Surface analysis of irradiated medical materials and evaluation of effects on cellular functions

Surface analysis of medical materials exposed to radiation was made and its effects on cellular functions were evaluated. The features of medical materials exposed to radiation under the practical conditions for sterilization and their effects on cellular functions were investigated to estimate the risk at the radiation exposure. Polyurethane frequently used as covering material for pace maker's lead, artificial blood vessel was used as the subject. Polyurethane film was exposed to γ-radiation at 25 kGy. High-pressure vapor sterilization, EOG sterilization and over-night immersion in 70% ethanol were made to compare the effects on cell functions. Then, the surface properties of polyurethane film submitted to those sterilization methods were compared using Wiehelmy method, ESCA and atomic force microscopy and the relation between the effects on cellular functions and the film properties was investigated. As regard film materials in which low molecular substances were produced by radiation exposure, some problems appeared in respects of toxicities of those low molecular substances. Therefore, it was thought that application of radiation exposure method was difficult for some of polymer materials tested. Next, PLLA sheet of 0.3 mm width was exposed to 10, 25 and 50 kGy followed by UV-exposure sterilization. Osteogenesis in osteoblasts cultured on PLLA sheet exposed to γ-ray was observed. A rapid evaluation method for osteogenetic ability in which the degree of calcification was used as an indicator was established and the molecular weight of PLLA was determined. The molecular weight after radiation exposure was decreased as an increase of radiation dose. The distribution of molecular weight (Mw/Mn) became larger as increasing of radiation dose and the degree of calcification in the osteoblastic cells was increased as raising the radiation dose. However, the total amount of protein and DNA content was not changed with an increase of radiation dose. Whereas HYP content and ALP activity was slightly increased with an increase of radiation dose. These results indicated that γ-ray sterilization of PLLA was useful from the aspect of enhancement of osteoblastic ability. (M.N.)