Pore formation of poly(ε-caprolactone) scaffolds with melting point reduction in supercritical CO2 foaming

Poly(epsilon-caprolactone)(PCL) is recently developed for bone tissue engineering applications due to its lasting degradation rate which matches the natural growth rate of a bone. In this work, batch foaming of PCL using supercritical CO2 was employed, and the effects of processing variables, namely soaking time, foaming temperature and pressure, depressurization rate on the pore morphology and structure were studied in detail. Results demonstrated that morphologies and structures of pores were significantly distinct astride foaming temperature of 40 degrees C, which were characterized by melt -state foaming and solid-state foaming respectively. The dramatic reduction of melting temperature (T-m) caused by the presence of supercritical CO2 was found to be the key for this specific phenomenon. Above 40 degrees C, the enhanced melting of PCL caused by the reduction of T-m led to wider pore size distribution, i.e. melt -state foaming, and the domino effect of variables on pore size was amplified; whilst below 40 degrees C the foams showed dense and small pore morphology, i.e. solid-state foaming. By tuning processing variables, scaffolds with diameter of 12.5 +/- 0.1 to 344 +/- 54 mu m and porosity of 60.8 +/- 3.2% to 83.4 +/- 1.3% were fabricated. Furthermore, the interconnectivity of neat PCL scaffolds were mostly around 70%, which showed potential application in bone tissue engineering. (C) 2016 Elsevier B.V. All rights reserved.