Abstract
INTRODUCTION
Ultra-High Molecular Weight Polyethylene (UHMWPE) wear debris is thought to be a main factor in the development of osteolysis (1). However, the method for the evaluation of the biological response to UHMWPE particles has not yet been standardized.
In this study, four different types of UHMWPE particles were generated using a mechanized pulverizing method and the biological responses of macrophages to the particles were investigated using an inverted cell culturing process (2).
MATERIALS & METHODS
Virgin samples were manufactured via Direct Compression Molding (DCM) technique from UHMWPE GUR1050 resin powder (Ticona, USA). For vitamin E (VE)-blended sample, the resin was mixed with VE at 0.3 wt% and the mixture was then molded using DCM. The crosslinked virgin samples were made by gamma ray irradiation to UHMWPE GUR1020 resin sheet (Meditech, USA) with doses of 95kGy ±10% and annealed. The VE-blended crosslinked samples were made by electron beam irradiation to VE-blended samples with doses of 300kGy and annealed. The material conditions were summarized in Figure 1. To pulverize the samples, the Multi-Beads Shocker (Yasui Kikai, Japan) was used.
After pulverization, samples were dispersed in an ethanol solution and sequentially filtered through polycarbonate filters. Over 100 sections of the filter were selected randomly and images of the particles were analyzed using scanning electron microscope (SEM).
To analyze the macrophage biological response, an inverted cell culturing process was used (2). The mouse macrophage-like cells were seeded at densities of 4×105cells per well in a 96-well culture plate and incubated for 1h. UHMWPE particles suspended in the culture medium were then added to each well in the appropriate amount. After that, fresh medium was added to fill the wells, and a sealing film was used to cover the culture plate. The culture plate was then inverted to cause the UHMWPE particles interact with the adhered macrophages. The inverted culture plate was incubated for 8h. The amount of TNF-α was measured by enzyme-linked immunosorbent assay (ELISA).
RESULTS & DISCUSSION
Geometric measurements showed no significant difference in the UHMWPE particles (Figure 2). The amount of TNF-α released stimulated by the crosslinked virgin particles showed significantly higher relative to the other UHMWPE particles (Figure 3).
During crosslinking irradiation, the carbon free radicals are generated in the main chain (3). In the presence of oxygen, these radicals can react to form peroxy radicals and when the peroxy free radicals react with hydrogen they form hydroperoxides, which can further degrade into other oxidation products (4). It has been reported that VE hinders this cascading in UHMWPE (5). Therefore, it is possible that oxidation of the crosslinked virgin UHMWPE was involved in the cytokine response observed in this study. However resin material, molding technique and the irradiation method were different between crosslinked virgin and VE-blended crosslinked samples. Further consideration will be needed to examine the relationship between residual radicals, hydroperoxides and biological response.
