WO2013155173A2

WO2013155173A2 - Methods and compositions relating to biodegradable epoxy elastomers

Info

Publication number: WO2013155173A2
Application number: PCT/US2013/035960
Authority: WO
Inventors: Chun Wang; Wenshou WANG
Original assignee: Regents Of The University Of Minnesota
Priority date: 2012-04-13
Filing date: 2013-04-10
Publication date: 2013-10-17
Also published as: WO2013155173A3

Abstract

A biodegradable epoxy elastomer comprising a residue of at least one first monomer, the first monomer including a diepoxide; and a residue of at least one second monomer, the second monomer comprising at least one hydrolytically degradable bond.

Description

METHODS AND COMPOSITIONS RELATING TO BIODEGRADABLE EPOXY

ELASTOMERS

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The work described herein was supported, in part, by grants from the Department of

Defense (Grant No. W81XWH-06- 1-0677) and the National Institutes of Health (Grant No. R01CA129189). The United States government may have certain rights in the invention.

BACKGROUND

Biodegradable synthetic elastomers have numerous potential applications in soft tissue repair and engineering. For example, the mechanical and degradative properties make the elastomers suitable for implantable devices, soft tissue repair, tissue engineering, and regenerative medicine. Other suitable applications include cardiovascular and orthopedic surgical interventions, surgical sutures, nerve regeneration and wound healing. In some applications it may be desirable to load the biodegradable synthetic elastomer with a drug or other therapeutic agent, which may be released from the elastomer under specified conditions.

Previously synthesized biodegradable synthetic elastomers include thermoset polyester elastomers and thermoplastic polyester elastomers and polyurethanes. Such polymers typically involve a complicated synthesis and stringent conditions. For example, thermoset polyester elastomers are synthesized at high temperatures (typically greater than 100°C) in high vacuum and an oxygen-free environment. Additionally thermoset polyester elastomers typically have a long reaction time (hours and days). The synthesis conditions make thermoset polyester elastomers unsuitable for loading fragile drug molecules. Thermoplastic polyester elastomers and polyurethanes also require stringent synthesis conditions. In addition, thermoplastic polyester elastomers and polyurethane synthesis require toxic catalysts, such as Sn(II) octoate and organic solvents. Still further, chain segregation may result in microscopic non-uniformity and non-uniform degradation. SUMMARY

A device including a biodegradable epoxy elastomer including residue of at least one first monomer, the first monomer including a diepoxide; and residue of at least one second monomer, the second monomer including at least one hydrolytically degradable bond.

Disclosed is a method that includes combining a first monomer with a second monomer, the first monomer having a diepoxide group, the second monomer having a diamine and a hydrolytically degradable group, wherein the first monomer and the second monomer have a molar ratio (of the first monomer to the second monomer) of about 0.1 to about 10.

These and various other features and advantages will be apparent from a reading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows one example synthesis for biodegradable epoxy elastomers (BEE). Figure 2 is an image of a BEE sample.

Figure 3 is a plot of temperature (°C) versus heat flow (mW) for BEE samples.

Figure 4 is a plot of strain (%) versus stress (MPa) for BEE samples.

Figure 5 is a plot of time (in days and weeks) versus mass loss (%) for BEE samples at pH 7.4 and pH 5.

Figure 6 is a plot of time (in days and weeks) versus water content (%) for BEE samples at pH 7.4 and pH 5.

Figure 7 is an image from a nuclear magnetic resonance analysis.

Figure 8 is a plot of polymer degradation products (mg/mL) versus cell viability (%).

Figure 9A and 9B are images of 3T3 fibroblasts on a standard tissue culture plate and BEE, respectively.

Figure 10 is a plot of temperature (°C) versus heat flow (mW) for BEE samples containing 0%, 5%, 10% and 20% ibuprofen by weight. Figures 11A, 1 IB and 11C are plots of cumulative release of Ibuprofen (%) over time (in days) for BEE samples containing 5%, 10% and 20% ibuprofen by weight, respectively.

Figure 12 shows an example synthesis for a non-degradable polymer.

Figure 13 is a plot of cumulative release of Ibuprofen (%) over time (in days) from the non-degradable polymer of Figure 12.

Figure 14 is a plot of time (in days and weeks) versus mass loss (%) for a BEE sample containing 10% ibuprofen by weight at pH 7.4 and pH 5.

Figure 15a is an image of a BEE rod and polycaprolactone (PCL) rod before implantation.

Figure 15B is an image of an implanted BEE rod after 2 weeks.

Figure 15C is an image of an implanted PCL rod after 2 weeks.

Figure 16 contains images of hematoxylin and eosin (H&E) stained tissue slices for the BEE and PLC rods after 1 and 2 weeks of implantation.

Figure 17 is a plot of time (seconds) versus load (Newtons) for a peel off test involving BEE.

Figure 18 is a scanning electron microscope (SEM) image of a BEE coated polyurethane substrate.

Figure 19 is a plot of a Fourier transform infrared spectroscopy (FTIR) spectra for BEE samples.

Figure 20 is an image from an X-ray photoelectron spectroscopy (XPS) analysis of BEE samples.

Figures 21 A, 21 B and 21 C are images showing a static water contact angle for BEE samples.

Figures 22A, 22B, 22BB, 22C, 22D, and 22DD are images of 3T3 fibroblasts on a standard tissue culture plate, BEE, a BEE surface containing isocyanate group, and a polyethylene glycol (PEG) grafted BEE, respectively.

The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. DETAILED DESCRIPTION

In the following description, reference is made to the accompanying set of drawings that form a part hereof and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. All numbers recited herein for a particular property can also be utilized with all other numbers recited for that particular property in order to form ranges.

As used in this specification and the appended claims, the singular forms "a", "an", and "the" encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

"Include," "including," or like terms means encompassing but not limited to, that is, including and not exclusive. It should be noted that "top" and "bottom" (or other terms like "upper" and "lower") are utilized strictly for relative descriptions and do not imply any overall orientation of the article in which the described element is located.

Biodegradable epoxy elastomers (BEEs) described can include a residue(s) of at least one first monomer and a residue of at least a second monomer. Exemplary BEEs described herein can comprise, consist of or consist essentially of a residue (or residues) of at least a first monomer, a residue (or residues) of at least a second and optionally at least one application specific agent, such as a therapeutic agent.

Exemplary first monomers can generally include at least two epoxy groups, or a diepoxide. Other characteristics or functional groups of the first monomer can be chosen based on other properties desired in the BEEs for example. Other functional groups in the first monomer may also be a function of the synthesis of the first monomer, for example. In some embodiments, the first monomer may include an ether group. Ether groups, if present, may be present because the synthesis route included a diol group.

Exemplary first monomers may also be chosen based on whether they are to be degradable or nondegradable. Other portions of the first monomer can also be chosen in order to obtain other desired properties, such as elasticity.

In some embodiments, exemplary first monomers can be of formula 1 below:

(1)

R¹ can be selected from (CrC^alkyl, (C₃-C₈)cycloalkyl, (C₁-C₆)alkyl(C₃-C₈)cycloalkyl, (C₃- C₈)cycloalkyl(C₁-C₆)alkyl, or (C₁-C₆)alkyl(C₃-C₈)cycloalkyl(C₁-C₆)alkyl, arylCd-C^alkyl, or (C₁-C₁₀)alkyl-O-(C₁-C₁₀)alkyl, wherein any of the alkyl or cycloalkyl groups may include one or more than one either, ester, amide, or urethane groups. For example, suitable first monomers include diepoxides such as diglycidyl ether.

