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 (XμT). Also measured were bulk density changes, pharmaceutic drug release and medium acidification for the degrading materials. m 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 t1/2 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. mposite 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 t1/2 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 cm2 s−1. Nevertheless, a t dependence is a necessary but not sufficient condition of a Fickian diffusion process. For all nanocomposite types both XμT data and bulk density measurements exhibited no variations with ceramic filler content.