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The technique bottleneck of repairing large bone defects with tissue engineered bone is the vascularization of tissue engineered grafts. Although some studies have shown that extracellular vesicles (EVs) derived from bone marrow mesenchymal stem cells (BMSCs) promote bone healing and repair by accelerating angiogenesis, the effector molecules and the mechanism remain unclear, which fail to provide ideas for the future research and development of cell-free interventions. Here, we found that Nidogen1-enriched EV (EV-NID1) derived from BMSCs interferes with the formation and assembly of focal adhesions (FAs) by targeting myosin-10, thereby reducing the adhesion strength of rat arterial endothelial cells (RAECs) to the extracellular matrix (ECM), and enhancing the migration and angiogenesis potential of RAECs. Moreover, by delivery with composite hydrogel, EV-NID1 is demonstrated to promote angiogenesis and bone regeneration in rat femoral defects. This study identifies the intracellular binding target of EV-NID1 and further elucidates a novel approach and mechanism, thereby providing a cell-free construction strategy with precise targets for the development of vascularized tissue engineering products.

Our previous studies found that sensory nerve tracts implanted in tissue-engineered bone (TEB) could result in better osteogenesis. To explore the mechanism of the sensory nerve promoting osteogenesis in TEB in vitro, a transwell coculture experiment was designed between dorsal root ganglion (DRG) cells and bone marrow mesenchymal stem cells (BMSCs). BMSC proliferation was determined by CCK8 assay, and osteo-, chondro-, and adipogenic differentiation were assessed by alizarin red, alcian blue, and oil red staining. We found that the proliferation and multipotent differentiation of BMSCs were all enhanced in the coculture group compared to the BMSCs group. Crystal violet staining showed that the clone-forming ability of BMSCs in the coculture group was also enhanced and mRNA levels of Sox2, Nanog, and Oct4 were significantly upregulated in the coculture group. Moreover, the autophagy level of BMSCs, regulating their stemness, was promoted in the coculture group, mediated by the AMPK/mTOR pathway. In addition, AMPK inhibitor compound C could significantly downregulate the protein expression of LC3 and the mRNA level of stemness genes in the coculture group. Finally, we found that the NK1 receptor antagonist, aprepitant, could partly block this effect, which indicated that substance P played an important role in the effect. Together, we conclude that DRG could maintain the stemness of BMSCs by enhancing autophagy through the AMPK/mTOR pathway in a transwell coculture system, which may help explain the better osteogenesis after implantation of the sensory nerve into TEB.

The prevascularization of tissue-engineered bone grafts (TEBGs) has been shown to accelerate capillary vessel ingrowth in bone defect remodeling and to enhance new bone formation. However, the exact mechanisms behind this positive effect remain unknown. Here, we report that basic fibroblast growth factor (FGF2)-Ras homolog gene family member A (RhoA)/Rho-associated protein kinase (ROCK) signaling functions as a molecular switch to regulate the lineage fate of bone mesenchymal stem cells (BMSCs) and that prevascularization promotes the cell fate switch, which contributes to increased bone regeneration with the use of prevascularized TEBGs compared with control TEBGs. Prevascularized TEBGs enhanced the in vivo endothelial differentiation of BMSCs by inhibiting RhoA/ROCK signaling. In vitro data more clearly showed that BMSCs differentiated into von Willebrand factor (vWF)-positive endothelial cells, and FGF2-induced inhibition of RhoA/ROCK signaling played a key role. Our novel findings uncovered a new mechanism that stimulates the increased vascularization of engineered bone and enhanced regeneration by promoting the endothelial differentiation of BMSCs implanted in TEBGs. These results offer a new molecular target to regulate TEBG-induced bone regeneration.

