# In Vivo Osteogenic Potential of Biomimetic Hydroxyapatite/Collagen Microspheres: Comparison with Injectable Cement Pastes

## TL;DR

This study compares bone-forming abilities of hydroxyapatite/collagen microspheres and injectable cement in rabbits, finding microspheres promote more bone growth.

## Contribution

The study introduces a novel biomimetic microsphere design that enhances bone ingrowth compared to traditional injectable cements.

## Key findings

- Microspheres showed tenfold greater bone ingrowth compared to cement pastes.
- Microspheres provided better cell accessibility and larger surface area for osteoconduction.
- Collagen presence did not significantly affect bone formation but caused more erosion in microspheres.

## Abstract

The osteogenic capacity of biomimetic calcium deficient hydroxyapatite microspheres with and without collagen obtained by emulsification of a calcium phosphate cement paste has been evaluated in an in vivo model, and compared with an injectable calcium phosphate cement with the same composition. The materials were implanted into a 5 mm defect in the femur condyle of rabbits, and bone formation was assessed after 1 and 3 months. The histological analysis revealed that the cements presented cellular activity only in the margins of the material, whereas each one of the individual microspheres was covered with osteogenic cells. Consequently, bone ingrowth was enhanced by the microspheres, with a tenfold increase compared to the cement, which was associated to the higher accessibility for the cells provided by the macroporous network between the microspheres, and the larger surface area available for osteoconduction. No significant differences were found in terms of bone formation associated with the presence of collagen in the materials, although a more extensive erosion of the collagen-containing microspheres was observed.