Biomedical Porous Shape Memory Alloys for Hard-Tissue Replacement Materials

Abstract

Porous shape memory alloys (SMAs), including NiTi and Ni-free Ti-based alloys, are unusual materials for hard-tissue replacements because of their unique superelasticity (SE), good biocompatibility, and low elastic modulus. However, the Ni ion releasing for porous NiTi SMAs in physiological conditions and relatively low SE for porous Ni-free SMAs have delayed their clinic applications as implantable materials. The present article reviews recent research progresses on porous NiTi and Ni-free SMAs for hard-tissue replacements, focusing on two specific topics: (i) synthesis of porous SMAs with optimal porous structure, microstructure, mechanical, and biological properties; and, (ii) surface modifications that are designed to create bio-inert or bio-active surfaces with low Ni releasing and high biocompatibility for porous NiTi SMAs. With the advances of preparation technique, the porous SMAs can be tailored to satisfied porous structure with porosity ranging from 30% to 85% and different pore sizes. In addition, they can exhibit an elastic modulus of 0.4–15 GPa and SE of more than 2.5%, as well as good cell and tissue biocompatibility. As a result, porous SMAs had already been used in maxillofacial repairing, teeth root replacement, and cervical and lumbar vertebral implantation. Based on current research progresses, possible future directions are discussed for “property-pore structure” relationship and surface modification investigations, which could lead to optimized porous biomedical SMAs. We believe that porous SMAs with optimal porous structure and a bioactive surface layer are the most competitive candidate for short-term and long-term hard-tissue replacement materials.

Enhancing the Elastocaloric Cooling Stability of NiFeGa Alloys via Introducing Pores

“…The porous NiTi SMAs exhibit different compressive stress–strain behavior as compared with their dense ones. However, when porosity is lower than 31%, it demonstrates a linear (without no apparent stress‐induced martensite transition [SIMT] plateau) superelastic behavior of almost 4% . But interestingly here, the foam with 53% porosity shows a small (not obvious) SIMT plateau during compressive stress–strain curves and it becomes almost linear at 308 K (above A f = 296 K).…”

Biocompatibility and Clinical Application of Porous TiNi Alloys Made by Self-Propagating High-Temperature Synthesis (SHS)

“…Deposited corrosion-resistant gradient coatings turn out not to remedy this challenge as they are usually nonelastic and have low fatigue strength [51,52]. The surface layer of the unwrought PTN alloy nevertheless withstands multicycle deformation and maintains its inherent integrity with the viscoelastic matrix [53].…”

Tissue Integration and Biological Cellular Response of SLM-Manufactured Titanium Scaffolds

“…SLM NiTi alloys are shape-memory alloys (SMA) (given the transformation of austenite state-stable after thermotreatment and martensitic state-stable at low temperature, allows the redimension after insertion in the receptor situs), resistant to corrosion, and possess non-ferromagnetic properties, which indicate them in bone implants, orthodontic arch wires, palatal expander, distracters, and dental drills [62]. This shape memory property refers to NiTi, β type Ni-free Ti materials and their ability to recover its shape after a heating process, due to the pseudoplastic deformation; whereas both non-deformed martensite and deformed martensite can be displayed at 23-24 • C temperature, the austenite phase is recorded at high temperature, meaning that the alloy can remember its initial morphology after it has been overheated [63,64]. At body's temperature, NiTi SLM porous plates are in the martensite phase and require little effort in inserting into the reconstruction area; maintenance of a constant temperature leads to austenite phase transformation, which produces a steady stress to compress the bone fragments [65].…”