Yue Song,1,* Kaifeng Lin,2,* Shu He,3,* Chunmei Wang,1 Shuaishuai Zhang,1 Donglin Li,1 Jimeng Wang,4 Tianqing Cao,1 Long Bi,1 Guoxian Pei1 1Department of Orthopedics, Xijing Hospital, The Fourth Military Medical University, Xi’an, China; 2Second Department of Orthopedics and Traumatology, Fuzhou General Hospital of Nanjing Military Area Command of Chinese PLA, Fuzhou, China; 3Department of Orthopedics, Xi’an Hong Hui Hospital, Xi’an, China; 4Department of Orthopedics, The 251st Hospital of Chinese PLA, Zhangjiakou, China *These authors contributed equally to this work Background and aim: As a newly emerging three-dimensional (3D) printing technology, low-temperature robocasting can be used to fabricate geometrically complex ceramic scaffolds at low temperatures. Here, we aimed to fabricate 3D printed ceramic scaffolds composed of nano-biphasic calcium phosphate (BCP), polyvinyl alcohol (PVA), and platelet-rich fibrin (PRF) at a low temperature without the addition of toxic chemicals.Methods: Corresponding nonprinted scaffolds were prepared using a freeze-drying method. Compared with the nonprinted scaffolds, the printed scaffolds had specific shapes and well-connected internal structures.Results: The incorporation of PRF enabled both the sustained release of bioactive factors from the scaffolds and improved biocompatibility and biological activity toward bone marrow-derived mesenchymal stem cells (BMSCs) in vitro. Additionally, the printed BCP/PVA/PRF scaffolds promoted significantly better BMSC adhesion, proliferation, and osteogenic differentiation in vitro than the printed BCP/PVA scaffolds. In vivo, the printed BCP/PVA/PRF scaffolds induced a greater extent of appropriate bone formation than the printed BCP/PVA scaffolds and nonprinted scaffolds in a critical-size segmental bone defect model in rabbits.Conclusion: These experiments indicate that low-temperature robocasting could potentially be used to fabricate 3D printed BCP/PVA/PRF scaffolds with desired shapes and internal structures and incorporated bioactive factors to enhance the repair of segmental bone defects. Keywords: three-dimensional printing, nano-biphasic calcium phosphate, polyvinyl alcohol, platelet-rich fibrin, bone substitutes, tissue engineering

CD31hiEmcnhi vessels were a subtype of vessels in the murine skeletal system, with high levels of platelet and endothelial cell adhesion molecule-1 (PECAM-1/CD31) and endomucin (Emcn). They were reported coupling angiogenesis and osteogenesis during bone development. We investigated the distribution of these vessels in rat tibiae and their temporal and spatial distribution during the bone defect repair process to improve our understanding of the importance of these vessels. We confirmed that CD31hiEmcnhi vessels were specially distributed around the trabecular bones near metaphysis and endosteum in rat tibiae. At 3 days post bone injury, CD31hiEmcnhi vessels proliferated and were extensively distributed across the entire repair area. At 7 and 14 days post-injury, these vessels decreased but were specially distributed around the growing trabecular bones near the frontier growth area, suggesting that these vessels support new bone formation. The distribution of CD31hiEmcnhi vessels and the transcriptions of Hif-1α and VEGFA, as well as BMP2 and Osterix decreased at 7 and 14 days post-injury under osteoporotic conditions, in combination with insufficient osteogenesis. Our research is of great significance to help understand the important role of CD31hiEmcnhi vessels in supporting new trabecular bones formation during bone defect repair process.

Let D(G) be the Drinfeld double of a finite group G and D(G;H) be the crossed product of C(G) and CH, where H is a subgroup of G. Then the sets D(G) and D(G;H) can be made C⁎-algebras naturally. Considering the C⁎-basic construction C⁎〈D(G),e〉 from the conditional expectation E of D(G) onto D(G;H), one can construct a crossed product C⁎-algebra C(G/H×G)⋊CG, such that the C⁎-basic construction C⁎〈D(G),e〉 is C⁎-algebra isomorphic to C(G/H×G)⋊CG.

