Bioabsorbable, biobeneficial polyester polymers for use in drug eluting stent coatings

[0001] A current paradigm in biomaterials research is the control of protein adsorption on the surface of implantable medical devices. Uncontrolled protein adsorption, leading to a mixed layer of partially denatured proteins, is a hallmark of current biomaterials when implanted. Current surfaces present different cell binding sites from adsorbed plasma proteins such as fibrinogen and immunoglobulin G. Platelets and inflammatory cells such as monocyte/macrophages and neutrophils adhere to these surfaces. When so activated, they secret a wide variety of pro-inflammatory and proliferative factors. These unfavorable events can be controlled by the use of non-fouling surfaces. Non-fouling surfaces are surfaces that absorb little or no protein, primarily due to their hydrophilic surface properties. One prior art approach is to use hyaluronic acid and polyethylene glycol to provide this non-fouling surface characteristic. Biobeneficial coatings are surface coatings that are intended to provide a biological benefit without releasing pharmaceutically active agents. Another type of biobeneficial coating contains free radical scavengers to preserve nitric oxide and prevent oxidative damage.

[0002] Langer et al. have published a type of bioabsorbable, polyester polymer that they have dubbed “Biorubber”. (Nature Biotechnology, vol. 20, p. 602, June 2002) This polymer is a polyester copolymer composed of sebacic acid and glycerol. It is a crosslinked elastomer, but possesses no biobeneficial or bioactive moieties. Improved polymers with non-fouling surfaces or with biobeneficial surfaces remain a goal in this art.

[0003] This invention relates to copolymers, some of which are useful in medical device applications. Some of these medical devices are implantable within a mammalian body, such as in a body lumen. The copolymers comprise at least one alcoholic moiety derived from a diol, triol, or polyol. Additionally, the copolymers comprise an acidic moiety, derived from a polycarboxylic acid, and a biobeneficial moiety. Some of these copolymers are biodegradable or bioerodable. Medical devices comprising these polymers and methods of making other polymers are within the scope of this invention.

[0004] A family of bioabsorbable, non-fouling (biobeneficial) polyester polymers is disclosed. In some embodiments, these polymers compose the base material for implantable medical devices. In some embodiments, implantable medical devices comprise these polymers. And in some embodiments, these polymers compose implantable medical device coatings. This family of polymers comprises the following basic components:

• • [0005] (1) moieties derived from aliphatic diols, triols, or polyols;
  • [0006] (2) moieties derived from polycarboxylic acids (carboxylic acids containing more than one acid functionality); and
  • [0007] (3) biobeneficial, non-fouling, or bioactive moieties.

[0008] Some invention embodiments are block copolymers of one or more diols, triols, or polyols with a toxicologically acceptable acid monomer (polycarboxylic acid) such as the following: C₂ to C₁₂ straight chain, aliphatic diacids, specifically oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azaleic acid, and sebacic acid. Longer chain lengths, such as found in dodecandioic acid, tetradecandioic acid, and hexadecandioic acid, are also possible. Polycarboxylic acids include citric acid and tartaric acid. Unsaturated polycarboxylic acids include fumaric acid and muconic acid. Lastly, useful aromatic polycarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 1,6-bis(p-carboxy phenoxy)hexane, 1,3-bis(p-phenoxy carboxy)propane, and 1,4-bis(p-phenoxy carboxy)butane. In some invention embodiments, the toxicologically acceptable polycarboxylic acid monomer specifically excludes sebacic acid.

[0009] Some invention block copolymers can be represented by the following formula: [AB]_n[A′B′]_m. In this formula A represents a moiety derived from an aliphatic diol, triol, or polyol. B represents a moiety derived from a polycarboxylic acid. In some embodiments these are limited to a toxicologically acceptable polycarboxylic acid monomer; in these or other embodiments, polycarboxylic acid monomers are selected from those specifically disclosed above. A′ represents a moiety derived from an aliphatic diol, triol, or polyol that is the same as or different from A. And B′ represents a moiety derived from a polycarboxylic acid that is the same as or different from B. n and m represent the relative length of each block in this block copolymer.

