Controlled BMP2 Release from Keratin‐based Hydrogels Modulates Osteoinduction

Abstract

Keratin biomaterials have potential for tissue engineering applications. When processed keratin is naturally non‐immunogenic, contains cell attachment sites, and has a tunable degradation rate, resulting in an effective scaffolding to simulate extracellular matrix (ECM). Keratose (oxidatively derived keratin) degrades in a period of weeks whereas kerateine (reductively derived keratin) degrades on an order of months to years, due to higher cysteine cross linking in kerateine. Clinically type 1 collagen sponge is soaked in bone morphogenetic protein (BMP2), which is a potent osteoinductive factor, in order to promote bone healing in orthopedic and craniofacial sites. The sponge, however, does not modulate BMP2 release in vivo, resulting in supraphysiological levels of the osteoinductive factor. Harmful ectopic bone formation and inflammation can result. In contrast, keratin degradation and BMP2 release rate are correlated. Modulation of BMP2 release by keratin, coupled with its inherent properties as an ECM substitute, could result in a suitable construct for osteoinduction via controlled osteogenic signal release, inflammatory mitigation, and cellular infiltration. The aim of this study was to examine the ability of keratin‐derived materials containing BMP2 to induce bone formation in vivo.Ectopic bone formation from collagen sponge, keratose gel, kerateine gel, and keratose: kerateine blends (30:70, 50:50, 70:30) ± 0.67μg BMP2/mg material was examined in a well‐known mouse model. Samples were placed in gelatin capsules and bilaterally implanted into pockets created in the gastrocnemius of 7w‐old male athymic nude mice (n=8 implants/variable). After 5w, new bone formation was ascertained by histology, microCT and histomorphometry. (Statistical significance: ANOVA with post‐hoc Bonferroni‐corrected t‐test).All +BMP2 samples produced new bone formation on microCT and histology, while there was no new bone in‐BMP2. On microCT, the most new bone was seen in 50:50+BMP2. 30:70+BMP2 had more new bone volume than collagen+BMP2 or keratose+BMP2. Histologically, 30:70+BMP2 contained greater total bone area than collagen+BMP2 and keratose+BMP2. 70:30+BMP2 had more cortical‐type bone and bone marrow than keratose+BMP2, but 30:70+BMP2 had more material still present than collagen+BMP2, keratose+BMP2, or 50:50+BMP2. Keratose (±BMP2) degraded completely. In‐BMP2 samples, remaining material increased with increasing kerateine. In conclusion, keratose/kerateine carriers facilitate greater BMP2‐induced bone than standard collagen or either biomaterial separately, suggesting their suitability as slow‐release BMP2 carriers for clinical bone regeneration.Support or Funding InformationNIH 5R01AR061391