Biomineralization of bone, a controlled process where hydroxyapatite nanocrystals preferentially deposit in collagen fibrils, is achieved by the interplay of the collagen matrix and noncollagenous proteins. Mimicking intrafibrillar mineralization in synthetic systems is highly attractive for the development of advanced hybrid materials with elaborated morphologies and outstanding mechanical properties, as well as understanding the mechanisms of biomineralization. Inspired by nature, intrafibrillar mineralization of collagen fibrils has been successfully replicated in vitro via biomimetic systems, where acidic polymeric additives are used as analogue of noncollagenous proteins in mediating mineralization. The development of synthetic templates that mimic the structure and functions of collagenous matrix in mineralization has yet to be explored. In this study, we demonstrated that self-assembled fibrils of elastin-like recombinamers (ELRs) can induce intrafibrillar mineralization. The ELRs displayed a disordered structure at low temperature but self-assembled into nanofibrils above its inverse transition temperature. In the presence of the self-assembled ELR fibrils, polyaspartate-stabilized amorphous calcium phosphates preferentially infiltrated into the fibrils and then crystallized into hydroxyapatite nanocrystals with their  axes aligned parallel to the long axis of the ELR fibril. As the recombinant technology enables designing and producing well-defined ELRs, their molecular and structural properties can be fine-tuned. By examining the ultrastructure of the self-assembled ELRs fibrils as well as their mineralization, we concluded that the spatial confinement formed by a continuum β-spiral structure in an unperturbed fibrillar structure rather than electrostatic interactions or bioactive sequences in the recombinamer composition played the crucial role in inducing intrafibrillar mineralization.
Bibliographical noteFunding Information:
This project was partially supported by a 3M Foundation NonTenured Faculty Award to C.A.. J.C.R.-C. wishes to thank the European Commission (HEALTH-F4-2011-278557, PITN-GA-2012-317306 MSCA-ITN-2014-642687, and NMP-2014-646075), the Ministry of Economy and Competitiveness (Spain; MAT2013-42473-R and MAT2015-68901R), and the Junta de Castilla y Leon (VA244U13, VA313U14, and VA015U16). Parts of this work were performed in the Univ. of Minnesota I. T. Characterization Facility, which receives partial support from NSF through the MRSEC program.
© 2017 American Chemical Society.
- amorphous calcium phosphate precursor
- biomimetic mineralization
- elastin-like recombinamer