This article aims to investigate the influence of reinforcing graphene oxide (GO) and graphite flakes (GF) fillers into ultrahigh molecular weight polyethylene (UHMWPE) for orthopedic application. These fillers were expected to physically bond to UHMWPE, thus can enhance the subsurface strength, improving the wear behavior of the composites. UHMWPE/GO and UHMWPE/GF composites were prepared at 0.1 and 1.0 wt% by melt‐blending, followed by a compression molding technique. A multidirectional pin‐on‐disc wear test was performed to simulate the kinematic of hip application. Whilst getting exposed in the artificial in‐vivo lubricant bath (30 v/v% diluted bovine serum). Following this, the wear mechanism fostered by each filler (GO and GF) was determined by wear features obtained from the optical microscope and scanning electron microscope (SEM). The crystallinity degree and crystal defect were assessed using x‐ray diffraction (XRD). The mechanical properties of fabricated composites were evaluated by using a universal testing machine and Vickers microhardness. We found that UHMWPE/GO has the lowest specific wear rate due to the improved subsurface strength, as the reduction of a weak adhesive point was observed on the worn surface. Meanwhile, higher GF content (1 wt%) in UHMWPE displayed a lower specific wear rate than neat UHMWPE after completing the 10 km sliding distance attributed to the filler resurfaced, responsible for providing a strong resistance of the shear stress applied upon sliding with the metal counterface. Interestingly, the hardness and tensile strength for both UHMWPE/GO and UHMWPE/GF increased, although the crystallinity percentage was declining compared to neat UHMWPE.

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Recent studies have found a rapid increase of ultrahigh molecular weight polyethylene (UHMWPE) wear in the presence of proteins from the synovial fluid. Due to UHMWPE's high hydrophobicity, it tends to adsorb a tremendous amount of proteins. Moreover, since UHMWPE has low thermal conductivity, a temperature rise in the center of the contact area due to frictional heating could cause protein denaturation from the synovial fluid. It has been shown that the denatured protein may increase the adhesive wear response. This study aimed to address the effects of graphite and graphene oxide (GO) addition on the wear properties of UHMWPE in protein environments. The surface properties were characterized using surface roughness profiler, surface energy evaluation, zeta potential, and Fourier transform infra-red (FTIR). Following that, wear properties of UHMWPE composite were evaluated using a multidirectional pin-on-disc wear test under a bovine serum lubricated condition. The worn surface of the UHMWPE composite sample was evaluated, and the dominating factors of wear properties were determined. The effect of protein adsorption on the composite surface was also assessed after the wear test. The hydrophilicity of UHWMPE/1.0GO is considered to be the dominant contribution determining protein adsorption in static conditions. UHMWPE composite's wear resistance improvement was primarily dominated by GO filler (1.0 wt%) near the sliding surface, which has improved the subsurface strength of the material and heat dissipation effect, which reduces the denaturation of the proteins.

Spinal cord injury (SCI) causes severe motor or sensory damage that leads to long-term disabilities due to disruption of electrical conduction in neuronal pathways. Despite current clinical therapies being used to limit the propagation of cell or tissue damage, the need for neuroregenerative therapies remains. Conductive hydrogels have been considered a promising neuroregenerative therapy due to their ability to provide a pro-regenerative microenvironment and flexible structure, which conforms to a complex SCI lesion. Furthermore, their conductivity can be utilized for noninvasive electrical signaling in dictating neuronal cell behavior. However, the ability of hydrogels to guide directional axon growth to reach the distal end for complete nerve reconnection remains a critical challenge. In this Review, we highlight recent advances in conductive hydrogels, including the incorporation of conductive materials, fabrication techniques, and cross-linking interactions. We also discuss important characteristics for designing conductive hydrogels for directional growth and regenerative therapy. We propose insights into electrical conductivity properties in a hydrogel that could be implemented as guidance for directional cell growth for SCI applications. Specifically, we highlight the practical implications of recent findings in the field, including the potential for conductive hydrogels to be used in clinical applications. We conclude that conductive hydrogels are a promising neuroregenerative therapy for SCI and that further research is needed to optimize their design and application.

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