Exemplary first monomers can include compounds of formulas 2 through 26:

(12)

(15)



In compounds 24 and 25, R can independently be selected from H, or an alkyl. In some embodiments, in compounds 24 and 25, R can independently be selected from H and CH₃.

In compound 26, R can be a cycloalkyl. In some embodiments, in compound 26,

R can be selected from: benzene (C₆H₆), toluene (CyH₈), hexane (C₆H₁₄), and 1,1,3,3- methylcyclohexane (C₁₀,H₂o).

Compound 14 is an example of a first monomer that would be degradable because of the presence of the ester group. Compound 26 is an example of a compound that includes a urethane group. First monomers that include monomeric, oligomeric, or polymeric groups therein can be utilized to form a BEE that is relatively elastic. The particular monomeric, oligomeric, or polymeric group can be chosen to tune the elasticity of the BEE. For example as the chain length increases, the BEE will be more elastic.

In some embodiments, R¹ may include at least one ester bond. For example, R¹ may contain a polymer of ε-caprolactone (PCL). In some embodiments, R¹ may include PCL having an average degree of polymerization of 1 to 50, in some embodiments from 1 to 20, or in some embodiments from 1 to 10. The synthesis of PCL diepoxide (an example of a first monomer including PCL in R¹) can be done according to methods known in the art (such as for example Zhou, Jiaxiang, Wang, Wenxin, Villarroya, Silvia, Thurecht, Kristofer J. and Howdle, Steven M. Epoxy functionalized poly(epsilon-caprolactone): Synthesis and application. Chem. Comm. 2008, 44, 5806-5808.). The PCL in such an embodiment of a first monomer can also be replaced with one or more polyesters. Exemplary polyesters can include, for example polylactic acid, polyglycolic acid, polyhydroxy butyrate, polyethylene succinate, polybutylene adipate terephthalate, polyhydroxy butyrate valerate, polybutylene succinate, polybutylene adipate, cellulose acetate butyrate, cellulose acetate propionate and combinations thereof. In some embodiments, the average degree of polymerization of such polymers can be from 1 to 50, in some embodiments from 1 to 20, and in some embodiments from 1 to 10.

Exemplary second monomers can generally include at least one hydrolytically degradable group or portion. Hydrolytic degradation is the process by which moisture, water, penetrates a degradable material and hydrolyzes one or more bonds (for example, ester bonds) thereby breaking down the material (for example polymers). Without being bound by theory, hydrolytic degradation of polymeric material is thought to proceed through a series of somewhat overlapping steps including: (1) diffusion of water into the material; (2) initial hydrolysis yielding polymers with reduced molecular weight (i.e., conversion of polymers to oligomers); (3) continued loss of molecular weight (i.e., formation of smaller oligomers); (4) initial loss of physical properties (e.g., pliability); (5) loss of further properties resulting in an opaque and hazy material; (6) major loss of physical properties, such as tensile strength and form-stability; (7) weight loss; and (8) volume loss, until the material is essentially degraded to monomers or small oligomers.

In some embodiments, the hydrolytically degradable group of the second monomer can be sensitive to pH. For example, a hydrolytically degradable group can be stable at one pH, but can be degraded at another pH. In some embodiments, a hydrolytically degradable group can be degraded within a physiologically relevant pH range. In some embodiments, a hydrolytically degradable group can be degraded at pHs from 4 to 7.5. In some embodiments, a hydrolytically degradable group can be degraded at pHs from 5 to 7.5. In some

embodiments, a hydrolytically degradable group can be degraded at pHs from 6 to 7.5. In some embodiments, portions of the second monomer can be chosen so that the hydrolytically degradable group will degrade at a desired rate, at a desired pH, or both.

In some embodiments, exemplary second monomers can include at least one hydrolytically degradable group and at least two amine groups, a diamine. In some embodiments, exemplary second monomers can be of formula 27 below:

H₂N R²— NH_{2 (27)} wherein R² can contain at least one portion that is hydrolytically degradable. In some embodiments, the hydrolytically degradable group can be a group that is degradable at a desired pH. In some embodiments, the hydrolytically degradable group can be independently selected from the following groups: imine, hydrazone, carboxylic hydrazone, vinyl ether, cis- aconityl amide, carboxy dimehtylmalic anhydride, trityl, ketal, acetal, diorthoester, orthoester, phosphoramidate, or silyl ether.

Exemplary ketals may have the following formulas (28 and 29):

Synthesis of ketal diamine structures can accomplished using methods described in

Bioconjug Chem. 2008 Apr;19(4):911-9. Fully acid-degradable biocompatible polyacetal microparticles for drug delivery. Paramonov SE, Bachelder EM, Beaudette TT, Standley SM, Lee CC, Dashe J, Frechet JM.

Exemplary acetals may have the following formulas (30 and 31):

Synthesis of acetal diamine structures can be accomplished using schemes analogous to that described in "In situ generation of bioreducible and acid labile nanogels/microgels simply via adding water into the polymerization system", Zhong-Kai Wang, Long-Hai Wang, Jiao-Tong Sun, Li-Fen Han and Chun-Yan Hong, Polym. Chem., 2013,4, 1694-1699.

Exemplary silyl ethers may have the following formulas (32):

R4

(32) wherein R3 and R4 are independently selected from hydrogen or alkyls such as, methyl, ethyl and isopropyl for example.

In some embodiments, second monomers that include silyl ethers can hydrolyze more quickly at slightly acidic pHs. The synthesis of diamine monomers containing silyl ether structures can be conducted using reaction schemes analogous to those found in the following published report: "Tunable Bifunctional Silyl Ether Cross-Linkers for the Design of Acid- Sensitive Biomaterials"; Parrott, M. C; Luft, J. C; Byrne, J. D.; Fain, J. H.; Napier, M. E.; DeSimone, J. M. J. Am. Chem. Soc. 2010, 132(50), 17928-17932.

The second monomer may experience an increased bond cleavage rate at mildly acidic conditions (i.e., pH below 7 at 37°C) as compared to the bond cleavage rate at a pH between 7 and 8 at 37°C. The second monomer introduces hydrolytic degradability into the BEE, which can be dependent on pH. The second monomer can provide an opportunity for fine-tuning the degradation rate of the elastomer. For example, the hydrolytic reactivity of the second monomer could be controlled by changing the chemical environment.

Suitable second monomers can include ortho ester diamines, which are pH sensitive (acid labile) and biocompatible. A specific exemplary ortho ester diamine includes 4- aminomethyl-2-aminopentyloxy-[l,3]-dioxolan. This ortho ester diamine is stable at room temperature and readily reacts with functional groups such as but not limited to epoxies, carboxylic acids, esters and the like to form biodegradable structures because of their high reactivity of amine groups.

In some embodiments, R² may include at least one ester bond. For example, R² may contain a polymer of ε-caprolactone (PCL). In some embodiments, R² may include PCL having an average degree of polymerization of 1 to 50, in some embodiments from 1 to 20, or in some embodiments from 1 to 10. The synthesis of PCL diamine (an example of a second monomer including PCL in R ) can be done according to methods known in the art (such as in Ozdemir Ozarslan, Emel Yildiz, Tulay Y. inan, Abdulkadir Kuyulu, Attila Giingor, Novel amine terminated elastomeric oligomers and their effects on properties of epoxy resins as a toughener. J. Appl. Polym. Sci. 2009 115, 37-45. The PCL in such an embodiment of a second monomer can also be replaced with one or more polyesters. Exemplary polyesters can include, for example polylactic acid, polyglycolic acid, polyhydroxy butyrate, polyethylene succinate, polybutylene adipate terephthate, polyhydroxy butyrate valerate, polybutylene succinate, polybutylene adipate, cellulose acetate butyrate, cellulose acetate propionate and combinations thereof. In some embodiments, the average degree of polymerization of such polymers can be from 1 to 50, in some embodiments from 1 to 20, and in some embodiments from 1 to 10.

In some embodiments, BEEs may also include optional third monomers. The optional third monomer may or may not include a hydrolytically degradable portion. The optional third monomer may include a hydrolytically degradable portion that degrades at a different H, for example, than the second monomer or may degrade at the same or a similar pH.

Optional third monomers may be chosen to provide various properties to the BEE. As an example, the optional third monomer could include a diacid, which could form a polyamide capable of hydrogen bonding to make the BEE stronger.

In some embodiments, a BEE can also include an optional application specific agent.

Exemplary application specific agents can include, for example therapeutic agents. In some embodiments, a BEE can also be used to form crosslinked particles having sizes ranging from 1 nm to 900 μηι. Such BEEs can be used as injectable drug delivery devices. In some embodiments, BEEs can also be used for soft tissue repair, scaffolds for tissue engineering, coating of implant and device surfaces, and biodegradable adhesives for example. In some embodiments, exemplary BEEs can be synthesized by combining a first monomer, which contains at least a diepoxide group, with a second monomer, which includes at least a hydrolytically degradable bond. In some embodiments, exemplary BEEs can be synthesized by combining a first monomer, which contains at least a diepoxide group, with a second monomer which includes at least a hydrolytically degradable bond and a diamine.

In some embodiments, BEEs may be synthesized under mild, solvent free conditions, at room temperature and without the use of a catalyst and/or initiator. The first monomer and the second monomer can react at room temperature without a solvent or catalyst. In some embodiments, after about 48 hours at room temperature the reaction may be complete and a BEE product is produced. The resulting BEE includes residues of at least one first monomer and at least one second monomer. It is recognized that the network formation could be accomplished in less time, such as between about 1 hour and about 6, 5, 4, 3, or 2 hours for example. One skilled in the art will recognize that the rate of reaction can be increased by increasing the synthesis temperature. In some embodiments, the synthesis can be maintained at mild temperatures, such as below about 50°C. As described above, the first and second monomers may react without a solvent, initiator or catalyst. In one example, the first monomer and the second monomer can be in a liquid state at room temperature, and can mix well with one another without the need for a solvent.

A therapeutic agent, such as a drug or bioactive agent, may also optionally be dispersed in the BEE at a molecular level, such as by in situ polymerization, without solvents. For example loading of small hydrophobic drug molecules or other therapeutic agents can be achieved by dissolving the therapeutic agent in the monomer mixture prior to polymerization. Alternatively, loading may be accomplished after polymerization by soaking the polymer in a solvent in which the therapeutic agent is dissolved.

In some embodiments, BEEs can be elastic and mechanically strong. Exemplary

BEEs can have a Young's Modulus of 4.8 to 8.0 MPa and an elongation of 98% to 137% at break. Control or modification of the synthesis can produce BEEs with modulus and elongation at break in the range of 10 kPa to 50 MPa and 4% to 1500%, respectively.

In some embodiments, BEEs can have a glass transition temperature (T_g) lower than zero. In some embodiments, typical medical applications occur around room temperature and physiological temperature (20 to 40 degrees Celsius). Low glass transition temperatures can allow the BEE to be elastic over typically utilized temperature ranges for medical

applications.

Mechanical properties and thermal properties of disclosed BEEs can be further controlled by adjusting the molar ratio of the first and second monomers as well as by using monomers of different chemical structures. When the molar ratio of the first monomer to the second monomer is larger than 1, resulting BEEs typically have a branched network structure. Higher molar ratios of the first monomer to the second monomer can lead to more

crosslinking in the network, which may impact the mechanical properties and degradation of the material as shorter chains will be produced. Suitable molar ratio ranges of the first monomer to the second monomer can be from 0.1 to 10. In some embodiments, suitable molar ratio ranges of the first monomer to the second monomer can be from 1 to 2. Outside this range, such as at monomer ratios (first monomer to second monomer) of 0.05 or 20, only very short polymer fragments will form. This may be due, in part, because a large excess of one monomer over the other may prohibit polymerization into long molecular chains.

In some embodiments, BEEs can exhibit pH-responsive degradation, which can enable mildly acidic microenvironments, such as those that exist in physiological and pathological situations, to be exploited to address medical problems, for example. Such situations may include tissues with inflammation, bone resorption due to osteoclast activity, bacterial infections, solid tumors, and late endosome and lysosome of cells. Additionally, BEE materials prepared from different monomer molar ratios, in spite of having different mechanical strength and elasticity, may have similar or the same degradation kinetics. That is, the mechanical properties and degradation rate of the BEE can be adjusted independently.

The second monomer can introduce hydrolytic degradability into the BEE. For example, in a BEE that includes an ortho ester as a hydrolytically degradable group, the rate of ortho ester hydrolysis may be faster at mildly acidic pHs than at neutral or basic pHs.

Thus, the pH-responsive degradation of BEEs may be tuned by adjusting the second monomer, including the monomer selection, the monomer amount, or both.

Cytotoxicity measurements have shown that synthesized BEEs and the degradation products of the BEEs may be non-toxic to fibroblast cells and cells may attach to the surface of the BEE fairly well. The BEE can be hydrophobic to encourage cell adhesion to the BEE. Alternatively, the BEE may be modified to be hydrophilic to prevent cell adhesion to the BEE. For example, the BEE may be modified with polyethylene glycol (PEG) to increase the hydrophilicity of the BEE surface. Whether a hydrophobic or hydrophilic surface is desired can depend on the application.

Exemplary BEEs may be used in various biomedical applications. Suitable applications can include for example, medical adhesives, sutures, and wound dressings. In one example, three-dimensional scaffolds for cell culture and tissue engineering (especially for elastic tissues for example) can be formed from BEEs. Soft tissue repair and replacement, especially for elastic tissues such as vascular grafts or drug eluding stents or balloons may also include BEEs.

BEEs may also be used as a coating or layer applied to a medical device. For example, a BEE coating may be formed on a substrate of a different nature than the coating. In one example, a BEE coating may be formed on a polymer substrate or a metal substrate. Suitable polymer substrates can include polyurethane and polyethylene. Suitable metal substrates can include stainless steel, titanium and nitinol. BEE coatings can be tailored to promote or inhibit cell adhesion. Further, BEE coatings can be tailored to release therapeutic agents such as anti-inflammatory or antimicrobial drugs.

The BEE may contain a therapeutic agent, such as drugs, bioactive compounds or combinations thereof. Additionally suitable therapeutic agents can include hydrophobic drugs. The therapeutic agent loading can be uniform or variable throughout the BEE.

