WO2018082722A1 - Polymeric thermoplastic biodegradable composition for production of inserts for treatment and prevention of local infections and a method of preparation thereof - Google Patents
Polymeric thermoplastic biodegradable composition for production of inserts for treatment and prevention of local infections and a method of preparation thereof Download PDFInfo
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- WO2018082722A1 WO2018082722A1 PCT/CZ2017/050052 CZ2017050052W WO2018082722A1 WO 2018082722 A1 WO2018082722 A1 WO 2018082722A1 CZ 2017050052 W CZ2017050052 W CZ 2017050052W WO 2018082722 A1 WO2018082722 A1 WO 2018082722A1
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- starch
- antibiotic
- esterified
- maltodextrin
- mixture
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K9/00—Medicinal preparations characterised by special physical form
- A61K9/0012—Galenical forms characterised by the site of application
- A61K9/0019—Injectable compositions; Intramuscular, intravenous, arterial, subcutaneous administration; Compositions to be administered through the skin in an invasive manner
- A61K9/0024—Solid, semi-solid or solidifying implants, which are implanted or injected in body tissue
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K47/00—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
- A61K47/30—Macromolecular organic or inorganic compounds, e.g. inorganic polyphosphates
- A61K47/34—Macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polyesters, polyamino acids, polysiloxanes, polyphosphazines, copolymers of polyalkylene glycol or poloxamers
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K47/00—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
- A61K47/30—Macromolecular organic or inorganic compounds, e.g. inorganic polyphosphates
- A61K47/36—Polysaccharides; Derivatives thereof, e.g. gums, starch, alginate, dextrin, hyaluronic acid, chitosan, inulin, agar or pectin
Definitions
- Polymeric thermoplastic biodegradable composition for production of inserts for treatment and prevention of local infections and a method of preparation thereof
- the invention relates to a polymeric thermoplastic biodegradable composition for the production of temporary inserts for the treatment and prevention of local infections in human and veterinary medicine.
- thermoplastic compositions of the present invention are designed to be suitable for applications complying with these trends.
- thermoplastic compositions according to the present invention may be useful in at least three fields of the current clinical practice: (i) a treatment and prevention of infections of joint replacements, (ii) a treatment of infections in various parts of the skeleton (ostheomyelitis of any known ethiology, pyogenic inflammations of joints and soft tissues), and (iii) a treatment of local infections in any other anatomical regions of the organism.
- the state-of-art treatment of deep infections of alloplastic implants is based on a two-step revision, wherein the first step is the extraction of the endoprosthesis, and the second step is the reimplantation taking place after the period necessary for infection healing.
- a temporary articulation insert a so-called intuitional spacer
- the main purpose of the spacer is to fix the necessary space taken up by the original anatomic joint for future reimplantation of joint replacement and to improve the function of the limb during the treatment of the infection.
- the spacer is made of cement filled with an antibiotic, it acts as a system locally releasing the antibiotic.
- Vancomycin, gentamicin, clindamycin or combinations thereof are applied for impregnation of the bone cement material.
- Antibiotic-impregnated spacers are manufactured from the cements either directly during the surgery or they are factory-made.
- the time course of antibiotics release from bone cement, which is a composite based on poly(methyl methacrylate) (PMMA) is often not compliant with the requirements of infection treatment.
- PMMA poly(methyl methacrylate)
- post-surgery infections of locomotor system represent a problem which requires removal of necrosing tissues, filling of the resulting dead space, and an adequate local and systemic treatment of the infection.
- the filling of the dead space may be done using the said PMMA-based composite with all the above-mentioned drawbacks, or the said fibrin foam which is too soft and releases the medicament too quickly due to its large surface.
- the treatment of the infection thus currently involves administering large doses of antibiotics, often of specific combinations of antibiotics, in the largest possible dose tolerable by the patient's organism. Another problem is caused by the fact that the distribution of an antibiotic into living tissues is limited under pathologic conditions.
- the PMMA-based and the fibrin-foam-based materials are characterized by unsuitable mechanical properties as well as by non-controllability of the medicament release rate.
- poly-8-caprolactone is well tolerated by living tissues and biodegradable. These properties predetermine poly- ⁇ - caprolactone for medical applications.
- Poly-8-caprolactone is employed in producing scaffolds for tissue engineering (an average time of poly-8-caprolactone resorption is 24 months [Gunatillake PA, Adhikari R. Biodegradable synthetic polymers for tissue engineering. Eur Cells Mater 2003;5: 1-16]), as well as a carrier for various drugs.
- thermoplastic compositions according to the invention are destined for direct insertion to the location of infection, but the release rate of the antibiotic can be controlled by the composition and the morphology of the thermoplastic composition.
- Antibiotics commonly used in clinical practice are generally very effective in the treatment of infections, if a sufficient local concentration is achieved. Achieving a high local concentration by systemic administration is impossible.
- An advantage of the thermoplastic composition according to the present invention resides in that the antibiotic is released locally, thus achieving a high local composition in the specific place, while avoiding the risk of systemic intoxication.
