Taking a leap in bioinspired robotics

Mechanical engineer Sangbae Kim builds animal-like machines for use in disaster response.“Say there are toxic gases leaking in a building, and you need to close a valve inside, but it’s dangerous to send people in,” says Sangbae Kim, associate professor of mechanical engineering at MIT. “Now, there is no single robot that can do this kind of job. I want to create a robotic first responder that can potentially do more than a human and help in our lives.”

“Say there are toxic gases leaking in a building, and you need to close a valve inside, but it’s dangerous to send people in,” says Sangbae Kim, associate professor of mechanical engineering at MIT. “Now, there is no single robot that can do this kind of job. I want to create a robotic first responder that can potentially do more than a human and help in our lives.”

In the not so distant future, first responders to a disaster zone may include four-legged, dog-like robots that can bound through a fire or pick their way through a minefield, rising up on their hind legs to turn a hot door handle or punch through a wall.

Such robot-rescuers may be ready to deploy in the next five to 10 years, says Sangbae Kim, associate professor of mechanical engineering at MIT. He and his team in the Biomimetic Robotics Laboratory are working toward that goal, borrowing principles from biomechanics, human decision-making, and mechanical design to build a service robot that Kim says will eventually do “real, physical work,” such as opening doors, breaking through walls, or closing valves.

“Say there are toxic gases leaking in a building, and you need to close a valve inside, but it’s dangerous to send people in,” Kim says. “Now, there is no single robot that can do this kind of job. I want to create a robotic first responder that can potentially do more than a human and help in our lives.”

To do this, Kim, who was awarded tenure this year, is working to fuse the two main projects in his lab: the MIT Cheetah, a four-legged, 70-pound robot that runs and jumps over obstacles autonomously; and HERMES, a two-legged, teleoperated robot, whose movements and balance is controlled remotely by a human operator, much like a marionette or a robotic “Avatar.”

“I imagine a robot that can do some physical, dynamic work,” Kim says. “Everybody is trying to find overlapping areas where you’re excited about what you’re working on, and it’s useful. A lot of people are excited to watch sports because when you watch someone moving explosively, it is hypothesized to trigger the brain’s  ‘mirror neurons’ and you feel that excitement at the same time. For me, when my robots perform dynamically and balance, I get really excited. And that feeling has encouraged my research.”

A drill sergeant turns roboticist

Kim was born in Seoul, South Korea, where he says his mother remembers him as a tinkerer. “Everything with a screw, I would take apart,” Kim says. “And she said the first time, almost everything broke. After that, everything started working again.”

He attended Yonsei University in the city, where he studied mechanical engineering. In his second year, as has been mandatory in the country, he and other male students joined the South Korean army, where he served as a drill sergeant for two and a half years.

“We taught [new recruits] every single detail about how to be a soldier, like how to wear shirts and pants, buckle your belt, and even how to make a fist when you walk,” Kim recalls. “The day started at 5:30 a.m. and didn’t end until everyone was asleep, around 10:30 p.m., and there were no breaks. Drill sergeants are famous for being mean, and I think there’s a reason for that — they have to keep very tight schedules.”

After fulfilling his military duty, Kim returned to Yonsei University, where he gravitated toward robotics, though there was no formal program in the subject. He ended up participating in a class project that challenged students to build robots to perform specific tasks, such as capturing a flag, and then to compete, bot to bot, in a contest that was similar to MIT’s popular Course 2.007 (Design and Manufacturing), which he now co-teaches.

“[The class] was a really good motivation in my career and made me anchor on the robotic, mechanistic side,” Kim says.

A bioinspired dream

In his last year of college, Kim developed a relatively cheap 3-D scanner, which he and three other students launched commercially through a startup company called Solutionix, which has since expanded on Kim’s design. However, in the early stages of the company’s fundraising efforts, Kim came to a realization.

“As soon as it came out, I lost excitement because I was done figuring things out,” Kim says. “I loved the figuring-out part. And I realized after a year of the startup process, I should be working in the beginning process of development, not so much in the maturation of products.”

After enabling first sales of the product, he left the country and headed for Stanford University, where he enrolled in the mechanical engineering graduate program. There, he experienced his first taste of design freedom.

