Rhodamine-loaded surface modified mesoporous silica particles embedded into a thermoresponsive composite hydrogel for prolonged release

In this manuscript, the synthesis and release capability of a composite system is presented. The composite consists of a surface polymerized mesoporous silica loaded with rhodamine B (RhB) embedded into a crosslinked thermoresponsive polymer. The mesoporous silica was synthesized using a hydrothermal procedure followed by surface functionalization and polymerization with PNiPAAm to obtain a thermoresponsive gated system. Further, the silica particles were loaded with rhodamine B and incorporated into a PNiPAAm hydrogel, yielding a composite system with drug delivery capabilities. Confocal fluorescence microscopy was used to confirm the mesoporous silica was effectively loaded with RhB and distributed within the hydrogel. Rhodamine release assays were carried out under equilibrium and non-equilibrium conditions for the polymerized silica, the pure PNiPAAM hydrogel and the PNiPAAm composites, and the materials were characterized at temperatures above and below the lower critical system temperature (LCST) of PNiPAAm. Three kinetic models were used to study the release performance: the power law, diffusion and relaxation, and Gallagher-Corrigan model. Fitting results of the experimental rhodamine-releasing data to the models strongly suggest the existence of a double diffusion barrier in which the composite prevents the burst release. The combination of the drug releasing properties of mesoporous silica and the stimuli responsiveness of poly(N-isopropylacrylamide) (PNiPAAm) in a single composite resulted in an interesting drug delivery system useful for applications where a prolonged temperature controlled release may be required.