Microspheres and Microcapsules

Microencapsulation is a technique which, as its name suggests, involves the encapsulation of small particles of dmg, or solution of dmg, in a polymer film or coat. Microspheres, on the other hand, are solid but not necessarily homogenous particles which can entrap drug. Although the terms tend to be used interchangeably, we retain the distinction here. Microspheres can be prepared also by a variety of techniques which are briefly discussed in the section on nanoencapsulation below. 

Typical photomicrographs of polyfe-caprolac-tone) microphores are shown in Fig. 8.30. 

Any method which will cause a coherent barrier to deposit itself on the surface of a liquid droplet or a solid particle of dmg may be applied to the formation of microcapsules. Many so-called microencapsulation procedures result in the formation of macroscopic beads which are simply coated granules. 

Coacervation is the term used to describe the separation of macromolecular solutions into colloid-poor and colloid-rich (coacervate) phases when the macromolecules are desol-vated. The liquid or solid to be encapsulated is 

Desolvation of water-insoluble macromolecules in nonaqueous solvents leads to the deposition of a coacervate layer around aqueous or solid disperse droplets. Table 8.13 lists both water-soluble and water-soluble macromolecules which have been used in coacervation processes. Desolvation, and thus coacervation, can be induced thermally and 

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Microparticulate systems present the advantage, in comparison with single-unit solid systems, to guarantee a wider contact area between the drug and the mucosa. Different microparticulate systems intended for vaginal administration were developed they include liposomes, microcapsules, and microspheres. Such systems can possess intrinsic bioadhesive properties or can be loaded in a vehicle with bioadhesive properties. 

The term microcapsule is defined, as a spherical particle with the size varying between 50 nm and 2 mm containing a core substance. Microspheres are, in a strict sense, spherically empty particles. However, the terms microcapsules and microspheres are often used synonymously. In addition, some related terms are used as well. For example, microbeads and beads are used alternatively. Spheres and spherical particles are also employed for a large size and rigid morphology. Due to attractive properties and wider applications of microcapsules and microspheres, a survey of their applications in controlled drug release formulations is appropriate. 

Several studies have utilized CLSM techniques to study the distribution and release of biomolecules incorporated in microcapsules and microspheres and to measure the encapsulation efficiency (9,10). Lipophilic fluorophores have been utilized to locate oil-rich regions within mixed-phase microspheres and to examine the distribution of polymeric components with microcapsules. Encapsulated oil could be differentiated from other components, and other fluorescent markers allowed visualization of polymer distribution in the capsule wall (11). The technique has also been used to explore the... 

Microparticles prepared in the presence of CyDs are shown in Fig. 15.2. In microcapsules and microspheres CyDs can either constitute a raw material for the shell of the capsules or the matrix of the spheres, or form with the active ingredient an inclusion complex dissolved or dispersed in the shell or the matrix [9-34]. 

Chitosan Beads, Microcapsules and Microspheres for Gastrointestinal Delivery Systems... 

A variety of different formulations for controlled release polymers exist including microparticles, microcapsules and microspheres. Microparticles range in size from 1-200 pm, while particles with a diameter smaller than 1 pm are called nanoparticles. Microcapsules are microparticles which have the substance of interest enclosed in a shell of degradable polymer. Microcapsules however are characterized by a relatively fast release of large amounts of the enclosed substance. Microspheres (Figi 1), on the other hand, are monolithic in structure, Le. have the substance unifomdy distributed within the polymer layer. This distribution results in a more uniform release over longer periods of time. We selected such microspheies prepared from poly(lactide-glycolide) copolymers to develop our sensors. 

A large variety of drug delivery systems are described in the literature, such as liposomes (Torchilin, 2006), micro and nanoparticles (Kumar, 2000), polymeric micelles (Torchilin, 2006), nanocrystals (Muller et al., 2011), among others. Microparticles are usually classified as microcapsules or microspheres (Figure 8). Microspheres are matrix spherical microparticles where the drug may be located on the surface or dissolved into the matrix. Microcapsules are characterized as spherical particles more than Ipm containing a core substance (aqueous or lipid), normally lipid, and are used to deliver poor soluble molecules... 

