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Inspired by nature, poly(acrylic acid) (PAA) and other polyelectrolytes have been used as noncollagenous proteins (NCPs) surrogates for biomimetic intrafibrillar mineralization of collagen fibrils and thus, to model the ultrastructure of bone, to study the mechanism of bone mineralization and, more scarcely to fabricate scaffolds for hard tissue engineering. The objective of this study was to systematically investigate the effect of the molecular weight (MW) and the concentration of PAA on the rate and pattern of biomineralization of collagen matrices. Densified type I collagen films were mineralized in supersaturated PAA-stabilized amorphous calcium-phosphate (PAA-ACP) solutions containing increasing MW (2 kDa, 50 kDA, 450 kDa) and concentrations (10, 25, 50 mg/L) of PAA up to 7 days. The stability and physical properties of collagen-free PAA-ACP solutions were also investigated. In our system, lowering PAA MW and increasing PAA concentration resulted in solutions with increasing stability. Over stable PAA-ACP solutions that fully inhibited mineralization of the collagen matrices were achieved using PAA 2k-50. Conversely, unstable solutions were obtained using high PAA MW at low concentrations. Nucleation and growth of significant amount of extrafibrillar minerals on the collagen fibrils was obtained using these solutions. In a wide range of combined MW and concentration of PAA we obtained intrafibrillar mineralization of collagen with hydroxyapatite crystals aligned parallel to the collagen fibril as in natural tissues. Intrafibrillar mineralization was correlated with PAA-ACP stability and growth of the PAA-ACP particles in solution. Our results support using PAA to surrogate NCPs function as selective inhibitors or promoters of biological mineralization and provide parameters to manufacture new biomimetic scaffolds and constructs for bone and dentin tissue engineering.

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Organic dyes undergo a variety of solid‐state chemical processes, including intra‐ and intermolecular reactions, gas‐solid reactions, and polymorphic transformations. The properties of dye solids are markedly affected by this chemistry. This paper reviews solid state dye chemistry from the literature and reports in detail the chemistry of two novel cyanine dye salts whose properties are controlled by the nature of their counterions. In cyanine‐oxonol salts, the oxonol counterion is a large planar dye which forms crystalline dye aggregates with cyanine ions. There is a multiplicity of polymorphic forms of these mixed dyes reflecting multiple favorable dye aggregate geometries. The cyanine‐borate salts undergo intermolecular solid‐state reactions. In either large single crystals or dispersions of the latter salts in polymer binders, alkyl transfer from the anion to the chromophore can be induced thermally or photochemically.