Cytotoxicity of poly(96L/4D-lactide): the influence of degradation and sterilization

The cytotoxicity of poly(96L/4D-lactide) (PLA96), and of its accumulated de gradation products, was investigated following different sterilization meth ods and pre-determined heat-accelerated degradation intervals. PLA96 sample s sterilized by either steam, ethylene oxide, or gamma irradiation were lef t untreated (SO samples), or were degraded for 30 h or 60 h (S30 and S60 sa mples) at 90 degrees C in water. Extracts of the samples and of the remaini ng degradation fluids (F30 and F60) were prepared. The toxicity of both unf iltered and filtered extracts was analyzed in a cell growth inhibition (CGI ) assay and a lactate dehydrogenase (LDH) leakage assay. Physical analysis of the extracted samples and of the degradation fluids also was performed. The S0 extracts demonstrated no significant CGI. The CGI of the S30 extract s ranged from 37 to 78%, whereas the CGI of the S60 extracts ranged from 6 to 33%. The CGI of the F30 extracts ranged from 19 to 38% and the CGI of th e F60 extracts was 98 to 123%. The LDH leakage assay only showed a high res ponse to the unfiltered F60 extracts. Neither sterilization nor filtration appeared to influence the cytotoxicity of the extracts. Particle accumulati on, however, might affect cell membrane permeability resulting in LDH leaka ge. The results of this study suggest that the cytotoxicity of PLA96 is rel ated to the pH and possibly the osmolarity of the tested extracts. The pH a nd osmolarity, in turn, may depend on variations in the amounts of solubili zed lactic acid and oligomers. These variations appear to result from degra dation stage-dependent differences in crystallinity, molecular weight and m olecular weight distribution of the PLA96 samples. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.