Preparation of Hydrogels

The resulting solution was injected between two silanized glasses separated by a silicon rubber spacer (0.1-1 mm) and heated at 37 °C for 4 hours, to give clear transparent films (Fig.l). 

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Tse JR, Engler AJ (2010) Preparation of hydrogel substrates with tunable mechanical properties. In Bonifacino JS (ed) Current protocols in cell biology. Wiley, Somerset... 

A method for preparing branched functionalized polymers containing polyol cores, (1 ), useful in the preparation of hydrogels, is described by McManus et al. (5). 

The reversible reaction between two thiol (sulfhydryl) groups that form a disulfide bridge under oxidative conditions, which is rapidly cleaved back to free thiols under reductive conditions [15, 16] (Scheme 1), has widely been used for the preparation of hydrogels and microgels. 

Michael addition is a facile reaction between nucleophiles and activated olefins and alkynes in which the nucleophile adds across a carbon-carbon multiple bond [25], For the preparation of hydrogels, the hydroxyl, thiol or amine functionalities have been reacted with vinyl sulfones [26-28], acrylates [29-31], acrylamides [32], and maleimides [33, 34] (Scheme 2). 

Peppas and Merrill [65] modified the Flory-Rehner theory to describe the preparation of hydrogels in the presence of water to obtain the following relationship ... 

Regarding the initiation process of polymerization, it can be started by y-radiation. It is a method that has been used for the synthesis of hydrogels of PEO as well as hydrogels based on vinyl monomers " in this latter case, azo-compounds such as 2,2-azo-isobutyroni-trile (AIBN)f or 2,2 -azobis (2-amidine-propane) dihydrochloride or V-SO, and aqueous salt solutions such as aqueous ammonium peroxodisulfate are also used. Among the monomers most used in the preparation of hydrogels through free-radical polymerization are 2-hydroxyethyl methacrylate (HEMA) and A-vinyl-2-pyrrolidone (VP). ... 

It is noteworthy that ageing has the same effect on the two kinds of gel (stirred or non stirred) increasing of pore volume, surface and mean diameter, and broadening of the pore range. As a consequence, to avoid these undesirable texture modifications, thermoporometry measurements must be carried out as soon as possible after the preparation of hydrogel samples (within 24 hours). 

Table 2 PEO-PHB-PEO triblock copolymers used for preparation of hydrogels with a-CD [71]...

Preparation of Hydrogel p-Nitrophenyl Carbamates. A 20 mL solution of hydrogel (2-3.0 g) in pyridine was treated with 3 g... 

Preparation of Hydrogel Arylsulfonyl Carbamates. To a solution of hydrogel (1-4.0 g) in dry pyridine (20-40 mL) was added eitherp-toluenesulfonyl Isocyanate (pTSI), 3.0 g, or p-nitro-benzenesulfonyl Isocyanate (p-NBSI), 0.5-3.0 g and the mixture was heated at 70 under nitrogen for 4 hr. The adduct was isolated by precipitation in benzene or ethanol. Repreclpltatlon from acetone or DMF yielded the desired products, IR (film) 3170 cm (-NH), 1530 cm" (-NO2), 1340, 1180 cm" (-SOj). The precise degree of substitution was determined by non-aqueous titration (Table II). 

Dcada, Y, Mita, T., Horii, F. et al. 1977. Preparation of hydrogels by radiation technique. Radial Phys Chem. 9 633-645. 

FIGURE 14.2 Schematic diagram showing conventional preparation of hydrogel microparticles. 

FIGURE 14.3 Schematic diagram showing spray-atomization provision for the preparation of hydrogel... 

Biodegradable Polymers Used in Preparation of Hydrogel Drug Delivery Systems and Their Application... 

Kim, K.H. Kim, J. Jo, W.H. Preparation of hydrogel nanoparticles by atom transfer radical polymerization of N-isopropylacrylamide in aqueous media using PEG macro-initiator. Polymer 2005, 46 (9), 2836-2840. 

PEG has been widely used for the preparation of hydrogels due to safety and FDA approval for internal use. Quick et al. prepared photocrossUnked PEG hydrogels for sustained DNA delivery. The results showed that plasmid DNA was released primarily in the relaxed and supercoiled forms for periods of 6-100... 

The ability of thiol-ene click chemistry to retain high efficiency under the most benign reaction conditions was exempHfied by Ritter and Bardts, in the preparation of hydrogels based on methacryhc acid [224]. In this study, poly(methacrylic acid) polymers were modified with cysteamine and aUyl amine to afford complementary thiol-ene reactive polymer chains. Solutions of the polymer pairs in water were mixed in the presence of a radical initiator, and the formation of a highly elastic gel was observed within only 2 h at room temperature. The authors noted that this approach might have broad application for a rapid and straightforward access to hydrogel materials for which the properties could easily be tailored by the choice of the amine modifiers. 

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