Preserving Microstructure Enhances Cohesion and Mechanical Performance in <i>Spirulina</i> -Based 3D-Printed Biomaterials

<i>Spirulina platensis</i> is a promising bioresource for developing structural materials, offering a renewable alternative to conventional polymers due to its rapid growth and characteristic helical microstructure. While its biochemical properties have been widely studied, the role of cellular morphology in determining macroscale mechanical performance remains underexplored. In this work, we examine how maintaining versus disrupting <i>Spirulina</i>'s native trichome structure and cell walls impacts the cohesion, rheology, and mechanical behavior of 3D-printed biomaterials. Using hydroxyethyl cellulose (HEC) as a binder, we developed two classes of bioinks: trichome biocomposites, based on freeze-dried <i>Spirulina</i> trichomes, and lysed biocomposites, formed from thermally lysed <i>Spirulina</i> cells. Differential scanning calorimetry revealed stronger molecular interactions between lysed cells and HEC, while trichomes contributed instead via physical interlocking and structural integrity of the cell wall. Despite weaker molecular interactions, trichome-based biocomposite bioinks exhibited higher viscosity, improved printability, and higher rheological yield stress by up to 499%. Upon dehydration, trichome biocomposites showed lower shrinkage and higher mechanical performance under compression, with normalized compressive modulus and yield strength significantly exceeding that of lysed biocomposites (by up to 107% and 108%, respectively). These effects are attributed to mechanical interlocking and enhanced stress transfer through intact cell walls. Our findings demonstrate that preserving biological microstructure may enable improved material cohesion and function, offering design principles for scalable, sustainable biofabrication of algae-based structural materials.