Dual Stimuli-responsive Hydrogel Research Articles

Assessing the effects of cellulose-inorganic nanofillers on thermo/pH-dual responsive hydrogels

The incorporation of renewable bio-based materials/eco-friendly inorganic nanofillers into stimuli-responsive hydrogels meets the need for biocompatible and non-toxic functional materials. However, it remains challenging to build a three-dimensional network with enhanced mechanical properties and desired stimuli-responsive performances. In this study, dual stimuli-responsive hydrogels with interpenetrating polymer network structure are fabricated by the crosslinking of N-isopropylacrylamide (NIPAM)11NIPAM: N-isopropylacrylamide and sodium alginate (SA)22SA: Sodium alginate. 2,2,6,6-tetramethyl-piperidine-1-oxyl-oxidized cellulose nanofibers (TOCNF)33TOCNF: 2,2,6,6-tetramethyl-piperidine-1-oxyl-oxidized cellulose nanofibers derived from energycane bagasse serves as a carrier material for nanosilicas (NS)44NS: Nanosilicas and nanoclays (NC)55NC: Nanoclays and the effects of TOCNF, TOCNF/NS and TOCNF/NC on the hydrogels are thoroughly explored. Among these hydrogels, PNIPAM/SA-TOCNF-NS possesses the largest compressive strength of 66.7 kPa and it is 5.65 times higher than that of PNIPAM/SA. The thermo-sensitivity and pH-sensitivity of hydrogels are evidenced by swelling behaviors, optical properties, contact angle measurements and fluorescence tests. PNIPAM/SA-TOCNF exhibits the largest contact angle and the swelling processes for all the hydrogels are well fitted by pseudo-second-order swelling kinetic model. In addition, after incorporating carbon quantum dots, all the hydrogels display temperature dependent on–off fluorescence properties and this process are fully reversible with the heating and cooling cycles. These novel hydrogels with pH and temperature responsive characteristics and remarkable mechanical properties will open the door for interesting applications in smart sensors etc.

A new dual stimuli responsive hydrogel: Modeling approaches for the prediction of drug loading and release profile

In this study, N-tert-butylmaleimic acid was designed for the first time and synthesized by reaction of maleic anhydride with tert-butylamine and evaluated as a new functional monomer for preparation of new pH-responsive hydrogels. Its structure was verified with FTIR, 1H and 13C NMR. A new pH- and temperature-responsive hydrogel p(TBMAC-co-NIPAM), based on TBMAC and NIPAM, was successfully prepared via free-radical copolymerization technique in an aqueous solution. The chemical and structural properties of the hydrogels were identified by FTIR and SEM. The swelling properties of these hydrogels were systematically investigated according to various parameters such as time, temperature, pH and salt effects, and the results show that they are strongly influenced by the content of TBMAC and exhibit strong pH, temperature and salinity sensitivity. In addition, swelling kinetics and water diffusion mechanisms in hydrogels were discussed. In addition, in vitro drug release studies were performed in simulated gastric, isotonic serum and intestinal fluid at two different temperatures (23 and 37 °C) by taking R6G as a model drug. Drug loading results were investigated with various isotherm models such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich. Various kinetic models such as zero-order, first-order, Higuchi model and Korsmeyer-Peppas models were applied to determine the drug release mechanism. The results indicated that drug release involves non-Fickian transport mechanism. These results suggest that this new pH- and thermo-responsive hydrogel may be used to improve sustained release of drugs.

Thermo- and pH-sensitive behavior of hydrogels based on oligo (ethylene glycol) methacrylates and acrylic acid

Novel dual stimuli-responsive hydrogels were prepared by free-radical polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and oligo (ethylene glycol) methacrylate (OEGMA), as thermosensitive monomers, and acrylic acid (AAc), as a pH-sensitive monomer. Due to the thermosensitive monomers introduced in the macromolecular network, the synthesized materials possessed tunable thermal behavior. In addition, as well as by introducing in the polymerization feed pH-sensitive monomer AAc, the equilibrium swelling properties of the hydrogels can be tuned by three comonomers. Moreover, the de-swelling kinetics was studied by changing temperature and/or pH, and they could be well described with a first-order kinetics equation. Especially, the faster shrinking rates of hydrogels were observed when the simultaneous temperature and pH stimuli changed from pH 8/18 to pH 2/55 °C because of the cooperative thermo-/pH responses. The prepared dual temperature-/pH-sensitive PMOA hydrogels as a new material candidate may provide significant valuable information for various potential applications.