Armor protects drug-releasing polymers

U. WARWICK (UK) — Chemists have figured out a way to add armor protection to polymer vesicles designed to carry a drug payload.

Researchers decorated the hollow structures—microscopic polymer-based sacks of liquid—with a variety of nanoparticles. The work suggests the possibility of designing drug-release vehicles with “stealth” capabilities that can go undetected by the body while releasing the drug. Details are reported in the Journal of the American Chemical Society.

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 that make these hollow structures potential drug-delivery vehicles.

Researchers at the University of Warwick were convinced that even more strength, and interesting tailored properties, could be given to the vesicles if they could add an additional layer of colloidal amour made from a variety of nanoparticles.

The work was inspired by the ability seen in some forms of plankton and bacteria to build an extra natural layer of nanoparticle-like armor.

“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,” says lead researcher Stefan Bon, an associate professor at Warwick.

“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.”

Bon and colleagues 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 that 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 a “stealth” armor to shield vesicles from unwanted attention from the body’s immune system while it slowly released its drug treatment.

This particular coating 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.

The researchers 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.

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