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

Poly(epsilon-caprolactone) (PCL), an aliphatic polyester, has received much attention because of its possible application as both a biocompatible and a biodegradable material. For biomedical purposes, PCL-based products can be used as drug delivery systems to the human body or tissue engineering scaffold material. In the latter case the three dimensional synthetic scaffolds, implanted at the tissue defect site, provide a frame-work for cells to attach, proliferate and form extra cellular matrix. To enhance bone regeneration process, hydroxyapatite (HA), the main component of the inorganic phase of bone, is generally added to the polymer material. Response of the organism to the implanted composite biomaterial depends on numerous factors, one of the most important is sterilisation. Different procedures can be utilised for sterilisation, among them high energy radiations present many benefits. In fact, because of excellent penetration characteristics of ionising radiations, radiation sterilisation eliminates problems associated with residual and ethylene oxide gas penetration, uniformity of sterilisation, etc. The doses for radiation sterilization for medical devices and health care products are established by procedures defined in standard ISO 11137. For tissue allografts, international tissue bank standard recommended 15 kGy* as a minimum dose for bacteria decontamination and 25 kGy as minimum dose for bacteria sterilization. These doses should be validated using procedures established by ISO 11137. Other international tissue banks recommended dose up to 35 kGy. However, high-energy radiation, in addition killing bacterial life, may also affect material properties and the interaction between the different phase of the material. This study was aimed at evaluating possible irradiation-induced effects on morphological and thermal properties of both inorganic and polymeric components of some PCL-HA composites. To this purpose PCL-HA samples with different PCL/HA ratios were exposed to gamma radiations. The sample irradiation was performed at 50 kGy, dose greater than the recommended sterilization dose range under N2 or air atmosphere. The samples were investigated by vibrational spectroscopy (IR and Raman spectroscopies) coupled to thermal analysis measurements (Differential Scanning Calorimetry and Thermogravimetry) which revealed to be highly sensible to structure variations.