In this podcast, my guests and I get into detailed discussion and debate on prosthetic limb use in modern-day, and future Paralympic and Olympic sport. We discuss the intricacies of the biomechanics of these devices, and we have ethical discussions as to what should and should not be allowed in sport. Furthermore, we expand our discussion to neurological implants, and their connection to advanced prosthetic limbs, finishing with a discussion of the implications of these devices to the future of society.
Whether or not you know someone who has lost a limb, we can all easily imagine the hardships that would follow such a tragedy. Thanks to scientific advancements, prosthetic limbs have become more and more available and functional over the past few decades. However, one of the greatest challenges—which has only recently been started to be addressed—still facing the industry is the question of how to restore tactility through prosthetic hands. Having the sense of touch in your hands is essential to everyday activities, such as putting on your clothes in the morning or drinking a glass of water; and, unfortunately, in the US alone there are over 100,000 persons registered who had an amputation of a complete arm, hand, or partial hand.
When it comes to tactility, there are three main pieces of information that need to be transferred to your somatosensory cortex, the part of your brain that receives and processes sensory information. Those three pieces of information are contact location, pressure, and timing (i.e., when the contact begins and ends). Most studies that have looked into transferring this information to a brain from a prosthesis have done so through a brain-machine interface using intracortical microsimulation (ICMS), which activates neurons though implanted microelectrodes within the somatosensory cortex. The brain-machine interface would work in the following way: First, the prosthesis would gather force data from mechanical stimuli to the prosthesis. Next, the prosthesis would send the data to a microelectrode array capable of ICMS via a computer processing unit. Finally, the microelectrode array would deliver electrical pulses to activate neurons within the somatosensory cortex, causing you to “feel” the mechanical stimuli.
The contact location and pressure of the mechanical stimuli would be determined from the force data gathered by the prosthesis; and the contact timing would be determined by having the force data be sent as a constant feed-back loop to the somatosensory cortex—that way a change of force from zero to some arbitrary, non-zero value and from some arbitrary, non-zero value to zero would indicate the beginning and end of the contact timing, respectively.
In studies by Tabot et al., O’Doherty et al., and Berg et al.; ICMS feedback has been shown to work with various species monkeys. Tabot’s and Bergs’s studies in particular are very promising, as both studies showed that the monkeys would respond in the same way when a mechanical stimulus was applied to either a prosthetic hand/finger or a native, biological hand/finger. Based on these works and others, there are now a few working prototypes of prosthetics arms and hands that can “feel” that have been given to the general population, such as the one that Marine veteran Claudia Mitchell has. Further work in this field of study will hopefully bring us to the point where all amputees are able to have a prosthetic limb that allows them to live out their daily lives just as easily as the rest of us. Additional readings on bioinspired prosthetic interfaces and prosthetic tactile feedback can be found here and here.
In media and science-fiction, robots have stereotypically, and perhaps somewhat unfairly, been depicted as mechanical, stiff assemblies of moving joints and complicated circuitry. While this still holds true for many robots designed today, whether for industry or research, the past few years have seen a growing interest in soft robotics in academia, industry, and popular culture. As the name implies, many research groups have begun investing in constructing robots from compliant, softer materials.
Inspired by the way organisms in nature survive and adapt to their surroundings (formally known as biomimicry), the advantages of soft robotic components lie in their flexibility, sensitivity, and malleability – delicate tasks or interactions involving other people would be better accomplished by robots made of compliant materials rather than one that could potentially cause harm to the object or person. To that end, many of the applications of soft robotic research have already seen results in the medical industry, from invasive surgery to assistive exosuits. By taking inspiration from biological creatures or mechanisms, softer materials like rubbers and plastics can be actuated to accomplish tasks conventional, “hard” robots could struggle with.
