasts that adhered to the test materials.

Cell growth inhibition results show that for polyurethane nanocomposites containing a 1% loading of modified montmorillonite (all modifications that were tested, Fig. 15 and Fig. 16) the materials were not cytotoxic. Comparing the % loading of nanocomposite, as the loading was increased the level of cell inhibition was also increased due to the increased concentration of organic modifier that was present. Surface Analysis

Time of flight secondary ion mass spectrometry (ToF-Sims) was used to analyse the surface of the nanocomposite materials. Two separate groups of nanocomposites were fabricated and analysed ToF-Sims. The two groups contained the following materials: 1. Carbon Chain Length

The materials that were tested included the base polyurethane, polyurethane loaded with 1% un-modified montmorillonite and polyurethane loaded with 1% montmorillonite modified with the following compounds:

• Octylamine (8CH3) • Dodecylamine (12CH3)

• Tetradecylamine (14CH3)

• Hexadecylamine (16CH3)

• Octadecylamine (18CH3) 2. Terminal Functional Group

The materials that were tested included the base polyurethane, polyurethane loaded with 1% and 3% un-modified montmorillonite and polyurethane loaded with 1% and 3% montmorillonite modified with the following compounds:

• Aminododecanoic Acid (12COOH) • Dodecylamine (12CH3)

Experimental Methods

All test materials were analysed by ToF-Sims and assessed for signs of ions associated with montmorillonite and the modification compounds being expressed on the surface of the materials. Results

Looking at the materials from the group looking at terminal functional group, the results showed that the nanocomposite that contained montmorillonite modified with dodecylamine showed ions present on the surface of the material that are associated with montmorillonite and the modification compound dodecylamine. The remaining nanocomposite materials, polyurethane loaded with unmodified montmorillonite and montmorillonite modified with aminododecanoic acid showed no signs ions associated with montmorillonite or the modification compound aminododecanoic acid. These results suggest that the presence of montmorillonite is associated with the modification compound. ToF-Sims analysis of the materials consisting of the carbon chain length set showed presence of ions associated with montmorillonite on the surface of nanocomposite materials contain montmorillonite modified with dodecylamine, tetradecylamine, hexadecylamine and octadecylamine. Ions associated with the modification compounds was only shown on the material containing montmorillonite modified with dodecylamine, due to the molecular weight tetradecylamine, hexadecylamine and octadecylamine being too large to be detected. Analysis of the nanocomposite materials that contained unmodified montmorillonite and montmorillonite modified with octylamine showed that ions associated with montmorillonite or octylamine were not present on the surface of the materials. The results obtained from ToF-Sims analysis of the materials supports the results obtain from the fibroblast adhesion to the nanocomposite materials, where materials that showed a significant decrease in fibroblast attachment showed the presence of ions associated with montmorillonite and where the molecular weight was at a detectable level, ions associated with the compound used to modify montmorillonite. Suggesting surface expression of the modification compound alters fibroblast adhesion to the nanocomposite materials.

