Yukimitsu Suzuki

In Situ Cross-Linkable Hydrogel of Hyaluronan Produced via Copper-Free Click Chemistry

Injectable hydrogels are useful in biomedical applications. We have synthesized hyaluronic acids chemically modified with azide groups (HA-A) and cyclooctyne groups (HA-C), respectively. Aqueous HA-A and HA-C solutions were mixed using a double-barreled syringe to form a hydrogel via strain-promoted [3 + 2] cycloaddition without any catalyst at physiological conditions. The hydrogel slowly degraded in PBS over 2 weeks, which was accelerated to 9 days by hyaluronidase, while it rapidly degraded in a cell culture media with fetal bovine serum within 4 days. Both HA-A and HA-C showed good biocompatibility with fibroblast cells in vitro. They were administered using the double-barreled syringe into mice subcutaneously and intraperitoneally. Residue of the hydrogel was cleared 21 days after subcutaneous administration, while it was cleared 7 days after intraperitoneal administration. This injectable HA hydrogel is expected to be useful for tissue engineering and drug delivery systems utilizing its orthogonality.

Preparation of Monodisperse Chitosan Microcapsules with Hollow Structures Using the SPG Membrane Emulsification Technique

We describe herein successful preparations of monodisperse chitosan microcapsules with hollow structures using the SPG membrane emulsification technique. Two preparation procedures were examined in this study. In the first method, monodisperse calcium alginate microspheres were prepared and then coated with unmodified chitosan. Subsequently, tripolyphosphate treatment was conducted to physically cross-link chitosan and solubilize the alginate core at the same time. In the second method, photo-cross-linkable chitosan was coated onto the monodisperse calcium alginate microspheres, followed by UV irradiation to chemically cross-link the chitosan shell and tripolyphosphate treatment to solubilize the core. For both methods, it was determined that the average diameters of the chitosan microcapsules depended on those of the calcium alginate microparticles and that the microcapsules have hollow structures. In addition, the first physical cross-linking method using tripolyphosphate was found to be preferable to obtain the hollow structure, compared with the second method using chemical cross-linking by UV irradiation. This was because of the difference in the resistance to permeation of the solubilized alginate through the chitosan shell layers.

Production of Cisplatin-Incorporating Hyaluronan Nanogels via Chelating Ligand-Metal Coordination.

Hyaluronan (HA) is a promising drug carrier for cancer therapy because of its CD44 targeting ability, good biocompatibility, and biodegradability. In this study, cisplatin (CDDP)-incorporating HA nanogels were fabricated through a chelating ligand-metal coordination cross-linking reaction. We conjugated chelating ligands, iminodiacetic acid or malonic acid, to HA and used them as a precursor polymer. By mixing the ligand-conjugated HA with CDDP, cross-linking occurred via coordination of the ligands with the platinum in CDDP, resulting in the spontaneous formation of CDDP-loaded HA nanogels. The nanogels showed pH-responsive release of CDDP, because the stability of the ligand-platinum complex decreases in an acidic environment. Cell viability assays for MKN45P human gastric cancer cells and Met-5A human mesothelial cells revealed that the HA nanogels selectively inhibited the growth of gastric cancer cells. In vivo experiments using a mouse model of peritoneal dissemination of gastric cancer demonstrated that HA nanogels specifically localized in peritoneal nodules after the intraperitoneal administration. Moreover, penetration assays using multicellular tumor spheroids indicated that HA nanogels had a significantly higher ability to penetrate tumors than conventional, linear HA. These results suggest that chelating-ligand conjugated HA nanogels will be useful for targeted cancer therapy.