Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/66—Polyesters containing oxygen in the form of ether groups
  • C08G63/668—Polyesters containing oxygen in the form of ether groups derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/672—Dicarboxylic acids and dihydroxy compounds
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K9/00—Medicinal preparations characterised by special physical form
  • A61K9/70—Web, sheet or filament bases ; Films; Fibres of the matrix type containing drug
  • A61K9/7007—Drug-containing films, membranes or sheets
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
  • A61L27/14—Macromolecular materials
  • A61L27/18—Macromolecular materials obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L31/00—Materials for other surgical articles, e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices
  • A61L31/04—Macromolecular materials
  • A61L31/06—Macromolecular materials obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/78—Preparation processes
  • C08G63/82—Preparation processes characterised by the catalyst used
  • C08G63/85—Germanium, tin, lead, arsenic, antimony, bismuth, titanium, zirconium, hafnium, vanadium, niobium, tantalum, or compounds thereof

Definitions

• the invention relates to a polymeric material, a process for the preparation of the polymeric material, a medical device comprising said polymeric material and the use of the medical device for the preparation of a medicament for guided tissue, as a scaffold for engineering tissue in vitro, or as a matrix for controlled release of a (bio)active substance.
• the European patent application 0 830 859 discloses a drug delivery system based on a copolymer of a polyalkylene glycol, preferably polyethylene glycol, and an aromatic polyester, preferably polybutylene terephthalate.
• This polymeric material has hydrogel-like properties and advantageously enables diffusion of even large molecules, such as proteins, through the polymeric matrix. Furthermore, the biocompatibility of this polymeric material has been found to be very good.
• tissue engineering a matrix, often referred to as scaffold, is provided with cells in vitro and the combined system of cells and scaffold is implanted into the body of a patient in need of tissue repair.
• the scaffold is intended to provide the mechanical properties and integrity to keep the implant together.
• the scaffold is intended to degrade so that the new tissue can take over its function.
• the cells are subjected to a culturing protocol in vivo to accelerate the process of formation of new tissue in vivo.
• the ideal material to serve as scaffold to be provided with cells in tissue engineering closely resembles the properties, in particular the mechanical properties, of the tissue which is in need of repair. Because some types of tissue require stronger and stiffer mechanical properties than others, it is desired to have a biodegradable and biocompatible material of which the mechanical properties may be advantageously adjusted to the need of the situation in tissue engineering. Also, depending on the type of tissue to be repaired, a slower or faster degradation of the scaffold may be desired. It is therefore a goal of the present invention to provide for a biomaterial which degrades over a favourably short period of time, while at the same time having excellent characteristics with respect to biocompatibility. Another goal of the present invention is to provide for a material which has a composition that allows for the adjustment of the degradation characteristics, while the biocompatibility and other characteristics related to the use of the material, for instance as drug delivery vehicle, are substantially not negatively affected by said adjustment.
• This polymeric material is based on a combination of a polyether component, a short chain diol and a mixture of aromatic and non-aromatic dicarboxylic acids or derivatives thereof.
• the invention is accordingly directed to a random copolymer comprising monomeric units wherein
• X represents a moiety containing an aromatic group
• Y is an alkylene moiety
• Z represents an alkylene or alkenylene moiety
• n is an integer in the range of 1 - 250, preferably 8 — 100
• m is an integer in the range of 2 - 16.
• a polymeric material according to the invention has been found to possess excellent characteristics with regard to biodegradability and biocompatibility. By varying the ratio between the different components of the multiblock copolymer, the biodegradability profile, as well as the mechanical properties, of the polymeric material may conveniently be adjusted.
• the degradation product of the polyester component, the dicarboxylic acid may catalyse the degradation of the other components of the present polymeric material.
• biocompatible is intended to refer to materials which may be incorporated into a human or animal body, e.g. in the form of a medical implant, substantially without unacceptable responses of the human or animal.
• biodegradable refers to materials which, after a certain period of time, are broken down in a biological environment.
• the rate of breakdown is chosen similar or identical to the rate at which the body generates autogenous tissue to replace an implant of which the biodegradable material is manufactured.
• random copolymer is intended to reflect that a polymeric material of the invention comprises monomeric units A, B, C, and D in any order an in any ratio.
