# Calcium Phosphate Mineralization of Bulk Alginate Hydrogels Composites With Metal and Metal Oxide Nanoparticles

## TL;DR

This study shows how adding metal nanoparticles to alginate hydrogels improves their strength and antibacterial properties, making them suitable for bone tissue engineering.

## Contribution

The study introduces a novel method of combining calcium phosphate mineralization with metal oxide nanoparticles in alginate hydrogels to enhance their biomedical potential.

## Key findings

- Calcium-deficient hydroxyapatite forms at pH 7.4, while amorphous calcium phosphate forms at pH 9.0.
- Mineralized hydrogels show earlier network breakdown, with strain values influenced by pH and nanoparticle type.
- Hydrogels at pH 9.0 significantly inhibit S. aureus, except those with CuONPs.

## Abstract

Alginate hydrogels are promising materials for biomedical applications due to their biocompatibility and ability to mimic the extracellular matrix. However, poor mechanical stability and limited bioactivity hinder their wider clinical application. This problem can be overcome by incorporating nanoparticles (NPs) and calcium phosphates (CaPs). In this study, the simultaneous gelation and CaP mineralization of bulk alginate hydrogels in the presence of antimicrobial silver (AgNP), copper oxide (CuONP), and zinc oxide (ZnONP) was investigated. Calcium‐deficient hydroxyapatite forms at pH 7.4, and stable amorphous calcium phosphate at pH 9.0. The incorporation of NPs influences the morphology of mineral phases but not composition. Rheological testing revealed that mineralized hydrogels exhibit earlier network breakdown compared to the non‐mineralized ones, with critical strain values dependent on both pH and NP type. Ion release is pH‐dependent, with generally higher metal ion release from non‐mineralized hydrogels. Antibacterial assays demonstrate significant inhibition of S. aureus by hydrogels prepared at pH 9.0, except for hydrogels containing CuONPs. For P. aeruginosa, the differences in inhibition rates between different hydrogels were less pronounced. The obtained results indicate that CaP‐mineralized alginate hydrogels incorporating metal and metal oxide NPs exhibit tunable properties, confirming their potential for bone tissue engineering applications and infection prevention.

This study explores alginate hydrogels simultaneously mineralized with calcium phosphates and embedded with antimicrobial nanoparticles (AgNPs, CuONPs, ZnONPs). The materials are synthesized at pH 7.4 and 9.0, and their structural, mechanical, ion release, and antibacterial properties were determined. Results highlight pH‐dependent properties and demonstrate the potential of these hydrogels for bone tissue engineering applications.