Biocompatible and bioabsorbable in vivo synthetic polymers are known for use in the manufacture of implantable medical devices. Many such bioabsorbable polymers belong to the polyester family. For example, aliphatic polyesters have been used in drug delivery systems.
Known biodegradable polyester polymer/copolymer materials include polydioxanone (PDS), polyglycolic acid (PGA), poly-L-lactic acid (PLA), and copolymers of polyglycolic acid and either L-lactic acid or trimethylene carbonate (TMC).
Linear polyesters may be synthesized by ring opening polymerization of cyclic esters or lactones, or by polycondensation of one or more difunctional monomers. Polycondensation of difunctional monomers include the esterification of diacid chlorides and diols, or the ester exchange reaction of diesters and diols. Crosslinked polyesters can be formed by including in the polycondensation reaction monomers with functionalities greater than two.
U.S. Pat. No. 1,779,367 discloses condensation reaction products of certain higher polybasic acids and polyhydric alcohols, notably glycerol. In one example, 1 mole equivalent gylcerol and 1.5 mole equivalents sebacic acid are reacted.
U.S. Pat. No. 2,012,267 discloses alkylene ester reaction products of polybasic acids. These esters are said to be formed by the esterification of dibasic acids and glycols of the formula:OH(CH2)mOH,where “m” is an integer greater than 2. In example 5, poly(ethylene sebacate) is prepared from 67.3 g of sebacic acid and 21.7 g of ethylene glycol.
U.S. Pat. No. 5,098,776 discloses fibrous sheets having shape memory properties. The sheet comprises a natural or synthetic fiber and a layer formed by applying a powder of shape memory polymer. The shape memory polymer may be a urethane polymer, a styrene butadiene polymer, a crystalline diene polymer, and a norbornane polymer. To impart shape memory properties, a powder of shape memory polymer is applied to a part of the sheet with the aid of adhesive.
U.S. Pat. No. 5,889,140 discloses molded articles made from crosslinkable polylactone-based compositions having biodegradability and shape memorizable properties. The compositions are made from 100 parts by weight of polylactone (A) having a number average molecular weight of 10,000 to 300,000 and 0.1 to 30 parts by weight of crosslinkable monomer (B). The crosslinkable polylactone-based composition is crosslinked by irradiating active energy radiation or by heating at 120° C. to 250° C.
U.S. Pat. No. 6,160,084 discloses biodegradable shape memory polymers. In one embodiment, the compositions contain hard and soft segments. The hard segments have a higher transition temperature than the soft segments. The hard segments have a transition temperature of between −30° C. and 270° C. Either the hard or soft segments are crosslinkable.
U.S. Pat. Publ. No. 2003/0118692 discloses biodegradable polymer condensation products of glycerol and diacid (e.g., sebacic acid). The degradation rate is reputed by this publication to be adjustable by modifying crosslink density. The molar ratio of glycerol to the diacid disclosed may be between (1 and 1.5):1. This publication reports the manufacture of a poly(glycerol-sebacate) by polycondensation of equi-molar amount of glycerol and sebacic acid. The publication also reports that the resulting polymer has two crystallization temperatures at −52.14° C. and −18.50° C., has two melting temperatures at 5.23° C. and 37.62° C., and is totally amorphous at 37° C. The disclosed polymer is suggested for use as a tissue engineering construct, or in other medical and non-medical applications. This publication does not report any shape memory properties for this material.
Chinese Pat. Publ. No. 1 640 909 A discloses biodegradable ternary aliphatic polyester elastomers. An esterification reaction is carried out between a dibasic acid and a diol to form a low-molecular weight linear prepolymer. In this reaction, the molar ratio of the dibasic acid to diol is between (1.5 and 3.5):1. An esterification crosslinking reaction then is carried out between that linear prepolymer and a monomeric polyol. This patent publication does not report any shape memory properties for this material, and instead describes the resulting polyester as an elastomer.