Balancing mechanical property and swelling behavior of bacterial cellulose film by in-situ adding chitosan oligosaccharide and covalent crosslinking with γ-PGA.

Bacterial cellulose (BC) is an ideal candidate material for drug delivery, but the disbalance between the swelling behavior and mechanical properties limits its application. In this work, covalent crosslinking of γ-polyglutamic acid (γ-PGA) with the chitosan oligosaccharide (COS) embedded in BC was designed to remove the limitation. As a result, the dosage, time, and batch of COS addition significantly affected the mechanical properties and the yield of bacterial cellulose complex film (BCCF). The addition of 2.25 % COS at the incubation time of 0.5, 1.5, and 2 d increased the Young's modulus and the yield by 5.65 and 1.42 times, respectively, but decreased the swelling behavior to 1774 %, 46 % of that of native BC. Covalent γ-PGA transformed the dendritic structure of BCCF into a spider network, decreasing the porosity and increasing the swelling behavior by 3.46 times. The strategy balanced the swelling behavior and mechanical properties through tunning hydrogen bond, electrostatic interaction, and amido bond. The modified BCCF exhibited a desired behavior of benzalkonium chlorides transport, competent for drug delivery. Thereby, the strategy will be a competent candidate to modify BC for such potential applications as wound dressing, artificial skin, scar-inhibiting patch, and so on.

ß-Alanine enhancing the crosslink of chitosan/poly-(γ-glutamic acid) hydrogel for a potential alkaline-adapted wound dressing.

Tiny crosslink in chitosan (CS)/poly-(γ-glutamic acid) (γ-PGA) hydrogel leads to some disadvantages including low mechanical strength and high swelling. To enhance the crosslink of CS/γ-PGA hydrogel, amino acid (AA) was introduced to remove the drawbacks. The results indicated that AA can dramatically increase the crosslink and mechanical properties of CS/γ-PGA hydrogel, and AA chain length and concentration have a drastic effect on them. Particularly, 0.5 % ß-Alanine (ß-Ala) decreased the hydrogel by 70 % in porosity, 52 % in water solubility, and 30 % in swelling, but increased by 2.2-fold in elastic modulus, 2.08-fold in stress, and 1.53-fold in water retention. The porosity of the hydrogel correlates positively with the elastic modulus but negatively with the crosslinking degree. The effect of pH on CS/ß-Ala/γ-PGA hydrogel was investigated in the load and release of benzalkonium chlorides (BAC). ß-Ala strengthened pH response of the hydrogel in BAC load and release. The loading capacity increased with pH value, and 0.5 % ß-Ala increased the hydrogel by 1.25-fold in the release capacity in alkaline environment, suggesting a good buffering effect of ß-Ala on pH variation to accelerate the transportation of BAC. CS/ß-Ala/γ-PGA hydrogel will be competently applied as a potential material for wound dressing in alkaline environment.

Electrocatalytic CO2 Reduction and H2 Evolution by a Copper (II) Complex with Redox-Active Ligand.

The process of electrocatalytic CO2 reduction and H2 evolution from water, regarding renewable energy, has become one of the global solutions to problems related to energy consumption and environmental degradation. In order to promote the electrocatalytic reactivity, the study of the role of ligands in catalysis has attracted more and more attention. Herein, we have developed a copper (II) complex with redox-active ligand [Cu(L1)2NO3]NO3 (1, L1 = 2-(6-methoxypyridin-2-yl)-6-nitro-1h-benzo [D] imidazole). X-ray crystallography reveals that the Cu ion in cation of complex 1 is coordinated by two redox ligands L1 and one labile nitrate ligand, which could assist the metal center for catalysis. The longer Cu-O bond between the metal center and the labile nitrate ligand would break to provide an open coordination site for the binding of the substrate during the catalytic process. The electrocatalytic investigation combined with DFT calculations demonstrate that the copper (II) complex could homogeneously catalyze CO2 reduction towards CO and H2 evolution, and this could occur with great performance due to the cooperative effect between the central Cu (II) ion and the redox- active ligand L1. Further, we discovered that the added proton source H2O and TsOH·H2O (p-Toluenesulfonic acid) could greatly enhance its electrocatalytic activity for CO2 reduction and H2 evolution, respectively.