Exploring and evaluating scaffolds for in-vivo application of TAT-BMP

Abstract

Although the need for bone regeneration is gradually increasing due to aging, clinical modality is not yet definite. Exogenous growth factors, like bone morphogenetic proteins (BMPs) should have sufficient bioactivity and be in harmony with the carrier system by controlled release of biological factors with mechanical support. Recombinant human BMP-2 (rhBMP-2) are currently used in clinics, but their efficacy remains obscure.Contrary to soluble hydrophilic rhBMP-2, inactive form TAT-BMP-2 fusion protein has a hydrophobic nature that requires an appropriate scaffold system toward in vivo application. In this regard, this study aims to explore the most proper scaffold among collagen, fibrin and hydrogel, which all have in-vivo biocompatibility, biodegradability by evaluating bone regeneration efficacy when combined with TAT-BMP-2 in the critical sized defect of a rabbit skull. Also, chemical residues of the most excellent scaffold,hydrogel, were detected by several methods to proceed into preclinical study. The results are as follows:1. The bone regeneration efficacy of hydrogel and collagen were in themselves comparable.2. 5μg of the TAT-BMP-2 and hydrogel composite induced 50% more efficient bone regeneration than blank, collagen and fibrin. Also it exhibited the most superior bone mineral density.3. Fibrin seemed to inhibit osteoinduction. Furthermore, the TAT-BMP-2 fibrin composite did not demonstrate significant bone regeneration compared to control or other experimental groups.4. The concentration dependency of the TAT-BMP-2 and hydrogel composite in bone regeneration needs further investigation.5. The elution buffer of hydrogel contained EDC and TCEP, which needs to be removed by serial dialysis.These results indicated that TAT-BMP-2 hydrogel composite showed the most effective in vivo mode of action to deliver secretory growth factors. Further treatments to remove the chemical residues in hydrogel should be done to move forward clinical application.