Preparation and biocompatibility of demineralized bone matrix/sodium alginate putty

Demineralized bone matrix (DBM) powder is widely used for bone regeneration due to its osteoinductivity and osteoconductivity. However, difficulties with handling, tendency to migrate from graft sites and lack of stability after surgery sometimes limit the clinical utility of this material. In this work, the possibility of using sodium alginate (ALG) carrier to deliver DBM powder was assessed. DBM-ALG putty with the DBM:ALG weight ratio of 5:5, 6:4, 7:3, 8:2 were prepared, respectively. The properties of the formed composite, including discrete degree, washout property, pH, equilibrium swelling as well as cytotoxicity in vivo, were adopted to ascertain the optimal ratio of DBM and ALG. The discrete diameter increased from 1.25 cm (5:5) to 2.08 cm (8:2) with the increase of DBM content. There was significant difference between the 8:2 group and the other groups in discrete diameter. The ratio of DBM had a significant effect on the swelling value. The pH of composites showed an increase trend with the DBM ratio's increase, when the ratio reached 7:3, the pH (7.22) was approximately equal to the body fluid. The proliferation of MC3T3-E1 cells was inhibited in the 5:5, 6:4 and 7:3 groups, while a slightly increased in the 8:2 group. The DBM-ALG with the optimal ratio of 7:3 was confirmed based on the results of the above mentioned. The histocompatibility of DBM-ALG (7:3) was examined using a rat model in which the materials were implanted subcutaneously, compared with the polyethylene, ALG and DBM. The study in vivo showed DBM-ALG (7:3) had a lower inflammatory response than DBM, a higher vascularization than ALG. The osteoinduction of DBM-ALG (7:3) was evaluated by co-culturing with MC3T3-E1 in vitro, compared with the DMEM, ALG and DBM. The results indicated calcification area in the DBM-ALG group was similar to that in the DBM group, larger than ALG group and DMEM group. The DBM-ALG (7:3) putty is promising as a directly injectable graft for repair of bone defect.