Semipermeable microcapsules

Chang TMS. In-vivo effects of semipermeable microcapsules containing L-asparaginase on 6C3HED lymphosarcoma. Nature 1971a 229 117-118. 

Transplantation of islets of Langerhans as a means of treating insulin-dependent diabetes mellitus has become an important field of interest [217-219]. However, tissue rejection and relapse of the initial autoimmune process have limited the success of this treatment. Immunoisolation of islets in semipermeable microcapsules has been proposed to prevent their immune destruction [220, 221]. Nevertheless, a pericapsular cellular reaction eventually develops around micro-encapsulated islets, inducing graft failure [222]. Since empty microcapsules elicit a similar reaction [223], the reaction is not related to the presence of islets within the capsule but is, at least partially, caused by the capsule itself. Consequently, microcapsule biocompatibility appears to constitute a major impediment to the successful microencapsulated islet transplantation. 

Semipermeable microcapsules of cellular dimensions (10-20 p. dia 200 A thick) can be formed, each containing enzyme, or some other large molecule. Useful membranes have been made of collodion or other polymeric materials. These membranes are permeable to the substrates and products of enzymic action, but the enzyme itself is too large to leak out. A great many enzymes have been successfully encapsulated, and the method appears to have general applicability. A limitation appears, however, in that large substrate molecules (proteins, polysaccharides) cannot permeate into the capsule, and the system is not applicable to such hydrolyses. 

Chang, T.M.S., Poznansky, M. J. Semipermeable microcapsules containing catalase for enzyme replacement in acatalasaemic mice. Nature 1968, 218 (5138), 243-245. 

In the case of microencapsulated cells and enzymes in biotechnology, high-molecular-weight components can be retained in microcapsules, while low-molecular by-products and substrate residues are extracted through semipermeable microcapsule walls. 

Goosen, M.F.A., O Shea, G.M., Gharapetian, M.M., and Sun, A.M., Immobilization of living cells in biocompatible semipermeable microcapsules biomedical and potential biochemical engineering applications, in Polymers in Medicine, Chiellini, E., Ed., Plenum Publ. Comp., New York, 1986, pp. 235-247. 

Chang T M S 1976 Biodegradable semipermeable microcapsules containing enzymes, hormones, vaccines, and other biologicals. J Bioeng 1 25-31... 

Microencapsulation refers to the formation of a spherical gel around each group of islets, cell cluster or tissue fragment. Microcapsules based on natural or synthetic polymers have been used for the encapsulation of both mammalian and microbial cells as well as various bioactive substances such as enzymes, proteins and drugs. A review of alternative semipermeable microcapsules prepared from oppositely charged water soluble polyelectrolyte pairs has been presented in recent papers. The main advantage of this approach is that cells, or bioactive agents, are isolated from the body by a microporous semipermeable membrane and the encapsulated material is thus protected against the attack of the immune system. In the case of microencapsulated pancreas islets, a suspension of microcapsules is typically introduced in the peritoneal cavity to deliver insulin to the portal circulation. 

Chang, T.M.S. (1977a), Experimental therapy using semipermeable microcapsules containing enzymes and other biologically active material. In Biomedical Applications of Immobilised Enzymes and Proteins Vol. 1 (ed. T.M.S. Chang), Plenum Press, New York and London, Chapter 11, pp. 147-162. 

Polyamide, collodion (cellulose nitrate), ethylcellulose, cellulose acetate butyrate or silicone polymers have been used for preparation of permanent microcapsules. This method offers a double specificity due to the presence of both the enzyme and a semipermeable membrane. Moreover, it allows simultaneous immobilization of many enzymes in a single step and the surface area for contacting the substrate and the catalyst is large. The need of high protein concentration and the restriction to low molecular weight substrates are the main limitations of enzyme microencapsulation. 

Defining inside from outside is a fundamental trait of living organisms. The creation of noimamral strucmres that can define in from out with nonpermeable or semipermeable barriers offers the potential of protecting the internal content from destmction, contamination, and unwanted dispersal until the content is dehvered to a defined location. Small spherical structures that define in and out are well known and come in forms ranging from microcapsules to vesicles to micelles. We refer to these structures collectively as polymeric capsules. 

Microcapsule properties make them attractive materials for a wide variety of practical applications. In the area of catalysts, microcapsules provide semipermeable membranes that are readily produced and dispersed. These properties, along with others, have inspired systems that include synthetic or man-made encapsulated catalysts, such as organocatalysts, metal particles, enzymes, and organometallic... 

