Thermoresponsive properties of porous poly(N‐isopropylacrylamide) hydrogels prepared in the presence of nanosized silica particles and subsequent acid treatment

Abstract

Porous poly(N‐isopropylacrylamide) hydrogels were prepared by the free‐radical polymerization of its monomer and a suitable crosslinker in the presence of spherical silica particles of different sizes (74 and 1600 nm) and by the subsequent acid extraction of silica. The yields were 81–83%, and the yields were not affected by the silica content. Scanning electron microscopy observations revealed the porous structure of the hydrogels. Porous and nonporous hydrogels showed volume phase transitions from swelling states to deswelling states at approximately 30 °C, as analyzed by the ratio of the diameter of cylinder‐shaped hydrogels to that of the glass tube used for the hydrogel preparation at the corresponding temperature. Deswelling, which was analyzed by rapid changes in the temperature of the aqueous media from 20 to 40 °C, was facilitated by decreased silica particle size and increased silica content. The deswelling rate constant of the hydrogel prepared with 74‐nm silica at 10 v/v % (silica/solvent) was more than 1500 times greater than that of conventional hydrogels. Swelling was similarly analyzed through changes in the temperature from 40 to 20 °C and was independent of the pore structure. The deswelling–swelling cycle was repeatable with reasonable reproducibility. Moreover, the mechanical strength of the porous hydrogels was significantly maintained compared with that of conventional nonporous hydrogels. This method produced thermoresponsive hydrogels of suitable mechanical strength and remarkable deswelling properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4228–4235, 2002

Ultrarapid Molecular Release from Poly(N‐isopropylacrylamide) Hydrogels Perforated Using Silica Nanoparticle Networks

“…These results were reproducible. Such cycling of deswelling and swelling was also characteristic of all nanoporous PNIPAAm hydrogels prepared thus far using silica particles, [9,21,22] whereas conventional, nonporous PNIPAAm hydrogels are known to form cracks in or on themselves during deswelling. The hydrogel reswelling process seems to be much slower than the deswelling process and was independent of pore morphology; when the temperature of the aqueous media was changed from 40 to 20 8C, it took approximately one hour to achieve equilibrium in the NT gel, SP gel, and nonporous hydrogels (data not shown).…”

“…[9,21,22] Subsequent silica extraction by HF treatment yielded hydrogels with nanosized spherical pores (SP gel) which showed very rapid deswelling. If the total volume of the silica used was kept constant, the smaller silica yielded a larger surface area of hydrogels.…”

“…It was previously shown that the deswelling rate of the hydrogels increased with silica content or with decreasing silica size, suggesting that the silica size successfully translated into hydrogel pore size. [9,22] If the morphological translation from the silica nanoparticles into the hydrogel pores is successful, then the networked silica nanoparticles should perforate the nanosized tracts into the hydrogels (NT gel), just like soft tissue containing a capillary vessel network. In the present study, nanoporous hydrogels were prepared by the method described above using silica particles with a morphology of column networks (mean diameter: 10 nm) and with spherical silica nanospheres (mean diameter: 10 nm) (Figure 1), and we investigated their morphological effects on hydrogel deswelling.…”

“…For a quantitative interpretation of these data, the deswelling process was fitted to an apparent first-order equation discussed previously. [9,21,22] The plots could be fitted linearly with a coefficient of variation of more than 0.99 for each case, suggesting that the process was governed by a first-order rate step. The rate constants estimated from the slope were plotted linearly against the silica content in the feed (Figure 7).…”

Preparation of Poly(γ-glutamic acid) Hydrogel / Apatite Composites and Their Application for Scaffold of Cell Proliferation

“…where is the compressibility of hydrogel, L and L0 are the measured and initial thickness values of the hydrogel, respectively [34,35]. The weight of the wet hydrogels (W0) was measured after equilibrating in deionized water for 2 days.…”