[0010] For purposes of this disclosure we define the soft block as having lower T_g or being highly water swellable. In some embodiments, the block labeled “n” contains the BB moiety and is, therefore the soft segment or soft block because most biobeneficial moieties are hydrophilic and absorb water. The other block, labeled by “m”, is referred to as the hard segment. For purposes of this disclosure, we define the hard blocks as the blocks with a lower water absorption or a higher T_g.

[0011] Invention copolymers can be linear or branched and can be crosslinked when desired. In some instances, crosslinking occurs through functional groups pendant from the polymer backbone. For instance, in some embodiments, the functional groups from acids in the backbone can serve as the crosslinking site. In other embodiments, the unsaturation in an unsaturated diacid serves as the crosslinking site. In yet other embodiments, hydroxyl groups are pendant from the polymer backbone and serve as the crosslinking site. Those of ordinary skill in the art will recognize that other ways of achieving crosslinks between polymer chains can be applied to invention copolymers. For example, to UV crosslink the polymers, some embodiments have UV polymerizable groups in the monomers. Such groups are typically acrylates or methacrylates. The general scheme would include replacing the hydroxyl and carboxylic acid groups with acrylate or methacrylate. This gives rise to another class of polymers.

[0012] Some invention block copolymers can be represented by the following formulas:

[0013]

[0014] In these formulas, Q represents a 1–18 carbon-atom hydrocarbon chain; W represents a 1–8 carbon-atom hydrocarbon chain; T represents a 1–16 carbon-atom hydrocarbon chain; and BB represents a biobeneficial moiety. For purposes of this disclosure, hydrocarbon chains are defined as chains containing 1–50 carbon atoms and include straight and branched alkyl chains, chains containing pendant or in-chain rings, chains containing pendant or in-chain rings and alky substitutions, and chains containing aromatic groups and alkyl substitutions. Suitable substituted hydrocarbyl chains are hydrocarbyl chains as defined above that are independently substituted with one or more halogen, amido, phosphido, alkoxy, ether, sulfide, phosphate ester, or other Lewis acidic or basic functionality. n and m represent the length of the blocks. In some embodiments, n takes any value from 2 to 1250. In some embodiments, m takes any value from 10 to 4500. n:m is usually within 1:2250 to 125:1. This means that in some embodiments the m-block is 2250 repeat units long while the n-block is 1 repeat unit long. Finally, L represents a crosslinking group for those blocks containing a crosslink, and L represents hydrogen for those blocks not containing a crosslink.

[0015] In the above formulas, a —CH₂— group can be substituted with a —Si(OR)₂— group in which R is an alkyl, phenyl, or halogenated alkyl containing 1–6 carbon atoms. A —CH₂— group can be substituted with a keto group, C═O. And sulfur can be substituted for oxygen, thereby converting ether linkages into sulfide linkages.

[0016] In some embodiments, the block copolymer may comprise non-fouling or biobeneficial moieties. The formulas shown below represent two specific classes of invention polymers.

[0017]

[0018] This polymer is comprised of moieties derived from glycerol, adipic acid, and mPEG. The diblock structure indicates that not all of the glycerol is derivatized with mPEG. A portion of the glycerol-derived moiety is involved in an ester crosslink as indicated by (R) or has a free hydroxyl as indicated by (H). In this structure, the PEG is pendant, but it can also be in the polymer backbone.

Diol, Triol, or Polyol

[0019] The diol, triol, or polyol component is a chain with one or more alcohol functionalities. In some embodiments this component is a mixture of di- or multi-alcoholic molecules such as mixtures with PEG diols, glycerol, other triols, etc. In some embodiments, this component is a mixture comprising PEG diols, PLURONIC (TM) diols, or glycerol or other triols.

[0020] In the diol, triol, or polyol, at least one hydroxy group should be present in order to form the hydrolyzable ester linkage. The hydrocarbyl groups T and W may have unsaturation. In polymer precursors containing groups T and W, sulfhydryl and amino groups can substitute for hydroxyl groups as long as at least one hydroxyl group remains to form an ester bond.

[0021] Here is a polymer with a sulfhydryl group substitution: one using mercaptoethanol, sebacic acid, and PEG300.

