Hydrogen-Bonded Layer-by-Layer Temperature-Triggered Release Films

• Published in: Langmuir 2009-12, Vol.25 (24), p.14025-14029
• Main Authors: Zhuk, Aliaksandr, Pavlukhina, Svetlana, Sukhishvili, Svetlana A
• Format: Article
• Language: English
• Subjects: Materials: Nano-and Mesostructured Materials, Polymers, Gels, Liquid Crystals, Composites
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la901478v

A hydrogen-bonded layer-by-layer (LbL) technique was used to build multilayers of neutral, temperature-responsive polymers such as poly(N-isopropylacrylamide) (PNIPAM), poly(N-vinylcaprolactam) (PVCL), poly(vinyl methyl ether) (PVME), or poly(acrylamide) (PAAm) with a polycarboxylic acid such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(ethacrylic acid) (PEAA). For all multilayers involving temperature-responsive polymers, the temperature used during or after self-assembly had a significant effect on film stability with pH changes. The proximity of the self-assembly or post-self-assembly temperature to the critical temperature of phase separation of a neutral polymer from solution resulted in a higher pH stability of multilayers. However, for polymers with a lower critical solution temperature (LCST) such as PNIPAM, PVCL, or PVME within PNIPAM/PMAA, PVCL/PMAA, or PVME/PMAA multilayers, the critical pH of film disintegration (pHcrit) increased in the temperature range from 10 to 37 °C, whereas for polymer films with an upper critical solution temperature (UCST), such as PAAm within PAAm/PMAA, the film showed the opposite trend. Using a hydrogen-bonded polyvinylpyrrolidone (PVPON)/PMAA system, which is not responsive to temperature changes, we constructed hybrid films with lower [PNIPAM/PMAA] n and higher [PVPON/PMAA] m strata and obtained free-floating [PVPON/PMAA] m films by temperature-triggered dissolution of the PNIPAM/PMAA layers at a constant pH value. The kinetics of [PVPON/PMAA] m film release was strongly dependent on the number of bilayers within the PNIPAM/PMAA stratum, indicating significant interpenetration between PNIPAM/PMAA and PVPON/PMAA bilayers. Importantly, the use of PEAA instead of PAA or PMAA in film assembly enabled the construction of hydrogen-bonded LbL films that can be released by applying temperature as a trigger at near-physiological pH values. This feature makes such release layers attractive candidates for future tissue engineering applications.