基质囊泡及其在骨矿化过程中的作用

基质囊泡(Matrix vesicles,MVs)是骨矿物初始形核生长的场所。骨矿化过程中,钙、磷酸根等离子经通道蛋白跨膜运输进入MVs内,当局部浓度达到一定值时,磷酸钙晶体开始沉积。磷酸钙的存在形态包括无定形磷酸钙、磷酸八钙及羟基磷灰石等。MVs可以调节细胞内外基质中的钙和磷酸根离子的稳态及无机磷酸盐/无机焦磷酸盐的比值,提供磷酸钙晶体成核位点,在骨矿化的初始启动过程中发挥重要作用。本文概述了MVs的生物来源、分子组分、提取方法,MVs介导的骨矿化过程,以及近年来利用囊泡作为体外矿化模型模拟MVs矿化过程的研究进展。     

Bioactive-Tissue-Derived Nanocomposite Hydrogel for Permanent Arterial Embolization and Enhanced Vascular Healing

Transcatheter embolization is a minimally invasive procedure that uses embolic agents to intentionally block diseased or injured blood vessels for therapeutic purposes. Embolic agents in clinical practice are limited by recanalization, risk of non-target embolization, failure in coagulopathic patients, high cost, and toxicity. Here, a decellularized cardiac extracellular matrix (ECM)-based nanocomposite hydrogel is developed to provide superior mechanical stability, catheter injectability, retrievability, antibacterial properties, and biological activity to prevent recanalization. The embolic efficacy of the shear-thinning ECM-based hydrogel is shown in a porcine survival model of embolization in the iliac artery and the renal artery. The ECM-based hydrogel promotes arterial vessel wall remodeling and a fibroinflammatory response while undergoing significant biodegradation such that only 25% of the embolic material remains at 14 days. With its unprecedented proregenerative, antibacterial properties coupled with favorable mechanical properties, and its superior performance in anticoagulated blood, the ECM-based hydrogel has the potential to be a next-generation biofunctional embolic agent that can successfully treat a wide range of vascular diseases.     

Application of the pack cementation process on SiC/SiC ceramic matrix composites

The potentials and limitations of a halide-activated pack cementation process on SiC/SiC Ceramic Matrix Composites for the development of bond coats as part of environmental barrier coating (EBCs) systems were investigated. Different pack compositions using chromium, aluminum and alloys of these elements were tested and the kinetics of coating formation were examined in addition to their microstructure. The results and their analogy to diffusion couples were discussed and it was shown that coating elements which form silicides and carbides are promising candidates for coatings deposited on SiC/SiC via pack cementation. Based on such considerations a two-step pack cementation was proposed, which used chromium, one of the suitable elements, in a first step, to finally achieve an alumina-forming coating. The oxidation resistance of the developed coating was tested via thermogravimetric analysis and compared to the uncoated material. The coating protected the fiber-matrix interface of the SiC/SiC Ceramic Matrix Composites from oxidation.     

Environmental effects on the strength and impact damage resistance of alumina based oxide/oxide ceramic matrix composites

In this study the effects of high temperature and moisture on the impact damage resistance and mechanical strength of Nextel 610/alumina silicate ceramic matrix composites were experimentally evaluated. Composite laminates were exposed to either a 1050°C isothermal furnace-based environment for 30 consecutive days at 6 h a day, or 95% relative humidity environment for 13 consecutive days at 67°C. Low velocity impact, tensile and short beam strength tests were performed on both ambient and environmentally conditioned laminates and damage was characterized using a combination of non-destructive and destructive techniques. High temperature and humidity environmental exposure adversely affected the impact resistance of the composite laminates. For all the environments, planar internal damage area was greater than the back side dent area, which in turn was greater than the impactor side dent area. Evidence of environmental embrittlement through a stiffer tensile response was noted for the high temperature exposed laminates while the short beam strength tests showed greater propensity for interlaminar shear failure in the moisture exposed laminates. Destructive evaluations exposed larger, more pronounced delaminations in the environmentally conditioned laminates in comparison to the ambient ones. External damage metrics of the impactor side dent depth and area directly influenced the post-impact tensile strength of the laminates while no such trend between internal damage area and residual strength could be ascertained.     

TGFβ-1 Induced Cross-Linking of the Extracellular Matrix of Primary Human Dermal Fibroblasts

Excessive cross-linking is a major factor in the resistance to the remodelling of the extracellular matrix (ECM) during fibrotic progression. The role of TGFβ signalling in impairing ECM remodelling has been demonstrated in various fibrotic models. We hypothesised that increased ECM cross-linking by TGFβ contributes to skin fibrosis in Systemic Sclerosis (SSc). Proteomics was used to identify cross-linking enzymes in the ECM of primary human dermal fibroblasts, and to compare their levels following treatment with TGFβ-1. A significant upregulation and enrichment of lysyl-oxidase-like 1, 2 and 4 and transglutaminase 2 were found. Western blotting confirmed the upregulation of lysyl hydroxylase 2 in the ECM. Increased transglutaminase activity in TGFβ-1 treated ECM was revealed from a cell-based assay. We employed a mass spectrometry-based method to identify alterations in the ECM cross-linking pattern caused by TGFβ-1. Cross-linking sites were identified in collagens I and V, fibrinogen and fibronectin. One cross-linking site in fibrinogen alpha was found only in TGFβ-treated samples. In conclusion, we have mapped novel cross-links between ECM proteins and demonstrated that activation of TGFβ signalling in cultured dermal fibroblasts upregulates multiple cross-linking enzymes in the ECM.     

