Transport and structural analysis of molecular imprinted hydrogels for controlled drug delivery

Molecular imprinting provides a rational design strategy for the development of controlled release drug delivery systems. We demonstrate that imprinting a hydrogel network results in macromolecular memory for the template molecule, indicated by the two or more times greater partitioning into these networks as compared to non-imprinted networks. Partitioning of drug into networks synthesized from multiple functional monomers was 8 times greater than networks synthesized from single monomers. One-dimensional permeation studies showed that the gel with maximum incorporated chemical functionality had the lowest diffusion coefficient, which was one to two orders of magnitude lower than all other gels studied. All imprinted networks had significantly lower diffusion coefficients than non-imprinted networks, in spite of comparable mesh sizes and equilibrium polymer volume fractions in the swollen state, which to our knowledge, is the first time that such a study has been conducted in the literature. We propose the "tumbling hypothesis", wherein a molecule tumbling through an imprinted network with multiple, organized functionalities and an appropriate mesh size, experiences heightened interactions with memory sites and shows delayed transport kinetics. Thus, the structural plasticity of polymer chains, i.e. the organization of functional groups into memory sites, may be responsible for enhanced loading and extended release.