Physical
and/or covalently linked (chemical) hydrogels were prepared
from chitin and cellulose extracted with ionic liquid from shrimp
shells and wood biomass, respectively, and compared with hydrogels
prepared from commercially available biopolymers, practical grade
chitin, and microcrystalline cellulose. The highly porous aerogels
were formed by initial dissolution of the biopolymers in NaOH/urea
aqueous systems using freeze/thaw cycles, followed by thermal treatment
(with or without epichlorohydrin as a cross-linker) and supercritical
CO2 drying. The ionic-liquid-extracted cellulose pulp and
chitin, as well as practical grade chitin could form both stable physical
and chemical hydrogels, whereas biopolymers of lower apparent molecular
weight such as microcrystalline cellulose required a covalent cross-linker
for hydrogel formation and commercially available pure chitin was
not suitable for the preparation of hydrogels of either type. Hydrogels
prepared from the ionic-liquid-extracted biopolymers exhibited properties
substantially different from those made from the commercially available
biopolymers. Loading of an active ingredient into the hydrogel and
its subsequent release was demonstrated using indigo carmine and revealed
that the release rate was controlled mainly by the biopolymer concentration
of the gel network.
An easy and efficient route to synthesize gel materials based on polymeric ionic liquids (PILs) is presented. The radical polymerization of imidazolium (Im)‐based ionic liquids (ILs) bearing a vinyl group ([VEIm][Br], [VEIm][Ac], [VBIm][Br], [VBIm][Cl]) with crosslinker (CL) N,N′‐methylenebisacrylamide (Bis) in water results in polyionic liquid hydrogels. Thermal and mechanical properties (tensile and compression tests) are investigated and compared with two different types of hydrogels. One is a polyacrylamide (PAAm) hydrogel having covalent‐type crosslinking. The other is an alginate‐based hydrogel having ionic‐type crosslinking. Prepared IL‐hydrogel materials provide favorable flexibility, adjustable by varying the CL ratio and water content. The higher the CL ratio is, the higher the fragility of the gel matrix. The gelation time of the hydrogels depends on the alkyl chain length, as well as the size of the anion.
Drug-coated balloon catheters are a novel clinical treatment alternative for coronary and peripheral artery diseases. Calcium alginate, poly(vinylethylimidazolium bromide) and polyacrylamide hydrogels were used as vessel models in this in vitro study. In comparison to a simple silicone tube their properties can be easily modified simulating different types of tissue. Local drug delivery after balloon dilation in the first crucial minute was determined in a vessel-simulating flow-through cell by a simulated blood stream.Balloon catheters were coated with paclitaxel using the ionic liquid cetylpyridinium salicylate as a novel carrier. Drug transfer from coated balloon catheters to different simulated vessel walls was evaluated and compared to a silicone tube. The highest paclitaxel delivery upon dilation was achieved with calcium alginate as the vessel model (60%) compared to polyacrylamide with 20% drug transfer. The silicone tube showed the least amount of wash-off (<1%) by a simulated blood stream after one minute from the vessel wall. The vessel-simulating flow-through cell was combined with a model coronary artery pathway to estimate drug loss during simulated use in an in vitro model. Calcium alginate and polyacrylamide hydrogels were used as tissue models for the simulated anatomic implantation process.In both cases, similar transfer rates for paclitaxel upon dilation were detected.
A novel strategy for the embedding of quinine-based organocatalysts in polymerized ionic liquids-based hydrogels is presented. With this technique, the encapsulated organocatalyst was successfully recovered and reused for four cycles without any loss of enantioselectivity (up to 91% ee) for the asymmetric nitroaldol (Henry) reaction. In this study, high catalyst leaching was significantly reduced (<0.01%) by controlling the water content. After catalyst removal, evaporation of the solvent affords the product in 98% purity without any further purification.
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