DEGRADABLE THIOL-ENE POLYMERS

Abstract

A thiol-ene polymeric material is disclosed. The material is produced by the photopolymerization of reactants having thiol and olefin moieties. The material can incorporate encapsulated components, including cells. Additionally, the material can be derivatized by reacting the polymeric material with components such as proteins.

Claims

1-15. (canceled)

16. A method for producing a hydrogel comprising a biocompatible cross-linked degradable thiol-ene polymer, the method comprising: subjecting a polymerization reaction mixture comprising at least one thiol compound and at least one olefin compound to a radical polymerization reaction under conditions sufficient to produce the biocompatible cross-linked degradable thiol-ene polymer, wherein (a) the at least one thiol compound comprises m number of reactive thiol groups; (b) the at least one olefin compound comprises n number of reactive ene groups, wherein at least one of the ene groups is a norbornene moiety; and (c) each of n and m is an integer of at least 2, provided that the sum of n+m is at least 5.

17. The method of claim 16, wherein the at least one olefin compound comprises a polymeric moiety selected from the group consisting of poly(lactic acid) (PLA); polyglycolide (PGA); a copolymer of PLA and PGA (PLGA); poly(vinyl alcohol) (PVA); poly(ethylene glycol) (PEG); poly(ethylene oxide); a poly(ethylene oxide)-co-poly(propylene oxide) block copolymer; a poloxamine; a polyanhydride; a polyorthoester; a poly(hydroxy acids); a polydioxanone; a polycarbonate; a polyaminocarbonate; a poly(vinyl pyrrolidone); a poly(ethyl oxazoline); a carboxymethyl cellulose; a hydroxyalkylated cellulose; a polypeptide; a polysaccharide; a carbohydrate; heparan sulfate; chondroitin sulfate; heparin, alginate; and a combination thereof.

18. The method of claim 16, wherein the at least one thiol compound comprises a polymeric moiety selected from the group consisting of poly(lactic acid) (PLA); polyglycolide (PGA); a copolymer of PLA and PGA (PLGA); poly(vinyl alcohol) (PVA); poly(ethylene glycol) (PEG); poly(ethylene oxide); a poly(ethylene oxide)-co-poly(propylene oxide) block copolymer; a poloxamine; a polyanhydride; a polyorthoester; a poly(hydroxy acids); a polydioxanone; a polycarbonate; a polyaminocarbonate; a poly(vinyl pyrrolidone); a poly(ethyl oxazoline); a carboxymethyl cellulose; a hydroxyalkylated cellulose; a polypeptide; a polysaccharide; a carbohydrate; heparan sulfate; chondroitin sulfate; heparin, alginate; and a combination thereof.

19. The method of claim 16, wherein the at least one thiol compound is a branched thiol compound.

20. The method of claim 16, wherein the at least at least one olefin compound is a branched olefin compound.

21. The method of claim 16, wherein the polymerization reaction mixture further comprises a chemical initiator.

22. The method of claim 16, wherein the polymerization reaction mixture further comprises a biologically active component.

23. The method of claim 22, wherein the biologically active component is selected from the group consisting of cells, tissues, and tissue aggregates.

24. The method of claim 22, wherein the biologically active component is selected from the group consisting of chondrocytes, immortalized cell lines, stem cells, hormone-producing cells and fibroblasts.

25. The method of claim 22, wherein the biologically active component is selected from the group consisting of a protein, a pharmacologically active agent, and an agricultural chemical.

26. The method of claim 25, wherein the biologically active component is a protein selected from the group consisting of an adhesion peptide, growth factor, hormone, antihormone, signaling compound, enzyme, serum protein, albumin, macroglobulin, globulin, agglutinin, lectin, extracellular matrix protein, antibody, antigen, and a combination thereof.

27. The method of claim 25, wherein the biologically active component is a pharmacologically active agent selected from the group consisting of an analgesic, antipyretic, nonsteriodal antiinflammatory drug, antiallergic, antibacterial drug, antianemia drug, cytotoxic drug, antihypertensive drug, dermatological drug, psychotherapeutic drug, vitamin, mineral, anorexiant, dietetic, antiadiposity drug, carbohydrate metabolism drug, protein metabolism drug, thyroid drug, antithyroid drug, coenzymes, and a combination thereof.