Background Vascularization is one of the most important processes in tissue-engineered bone graft (TEBG)-mediated regeneration of large segmental bone defects. We previously showed that prevascularization of TEBGs promoted capillary vessel formation within the defected site and accelerated new bone formation. However, the precise mechanisms and contribution of endogenous cells were not explored. Methods We established a large defect (5 mm) model in the femur of EGFP+ transgenic rats and implanted a β-tricalcium phosphate (β-TCP) scaffold seeded with exogenous EGFP− cells; the femoral vascular bundle was inserted into the scaffold before implantation in the prevascularized TEBG group. Histopathology and scanning electron microscopy were performed and connective tissue growth factor (CTGF) and fibrin expression, exogenous cell survival, endogenous cell migration and behavior, and collagen type I and III deposition were assessed at 1 and 4 weeks post implantation. Results We found that the fibrinogen content can be increased at the early stage of vascular bundle transplantation, forming a fibrin reticulate structure and tubular connections between pores of β-TCP material, which provides a support for cell attachment and migration. Meanwhile, CTGF expression is increased, and more endogenous cells can be recruited and promote collagen synthesis and angiogenesis. By 4 weeks post implantation, the tubular connections transformed into von Willebrand factor-positive capillary-like structures with deposition of type III collagen, and accelerated angiogenesis of endogenous cells. Conclusions These findings demonstrate that prevascularization promotes the recruitment of endogenous cells and collagen deposition by upregulating fibrinogen and CTGF, directly resulting in new blood vessel formation. In addition, this molecular mechanism can be used to establish fast-acting angiogenesis materials in future clinical applications. Electronic supplementary material The online version of this article (10.1186/s13287-018-0925-y) contains supplementary material, which is available to authorized users.

Massive bone defects are a challenge in orthopaedic research. Defective regeneration leads to bone atrophy, non-union of bone, and physical morbidity. Large animals are important models, however, production costs are high, nursing is complex, and evaluation methods are limited. A suitable laboratory animal model is required to explore the underlying molecular mechanism and cellular process of bone tissue engineering. We designed a stainless steel plate with 8 holes; the middle 2 holes were used as a guide to create a standardized critical size defect in the femur of anaesthetized rats. The plate was fixed to the bone using 6 screws, serving as an inner fixed bracket to secure a tricalcium phosphate implant seeded with green fluorescent protein-positive rat bone marrow mesenchymal stem cells within the defect. In some animals, we also grafted a vessel bundle into the lateral side of the implant, to promote vascularized bone tissue engineering. X-ray, microcomputed tomography, and histological analyses demonstrated the stainless steel plate resulted in a stable large segmental defect model in the rat femur. Vascularization significantly increased bone formation and implant degradation. Moreover, survival and expansion of green fluorescent protein-positive seeded cells could be clearly monitored in vivo at 1, 4, and 8 weeks postoperation via fluorescent microscopy. This standardized large segmental defect model in a small animal may help to advance the study of bone tissue engineering. Furthermore, availability of antibodies and genetically modified rats could help to dissect the precise cellular and molecular mechanisms of bone repair.

Están disponibles los registros digitales obtenidos para uso de los investigadores interesados en estudiar la severidad del terremoto desde el punto de vista instrumental. Se incluyen los acelerogramas obtenidos con equipo Kinemetrics SMA-1 y sus correspondientes integraciones, velocidades y desplazamientos. Se trata de archivos de caracteres ASCII fácilmente legible por medio de diferentes rutinas de análisis de datos. Strong-motion records were recovered from 15 accelerographs at 14 stations operated by the Strong Motion Instrumentation Program of the Earthquake Engineering Laboratory (EEL) at the University of Costa Rica (Santana and others, 1991) following the damaging Limón, Costa Rica earthquake of April 22, 1991. The sites range in epicentral distance from 73 to 160 km; peak horizontal accelerations at ground level ranged from 0.03 to 0.27 g. The accelerograms are characterized by long duration of strong shaking, of approximately 30 seconds. An extensive strong motion data set from a moment magnitude (Mw) 7.5 earthquake is rare. Because of the importance of these data not only to Costa Rica but also to California, the California Strong Motion Instrumentation Program (CSMIP), in cooperation with the University of Costa Rica, digitized and processed these data for distribution to engineers, seismologists and others concerned with the seismic safety problem. This processed data is the second extensive set of data from an earthquake with magnitude between the magnitude 7 Lorna Prieta earthquake and the magnitude 7.8 Chile and Tabas, Iran earthquakes. Universidad de Costa Rica/[]/UCR/Costa Rica UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ingeniería::Instituto Investigaciones en Ingeniería (INII)