[Preparation of decellularized bone graft material with supercritical carbon dioxide extraction technique]

To evaluate the immunogenicity and osteogenic ability of animal-derived bone graft material decellularized with supercritical carbon dioxide.

Porcine femurs were randomly divided into two groups after preliminary treatment, and decellularized with conventional method (control group) or supercritical carbon dioxide (experimental group). Allogenic demineralized bone matrix was used as positive control. Clearance rate of galactose-α-1, 3-galactose (α-Gal) antigen was determined by enzyme-linked immunosorbent assay and residual DNA was detected by a fluorescence method. Nine SPF-grade male athymic nude mice of 6 weeks old were randomly divided into experimental, control and positive control groups. Samples were implanted over biceps femoris muscle of athymic nude mice. The explants were collected 4 weeks post implantation. Hematoxylin and eosin (HE) staining and immunohistochemistry were applied to determine the osteogenic ability and bone tissue-associated protein expressions of the implants.

The clearance rates of α-Gal antigen in the experimental group and the control group were (99.09±0.26)% and (30.18±2.02)%, respectively (t=58.67, P<0.01). The residual DNA of the experimental, control and positive control groups were (13.49±0.07), (15.20±0.21) and (14.70±0.17) ng/mg. The residual DNA in the experimental group was significantly lower than that in the control group (t=－13.41, P<0.01) and positive control group (t=－11.30, P<0.01). HE staining results showed that multiple bone formation centers with active osteogenesis and rich bone marrow were observed in experimental group 4 weeks after implantation, but only a small number of bone formation centers were observed in the control and positive control groups, with no obvious osteoblasts present. Immunohistochemistry results indicated that the expressions of alkaline phosphatase, Runt-related transcription factor 2, collagen typeⅠand osteocalcin in the experimental group showed an increasing trend compared with those in the control and positive control groups.

Compared with clinically used allogenic demineralized bone matrix and bone graft material decellularized with conventional method, bone graft material decellularized with supercritical carbon dioxide exhibits lower immunogenicity and better osteogenic ability.