[0022]

[0023] Criteria for choosing the polyol component depends on whether the component is for hydrocarbyl group T or group W. In addition to two hydroxyl groups, in order to be a part of the polymer backbone, group W requires a third, pendant functionality to attach to the biobeneficial moiety. If group T is to have a pendant hydroxyl or alkoxy group, it must also have this third functionality. However, when group T does not have or is not desired to have any pendant functional groups, it can be difunctional. In some embodiments having excellent biocompatibility, the polyol or polyols are endogenous or have established biocompatibilities.

[0024] Suitable polyols are ethylene glycol, 1,2-propane diol, 1,3-propane diol, 1,4-butanediol, 1,5-butanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, higher diols up to C₁₆, glycerol, trimethylol propane, pentaerythritol, cyclohexanedimethanol, serinol, diethanolamine, and saccharides such as erythrose, threose, ribose, arabinose, xylose, lyxose, dihydroxyacetone, erythrulose, xylulose, aldoses, and ketoses. In some embodiments, polyols are 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, 1,12-dodecanediol, glycerol, serinol, diethanolamine, trimethylol propane, or pentaerythritol.

[0025] One embodiment uses phosphoryl choline-co-HEMA a biobeneficial, methacrylate copolymer. In this polymer, the phosporyl choline group is attached to a methacrylate. These polymers are not usually hydroxy terminated, but certain living polymerization schemes will function with these hydroxy terminated polymer.

[0026] Tri- or multi-functional —OH can copolymerize in the backbone such that two of the hydroxyl groups act to incorporate the polyol chain into the polymer. This leaves one or more remaining hydroxyl groups to conjugate a bioactive moiety. Or, one or more of the remaining hydroxyl groupscan serve as a crosslinking site.

Polycarboxylic Acid

[0027] The polycarboxylic acid is a compound with at least two carboxylic acid groups. For implant use, polycarboxylic acid used in this invention should be toxicologically acceptable. This means the toxicity it imparts to the polymer, and the toxicity of the monomer itself when released, should be low enough that the polymer can be used within a mammalian body. Specific examples of these include C₂ to C₁₂ straight chain aliphatic diacids, specifically oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azaleic acid, sebacic acid, and citramalic acid. Longer chain lengths, such as found in dodecanedioic acid, tetradecanedioic acid, and hexadecanedioic acid, are useful in the practice of this invention. Polycarboxylic acids include citric acid, tricarballylic acid, and tartaric acid. Unsaturated polycarboxylic acids include fumaric acid and muconic acid. Lastly, useful aromatic polycarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 1,6-bis(p-carboxy phenoxy)hexane, 1,3-bis(p-phenoxy carboxy)propane, and 1,4-bis(p-phenoxy carboxy)butane.

[0028] Specific examples of polycarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azaleic acid, sebacic acid, terephthalic acid, and citric acid. Particularly suitable examples include succinic acid, adipic acid, sebacic acid, tricarballylic acid, citric acid, fumaric acid, terephthalic acid, and 1,3-bis(p-phenoxy carboxy)propane.

Biobeneficial Moiety

[0029] For purposes of this disclosure, the term “biobeneficial” is an umbrella description for any surface that provides biological benefit for an implantable medical device without the release of a pharmacologically active agent. Following this definition of “biobeneficial”, the term biobeneficial moiety is a moiety that imparts, either by itself or with another moiety, to a polymer or surface the characteristic of being “biobeneficial”. Within this umbrella definition, some surfaces may be regarded as non-fouling and some as bioactive, whereas others may be regarded as hemocompatible or non-thrombogenic. Also, biobeneficial moieties include moieties that have any combination of bioactive, non-fouling, or hemocompatible characteristics.

[0030] Biobeneficial moieties that are primarily non-fouling are poly(ethylene glycol), polypropylene glycol, PLURONIC (™) surfactants—block copolymers of polyethylene glycol and polypropylene glycol, hydroxy functional poly(vinyl pyrrolidone)dextran, dextrin, sodium hyaluronate, hyaluronic acid, elastin, chitosan, water-soluble chitosan, water-soluble heparin, water-soluble elastin, tropoelastin, Albumin, and poly(2-hydroxyethyl methylmethacrylate). Biobeneficial moieties that are primarily hemocompatible are heparin, hirudin, and sulfonated polystyrene. Particular bioactive agents would include superoxide dismutase mimetics, anti-oxidants, and free radical scavengers. Biobeneficial moieties can possess a combination of these or other properties.

