1 Enhancement of biomimetic enzymatic 2 mineralization of gellan gum polysaccharide 3 hydrogels by plant-derived gallotannins 4

Mineralization of hydrogel biomaterials with calcium phosphate (CaP) is considered 30 advantageous for bone regeneration. Mineralization can be both induced by the enzyme alkaline 31 phosphatase (ALP) and promoted by calcium-binding biomolecules such as plant-derived 32 polyphenols. In this study, ALP-loaded gellan gum (GG) hydrogels were enhanced enriched with 33 gallotannins, a subclass of polyphenols. Five preparations were compared, namely three tannic 34 acids of differing molecular weight (MW), pentagalloyl glucose (PGG) and a gallotannin-rich 35 extract from mango kernel (Mangifera indica L.). Certain gallotannin preparations promoted 36 mineralization to a greater degree than others. The various gallotannin preparations bound 37 differently to ALP and influenced the size of aggregates of ALP, which may be related to ability to 38 promote mineralization. Human osteoblast-like Saos-2 cells grew in eluate from mineralized 39 hydrogels. Gallotannin incorporation impeded cell growth on hydrogels and did not impart 40 antibacterial activity. In conclusion, gallotannin incorporation aids mineralization but reduces 41 cytocompatibility. 42