Study On UHMWPE Wear Debris Loaded With Alendronate Sodium

Ultra high molecular weight polyethylene (UHMWPE) has been used for total joint arthroplasty bearings due to its excellent mechanical properties and wear properties. However wear debris of artifical joint, in particular the wear debris of UHMWPE, would result in a series of biological reactions and lead to the periprosthetic osteolysis, which are the major reasons for the late failure of artifical joint. Various approaches have been attempted to reduce UHMWPE wear, such as improving the wear performance of UHMWPE, alternative articulating surfaces and the use of pharmaceuticals to inhibit abnormal bone resorption. In our previous study, UHMWPE loaded with anti-resorptive drugs, estradiol and alendronate sodium (ALN) have been studied, which have potential application in clinics to treat particle-induced osteolysis after artifical joint replacement. Preliminary study showed that ALN did not agglomerate in UHMWPE-0.22 wt% ALN. and incorporation of a certain amount of ALN (0.22 wt%) in UHMWPE had little impact on the mechanical and tribological properties of UHMWPE. However, it has not studied how to fabricate and characterize UHMWPE-ALN wear debris, and how the size and ALN loading ratio of UHMWPE-ALN wear debris influence the in vitro ALN release and cellular response. In this study, UHMWPE-ALN wear debris were prepared and characterized, and the in vitro ALN release and the cellular response of the UHMWPE-ALN wear particles were also studied.In this study, three groups of samples (UHMWPE, UHMWPE-0.5% ALN and UHMWPE-1.0% ALN) were hot compressed in the Manual Hydraulic Press. The functional group, crystal structure and crystallinity of UHMWPE-ALN were characterized by fourier transform infrared spectroscopy (FT-IR), X ray diffraction (XRD), differential scanning calorimetry (DSC) analysis. The UHMWPE-ALN wear debris with the size range of<45μm and 45μm～75μm were acquired by means of filtration, and the size, morphology and number of UHMWPE-ALN wear debris were examined by Laser diffraction wear particle analyzer, scanning electron microscopy(SEM) and blood cell analyzer, and the in vitro release properties of the UHMWPE-ALN wear debris with different size and ALN loading ratio were studied by ninhydrin colorimetric method. Osteoblast cells (MC3T3-E1) and macrophage cells (RAW 264.7) were challenged with UHMWPE-ALN wear debris respectively in vitro to study the biological reaction to the wear debris. Cell morphology was observed by optical microscope and SEM. Cell proliferation of osteoblast cells and macrophage cells were investigated by Methyl thiazolyl tetrazolium(MTT) assay. The differentiation of osteoblast cells was studied by determining the activity of alkaline phosphatase (ALP), and the expression of pro-osteolytic cytokines (interleukin-6. IL-6 and tumor necrosis factor-a. TNF-a) were investigated by enzyme-linked immunosorbnent assay (ELISA).The FTIR spectrum of UHMWPE-ALN contained characteristic peaks of ALN, such as peaks at 1230 cm-1～1265 cm-1 owing to P=O stretching vibration. peaks at 1178 cm-1 owing to C-O stretching vibration, peaks at 1095 cm-1 owing to C-N stretching vibration. The position of P=O peaks shifted from 1238 cm-1 to 1265 cm-1 resulting from the lose three crystalliferous water of ALN in the process of hot compression moulding, the position of C-O and C-N peaks did not shift, which demonstrated that hot compression procedure had no impact on the chemical structure of ALN. However, UHMWPE was oxidized during hot compression procedure as demonstrated by the peaks at 1720 cm-1 owing to ketone/carboxylic acid groups in the FTIR spectrum of UHMWPE-ALN. The results of the XRD showed that the position of the diffraction peaks of UHMWPE crystal plane (110) and (200) were not displaced, no new diffraction peaks were appeared, but the intensity of the diffraction peaks was decreased in the presence of ALN. It indicated the presence of ALN had no impact on the crystal structure of UHMWPE but could decreased the crystallinity degree of UHMWPE. There was only one melting peak in DSC spectrum of UHMWPE and UHMWPE-ALN, the location of melting peak was shifted to high-melting temperature and the melting enthalpy was decreased in the presence of ALN, which revealed that the speed of UHMWPE crystallization was accelerated and the crystallinity was decreased in the presence of ALN.The mean sizes of UHMWPE and UHMWPE-ALN wear debris (< 45μm,45μm-75μm) were 36.98±1.88μm,66.7±2.61μm respectively after filtration. The minimum size is about 5μm and the size distribution ranged from 5μm to 250μm, which is different from that of UHMWPE wear debris in vivo. The SEM images showed that the morphology of the UHMWPE-ALN wear debris were irregularly form of block or fibril, which is similar with that of UHMWPE wear debris in vivo.It was observed that the ALN released from the UHMWPE-ALN wear debris by a three-step profile, the burst release which was mainly influenced by the size of wear debris, the rapid release which was mainly influenced by ALN loading ratio and the slow release, in which the release rate reduced to the same low level for different size and different ALN loading ratio. The oxidation index of the UHMWPE-ALN wear debris incresed from 1.29±0.014 to 1.33±0.007 after soaked in the PBS for 100 days, no significant difference was observed, which demonstrated that the release of ALN was mainly controlled by the diffusion from the swollen UHMWPE. The release of ALN from the UHMWPE-ALN wear debris extended beyond 100 d with maximum percentage release ranging from 49.77%. 38.76%(45μm-75μm, UHMWPE-1.0% ALN. UHMWPE-0.5% ALN) to 63.90%.49.39% (< 45μm, UHMWPE-1.0% ALN, UHMWPE-0.5% AL) in 100 d. There are still some ALN contained in the wear debris.The results of cell culture indicated that ALN within a certain range of concentrations (10-6～3×10-6 mol/L) inhibited the proliferation of macrophage cells, improved the proliferation and differentiation of osteoblast cells, whereas had no influence on the secretion of TNF-αand IL-6 of macrophage cells. The similar influence was also observed as well as the size of UHMWPE-ALN wear debris. As the size of UHMWPE-ALN wear debris decreasing, the differentiation of osteoblast cells and the proliferation of macrophage cells were decreased, but the secretion of TNF-αof macrophage cells were improved.It was summarized that it was feasible to prepared the UHMWPE-ALN wear debris, in which the chemical structure of ALN was stable. ALN could released from the wear debris and affected the macrophage and osteoblast cells. The UHMWPE-ALN wear debris possessed the potential inhibition of osteolysis. However, the size of UHMWPE/UHMWPE-ALN wear debris prepared in this experiment is different from that of UHMWPE wear debris in vivo. It need for improvement in the fabrication of UHMWPE wear debris to simulate the reaction between UHMWPE wear debris and cells in vivo.