Microcapsule-type entrapment

For the microcapsule-type entrapment method, a semi-permeable polymer membrane is used to surround the enzymes. As with lattice-type entrapment, control of the conditions is very important as they can have a detrimental effect on the preparation of the enzyme microcapsules. There... 

The enzyme can be entrapped into the growing polymer or gel materials or microcapsules (microcncapsu-lation). The retention of enzymes in the reaction vessel can also be achieved by an ultrafiltration membrane. All these immobilization types have in common that the enzymes are not modified and are still acting in their soluble form, so that they should be freely mobile in their cage . An older but good review of these techniques is given by Tramper [72], Frequently used matrices for gel entrapment are polyacrylamide and collagen [41]. The membrane inclusion method is a broadly applicable one. 

The solvents used to dissolve the polymeric materials are chosen according to the polymer and drug solubilities and stabilities, process safety, and economic considerations. Substances can be incorporated within microspheres in the liquid or solid state during manufacture or subsequently by absorption. Fig. 1 shows two types of microspheres Microcapsules, where the entrapped substance is completely surrounded by a distinct capsule wall, and micromatrices, where the entrapped substance is dispersed throughout the microsphere matrix. 

The adsorption of polymers, poly(vinyl pyridine) or poly(acrylonitrile) either to coordinate metal atoms or to adsorb biopolymers has been used to prepare chemically modified electrodes for immobihzation of enzymes either by physical or by chemical adsorption (carrier binding), cross-linking, and entrapping at lattice sites or in microcapsules [43]. A wide application of these types of electrodes has been made for electrochemical reactions of biological interest [44]. 

Encapsulation is a formulation technique in which an active compound can be enclosed inside a second material, such as polymeric or nonpolymeric carrier. The product obtained by this process is referred to as microcapsules. These microcapsules are obtainable in two types of morphology— either matrix type or core-shell (Figure 11.8). Matrix-type microcapsules are in which the API is homogeneously distributed within the carrier system. In contrast, core-shell microcapsules consist of a solid shell made up of polymeric materials surrounding a core-forming space, which entraps the API. 

In encapsulation process, microspheres and microcapsules can be obtained. Microspheres are microbeads composed of a biopolymer gel network entrapping an active, whereas microcapsules are constituted by an active ingredient (small droplets of liquid or particles) that is inside a hollow and involved by thin walls(s) (Madene et al 2006 Umer et al 2011). The simplest of the microcapsules may have a core surrounded by a wall of uniform or nonuniform thickness. The core material may have one or several different types of ingredients. The wall may be single or multilayered (Madene et al., 2006). 

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