Chang TMS. Semipermeable aqueous microcapsules (artificial cells)—with emphasis on experiments in an extracorporeal shunt system. Trans Am Soc Artif Internal Organs 1966 12 13-19. 

Chang TMS, Macintosh FC, Mason SG. Semipermeable aqueous microcapsules. I. Preparation and properties. Can J Physiol Pharmacol 1966 44 115-128. 

In the biotechnology industry microencapsulated microbial cells are being used for the production of recombinant proteins and peptides. The retention of the product within the microcapsule can be beneficial in the collection and isolation of the product. Encapsulation of microbial cells can also increase the cell-loading capacity and the rate of production in bioreactors. Smaller microcapsules are better for these purposes they have a larger surface area that is important for the exchange of gases across the microcapsule membrane. Microcapsules with semipermeable membranes are being used in cell culture. A feline breast... 

Lee outlines three different physical methods that are commonly utilized for enzyme immobilization. Enzymes can be adsorbed physically onto a surface-active adsorbent, and adsorption is the simplest and easiest method. They can also be entrapped within a cross-linked polymer matrix. Even though the enzyme is not chemically modified during such entrapment, the enzyme can become deactivated during gel formation and enzyme leakage can be problematic. The microencapsulation technique immobilizes the enzyme within semipermeable membrane microcapsules by interfacial polymerization. All of these methods for immobilization facilitate the reuse of high-value enzymes, but they can also introduce external and internal mass-transfer resistances that must be accounted for in design and economic considerations. 

Encapsulation. Immobilization of enzymes by encapsulation within semipermeable structures dates back to the 1970s. There are three fundamental variations of this approach. In coacervation, aqueous microdroplets containing the enzyme are suspended in a water-immiscible solvent containing a polymer, such as cellulose nitrate, polyvinylacetate, or polyethylene. A solid film of polymer can be induced to form at the interface between the two phases, thereby producing a microcapsule containing the enzyme. A second approach involves interfacial polymerization in which an aqueous solution of the enzyme and a monomer are dispersed in an immiscible solvent with the aid of a surfactant. A second (hydrophobic) monomer is then added to the solvent and condensation polymerization is allowed to proceed. This approach has been used extensively with nylons, but is also applicable to polyurethanes, other polyesters, and polyureas. 

Wallace, A. M. Wood, D. A. Development of a simple procedure for the preparation of semiperme-able antibody-containing microcapsules and their analytical performance in a radioimmunoassay for 17-hydroxyprogesterone. Clinica Chimica Acta (1984), 140(2), 203-212. 

Bugarski, M.B., Sajc, L., Plavsic, M., Goosen, M.F.A., and Jovanovic, G., Semipermeable alginate-PLO microcapsules as a bioartificial pancreas, in Animal Cell Technology, Basic and Applied Aspects, Vol. 8, Funatsu, K., Shirai, Y., and Matsushita, T., Eds., Kluwer Academic Publishers, Dordrecht, 1997, pp. 479-486. 

Materials and Methods. Stable microcapsules (mean diameter, 8 10 pm) with a semipermeable membrane of poly(styrene) (PSt) were prepared by depositing the polymer around emulsified aqueous droplets using the following three procedures (i) primary emulsification of an aqueous solution of sodium dodecylbenzenesulfonate or Triton X-100 as an emulsifier in dichloromethane containing PSt with a homoblender ... 

Methods for forming microparticles containing encapsulated cells have been described. The cells may be encapsulated in a microcapsule that includes an internal cell core containing polysaccharide gum surrounded by a semipermeable membrane (22). The microcapsule is made from alginate in combination with polylysine, poly-omithine. 

Microencapsulation of enzymes (and other biomolecules) has been extensively studied. The microcapsules have semipermeable walls that allow small substrate and product molecules to pass through freely, while large enzyme molecules are retained in solution within the capsules. However, the polymerization process used in forming the capsules generates heat that may damage the enzymes. 

Microencapsulation involves surrounding a collection of cells with a thin generally micrometer sized, semipermeable membrane. Its primary purpose is to protect the encapsulated cells from the host s immune system, while allowing the exchange of small molecules and thereby ensuring cell survival and function. There are several requirements for polymer capsules or hydrogels used as components of microcapsules ... 

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