Search for: All records

Abstract ObjectiveFluid shear stress is thought to be a regulator of endothelial cell behavior during angiogenesis. The link, however, requires an understanding of stress values at the capillary level in angiogenic microvascular networks. Critical questions remain. What are the stresses? Do capillaries experience similar stress magnitudes? Can variations explain vessel‐specific behavior? The objective of this study was to estimate segment‐specific shear stresses in angiogenic networks. MethodsImages of angiogenic networks characterized by increased vascular density were obtained from rat mesenteric tissues stimulated by compound 48/80‐induced mast cell degranulation. Vessels were identified by perfusion of a 40 kDa fixable dextran prior to harvesting and immunolabeling for PECAM. Using a network flow‐based segment model with physiologically relevant parameters, stresses were computed per vessel for regions across multiple networks. ResultsStresses ranged from 0.003 to 2328.1 dyne/cm²and varied dramatically at the capillary level. For all regions, the maximum segmental shear stresses were for capillary segments. Stresses along proximal capillaries branching from arteriole inlets were increased compared to stresses along capillaries in more distal regions. ConclusionsThe results highlight the variability of shear stresses along angiogenic capillaries and motivate new discussions on how endothelial cells may respond in vivo to segment‐specific microenvironment during angiogenesis. 

Various biomacromolecule components of extracellular matrix (ECM) link together to form a structurally stable composite. Monitoring of such matrix microstructure can be very important in studying structure-associated cellular processes, improving cellular function, and ensuring sufficient mechanical integrity in engineered tissues. This paper describes a novel method to study microscale alignment of matrix in engineered tissue scaffolds (ETS) that were usually composed of a variety of biomacromolecules derived by cells. as the organization of overall biomacromolecule network has been seldomly examined. First, a trained loading function was derived from Raman spectra of highly aligned native tissue via PCA, where prominent changes associated with Raman bands (e.g., 1444, 1465, 1605, 1627-1660 and 1665-1689 cm−1) were detected with respect to the polarized angle. These changes were mainly caused by the aligned matrix of many compounds within the tissue relative to the laser polarization, including proteins, lipids and carbohydrates. Hence this trained function was applied to quantify the alignment within ETS of various matrix components derived by cells. A simple metric called Amplitude Alignment Metric was derived to correlate the orientation dependence of polarized Raman spectra of ETS to the degree of matrix alignment. By acquiring polarized Raman spectra of ETS at micrometer regions, the Amplitude Alignment Metric was significantly higher in anisotropic ETS than isotropic ones. The PRS method showed a lower p-value for distinguishing the alignment between the two types of ETS as compared to the microscopic method for detecting fluorescently labeled protein matrices at similar microscopic scale. These results indicate the anisotropy of complex matrix in engineered tissue can be assessed at microscopic scale using a PRS-based simple metric, superior to traditional microscopic method. This PRS-based method can serve as a complementary tool for the design and assessment of engineered tissues that mimic the native matrix organizational microstructures.