LATE DEGRADATION SIMULATION OF POLY(L-LACTIDE)

High molecular weight as-polymerized poly(l-lactide) (PLLA) has been s uccessfully used for fracture fixation and orbital floor reconstructio n in animals and humans. As this PLLA takes more than 3 years to resor b, a method was developed to obtain insight into the final cellular de gradation process of the PLLA by means of short-lasting animal experim ents. Pre-degraded PLLA particles (< 500 mu m) were implanted subcutan eously in the backs of 14 rats. Two different methods of sterilization (regular steamsterilization and gamma-irradiation) and implantation v ehicles (gelatin capsules and hydroxypropyl-methylcellulose (HPMC)) we re used to examine the biological behaviour of the pre-degraded PLLA. Two rats were sacrificed at 48 h, 3 days and 1, 2, 4, 8, 16 weeks foll owing the operation. The tissues were examined using light microscopy and transmission electron microscopy. Gel permeation chromatography (G PC) and differential scanning calorimetry (DSC) were used to character ize the PLLA material. GPC measurements of the pre-degraded PLLA revea led a (M) over bar(n) of 5500. Upon hydrolysation the crystallinity of the PLLA increased by about 60% and the heat of fusion was 86 J g(-1) . Deterioration of the mechanical and physical properties due to the t wo sterilization methods was negligible. No differences in cellular re sponse were observed between the densely packed PLLA particles (gelati n capsules) and the particles scattered over the tissue (HPMC-gel). Th e present study enabled an early observation of the late degradation p hase of PLLA.