Release of the therapeutic agent may be pH dependent. As described above, degradation of BEEs can be pH dependent. As the BEE degrades, the therapeutic agent can be released. More specifically, at pathological conditions, under which BEEs are relatively stable, release of the therapeutic agent may be controlled by diffusion, and at mildly acidic conditions (i.e., pH below 7.0 and 37°C) release of the therapeutic agent may be controlled by degradation of BEE and diffusion. Thus, tailoring the degradation of the BEE also tailors the release rate of the therapeutic agent. In one example, the BEE is tailored to release a therapeutic agent for a time period of 24 hours to several days based on the environment, including temperature and pH. The therapeutic agent may present in amount sufficient to release a therapeutically significant amount during use. Suitable loadings vary depending on the application. Examples loadings can range from 1 to 99% by weight of the BEE. Additional suitable loadings include 5%, 10% and 20% therapeutic agent by weight of the BEE.

A macromolecule can be grafted on the BEE. Suitable macromolecules can be a protein, peptide or polysaccharide. Suitable macromolecules can also contain one or more than one functional groups which are reactive with isocyanate. For example the

macromolecule can include an amine or hydroxyl.

Figure 1 illustrates the synthesis of BEE in which the first monomer is 1,4-Butanediol diglycidyl ether (BDGE) and the second monomer is 4-Aminomethyl-2-aminopentyloxy- [1 ,3]-dioxolan (AMAD). The resulting product is a branched network of elastomers with various degrees of crosslinking. Such an exemplary BEE can form films that may be homogeneous and optically transparent for example.

As will be more clearly explained through the Examples below, the biodegradable epoxy elastomers described herein can be produced through a mild and facile synthesis. The BEE is produced through a solvent-free, catalyst-free synthesis at room temperature and pressure. Further, the BEE can be produced in a single-step one-pot reaction without the need for a curing step.

The present disclosure is illustrated by the following examples. It is to be understood that the particular examples, assumptions, modeling, and procedures are to be interpreted broadly in accordance with the scope and spirit of the disclosure as set forth herein.

EXAMPLES

The present disclosure is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present disclosure will be apparent to those of skill in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight bases, and all reagents used in the examples were obtained, or are available, from the chemical suppliers described below, or may be synthesized by conventional techniques.

Materials Used

1 ,4-butanediol diglycidyl ether (>95%) (BDGE)

4,7,10-trioxa-l,13-tridecacnediamine (97%) (TTDA)

Ibuprofen (>98%) (Ibu)

Each of the above materials is available from Sigma-Aldrich, St. Louis, MO. Synthesis of 4-Aminomethyl-2-aminopentyloxy-[l ,3]-dioxolan (AMAD)

The synthesis of 4-Aminomethyl-2-aminopentyloxy-[l,3]-dioxolan (AMAD) is described in the publication entitled "Poly(ortho ester amides): acid-labile temperature- responsive copolymers for potential biomedical applications" by Rupei Tang, R. Noelle Palumbo, Weihang Ji and Chun Wang in Biomacromolecules, volume 10 (2009), pages 722- 727, which is herein incorporated by reference in its entirety. This synthesis can also be described as below:

The monomer AMAD was synthesized via four steps as show above. Reaction conditions: (i) ethyl trifluoroacetate, acetonitrile; ii) trimethyl orthoacetate, j?-toluene sulfonic acid (p-TSA), acetonitrile; (iii) 5-trifluoroacetylamino-l-pentanol, pyridinium ^»-TSA; (iv) NaOH/H₂0/THF.

2,2,2-Trifluoro-iV-(2,3-dihydroxypropyl) acetamide (1). To a stirred mixture of 3- amino-l,2-propanediol (18.80 g, 0.21 mol) in acetonitrile (120 mL) under argon was added dropwise ethyl trifluoroacetate (34.30 g, 0.24 mol). After 4 h, the solvent was evaporated, and the residue was dissolved in ethyl acetate (200 ml), washed with aqueous KHS0₄ and brine, then dried over MgS0 , and concentrated to yield 34.90 g (91%) of 2,2,2-trifluoro-N-(2,3- dihydroxypropyl)-acetamide as colorless oil. 1H NMR (300MHz, CD₃OD): £(ppm) 3.27-3.29 (m, 2H, NH-G¾), 3.47-3.49 (m, 2H, C¾-OH), 3.70-3.78 (m, 1H, CH-OH), 7.60 (b, 1H, NH).

2,2,2-Trifluoro-7V-(2-methoxy-2-methyl-[l,3]-dioxolan-4-ylmethyl) acetamide (2). To a stirred mixture of 1 (10.16 g, 54.30 mmol), trimethyl orthoacetate (30.00 g, 0.25 mol), and acetonitrile (80 mL) was added j^-toluene sulfonic acid (p-TSA; a trace amount). The mixture was reacted for 6 h at room temperature, followed by evaporation of most of volatile components. The residue was dissolved in ethyl acetate (250 ml), washed successively with saturated aqueous sodium hydrogen carbonate and brine, dried over MgS0₄, and concentrated to yield 1 1.32 g (86%) of 2,2,2-trifluoro-N-(2-methoxy-2-methyl-[l,3] dioxolan-4-ylmethyl) acetamide as oil. 1H NMR (300MHz, CDC1₃): (ppm) 1.67-1.69 (d, 3H, C¾), 3.27-3.30 (d, 3H, O-CH3), 3.37-3.72 (m, 2H, NH-CH₂), 4.14-4.21 (m, 2H, 0-CH₂), 4.43-4.51 (m, 1H, O- CH), 6.86-7.89 (b, 1H, NH).

5-Trifluoroacetylaminopentanol. To a stirred mixture of 5-amino-l-pentanol (10.00 g, 96.94 mmol) in THF (100 mL) under argon was added dropwise ethyl trifluoroacetate (15.98 g, 112.45 mmol). After 4 h, the solvent was evaporated, and the residue was dissolved in ethyl acetate (200 ml), washed with aqueous KHS0₄ and brine, then dried over MgS0₄, and concentrated to yield 17.33 g (90%) of 5-trifluoroacetylaminopentanol as colorless oil. 1H NMR (300MHz, CDC1₃): S ppm) 1.41-1.49 (m, 2H, CH₂), 1.56-1.68 (m, 4Η, CH₂), 2.19 (b, 1Η, O-H), 3.34-3.41 (q, 2Η, CH-NH), 3.64-3.68 (q, 2H, CH-OH), 6.90 (b, 1H, NH).

2,2,2-Trifluoro-N-(2-(5'-trifluoroacetylaminopentyloxy)-2-methyl-[l ,3]-dioxolan-4- ylmethyl) acetamide (3). A mixture of 2 (4.18 g, 17.19 mmol), 5-trifluoroacetylaminopentanol (3.42 g, 17.19 mmol), and pyridinium -toluene sulfonate (45.00 mg, 0.17 mmol) was heated at 130°C until no volatile component was distilled. After cooling to room temperature, the residue was purified with column chromatography (silica gel, ethyl acetate/hexane (1/1) as eluent) to yield 5.99 g (85%) of 2,2,2-trifluoro-iV-(2-(5'- trifluoroacetylaminopentyloxy)-2- methyl-[l ,3]dioxolan-4-ylmethyl) acetamide as oil. 1H NMR (300MHz, CDC1₃): S(ppm) 1.41-1.44 (t, 2H, C¾), 1.55-1.63 (m, 4H, C¾), 2.08-2.09 (d, 3H, C¾), 3.34-3.36 (m, 2H, NH-C¾), 3.61-3.65 (m, 2H, NH-G¾), 4.02-4.16 (m, 2H, 0-G¾), 4.30-4.36 (m, 1H, O-CH), 6.75-6.91 (b, 1H, NH), 7.24-7.48 (b, 1H, NH).