The most common method of moving these robotic parts is with changes in internal pressure. By creating a “hard”, skeletal frame, and surrounding it with soft, sealed membranes, changes in pressure allow the designer to control its components precisely. By decreasing the pressure and creating a vacuum, the robotic section would shrink or crumple, and increasing it would do the opposite. Researchers at Harvard developed “artificial muscles” by taking this concept a step further; using origami, they were able to design soft robotic mechanisms that could orient themselves into tunable positions as the pressure was changed inside the membrane (as a side note, origami is used in a surprising number of research fields, one of the most famous being satellite deployment). Compared to the challenge of precisely controlling prismatic (sliding) joints and servos in conventional robotics, the compliance of the materials used allow for finer control and smaller ranges of applied forces that are better suited for precise tasks.
Another significant advantage of soft robots over their stiff counterparts is their adaptability to environmental conditions. Generally speaking, robots do not do well in water (or lava, for that matter), but it would have little effect on robots covered in a sealed, pressurized “skin”. This is what inspired NASA in 2015 to fund research into soft robots that could explore the oceans of one of Jupiter’s moons, Europa. Similarly, a light-activated underwater robotic manta ray was designed at a centimeter scale to study the effect of environmental cues on controllable robots.
While research in soft robotics is still relatively new, it has the potential to significantly affect the role of robots in our daily lives. As a softer, safer, and more environmentally robust alternative to “hard” robots, wearable robotic devices, exploratory robotic fish, and personal medical attendants could soon become commonplace for the general public.
Can you imagine a world where amputees receive replacement limbs which are able to detect temperature and pressure like an actual limb? How about a world where when you get a cut, you can 3D print some of your own skin to patch the wound?
To the average citizen, this might seem like something out of a science fiction movie. To researchers at the Graz University of Technology, the Wake Forest School of Medicine, and the Universidad Carlos III de Madrid, this is a reality that they are helping bring ever closer. Both of these scenarios are discussed in a recent article by Mark Crawford, who investigated the recent breakthroughs in 3D printing human skin and creating sense-sensitive artificial skin.
At the Graz University of Technology, researchers are working on creating an artificial skin that can sense temperature, humidity, and pressure. Currently, artificial skins can measure one sense at best, but with the use of the nanoscale sensors that these researchers are developing, sensing all three at once could be possible. This is achieved through the materials that the nanosensors are created out of: a smart polymer core and a piezoelectric shell. The smart polymer core can detect humidity and temperature through expansion, and the piezoelectric shell detects pressure through an electric signal that is created when pressure is applied. With this technology, prosthetics could be made which could allow the wearer to retain some of their lost senses.
At the Wake Forest School of Medicine, researchers have created a handheld 3D printer which produces human skin. This device could be used to replace skin grafts, as it can apply layers of skin directly onto the wound. Through the use of bioink, this handheld printer can create different types of skin cells. After scanning the wound to see what layers of tissue have been disrupted, it can print the appropriate skin needed to correct the injury.
At the Universidad Carlos III de Madrid, researchers are also 3D printing human skin using bioink. They are creating both allogenic and autologous skin to create the optimal skin, which is a combination of the patient’s own cells and cells created from a stock. Although they have managed to print functioning skin in its natural layered state, it is tricky to create the cells in such a way that they do not deteriorate.
It is also tricky to correctly deposit the product. To illustrate, more research needs to be done on the mechanical properties of artificial skin before it could be used on humans. The artificial skin must be able to stretch and react to tension in a similar manner to the real skin it will be connected to. Additionally, researchers must figure out how to safely send the signals the artificial skin is detecting to the brain.
Overall, both advancing artificial skins and 3D printing human skins could largely impact humanity. Even though we have yet to use these skins on people, they are already being used in industries, such as L’Oreal, to limit testing on humans and animals. Already, these skins are being used on robots, as seen in this video, to help prepare the skin for human transplant:
3-D printing is a quite exciting technology that has come to light in recent years. The process involves a nozzle much like in a regular inkjet printer that layers material upon material to build up a 3D structure. The printer receives this data from a computer designed file that maps out where the printer should add material. Combine this with filler material that serves to hold everything in its final upright position, and the final product is born, after setting and clearing off the filler. This process has been used to make many different things, from simple objects like phone cases and luggage tags to complex scaffolds used to hold cells for tissue engineering, or as in this post, specific implants for dogs and other animals. The usual types of orthopedic implants that have somewhat of a cookie cutter size distribution for humans do not always fit in dogs or other animals. So, 3-D printing has been employed to create implants used to repair and replace bones in veterinary situations.
