Transforming growth factor (TGF)-beta1 releasing tricalcium phosphate/chitosan microgranules as bone substitutes

Tricalcium phosphate (TCP)/chitosan composite microgranules were developed as bone substitutes and tissue engineering scaffolds with the aim of obtaining a high bone forming efficacy. The microgranules have the ability to fill various types of defect sites with closer packing. In addition, the transforming growth factor-beta 1 (TGF-beta1) was added to the microgranules in order to improve bone-healing efficacy.

TCP/chitosan microgranules were fabricated by dropping a TCP suspended chitosan solution into a NaOH/ethanol solution. TGF-beta1 was incorporated into the TCP/chitosan microgranules by soaking the microgranules into the TGF-beta1 solution. Scanning electron microscopy (SEM) observations as well as experiments examining the release of TGF-beta1 from chitosan and TCP/chitosan microgranules were performed. SEM was used to examine the cell morphologies on the microgranules, and the extent of cell proliferation was evaluated using a dimethyl-thiazol tetrazolium bromide (MTT) assay. The differentiated cell function was assessed by measuring the alkaline phosphatase activity as well as performing an osteocalcin assay.

The size of the prepared microgranules was 350-500 microm and TCP powders were observed on the surface of the microgranules. TGF-beta1 was released from the TCP/chitosan microgranules at a therapeutic concentration for 4 weeks. The proliferation of osteoblasts on the TGF-beta1 loaded microgranules was the highest among the microgranules. SEM indicated that the seeded osteoblastic cells were firmly attached to the microgranules and proliferated in a multilayer fashion. The ALPase activity and osteocalcin content of all the samples increased during the culture period.

These results suggest that the TCP/chitosan microgranules are potential bone substitutes with a drug releasing capacity and a osteoblastic cells culture scaffold.