• the ratio of the number a of monomeric units A to the number b of monomeric units B (a b) will typically be the same as the ratio of the number c of monomeric units C to the number d of monomeric units D (c/d). It is preferred that a copolymer according to the invention does not contain any other monomeric units than the units A, B, C, and/or D.
• the polymeric material comprises both hard and soft fragments.
• the weight fraction of soft fragments may be defined as x and be determined by the combined weight fraction of the monomeric units A and C in the polymeric material.
• the weight fraction of hard fragments is then defined as 1-x and is determined by the combined weight fraction of the monomeric units B and D in the polymeric material.
• the weight fraction of soft segments x preferably is in the range of 0.1 to 1, more preferably 0.4 to 1, yet more preferably 0.5 to 0.9.
• the fraction of the sum of the number of monomeric units C and the number of monomeric units D (c + d) is preferably from 0.01 to 1, more preferably from 0.05 to 0.99.
• X is a moiety comprising an aromatic group.
• the aromatic group may in principle be any aromatic group such as a phenyl, naphtyl, or cyclopentadienyl group.
• the aromatic group is a phenyl group.
• the aromatic group may carry one or more substituents, such as chloro, bromo, iodo, fluoro, nitro, methoxy groups or alkyl groups containing 1-3 carbon atoms.
• moiety X comprises other atomic groups, such as methylene groups. Examples of such possibilities include -(CH2) P -aromatic group-(CH2)q, wherein p and q are independently chosen from the group of integers in the range of 0-3. Preferably, both p and q are 0.
• Moiety Y is an alkylene group.
• alkylene and polyalk lene generally refer to any isomeric structure, i.e. propylene comprises both 1,2-propylene and 1,3-propylene, butylene comprises 1,2- butylene, 1,3-butylene, 2,3-butylene, 1,2-isobutylene, 1,3-isobutylene and 1,4- isobutylene (tetramethylene) and similarly for higher alkylene homologues.
• this alkylene group is chosen from the group of ethylene, propylene, butylene and combinations thereof.
• moiety Y forms a repeating unit that occurs n times in the monomeric units A and C.
• This repeating unit is preferably derived from a poly(alkylene glycol).
• the poly (alkylene glycol) is preferably chosen from the group of poly(ethylene glycol), poly (propylene glycol), and poly(butylene glycol) and copolymers thereof, such as poloxamers.
• a highly preferred poly(alkylene glycol) is poly(ethylene glycol).
• the poly(alkylene glycol) may have a weight average molecular weight of about 200 to about 10,000 g/mol.
• the poly(alkylene glycol) has a weight average molecular weight of 300 to 4,000 g/mol. Accordingly, integer n is preferably chosen in the range of 1 - 250, more preferably 8 - 100.
• a weight average molecular weight may suitably be determined by gel permeation chromatography (GPC).
• GPC gel permeation chromatography
• This technique which is known per se, may for instance be performed using chloroform, hexafluoro isopropanol or m-cresol as a solvent and polystyrene or poly(methyl methacrylate) as external standard.
• a measure for the weight average molecular weight may be obtained by using viscometry (see NEN-EN-ISO 1628-1).
• This technique may for instance be performed at 25°C using chloroform, hexafluoro isopropanol or a mixture of both as a solvent.
• the intrinsic viscosity of the copolymer lies between 0.2 and 2.0 dL/g.
• the more preferred ranges for the weight average molecular weight measured by GPC mentioned above can also be expressed in terms of the intrinsic viscosity, when the appropriate physical data for the polymers are known.
• Moiety Z is an alkylene or alkenylene group.
• alkylene group the term alkenylene group is intended to refer to any isomeric structure.
• a propenylene group can be a 1,2-propenylene group, a 2,3-propenylene group, or an isopropenylene group.
• moiety Z, together with the two attached carbonyl groups will be derived from a dicarboxylic acid or a derivative thereof.
• the dicarboxylic acid is an alkanedioic acid having from 4 to 18 carbon atoms.
• the dicarboxylic acid is an unbranched dicarboxylic acid, as it has been found that this leads to a copolymer having superior processability, wherein a biologically active agent can be incorporated in a convenient manner.
• dicarboxylic acids chosen from the group of maleic acid, succinic acid, adipic acid, sebacic acid, glutaric acid, and suberic acid.
