Gelling, in situ

Melamine resins [1617] and phenol-formaldehyde resins [1620] can be gelled in situ to reduce the permeability. Various classes of polymers can be gelled by similar principles [882]. 

However, 1 have discovered that effective mixing and binding effect is obtained with sand if the concentrated silica sol is mixed first with the sand to form a uniform and continuous film on the surface of the sand grains. The concentrated sodium silicate solution is then added to the sand mass in a second, separate step and the sodium silicate then mixed with the colloidal silica film on the surface of the sand, gelling in situ to form an intimately and uniformly mixed binder within the sand mass. The sand mix thus formed in the mixer can be molded by any of the various processes available in foundry practice and hardened to form strong molds or cores. 

A clear solution of aluminum citrate neutralized to pH 7 is used for in situ gelling of polymers in polymer flooding and well stimulation in enhanced oil recovery techniques (128—132). The citrate chelate maintains aluminum ion solubiUty and controls the rate of release of the aluminum cross-linker. 

Figure 4. (a) Adsorption-desorption isotherms of N2 at -196°C of 80°C-outgassed (empty squares) chitosan, (filled trangles) zeolite X-chitosan composite from in-situ zeolite synthesis and (empty triangles) zeolite Y-chitosan composite from encapsulation of the zeolite in the gelling chitosan. (b) Scanning electron micrographs of a calcined zeolite-chitosan bead prepared by zeolitisation of a silica-chitosan composite. 

Van Tomme SR, Storm G, Hennink WE (2008) In situ gelling hydrogels for pharmaceutical and biomedical applications. Int J Pharm 355 1-18... 

Jain A Kim YT, Mckeon RJ, Bellamkonda RV (2006) In situ gelling hydrogels for conformal repair of spinal cord defects, and local delivery of BDNF after spinal cord injury. Biomaterials 27 497-504. 

All the above mentioned polymers have been evaluated mainly for application in the intestine. Finally, the last part of the gastrointestinal tract, the rectum should also be mentioned as a suitable site for delivery and fast absorption of therapeutics. Kim et al. [88] developed an in situ gelling and mucoadhesive acetaminophen liquid suppository prepared with poloxamers and sodium alginate. It was found that this particular formulation of acetaminophen in humans resulted in shorter T ax and higher maximum plasma concentrations of dmg (C ax) than the conventional acetaminophen suppositories. 

J. Winkler, USP 3460922 (1969) CA 71, 93351 (1969) claims a thixotropic-gelled flammable hydrocarbon compsn, containing powdered metals and/or AN, for use in flamethrowers, rocket fuel and napalm. The hydrocarbon gel is prepd by an in situ cross-linking of a polyurethane... 

Choi HK, Oh YK, Kim CK. In-situ gelling and mucoadhesive liquid suppository containing acetaminophen enhanced bioavailability. Int J Pharm 1998 165 23-32. 

CA 68, 88704v(1968) [Expl slurries of conventional oxidizers fuels and water which can be gelled by polymerization, in situ, are described. For example, NaN03 14.7,... 

Another way is to entrap cells within porous matrices formed in situ. Various gelatinous materials such as acrylamide, alginate, collagen and K-carrageenan, can be mixed with cell suspensions and be gelled into various shape and sizes. 

The introduction in the early 1980s of the concept of in situ gel systems demonstrated that a considerable prolongation in duration of action could be obtained. In situ gelling systems have unique properties, which can make a liquid change phase to a gel or sohd phase in the culde-sac upon its instillation into the eye. Three methods have been employed to induce phase transition on the eye surface change in pH and temperature as well as activation by ions. 

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