Pharmaceutical Applications of Polymeric Membranes

Both W/O/W and O/W/O emulsions have attracted considerable attention because of their potential applications in food science [4-7], cosmetics [8-10] and pharmaceutics [11]. In particular, there have been many studies on the pharmaceutical applications of W/O/W emulsions because the internal aqueous droplets can contain water-soluble drugs for controlled release or targetable delivery [12-14]. Solid microcapsules loaded vhth bioactive polymers are also prepared from W/O/W droplets by the solvent evaporation method [15-18]. Other applications studied thus far include the synthesis of shaped polymeric microparticles [19] and the use of the intermediating phase as the permeation membrane in separation technology [20-25]. 

The main application of this technology for metal extraction will probably be in the treatment of effluents and wastewaters as shown by the many research papers that have been published. This is particularly true of the supported liquid membrane because of the many modules required to treat significant volumes of feed solution. This then creates a large capital expenditure, aud, although lifetimes of polymeric membranes have now been increased considerably, the initial outlay will probably be too great for the value of any benefits or metal recovered. However, if this process can be used for high-value products, then the expenditure can be more easily justified— hence, the potential use of such systems for recovery of pharmaceutical compounds. 

Hydration can be an important factor in diffusion and mass transport phenomena in pharmaceutical systems. It may alter the apparent solubility or dissolution rate of the drug, the hydrodynamic radii of permeants, the physicochemical state of the polymeric membrane through which the permeant is moving, or the skin permeability characteristics in transdermal applications. 

Generally, a distinction can be made between membrane bioreactors based on cells performing a desired conversion and processes based on enzymes. In ceU-based processes, bacteria, plant and mammalian cells are used for the production of (fine) chemicals, pharmaceuticals and food additives or for the treatment of waste streams. Enzyme-based membrane bioreactors are typically used for the degradation of natural polymeric materials Hke starch, cellulose or proteins or for the resolution of optically active components in the pharmaceutical, agrochemical, food and chemical industry [50, 51]. In general, only ultrafiltration (UF) or microfiltration (MF)-based processes have been reported and little is known on the application of reverse osmosis (RO) or nanofiltration (NF) in membrane bioreactors. Additionally, membrane contactor systems have been developed, based on micro-porous polyolefin or teflon membranes [52-55]. 

Membrane polymeric materials for separation applications are made of polyamide, polypropylene, polyvinylidene fluoride, polysulfone, polyethersulfone, cellulose acetate, cellulose diacetate, polystyrene resins cross-linked with divinylbenzene, and others (see Section 2.9) [59-61], The use of polyamide membrane filters is suggested for particle-removing filtration of water, aqueous solutions and solvents, as well as for the sterile filtration of liquids. The polysulfone and polyethersulfone membranes are widely applied in the biotechnological and pharmaceutical industries for the purification of enzymes and peptides. Cellulose acetate membrane filters are hydrophilic, and consequently, are suitable as a filtering membrane for aqueous and alcoholic media. 

Microporous polymeric membranes are used widely for filtration and purification processes, such as filtration of wastewater, preparation of ultra-pure water, and in medical, pharmaceutical or food applications, including removal of microorganisms, dialysis and protein filtration. 

Other relevant examples of application for ceramic nanofilters have been reported [124], The first separation problem in which ceramic NF membranes are likely to compete with polymeric membranes is the concentration of pharmaceutical components in their reaction solvents. Ceramic nanofllters are also of interest in the agrofood indnstry for separation processes working at relatively high temperatnre and/or in the presence of organic solvents. Another potential application is in the production of chemically modified sugars in which the N-methyl-pyrrolidone (NMP), nsed as the solvent for the reaction, needs to be removed from the product (minimum molecular weight about 1000 Da) down to 0.1%. In this case, diaflltration with a ceramic NF membrane has shown to be an efficient way of decreasing the NMP content down to the intended low NMP residual... 

Many membrane separation applications have already benefitted from membrane modification strategies. Chapter 10 describes how bespoke polymeric membranes have been used to improve the crystallization of biomolecules. Membrane crystallization allows through a careful control of the process parameters the production of crystals with controlled shape, size, size distribution, and polymorphism. Further research is required to provide comprehensive understanding of the complex relationships between membrane process parameters and crystal structure. The control of product polymorphism will continue to be important in the pharmaceutical industry, which, as the range of drugs and their specificity increase, will reqnire improved... 

Microencapsulation, a formulation technique much used in the pharmaceutical industry, is beginning to have limited application for farm chemicals. It consists of surrounding the toxicant with a polymeric membrane. In one example of this technique, known as interfacial encapsulation, a compatible oil-soluble toxicant... 

Surfactant aggregates (microemulsions, micelles, monolayers, vesicles, and liquid crystals) are recently the subject of extensive basic and applied research, because of their inherently interesting chemistry, as well as their diverse technical applications in such fields as petroleum, agriculture, pharmaceuticals, and detergents. Some of the important systems which these aggregates may model are enzyme catalysis, membrane transport, and drug delivery. More practical uses for them are enhanced tertiary oil recovery, emulsion polymerization, and solubilization and detoxification of pesticides and other toxic organic chemicals. 

Polymeric microencapsulates and lipid microencapsulates have extensive potential applications in food, cosmetics and pharmaceutics [1-5]. Microencapsulates can protect and conserve an active component until its release is desired and stimulated. Polymeric microencapsulates consist of a (biocompatible) polymer matrix in which an active component is encapsulated. Most frequently poly(lactic add) (PLA) or poly (lactic-co-glycolic acid) (PLGA) is used as the polymer [6,7], but alternatives have been investigated [8, 9]. Lipid microencapsulates, lipid vesicles and liposomes are composed of a (phospho-)lipid bilayer membrane that encapsulates an aqueous volume, thus mimicking a cell structure. 

Membranes, both polymeric and ceramic, play an important role in pharmaceutical and medical sciences and have a great future in many different directions of their applications, such as artificial organs, drug delivery and others. Many other applications also seem to remain unexplored. 

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