01 February 2011

Drug delivery using stealth nanotechnology

Plankton inspired chemists to create "stealth armor" for microscopic drug delivery vehicles
Nanonews Network based on the materials of the University of Warwick:
Plankton inspires creation of stealth armour for slow release microscopic drug vehicles

The ability of some forms of plankton and bacteria to form an additional natural protective layer of nanoscale particles inspired chemists from the University of Warwick to develop a strikingly simple way to create a coating-"armor" for polymer bubbles containing drugs.

Scientists have been able to link these hollow structures to a range of nanoparticles, developing a new strategy for creating drug delivery vehicles. Their "stealth technology" makes microscopic polymer bubbles containing liquid medicinal substances invisible to the body's defense systems.

Advances in the field of polymerization have caused a whole wave of work to create bubbles from polymer molecules. Such hollow structures have a number of interesting chemical and physical properties that make them potential means of drug delivery.

Scientists from the University of Warwick were convinced that if such bubbles were "dressed" in an additional layer of colloidal "armor" made of various nanoparticles, they could be given even greater strength and achieve predetermined properties.

"We were inspired by nature's ability to provide protection and mechanical strength to certain classes of cells and organisms. In addition to the mechanical strength given to cells by the cytoskeleton, plants, fungi and some bacteria have an additional cell wall acting as an external barrier. Organisms with a cell wall consisting of protective colloidal objects have particularly attracted our attention.

These are, for example, bacteria covered with an S-layer of proteins, or phytoplankton, such as coccolithophorids, which has its own colloidal "nanobrony" based on CaCO3," says associate Professor Stefan Bon, head of the work published in the Journal of American Chemical Society (Rong Chen et al al., Polymer Vesicles with a Colloidal Armor of Nanoparticles).

Scientists have found a surprisingly simple and highly effective method of adding a number of different types of additional protection to polymer bubbles. One of them was a layer of microscopic polystyrene beads with a high degree of packaging organization. This meant that the researchers were able to create a bubble having not only an additional reinforced external protective barrier, but also having precise permeability characteristics essential for the release of the drug, determined by a crystal-like structure of polystyrene beads.

Using the same technique, the scientists managed to add a gelatinous polymer to the bubble. This technology provided the bubbles with a "stealth armor" that protects them from unwanted attention from the immune system. This coating (a hydrogel made of a copolymer of ethyl acrylate and methacrylic acid) absorbs so much of the surrounding water that it is able to "deceive" the body's defense mechanisms, making them believe that it is really ordinary water.

Four different types of coatings created by scientists at the University of Warwick.

In order to bind polymers, scientists came up with the idea to give colloidal or latex particles an electric charge opposite to bubbles. It turned out to be even more efficient and simple than they had expected. However, to make sure their plan worked, they needed a new way to observe the bubbles.

Previously used electron microscopic methods required preliminary drying of the bubbles. Drying significantly deforms their structure, as a result of which this technology provides little useful data. However, the University of Warwick has recently acquired a cryoelectronic microscope. This allowed the scientists to quickly freeze the bubbles to -150 degrees, preserving their shape, and make sure that the charge-changing method worked as planned.

Polymer bubbles with "stealth armor" (cryoelectronic microscopy) that are "invisible" to the body's immune system.

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