Special issue – recent advances in nanostructured implantable biomaterials

Recently, different surface modification methods have been employed to enhance the important mechanical and functional properties of biomedical alloys. The purpose of this special issue is to establish a forum for the discussion of recent advances either through change in grain structure or understanding of surface modification techniques that are used for improving the performance of a variety of implantable biomaterials.

Synthesis of nano/ultrafine-grained materials to enhance biofunctionalisation of the orthopaedic implants has been the focus of research and development. Significant advancement has been made in the field towards improving the mechanical properties of biomedical alloys including titanium and magnesium alloys and stainless steels. Novel techniques like severe plastic deformation (SPD) to obtain an ultra-fine grained (UFG) microstructure have gained significant attention in the materials research. Kumar et al.¹ discussed the use of SPD process in developing nano/ultrafine-grained titanium and magnesium alloys. Similarly, Sabirov et al.² used SPD process to obtain an UFG microstructure which enhances the mechanical and functional properties of Ti-based alloy. Nune et al.³ described the state-of-art knowledge on the biological activity of the nanostructured materials with focus on the effect of phase reversion-induced nano-grained structure on protein adsorption and cell–material interactions. Mali et al.⁴ in their review article comprehensively discussed recent advances in biomedical applications of nanostructured hydroxyapatite coatings on stainless steel implants with particular emphasis on the electrochemical deposition of hydroxyapatite and their cellular activity. Zhang et al.⁵ described an interesting approach to develop a highly ordered TiO₂ nanotube arrays which were fabricated by anodisation of titanium and modification in calcium-containing solution using ultrasound-assisted impregnation. These calcium-ion-modified nanotubes arrays were highly effective in promoting apatite formation. Biazar et al.⁶ presented an interesting study on nanofibers that were developed via an electrospinning process and surface modified by crosslinking CO₂ plasma and collagen. These nanofibers significantly enhance the performance of biomaterials and are potentially suitable for manufacturing scaffolds for enhancing the cell adhesion in tissue engineering. In a review article by Shadjou et al.⁷, the application of graphene mesoporous silica nanoparticles in orthopedic implants is discussed.

Most implantable materials used in medical implants are vulnerable to degradation due to corrosion during their service life. The electrochemical and mechanical aspects of corrosion processes and related issues in nanostructured metallic biomaterials are comprehensively discussed by Chaudhari et al.⁸. Magnesium (Mg) alloys are emerging as important candidates for biodegradable temporary implant applications given their strength-to-weight ratio and biocompatibility. However, in spite of significant research and improvement, problems of fast degradation rates for Mg-based alloys continue to be a challenge for their successful implementation for variety of applications in the physiological system. Current research is now focused on developing improved Mg alloys with lower biodegradation rates by utilizing surface modification techniques. Mahapatro et al.⁹ have described an interesting method to develop a self-assembled monolayers (SAMs) on the surface of magnesium alloy. Similarly, Wang et al.¹⁰ developed Si-containing coatings through a chemical deposition method on the surface of AZ31B alloy to decrease the biodegradation rate of the alloy. Trivedi et al.¹¹ combined the material science and engineering and cellular biology to develop our understanding of inhibition of bacterial colonization and biofilm formation on Mg-2Zn-3Gd surface with different grain structures. The study demonstrated that grain size has a significant impact on the antimicrobial behaviour of the alloy.

I sincerely hope that the material presented in this collection of 11 original review and research articles will provide a glimpse of ongoing research and development activities in the biomaterials field.

The Editor, Professor Devesh Misra would like to dedicate this special issue to Professor P. Rama Rao on his forthcoming 80th birthday, given that in under his guidance, the Editor acquired experience in editorial activities.