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Super Soldiers: 3D Bioprinting and the Future Fighter
How can the military best give soldiers an advantage on the future battlefield? This is the question that drives human performance enhancement (HPE) researchers to discover ways to make soldiers faster and stronger, with increased endurance and awareness. 1 The goal of this paper is to briefly discuss the value of HPE, the current capabilities of 3d bioprinting technology, and the possible application of those capabilities to solve the HPE problem in the future military.
Though there are many who feel that the human factor will become less relevant in our age of advanced robotics, drones, and autonomous vehicle technology, those technologies are still a ways away from being fully operational, and that humans with their decision-making capabilities will continue to be an integral part of armed conflicts, and will likely have a presence on the ground for the foreseeable future. HPE and Ethics researcher Patrick Lin says “one of the weakest links in armed conflicts-as well as one of the most valuable assets-continues to be the warfighters themselves,” which seems to be a view shared by the current military, as the Defense Advanced Research Projects Agency (DARPA) has spent millions of dollars in the recent years on a variety of projects focused on HPE. 2, 3
Many current HPE efforts include external modifications, like robotic exoskeletons for heavy lifting, telescoping contact lenses to improve vision, and use of stimulants like amphetamines to keep pilots alert on long missions . 4, 5 Though these efforts may be promising, they each encounter limitations: the external modifications can be expensive and time consuming to fabricate, and like all technology, are subject to equipment failures and require an external power source to operate, which may only have a short battery life. The stimulants and drugs can have negative side effects, as shown in a 2002 incident where USAF pilots accidentally dropped bombs on a group of Canadians in Afghanistan after being given amphetamines to prevent fatigue during long missions, which some argued impaired their vision. 6, 7 These limitations suggest that even though there are many current HPE efforts already being researched, it may be worth continuing to consider possible alternatives.
Though 3d bioprinting is very much still an emerging technology, with the first patent being granted in 2006, it offers unique possibilities for HPE. 8 By using this technology, would it be possible to print not just replacement body parts for repairing the system, but augmented or enhanced parts to improve performance? Of course that issues carries with it a host of moral and ethical implications, but the military has already shown interest in using traditional 3d printers for printing on-site repairs of equipment, so using additive manufacturing for HPE might not be that far-fetched. 9
Understanding the current 3d bioprinting process is a starting point for planning possible augmented enhancements in the future. There are currently six steps to bioprint tissues:
Imaging- Before making a print, a researcher needs to scan an existing body part or the surrounding area to guide the fabrication process and ensure that all printed tissues will fit well within the available area and work well with the surrounding tissues. Current scanning is done using x-ray, computed tomography (CT), and magnetic resonance imaging (MRI). This information creates a digital blueprint with computer assisted design (CAD) software, which can then be customized or altered. 10
Design- Once the information has been gathered, the researcher generates a process plan. Because bioprinting technology is not advanced enough to print at the cellular level, there are three current approaches to create tissues:
- Biomimicry- this method involves manipulating a new cell to mimic properties of a cell in the organ the researcher hopes to print. 11
- Autonomous self-assembly- this method uses embryonic development as a guide. Just as cells in a developing embryo know how to form themselves into complicated organ as the embryo develops, once the relevant cells are placed in the right place, nature completes the process and the cells move into the correct places and take on the correct properties in order to form a functional tissue. 12
- Mini-tissues- this method is similar to self-assembly, where small parts of organs or tissues are allowed to self-assemble, and then placed together to then self-assemble into a larger tissue. 13
Material Selection- A bioink requires not just the cells that are going to be printed, but also a type of matrix to help them communicate, differentiate, and adhere to one another as they develop into a tissue. The most common types of ‘matrix’ materials are synthetic polymers, natural polymers, and extracellular matrix, which is found in the human body. 14
Cell Selection- Once the matrix material has been determined, researchers choose which types of cells are most appropriate for that particular printing. 15 There are three different types:
- Differentiated cells- these cells already have their assigned specialized properties in a tissue or organ.