4-Aminomethyl-2-aminopentyloxy-2-methyl-[l ,3]-dioxolan (AMAD). The trifluoroacetamide 3 (5.98 g, 14.57 mmol) was dissolved in THF (40 ml), and sodium hydroxide (1.6 M, 40 ml) was added. The mixture was vigorously stirred overnight, extracted with diethyl ether, dried over MgS0 , and evaporated. The residue was purified with column chromatography (silica gel, methanol/dichloromethane (1/10) as eluent) to yield 1.91 g (60%) of 4-aminomethyl-2-aminopentyloxy- 2-methyl-[l,3]-dioxolan as oil. ¹H NM (300MHz, CDC1₃): S ppm) 1.45-1.71 (m, 9H, Ci¾, CH₃), 2.67-2.90 (m, 4H, G¾-NH₂), 3.48-3.50 (m, 1H, 0-G¾), 3.58-3.62 (t, 2H, 0-G¾), 3.71 -3.72 (m, 1H, 0-G¾), 4.06-4.16 (m, 1H, O-CH). ¹³C NMR (CDC1₃, fppm): 22.02, 22.32, 23.57, 23.60, 29.63, 32.58, 33.32, 33.60, 44.72, 44.77, 62.21 , 62.60, 67.19, 67.27, 78.44 (CH), 121.68, 121.90. Calcd: (C₁₀H2₂N₂O₃) 218.3, found m/z 219.2 (M + H⁺), 241.2 (M + Na⁺). Anal. Calcd for (C₁₀H₂₂N2O₃): C, 55.02; H, 10.16; N, 12.83. Found: C, 54.87; H, 10.06; N, 12.73.

Example 1 - BDGE:AMAD ratios

Samples BEE-a, BEE-b and BEE-c were formed with varying BDGE:AMAD ratios. Sample BEE-a had a molar ratio of 1.2: 1, Sample BEE-b had a molar ratio of 1.5:1, and Sample BEE-c had a molar ratio of 1.8: 1, where BDGE had a molecular weight of 202.3 grams/mol and AMAD had a molecular weight of 204.3 grams/mol.

Each Sample was synthesized by combining the appropriate amount of BDGE with AMAD, both in liquid form, and mixing gently in a 10-mL glass vial with lid. The mixture was then poured into a Teflon-line, 55 mm diameter Petri dish and was covered. After 48 hours a room temperature, a transparent film was obtained. Figure 2 is an image of Sample BEE-a. As shown, Sample BEE-a was optically clear or transparent, suggesting that the material was highly homogeneous on the micro-scale and that the polymer chains were largely amorphous at room temperature.

Gel fractions of the samples were measured in tetrahydrofuran (THF). A 10mm x 10 mm x 1 mm (LxWxH) sample having weight W₀ was immersed in 200 mL of THF for 72 hours, and then dried under vacuum at room temperature until a constant weight, W_l5 was reached. The gel fraction was calculated as Wi/W₀.

The thermal properties were characterized by Differential Scanning Calorimetry (DSC) carried out over a temperature range of 100°C to 150°C using a TA Q100 differential scanning calorimeter (available from TA Instruments) purged with nitrogen. The heating or cooling rate was 10 °C per minute. The midpoint of the transition zone was taken as the glass transition temperature (T_g). The results are shown in Figure 3.

Only one glass transition temperature was observed for each sample in the temperature range tested. None of the samples had a melting point within the temperature range tested. The glass transition temperature of each sample was below 0 °C and increased slightly with the increase of feed molar ratio.

Static mechanical tensile stress-strain measurements were performed using a

Rheometrics minimat 2000 instrument and a MTS Testworks 4 computer software package for automatic control of test sequences and data acquisition and analysis. Dumbbell-shaped test specimens were cut from synthesized polymer films and tested at room temperature with a crosshead speed of 20 mm/min according to the ASTM D882-88 standard method. The tests were performed in triplicate to give mean values of tensile strength, Young's modulus, and elongation at break. The stress-strain curves of Samples BEE-a, BEE-b and BEE-c are shown in Figure 4. These curves are linear and reversible without yield point or hysteresis before failing at large strain, indicating that the polymers underwent elastomeric deformation.

Samples containing higher BDGE:AMAD molar ratios were more densely crosslinked and therefore were stiffer and less elastic.

The tensile strength, Young's modulus, elongation at break, glass transition temperature, and gel fraction results for Samples BEE-a, BEE-b and BEE-c are presented in Table 1. Table 1

With increasing feed molar ratio of monomers, the average values of both tensile strength and Young's modulus increased, and the elongation at break decreased. Stiffer and less elastic polymers formed at the higher molar feed ratios which suggest more densely cross-linked chains.

The high gel fractions indicate that the network formation was extremely efficient. The identification of only one glass transition temperature below 0°C and no melting point for each sample suggests that the samples were highly homogeneous on the micro-scale and that the polymer chains were largely amorphous at room temperature.

The ranges of Young's modulus and elongation at break (4.8-8.0 MPa, and 98-137%, respectively) were on par with many polyester-based thermoset and thermoplastic elastomers.

Example 2 - Hydrolytic Degradation in Vitro

Behavior of Samples BEE-a, BEE-b and BEE-c was evaluated in aqueous buffer solutions of physiological pH 7.4 (50 mM phosphate buffer saline, PBS) and mildly acidic pH 5.0 (50 mM sodium acetate) at 37 °C. The degradation process over 6 weeks was

characterized in terms of mass loss and change in water content of the polymers.

Samples having dimensions of 10 mm x 10 mm x 1 mm (LxWxH) were cut and the initial dry weight was recorded as W₀. The samples were completely immersed in 10 mL of the respective buffer solution. At predetermined time points, the samples were removed from the buffer solution, lightly blotted with tissue paper to remove excess water from the sample surface, and weighed (W]). The sample was dried in a vacuum oven at 30 °C for at least 48 hours and its weight was recorded as W₂. The polymer weight loss (Wi_oss) was calculated in percentage from 100 x (W₀- W₂)/W₀. The water content of the polymer (W_ab) was calculated in percentage from 100 x (W₁-W₂)/W₂. Triplicate polymer samples were measured as each point and the mean value was reported.

The results after 6 weeks are shown in Figure 5 and Figure 6. As illustrated by Figure

5, the degradation was distinctly pH-dependent. At physiological pH 7.4 the mass loss was consistently no more than 10% during 6 weeks (Figure 5) and the water content remained low as well— less than 20% (Figure 6). At mildly acidic conditions, the mass loss and the water content was increased. After an initial 3-4 days, the mass loss and water content increased almost linearly until complete polymer degradation at about day 7. It is noted that in contrast to the BEE thermal and mechanical properties described above, the rate of BEE degradation at both pH 7.4 and 5.0 (as measured by both mass loss and changes in water content) appear to be independent of the monomer molar ratio. Further, despite a higher water content, the trend of mass loss at pH 5.0 was still quite liner. This suggests that erosion of these water- absorbing BEE samples at acidic pH was governed primarily by the reactivity of the ortho ester bond with water. This is a distinctly different mechanism than the classic surface erosion behavior of POEs (poly ortho esters) that rely on excluding water from the highly

hydrophobic polymer bulk.

Additionally, the mass loss and the water content appear to be independent of the BDGE:AMAD molar ratio of the feed. This was true at pH 7.4 and pH 5.0.

