Mechanical and Biotribological Properties of PVA/SB Triple-Network Hydrogel for Biomimetic Artificial Cartilage

Poly (vinyl alcohol) hydrogel has been perceived as a promising replacement for articular cartilage due to its superior water-absorption ability and excellent biocompatibility, but its mechanical properties are still insufficient. In this study, the poly (vinyl alcohol)/sodium tetraborate triple-network (PVA/SB TN) hydrogel was developed by repeated freeze–thaw method. Scanning electron microscopy images demonstrated that the structure of as-prepared hydrogels was three-dimensional porous network structure similar to that of natural articular cartilage. Compared to the pure PVA hydrogel, the mechanical performance of the PVA/SB TN hydrogels were improved by 116% and 461% in tensile and compressive strengths, respectively. This was mainly because that the complexation reaction between the PVA and SB strengthened the stability of the hydrogel network. Notably, the biotribological performance of PVA hydrogel has also been improved significantly. Even at high load, the friction coefficient of the PVA/SB TN hydrogel was both very low in calf serum or deionized water. This PVA/SB TN hydrogel with good mechanical property and low friction has high application potential in cartilage repair.

Two RING-Finger Ubiquitin E3 Ligases Regulate the Degradation of SPX4, An Internal Phosphate Sensor, for Phosphate Homeostasis and Signaling in Rice

SPX-domain-containing proteins (SPXs) play an important role in inorganic phosphate (Pi) sensing,signaling,and transport in eukaryotes.In plants,SPXs are known to integrate cellular Pi status and negatively regulate the activity of Pi central regulators,the PHOSPATE STARVATION RESPONSE proteins (PHRs).The stability of SPXs,such as SPX4,is reduced under Pi-deficient conditions.However,the mechanisms by which SPXs are degraded remain unclear.In this study,using a yeast-twhybrid screen we iden.tified two RING-finger ubiquitin E3 ligases regulating SPX4 degradation,designated SDEL1 and SDEL2,which were post-transcriptionally induced by Pi starvation.We found that both SDELs were located in the nucleus and cytoplasm,had ubiquitin E3 ligase activity,and directly ubiquitinated the K^213 and K^299 lysine residues in SPX4 to regulate its stability.Furthermore,we found that PHR2,a Pi central regulator in rice,could compete with SDELs by interacting with SPX4 under Pi-sufficient conditions,which protected SPX4 from ubiquitination and degradation.Consistent with the biochemical function of SDEL1 and SDEL2,overexpression of SDEL1 or SDEL2 resulted in Pi overaccumulation and induced Pi-starvation signaling even under Pi-sufficient conditions.Conversely,their loss-of-function mutants displayed decreased Pi accumulation and reduced Pi-starvation signaling.Collectively,our study revealed that SDEL1 and SDEL2 facilitate the degradation of SPX4 to modulate PHR2 activity and regulate Pi homeostasis and Pi signaling in response to external Pi availability in rice.

Laser textured dimple-patterns to govern the surface wettability of superhydrophobic aluminum plates

A laser texturing technique herein can endow bare aluminum alloy surface with regular dimple-pattern array and thus generates a case hardening.After STA treatment,these laser-textured samples become superhydrophobic.The surface wettability of the laser-textured samples can be regulated by controlling the dimple-pattern dimensions during the laser processing.It is noteworthy that a fluorescence method is utilized to record the zones on the superhydrophobic surface penetrated by small enough water molecules.Compared with a general method of the Cassie-Baxter theoretical calculation,this fluorescence method intuitively exhibits the air trapping ability of the superhydrophobic surface.Furthermore,the laser-textured superhydrophobic samples have a notable hysteresis phenomenon at the initial period of UMT friction because the air cushion trapped within superhydrophobic samples have strong repellency against water droplets on the hydrophilic steel ball.Additionally,such samples display strong mechanical stability in comparison with bare aluminum alloy because of the presence of case hardening on the surface of the laser patterns.The research results above provide a valuable reference for designing a surface with different wettability,which may inspire practical applications in the fields of fluid transport,droplet manipulation,water harvesting and microfluidic devices.

Mechanical and Tribological Study of PVA–pMPDSAH Double-Network Hydrogel Prepared by Ultraviolet Irradiation and Freeze–Thaw Methods for Bionic Articular Cartilage

Hydrogel has been widely used in the research of bionic articular cartilage due to their similarity in structure and functional properties to natural articular cartilage.In this research,polyvinyl alcohol and betaine monomer were used as raw materials to prepare a high-strength double-network hydrogel by a combination of ultraviolet(UV)irradiation and freeze–thaw methods.The structure of samples was characterized by Fourier transform infrared spectroscopy and X-ray diff raction,and the morphology of the samples was characterized by scanning electron microscope and three-dimensional white light interferometer.In addition,we also studied the swelling ratio,water content,mechanical properties and tribological properties of the samples.We found that the addition of betaine monomer and the UV irradiation time had a positive eff ect on the mechanical properties and tribological properties of the samples.

Identification of molecular markers linked to rice bacterial blight resistance genes from Oryza meyeriana

Y73 is a progeny of asymmetric somatic hybridization between Oryza sativa cv.Dalixiang and the wild rice species Oryza meyeriana.Inoculation with a range of strains of Xanthomonas oryzae pv.oryzae showed that Y73 had inherited a high level of resistance to rice bacterial blight(BB)from its wild parent.An F2 population of 7125 individuals was constructed from the cross between Y73 and a BB-susceptible cultivar IR24.After testing 615 SSR and STS markers covering the 12 rice chromosomes,186 markers were selected that showed polymorphism between Y73 and IR24.Molecular markers linked to the BB resistance genes in Y73 were scanned using the F2 population and the polymorphic markers.The SSR marker RM128 on chromosome 1,the STS marker R03D159 on chromosome 3 and the STS marker R05D104 on chromosome 5 were found to be linked to the rice BB resistance genes in Y73.