- the invention is based on the surprising experimental finding that thermoplastic heterogenous mixture of starch or starch ester and poly-8-caprolactone releases an antibiotic contained in the starch component, even when the starch component is discrete or semi- continuous phase of the mixture, and thus not in direct contact with the surrounding medium. It was further discovered that the antibiotic release rate can be effectively controlled by adjusting the ratio of the components in the mixture, the morphology of the mixture and/or esterification of the starch component.
- a plastified polysaccharide component which is at least one plastified polysaccharide selected from starch, a mixture of starch and maltodextrin, esterified starch, and a mixture of esterified starch and esterified maltodextrin, wherein maltodextrin is a mixture of oligosaccharides having the dextrose equivalent of at most 25, whereas the polysaccharide component further contains an antibiotic, and
- polyester component which is poly-8-caprolactone and/or poly[(8-caprolactam)-co-(8- caprolactone)] containing at least 10 % of crystalline phase and having the crystalline phase melting temperature lower than 65 °C,
- the mixture of components (a) and (b) is heterogenous.
- the component (b) is always continuous.
- the component (a) can be in the form of discrete particles dispersed in component (b) matrix.
- the component (a) can be continuous, and the morphology of the materials as a whole then corresponds to interpenetrating matrices of components (a) and (b), i.e., irregularly alternating regions of component (a) and component (b).
- the continuous phase of the composition is poly-8-caprolactone and/or poly[(8- caprolactam)-co-(8-caprolactone)] with the crystalline phase melting temperature lower than 65 °C.
- the low crystalline phase melting temperature of the polyester component of the composition is important for the direct shaping of the material during the surgery according to the individual needs.
- the starch component can be plastified during its processing.
- the term tauplastification means a process during which the grains of the native starch disintegrate as a result of increased temperature, shear forces, absorbed air humidity, and optionally added plastifier; the amylase crystalline phase melts and a homogenous amorphous mixture of amylose and amylopectin is formed.
- Esters of starch and maltodextrin are thermoplastic and amorphous and are thus always plastified when undergoing processing at a temperature above the glass transition temperature, T g .
- the temperatures T g can be found in reference literature or determined by known methods, e.g. by calorimetry (DSC).
- Rheological properties of the plastified starch are determined by its molecular parameters. Rheological properties of the polysaccharide component can be effectively controlled within a broad range by the incorporation of maltodextrin which is a starch oligomer. Furthermore, rheological properties of the polysaccharide phase of the mixture can be controlled by incorporation of further plastifiers, in order to form a finer structure of the heterogenous mixture with a larger interphase surface.
- a preferred plastifier of starch is glycerol which can optionally be combined with polyvinyl alcohol.
- Preferred plastifiers for starch esters are glycerol acetates or propionates or citric acid ethyl esters.
- Weight ratio of plastifiers to the total content of starch, maltodextrin, esterified starch and esterified maltodextrin in the composition according to the present invention is preferably between 1:20 and 1: 1.5.
- Interaction between the antibiotic and the starch component is determined predominantly by the chemical nature of the starch component. Esterification of starch by acetic, propionic or butyric acid is advantageous.
- solvents capable of dissolving the antibiotics as well as starch or starch esters, respectively.
- the solvents should have a high boiling point; thus they correspond to starch plastifiers or starch softeners.
- morphology of the mixture and thus the interphase surface of the mixture can be optimized so that the antibiotic migrates from the starch phase of the composition into the surrounding tissue at a desired rate.
- biocompatible Ti0 2 -based nanoparticles can be added into the composition to moderately affect mechanical and rheological properties of the components, morphology, and to affect the antibiotic release rate.
- Biocompatible Ti0 2 particles affecting the final mechanical properties, the rheology of the components, the morphology of the mixture and thus the antibiotic release rate may be isometric micro- or nanoparticles of titanium dioxidide having the size of 0.01 to 10 ⁇ , or titanate nanotubes (TiNT) having the mean diameter of at most 40 nm and aspect ratio width:length at least 10, as described in the patent document CZ 302299 B6.
- TiNT titanate nanotubes
- Mass ratio of Ti0 2 -based nanoparticles and/or titanate nanotubes with respect to the total amount of starch, maltodextrin, esterified starch and esterified maltodextrin is 1:20 to 1:2.
- the antibiotic is at least one antibiotic selected from the group comprising cyclins, aminoglycosidic and glycopeptidic antibiotics, and is present in the amount of 2 to 20 wt. %, relative to the total weight of the mixture; preferably the antibiotic is selected from tetracycline, gentamicine and vancomycine.
- the object of the invention is also a method of preparation of the thermoplastic biodegradable composition, comprising the steps of
- step (b) melt-mixing of the mixture obtained in step (a) with poly-8-caprolactone and/or poly[(s- caprolactam)-co-(8-caprolactone)] containing at least 10 % of crystalline phase and having the crystalline phase melting temperature lower than 65 °C.
- the plastification conditions include melt-mixing (i.e., shear force) and heating above 60 °C or above T g of the polysaccharide material.
- the starch and/or starch and maltodextrin mixture and/or esterified starch and/or esterified starch and esterified maltodextrin mixture is mixed with the antibiotic and with a plastifier selected from the group comprising polyvinyl alcohol, glycerol, glycerol acetates, glycerol propionates, citric acid ethyl esters.