28. The method of claim 25, wherein the biologically active component is an agricultural chemical selected from the group consisting of a fungicide, herbicide, fertilizer, pesticide, carbohydrate, nucleic acid, organic molecule, inorganic biologically active molecule, and a combination thereof.

29. The method of claim 22, wherein the radical polymerization reaction encapsulates the biologically active component within the biocompatible cross-linked degradable thiol-ene polymer.

30. The method of claim 17, wherein the polymeric moiety has a molecular weight ranging from about 30 Da to about 50,000 Da.

31. The method of claim 18, wherein the polymeric moiety has a molecular weight ranging from about 30 Da to about 50,000 Da.

32. The method of claim 17, wherein the polymeric moiety is biodegradable.

33. The method of claim 18, wherein the polymeric moiety is biodegradable.

34. The method of claim 17, wherein the polymeric moiety selected from the group consisting of poly(lactic acid) (PLA), poly(vinyl alcohol) (PVA), and poly(ethylene glycol) (PEG), and a combination thereof.

35. The method of claim 18, wherein the polymeric moiety selected from the group consisting of poly(lactic acid) (PLA), poly(vinyl alcohol) (PVA), and poly(ethylene glycol) (PEG), and a combination thereof.

36. A method for producing a biocompatible thiol-ene hydrogel, the method comprising subjecting a polymerization reaction mixture comprising at least one thiol compound and at least one olefin compound to a radical polymerization reaction under conditions sufficient to produce the biocompatible thiol-ene hydrogel, wherein: (a) the at least one thiol compound comprises m number of reactive thiol groups; (b) the at least one olefin compound comprises n number of reactive ene groups; and (c) each of n and m is an integer of at least 2, provided the sum of n+m is at least 5.

37. The method of claim 36 wherein the at least one thiol compound comprises a polymeric moiety selected from the group consisting of poly(lactic acid) (PLA), polyglycolide (PGA), a copolymer of PLA and PGA (PLGA), poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), poly(ethylene oxide), a poly(ethylene oxide)-co-poly(propylene oxide) block copolymer, a poloxamine, a polyanhydride, a polyorthoester, a poly(hydroxy acids), a polydioxanone, a polycarbonate, a polyaminocarbonate, a poly(vinyl pyrrolidone), a poly(ethyl oxazoline), a carboxymethyl cellulose, a hydroxyalkylated cellulose, a polypeptide, a polysaccharide, a carbohydrate, heparan sulfate, chondroitin sulfate, heparin, alginate, hyaluronic acid, gelatin, and a combination thereof.

38. The method of claim 37, wherein the at least one thiol compound comprises a polymeric moiety selected from the group consisting of hyaluronic acid and gelatin.

39. The method of claim 38, wherein the polymeric moiety of the at least one thiol compound is hyaluronic acid.

40. The method of claim 38, wherein the polymeric moiety of the at least one thiol compound is gelatin.

41. The method of claim 36, wherein the at least one olefin compound comprises a polymeric moiety selected from the group consisting of poly(lactic acid) (PLA), polyglycolide (PGA), a copolymer of PLA and PGA (PLGA), poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), poly(ethylene oxide), a poly(ethylene oxide)-co-poly(propylene oxide) block copolymer, a poloxamine, a polyanhydride, a polyorthoester, a poly(hydroxy acids), a polydioxanone, a polycarbonate, a polyaminocarbonate, a poly(vinyl pyrrolidone), a poly(ethyl oxazoline), a carboxymethyl cellulose, a hydroxyalkylated cellulose, a polypeptide, a polysaccharide, a carbohydrate, heparan sulfate, chondroitin sulfate, heparin, alginate, and a combination thereof.

42. The method of claim 41, wherein the at least one olefin compound comprises a polymeric moiety selected from the group consisting of polypeptide, poly(lactic acid) (PLA), poly(vinyl alcohol) (PVA), and poly(ethylene glycol) (PEG), and a combination thereof.

43. The method of claim 42, wherein the polymeric moiety of the at least one olefin compound is poly(ethylene glycol) (PEG).

44. The method of claim 36, wherein the at least one olefin compound comprises an ene group selected from the group consisting of a vinyl moiety, a vinyl ether moiety, an allyl moiety, an acrylate moiety, a methacrylate moiety, a maleimide moiety, and a norbornene moiety.

