Concept of Drug Delivery Matrix

Controlled release of a drug has been achieved till now by enclosing it in a hydro-phobic matrix (wax, polyethylene, polypropylene, and ethyl cellulose) or hydrophilic matrix (such as carboxymethyl tamarind, hydroxyl propyl cellulose, hydroxyl propyl methylcellulose, methylcellulose, sodium carboxymethylcellulose and alginates) [62,63]. 

Various techniques of drug loading into the matrix are in practice. Some of the most commonly used are  

Solvent swelling technique The matrix can be left to swell in the highly concentrated drug solution. Afterwards, the solvent is removed by suitable physical treatment (e.g., evaporation) [64]. 

Supercritical fluid technique Supercritical fluids are dense as liquids but have viscosity as low as that of gas. In this technique, a solution of the drug efficiently swells the matrix the solvent is then easily removed by decreasing the pressure, leaving the drug behind in the matrix [65]. 

Direct compression method In this method, the drug is grounded and mixed with the matrix and a binder in a definite proportion in the presence of a volatile solvent. Next they are compressed into tablets under high pressure (2-3 tons/cm ) [66]. 

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