- a plastifier selected from the group comprising polyvinyl alcohol, glycerol, glycerol acetates, glycerol propionates, citric acid ethyl esters.
- TPS thermoplastified starch
- PCL poly(8-caprolactone)
- ATB vancomycin.
- the SEM samples were prepared by cutting and smooting in liquid nitrogen, followed by etching the starch phase.
- the micrographs show that the morphology can be controlled by the composition which changes the structure of the TPS phase from continuous (a), through partly continuous (b) to particulate or discrete (c).
- the starting substances were wheat starch type A (Soltex NP1; producer: Amylon a.s., Czech Republic) and poly(8-caprolactone) (Capa 6800; producer: Perstorp, Sweden) and the antibiotic vancomycin (Vancomycin Mylan; producer: Biologici Italia).
- a mixture of plastified starch with vancomycin was prepared: the starch was pre-mixed with glycerol in weight ratio 7:3 at room temperature and subsequenently mixed with a vancomycin aqueous solution. This mixture was plastified at 85 °C and then dried. The resulting mixture had weight ratio TPS vancomycin equal to 63: 10.
- the final composition TPS/PCL/ATB was prepared by melt-mixing in a twin-screw microextruder at 120 rpm and temperature 110 °C. The ratio of components in the resulting composition TPS/PCL/ATB was 63/27/10.
- TPS thermoplastic starch
- PCL poly(8-caprolactone)
- ATB vancomycin antibiotic
- TPS thermoplastic starch
- PCL poly(8-caprolactone)
- ATB antibiotic vancomycin
- the starting substances were wheat starch type A (Soltex NP1; producer: Amylon a.s., Czech Republic) acetylated to the degree of substitution 2,8 and poly(8-caprolactone) (Capa 6800; producer: Perstorp, Sweden) and the antibiotic vancomycin (Vancomycin Mylan; producer: Biologici Italia).
- acetylated starch with vancomycin was prepared.
- the powdered acetylated starch was pre-mixed with triethyl citrate in weight ratio 7:3 at room temperature, and subsequenently mixed with vancomycin acetone solution. This mixture was dried to remove acetone and plastified at 110 °C for 7 minutes in laboratory kneader. The resulting mixture had weight ratio TPS: vancomycin 63: 10.
- the final composition ATPS 1/PCL/ATB was prepared by melt-mixing in twin-screew microextruder at 120 rpm and temperature 110 °C.
- the antibiotic release rate was determined in the same manner as in Examples 1-3, it had logarithmic character, but it was significantly slower than for the composition of Example 2. The times corresponding to the release of 25%, 50% and 75% of vancomycin are shown in Table 2. After 30 days, when the experiment ended, 58% of vancomycin was released.
- the antibiotic release rate was determined in the same manner as in Examples 1-4, it had logarithmic shape, and it was significantly slower in comparison with the system in Example 2. The times corresponding to the release of 25%, 50% and 75% of vancomycin are shown in Table 2. After 30 days, when the experiment ended, 62% of vancomycin was released.
- TPS thermoplastic starch
- PCL poly(8-caprolactone)
- TiNT titanate nanotubes
- ATB 1 antibiotic vancomycin
- TPS thermoplastic starch
- PCL poly(8-caprolactone)
- TiNT titanate nanotubes
- ATB2 antibiotic tetracyclin
- the release rate of the antibiotics in polymeric systems comprising various components according to the invention was measured.
- TPS thermoplastified starch
- PCL poly(8-caprolactone)
- ATB vancomycin or tetracyclin
- SBF simulated body fluid containing in particular Na + and CI " ions together with other salts in physiological concentrations in aqueous solutions
- P.N. Chavan, M. M. Bahir, R. U. Mene, M. P. Mahabole, R. S. Khairnar Study of nanobiomaterial hydroxyapatite in simulated body fluid: Formation and growth of apatite.
- the concentration of the released antibiotic was determined by means of UV/VIS spectroscopy based on the previously established calibration curve.
- Table 1 The antibiotic release rate as a function of the composition of the polymeric systems TPS/PCL/ATB according to the invention, wherein TPS is thermoplastified starch, PCL is poly(8-caprolactone) and ATB is vancomycin.
- TPS thermoplastified starch
- PCL poly(8-caprolactone)
- ATB vancomycin
- TPS thermoplastified starch
- PCL poly(s- caprolactone)
- ATB vancomycin
- ATB2 tetracyclin
- TiNT titanate nanotubes having the diameter of 20 nm and the aspect ratio (width: length) more than 50.
- the lines of the table correspond to examples 6 and 7.
- Thermoplastic biodegradable polymeric composition for the production of temporary inserts designed for the treatment and prevention of local infections of skeleton or other anatomical structures, in human as well as veterinary medicine.
