Injectable Cell-based Tissue Engineered Bone Formulations

Abstract

Current golden standard therapy for bone repair and regeneration involves the use of auto grafts. Nevertheless, there are many drawbacks associated with auto grafts including donor site morbidity, requirement for an invasive surgery, post-operative pain and infection. The use of injectable tissue engineered bone is an attractive alternative, providing a minimally invasive approach to regenerate bone. It offers faster healing, less pain and exact conformation to irregular defects. The present work is designed to achieve injectable formulations of tissue engineered bone that fulfil the requirements needed. It involves investigation of potential polymeric binders that are biocompatible, biodegradable and allow bone formation when combined with cells. Chitosan binders were tested for biocompatibility, biodegradability, gelation, angiogenic potential and osteogenic differentiation and bone formation when mixed with goat and human bone marrow derived mesenchymal stem cells (gMSCs, hMSCs). An in vivo bone formation study was performed to investigate the bone formation ability of gMSCs in contact with chitosan binder. Chick chorioallantoic membrane assay was carried out to examine the angiogenic potential of the chitosan binder combined with/without hMSCs. Furthermore, MC3T3-El cells were employed to assess the osteogenic potential of cells exposed to chitosan polymeric systems. Chitosan binder was proved to be an attractive polymer to carry cell-scaffold combination. hMSCs were able to survive and differentiate along the osteogenic lineage when encapsulated with 1.5% (w/v) chitosan-15% (w/v) glycerol phosphate (GP)-0.18% (w/v) hydroxyethyl cellulose (HEC) in a 14-day study. Furthermore, chitosan-GP-HEC solutions demonstrated fast gelation at 37°C. Chitosan was biodegradable following 42 days in the presence/absence of lysozyme. Moreover, gMSCs combined with chitosan binder produced 24.6 ± 13.7% bone comparable to the control group after a 6-week implantation in mice. Chitosan was shown to be nonangiogenic unlike hMSCs which showed angiogenic potential. Also, chitosan was found to be osteogenic at 2 and 0.05 mg/ml concentrations.