Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief

This work shows that a soft,thin film comprising randomly aligned carbon nanotubes(CNTs)can reduce surface wear more effectively than a homogeneous thin film because of enhanced elastic recoverability and contact stress relief originating from its mesh structure.To investigate the wear characteristics of the mesh structure compared to those of the homogeneous thin film,multi-walled CNTs(MWCNTs)and diamond-like carbon(DLC)thin films were prepared to conduct nanoscale tribological experiments using the atomic force microscopy(AFM).The MWCNT thin film showed unmeasurably low wear compared with the DLC thin film under a certain range of normal load.To demonstrate the wear reduction mechanism of the MWCNT thin film,its indentation and frictional behaviors were assessed.The indentation behavior of the MWCNT thin film revealed repetitive elastic deformation with a wide strain range and a significantly lower elastic modulus than that of the DLC thin film.The permanent deformation of the MWCNT thin film was observed through frictional experiments under relatively high normal load conditions.These results are expected to provide insights into the design of highly wear-resistant surfaces using nanostructures.

Development of polyimide films reinforced with boron nitride and boron nitride nanosheets for transparent flexible device applications

The benefits of reinforcing polyimide （PI） films with boron nitride （BN） particles and boron nitride nanosheets （BNNSs） were assessed with the aim of enhancing their thermal, optical, and mechanical properties for flexible device applications. BNNSs were prepared from BN particles using a liquid-phase exfoliation method assisted by an ultrasonic probe-type sonicator and centrifugator. PI-based composite films blended with BNNSs and BN particles were fabricated at various concentrations via mechanical stirring and spin coating. The transparency of the PI/BNNS composite films remained almost the same as that of pure PI films up to 3 wt.% whereas the transparency of the PI/BN composite films decreased with increasing concentration of the BN fillers at 550 nm. The thermal stability improved significantly with increasing concentrations of both BN and BNNS relative to that of pure PI films. The temperature for 5% weight loss of the PI/BNNS composite film was higher than that of the PI/BN composite film at the same filler concentration. The composite films with 2 wt.% BN or BNNS showed the lowest wear rate, and the PI/BNNS composite films showed more stable frictional behavior compared to the PI/BN composite films. In addition, bending tests showed that the PI/BNNS composite films exhibited excellent flexibility compared to the PI/BN composite films. Overall, the results indicate that the BNNS can be effectively used as a filler that can enhance the thermal and mechanical properties of polymer materials for flexible device applications.

One-step method to enhance biotribological properties and biocompatibility of DLC coating by ion beam irradiation

A one-step method was developed to create a highly biocompatible micropatterned surface on a diamond-like carbon(DLC)through irradiation with a nitrogen ion beam and thus enhance the biocompatibility of osseointegrated surfaces and biotribological performance of articular surfaces.The biocompatibility and biotribological mechanisms were analyzed in terms of the structure and morphology of DLC.It was demonstrated that a layer enriched in sp^(3) C-N bonds was formed on the surface of the DLC after nitrogen ion beam irradiation.Moreover,with an increase in the radiation dose,the content of sp^(3) C-N on the DLC surface increased significantly,and the biocompatibility was positively correlated with it.The adhesion of the MC3T3 osteoblasts increased significantly from 32%to 86%under an irradiation dose of 8×10^(15) ions/cm^(2).In contrast,the micropattern had a significant negative effect on the adhesion of the osteoblasts as it physically hindered cell expansion and extension.The micropattern with a depth of 37 nm exhibited good friction properties,and the coefficient of friction was reduced by 21%at relatively high speeds.

Dendritic cell-based immunotherapy for colon cancer using an HLA-A＊0201-restricted cytotoxic T-lymphocyte epitope from tumor-associated antigen 90K

