The Induced Membrane Technique—The Filling Matters: Evaluation of Different Forms of Membrane Filling with and without Bone Marrow Mononuclear Cells (BMC) in Large Femoral Bone Defects in Rats

Targeting micromotion for mimicking natural bone healing by using NIPAM/Nb2C hydrogel

Natural fracture healing is most efficient when the fine-tuned mechanical force and proper micromotion are applied. To mimick this micromotion at the fracture gap, a near-infrared-II (NIR-II)-activated hydrogel was fabricated by integrating two-dimensional (2D) monolayer Nb2C nanosheets into a thermally responsive poly(N-isopropylacrylamide) (NIPAM) hydrogel system. NIR-II-triggered deformation of the NIPAM/Nb2C hydrogel was designed to generate precise micromotion for co-culturing cells. It was validated that micromotion at 1/300 Hz, triggering a 2.37-fold change in the cell length/diameter ratio, is the most favorable condition for the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Moreover, mRNA sequencing and verification revealed that micromotion-induced augmentation was mediated by Piezo1 activation. Suppression of Piezo1 interrupts the mechano-sensitivity and abrogates osteogenic differentiation. Calvarial and femoral shaft defect models were established to explore the biocompatibility and osteoinductivity of the Micromotion Biomaterial. A series of research methods, including radiography, micro-CT scanning, and immunohistochemical staining have been performed to evaluate biosafety and osteogenic efficacy. The in vivo results revealed that tunable micromotion strengthens the natural fracture healing process through the sequential activation of endochondral ossification, promotion of neovascularization, initiation of mineral deposition, and combinatory acceleration of full-thickness osseous regeneration. This study demonstrated that Micromotion Biomaterials with controllable mechanophysical characteristics could promote the osteogenic differentiation of BMSCs and facilitate full osseous regeneration. The design of NIPAM/Nb2C hydrogel with highly efficient photothermal conversion, specific features of precisely controlled micromotion, and bionic-mimicking bone-repair capabilities could spark a new era in the field of regenerative medicine.

Systematic literature review of in vivo rat femoral defect models using biomaterials to improve the induced membrane technique: a comprehensive analysis

Purpose

The aim of this study was to conduct a systematic literature review analyzing the results of in vivo rat femoral defect models using biomaterials for improving the induced membrane technique (IMT).

Methods

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, the PubMed, Embase, and Web of Science databases were searched. Inclusion criteria were studies reporting results of the IMT in in vivo rat femoral critical-sized defect models using a biomaterial possibly combined with molecules. Methodologic quality was assessed with the Animal Research: Reporting In Vivo Experiments guidelines.

Results

Twenty studies met the inclusion criteria. Femoral stabilization with plate and screws was the most frequent. Histologic, biomechanical, and/or radiologic analyses were performed. In two-stage strategies, the PMMA spacer could be associated with bioactive molecules to enhance IM growth factor expression and improve bone formation. Modulating the roughness of spacers could increase IM thickness and accelerate its formation. In one-stage strategies, human tissue-derived membranes combined with bone grafting achieved bone formation comparable to a standard IMT. All calcium phosphate grafts seemed to require a functionalization with growth factors or bone marrow mononuclear cells to improve outcomes compared with non-functionalized grafts.

Conclusion

This systematic review described the main parameters of the in vivo rat femoral defect models using biomaterials to improve the induced membrane technique. Although the studies included had several methodological limitations that may limit the scope of these conclusions, one- and two-stage strategies reported promising results with biomaterials to improve the IMT.

Measuring Bone Healing: Parameters and Scores in Comparison

(1) Background: Bone healing is a complex process that can not be replicated in its entirety in vitro. Research on bone healing still requires the animal model. The critical size femur defect (CSFD) in rats is a well-established model for fractures in humans that exceed the self-healing potential. New therapeutic approaches can be tested here in vivo. Histological, biomechanical, and radiological parameters are usually collected and interpreted. However, it is not yet clear to what extent they correlate with each other and how necessary it is to record all parameters. (2) Methods: The basis for this study was data from three animal model studies evaluating bone healing. The µCT and histological (Movat pentachrome, osteocalcin) datasets/images were reevaluated and correlation analyses were then performed. Two image processing procedures were compared in the analysis of the image data. (3) Results: There was a significant correlation between the histologically determined bone fraction (Movat pentachrome staining) and bending stiffness. Bone fraction determined by osteocalcin showed no prognostic value. (4) Conclusions: The evaluation of the image datasets using ImageJ is sufficient and simpler than the combination of both programs. Determination of the bone fraction using Movat pentachrome staining allows conclusions to be drawn about the biomechanics of the bone. A standardized procedure with the ImageJ software is recommended for determining the bone proportion.

One Stage Masquelets Technique: Evaluation of Different Forms of Membrane Filling with and without Bone Marrow Mononuclear Cells (BMC) in Large Femoral Bone Defects in Rats

The classic two-stage masquelet technique is an effective procedure for the treatment of large bone defects. Our group recently showed that one surgery could be saved by using a decellularized dermis membrane (DCD, Epiflex, DIZG). In addition, studies with bone substitute materials for defect filling show that it also appears possible to dispense with the removal of syngeneic cancellous bone (SCB), which is fraught with complications. The focus of this work was to clarify whether the SCB can be replaced by the granular demineralized bone matrix (g-DBM) or fibrous demineralized bone matrix (f-DBM) demineralized bone matrix and whether the colonization of the DCD and/or the DBM defect filling with bone marrow mononuclear cells (BMC) can lead to improved bone healing. In 100 Sprague Dawley rats, a critical femoral bone defect 5 mm in length was stabilized with a plate and then encased in DCD. Subsequently, the defect was filled with SCB (control), g-DBM, or f-DBM, with or without BMC. After 8 weeks, the femurs were harvested and subjected to histological, radiological, and biomechanical analysis. The analyses showed the incipient bony bridging of the defect zone in both groups for g-DBM and f-DBM. Stability and bone formation were not affected compared to the control group. The addition of BMCs showed no further improvement in bone healing. In conclusion, DBM offers a new perspective on defect filling; however, the addition of BMC did not lead to better results.