Perpendicular growth of a tip-growing polymer precipitate on parallel line-patterned surfaces

Growth on surfaces with parallel line patterns typically results in longitudinal alignment, whether in living cells or nonliving crystals. However, unlike many other cells, tip-growing fungal germ tubes grow perpendicular to these line patterns. Here, we show that a recently reported artificial system that mimics the tip growth of germ tubes also exhibits similar perpendicular growth on grooved or ridged surfaces. Our experiments using tip-growing polymer precipitates reveal that the soft growing tip can be partially trapped by substrate patterns, and that the tip can change its growing direction when encountering the surface pattern obliquely. We theoretically rationalize this change in growth direction induced by physical interaction between the soft growing system and the substrate topography. Our physical explanation of the unique growth behavior based on material characteristics without external control suggests a way to achieve embedded physical intelligence in soft mechanical systems interacting with the surrounding objects.