E-beam sterilization of microstructures in titanium surfaces for medical implants

摘要

Due to its biocompatibility titanium is the metal of choice for most medical implants. The surface in contact with the human body may be equipped with a functional microstructure for various purposes such as bone ingrowth. All implants must be sterilized before operation. Among other processes, the sterilization by low energy electron beam (e-beam-sterilization) offers a lot of advantages. The non-thermal sterilization works with short process times (milliseconds) and without microbicide gases. The radiation sterilization is a regulated process according to DIN EN ISO 11137, which describes a killing effect of microorganism after the validation of a dose of 25 kGy. In principal it is possible to sterilize all material classes, electronic devices and different geometries, so that the low energy e-beam-sterilization is a suitable method for multifunctional implants. The sterilization of surface microstructures with low energy e-beam-sterilization is challenging because of the limited penetration depth. The influence of high aspect ratio microstructures on low energy e-beam-sterilization was investigated experimentally. A microhole array with 230 μm hole diameter served as a model structure and was manufactured in the titanium surface by electrical discharge machining. Other surface microstructures were generated by laser machining and blasting. All samples were contaminated with 10~7 CFU/sample Escherichia coli (E. coli) K12, sterilized by e-beam and incubated in a culture medium in order to prove that the sterilization was successful. The microhole depth was varied to determine the critical depth for low energy e-beam-sterilization.