Stretch-induced reversible self-growth of high aspect ratio microstructures scribed by femtosecond laser.

Inspired by the intricate surface patterns in nature, the concept of polymer self-growth has recently been applied to construct synthetic structures. However, existing techniques, whether driven by chemical reactions or physical mass transport, fail to offer rapid and reversible tuning, and typically can only produce structures with low aspect ratios. Here, we present a generalized stretch-induced polymer self-growth (SIPS) method for reversibly constructing structures on a wide range of pre-stretched elastic membranes, including silicone, PU, PDMS, dielectric elastomer (VHB), and hydrogel. High aspect ratio (~1.4, much larger than the previously reported value ~ 0.25) straight and bent micropillars with different cross-sections are facilely fabricated by femtosecond laser cutting. By releasing and subsequent re-stretching the membrane, tuning of the grown structures is readily achievable, enabling a rapid (~ 30 s) and reversible transition between structured and flat surface. Experimental and simulation results confirm that the micropillar height is governed by the stretch ratio and laser scribing depth. The high aspect ratio enhances tactile perception and allows directional bending for encoding information. These capabilities are demonstrated through proof-of-concept applications in Braille training and information encryption/decryption. The presented SIPS method that combines femtosecond laser cutting and the stretching of elastic membranes, offers an efficient approach for fabricating tunable functional microstructures with great potential in the fields of micro/nanofabrication and adaptive surface engineering.