Biomimicry of Aquatic Organisms in Engineering

Drifting continents and changing environments have driven nature to adapt accordingly and survive the countless challenges of life itself. These adaptations have been tested over 3.8 billion years of evolution and natural selection [1]. Although engineering can create outstanding products for human convenience, it often cannot compete with nature's abilities.  As a result, engineers are developing the concept of mirroring the mechanisms underlying desirable characteristics in living organisms to solve complex problems - a process known as biomimicry [2]. Biomimicry can be seen throughout human history, from using the simple idea of sharp animal teeth to inspire spears in prehistoric times, to pain-free injections inspired by the mosquito’s proboscis [3].

Due to the complexity and variety of biological systems, inspiration for engineering has been taken from all aspects of nature. One of which with tremendous potential is aquatic habitats. The ocean can be a challenging environment for survival, due to factors such as extreme pressures, strong underwater currents and scarcity of light at great depths. This leads to aquatic organisms being inventive, strategic and resilient, making them excellent inspiration for futuristic technologies. A remarkable example is the iconic Gherkin building in London, which was inspired by the Venus Flower Basket Sponge - an inhabitant of the deep ocean. Imitating its sturdy lattice structure and its means of channelling water, the need for its air conditioning was cut by an impressive 50% [4].

Furthermore, there is enormous scope for discovery in aquatic environments as 80% of all life on Earth is found in the ocean, whilst only 20% of it has been explored [5]. Thus, there is incredible potential to expand the biomimicry of today, as we discover new resilient oceanic organisms [6].  

Aquatic Biomimicry in Energy Engineering

Comparing the clean, healthy environment maintained by nature for four billion years with the damage caused by industrialisation in the last 200 years, it is indisputable that solutions to the environmental crisis must be produced [7]. It is argued that biomimicry could be the key to environmental sustainability. The environmental crisis has been recognised as a global issue since the 19th century, one primary way to tackle it is to increase human reliance on renewable forms of energy [8].

Among many others, aquatic biomimicry has contributed to environmental sustainability in extremely successful ways. For example, WhalePower, a Toronto-based company, constructed a wind turbine with bumpy-blades inspired by whale flippers, reducing the drag experienced by the blades by 32% and made the turbines - which are in use today - far more efficient [9]. While mimicking aquatic life has enhanced wind turbine efficiency, its potential has not been fully utilised in hydroelectric energy.  Although the International Energy Agency estimates that the constant movement of the ocean could produce between 20,000 and 80,000 TWh of energy, little of this is currently being harnessed [10]. This is due to the fact that there are very few wave power systems (WPS) that are cost-effective and efficient. 

To increase the efficiency of WPSs, Timothy Finnigan founded bioWAVE - a wave energy converter that imitates the flexible stems of undersea flora, altering its orientation relative to the wave force [11]. The blades are connected to a column by a hinged pivot which allows the blades to move and rotate freely in rhythm with the motion of the waves, both above and underwater. This furthermore allows the WPS to orient itself to maximise natural wave energy capture [12]. This invention was a huge step forward for SDG 7: Affordable and Clean Energy,  as the design is not only much more effective but also more environmentally friendly than traditional WPSs as it creates minimum seabed disturbances due to its smooth motion [13].  

A major setback to the design of traditional WPSs is their survivability. In strong currents, the base of tidal turbines become weak, leading to parts of the turbine breaking off, making the device an economic burden due to higher maintenance costs [14]. To avoid this technical hurdle, Finnigan used bioBASE to secure the 90-ton, 100-foot by 100-foot bioWAVE system to the seabed [11].  BioBASE is a mounting system that mimics the intelligent mechanism -  known as the holdfast - that large undersea flora, such as giant kelp, use to clasp onto the seabed. The mechanism wields many small "root"-like elements instead of one main shaft to distribute the load of the device equally. This helps relieve excessive force on one root, providing a stable base to the bioWAVE. In addition, the unit also mimics the natural protective measures of undersea vegetation by collapsing and laying against the seabed to avoid damage from excessively violent wave conditions. This allows the engineers to use lighter and less expensive materials in the system, as it would not need to function in extremely rough conditions [13].   

