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.

Fabrication of three-dimensional proteinaceous micro- and nano-structures by femtosecond laser cross-linking

“…It allows to become a standard to introduce and discuss variation of the major factors including laser properties, irradiation conditions, solvent, photoactivator and protein concentration, that can affect the outcome of the process. BSA is also often used due to its unique properties, one of which is pH actuation capability 39,40,62 , as discussed later. Kaehr et al have also shown its potential to be mixed with other …”

“…These functions include not only the diverse intrinsic properties of native proteins such as charge transfer, molecule modification and cell-cell communication, but also engineered functions of synthetic proteins. Consequently, the resulting protein structures have been applied to fabricate functional microdevices, including pH-sensitive actuators 39,40 and optical microcomponents 41,42 . The integration of proteinaceous microstructures into commercial polymers 43 and protein-polymer hybrids 44 has also been found to increase mechanical strength.…”

Femtosecond Laser Direct Write Integration of Multi-Protein Patterns and 3D Microstructures into 3D Glass Microfluidic Devices

“…Protein molecules in aqueous solution can be cross-linked to construct 3D proteinaceous microstructures by the exposure of a focused femtosecond laser along its trajectory in well-resolved and controlled manners [7][8][9]. Such microstructures made of protein have been applied for cell culture scaffolds [10,11], pH-actuators [9,12,13] and optical elements [13,14].…”

“…Such microstructures made of protein have been applied for cell culture scaffolds [10,11], pH-actuators [9,12,13] and optical elements [13,14]. 3D microstructures made of collagen have been shown to promote cell adhesion [10,11].…”

“…3D microstructures made of collagen have been shown to promote cell adhesion [10,11]. pH-change has been shown to cause the expansion or shrinking of microstructures made of bovine serum albumin (BSA) and other proteins [9,12]. This pH-actuation of BSA was applied to create pH-tunable lenses [13].…”