Physical Encapsulation Systems

Most DDS belong to one of two main categories physical encapsulation systems and covalent encapsulation systems. These two DDS will be described in more detail in 

Physical encapsulation systems use polymer nanostructures as formulation systems, and the polymer can have different uses. It may prevent dissolution or it may control diffusion. Polymers that delay drug dissolution slow the rate at which drug molecules are exposed to water from the aqueous environment surrounding the DDS. This may be achieved by using a polymer coating or a matrix that dissolves at a slower rate than the drug [30-32]. 

Most polymer systems used in physical encapsulation systems are based on biopolymers such as chitosan, dextran, polylactides, or copolymers of lactide and glycolic acid. These are often prepared with PEG chains to enhance circulation and avoid rapid protein deposition. These polymers have good biodegradation properties, they are hiocompatible and biodegradable, and produce well-tolerated degradation 

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Figure 3.2 Physical encapsulation systems [33]. Reproduced with permission from L.M. Kaminskas, V.M. McLeod, C.J.H. Porter, and B.J. Boyd, Molecular Pharmaceutics, 2012, 9, 3, 355. 2012, ACS...

The various cabinet systems described above were all of rigid construction. Experience shows that rigid cabinets offer many advantages they are robust, can support heavy items of equipment and peripherals such as pass boxes and interface panels. However, it is practical to consider the use of plastic film isolator technology as an alternative approach to providing physical encapsulation. ... 

Preencapsulation Steps 1. Encapsulation of bioactive molecules in micro/nanospheres or hydrogels 2. Loading of encapsulating system into the polymer nanocomposite carrier system ++++ Polymer matrix degradation Uncontrolled diffusion of bioactive molecule is prevented through a physical barrier until the encapsulation system has been sufficiently degraded... 

The HLB system has made it possible to organize a great deal of rather messy information and to plan fairly efficient systematic approaches to the optimiza-tion of emulsion preparation. If pursued too far, however, the system tends to lose itself in complexities [74]. It is not surprising that HLB numbers are not really additive their effective value depends on what particular oil phase is involved and the emulsion depends on volume fraction. Finally, the host of physical characteristics needed to describe an emulsion cannot be encapsulated by a single HLB number (note Ref. 75). 

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

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