| Polyglycolic acid (PGA) and Polylactic acid (PLA) are well-established bioabsorbable polymers. Polyglycolic acid sutures were first introduced in 1970. PLA or polylactide is derived from the cyclic diester of lactic acid (lactide) by ring opening polymerization. PLA’s performance can be varied by the optical purity of the lactic acid monomer and its molecular weight. L-polylactide fibers (mp 170°C) have high crystallinity, whereas those from poly-DL-lactide are amorphous. Crystalline poly-L-lactide is more resistant to hydrolytic degradation than the amorphous DL form. The rate of poly-L-lactide degradation can be enhanced by plasticization with triethyl citrate, but results in a less crystalline, more flexible material. The absorption rate of poly-L-lactide implants is relatively long and is a function of polymer quality, processing conditions, implant site, and physical implant dimensions. Unlike PLA, PGA is absorbed within a few months postimplantation based on its higher hydrolytic susceptibility. Poly(lactide-co-glycolide) are copolymers of PGA/PLA that can be tailored for a variety of applications, e.g., surgical clips and staples. Copolymers are amorphous in the compositional range 25-70 mole percent glycolide. Pure polyglycolide is ~50% crystalline, whereas pure poly-L-lactide is ~37% crystalline. |
