Bioprinting of pre-vascularized constructs for enhancedin vivoneo-vascularization.

Pre-vascularization has been receiving significant attention for developing implantable engineered 3D tissues. While various pre-vascularization techniques have been developed to improve graft vascularization, the effect of pre-vascularized patterns onin vivoneo-vessel formation has not been studied. In this study, we developed a functional pre-vascularized construct that significantly promotes graft vascularization and conductedin vivoevaluations of the micro-vascular patterns (µVPs) in various printed designs.µVP formation, composed of high-density capillaries, was induced by the co-printing of endothelial cells and adipose-derived stem cells (ADSC). We implanted the printed constructs with variousµVP designs into a murine femoral arteriovenous bundle model and evaluated graft vascularization via 3D visualization and immune-histological analysis of the neo-vessels. TheµVP-distal group (µVP located away from the host vessel) showed approximately two-fold improved neo-vascularization compared to theµVP-proximal group (µVP located near the host vessel). Additionally, we confirmed that theµVP-distal group can generate the angiogenic factor gradient spatial environment for graft vascularization via computational simulations. Based on these results, the ADSC mono pattern (AMP), which secretes four times higher angiogenic factors thanµVP, was added to theµVP + AMP group design. TheµVP + AMP group showed approximately 1.5- and 1.9-fold higher total sprouted neo-vessel volume than theµVP only and AMP only groups, respectively. In immunohistochemical staining analysis, theµVP + AMP group showed two-fold improved density and diameter of the matured neo-vessels. To summarize, these findings demonstrate graft vascularization accelerated due to design optimization of our pre-vascularized constructs. We believe that the developed pre-vascularization printing technique will facilitate new possibilities for the upscaling of implantable engineered tissues/organs.

Blockade of Activin Receptor IIB Protects Arthritis Pathogenesis by Non-Amplification of Activin A-ACVR2B-NOX4 Axis Pathway.

Although activin receptor IIB (ACVR2B) is emerging as a novel pathogenic receptor, its ligand and assembled components (or assembly) are totally unknown in the context of osteoarthritis (OA) pathogenesis. The present results suggest that upregulation of ACVR2B and its assembly could affect osteoarthritic cartilage destruction. It is shown that the ACVR2B ligand, activin A, regulates catabolic factor expression through ACVR2B in OA development. Activin A Tg mice (Col2a1-Inhba) exhibit enhanced cartilage destruction, whereas heterozygous activin A KO mice (Inhba+/- ) show protection from cartilage destruction. In silico analysis suggests that the Activin A-ACVR2B axis is involved in Nox4-dependent ROS production. Activin A Tg:Nox4 KO (Col2a1-Inhba:Nox4-/- ) mice show inhibition of experimental OA pathogenesis. NOX4 directly binds to the C-terminal binding site on ACVR2B-ACVR1B and amplifies the pathogenic signal for cartilage destruction through SMAD2/3 signaling. Together, the findings reveal that the ACVR2B assembly, which comprises Activin A, ACVR2B, ACVR1B, Nox4, and AP-1-induced HIF-2α, accelerates OA development. Furthermore, it is shown that shRNA-mediated ACVR2B knockdown or trapping ligands of ACVR2B abrogate OA development by competitively disrupting the ACVR2B-Activin A interaction. These results suggest that the ACVR2B assembly is required to amplify osteoarthritic cartilage destruction and could be a potential therapeutic target in efforts to treat OA.

Spiral scanning imaging and quantitative calculation of the 3-dimensional screw-shaped bone-implant interface on micro-computed tomography.

PURPOSE: Bone-to-implant contact (BIC) is difficult to measure on micro-computed tomography (CT) because of artifacts that hinder accurate differentiation of the bone and implant. This study presents an advanced algorithm for measuring BIC in micro-CT acquisitions using a spiral scanning technique, with improved differentiation of bone and implant materials. METHODS: Five sandblasted, large-grit, acid-etched implants were used. Three implants were subjected to surface analysis, and 2 were inserted into a New Zealand white rabbit, with each tibia receiving 1 implant. The rabbit was sacrificed after 28 days. The en bloc specimens were subjected to spiral (SkyScan 1275, Bruker) and round (SkyScan 1172, SkyScan 1275) micro-CT scanning to evaluate differences in the images resulting from the different scanning techniques. The partial volume effect (PVE) was optimized as much as possible. BIC was measured with both round and spiral scanning on the SkyScan 1275, and the results were compared. RESULTS: Compared with the round micro-CT scanning, the spiral scanning showed much clearer images. In addition, the PVE was optimized, which allowed accurate BIC measurements to be made. Round scanning on the SkyScan 1275 resulted in higher BIC measurements than spiral scanning on the same machine; however, the higher measurements on round scanning were confirmed to be false, and were found to be the result of artifacts in the void, rather than bone. CONCLUSIONS: The results of this study indicate that spiral scanning can reduce metal artifacts, thereby allowing clear differentiation of bone and implant. Moreover, the PVE, which is a factor that inevitably hinders accurate BIC measurements, was optimized through an advanced algorithm.