Calcium phosphate nucleation and crystallization in and on biological proteins such as collagen are important for the mechanical functioning of bones and teeth. In collagenous structures, these processes follow distinctly different patterns, depending on whether they occur in highly confined gap regions at nanoscale or in less confined extrafibrillar spaces. Although the mechanism(s) driving these differences are still largely unknown, differences in the free energy for calcium phosphate nucleation may explain them. Hence, using polyaspartic acid as an extrafibrillar nucleation inhibitor, we separately evaluated the nucleation energy barriers for intra- and extrafibrillar calcium phosphate mineralization. Using <i>in situ</i> X-ray scattering techniques, we quantified nucleation rates at different supersaturations in simulated body fluid. With the nucleation inhibitor protein, the interfacial energies between calcium phosphate nuclei and mineralization fluids were increased in unconfined spaces. In contrast, the confined gap spaces inside collagen fibrils lowered the energy barrier by reducing the reactive surface area of nuclei, decreasing the surface energy penalty. Beyond the conventionally accepted role of collagen as a substrate for nucleation, we found that the confined gap geometry indeed actively guides the 2-dimensional morphology and structure of calcium phosphate and changes the nucleation and crystallization pathway by reducing the total energy barrier. To better describe these experimental findings, we developed a new modification of classical nucleation theory. Our findings clarify how nucleation behaviors in nanoscale confined spaces differ from those in the bulk, and they highlight the importance of interfacial chemistry in confined spaces on calcium phosphate nucleation and crystallization.

Calcium phosphate crystallization pathway in confined collagen spaces

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.