Jonathan C. Y. Chung

Relationship between osseointegration and superelastic biomechanics in porous NiTi scaffolds

The superelastic nature of bones requires matching biomechanical properties from the ideal artificial biomedical implants in order to provide smooth load transfer and foster the growth of new bone tissues. In this work, we determine the biomechanical characteristics of porous NiTi implants and investigate bone ingrowth under actual load-bearing conditions in vivo. In this systematic and comparative study, porous NiTi, porous Ti, dense NiTi, and dense Ti are implanted into 5 mm diameter holes in the distal part of the femur/tibia of rabbits for 15 weeks. The bone ingrowth and interfacial bonding strength are evaluated by histological analysis and push-out test. The porous NiTi materials bond very well to newly formed bone tissues and the highest average strength of 357 N and best ductility are achieved from the porous NiTi materials. The bonding curve obtained from the NiTi scaffold shows similar superelasticity as natural bones with a deflection of 0.30-0.85 mm thus shielding new bone tissues from large load stress. This is believed to be the reason why new bone tissues can penetrate deeply into the porous NiTi scaffold compared to the one made of porous Ti. Histological analysis reveals that new bone tissues adhere and grow well on the external surfaces as well as exposed areas on the inner pores of the NiTi scaffold. The in vitro study indicates that the surface chemical composition and topography of the porous structure leads to good cytocompatibility. Consequently, osteoblasts proliferate smoothly on the entire implant including the flat surface, embossed region, exposed area of the pores, and interconnected channels. In conjunction with the good cytocompatibility, the superelastic biomechanical properties of the porous NiTi scaffold bodes well for fast formation and ingrowth of new bones, and porous NiTi scaffolds are thus suitable for clinical applications under load-bearing conditions.

Fabrication of FeF3 nanocrystals dispersed into a porous carbon matrix as a high performance cathode material for lithium ion batteries

FeF3/C nanocomposites, where FeF3 nanocrystals had been dispersed into a porous carbon matrix, were successfully fabricated by a novel vapour–solid method in a tailored autoclave. Phase evolution of the reaction between the precursor and HF solution vapour under air and argon gas atmospheres were investigated. The results showed that the air in the autoclave played an important role in driving the reaction to form FeF3. The as-prepared FeF3/C delivered 134.3, 103.2 and 71.0 mA h g−1 of charge capacity at a current density of 104, 520, and 1040 mA g−1 in turn, exhibiting superior rate capability to the bare FeF3. Moreover, it displayed stable cycling performance, with a charge capacity of 196.3 mA h g−1 at 20.8 mA g−1. EIS and BET investigations indicated that the good electrochemical performance can be attributed to the good electrical conductivity and high specific surface area that result from the porous carbon matrix.

Hydrogen release from titanium hydride in foaming of orthopedic NiTi scaffolds

Titanium hydride powders are utilized to enhance the foaming process in the formation of orthopedic NiTi scaffolds during capsule-free hot isostatic pressing. In order to study the formation mechanism, the thermal behavior of titanium hydride and hydrogen release during the heating process are systematically investigated in air and argon and under vacuum by X-ray diffraction (XRD), thermal analysis, including thermogravimetric analysis and differential scanning calorimetry, energy dispersive X-ray spectroscopy, and transmission electron microscopy. Our experiments reveal that hydrogen is continuously released from titanium hydride as the temperature is gradually increased from 300 to 700 °C. Hydrogen is released in two transitions: TiH1.924→TiH1.5/TiH1.7 between 300 °C and 400 °C and TiH1.5/TiH1.7→α-Ti between 400 °C and 600 °C. In the lower temperature range between 300 °C and 550 °C the rate of hydrogen release is slow, but the decomposition rate increases sharply above 550 °C. The XRD patterns obtained in air and under vacuum indicate that the surface oxide layer can deter hydrogen release. The pressure change is monitored in real time and the amount of hydrogen released is affected by the processing temperature and holding time. Holding processes at 425 °C, 480 °C, 500 °C, 550 °C, and 600 °C are found to significantly improve the porous structure in the NiTi scaffolds due to the stepwise release of hydrogen. NiTi scaffolds foamed by stepwise release of hydrogen are conducive to the attachment and proliferation of osteoblasts and the resulting pore size also favor in-growth of cells.

Large-scale fabrication of hierarchical α-Fe2O3 assemblies as high performance anode materials for lithium-ion batteries

Hierarchical flower- and cube-like α-Fe2O3 assemblies consisting of nanoparticles with sizes of around 150 nm have been successfully synthesized by a precipitation–calcination strategy. The as-prepared assemblies exhibit superior electrochemical performance, with respective reversible capacities of 570 and 675 mA h g−1 at 0.2 C after 100 cycles.

Tannic Acid/Fe3+/Ag Nanofilm Exhibiting Superior Photodynamic and Physical Antibacterial Activity

Silver nanoparticles (AgNPs) enwrapped in the biologically safe tannic acid (TA)/Fe3+ nanofilm are synthesized by an ultrafast, green, simple, and universal method. The physical antibacterial activity and photodynamic antibacterial therapy (PAT) efficacy of the TA/Fe3+/AgNPs nanofilm were investigated for the first time, which exhibited a strong physical antibacterial activity as well as great biocompatibility, through in vitro and in vivo studies. The results disclosed that this hybrid coating could possess high PAT capabilities upon irradiation under a visible light of 660 nm, which is longer than those of previously reported green and blue sensitization light, thus allowing deeper light penetration into biological tissues. Electron spin resonance (ESR) spectra proved that the PAT efficacy of the TA/Fe3+/AgNPs nanofilm was associated with the yields of singlet oxygen (1O2) under the irradiation of visible light (660 nm). A higher PAT efficiency of 100 and 94% against Escherichia coli and Staphylococcus aureus could be achieved within 20 min of illumination under 660 nm visible light, whereas the innate physical antibacterial activity of AgNPs could endow the implants with long-term prevention of bacterial infection. The mechanism of PAT may be associated with the formation of oxidative stress and oxidative damage to key biomolecules (proteins and lipids) in bacteria. Our results reveal that the synergistic action of both PAT and physical action of AgNPs in this hybrid nanofilm is an effective way to inactivate bacteria, with minimal side effects.

