Influences of laser powers on microstructure and properties of the coatings on the AZ91HP magnesium alloy

Al-Si alloy coatings were prepared on AZ91HP magnesium alloy by broad-beam laser cladding; the influences of the powers on the microstructure and properties of the coatings were discussed. It was found that the microstructure of the coatings at the powers of 3 and 3.5 kW was characterized by Mg2Si dendrites, and needle-like Mg2Al3 （hcp） dispersing in the Mg17Al12 matrix, whereas the coating at the power of 2.5 kW was composed of the petal-like Mg2Al3 （fcc） as well as the needle-like Mg2Al3 （hcp）. The coating at the power of 4 kW appeared as α-Mg solid solution and Mg2Si, Mg17Al12, as well as Mg2Al3 （hcp）. The coatings with the powers of 3 and 3.5 kW exhibited higher microhardness and better wear resistance because of more Mg2Si and Mg17Al12. However, the coating at the power of 2.5 kW displayed better corrosion resistance.

Recent Progress in Bionic Hydrogels for Articular Cartilage:Tribological and Mechanical Characteristics

Cartilage regeneration and repair are considered clinical challenges since cartilage has limited capability for reconstruction.Although tissue-engineered materials have the ability to repair cartilage,they have weak mechanical characteristics and cannot resist long-term overload.On the other hand,surgery to replace the joint is frequently done to treat significant cartilage deterioration these days.However,the materials that are being used for replacement have high friction coefficients,lack shock absorption functions,and lack cushioning.Further research on natural articular cartilage structure and function may lead to bionic hydrogels,which have suitable physicochemical and biological characteristics(e.g.,tribological and mechanical properties and the ability to support loadbearing capability),but need improvements.Based on their tribological and mechanical characteristics,the current review highlights the most recent advancements of bionic hydrogels used for articular cartilage,highlighting both the field's recent progress and its potential for future research.For this reason,firstly,some important property improvement methods of bionic hydrogels are discussed and then,the recent findings of various research on the making of those bionic materials are provided and compared.It seems that by using some modifications such as product design,surface treatments,animal tests,controlling the isoelectric point of hydrogels,and computer simulation,the intended mechanical and tribological characteristics of natural articular cartilage may be attained by the bionic hydrogels.

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.

Effects of Surface Oxidation Treatment of Carbon Fibers on Biotribological Properties of CF/PEEK Materials

Carbon Fiber （CF） reinforced polyetheretherketone （PEEK） composite is one of the most promising implant biomaterials used in orthopedics. In this article, unfilled PEEK and CF/PEEK specimens were prepared by vacuum hot pressing method, and their tribological properties were evaluated by sliding against a cobalt-chromium-molybdenum （Co-Cr-Mo） alloy block. The influences of mass fraction of carbon fibers in CF/PEEK and the surface oxidation treatment of carbon fibers were explored. The results showed that the water contact angles on the surfaces of CF/PEEK specimens decreased, indicating that their surface wettability was improved. The hardness value of CF/PEEK was significantly improved, the friction coefficients of CF/PEEK were effectively reduced and its wear resistance was enhanced compared with unfilled PEEK. The leading effect on CF/PEEK tribological properties was the mass fraction of CF, followed by surface oxidation of CF, and the calf serum solution had better lubricity than that of saline and deionized water.

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.