Abstract Over the past few decades there has been great interest in the use of orthopedic and dental implants that integrate into tissue by promoting bone ingrowth or bone adhesion, thereby ...eliminating the need for cement fixation. However, strategies to create bioactive implant surfaces to direct cellular activity and mineralization leading to osteointegration are lacking. We report here on a method to prepare a hybrid bone implant material consisting of a Ti–6Al–4V foam, whose 52% porosity is filled with a peptide amphiphile (PA) nanofiber matrix. These PA nanofibers can be highly bioactive by molecular design, and are used here as a strategy to transform an inert titanium foam into a potentially bioactive implant. Using scanning electron microscopy (SEM) and confocal microscopy, we show that PA molecules self-assemble into a nanofiber matrix within the pores of the metallic foam, fully occupying the foam's interconnected porosity. Furthermore, the method allows the encapsulation of cells within the bioactive matrix, and under appropriate conditions the nanofibers can nucleate mineralization of calcium phosphate phases with a Ca:P ratio that corresponds to that of hydroxyapatite. Cell encapsulation was quantified using a DNA measuring assay and qualitatively verified by SEM and confocal microscopy. An in vivo experiment was performed using a bone plug model in the diaphysis of the hind femurs of a Sprague Dawley rat and examined by histology to evaluate the performance of these hybrid systems after 4 weeks of implantation. Preliminary results demonstrate de novo bone formation around and inside the implant, vascularization around the implant, as well as the absence of a cytotoxic response. The PA–Ti hybrid strategy could be potentially tailored to initiate mineralization and direct a cellular response from the host tissue into porous implants to form new bone and thereby improve fixation, osteointegration, and long term stability of implants.
This dataset contains 82 unique refractory alloys experimentally synthesized via arc melting and subject to screening tests for hardness and room temperature ductility. Most compositions fall under ...the definition of high entropy or complex concentrated alloys, but simpler ternary compositions are also included. Hardness was collected via a standard indentation technique while compressive ductility was quantified using a custom high throughput experimental approach yielding a ductility ranking from 0 to 5. The unique ductility screening test was developed to provide directional information for alloy development at a low cost and rapid pace using conventional test equipment. Predicted solidus temperature for all alloys is also included based on thermodynamic modelling. The dataset should be of interest to those exploring the emerging class of refractory high entropy alloys and particularly useful where optimization is sought balancing strength, ductility, and high melting temperature.
Near-stoichiometric NiTi with up to 18% closed porosity was produced by expansion at 1200
°C of argon-filled pores trapped by powder metallurgy within a NiTi billet. When optimally heat-treated, NiTi ...with 6–16% porosity exhibits superelasticity, with recoverable compressive strains up to 6% at a maximum compressive stress up to 1700
MPa. The apparent Young’s modulus of NiTi with 16% porosity, measured during uniaxial compression, is in the range of 15–25
GPa (similar to human bone), but is much lower than measured ultrasonically (∼40
GPa), or predicted from continuum elastic mechanics. This effect is attributed to the reversible stress-induced transformation contributing to the linear elastic deformation of porous NiTi. The unique combination of low stiffness, high strength, high recoverable strains and large energy absorption of porous superelastic NiTi, together with the known biocompatibility of NiTi, makes this material attractive for bone–implant applications.
Porous NiTi by creep expansion of argon-filled pores Oppenheimer, Scott M.; Dunand, David C.
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
10/2009, Letnik:
523, Številka:
1
Journal Article
Recenzirano
NiTi powders are densified in the presence of argon gas, whose initial pressure is varied between 1 and 33
atm, to create NiTi billets containing isolated Ar-filled pores. Upon vacuum annealing, the ...pressurized pores expand by creep of the surrounding NiTi matrix at rates which are in agreement with a simple analytical model up to 16% porosity. Beyond this porosity, foaming becomes very slow, as pores connect with each other and with the specimen surface where the gas escapes. This is due to failure of previous NiTi powder boundaries weakened by oxides insoluble in NiTi; this mechanism does not occur in Ti foams which dissolve their oxides at high temperature, allowing higher levels of pore expansion and foam porosity. NiTi with 10–16% porosity exhibits Young's moduli of 48–57
GPa, and may be useful for high-strength, low stiffness biomedical implants with superelastic or shape-memory properties.
