Temperature-responsive microcapsules

Encapsulation of PNIPAM inside non-temperature-sensitive (PSS/PAH) capsules templated on PS cores was achieved by the same ship in a bottle synthesis [37], providing temperature-responsive microcapsules. Encapsulated PNIPAM collapsed when the temperature of the system increased above 34 °C, forming discrete particles inside the capsule, without modification of the shell (Fig. 3.6). This prop-... 

A method to prepare well-defined responsive microcapsules and nanocapsules with engineered walls is reported. A decomposable colloidal template is coated by polyelectrolyte multilayers, and after core removal a hollow capsule, refillable with drugs, is obtained. The release of the capsule as well as mechanical properties can be tuned by adjusting pH and temperature. 

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. 

The membranes of the thermosensitive controlled-release microcapsules were constructed by a random mixing Aquacoat (Table 1) with the latex particles having poly(EA/MMA/2-hydroxyethyl methacrylate) core and poly(A-isopropylacrylamide (NIPAAm)) shell. This is an example where the membrane has the random two-phase structure as shown in Fig. 5. The microcapsules exhibited a thermosensitive release of water-soluble drug. The mechanism is explained in Fig. 6. When the temperature was changed in a stepwise manner between 30 and 50°C, the microcapsules showed an on-off pulsatile release. This on-off response was reversible. 

Figure 5.5 pH-responsive volume change ratios of PDMAEMA microcapsules prepared at different pH values. The test temperature is 37 °C. The compositions of the middle fluid are 1.0 mol DMAEMA, 0.05 mol IT MBA, 0.05% w/v V50, 1% w/v Pluronic F127, 5% w/v glycerin. (Reproduced from Wei et aiy with permission from Elsevier.)... 

C. Gao, S. Leporatti, S. Moya, E. Donath and H. Moehwald, Swelling and shrinking of polyelectrolyte microcapsules in response to changes in temperature and ionic strength. Chemistry — A European Journal, 9(4), 915-920 (2003). 

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