“That was a life-changing experience,” Kim says. “It was a more free, creativity-respecting environment — way more so than Korea, where it’s a very conservative culture. It was quite a culture shock.”

Kim joined the lab of Mark Cutkosky, an engineering professor who was looking for ways to design bioinspired robotic machines. In particular, the team was trying to develop a climbing robot that mimicked the gecko, which uses tiny hairs on its feet to help it climb vertical surfaces. Kim adapted this hairy mechanism in a robot and found that it worked.

“It was 2:30 a.m. in the lab, and I couldn’t sleep. I had tried many things, and my heart was thumping,” Kim recalls. “On some replacement doors with tall windows, [the robot] climbed up smoothly, using the world’s first directional adhesives, that I invented. I was so excited to show it to the others, I sent them all a video that night.”

He and his colleagues launched a startup to develop the gecko robot further, but again, Kim missed the thrill of being in the lab. He left the company soon after, for a postdoc position at Harvard University, where he helped to engineer the Meshworm, a soft, autonomous robot that inched across a surface like an earthworm. But even then, Kim was setting his sights on bigger designs.

“I was moving away from small robots because it’s very difficult for them to do to real, physical work,” Kim says. “And so I decided to develop a larger, four-legged robot for human-level physical tasks — a long-term dream.”

Searching for principles

In 2009, Kim accepted an assistant professorship in MIT’s Department of Mechanical Engineering, where he established his Biomimetic Robotics Lab and set a specific research goal: to design and build a four-legged, cheetah-inspired robot.

“We chose the cheetah because it was the fastest of all land animals, so we learned its features the best, but there are many animals with similarities [to cheetahs],” Kim says. “There are some subtle differences, but probably not ones that you can learn the design principles from.”

In fact, Kim quickly learned that in some cases, it may not be the best option to recreate certain animal behaviours in a robot.

“A good example in our case is the galloping gait,” Kim says. “It’s beautiful, and in a galloping horse, you hear a da-da-rump, da-da-rump. We were obsessed to recreate that. But it turns out galloping has very few advantages in the robotics world.”

Animals prefer specific gaits at a given speed due to a complex interaction of muscles, tendons, and bones. However, Kim found that the cheetah robot, powered with electric motors, exhibited very different kinetics from its animal counterpart. For example, with high-power motors, the robot was able to trot at a steady clip of 14 miles per hour — much faster than animals can trot in nature.

“We have to understand what is the governing principle that we need, and ask: Is that a constraint in biological systems, or can we realize it in an engineering domain?” Kim says. “There’s a complex process to find out useful principles overarching the differences between animals and machines. Sometimes obsessing over animal features and characteristics can hinder your progress in robotics.”

A “secret recipe”

In addition to building bots in the lab, Kim teaches several classes at MIT, including 2.007, which he has co-taught for the past five years.

“It’s still my favourite class, where students really get out of this homework-exam mode, and they have this opportunity to throw themselves into the mud and create their own projects,” Kim says. “Students today grew up in the maker movement and with 3-D printing and Legos, and they’ve been waiting for something like 2.007.”

Kim also teaches a class he created in 2013 called Bioinspired Robotics, in which 40 students team up in groups of four to design and build a robot inspired by biomechanics and animal motions. This past year, students showcased their designs in Lobby 7, including a throwing machine, a trajectory-optimizing kicking machine, and a kangaroo machine that hopped on a treadmill.

Outside of the lab and the classroom, Kim is studying another human motion: the tennis swing, which he has sought to perfect for the past 10 years.

“In a lot of human motion, there’s some secret recipe, because muscles have very special properties, and if you don’t know them well, you can perform really poorly and injure yourself,” Kim says. “It’s all based on muscle function, and I’m still figuring out things in that world, and also in the robotics world.”- Jennifer Chu

Bioinspired robots: Examples and the state of the art

Researchers at Carnegie Mellon University attempts to mimic animal motion have resulted in many technological advances that have revolutionized how manmade machines move through the air, in water, and over land.  Despite numerous achievements, engineers and scientists have yet to closely replicate the grace and fluidity of animal movement. This suggests the biological world still has much in the way of suggestions for how to build, design, and program robotic systems whose locomotive capabilities will far outpace what is possible today. The question then becomes: How deeply should we look at biology? Take the transition from snake to snake robot as an example. On the surface, one can see a snake, say, on a hike in the woods and then build an elongated mechanical creature. However, we can go deeper: One can study the fundamental macroscopic principles that can be transferred from muscles and skeleton to conventional motors and mechanical linkages. Going even deeper, one can try to create new muscle-like actuators and controllers based on neural networks in an attempt to accurately copy biological function and control.  The right choice of where to focus on this spectrum remains an open question.

