Injectable and moldable hydrogels for use in sensitive and wide range strain sensing applications

Area of Science:

• Materials Science
• Polymer Chemistry
• Biomaterials Engineering

Background:

• Hybrid double network (DN) hydrogels offer enhanced mechanical properties for soft material applications.
• Few existing hydrogels possess both injectability and moldability.
• Gelatin/polyacrylamide DN hydrogels are a promising area for advanced material development.

Purpose of the Study:

• To report the mechanical properties, gauge factor (GF) values, injectability, and moldability of a gelatin/polyacrylamide DN hydrogel.
• To optimize parameters for superior mechanical performance.
• To evaluate the potential of these hydrogels as strain sensors.

Main Methods:

• Optimization of gelatin to polyacrylamide ratio, reactant concentrations, and metal ion concentration.
• Assessment of mechanical properties, including tensile strength and strain tolerance.
• Evaluation of injectability and moldability through shape-changing experiments.
• Measurement of electrical conductivity and gauge factor (GF) for strain sensing capabilities.

Main Results:

• The optimized hydrogel exhibited high water content and withstood strains up to 5000%.
• Gels were successfully injected into molds, maintaining properties after remolding.
• Calcium doping (20 mM) enhanced tensile strength to 1.71 MPa and improved conductivity.
• Gauge factor (GF) values ranged from 1.63 to 6.85 for the Ca2+-doped hydrogel at various strains.
• The hydrogel strain sensors demonstrated good stability under cyclic stretching.

Conclusions:

• A gelatin/polyacrylamide DN hydrogel with excellent mechanical properties, injectability, and moldability has been developed.
• Metal ion doping (Ca2+, Mg2+) significantly enhances mechanical strength and electrical conductivity.
• These hydrogels show great promise as reliable and sensitive strain sensors for various applications.