Calcium spraying for fabricating collagen-alginate composite films with excellent wet mechanical properties

Abstract Two spray processes for adding calcium were designed to improve the mechanical properties of collagen fiber films in wet conditions. The processes were applied after immersion of the films in sodium alginate (SA) and glycerol solution. One process (P1) involved spraying after immersion but before but before the film had dried the film and the other process (P2) involved spraying after drying the film. Both processes significantly improved the wet mechanical properties of the films. However, P1 mainly enhanced the elasticity and stiffness, whereas P2 mainly enhanced the toughness. Ca-alginate complexes gradually formed in the samples after the addition of Ca2+, improving the water resistance of the samples. For the samples prepared using P1, Ca2+ penetrated inside the film and chelated SA and collagens to form a dense network, but further damaged the triple helix structures of collagens. For the samples prepared using P2, the sprayed calcium ions generated a protective layer of calcium alginate on the surface of the membrane and the secondary structure of the collagen was better maintained.