Tumor-associated antigen 90K is implicated in cell-cell and cell-extracellular matrix adhesion through its interaction with galectin-3 and integrin-β 1 and is highly expressed in malignant tissues, making it a novel target for the development of new immunotherapies. We investigated a potential immunotherapy treatment for colon cancer using 90K-specific cytotoxic T lymphocytes induced by autologous dendritic cells and pulsed with 90K peptides. We selected three peptides （90K3s1, 90K5 and 90K523） that bind to HLA-A＊0201 molecules on the basis of their binding affinity, as determined by a peptide-T2 binding assay. Dendritic cells pulsed with 90K peptides resulted in the efficient generation of mature dendritic cells and exhibited enhanced T-cell stimulation and polarization of naive T cells toward Thl. Dendritic cells pulsed with 90K peptides generated potent cytotoxic T-lymphocytes that lysed T2 cells loaded with each 90K peptide, and 90K＋/HLA-A2＋ colon cancer cell lines, including HCT116 and SW480, in a dose-dependent and HLA-A＊O2Ol-restricted manner. No killing was observed in 90K＋/HLA-A2- DLD1 or 90K-/HLA-A2- K562 cells. Therefore, we believe that cytotoxic T-lymphocytes stimulated by 90K peptide-pulsed dendritic cells naturally recognize the 90K peptide presented by colon cancer cells in the context of HLA-A2, and kill 90K-positive tumor cells. Dendritic cells pulsed with 90K peptides led to the induction of granzyme B and perforin positive CD8＋ T cells against HCT116 and SW480 cells, but not DLD1 cells. In conclusion, 90K-specific cytotoxic T lymphocytes, generated by stimulating T cells with 90K peptide-pulsed dendritic cells, could be useful effector cells for the immunotherapv treatment of colon cancer.

Effect of friction on the contact stress of a coated polymer gear

Polymer gears are used extensively in various applications.However,durability issues have been emerging because of friction at gear tooth contact areas.To extend the lifetime of polymer gears,a low-frictional coating has been considered as a possible strategy.In this study,a finite element simulation method was performed to investigate the contact stress between a pair of coated polymer gears.The simulation included various friction coefficients(COFs)for studying the effects of friction during the operation.Numerical results revealed that the friction causes the contact stress to shift over the roll angle,which is attributed to the direction of the sliding friction based on a free-body diagram.We also investigated the effects of coating and found that a thin coating has little effect on the bulk deformation behavior of the gear.Moreover,the stress distribution in the coating at the pitch point was investigated as the COF increased.Under zero friction,three notable stress regions were observed:1)the center of the surface,2)the end of the contact,and 3)the overall contact area.As COF was increased in the micro-slip region of the contact interface,both tensile and compressive stresses in the coating increased.This study provides significant aid to engineers for understanding the stress response of the coating applied to polymer gears to achieve an optimal design.

60 years of Rabinowicz' criterion for adhesive wear

60 years ago, in 1958, Ernest Rabinowicz published a 5 page paper titled "The effect of size on the looseness of wear fragments" where he suggested a criterion determining the minimum size of wear particles. The criterion of Rabinowicz is based on the consideration of the interplay of elastic energy stored in "asperities" and the work of separation needed for detaching a wear particle. He was probably the first researcher who explicitly emphasized the role of adhesion in friction and wear. In a recent paper in Nature Communications, Aghababaei, Warner and Molinari confirmed the criterion of Rabinowicz by means of quasi-molecular dynamics and illustrated the exact mechanism of the transition from plastic smoothing to formation of wear debris. This latter paper promoted the criterion of Rabinowicz to a new paradigm for current studies of adhesive wear. The size arguments of Rabinowicz can be applied in the same form also to many other problems, such as brittle-ductile transition during indentation, cutting of materials or ultimate strength of nano-composites.

Propagating acoustic waves on a culture substrate regulate the directional collective cell migration

Collective cell migration plays a critical role in physiological and pathological processes such as development,wound healing,and metastasis.Numerous studies have demonstrated how various types of chemical,mechanical,and electrical cues dictate the collective migratory behaviors of cells.Although an acoustic cue can be advantageous because of its noninvasiveness and biocompatibility,cell migration in response to acoustic stimulation remains poorly understood.In this study,we developed a device that is able to apply surface acoustic waves to a cell culture substrate and investigated the effect of propagating acoustic waves on collective cell migration.The migration distance estimated at various wave intensities revealed that unidirectional cell migration was enhanced at a critical wave intensity and that it was suppressed as the intensity was further increased.The increased migration might be attributable to cell orientation alignment along the direction of the propagating wave,as characterized by nucleus shape.Thicker actin bundles indicative of a high traction force were observed in cells subjected to propagating acoustic waves at the critical intensity.Our device and technique can be useful for regulating cellular functions associated with cell migration.