Soft and Stiff 3D Microstructures by Step‐Growth Photopolymerization Using a Single Photoresin and Multi‐Photon Laser Printing

Abstract Manufacturing three‐dimensional (3D) microstructures with multi‐material properties via two‐photon 3D laser printing (2PLP) remains a significant challenge due to restrictions inherent to conventional chain‐growth photoresins. Herein, an additive‐ and initiator‐free resin formulation is introduced that allows for the printing of 3D microstructures with disparate mechanical properties via the step‐growth photopolymerization‐based self‐dimerization of visible‐light‐active ortho ‐methylbenzaldehydes ( o MBA) within a single fabrication step in 2PLP by altering the printing parameters (i.e., laser power, scan speed). It is established that the laser exposure dose ( D exp ) directly influences the material properties by varying the degree of crosslinking. While stiff materials with a Young's modulus above 1300 MPa at the higher edge of the D exp can be produced, soft materials with a Young's modulus of < 10 MPa at the lower edge of the D exp can also be fabricated. Thus, the herein pioneered resin offers a very broad material property window – spanning more than two orders of magnitude in Young's modulus – for multi‐material printing via 2PLP, which is not achievable with conventional resins. The capabilities of the advanced resin are demonstrated by printing structures with hard and soft segments in a single fabrication step, visualizing their unique mechanical response to compression via in situ measurements.