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    Synthesis and characterization of stiff, self-crosslinked thermoresponsive DMAA hydrogels
    (MDPI, 2020-06-01)
    Stiff thermosensitive hydrogels (HG) were synthesized by self-crosslinking free radical polymerization of N, N-dimethylacrylamide (DMAA) and N-isopropylacrylamide (NIPAAm), adjusting the degree of swelling by carboxylate-containing sodium acrylate (NaAc) or a 2-oxazoline macromonomer (MM). The formation of hydrogels was possible due to the self-crosslinking property of DMAA when polymerized with peroxodisulfate initiator type. The MM was synthetized by the ring-opening cationic polymerization of 2-methyl-2-oxazoline (MeOxa) and methyl-3-(oxazol-2-yl)-propionate (EsterOxa), and contained a polymerizable styryl endgroup. After ester hydrolysis of EsterOxa units, a carboxylate-containing MM was obtained. The structure of the hydrogels was confirmed by 1Hhigh-resolution (HR)-MASNMRspectroscopy. Suitable conditions and compositions of the comonomers have been found, which allowed efficient self-crosslinking as well as a thermoresponsive swelling in water. Incorporation of both the polar comonomer and the macromonomer, in small amounts furthermore allowed the adjustment of the degree of swelling. However, the macromonomer was better suited to retain the thermoresponsive behavior of the poly (NIPAAm) due to a phase separation of the tangling polyoxazoline side chains. Thermogravimetric analysis determined that the hydrogels were stable up to ~ 350 ffiC, and dynamic mechanical analysis characterized a viscoelastic behavior of the hydrogels, properties that are required, for example, for possible use as an actuator material.
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    Improved resistance to water erosion and self-healing capacity of earthen-based 3D printed elements using enzyme-induced carbonate precipitation (EICP)
    (Springer, 2026-03-30)
    Cracking in earth-based construction materials poses significant durability challenges, necessitating sustainable solutions. 3D printing offers efficient, scalable construction with earthen materials, but requires durable, eco-friendly matrices. This study explores enzymatic-induced carbonate precipitation (EICP) using urease to improve water resistance and self-healing in earthen-based 3D printed elements containing cement and rice husk fibers. Urease catalyzes urea hydrolysis, forming calcium carbonate (CaCO3) to fill pores and seal cracks. EICP was applied as a soil additive for water resistance and as a surface treatment for crack repair. The optimized formulation (1 M CaCl2-urea 4 U/L urease, Mod. B1-E4) achieved 25.5% less mass loss than 24. 7% for nonenzymatic controls after 60 min of immersion in water and sealed cracks up to 0.45 mm wide within 48 h. SEM, EDS, and XRD analysis confirmed a reduction in porosity 15% through CaCO3 formation, which improved resistance to erosion. The formulation yielded 0.75 g of CaCO3 per reaction cycle, demonstrating efficient biocementation. EICP offers a low carbon alternative for improving the durability of 3D printed earthen structures as a pore-filler and crack-sealer, with potential for sustainable and scalable repairs in construction.
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