Protein crystals: How the weak become strong.

The use of the nanoparticle as a delivery vehicle, demonstrated by Soike and co-workers, in effect eliminates these issues; the nanoparticle surface functionality can be manipulated independently of the molecule that it contains. As a rigid and self-contained structure it can retain its integrity, and its degradation behaviour can be manipulated by the choice of degradable polymer used to encapsulate the cargo. By removing the aforementioned constraints, one can imagine integrating a very broad range of drug systems that release at tunable but independent rates. The alternating assembly of charged microparticles using electrostatic assembly was introduced by Iler 9 , and has since been extended to nanoparticles 10. Soike et al. now show that by using a nanoparticle loaded with cargo, the out-diffusion of the cargo from the assembled nanoparticle film is influenced by its position within the film layers: the outermost layers release cargo at a higher flux than layers in the middle or at the bottom. This discovery might be used to tune the relative release rates of different drugs from different parts of a surface. This capability would allow greater control of an assortment of therapeutics for vascular stents (artificial tubes designed to maintain flow in blood vessels), hip or joint implants, and a wealth of other implant devices for which, for example, there is a desire to elute one drug fairly rapidly, and a second drug at a slower pace. Another interesting finding of this work 2 is that the diffusion rates of drug molecules from the nanoparticle cores are also influenced by the drug diffusion path within the polyelectrolyte ionically crosslinked film network. As cargo is released and the nanoparticles begin to break down, several diffusion channels for molecules of various size open up, and thus co-delivery of two drugs can lead to synergistic release behaviour. In all cases, drug release rates were affected depending on the layer in which the drug nanoparticle was located, but the time point at which release begins did not change regardless of particle position or release of other drugs in the multilayer. This implies that diffusion through the LbL network is a key factor of release kinetics regardless of whether and how the principal components are encapsulated. The observation underlines the fact that the only way to acquire a staged release profile in these systems is to effectively block diffusion of molecules throughout the film, as demonstrated with the …