- Pluripotent stem cells- these are normal cells that have been modified to behave like embryonic stem cells using chemicals.
- Multipotent stem cells- these cells have the capacity to self-renew by dividing and to develop into multiple specialized cell types present in a specific tissue or organ.
Bioprinting- After the bioink has been created, there are several types of printers currently used. The most commonly used is an inkjet printing method, where drops of bioink are dripped out of the printer into a hydrogel scaffold which allows the structure to keep its shape while the self-assembly process takes place and the cell groups fuse into their completed structure. 16 The second method, which is more expensive and less widely-used, is the microextrustion method, which operates very similarly to the inkjet method except that instead of depositing individual drops of a cell solution, the microextrusion printer deposits a continuous stream of material. This method of printing is good for high-viscosity materials, but has a lower rate of cell survival. 17 The last method is the laser printing method, where cells to be printed are placed in a ribbon above a gold or titanium sheet, with the hydrogel facing it. A laser pulse focuses on the metal layer which creates high pressure bubbles, which will propel cells toward the receiving hydrogel scaffold. This is a very expensive method, but can achieve a very high resolution. 18
Application- After the bioink solution has been successfully printed and fused into the finished tissue, the printed cells need a period of time to mature and fuse into the finished, functional tissue. After this process, the tissue can either be implanted in a patient, or kept in a lab environment for further testing. 19
Though bioprinting has successfully produced simple tissue products, like skin, cartilage, and hollow tubes, there are some limitations that will need to be overcome before bioprinting could to advance to the point of printing fully functional organs that could be used for HPE. The first limitation is functionality- how can a researcher ensure that a printed organ would work when actually inserted into the body, communicate with the surrounding tissues, and receive signals from the body. Currently, lab-printed tissue does not include nerves or vasculature to allow the printed organ to receive nutrients from the blood. Both of these omissions would need to be included in a functional organ. 20
Another limitation is size and complexity. Currently, many printed tissues of a large size will collapse on themselves before they have a chance to fuse together. In very complicated organs, sometimes certain types of cells must be in certain places exactly, and it’s not just enough to leave them to develop and shift around on their own as with the embryonic model. Until bioprinters can print on the cellular level or researchers find a better way to ensure specific diversification of a group of cells in a printed organism, this will be a limiting factor for certain types of organisms. (REF). A last limitation is contamination and immunity. Currently, some labs use fetal bovine serum and other chemicals to grow cells and keep bioengineered tissues alive. To use printed tissues in humans, they would need to be 100% pure and uncontaminated. 21
Projected Capabilities and Types of Enhancements- As the technology develops and the limiting factors previously identified are resolved, bioprinting may be able to create modified body parts for HPE. When considering how bioprinting seems to offer an endlessly customizable array of options for HPE, there are two criteria that are useful to keep in mind when determining which enhancements make the most sense. First, the human body already works very well the way it is. The enhancements with the greatest chance of success are those that most closely resemble the existing body parts. The more radically an enhancement diverges from the original body part, the less likely it is to function well with the other surrounding tissues in the body. Secondly, the human body has a finite amount of space inside it, and therefore any enhancement must be sized appropriately to fit. Keeping these two criteria in mind helps narrow down the range of potential enhancements to those that would be the most realistically successful. Below are three examples of enhancements that might have a high chance of success as well as a high impact on the fighting force:
Muscles- There are many factors that contribute to muscle exhaustion, including composition (fast/slow twitch fibers), lactic threshold (the point at which the buildup of lactic acid causes the muscle to stop contracting), and muscle cross section, which is simply the size of a muscle group. If additional muscle tissue could be printed identical to the military member’s existing tissue, it would immediately increase the muscle cross section. Depending on the advancement of the technology with regard to cellular differentiation, in the long term future a bioprinter might be able to fabricate fast or slow twitch fiber exclusively, which would change the ratio of the type of fiber in the muscle to be more appropriate for certain tasks. 22, 23
Heart- The hearts of athletes in peak physical condition are often between 20 and 40% larger than their nonathletic counterparts, a condition known as “athlete’s heart.” 24 Athletes’ hearts adapt to the increased demands of intense training by growing larger and contracting more strongly. These athletic hearts can beat over 200 times a minute and thus pump an extraordinarily large volume of blood and oxygen to the body to support strenuous exertion over a lengthy period of time, as seen in marathon runners and long distance cyclists, and scientific study shows that health risks associated with athlete’s heart are small. 25 With a 3D bioprinter, a medical professional could create a digital scan of a soldier’s heart, increase the scale of the model, and enable the soldier to benefit from the more powerful organ without having to alter the design. Of course this stronger heart would need to be accompanied by a more robust network of blood vessels as well to support the greater amount of force.
