X-ray microtomographic analysis of α-tricalcium phosphate-poly(lactic-co-glycolic) acid nanocomposite degradation

The degradation characteristics of αTCP-PLGA(50:50) nanocomposites containing varying ceramic weight loadings in an aqueous medium have been assessed using X-ray microtomography (X μ T). Also measured were bulk density changes, pharmaceutic drug release and medium acidification for the degrading materials. Calcium phosphate addition to the polymer leads to increasing delays in the onset of degradation medium acidification and tetracycline release. Bulk density changes with time for all composite materials measured using a buoyancy method were well described during the initial degradation regime by a t 1/2 function. PLGA density evolution follows a linear function of time which indicates a differing water absorption process occurring in the pure polymer compared with the nanocomposites. Nanocomposite microtomographic analysis over the same period elucidated a core-periphery structure caused by water imbibition. Peripheral regions closest to the specimen surface exhibit reduced attenuation coefficients compared with the core which may be characteristic of a frontal system caused by a polymer phase transition. The front position and specimen swelling are adequately described by a t 1/2 and complementary error function respectively which if assessed under the assumption of a diffusion controlled process yields a diffusion coefficient of water in all nanocomposites at 37 °C of 4.8 × 10 −14  cm 2  s −1. Nevertheless, a t dependence is a necessary but not sufficient condition of a Fickian diffusion process. For all nanocomposite types both X μ T data and bulk density measurements exhibited no variations with ceramic filler content.