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Abstract
The invention provides a polymeric thermoplastic biodegradable composition incorporating an antibiotic, in particular for production of inserts for the treatment and prevention of local infections, consisting of (a) at least one plastified polysaccharide component, which is selected from starch, a mixture of starch and maltodextrin, esterified starch, and a mixture of esterified starch and esterified maltodextrin, wherein maltodextrin is a mixture of oligosaccharides having the dextrose equivalent of at most 25, whereas the polysaccharide component further contains an antibiotic, and (b) a polyester component which is poly-ε-caprolactone and/or poly[(ε-caprolactam)-co-(ε-caprolactone)] containing at least 10 % of crystalline phase and having the crystalline phase melting temperature lower than 65 °C, in the weight ratio (a):(b) in the range of 4:1 to 1:9. Additionally, method of preparation of such composition is described.
Description
Polymeric thermoplastic biodegradable composition for production of inserts for treatment and prevention of local infections and a method of preparation thereof
Field of Art
The invention relates to a polymeric thermoplastic biodegradable composition for the production of temporary inserts for the treatment and prevention of local infections in human and veterinary medicine. Background Art
Systems with controlled local release of an active components represent a modern trend in current human and veterinary medicine. They offer a number of advantages over classical pharmaceutical treatments, in particular the possibility to administer lower doses of the active component directly in the target location, reduction of fluctuations of plasma levels of the active component, reduction of undesired side effects, and overall a lower burden for the patient's organism. Due to these advantages, many local release systems are currently being introduced into medical practice, including systems for local release of hormones, antiinflammatory agents, antibiotics and cytostatics. The thermoplastic compositions of the present invention are designed to be suitable for applications complying with these trends. The thermoplastic compositions according to the present invention may be useful in at least three fields of the current clinical practice: (i) a treatment and prevention of infections of joint replacements, (ii) a treatment of infections in various parts of the skeleton (ostheomyelitis of any known ethiology, pyogenic inflammations of joints and soft tissues), and (iii) a treatment of local infections in any other anatomical regions of the organism.
As regards the first field (the treatment and prevention of infections of joint replacements), the state-of-art treatment of deep infections of alloplastic implants is based on a two-step revision, wherein the first step is the extraction of the endoprosthesis, and the second step is the reimplantation taking place after the period necessary for infection healing. For spanning the period of time between the first and the second step, a temporary articulation insert, a so-called„spacer", made of bone cement, is applied. The main purpose of the spacer is to fix the necessary space taken up by the original anatomic joint for future reimplantation of joint replacement and to improve the function of the limb during the treatment of the
infection. When the spacer is made of cement filled with an antibiotic, it acts as a system locally releasing the antibiotic. Vancomycin, gentamicin, clindamycin or combinations thereof are applied for impregnation of the bone cement material. Antibiotic-impregnated spacers are manufactured from the cements either directly during the surgery or they are factory-made. The time course of antibiotics release from bone cement, which is a composite based on poly(methyl methacrylate) (PMMA), is often not compliant with the requirements of infection treatment. In the rather short time period immediately after the spacer application, the antibiotic from the surface layer of the materials is quickly released, and then the release of the antibiotic is significantly slowed down, almost stopped. However, it is highly desirable for the treatment of the infection that the antibiotic is continually released in a sufficient concentration into the tissues surrounding the spacer throughout the whole time period between the first and the second step of the reimplantation. A significant drawback of the currently used PMMA-based or fibrin-foam based spacer materials is insufficient control of the antibiotic release.
Regarding the second field (the treatment of infections in various parts of the skeleton such as ostheomyelitis of any known ethiology, or pyogenic inflammations of joints and soft tissues), post-surgery infections of locomotor system represent a problem which requires removal of necrosing tissues, filling of the resulting dead space, and an adequate local and systemic treatment of the infection. The filling of the dead space may be done using the said PMMA-based composite with all the above-mentioned drawbacks, or the said fibrin foam which is too soft and releases the medicament too quickly due to its large surface. The treatment of the infection thus currently involves administering large doses of antibiotics, often of specific combinations of antibiotics, in the largest possible dose tolerable by the patient's organism. Another problem is caused by the fact that the distribution of an antibiotic into living tissues is limited under pathologic conditions.
A similar situation exists in the third field(the treatment of local infections in any other anatomical regions of the organism). The PMMA-based and the fibrin-foam-based materials are characterized by unsuitable mechanical properties as well as by non-controllability of the medicament release rate.
One of possible materials for all above-mentioned applications is poly-8-caprolactone. It is well tolerated by living tissues and biodegradable. These properties predetermine poly-ε- caprolactone for medical applications. Poly-8-caprolactone is employed in producing
scaffolds for tissue engineering (an average time of poly-8-caprolactone resorption is 24 months [Gunatillake PA, Adhikari R. Biodegradable synthetic polymers for tissue engineering. Eur Cells Mater 2003;5: 1-16]), as well as a carrier for various drugs. Recently, numerous processes were published for production of drug carriers in the form of spherical micro- and nanoparticles. However, only a fraction of the published research results relates to treatment of local tissue infections. A predominant work is the article of Teo et al. [E.Y. Teo, S.Y. Ong, M.S. Chong, Z. Zhang, J. Lu, S. Moochhala, B. Ho, S.H. Teoh, Polycaprolactone -based fused deposition modeled mesh for delivery of antibacterial agents to infected wounds, Biomaterials 32 (1) (2011) 279-287], studying the effect of poly-ε- caprolactone/calcium phosphate composite-based scaffold with incorporated gentamicin sulfate on bacteria elimination and wound healing in mice.
