Poly(acrylic acid) is considered to be an important mucoadhesive for controlled release applications. Yet, the specific mechanisms responsible for its bioadhesive behavior are not well understood. Attenuated total reflection infrared spectroscopy (ATR-FTIR) was developed for investigation of chain interpenetration at a poly(acrylic acid) (PAA) and mucin interface. A thin film of acrylic acid, polymerized below the gelation point, was cross-linked directly on an ATR crystal. The cross-linked PAA film was contacted with a buffered mucin solution and the ATR-FTIR spectrum was collected in situ as a function of time. The experimental results show evidence in support of chain interpenetration at the PAA/mucin interface. The experimental results indicate that as PAA and mucin are compatible in the 5-7 pH range, an important mechanism of mucoadhesion is the swelling of PAA by mucin and adhesion is limited by the extent of chain interpenetration across the biointerface.
