Humidity-Sensitive Hydraulic Actuator Inspired by Pine Cones

Innovation: Academia

Technical University of Munich

2017

Image: Aaron Burden / Unsplash / CC BY SA - Creative Commons Attribution + ShareAlike

Sense Temperature Cues From the Environment

Some living systems use their ability to perceive temperature to find prey or avoid predators, or as a way to gain information about their environment, such as whether they are near a warm or cold place. Temperature gradients can be subtle and modulate as they travel through water, air, or solids. Living organisms must therefore have a variety of thermal sensors appropriate to a given medium (liquid, gas, solid). Some even have a way to “visualize” a signal’s source. For example, the rattlesnake has heat sensors with thousands of nerve endings located in pit-shaped holes on each side of its face. The sensitivity of the pits overlaps, giving the snake a bifocal image of the heat’s source.

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Sense Atmospheric Conditions

For some living systems, the ability to detect changes in atmospheric conditions can be very valuable. By predicting changes in regional weather or in very localized conditions, living systems can avoid or take advantage of those changes. Since such adjustments can be very subtle, living systems must be able to detect miniscule variations in moisture, barometric pressure, ions in the air, and other environmental cues. Many insects and birds, for example, can predict oncoming storms and take cover before their lives are put at risk.

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Modify Size/Shape/Mass/Volume

Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Hydraulic actuator from Technical University of Munich can passively swell to change shape, reducing energy usage.

Benefits

Autonomous
Reduced energy usage
Sustainable

Applications

Building design
Architecture
Heating and cooling systems

UN Sustainable Development Goals Addressed

Goal 11: Sustainable Cities & Communities
Goal 12: Responsible Production & Consumption

Bioutilization

Cellulose

The Challenge

Common actuators used in many different industries require electricity, which can amount to a large expense. Additionally, critical actuators, like those in medical applications, can fail during power outages, resulting in safety hazards.

Innovation Details

The hydraulic actuator responds dynamically to changes in the air’s humidity. It is composed of two layers that absorb varying amounts of liquid to control the mechanical properties of the system. One of the layers contains , a polysaccharide, that is considered one of the most abundant biopolymers in the world. The other layer maintains the structural integrity of the system. The actuator can be used in smart buildings to allow heat exchange with the environment, reducing energy usage and costs.

Biomimicry Story

Pine cones respond naturally to different degrees of humidity by opening and closing. The scales flex passively in response to changes in moisture levels via a two‑layered structure. The first layer is composed of cell walls made of lignin, a rigid found in plants. The second component is cellulose, a fiber found in most plants. The pine cone scales are arranged so that when the air is humid, the outer cells expand toward the core, pinching the pine cone shut. When the atmosphere is dry, the pine cone stays open with bent scales to allow the wind to scatter its seeds.

References

Journal article

Toward a New Generation of Smart Biomimetic Actuators for Architecture

Advanced Materials

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