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Biological mineralization of tissues in living organisms relies on proteins that preferentially nucleate minerals and control their growth. This process is often referred to as ''templating,'' but this term has become generic, denoting various proposed mineralorganic interactions including both chemical and structural affinities. Here, we present an approach using self-assembled networks of elastin and fibronectin fibers, similar to the extracellular matrix. When induced onto negatively charged sulfonated polystyrene surfaces, these proteins form fiber networks of Ϸ10-m spacing, leaving open regions of disorganized protein between them. We introduce an atomic force microscopy-based technique to measure the elastic modulus of both structured and disorganized protein before and during calcium carbonate mineralization. Mineralinduced thickening and stiffening of the protein fibers during early stages of mineralization is clearly demonstrated, well before discrete mineral crystals are large enough to image by atomic force microscopy. Calcium carbonate stiffens the protein fibers selectively without affecting the regions between them, emphasizing interactions between the mineral and the organized protein fibers. Late-stage observations by optical microscopy and secondary ion mass spectroscopy reveal that Ca is concentrated along the protein fibers and that crystals form preferentially on the fiber crossings. We demonstrate that organized versus unstructured proteins can be assembled mere nanometers apart and probed in identical environments, where mineralization is proved to require the structural organization imposed by fibrillogenesis of the extracellular matrix.calcium carbonate ͉ elastic modulus ͉ extracellular matrix ͉ secondary ion mass spectroscopy B iomineralization is the process by which living organisms build inorganic mineral-based structures. This process has been of vital interest for over a century, because nature is known to produce mineral architectures, which exhibit superior mechanical strength and other specialized properties. Understanding and mimicking this process is critical to ''biomimetic'' materials science for inorganic-organic hybrid materials (bioceramics), low-temperature materials for electronics and semiconductor applications, and medical engineering of bone, teeth, and cartilage (1-6). A large body of literature already exists describing the process, but even the most recent reviews emphasize the diversity of biominerals rather than the shared underlying mechanisms (7-9). Yet to understand the fundamental processes leading to biomineralization, we must first focus on the phenomena that many systems have in common. Arguably it is the very early stages of tissue organization and mineral nucleation that are the most general, after which specific controls of mineral growth allow differentiation into characteristics unique to each organism. In this article, we present an approach that we have developed to probe these early mineralization stages.The most intricate and organized biomineral ...

Nacre, the crown jewel of natural materials, has been extensively studied owing to its remarkable physical properties for over 160 years. Yet, the precise structural features governing its extraordinary strength and its growth mechanism remain elusive. In this paper, we present a series of observations pertaining to the red abalone (Haliotis rufescens) shell's organic-inorganic interface, organic interlayer morphology and properties, large-area crystal domain orientations and nacre growth. In particular, we describe unique lateral nanogrowths and paired screw dislocations in the aragonite layers, and demonstrate that the organic material sandwiched between aragonite platelets consists of multiple organic layers of varying nano-mechanical resilience. Based on these novel observations and analysis, we propose a spiral growth model that accounts for both [001] vertical propagation via helices that surround numerous screw dislocation cores and simultaneous h010i lateral growth of aragonite sheet structure. These new findings may aid in creating novel organic-inorganic micro/nano composites through synthetic or biomineralization pathways. Keywords: nacre; biomineralization; crystal growthBiomaterials provide fascinating examples of nature's ability to assemble structures of remarkable strength and toughness (Aksay et al. 1996;Addadi & Weiner 1997;Sanchez et al. 2005). Particularly well studied is nacre, or mother of pearl, a composite of aragonite CaCO 3 and organic matrix that is 3000 times more fracture resistant than the pure mineral (Currey 1977;Jackson et al. 1988). Its unique mechanical properties are attributed to a structure of polygonal aragonite platelets, approximately 5 mm across by 0.5 mm thick, wrapped in polysaccharide and protein fibres ( Weiner 1986;Jackson et al. 1989). There exist two principal types of nacre structure: columnar, composed of stacked platelets of rather uniform size with coinciding centres, and sheet, in which the centres of platelets rest on the interfaces between underlying platelets, as in a brick wall. Columnar nacre is known to be deposited in a narrow zone at the margin of the shell, while sheet nacre is deposited over most of the inner surface (Hedegaard 1997). Yet, after 160 years of scientific investigation (Carpenter 1847), the precise features governing nacre's extraordinary strength remain elusive. This is largely due to the lack of structural characterization at the atomic and nanometre scale. Understanding the physical and mechanical properties of nacre at nanometre scale dimensions could lead to the synthesis of novel materials with unprecedented performance.Here, we present a series of observations, using highresolution imaging and nanoscale force measurements, on structural features at the organic-inorganic interface, morphological and mechanical properties of the organic matrix, crystal directions and ultimately sheet nacre growth. We reveal nanometre-scale growths on vertical (010) platelet faces and new details of asperities, i.e. small protrusions, on horizonta...