Mussel-Inspired Carboxymethyl Chitosan Hydrogel Coating of Titanium Alloy with Antibacterial and Bioactive Properties

Infection-related titanium implant failure rates remain exceedingly high in the clinic. Functional surface coating represents a very promising strategy to improve the antibacterial and bioactive properties of titanium alloy implants. Here, we describe a novel bioactive surface coating that consists of a mussel-inspired carboxymethyl chitosan hydrogel loaded with silver nanoparticles (AgNPs) to enhance the bioactive properties of the titanium alloy. The preparation of hydrogel is based on gallic acid grafted carboxymethyl chitosan (CMCS-GA) catalyzed by DMTMM (4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride). To build a firm bonding between the hydrogel and titanium alloy plate, a polydopamine layer was introduced onto the surface of the titanium alloy. With HRP/H2O2 catalysis, CMCS-GA can simply form a firm gel layer on the titanium alloy plate through the catechol groups. The surface properties of titanium alloy were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and water contact angle. Silver nanoparticles were loaded into the gel layer by in situ reduction to enhance the antibacterial properties. In vitro antibacterial and cell viability experiments showed that the AgNPs-loaded Ti-gel possesses excellent antibacterial properties and did not affect the proliferation of rabbit mesenchymal stem cells (MSCs).

Osteogenesis and degradation behavior of magnesium alloy plate in vivo

Introduction: The magnesium alloy was fabricated into orthopedic plates, and used to repair tibial fractures of New Zealand white rabbits. The osteogenesis and degradation behavior of magnesium alloy plates were investigated in vivo. Methods: 38 rabbits were randomly divided into an experimental group using the magnesium alloy plate and control group using a titanium alloy plate. Tibial fractures in the experimental group and control group were fixed with magnesium alloy plates and titanium alloy plates, respectively. An X-ray of the fracture site was taken at 1, 2, 4, 8, and 16 weeks after surgery. The formation of callus and expression of bone morphogenetic protein (BMP-2) in each group were examined at 4, 8, and 16 weeks postoperatively. The degradation behavior of the magnesium alloy plate was observed using a scanning electron microscope with an energy dispersive spectroscopy system. Results: The results of X-ray showed that the fracture healed gradually and there was significant callus around the plate in the magnesium alloy plate group than that in the titanium alloy plate groups. The formation of callus and the expression of BMP-2 in the magnesium alloy plate group were more significant than that in the titanium plate group. The degradation behavior of the magnesium alloy plates deepened in vivo with the implantation time. Conclusion: The results demonstrated that the magnesium alloy plate implanted into the rabbit tibia could promote the formation of callus and result in osteogenesis in vivo. Meanwhile, the magnesium alloy plate was absorbed gradually in vivo.

Study on bubble morphology at interface of laser direct joint between carbon fiber reinforced thermoplastic (CFRTP) and titanium alloy

Laser direct joining of carbon fiber reinforced thermoplastic (CFRTP) composite plate and titanium alloy plate with a thickness of 2 mm was performed with swing laser. Numerous air bubble of submillimeter size were observed inside the fusion zone of CFRTP and titanium alloy at the cross section of the joints. The air bubble characteristics were analyzed based on the morphology and size, while the formation mechanism of air bubble was further elucidated according to the nucleation mode, nucleation site and nucleation position. The results demonstrated that the nucleation modes of air bubble are substantially divided into homogeneous nucleation and heterogeneous nucleation, which is related to the nucleation sites. The nucleation mode presents a crucial factor influencing the position and morphology of air bubble. In addition, the air bubble characteristics are also determined by the clamp pressure and resin flow. The final morphology of air bubble is primarily represented by four typical types.

