Bio-inspiration: necessary abstraction in the study of biological adaptive structures (1/2)

In this first post of 2-part series on bio-inspiration I detail the design philosophy that has guided the study of plant movements reported in a recent publication on amplification of actuation in plants. The second post of the series details the 5 abstracted mechanisms of amplification of actuation in plant movements identified in the publication.

The bustling trend of bio-mimicry has gotten the world of shape shifting structures in a bit of a frenzy in the past decade. Engineered structures whose shape changes to perform a task have been traditionally inspired by the scissor mechanics (cf the picture of the pentograph lift). As materials available for building shape shifting structures evolve (reinforced plastics, elastomers…) many examples of scaled-up biological structures have appeared resulting in the increase of “organic shapes” being found in some of today’s most advanced shape shifting structures.

scissor
Pentograph lift based on scissor mechanism. The displacement range of the hydraulic actuators is amplified by the scissor mechanism. src: skodtecelevators.com

Bio-mimicry can be defined as the reproduction of natural artifacts to engineering scale. The goal of mimicking nature is to solve engineering problems in a way that did not occur to engineers before. In this post I defend the idea that such a direct translation from nature to engineering  will probably fail in the long run. Natural solutions are answers to problems specific to nature. This simple fact is the basis of any successful design inspired by nature. To be able to use the natural solutions, the designers extract the mechanism and understand its purpose. As a consequence, there is a necessary level of abstraction of natural movements necessary to the reproduction of natural principles. This necessity stems from the overwhelming number of biological structures that produce movements.

For instance, this abstraction exercise allows us to summarize all musculo-skeletal movements, movements in animals created by the shortening of a muscle and a rigid skeleton, in one category of mechanisms: lever mechanism.

lever3
Most of animal locomotion relies on the lever mechanism. src: alexeinstein.wordpress.com/2014/09/03/lever-of-human-body/

Designers search nature for solutions to particular engineering problems with a specific idea in mind. This direct approach has provided many successful engineering products (think of velcro) but has constrained us, engineers, to the role of observers. The solutions provided by biology to problems challenge our rational, rigorous problem solving approaches. In order to go beyond the limitation of the observer’s approach, we need to rationalize biology, categorize the problems solved and their solutions, in engineering terms. Such a methodology has notably been developed by Julian F.V Vincent who cite the advantages of biological structure over engineered structures as twofold:

First, all biological functions have to evolve from pre-existing conditions. Thus any function (such as adaptive morphological change) will be achieved in a number of different ways depending on the ancestor’s adaptation, phylogenetic freedom, biochemical and physiological mechanisms, etc. This variety may suggest useful alternatives to an engineer faced with specific design problems. This is illustrated here by the discussion of how plants move. Second, the tendency is for biological mechanisms to be only just good enough (taking into account the familiar optimizations of expense, safety, repair, etc.), so quite often some intriguingly simple solutions appear.

The difference between abstracted inspiration and direct mimicry can be illustrated  by two shape shifting robotic grippers. Both are incredible in their own right. One is the the octopus inspired gripper by Festo. It closely resembles an octopus limb. A more abstract structure with a similar purpose is found in gripper from Soft Robotics. The two videos below display the incredible possibilities of the two systems.

Besides the similar color, both systems differ in appearance. One is very faithful in appearance to the octopus. Suction cups cover its gripping surface for maximal adherence. It mixes two action, wrapping of the arm around the object and grip from suction cups. The other one is conceptually simpler. The actuation is well documented (here) and entails only one action, wrapping of the arm around the object. In this case the first gripper is a text-book example of bio-mimicry while the second on is bio-inspired. The reference to biology is implicit but the parallels to hydrostats (animals & plants) are acute.

abstract
Understand a biological mechanism

In the next chapter of the series, I will present what this abstraction yields when applied to the categorization of plant movements. Specifically, the next post will be based on the idea that even the most basic generations of plant movement involve some degree of amplification of actuation.

– Victor Charpentier, Form Finding Lab PhD candidate

Reference:

 

Charpentier, V., Hannequart, P., Adriaenssens, S., Baverel, O., Viglino, E., & Eisenman, S. (2017). Kinematic amplification strategies in plants and engineering. Smart Materials and Structures26(6), 063002.

Wagg, D., Bond, I., Weaver, P., & Friswell, M. (Eds.). (2008). Adaptive structures: engineering applications. John Wiley & Sons.

 

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