Interfacial assembly of collagen and poly(acrylic acid) forms a dense and low-permeable collagen membrane

Artificial hydrated membranes capable of regulating molecular permeability are useful extracellular matrix-inspired barriers. Here, we report a simple aqueous method for forming dense collagen membranes through liquid-liquid interfacial assembly of type I collagen and poly(acrylic acid) (PAA). The interfacially assembled membrane had thicknesse of 40 μm in the dry state and 350 μm in the hydrated state. Compared with a commercial atelocollagen membrane, the membrane prepared by the type I collagen/PAA (Col I/PAA) method showed a denser hydrated collagen structure, higher dry mass per hydrated volume, and lower permeability to fluorescent tracers. Mechanistic analysis using NaCl and urea indicated that collagen accumulation was not governed solely by electrostatic complexation. NaCl alone caused only a modest increase at high concentration, consistent with partial salting-out, whereas collagen accumulation was observed at 0-2.0 M urea but was markedly reduced at 4.0 M urea. Combined NaCl/urea conditions revealed maximal accumulation at 0.5 M urea with 0.1 and 0.5 M NaCl. Circular dichroism (CD) and turbidity measurements suggested that moderate urea concentration preserves the collagen triple-helical signature and suppresses coarse aggregation, while NaCl promotes light-scattering aggregate formation. These results show that the Col I/PAA interfacial assembly method enables dense hydrated collagen membranes with low molecular permeability for molecular barrier assembly in pharmaceutical applications.