• Z is preferably chosen from the group of ethenylene, propylene, butylenes, hexylene, and octylene.
• a copolymer having increased swelling behaviour is obtained when the amount of (aliphatic) dicarboxylic acid used to prepare the copolymer is increased.
• a derivative of a dicarboxylic acid which will be incorporated into the copolymer structure by way of the same carboxylic functionalities.
• examples of such derivatives can easily be conceived by the skilled person and include anhydrides, mono- and diesters, mono- and diacid chlorides, and the like.
• the carboxylic acid group is preferably esterified to an alkyl group having from 1 to 4 carbon atoms.
• Preferred derivatives are dimethyl esters.
• Integer m is chosen in the range of 2 — 16.
• the 2 — 16 repeating methylene groups are preferably derived from a diol.
• the diol is chosen from the group of dihydroxy ethane, dihydroxy propane or dihydroxy butane.
• a highly preferred short chain diol is dihydroxy butane.
• the weight average molecular weight of a random copolymer according to the invention preferably lies between 10,000 and 500,000 g/mol, more preferably between 40,000 and 300,000 g/mol.
• the invention further relates to a process for preparing a copolymer as described above comprising the steps of a) reacting an aromatic dicarboxylic acid or a derivative thereof, a non- aromatic dicarboxylic acid or a derivative thereof with a poly (alkylene glycol) and an alkanediol; and b) carrying out a polycondensation under removal of the alkanediol.
• the aromatic dicarboxylic acid or derivative thereof is chosen such that it gives moiety X described above.
• a preferred example of the aromatic dicarboxylic acid is terephthalic acid or a derivative thereof.
• Examples of such derivatives can easily be conceived by the skilled person and include anhydrides, mono- and diesters, mono- and diacid chlorides, and the like.
• the carboxylic acid group is preferably esterified to an alkyl group having from 1 to 4 carbon atoms.
• Preferred derivatives are dimethyl esters.
• the non-aromatic dicarboxylic acid or derivative thereof, as discussed above, is chosen such that it gives moiety Z in the copolymer.
• the non-aromatic is chosen from the group of aleic acid, succinic acid, adipic acid, sebacic acid, glutaric acid, and suberic acid.
• suitable derivatives can easily be conceived by the skilled person and include anhydrides, mono- and diesters, mono- and diacid chlorides, and the like.
• the carboxylic acid group is preferably esterified to an alkyl group having from 1 to 4 carbon atoms.
• Preferred derivatives are dimethyl esters.
• the poly(alkylene glycol) is chosen such that it gives moiety Y in the copolymer.
• the poly(alkylene glycol) is preferably chosen from the group of poly(ethylene glycol), polypropylene glycol), and poly(butylene glycol) and copolymers thereof, such as poloxamers.
• a highly preferred poly (alkylene glycol) is poly(ethylene glycol).
• the poly(alkylene glycol) may have a weight average molecular weight of about 200 to about 10,000 g/mol.
• the poly(alkylene glycol) has a weight average molecular weight of 300 to 4,000 g/mol.
• the alkanediol is preferably a short chain diol and is chosen such that it gives the group carrying the index m in the formulas above.
• the diol is chosen from the group of dihydroxy ethane, dihydroxy propane or dihydroxy butane.
• a highly preferred short chain diol is dihydroxy butane.
• a preferred preparation of a multiblock copolymer according to the invention will now be explained by way of example for a multiblock copolymer synthesized from poly(ethylene glycol), butanediol, dimethyl terephthalate, and dimethyl succinate. Based on this description, the skilled person will be able to prepare any desired multiblock copolymer within the above described class.
• a typical poly(ether ester) multiblock copolymer may be synthesized from a mixture of dimethyl terephthalate, an alkanediol such as 1,4-butanediol (in excess), poly(ethylene glycol), dimethyl succinate, an antioxidant and a catalyst.
• An example of a suitable catalyst is tetrabutyloxy titanium. The mixture is placed in a reaction vessel and preferably heated to at least about 160°C, and methanol is preferably distilled as transesterification proceeds.
• the temperature is preferably raised slowly to about 245°C, and a vacuum (finally less than 0.1 mbar) is preferably achieved.
