Coacervation conditions and crosslinking determines availability of carbonyl groups on elastin and its calcification

During medial calcification, calcium phosphate minerals deposit in the medial layer of arteries, causing their stiffening. Although elastin (ELN) has been shown to be the main site for mineral deposition, the sites for mineral nucleation are not clear since ELN is nearly neutral, thus intrinsically lacking binding sites for Ca2+ or PO43–. Using a three-dimensional ELN hydrogel model, this study finds that binding of Ca2+ on the carbonyl groups initiates the mineralization. Coacervation and cross-linking, which are the two steps for the gel synthesis and also intrinsic processes for in vivo ELN fiber formation, are positively correlated with the mineralization. Both processes increase the percentage of exposed carbonyl groups that are available for Ca2+ binding and subsequent mineralization. This study provides insights into the initiation of ELN mineralization as well as a new perspective on the inherent weakness of elastic tissues.

Stress-relaxation tests were performed using a Biomomentum Mach-1 (Biomomentum Inc. Laval, Canada) micromechanic testing device.