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Plankton inspired stealth armor for slow release microscopic drug vehicles

By Rob Aid
29 January 2011

stefan-bon-plankton-biomimicrySome forms of plankton and bacteria have the ability to build an extra natural layer of nanoparticle-like armor. That ability has inspired chemists at the University of Warwick to create a remarkably simple way to give drug bearing polymer vesicles (microscopic polymer based sacs of liquid) their own armored protection. The technology could be used to enable “stealth” capabilities of the vesicle which could avoid the body’s defenses while releasing the drug.

Advances in polymerization have led to a surge in the creation of vesicles made from polymer molecules. Such vesicles have interesting chemical and physical properties which makes these hollow structures potential drug delivery vehicles. The University of Warwick team was convinced that even more strength, and interesting tailored properties, could be given to the vesicles if they could add an additional layer of colloidal armor made from a variety of nanoparticles.

“We took our inspiration from nature, in how it adds protection and mechanical strength in certain classes of cells and organisms. In addition to the mechanical strength provided by the cytoskeleton of the cell, plants, fungi, and certain bacteria have an additional cell wall as outermost boundary. Organisms that particularly attracted our interest were those with a cell wall composed of an armor of colloidal objects – for instance bacteria coated with S-layer proteins, or phytoplankton, such as the coccolithophorids, which have their own CaCO3-based nano-patterned colloidal armor”, said Stefan Bon, lead researcher and Associate Professor at the University of Warwick.

The Warwick researchers hit on a surprisingly simple and highly effective method of adding a range of different types of additional armor to the polymer based vesicles. One of those armor types was a highly regular packed layer of microscopic polystyrene balls. This configuration meant the researchers could design a vesicle which had an additional and precise permeable reinforced barrier for drug release, as a result of the crystalline-like ordered structure of the polystyrene balls.

The researchers also succeeded in using the same technique to add a gelatine-like polymer to provide “stealth” armor to shield vesicles from unwanted attention from the body’s immune system while it slowly released its drug treatment. This particular coating (a poly((ethyl acrylate)-co-(methacrylic acid)) hydrogel) absorbs so much surrounding water into its outer structure that it may be able to fool the body’s defense mechanism into believing it is in fact just water.

Bon had the idea of simply giving their chosen colloidal particles, or latex, based armor the opposite charge to that of the polymer vesicles, to bind them together. This turned out to be even more effective and easy to manipulate and tailor than the researchers had hoped for.  However the researchers needed a new way of actually observing the vesicles to see if their plan had worked.

Previous observational methods required researchers to dry out the vesicles before examining then under an electron microscope, but this seriously deformed the vesicles and thus provide little useful data. However, the folks from University of Warwick have recently acquired a cryo-electron microscope which allowed the research team to quickly freeze the vesicles and preserve their shape before an observation by the electron microscope. This method confirmed the hypothesis of the researchers.

For more information, read the paper published in the Journal of the American Chemical Society named: “Polymer Vesicles with a Colloidal Armor of Nanoparticles”.

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