Synthesis, characterization, and drug release properties of poly(N‐isopropylacrylamide) gels prepared in methanol–water cononsolvent medium

Abstract

Poly(N‐isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol–water mixture. A scanning electron microscopy study revealed that the freeze‐dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X0.43>X0.21>X0.76 ≈ X0.57>X0.31>X0.13>X0.06>X0, where Xm denotes a gel prepared in a methanol–water mixture with m mole fraction of methanol (xm). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all the PNIPAM gels in the methanol–water mixtures with different xm values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.43> X0.31> X0.21> X0.57> X0.76 ≈ X0.13> X0.06> X0. The reswelling rates of these hydrogels decreased in the following order: X0> X0.31> X0.06 ≈ X0.13 > X0.76> X0.57> X0.21> X0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug‐loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Space-resolved quantitative mechanical measurements of soft and supersoft materials by atomic force microscopy

“…This is mainly due to the cononsolvency of the solvent mixture for the PNIPAM chain segment. 11 As a result, polymerization occurs in the heterogeneous phase, and, furthermore, the decomposition of the APS initiator is also significantly faster in the water-methanol mixture. Consequently, a highly porous gel was formed.…”

“…11,12 In this way, the internal structure of the hydrogel undergoes a structural modification, which results in greatly tunable mechanical properties of the hydrogels (from the 100 Pa to 10 kPa range). The mechanical properties of these gels are frequency-independent in the accessible range, homogeneous and linear; the gels represent a good model material to compare quantitatively and validate AFM results with macroscopic mechanical measurements obtained using a rheometer.…”

Modular microfluidic valve structures based on reversible thermoresponsive ionogel actuators

“…As demonstrated by Gallagher et al [23] the highly porous morphology of the ionogel compared with the hydrogel (just poly-NIPAAm) has a significant effect on the hydration mechanism and therefore on the degree of swelling-shrinking. [24] The shrinking process (50 °C) proved to be quite fast, with a complete actuation of the ionogel discs after 3.5 min. The shrinking rate constant was found to be k sh = 3.5 ± 0.2 × 10 -3 s -1 for the ionogel, while in the case of the hydrogel a slightly higher k sh was obtained 4.44 ± 0.03 × 10 -3 s -1 , with a complete actuation after ∼ 3 min (Figure 6, bottom).…”

Versatile Mechanical and Thermoresponsive Properties of Macroporous Copolymer Gels

“…There were also reports of synthesis and characterization of PNIPAM hydrogels in different ethanol–water, and methanol–water mixtures . Recently, the synthesis of the PNIPAM hydrogels by tuning the stereoregularity of the PNIPAM gels was reported by using the rare earth Lewis acid Y(OTf) 3 in different methanol–water mixtures and their LCST was reported and it varied only in between 25 and 34 °C .…”