Abstract
The collagen architecture is the major determinant of the function and mechanical behavior of cardiovascular tissues. In order to engineer a functional and load-bearing cardiovascular tissue with a structure that mimics the native tissue to meet in vivo mechanical demands, a complete understanding of the collagen orientation mechanism is required. Several methods have been used to visualize collagen architecture in tissue-engineered (TE) constructs, but they either have a limited imaging depth or have a complicated set up. In this study, Diffusion Tensor Imaging (DTI) is explored as a fast and reliable method to visualize collagen arrangement, and Confocal Laser Scanning Microscopy (CLSM) was used as a validation technique. Uniaxially constrained TE strips were cultured for 2 days, 10 days, 3 and 6 weeks to investigate the evolution of the collagen orientation with time. Moreover, a comparison of the collagen orientation in high and low aspect ratio (length/width) TE constructs was made with both methods. Both methods showed similar fiber orientation in TE constructs. Collagen fibers in the high aspect ratio samples were mostly aligned in the constrained direction, while the collagen fibers in low aspect ratio strips were mainly oriented in the oblique direction. The orientation changed to the oblique direction by extending culture time and could also be visualized. DTI captured the collagen orientation differences between low and high aspect ratio samples and with time. Therefore, it can be used as a fast, non-destructive and reliable tool to study the evolution of the collagen orientation in TE constructs.
Highlights
Collagen is a major fibrous protein of the extracellular matrix (ECM)
The fibers were aligned in the constrained direction after 3 weeks (Fig 4D) and by extending the culture time, the fiber orientation changed to oblique in the areas where the compaction in width was accentuated (Fig 4F)
Collagen fibers in low aspect ratio strips were mainly oriented in the oblique direction
Summary
Collagen is a major fibrous protein of the extracellular matrix (ECM) It is the main load-bearing constituent of cardiovascular tissues and provides the tissue with the capacity to withstand hemodynamic forces [1]. Tissue engineering of load-bearing cardiovascular tissues requires the complete understanding of the mechanisms that underlie the formation and evolution of the fibrous architecture of the ECM to be able to replicate the structure and functional behavior of native tissues [5]. Tissue cells generate traction forces when tissue is developing and the exerted force on the ECM is demonstrated more predominant in the direction of cell alignment [6,7,8]. The traction forces generated by the cells may cause the collagen to align in the direction of the cells [12,13,14,15,16]
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