• a vacuum finally less than 0.1 mbar
• Excess alkanediol may be distilled off and the objective multiblock copolymer is formed in a polycondensation step.
• a polymeric material according to the invention can be used for the manufacture of various medical devices, such as scaffolds for artificial skin, bone implants, cement restrictors, or for tissue engineering cartilage or muscle.
• the invention therefore also encompasses a medical device comprising a polymeric material as described above.
• the medical device can be used for tissue repair or controlled drug release.
• Preferred forms of the medical device include a scaffold for engineering tissue in vitro, a matrix for controlled drug release, a substitute for tissue repair, a suture, a bone screw, a suture anchor, a tapered or non-tapered pin, or a staple.
• a polymeric material according to the invention its composition and its preparation
• the skilled person can adjust the properties of the material to suit his particular needs in the context of a specific application or device.
• a more flexible material may be desired for scaffolds for tissue engineering skin or for sutures, which property is positively affected by increasing the amount of the poly(alkylene glycol) component in the multiblock copolymer.
• an even faster degradation profile is desired in which case higher amounts of the non- aromatic dicarboxylic acid or derivative thereof may be incorporated.
• a given wt.% of poly (alkylene glycol) component in the multiblock copolymer can be incorporated in two different ways.
• One possibility is to use a lower number of larger blocks, i.e. poly(alkylene glycol) of a higher weight average molecular weight; another is to incorporate more blocks of a lower weight average molecular weight.
• the polymeric material is prepared by conventional processing step for such as extrusion, injection-molding, blow-molding, solution molding and other techniques for the shaping and processing of polymeric materials.
• the medical device it is possible to include pharmaceuticals or pharmaceutically active components in the polymeric composition.
• the device can be used for the controlled release of medicaments. This can be performed in conjunction with the other functions of the polymeric composition of the present invention, but it may also be the sole purpose of this specific embodiment.
• the polymer of the present invention can also be used to prepare controlled release formulations for the release of biologically active agents, including protein and peptides.
• Such delivery systems may be formulated into microspheres, injectable gels, sheets etc., by methods known to those skilled in the art.
• biologically active agent means an agent which provides a therapeutic or prophylactic effect.
• agents include, but are not limited to, antimicrobial agents (including antibacterial and anti- fungal agents), anti-viral agents, anti-tumor agents, hormones immunogenic agents, growth factors, hpids, and lipopolysaccharides.
• biologically active agents that can be incorporated into the polymeric material may vary widely in nature; in principle any type of additive may be incorporated.
• the polymeric material is biodegradable in vivo, and allows diffusion of molecules, the additives will be released to the surroundings of the material in a controlled manner.
• These additives may be added to the solution in amounts ranging from 0 to 50 wt.%, preferably from 1 to 20 wt.%.
• Biologically active agents which may be incorporated include, but are not limited to, non-peptide, non-protein small-sized drugs. They have a molecular weight which in general is less than 1500, and in particular less than 500.
• a second important group of biologically active agents are biologically active peptides and proteins.
• a biologically active agent may be incorporated into the polymeric material by dissolving it in a solution of the polymeric material.
• Suitable solvents are chloroform, dichloromethane, N-methyl-2-pyrrolidone, dimethyl sulfoxide, acetone, hexafluoroisopropanol and the like. The selection of a suitable solvent will be dependent on the composition of the chosen copolymer. Hence, a homogeneous solution is formed or a suspension is formed by dispersion.
• a solution of a biologically active agent may be mixed with the copolymer solution to form a homogeneous mixture, or an emulsion.
• a biologically agent can be incorporated by physically mixing with the copolymer, for example by extrusion. Since in the latter case heat is applied, care must be taken not to harm the stabihty and/or activity of the biologically active agent.
• Pore-forming agents may include organic solvents, water, salts (sodium chloride, sodium citrate, and the like), sugars and water-soluble synthetic polymers. Using such pore-forming agents, pores can be created by leaching-out of the agent, or by phase separation.
• Example 1 The invention will now be further elucidated by the following, non- restrictive examples.
• Example 1 The invention will now be further elucidated by the following, non- restrictive examples.
• Example 1 The invention will now be further elucidated by the following, non- restrictive examples.
• Example 1 The invention will now be further elucidated by the following, non- restrictive examples.
