Stepwise Preparation and Characterization of Ultrathin Hydrogels Composed of Thermoresponsive Polymers

Abstract

Sequential surface chemical reactions of poly(acrylic acid-co-N-isopropylacrylamide) [poly(AAc-co-NIPAAm)] with AAc contents of 5, 10, and 15 mol %, of which carboxyl groups were previously activated by 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDC), plus poly(vinylamine hydrochloride) through amide linkages produced ultrathin films on a solid substrate. Assembly processes were quantitatively monitored by a quartz crystal microbalance as substrates. Assembled amounts increased with decreasing both AAc and EDC amounts. Subsequent immersion of ultrathin films into aqueous media resulted in the thickness increases, producing ultrathin hydrogels. Swelling ratios were estimated by percent increases in the thickness and increased with increasing AAc and EDC amounts. Swelling ratios were regularly changed by varying the ionic strength and pH of aqueous media. Swelling properties were interpreted on the basis of structural information on ultrathin hydrogels. Cyclic voltammetries using potassium ferricyanide revealed that ions permeated ultrathin hydrogels, and permeabilities were clearly suppressed above a lower critical solution temperature (LCST) of polyNIPAAm. Reversible on−off changes in permeabilities below and above a LCST were potentially observed. Not only structural control but also stimuli responsive functions of ultrathin hydrogels were realized within the present study.

Covalent Layer‐by‐Layer Assembly Using Reactive Polymers

“…Examples of amide-bond-forming reactions that have proved particularly useful for covalent LbL assembly include reactions between amine-functionalized agents and building blocks functionalized with (i) anhydrides [66][67][68][69][70][71][72][73], (ii) acid chlorides [81,82], (iii) activated esters (e.g., polymers bearing reactive pentafluorophenyl ester groups) [74][75][76][77], and, in the presence of a carbodiimide coupling agent, (iv) carboxylic acids [78][79][80]. The reactivity of anhydride and acid chloride functionalities generally restricts the first two of these approaches to the use of aprotic organic solvents and film components that do not contain other protic groups that could lead to unwanted side reactions.…”

Layer‐by‐Layer Self‐Assembled Multilayer Stimuli‐Responsive Polymeric Films

“…An alternative approach to introduce thermoresponsive polymers into multilayer films was based on chemical reactions between activated polymers (i.e., PAA) during sequential deposition of temperature-responsive copolymers containing amino or carboxylic groups [10,100] or polymerization grafted from activated polymers [3]. A fully integrated microfluidic valve with a switchable, thermosensitive polymer surface has been fabricated through the combination of the responsive PEMs and microfabrication.…”

“…First developed by Decher in the early 1990s, the LBL assembly technique has made rapid progress in film-preparative methodologies and functional film materials [7]. Advanced multilayer films with components such as synthetic linear polymers [8], polymeric microgels [9][10][11][12], biomacromolecules [13][14][15][16][17][18], particles [19][20][21], dendritic molecules [22,23], organic components [24][25][26][27][28], block copolymers [29][30][31][32], and polyelectrolyte stabilized micelles [33] have been successfully fabricated. The driving force for multilayer film fabrication is diverse, including electrostatic interaction [34,35], hydrogen-bond [36][37][38][39][40][41], coordination-bond [42][43][44], charge-transfer interactions [45], biospecific interaction (e.g., sugar-lectin interactions) [46,47], guest-host interaction [48,49], cation-dipole interaction [50,…”

Effective surface modification by stimuli-responsive polymers onto the magnetite nanoparticles by layer-by-layer method

“…It was followed by the cross-linking reaction at each step. The chemical reaction was very effective to get good stability [13]. These materials would be very useful for biomedical applications such as drug delivery system and diagnosis.…”