The involvement of collagen in bone biomineralization is commonly admitted, yet its role remains unclear. Here we show that type I collagen in vitro can initiate and orientate the growth of carbonated apatite mineral in the absence of any other vertebrate extracellular matrix molecules of calcifying tissues. We also show that the collagen matrix influences the structural characteristics on the atomic scale, and controls the size and the three-dimensional distribution of apatite at larger length scales. These results call into question recent consensus in the literature on the need for Ca-rich non-collagenous proteins for collagen mineralization to occur in vivo. Our model is based on a collagen/apatite self-assembly process that combines the ability to mimic the in vivo extracellular fluid with three major features inherent to living bone tissue, that is, high fibrillar density, monodispersed fibrils and long-range hierarchical organization.

Low efficiency of charge extraction (and conversely charge injection) across biotic-abiotic interfaces constitutes an obstacle to the integration of biological and electronic systems in high-performance bioelectronic devices. Advances in the promotion of charge transport across these typically non-conductive interfaces will have far-reaching implications in important applications such as alternative energy generation, bioelectrosynthesis, diagnostics, and environmental monitoring. This review highlights the use of synthetic materials to improve electrical interfacing between biological systems and electrodes, focusing specifically on whole cell bioelectrochemical systems. By taking advantage of a rich variety of materials chemistry and synthetic methodologies, significant improvements to the facilitation of charge transport across abiotic-biotic interfaces have been realized. The modifications of the bioelectronic interfaces presented herein include the use of organic small molecules, semiconducting and redox active polymers, inorganic nanoparticles, carbon nanotubes, graphene, hybrid organic-inorganic systems, and micro-/nanoelectrodes. However, design rules to guide material selection and choices regarding device architecture remain ambiguous. Establishment of a clearer understanding of bioelectronic charge transfer phenomena, their constituent pathways, and means of stimulating or selecting for different pathways is still work in progress. As such, great opportunities exist for materials scientists to contribute to these topics through design and implementation.