ABSTRACT
Porous NiTi alloy samples were fabricated with 12-36% porosity from equiatomic NiTi alloy powder using laser engineered net shaping (LENS). The effects of processing parameters on density and properties of laser-processed NiTi alloy samples were investigated. It was found that the density increased rapidly with increasing the specific energy input up to 50 J/mm(3). Further increase in the energy input had small effect on density. High cooling rates associated with LENS processing resulted in higher amount of cubic B2 phase, and increased the reverse transformation temperatures of porous NiTi samples due to thermally induced stresses and defects. Transformation temperatures were found to be independent of pore volume, though higher pore volume in the samples decreased the maximum recoverable strain from 6% to 4%. Porous NiTi alloy samples with 12-36% porosity exhibited low Young's modulus between 2 and 18 GPa as well as high compressive strength and recoverable strain. Because of high open pore volume between 36% and 62% of total volume fraction porosity, these porous NiTi alloy samples can potentially accelerate the healing process and improve biological fixation when implanted in vivo. Thus porous NiTi is a promising biomaterial for hard tissue replacements.
Subject(s)
Alloys/chemistry , Biocompatible Materials/chemistry , Lasers , Nickel/chemistry , Titanium/chemistry , Compressive Strength , Materials Testing , Porosity , Tensile Strength , X-Ray DiffractionABSTRACT
The Laser Engineered Net Shaping (LENS) method was used to fabricate porous Ti implants. Porous Ti structures with controlled porosity in the range of 17-58 vol.% and pore size up to 800 microm were produced by controlling LENS parameters, which showed a broad range of mechanical strength of 24-463 MPa and a low Young's modulus of 2.6-44GPa. The effects of porous structure on bone cell responses were evaluated in vitro with human osteoblast cells (OPC1). The results showed that cells spread well on the surface of porous Ti and formed strong local adhesion. MTT assay indicated LENS processed porous Ti provides a preferential surface for bone cell proliferation. Porous Ti samples also stimulated faster OPC1 cell differentiation compared with polished Ti sheet, which could be due to the change in cell morphology within the pores of Ti samples. More extracellular matrix and a higher level of alkaline phosphatase expression were found on the porous samples than on the Ti sheet. This can be beneficial for faster integration of porous implant with host bone tissue. The results obtained also indicated that a critical pore size of 200 microm or higher is needed for cell ingrowth into the pores, below which OPC1 cells bridged the pore surface without any growth in the pores.
Subject(s)
Biocompatible Materials/chemistry , Biocompatible Materials/pharmacology , Lasers , Titanium/chemistry , Titanium/pharmacology , Apoptosis/drug effects , Cell Shape , Cells, Cultured , Humans , Immunohistochemistry , Materials Testing , Microscopy, Confocal , Microscopy, Electron, Scanning , PorosityABSTRACT
The need for unique mechanical and functional properties coupled with manufacturing flexibility for a wide range of metallic implant materials necessitates the use of novel design and fabrication approaches. In this work, we have demonstrated that application of proposed design concepts in combination with laser-engineered net shaping (LENStrade mark) can significantly increase the processing flexibility of complex-shaped metallic implants with three-dimensionally interconnected, designed and functionally graded porosities down to 70vol.%, to reduce effective stiffness for load-bearing implants. Young's modulus and 0.2% proof strength of these porous Ti samples having 35-42vol.% porosity are found to be similar to those of human cortical bone.
