Degradable poly(2-hydroxyethyl methacrylate) hydrogels were prepared from a linear copolymer (M = 49 kDa) of 2-hydroxyethyl methacrylate (HEMA), 2-(acethylthio)ethyl methacrylate (ATEMA), and zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC). The deprotection of ATEMA thiol groups by triethylamine followed by their gentle oxidation with 2,2'-dithiodipyridine resulted in the formation of reductively degradable polymers with disulfide bridges. Finally, a hydrogel 3D structure with an oriented porosity was obtained by gelation of the polymer in the presence of needle-like sodium acetate crystals. The pore diameter and porosity of resulting poly(2-hydroxyethyl methacrylate-co-2-(acethylthio)ethyl methacrylate-co-2-methacryloyloxyethyl phosphorylcholine) [P(HEMA-ATEMA-MPC)] hydrogels varied between 59 and 65 μm and between 70 and 79.6 vol % according to Hg porosimetry, and complete degradation of these materials was reached in 86 days in 0.33 mmol solution of l-cysteine/L in phosphate buffer. The cross-linked P(HEMA-ATEMA-MPC) hydrogels were evaluated as a possible support for human mesenchymal stem cells (MSCs). No cytotoxicity was found for the un-cross-linked thiol-containing and protected P(HEMA-ATEMA-MPC) chains up to a concentration of 5 and 1 wt % in α-minimum essential medium, respectively.
A series of macroporous amphoteric cryogels based on allylamine, methacrylic acid and acrylamide were synthesized by radical copolymerization of monomers in cryoconditions. The average molar composition of amphoteric cryogels was found from the potentiometric and conductimetric titration curves. The morphology of cryogels was evaluated by SEM. Cryogels are highly elastic and have continuous macroporous structure with 50-200 mm pores. The values of the isoelectric pH determined from the swelling experiments arranged between 3.5 and 4.3. Complexation of amphoteric with transition metal ions was studied. Cryogels with adsorbed copper, nickel, or cobalt ions have an intense colour due to formation of coordination and ionic bonds between metal ions and amine and/or carboxylic groups of cryogels. Metal ions entrapped within the pores of cryogels were reduced by treating aqueous solution of NaBH 4 . Formation of micron sized metals on the inner surface of cryogels was observed by SEM.
Summary
The interpenetrating network structure was used to control mechanical properties of hydrogels based on poly(2‐hydroxyethyl methacrylate) (PHEMA) (first network (A) or second network (B)) and poly(glycerol methacrylate) (PGMA) (network B). In order to understand the structure, mechanical and swelling properties of sequentially made IPN hydrogels, the swollen PHEMA network microstructure and its formation was investigated by means of swelling and SWAXS experiments. Visually clear and microscopically homogenous hydrogel networks based on poly(2‐hydroxyethyl methacrylate) revealed presence of domains of size 1–10 nm formed during polymerization in the presence of water. The study was carried out to understand conditions under which the hydrophobic interactions are operative and their effect on the microstructure as well as how they change when the double network structure is introduced. The morphologies of network A ranged from homogenous, non‐porous, and optically clear gels, to macroporous gels resulting from phase separation and offering fused‐sphere morphology. A cryogel characterized by large elongated and partially interconnected pores of tens to hundreds micrometers were another object for comparison. In most cases, an increase of tensile moduli and improvement of ultimate tensile properties was achieved. A surprisingly high increase in true strength (by a factor of 10 – 30) was achieved when the macroporous PHEMA network A was reinforced by weak PHEMA or PGMA networks B. All these weakly crosslinked IPN gels were optically clear.
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