Comparison of surface properties of polydopamine and polydopamine-tannic acid-based multilayer films

The surface properties of various multilayers obtained by codeposition of polydopamine (PDA) and tannic acid (TA), referred to as PDATA, were investigated in comparison with PDA multilayers. Two different approaches were used in the preparation of multilayers. First, multilayers composed solely of either PDATA or PDA were constructed. Second, they were self-assembled through a layer-by-layer (LbL) technique using various counter polymers: branched poly(ethylenimine) (BPEI), TA or poly(N-vinyl caprolactam) (PVCL). Self-assembly of PDATA with itself could not go beyond a few layers and did not form true multilayers, whereas PDA formed multilayer films. LbL growth was obtained using counter polymers, except for PDATA and TA pair. In general, PDATA formed thinner and smoother films with enhanced wettability. Films composed solely of PDATA or PDA exhibited superhydrophilic properties, whereas LbL films, despite being hydrophilic, were not superhydrophilic. The stability of PDATA-based films was lower compared to PDAs under pH 7.4/37 °C conditions and could be enhanced when self-assembled using a counter polymer. Among the counter polymers, PVCL produced the smoothest and most stable multilayers, while BPEI and TA provided films with higher wettability.