Biopolymers are essential building blocks that constitute cells and tissues with well-defined molecular structures and diverse biological functions. Their three-dimensional (3D) complex architectures are used to analyze, control, and mimic various cells and their ensembles. However, the free-form and high-resolution structuring of various biopolymers remain challenging because their structural and rheological control depend critically on their polymeric types at the submicron scale. Here, direct 3D writing of intact biopolymers is demonstrated using a systemic combination of nanoscale confinement, evaporation, and solidification of a biopolymer-containing solution. A femtoliter solution is confined in an ultra-shallow liquid interface between a fine-tuned nanopipette and a chosen substrate surface to achieve directional growth of biopolymer nanowires via solvent-exclusive evaporation and concurrent solution supply. The evaporation-dependent printing is biopolymer type-independent, therefore, the 3D motor-operated precise nanopipette positioning allows in situ printing of nucleic acids, polysaccharides, and proteins with submicron resolution. By controlling concentrations and molecular weights, several different biopolymers are reproducibly patterned with desired size and geometry, and their 3D architectures are biologically active in various solvents with no structural deformation. Notably, protein-based nanowire patterns exhibit pin-point localization of spatiotemporal biofunctions, including target recognition and catalytic peroxidation, indicating their application potential in organ-on-chips and micro-tissue engineering.
Keywords: 3D writing; biopolymers; nanoscale confinement; solvent-exclusive evaporation; sub-micron resolution.
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