Technique to control pH in vicinity of biodegrading PLA-PGA implants

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Abstract
This in vitro study was performed to examine if the pH decrease in the vicinity of degrading polylactic acid (PLA) and polyglycolic acid (PGA) polymers can be offset by incorporation of basic salts within PLA‐PGA implants. It has been suggested that such pH lowering results in adverse effects, which may be responsible for biocompatibility concerns raised recently about PLA and PGA polymers. The results indicated that all three salts investigated in this study were successful in controlling the decrease in pH due to the acidic degradation products of the copolymer. The pH of the test media for the control group fell to a value of 3.0 at 9 weeks. Implants containing calcium carbonate maintained the pH value between 7.4 and 6.3 throughout the degradation process. Implants with calcium hydroxyapatite and sodium bicarbonate controlled the pH values between 6.9 and 4.3 and 8.2 and 4.5, respectively. At 3 weeks, marked swelling of implants containing calcium carbonate or sodium bicarbonate was observed relative to the control implants. The molecular weight and mass changes in the implants did not show any significant differences at 9 weeks. Thus, results from this in vitro model show that a significant decrease in pH in the vicinity of PLA‐PGA implants can be avoided by incorporating basic salts. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 38: 105–114, 1997