To Improve Total Knee Prostheses Performance Using Three-Phase Ceramic-Based Functionally Graded Biomaterials

One of the common issues that occur after total knee replacement surgery is the aseptic loosening. The problem usually occurs after about 15 years from the surgery. The destructive effects of residual particles due to wear, the stress shielding effect, and micro-movements are the causative factors for this type of loosening. In this research, using the advantages of functionally graded biomaterials (FGBM), it is tried to design a prosthetic system that can reduce the above-mentioned effects. For this purpose, the materials used in the most important part of the prosthesis system, i.e., the femoral part are redesigned so that the bioactivity between the prosthesis and bone, and the stress applied to the adjacent tissues increase simultaneously. In addition, to reduce the effect of wear at contact areas, wear-resistant biocompatible ceramics such as alumina and zirconia are used. The value of stress at the bone-prosthesis interface and adjacent tissues is the most important parameters. Two types of three-phase ceramic-based FGBMs are recommended. The prosthesis with three-phase hydroxyapatite-titanium-zirconia has increased the average stress in the bone tissues around high-risk areas up to 71.8% with respect to a commonly used Cr-Co prosthesis. The result for the prosthesis with three-phase hydroxyapatite-titanium-alumina is up to 65%, respectively. At bone-prosthesis interfaces, an increase of 92% in the stress for both zirconia-based and alumina-based is seen. Briefly, the recommended FGBMs can improve the bone-prosthesis performance in all desired indices

Complexation between porcine gastric mucin (PGM) and lysozyme: Influence of heat treatment of lysozyme on the tribological properties

The influence of complexation between porcine gastric mucin (PGM) and lysozyme (LYZ) solutions (pH⁓7.0) on their lubricating properties was studied at a hydrophobic self-mated polydimethylsiloxane (PDMS) tribopair. To this end, LYZ solutions with varying heating time, namely 1hr, 3hr-, and 6hr at 90 °C, as well as unheated LYZ solution, were prepared. The lubricating capability of PGM and LYZ solutions and also their mixtures was characterized using pin-on-disk tribometry. In parallel, to precisely investigate the interaction between PGM and LYZ solutions, an array of the well-known experiments including electrophoretic-dynamic light scattering, circular dichroism spectroscopy and optical waveguide light-mode spectroscopy were employed. These experiments were utilized to elucidate the key features e.g. zeta potential, hydrodynamic diameter, conformational structure and mass adsorption. The tribometry results indicated that both PGM and unheated LYZ solutions had poor lubricating properties in the boundary lubrication regime (sliding speed lower than 10 mm/s). Mixing PGM with unheated LYZ led to a slight decrease in the friction coefficient, but no desirable lubricity was observed. An optimum slippery characteristic was achieved by incorporating 1hr heated LYZ solution into PGM one. Excellent lubricity of PGM/1hr heated LYZ may stem from surface charge compensation, tenaciously compact aggregation, unique conformational structure and considerable mass adsorption onto PDMS. This finding revealed that a strong interaction between PGM and LYZ molecules and as a result, the promising lubricating capability of PGM/LYZ mixtures, can be administered by varying heat-treatment duration of LYZ proteins

Elastic-plastic properties of titanium and its alloys modified by fibre laser surface nitriding for orthopaedic implant applications

Laser nitriding is one of the most promising approaches to improve wear resistance of Ti alloy surfaces and may extend the use in orthopaedic implants. In this study, three types of Ti alloys, namely alpha commercially pure Ti (“TiG2”), alpha-beta Ti–6Al–4V (“TiG5”), and beta Ti-35.5Nb-7.3Zr-5.7Ta (“βTi”), were subjected to an open-air laser nitriding treatment. Essential elastic-plastic mechanical properties including elastic modulus, hardness, elastic energy, plasticity index, and hardness-to-elasticity ratio of the laser-treated Ti alloys were characterized using nanoindentation experiment. The results showed that the elastic modulus, hardness and elastic energy values of all Ti samples significantly increased in the nitrided layer compared to respective bare substrates for all three Ti materials. Across different Ti samples, βTi sustained its relatively lower elastic modulus, but presented comparable hardness, elastic energy, plasticity index, as well as hardness-to-elasticity ratio in the nitrided layer compared to the other two Ti alloys. Overall, amongst three medical grade Ti alloys in this study, βTi appeared as the most appealing candidate for joint replacement applications even solely in view of mechanical compatibility when combined with surface laser nitriding. Nevertheless, laser nitriding treatment in this study tended to cause a residual compressive stress on all Ti alloys as displayed by cracks developed in the nitrided layer and analyzed on βTi by X-ray diffraction (XRD) and further nanoindentation tests

Mechanical and tribological properties of hydroxyapatite nanoparticles extracted from natural bovine bone and the bone cement developed by nano-sized bovine hydroxyapatite filler

The aim of this study is twofold. Firstly, it provides a nano-sized hydroxyapatite derived from bovine bone (BHA), as a raw material and natural source of HA, and to obtain the mechanical and tribological properties of sintered BHA ceramic. Secondly, it evaluates the mechanical and tribological properties of a commercially available bone cement by incorporating nano-sized BHA as a bone compatible nano-filler. In order to achieve these two goals, the mechanical and tribological properties of sintered BHA ceramic and nano-composite cements were measured using nano-indentation and nano-scratch experiments. The results indicated that the nano- hydroxyapatite of single phase with high crystallinity and appropriate mechanical and tribological properties could be produced from the natural bovine bone. Moreover, it was found that the nano-composite with 10. wt% BHA exhibited a good improvement in mechanical and tribological properties in comparison with other examined PMMA/BHA nano-composites