45. The method of claim 36, wherein the at least one thiol compound is a branched thiol compound.

46. The method of claim 36, wherein the at least at least one olefin compound is a branched olefin compound.

47. The method of claim 36, wherein the ene group is a norbornene moiety.

48. The method of claim 36, wherein the molecular weight of the at least one thiol compound is from about 30 Da to about 50 kDa.

49. The method of claim 36, wherein the molecular weight of the at least one olefin compound is from about 30 Da to about 50 kDa.

50. The method of claim 36, wherein the at least one thiol compound is biodegradable.

51. The method of claim 36, wherein the at least one olefin compound is biodegradable.

52. The method of claim 36, wherein the polymerization reaction mixture further comprises a chemical initiator.

53. The method of claim 36, wherein the polymerization reaction mixture further comprises a biologically active component.

54. The method of claim 53, wherein the biologically active component is selected from the group consisting of cells, tissues, and tissue aggregates.

55. The method of claim 54, wherein the biologically active component is selected from the group consisting of chondrocytes, immortalized cell lines, stem cells, hormone-producing cells and fibroblasts.

56. The method of claim 54, wherein the biologically active component is selected from the group consisting of a protein, a pharmacologically active agent, and an agricultural chemical.

57. The method of claim 56, wherein the biologically active component is a protein selected from the group consisting of an adhesion peptide, growth factor, hormone, antihormone, signaling compound, enzyme, serum protein, albumin, macroglobulin, globulin, agglutinin, lectin, extracellular matrix protein, antibody, antigen, and a combination thereof.

58. The method of claim 56, wherein the biologically active component is a pharmacologically active agent selected from the group consisting of an analgesic, antipyretic, nonsteriodal antiinflammatory drug, antiallergic, antibacterial drug, antianemia drug, cytotoxic drug, antihypertensive drug, dermatological drug, psychotherapeutic drug, vitamin, mineral, anorexiant, dietetic, antiadiposity drug, carbohydrate metabolism drug, protein metabolism drug, thyroid drug, antithyroid drug, coenzymes, and a combination thereof.

59. The method of claim 56, wherein the biologically active component is an agricultural chemical selected from the group consisting of a fungicide, herbicide, fertilizer, pesticide, carbohydrate, nucleic acid, organic molecule, inorganic biologically active molecule, and a combination thereof.

60. The method of claim 53, wherein the radical polymerization reaction encapsulates the biologically active component within the biocompatible thiol-ene hydrogel.

Description

BRIEF DESCRIPTION OF TUE DRAWINGS

[0016] FIG. 1 shows the general scheme for thiol-ene polymerization.

[0017] FIG. 2 shows a scheme for the formation of a thiol-ene hydrogel formed from derivatized PLA, PEG and PVA monomers,

[0018] FIG. 3 shows schemes for derivatizations of poly(vinyl alcohol).

[0019] FIG. 4 shows schemes for derivatizations of poly(lactic acid).

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention is directed to a novel class of degradable scaffolds which are biocompatible thiol-ene hydrogels built upon degradable materials, such as PVA, PEG and PLA blocks, that can incorporate chemicals and live cells within the polymer matrix.

[0021] Thiol-ene polymerizations are photochemically initiated, step growth, free-radical processes that take place between thiols and olefins via a sequential propagation/chain-transfer process. For polymerization to occur, each thiol-containing component must have an average of at least two thiol groups and each olefin-containing component must have at least two ene functional groups, (i.e. the monomer must contain two or more double bonds). Polymerization of a dithiol and a diene results in the formation of a linear polymer, rather than a crosslinked polymer. Crosslinked gels can be readily formed by increasing the functionality, i.e., increasing the degree of branching, of one or both of the monomers to be greater than two. Thiol-ene polymerizations have a number of significant and unique advantages that make them particularly beneficial. These benefits include a step growth polymerization that causes the molecular weight to build up more slowly, the ability to photoinitiate the sample without any need for a distinct (and possibly cytotoxic) initiator specie, the ability to polymerize extremely thick (more than 30 cm) samples because of a self-eliminating light intensity gradient, the very low radical concentration present during polymerizations producing less cellular damage from the free radicals, the lack of oxygen inhibition and the ease with which monomers of significantly varying chemistry can be copolymerized.