The creep of reticulated metallic foams is studied through the finite element method using three-dimensional, periodic unit cells with four different architectures characterized by struts which ...deform primarily by: (i) simple bending, (ii) compression, (iii) a combination of simple bending and compression and (iv) double bending (for Kelvin space-filling tetrakaidecahedra). The creep behavior of each of these models is examined with respect to temperature, stress and foam relative density. Calculated creep rates for both bending and compression models are below those predicted from simplified analytical models and bracket those of the combination model. The simple and double bending models predict nearly identical strain rates despite very different geometries, because in both cases the deflection rates of the fastest deforming struts are similar. Both analytical and numerical predictions are compared to published creep data for metallic foams.
The compressive creep behavior of nickel-rich B2–NiTi (with 50–140
μm grain size) was studied over the stress range 3–11
MPa and the temperature range 950–1100
°C. The stress exponent (
n
=
2.7) and ...activation energy (
Q
=
155
kJ
mol
−1) are compared with a literature review of NiTi creep studies performed over lower temperature and/or higher stresses. Possible explanations for discrepancies between studies are discussed.
Ru-based B2 phases present an opportunity to design two-phase BCC + B2 refractory multi-principal element alloys (RMPEAs) with higher temperature stability compared to B2 phases observed in RMPEAs. ...In this investigation, seven equiatomic Ru-containing RMPEAs were characterized in the as-cast and annealed conditions. Of the two Hf-free alloys, Mo
25
Nb
25
Ta
25
Ru
25
was determined to be a single-phase B2 alloy and Mo
20
Nb
20
Ta
20
W
20
Ru
20
was single-phase BCC. Within all five Hf-containing alloys, phases formed during solidification included HfRu–B2, disordered BCC, and HfO
2
phases. The Hf-containing alloys also precipitated B2 nanoparticles within the BCC phases after further cooling in the solid. All phases were still present after annealing at 1500
∘
C to 1600
∘
C. The HfRu–B2 nanoparticles in as-cast Hf
20
Mo
20
Nb
20
Ta
20
Ru
20
were characterized by transmission electron microscopy (TEM), and a lattice misfit of < 1 pct between the BCC phase and B2 nanoparticles was calculated. Room-temperature micropillar compression tests were performed on BCC + B2 nanoparticle regions in annealed Hf
20
Mo
20
Nb
20
Ta
20
Ru
20
. Post-mortem TEM analysis revealed precipitate shearing by dislocations, resulting in paired dislocations, along with bowing of dislocations around precipitates. Utilizing the insights from this investigation, compositions for RMPEAs with solutionable B2 precipitates stable above 1200
∘
C are suggested.
Ti–6Al–4V foams are produced by the expansion of pressurized argon pores trapped in billets created by powder metallurgy. Pore expansion during thermal cycling (840–1030
°C, which induces ...transformation superplasticity in Ti–6Al–4V) improves both the foaming rate (by reducing the flow stress) and the final porosity (by delaying fracture of the pores and subsequent escape of the gas), as compared to isothermal pore expansion at 1030
°C, where Ti–6Al–4V creep is the controlling mechanism. Raising the argon content in the billet increases the foaming rates for both creep and superplastic conditions, in general agreement with an analytical model taking into account the non-ideal behavior of high-pressure Ar and the pore size dependence of surface tension. Superplastically foamed Ti–6Al–4V with 52% open porosity exhibits a combination of high strength (170
MPa) and low stiffness (18
GPa), which is useful for bone implant applications.
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