Thermo‐ and pH‐sensitive hydrogels based on 2‐(2‐methoxyethoxy)ethyl methacrylate and methacrylic acid

Abstract

Hydrogels based on commercially available 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO2MA), with methacrylic acid (MAA) as comonomer, are studied. The incorporation of an ionizable monomer, such as MAA, in a thermosensitive system leads to the formation of hydrogels able to respond to pH and temperature according to their monomeric composition. Thus, at low pH, the acid groups of MAA are protonated, and they do not contribute to increase the hydrophilic balance, and collapse of the hydrogels occurs around room temperature. For temperatures below that of collapse, the degree of swelling increases with increasing MEO2MA content. In contrast, at neutral or basic pH, the ionization of the acid groups contributes to increase the hydrophilicity and the osmotic pressure, leading to polyelectrolyte behaviour. In this regime, the swelling capacity increases and the thermosensitivity decreases with increasing MAA content in the hydrogels. These properties make poly(MEO2MA‐co‐MAA) hydrogels suitable candidates for use in oral controlled delivery of hydrophobic drugs. This possibility is explored using ibuprofen as a model drug, after a complete study of the swelling kinetics. Copyright © 2010 Society of Chemical Industry

Swelling control in thermo-responsive hydrogels based on 2-(2-methoxyethoxy)ethyl methacrylate by crosslinking and copolymerization with N-isopropylacrylamide

“…In previous investigations, 19,20,22 it was shown that the VTT of the MEO 2 MA-based hydrogels occurred with a very fast change in the sample transparency. Thus, these hydrogels were completely transparent at low temperatures but became opaque above the transition temperature.…”

“…Furthermore, it is possible that not all of the double bonds in POSS-meth 8 functioned as crosslinker points because of steric effects according to Sastre et al 35 One of the most interesting features of the MEO 2 MA-based hydrogels is their thermo-responsiveness. 19,20,22,28 Thus, the waterswelling capacity of the samples was evaluated as a function of temperature. The experimental results are collected in Figure 2.…”

“…Thus, such stimuli-sensitive hydrogels have been intensively studied with respect to drug delivery 9,10 and other biomedical applications. [11][12][13][14][15][16][17] Recently, hydrogels based on oligo(ethylene glycol) side chains methacrylic monomers, [18][19][20][21][22] such as 2-(2-methoxyethoxy)ethyl methacrylate (MEO 2 MA), were highlighted as a successful alternative to poly(N-iPAAm)-based hydrogels because of the advantages of a controllable lower critical solution temperature, 23,24 high biocompatibility/ low cytotoxicity 25,26 and facile polymerization by both the free radical and the anionic polymerization mechanisms. 27 The previous investigations on MEO 2 MA-based hydrogels were mainly focused on controlling the thermo-responsive behavior for biomedical applications.…”

“…28 In other cases, they have been copolymerized with ionic monomers to obtain additional pH responsiveness. 20,22 A major issue that remains almost unexplored for this interesting system is the study of modulating its ability of water uptake or the control of its swelling. It is important to remark that, for many real applications such as drug delivery, the swelling capacity of the thermoresponsive hydrogels before their collapse could be as important as the temperature at which the volume transition takes place.…”

“…28 In other cases, they have been copolymerized with ionic monomers to obtain additional pH responsiveness. 20,22 …”