Water-insoluble hydrogels

A variety of polymers including water-soluble and insoluble, ionic and nonionic hydrocolloids, and water-insoluble hydrogels can be used in bioadhesive systems [31]. The bioadhesive properties of the polymer are affected by the ... 

Oil that is deposited on a water-insoluble hydrogel, such as agar and con-nyaku, can be readily separated. This is because the water film on the hydrogel surface inhibits adhesion of oil onto the gel networks. Based on this mechanism shown as model 2) in Fig. 1, the authors attempted separation of collected oil by making the substrate of coalesced oil particles unstable. 

Superabsorbents. Water-sweUable polymers are used extensively in consumer articles and for industrial appUcations. Most of these polymers are cross-linked acryUc copolymers of metal salts of acryUc acid and acrylamide or other monomers such as 2-acrylamido-2-methylpropanesulfonic acid. These hydrogel forming systems can have high gel strength as measured by the shear modulus (134). Sometimes inorganic water-insoluble powder is blended with the polymer to increase gel strength (135). Patents describe processes for making cross-linked polyurethane foams which contain superabsorbent polymers (136,137). 

As a polycation, chitosan spontaneously forms macromolecular complexes upon reaction with anionic polyelectrolytes. These complexes are generally water-insoluble and form hydrogels [90,91]. A variety of polyelectrolytes can be obtained by changing the chemical structure of component polymers, such as molecular weight, flexibility, fimctional group structure, charge density, hydrophilicity and hydrophobicity, stereoregularity, and compatibility, as... 

Hydrogel and water-soluble ointment achieve their consistency by means of different gel-forming agents (gelatin, methylcellulose, polyethylene glycol). Lotions are aqueous suspensions of water-insoluble and solid constituents. 

Corpart and Candau [68, 69] described the formulation of polyampholytes containing both positive and negative charges in inverse microemulsions. The copolymers can show very different behaviors in the aqueous solution, ranging from insoluble, water-swollen hydrogels to water-soluble compounds, depending on the monomer composition. For polyampholytes with balanced stoichiometry, the polymer behavior is controlled by attractive electrostatic forces. The compound is usually insoluble in water, but becomes soluble upon the addition of salt. 

III), formed a hydrogel that could be used to encapsulate water-insoluble materials. Soybean-based materials prerpared by Liu [4] were also effective as hydrogels and used as drug delivery agents. 

Water-soluble polymers can be crosslinked electrostatically or covalently to give hydrogels. Crosslinked hydrogels absorb water but do not dissolve. The differences in release of drugs from water-insoluble matrices and from swelling hydrogels should be appreciated. 

The first report on a CD inclusion polymer forming hydrogels dates back to 1994, which describes the discovery of the sol-gel transition during the inclusion complex formation between a-CD and high molecular weight PEO in aqueous solution [59]. The gelation was induced by the partially formed a-CD-PEO inclusion complexes, which self-assembled into water-insoluble domains acting as a kind of... 

Physical hydrogels were formed induced by self-assembled water-insoluble and crystalline polypseudorotaxane domains which act as physical crosslinking points. Such physical hydrogels include the polypseudorotaxane systems of a-CD threading on PEO or its copolymers, a-CD threaded on PEI, PL, or their copolymers, and even 3-CD or y-CD threaded PPO or PEI copolymers. The thermo-reversible and thixotropic properties of these supramolecular hydrogels have inspired their applications as injectable drug delivery systems. Physical hydrogels induced by physical interaction of threaded CD molecules in polyrotaxanes were also developed. 

Possibly the best way to obtain transmission spectra from hydrogels is to prepare a capillary thin film onto a water-insoluble and IR-transparent window. The preparation of capillary films is simple a drop or smear of the hydrogel sample is placed onto the window and a second window is placed on the top of the first. The resulting sandwich is placed in the IR beam. 

Gitsov et al 10) produced a nanoreactor fi om laccase and linear poly(ethylene oxide)-dendritic poly(benzyl ether) diblock copolymers. A notable feature of this system is the presence of hydrophobic dendritic pockets that increase the local concentration of water-insoluble organic compounds near the active site where they are oxidized. Li and Hsieh (77) employed a hydrogel fiber membrane, with a large surface area and improved organic solvent solubility in order to facilitate lipase reactions. He (72) grafted lipase onto silica particles, which permitted him to carry out synthesis of polyesters, polycarbonates, polyphosphates, and their copolymers at temperatures up to 150°C. 

---