Experimental investigation of collagen waviness and orientation in the arterial adventitia using confocal laser scanning microscopy

Mechanical properties of the adventitia are largely determined by the organization of collagen fibers. Measurements on the waviness and orientation of collagen, particularly at the zero-stress state, are necessary to relate the structural organization of collagen to the mechanical response of the adventitia. Using the fluorescence collagen marker CNA38-OG488 and confocal laser scanning microscopy, we imaged collagen fibers in the adventitia of rabbit common carotid arteries ex vivo. The arteries were cut open along their longitudinal axes to get the zero-stress state. We used semi-manual and automatic techniques to measure parameters related to the waviness and orientation of fibers. Our results showed that the straightness parameter (defined as the ratio between the distances of endpoints of a fiber to its length) was distributed with a beta distribution (mean value 0.72, variance 0.028) and did not depend on the mean angle orientation of fibers. Local angular density distributions revealed four axially symmetric families of fibers with mean directions of 0°, 90°, 43° and ?43°, with respect to the axial direction of the artery, and corresponding circular standard deviations of 40°, 47°, 37° and 37°. The distribution of local orientations was shifted to the circumferential direction when measured in arteries at the zero-load state (intact), as compared to arteries at the zero-stress state (cut-open). Information on collagen fiber waviness and orientation, such as obtained in this study, could be used to develop structural models of the adventitia, providing better means for analyzing and understanding the mechanical properties of vascular wall.     

Evaluation of a Continuous Quantification Method of Apoptosis and Necrosis in Tissue Cultures

In tissue-engineering and other life sciences, there is a growing need for real-time, non-destructive information on apoptosis and necrosis in 2D and 3D tissue cultures. Previously, propidium iodide was applied as a fluorescent marker for monitoring necrosis. In the current study this technique was extended with a fluorescent apoptosis marker, YO-PRO-1, to discriminate between both stages of cell death. The main goal was to evaluate the performance of YO-PRO-1 and propidium iodide during monitoring periods of up to 3 days. Apoptosis was induced in C2C12 cultures and the numbers of YP-positive and PI-positive nuclei were counted in time. The performance of the dual staining was evaluated with a metabolic measure and a probe intensity study. Cell metabolism was unaffected during the first 24 h of testing. In conclusion, the YP/PI dual staining method was found to be a powerful tool in obtaining real-time spatial information on viability in cell and tissue culture without culture disruption.