Example 3 - Hydrolytic Degradation Products of AM AD and BEE

To identify the degradation products of the ortho ester diamine monomer AMAD, 20 mg of AMAD was added to 4 mL of CD₃COOD-CD₃COONa buffer solution (50 mN, pH 5.0) and mixed by constant stirring. After the solution became clear, proton nuclear magnetic resonance spectroscopy (NMR) measurement was conducted to identify the possible degradation products.

Figure 7 is an image of the NMR results. The NMR peaks of the hydrolytic products could be assigned to protons of the compounds resulting for exocyclic cleavage of the ortho ester group. These peaks include those with chemical shifts around 8 ppm (formate protons), below 2 ppm (methylene protons of 5-hydroxy-pentylamine, and between 3 and 4 ppm (other methylene protons of the exocyclic products). The proton NMR trace of 3-amino-l,2-propane diol, one of the endocyclic products, was also shown in Figure 7. Comparing these two NMR traces, it is noted that peaks corresponding to the methylene protons of 3-amino-l,2-propane diol (with chemical shifts around 2.5 ppm, highlighted in Figure 7 by a dotted box) were not found in the hydrolytic products. This suggests that the hydrolysis of the ortho ester structure involved solely the exocyclic cleavage of the bond, generating a pair of stereo-isomers of amino alcohol formate and a primary alcohol. This also suggests that the final hydrolytic products of the BEE network includes a number of structurally similar linear and branched molecules containing hydroxyls and formates.

Example 4 - Cytocompatibility of BEE degradation products

To determine the cytotoxicity of the hydrolytic degradation products of BEE, various amounts of water-soluble degradation products were incubated with 3T3 cell for 24 hours, and the metabolic cell viability was quantified using an MTT (3-(4,5-dimethyl-thiazol-2-yl)- 2,5-diphenyl tetrazolium bromide) assay.

To generate the hydrolytic products of BEE, a small amount of polymer sample was placed in buffer of pH 5.0 and incubated at 37 °C for two days until the polymer completely disappeared, signifying degradation. The solution containing the polymer degradation products was adjusted to pH 7.4 using 1 N NaOH. To test cytocompatibility of the degradation products, murine fibroblasts (NIH 3T3) were seeded into 96- well plates at 10000 cells/well and cultured with the degradation products of various concentrations for 24 hours in Dulbecco's Modified Eagle Medium supplemented with 10% fetal Bovine serum, 10 mM HEPES, 100 U/mL penicillin/streptomycin at 5% C0₂ and 37 °C. MTT in PBS (5 mg/mL) was added to each well reaching a final concentration of 0.5 mg/mL. After 4 hours, unreacted MTT was removed by aspiration. The formazan crystals were dissolved in 100 μ∑ of DMSO and the absorbance was measured at 570 nm using a Bio-Tek Synergy HT plate reader. Cell viability was calculated by [absorbence of cells exposed to degradation product]/[absorbence of cells cultured without degradation products] in percentage. Morphology of cells exposed to various concentrations of the degradation products was also examined using an optical microscope. Figure 8 is a plot of polymer degradation product in mg/mL versus percent cell viability. There was no apparent cell toxicity to BEE degradation products of up to 500 g/mL in comparison to cells cultured in media alone. Example 5 - Cell Adhesion and Cytocompatibility of BEE in Direct Contact

BEE films were sterilized for cell culture by immersing 10 mm x 10mm x 1mm (LxWxH) samples in ethanol for 3 hours, dried and irradiated under UV for 3 hours. The 3T3 fibroblasts were added onto the sterilized BEE films and immersed in cell culture medium in 12-well plates (1 mL of media in each well, 100000 cells per well). The cells were also cultured on tissue culture plates (TCP) without the polymer as comparison. Cell culture was conducted at 37 °C and in 0.5% C0₂ for 24 hours. To observe the morphology of cells adhered to the BEE films for comparison with TCP surface, white-light images of cells were taken with an Olympus microscope with phase contrast. Cell viability in percentage was quantified using MTT assay as described above. Viability of cells cultured on TCP was taken as 100%.

Figures 9 A and 9B are images of T3T fibroblasts seeded on TCP and on BEE for 24 hours, respectively. Cell adhesion was observed for the T3T fibroblasts seeded on BEE with normal cell morphology and cell density comparable to cells on a TCP surface. BEE surface supported the cells with comparably high viability (91±19%) relative to that of the TCP surface (100±9%). The excellent cell adhesive capacity of the BEE was likely due to the presence of the positively charged amino groups in the polymer and would be a highly desirable property if the BEE is to be used in applications that require intimate cell-material interactions (such as wound dressing, cardiovascular prosthetics, and tissue engineering scaffold). Furthermore, the secondary amines and the hydroxyls in the BEE could be modified chemically so as to introduce new chemical or biological functionalities (such as cell-binding ligand) that would endow the BEE with new properties.

Example 6 - Solvent Free Loading Of Ibuprofen in BEE

Samples BEE-b/Ibu were synthesized similar to Sample BEE-b with a BDGE:AMAD ratio of 1.5:1 except prior to combining BDGE and AMAD, Ibuprofen was dissolved directly into the BDGE without the use of a solvent. The Ibu/BDGE mixture combined with AMAD to synthesize a drug-loaded (Ibu-loaded) BEE.

Table 2

Ibuprofen was dissolved directly and completely into the liquid BDGE monomer.

Therefore the loading efficiency was essentially 100%. The drug-loaded BEE samples maintained homogeneous appearance and optical transparency even with drug content as high as 20% by weight. To further examine the dissolution state of the drug within the polymer, free Ibuprofen itself (Ibu) and the BEE samples loaded with 5 to 20% Ibuprofen (BEE-b/Ibu- 5%, BEE-b/Ibu-10%and BEE-b/Ibu-20%) were analyzed by differential scanning calorimetry (DSC) using a TA Q100 differential scanning calorimeter (available from TA Instruments) and the results shown in Figure 10. The melting point of free Ibuprofen at 76°C disappeared in all the Ibu-loaded samples. The loading of Ibuprofen did increase slightly the T_g of the BEE samples from -9.5 °C to approximately -7 °C.

Example 7 - Kinetics and mechanisms of Ibuprofen release from BEE

The release kinetics of Ibuprofen from Samples BEE-b/Ibu-5%, BEE-b/Ibu-10% and BEE-b/Ibu-20%) were determined by measuring the cumulative amount of released Ibuprofen through 7 days.

Samples having a size of 10 mm x 10 mm x 1mm (LxWxH) were incubated at 37 °C in glass vials containing 10 mL aqueous buffers of physiological pH 7.4 and mildly acidic pH 5.0. The buffer media were collected periodically and replaced by fresh buffer of the volume. The amount of Ibuprofen released in the media was measured by UV spectroscopy (Beckman Coulter, DU 640B spectrophotometer) with absorbance at 263 nm. The results are shown in Figures 11A, 1 IB and 11C for Samples BEE-b/Ibu-5%, BEE-b/Ibu-10% and BEE-b/Ibu-20%, respectively.

The release of Ibuprofen was not linear for each sample at pH 7.4. More specifically, at pH 7.4, the Ibuprofen release was faster during the initial 2 days, and lasted for 7 days. Despite difference in amounts of Ibuprofen loaded, the release profiles at pH 7.4 were quite similar; the cumulative Ibuprofen released by day 2 were 68±5%, 64±5%, 67±5%, for 5% (BEE-b/Ibu-5%), 10% (BEE-b/Ibu-10%), and 20% (BEE-b/Ibu-20%Ibu loading),

respectively.

