Delivery with Microcapsules

Dehvering pharmaceutical agents to specific cells in the body is a difficult task involving complex interactions between many elements. Delivery systems have several fundamental requirements to achieve this task. The delivery vehicle must be ingesti-ble, implantable, or injectable to introduce the dmg into the body. The system must then protect the drug from the body s defense mechanisms in order to accumulate in selected cells. Once at the target, the delivery system should release the enclosed pharmaceutical agent with a controllable and predictable profile. Finally, the delivery vehicle should be biocompatible, nontoxic, and easily eliminated from the body. 

---

Figure 5.11 Nude mice skin experiment was performed to demonstrate the possible delivery of 5-FU from microcapsule-fabricated cotton (a) nude mouse (b) nude mouse skin treated with microcapsule-fabricated cotton samples (right-hand side 5-FU microcapsules treated cotton left-hand side blank microcapsules treated cotton) (c) nude mouse skin treated with microcapsule-fabricated cotton after 24 h (d) release of 5-FU from microcapsule-fahricated cotton after 24 h. For (b) and (c), the left sample represents the microcapsule without dmgs and the right sample represents the 5-FU-loaded microcapsules (Lam et al., 2012).

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. 

Oil-in-water emulsions lend themselves readily to the delivery of oils and oil-soluble bioactives. The surfactant or biopolymer provides a means of isolating and protecting the lipophihc cores. Many types of materials with emulsifying capacity have been used to encapsulate oils and oil-soluble bioactives in single and multiple emulsion systems. Multilayered interfaces have also been used to improve the robustness of microcapsules. 

Poly(amino acid)s (PAAs) have also been used in drug delivery PEO-(l-aspartic acid) block copolymer nano-associates , formed by dialysis from a dimethyl acetamide solution against water, could be loaded with vasopressin. PLA-(L-lysine) block copolymer microcapsules loaded with fluorescently labelled (FITC) dextran showed release profiles dependent on amino acid content. In a nice study, poly(glutamate(OMe)-sarcosine) block copolymer particles were surface-grafted with poly(A-isopropyl acrylamide) (PNIPAAm) to produce a thermally responsive delivery system FITC-dextran release was faster below the lower critical solution temperature (LCST) than above it. PAAs are prepared by ring-opening polymerisation of A-carboxyanhydride amino acid derivatives, as shown in Scheme 1. 

Live rotavirus vaccine was developed for oral delivery to prevent infections by the virus in young children. However, incorporation of live rotavirus into poly (oL-lactide-co-glycolide) microspheres or alginate microcapsules was reported to result in a significant loss of rotavirus infectivity. The loss was reduced by stabilization of the rotavirus vaccine with an excipient blend of cellulose, starch, sucrose, and gelatin at a mass ratio of 30 30 30 10 in granules or tablets. ... 

---