ABSTRACT
Life affords no higher pleasure than that of surmounting difculties, passing from one stage of success to another, forming new wishes and seeing them gratied.
Samuel Johnson
Several chemically and physically based techniques of microencapsulation have been developed over decades,1-3 aiming to protect small drug molecules, proteins, and DNA from the environment,4-7 to spatially or temporally control their release rates and patterns,8 to mask their undesirable tastes and odours,9 and to encapsulate cells.10,11 Being a versatile and straightforward way, the solvent removal (evaporation/extraction) methods are the simplest and the most popular way for microspheres preparation to accomplish these goals. Microsphere/microcapsule formation by the solvent evaporation and extraction methods were patented early in 1970s by Vranken and Claeys,12,13 and the rst appearance of the technique in literature goes back to late seventies.14 A wide variety of active pharmaceutical ingredients have been encapsulated; unionized and lipophilic small drug molecules are commonly encapsulated using simple emulsion technique, while hydrophilic or ionized compounds, such as proteins and peptides are often incorporated using double complex emulsion.15-17 Despite the fact that controlled release can be achieved using common dosage forms such as tablets, rugged matrix microspheres manufactured by the emulsion solvent removal technique offer incentives in preparing liquid suspensions and injectable dosage forms with better control of drug release.18,19 Efforts have been made to develop drug carriers capable of delivering the active molecules specically to the intended target organ (drug targeting), while increasing the therapeutic efcacy and reducing the total amount of drug administered. Lupron Depot® (leuprolide acetate, TAP Pharmaceuticals Inc.), indicated for the treatment of prostate cancer, endometriosis, uterine broids, and central precocious puberty, is the rst commercial product based on poly(lactic-co-glycolic) acid (PLGA) polymers20 manufactured via the double emulsion solvent evaporation method. Later, more products were introduced, such as Vivitro® (naltrexone, Cephalon)21,22 and Consta Risperdal® (Risperidone, Janssen Pharmaceuticals),23-26 which were manufactured using the simple oil-in-water (O/W) emulsion solvent removal methods.
