Surface structure and apatite-forming ability of polyethylene substrates irradiated by oxygen cluster ion beams

Polyethylene (PE) substrates were irradiated at a dose of 1 x 10(15) ions/cm(2) by the simultaneous use of oxygen (O(2)) cluster and monomer ion beams. The acceleration voltage for the ion beams was varied from 3 to 9 kV. Unirradiated and irradiated PE substrates were soaked for 7 days in a metastable calcium phosphate solution (1.5SBF) that had 1.5 times the ion concentrations of a normal simulated body fluid. The irradiated PE substrates formed apatite on their surfaces, irrespective of the acceleration voltage, whereas unirradiated substrates did not form apatite. This is attributed to the formation of functional groups that are effective for apatite nucleation, such as --COOH groups, on the substrate surface by the simultaneous use of O(2) cluster and monomer ion beams. The apatite-forming ability of the irradiated PE substrates was improved greatly by a subsequent CaCl(2) solution treatment. This suggests that Ca(2+) ions introduced on the substrate surface by the CaCl(2) solution treatment accelerated the apatite nucleation. It is concluded that apatite-forming ability can be induced on the surface of PE by the simultaneous use of O(2) cluster and monomer ion beams.