[0031] A caveat is that the maximum molecular weight of this component should be low enough so that the released molecule can pass through the kidneys, e.g., in some embodiments the maximum molecular weight of this component is less than or equal to 40,000 Daltons, if the polymer is not absorbable by hydrolysis or enzymolysis. In this respect, a maximum molecular weight of 20,000 Daltons is more preferred. If the biobeneficial moiety itself is hydrolyzed or metabolized by the body, as would be the case with heparin, then the maximum molecular weight could be larger than the renal passage cutoff of approximately 40,000 Daltons.

[0032] Invention polymers can be linear or crosslinked. The biobeneficial components can be pendant or in the polymer backbone. A polymer of this invention can contain more than one type of biobeneficial moiety. For example, a non-fouling moiety can be pendant on select repeat units designated by “n” while a bioactive moiety could be present on other repeat units designated by “m”. Bioactive moieties can be selected from PEG diols with molecular weights from 300–30,000.

[0033] The choice of values for “n” and “m” determines the total weight fraction of each block in the final polymer. For linear polymers there are limits to the amount of biobeneficial moiety that can be incorporated while retaining acceptable mechanical properties. For example, the non-fouling biobeneficial moieties are largely very hydrophilic and many are water-soluble. If the weight fraction of non-fouling component moieties becomes greater than approximately 80% by weight, then the linear polymer can swell excessively, or even dissolve, in water. Therefore, the weight fraction of non-fouling component moieties is chosen to be less than approximately 80 percent by weight in some embodiments. But if the weight fraction of the non-fouling moiety is too low, not enough will be present to modify the surface properties of the polymer. This level depends of the particular polymer, but is in the range of 1–10 percent by weight, below which biobeneficial, non-fouling properties will be subtle. Therefore, the weight fraction of non-fouling component moieties is chosen to be greater than 1–10 percent by weight in some embodiments. In the case of crosslinked systems, the problems of polymer dissolution are eliminated. Excessive swelling can still occur, which can weaken the polymer coating in some embodiments. In the case of hemocompatible, biobeneficial moieties, similar concerns apply because larger amounts of these moieties give higher surface concentrations at the expense of mechanical properties due to excessive water swelling. Bioactive, biobeneficial moieties are not necessarily hydrophilic. In some embodiments, as much hemocompatible, biobeneficial moiety is incorporated into the polymer as can be incorporated into the polymer and still have the polymer retain acceptable mechanical properties for use in medial devices. For some embodiments, appropriate values of n are between 2 and 1250. For some embodiments, appropriate values of m are between 10 and 4500.

[0034] One specific embodiment of invention copolymers is the crosslinked terpolymer of glycerol, sebacic acid, and polyethylene glycol (PEG300). This polymer has the structure shown below.

[0035]

[0036] The reactivities of PEG300 and glycerol are quite different, so it is advantageous to produce this polymer in a two-step process. Generally, one equivalent of PEG300 is combined with two equivalents of sebacic acid. This is heated under vacuum to produce a sebacic-acid-terminated PEG300. Useful reaction temperatures range from 80 to 140° C., under vacuum of 10 mtorr to 760 torr. Then, depending on the n:m target ratio and the final molecular weight desired in the copolymer, an additional amount of sebacic acid and glycerol, in a. 1:1 mole ratio, is added, and the reaction is continued. Useful reaction parameters in this step include reaction temperatures of from 80 to 140° C., under pressures of 10 mtorr to 760 torr, for reaction times of 2–48 hours.

[0037] Another specific embodiment of invention copolymers is a grafted terpolymer of citric acid, succinic acid, butanediol, and mPEG. This polymer has the structure.