[0022] Thiol-ene systems form ground state charge transfer complexes, and therefore photopolymerize even in the absence of initiators in reasonable polymerization times. Since the complex which absorbs the light is consumed by the polymerization, the polymer itself does not absorb light. Thus, polymerization can proceed to extremely great depths, and no potentially toxic initiator is required to initiate the polymerization. The polymer properties can be tailored by appropriate monomer choices since the products are regular, alternating copolymers. Nearly any unsaturated monomer can polymerize via this mechanism in the presence of a suitable polythiol and light.

[0023] The scheme shown in FIG. 1 is the general polymerization mechanism. The charge transfer complex forms by the interaction of the thiol group with the double bond of the ene followed by electron transfer and formation of a thiyl radical upon exposure to light. The thiyl radical then initiates the polymerization. Termination involves radical-radical combinations of either -carbon radicals or thiyl radicals.

[0024] One embodiment of the present invention is a polymeric material comprising repeating units of the formula:

[SR.sub.1SCCR.sub.2CC]

wherein R.sub.1 and R.sub.2 are independent linkers, and at least one of R.sub.1 and R.sub.2 are degradable. Thus, the chemical natures of R.sub.1 and R.sub.2 are independent, that is, they can be the same or different. R.sub.1 and R.sub.2 function as linkers to link together the thiol-ene junctures. In accordance with the present invention, the polymeric material is preferably produced by a process of combining a first reactant of the formula R.sub.1(CC).sub.n with a second reactant of the formula R.sub.2(SH).sub.m, wherein n and m are independently integers greater than one and R.sub.1 and R.sub.2 are as defined above. The first and second reactants are then irradiated with light to cause reaction between the first and second reactants to form the polymeric material. In alternative embodiments, the polymeric material of the present invention can include additional linker segments, R.sub.3 . . . R.sub.n. Such additional linker segments meet the requirements set forth herein for R.sub.1 and R.sub.2. For example, a polymeric material having the repeating unit described above can further comprise repeating units of the formula:

[SR.sub.3SCCR.sub.4CC]

wherein R.sub.3 and R.sub.4 are independent linkers.

[0025] As used herein, the term degradable, with reference to the R.sub.1 and R.sub.2 segments and the polymeric materials of the present invention refers to a segment or material having a molecular structure which can decompose to smaller molecules. Such degradation or decomposition can be by various chemical mechanisms. For example, a degradable polymer can be hydrolytically degradable in which water reacts with the polymer to form two or more molecules from the polymer by chemical bonds in the molecule being hydrolyzed, thus producing smaller molecules. In a further embodiment of the present invention, the segments or materials are biodegradable. Biodegradability refers to a compound which is subject to enzymatic decomposition, such as by microorganisms, or to a compound, portions of which are subject to enzymatic decomposition, such as by microorganisms.

[0026] R.sub.1 and R.sub.2, while at least one is degradable, can be chemically diverse. In preferred embodiments, R.sub.1 and R.sub.2 can be selected from poly(lactic acid) (PLA), polyglycolide (PGA), copolymers of PLA and PGA (PLGA), poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), poly(ethylene oxide), poly(ethylene oxide)-co-poly(propylene oxide) block copolymers (poloxamers, meroxapols), poloxamines, polyanhydrides, polyorthoesters, poly(hydroxy acids), polydioxanones, polycarbonates, polyaminocarbonates, poly(vinyl pyrrolidone), poly(ethyl oxazoline), carboxymethyl cellulose, hydroxyalkylated celluloses such as hydroxyethyl cellulose and methylhydroxypropyl cellulose, and natural polymers such as polypeptides, polysaccharides or carbohydrates such as polysucrose, hyaluranic acid, dextran and similar derivatives thereof, heparan sulfate, chondroitin sulfate, heparin, or alginate, and proteins such as gelatin, collagen, albumin, or ovalbumin, or copolymers, or blends thereof. In particularly preferred embodiments, R.sub.1 and R.sub.2 can be selected from polylactic acid) (PLA), poly(vinyl alcohol) (PVA), and poly(ethylene glycol) (PEG). PLA monomers provide degradability to the system while PVA and PEG enhance the hydrophilic nature of the hydro gel and provide for the possibility of further derivatization and/or extensive crosslinking.