Disclosure of the Invention The drawbacks of the materials currently used in the local infection treatment (i.e., in particular of PMMA-based or fibrin-foam-based bone cement) are eliminated by the thermoplastic compositions according to the invention. Similarly to PMMA and fibrin foam, the thermoplastic composition according to the invention is destined for direct insertion to the location of infection, but the release rate of the antibiotic can be controlled by the composition and the morphology of the thermoplastic composition. Antibiotics commonly used in clinical practice are generally very effective in the treatment of infections, if a sufficient local concentration is achieved. Achieving a high local concentration by systemic administration is impossible. An advantage of the thermoplastic composition according to the present invention resides in that the antibiotic is released locally, thus achieving a high local composition in the specific place, while avoiding the risk of systemic intoxication.
The invention is based on the surprising experimental finding that thermoplastic heterogenous mixture of starch or starch ester and poly-8-caprolactone releases an antibiotic contained in the starch component, even when the starch component is discrete or semi- continuous phase of the mixture, and thus not in direct contact with the surrounding medium. It was further discovered that the antibiotic release rate can be effectively controlled by adjusting the ratio of the components in the mixture, the morphology of the mixture and/or esterification of the starch component. These findings allow to prepare a
system for long-term dosing of an antibiotic into the surrounding living tissues in various anatomic regions of the organism, said system being prepared from heterogenous mixture of plastified starch or esterified starch, and polyester, poly-8-caprolactone -based component. The object of the invention is a polymeric thermoplastic biodegradable composition incorporating an antibiotic, consisting of
(a) a plastified polysaccharide component, which is at least one plastified polysaccharide selected from starch, a mixture of starch and maltodextrin, esterified starch, and a mixture of esterified starch and esterified maltodextrin, wherein maltodextrin is a mixture of oligosaccharides having the dextrose equivalent of at most 25, whereas the polysaccharide component further contains an antibiotic, and
(b) a polyester component which is poly-8-caprolactone and/or poly[(8-caprolactam)-co-(8- caprolactone)] containing at least 10 % of crystalline phase and having the crystalline phase melting temperature lower than 65 °C,
in the weight ratio (a):(b) in the range of 4: 1 to 1:9.
The mixture of components (a) and (b) is heterogenous. The component (b) is always continuous. The component (a) can be in the form of discrete particles dispersed in component (b) matrix. Alternatively, the component (a) can be continuous, and the morphology of the materials as a whole then corresponds to interpenetrating matrices of components (a) and (b), i.e., irregularly alternating regions of component (a) and component (b).
The continuous phase of the composition is poly-8-caprolactone and/or poly[(8- caprolactam)-co-(8-caprolactone)] with the crystalline phase melting temperature lower than 65 °C. The low crystalline phase melting temperature of the polyester component of the composition is important for the direct shaping of the material during the surgery according to the individual needs. The starch component can be plastified during its processing. The term„plastification" means a process during which the grains of the native starch disintegrate as a result of increased temperature, shear forces, absorbed air humidity, and optionally added plastifier; the amylase crystalline phase melts and a homogenous amorphous mixture of amylose and
amylopectin is formed. Esters of starch and maltodextrin are thermoplastic and amorphous and are thus always plastified when undergoing processing at a temperature above the glass transition temperature, Tg. The temperatures Tg can be found in reference literature or determined by known methods, e.g. by calorimetry (DSC).
Rheological properties of the plastified starch are determined by its molecular parameters. Rheological properties of the polysaccharide component can be effectively controlled within a broad range by the incorporation of maltodextrin which is a starch oligomer. Furthermore, rheological properties of the polysaccharide phase of the mixture can be controlled by incorporation of further plastifiers, in order to form a finer structure of the heterogenous mixture with a larger interphase surface. A preferred plastifier of starch is glycerol which can optionally be combined with polyvinyl alcohol. Preferred plastifiers for starch esters are glycerol acetates or propionates or citric acid ethyl esters. Weight ratio of plastifiers to the total content of starch, maltodextrin, esterified starch and esterified maltodextrin in the composition according to the present invention is preferably between 1:20 and 1: 1.5. Interaction between the antibiotic and the starch component is determined predominantly by the chemical nature of the starch component. Esterification of starch by acetic, propionic or butyric acid is advantageous. For transferring some types of antibiotics into the starch component solid phase, it may be necessary to use solvents capable of dissolving the antibiotics as well as starch or starch esters, respectively. However, the solvents should have a high boiling point; thus they correspond to starch plastifiers or starch softeners.