[0038]

[0039] Another specific embodiment of the invention copolymers is a grafted terpolymer of tricarballylic acid, succinic acid, 1,4-butanediol and the monomethyl ether of polyethylene glycol MW=600 (mPEG600). Again, one method of making this polymer is a two-step process where the mPEG is reacted first due to its lower reactivity. Generally, the mPEG is coupled to the tricarballylic acid by coupling an amine-terminated mPEG (such as available from Nektar, formerly Shearwater Polymers) to tricarballylic acid via carbodiimide chemistry. This mPEG-derivatized diacid is then combined with the desired amount of 1,4-butanediol and succinic acid in a 1:1 mole ratio. Instead of ester formation via dehydration using heat and vacuum, further addition of an appropriate carbodiimide, such as 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) or 1,3-dicyclohexylcarbodiimide (DCC), will couple the carboxylic acid and hydroxyl groups to form the polyester. In some embodiments, this yields a linear polymer that is solvent soluble and amenable to current stent coating processes.

[0040] Another specific embodiment of invention copolymers is a terpolymer of 1,3-propanediol, adipic acid, and PEG600. This polymer has the following structure.

[0041]

[0042] Generally, this type of copolymer can also be synthesized in a two-step process. First, the total amount of adipoyl chloride is added to the reaction vessel under anhydrous conditions with an appropriate amount of pyridine to absorb the released HCl. The solvent is toluene. Next, dry PEG600 is added. After the PEG600 has reacted (which results in a adipoyl-chloride-terminated PEG600), 1,3-propanediol is added. 1,3-propanediol is a breakdown product of all biodegradable polymers containing the monomer trimethylene carbonate. 1,3-propanediol is biocompatible. In various embodiments, the molecular weight of the PEG can be varied, the diol can be varied, and the diacid can be varied. In some embodiments, the diacid is one or more of succinic, adipic, or sebacic acids. In some embodiments, this type of polymer is linear and solvent soluble. It is also possible to make copolymers with both pendant and in-chain biobeneficial moieties. This is particularly true in two-step reaction schemes where two different types of acid terminated, biobeneficial derivatized blocks can be synthesized separately, and then combined and further reacted with additional diacid and diol.

[0043] In various embodiments, the molecular weight of the PEG can be varied, the diol can be varied, and the diacid can be varied. In some embodiments, the diacid is one or more of adipic, succinic, and sebacic acid. In some embodiments this type of copolymer is linear and solvent soluble.

[0044] In some invention embodiments, the bioactive moiety is selected to have or to also have free-radical scavenging characteristics. Specific examples of useful bioactive moieties that have free-radical scavenging characteristics include superoxide dismutase or a nitric oxide donor.

[0045] In addition to being used as a non-fouling coating, invention copolymers may be coated onto a polymeric stent, a metal stent, or a bare metal stent, or they may be coated on top of a drug eluting coating already present on a stent. Alternatively, invention copolymers may be disposed between a stent and a drug-eluting coating. Also, invention copolymers can be used to construct polymer-based medical devices or can serve as the substrate from which medical devices (implantable or not) are constructed.

[0046] Invention copolymers can also be used as mixtures with other polymers. For example, invention polymers can be physically blended with PEG, POLYACTIVE(™), or other biobeneficial polymers. These blends could be formulated to modulate biological outcome.

[0047] For purposes of this disclsoure, “modulate biological outcome” means adjusting the polymer biobeneficial-component content in order to minimize fibrinogen absorption, platelet binding, the number of adherent macrophages and inflammatory cells, and the degree to which inflammatory cells are activated.

[0048] These blends could also be formulated to modulate or tune the release rate of drugs from coatings, reservoirs, or particles composed of these blends and drugs or therapeutic agents. Blends with other polymers can be formulated to modulate the mechanical properties of invention polymers. For instance, other polymers could be blended into invention polymers to modify mechanical properties or vice versa. Useful polymers for preparing such blends include polycaprolactone, poly(D,L-lactide), poly(L-lactide), poly(D,L-lactide-co-L-lactide), poly(glycolide), poly(D,L-lactide-co-glycolide), poly(dioxanone), poly(4-hydroxybutyrate), poly(3-hydroxybutyrate), poly(3-hydroxy valerate), poly(hydroxybutyrate-co-hydroxyvalerate), poly(tyrosine derive carbonates), poly(tyrosine arylates), poly(imino carbonates), poly(trimethylene carbonate), poly(anhydrides), poly(orthoesters), and poly(ester amides).