The Ibuprofen release at pH 5.0 was much accelerated for all the samples compared to that of pH 7.4. Each sample at pH 5.0 reached completion within one day. Increasing

Ibuprofen loading from 5% (BEE-b/Ibu-5%) to 10% (BEE-b/Ibu-10%) to 20% (BEE-b/Ibu- 20%) resulted in a slightly faster release rate, for example, the cumulative Ibuprofen released by half a day were 57±15%, 63±15%, 75±15%, respectively.

To evaluate the effect of acid catalyzed polymer degradation on Ibuprofen release, a non-degradable polymer NBEE was synthesized by replacing the ortho ester diamine monomer AMAD with a non-hydrolyzable diamine TTDA (Figure 12). The composition of Sample NBEE-b/Ibu-10% is presented in Table 3.

Table 3

The release of Ibuprofen from Sample NBEE-b/Ibu-10% was characterized as described above and compared with that of Sample BEE-b/Ibu-10%, which also contained 10% Ibuprofen loading. The results for Sample NBEE-b/Ibu-10% are shown in Figure 13. The release profiles from Sample NBEE-b/Ibu-10% were almost identical between pH 7.4 and 5.0, and were also very similar to the release profile from Sample BEE-b at pH 7.4. The similarity of release profiles from Sample BEE-b at pH 7.4 and 5.0 suggest that release of Ibuprofen from Sample NBEE-b/Ibu-10% is only controlled by the diffusion and that there was no pH-sensitivity due to the nature of the Sample NBEE-b/Ibu-10% polymer. This further suggests that the release behavior difference between Sample BEE-b/Ibu-10% and Sample NBEE-b/Ibu-10% at pH 5.0 is related to the structure of the elastomers. That is, the presence of AMAD in Sample BEE-b/Ibu-10% leads to degradation of the elastomer and release of Ibuprofen.

To examine possible influence on BEE polymer degradation rate due to the presence of the drug, mass loss over time of Sample BEE-b/Ibu-10% was determmed at pH 7.4 and 5.0. The results are shown in Figure 14. As shown, Sample BEE-b/Ibu-10% degrades completely in one day at pH 5, which is consistent with the drug release behavior of Sample BEE-b/Ibu- 10% and confirms the conclusion that the release of Ibuprofen from the synthesized biodegradable epoxy elastomer was controlled by degradation of polymer at pH 5. At pH 7.4, there is a much less weight loss of Sample BEE-b/Ibu-10% compare with that at pH 5 at the same time point. The weight loss of Sample BEE-b/Ibu-10% at pH 7.4 appears to be caused by the release of drug, because the polymer is fairly intact for the first days. Example 8 - Evaluation of BEE biocompatibility in vivo

Mini-rods of BEE-b (Table 1) were prepared by conducting the crosslinking polymerization reaction in side glass capillary tubes. The mini-rod (diameter: -0.8 mm) were retrieved by breaking the glass tubes and cutting the rods to about 5-6 mm in length.

Polycaprolactone (PCL) (Mw 45000, available from Sigma) mini-rods of a similar size were prepared by melt-molding in glass capillary tubes. Before implantation, each mini-rod was sterilized by immersing in 75% ethanol for three hours followed by UV irradiation for an additional three hours. The mini-rods were placed in the subcutaneous tissue in the back of 10~16-week-old male C57BL/6 mice using a 18-G needle (inner diameter -0.84 mm). After 1 or 2 weeks, the mice were sacrificed and the implant site was opened, examined under a Leica dissection microscope and photographed. Figure 15A is an image of the BEE-b and PCL mini-rods before implantation. Figures 15B and 15C are images of the BEE rod and the PCL rod, respectively, 2 weeks after implantation. Both BEE and PCL rods were seen underneath the skin without any apparent adverse effect on the surrounding tissue.

The polymer mini-rods and surrounding tissue were excised, embedded in OCT, frozen, and sectioned with a cryotome into ΙΟ-μπι-fhick slices along the direction

perpendicular to the length of the mini-rods. After fixing with 10% paraformaldehyde, the tissue sections were stained with haemotoxylin and eosin (H&E). Figure 16 contains images of H&E-stained tissue slices for the BEE and PCL rods 1 and 2 weeks after implantation. The BEE and PCL rods elicited similar degree of minor inflammatory response after 1 and 2 weeks of implantation. All the mice were housed under specific pathogen-free conditions and cared for in accordance with the University of Minnesota and NIH guidelines

Example 9 - BEE as a Coating

1,4-butanediol diglycidyl ether (BDGE) and 4-aminomethyl-2-aminopentyloxy-[l,3]- dioxolan (AMAD) were mixed together at room temperature. Polyethylene (PE),

polyurethane (PU) and stainless steel (SS) plates were prepared by treating with sandpaper to roughen the surface and wiping the surfaces with acetone. The cleaned plates were dipped into the monomer mixture solution for 3 min, and then taken out to cure at 40 C overnight.

The BEE coating on the SS plate was characterized by a peel-off test using a custom- built instrument according to ASTM D3330/D3330M-04(2010) Standard Test Method for Peel Adhesion of Pressure-Sensitive Tape (Test method F). The BEE-coated SS plate was fastened and the BEE film was peeled at 90° angle at a speed of 25 mm per minute. The load was recorded with time until the coating was completely detached from the substrate. Figure 17 is a plot of time in seconds versus the load in Newtons. The coating began to peel off at 20 seconds. A load of approximately 40-50 mN (about 70-100 seconds) was needed to peel off the coating. After 100 seconds, the coating detached completely and the load returned to zero.

The BEE coating on the PU plate was characterized by SEM. The BEE coated PU plate was frozen by liquid nitrogen and broken by a hammer. The cross-section was coated with platinum and observed by scanning electron microscope (SEM). Figure 18 is the SEM image. The image shows a strong adhesion between the BEE coating and PU substrate, which is likely due to BEE chains penetrating part of the PU and forming a tightly interwoven region at the interface. Example 10 - BEE modified with PEG

BEE can be chemically modified to change its properties. This example shows that PEG can be grafted to the BEE surface so that the BEE changes from a cell-adhesive surface to a cell-repulsive surface.

A BEE-b (see table 1) film sample (10 mm x 10mm x 1 mm) (LxWxH) was dipped into hexane diisocyanate (HDI) for 1 hour, and then washed three times with acetone to remove the physically absorbed HDI. The samples were dried under vacuum for 24 hours to obtain a BEE-b surface containing isocyanate group (denoted "BEE-NCO"). The BEE-NCO was dipped into a PEG (Mw: 2000) /chloroform solution (10 wt%) for 1 hour, washed with chloroform, and dried under vacuum for 24 hours to obtain PEG grafted BEE (denoted "BEE- PEG").

The unmodified BEE-b, BEE-NCO, BEE-PEG were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and water contact angle measurement. To determine cell adhesive properties of the materials, NIH3T3 fibroblast cells were seeded in wells of tissue culture plates at 50000 cells per well and cultured on either the bare tissue culture plate or on the different BEE surfaces for 24 hours. After repeated washing, the cells that adhered on these surfaces were observed under a microscope.

Figure 19 is an image of the FTIR spectra of BEE-b, BEE-NCO, and BEE-PEG.