Wang, Y., Angelatos, A.S. and Caruso, F. (2008) Chemistry of Materials, 20,848-858. Sukhorukov, G.B. (2002) (eds R. Arshady, and A. Guyot), Microspheres, Microcapsules and Liposomes, Vol. 5 Dendrimers, Assemblies and Nanocomposites, Citus Books, London, Author are the amended details correct ... 

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... 

Bornscheuer UT, Padmanabhan P, Scheper T (1999) In Arshady R (ed) The MML Series Microspheres, microcapsules and liposomes. Citus Books, London, vol 1, p 541... 

Thies C (1999) Microspheres, microcapsules and liposomes. Citus Books, London... 

It has been shown that a modified drug release can be obtained from calcium alginate microcapsules, pellets, and microspheres. When biodegradable bone implants composed of calcium alginate spheres and containing gentamicin were introduced into the femur of rats, effective drug levels in bone and soft tissue were obtained for 30 days and 7 days, respectively. ... 

Suspensions of liposomes, microspheres and microcapsules, and nanospheres and nanocapsules formed from a variety of polymers or proteins, as discussed in section 8.6.3 form a new class of pharmaceutical suspension in which physical stability is paramount. It is important that on injection these carrier systems do not aggregate, as this will change the effective size and the fate of the particles. The exception to this is the deliberate flocculation of latex particles administered to the eye, where aggregation leads to agglomerated... 

Martin, F. J. 1999. Stealth liposomes A pharmaceutical perspective. In Microspheres, microcapsules and liposomes, edited by R. Arshady. London Citus. 

S.V. Mikhalovsky, in Microspheres, Microcapsules and Liposomes, TTie MML Series, Vol. 2 Medical Biotechnology Applications, R Arshady (ed.), Citus Books, London, 1999, 133. 

As the filler of the dismantlable adhesive, thermally expansive microcapsules (Matsumoto Microsphere F-30 Matsumoto Yushi-Seiyaku Co. Ltd.) were used. They consisted of a poly(vinyl chloride) shell filled with liquid hydrocarbon (H-quefied isobutane) as shown in Fig. 34.2. The diameter of the microcapsule was 10-30 pm and the average was 20 pm. The shell thickness was 3—4 pm at room... 

The morphology of the resulting solid material depends both on the material structure (crystalline or amorphous, composite or pure, etc.) and on the RESS parameters (temperature, pressure drop, distance of impact of the jet against the surface, dimensions of the atomization vessel, nozzle geometry, etc.)[ l It is to be noticed that the initial investigations consisted of pure substrate atomization in order to obtain very line particles (typically of 0.5-20 m diameter) with narrow diameter distribution however, the most recent publications are related to mixture processing in order to obtain microcapsules or microspheres of an active ingredient inside a carrier. 

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. 

Gutcho, M.M. (Ed.). Microcapsules and Microencapsulation Techniques, Noyes Data Co., New Jersey, 1976 Arshady, R. (Ed.). Microspheres, Microcapsules and Liposomes, Citrus Books, London, U.K.,... 

Agitated gelling bath to enable controlled gelification/polymerization of the droplet to form microspheres/microcapsules and... 

Bioencapsulation is an emerging technology applied to bioactive molecules to be protected and released under controlled conditions. It has many potential uses in agriculture, food industry, pharmacy, and biomedicine, actually not fully exploited. The most used matrices to build microcapsules or microspheres are polymers, either synthetic or natural, the last ones, known as biopolymers, being preferred for their biocompatibility and good acceptance in food and cosmetics. 

The active constituent/encapsulating material ratio is usually high in reservoir systems (between 0.70 and 0.95), whereas for matrix systems, this ratio is generally lower than 1.5 (more commonly between 0.2 and 0.35). The delivery devices defined in 1 are often referred to as microcapsules and those described in 2 are called microspheres. 

Arshady R. Microspheres Microcapsules and Liposomes Preparation and Chemical Applications. London, U.K. Citus Books 1999. 616p. 

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