[0027] R.sub.1 and R.sub.2 can vary in size depending upon desired properties for the resulting polymeric material. More particularly, the molecular weight for R.sub.1 and R.sub.2 can range from about 30 DA to about 50000 Da. Prior to formation of the polymeric material of the present invention, R.sub.1 and R.sub.2 are derivatized to include thiol or olefin moieties such that they can participate in photo-initiated thiol-ene polymerization. Thiolated macromers such as polyethylene glycol) dithiol are available commercially. The olefin moieties can be selected from any suitable compound having a carbon double bond. For example, the olefin moiety can be selected from any suitable ethylenically unsaturated group such as vinyl, acetyl, vinyl ether, ally, acrylate, methacrylate, maleimide, and norbornene. Thus, it will be appreciated that in the repeating unit shown above, the carbons can be CH.sub.2 or can be substituted at one or more than one of the carbons within the repeating group, even including ring structures incorporating a double bond. If each of R.sub.1 and R.sub.2 are derivatized with either two thiol or two olefin moieties, the resulting thiol-ene polymer would be a linear copolymer composed of alternating R.sub.1 and R.sub.2 segments. However, the thiol-ene polymeric material is preferably formed to contain cross-linking and branching. Thus, the derivatized R.sub.1 and R.sub.2 segments preferably have more than two thiol or olefin moieties per molecule that can participate in crosslinking and polymerization. The extent of the branching and crosslinking can be controlled by the use of differently derivatized R.sub.1 and R.sub.2 segments and control over the concentration of the starting materials.

[0028] By photoinitiation of the thiol-ene polymerization reaction with these monomeric, oligomeric or polymeric starting materials, high molecular weight, crosslinked networks are obtainable in the presence or absence of a chemical initiator within reasonable reaction times. This is a very important property inherent to the polymerization reactions, which can eliminate the adverse effects of chemical initiators and still obtain rapid curing. Because of the step growth nature of the polymerization, these polymers have significantly lower glass transition temperatures and higher degrees of swelling than homopolymer diacrylate analogues. Thus, simple changes in molecular weight, number of functional groups, and the chemistry of the monomer between the functional groups allow facile control of the polymer properties over a wide range.

[0029] FIG. 2 illustrates an example of a thiol-ene hydrogel that can be formed from derivatized PLA, PEG and PVA monomers. The resulting hydrogel is formed from the PLA triene (e.g., made from glycerol with three lactide arms and subsequent ene attachment), the PEG dithiol (such as the commercially available PEG dithiol), and the partially acrylated PVA derivatized to include the well-known RGD adhesion sequence. Hydrogel matrices of this type facilitate independent control of the (i) mechanical properties by adjusting the PVA and PLA functionality, (ii) swelling through adjustments to the relative amount of PEG, (iii) the degradation timescale through adjustments in the molecular weight of the PLA arms, and (iv) attachment of biomolecules such as signaling compounds to the PVA backbone. The resulting networks will be three dimensional, hydrophilic, porous structures that can be further modified by the attachment of molecules of interest to the pendant OH groups of PVA to impart therapeutic or other properties to the hydrogel. Thiol-ene polymers are alternating copolymers, but because a monomer can be derivatized in numerous ways, the ability to vary the composition of the copolymers exists.

[0030] A list of some properties of the thiol-ene hydrogel illustrated in FIG. 2 that can be influenced by modifying parameters of the individual monomers is shown in Table 1. Degradation rate, mechanical properties, crosslink density and swelling can each be controlled with systematic changes in the amounts, molecular weights or functionality of the various monomers. For example, in considering control of the degradation rate of the polymer matrix, the simplest method for controlling this feature is to change the molecular weight of the oligomeric PLA branches. The higher the molecular weight of the branch, the more rapidly the system will degrade. This phenomena, which is different from what might be observed in linear PLA systems, arises because the PLA segments may act as crosslinks in the system. As the molecular weight of the PLA crosslink increases, the probability that any one of the repeat units and hence the crosslink will be degraded is higher, thus leading to more rapid degradation of the PLA crosslinks.

