Tailoring the Mechanical Properties of 3D Microstructures Using Visible Light Post‐Manufacturing

Abstract

the laser, where the square of the optical intensity exceeds the threshold needed to initiate polymerization. In this way, very small feature sizes of less than 100 nm can be achieved. [3,4] Microstructures pre pared via DLW have for example been used in microfluidic chips, [5,6] metama terials, [7] or as 3D microscaffolds for cell and tissue engineering. [8] Commercial resist mixtures are available that are well suited for the rapid generation of stable structures. However, when using standard resists, the resulting microstructures are static. In order to further expand the rep ertoire of applications of DLW, new photo resists have to be designed that directly impart functionality onto the structures emerging from the writing process. [9] Our group has been pursuing this goal, pro ducing resists that, e.g., lead to conduc tive, [10] stimuliresponsive, [11] and erasable structures. [12] The mechanical properties of microstructures are critical for their application, especially when used as cell scaf folds. [13] The mechanical properties of microstructures created via DLW can certainly be tuned by careful adjustment of the writing parameters (i.e., laser power and scan speed), but only to a limited extent. [14] Herein, we present the first photoresist for DLW that is capable of generating microstructures whose mechanical properties can be adjusted postwriting, solely The photochemistry of anthracene, a new class of photoresist for direct laser writing, is used to enable visible-light-gated control over the mechanical properties of 3D microstructures post-manufacturing. The mechanical and viscoelastic properties (hardness, complex elastic modulus, and loss factor) of the microstructures are measured over the course of irradiation via dynamic mechanical analysis on the nanoscale. Irradiation of the microstructures leads to a strong hardening and stiffening effect due to the generation of additional crosslinks through the photodimerization of the anthracene functionalities. A relationship between the loss of fluorescence-a consequence of the photodimerization-and changes in the mechanical properties isestablished. The fluorescence thus serves as a proxy read-out for the mechanical properties. These photoresponsive microstructures can potentially be used as "mechanical blank slates": their mechanical properties can be readily adjusted using visible light to serve the demands of different applications and read out using their fluorescence. 3D MicrostructuresDirect laser writing (DLW) is the only manufacturing tech nique capable of producing truly 3D structures on the micro scopic scale. [1] What differentiates DLW from conventional 3Dprinting techniques is the fact that it exploits twophoton absorption (TPA) to initiate polymerizations. While single photon absorption (SPA) is proportional to the optical inten sity, TPA is proportional to the square of the optical intensity. [2] Thus, polymerization will only take place in the focal volume of

Light‐Powered Microrobots: Challenges and Opportunities for Hard and Soft Responsive Microswimmers

“…In addition to the photoresist selection and printing parameters' optimization, postprocessing of 2PP 3D-printed structures can contribute to achieving the desired material properties. For example, postprint curing can help improve the mechanical properties of hard polymers by increasing the degree of crosslinking, [99,100] thermal reflow can reduce surface roughness for fast printed structures, [101] and isotropic plasma etching and/or pyrolysis can be used to improve the resolution beyond 100 nm. [102]…”

Challenges and limits of Mechanical Stability in 3D Direct Laser Writing

“…While the control of the degree of polymerization in the voxel during the actual writing process is of utmost importance for further improvements of DLW, it has been a challenge to directly measure the level of chemical conversion in the printed area. A few studies investigate the effect of the writing condition on the properties of the printed polymer network 28,[42][43][44][45][46] . By using different detection instrumentations, for non-commercial resists based on a mixture of two different tri-acrylates, a monomer conversion degree of 60%-75% has been obtained while for organic-inorganic hybrid resists, degree of conversion has been reported to be 35%-75% 42,43 .…”

“…Recent developments in nano-scale devices take advantage of many complex patterns with high aspect ratio structures in its design 45,[53][54][55][56] . High strength along with high deformability is an essential property for the design and reliability of novel nano devices 57 .…”

Wavelength‐Selective Folding of Single Polymer Chains with Different Colors of Visible Light

“…[40,41] However, we have recently observed that even the non-extended anthracene that is traditionally dimerized with highly energetic UV-light, can be efficiently brought to reaction with visible light up to 415 nm. [42] In order to induce the second folding step as well with mild visible light, the partially folded SCNP1 was irradiated in THF (0.25 mg mL -1 ) with a violet LED (centered at λ = 415 nm, emitting between λ = 390 nm and λ = 440 nm). The hydrodynamic volume of SCNP1 underwent a This article is protected by copyright.…”