Probing the Influence of γ-Sterilization on the Oxidation, Crystallization, Sliding Wear Resistance, and Cytocompatibility of Chemically Modified Graphene-Oxide-Reinforced HDPE/UHMWPE Nanocomposites and Wear Debris

Abstract

Osteolysis and aseptic loosening due to wear at the articulating interfaces of prosthetic joints are considered to be the key concerns for implant failure in load-bearing orthopedic applications. In an effort to reduce the wear and processing difficulties of ultrahigh-molecular-weight polyethylene (UHMWPE), our research group recently developed high-density polyethylene (HDPE)/UHMWPE nanocomposites with chemically modified graphene oxide (mGO). Considering the importance of sterilization, this work explores the influence of γ-ray dosage of 25 kGy on the clinically relevant performance-limiting properties of these newly developed hybrid nanocomposites in vitro. Importantly, this work also probes into the cytotoxic effects of the wear debris of different compositions and sizes on MC3T3 murine osteoblasts and human mesenchymal stem cells (hMSCs). In particular, γ-ray-sterilized 1 wt % mGO-reinforced HDPE/UHMWPE nanocomposites exhibit an improvement in the oxidation index (16%), free energy of immersion (−12.1 mN/m), surface polarity (5.0%), and hardness (42%). Consequently, such enhancements result in better tribological properties, especially coefficient of friction (+13%) and wear resistance, when compared with UHMWPE. A spectrum of analyses using transmission electron microscopy (TEM) and in vitro cytocompatibility assessment demonstrate that phagocytosable (0.5–4.5 μm) sterilized 1 mGO wear particles, when present in culture media at 5 mg/mL concentration, induce neither significant reduction in MC3T3 murine osteoblast and hMSC growth nor cell morphology phenotype, during 24, 48, and 72 h of incubation. Taken together, this study suggests that γ-ray-sterilized HDPE/UHMWPE/mGO nanocomposites can be utilized as promising articulating surfaces for total joint replacements.

Overview of sterilization methods for UHMWPE through surface analysis

“…19,20 In the last 10 years, a great number of failure reports involving polymeric pieces in arthroplasty applications have been published. 10,21,22 The main factor behind this is described as oxidative degradation of the material, induced by sterilization processes. [22][23][24][25] Overall, sterilization processes remain a major problem when it comes to the use of polymeric materials in biomedical applications, since the employed energy induces rapid aging, oxidation and other surface phenomena that lead to materials fragilization.…”

“…10,21,22 The main factor behind this is described as oxidative degradation of the material, induced by sterilization processes. [22][23][24][25] Overall, sterilization processes remain a major problem when it comes to the use of polymeric materials in biomedical applications, since the employed energy induces rapid aging, oxidation and other surface phenomena that lead to materials fragilization. In practice, this means that a recipient of a load bearing polymeric part may be subjected to implant mechanical failure or problems with the formation of debris that accumulate around the tibial, patellar and acetabular components, causing bone inflammation and degradation.…”

Effects of reinforcements and gamma‐irradiation on wear performance of ultra‐high molecular weight polyethylene as acetabular cup liner in hip‐joint arthroplasty: A review

“…A 20% and 43% decreased tensile strength and percentage of elongation was observed, respectively, for UHMWPE‐1 wt.% GO than UHMWPE‐0.5 wt.% nanocomposite. Irrespective of various graphene products utilized in nanocomposites, the best mechanical performances can be obtained at an optimal filler content, 20–22 and the optimum GO content in UHMWPE is fixed to 0.5 wt% 112 …”

“…To decrease the CoF, the accelerated thermal aging of irradiated U‐GO at 180°C for 21 days, undergoes oxidative degradation, which will again weaken the interface and release graphene sheets, which act as lubricating agent at the mating surface, thus 11% reduced CoF 217 . The improved crystallinity and hardness of gamma‐irradiated UHMWPE‐HDPE‐GO (UHG) nanocomposites attributed to 30% decreased CoF and wear rate than that of un‐irradiated UHG 22 . Carbon fibers reinforced UHMWPE also showed improved mechanical properties, when gamma‐irradiated at 25 kGy dose level 218 .…”

“…The high mechanical strength and resistance to wear 20,21 of the UHMWPE are the important attributes to increase the longevity of THR 22 . During the articulation of THR, the polyethylene acetabular cup liner experiences joint force due to the multidirectional sliding of femoral head (metallic/ceramic) against it (Figure 1(b)).…”