[0049] In some embodiments coatings may be formed on medical devices using invention copolymers as the coating material base. In some embodiments this is accomplished by applying the copolymer of the drugs, polyol(s), and diacid(s) to the surface of the medical device before the copolymer has been substantially crosslinked. Then the coating can be crosslinked slowly by heating the coating. Slow crosslinking is facilitated by the presence of the “third” hydroxyl group, which is a secondary (or tertiary) hydroxyl. Alternatively, a crosslinking step can be carried out simultaneously during sterilization, such as heat or electron-beam sterilization.

[0050] Crosslinking (in bulk invention polymer or in coatings comprising invention polymer) can be carried out so that the crosslinks form mainly between invention copolymer chains. Alternatively, the crosslinks can form between invention copolymer chains in blends, or between invention copolymers in one layer and the molecules or polymer chains in primer layers or in other polymer layers.

[0051] Conventional therapeutic agents, such as small-hydrophobic drugs, may also be added to invention copolymers, making them bioabsorbable, drug-eluting systems. Conventional therapeutic agents can be grafted on to the invention copolymers or can be mixed in the invention copolymers. Invention copolymers can be coated as blends with a variety of other biobeneficial polymers. Moreover, they can serve as base or topcoat layers for other biobeneficial polymer layers.

[0052] The therapeutic agent can be for inhibiting the activity of vascular smooth muscle cells. More specifically, the therapeutic agent can be aimed at inhibiting abnormal or inappropriate migration or proliferation of smooth muscle cells to prevent, inhibit, reduce, or treat restenosis. The therapeutic agent can also include active agent may be any substance capable of exerting a therapeutic or prophylactic effect in the practice of the present invention. Examples of such active agents include antiproliferative, antineoplastic, antiinflammatory, antiplatelet, anticoagulant, antifibrin, antithrombin, antimitotic, antibiotic, and antioxidant substances as well as combinations thereof. An example of an antiproliferative substance is actinomycin D, or derivatives and analogs thereof (manufactured by Sigma-Aldrich 1001 West Saint Paul Avenue, Milwaukee, Wis. 53233; or COSMEGEN available from Merck). Synonyms of actinomycin D include dactinomycin, actinomycin IV, actinomycin I₁, actinomycin X₁, and actinomycin C₁. Examples of antineoplastics include paclitaxel and docetaxel. Examples of antiplatelets, anticoagulants, antifibrins, and antithrombins include aspirin, sodium heparin, low molecular weight heparin, hirudin, argatroban, forskolin, vapiprost, prostacyclin and prostacyclin analogs, dextran, D-phe-pro-arg-chloromethylketone (synthetic antithrombin), dipyridamole, glycoprotein IIb/IIIa platelet membrane receptor antagonist, recombinant hirudin, thrombin inhibitor (available from Biogen), and 7E-3B® (an antiplatelet drug from Centocor). Examples of antimitotic agents include methotrexate, azathioprine, vincristine, vinblastine, fluorouracil, adriamycin, and mutamycin. Examples of cytostatic or antiproliferative agents include angiopeptin (a somatostatin analog from Ibsen), angiotensin converting enzyme inhibitors such as CAPTOPRIL (available from Squibb), CILAZAPRIL (available from Hoffman-LaRoche), or LISINOPRIL (available from Merck & Co., Whitehouse Station, N.J.), calcium channel blockers (such as Nifedipine), colchicine, fibroblast growth factor (FGF) antagonists, histamine antagonist, LOVASTATIN (an inhibitor of HMG-CoA reductase, a cholesterol lowering drug from Merck & Co.), monoclonal antibodies (such as PDGF receptors), nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitor (available form Glazo), Seramin (a PDGF antagonist), serotonin blockers, thioprotease inhibitors, triazolopyrimidine (a PDGF antagonist), and nitric oxide. Other therapeutic substances or agents that may be appropriate include alpha-interferon, genetically engineered epithelial cells, dexamethasone, estradiol, clobetasol propionate, cisplatin, insulin sensitizers, receptor tyrosine kinase inhibitors and carboplatin. Exposure of the composition to the active agent should not adversely alter the active agent's composition or characteristic. Accordingly, the particular active agent is selected for compatibility with the blended composition. Rapamycin is a suitable active agent. Additionally, 40-O-(2-hydroxy)ethyl-rapamycin, or a functional analog or structural derivative thereof, is suitable, as well. Examples of analogs or derivatives of 40-O-(2-hydroxy)ethyl-rapamycin include but are not limited to 40-O-(3-hydroxy)propyl-rapamycin and 40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin. The release rate active agents, such as 40-O-(2-hydroxy)ethyl-rapamycin, can be advantageously controlled by various methods and coatings as is known in the art.