The most prominent veterinary application for 3-D printed implants is dogs. This is due to their slight differences in body type, even within breeds, that can make finding a pre-sized and pre-made implant difficult to find. One such example of this is a dachshund, named Patches, that received a custom made skull implant after other implants were found to be ineffective or dangerous to her long term health. Patches had a brain tumor, one that grew to a very large size and began encroaching on her eyes. The tumor was successfully removed, but the process involved the removal of large portions of her skull, leaving her brain unprotected. If a preexisting implant were tried, the way it would fit would leave her head vulnerable to an impact, making the implant quite pointless. A 3-D printed implant was made, and old Patches made a full recovery.
The process involves taking a CT scan of the area in question and gaining an understanding as to the layout of the area. This allows designers to make a 3-D model of the implant using a computer, and that model can be printed out using a 3-D printer. In the case of implants, titanium is usually used due to its biocompatibility and great mechanical strength. The implants can be used for surgery and repair, or an array of other applications, even studying the cranial activities of primates. In any case, these exciting new developments in 3-D printing are leading to advancements in the medical and biological fields. So, the next time you fire up you 3-D printer to make a cool-looking hood ornament, know that the same technology is at work, saving lives and giving scientists new knowledge about animals they previously had no good way of studying.
In 2012, the “Blade Runner” Oscar Pistorius became the first double amputee to compete in the Olympics. Ever since this historic occasion, the issue of whether prosthetics should be allowed in athletics has been a topic of controversy in the media. Do prosthetics give amputees an advantage over able-bodied athletes? Are athletes with prosthetics capable of running faster and performing better than able-bodied athletes?
In a recent article, physiology and biomechanics professor Alena Grabowski attempts to answer some of these questions. Grabowski was part of a research group that conducted a study to see if Pistorius’s prosthetics gave him any advantages after he was banned from competing in the 2008 Olympics. The group focused on comparing the abilities of Pistorius to those of able-bodied track athletes. The study involved testing Pistorius’ energy cost in running, his endurance, and his general running mechanics. In order to test for energy costs, the researchers measured breathing and metabolic rates of able-bodied runners who were similar in ability to Pistorius as they ran a series of short sprints. To test endurance, runners were placed on treadmills set at their max speed to measure how long they could maintain that speed. To test the running mechanics, each runner was asked to continue increasing their speed on a treadmill until they could no longer take eight consecutive strides on the treadmill without maintaining their position on the treadmill. Based on the study, the group was able to determine that Pistorius’ running abilities are very similar to able-bodied runners, thus allowing his ban to be lifted and for him to ultimately compete in the 2012 Olympics.
After the initial research, Grabowski decided to conduct research of her own into prosthetics. Her study involved how changing key parameters in a prosthetic affected a runner’s abilities. In order to conduct the tests, she first modeled the foot as a spring system. This allowed her to pick the key parameters to change: stiffness, height, and speed of a prosthetic. Five participants were chosen to be tested. The study consisted of a participant using a set prosthetic to run on a treadmill, increasing the speed on each trial until they could no longer hold their position in the treadmill. This was repeated for different parameter changes in the prosthetics until enough data was collected to compare. From her study, Grabowski found that the length of the prosthetic had no overall effect on running speed. However, stiffness did appear to aid runners, but the effects were negligible at high running speeds. Thus, the advantages of having prosthetics come into play more for long distance running than for sprints. Based on her research finding, Grabowski hopes that future prosthetic development can be more tailored to match the specific wearers abilities before amputation.
The world of prosthetics opens up the door for many amputees to compete in an able-bodied society: from being able to complete just simple day-to-day tasks to competing alongside able-bodied athletes in the Olympics. Though many may still be skeptical of the use of prosthetics in competition—namely running, the evidence says that the effects are minimal or even no-existent in the case of sprinters. With the help of researchers like Alena Grabowski, more athletes like Oscar Pistorius are and hopefully will be making great strides in the future.