Biomaterials developed to treat bone defects have classically focused on bone healing via direct, intramembranous ossification. In contrast, most bones in our body develop from a cartilage template via a second pathway called endochondral ossification. The unsolved clinical challenge to regenerate large bone defects has brought endochondral ossification into discussion as an alternative approach for bone healing. However, a biomaterial strategy for the regeneration of large bone defects via endochondral ossification is missing. Here we report on a biomaterial with a channel-like pore architecture to control cell recruitment and tissue patterning in the early phase of healing. In consequence of extracellular matrix alignment, CD146+ progenitor cell accumulation and restrained vascularization, a highly organized endochondral ossification process is induced in rats. Our findings demonstrate that a pure biomaterial approach has the potential to recapitulate a developmental bone growth process for bone healing. This might motivate future strategies for biomaterial-based tissue regeneration.
Wound contraction is an ancient survival mechanism of vertebrates that results from tensile forces supporting wound closure. So far, tissue tension was attributed to cellular forces produced by tissue‐resident (myo‐)fibroblasts alone. However, difficulties in explaining pathological deviations from a successful healing path motivate the exploration of additional modulatory factors. Here, it is shown in a biomaterial‐based in vitro wound healing model that the storage of tensile forces in the extracellular matrix has a significant, so‐far neglected contribution to macroscopic tissue tension. In situ monitoring of tissue forces together with second harmonic imaging reveal that the appearance of collagen fibrils correlates with tissue contraction, indicating a mechanical contribution of tensioned collagen fibrils in the contraction process. As the re‐establishment of tissue tension is key to successful wound healing, the findings are expected to advance the understanding of tissue healing but also underlying principles of misregulation and impaired functionality in scars and tissue contractures.
Mechanical boundary conditions critically influence the bone healing process. In this context, previous in vitro studies have demonstrated that cyclic mechanical compression alters migration and triggers osteogenesis of mesenchymal stromal cells (MSC), both processes being relevant to healing. However, it remains unclear whether this mechanosensitivity is a direct consequence of cyclic compression, an indirect effect of altered supply or a specific modulation of autocrine bone morphogenetic protein (BMP) signaling. Here, we investigate the influence of cyclic mechanical compression (ε = 5% and 10%, f = 1 Hz) on human bone marrow MSC (hBMSC) migration and osteogenic differentiation in a 3D biomaterial scaffold, an in vitro system mimicking the mechanical environment of the early bone healing phase. The open-porous architecture of the scaffold ensured sufficient supply even without cyclic compression, minimizing load-associated supply alterations. Furthermore, a large culture medium volume in relation to the cell number diminished autocrine signaling. Migration of hBMSCs was significantly downregulated under cyclic compression. Surprisingly, a decrease in migration was not associated with increased osteogenic differentiation of hBMSCs, as the expression of RUNX2 and osteocalcin decreased. In contrast, BMP2 expression was significantly upregulated. Enabling autocrine stimulation by increasing the cell-to-medium ratio in the bioreactor finally resulted in a significant upregulation of RUNX2 in response to cyclic compression, which could be reversed by rhNoggin treatment. The results indicate that osteogenesis is promoted by cyclic compression when cells condition their environment with BMP.Our findings highlight the importance of mutual interactions between mechanical forces and BMP signaling in controlling osteogenic differentiation.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Our findings support the new concept that occludin acts as a hypoxiasensor and contributes toward regulating the TJ assembly redox dependently. This is of pathogenic relevance for tissue barrier injury with reducing conditions. The ECL2 disulfide might be a model for four TMD proteins in TJs with two conserved cysteines in an ECL.
Yes-associated protein (YAP) acts as a mechanotransducer in determining the cell fate of murine C2C12 mesenchymal precursors as investigated after stimulation with ultrasound. We applied Focused Low-Intensity Pulsed Ultrasound (FLIPUS) at a sound frequency of 3.6 MHz, 100 Hz pulse repetition frequency (PRF), 27.8% duty cycle (DC), and 44.5 mW/cm2 acoustic intensity ISATA for 5 minutes and evaluated early cellular responses. FLIPUS decreased the level of phosphorylated YAP on Serine 127, leading to higher levels of active YAP in the nucleus. This in turn enhanced the expression of YAP-target genes associated with actin nucleation and stabilization, cytokinesis, and cell cycle progression. FLIPUS enhanced proliferation of C2C12 cells, whereas silencing of YAP expression abolished the beneficial effects of ultrasound. The expression of the transcription factor MyoD, defining cellular myogenic differentiation, was inhibited by mechanical stimulation. This study shows that ultrasound exposure regulates YAP functioning, which in turn improves the cell proliferative potential, critical for tissue regeneration process.
Successful fracture healing requires a tight interplay between mechanical and biological cues. In vitro studies illustrated that mechanical loading modulates bone morphogenetic protein (BMP) signaling. However, in the early phases of large bone defect regeneration in vivo, the underlying mechanisms leading to this mechanosensation remained unknown. We investigated the interaction of BMP2 stimulation and mechanical boundary conditions in a rat critical‐sized femoral defect model (5 mm) stabilized with three distinctly different external fixator stiffness. Defects were treated with 5 μg rhBMP2 loaded on an absorbable collagen sponge. Early matrix alignment was monitored by second‐harmonic generation imaging. Bony bridging of defects and successive healing was monitored by histology at day 7 and day 14 as well as in vivo microCT at days 10, 21, and 42 post‐operation. Femora harvested at day 42 were characterized mechanically assessing torsional load to failure ex vivo. At tissue level, differences between groups were visible at day 14 with manifest bone formation in the microCT. Histologically, we observed prolonged chondrogenesis upon flexible fixation, whereas osteogenesis started earlier after rigid and semirigid fixation. At later time points, there was a boost of bone tissue formation upon flexible fixation, whereas other groups already displayed signs of tissue maturation. Based on gene expression profiling, we analyzed the mechanobiological interplay. Already at day 3, these analyses revealed differences in expression pattern, specifically of genes involved in extracellular matrix formation. Gene regulation correlating with fixator stiffness was pronounced at day 7 comprising genes related to immunological processes and cellular contraction. The influence of loading on matrix contraction was further investigated and confirmed in a 3D bioreactor. Taken together, we demonstrate an early onset of mechanical conditions influencing BMP2‐induced defect healing and shed light on gene regulatory networks associated with extracellular matrix organization and contraction that seemed to directly impact healing outcomes. © 2018 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.