Ears- 3d bioprinting could potentially combat the effects of hearing loss through aging and service-related causes. Among military veterans, the most common service-connected disabilities are hearing impairments, and if a soldier’s inner ear could be restored to its original undamaged state, it could be an advantage. 26
Possible Enhancement Process- If the future military decided to employ 3D bioprinted modifications, what might the process look like?
Donation: As soldiers begin basic training, they provide cellular samples as part of their medical screening and in-processing. Organs and tissues are scanned using an MRI or similar technology, and saved as digital blueprints. This material follows soldiers to each new duty station or deployment as part of the medical record.
Selection: Upon completion of basic training, or at any other time in the soldier’s career, the soldier is identified as a candidate for an enhancement.
Modeling: The digital blueprint data and cellular samples are provided to the nearest medical facility, whether traditional or expeditionary, and the file is customized to create an enhancement designed to complement the soldier’s existing musculature.
Fabrication: The enhancement is printed and surgically inserted. The soldier undergoes a period of familiarization and adjustment training to become comfortable with her/his new capability.
Maintenance: If at any time the enhancement becomes damaged, a new one is created locally from the saved digital blueprint which is transmitted to a printer nearest to the soldier’s location.
Support: Enhanced soldiers leaving the military service are offered transition support as they return to civilian life.
The possible advantages of using printed enhancements could be reduced training costs, a low rate of implant rejection if the tissues were printed with a soldier’s own genetic material, and the fact that the printing may not require an entire laboratory facility and might be more mobile, as we are seeing traditional 3d printers become small and more mobile as the technology develops. If the military chose to give enhancements to members of the Special Forces community, a group with a very high rate of physical injury, instead of new recruits, then it might allow the military to benefit from their experience for a longer amount of time. This could potentially reduce new Special Forces recruits needed every year and the associated cost of training them.
Concerns- Some issues to consider involve foreign country competition, security, and moral/ethical concerns. Many foreign countries are investing heavily in this technology. If the U.S. begins using bioprinting to improve the military, what are the odds that other countries may attempt to do the same? If so, would we lose whatever advantage enhanced forces provided? Additionally, because part of the process involves digital information, would it be vulnerable to hacking? Could another country or cyber actor access and steal digital blueprints? Some ethics researchers expressed hesitation when considering an enhanced or augmented military with soldiers whose capabilities far exceeded the human baseline, and posed the question of whether an enhanced soldier would count as a weapon under the Geneva Conventions. 27 Some with religious concerns might feel that this type of modification could be inappropriate because improving the human body outside of what is naturally possible could be seen as “playing God.” Reassuring and educating this part of the population might help popular opinion in this area.
In conclusion, human beings will likely to continue to play a direct role in combat, even with recent technological advancements, and performance enhancement is an important concern for the future. Though the bioprinting technology still has to advance beyond some current obstacles, future bioprinting may offer the possibility of a customizable enhancement process with a low rate of rejection.
The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of any agency of the U.S. government. Assumptions made within the analysis are not reflective of the position of any U.S. government entity.
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