To help address these fundamental questions, the biologically inspired robotics community has to date produced many great works, far too many to summarize in one brief article.  Instead, we focus the attention of this short comment on what works have specifically inspired our research in the Biorobotics lab at Carnegie Mellon University over the past 20 years. In this time, we have built a number of different robots but are perhaps best known for novel snake-like robots (see http://biorobotics.org).

In our opinion, the single biggest influence in biological inspiration is Bob Full.  His group at Berkeley studies cockroaches, crabs, and geckos, just to name a few.  Full’s research interest is primarily in comparative biomechanics and physiology [1, 2].  He collaborates with a number of different engineers and other scientists to elucidate biological principles that inspire the design of advanced robotic components, control algorithms, and novel system designs.

Full’s work on geckos leads to a fundamental understanding of how their feet stick to nearly any surface and yet not are encumbered by dirt and other particles. His collaborator Ron Fearing, also at Berkeley, developed new MEMS manufacturing technology to replicate the capabilities of geckos’ feet.  Fearing’s work harnesses features of animal manipulation, locomotion, sensing, actuation, mechanics, dynamics, and control strategies to radically improve robotic capabilities, especially at very small scales.  Fearing’s research ranges from the fundamental understanding of mechanical principles to novel fabrication techniques and system integration for autonomous machines [3, 4].

At Harvard University, Rob Wood also develops novel robotic mechanisms at very small scales [5, 6].  His work uses microfabrication techniques to develop biologically inspired robots with features on the micrometre to centimetre scales. His specific interests include new micro- and mesoscale manufacturing techniques, fluid mechanics of flapping wings, control of sensor-limited and computation-limited systems, active soft materials, and morphable soft-bodied robots.

In addition to novel designs and methods for constructing robot morphologies, biology also inspires us to design improved software to enable robots to better interact with complex environments. Shigeo Hirose is one of the early pioneers in the creation of numerous biologically inspired robotic systems that specialize in weaving their way through complex terrains.  He is probably best known for his original work on serpentine locomotion, both analyzing the fundamental physics governing how biological snakes move as well as employing the lessons learned therein to create and control numerous mechanisms over the years [7].  His ground-breaking insight into biologically inspired control has naturally influenced his robot’s designs.

Dan Koditschek’s name is synonymous with robot control, especially in the area of dynamic legged locomotion [8, 9].  He has played a major role in several seminal works in the area of bioinspired robots throughout his career (many in collaboration with Bob Full).  In addition, he has overseen the construction of biologically inspired robots that have helped roboticists better understand mechanized locomotion as well as offered biologists better insight into the natural world.  Additionally, Full’s observations on the role of compliance in mechanisms and control inspired Koditschek’s group to develop the family of RHex robots. Moreover, Koditschek and Full developed the concept of templates and anchors, a now-ubiquitous method for abstracting the motion of complex systems.  Koditscheck’s more recent work with Full has started to explore both the design and the control of aerial acrobatics using tail-like appendages, originally inspired by the observation of geckos that control the orientation of their bodies using their tails in midair.

Related to the work by Full and Koditschek, the incorporation of compliance in robot mechanisms and control design can also be attributed to Gill Pratt. Pratt, in part, developed a new paradigm for robotic actuation–the series elastic actuator–as well as controllers that employ this technology [10].  This work has directly affected and certainly inspired several generations of robotic devices with different morphologies that move by slithering, crawling, and walking.

A. E. Hosoi’s research covers a diverse set of topics, from fundamentals of materials science and fluid dynamics to the control and practical application of locomotion and manipulation systems [11, 12].  Two projects that are particularly relevant to the study of biologically inspired robots are those that consider the Roboclam and the Robosnail.  Both systems were constructed using direct biological inspiration aimed at practical real-world applications.

