The serum protein fetuin-A is a potent systemic inhibitor of soft tissue calcification. Fetuin-A is highly effective in the formation and stabilization of protein-mineral colloids, referred to as calciprotein particles (CPPs). These particles ripen in vitro in a two-step process, indicated by a morphological conversion from spheres to larger prolate ellipsoids. Using a combined light scattering and electron microscopic imaging approach we determined that the second-stage particles resulted from a highly anisotropic outgrowth of the first-stage particles. Electron microscopy of ascites fluid from a patient with calcifying peritonitis revealed particles reminiscent of secondary CPPs. Thus, CPPs form in the body and undergo the two-step ripening at least in pathological conditions. Unlike in vitro generated CPPs, ascites-derived CPPs contained little fetuin-A but large amounts of albumin. This prompted us to study the role of fetuin-A combined with other serum proteins in CPP formation. Fetuin-A was indispensable for primary CPP formation. Albumin and acidic proteins in general greatly enhanced the fetuin-A triggered formation of secondary CPPs and, thus, substituted substantial amounts of fetuin-A without loss of inhibition of calcium phosphate precipitation. Thus, direct mineral deposition from solute in the body is unlikely even at low fetuin-A serum levels as long as sufficient bulk acidic protein is available. Collectively fetuin-A and other acidic bulk plasma proteins may be considered as mineral chaperones mediating the stabilization, safe transport, and clearance in the body of calcium and phosphate as colloidal complexes, thus, preventing ectopic calcification.

Zn-based biodegradable metallic materials have been regarded as new potential biomaterials for use as biodegradable implants, mainly because of the ideal degradation rate compared with those of Mg-based alloys and Fe-based alloys. In this study, we developed and investigated a novel Zn-4 wt % Ag alloy as a potential biodegradable metal. A thermomechanical treatment was applied to refine the microstructure and, consequently, to improve the mechanical properties, compared to pure Zn. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the Zn-4Ag alloy are 157 MPa, 261 MPa, and 37%, respectively. The corrosion rate of Zn-4Ag calculated from released Zn ions in DMEM extracts is approximately 10.75 ± 0.16 μg cm^–2 day^–1, which is higher than that of pure Zn. In vitro cytotoxicity tests showed that the Zn-4Ag alloy exhibits acceptable toxicity to L929 and Saos-2 cells, and could effectively inhibit initial bacteria adhesion. This study shows that the Zn-4Ag exhibits excellent mechanical properties, predictable degradation behavior, acceptable biocompatibility, and effective antibacterial properties, which make it a candidate biodegradable material.

The concentration of mineral solutes in mammalian blood is considerably higher than that predicted by their solubility product. The plasma protein fetuin-A inhibits calcium phosphate deposition by forming colloidal calciprotein particles (CPPs). In this article the authors present a detailed small angle neutron scattering study including contrast variation analysis providing detailed quantitative information on the three-dimensional topology of the CPPs and on their morphogenesis. In detail the authors found the following: (i) A two stage growth process showing spontaneously formed primary particles with a size of about 500 Å diameter that subsequently transformed to 1000 Å sized particles which were stable for at least 24 h. (ii) A particular shielding topology was observed for the second CPP state, namely, that a densely packed fetuin-A monolayer covers a mineral core and thereby prevents further crystal growth. (iii) Transmission electron microscopy analysis of in vitro synthesized second state CPPs re...

Fetuin-A/α₂-HS glycoprotein is a major systemic inhibitor of unwanted calcium phosphate deposition in the soft tissue. Fetuin-A mediates the formation of initially ∼100 nanometre sized colloidal protein–mineral particles, denoted as calciprotein particles. After a lag period, these particles rapidly grow to elongated particles of about twice the initial size. Similar particles can be generated with other acidic macromolecules as well. However, fetuin-A is more potent regarding activity and specificity of inhibition. Given the widely recognized physiological relevance of fetuin-A as an inhibitor of pathological mineralization both in vitro, in cells, in animals and in humans, and its ready availability in large quantities, fetuin-A is a prototypic model protein to investigate protein–calcium phosphate interactions and mineral colloid stabilization, respectively. Several studies have concentrated on the pathophysiological relevance and the structural details of particle formation and mineral ripening. The principles governing calciprotein particle formation and ripening are nevertheless poorly understood. Here we present a systematic and quantitative investigation by time-resolved dynamic light scattering of the three major parameters: fetuin-A concentration, mineral ion concentration and temperature. Changes in temperature had only a weak effect on calciprotein particle size. Increased mineral ion concentrations and especially increased fetuin-A concentration led to smaller particles. An increased temperature, mineral ion concentration and a reduced fetuin-A concentration, respectively, all accelerated the particle ripening process. Our investigation demonstrates that calciprotein particle formation and ripening are two separate and successive processes and that particle ripening follows Arrhenius law. Furthermore it provides concepts to control the particle size and stability.