By controlling the rheological properties of the starch phase of the mixture, morphology of the mixture and thus the interphase surface of the mixture can be optimized so that the antibiotic migrates from the starch phase of the composition into the surrounding tissue at a desired rate. Furthermore, biocompatible Ti02-based nanoparticles can be added into the composition to moderately affect mechanical and rheological properties of the components, morphology, and to affect the antibiotic release rate. Biocompatible Ti02 particles affecting the final mechanical properties, the rheology of the components, the morphology of the mixture and thus the antibiotic release rate, may be isometric micro- or nanoparticles of titanium dioxidide having the size of 0.01 to 10 μιη, or titanate nanotubes (TiNT) having the mean diameter of at most 40 nm and aspect ratio width:length at least 10, as described in the patent document CZ 302299 B6. Biocompatibility of TiNT in bone implants has been
established [T. Kasuga, Thin Solid Films 2006, 496, 141- 145; Oh S., Daraio C, Chen LH., Pisanic TR., Finones R., Jin S. J Biomed Mater Res Pt A 2006, 78, 97-103]. Mass ratio of Ti02-based nanoparticles and/or titanate nanotubes with respect to the total amount of starch, maltodextrin, esterified starch and esterified maltodextrin is 1:20 to 1:2.
Preferably, the antibiotic is at least one antibiotic selected from the group comprising cyclins, aminoglycosidic and glycopeptidic antibiotics, and is present in the amount of 2 to 20 wt. %, relative to the total weight of the mixture; preferably the antibiotic is selected from tetracycline, gentamicine and vancomycine.
The object of the invention is also a method of preparation of the thermoplastic biodegradable composition, comprising the steps of
(a) mixing of starch and/or starch and maltodextrine mixture and/or esterified starch and/or esterified starch and esterified maltodextrin mixture with an antibiotic under plastification conditions, and
(b) melt-mixing of the mixture obtained in step (a) with poly-8-caprolactone and/or poly[(s- caprolactam)-co-(8-caprolactone)] containing at least 10 % of crystalline phase and having the crystalline phase melting temperature lower than 65 °C.
The plastification conditions include melt-mixing (i.e., shear force) and heating above 60 °C or above Tg of the polysaccharide material.
Preferably, in step (a), the starch and/or starch and maltodextrin mixture and/or esterified starch and/or esterified starch and esterified maltodextrin mixture is mixed with the antibiotic and with a plastifier selected from the group comprising polyvinyl alcohol, glycerol, glycerol acetates, glycerol propionates, citric acid ethyl esters.
Brief description of Drawings
Figure 1. SEM micrograph of the polymeric systems TPS/PCL/ATB according to the invention, wherein TPS = thermoplastified starch, PCL = poly(8-caprolactone) and ATB is vancomycin. The SEM samples were prepared by cutting and smooting in liquid nitrogen, followed by etching the starch phase. The micrographs show that the morphology can be
controlled by the composition which changes the structure of the TPS phase from continuous (a), through partly continuous (b) to particulate or discrete (c).
Example of carrying out the Invention
Example 1
A thermoplastic composition of thermoplastic starch (TPS), poly(8-caprolactone (PCL) and the antibiotic vancomycin (ATB) in weight ratio TPS/PCL/ATB = 63/27/10 was prepared. The starting substances were wheat starch type A (Soltex NP1; producer: Amylon a.s., Czech Republic) and poly(8-caprolactone) (Capa 6800; producer: Perstorp, Sweden) and the antibiotic vancomycin (Vancomycin Mylan; producer: Biologici Italia). In the first step, a mixture of plastified starch with vancomycin was prepared: the starch was pre-mixed with glycerol in weight ratio 7:3 at room temperature and subsequenently mixed with a vancomycin aqueous solution. This mixture was plastified at 85 °C and then dried. The resulting mixture had weight ratio TPS vancomycin equal to 63: 10. In the second step, the final composition TPS/PCL/ATB was prepared by melt-mixing in a twin-screw microextruder at 120 rpm and temperature 110 °C. The ratio of components in the resulting composition TPS/PCL/ATB was 63/27/10. Morphology of the resulting composition was determined by scanning electron microscopy which showed that the two main components (TPS/ATB and PCL) form a co-continuous structure. The vancomycin release rate was determined by UV/VIS spectroscopy in an experiment in which 10 mg of thermoplastic composition with the shape of a small cube was immersed in 30 mL of simulated body fluid (SBF; the composition of SBF was adjusted according to literature [P.N. Chavan, M. M. Bahir, R. U. Mene, M. P. Mahabole, R. S. Khairnar: Study of nanobiomaterial hydroxyapatite in simulated body fluid: Formation and growth of apatite. Materials Science and Engineering B 168 (2010) 224-230]). The dependence of the antibiotic release rate on time was logarithmic. The times corresponding to therelease of 25%, 50% and 75% of vancomycin are shown in Table 1. After 5 days, when the experiment ended, 95% of vancomycin was released.
Example 2
A thermoplastic composition consisting of thermoplastic starch (TPS), poly(8-caprolactone) (PCL) and vancomycin antibiotic (ATB), in weight ratios of the components TPS/PCL/ATB = 45/45/10, was prepared by procedure described in Example 1. Morphology of the mixture was observed by SEM microscopy and is shown in Fig. lb, the starch component formed semi-continuous phase of the mixture. The antibiotic release rate was determined in the same manner as in Example 1, it had logarithmic character, but the overall rate was significantly slower than for the composition in Example 1. The measured times corresponding to the release of 25%, 50% and 75% of vancomycin are shown in Table 1. After 30 days, when the experiment ended, 68% of vancomycin was released.
