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Abstract This study explores a novel multi-material 3D printing technique for fabricating bioinspired hydrogel-Rochelle salt composites, focusing on optimizing concentration, cooling, and coating parameters to enhance material performance. The hydrogel-Rochelle salt composite is a promising material due to its lightweight, mechanical robustness, and piezoelectric properties, making it suitable for applications in sensors, medical devices, and structural materials. A series of concentration tests was conducted to determine the optimal Rochelle salt concentration for achieving efficient curing depth and exposure time. The results identified 50wt% hydrogel/50wt% Rochelle salt as the optimal concentration, providing a balanced curing profile essential for ensuring reliable layer adhesion and structural consistency. To enable controlled crystallization, a cooling process was introduced, with a cooling time of 15 minutes found to be sufficient for complete crystallization to a depth of 500 microns. Thermal imaging and microscopy confirmed the stability of the crystalline structure within the hydrogel matrix, ensuring the material’s functional integrity. Additionally, applying a coating to the printed structure significantly improved surface uniformity and durability, embedding the crystalline elements more effectively within the hydrogel matrix and enhancing the composite’s overall structural integrity. This coating process allowed the composite to withstand repeated printing cycles, facilitating the construction of layered, multi-material structures with improved mechanical and functional properties. The results highlight the importance of fine-tuning concentration, cooling time, and coating techniques to achieve optimal performance in multi-material 3D printing. By addressing these factors, the study demonstrates a reliable approach to producing hydrogel-Rochelle salt composites with high structural quality and piezoelectric functionality. This method not only enhances the material’s durability and adhesion between layers but also opens new possibilities for creating customized, multifunctional materials. The developed process holds significant promise for applications that require precise control over material properties, such as wearable electronics, medical implants, and lightweight structural components. In conclusion, this research provides valuable insights into the fabrication of hydrogel-Rochelle salt composites through advanced 3D printing techniques. The findings offer a foundation for future exploration in multi-material printing and composite fabrication, paving the way for the development of versatile materials with tailored properties for diverse applications. 

Deep carbon cycle is crucial for mantle dynamics and maintaining Earth’s habitability. Recycled carbonates are a strong oxidant in mantle carbon-iron redox reactions, leading to the formation of highly oxidized mantle domains and deep carbon storage. Here we report high Fe³⁺/∑Fe values in Cenozoic intraplate basalts from eastern China, which are correlated with geochemical and isotopic compositions that point to a common role of carbonated melt with recycled carbonate signatures. We propose that the source of these highly oxidized basalts has been oxidized by carbonated melts derived from the stagnant subducted slab in the mantle transition zone. Diamonds formed during the carbon-iron redox reaction were separated from the melt due to density differences. This would leave a large amount of carbon (about four times of preindustrial atmospheric carbon budget) stored in the deep mantle and isolated from global carbon cycle. As such, the amounts of subducted slabs stagnated at mantle transition zone can be an important factor regulating the climate.