About drugs in hydrogel drug delivery systems
In relation to drug release properties the lateral and rotational mobility of both water soluble and water insoluble drugs in photopolymerized poly(ethylene glycol) diacrylate (PEGDA) networks were investigated by nuclear magnetic resonance as a function of the network cross-link density and temperature. The network mesh size affects the lateral diffusivity for all drugs, even if the mesh size is an order of magnitude larger than the drug molecular size. The rotational diffusional motion is only appreciably affected when the drug size and network mesh size are of the same order of magnitude. By complexing the drug to cyclodextrin (CD) it is found that in some cases, depending on network mesh size and complex size, the complex is absorbed by the PEGDA gel, but that the diffusion of the drug in the gel is not necessarily slower than in the absence of the CD. This is explained by a theoretical model. It has been shown that the network cross-link density represents an important tuning parameter in the polymeric drug delivery. It affects polymer morphology and surface properties of these materials (as shown by AFM), swelling behavior, diffusional mobility of the drug molecules in the gel and thereby the drug release rate. Further in this work it was found that in the case of the water insoluble drug amiodarone and γ-cyclodextrin the drug-CD complexation leads to large, rigid supramolecular structures. This finding is of great importance for improvements in the delivery formulations of this important antiarrhythmic drug.