# Subchondral bone repair potential of an osteochondral scaffold augmented with BMP-2 or strontium-enriched amorphous calcium phosphate: a co-culture in vitro model

## TL;DR

Researchers tested two ways to improve bone repair in a lab model, finding that one method better supports bone cell development.

## Contribution

The study introduces and compares two augmentation strategies for an osteochondral scaffold to enhance subchondral bone repair.

## Key findings

- BMP-2-modified scaffolds showed higher metabolic activity and better osteoblast differentiation than controls and Sr-ACP scaffolds.
- Sr-ACP scaffolds tended to stimulate osteoclast activity more than BMP-2 scaffolds.
- Both modified scaffolds improved MSC adhesion and growth compared to the unmodified scaffold.

## Abstract

A collagen/collagen-magnesium-hydroxyapatite (Col/Col-Mg-HA) scaffold is currently used in the clinical practice to address osteochondral lesions (OCL). However, suboptimal bone regeneration still limits its overall reparative potential. The aim of this study was to test in vitro the osteoinductive potential of two different augmentation strategies: the addition of Bone Morphogenetic Protein-2 (BMP-2) or the incorporation of strontium ions-enriched amorphous calcium phosphate (Sr-ACP) granules.

Human mesenchymal stromal cells (MSCs) were seeded on the differently modified scaffolds and unmodified material used as a control, and grown for 14 days in a co-culture system in the presence of primary osteoclasts and conditioned medium of endothelial cells. The potential of the BMP-2- and Sr-ACP-enriched scaffolds compared to the control was then evaluated in terms of MSCs adhesion and morphology, metabolic activity, osteogenic differentiation, and osteoclasts’ markers expression.

Morphologically, both modified scaffolds sustained good cell adhesion. More secreted matrix was observed on the BMP-2 scaffold, together with higher metabolic activity and an upregulation of most of the evaluated osteoblast-related genes compared to the control and the Sr-ACP scaffold. Conversely, in the presence of the Sr-ACP scaffold, lower metabolic activity and a slower activation of osteoblast-related markers, together with a tendency to stimulate the osteoclasts’ activity, was observed.

Overall, both augmentation strategies were able to favor the adhesion and growth of MSCs compared to the unmodified scaffold, with the BMP-2-modified scaffold promoting more the differentiation of MSCs toward a mature osteoblastic phenotype than the Sr-ACP-modified scaffold, and the latter promoting more osteoclast activation.