• Example 1 The invention will now be further elucidated by the following, non- restrictive examples.
• the poly(ether ester) multiblock copolymer described in the following example is composed from poly(ethylene gycol), butanediol, dimethyl terephthalate as the aromatic dicarboxylic acid derivative and dimethyl succinate as non-aromatic dicarboxylic acid.
• a polymer (1-A) that contains approximately 60% by weight of poly(ethylene glycol) and terephthaliite and succinate in a 50/50 molar ratio is prepared by placing the following materials in a reactor suitable to perform both atmospheric distillations and distillations under reduced pressure:
• the reactor is equipped with a mechanical stirrer with torque readout, a nitrogen inlet tube, a PtlOO temperature sensor connected to a digital read-out device and a condensor, which can be heated by a thermostatic water bath.
• the reactor is heated by a thermostatic oil bath.
• the transesterfication reaction begins at 140 to 145°C. Methanol is distilled off for approximately one hour. After this the temperature is slowly increased to 240°C. As the temperature of the reaction mixture reaches 230 to 240°C, the pressure is gradually reduced to 0,5-1,5 mbar in approximately 30 minutes. During 3-4 hours, until the reaction mixture has reached the desired viscosity, the condensation product 1,4-butanediol is distilled off. The polymer is then extruded and quenched in cold water follow by drying and grinding.
• the intrinsic viscosity of the product measured in chloroform at 25°C is 0,990 dl/g.
• H-NMR measurements were used to calculate the polyether wt.% and the diacid ratio (T/S).
• T/S diacid ratio
• 1-A the poly(ethylene glycol) content was 58.3 wt.%.
• the diacid ratio (T/S) is 55/45 mole%.
• a multiblock copolymer (1-B) was synthesized that contains approximately the same polyether content as 1-A.
• the diacid used was only succinate, no aromatic diacid was incorporated. It is prepared in the same way as described in example 1, by placing the following materials in a reactor:
• the intrinsic viscosity of the product measured in chloroform at 25 °C is 1,166 dl/g. H-NMR measurements showed that 63.5 w/w% poly(ethylene glycol) was incorporated.
• a 10% by weight solution of the polymers described in examples 1 and 2 were used to cast films to be used for in-vitro degradation studies. Dry films (approximately 0.5 gram, 50-100 ⁇ m thickness) were immersed in 50 ml phosphate buffered saline (PBS, pH 7.4, containing 1.06 mM KH2PO4, 155.17 mM NaCl, and 2.96 mM Na 2 HP0 4 - 7 H 2 0) at 37°C in a shaking bath for 1, 2, 4 and 8 weeks. Each week, the buffer was refreshed. The films were freeze-dried and subsequently analysed by Gel Permeation Chromatography (GPC).
• GPC Gel Permeation Chromatography
• PEG polyethyelene glycol
• PB polybutylene
• T terephthalate
• S succinate
• Films were prepared from a water-in-oil emulsion (w/o).
• the oil phase was constituted of 1 gram of polymer dissolved in at least 5 mL of dichloromethane (for the exact amounts, see appendix 1).
• the water phase consisted of the protein dissolved in PBS (55 mg/mL).
• the 3 different proteins used were Lysozyme, Carbonic Anhydrase and Bovine Serum Albumin (BSA). 0.6mL of this protein solution was added to the polymer solution and stirred a few seconds with a stirring plate. Then, the mix was put in a 50 mL centrifuge tube and the emulsion was prepared using the Ultra Turrax for 30 seconds at 19000 rpm.
• the emulsion was cast using an adjustable film applicator (setting: 700 ⁇ m) on a glass plate. After evaporation of the dichloromethane, the films were stripped from the glass plate and dried further in the air for some hours. Subsequently, the films were dried in the freeze-dryer for at least 10 hours.
• Graphs 1A and B Cumulated release (%) of lysozyme from 1000PEG(T/S)60PB(T/S)40 when the percentage of succinate was 10%, 50%, 100% and from the 'reference' 1000PEGT65PBT35.
• the copolymer which contains 100% of succinate showed a very fast release of lysozyme (graph 1A): 100% of the protein is released within 20 minutes. When the succinate percentage is only 50%, the release was finished after 5 hours.
