Wei He

Biocompatible Ni-free Zr-based bulk metallic glasses with high-Zr-content: compositional optimization for potential biomedical applications.

The present study designs and prepares Ni-free Zr60+xTi2.5Al10Fe12.5-xCu10Ag5 (at.%, x=0, 2.5, 5) bulk metallic glasses (BMGs) by copper mold casting for potential biomedical application. The effects of Zr content on the in vitro biocompatibility of the Zr-based BMGs are evaluated by investigating mechanical properties, bio-corrosion behavior, and cellular responses. It is found that increasing the content of Zr is favorable for the mechanical compatibility with a combination of low Youngs modulus, large plasticity, and high notch toughness. Electrochemical measurements demonstrate that the Zr-based BMGs are corrosion resistant in a phosphate buffered saline solution. The bio-corrosion resistance of BMGs is improved with the increase in Zr content, which is attributed to the enrichment in Zr and decrease in Al concentration in the surface passive film of alloys. Regular cell responses of mouse MC3T3-E1 cells, including cell adhesion and proliferation, are observed on the Zr-Ti-Al-Fe-Cu-Ag BMGs, which reveals their general biosafety. The high-Zr-based BMGs exhibit a higher cell proliferation activity in comparison with that of pure Zr and Ti-6Al-4V alloy. The effects of Zr content on the in vitro biocompatibility can be used to guide the future design of biocompatible Zr-based BMGs.

Laser pulse dependent micro textured calcium phosphate coatings for improved wettability and cell compatibility

Surface wettability of an implant material is an important criterion in biological response as it controls the adsorption of proteins followed by attachment of cells to its surface. Hence, micro-textured calcium phosphate coatings with four length scales were synthesized on Ti–6Al–4V substrates by a laser cladding technique and their effects on wettability and cell adhesion were systematically evaluated. Microstructure and morphological evolutions of the coatings were studied using scanning electron and light optical microscopes respectively. The surface texture of coating defined in terms of a texture parameter was correlated to its wetting behavior. The contact angle of simulated body fluid measured by a static sessile drop technique, demonstrated an increased hydrophilicity with decreasing value of texture parameter. The influence of such textures on the inxa0vitro bioactivity and inxa0vitro biocompatibility were studied by the immersion of the samples in simulated body fluid and mouse MC3T3-E1 osteoblast-like cell culture respectively.

Wetting effects on in vitro bioactivity and in vitro biocompatibility of laser micro-textured Ca-P coating

Calcium phosphate (Ca-P) coating on the Ti-6Al-4V alloy enhances osteoblast adhesion and tissue formation at the bone implant interface. In light of this, in the current work a laser-based coating technique was used to synthesize two different micro-textured (100 microm and 200 microm spaced line patterns) Ca-P coatings on the Ti-6Al-4V alloy and its effect on wettability and osteoblast cell adhesion were systematically studied. X-ray diffraction (XRD) analysis of the coated samples indicated the presence of precursor material, Ca10(PO4)6(OH)2 (HA) and various other additional phases such as CaTiO3, Ca3(PO4)2, TiO2 (anatase) and TiO2 (rutile) owing to the reaction between the precursor (HA) and substrate (Ti-6Al-4V) during laser processing. Confocal laser scanning microscopy-based characterization of coated samples indicated that the samples processed at 100 microm line spacing demonstrated a reduced surface roughness and smaller texture parameter value as compared to the samples processed at 200 microm spacing. The surface energy and wettability of the 100 microm spaced samples measured using a static sessile drop technique demonstrated higher surface energy and increased hydrophilicity as compared to the control (untreated Ti-6Al-4V) and the samples processed at 200 microm spacing. The tendency of coated samples for mineralization through generation of an apatite-like phase during immersion in a simulated body fluid was indicative of their in vitro bioactive nature. In light of higher surface energy and increased hydrophilicity the in vitro biocompatibility of the samples with 100 microm line spacing was demonstrated through increased cell proliferation and cell adhesion of mouse MC3T3-E1 osteoblast-like cells.

