Biofunctionalization of synthetic bone substitutes with angiogenic stem cells: Influence on regeneration of critical-size bone defects in an in vivo murine model

Improving material properties of a poloxamer P407 hydrogel-based hydroxyapatite bone substitute material by adding silica-A comparative in vivo study

The structure and handling properties of a P407 hydrogel-based bone substitute material (BSM) might be affected by different poloxamer P407 and silicon dioxide (SiO2) concentrations. The study aimed to compare the mechanical properties and biological parameters (bone remodeling, BSM degradation) of a hydroxyapatite: silica (HA)-based BSM with various P407 hydrogels in vitro and in an in vivo rat model. Rheological analyses for mechanical properties were performed on one BSM with an SiO2-enriched hydrogel (SPH25) as well on two BSMs with unaltered hydrogels in different gel concentrations (PH25 and PH30). Furthermore, the solubility of all BSMs were tested. In addition, 30 male Wistar rats underwent surgical creation of a well-defined bone defect in the tibia. Defects were filled randomly with PH30 (n = 15) or SPH25 (n = 15). Animals were sacrificed after 12 (n = 5 each), 21 (n = 5 each), and 63 days (n = 5 each). Histological evaluation and histomorphometrical quantification of new bone formation (NB;%), residual BSM (rBSM;%), and soft tissue (ST;%) was conducted. Rheological tests showed an increased viscosity and lower solubility of SPH when compared with the other hydrogels. Histomorphometric analyses in cancellous bone showed a decrease of ST in PH30 (p = .003) and an increase of NB (PH30: p = .001; SPH: p = .014) over time. A comparison of both BSMs revealed no significant differences. The addition of SiO2 to a P407 hydrogel-based hydroxyapatite BSM improves its mechanical stability (viscosity, solubility) while showing similar in vivo healing properties compared to PH30. Additionally, the SiO2-enrichment allows a reduction of poloxamer ratio in the hydrogel without impairing the material properties.

Osteogenic potential of calcium silicate-doped iron oxide nanoparticles versus calcium silicate for reconstruction of critical-sized mandibular defects: An experimental study in dog model

Objective

To evaluate bioactivity and osteogenic potential of calcium silicate (CS)-doped iron oxide (Fe₂O₃) nanoparticles versus pure CS in the reconstruction of induced critical-sized mandibular defects.

Design

CS-doped Fe₂O₃ was prepared; morphological and microstructure identification of nanoparticles were made. An in vivo randomised design was developed on 24 adult male dogs where four critical-sized mandibular defects were created in each dog. Bone defects were allocated into control, CS, CS-3% Fe₂O₃ and CS-10% Fe₂O₃ group. Dogs were euthanized at 1 and 3 months (12 dog/time) for histopathologic and histomorphometric evaluation.

Results

At three months, bone formation and maturation were evident where mean ± SD percent of mature bone was 2.66 ± 1.8, 9.9 ± 2.5, 22.9 ± 4.9, and 38.6 ± 8.1 in control, CS, CS-3% Fe₂O₃, and CS-10% Fe₂O₃ groups respectively. A high significant (P < 0.001) increase in area percent of mature bone was recorded in CS, CS-3% Fe₂O₃, and CS- 10% Fe₂O₃ groups compared to control group (73%, 88% and 93.3% respectively). Significant increase (P < 0.001) in area of mature bone was recorded in CS-3% Fe₂O₃ and CS-10% Fe₂O₃ groups compared to CS group. A significant increase (P < 0.001) in area of mature bone formation was detected in CS-10% Fe₂O₃ group compared to other groups.

Conclusion

CS-doped Fe₂O₃ has good osteoconductive, biocompatible properties with promoted bone regeneration. Fe₂O₃ has synergistic effect in combination with CS to promote bone formation. Increasing concentration of Fe₂O₃ nanoparticles resulted in improved osteogenesis and maturation. Results suggests that the novel CS-Fe₂O₃ alloplasts could be used for reconstruction of critical-sized bone defects.

Bone marrow aspirate concentrate and platelet-rich fibrin in fresh extraction sockets: A histomorphometric and immunohistochemical study in humans

The aim of this study was to evaluate the level of mineralized tissue and expression of bone markers in sockets grafted with platelet-rich fibrin and bone marrow aspirate concentrate (BMAC). Patients requiring extraction of one maxillary anterior tooth were randomized into three groups. After tooth extraction, the sockets in the control group (CG) were permitted to fill with blood clot. In the platelet-rich fibrin group (PRFG), after blood processing, the sockets were grafted with PRF plug. In the bone marrow aspirate concentrate combined with platelet-rich fibrin group (BM/PG), after blood and bone marrow processing, the sockets were grafted with a mixture of PRF plug and BMAC. After 6 months, the sites were reopened and bone cores were harvested and prepared for histomorphometric and immunohistochemical evaluation. The following levels were measured: mineralized tissue, expression of RUNX-2, and osteocalcin. Fifteen patients were included in this study. The histomorphometric analysis showed a more pronounced level of mineralized tissue in PRFG and BM/PG (54.20 ± 4.31% and 64.70 ± 6.74%, respectively) when compared with CG (40.60 ± 5.98%) (p = 0.0283 and p = 0.0090, respectively). The expression of RUNX-2 was very low in BM/PG (0.80 ± 0.84%) and absent in CG and PRFG (p = 0.0528). Osteocalcin expression was higher for BM/PG (23.40 ± 1.52%) when compared with CG and PRFG (18.40 ± 2.07% and 16.20 ± 1.92%, respectively) (p = 0.0117 and p = 0.0088, respectively). This preliminary study indicates that clinical use of bone marrow aspirate concentrate, when combined with platelet-rich fibrin as a carrier, might have some potential to increase mineralization in fresh extraction sockets.

Vascularization Strategies in the Prevention of Nonunion Formation

Delayed healing and nonunion formation are major challenges in orthopedic surgery, which require the development of novel treatment strategies. Vascularization is considered one of the major prerequisites for successful bone healing, providing an adequate nutrient supply and allowing the infiltration of progenitor cells to the fracture site. Hence, during the last decade, a considerable number of studies have focused on the evaluation of vascularization strategies to prevent or to treat nonunion formation. These involve (1) biophysical applications, (2) systemic pharmacological interventions, and (3) tissue engineering, including sophisticated scaffold materials, local growth factor delivery systems, cell-based techniques, and surgical vascularization approaches. Accumulating evidence indicates that in nonunions, these strategies are indeed capable of improving the process of bone healing. The major challenge for the future will now be the translation of these strategies into clinical practice to make them accessible for the majority of patients. If this succeeds, these vascularization strategies may markedly reduce the incidence of nonunion formation. Impact statement Delayed healing and nonunion formation are a major clinical problem in orthopedic surgery. This review provides an overview of vascularization strategies for the prevention and treatment of nonunions. The successful translation of these strategies in clinical practice is of major importance to achieve adequate bone healing.