Living organisms have structured surfaces with specific wettability that allows their efficient adaptation to the environment and improves their survival rate. For example, the rice leaves have micro- and nanoscale structures on their surface that form a superhydrophobic surface for self-cleaning and water repellence [1]. Bioinspiration of these natural surfaces in science can be beneficial for applications in biotechnology, microfluidics, textiles, fabrication of sensors, etc [2]. Addressing these challenging goals requires the development of both materials with tailored properties and methods for the fabrication of structured surfaces. In comparison to previously reported surface patterning techniques, melt-electrowriting is a novel and solvent-free technique that is based on 3D printing and electrospinning which allows programmed deposition of polymeric microfibers [3]. Shape memory polymers offer a very interesting combination of properties such as switching of mechanical properties and the capability of stimuli-induced restoration of shape after deformation [4, 5].

In the present study, we report the fabrication of structured surfaces with shape-memory features (continuous vertical lamellae) with a high aspect ratio using melt-electrowriting as well as an investigation of their wetting behavior. It was found that the lamellae presented softness and hardness memory at room temperature. This depends on the previous temperature that the polymer was exposed. It was as well observed that wetting behavior depends on the state of features, which could be either soft or hard depending on temperature, height, and distance between them. While increasing the volume of the droplet, water can jump to the next lamella that results in a lower contact angle. This water jumping of lamellae at higher temperatures also produces deformation of the structure. Deformed surfaces can be frozen by cooling. The deformed state can be completely recovered at an elevated temperature. This feature opens the possibility to apply such topographies for the design of smart elements of microfluidic devices, as for example smart valves.

Figure 1. Shape memory behavior of the lamellae surfaces conducted by the advancing volume of water drop.

References

[1] D.H. Kwon, H.K. Huh, S.J. Lee, Exp. Fluids 2014, 55(3), 1691.

[2] Z. Cheng, D. Zhang, X. Luo, H. Lai, Y. Liu, L. Jiang, Adv. Mater, 2021,. 33(6), 2001718.

[3] P.D. Dalton, Current Opinion in Biomedical Engineering 2, 2017, 49-57.

[4] L. Ionov, G. Stoychev, D. Jehnichen, J.U. Sommer, ACS Applied Materials & Interfaces, 2017, 9(5), 4873-4881.

[5] G. Stoychev, M.J. Razavi, X. Wang, L. Ionov, Macromol. Rapid Commun., 2017, 38(18), 1700213.