pH-compensation effect of bioactive inorganic fillers on the degradation of PLGA

It has been suggested that acidic degradation product of the poly (α-hydroxy acids) results in pH decrease in the vicinity of the scaffolds, which may be responsible for biocompatibility concerns rose recently about polylactide acid (PLA), polyglycolic acid (PGA) polymers and their copolymer poly (lactic acid-co glycolic acid) (PLGA). This in vitro study was performed to evaluate the pH-compensation ability of bioactive inorganic fillers (BIFs) such as wollastonite (W), bioglass 45S5 (BG 45S5) and hydroxyapatite (HA) on the acidic degradation products of PLGA. Three composite scaffolds of PLGA incorporated with BIFs were fabricated and immersed in phosphate buffered saline (PBS, pH 7.4) solution at 37 °C for 8 weeks to evaluate the pH changes of the PBS, the mass loss and water absorption of the scaffolds, and the molecular weight loss of the PLGA in the scaffolds. The results indicated that the pH of the PLGA group fell to a value of 4.3 in 8 weeks while the pH of the composite groups containing W and BG 45S5 was maintained between 7.7–7.3 and 8.15–7.1 throughout the soaking period, respectively. However, the pH of the composite group containing HA exhibited an almost linear decrease from 7.4 to 5.6 at an average rate of 0.05 per day. In addition, the incorporation of W and BG delayed the degradation of the PLGA in the composites while the incorporation of HA accelerated the degradation. Furthermore, the W and BG in the composite scaffolds accelerated weight loss of the scaffolds and increased their capacity to absorb water during the initial incubation period. All of these results suggested that incorporations of both W and BG 45S5 into PLGA strongly affected the degradation behavior of scaffolds and were effective in compensation of the pH decrease caused by the acidic degradation products of the PLGA.