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.
Highlights
The average life-span of modern person has been greatly elongated by the advanced medical technology and living condition
We review recent progress on the mechanical and biological properties of porous SMAs in relation to their porous structures and microstructures in three sections
The porous NiTi SMAs have a great advantage, because their modulus can be adjusted by controlling the pore structure, and they were firstly developed at the end of the 1980s in Russia
Summary
The average life-span of modern person has been greatly elongated by the advanced medical technology and living condition. We review recent progress on the mechanical and biological properties of porous SMAs in relation to their porous structures and microstructures in three sections. It covers (1) the brief description on the fundamentals of SME and SE; (2) the fabrication methods and pore structMuarteeriaclos 2n0t1r8o, 1l1l,inx gFO, RmPeEEcRhaRnEVicIEaWl and biological performances of porous NiTi SMAs in r3eolaf t5i3on to their tphoerboruiesfsdtreusccrtiuprtieonanodn mthiecrfousntdruamcteunrtea,lssuorffSaMceEmaonddifiSEc;at(i2o)nt,heanfadbbriicoamtioendimcaelthaopdpsliacnadtiopnorse; and, (3) thestrmucetcuhraenciocnatlraonllidngb,iomloecghicaanlicparloapnedrtbiieosloogficdaelnpseerfaonrmd apnocreosuosfNpoi-rforuees NTii-TbiaSsMedASsMinArse.laFtiionnaltloy, this reviewthesiurmpomroauriszestsrupcatsutrwe aonrdksmaincdrogstirvuecstuarfeu, tsuurefapceromspoedcifti.cIattisohno, ualnddbbeiommeendtiicoanl eadppthliacattsieovnse;ralnrde,view article(3s) hthaevme ebceheannipcaulbanlidshbeiodlowgiictahl panropemertpiehsaosfisdeonnsedainffderpeonrot uasspNei-cftrseeoTf it-hbaespedorSoMuAssN. They should possess functionality that is similar to the hard-tissue, such as enough Tsphaecemtaotearllioawls aforre ceexllpeactttaecdhmtoenhta, vsperaeasdiimngil,aarnmd ipcrroolsitfreuracttiuonre, owr itshuffbicoinenets nourttreieentth,traasnssphoorwt n in.
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