In the future, the ambitious design of bioWAVE is to be scaled up to one megawatt, which is enough to power up to 800 homes annually [12]. However, two general difficulties for marine energy are the struggle of obtaining permission to test within the ocean and creating large test facilities. Furthermore, the process and development of hardware is expensive, as well as slow, hence it requires a lot of funding. This ultimately means that the progress of marine energy is limited by the economic support received [15].  

Aquatic Biomimicry in Biomedical Engineering 

Although humans have evolved to be highly intelligent, which has led to their great success, many species possess other favourable traits that are beneficial for their survival. For instance, humans have a limited regenerative capacity, which allows them to only heal minor wounds, such as cuts and scratches. Meanwhile, many aquatic species - including starfish and sea cucumbers - have inherent abilities to regenerate entire body parts and organs [16]. These properties are especially attractive to researchers in medical technology who are constantly looking to develop more innovative solutions in order to move forward with SDG 3: Health and Wellbeing. The development of the scanning electron microscope, along with advances in nanotechnology, allow scientists to analyse the internal structure and hidden characteristics of these aquatic organisms and processes [2]. 

Each year, 1.6 million people have an amputation in the USA alone, and the leading solution to this problem is prosthetic limbs [16]. Most scientists try to mimic the movement of human arms in prosthetics. However, researchers have discovered that the capacity of an octopus to grip something is much stronger than that of a human’s ability, as two-thirds of an octopus’s neurons are in its arms [17]. As a result, a  team of researchers backed by the Italian Institute of Technology made the decision to emulate the tentacles of an octopus. Unlike bioWAVE, these scientists delved deeper into the biology of the octopus, rather than simply studying the overall structure of the organism. They used microanatomy and ultrasounds to investigate the morphology of the internal tissues in order to understand how the suction and movement of octopus tentacles worked [18].

They found that the tentacles were made of muscles along with soft tissue and lacked any skeletal structure. This hydrostat structure was soft and compliant but had the ability to stiffen, allowing the tentacles to have virtually unlimited degrees of freedom to elongate, shorten, bend, or twist - making them an excellent inspiration for soft robotics [19]. Researchers found that the tentacles had densely packed transverse and longitudinal muscles. Elongation of the arm could be achieved by contraction of the transverse muscles (TMs), whereas shortening of the arm results from the contraction of the longitudinal muscles (LMs).  

To design the body of the robotic tentacle, the researchers embedded cylindrical cables, that can be controlled by a motor, to act as the LMs running all along the silicone tentacle. The TMs were arranged perpendicularly to the LMs in order to mimic their reciprocal action [18].

Festo, a German company, conducted a separate study focused on the gripping properties of a robotic octopus tentacle. They used a soft silicone structure with two rows of suction cups along its length, which could be controlled pneumatically, bending inwards when compressed air is put into it. In an octopus, the sucker attaches to the object and forms a watertight seal, reducing the pressure in the chamber and creating suction [21]. Festo mimics this through an artificial vacuum applied at the larger suction cups, while the smaller ones work passively, firmly attaching the object to the gripper. The ability to change the pressure and vacuum allows the arm to grip onto objects of almost any shape and size, making it more effective than a human version of the robotic arm [22]. These advancements in the biomimicry of octopus tentacles have immense potential, both in the field of prosthetics and as assistant robots in the medical industry.  

Aquatic Biomimicry in Tissue Engineering

Delving even deeper, to a molecular level, a very promising field of research is that of the use of biomimicry in tissue engineering. Some natural aquatic materials, such as mollusc nacre and shark skin, have already had a substantial impact on innovating unconventional tissue engineering technologies [23].  A specific example of these aquatic materials are crustacean shells; their unique structure gives them mechanical properties that allow them to strongly cling to their surroundings. Hence, replicating their molecular structure to engineer multifunctional fibrous scaffolds has had applications in bioactive bone or dental regeneration [23].  

Currently, bioengineers are trying to understand the ability of aquatic animals - such as starfish and salamanders - to regenerate lost tissue in the hope of mimicking it to restore lost limbs and organs in humans. The first stage to understanding this process is to identify the genetic characteristics these species possess that are different to the human genome [24].  

