title: An enhanced strength retention poly(glycolic acid)-poly(L-lactic acid) copolymer for internal fixation: in vitro characterization of hydrolysis.
abstract: In general, most bioabsorbable polymers used for internal fixation are composed of copolymers of glycolic acid and lactic acid (L and/or DL). Within this family of polymers resides the latitude to design materials with specific degradation properties to meet a variety of clinical needs. One material with an extensive clinical history is LactoSorb copolymer, which is composed of a molar ratio of 82:18 poly(L-lactic acid)-poly(glycolic acid). Fixation devices derived from this copolymer have been used in orthopedic and craniofacial surgeries. With a strength loss profile of approximately 12 weeks, it mirrors the profile of normal healing; however, in cases in which delayed healing is anticipated, a copolymer with a longer strength retention profile may be desirable. This study compared the hydrolytic degradation, in vitro, of the 82:18 copolymer with a related 85:15 poly(L-lactic acid)-poly(glycolic acid) copolymer. In addition to a difference in the copolymer ratio, the latter had a larger inherent viscosity (molecular weight) and a smaller polydispersity (molecular weight distribution). This copolymer had an equivalent initial tensile modulus as the 82:18 copolymer (0.8 GPa) but a strength retention profile that spanned 44 weeks. The activation energy of hydrolysis for the 85:15 copolymer was 38.8 kcal/mol, which was greater than the 23.8 kcal/mol historical value for the 82:18 copolymer. This suggests that hydrolysis of the 85:15 copolymer is more temperature-sensitive than that of the 82:18 copolymer. These results were interpreted in the context of the differences in the compositions of these 2 copolymers.
authors.affiliation: Biomet, Inc., 56 E Bell Drive, Warsaw, IN 46581, USA. bill.pietrzak@biomet.com
authors.forename: William S
authors.initials: WS
authors.lastname: Pietrzak
authors.forename: Mukesh
authors.initials: M
authors.lastname: Kumar
mesh_terms: D020341:Absorbable Implants; D001672:Biocompatible Materials / Q000737:chemistry*; D055119:Elastic Modulus; D006358:Hot Temperature; D006801:Humans; D006868:Hydrolysis; D016268:Internal Fixators; D019344:Lactic Acid / Q000737:chemistry*; D008422:Materials Testing; D008970:Molecular Weight; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011474:Prosthesis Design; D013314:Stress, Mechanical; D013718:Tensile Strength; D013997:Time Factors; D044366:Transition Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D001672:Biocompatible Materials; D014867:Water; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid