Mineralized collagen fibrils constitute a basic structural unit of collagenous mineralized tissues such as dentin and bone. Understanding of the mechanisms of collagen mineralization is vital for development of new materials for the hard tissue repair. We carried out bio-inspired mineralization of reconstituted collagen fibrils using poly-l-aspartic acid, as an analog of non-collagenous acidic proteins. Transmission electron microscopy and electron diffraction studies of the reaction products revealed stacks of ribbon-shaped apatitic crystals, deposited within the fibrils with their c-axes coaligned with the fibril axes. Such structural organization closely resembles mineralized collagen of bone and dentin. Initial mineral deposits formed in the fibrils lacked a long range crystallographic order and transformed into crystals with time. Interestingly, the shape and organization of these amorphous deposits was similar to the crystals found in the mature mineralized fibrils. We demonstrate that the interactions between collagen and poly-l-aspartic acid are essential for the mineralized collagen fibrils formation, while collagen alone does not affect mineral formation and poly-l-aspartic acid inhibits mineralization in a concentration dependant manner. These results provide new insights into basic mechanisms of collagen mineralization and can lead to the development of novel bio-inspired nanostructured materials.

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Abstract:Ce 1-x Zr x O 2 nanoparticle sols (x = 0-1) are synthesized by hydroxide coprecipitation of a mixed precursor solution of cerium ammonium nitrate and zirconyl chloride followed by redispersion in an aqueous medium by sonication using nitric acid as the peptizing agent. The obtained sols are highly concentrated and stable for weeks. Analytical ultracentrifugation measurements show a particularly narrow particle distribution with an average particle size of about 3.5 nm for pure CeO 2 and 2.5 nm for pure ZrO 2 nanoparticles. Wide-angle X-ray scattering (XRD) as well as high-resolution transmission electron microscopy give evidence that all of the as-synthesized nanoparticle sols with a ceria content larger than 20 mol % are well crystalline. The formation of a solid solution with an increasing amount of Zr was monitored by XRD and Raman spectroscopy.