Laser surface modification for synthesis of textured bioactive and biocompatible Ca-P coatings on Ti-6Al-4V

A textured calcium phosphate based bio-ceramic coating was synthesized by continuous wave Nd:YAG laser induced direct melting of hydroxyapatite precursor on Ti–6Al–4V substrate. Two different micro-textured patterns (100xa0μm and 200xa0μm line spacing) of Ca–P based phases were fabricated by this technique to understand the alignment and focal adhesion of the bone forming cells on these surfaces. X-ray diffraction studies of the coated samples indicated the presence of CaTiO3, α-Ca3(PO4)2, Ca(OH)2, TiO2 (anatase) and TiO2 (rutile) phases as a result of the intermixing between the precursor and substrate material during laser processing. A two dimensional elemental mapping of the cross-section of the coated samples exhibited the presence of higher phosphorous concentration within the coating and a thin layer of calcium concentration only at the top of the coating. Improved in vitro bioactivity and in vitro biocompatibility was observed for the laser processed samples as compared to the control.

Antimicrobial behavior of Cu-bearing Zr-based bulk metallic glasses

The antimicrobial behavior of Cu-bearing Zr-based bulk metallic glasses (BMGs) was investigated for the first time against the Gram positive bacterium Staphylococcus aureus to evaluate their potential applications in healthcare settings. Despite their lack of bacteria-killing effect under a relatively severe experimental setting of dynamic immersion, the biocidal potency of the two Zr-based BMGs was demonstrated via a moist contact assay. There was a significant reduction in viable bacterial populations after 4h of contact on the Zr-based BMGs, which was evidenced by the pronounced reduction in viable bacterial populations. To understand the mechanism of cell death, a direct relationship was established between the killing efficiency and the ability of the substrate to release Cu ions. Findings in this study will direct the future design of antimicrobial BMGs with enhanced killing efficacy.

Laser Induced Nitrogen Enhanced Titanium Surfaces for Improved Osseo-Integration

The osseo-integration, corrosion resistance, and tribological properties of the commonly used bioimplant alloy Ti–6Al–4V were enhanced using a laser-based surface nitridation process. The biomedical properties of the laser nitrided Ti–6Al–4V were investigated using experimental and computational methodologies. Electrochemical analysis of laser nitrided titanium in simulated body fluid (SBF) was performed to assess the biomedical characteristics in near-human body conditions. Additionally, the corrosive wear performance of these laser nitrided samples was evaluated using pin-on-disk geometry with a zirconia pin counter surface in SBF to mimic the biological scenario. Osteoblast studies were conducted to evaluate cell affinity towards titanium nitrided bioimplant material. Cells adhered to all substrates, with high viability. Initial cell adhesion was revealed by focal adhesion formation on all substrates. Cells can proliferate on samples treated with 1.89 and 2.12xa0×xa0106 J/m2 laser conditions, while those treated with 1.70xa0×xa0106 J/m2 inhibited proliferation. Thus, microstructural and phase observations, electrochemical analyses, corrosive wear evaluation, and cell behavior analysis of laser nitrided surface of bioimplant material (Ti–6Al–4V) indicated that laser nitriding greatly improves the performance of bioimplant material.

In vitro responses of bone-forming MC3T3-E1 pre-osteoblasts to biodegradable Mg-based bulk metallic glasses

In light of the superior property profile of favorable biocompatibility, proper corrosion/degradation behavior and good mechanical properties, Mg-based bulk metallic glasses (BMGs) are considered as potential biodegradable biomaterials. In the present study, in vitro responses of bone-forming MC3T3-E1 pre-osteoblasts to Mg-Zn-Ca-Sr BMGs were studied in order to assess their feasibility to serve as orthopedic implants. The Mg-Zn-Ca-Sr BMGs were much more capable of supporting cell adhesion and spreading in comparison with crystalline AZ31B Mg alloy. The Mg-Zn-Ca-Sr BMG extracts showed no cytotoxicity to and slightly stimulated the proliferation of pre-osteoblasts. The cells cultured in 100% BMG extracts exhibited lower alkaline phosphatase activity as compared with that in negative control, which could be mainly ascribed to the inhibition of high concentrations of Zn ions on cell differentiation. With decreasing the extract concentration, the inhibitory effect was diminished and the 5% BMG extract exhibited slight stimulation in cell differentiation and mineralization. The high corrosion resistance of BMGs contributed to smaller environmental variations, compared with AZ31B alloy, thus lowering the unfavorable influences on cellular responses. A comparison among the biodegradable Mg-, Ca- and Sr-based BMGs for their biomedical applications is presented.

