Univ. of Warwick
The ability of some forms of plankton and bacteria to
build an extra natural layer of nanoparticle-like armor has inspired chemists
at the Univ. of Warwick to devise a simple way to give
drug bearing polymer vesicles (microscopic polymer based sacs of liquid) their
own armored protection.
researchers have been able to decorate these hollow structures with a variety
of nanoparticles opening a new strategy in the design of vehicles for drug
release, for example by giving the vesicle “stealth” capabilities which can
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.
of Warwick team 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
armor made from a variety of nanoparticles.
Lead researcher on the Univ. of Warwick
team Associate Professor Stefan Bon said:
“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
researchers hit on a 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 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 (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.
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 than they even they 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 Univ.
of Warwick had recently acquired a
cryo electron microscope thanks to funding from the Science City
program. This allowed the research team to quickly freeze the vesicles to -150oc
preserving the vesicles shape before observation by the electron microscope.
This revealed that the researchers’ simple charge based method had worked
exactly as planned.
The research has just been published in a paper entitled Polymer Vesicles with a Colloidal Armor of
Nanoparticles by Rong
Chen, Daniel J. G. Pearce, Sara Fortuna, David L. Cheung, and Stefan A. F. Bon* Department
of Chemistry, University of Warwick in the Journal of the American Chemical Society http://dx.doi.org/10.1021/ja110359f.