Friederike Dehli

Abstract

The influence of gelatin methacryloyl hydrogel morphology on the sorption and release behavior of metoprolol was studied for both equilibrium and non-equilibrium conditions. For samples examined in equilibrium conditions, no influence of the sample morphology was observed. The maximum sorption capacity qmax was determined to be 530 μmol g–1. Furthermore, up to 100\% of the sorbed drug was released from both foamed and non-foamed samples upon immersion into salt solutions, which demonstrates the regenerability of the material. By contrast, the sample morphology strongly influenced the sorption and release kinetics. We found that the sorption and release rate coefficients k increased up to 10 times for foamed hydrogels as compared to non-foamed hydrogels. Furthermore, k increased with increasing ion concentration in the sorption and release medium. This effect was more pronounced for non-foamed hydrogels. The obtained results indicate that the sorption and release rate can be controlled by the morphology of the sorbents and, to some extent, by the ion concentration of the surrounding medium.

Abstract

Hypothesis While tailoring the pore diameters in hydrogel foams has been demonstrated in numerous studies, fine control over the diameters of the pore openings is still a challenge. We hypothesise that this can be achieved by controlling the size of the thin films which separate the bubbles in the liquid foam template. If this is the case, systematic changes of the template’s gas fraction ϕ (the higher ϕ, the larger are the thin films) will lead to corresponding changes of the pore opening diameter. Experiments Since the size of the thin films depends on both bubble size 〈Db〉 and gas fraction ϕ, we need to decouple both parameters to control the film size. Thus, we generated foams with constant bubble sizes via microfluidics and adjusted the gas fractions via two different techniques. The foams were solidified using UV light. Subsequently, they were analysed with confocal fluorescence microscopy. Findings We were able to change the pore opening diameter 〈dp〉 at a constant pore diameter 〈Dp〉 by adjusting the gas fraction of the foam template. The obtained 〈dp〉/〈Dp〉 ratios are between those obtained theoretically for disordered foams and FCC ordered foams, respectively.

Abstract

Hypothesis It is possible to generate fairly monodisperse liquid foams by a dispersion cell, which was originally designed for the generation of fairly monodisperse emulsions. If this is the case, scaling-up the production of monodisperse liquid and solid foams will be no longer a problem. Experiments We used the dispersion cell - a batch process - and examined the influence of stirrer speed, membrane pore diameter and injection rate on the structure of the resulting liquid foams. We used an aqueous surfactant solution as scouting system. Once the experimental conditions were known we generated gelatin-based liquid foams and methacrylate-based foamed emulsions. Findings We found that (a) the bubble size of the generated liquid foams can be adjusted by varying the membrane pore diameter, (b) no stirrer should be used to obtain monodisperse foams, and (c) the bubble size is not influenced by the air injection rate. Since (i) the output for all investigated systems is up to two orders of magnitude larger compared to microfluidics and (ii) the membrane technology can very easily be scaled-up if run in a continuous process, the use of membrane foaming is expected to be heavily used for the generation of monodisperse liquid and solid foams, respectively.