George Lauder’s work on fish-like robots has resulted in a series of robotic test platforms that examine fin and body kinematic and hydrodynamic functions during locomotion [13]. Robotic devices have a considerable advantage over studying live fish in the sense that a variety of programmable motions permit the careful investigation of the discrete components of naturally coupled movements.

The idea of using a robot to serve as a surrogate to study biology is also present in Daniel Goldman’s work that focuses on studying systems that locomote on granular media [14-17].  Goldman, faculty and director of the Crablab at Georgia Tech, has recently coined the term “robot physics,” which relates to the practice of using robots as the basis for modelling biological systems in extremely complex terrains.  Goldman’s team uses robots to help study snakes, lizards, ants, and turtles, just to name a few. Goldman’s group specializes in the interaction of physical and biological systems with complex materials, like granular media.  His group looks investigate how organisms like lizards, crabs, and cockroaches generate appropriate musculoskeletal dynamics to scurry rapidly over substrates like sand, bark, leaves, and grass.

Noah Cowan has also applied and made novel advances in the application of control theory to the study of sensorimotor control of animal movement [18, 19].  He and his collaborators study weakly electric fish as well as cockroach antennae. At Northwestern, Malcolm MacIver, one of Cowan’s and Lauder’s collaborators, pursues a research program in the mechanical and neural basis of animal behaviour, particularly at the intersection of information harvesting and biomechanics [20].

Finally, A. Ijspeert’s work on biologically inspired robots focuses on the computational aspects of locomotion control, sensorimotor coordination, and learning in animals and in robots [21, 22]. His group is interested in using robots and numerical simulation to study the neural mechanisms underlying movement control and learning in animals.

In the Biorobotics lab at Carnegie Mellon, inspiration has also been drawn from the works of J. Ostrowski and S. D. Kelly that employ concepts from the field of geometric mechanics to the study of undulatory locomotion [23-26]. In their respective works, Ostrowski and Kelly perform mathematical modeling, analysis, simulation, and control of systems that exhibit nonlinear dynamics. Former CMU student Elie Shammas, now faculty at the American University of Beirut, took this early work and developed visualization tools that enable intuition to guide the design of gaits for idealized articulated systems. Ross Hatton, who succeeded Shammas, took this work to the next level, generating results at the interface of robotics and applied mechanics [27, 28]. Hatton, now faculty at Oregon State University, provided a wealth of analytic tools to study snake-like locomotion as well as other locomoting systems. Recently, Hatton began new work that looks at sensing and control in spiders.  Adding to the work of Goldman’s and Choset’s previous students, Chaohui Gong has recently created a new approach that brings to bear all of the analytic tools, developed by one of Choset’s students, to study both natural as well as robotic systems that locomote in granular media. Gong’s demonstrations include snake robots locomoting on rocks, sandy inclines, and in tight spaces- Matt Travers and Howie Choset

1. T. Libby et al., Tail-assisted pitch control in lizards, robots and dinosaurs. Nature 481, 181 (2012).

2. R. J. Full, T. Kubow, J. Schmitt, P. Holmes, D. Koditschek.  Quantifying dynamic stability and maneuverability in legged locomotion. Int. Comp. Biol. 42, 149 (2002).

3. C. Li et al., Terradynamically streamlined shapes in animals and robots enhance traversability through densely cluttered terrain. Bioinspir. Biomim10, 046003 (2015).

4. A. G. Gillies et al.Gecko toe and lamellar shear adhesion on macroscopic, engineered rough surfaces. J. Exp. Biol. 217, 283 (2014).

5. M. A. Graule et al.Perching and takeoff of a robotic insect on natural and artificial overhangs using switchable electrostatic adhesionScience 352, 978 (2016).

6. J.-S. Koh et al.Jumping on water: Surface tension–dominated jumping of water striders and robotic insectsScience 349, 517 (2015).

‪7. S. Hirose, Biologically Inspired Robots: Snake-Like Locomotors and Manipulators (Oxford University Press, Oxford, 1993).

8. A. Altendorfer et al., RHex: A biologically inspired hexapod runner. J. Autonomous Robots 11, 207 (2002).

9. G. A. Lynch, J. E Clark, P.-C. Lin, D. E. KoditschekA bioinspired dynamical vertical climbing robot. Int. J. Robotics 31, 974 (2012).

