BiFACIAL (<i>Bi</i>omimetic <i>F</i>reestanding <i>A</i>nisotropic <i>C</i>atechol‑<i>I</i>nterfaces with <i>A</i>symmetrically <i>L</i>ayered) Films as Versatile Extracellular Matrix Substitutes

Biological naïve extracellular matrices (ECMs) exhibit anisotropic functions in their physical, chemical, and morphological properties. Representative examples include anisotropic skin layers or blood vessels simultaneously facing multiphasic environments. Here, anisotropically multifunctional structures called BiFACIAL (<i>bi</i>omimetic <i>f</i>reestanding <i>a</i>nisotropic <i>c</i>atechol-<i>i</i>nterfaces with <i>a</i>symmetrically <i>l</i>ayered) films were developed simply by contacting two polysaccharide solutions of heparin-catechol (Hep-C) and chitosan-catechol (Chi-C). Such anisotropic characters were due to controlling catechol cross-linking by alkaline pH, resulting in a trimodular structure: a rigid yet porous Hep-C exterior, nonporous interfacial zone, and soft/highly porous Chi-C interior. The anisotropic features of each layer, including the porosity, rigidity, rheology, composition, and ionic strength, caused the BiFACIAL films to show spontaneously biased stimuli responses and differential behaviors against biological substances (e.g., blood plasma). The films could be created in situ in live animals and imitated the structural/functional aspects of the representative anisotropic tissues (e.g., skin and blood vessels), providing valuable ECM-like platforms for the creation of favorable environments or for tissue regeneration or disease treatment by effectively manipulating cellular behaviors