title: Shape-shifting 3D protein microstructures with programmable directionality via quantitative nanoscale stiffness modulation.
abstract: The ability to shape-shift in response to a stimulus increases an organism's survivability in nature. Similarly, man-made dynamic and responsive "smart" microtechnology is crucial for the advancement of human technology. Here, 10-30 μm shape-changing 3D BSA protein hydrogel microstructures are fabricated with dynamic, quantitative, directional, and angle-resolved bending via two-photon photolithography. The controlled directional responsiveness is achieved by spatially controlling the cross-linking density of BSA at a nanometer lengthscale. Atomic force microscopy measurements of Young's moduli of structures indicate that increasing the laser writing distance at the z-axis from 100-500 nm decreases the modulus of the structure. Hence, through nanoscale modulation of the laser writing z-layer distance at the nanoscale, control over the cross-linking density is possible, allowing for the swelling extent of the microstructures to be quantified and controlled with high precision. This method of segmented moduli is applied within a single microstructure for the design of shape-shifting microstructures that exhibit stimulus-induced chirality, as well as for the fabrication of a free-standing 3D microtrap which is able to open and close in response to a pH change.
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371.
authors.forename: Mian Rong
authors.initials: MR
authors.lastname: Lee
authors.forename: In Yee
authors.initials: IY
authors.lastname: Phang
authors.forename: Yan
authors.initials: Y
authors.lastname: Cui
authors.forename: Yih Hong
authors.initials: YH
authors.lastname: Lee
authors.forename: Xing Yi
authors.initials: XY
authors.lastname: Ling
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry; D055119:Elastic Modulus; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000138:chemical synthesis* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D055595:Mechanical Phenomena; D018625:Microscopy, Atomic Force; D055616:Microtechnology / Q000379:methods; D010316:Particle Size; D058105:Polymerization; D012710:Serum Albumin, Bovine / Q000737:chemistry*
chemical_list: D003432:Cross-Linking Reagents; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D012710:Serum Albumin, Bovine
keywords: BSA; chirality; modulation cross-linking density; pH responsive; programmable directionality; shape-shifting materials; two-photon lithography