Mimicking the extraordinary performances of natural materials presents an attractive, but challenging approach in the synthesis of advanced functional materials. In the field of separation techniques, the design of a low-cost, regenerative, environmentally friendly sorbent and the utilization of most of its active centers to remove the targeted pollutant are everyday challenges. The combination of casein and poly(sodium methacrylate) (PMANa) in the form of a soft polymer network is proposed as a promising sorbent for the removal of Ni²⁺ from wastewater. Such a combination and an applied synthetic route form hybrid materials with better sorption properties than both their components alone. SEM and TEM show that caseinate micelles are dissociated and the more exposed protein structure is stabilized by the PMANa network and able to form various stable complexes. The achieved sorption capacity (224 mg g⁻¹) is among the highest reported in the literature. The very high removal efficiency in the wide range of the initial Ni²⁺ concentrations (0.05–200 ppm) and easy and complete regeneration without decrease in sorption capacities make these low-cost materials highly sensitive sorbents attractive for use under real conditions where it is necessary to avoid environmental risks and provide the recovery and reuse of the metal.

Hydrogels endure various dynamic stresses, demanding robust mechanical properties. Despite significant advancements, matching hydrogels’ strength to biological tissues and plastics is often challenging without applying potentially harmful crosslinkers. Using hydrogen bonds as sacrificial bonds offers a promising strategy to produce tough, versatile hydrogels for biomedical and industrial applications. Poly(methacrylic acid) (PMA)/gelatin hydrogels were synthesized by thermally induced free-radical polymerization and crosslinked only by physical bonds, without adding any chemical crosslinker. The addition of gelatin increased the formation of hydrophobic domains in the structure of the hydrogels, which acted as permanent crosslinking points. The increase in PMA and gelatin contents generally led to a lower equilibrium water content (WC), higher thermal stability and better mechanical properties. The values of tensile strength and toughness reached up to 1.44 ± 0.17 MPa and 4.91 ± 0.51 MJ m⁻³, respectively, while the compressive modulus and strength reached up to 0.75 ± 0.06 MPa and 24.81 ± 5.85 MPa, respectively, with the WC being higher than 50 wt.%. The obtained values for compressive mechanical properties are comparable with super-strong hydrogels reported in the literature. In addition, hydrogels exhibited excellent fatigue resistance and biocompatibility, as well as great shape memory properties, which make them prominent candidates for a wide range of biomedical applications.

Externally governed hydrogel swelling is a highly convenient yet inherently challenging process, as it requires both responsive materials and appropriately tuned external stimuli. In this work, for the first time, the influence of simultaneous action of external physical fields—ultrasound (US) and microwave heating (MW), combined with cooling—on the isothermal swelling kinetics of poly(methacrylic acid) (PMAA) hydrogel was investigated and compared with swelling under conventional thermal heating (TH) under isothermal conditions. Swelling kinetics were monitored over a temperature range of 248–318 K, under simultaneous cooling with either US, MW, or TH. The well-established Peppas model was used to determine swelling kinetics parameters, revealing a significant acceleration in the swelling process under MW (up to 48.8 times at 313 K), as well as different water penetrating mechanisms (non-Fickian diffusion) compared to TH and US (Super-case II). Additionally, it was demonstrated that the swelling conversion curves could be mathematically described using a “shrinking boundary surfaces” model. Isothermal swelling constants and the corresponding kinetic parameters (activation energy E_a and pre-exponential factor ln A) were calculated. The results confirmed that external physical fields significantly influence the thermal activation and swelling behavior of PMAA xerogels, offering insight into field-responsive transport processes in hydrogel networks.