Capsules enable on demand drug release

Capsules that can release their contents at a selected temperature have been developed by researchers in France, and could lead to the development of therapeutic agents that are applied to the skin and triggered locally by rubbing.

According to a news release from the CNRS Paul Pascal Research Centre (France), published via AlphaGalileo, silica substrates, which are often used to deliver encapsulated therapeutic agents, lead to uncontrolled, or practically uncontrolled, drug release. The new capsules, however, offer on demand drug release that is activated by raising the temperature.

The dosage form is created by dispersing oil, which can contain a specific agent, in water. When stabilized into droplets by silica particles, the emulsion offers the distinct characteristic of being made of oil that is liquid at the production temperature, but solid at ambient temperature. A silica shell is then polymerized around the cooled droplets and the contents can be released by warming the capsule to above the melting temperature of the selected oil; the transition from the solid state to the liquid state leads to expansion of the confined oil, which breaks the silica shell.

Release temperatures between 35 °C and 56 °C can be selected by choosing the appropriate oil or by mixing several types of oil. The way in which the capsule contents are released, such as a string of droplets or all in one go, can also be controlled.

According to the news release, the principle is very simple and cheap. As well as possibly aiding the drug delivery of therapeutic agents onto the skin, which are then triggered locally by rubbing to generate heat, the capsules could also be used to monitor the freshness of foods or to release perfume into the air, onto the fabric or onto the skin. The researchers are now working on designing double emulsion systems that could be used to extend the technique to multitherapy.