Reinforcing hydrogels with in situ formed amorphous CaCO₃

Area of Science:

• Materials Science
• Biomaterials Engineering
• Polymer Chemistry

Background:

• Hydrogels are limited in load-bearing applications due to poor stiffness and the stiffness-toughness compromise.
• Nature reinforces hydrogel-based materials with minerals for load-bearing and protection.
• Current synthetic hydrogel reinforcement with calcium carbonate (CaCO3) shows limited improvements.

Purpose of the Study:

• To investigate the influence of CaCO3 size, structure, and morphology on the mechanical properties of reinforced poly(acrylamide) (PAM) hydrogels.
• To explore methods for enhancing hydrogel stiffness and toughness beyond current limitations.
• To understand the structure-property relationships in mineralized hydrogels.

Main Methods:

• In situ formation of CaCO3 biominerals within a model PAM hydrogel.
• Systematic investigation of CaCO3 size, structure (e.g., amorphous calcium carbonate nano-structures), and morphology.
• Functionalization of PAM with acrylic acid (AA) to enhance affinity with CaCO3.

Main Results:

• Reinforcement with micro-sized CaCO3 crystals increased PAM hydrogel fracture energy 3-fold.
• Percolating amorphous calcium carbonate (ACC) nano-structures, formed with Mg2+, increased fracture energy 13-fold.
• Functionalization with AA significantly enhanced ACC affinity, increasing hydrogel stiffness by a factor of 50.

Conclusions:

• The structure of CaCO3 biominerals and their affinity to the hydrogel matrix are critical for mechanical reinforcement.
• Tailoring CaCO3 structure and matrix interaction allows for a wider tuning range of mineralized hydrogel mechanical properties.
• This approach offers potential for developing advanced load-bearing hydrogel materials inspired by natural biomineralization.