Example 3
A thermoplastic composition consisting of thermoplastic starch (TPS), poly(8-caprolactone) (PCL) and the antibiotic vancomycin (ATB) in weight ratios of the components TPS/PCL/ATB = 27/63/10 was prepared by procedure described in Example 1. Morphology of the mixture was observed by SEM microscopy and is shown in Fig. lc, the starch component formed particles in the PCL matrix. The antibiotic release rate was determined in the same manner as in Examples 1 and 2, it had logarithmic character, but the overall release rate was significantly slower than for the composition of Example 2. The measured times corresponding to the release of 25%, 50% and 75% of vancomycin are shown in Table 1. After 30 days, when the experiment ended, 43% of vancomycin was released.
Example 4
Thermoplastic composition consisting of acetylated thermoplastic starch (ATPS 1), poly(s- caprolactone) (PCL) and the antibiotic vancomycin (ATB) in weight ratio ATPS 1/PCL/ATB = 45/45/10 was prepared. The starting substances were wheat starch type A (Soltex NP1; producer: Amylon a.s., Czech Republic) acetylated to the degree of substitution 2,8 and poly(8-caprolactone) (Capa 6800; producer: Perstorp, Sweden) and the antibiotic vancomycin (Vancomycin Mylan; producer: Biologici Italia). In the first step, a mixture of acetylated starch with vancomycin was prepared. The powdered acetylated starch was pre-mixed with triethyl citrate in weight ratio 7:3 at room temperature, and subsequenently mixed with vancomycin acetone solution. This mixture was dried to remove
acetone and plastified at 110 °C for 7 minutes in laboratory kneader. The resulting mixture had weight ratio TPS: vancomycin 63: 10. In the second step, the final composition ATPS 1/PCL/ATB was prepared by melt-mixing in twin-screew microextruder at 120 rpm and temperature 110 °C. The antibiotic release rate was determined in the same manner as in Examples 1-3, it had logarithmic character, but it was significantly slower than for the composition of Example 2. The times corresponding to the release of 25%, 50% and 75% of vancomycin are shown in Table 2. After 30 days, when the experiment ended, 58% of vancomycin was released. Example 5
A thermoplastic composition consisting of acetylated mixture of thermoplastic starch and maltodextrin having dextrose equivalent 22 in weight ratio starch:maltodextrin equal to 7:3 (ATPS2), poly(8-caprolactone) (PCL) and the antibiotic vancomycin (ATB) in weight ratio ATPS2/PCL/ATB = 45/45/10 was prepared in the same way as in Example 4. The antibiotic release rate was determined in the same manner as in Examples 1-4, it had logarithmic shape, and it was significantly slower in comparison with the system in Example 2. The times corresponding to the release of 25%, 50% and 75% of vancomycin are shown in Table 2. After 30 days, when the experiment ended, 62% of vancomycin was released. Example 6
A thermoplastic composition consisting of thermoplastic starch (TPS), poly(8-caprolactone) (PCL), titanate nanotubes (TiNT) and the antibiotic vancomycin (ATB 1) in weight ratio TPS/PCL/TiNT/ATB 1 = 56/24/10/10 was prepared in the same way as in Example 1, but titanate nanotubes having mean diameter of 20 nm and aspect ratio width:length equal to 60 were dispersed in aqueous solution of vancomycin. Due to TiNT, the release of vancomycin from the system was faster than from the analogical system in Example 1, as determined by UV/VIS spectroscopy (the ATB release experiments were carried out in the same way as in Examples 1-5). The times corresponding to the release of 25%, 50% and 75% of vancomycin are shown in Table 3. After 5 days, when the experiment ended, 100% of vancomycin was released.
Example 7
A thermoplastic composition consisting of thermoplastic starch (TPS), poly(8-caprolactone) (PCL), titanate nanotubes (TiNT) and the antibiotic tetracyclin (ATB2) in weight ratio TPS/PCL/TiNT/ATB2 = 56/24/10/10 was prepared in the same way as in Example 6. The times corresponding to the release of 25%, 50% and 75% of vancomycin are shown in Table 3. After 5 days, when the experiment ended, 100% of tetracyclin was released.
Example 8
The release rate of the antibiotics in polymeric systems comprising various components according to the invention (e.g. TPS/PCL/ATB, wherein TPS = thermoplastified starch, PCL = poly(8-caprolactone) and ATB is vancomycin or tetracyclin) was measured. The antibiotic was released into SBF solution (SBF = simulated body fluid containing in particular Na+ and CI" ions together with other salts in physiological concentrations in aqueous solutions [P.N. Chavan, M. M. Bahir, R. U. Mene, M. P. Mahabole, R. S. Khairnar: Study of nanobiomaterial hydroxyapatite in simulated body fluid: Formation and growth of apatite. Materials Science and Engineering B 168 (2010) 224-230]).]). The concentration of the released antibiotic was determined by means of UV/VIS spectroscopy based on the previously established calibration curve. The values of ATB release rate in the SBF solution were fitted with the function y = a*ln(t) + b, where y = released antibiotic amount (in %) and t = time. If the ATB release time exceeded the measurement time, the values were obtained by interpolation from the fitted curve; the approximated values are always marked by asterisk in Tables 1-3.
