Enzymatically cross-linkable sulfated bacterial polyglucuronic acid as an affinity-based carrier of FGF-2 for therapeutic angiogenesis.

The fibroblast growth factor-2 (FGF-2) is a critical protein for biological processes such as angiogenesis and tissue regeneration. Recently, hydrogels based on semi-synthetic sulfated polysaccharides have been developed for the controlled delivery of FGF-2. These affinity-based FGF-2 carriers utilizing hydrogels based on sulfated polysaccharides enable sustained delivery of FGF-2, yet choice of materials is limited. Here, we demonstrate a novel synthetic sulfated polysaccharide-based hydrogel based on bacterial polyglucuronic acid (PGU). We synthesized phenol-grafted sulfated PGU (PGUS-Ph), an enzymatically cross-linkable PGU derivative that exhibited an enhanced affinity for FGF-2. The aqueous solution of PGUS-Ph, when combined with FGF-2, could be injected into affected sites and form a hydrogel in a minimally invasive manner. The FGF-2 released from the PGUS-Ph hydrogel induced blood vessel formation, as proven by a chick embryo-based angiogenesis assay. Our results indicate that the PGUS-Ph has the potential as an enzymatically cross-linkable and minimally invasively injectable affinity-based FGF-2 delivery system.

Fabrication of cell-laden microbeads and microcapsules composed of bacterial polyglucuronic acid.

In the past decades, the microencapsulation of mammalian cells into microparticles has been extensively studied for various in vitro and in vivo applications. The aim of this study was to demonstrate the viability of bacterial polyglucuronic acid (PGU), an exopolysaccharide derived from bacteria and composed of glucuronic acid units, as an effective material for cell microencapsulation. Using the method of dropping an aqueous solution of PGU-containing cells into a Ca2+-loaded solution, we produced spherical PGU microbeads with >93 % viability of the encapsulated human hepatoma HepG2 cells. Hollow-core microcapsules were formed via polyelectrolyte complex layer formation of PGU and poly-l-lysine, after which Ca2+, a cross-linker of PGU, was chelated, and this was accomplished by sequential immersion of microbeads in aqueous solutions of poly-l-lysine and sodium citrate. The encapsulated HepG2 cells proliferated and formed cell aggregates within the microparticles over a 14-day culture, with significantly larger aggregates forming within the microcapsules. Our results provide evidence for the viability of PGU for cell microencapsulation for the first time, thereby contributing to advancements in tissue engineering.

Development of phenol-grafted polyglucuronic acid and its application to extrusion-based bioprinting inks.

In this present work, we developed a phenol grafted polyglucuronic acid (PGU) and investigated the usefulness in tissue engineering field by using this derivative as a bioink component allowing gelation in extrusion-based 3D bioprinting. The PGU derivative was obtained by conjugating with tyramine, and the aqueous solution of the derivative was curable through a horseradish peroxidase (HRP)-catalyzed reaction. From 2.0 w/v% solution of the derivative containing 5 U/mL HRP, hydrogel constructs were successfully obtained with a good shape fidelity to blueprints. Mouse fibroblasts and human hepatoma cells enclosed in the printed constructs showed about 95% viability the day after printing and survived for 11 days of study without a remarkable decrease in viability. These results demonstrate the great potential of the PGU derivative in tissue engineering field especially as an ink component of extrusion-based 3D bioprinting.