Sustained Release of BMP-2 in Bioprinted Alginate for Osteogenicity in Mice and Rats

Michelle T Poldervaart,Harrie Weinans,F Cumhur Öner,Jacqueline Alblas,Huanan Wang,Sander C G Leeuwenburgh,Johan Van Der Stok,Wouter J A Dhert,Pandit Abhay

doi:10.1371/journal.pone.0072610

Abstract

The design of bioactive three-dimensional (3D) scaffolds is a major focus in bone tissue engineering. Incorporation of growth factors into bioprinted scaffolds offers many new possibilities regarding both biological and architectural properties of the scaffolds. This study investigates whether the sustained release of bone morphogenetic protein 2 (BMP-2) influences osteogenicity of tissue engineered bioprinted constructs. BMP-2 loaded on gelatin microparticles (GMPs) was used as a sustained release system, which was dispersed in hydrogel-based constructs and compared to direct inclusion of BMP-2 in alginate or control GMPs. The constructs were supplemented with goat multipotent stromal cells (gMSCs) and biphasic calcium phosphate to study osteogenic differentiation and bone formation respectively. BMP-2 release kinetics and bioactivity showed continuous release for three weeks coinciding with osteogenicity. Osteogenic differentiation and bone formation of bioprinted GMP containing constructs were investigated after subcutaneous implantation in mice or rats. BMP-2 significantly increased bone formation, which was not influenced by the release timing. We showed that 3D printing of controlled release particles is feasible and that the released BMP-2 directs osteogenic differentiation in vitro and in vivo.

Highlights

For the treatment of large bone defects currently auto- or allograft bone grafts are being used
To accomplish such a gradual and sustained release many controlled release vehicles have been described in literature; gelatin microparticles (GMPs) are promising because growth factors can be incorporated into these microspheres by simple post-loading, thereby avoiding chemical reactions that can damage the activity of fragile proteins such as bone morphogenetic protein 2 (BMP-2)
We investigated whether prolonged BMP-2 presence in scaffolds promotes osteogenic differentiation and bone formation compared to fast growth factor release

Summary

Introduction

For the treatment of large bone defects currently auto- or allograft bone grafts are being used. The gene coding for BMP-2 is upregulated for about four weeks after fracture, which supports the approach to strive for a more sustained release of the BMP-2 protein at lower dosage, as an alternative and effective strategy in enhancing osteogenic differentiation and bone formation while reducing the risk of side effects and complications [11,12,13] To accomplish such a gradual and sustained release many controlled release vehicles have been described in literature; gelatin microparticles (GMPs) are promising because growth factors can be incorporated into these microspheres by simple post-loading, thereby avoiding chemical reactions that can damage the activity of fragile proteins such as BMP-2. GMPs are non-cytotoxic, biodegradable and have already been used in numerous formulations as isolated particles or incorporated as dispersed phase into hydrogels to deliver BMP-2 and other growth factors such as TGF-b1 and bFGF [14,15]

Methods

Results

Conclusion