The Microstructural Difference and Its Influence on the Ballistic Impact Behavior of a Near β-Type Ti5.1Al2.5Cr0.5Fe4.5Mo1.1Sn1.8Zr2.9Zn Titanium Alloy

In this work, a near β-type Ti5.1Al2.5Cr0.5Fe4.5Mo1.1Sn1.8Zr2.9Zn alloy was hot-rolled at the temperature of 800–880 °C with a thickness reduction of 87.5% and then heat-treated with the strategy of 880 °C/1 h/air cooling (AC) + 650 °C/3 h/AC. The microstructure difference between the hot-rolled and heat-treated titanium alloys and its influence on the ballistic impact behavior of the hot-rolled and heat-treated titanium alloys were analyzed. The microstructural investigation revealed that the average size of the acicular secondary α phase (αs) dropped from 75 to 42 nm, and the corresponding amount of this phase increased significantly after heat treatment. In addition, the dislocation density of the α and β phases decreased from 0.3340 × 1015/m2 and 4.6746 × 1015/m2 for the hot-rolled titanium alloy plate to 0.2806 × 1015/m2 and 1.8050 × 1015/m2 for the heat-treated one, respectively. The high strength of the heat-treated titanium alloy was maintained, owing to the positive contribution of the acicular secondary α phase. Furthermore, the critical fracture strain increased sharply from 19.9% for the hot-rolled titanium alloy plate to 23.1% for the heat-treated one, thereby overcoming (to some extent) the constraint of the strength–ductility trade-off. This is mainly attributed to the fact that the dislocation density and the difference between the dislocation densities of the α and β phases decreased substantially, and deformation localization was effectively suppressed after heat treatment. Damage to the hot-rolled and heat-treated titanium alloy plates after the penetration of a 7.62 mm ordinary steel core projectile at a distance of 100 m was assessed via industrial computer tomography and microstructure observation. The results revealed that a large crack (volume: 2.55 mm3) occurred on the rear face and propagated toward the interior of the hot-rolled titanium alloy plate. The crack tip was connected to a long adiabatic shear band with a depth of 3 mm along the thickness direction. However, good integrity of the heat-treated titanium alloy plate was maintained, owing to its excellent deformation capability. Ultimately, the failure mechanism of the hot-rolled and heat-treated titanium alloy plates was revealed by determining the crack-forming reasons in these materials.

The Effect of annealing temperature on corrosion resistance and microstructure of Zr-Sn-Nb-Fe alloy

The Ti-2Al-2.5Zr titanium alloy plate in beta phase water quench at different times of the reentry after annealing is implemented while primary phase number and size distribution of samples are obtained. This research is carried out on corrosion behavior in 3.5% [mass fraction] NaCl solution. Experimental study showed that after the beta phase water quenching Ti-2Al-2.5Zr titanium alloyed after 500 oC annealing when partial recrystallization happened. There seems to be lots of tiny dispersion in the alloy that was annealed with its samples of six-party [HCP] structure of Ti, Zr, Al phase 2 with the dimension below 100 nm. Reaching 500 oC when the rate of annealing at a primary phase of the sample at 550 oC is low 90% of the primary phase is less than 100 nm. The changing of the rule of present decreasing also triggers little difference overall. Precipitation in the process of annealing Zr [Nb,Fe,Cr] 2is less that proves to be good for corrosion resistance.

An Experimental Study for the Development of Mandrel-Free Hot-Spinning for Large Size Titanium Alloy Plate Forming

A mandrel-free hot-spinning was developed as a near-net-shape titanium alloy plate forming technique. In this work, a Ti–6Al–4V alloy conical product with a wall angle of 34 deg and 170 mm height was formed from a large size Ti–6Al–4V plate (890–920 mm diameter × 30 mm thick). The product was characterized metallurgically and mechanical properties were measured, and the shape of formed products was investigated. It was found that the mandrel-free hot-spinning is able to form a large size titanium alloy plate. Material properties including tensile strength and microstructure of the formed products satisfied the material specifications. Fatigue stress of the formed product was higher than that of the typical Ti–6Al–4V material. For a further improvement, a forming method using preformed material was proposed and which was successfully conducted with two types of preforms and found to be effective in the forming process.