Temperature-Triggered Release

To verify this, we performed experiments of release in the presence of anionic SDS (sodium dodecyl sulfeite), cationic CTAB, or nonionic Ifralan D205 (mixture of poly(oxyethylene) molecules C12E5 and C10E5) at a concentration of about 60 times the critical micellar concentration. As expected, the addition of SDS 

The differences of release could be exploited for various applications. One could take advantage of the release of large drops (in the absence of surfactant) for a sudden release as soon as a given temperature threshold is reached. Otherwise, the formation of very small drops containing a water-insoluble monomer or initiator could be used in order to provoke a controlled and spatially uniform release to start a polymerization. The only drawback, which is the inability to encapsulate hydrophihc compounds, will be addressed in the next part 

Using the same concepts, we moved on to double emukions instead of simple wax in water emukions in order to dkpose of several compartments in the capsules. Double emukions, simply put, are emukions in which each droplet 

Rhodamine B is exclusively present in the inner water droplets and not in the wax (the fluorescence that seems to come from the wax originates in fact in water droplets located below the observed slice), nor in the outer water phase. This indicates that during the second emulsification step, no contact between the two aqueous phases occurred. Fluorescence is even more visible at the water-wax interface, likely due to a Rhodamine B affinity for the interface because of the presence of aromatic cycles. During mineralization, Rhodamine present at the interface has been embedded inside the newly formed silica shell. 

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Fig. 4.9 Temperature and pH-value (qualitatively) in the different cycles of an automatic dishwashing program and the dissolution of a tablet with temperature triggered release of rinse aid.

Thermosensitive HPMA mono/dilactate polymer was prepared and the temperature-triggered release of content from polymer-coated liposomes studied. HPMA mono/ dilactate polymer was synthesized with a cholesterol anchor suitable for incorporation in the liposomal bilayers and with a cloud point temperature of the polymer slightly above normal body temperature (42°C)... 

Layer-by-layer electrostatic deposition of biopolymers at interface of emulsion droplets Polyelectrolyte capsules microparticles with novel functionality and triggered release multiple layers around oil droplets exhibiting improved stability towards environmental stresses (temperature, ionic strength, pH, freezing, dehydration) McClements, 2005, 2006 Sanguansri and Augustin, 2006... 

That crosslinking has indeed occurred is confirmed by the very existence of aggregates at 25 °C, as in its absence the diblock copolymers are completely soluble at this temperature. Tunability of the solubility of the PMEMA block in water arises from the fact that its lower critical solution temperature (LCST) lies between 25 and 60 °C. This reversible hydration of the core could be a very useful feature to trigger release of occluded guest molecules from the core interior. More recently, utilizing a similar methodology, zwitterionic shell-crosslinked systems have also been prepared wherein the core and shell domains contain amine and carboxylic acid groups, respectively, or vice versa. Such systems exhibit an isoelectric point, at a pH wherein the crosslinked micelles ( 40 nm) become electrically neutral and precipitate out in water addition of acid or base causes complete redissolution of these nanospheres [58]. 

Nevertheless, this is a challenge which often stretches the capability of formulation scientists to generate solutions. Opportunities clearly exist for truly triggered release formulations that deliver free pesticide on the basis of a temperature, a biological or another environmental trigger. 

Alternatively, based on the fact that the local temperature in sohd tumors is sHghtly higher than the regular body temperature, polymer chemists have designed hydrophobic blocks that are able to react to an increase in temperature. It is well known that polymers can undergo relatively well-defined transitions, from a water-soluble to a water-insoluble material, and vice versa. Hence, if the transition temperature of the hydrophobic block is tuned in a suitable way, then a thermally triggered release of the drug can be achieved. 

Lee, S.Y., et al. Shell cross-linked polyethylenimine-modified micelles for temperature-triggered drug release and gene delivery. Rsc Advances 4(101), 57702-57708 (2014)... 

The study demonstrates that liposomes surface-modified with A-(2-hydroxypropyl)methacrylamide (HPMA) mono/dilactate copolymer are attractive systems for achieving temperature-triggered content release... 

Some disease states are associated with local hyperthermia. Alternatively, local increases in body temperature can be induced by exterior means, making temperature-directed drug release another viable triggered release strategy. To that aim, polymers... 

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