Effect of poly(vinyl alcohol) (PVA) wear particles generated in water lubricant on immune response of macrophage

To develop a novel biotribological material for artificial cartilage implant with a lubricity supplement of the joint surface, we focused on two types of poly(vinyl alcohol) (PVA) hydrogel: repeated freeze–thawing (PVA-FT) and cast-drying (PVA-CD) gels. Here we observed the morphology of wear particles generated during a reciprocating wear test and assessed macrophage immune responses by applying hydrogel wear particles. As a result, PVA-CD had a significantly lower total amount of wear than did PVA-FT. The size distributions of PVA-FT and -CD wear particles were similar. Most of the particles were nanoparticles up to approximately 50 nm in diameter. Considering the particle volume distribution, there were very few micron- and submicron-sized wear particles around 1 μm in diameter. In SEM observations of dried PVA wear particles, both distributions of wear particles of PVA-FT and -CD were similar. Micron-sized wear particles were chiefly formed by close packing of 20- to 50-nm-sized particles. Biochemical and immunological evaluations revealed no cytotoxic effects of wear particles on macrophages. Cytokine synthesis of both wear particle-stimulated groups was significantly lower than that of the lipopolysaccharide-stimulated positive control. Therefore, it is suggested that PVA wear particles do not affect the macrophage immune response

Purification of Pneumocystis carinii trophozoites and identification of their circulating antigens.

We have developed a new method to isolate Pneumocystis carinii trophozoites from experimental rat bronchoalveolar lavage specimens by using a Percoll discontinuous gradient and have identified the circulating antigens in experimental rat P. carinii pneumonia. The antigenic components of the trophozoites were compared with those of cysts by immunoblotting. A major immunoreactive band of 90,000 Da and some others of lower molecular mass were found in trophozoites. On the other hand, bands of 110,000, 50,000, and 45,000 Da were observed in cysts. The band of 50,000 Da was not identified when antitrophozoite rabbit serum preabsorbed with P. carinii-infected rat serum was used for immunoblotting. These results suggest that the molecule of 50,000 Da is the major circulating antigen in P. carinii-infected rats

The relations between wear behavior and basic material properties of graphene-based materials reinforced ultrahigh molecular weight polyethylene

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

A functional effect of the superficial mechanical properties of articular cartilage as a load bearing system in a sliding condition

The structure and composition of articular cartilage show depth-wise inhomogeneity and anisotropy. In particular, the dense collagen network covers and reinforces the superficial tangential zone of the tissue. It is thought that this peculiar structure offers the excellent tribological property of articular cartilage. The purpose of this study was to investigate the functionality of the superficial tangential zone (STZ) of articular cartilage as a load bearing system. The 2-dimensional finite element (FE) model was accepted for sliding configuration with sufficient extent of sliding distance. The standard model as a control was carried from our previous study, which included depth-dependent Young׳s modulus of the solid phase, fiber reinforcement with strain-dependency and permeability with compaction effect. The mechanical property of the superficial layer was modified for a parametric study of its functionality. According to research results in the past, the tangential stiffness of the fiber reinforcement of the STZ model was enhanced, and the following anisotropic permeability was also modified. The stationary contact condition and the migrating contact condition were examined to compare the effect of the superficial tangential layer. The result showed that the significant reduction of friction coefficient was found in migrating contact condition of the STZ model. In the observation of field output of FE analysis, the contacting surface formed a thin low permeability layer, which would enable the high fluid pressure and the low fluid flow at the same time. It seemed that the stiffening of the fiber reinforcement of the superficial layer promoted the formation of the low permeability layer. Beyond the effectivity of the fiber reinforcement of biphasic matrix on the interstitial fluid pressurization, the findings of this study indicated that the compaction effect on the permeability would involve a quite complex phenomenon in long term migrating contact sliding