Secondary Structure

The secondary structure ratios of Col-TPU composite nanofiber membranes were associated with the amide I band including an α-helix structure, a β-sheet structure, and a β-turn structure. Figure 3C shows that the ratio of β-sheet for collagen decreased from 45% to 21% with increasing TPU ratios, thus suggesting that a more compact structure of the composite nanofiber membrane was formed due to the interactions from larger volumes of side-chain amino acids between collagen and TPU [28]. All Col-TPU composite nanofiber membranes lacked a random collagen structure, suggesting that TPU would not destroy the overall conformation of the secondary structure of collagen. The α-helix ratio of composite nanofiber membranes increased from 40% to 59% with increasing TPU, thus suggesting that the addition of TPU makes sense for the formation of the α-helix. The ratio of the β-turn of Col100 is 14.18%. With increasing TPU ratio, the β-turn of Col-TPU composite nanofiber membranes increased from 15% to 20%. The β-turn mostly transformed into a β-sheet resulting from more -NH groups forming hydrogen bonds, thus indicating that the composite reaction between collagen and TPU is conducive to the formation of an ordered secondary structure leading to a stable collagen structure [29].
