The Poor Osteoinductive Capability of Human Acellular Bone Matrix

Combined therapy of adipose-derived stem cells and photobiomodulation on accelerated bone healing of a critical size defect in an osteoporotic rat model

We investigated the impact of human demineralized bone matrix (hDBM) plus adipose-derived stem cells (hADS) plus photobiomodulation (PBM) on a critical-sized femoral defect (CSFD) in ovariectomy induced osteoporosis in rats. There were 6 groups as follows. In group 1 (control, C), only CSFDs were created. Groups 2-6 were implanted with DBM into the CSFD (DBM-CSFD). In group 2 (S), only DBM was transplanted into the CSFD. In group 3 (S + PBM), the DBM-CSFDs were treated with PBM. In group 4, the DBM-CSFDs were treated with alendronate (S + ALN). In group 5, ADSs were seeded into DBM-CSFD (S + ADS). In group 6, ADSs were seeded into DBM-CSFD and the CSFDs were treated with PBM (S + PBM + ADS). At week eight (catabolic phase of bone repair), the S + ALN, S + PBM + ADS, S + PBM, and S + ADS groups all had significantly increased bone strength than the S group (ANOVA, p = 0.000). The S + PBM, S + PBM + ADS, and S + ADS groups had significantly increased Hounsfield unit than the S group (ANOVA, p = 0.000). ALN, ADS, and PBM significantly increased healed bone strength in an experimental model of DBM-treated CSFD in the catabolic phase of bone healing in osteoporotic rats. However, ALN alone and PBM plus ADS were superior to the other protocols.

Preconditioning adipose-derived stem cells with photobiomodulation significantly increased bone healing in a critical size femoral defect in rats

We assessed the combined impacts of human demineralized bone matrix (hDBM) scaffold, adipose-derived stem cells (hADS), and photobiomodulation (PBM) on bone repair of a critical size femoral defect (CSFD) in 72 rats. The rats were divided into six groups: control (group 1); ADS (group 2 - ADS transplanted into hDBM); PBM (group 3 - PBM-treated CSFDs); ADS + PBM in vivo (group 4 - ADS transplanted into hDBM and the CSFDs were treated with PBM in vivo); ADS + PBM in vitro (group 5 - ADS were treated with PBM in vitro, then seeded into hDBM); and ADS + PBM in vitro+in vivo (group 6 - PBM-treated ADS were seeded into hDBM, and the CSFDs were treated with PBM in vivo. At the anabolic phase (2 weeks after surgery), bone strength parameters of the groups 5, 6, and 4 were statistically greater than the control, ADS, and PBM in vivo groups (all, p = 0.000). Computed tomography (CT) scans during the catabolic phase (6 weeks after surgery) of bone healing revealed that the Hounsfield unit (HU) of CSFD in the groups 2 (p = 0.000) and 5 (p = 0.019) groups were statistically greater than the control group. The groups 5, 4, and 6 had significantly increased bone strength parameters compared with the PBM in vivo, control, and ADS groups (all, p = 0.000). The group 5 was statistically better than the groups 4, and 6 (both, p = 0.000). In vitro preconditioned of hADS with PBM significantly increased bone repair in a rat model of CSFD in vivo.

The involvement of mitochondrial fission in maintenance of the stemness of bone marrow mesenchymal stem cells

IMPACT STATEMENT

How to maintain the stemness of bone marrow mesenchymal stem cells (BMSCs) in cultures is a long-standing question. The present study found that mitochondrial dynamics affects the stemness of BMSCs in cultures and the retaining of mitochondrial fission enhances the stemness of BMSCs. This work thus provides a novel insight into strategic approaches to maintain the stemness of BMSCs in cultures in relation to the clinical application of bone-marrow stem cells.

Demineralized Bone Scaffolds with Tunable Matrix Stiffness for Efficient Bone Integration

As a biophysical cue, matrix stiffness can decide the stem cell fate. However, most methods to construct three-dimensional (3D) scaffolds may change the 3D microstructure while altering their mechanical properties. In this study, demineralized bone matrix scaffolds with different compressive modulus (66.06 ± 27.83 MPa (high), 26.90 ± 13.16 MPa (medium), and 0.67 ± 0.14 MPa (low)) were constructed by controlling the decalcification duration (1 h, 12 h, and 5 days), respectively. The pore size and porosity have no significant difference between the scaffolds before and after decalcification. Cell experiments indicated that the low scaffolds could promote the osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) in vitro. Rat subcutaneous implantation experiments further demonstrated that the low scaffolds could efficiently improve the cell infiltration, deposition of collagen fibers, and positive osteocalcin and osteopontin expression of endogenous cells as well as angiogenesis. Finally, rabbit femoral condylar defect experiments proved that the low scaffolds could significantly promote the bone repair and integration and stromal cell derived factor-1α/CXC chemokine receptor signal pathway was essential for the stiffness-mediated bone repair. These investigations provided a novel method for fabricating 3D bone grafts with different stiffness, which is also of great significance for studying the effect of stiffness on the biological behavior of MSCs in three dimensions.