Claims

Claims:
1. A nanocomposite comprising an active substance, said nanocomposite comprising:
• a polymer matrix; • a nanoparticulate filler dispersed through said polymer matrix; and
• a dispersant for aiding dispersion of the filler in the matrix; wherein:
• the active substance is the dispersant, and the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite, or • the active substance is not the dispersant but is associated with the filler or with the dispersant or with both the filler and the dispersant, and the polymer matrix and the filler are such that the active substance is releasable from the nanocomposite, or
• the active substance is the filler, and the polymer matrix is such that the active substance is releasable from the nanocomposite.
2. A nanocomposite comprising at least two active substances, said nanocomposite comprising:
• a polymer matrix, wherein said matrix is not a hydrogel;
• a nanoparticulate filler dispersed through said polymer matrix; and • a dispersant for aiding dispersion of the filler in the matrix; wherein the polymer matrix and the filler are such that the active substances are releasable from the nanocomposite.
3. The nanocomposite of claim 1 or claim 2 wherein the active substance is the dispersant.
4. The nanocomposite of claim 1 or claim 2 wherein the active substance is not the dispersant but is associated with the filler or with the dispersant or with both the filler and the dispersant.
5. The nanocomposite of claim 1 or claim 2 wherein the active substance is the particulate filler.
6. The nanocomposite of any one of claims 1 to 5 wherein the dispersant is chlorhexidine or 1-aminoundecanoic acid or Ethoquad® O/12PG.
7. The nanocomposite of any one of claims 1 to 6 wherein the dispersant is a surfactant.
8. The nanocomposite of any one of claims 1 to 7 wherein the polymer matrix is not a hydrogel.
9. The nanocomposite of any one of claims 1 to 8 wherein the polymer matrix has a low water content.
10. The nanocomposite of any one of claims 1 to 9 wherein the polymer matrix has a water content of less than about 10% by weight.
11. The nanocomposite of any one of claims 1 to 10 wherein the polymer matrix is an elastomer.
12. The nanocomposite of any one of claims 1 to 11 wherein the polymer matrix is a polyurethane.
13. The nanocomposite of claim 12 wherein the polyurethane is a polyetherurethane.
14. The nanocomposite of any one of claims 1 to 13 wherein the nanoparticulate filler is intercalated.
15. The nanocomposite of any one of claims 1 to 13 wherein the nanoparticulate filler is exfoliated.
16. The nanocomposite of any one of claims 1 to 15 wherein the filler comprises nanoparticles having an aspect ratio of at least about 100.
17. The nanocomposite of any one of claims 1 to 15 wherein the filler comprises nanoparticles having an aspect ratio of between about 1 and about 10.
18. The nanocomposite of any one of claims 1 to 17 wherein the filler is an inorganic filler.
19. The nanocomposite of any one of claims 1 to 17 wherein the filler is an organic filler.
20. The nanocomposite of any one of claims 1 to 16 or 18 wherein the filler comprises montmorillonite.
21. The nanocomposite of any one of claims 1 to 16 wherein the filler comprises carbon nanotubes.
22. The nanocomposite of any one of claims 1 to 21 wherein the filler is present in the nanocomposite at a level of between about 0.1 and about 10% by weight.
23. The nanocomposite of any one of claims 1 to 22 wherein the nanoparticulate filler causes a release inhibition (as defined herein) of up to about 95%.
24. The nanocomposite of any one of claims 1 to 23 wherein the active substance is a drug.
25. The nanocomposite of claim 24 wherein the drug is an antibiotic, an antithrombotic agent or an anticancer drug.
26. The nanocomposite of any one of claims 1 to 25 wherein the active substance is present in the nanocomposite at a level of at least about 0.1%.
27. The nanocomposite of any one of claims 1 to 26 wherein the active substance is releasable from the nanocomposite over a period of at least one week.
28. An article for direct or indirect contact with body fluids and/or tissues, said article compήsing a nanocomposite of any one of claims 1 to 21.
29. Use of a nanocomposite according to any one of claims 1 to 28 for the fabrication of an article for direct or indirect contact with body fluids and/or tissues.
30. Use of an article according to claim 28 for a purpose selected from prevention of blood clotting, treatment of heart disease, treatment or prevention of an infection and treatment or prevention of cancer.
31. A method of treating or preventing a condition in a patient comprising the step of implanting an article according to claim 28 into said patient, wherein the active substance is indicated for said treatment or prevention.
32. A method of delivering an active substance comprising exposing an article according to claim 28 to a medium capable of releasing the active substance therefrom.
33. The nanocomposite of claim 1 wherein the polymer matrix comprises a polyetherurethane and the active substance is an antimicrobial agent and the concentration of the active substance in the polymer matrix is such that the nanocomposite resists growth of microbes on the surface thereof for at least 2 days.
34. The nanocomposite of claim 33 wherein the active substance is chlorhexidine or a salt thereof.
35. An article for implantation into a patient, said article comprising the nanocomposite of claim 33 or claim 34.
36. The article of claim 35, said article being an artificial portion of a urinary tract.
37. The nanocomposite of claim 1 wherein the polymer matrix comprises a polyetherurethane and the active substance is a substance for reducing surface cell adhesion, and concentration of the active substance in the polymer matrix is such that the nanocomposite shows a reduction in fibroblast adhesion relative to a nanocomposite having the same composition except for the absence of the active substance.
38. The nanocomposite of claim 37 wherein the active substance is montmorillonite modified with an alkylamine having at least 12 carbon atoms.
39. The nanocomposite of claim 38 wherein the alkylamine is C12, C14, C16 or Cl 8 alkylamine.
40. The nanocomposite of any one of claims 37 to 39 wherein the reduction in fibroblast adhesion is at least about 95% after about 72 hours.
41. An article for implantation into a patient comprising the nanocomposite of any one of claims 37 to 40.
42. The article of claim 41 wherein the entire external surface of said article comprises said nanocomposite.
43. The article of any one of claims 35, 36, 41 or 42 wherein the concentration of the active substance is between about 1 and about 5% by weight.
PCT/AU2008/000493 2007-04-04 2008-04-04 Nanocomposites WO2008122085A1 (en)

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