Microcapsule designs

De Geest BG, Van Camp W, Du Prez FE, De Smedt SC, Demeester J, Hennink WE (2008) Biodegradable microcapsules designed via click chemistry. Chem Commun 2 190-192... 

Figure 16.2. Some possible microcapsule designs microspheres top left) versus true microcapsules (Arshady 1993 Gibbs et al. 1999).

A majority of the fasteners used in automobiles in the United States are coated with microcapsules loaded with an adhesive. When the fastener is installed, a fraction of the capsules in the coating mpture releasing the adhesive payload. The adhesive essentially glues the fasteners in place preventing them from becoming loose and causing rattles. The capsules are designed so that only a fraction of them break each time a fastener is taken off and put back. The on/off cycle can be repeated three or four times. 

The resulting enzyme-containing microcapsules (which can contain different enzymes in different capsules, as was the case here) were then embedded within a Ca-alginate bead, designated a capsules-in-bead structured microreactor (Scheme 5.7). 

These two seemingly dissimilar applications have a common basis—both are examples of the pressure-sensitive release of a chemical. How are these products designed Tiny spherical capsules (microcapsules or microspheres) with a glass or polymer shell are filled with a liquid core and glued onto paper. For a scratch-and-sniff ad, the core of the microcapsules contains a liquid with the desired scent for carbonless paper, a liquid ink or dye is encapsulated within the... 

Coradin, T., Mercey, E., Lisnard, L. and Livage, J. (2001) Design of silica-coated microcapsules for bioencapsulation. Chemical Communications, 2496-2497. 

Consider the following product design and evaluation problem from the agrochemical industry. A pesticide product consisting of an active ingredient and an additive need to be evaluated in terms of its controlled release characteristics from a polymeric microcapsule to a release medium. Here, since the AI and the additives (solvent and surfactant) are known, the product-evaluation problem consists of designing the microcapsule and identification of... 

If the cere material Is an Irregular material, such as occurs with a ground particle, then the wall will somewhat follow the contour of the Irregular particle and one achieves an Irregular microcapsule. The last well known design for a microcapsule Is that of a multiple wall. In this case the multiple walls are placed around a core to achieve multiple purposes related to the manufacture of the capsules, their subsequent storage and controlled release. 

Haynie, D.T. Method for Designing Polypeptides for the Nanofabrication of Thin Films, Coatings, and Microcapsules by Electrostatic Layer-by-Layer Self Assembly for Use in Medicine, 2003-652364 2005069950 (2005). 

Table 24.1. Properties of the core, encapsulant material and microcapsule of importance in the design of encapsulated bioactives.

In cell encapsulation, ultrathin polymeric membranes microcapsules are used for the immunoprotection of transplanted cells. The membrane must allow the selective passage of some molecules but must act as a barrier to others. As a consequence, a careful material design is fundamental. 

Design of delivery device Shape/geometry Cylinder or rod Microparticles (microsphere, microcapsule, nanoparticle) Film or sheet Viscous gel or liquid... 

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. 

Takada S, Ogawa Y. [Design and development of controlled release of drugs from injectable microcapsules]. Nippon Rinsho 1998 Mar 56(3) 675-679. 

Brungenberg de Jong and coworkers carried out the first extensive studies of complex coacervation (1). They characterized the gelatin-gum arabic coacervation system, a system that later was developed into a process capable of producing microcapsules loaded with a variety of lyophobic materials (2). More recently, an encapsulation process based on the coacervation of gelatin with a polyphosphate has been reported (3). The present paper describes results of a study designed to characterize the gelatin-polyphosphate coacervation interaction and define how various experimental paramenters affect it. 

The expansion behavior of the microcapsules was measured by a PVT (pressure-volume-temperature) apparatus [12, 13] since it is also very important for the design or for modification of the microcapsules. The expansion behavior of the adhesive is discussed on the basis of the experimental results. 

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