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

Abstract

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 (pH(crit)) increased in the temperature range from 10 to 37 degrees 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.

Functionalized Biocompatible Poly(N‐vinyl‐2‐caprolactam) With pH‐Dependent Lower Critical Solution Temperature Behaviors

“…[ 7 ] The unique temperature dependent behavior of PVCL has been employed to prepare thermoresponsive microgels for a variety of applications, including thermalsensitive drug delivery [ 8 ] and template for oxidative polymerization of pyrrole. [ 9 ] Furthermore, thermosensitive PVCL was recently employed by Zhuk et al [ 10 ] for constructing pH responsive multilayers, which can be delaminated at high pH values. It also has been used to stabilize proteases.…”

Construction and deconstruction of multilayer films containing polycarboxybetaine: Effect of pH and ionic strength

“…Fig. 10a shows the thickness growth of (PVPMC/PSS) 10 -(PEC/ PSS) 30 as the function of bilayer number measured by QCM. Two typical growth behaviors were observed for two different LbL assembly component pairs.…”

“…Fig. 10b shows the photographs of the obtained (PVPMC/PSS) 10 -(PEC/PSS) 30 multilayer film deposited on the quartz substrate. The size of the multilayer film was approximately 15 Â 10 mm 2 .…”

“…Although some polyelectrolyte LbL multilayer films could be destroyed completely in high salt solution by deconstructing polyanion/polycation ion pairs with external salt ions, such as 0.6 M NaCl solution for poly(diallyldimethylammonium) (PDDA)/poly(acrylic acid) (PAA) and 3.5 M NaCl solution for PDDA/poly(sodium 4-styrenesulfonate) (PSS), the disintegration rate of these multilayer films was uncontrollable [28,29]. Moreover, to our knowledge, there are few reports about the influence of experimental assembly condition on the deconstruction of multilayered films [30]. Therefore, it is important and necessary to fabricate the disintegrable LbL multilayer films in a controllable manner and investigate effects of experimental variables on the deconstruction of multilayer films.…”

Temperature Response of PNIPAM Derivatives at Planar Surfaces: Comparison between Polyelectrolyte Multilayers and Adsorbed Microgels

“…[15] Besides this entropically driven build-up of polyelectrolyte multilayers containing NIPAM, PNIPAM was also incorporated into multilayers by chemical reactions, [16] for example, by click chemistry. [17] Polyelectrolyte multilayers were also constructed via hydrogen bonding between PNIPAM and polyacid [18,19] or between a PNIPAM block copolymer and a second homopolymer. [20] These multilayers are of interest since their release or disintegration can be easily controlled by pH and temperature.…”