A microfluidic approach for development of hybrid collagen-chitosan extracellular matrix-like membranes for on-chip cell cultures

To advance organ-on-a-chip development and other areas befitting from physiologically-relevant biomembranes,a microfluidic platform is presented for synthesis of biomembranes during gelation and investigation into their role as extracellular matrix supports.In this work,high-throughput studies of collagen,chitosan,and collagen-chitosan hybrid biomembranes were carried out to characterize and compare key properties as a function of the applied hydrodynamic conditions during gelation.Specifically,depending on the biopolymer material used,varying flow conditions during biomembrane gelation caused width,uniformity,and swelling ratio to be differently affected and controllable.Finally,cell viability studies of seeded fibroblasts were conducted,thus showing the potential for biological applications.     

Leader-following consensus of fractional-order multi-agent systems via adaptive control

This article focuses on the consensus problem of leader-following fractional-order multi-agent systems (MASs) with general linear and Lipschitz nonlinear dynamics. First, the distributed adaptive protocols for linear and nonlinear fractional-order MASs are constructed, respectively. We allow the control coupling gains to be time varying for each agent. Moreover, the adaptive modification schemes for the control gain are designed, which renders smaller control gains and thus requires smaller amplitude on the control input without sacrificing consensus convergence. Second, based on fractional-order Lyapunov stability theorem and Barbalat's lemma, two novel sufficient conditions in terms of linear matrix inequalities are provided to ensure that the leader-following consensus can be obtained in the case for any undirected connected communication graph. Furthermore, we show that the proposed algorithm also works for consensus of agents with intrinsic Lipschitz nonlinear dynamics. As a result, the proposed framework requires no global information and thus can be implemented in a fully distributed manner. Finally, the numerical simulations are given to demonstrate the effectiveness of obtained the theoretical results.     

Sintering Mechanism and Microstructure of TaC/SiC Composites Consolidated by plasma-activated sintering

TaC/SiC composites with 5 wt% SiC addition were densified by plasma-activated sintering (PAS) at 1500–1800 °C for 5 min under 30 MPa. The effects of plasma-activated sintering on microstructures, densification and mechanical properties of the composites were investigated. The results showed that TaC/SiC composites achieved a relative density more than 99% of the theoretical density at 1600 °C. A low eutectic liquid phase generated by the oxide on the particle surface was observed in the composite to realize a relatively low temperature sintering densification. While the TaC particle size decreased insignificantly with increasing sintering temperature, the transformation of morphology of SiC particles changing from equiaxed to elongated grain was activated, accompanying with a slight particle size decreasing of the SiC phase, thus promoting a relatively high flexural strength of 550 MPa under 1800 °C. Besides, some ultra-fine 2 nm Ta₂Si was observed in the glassy pockets, strengthening the amorphous phase and thus increasing the flexural strength.     

Crack initiation and propagation in braided SiC/SiC composite tubes: Effect of braiding angle

Crack initiation and propagation in three braided SiC/SiC composite tubes with different braiding angles are investigated by in situ tensile tests with synchrotron micro-computed tomography. Crack networks are precisely detected after an image subtraction procedure based on Digital Volume Correlation. FFT based simulations are performed on the full-resolution 3D images to assess elastic stress/strain fields. Quantitative measurements of the crack geometries are performed using a novel method based on grey levels. The results show that braiding angle has no obvious effect on the location of crack onsets (initiation always occurs at tow interfaces), whereas it significantly affects the paths of crack propagation. This work provides an explicit demonstration of the crack propagation scenarios with respect to the mesoscopic fibre architectures.     

Microstructure and mechanical properties of Si3N4f/BN composites with BN interphase prepared by chemical vapor deposition of borazine

The boron nitride (BN) interphase of silicon nitride (Si₃N₄) fiber-reinforced BN matrix (Si₃N_4f/BN) composites was prepared by chemical vapor deposition (CVD) of liquid borazine, and the microstructure, growth kinetics and crystallinity of the BN coating were examined. The effects of coating thickness on the mechanical strength and fiber/matrix interfacial bonding strength of the composites were then investigated. The CVD BN coating plays a key role in weakening the interfacial bonding condition that improves the mechanical properties of the composites. The layering structure of the BN coating promotes crack propagation within the coating, which leads to a variety of toughening mechanisms including crack deflection, fiber bridging and fiber pull out. Single-fiber push-out experiments were performed to quantify the fiber/matrix bonding strength with different coating thicknesses. The physical bonding strength due to thermal mismatch was discussed.