Porous TiNbZr alloy scaffolds for biomedical applications

In the present study, porous Ti–10Nb–10Zr alloy scaffolds with different porosities were successfully fabricated by a ‘‘space-holder” sintering method. By the addition of biocompatible alloying elements the porous TiNbZr scaffolds achieved significantly higher strength than unalloyed Ti scaffolds of the same porosity. In particular, the porous TiNbZr alloy with 59% porosity exhibited an elastic modulus and plateau stress of 5.6 GPa and 137 MPa, respectively. The porous alloys exhibited excellent ductility during compression tests and the deformation mechanism is mainly governed by bending and buckling of the struts. Cell cultures revealed that SaOS2 osteoblast-like cells grew on the surface and inside the pores and showed good spreading. Cell viability for the porous scaffold was three times higher than the solid counterpart. The present study has demonstrated that the porous TiNbZr alloy scaffolds are promising scaffold biomaterials for
bone tissue engineering by virtue of their appropriate mechanical properties, highly porous structure and excellent biocompatibility.

Ti6Ta4Sn alloy and subsequent scaffolding for bone tissue engineering

Porous titanium (Ti) and titanium alloys are promising scaffold biomaterials for bone tissue engineering, because they have the potential to provide new bone tissue ingrowth abilities and low elastic modulus to match that of
natural bone. In the present study, a new highly porous Ti6Ta4Sn alloy scaffold with the addition of biocompatible alloying elements (tantalum (Ta) and tin (Sn)) was prepared using a space-holder sintering method. The
strength of the Ti6Ta4Sn scaffold with a porosity of 75% was found to be significantly higher than that of a pure Ti scaffold with the same porosity. The elastic modulus of the porous alloy can be customized to match that of
human bone by adjusting its porosity. In addition, the porous Ti6Ta4Sn alloy exhibited an interconnected porous structure, which enabled the ingrowth of new bone tissues. Cell culture results revealed that human SaOS₂
osteoblast-like cells grew and spread well on the surfaces of the solid alloy, and throughout the porous scaffold. The surface roughness of the alloy showed a significant effect on the cell behavior, and the optimum surface
roughness range for the adhesion of the SaOS2 cell on the alloy was 0.15 to 0.35 mm. The present study illustrated the feasibility of using the porous Ti6Ta4Sn alloy scaffold as an orthopedic implant material with a special
emphasis on its excellent biomechanical properties and in vitro biocompatibility with a high preference by osteoblast-like cells.

Biomimetic modification of porous TiNbZr alloy scaffold for bone tissue engineering

Porous titanium (Ti) and Ti alloys are important scaffold materials for bone tissue engineering. In the present study, a new type of porous Ti alloy scaffold with biocompatible alloying elements, that is, niobium (Nb) and zirconium (Zr), was prepared by a space-holder sintering method. This porous TiNbZr scaffold with a porosity of 69% exhibits a mechanical strength of 67MPa and an elastic modulus of 3.9GPa, resembling the mechanical properties of cortical bone. To improve the osteoconductivity, a calcium phosphate (Ca/P) coating was applied to the surface of the scaffold using a biomimetic method. The biocompatibility of the porous TiNbZr alloy scaffold before and after the biomimetic modification was assessed using the SaOS2 osteoblast–like cells. Cell culture results indicated that the porous TiNbZr scaffold is more favorable for cell adhesion and proliferation than its solid counterpart. By applying a Ca/P coating, the cell proliferation rate on the Ca/P-coated scaffold was significantly improved. The results suggest that high-strength porous TiNbZr scaffolds with an appropriate osteoconductive coating could be potentially used for bone tissue engineering application.

Compressibility of porous magnesium foam: dependency on porosity and pore size

Mechanical properties of porous magnesium with the porosity of 35–55% and the pore size of about 70–400 μm are investigated by compressive tests focusing on the effects of the porosity and pore size on the Young's modulus and strength. Results indicated that the Young's modulus and peak stress increase with decreasing porosity and pore size. The mechanical properties of the porous magnesium were in a range of those of cancellous bone. Therefore, it is suggested that the porous magnesium is one of promising scaffold materials for hard tissue regeneration.

Ingrowth of human mesenchymal stem cells into porous silk particle reinforced silk composite scaffolds : an in vitro study

Silk fibroin protein is biodegradable and biocompatible, exhibiting excellent mechanical properties for various biomedical applications. However, porous three-dimensional (3-D) silk fibroin scaffolds, or silk sponges, usually fall short in matching the initial mechanical requirements for bone tissue engineering. In the present study, silk sponge matrices were reinforced with silk microparticles to generate protein-protein composite scaffolds with desirable mechanical properties for in vitro osteogenic tissue formation. It was found that increasing the silk microparticle loading led to a substantial increase in the scaffold compressive modulus from 0.3 MPa (non-reinforced) to 1.9 MPa for 1:2 (matrix:particle) reinforcement loading by dry mass. Biochemical, gene expression, and histological assays were employed to study the possible effects of increasing composite scaffold stiffness, due to microparticle reinforcement, on in vitro osteogenic differentiation of human mesenchymal stem cells (hMSCs). Increasing silk microparticle loading increased the osteogenic capability of hMSCs in the presence of bone morphogenic protein-2 (BMP-2) and other osteogenic factors in static culture for up to 6 weeks. The calcium adsorption increased dramatically with increasing loading, as observed from biochemical assays, histological staining, and microcomputer tomography (μCT) analysis. Specifically, calcium content in the scaffolds increased by 0.57, 0.71, and 1.27 mg (per μg of DNA) from 3 to 6 weeks for matrix to particle dry mass loading ratios of 1:0, 1:1, and 1:2, respectively. In addition, μCT imaging revealed that at 6 weeks, bone volume fraction increased from 0.78% for non-reinforced to 7.1% and 6.7% for 1:1 and 1:2 loading, respectively. Our results support the hypothesis that scaffold stiffness may strongly influence the 3-D in vitro differentiation capabilities of hMSCs, providing a means to improve osteogenic outcomes.