• Two release behaviours are clearly visible on the overall graph of the experiment (graph IB): in contrast to the fast release from polymers with 50 or 100% succinate, the release from polymers with 0 or 10% succinate continued for more than 30 days.
• the fast release is due to the swelling of the copolymers.
• the degradation of the matrix is also involved because the release takes more time.
• the degradation of the 0 and 10% succinate compositions have the same profile which explains also the similar profile of their release.
• the combination of degradation and diffusion explains the zero order profile observed for the 0 and 10% of succinate compositions. For highly swollen matrices, in which diffusion is fast compared to degradation, no effect of polymer degradation can be expected and a first order profile of release is observed.
• the determination of the diffusion coefficient of each copolymer is interesting.
• the diffusion coefficient expresses the capability of the molecule entrapped to diffuse through the polymer matrix into the release medium.
• the release was plotted as a function of t (time in seconds). The diffusion coefficients were calculated using equations 2 and 3, after rearranging.
• succinate copolymers have a higher diffusion coefficient [Bezemer J.M., Protein Release Systems based on Biodegradable Amphiphilic Multiblock copolymers, Thesis University of Twente; 1992 p.65].
• the release of lysozyme was complete within only 5 hours for the 1000PEG(T/S)60PB(T/S)40 (graph 3), and within 1 hour for the 4000PEG(T/S)60PB(T/S)40.
• the 600PEG(T/S)60PB(T/S)40 needs 10 days to release all the Lysozyme entrapped, whereas only 5% of the protein is released in 25 days from the 300PEG(T/S).
• the lysozyme must be retained inside of the matrix of the 300PEG(T/S). As the release is fast for the copolymers containing PEG segments of 1000 and 4000 g/mol, the release is mostly determined by the matrix swelling instead of degradation.
• the 4000PEG showed the fastest release because it swells more than the other compositions (appendix 1), resulting in the highest diffusion coefficient.
• BSA is the biggest protein (67kD) used for this release study (graph 4).
• the 1000PEG polymer has a complete release in 80 days and the 4000PEG in 100 days, whereas the BSA release from the 600PEG polymer is not finished yet at day 125.
• the large size of the protein induces a lag-time at the beginning: there is no initial diffusion out of the matrix. If the release was mainly determined by the swelling of the matrix, an increasing release rate would be expected with increasing PEG segment length. Surprisingly, the release from the 1000 composition is the fastest and is therefore linked to the degradation scheme. Around 40-50 days, the matrix is more open for protein diffusion, due to degradation. Moreover, the release of the 4000 composition is faster than the 600 composition whereas the degradation profiles were the same. This is due to a combination of swelling and degradation effects.
• New succinate containing copolymers were evaluated for release purposes because the degradation rate of PEGT/PBT copolymers was too slow for some applications. It was shown that protein release was faster for succinate containing polymers than for the aromatic poly(ether ester)s. Lysozyme was released from the 1000PEG(T/S)60PB(T/S)40 (50% succinate) within 5 hour, whereas for the comparable PEGT/PBT composition it takes 30 days. When the PEG molecular weight increased, the release was faster. By the same way, when the percentage of succinate was higher, the release was also faster. Two release profiles were observed. For small proteins (lysozyme, carbonic anhydrase), the release was fast through the swollen matrix and a first order release was obtained. For larger protein (BSA), the release was correlated to the degradation behaviour of the copolymer and a delayed release profile was observed.
• Porous discs (d ⁇ l ⁇ mm) were prepared using a solvent casting/salt leaching process. Gamma irradiated samples were implanted subcutaneous on the back along the dorso-medial line of large Wistar rats. Samples were explanted after 2, 8 and 15 weeks. GPC analysis on the copolymers was performed after extraction from the tissue using chloroform.
• copolymer compositions have been synthesized as described in example 1.
• the copolymer had a fixed PEG Mw (1000D) and PEG(T/S)/PB(T/S) ratio (65/35) and variable succinate substitution ratio.
• a substitution of for example 10% indicates that 10 mol % of the diacid groups consist of succinate, the remaining 90 mole % is terephthalate.
• the swelling of the films is determined by weighing them before and after incubation in the release buffer for three days.
• the equation used to calculate the equihbrium volume-swelhng ratio is shown below in the equation 1:
• Equation 1 equilibrium swelling ratio

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