Organic composite-mediated surface coating of human acellular bone matrix with strontium

Acellular bone matrix (ACBM) provides an osteoconductive scaffold for bone repair, but its osteoinductivity is poor. Strontium (Sr) improves the osteoinductivity of bone implants. In this study, we developed an organic composite-mediated strontium coating strategy for ACBM scaffolds by using the ion chelating ability of carboxymethyl cellulose (CMC) and the surface adhesion ability of dopamine (DOPA). The organic coating composite, termed the CMC-DOPA-Sr composite, was synthesized under a mild condition, and its chemical structure and strontium ion chelating ability were then determined. After surface decoration, the physicochemical properties of the strontium-coated ACBM (ACBM-Sr) scaffolds were characterized, and their biocompatibility and osteoinductivity were determined in vitro and in vivo. The results showed that the CMC-DOPA-Sr composite facilitated strontium coating on the surface of ACBM scaffolds. The ACBM-Sr scaffolds possessed a sustained strontium ion release profile, exhibited good cytocompatibility, and enhanced the osteogenic differentiation of mesenchymal stem cells in vitro. Furthermore, the ACBM-Sr scaffolds showed good histocompatibility after subcutaneous implantation in nude mice. Taken together, this study provided a simple and mild strategy to realize strontium coating for ACBM scaffolds, which resulted in good biocompatibility and improved osteoinductivity.

Combination therapy with PTH and DBM cannot heal a critical sized murine femoral defect

Orthopaedic surgeons continue to search for cost-effective bone graft substitutes to enhance bone repair. Teriparatide (PTH 1-34) and demineralized bone matrix (DBM) have been used in patients to promote bone healing. We evaluated the efficacy of PTH and DBM in healing a critical sized femoral defect in three lineage-specific transgenic mice expressing Col3.6GFPtopaz (pre-osteoblastic marker), Col2.3GFPemerald (osteoblastic marker) and α-SMA-Cherry (pericyte/myofibroblast marker). Mid-diaphyseal defects measuring 2 mm in length were created in the central 1/3 of mice femora using a circular saw and stabilized with an alveolar distractor device and cerclage wires. Three groups were evaluated: Group I, PTH 30 μg/kg injection daily, Group II, PTH 30 μg/kg injection daily + DBM, and Group III, DBM + 30μL saline injection. PTH was given for 28 days or until the time of sacrifice. Animals were sacrificed at 7, 14, 28, and 56 days. Radiographs at the time of sacrifice were evaluated using a 5-point scaled scoring system. Radiographs showed a lack of healing across all treatment groups at all time points: Group I, 1.57 +/- 0.68; Group II, 3.00 +/- 1.29; and Group III, 2.90 +/- 1.03. Bone formation in the defect as measured by radiographic healing score was significantly better at 56 days in Groups II (p = 0.01) and III (p < 0.01) compared to Group I. Across all treatment groups and time points the defects were largely absent of osteoprogenitor cells based on gross observation of frozen histology and quantitation of cellular based histomorphometric parameters. Quantitation of frozen histologic slides showed a limited osteoprogenitor response to PTH and DBM. Our results suggest that the anabolic agent teriparatide is unable to induce healing in a critical sized mouse femoral defect when given alone or in combination with the DBM preparation we used as a local bone graft substitute.

Evaluation of osteogenic cell differentiation in response to bone morphogenetic protein or demineralized bone matrix in a critical sized defect model using GFP reporter mice

We evaluated the osteoprogenitor response to rhBMP-2 and DBM in a transgenic mouse critical sized defect. The mice expressed Col3.6GFPtopaz (a pre-osteoblastic marker), Col2.3GFPemerald (an osteoblastic marker) and α-smooth muscle actin (α-SMA-Cherry, a pericyte/myofibroblast marker). We assessed defect healing at various time points using radiographs, frozen, and conventional histologic analyses. GFP signal in regions of interest corresponding to the areas of new bone formation was quantified using a novel computer assisted algorithm. All defects treated with rhBMP-2 healed. In contrast, the majority of the defects in the DBM (27/30) and control (28/30) groups did not heal. Quantitation of pre-osteoblasts demonstrated a maximal response (% GFP + cells/TV) in the Col3.6GFPtopaz mice at day 7 (7.2% ± 6.0, p < 0.05 compared to days 14, 21, 28, and 56). The maximal response of the Col2.3GFP cells was seen at days 14 (8.04% ± 5.0) and 21 (8.31% ± 4.32), p < 0.05. In contrast, DBM and control groups showed a limited osteogenic response at all time points. In conclusion, we demonstrated that the BMP and DBM induce vastly different osteogenic responses which should influence their clinical application as bone graft substitutes.