Figure 19 confirms the presence of the isocyanate group on BEE-NCO. The NCO signal completely disappeared after PEG grafting, suggesting that the grafting reaction was highly efficient.

Figure 20 is an image of the XPS analysis. Table 4 summarizes the C, N and O percentages as measured by XPS. The number in parentheses was calculated from the feed ratio. Table 4

Figures 21 A, 21B and 21 C are images showing the static water contact angle of the surfaces of BEE-b, BEE-NCO, BEE-PEG. Table 5 provides the static water contact angle of the surface of BEE-b, BEE-NCO and BEE-PEG, respectively.

Table 5

The lower contact angle of BEE-PEG compared to BEE-NCO indicated that grafting PEG increased the hydrophilicity of the surface.

Figures 22 A, 22B, 22C and 22D are images of 3T3 fibroblasts on a standard tissue culture plate, BEE-b, Bee-NCO, and BEE-PEG, respectively. Figure 22BB is an enlarged image of a portion of Figure 22B and Figure 22DD is an enlarged image of a portion of Figure 22DD to show additional detail. As shown, PEG-grafted BEE (BEE-PEG) dramatically reduced adhesion and spreading of NIH3T3 fibroblasts.

Thus, embodiments of methods and compositions relating to biodegradable epoxy elastomers are disclosed. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the present disclosure can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation.

Claims

The following is claimed:

A biodegradable epoxy elastomer comprising:

residue of at least one first monomer, the first monomer comprising a

diepoxide; and residue of at least one second monomer, the second monomer comprising at least one hydrolytically degradable bond.

The biodegradable epoxy elastomer of claim 1, wherein the first monomer is

wherein R¹ is selected from (C₁-C₁o)alkyl, (C₃-C₈)cycloalkyl, (C₁-C₆)alkyl(C₃- C₈)cycloalkyl, (C₃-C₈)cycloalkyl(Ci-C₆)alkyl, or (C₁-C₆)alkyl(C₃-C₈)cycloalkyl(C₁-C₆)alkyl, ary^C Ci^alkyl, or (C₁-C₁₀)alkyl-O-(C₁-C₁₀)alkyl, wherein any of the alkyl or cycloalkyl groups may independently include one or more than one ether, ester, amide, or urethane groups.

3. The biodegradable epoxy elastomer of claim 1 or 2, wherein R¹ includes one or more ether groups.

4. The biodegradable epoxy elastomer of claim 1, wherein the first monomer is diglycidyl ether.

5. The biodegradable epoxy elastomer of any one of claims 1 to 4, wherein the second monomer has the formula:

H₂N R²— NH₂ wherein R² is selected from the group consisting of imine, hydrazone, carboxylic hydrazone, vinyl ether, cis-aconityl amide, carboxy dimehtylmalic anhydride, trityl, ketal, acetal, diorthoester, orthoester, phosphoramidate, and silyl ether.

6. The biodegradable epoxy elastomer of any one of claims 1 to 5, wherein the second monomer comprises an orthoester.

7. The biodegradable epoxy elastomer of any one of claims 1 to 4, wherein the second monomer is 4-aminoethyl-2-aminopentyloxy-[l,3]-dioxolan.

8. The biodegradable epoxy elastomer of any one of claims 1 to 7, wherein a molar ratio of the first monomer to the second monomer is between about 0.1 to about 10.

9. The biodegradable epoxy elastomer of any one of claims 1 to 8, wherein a molar ratio of the first monomer to the second monomer is between about 1 to about 2.

10. The biodegradable epoxy elastomer of any one of claims 1 to 9, wherein the biodegradable epoxy elastomer further comprises a therapeutic agent.

11. A device comprising:

a biodegradable epoxy elastomer comprising: residue of at least one first monomer, the first monomer comprising a

12. The device of claim 1, wherein the first monomer is

wherein R¹ is selected from (C₁-C₁₀)alkyl, (C3-C₈)cycloalkyl, (Q-C^alky^ }- C₈)cycloalkyl, (C₃-C₈)cycloalkyl(C₁-C₆)alkyl, or (C₁-C₆)alkyl(C₃-C₈)cycloalkyl(Ci-C₆)alkyl, aryl(C₁-Ci₀)alkyl, or (C₁-C₁₀)alkyl-O-(C₁-C₁₀)alkyl, wherein any of the alkyl or cycloalkyl groups may independently include one or more than one ether, ester, amide, or urethane groups.

13. The device of claims 11 or 12, wherein R includes one or more ether groups.

14. The device of claim 11, wherein the first monomer is diglycidyl ether.

15. The device of any one of claims 11 to 14, wherein the second monomer has the formula:

H₂N R²— NH₂ wherein R is selected from the group consisting of imine, hydrazone, carboxylic hydrazone, vinyl ether, cis-aconityl amide, carboxy dimehtylmalic anhydride, trityl, ketal, acetal, diorthoester, orthoester, phosphoramidate, and silyl ether.

16. The device of any one of claims 11 to 15, wherein the second monomer comprises an orthoester.

17. The device of any one of claims 11 to 14, wherein the second monomer is 4- aminoethyl-2-aminopentyloxy- [ 1 ,3] -dioxolan.

18. The device of any one of claims 11 to 17, wherein a molar ratio of the first monomer to the second monomer is between about 0.1 to about 10.

19. The device of any one of claims 11 to 18, wherein a molar ratio of the first monomer to the second monomer is between about 1 to about 2.

20. The device of any one of claims 11 to 19, wherein the biodegradable epoxy elastomer further comprises a therapeutic agent.

21. The device of any one of claims 11 to 20, wherein the device is an adhesive, a three- dimensional scaffold, a wound dressing, or a soft tissue replacement.

22. The device of any one of claims 11 to 21 further comprising a residue of polyethylene glycol (PEG) grafted on the biodegradable epoxy elastomer.

23. The device of any one of claims 11 to 22, wherein the second monomer has accelerated bond cleavage at 37 degrees Celsius and a pH below about 7 compared to a bond cleavage at 37 degrees Celsius and a pH between about 7 and about 8.

24. The device of any one of claims 11 to 23 further comprising a substrate comprising at least one member selected from the group consisting of polymers and metals, wherein the BEE is a coating on the substrate.

25. The device of any one of claims 11 to 24, wherein the substrate comprises at least one member selected from the group consisting of polyurethane, polyethylene and stainless steel.

26. The device of any one of claims 11 to 25 further comprising a residue of a

macromolecule grafted on the biodegradable epoxy elastomer.

27. The device of any one of claims 11 to 26, wherein the macromolecule is selected from the group consisting of proteins, peptides, and polysaccharides.

28. A method comprising: combining a first monomer with a second monomer, the first monomer comprising a diepoxide group, the second monomer comprising a diamine and a hydrolytically degradable group, wherein the first monomer and the second monomer have a molar ratio (of the first monomer to the second monomer) of about 0.1 to about 10.

29. The method according to claim 28, wherein the step of combining a first monomer and the second monomer is essentially free of solvent.

30. The method according to any one of claims 28 or 29, wherein the step of combining a first monomer and the second monomer is conducted at room temperature and normal atmospheric pressure.

31. The method according to any one of claims 28 to 30, wherein the first monomer and second monomer are combined in a molar ratio of about 1 to about 2.

32. The method according to any one of claims 28 to 31 further comprising mixing a therapeutic agent with the first monomer before the first monomer is mixed with the second monomer.