Processing of biocompatible porous Ti and Mg

A new powder manufacturing process for Ti and Mg metallic foams designs porosity, pore size and morphology. These open-cellular foams (pores: 200–500 μm) have exceptional characteristics (e.g., Ti foam porosity 78%, compressive strength 35 MPa, Young's modulus 5.3 GPa). Anticipated applications include biocompatible implant materials.

Empirical generalisation as an inadequate cognitive scaffold to theoretical generalisation of a more complex concept

The impact of prior learning on new learning is highlighted by the case of Dean, a Year 8 student who developed his own method to find the sum of the interior angles of a polygon without knowing why his method worked. Enriched transcripts and visual displays of the cognitive, social (Dreyfus, Hershkowitz, & Schwarz, 2001) and affective elements (Williams, 2002) of Dean's interrupted abstraction process informed the identification of factors that inhibited Dean's constructing process. It was found Dean possessed an empirical, not theoretical, generalization (Davydov, 1990) about sums of interior angles of triangles that was an inadequate cognitive artifact for constructing the new more complex theoretical generalization. The study suggests use of tasks designed with the opportunity develop assumed knowledge in conjunction with new concepts.

Porous titanium with porosity gradients for biomedical applications

Highly porous titanium and titanium alloys with an open cell structure are promising implant materials due to their low elastic modulus, excellent bioactivity, biocompatibility and the ability for bone regeneration. However, the mechanical strength of the porous titanium decreases dramatically with increasing porosity, which is a prerequisite for the ingrowth of new bone tissues and vascularization. In the present study, porous titanium with porosity gradients, i.e. solid core with highly porous outer shell was successfully fabricated using a powder metallurgy approach. Satisfactory mechanical properties derived from the solid core and osseointegration capacity derived from the outer shell can be achieved simultaneously through the design of the porosity gradients of the porous titanium. The outer shell of porous titanium exhibited a porous architecture very close to
that of natural bone, i.e. a porosity of 70% and pore size distribution in the range of 200 - 500 μm. The peak stress and the elastic modulus of the porous titanium with a porosity gradient (an overall porosity 63%) under compression were approximately 152 MPa and 4 GPa, respectively. These
properties are very close to those of natural bone. For comparison, porous titanium with a uniform porosity of 63% was also prepared and haracterised in the present study. The peak stress and the elastic modulus were 109 MPa and 4 GPa, respectively. The topography of the porous titanium
affected the mechanical properties significantly.

Micro-porous nickel produced by powder metallurgy

Micro-porous nickel (Ni) with an open cell structure was fabricated by a special powder metallurgical process, which includes the adding of a space-holding material. The average pore size of the micro-porous Ni samples approximated 30 μm and 150 μm, and the porosity ranged from 60 % to 80 %. The porous characteristics of the Ni samples were observed using scanning electron microscopy (SEM) and the mechanical properties were evaluated using compressive tests. For comparison, porous Ni samples with a macro-porous structure prepared by both powder metallurgy
(pore size 800 μm) and the traditional chemical vapour deposition (CVD) method (pore size 1300 μm) were also presented. Results indicated that the porous Ni samples with a micro-porous structure exhibited different deformation behaviour and dramatically increased mechanical properties,
compared to those of the macro-porous Ni samples.

Processing and mechanical properties of porous titanium-niobium shape memory alloy for biomedical applications

Ti-26 at.%Nb (hereafter Ti-26Nb) alloy foams were fabricated by space-holder sintering process. The porous structures of the foams were characterized by scanning electron microscopy (SEM). The mechanical properties of the Ti-26Nb foam samples were investigated using compressive test. Results indicate that mechanical properties of Ti-26Nb foam samples are influenced by foam porosity. The plateau stresses and elastic moduli of the foams under compression decrease with the increase of their porosities. The plateau stresses and elastic moduli are measured to be from 10~200 MPa and 0.4~5.0 GPa for the Ti-26Nb foam samples with porosities ranged from 80~50 %, respectively.

Mechanical properties of micro-porous metals produced by space-holding sintering

Micro-porous nickel foams with an open cell structure were fabricated by the space-holding sintering. The average pore size of the micro-porous nickel specimens ranged from 30 μm to 150 μm, and the porosity ranged from 60 % to 80 %. The porous characteristics of the nickel specimens were observed using scanning electron microscopy (SEM). The mechanical properties were studied using compressive tests. For comparison, macro-porous nickel foams prepared by the chemical vapour deposition method with pore sizes of 800 μm and 1300 μm and porosity of 95 % were also presented. Results indicated that the ratio value of 6 and higher for the specimen length to cell size (L/d) is satisfying for obtaining stable compressive properties. The micro-porous nickel specimens exhibited different deformation behaviour and dramatically increased mechanical properties, compared to those of the macro-porous nickel specimens.

Viscoplastic behaviour of porous bronzes and irons

An experimental investigation is presented for the viscoplastic behaviour of porous metals. The interest is in the influence of porosity on the deformation behaviour of such materials under loading at various strain rates. Material samples of bronze with 10% tin and pure iron were fabricated by powder metallurgy technology with porosity ranging from 10 to 40%. The samples were then subjected to a large uniaxial compression under both quasi-static and dynamic loading with the maximum strain rate at 10 s−1. The materials show behaviour in an approximately bi-linear nature for strain up to 0.4. The data will be used to develop simple phenomenological constitutive models, which incorporate the volume fraction as a control factor.