10. G. A. Pratt, M. M. Williamson, Series elastic actuators, in vol. 1 of IEEE International Conference on Intelligent Robots and Systems (1995), pp. 399–406.

11. A. G. Winter et al., Razor clam to RoboClam: Burrowing drag reduction mechanisms and their robotic adaptation. Bioinspir. Biomim9, 036009 (2014).

12. B. Chan, N. J. Balmforth, A. E. Hosoi, Building a better snail: Lubrication and gastropod locomotion. Phys. Fluids 17, 113101 (2005).

13. G. V. Lauder, E. J. Anderson, J. Tangorra, P. G. A. Madden, Fish bio robotics: Kinematics and hydrodynamics of self-propulsionJ. Exp. Biol. 210, 2767 (2007).

14. B. McInroe et al., Tail use improves soft substrate performance in models of early vertebrate land locomotors. Science 353, 154 (2016).

15. H. C. Astley et al., Modulation of orthogonal body waves enables high maneuverability in sidewinding locomotion, Proc. Natl. Acad. SciU.S.A. 112, 6200 (2015).

16. J. Aguilar et al., A review on locomotion robophysics: The study of movement at the intersection of robotics, soft matter and dynamical systems. Rep. Prog. Phys. 79, 110001 (2016).

17. Tingnan Zhang, Daniel I. Goldman, The effectiveness of resistive force theory in granular locomotion. Phys. Fluids 26, 101308 (2014).

18. J. M. Mongeau, A. Demir, J. Lee, N. J. Cowan, R. J. Full, Locomotion and mechanics mediated tactile sensing: Antenna reconfiguration simplifies control during high-speed navigation in cockroaches. J. Exp. Biol. 216, 4530 (2013).

19. S. Sefati et al., Mutually opposing forces during locomotion can eliminate the tradeoff between maneuverability and stability. Proc. Natl. Acad. SciU.S.A. 110, 18798 (2013).

20. Y. Bai, J. B. Snyder, M. A. Peshkin, M. A. MacIver, Finding and identifying simple objects underwater with active electrosense. Int. J. Robotics Res. 34, 1255 (2015).

21. K. Karakasiliotis et al., From cineradiography to biorobots: An approach for designing robots to emulate and study animal locomotion, in J. R. Soc. Interface13, 119, (2016).

22. A. Ijspeert. Biorobotics: Using robots to emulate and investigate agile animal locomotionScience346, 196 (2014).

23. J Ostrowski, J. Burdick, Gait kinematics for a serpentine robot, in IEEE International Conference on Robotics and Automation (IEEE, 1996).

24. J Ostrowski, J Burdick, The geometric mechanics of undulatory robotic locomotion. Int. J. Robotics Res. 17, 683 (1998).

25. S. D. Kelly, H. Xiong, Self-propulsion of a free hydrofoil with localized discrete vortex shedding: analytical modeling and simulation. Theor. Comput. Fluid Dyn24, 45 (2010).

26. P. Tallapragada, S. D. Kelly, Dynamics and self-propulsion of a spherical body shedding coaxial vortex rings in an ideal fluid. Dynamics 18, 21 (2013).

27. H. Faraji, R. L. Hatton, Aiming and vaulting: Spider-inspired leaping for jumping robots, in Proceedings of the IEEE International Conference on Robotics and Automation (IEEE, 2016).

28. H. Faraji et al.Impulse redirection of a tethered projectile, in Proceedings of the ASME Dynamic Systems and Controls Conference (DSCC), (ASME, 2015).

Biomechanics

Biomechanics is the study of the structure and function of the mechanical aspects of biological systems, at any level from whole organisms to organscells and cell organelles,[1] using the methods of mechanics.[2]. . The word “biomechanics” (1899) and the related “biomechanical” (1856) come from the Ancient Greek βίος bios “life” and μηχανική, mēchanikē “mechanics”, to refer to the study of the mechanical principles of living organisms, particularly their movement and structure.[3]

Methods


Biomechanics is closely related to engineering because it often uses traditional engineering sciences to analyze biological systems. Some simple applications of Newtonian mechanics and/or materials sciences can supply correct approximations to the mechanics of many biological systems.

