Synthesis of hydroxyapatite for biomedical applications

Joint replacement is a major orthopaedic procedure used to treat joint osteoarthritis. Aseptic loosening and infection are the two most significant causes of prosthetic implant failure. The ideal implant should be able to promote osteointegration, deter bacterial adhesion and minimize prosthetic infection. Recent developments in material science and cell biology have seen the development of new orthopaedic implant coatings to address these issues. Coatings consisting of bioceramics, extracellular matrix proteins, biological peptides or growth factors impart bioactivity and biocompatibility to the metallic surface of conventional orthopaedic prosthesis that promote bone ingrowth and differentiation of stem cells into osteoblasts leading to enhanced osteointegration of the implant. Furthermore, coatings such as silver, nitric oxide, antibiotics, antiseptics and antimicrobial peptides with anti-microbial properties have also been developed, which show promise in reducing bacterial adhesion and prosthetic infections. This review summarizes some of the recent developments in coatings for orthopaedic implants.

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Bioactive Coatings for Orthopaedic Implants—Recent Trends in Development of Implant Coatings

New promising techniques for depositing biocompatible hydroxyapatite-based coatings on biocompatible metal substrates for biomedical applications have continuously been exploited for more than two decades. Currently, various experimental deposition processes have been employed. In this review, the two most frequently used deposition processes will be discussed: a sol-gel dip coating and an electrochemical deposition. This study deliberates the surface morphologies and chemical composition, mechanical performance and biological responses of sol-gel dip coating as well as the electrochemical deposition for two different sample conditions, with and without coating. The review shows that sol-gel dip coatings and electrochemical deposition were able to obtain the uniform and homogeneous coating thickness and high adherent biocompatible coatings even in complex shapes. It has been accepted that both coating techniques improve bone strength and initial osseointegration rate. The main advantages and limitations of those techniques of hydroxyapatite-based coatings are presented. Furthermore, the most significant challenges and critical issues are also highlighted.

A review of hydroxyapatite-based coating techniques: Sol-gel and electrochemical depositions on biocompatible metals.

A comprehensive review of hydroxyapatite-based coatings adhesion on metallic biomaterials

Calcium orthophosphate deposits: Preparation, properties and biomedical applications.

Comparative investigation on the adhesion of hydroxyapatite coating on Ti–6Al–4V implant: A review paper

Ti/TiN/HA coating on Ti–6Al–4V for biomedical applications

Aircraft engines, fuselage, automobile parts, and energy saving strategies in general have promoted the interest and research in the field of lightweight materials, typically on alloys based on aluminum. Aluminum alloy itself does not have suitable wear resistance; therefore, it is necessary to enhance surface properties for practical applications, particularly when aluminum is in contact with other parts. Fretting fatigue phenomenon occurs when two surfaces are in contact with each other and one or both parts are subjected to cyclic load. Fretting drastically decreases the fatigue life of materials. Therefore, investigating the fretting fatigue life of materials is an important subject. Applying surface modification methods is anticipated to be a supreme solution to gradually decreasing fretting damage. In this paper, the authors would like to review methods employed so far to diminish the effect of fretting on the fatigue life of Al7075-T6 alloy. The methods include deep rolling, shot peening, laser shock peening, and thin film hard coatings. The surface coatings techniques are comprising physical vapor deposition (PVD), hard anodizing, ion-beam-enhanced deposition (IBED), and nitriding.

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A Study on Surface Modification of Al7075-T6 Alloy against Fretting Fatigue Phenomenon

We developed a theoretical model that estimates the bubble size from sub-millimeter orifices under variable gas flow conditions. The model is successfully tested for orifices with diameters in the range of 0.2 mm to 1 mm under both quasi-static and dynamic bubbling regimes. The model is able to predict the final bubble radius with an accuracy better than 20% compared with the experimental results. Moreover, we explicitly look into the influence of the gas reservoir volume Vc upstream of the orifice on the gas reservoir pressure Pc by simultaneously monitoring the events, i.e. changes in the state of bubble, upstream and downstream of orifices. We found that, variations in Pc reduce as Vc increases. Analysis of the dynamics of the dominating forces acting on a bubble show that, enlarging Vc mainly amplifies the gas momentum force and the liquid inertia force. Hence, the bubble detachment mechanism may no longer be only buoyancy driven. 

Bubble formation from sub-millimeter orifices: Experimental analysis and modeling

The application of liquid nitrogen is being considered nowadays because it is clean and environmentally friendly and improves product quality. The cryogenic cooling can also be useful in hard machining process where workpiece is exposed to high thermo-mechanical loads. Thermal loads are one of the factors affecting residual stresses and microstructural changes in a material. There is no study in literature to evaluate the effect of cryogenic cooling for evaluation of thermo-mechanical loads during the machining of the hardened AISI H13 steel. Therefore, in the present study, to control and investigate the thermal loads, microhardness, white layer thickness, and surface quality in hard machining of AISI H13 steel, the cryogenic cooling system was employed during the process. Results indicated that depth of cut was the most influential item on temperature enhancement of cutting zone, while high feed rates were responsible for enhancement of microhardness surface roughness. Intense and rapid cooling using the liquid nitrogen spraying was found effective strategy to reduce white layer thickness and improve surface quality at the machined surface. 

E. Mohseni

Papers

Comparative investigation on the adhesion of hydroxyapatite coating on Ti–6Al–4V implant: A review paper

Ti/TiN/HA coating on Ti–6Al–4V for biomedical applications

A Study on Surface Modification of Al7075-T6 Alloy against Fretting Fatigue Phenomenon

Bubble formation from sub-millimeter orifices: Experimental analysis and modeling

Liquid nitrogen spraying in hard machining process of AISI H13 steel