With material consumption increasing, the need for biodegradable materials derived from renewable resources becomes urgent, particularly in the popular field of 3D-printing. Processed natural fibers have been used as fillers for 3D-printing filaments and slurries, yet reports of utilizing pure biomass to 3D-print structures that reach mechanical properties comparable to synthetic plastics are scarce. Here, we develop and characterize slurries for extrusion-based 3D-printing comprised of unprocessed spirulina and varying amounts of cellulose fibers (CFs). Tuning the micro-morphology, density, and mechanical properties of multilayered structures is achieved by modulating the CF amount or drying method. Densified morphologies are obtained upon desiccator-drying, while oven incubation plasticizes the matrix and leads to intermediate densities. Freeze-drying creates low-density foam microstructures. The compressive strengths of the structures follow the same trend as their density. CFs are critical in the denser structures, as without the fibers, the samples do not retain their shape while drying. The compressive strength and strain to failure of the composites progressively increase with increasing filler content, ranging between 0.8 and 16 MPa and 12%-47%, respectively, at densities of 0.51-1.00 g/cm 3 . The measured properties are comparable to other biobased composites and commercial plastic filaments for 3D-printing.

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The increasing consumption of nonrenewable materials urgently calls for the design and fabrication of sustainable alternatives. New generations of materials should be derived from renewable sources, processed using environmentally friendly methods, and designed considering their full life cycle, especially their end-of-life fate. Here, we review recent advances in developing sustainable polymers from biological matter (biomatter), including progress in the extraction and utilization of bioderived monomers and polymers, as well as the emergence of polymers produced directly from unprocessed biomatter (entire cells or tissues). We also discuss applications of sustainable polymers in bioplastics, biocomposites, and cementitious biomaterials, with emphasis on relating their performance to underlying fundamental mechanisms. Finally, we provide a future outlook for sustainable material development, highlighting the need for more accurate and accessible tools for assessing life-cycle impacts and socioeconomic challenges as this field advances. Expected final online publication date for the Annual Review of Materials Research, Volume 53 is July 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The mass production and disposal of non‐degradable fossil‐based plastics is responsible for alarming environmental and social issues when not managed responsibly. Towards manufacturing environmentally‐friendly materials, biopolymers, that is, polymers synthesized by living organisms, emerge as promising sustainable alternatives as they combine attractive mechanical properties, compostability, and renewable sourcing. In this review, we analyze the structural and mechanical properties of three of the most studied biopolymer classes: cellulose, chitin, and protein beta‐sheet structures. We first discuss the hierarchical structure of the biopolymers and how their rich interaction networks induce appealing mechanical properties. Then, we review different fabrication and processing methods to translate these attractive properties into macroscopic materials and composites. Finally, we discuss a nascent approach, which leverages the direct use of microorganisms, in the form of intact cells, tissues or dissociated biological matter (biomatter), as meso‐scale material building blocks. These non‐ or little pre‐processed biomatter building blocks are composed of the biopolymer structural elements (molecular‐nano scale), but also inherit the higher‐scale hierarchical characteristics. Processing‐structure–property relationships for biomatter‐based materials are discussed, emphasizing on the role of hierarchical arrangement, processing‐induced transformations, and intermolecular bonding, on the macroscopic mechanical properties. Finally, we present a perspective on the role of biopolymers in a circular economy.