Application of Hierarchically Porous Chitosan Monolith for Enzyme Immobilization.

Enzyme immobilization is a crucial technique for improving the stability of enzymes. Compared with free enzymes, immobilized enzymes offer several advantages in industrial applications. Efficient enzyme immobilization requires a technique that integrates the advantages of physical absorption and covalent binding while addressing the limitations of conventional support materials. This study offers a practical approach for immobilizing α-amylase on a hierarchically porous chitosan (CS) monolith. An optimized CS monolith was fabricated using chemically modified chitin by thermally induced phase separation. By combining physical adsorption and covalent bonding, this technique leverages the amino and hydroxy groups present in CS to facilitate effective enzyme binding and stability. α-Amylase immobilized on the CS monolith demonstrated excellent stability, reusability, and increased activity compared to its soluble counterpart across various pH levels and temperatures. In addition, the CS monolith exhibited a significant potential to immobilize other enzymes, namely, lipase and catalase. Immobilized lipase and catalase exhibited higher loading capacities and enhanced activities than their soluble forms. This versatility highlights the broad applicability of CS monoliths as support materials for various enzymatic processes. This study provides guidelines for fabricating hierarchical porous monolith structures that can provide efficient enzyme utilization in flow systems and potentially enhance the cost-effectiveness of enzymes in industrial applications.

Cellulose Nanocrystal-Based Gradient Hydrogel Actuators with Controllable Bending Properties.

Stimuli-responsive hydrogel actuators are being increasingly used in microtechnology, but typical bilayer hydrogel actuators have significant drawbacks due to weak adhesive interface between the two layers. In this study, thermoresponsive single-layer hydrogel actuators are produced by generating a gradient distribution of cellulose nanocrystals (CNCs) in a poly(N-isopropylacrylamide) (PNIPAAm) hydrogel network by electrophoresis. Tunable bending properties of the composite hydrogels, such as the thermoresponsive bending speed and angle, are realized by varying the electrophoresis time, applied voltage, and CNC concentration. By varying these conditions, the gradient distribution of the CNCs can be optimized, leading to fast bending and large bending angles of the hydrogels. Bending properties are attributed to the gradient distribution of CNCs causing different deswelling rates across the hydrogel network owing to reinforcing effects. Bending ability is also influenced by differences in the CNC dimensions based on the sources of cellulose, which determine the rigidity of the CNC-rich layer of the polymer composite. It is thus shown that thermoresponsive single-layer gradient hydrogels with tunable bending properties can be realized.

Fabrication of chitin monoliths with controllable morphology by thermally induced phase separation of chemically modified chitin.

As a natural polymer, chitin has excellent biological properties such as biodegradability and immunological, antibacterial, and wound-healing activities and has numerous applications in cosmetics, drug delivery, and pharmaceuticals. Organic polymer monoliths have also drawn significant attention, owing to their high permeability, large surface area, and high mechanical strength. They are usually applied to separation, ion exchange, catalysis, and chromatography. We have previously prepared cellulose monoliths using biopolymers; however, because chitin possesses amide groups on its side chain, it is superior to cellulose for further chemical modification and applications. However, the utilization of chitin is restricted by its insolubility in water and common organic solvents. In this study, for the first time, a monolith was prepared by chemical modification of chitin using a thermally induced phase separation (TIPS) method. First, we prepared dibutyrylchitin (DBC) as a starting polymer that is soluble in organic solvents. To prepare the monolith, DBC was dissolved completely in dimethyl sulfoxide (DMSO) while heating, and deionized water was added to the solution. It was then cooled at 20 °C to form a monolith via phase separation. The porous morphology of the DBC monolith was altered by regulating the DBC concentration, DMSO/H2O ratio, and aging temperature. The DBC monolith was converted to a chitin monolith by the alkaline hydrolysis of butyryl ester. The successful hydrolysis of butyryl ester was confirmed by the disappearance of the peak at 1735 cm-1 in the FT-IR spectra, which is related to the ester moiety of DBC. The chitin monolith has the potential to be utilized under water flow for catalysis, metal capture from wastewater, dye sorption, and drug delivery systems.

Mechano-Responsive Hydrogels Driven by the Dissociation of a Host-Guest Complex.

We developed a mechano-responsive hydrogel that is driven by the dissociation of a host-guest complex. The hydrogel comprised a thermoresponsive linear polymer with adamantane as a guest molecule in its side chain and a nonthermoresponsive network structure with ß-cyclodextrin as a host molecule. Immobilization of the thermoresponsive polymer in the hydrogel via host-guest interaction resulted in a partial restriction of its phase transition, even above its lower critical solution temperature (LCST). The hydrogel demonstrated a decrease in transmittance when mechanical stress was applied at a temperature above its LCST, indicating that the phase transition of the thermoresponsive polymer was induced by the dissociation of the host-guest complex under mechanical stress. Moreover, this mechano-responsive behavior was repeatable by cooling the hydrogel to redissolve the thermoresponsive polymer. The strategy of the mechano-responsive phase transition will be useful for various applications that demand the control of desired functions by applied stress.