Cyclodextrin triggered dimensional changes of polysaccharide nanogel integrated hydrogels at nanometer resolution

High resolution monitoring of dimensional changes of cholesterol bearing pullulan (CHP) hydrogels was performed as a model for materials' dimensional changes associated with drug delivery. Hydrogels consisting of methacryloyl group-modified cholesterol bearing pullulan (CHPMA) were covalently attached at the end of an optical fibre for interferometric monitoring of dimensional changes. Hydrogels polymerized by CHPMA self-assembled nanogels with different methacryloyl groups (4 and 7 methacryloyl groups per 100 glucose units) at different original CHP concentrations (35, 45 and 55 mg ml−1) were employed to prepare soft materials with various swelling properties. The substituted cholesteryl groups in CHP gels affect the hydrogel swelling by forming association domains by hydrophobic interaction that can also be destabilized by host–guest interactions with cyclodextrins. The swelling properties were determined with 2 nm resolution in optical length and sampled at a frequency of approximately 1 Hz for the 50 μm radius hemispherical hydrogels. The results show that the equilibrium swelling and swelling kinetics of the CHP depend on its composition and the exposure to cyclodextrin types and concentrations. CHP hydrogels with the least number of methacryloyl groups and the lowest CHP concentration yielded the largest swelling changes on exposure to methyl-β-cyclodextrin. The swelling rate induced by cyclodextrin was independent of CHP concentration and type of cyclodextrin. The interferometric investigation of CHP hydrogel swelling associated with the disassociation of cholesterol group aggregates has proved its potential in providing information on hydrogel swelling relevant to materials' dimensional changes associated with controlled drug delivery.