Spectroscopic and calorimetric study on different gamma-irradiated poly-epsilon-caprolactone/hydroxyapatite (PCL/HA) composite biomaterials.

Different studies haave underlined that gamma-irradiation, a common method for sterilization, can induce structural changes on biomaterials (cross-linking, changes in molecular weight and cristallinity) through the formation of aggressive radicals (OH, COO, O2). Poly-epsilon-caprolactone/hydroxyapatite (PCL/HA) samples (synthesized at IMCB-CNR Napoli, Italy) with different composition (100%, 70%, 60%, 50% w/w of PCL) were irradiated in air or under nitrogen at doses of 10, 25 and 50 kGy (dose to water) with gamma-rays from a 60Co Nordion 220 Gammacell at a dose rate of 0.7 kGy/h. Irradiation does were chosen as recommended for sterilization of bone tissue for inactivation of bacteria. The samples were analyzed after each dose with Raman and FT-IR/ATR spectroscopies to study morphology through changes in area, width, intensity and position of bands associated to crystalline and amorphous phases of PCL and HA; spectroscopic data about cristallinity and relative PCL/HA ratios were confirmed by calorimetric methods (TG and DSC). We find out that both PCL and HA were affected by irradiation: amorphous content increased with irradiation, in particular in air. Relevant changes were observed in the IR spectra of HA in carbonate bands. Samples treated under nitrogen showed smaller changes because of the lower concentration of radicals originated from oxygen and water. This study helps to understand how composite biomaterials can react to gamma-sterilization and could be the starting point of further studies on the effect of different types of irradiation and radicals on biomaterials.