Collagen films with improved wet state mechanical properties by mineralization

Collagen films have weak wet mechanical properties due to poor water resistance. Herein, two mineralization processes were designed to improve the mechanical properties of collagen fibers under wet conditions for use as packaging materials. One scheme (S1) involved preparing carboxymethyl chitosan amorphous calcium orthophosphate (CMCS-ACP) nanoparticles, dispersing them in an aqueous solution and then immersing the collagen film in the dispersion to introduce the inorganic phase. Another scheme (S2) introduced the inorganic phase by alternately soaking in a CaCl2 and a Na2HPO4 solution. S1 introduced an amorphous inorganic phase and enhanced the wet tensile strength of collagen films from 2.71 MPa (Control) to 4.08 MPa (1.0%C-A). S2 introduced a large number of inorganic phases, which did not significantly enhance the wet tensile strength of the film, but reduced its swelling ratio from 176.15% to 112.87%. The amorphous inorganic phase from S1 did not destroy the triple helix structure of the collagen film, whereas the direct calcium phosphate deposition from S2 greatly damaged the original structure of the collagen film, resulting in poorer mechanical properties from 2.71 MPa (Control) to 1.55 MPa (N3).