The axolotl, an aquatic salamander, has the ability to regrow a tail. Scientists suspect this is because it has certain genes that are "turned off" in humans. It is possible that those genes enable regeneration or aid the process by allowing axolotls to form a wound epidermis. The wound epidermis sends chemical signals for the formation of a blastema (a cluster of stem cells) at the site of amputation, whilst in humans scar tissue is formed. These stem cells can then multiply and differentiate to form tissue eventually forming a tail [25]. Genetic engineers aim to find a way to send a signal to these genes in humans, turning them on and activating the ability to regenerate tissue, allowing a human limb to regrow similarly to the axolotl’s tail. There are several propositions on how to achieve this, such as drugs administered through a “smart bandage” that can alter these genes, or triggering the process using a genetic engineering tool such as CRISPR-Cas9 [26].   

Successful limb regeneration in humans could also allow bioengineers to develop natural limbs in an artificial environment, such as a lab. A fundamental challenge is that a human limb has many more complexities than that of a salamander, making it much more difficult to regrow. However, if limb regeneration could be realistically executed, it is possible to eliminate the need for prosthetics and organ transplants. Medical costs could thus be lowered and complications of surgery could also be minimised. 

Progression of Biomimicry and the Challenges

In 1997 Janine Benyus wrote the book Biomimicry: Innovation Inspired by Nature, provoking a surge in biomimicry research [27]. Since then, biomimetics has grown exponentially in the last decade due to the need for solutions to environmental and health-related concerns [28].

Bio-mimicked products have the potential to replace traditional engineering technologies by making products more compatible with nature, rather than destructive. Consequently, the market size for products and projects that applied biomimetics was estimated to be more than £1 million between 2005 and 2008. By 2025, industry analysts predict that this figure will increase to about £723 billion [2]. 

It is evident that biomimicry has the solutions for many challenges and there is considerable interest in researching biomimetic solutions, so what is the reason for the slow commercialisation of these ideas? 

The basic challenge for biomimicry researchers is that of conducting numerous studies on several organisms to identify the one with the most potential, which is especially difficult when several organisms exhibit similar characteristics [29]. This may cause a delay in the development of biomimetic products. Meanwhile, traditional solutions are built and applied quicker and support today's fast-paced industrial growth.

Being a new field of research, there is a lack of tools, methods, educational institutions and training specifically designed for research and innovation in biomimicry. Consequently, scientists do not have a systematic methodology to bridge the gap between materials science, engineering and the application of biomimicry [29]. This lack of collaboration between engineers and biologists is a major hurdle in applying engineering principles to biomimetic designs.

 Furthermore, large firms trust numerical results to decide where to invest money for better economic returns, but with the obvious difficulty in quantifying nature’s efficiency, it can be difficult to convince corporations to invest in biomimicry [31]. Nevertheless, its potential has been recognised by some major multinational firms like Boeing, Procter and Gamble (P&G), Nike, and Interface. Each of these firms are trying to incorporate biomimetic ideas to try and reduce their environmental impact, for example, Boeing has been researching biomimetic ways to try and increase plane efficiency [30].

How Can the Challenges be Overcome? 

Any drastically new way of thinking is always embraced gradually as society is often hesitant to change its mindset towards traditionally functioning practices. In order to encourage biomimicry adoption, it is imperative to increase awareness about biomimicry through workshops, training and integration into the university curriculum. To proceed with this, the establishment of a government body with the sole responsibility of urging multidisciplinary collaboration between these fields is necessary. The government body should also support and encourage the application of biomimetic materials and technologies by implementing necessary legislation and incentivise biomimetic projects in order to replace inefficient or unsustainable technologies.

Conclusion

Scientists believe that a mere 14% of earth's species have been discovered, and even these organisms are not understood enough to emulate all their special properties [32]. The potential of basic organisms is massively undermined, for instance, simple kelp can inspire major solutions. Thus, the extent of biomimetic application is unimaginable. Even though there are complications in the adoption of biomimicry, it is now more crucial than ever to take advantage of the lessons that nature has already learnt to make engineering efficient with reduced environmental damage.

Once biomimicry is broadly established, the many novel concepts on the brink of invention will have the potential to be fully explored and developed, to address the challenges experienced by humankind on both an individual and global scale now and in the future. 

The ever-changing issues in climate change and healthcare push humans to broaden their horizons and look for solutions further than man-made inventions. Moving forward, it is essential to utilise hugely unexplored areas, such as deep aquatic environments and the organisms living within them, allowing the development of SDG 14: Life Below Water, and other SDGs that benefit from this.

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