Thermo-mechanical Properties of Hierarchical Biocomposite Materials from Photosynthetic Microorganisms

Abstract: Extrusion 3D-printing of biopolymers and natural fiber-based biocomposites allows for the fabrication of complex structures, ranging from gels for healthcare applications to eco-friendly structural materials. However, traditional polymer extrusion demands high-energy consumption to pre-heat the slurries and reduce material viscosity. Additionally, natural fiber reinforcement often requires harsh treatments to improve adhesion to the matrix. Here, we overcome these challenges by introducing a systematic framework to fabricate natural biocomposite materials via a sustainable and scalable process. Using Chlorella vulgaris microalgae as the matrix, we optimize the bioink composition and the 3D-printing process to fabricate multifunctional, lightweight, hierarchical materials. A systematic dehydration approach prevents cracking and failure of the 3D-printed structure, maintaining a continuous morphology of aggregated microalgae cells that can withstand high shear forces during processing. Hydroxyethyl cellulose acts as a binder and reinforcement for Chlorella cells, leading to biocomposites with a bending stiffness above 1.5 GPa. The Chlorella biocomposites demonstrate isotropic heat transfer, functioning as effective thermal insulators with a thermal conductivity of 0.10 W/mK at room temperature. These materials show promise in applications requiring balanced thermal insulation and structural capabilities, positioning them as a sustainable alternative to conventional materials in response to increasing global materials demand.