Unveiling the Compression Mechanical Properties of AMPS–APTAC–DMAAm Terpolymeric Hydrogels

Polyampholyte hydrogels are promising for load-bearing biomedical applications, but the link between composition and compression behavior remains unclear. In this study, we investigate how initial monomer concentration and a neutral comonomer influence swelling and mechanical properties in AMPS-APTAC networks. Terpolymeric AMPS-APTAC-DMAAm hydrogels were prepared with monomer concentrations from 1 to 2 M, MBAAm levels from 1 to 5 mol%, and DMAAm fractions from 0 to 0.16. Swelling was measured in water. Unconfined compression tests at 3 mm·min^-1 provided stress-strain curves, Young's modulus (E), fracture stress (σ_f), fracture strain (ε_f), and toughness (W) up to 99% strain. Increasing the monomer concentration produced denser networks, lower swelling, and higher stiffness. For C2M1, E reached 35.4 kPa, σ_f reached 0.8 MPa, ε_f was 82%, and W was 65.6 kJ·m^-3. Adding DMAAm strengthened the gels through reversible associative interactions. At z = 0.06, σ_f increased to 4.28 MPa and W to 196.0 kJ·m^-3. At z = 0.16, E increased to 103.0 kPa, while σ_f was 2.34 MPa and W was 191.6 kJ·m^-3. Swelling decreased when monomer or crosslinker content increased. These results show that monomer concentration and DMAAm-mediated associations act as separate design variables that can be tuned to optimize stiffness, strength, and toughness in AMPS-APTAC polyampholyte hydrogels.