Alginate encapsulation agents

In a trial, alginate was crosslinked with hyaluronate, which are both pH-responsive biomaterials, as encapsulation agents in the form of microspheres. The spherical micro-spheres presented promising loading and release behaviors in the simulated gastrointestinal tract media [69]. 

More robust enz5mies have been obtained [95] by encapsulation. TEOS is better used with Ca-alginate as agent for producing a Ca-silicate cage, as it avoids any interference with the production of methanol in the case of non-complete hydrolysis of TMOS [97, 98]. Co-encapsulated enzymes work better than singly encapsulated ones [99]. 

Another biomedical appHcation of mictocapsules is the encapsulation of Hve mammalian ceUs for transplantation into humans. The purpose of encapsulation is to protect the transplanted ceUs or organisms from rejection by the host. The capsule sheU must prevent entrance of harmful agents into the capsule, aUow free transport of nutrients necessary for ceU functioning into the capsule, and aUow desirable ceUular products to freely escape from the capsule. This type of encapsulation has been carried out with a number of different types of Hve ceUs, but studies with encapsulated pancreatic islets or islets of Langerhans ate most common. The alginate—poly(L-lysine) encapsulation process originally developed in 1981 (54) catalyzed much of the ceU encapsulation work carried out since. A discussion of the obstacles to the appHcation of microencapsulation in islet transplantation reviewed much of the mote recent work done in this area (55). Animal ceU encapsulation has also been researched (56). 

In the dual liposome-microcapsule system, two factors control the release of the active substance escape from lipsomes into the microcapsule interior, and diffusion across a rate limiting capsule wall into the external environment. This system can take advantage of the inherent instability of some lipsomes while over-coming many of the problems associated with their use by protecting them from the environment by the capsule. At the same time, a new measure of control over the time at which a microcapsule will commence delivery of the enclosed agent is introduced by careful choice of the liposome composition. By changing the nature of the liposomes or of the encapsulant (e.g. alginate) different release times and patterns can be obtained. 

The gelation technology employs chemical interactions to cause liquid droplets to gel, forming microcapsules or microspheres. This technique is used by the pharmaceutical industry to encapsulate active agents and also to immobilize live cells and organisms. In one process, live cells are first entrapped in gel matrix beads produced by the reaction of sodium alginate with calcium ions. The outer layer of the beads is then hardened by treatment with a polycation to form a polyelectrolyte complex, while the interior of the beads is solubilized by treating with sodium nitrate to form a soluble complex. 

One can entrap into microcapsules not therapeutic agents but alive cells which can produce these compounds (recombinant proteins, including enzymes, hormones, peptide immunostimulators or immunomodulators, etc.). One of the most widely used techniques for animal cell encapsulation into alginate-polycation microcapsules has been described earlier (see Section lll.A). 

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