Semi-solid gels

In a 3-I. round-bottomed flask 250 g. of commercial calcium hypochlorite is dissolved in i 1. of warm water and a warm solution of 175 g. of potassium carbonate and 50 g. of potassium hydroxide in 500 cc. of water is added. The flask is stoppered and shaken vigorously until the semi-solid gel which first forms become quite fluid. The suspended solid is removed by filtration on a large Buchner funnel, washed with 200 cc. of water, and sucked as dry as possible with the aid of a rubber dam and an efficient suction pump. The filtrate of approximately 1500 cc. is placed in a 3-I. round-bottomed flask and is ready for the addition of methyl /3-naphthyl ketone. 

First melt, 71.9 °C second melt, 86-95°C Amber semi-solid gel... 

When phosphorus pentoxide is added to isobutyronitrile, the liquid sets to a semi-solid gel which is difficult to transfer from a flask. Hence, the addition of one to the other should be made only in the flask from which the distillation is to be made. 

Semi-solid gel type preparations have also been developed for ophthalmic delivery as an alternative to traditional ointments, based on the effect of increasing the viscosity to prolong the retention of drug in the eye (for example, Pilopine HS gel, Alcon Laboratories, Inc.). Several types of gelling agents have been used, such as polyacrylic acid derivatives, carbomer and hypromellose. 

The choice of packaging for ophthalmic products will depend on the type of dosage form, such as whether it is a liquid solution/suspension or semi-solid gel or ointment. Also, choice will depend on how the product is to be used by the patient, such as whether it is intended to... 

The exact product optimisation studies to be conducted will depend on the type of ophthalmic dosage form to be developed (liquid drops, semi-solid gel/ointment or solid device). However, the dosage form type should be clearly defined from the product design evaluation and supporting preformulation studies, to enable the formulator to focus on the most relevant product optimisation studies. 

Starch Gels The first gel media to receive attention was starch. Starch gels are prepared by heating and cooling a mixture of partially hydrolyzed starch in an appropriate buffer. This causes the branched chains of the amylopectin component of the starch to intertwine and form a semi-solid gel. 

Once the film is metered onto the carrier surface it is conveyed into the drying chamber, where the actual solvent removal takes place. For a period of time, depending upon the thickness of the cast and the drying rate, the fluid film on the surface of the carrier is free to flow Therefore the surface it rides on must be flat, smooth, and level. During the first stage of drying, the fluid suspension of particles in the slip forms a semi-solid, gel-like structure. When this gel forms, the... 

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