Evaluation of biodegradable Zn-1%Mg and Zn-1%Mg-0.5%Ca alloys for biomedical applications.

Increasing interest in biodegradable metals (Mg, Fe, and Zn) as structural materials for orthopedic and cardiovascular applications mainly relates to their promising biocompatibility, mechanical properties and ability to self-remove. However, Mg alloys suffer from excessive corrosion rates associated with premature loss of mechanical integrity and gas embolism risks. Fe based alloys produce voluminous corrosion products that have a detrimental effect on neighboring cells and extracellular matrix. In contrast, Zn does not appear to exhibit a harmful mode of corrosion. Unfortunately, pure zinc possesses insufficient mechanical strength for biomedical structural applications. The present study aimed at examining the potential of two new zinc based alloys, Zn-1%Mg and Zn-1%Mg-0.5%Ca to serve as structural materials for biodegradable implants. This examination was carried out under in vitro conditions, including immersion testing, potentiodynamic polarization analysis, electrochemical impedance spectroscopy (EIS), and stress corrosion cracking (SCC) assessments in terms of slow strain rate testing (SSRT). In order to assess the cytotoxicity of the tested alloys, cell viability was evaluated indirectly using Saos-2 cells. The results demonstrate that both zinc alloys can be considered as potential candidates for biodegradable implants, with a relative advantage to the Zn-1%Mg alloy in terms of its corrosion resistance and SCC performance.

Albumin-Enriched Fibrin Hydrogel Embedded in Active Ferromagnetic Networks Improves Osteoblast Differentiation and Vascular Self-Organisation.

Porous coatings on prosthetic implants encourage implant fixation. Enhanced fixation may be achieved using a magneto-active porous coating that can deform elastically in vivo on the application of an external magnetic field, straining in-growing bone. Such a coating, made of 444 ferritic stainless steel fibres, was previously characterised in terms of its mechanical and cellular responses. In this work, co-cultures of human osteoblasts and endothelial cells were seeded into a novel fibrin-based hydrogel embedded in a 444 ferritic stainless steel fibre network. Albumin was successfully incorporated into fibrin hydrogels improving the specific permeability and the diffusion of fluorescently tagged dextrans without affecting their Young's modulus. The beneficial effect of albumin was demonstrated by the upregulation of osteogenic and angiogenic gene expression. Furthermore, mineralisation, extracellular matrix production, and formation of vessel-like structures were enhanced in albumin-enriched fibrin hydrogels compared to fibrin hydrogels. Collectively, the results indicate that the albumin-enriched fibrin hydrogel is a promising bio-matrix for bone tissue engineering and orthopaedic applications.

Stimulation of Human Osteoblast Differentiation in Magneto-Mechanically Actuated Ferromagnetic Fiber Networks.

There is currently an interest in "active" implantable biomedical devices that include mechanical stimulation as an integral part of their design. This paper reports the experimental use of a porous scaffold made of interconnected networks of slender ferromagnetic fibers that can be actuated in vivo by an external magnetic field applying strains to in-growing cells. Such scaffolds have been previously characterized in terms of their mechanical and cellular responses. In this study, it is shown that the shape changes induced in the scaffolds can be used to promote osteogenesis in vitro. In particular, immunofluorescence, gene and protein analyses reveal that the actuated networks exhibit higher mineralization and extracellular matrix production, and express higher levels of osteocalcin, alkaline phosphatase, collagen type 1α1, runt-related transcription factor 2 and bone morphogenetic protein 2 than the static controls at the 3-week time point. The results suggest that the cells filling the inter-fiber spaces are able to sense and react to the magneto-mechanically induced strains facilitating osteogenic differentiation and maturation. This work provides evidence in support of using this approach to stimulate bone ingrowth around a device implanted in bone and can pave the way for further applications in bone tissue engineering.

Cytotoxic characteristics of biodegradable EW10X04 Mg alloy after Nd coating and subsequent heat treatment.

Porous Mg scaffolds are considered as potential bone growth promoting materials. Unfortunately, the high rate of biocorrosion inherent to Mg alloys may cause a premature loss of mechanical strength, excessive evolution of hydrogen gas, and a rapidly shifting surface topography, all of which may hinder the ability of native cells to attach and grow on the implant surface. Here we investigated the cell cytotoxicity effects during corrosion of a novel magnesium alloy, EW10X04 (Mg-1.2%Nd-0.5%Y-0.5%Zr-0.4%Ca), following diffusion coating (DC) and heat treatment to reduce the corrosion rate. Cells were exposed either to corrosion products or to the corroding scaffold surface, in vitro. The microstructure characterization of the scaffold surface was carried out by scanning electron microscopy (SEM) equipped with a Noran energy dispersive spectrometer (EDS). Phase analyses were obtained by X-ray diffraction (XRD). We found that cell viability, growth, and adhesion were all improved when cultured on the EW10X04+DC surface or under corrosion product extracts due to lower corrosion rates relative to the EW10X04 control samples. It is therefore believed that the tested alloy after Nd coating and heat treatment may introduce a good balance between its biodegradation characteristics and cytotoxic effects towards cells.