Porous NiTi for bone implants: A review

Abstract

NiTi foams are unique among biocompatible porous metals because of their high recovery strain (due to the shape-memory or superelastic effects) and their low stiffness facilitating integration with bone structures. To optimize NiTi foams for bone implant applications, two key areas are under active study: synthesis of foams with optimal architectures, microstructure and mechanical properties; and tailoring of biological interactions through modifications of pore surfaces. This article reviews recent research on NiTi foams for bone replacement, focusing on three specific topics: (i) surface modifications designed to create bio-inert porous NiTi surfaces with low Ni release and corrosion, as well as bioactive surfaces to enhance and accelerate biological activity; (ii) in vitro and in vivo biocompatibility studies to confirm the long-term safety of porous NiTi implants; and (iii) biological evaluations for specific applications, such as in intervertebral fusion devices and bone tissue scaffolds. Possible future directions for bio-performance and processing studies are discussed that could lead to optimized porous NiTi implants.

An original architectured NiTi silicone rubber structure for biomedical applications

“…Each of the two constitutive materials are well known for their typical behavior: NiTi exhibits superelasticity and shape memory behavior, and silicone rubber exhibits hyperelasticity allowing large deformations without permanent set. The use of NiTi was investigated for many applications during the last few years, especially in the medical field [4,5,6,7] due to its biocompatibility [8,9,10,11,12]. Also, similarly to SMA, elastomers are often considered to make composites [13,14].…”

Biomedical Applications of Shape Memory Alloys

“…Notwithstanding a porous form of NiTi was discovered at the end of the 60's [35] and immediately the high potentialities were recognized, the effective use of NiTi foams ( Figure 14) started only recently after deep studies of biocompatibility and corrosion resistance [36][37][38]. From these studies, the importance of the fabrication processes for creating foams with desirable architectures and microstructures, and of the pore surface modifications for tailoring the biological interactions was underlined.…”

“…The disadvantage, in case of calcified Figure 14: Scanning electron microscope images of porous NiTi produced using three different methods: (a) self-propagating hightemperature synthesis process (porosity 65 ± 10%, 100-360 μm) (b) capsule-free hot isostatic pressing with argon expansion (porosity 42%, 50-400 μm) (c) metal injection molding (porosity 70%, 355-500 μm). (d) Commercial porous NiTi implant (Actipore, Biorthex, Canada) for spinal fusion produced by SHS process [38].…”

Open-cell aluminium foams with graded coatings as passively controllable energy absorbers

“…They can amongst others be used as catalyst support [1,2], implant material [3], heat exchanger [4], sound absorber [5] and energy/impact absorbers [6,7,8,9,10,11,12,13]. In the future OCMFs may have the potential to partially replace the relatively heavy bulk metals used in crumple zones of cars as low-weight energy absorbers [14].…”