An Efficient and Reproducible Protocol for Distraction Osteogenesis in a Rat Model Leading to a Functional Regenerated Femur

Mechanical Characterization at the Microscale of Mineralized Bone Callus after Bone Lengthening

Distraction osteogenesis (DO) involves several processes to form an organized distracted callus. While bone regeneration during DO has been widely described, no study has yet focused on the evolution profile of mechanical properties of mineralized tissues in the distracted callus. The aim of this study was therefore to measure the elastic modulus and hardness of calcified cartilage and trabecular and cortical bone within the distracted callus during the consolidation phase. We used a microindentation assay to measure the mechanical properties of periosteal and endosteal calluses; each was subdivided into two regions. Histological sections were used to localize the tissues. The results revealed that the mechanical properties of calcified cartilage did not evolve over time. However, trabecular bone showed temporal variation. For elastic modulus, in three out of four regions, a similar evolution profile was observed with an increase and decrease over time. Concerning hardness, this evolves differently depending on the location in the distracted callus. We also observed spatial changes in between regions. A first duality was apparent between regions close to the native cortices and the central area, while latter differences were seen between periosteal and endosteal calluses. Data showed a heterogeneity of mechanical properties in the distracted callus with a specific mineralization profile.

Experimental Modeling of Combined and Sequential Use of Transosseous and Intramedullary Blocking Osteosynthesis

Background. The introduction of the combined and sequential application of transosseous and intramedullary blocked osteosynthesis in limb lengthening requires an experimental study of the features of distraction regenerate. For small animals (in particular rabbits), special models are required.

Aims. To develop experimental models of sequential and combined use of transosseous and intramedullary osteosynthesis in limb lengthening and substantiate their effectiveness.

Materials and methods. A comparative study was carried out on 30 rabbits of the Soviet Chinchilla breed. Experimental models of sequential (EM-1) and combined (EM-2) application of transosseous and intramedullary osteosynthesis with preservation of the apparatus during the fixation period to simulate blockage were studied in the main groups. For comparison, sequential (comparison model 1 – CM-1) and combined (comparison model 2 – CM-2) use of transosseous and intramedullary osteosynthesis with dismantling of the apparatus at the end of distraction were modeled. The control was a regenerate formed according to the classical Ilizarov method. Radiographs were performed in dynamics, CT and morphological studies – at the end of the fixation period.

Results. It was noted that regenerates of the same type in structure were formed in the EM-1 and CM-1 groups, as in the EM-2 and CM-2 groups. With successive methods, the spindle-shaped form of the regenerate prevailed, the formation of a pronounced periosteal component was noted. Powerful cortical plates, according to morphological studies, are formed from the periosteal and intermediate zones. With combined techniques, the cortical plates are formed thinner and predominantly from the periosteal component, the shape of the regenerate is closer to fusiform. In the comparison groups, the total time of surgical interventions was 25–50 % longer, in 50 % of cases there was a loss of length or deformation of the regenerate.

Conclusions. The developed models of sequential and combined use of transosseous and intramedullary osteosynthesis for limb lengthening with preservation of fixation with an apparatus to simulate blocking have proven to be reliable in terms of fixation and easy to use on small laboratory animals.. 

Systemic Administration of G-CSF Accelerates Bone Regeneration and Modulates Mobilization of Progenitor Cells in a Rat Model of Distraction Osteogenesis

Granulocyte colony-stimulating factor (G-CSF) was shown to promote bone regeneration and mobilization of vascular and osteogenic progenitor cells. In this study, we investigated the effects of a systemic low dose of G-CSF on both bone consolidation and mobilization of hematopoietic stem/progenitor cells (HSPCs), endothelial progenitor cells (EPCs) and mesenchymal stromal cells (MSCs) in a rat model of distraction osteogenesis (DO). Neovascularization and mineralization were longitudinally monitored using positron emission tomography and planar scintigraphy. Histological analysis was performed and the number of circulating HSPCs, EPCs and MSCs was studied by flow cytometry. Contrary to control group, in the early phase of consolidation, a bony bridge with lower osteoclast activity and a trend of an increase in osteoblast activity were observed in the distracted callus in the G-CSF group, whereas, at the late phase of consolidation, a significantly lower neovascularization was observed. While no difference was observed in the number of circulating EPCs between control and G-CSF groups, the number of MSCs was significantly lower at the end of the latency phase and that of HSPCs was significantly higher 4 days after the bone lengthening. Our results indicate that G-CSF accelerates bone regeneration and modulates mobilization of progenitor cells during DO.

Comprehensive In Vitro Testing of Calcium Phosphate-Based Bioceramics with Orthopedic and Dentistry Applications

Recently, a large spectrum of biomaterials emerged, with emphasis on various pure, blended, or doped calcium phosphates (CaPs). Although basic cytocompatibility testing protocols are referred by International Organization for Standardization (ISO) 10993 (parts 1-22), rigorous in vitro testing using cutting-edge technologies should be carried out in order to fully understand the behavior of various biomaterials (whether in bulk or low-dimensional object form) and to better gauge their outcome when implanted. In this review, current molecular techniques are assessed for the in-depth characterization of angiogenic potential, osteogenic capability, and the modulation of oxidative stress and inflammation properties of CaPs and their cation- and/or anion-substituted derivatives. Using such techniques, mechanisms of action of these compounds can be deciphered, highlighting the signaling pathway activation, cross-talk, and modulation by microRNA expression, which in turn can safely pave the road toward a better filtering of the truly functional, application-ready innovative therapeutic bioceramic-based solutions.