Applied mechanics, most notably mechanical engineering disciplines such as continuum mechanicsmechanism analysis, structural analysis, kinematics and dynamics play prominent roles in the study of biomechanics.[4] Usually, biological systems are much more complex than man-built systems. Numerical methods are hence applied in almost every biomechanical study. Research is done in an iterative process of hypothesis and verification, including several steps of modellingcomputer simulation and experimental measurements.

Subfields


Applied subfields of biomechanics include:

Sports biomechanics


sports biomechanics, the laws of mechanics are applied to human movement in order to gain a greater understanding of athletic performance and to reduce sport injuries as well. It focuses on the application of the scientific principles of mechanical physics to understand movements of action of human bodies and sports implements such as cricket bat, hockey stick and javelin etc. Elements of mechanical engineering (e.g., strain gauges), electrical engineering (e.g., digital filtering), computer science (e.g., numerical methods), gait analysis(e.g., force platforms), and clinical neurophysiology (e.g., surface EMG) are common methods used in sports biomechanics.[5]

Biomechanics in sports can be stated as the muscular, joint and skeletal actions of the body during the execution of a given task, skill and/or technique. Proper understanding of biomechanics relating to sports skill has the greatest implications on: sport’s performance, rehabilitation and injury prevention, along with sport mastery. As noted by Doctor Michael Yessis, one could say that best athlete is the one that executes his or her skill the best.[6]

Continuum biomechanics


The mechanical analysis of biomaterials and biofluids is usually carried forth with the concepts of continuum mechanics. This assumption breaks down when the length scales of interest approach the order of the micro structural details of the material. One of the most remarkable characteristic of biomaterials is their hierarchical structure. In other words, the mechanical characteristics of these materials rely on physical phenomena occurring in multiple levels, from the molecular all the way up to the tissue and organ levels.

Biomaterials are classified in two groups, hard and soft tissues. Mechanical deformation of hard tissues (like woodshell and bone) may be analysed with the theory of linear elasticity. On the other hand, soft tissues (like skintendonmuscle and cartilage) usually undergo large deformations and thus their analysis rely on the finite strain theory and computer simulations. The interest in continuum biomechanics is spurred by the need for realism in the development of medical simulation.[7]:568

Biofluid mechanics


Biological fluid mechanics, or biofluid mechanics, is the study of both gas and liquid fluid flows in or around biological organisms. An often studied liquid biofluids problem is that of blood flow in the human cardiovascular system. Under certain mathematical circumstances, blood flow can be modelled by the Navier–Stokes equationsIn vivo whole blood is assumed to be an incompressible Newtonian fluid. However, this assumption fails when considering forward flow within arterioles. At the microscopic scale, the effects of individual red blood cells become significant, and whole blood can no longer be modelled as a continuum. When the diameter of the blood vessel is just slightly larger than the diameter of the red blood cell the Fahraeus–Lindquist effect occurs and there is a decrease in wall shear stress. However, as the diameter of the blood vessel decreases further, the red blood cells have to squeeze through the vessel and often can only pass in single file. In this case, the inverse Fahraeus–Lindquist effect occurs and the wall shear stress increases.

An example of a gaseous biofluids problem is that of human respiration. Recently, respiratory systems in insects have been studied for bioinspiration for designing improved microfluidic devices.[8]

Biotribology


The main aspects of Contact mechanics and tribology are relate to frictionwear and lubrication. When the two surfaces come in contact during motion i.e. rub against each other, friction, wear and lubrication effects are very important to analyze in order to determine the performance of the material. Biotribology is a study of friction, wear and lubrication of biological systems especially human joints such as hips and knees.[9] For example, femoral and tibial components of knee implant routinely rub against each other during daily activity such as walking or stair climbing. If the performance of tibial component needs to be analyzed, the principles of bio-tribology are used to determine the wear performance of the implant and lubrication effects of synovial fluid. In addition, the theory of contact mechanics also becomes very important for wear analysis. Additional aspects of bio-tribology can also include analysis of subsurface damage resulting from two surfaces coming into contact during motion, i.e. rubbing against each other, such as in the evaluation of tissue-engineered cartilage.[10]

Comparative biomechanics

Chinstrap penguin leaping over water


Comparative biomechanics is the application of biomechanics to non-human organisms, whether used to gain greater insights into humans (as in physical anthropology) or into the functions, ecology and adaptations of the organisms themselves. Common areas of investigation are Animal locomotion and feeding, as these have strong connections to the organism’s fitness and impose high mechanical demands. Animal locomotion, has many manifestations, including runningjumping and flying. Locomotion requires energy to overcome frictiondraginertia, and gravity, though which factor predominates varies with environment.

