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

High resolution monitoring of dimensional changes of cholesterol bearing pullulan (CHP) hydrogel was performed as a model for materials dimensional changes associated with drug delivery. Hydrogels consisting of methacryloyl groups modified cholesterol bearing pullulan (CHPMA) were covalently attached to 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) in different original CHP concentrations (35, 45 and 55 mg/ml) 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 also can be destabilized by host- guest interaction with cyclodextrins. The swelling properties were determined with 2 nm resolution in optical length and sampled at frequency of approximately 1 Hz for the 50 m radius hemispherical hydrogels. The results show that the equilibrium swelling and swelling kinetics of the CHP depend on their composition and the exposure to cyclodextrins type and concentrations. Hydrogels with the lowest methacryloyl groups and lowest CHP concentration yielded the largest swelling changes on exposure to methyl--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 of hydrogel swelling relevant of materials dimensional changes associated with controlled drug delivery