Post-polymerization of urease-induced calcified, polymer hydrogels

Area of Science:

• Materials Science
• Biomaterials Engineering
• Nanotechnology

Background:

• Urease-induced calcification offers a novel route for creating calcium carbonate (CaCO3)-based composite materials via hydrogel mineralization.
• Initial hybrid materials exhibit poor mechanical properties, necessitating optimization strategies.
• The stiffness of these materials is critically dependent on the interplay between the hydrogel matrix and CaCO3 crystals.

Purpose of the Study:

• To investigate methods for enhancing the mechanical properties, specifically Young's modulus (YM), of urease-induced calcified hydrogel composites.
• To determine the key factors influencing the stiffness of CaCO3-based hybrid materials.
• To explore the impact of hydrogel matrix composition and post-treatment on material performance.

Main Methods:

• Synthesizing CaCO3-based hydrogel composites using urease-induced calcification.
• Varying the degree of calcification (up to 94 wt%) and hydrogel matrix composition (e.g., poly(2-hydroxyethylacrylate), poly(N,N-dimethyl acrylamide)).
• Employing post-polymerization (PP) techniques and analyzing the influence of crystal-matrix contact area on mechanical properties.

Main Results:

• Increasing calcification content improved YM from ~40 MPa to over 300 MPa.
• Incorporating CaCO3-affine groups into the hydrogel matrix did not enhance stiffness.
• Post-polymerization (PP) of calcified hydrogels achieved YM > 1 GPa, highlighting the importance of crystal-matrix contact area.
• Switching to high glass transition temperature (Tg) hydrogel matrices (poly(N,N-dimethyl acrylamide)) resulted in YM up to 3.5 GPa after PP.

Conclusions:

• The size of the contact area between the hydrogel matrix and CaCO3 crystals is paramount for controlling composite stiffness.
• Post-polymerization is an effective strategy for significantly enhancing the Young's modulus of these materials.
• High Tg hydrogel matrices, when combined with PP, offer a promising pathway to achieving ultra-stiff CaCO3-based composites.