[0053] As stated above, invention block copolymers can be used with other polymers and biopolymers. Representative examples of polymers useful with invention block copolymers include ethylene vinyl alcohol copolymer, poly(hydroxyvalerate); poly(L-lactic acid); polycaprolactone; poly(lactide-co-glycolide); poly(hydroxybutyrate); poly(hydroxybutyrate-co-valerate); polydioxanone; polyorthoester; polyanhydride; poly(glycolic acid); poly(D,L-lactic acid); poly(glycolic acid-co-trimethylene carbonate); polyphosphoester; polyphosphoester urethane; poly(amino acids); cyanoacrylates; poly(trimethylene carbonate); poly(iminocarbonate); copoly(ether-esters) (e.g. PEO/PLA); polyalkylene oxalates; polyphosphazenes; biomolecules, such as fibrin, fibrinogen, cellulose, starch, collagen and hyaluronic acid; polyurethanes; silicones; polyesters; polyolefins; polyisobutylene and ethylene-alphaolefin copolymers; acrylic polymers and copolymers; vinyl halide polymers and copolymers, such as polyvinyl chloride; polyvinyl ethers, such as polyvinyl methyl ether; polyvinylidene halides, such as polyvinylidene fluoride and polyvinylidene chloride; polyacrylonitrile; polyvinyl ketones; polyvinyl aromatics, such as polystyrene; polyvinyl esters, such as polyvinyl acetate; copolymers of vinyl monomers with each other and olefins, such as ethylene-methyl methacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins, and ethylene-vinyl acetate copolymers; polyamides, such as Nylon 66 and polycaprolactam; alkyd resins; polycarbonates; polyoxymethylenes; polyimides; polyethers; epoxy resins; polyurethanes; rayon; rayon-triacetate; cellulose; cellulose acetate; cellulose butyrate; cellulose acetate butyrate; cellophane; cellulose nitrate; cellulose propionate; cellulose ethers; and carboxymethyl cellulose.

[0054] Examples of implantable devices for the present invention include self-expandable stents, balloon-expandable stents, stent-grafts, grafts (e.g., aortic grafts), vascular grafts, artificial heart valves, cerebrospinal fluid shunts, pacemaker electrodes, guidewires, ventricular assist devices, artificial hearts, cardiopulmonary by-pass circuits, blood oxygenators, and endocardial leads (e.g., FINELINE and ENDOTAK, available from Guidant Corporation, Santa Clara, Calif.). The underlying structure of the device can be of virtually any design. The device can be made of a metallic material or an alloy such as, but not limited to, cobalt chromium alloy (ELGILOY), stainless steel (316L), high nitrogen stainless steel, e.g., BIODUR 108, cobalt chrome alloy L-605, “MP35N,” “MP20N,” ELASTINITE (Nitinol), tantalum, nickel-titanium alloy, platinum-iridium alloy, gold, magnesium, or combinations thereof. “MP35N” and “MP20N” are trade names for alloys of cobalt, nickel, chromium, and molybdenum available from Standard Press Steel Co., Jenkintown, Pa. “MP35N” consists of 35% cobalt, 35% nickel, 20% chromium, and 10% molybdenum. “MP20N” consists of 50% cobalt, 20% nickel, 20% chromium, and 10% molybdenum. Devices made from bioabsorbable or biostable polymers could also be used with the embodiments of the present invention.