Comparative biomechanics overlaps strongly with many other fields, including ecologyneurobiologydevelopmental biologyethology, and palaeontology, to the extent of commonly publishing papers in the journals of these other fields. Comparative biomechanics is often applied in medicine (with regards to common model organisms such as mice and rats) as well as in biomimetics, which looks to nature for solutions to engineering problems.

Plant biomechanics


application of biomechanical principles to plants, plant organs and cells has developed into the subfield of plant biomechanics.[11] Application of biomechanics for plants ranges from studying the resilience of crops to environmental stress[12] to development and morphogenesis at cell and tissue scale, overlapping with mechanobiology.[13]

Computational biomechanics


Computational biomechanics is the application of engineering computational tools, such as the Finite element method to study the mechanics of biological systems. Computational models and simulations are used to predict the relationship between parameters that are otherwise challenging to test experimentally, or used to design more relevant experiments reducing the time and costs of experiments. Mechanical modelling using finite element analysis has been used to interpret the experimental observation of plant cell growth to understand how they differentiate, for instance.[13] In medicine, over the past decade, the Finite element method has become an established alternative to in vivo surgical assessment. One of the main advantages of computational biomechanics lies in its ability to determine the endo-anatomical response of an anatomy, without being subject to ethical restrictions.[14] This has led FE modelling to the point of becoming ubiquitous in several fields of Biomechanics while several projects have even adopted an open source philosophy (e.g. BioSpine).

History

Antiquity


Aristotle, a student of Plato can be considered the first bio-mechanic, because of his work with animal anatomy. Aristotle wrote the first book on the motion of animals, De Motu Animalium, or On the Movement of Animals.[15] He not only saw animals’ bodies as mechanical systems but pursued questions such as the physiological difference between imagining performing an action and actually doing it.[16] In another work, On the Parts of Animals, he provided an accurate description of how the ureter uses peristalsis to carry urine from the kidneys to the bladder.[7]:2

With the rise of the Roman Empire, technology became more popular than philosophy and the next bio-mechanic arose. Galen (129 AD-210 AD), physician to Marcus Aurelius, wrote his famous work, On the Function of the Parts (about the human body). This would be the world’s standard medical book for the next 1,400 years.[17]

Renaissance


The next major biomechanic would not be around until 1452, with the birth of Leonardo da Vinci. Da Vinci was an artist and mechanic and engineer. He contributed to mechanics and military and civil engineering projects. He had a great understanding of science and mechanics and studied anatomy the mechanics’ context. He analyzed muscle forces and movements and studied joint functions. These studies could be considered studies in the realm of biomechanics. Leonardo da Vinci studied anatomy in the context of mechanics. He analyzed muscle forces as acting along lines connecting origins and insertions and studied joint function. Da Vinci tended to mimic some animal features in his machines. For example, he studied the flight of birds to find means by which humans could fly; and because horses were the principal source of mechanical power in that time, he studied their muscular systems to design machines that would better benefit from the forces applied by this animal.[18] standard medical book for the next 1,400 years.

In 1543, Galen’s work, On the Function of the Parts was challenged by Andreas Vesalius at the age of 29. Vesalius published his own work called, On the Structure of the Human Body. In this work, Vesalius corrected many errors made by Galen, which would not be globally accepted for many centuries. With the death of Copernicus came a new desire to understand and learn about the world around people and how it works. On his deathbed, he published his work, On the Revolutions of the Heavenly Spheres. This work not only revolutionized science and physics, but also the development of mechanics and later bio-mechanics.[19]