Table 1. The antibiotic release rate as a function of the composition of the polymeric systems TPS/PCL/ATB according to the invention, wherein TPS is thermoplastified starch, PCL is poly(8-caprolactone) and ATB is vancomycin. The lines of the table correspond to examples 1, 2 and 3.
Table 2. The antibiotic release rate as a function of the composition of the acetylated starch in the polymeric systems ATPS/PCL/ATB according to the invention, wherein ATPS is acetylated thermoplastified starch, PCL is poly(8-caprolactone) and ATB is vancomycin.
The lines of the table correspond to examples 4 and 5.
Time until release of the Proportion of indicated proportion released ATB
Measurement
Composition Example at the end of
25% 50% 75% total time
the
measurement
ATPS 1/PCL/ATB
4 0.5 d 10.8 d >100 d * 30 days 58%
(45/45/10)
ATPS2/PCL/ATB
5 0.4 d 4.6 d >100 d * 30 days 62%
(45/45/10)
Table 3. The antibiotic release rate in the polymeric systems TPS/PCL/ATB/TiNT according to the invention, wherein TPS is thermoplastified starch, PCL is poly(s- caprolactone) and ATB is vancomycin (ATB 1, Example 6) or tetracyclin (ATB2, Example 7) and TiNT are titanate nanotubes having the diameter of 20 nm and the aspect ratio (width: length) more than 50. The lines of the table correspond to examples 6 and 7.
Industrial Applicability
Thermoplastic biodegradable polymeric composition for the production of temporary inserts designed for the treatment and prevention of local infections of skeleton or other anatomical structures, in human as well as veterinary medicine.
Claims
1. A polymeric thermoplastic biodegradable composition incorporating an antibiotic, in particular for production of inserts for the treatment and prevention of local infections, consisting of
(a) at least one plastified polysaccharide component, which is selected from starch, a mixture of starch and maltodextrin, esterified starch, and a mixture of esterified starch and esterified maltodextrin, wherein maltodextrin is a mixture of oligosaccharides having the dextrose equivalent of up to 25, whereas the polysaccharide component further contains an antibiotic, and
(b) a polyester component which is poly-8-caprolactone and/or poly[(8-caprolactam)-co-(8- caprolactone)] containing at least 10 % of crystalline phase and having the crystalline phase melting temperature lower than 65 °C,
in the weight ratio (a):(b) in the range from 4: 1 to 1:9.
2. The polymeric thermoplastic biodegradable composition incorporating an antibiotic according to claim 1, wherein the esterified starch and/or esterified maltodextrin in the polysaccharide component (a) are acetates and/or propionates and/or butyrates of starch and/or maltodextrin.
3. The polymeric thermoplastic biodegradable composition incorporating an antibiotic according to claim 1, wherein the antibiotic is at least one antibiotic selected from the group comprising cyclins, aminoglycosidic and glycopeptide antibiotics, and is present in the amount of 2 to 20 wt. %, relative to the total weight of the composition; preferably, the antibiotic is selected from gentamicin, tetracycline and vancomycin.
4. The polymeric thermoplastic biodegradable composition incorporating an antibiotic according to claim 1, wherein the polysaccharide component (a) further comprises plastifiers selected from the group comprising polyvinyl alcohol, glycerol, glycerol acetates, glycerol propionates, citric acid ethylesters, wherein the total amount of the plastifiers in the polysaccharide component (a) is in weight ratio 1:20 to 1: 1.5, relative to the total amount of starch, maltodextrin, esterified starch and esterified maltodextrin.
5. The polymeric thermoplastic biodegradable composition incorporating an antibiotic according to claim 1, wherein the polysaccharide component (a) further comprises titanate nanotubes having the mean diameter of at most 40 nm and aspect ratio width:length at least 10, or isometric Ti02 particles having the size of 0.01 to 10 μιη, wherein the weight ratio of the nanotubes or particles to the total amount of starch, maltodextrin, esterified starch and esterified maltodextrin is 1:20 to 1:2.
6. Use of the polymeric thermoplastic biodegradable composition according to any one of the preceding claims for the production of temporary inserts destined for the treatment and prevention of local infections in anatomical structures, in particular in skeleton, in human or veterinary medicine.
7. A method of preparation of the thermoplastic biodegradable composition according to claim 1, comprising the steps of
(a) mixing starch and/or starch and maltodextrine mixture and/or esterified starch and/or esterified starch and esterified maltodextrin mixture with an antibiotic under plastification conditions, and
(b) melt-mixing of the mixture obtained in step (a) with poly-8-caprolactone and/or poly[(s- caprolactam)-co-(8-caprolactone)] containing at least 10 % of crystalline phase and having the crystalline phase melting temperature lower than 65 °C.
8. The method according to claim 7, wherein in step (a), starch or starch and maltodextrine mixture or esterified starch or esterified starch and esterified maltodextrin mixture is mixed with the antibiotic and with a plastifier selected from the group comprising polyvinyl alcohol, glycerol, glycerol acetates, glycerol propionates, citric acid ethyl esters.
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