Autoclaving-Triggered Hydrogelation of Chitosan-Gluconic acid Conjugate Aqueous Solution for Wound Healing.

Moist wound healing is known to heal wounds faster than dry wound healing. Hydrogel wound dressings are suitable for moist wound healing because of their hyperhydrous structure. Chitosan, a natural polymer, promotes wound healing by stimulating inflammatory cells and releasing bioactive compounds. Therefore, chitosan hydrogel has great potential as a wound dressing. In our previous study, physically crosslinked chitosan hydrogels were successfully prepared solely by freeze-thawing of chitosan-gluconic acid conjugate (CG) aqueous solution without using any toxic additives. Furthermore, the CG hydrogels could be sterilized by autoclaving (steam sterilization). In this study, we showed that autoclaving (121 °C, 20 min) of a CG aqueous solution simultaneously achieved gelation of the solution and sterilization of the hydrogel. Hydrogelation of CG aqueous solution by autoclaving is also physically crosslinking without any toxic additives. Further, we showed that the CG hydrogels retained favorable biological properties of the CG hydrogels prepared by freeze-thawing and subsequent autoclaving. These results indicated that CG hydrogels prepared by autoclaving were promising as wound dressings.

Hydrophobically-modified gelatin hydrogel as a carrier for charged hydrophilic drugs and hydrophobic drugs.

Gelatin molecules have been chemically crosslinked using potentially cytotoxic reagents to prepare stable hydrogels. Hydrophobic interaction is a means of forming physical crosslinks that is a good candidate for enhancing the stability of gelatin hydrogels without using cytotoxic chemicals. In this study, we proposed a new method to fabricate hydrogels from hydrophobically-modified gelatin (HMG) with high content of hydrophobic segments. HMG was first dissolved in dimethyl sulfoxide and poured into a vial with the desired shape. After the solution was freeze-dried, the solid construct was hydrated. The HMG hydrogel containing basic fibroblast growth factor promoted angiogenesis in vivo, indicating that the positively charged hydrophilic growth factor formed an electrostatic complex with negatively charged HMG hydrogel and was gradually released in vivo with the degradation of the hydrogel. In addition, we showed that the hydrophobic segments of HMG enhanced the adsorption of fluorescein sodium, a model for hydrophobic therapeutic agents, to the hydrogel through hydrophobic interaction. Furthermore, in vitro experiments indicated that the hydrophobic agents would be released from the hydrogel in a controlled manner in vivo. These results show that the HMG hydrogel has significant potential as a carrier for both charged hydrophilic drugs and hydrophobic drugs.

Millimeter-sized capsules prepared using liquid marbles: Encapsulation of ingredients with high efficiency and preparation of spherical core-shell capsules with highly uniform shell thickness using centrifugal force.

HYPOTHESIS: In our previous study, we prepared millimeter-sized spherical hard capsules by solidifying droplets of liquid monomer or polymer solution placed on superamphiphobic surface. Application of liquid marbles in place of the naked droplets for capsule preparation has a great potential to increase encapsulation efficiency of high volatile ingredients. Further, interfacial thermodynamic prediction of internal configuration of capsules from spreading coefficients may be effective to prepare core/shell capsule. EXPERIMENTS: Droplets of liquid monomer containing a volatile ingredient were rolled on superamphiphobic powders to prepare liquid marbles and solidified by photopolymerization. For preparation of core/shell capsules, the liquid marbles injected with an immiscible water droplet were also solidified. FINDINGS: A volatile ingredient could be encapsulated with higher efficiency than our previous method. Interfacial thermodynamic prediction of internal configuration of capsules from spreading coefficients indicated successful formation of core/shell capsules. However, photopolymerization of the liquid marbles in a static condition resulted in formation of not only core/shell capsules but also acorn-type capsules. Furthermore, the core/shell capsules were distorted and the shell thickness was not uniform. Rolling of the liquid marbles, which generated centrifugal force inside of the liquid marbles, was effective to prepare spherical capsules with highly uniform shell thickness.