Macrophage responses to a Zr-based bulk metallic glass: Macrophage Responses To A Zr-Based Bulk Metallic Glass

Bulk metallic glasses (BMGs) are considered to be a competitive candidate of biomedical materials, owing to their appealing mechanical properties and high thermal processability. Based on the established biosafety of the Zr-based BMGs, macrophage responses to (Zr₅₅ Al₁₀ Ni₅ Cu₃₀)₉₉ Y₁ (atomic percent) BMG were investigated in the present study, in comparison with Ti-6Al-4V alloy. The adhesion of RAW 264.7 macrophages to both alloys was found to be mediated by protein adsorption. The Zr-based BMG is capable of supporting regular adhesion and proliferation of macrophages, indicating its good biocompatibility, which agrees with previous findings using other mammalian cells. A lower degree of morphological activation was revealed on Zr-based BMG substrates than on Ti-6Al-4V substrates, which is evidenced by smaller spreading areas and less ruffling on cell surfaces. Smaller amount of proinflammatory cytokine, tumor necrosis factor-alpha, was secreted by macrophages cultured on Zr-based BMGs, which further confirms the lower level of inflammation induced by BMG than by Ti alloys.

Surface engineering of a Zr-based bulk metallic glass with low energy Ar- or Ca-ion implantation

In the present study, low energy ion implantation was employed to engineer the surface of a Zr-based bulk metallic glass (BMG), aiming at improving the biocompatibility and imparting bioactivity to the surface. Ca- or Ar-ions were implanted at 10 or 50 keV at a fluence of 8 × 10(15)ions/cm(2) to (Zr0.55Al0.10Ni0.05Cu0.30)99Y1 (at.%) BMG. The effects of ion implantation on material properties and subsequent cellular responses were investigated. Both Ar- and Ca-ion implantations were suggested to induce atom displacements on the surfaces according to the Monte-Carlo simulation. The change of atomic environment of Zr in the surface regions as implied by the alteration in X-ray absorption measurements at Zr K-edge. X-ray photoelectron spectroscopy revealed that the ion implantation process has modified the surface chemical compositions and indicated the presence of Ca after Ca-ion implantation. The surface nanohardness has been enhanced by implantation of either ion species, with Ca-ion implantation showing more prominent effect. The BMG surfaces were altered to be more hydrophobic after ion implantation, which can be attributed to the reduced amount of hydroxyl groups on the implanted surfaces. Higher numbers of adherent cells were found on Ar- and Ca-ion implanted samples, while more pronounced cell adhesion was observed on Ca-ion implanted substrates. The low energy ion implantation resulted in concurrent modifications in atomic structure, nanohardness, surface chemistry, hydrophobicity, and cell behavior on the surface of the Zr-based BMG, which were proposed to be mutually correlated with each other.

Surface Mechanoengineering of a Zr-Based Bulk Metallic Glass via Ar-Nanobubble Doping To Probe Cell Sensitivity to Rigid Materials

In this study, a new materials platform, utilizing the amorphous microstructure of bulk metallic glasses (BMGs) and the versatility of ion implantation, was developed for the fundamental investigation of cell responses to substrate-rigidity variations in the gigapascal modulus range, which was previously unattainable with polymeric materials. The surface rigidity of a Zr-Al-Ni-Cu-Y BMG was modulated with low-energy Ar-ion implantation because of the impartment of Ar nanobubbles into the amorphous matrix. Surface softening was achieved due to the formation of nanobubble-doped transitional zones in the Zr-based BMG substrate. Bone-forming cell studies on this newly designed platform demonstrated that mechanical cues, accompanied by the potential effects of other surface properties (i.e., roughness, morphology, and chemistry), contributed to modulating cell behaviors. Cell adhesion and actin filaments were found to be less established on less stiff surfaces, especially on the surface with an elastic modulus of 51 GPa. Cell growth appeared to be affected by surface-mechanical properties. A lower stiffness was generally related to a higher growth rate. Findings in this study broadened our fundamental understanding concerning the mechanosensing of bone cells on stiff substrates. It also suggests that surface mechanoengineering of metallic materials could be a potential strategy to promote osseointegration of such materials for bone-implant applications. Further investigations are proposed to fine-tune the ion implantation variables in order to further distinguish the surface-mechanical effect on bone-forming cell activities from the contributions of other surface properties.