Tiny Containers That Make and Pack Themselves

Associate Professor Srinivasa Raghavan and his team at the Complex Fluids and Nanomaterials Group are developing new kinds of fluids and materials at the nano scale, both through the synthesis of new molecules, and through self-assembly, the ability of some molecules to bind into new, more complex forms without a chemical reaction.

Left: A conceptual drawing of a vesicle containing a dissolved drug.  Right: Actual vesicles, measuring approximately 150 nanometers in diameter.

Dr. Raghavan has been working with lipid molecules, which look something like a head with two tails. The lipids' "heads" are attracted to water, while their "tails" are adverse to it. When put into water, the "heads" naturally cluster as they seek water, while the "tails" cluster to avoid it. The "heads" form two walls, with all of the "tails" between them, protected from the water. This bilayer material naturally forms into a sphere with a hollow center, called a vesicle. (See illustration.)

As a vesicle forms, water is captured in its hollow center, turning it into a tiny container. Light and temperature can then be used to reconfigure the vesicle, which causes it to break apart and release the water trapped inside.

A capsule made from biopolymers (e.g. chitosan and gelatin) that contains drugs and magnetic particles.  The capsule can be used for drug delivery to specific locations in the body by guiding it with magnetic fields.  Antibodies, added to the capsule’s outer surface, also assist in targeted delivery by latching onto corresponding antigens in tumors.

One of the most promising applications of this procedure, still being developed, is drug delivery: if a drug is suspended in water, it is trapped inside the vesicles when they form. The vesicles would then travel through the body, breaking apart and releasing the drugs inside under specific conditions. If iron particles are also trapped inside the vesicles, their path through the body could be controlled by magnetic fields. The potential benefits to a patient are groundbreaking: chemotherapy drugs, for example, could be delivered only to the site of a cancer, reducing the strain they put on the body.

	A student loads a sample into a UV-to-visible light (UV-VIS) spectrometer.  The spectrometer is used to determine what sort of light self-assembled systems (such as vesicles) react to, so researchers can control their behavior.

These principles can also be applied to larger forms of self-assembly, such as positively-charged polymers which self-assemble into capsules when placed in a negatively-charged solution. These, in turn, can contain vesicles.

The group also studies "smart" fluids, which can rearrange their molecules to alternate between fluid and gel states when exposed to light or heat; and gels which swell and shrink when stimulated by light, heat, or changes in pH. Smart fluids have the potential to act as tiny valves within nano-scale channels, while the exapanding and contracting gels could be used to create artificial muscles.

To learn more about Dr. Raghavan's research interests, publications, visit the Complex Fluids and Nanomaterials Group site »