Green techniques for biomedical metallic materials with nanotechnology

Abstract

From a clinic or medical viewpoint, it is important that the surgical implant retains a combination of high strength (including surface wear resistance), good biocompatibility, and chemical stability. To enable safe interactions between the surgical implants and tissues, surface modification and functionalization are commonly employed. Biological coatings such as TiN and titanium oxides are widely adopted and functionalized with various biological properties such as corrosion resistance, bioactivity, cytocompatibility, and bioconductivity. However, failure of the biological coatings due to the long term corrosion and wear or fretting is the main problem and debris from the materials is the main cause of joint replacement failure. Since the surgical implants are implanted into the human body for a long time, cyclic motions between the surgical implants and human tissues may disrupt the protective biological coatings accelerating corrosion and increasing the risks of immunological response by the leached metallic ions. Therefore, improved metallic biomaterials and the relevant manufacturing techniques are being introduced to meet this demand. Apart from the biocompatibility requirement, metallic biomedical materials also have to meet high standards regarding its performance (functionality, reliability) and selection criteria (cost, manufacturing ability). Up to now, the most often used metallic biomedical materials include stainless steel, cobalt-based alloys, and commercially pure titanium or titanium-based alloys. However, the implant metallic biomaterials, like all mechanical components, are subjected to degradation and have limited lifetime. Damaged implant requires successive operation to replace worn components and so intensive efforts are made to increase durability of implants metallic biomaterials. For enhancing the mechanical retention, engineered nanostructures on the surface are normally taken to increase effective surface area on implant surfaces (such as both dental and orthopedic applications) to exhibit biological, mechanical, and morphological compatibilities to receiving vital hard/soft tissue, resulting in promoting osseointegration. The surface engineered nanostructures play a crucial role in biomedical metallic materials because (1) the surface of a biomaterials is the only part contacting with the bioenvironment, (2) the surface region of a biomaterial is almost always different in morphology and composition from the bulk, (3) for biomaterials that do not release or leak biologically active or toxic substance, the characteristics of the surface governs the biological response (foreign material vs. host tissue), and (4) surface properties such as topography affect the mechanical stability of the implant-tissue interface. Therefore, aim to provide vital information about the growing field of engineered nanostructures on the surface of metallic biomedical materials, the relevant green technologies such as equal channel angular extrusion (ECAE), high pressure torsion (HPT), cold rolling, heat rolling, high energy ball milling, sandblasting, and shot peening are reviewed. At the same time, implant industry is experiencing rapid growth mainly due to age-related degenerative diseases. with the increase of the need to diagnose diseases at an early stage in accordance with the saying: prevention is better than cure, the future prospects related to the significantly feasible surface nanostructured technology for the foreseeable future are also pointed out. It indicates that new surface bioengineering technologies should be explored to help the scientists and clinicians in the initiation of targeted treatments and in the follow-up of treatment responses.