Lateral and Rotational Mobility of Some Drug Molecules in a Poly(Ethylene Glycol) Diacrylate Hydrogel and the Effect of Drug-Cyclodextrin Complexation

In relation to drug release properties the lateral and rotational mobility of two drugs and one drug mimic 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.