Ectopic Bone Formation in Muscles Using Injectable Bone-forming Material Consisting of Cross-linked Hyaluronic Acid, Bone Morphogenetic Protein, and Nano-hydroxyapatite

Abstract

To accelerate bone formation, we prepared an injectable bone-inducing sol-gel material. Bone morphogenetic protein (BMP) was incorporated into a cross-linkable hyaluronic acid (cHLA) sol with –SH functional groups with and without nano-hydroxyapatite (nHAP). The test cHLA/BMP/nHAP and control cHLA/BMP sols were injected into the back subcutaneous and thigh intra-muscular tissues of 10-week-old male mice (n=10 each), and allowed to gel for 20 min. After feeding for 8 weeks, calcification at the injection sites was evaluated by micro-computed tomography (CT) and histological examination. CT revealed calcification at the sites of test cHLA/BMP/nHAP sol-gel injection in 80–90% of the mice, while control cHLA/BMP sol-gel could not induce any calcification. Histological observations clarified that new bone formed in the calcification zones at both sites by endochondral ossification. It was thought that nHAP functioned as a carrier that retains and slowly release osteo-inductive BMP. The cHLA/BMP/nHAP sol-gel has potential as an injection-type osteo-inductive biomaterial.