Fabrication of Thermo-Responsive Controllable Shape-Changing Hydrogel.

Area of Science:

• Materials Science
• Polymer Chemistry
• Biomedical Engineering

Background:

• Double network (DN) hydrogels offer enhanced mechanical properties compared to single network hydrogels.
• Thermoresponsive hydrogels can change their volume in response to temperature variations, enabling smart material applications.
• Polyvinyl alcohol (PVA) and N-isopropylacryl amide (NIPAM) are common components in hydrogel formulations, but their combination in a DN structure requires specific preparation methods.

Purpose of the Study:

• To synthesize and characterize novel temperature-responsive double network (DN) hydrogels.
• To investigate the influence of a dual-network structure on the mechanical properties and thermal responsiveness of the hydrogel.
• To explore the potential of these hydrogels in applications requiring controlled swelling and deswelling behavior.

Main Methods:

• Preparation of DN hydrogels using a 3D printed mold, involving radical photo-initiated polymerization of methacrylic acid (MA) modified PVA and NIPAM, followed by a freezing-thawing process to induce PVA crystallization.
• Characterization of hydrogel properties including tensile strength, compressive strength, and thermoresponsive behavior through thermal cycling.
• Swelling-deswelling studies to evaluate the hydrogel's response to temperature changes.

Main Results:

• The synthesized DN hydrogels demonstrated good mechanical properties with tensile strength of 1.23 MPa and compressive strength of 1.47 MPa.
• The hydrogels exhibited thermoresponsive behavior due to the phase transition of PNIPAAm segments around 32 °C.
• Thermal cycling revealed a transition from a virgin state to a steady state, likely due to PVA crystal reorganization, with clear swelling-deswelling cycles showing a 13% length change.

Conclusions:

• The developed DN hydrogels possess a promising combination of mechanical robustness and tunable thermoresponsiveness.
• The unique dual-network structure, formed by in-situ polymerization and PVA crystallization, contributes to the observed properties.
• These hydrogels are suitable for applications where controlled volume changes with temperature are desired, such as in drug delivery or soft robotics.