Combining gellan gum with a functional low-molecular-weight gelator to assemble stiff shaped hybrid hydrogels for stem cell growth

Abstract

We report hybrid hydrogels that combine gellan gum (GG) polymer gelator (PG) with a low-molecular weight gelator (LMWG) based on 1,3:2,4-dibenzylidene sorbitol (DBS). We fabricate these gels into beads using a heat–cool cycle to set the LMWG gel and then using different calcium sources (CaCl₂ and CaCO₃) to subsequently crosslink the gellan gum. In the case of CaCO₃, glucono-δ-lactone (GdL) is used as a slow acidification agent to slowly solubilise calcium ions and induce GG crosslinking. Alternatively the photoacid generator, diphenyliodonium nitrate (DPIN) can be used with UV irradiation to solubilise CaCO₃ and induce GG gelation, in which case, a photomask applied to gels made in trays yields photopatterned gels. Combining the LMWG with gellan gum further enhances the stiffness of GG, and importantly, makes the gels significantly more resistant to shear strain. LMWG/GG hybrid gels are considerably stiffer than equivalent LMWG/alginate gels. The DBS-CONHNH₂ LMWG retains its unique ability to reduce precious metal salts to nanoparticles (NPs) within the hybrid gel beads, as demonstrated by the in situ fabrication of AgNPs. The hybrid gel beads support the growth of human mesenchymal stem cells for extended periods of time. We suggest that the favourable rheological properties of these hybrid gels, combined with the ability of the LMWG to form AgNPs in situ, may enable potential future orthopedic applications.