Fully plant-derived flaxseed mucilage-soy protein inks for extrusion-based 3D printing of tunable hydrogel scaffolds

The development of sustainable, biocompatible bioinks is essential to advancing extrusion-based 3D printing. This study introduces a fully plant-derived ink system integrating flaxseed mucilage (FSM) and soy protein isolate (SPI) and systematically assesses its printability and scaffold performance. FSM was prepared at concentrations of 5%, 6%, and 7% (w/v), both independently and in combination with 4% SPI, followed by EDC-NHS crosslinking. Rheological analysis indicated a pronounced shear-thinning behavior across all formulations with increased FSM concentration and SPI incorporation; with the 7% FSM + 4% SPI blend exhibiting the highest consistency index (3684.31 Pa s), the lowest flow index (0.1605), and superior viscoelastic properties (G' > G″). Printability studies demonstrated improved filament fidelity and grid resolution with higher FSM content and SPI addition, with the 7% FSM + 4% SPI formulation exhibiting superior shape retention. Scanning electron microscopy (SEM) analysis confirmed the formation of interconnected porous architectures, while degradation studies in a phosphate-buffered saline (PBS) solution showed controlled structural erosion influenced by FSM concentration and SPI presence. FSM-only scaffolds exhibited high swelling capacity, which was substantially reduced upon SPI incorporation. Mechanical and thermal analyses demonstrated that SPI incorporation influenced scaffold stability and elasticity. Structural characterization through attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray diffraction (XRD) confirmed intermolecular interactions between FSM and SPI. Studies on the release of antibacterial drugs from ciprofloxacin-loaded scaffolds have shown concentration-dependent inhibition zones against Bacillus subtilis. Overall, this study demonstrates that FSM-SPI composite hydrogels offer tunable rheological, mechanical, and degradation properties, rendering them promising, sustainable inks for extrusion-based 3D printing applications.