Biomedical Porous Shape Memory Alloys for Hard-Tissue Replacement Materials

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.

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Sintering and Morphology of Porous Structure in NiTi Shape Memory Alloys for Biomedical Applications

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.570.87 ◽

2012 ◽

Vol 570 ◽

pp. 87-95 ◽

Cited By ~ 3

Author(s):

Irfan Haider Abidi ◽

Fazal Ahmad Khalid

Keyword(s):

Elastic Modulus ◽

Shape Memory Alloys ◽

Porous Structure ◽

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

Biomedical Implants ◽

Recoverable Strain ◽

Porous Niti ◽

Niti Shape Memory Alloys

The combination of attractive properties of porous NiTi shape memory alloys like high recoverable strain due to superelasticity and shape memory effect, good corrosion resistance, improved biocompatibilty, low density and stiffness along with its porous structure similar to that of bone make them best materials for biomedical implants. In current study porous NiTi SMAs have been fabricated successfully by space holder technique via pressureless sintering using NaCl powder as a spacer. Various volume fractions of NaCl powders have been involved to study their effect on the pore characteristics as well as on mechanical properties of foam. Porous NiTi with average porosity in the range of 44.3%-63.5% have been fabricated having average pore size 419µm which were very appropriate for various biomedical implants. Porous NiTi SMAs exhibited superelasticity at room temperature and shape memory effect was also determined. Maximum recoverable strain of 6.79% was demonstrated by the porous NiTi alloy with 44.3% porosity and it was diminishing with increasing porosity. Compression strength and elastic modulus have shown a decreasing trend with increasing porosity content. Elastic modulus of porous NiTi extends from 1.38 to 5.42GPa depending upon the pore volume which was very much comparable to that of various kinds of bones.

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Mechanical and Microstructural Characterization of Porous NiTi Shape Memory Alloys

Metallurgical and Materials Transactions A ◽

10.1007/s11661-009-9906-1 ◽

2009 ◽

Vol 40 (9) ◽

pp. 2061-2070 ◽

Cited By ~ 21

Author(s):

O. Scalzo ◽

S. Turenne ◽

M. Gauthier ◽

V. Brailovski

Keyword(s):

Shape Memory Alloys ◽

Shape Memory ◽

Microstructural Characterization ◽

Porous Niti ◽

Niti Shape Memory Alloys

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Numerical implementation of the microplane constitutive model for shape memory alloys

Proceedings of the Institution of Mechanical Engineers Part L Journal of Materials Design and Applications ◽

10.1177/1464420717708486 ◽

2017 ◽

Vol 233 (6) ◽

pp. 1117-1133 ◽

Cited By ~ 2

Author(s):

MR Karamooz-Ravari ◽

B Shahriari

Keyword(s):

Shape Memory Alloy ◽

Constitutive Model ◽

Shape Memory Alloys ◽

Shape Memory ◽

Numerical Integration ◽

Biological Properties ◽

Industrial Applications ◽

Stress Increment ◽

Integration Formulas

With the advent of shape memory alloys, several industrial applications were proposed due to their superior mechanical and biological properties. Since the fabrication and characterization of shape memory alloy devices is challenging and expensive, it is necessary to simulate their thermomechanical responses before fabrication. To do so, a powerful constitutive model capable of simulation of the important features of these materials is necessary. To be able to simulate a shape memory alloy device, it is vital to implement a suitable constitutive model in such a way to be used in finite element models. In this paper, an existing constitutive model based on microplane theory is numerically implemented and the effects of stress increment, different numerical integration formulas, and loading direction on the thermomechanical response of shape memory alloy is investigated through superelastic and shape memory proportional and nonproportional loadings. The obtained results show that the stress increment may have significant effect on the results if the forward Euler scheme is utilized. In addition, for the case of numerical integration over the surface of a unit hemisphere, 61 points integration formula without orthogonal symmetry provides the best results while 21 orthogonally symmetric one is the most inaccurate one. Also, the orthogonally symmetric numerical integration formulas predict the isotropic material response while those without orthogonal symmetry predict a little anisotropy.

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