TABLE-US-00001 TABLE 1 Influence of Monomer Amounts and Structural Features on the Polymer Matrix Properties Monomer Parameters to be Varied Primary Influence Secondary Influence Molecular Weight of PLA Branches Degradation Rate Swelling (minor) Number of PLA Branches per PLA Crosslink Density Swelling Monomer (i.e., the functionality) Mechanical Properties Amount of PLA Monomer Crosslink Density Swelling (minor) Mechanical Properties Degree of Substitution on PVA Crosslink Density Swelling - also changes Backbone Mechanical Properties because of consumption of hydrophilic OH functional groups Amount of PEG Monomer Swelling Crosslink Density (minor)

[0031] Another parameter that dictates the network properties is monomer functionality. For example, in the example shown in FIG. 2, as the number of reactive functional groups on the PLA branched oligomer or PVA increases, the extent of crosslinking increases, giving more rigid hydrogels. Increasing the functionality of the PVA monomers requires consuming additional OH functional groups and converting them to thiols or vinyl substituents. The loss of hydroxyl functional groups reduces the network hydrophilicity to a minor degree, thus impacting the swelling. Additionally, for both of these changes, the increase in crosslink density impacts the initial equilibrium swelling; however, the swelling is more easily controlled by the amount of PEG added to the matrix. The functionality of the PLA will be adjusted by starting with di-, tri-, and tetra-functional alcohols in the PLA synthesis to obtain di-, tri- and tetra-functional oligomers oligomers with two, three and four branches). The size of the oligomer chains is controlled during the synthesis by changing the ratio of hydroxyl groups to lactides. The PVA functionality can be manipulated by replacing between about 2% and about 10% of the hydroxyl functional groups with vinyl or thiol groups.

[0032] As noted above, the thiol-ene hydrogels of the present invention are prepared from biocompatible monomers. A biocompatible material does not promote an immune, allergenic or inflammatory response in the body. The resulting hydrogels are therefore biocompatible as well and can be used internally for the purposes of tissue engineering. Because the individual monomers are biocompatible and the polymerization process itself can be free of toxic chemical initiators, it is also possible to encapsulate biologically active materials, such as cells, tissue and tissue aggregates during the polymerization process thereby trapping such materials within the biocompatible hydrogel matrix. These materials are then supported within the matrix and can function within the correct temperature, water and nutrient environment. Cells of interest for encapsulation include chondrocytes, immortalized cell lines, stem cells, hormone-producing cells, fibroblasts and the like. To have an optimal cell environment, the hydrophilicity and transport properties (e.g. diffusion) must be controlled. In particular, the matrices must allow for the ready transport of nutrients and oxygen to encapsulated cells, as well as the removal of cellular waste products. Suitable matrices include multi-branched PLA and PVA chains either linked to each other or to PEG segments to form a three dimensional structure. PEG is extremely hydrophilic. Therefore, the presence of large amounts of PEG (as well as the remaining hydroxyls from the PVA) assure that the degree of swelling of the hydrogel is high and that transport is facile.

[0033] In a further embodiment of the present invention, monomers are synthesized that contain chemical links to allow for derivatization of the polymeric material with functional molecules as well as the necessary thiol and olefin moieties for formation of the hydrogel. For example, the monomers could be derivatized to contain multiple thiol groups, some of which are derivatized to link a protein while others are left free to participate in the thiol-ene polymerization thereby forming a thiol-ene hydrogel containing bound protein. Alternatively, a thiol-ene hydrogel can be produced with monomers having an excess of thiol groups and after formation, the hydrogel can be derivatized with a protein.

[0034] Knowledge of the biological events that occur at the cell-scaffold interface plays a key role in tissue engineering. Vital interactions occur on the molecular scale, and the proteins and factors that are responsible for these interactions may be incorporated into suitable scaffolding materials by derivatization of the polymeric material of the present invention. For example, signaling molecules, hormones, and growth factors each can be integrated into the hydrogel through derivatization of the monomers, macromers or polymers, thereby mimicking the native environment (i.e., in the body) of those cells, resulting in more efficient production of extracellular matrix and improved tissue-like properties of the final material. One of the significant advantages of the thiol-ene approach is the simplicity with which the resulting polymeric networks can be derivatized. The thiols can be easily modified either before or after polymerization (if a slight excess of thiol is added to the polymerization, a significant number of thiols will remain unreacted and derivatizable).

