Abstract
This study aims to characterize and understand the effects of freezing on collagen structures and functionality. Specifically, thermodynamic destabilization of collagen at molecular- and fibril-levels by combination of low temperatures and freezing were experimentally characterized using modulated differential scanning calorimetry. In order to delineate the effects of sub-zero temperature and water-ice phase change, we hypothesized that the extent of destabilization can be determined based on post-thaw heat induced thermal denaturation of collagen. It is found that thermal denaturation temperature of collagen in hydrogel decreases by 1.4–1.6°C after freeze/thaw while no such decrease is observed in the case of molecular solution. The destabilization is predominantly due to ice formation. Exposure to low temperatures in the absence of ice has only minimal effect. Calorimetry measurements combined with morphological examination of collagen matrices by scanning electron microscopy suggest that freezing results in destabilization of collagen fibrils due to expansion of intrafibrillar space by ice formation. This fibril-level damage can be alleviated by use of cryoprotectant DMSO at concentrations as low as 0.5 M. A theoretical model explaining the change in collagen post-thaw thermal stability by freezing-induced fibril expansion is also proposed.
Highlights
Collagen is the primary structural component of tissue extracellular matrix (ECM) and plays a critical role for tissue mechanical integrity and functionality [1, 2]
We address the above gaps by providing measurements of post-thaw thermal stability of collagen at multiple levels of its hierarchy using modulated temperature differential scanning calorimetry (MTDSC)
Heat absorbed by collagen during thermal denaturation is observed as an endothermic peak in a DSC thermogram [39]
Summary
Collagen is the primary structural component of tissue extracellular matrix (ECM) and plays a critical role for tissue mechanical integrity and functionality [1, 2]. Collagen ECM is a porous mesh of collagen fibrils, saturated by an interstitial fluid where individual fibrils are formed by self-assembly of tropocollagen molecules [3]. This hierarchical structure of collagen regulates various cell-cell and cell-matrix interactions [4,5,6]. Collagen’s stability is critical to the functionality of native and engineered tissues. Thermal treatments where native/engineered biomaterials are exposed to a combination of sub-zero temperatures and freezing conditions have drawn less
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