Chemical Characterization of Ultra High Molecular Weight Polyethylene Based Tibial Inserts After Ethylene Oxide Sterilization

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) has become the gold standard for total joint replacements such as tibial inserts because of its chemical inertness, superior mechanical properties, and biocompatibility. Ethylene oxide sterilization is one of the most common and effective methods used, especially for the sterilization of polyethylene-based polymeric implants. However, variable sterilization conditions can cause a change in the chemical structure of the polymeric material, which affects its mechanical properties and lifetime. The aim of this study is to investigate whether the chemical structure of UHMWPE tibial inserts sterilized with ethylene oxide undergoing certain conditions remains the same. Chemical characterization studies were performed with Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffractometer, differential scanning calorimetry, thermogravimetric analysis, mass spectrometry and elemental analysis techniques recommended for polymeric materials in ISO 10993-8:2020 standard. According to the FTIR results, the spectra of the non-sterile and sterile tibial inserts were compared, and it was determined that the similarity between them was 99.97%. XRD results revealed that after ethylene oxide sterilization, there was no significant shift in the Bragg (1 0 0) peak. The percentages of crystallinity calculated from the fusion enthalpies determined by DSC of sterile and non-sterile samples are 54.3% and 53.3%, respectively. Characterization results revealed that there was no significant change in molecular structure, crystallinity, elemental composition of UHMWPE materials after ethylene oxide sterilization. These results can provide assurance that tibial inserts keep their physical, chemical, and mechanical properties after sterilization.