Biobased artificial spider silk captures moisture and generates triboelectric power using simple water-based processing, offering an efficient and sustainable approach for water harvesting and low power energy needs.
(Nanowerk Spotlight) Atmospheric humidity is one of the most widespread sources of untapped water. Many regions experience regular fog or persistently damp air, yet the tools that could capture moisture in a practical and sustainable way remain limited.
Engineers and material scientists have proposed surfaces that gather droplets, fibers that guide them, and coatings that speed their movement. These ideas showed potential but often relied on complex synthetic polymers or chemical treatments that restricted real world use.
Water collection itself is only half the story. Another branch of research has explored how moving droplets can create electricity when they make and break contact with a solid surface. This process, known as the triboelectric effect, involves the exchange of electrons when two materials touch and then separate. Devices that use this effect can power small electronics, but they also tend to require detailed surface designs or specialized materials.
These separate efforts highlight a shared obstacle. Many proposed systems can either harvest water or generate electrical power, but not both. Attempts to combine these functions often increase fabrication steps or introduce materials that conflict with sustainability goals.
Meanwhile, natural systems reveal much simpler methods for managing moisture. One example is spider dragline silk. The repeating pattern of thick spindle knots and thin joints guides droplets along the thread due to differences in curvature that create variations in internal pressure known as Laplace pressure. Laplace pressure describes how the pressure inside a curved liquid surface increases when the radius of curvature decreases. This pushes droplets toward regions with lower curvature and lower pressure. Biological spider silk can perform this task without coatings, solvents, or external power.
Researchers have tried to imitate this behavior with synthetic fibers, but many approaches still depend on equipment or materials that limit broad use. This creates interest in methods that recreate the essential geometry of spider silk using simpler ingredients and cleaner processing.
The paper reports artificial spider silk made entirely from biobased polymers that can harvest moisture from humid air and deliver droplets to a triboelectric nanogenerator. The fibers form through electrostatic complexation, which is the attraction between molecules that carry opposite electrical charges. Because the method uses only water-based solutions and common natural polymers, it avoids the chemical and structural demands that restricted earlier designs.
The study demonstrates that a straightforward process can yield fibers with controlled structure and practical use in both water harvesting and energy generation.
Design of fog-harvesting and triboelectric power generation systems. a) Image of a spider. b) Image of water harvesting of natural spider silk. c) Schematic of the water-collection mechanism of spider silk. d) Photograph of a chitosan–sodium alginate filament (CSF) prepared in this study. e) Schematic of the CSF preparation process. f) Conceptual diagram of water harvesting of CSF for triboelectric energy generation. (Image: Reproduced from DOI:10.1002/adfm.202522750, CC BY ) (click on image to enlarge)
The artificial silk is made from chitosan and sodium alginate. Chitosan is a positively charged polymer derived from chitin, the structural material found in crustacean shells. Sodium alginate is a negatively charged polymer obtained from seaweed. When these two polymers meet in solution, they form a polyelectrolyte complex. A polyelectrolyte complex is a stable material created through the attraction of opposite charges rather than chemical reactions.
To make the fibers, the researchers placed droplets of chitosan solution and sodium alginate solution on a polystyrene surface. When the droplets touched, a thin liquid film formed at their boundary. Pulling this film produced a filament with evenly spaced droplets along its length. These droplets appeared because of Plateau-Rayleigh instability, which is a fluid behavior in which a cylindrical thread of liquid breaks into beads to lower its surface energy. As the filament dried, the droplets solidified into spindle shaped knots, and the thinner connecting regions formed joints. This created a structure similar to natural spider silk.
Microscopy revealed smooth surfaces on the knots and rougher, oriented surfaces on the joints. This contrast in texture helps direct droplet movement. Zeta potential measurements, which track the electrical potential at the boundary of dispersed particles or polymers in liquid, showed positive values of +33.4 mV for chitosan and negative values of −47.25 mV for sodium alginate.
These values indicate strong electrostatic attraction. The composite fibers stayed intact when immersed in 1 wt.% acetic acid for 24 hours, although they swelled. This stability confirms that the two polymers formed a true complex. Infrared spectroscopy detected a new absorption peak at 1712 cm⁻¹, a signal of protonated carboxyl groups that supports complex formation. Thermal analysis showed a degradation profile distinct from either pure polymer.
Polymer concentration influenced fiber formation. Concentrations from 0.2 to 1.4 wt.% produced stable filaments, and fibers made from 1.0 wt.% solutions showed strong fog harvesting performance. The surface used to support the droplets also mattered. Bare glass held droplets too strongly and caused filament breakage. Hydrophobic glass held them too weakly and prevented drawing. Polystyrene provided the right balance and produced a yield of 89.79 percent. Adjusting the mass ratio of chitosan to sodium alginate to 3.2 increased this yield to 99.36 percent.
Fog harvesting tests used an ultrasonic humidifier to create air at about 90 percent relative humidity. Droplets formed along the fibers and moved toward the spindle knots. Larger droplets formed when fibers were made from higher concentration solutions. Fibers made from 1.4 wt.% solutions produced first droplet volumes of 26.3 µL. These droplets required more time to form, so overall harvesting rate was highest for 1.0 wt.% fibers. These achieved a maximum fog harvesting efficiency of 1552.83 mg cm⁻¹ h⁻¹.
The fibers also supported energy generation. They were woven into web-like structures that directed collected water through a funnel and onto a slanted sheet of polytetrafluoroethylene backed with aluminum electrodes. When droplets touched and then moved along this surface, they produced electrical charge through the triboelectric effect. The output voltage increased as the tilt angle rose to 45°, then declined.
Larger droplets produced higher voltage because they contacted more surface area. Droplets released from greater height hit with more speed and increased electrical output. Frequency had a smaller effect. Under optimized conditions, the device produced an open circuit voltage of 180 V and a maximum power of 72.25 µW at a resistance of 108 Ω.
Scaling the system increased water production. Four webs collected 45.06 g h⁻¹ in the fog chamber. Durability tests cycled the webs through wetting, fog exposure, and drying. After 30 cycles, the webs kept 83 percent of their initial fog harvesting efficiency. High humidity exposure for nearly two weeks caused no visible damage.
The integrated system powered small electronics by charging a 4.6 µF capacitor to 6 V after 360 seconds. This output powered 80 light emitting diodes in series. In a greenhouse like environment with sustained humidity, the device powered a hygrometer, thermometer, and stopwatch.
This study shows that artificial spider silk made from simple biobased ingredients can gather water from humid air and supply droplets to a triboelectric nanogenerator. The fibers form through water-based processing and gain their structure from natural fluid behavior rather than complex manufacturing. The work points toward systems that provide local water collection and small-scale electrical power in humid environments using accessible materials and straightforward fabrication.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
