Molecular Imprinting of Cyclodextrin Supramolecular Hydrogels Improves Drug Loading and Delivery

Abstract

Cyclodextrin-based controlled delivery materials have previously been developed for controlled release of different therapeutic drugs. In this study, a supramolecular hydrogel made from cyclodextrin-based macromonomers is subjected to molecular imprinting to investigate the impact on release kinetics and drug loading, when compared with non-imprinted, or alternately imprinted hydrogels. Mild synthesis conditions are used to molecularly imprint three antibiotics-novobiocin, rifampicin, and vancomycin-and to test two different hydrogel chemistries. The release profile and drug loading of the molecularly imprinted hydrogels are characterized using ultraviolet spectroscopy over a period of 35 days and compared to non-imprinted, and alternately imprinted hydrogels. While only modest differences are observed in the release rate of the antibiotics tested, a substantial difference is observed in the total drug-loading amount possible for hydrogels releasing drugs which has been templated by those drugs. Hydrogels releasing drugs which are templated by other drugs do not show improved release or loading. Analysis by FTIR does not show substantial incorporation of drug into the polymer. Lastly, bioactivity assays confirmed long-term stability and release of incorporated antibiotics.

Keywords: affinity; cyclodextrin; drug delivery; infection; molecular imprinting.

Figure 1.

Basic molecular imprinting scheme for higher order complexes, demonstrating how templating could result in geometrically higher affinities, than a linear polymer could.

Figure 2.

Chemical Synthesis of CD-HDI Networks

Figure 3.

Chemical Synthesis of CD-EGDE Networks

Figure 4.

FTIR spectra of (a) Pure rifampicin (RM), (b) CD polymer made without imprinting, then loaded with RM, then subjected to extensive non-polar solvent washing and drug release, (c) CD polymer made from RM imprinting, loaded with RM, and subjected to extensive non-polar solvent washing and drug release, (d) Pure CD polymer. The existence of 1701 and 1541cm⁻¹(δ(N-H) peaks, indicates the CD polymer urethane bond. Unique RM peaks (e.g. aromatic region peaks of rifampin at around 700–800cm⁻¹) demonstrate low background presence of RM.

Figure 5.. Cumulative Release and Total Loading of Novobiocin from Novobiocin- Templated Hydrogels.

The panel on the left shows overall release as a function of time for the various novobiocin-loaded hydrogels. The panel on the right shows percent loading for each MI hydrogel, where higher MI % corresponds to higher loading (p< 0.05). Samples are in triplicate. Error bars show ± standard deviation.

Figure 6.. Cumulative Release and Total Loading of Vancomycin from Vancomycin-Templated Hydrogels.

The panel on the left shows overall release as a function of time for the various vancomycin-loaded hydrogels. The panel on the right shows percent loading for each MI hydrogel, where higher MI % corresponds to higher loading (p< 0.05). Samples are in triplicate. Error bars show ± standard deviation.

Figure 7.. Cumulative Release and Total Loading of Rifampicin from Rifampicin-Templated Hydrogels.

The panel on the left shows overall release as a function of time for the various rifampicin-loaded hydrogels. The panel on the right shows percent loading for each MI hydrogel, where higher MI % corresponds to higher loading (p< 0.05). Samples are in triplicate. Error bars show ± standard deviation.

Figure 8.. Release of Drugs from Alternately Templated Hydrogels.

Shown above are the overall release profiles over time for the various drug loaded hydrogels. Novobiocin (top left) showed the least amount of change, where release was statistically comparable, regardless of templating molecule. Vancomycin (top right) showed some change, where release from vancomycin-templated hydrogels was statistically different, particularly in early time points. However release from rifampicin was significantly different depending on whether the hydrogel was templated with the large, hydrophilic VM; the small, moderately hydrophobic NB; or with RM itself (p<0.05). All the hydrogels used were initially imprinted with 9 wt% drug (9% MI). Samples are in triplicate. Error bars show ± standard deviation.

Figure 9.. Total Drug-Loading in Alternately Templated Hydrogels.

Shown above are the total drug loading amounts over 72hrs for the various drug-loaded hydrogels. All three drug: novobiocin (top left), vancomycin (top right) and rifampicin (bottom) showed total drug-loading that was statistically significantly different depending on whether the hydrogel was templated with VM; NB; or RM (p<0.05) All the hydrogels used were initially imprinted with 9 wt% drug (9% MI). Samples are in triplicate. Error bars show ± standard deviation.

Figure 10.. Kirby-Bauer Disk Diffusion Susceptibility Test of Templated Hydrogels.

Shown above are the total drug loading amounts over 72hrs for the various drug-loaded hydrogels. All three drug: novobiocin (top left), vancomycin (top right) and rifampicin (bottom) showed total drug-loading that was statistically significantly different depending on whether the hydrogel was templated with VM; NB; or RM (p<0.05) All the hydrogels used were initially imprinted with 9 wt% drug (9% MI).