Microencapsulation processes

Fig. 6. Flow diagram of microencapsulation process that utilises acid-cataly2ed in situ polymerisation of melamine or urea with formaldehyde to form a...

J.E. Vandegaer, Ed, Microencapsulation — Processes and Applications , Plenum Press, NY (1974) [Proceedings of the American Chemical Society Symposium on Microencapsulation Processes and Applications, held in Chicago,... 

The steroid microsphere systems are probably the most successful drug delivery formulations thus far ba.sed on lactide/glycolide polymers. Several of these products appear to be on track for human and animal applications in the 1990s. The success of these formulations is due to the known safety of the polymer, the reproducibility of the microencapsulation process, reliability in the treatment procedure, and in vivo drug release performance (80). 

The typical microencapsulation process via complex coacervation is illustrated in Figure 6.7. 

Several patent applications have been granted to SGT covering its sol gel microencapsulation process and its implementation for... 

The microencapsulation process can be classified into two main categories (as defined by Thies [38] and reported in Table 21.3) (a) chemical process and (b) mechanical process. 

Thies, C. (1996) A survey of microencapsulation processes, in Microencapsulation Methods and Industrial Applications (ed. S. Benita), vol. 17, Marcel Dekker, New York, pp. 1-21. 

Enhancing Drug Release from Folylactide Microspheres by Using Base in the Microencapsulation Process... 

The solvent evaporation microencapsulation process using sodium oleate as the emulsifier produced microspheres in high yields (75-95%), essentially free of agglomeration (1). Drugs with low solubility in water (0.02 mg/ml or less) e.g. thioridazine, were incorporated with 80-99% efficiency. Core loadings up to 60% were attained along with prolonged in vitro release. 

Vandegaer, Jan E. "Microencapsulation—Processes and Applications." 180 p., Plenum Press, New York, 1973. 

Another innovation in in-situ microencapsulation is aminoplast shellwalls containing base-cleavable ester moiety [15]. Polyols reacted with diacids that contain thiol or hydroxy functionality produce crosslinking groups. These crosslinking groups along with urea-formaldehyde prepolymer are dissolved into the pesticide and the in-situ microencapsulation process is completed. The resultant microcapsules may contain an insecticide that is safer to handle under acidic conditions yet will rapidly release the insecticide in the alkaline gut of an insect. Alternately, base could be added to the spray tank to rapidly release capsule contents prior to application. 

R. E. Sparks, I. C. Jacobs, Selection of Coating And Microencapsulation Processes, Controlled Release Delivery Systems, Marcel Dekker, Inc., USA, 1999, pp. 3-29. 

H. B. Scher and M. Rodson, Microencapsulation Process, United States Patent 4,956,129, 1990. 

M. Rodson and H. B. Scher, Water-in-oil Microencapsulation Process and Microcapsules produced thereby. United States Patent 6,113,935, 2002. 

Vandegaer, J. E. (ed.) Microencapsulation - process and applications. New York Plenum Press 1974... 

Ransone CM, Eyman IV, Litzinger D, CoUoton M, and Shah SS. 1999, A novel microencapsulation process for sustained dehvery of proteins. Proc. Inter. Symp. Control. Release Bioact. Mater. 1999 26 603-604. 

Robinson, D.H. Ethyl cellulose-solvent phase relationships relevant to coacervation microencapsulation processes. Drug Dev. Ind. Pharm. 1989, 15 (14-16), 2597-2620. 

Kaeser-Liard, B. Kissel, T. Sucker, H. Manufacture of controlled-release formulations by a new microencapsulation process, the emulsion-induction technique. Acta Pharm. Technol. 1984, 30 (4), 294-301. 

Exposure to w/o interfaces Reducing or avoiding denaturation at w/o interfaces by including protective excipients/ employing anhydrous microencapsulation processes. 

Thies, C. A survey of microencapsulation processes. In Microencapsulation Methods and Industrial Applications ... 

The internal structure of microspheres may vary as a function of the microencapsulation process employed. " Reservoir microcapsules have a core of... 

Tice, T.R. Gilley, R.M. Microencapsulation Process and Products Therefrom. US Patent 5,407,609, Apr 18, 1995 Southern Research Institute Birmingham, AL. 

Hydroxypropyl cellulose is also used in microencapsulation processes and as a thickening agent. In topical formulations, hydroxypropyl cellulose is used in transdermal patches and ophthalmic preparations. ... 

Debenedetti and coworkers (88,89) provided one of the first examples of microencapsulation of a drug in the polymeric matrix. Richard and coworkers (90) provided a recent example of the microencapsulation process when they produced microparticles with the encapsulated model protein that showed sustained release. Foster and coworkers (87) also reported precipitation of copper-indomethacin by PVP with a 96-fold enhancement in the dissolution rate of indomethacin. These examples clearly demonstrated the advantages of using supercritical fluid processing for the preparation of polymer-drug formulations with potentially improved therapeutic properties. 

Shine AD, Gelb J Jr. Microencapsulation process using supercritical fluids. US patent 5766637, 1998. 

Regarding nucleation of solid particles from liquid droplets (antisolvent, nebulization, PGSS, microencapsulation processes), it is obvious that the droplets size is a basic parameter in the process. Some investigators reported results of experimental works supported by theoretical considerations on droplet formation by injection of a liquid into a pressurized fluid using a simple capillary nozzle (78) or a coaxial nozzle (79). Both articles, following previous works on liquid droplets formation into an insoluble liquid or into a gas, suggest the correlation of the experimental results with two dimensionless numbers... 

Large lots can be prepared on a commercial-scale plant (XlOO, Fig. 8), where several tens of kilograms of particles can be obtained daily, either by RESS, antisolvent, or microencapsulation processes. For a nonpharmaceutical application, we envisage modifying a large SFE plant (XIOOO, Fig. 9) for processing at least 1000 kg of powder per day by an antisolvent process. 

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