[0035] A wide variety of molecules can be incorporated into the polymeric material through OH groups or SH groups including, but not limited to, proteins, pharmacologically active agents, and agricultural chemicals. Alternatively, such molecules can be encapsulated in the polymeric material in the event such molecules would lose functionality if chemically bound to the polymeric material. For example, types of proteins that can be incorporated into the polymeric material include adhesion peptides (such as RGD adhesion sequence), growth factors, hormones, antihormones, signaling compounds, enzymes, serum proteins, albumins, macroglobulins, globulins, agglutinins, lectins, extracellular matrix proteins, antibodies, and antigens. Types of pharmacologically active agents that can be incorporated into the polymeric material include analgesics, antipyretics, nonsteriodal antiinflammatory drugs, antiallergics, antibacterial drugs, antianemia drugs, cytotoxic drugs, antihypertensive drugs, dermatological drugs, psychotherapeutic drugs, vitamins, minerals, anorexiants, dietetics, antiadiposity drugs, carbohydrate metabolism drugs, protein metabolism drugs, thyroid drugs, antithyroid drugs, and coenzymes. Types of agricultural chemicals that can be incorporated into the polymeric material include fungicides, herbicides, fertilizers, pesticides, carbohydrates, nucleic acids, organic molecules, and inorganic biologically active molecules. In a further embodiment, the polymeric material of the present invention can be formed as commodity plastic products that are typically considered to be disposable products. Because the polymeric material of the present invention is degradable, such products, when disposed of, will more rapidly degrade in the environment. Such products include, for example, eating utensils, plates, bowls, cups, food and beverage containers and packaging.

[0036] The following experimental results are provided for purposes of illustration and are not intended to limit the scope of the invention.

EXAMPLES

Example 1

[0037] This example shows two possible derivatizations of polyvinyl alcohol).

[0038] Synthesis of a thiol macromer can proceed via several approaches, two of which are presented in the scheme shown in FIG. 3. Both progress via a tosylate intermediate. Poly(vinyl alcohol) was tosylated in anhydrous pyridine at 85 C. overnight. The insoluble PVA was pulled into solution as the reaction proceeded. This tosylated PVA was then be reacted with dithiothreitol (DTT), in one instance, and potassium thioacetate, in another instance, at room temperature. Nucleophilic attack of the thiolate anion displaced the tosyl group, covalently linking these molecules to the PVA backbone through a thioether bond. PVA-thioacetate was hydrolyzed via simple methanolysis, yielding the thiol macromer (PVA-SH) in which the thiol groups have replaced some of the hydroxyl groups. Using an excess of DTT in the other mechanism guarantees that there will be free thiol groups in the resulting molecule (PVA-DTT).

[0039] Once formed, the thiolated PVA can then be photopolymerized in the presence of a multi-ene in an aqueous solution to provide a crosslinked hydrogel network. Polymerizations of the thiolated. PVA with the PLA triacrylate or PLA triallyl yield a degradable, hydrogel network in which the swelling and degradation time are controlled by the amount and molecular weight of the trifunctional PLA, respectively.

Example 2

[0040] This example demonstrates the feasibility of synthesizing PLA multi-ene and PLA multithiol monomers for use in the present invention.

[0041] A major advantage of thiol-ene hydrogels is the ability to use a wide range of precursor molecules with varying structures and chemistries. In particular, the technique affords the possibility of having largely polylactic acid) polymers in which the degradation rate is controlled by the PLA segment molecular weight. To obtain this control, it is necessary to synthesize PLA multi-enes and PLA multithiols. FIG. 4 shows the scheme for the synthesis of PLA trithiol and PLA triacrylate.

[0042] Lactic acid oligomers with three branches were prepared with glycerol used as an initiator to polymerize the lactide using stannous octoate as the catalyst. Oligomers with different chain lengths were obtained by adjusting the initiator/facade ratio. This oligomer was used to derivatize the hydroxyl end groups of the three branches either with acrylates or with thiols. None of the PLA thiol derivatives have previously been synthesized. Synthesized macromers were characterized by FTIR and NMR. PLA triacrylate showed all the reported IR and .sup.1H-NMR bands.

[0043] While various embodiments of the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. It is to be expressly understood, however, that such modifications and adaptations are within the scope of the present invention, as set forth in the claims below.