Shrinking mechanism of a porous collagen matrix immersed in solution.

The porous structure of collagen-based matrices enables the infiltration of cells both in in vitro and clinical applications. Reconstituted porous collagen matrices often collapse when they are in contact with aqueous solutions; however, the mechanism for the collapse of the pores is not understood. We, therefore, investigated the interactions between the collagen matrix and different solutions, and discuss the mechanisms for the change in microstructure of the matrix on immersing it in solution. When a dried collagen matrix was immersed in aqueous solutions, the matrix shrunk and pores close to the surface closed. The shrinkage ratio and thickness of the compact microstructure close to the superficial area decreased with increasing ethanol content in the solution. The original porous structure of the collagen matrix was preserved when the matrix was immersed in absolute ethanol. The shrinkage of a porous collagen matrix in contact with aqueous solutions was attributed to the liquid/gas interfacial tension. The average pore diameter of the matrix also significantly affected the shrinkage of the matrix. The shrinkage of the matrix, explained using the Young-Laplace equation, was found to result from the pressure drop, and especially in the pores located superficially, leading to the collapse of the matrix microstructure. The integrity of the porous microstructure allows better penetration of cells in medical applications. The numbers of NIH/3T3 fibroblasts penetrated through the hydrated Col/PBS porous collagen matrices pre-immersed in absolute ethanol with subsequent water and DMEM culture medium replacements were significantly higher than those through matrices hydrated directly in DMEM.