Galileo Galilee, the father of mechanics and part-time biomechanic was born 21 years after the death of Copernicus. Galileo spent many years in medical school and often questioned everything his professors taught. He found that the professors could not prove what they taught so he moved onto mathematics where everything had to be proven. Then, at the age of 25, he went to Pisa and taught mathematics. He was a very good lecturer and students would leave their other instructors to hear him speak, so he was forced to resign. He then became a professor at an even more prestigious school in Padua. His spirit and teachings would lead the world once again in the direction of science. Over his years of science, Galileo made a lot of biomechanical aspects known. For example, he discovered that  “animals’ masses increase disproportionately to their size, and their bones must consequently also disproportionately increase in girth, adapting to loadbearing rather than mere size. [The bending strength of a tubular structure such as a bone is increased relative to its weight by making it hollow and increasing its diameter. Marine animals can be larger than terrestrial animals because the water’s buoyancy [sic] relieves their tissues of weight.”[20]

Galileo Galilei was interested in the strength of bones and suggested that bones are hollow because this affords maximum strength with minimum weight. He noted that animals’ bone masses increased disproportionately to their size. Consequently, bones must also increase disproportionately in girth rather than mere size. This is because the bending strength of a tubular structure (such as a bone) is much more efficient relative to its weight. Mason suggests that this insight was one of the first grasps of the principles of biological optimization.[18]

In the 16th century, Descartes suggested a philosophic system whereby all living systems, including the human body (but not the soul), are simply machines ruled by the same mechanical laws, an idea that did much to promote and sustain biomechanical study. Giovanni Alfonso Borelli embraced this idea and studied walking, running, jumping, the flight of birds, the swimming of fish, and even the piston action of the heart within a mechanical framework. He could determine the position of the human centre of gravity, calculate and measured inspired and expired air volumes, and showed that inspiration is muscle-driven and expiration is due to tissue elasticity. Borelli was the first to understand that the levers of the musculoskeletal system magnify motion rather than force so that muscles must produce much larger forces than those resisting the motion. Influenced by the work of Galileo, whom he personally knew, he had an intuitive understanding of static equilibrium in various joints of the human body well before Newton published the laws of motion.[21]

Industrial era


It was many years after Borelli before the field of biomechanics made any major leaps. After that time, more and more scientists took to learning about the human body and its functions. There are not many notable scientists from the 19th or 20th century in bio-mechanics because the field is far too vast now to attribute one thing to one person. However, the field is continuing to grow every year and continues to make advances in discovering more about the human body. Because the field became so popular, many institutions and labs have opened over the last century and people continue doing research. With the Creation of the American Society of Biomechanics in 1977, the field continues to grow and make many new discoveries.[23]

In the 19th century, Étienne-Jules Marey used cinematography to scientifically investigate locomotion. He opened the field of modern ‘motion analysis’ by being the first to correlate ground reaction forces with movement. In Germany, the brothers Ernst Heinrich Weber and Wilhelm Eduard Weber hypothesized a great deal about human gait, but it was Christian Wilhelm Braune who significantly advanced the science using recent advances in engineering mechanics. During the same period, the engineering mechanics of materials began to flourish in France and Germany under the demands of the industrial revolution. This led to the rebirth of bone biomechanics when the railroad engineer Karl Culmann and the anatomist Hermann von Meyer compared the stress patterns in a human femur with those in a similarly shaped crane. Inspired by this finding Julius Wolff proposed the famous Wolff’s law of bone remodelling.[24]

Applications


The study of biomechanics ranges from the inner workings of a cell to the movement and development of limbs to the mechanical properties of soft tissue,[25] and bones. Some simple examples of biomechanics research include the investigation of the forces that act on limbs, the aerodynamics of bird and insect flight, the hydrodynamics of swimming in fish, and locomotion in general across all forms of life, from individual cells to whole organisms.

With growing understanding of the physiological behaviour of living tissues, researchers are able to advance the field of tissue engineering, as well as develop improved treatments for a wide array of pathologies.

Biomechanics is also applied to studying human musculoskeletal systems. Such research utilizes force platforms to study human ground reaction forces and infrared videography to capture the trajectories of markers attached to the human body to study human 3D motion. Research also applies electromyography to study muscle activation, investigating muscle responses to external forces and perturbations.[26]

Biomechanics is widely used in orthopaedic industry to design orthopaedic implants for human joints, dental parts, external fixations and other medical purposes. Biotribology is a very important part of it. It is a study of the performance and function of biomaterials used for orthopaedic implants. It plays a vital role to improve the design and produce successful biomaterials for medical and clinical purposes. One such example is in tissue-engineered cartilage.[27]

References

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