Be careful not to SLIP

Biomimicry is an interdisciplinary field that combines engineering and biology to design machines and tools based on plant traits (Hayakawa et al. 2024). One of the major challenges for scientists was creating an extremely water-repellent material that would prevent liquids from adhering to surfaces (Xue et al. 2010). Scientists created superhydrophobic surfaces which were surfaces with small bumps and ridges designed to capture air under water droplets, minimizing the physical contact between the liquid and solid (Ma and Hill 2006). Although water repels well from superhydrophobic surfaces, external factors could easily damage them or cause them to lose their abilities over time (Wan et al. 2022). The search for a more effective slippery surface led research towards an unexpected biological model: the pitcher plant (Li et al. 2024). 

The carnivorous pitcher plant possesses highly specialized modified leaves that trap insects (Scholz et al. 2010). They have a rounded rim surrounding the opening of the pitcher, called the peristome. One of its primary functions is to attract insects, specifically because of its bright leaves, odours, and moisture absorbing nectar (Scholz et al. 2010; Li et al. 2024). When wet, the peristomes get extremely slippery, causing the insects to lose their footing and fall into the pitcher (Figure 1) (Li et al. 2024). Below the peristome is the conductive zone. The inner walls of the conductive zone feature downward-facing lunate cells coated with a thick layer of tiny epicuticular wax crystals. These crystals form a rough structure on the pitcher walls, reducing the adhesive on the insect’s feet, making climbing back out difficult (Li et al. 2024). The fluid in the pitcher then digests the insects, and special glands on the inner surface of the pitcher absorb the released nutrients (Mithöfer 2011).

In 2011, taking inspiration from the trapping mechanism of pitcher plants, the Aizenberg research group created a novel method to substitute superhydrophobic surfaces, called slippery liquid infused porous surfaces, or SLIPS (Li et al. 2024). Instead of using trapped air, SLIPS replaced it with a thin layer of lubricating fluid that was held in place using capillary and van der Waal forces. This created a very smooth and continuous liquid composite lubrication layer that lowered friction resistance between the solid substrate and the external liquid. Additionally, unlike superhydrophobic surfaces, if mechanical damage occurs to the lubricant layer on SLIPS, the lubricant redistributes across the surface and restores the slippery properties, demonstrating excellent repairability (Li et al. 2024)

The distinctive characteristics of SLIP have enabled its use in various applications, including self-cleaning surfaces and anti-icing materials, which maintain surfaces clean and functional without frequent upkeep (Scholz et al. 2010; Zhang et al. 2019) SLIPS and the pitcher plant demonstrates how studying biological adaptations can lead to innovative technological solutions.

Bibliography

Hayakawa, Takahiko, Hayato Suzuki, Hiroshi Yamamoto, and Nobutaka Mitsuda. 2024. “Synthetic Biology in Plants.” Plant Biotechnology 41 (3): 173–93. https://doi.org/10.5511/plantbiotechnology.24.0630b.

Li, Junwei, Bin Lu, Zhengbai Cheng, Haibing Cao, and Xingye An. 2024. “Designs and Recent Progress of ‘Pitcher Plant Effect’ Inspired Ultra-Slippery Surfaces: A Review.” Progress in Organic Coatings 191 (June): 108460. https://doi.org/10.1016/j.porgcoat.2024.108460.

Ma, Minglin, and Randal M. Hill. 2006. “Superhydrophobic Surfaces.” Current Opinion in Colloid & Interface Science 11 (4): 193–202. https://doi.org/10.1016/j.cocis.2006.06.002.

Mithöfer, Axel. 2011. “Carnivorous Pitcher Plants: Insights in an Old Topic.” Phytochemistry, Plant-Insect Interactions, vol. 72 (13): 1678–82. https://doi.org/10.1016/j.phytochem.2010.11.024.

Scholz, I., M. Bückins, L. Dolge, et al. 2010. “Slippery Surfaces of Pitcher Plants: Nepenthes Wax Crystals Minimize Insect Attachment via Microscopic Surface Roughness.” The Journal of Experimental Biology 213 (Pt 7): 1115–25. https://doi.org/10.1242/jeb.035618.

Wan, Tao, Bo Wang, Qing Han, Jianshe Chen, Binchuan Li, and Shicheng Wei. 2022. “A Review of Superhydrophobic Shape-Memory Polymers: Preparation, Activation, and Applications.” Applied Materials Today 29 (December): 101665. https://doi.org/10.1016/j.apmt.2022.101665.

Xue, Chao-Hua, Shun-Tian Jia, Jing Zhang, and Jian-Zhong Ma. 2010. “Large-Area Fabrication of Superhydrophobic Surfaces for Practical Applications: An Overview.” Science and Technology of Advanced Materials 11 (3): 033002. https://doi.org/10.1088/1468-6996/11/3/033002.

Zhang, Dong, Yuzheng Xia, Xiaonong Chen, Shuxian Shi, and Lei Lei. 2019. “PDMS-Infused Poly(High Internal Phase Emulsion) Templates for the Construction of Slippery Liquid-Infused Porous Surfaces with Self-Cleaning and Self-Repairing Properties.” Langmuir 35 (25): 8276–84. https://doi.org/10.1021/acs.langmuir.9b01115.