Characterization study of modified Cu-Zn-Al shape memory alloy with the addition of Mn and Zr

As a modification of Cu-Zn-Al shape memory alloy (SMA), the characteristics of Cu-21Zn-6Al-1Mn-0.5Zr (wt%) SMA are examined and compared with that of Cu-21Zn-6Al (wt%) SMA in the present work. After added Zr into the Cu-Zn-Al alloy, the average grain size of Cu-Zn-Mn-Zr alloy is reduced from 300 micrometers (that of Cu-Zn-Al alloy) to 75 micrometers . Two Zr-rich new phases were found in Zr added alloy by means of transmission electron microscopy. The tensile testing results and scanning electron microscopy observations show that the strength of grain boundary and the ductility of the Mn, Zr added alloy were enhanced. This has made the alloy exhibit better mechanical property than ordinary Cu-Zn-Al SMA. Moreover, upon ageing, the reordering phenomenon was not serious when the aging temperature was below 200 degree(s)C in Cu-Zn-Al-Mn-Zr alloy while significant decrease of order degree and shape memory capacity were found for Cu-Zn-Al alloy.

Preparation of Ni current collector and MoS 2 cathode in three-dimensional Li ion microbattery based on silicon MCP

Three-dimensional Li ion microbatteries are known for their high surface area which leads to high current and capacity compared to traditional planar batteries. This paper describes economical approaches to prepare half 3D microbatteries based on silicon microchannel plates (MCP). The high aspect ratio silicon MCP is formed by electrochemical etching and a nickel layer is coated onto the silicon MCP as a current collector by electroless deposition. A molybdenum sulfide layer is electro-deposited onto the nickel coated silicon MCP as a cathode. The as-deposited molybdenum sulfide film is amorphous whereas the film annealed at a high temperature appears to be highly textured.

Novel far infrared imaging sensor based on the use of titanium-nickel shape memory alloys

In this paper we describe a novel imaging sensor design1 that uses the thermo-mechanical properties of nickel-titanium (NiTi) shape memory alloys (SMAs) for detecting far infrared radiation (FIR). A thin NiTi SMA cantilever is coated with a FIR absorbing layer on one surface, while the other is coated with a highly reflecting metallic layers such as gold. Upon absorption of FIR, the temperature of the cantilever changes. This causes the tilt angle of the cantilever to change as well. The deflection is very large if the temperature change coincides with the temperature range of the phase transformation of the NiTi SMA. The detection of the mechanical movements in the cantilever is achieved by illuminating the reflective side using a visible laser beam. A Michelson interferometer is used to covert the reflected light into optical modulation. In doing this, very small displacement in the cantilever can be visualized as laser intensity variation. A single element device has been fabricated for this purpose and our initial experimental results have demonstrated the successful detection of FIR. An estimation of angular deflection per unit change of temperature suggests that our approach can offer sensitivity higher than the reported design based on the use of bi-material strips. We envisage that a two-dimensional array of such devices can lead to the possibility of realizing a practical low-cost infrared imaging device operating under room temperature conditions.

Pulsed laser deposition of high purity TiN thin films

TiN thin films were deposited on glass substrates by KrF excimer laser ablation of Ti in very broad N2 pressure range with different target-substrate distance at room temperature. The as-deposited TiN thin films were analyzed by x-ray diffraction and transmission electron microscopy. It is found that normally the as-deposited thin films are the mixture of TiN and Ti and the ratio of TiN to Ti of the as- deposited thin film depends on both the N2 pressure and the target-substrate distance. The high purity TiN thin films can be obtained only in a very narrow deposition parameter range. A compound parameter (the product of the N2 pressure and the target-substrate distance) is proposed to optimize deposition for high purity TiN thin films and the possible mechanism is also discussed. It is also revealed that the as-deposited TiN thin films were polycrystalline with an average grain size about 20 nm.

Effects of Temperature on the Effectiveness of the Surface Barrier Layers on Orthopedic Nickel-Titanium Shape Memory Alloys Fabricated by Nitrogen Plasma Implantation

Summary form only given. Nickel-titanium shape memory alloys (NiTi SMA) are potential orthopedic materials due to their super-elastic properties and shape memory effects. However, there are health and safety concerns with regard to the leakage of harmful Ni ions from the surface during prolonged use inside human beings. To mitigate this effect, we modified the alloy surface by plasma implantation of gas species such as nitrogen and oxygen. Our objection is to create barrier surface layers with graded interface to reduce Ni leaching from the NiTi substrate. The modified surfaces possess much improved electrochemical corrosion resistance, diminished Ni out-diffusion, and good biocompatibility according to our previous works. Since high temperature can degrade the elasticity of the NiTi SMA, suitable implantation parameters must be used to retain the mechanical properties of the bulk NiTi. In this work, we investigate the effects of the temperature on the effectiveness of the treatment process as well as the shape recovery. Our results show dependence of the shape recovery and surface barrier effectiveness on the treatment temperature