Abstract
Mineralization of hydrogel biomaterials with calcium phosphate (CaP) is considered advantageous for bone regeneration. Mineralization can be both induced by the enzyme alkaline phosphatase (ALP) and promoted by calcium-binding biomolecules, such as plant-derived polyphenols. In this study, ALP-loaded gellan gum (GG) hydrogels were enriched with gallotannins, a subclass of polyphenols. Five preparations were compared, namely three tannic acids of differing molecular weight (MW), pentagalloyl glucose (PGG), and a gallotannin-rich extract from mango kernel (Mangifera indica L.). Certain gallotannin preparations promoted mineralization to a greater degree than others. The various gallotannin preparations bound differently to ALP and influenced the size of aggregates of ALP, which may be related to ability to promote mineralization. Human osteoblast-like Saos-2 cells grew in eluate from mineralized hydrogels. Gallotannin incorporation impeded cell growth on hydrogels and did not impart antibacterial activity. In conclusion, gallotannin incorporation aided mineralization but reduced cytocompatibility.
Highlights
To adapt hydrogels for applications in bone regeneration, they are enriched with a mineral phase, most commonly a form of calcium phosphate (CaP)
One biomimetic mineralization method is the incorporation of alkaline phosphatase (ALP), the enzyme responsible for mineralization of bone tissue, followed by incubation in a mineralization solution of calcium glycerophosphate (CaGP)
Calculation of dry mass percentage (Figure 1F) demonstrated that values were clearly higher in the presence of the enzyme ALP
Summary
To adapt hydrogels for applications in bone regeneration, they are enriched with a mineral phase, most commonly a form of calcium phosphate (CaP) (for a review, see [1]). ALP-mediated mineralization of gellan gum (GG) hydrogels with CaP reinforced the hydrogel mechanically and promoted the adhesion and growth of bone-forming cells, which is a pre-requisite for new bone formation [2]. Strategies to increase mineralizability include the incorporation of calcium-binding biomolecules [2,3] or phosphate-binding biomolecules [1,4]. It can be noted that ALP itself has been shown to increase the local inorganic phosphate concentration [5], but its combination with CaP results in the formation of hybrid organic–inorganic materials [6] reported to promote cell growth
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