Intelligent membranes to control moisture flow

Researchers at the Adolphe Merkle Institute and Chulalongkorn University in Thailand have developed a new class of nature-inspired membranes that autonomously control the extent of water transport in response to environmental conditions, with potential applications ranging from healthcare to packaging.

Nature has developed countless strategies for collecting and retaining water, including mechanisms to prevent water loss through transpiration. For example, most land plants are covered by thin protective layers, known as cuticles, that prevent desiccation. Olive trees and ivy leaves possess cuticles that act as intelligent barriers, regulating moisture transport in response to changing environmental conditions. Supported by a Swiss National Science Foundation SPIRIT grant, aimed at fostering international research partnerships, the Swiss-Thai team sought to understand the design principles underlying this remarkable behavior and translate them into synthetic materials. "Our goal was to exploit the principles at play in the olive cuticle as blueprints for the bio-inspired design of artificial membranes, and if possible, improve on nature," explains Prof. Christoph Weder, AMI's Chair of Polymer Chemistry and Materials.

Like their biological counterparts, the synthetic membranes developed by the team adapt dynamically to humidity and, owing to their asymmetric structure, preferentially transport water in one direction. Earlier studies by AMI's polymer researchers had revealed that this directional transport in plant cuticles arises from a subtle interplay between the compositionally graded architecture of the cuticle and humidity-induced softening of its central layer. By recreating these features in artificial membranes, the scientists established a versatile platform for investigating the underlying transport mechanisms and tailoring them through material design.

Working closely across disciplines and continents, the researchers subsequently developed membranes whose directional water transport can be switched on or off simply by changing the surrounding humidity. Rather than relying on pumps, valves, or external power sources, the membranes autonomously regulate water permeation as environmental moisture changes the mobility of selected polymers within them. By carefully controlling the membrane composition and architecture, the team demonstrated that both the magnitude and the directionality of water transport can be tuned over a wide range. These findings not only provide new insights into how plants regulate water loss but also demonstrate adaptive membranes with programmable transport properties and world-record asymmetries.

However, despite the promising results, the researchers acknowledge that hurdles remain. "Predicting exactly how these membranes will behave under different conditions is still difficult," adds former PhD student, Dr. Luca Grillo. "And the humidity range in which we get our membranes to switch is still somewhat limited."

The responsive membranes could be used wherever passive moisture control is desirable. Potential applications for this new class of membranes are wide-ranging, including packaging that could regulate moisture to extend the shelf life of food or protect electronics, wound dressings that maintain optimal moisture for healing, and systems for oil–water separation and water harvesting in dry regions. Because the membranes operate autonomously and require no electronic control or external energy input, they represent an attractive strategy for developing sustainable materials inspired by the elegant solutions evolved by nature over millions of years. The project also illustrates how international collaboration, bringing together complementary expertise in plant biology, polymer science, and materials engineering, can transform fundamental biological discoveries into innovative technologies with real societal impact.

References:

Grillo, L.; Weder, C. Directional Water Transport in Laminated Polymer. Journal of Membrane Science 2025, 733, 124379.

Rattanaphong, N.; Grillo, L.; Weder, C.; Dubas, S. T. Directional Moisture Transport in Compositionally Graded Multilayer Membranes. ACS Appl. Polym. Mater. 2025, 7 (24), 16628–16636.