When thinking about space missions, the health concerns of astronauts are not typically top-of-mind. However, there are a lot of physiological and psychological changes that occur when humans are in an isolated condition with no gravitational forces.

Some of these effects are more minor, such as motion sickness. Others are more severe, such as the loss of muscle and bone mass, which occur due to being in a weightless environment. The heart can start to atrophy because astronauts lose a substantial amount of their blood volume, which results in less blood to pump. The senses can be disrupted, including changes in vision and taste. Psychological consequences, such as anxiety, insomnia and depression, can occur.

The immune system is also affected by space travel, which is of particular interest to Jorge M Zuniga, assistant professor and research project lead at the University of Nebraska Omaha. He noticed, in previous research conducted by Nasa, that almost all astronauts studied had immune dysregulation. Although disruption to the immune system was not new information, the paper highlighted the significant impact of carriers and viruses in space. “When you put up a carrier and a virus in space, the virus reproduces much, much faster and it is hard to predict the rate of development, which is kind of dangerous, and they become antibiotic resistant,” explains Zuniga. “To put this in perspective, a nurse in the ER will have less chance to get an infection than astronauts.”

Exact reasons for the immune dysregulation has not yet been established. “People usually attribute this to radiation exposure, to isolation, to the distress of being by yourself and being responsible for everything,” says Zuniga. “The lack of exercise and movement in the lymphatic system – the system that has all our immune responses – means that if we don’t move as much, that could affect it, but nobody knows for sure. This is just one hypothesis.”

It’s not just the lack of movement that is problematic, the nature of it also raises the risk of certain injuries. “Astronauts in the International Space Station (ISS) don’t really walk, because there are no gravitational forces, so there is no ability to walk,” explains Zuniga. “They move with their hands, they push into things, they grab things and they float around. So, one of the main injuries astronauts get are fractures and jammed fingers.”

“[Astronauts] move with their hands, they push into things, they grab things and they fl oat around. So, one of the main injuries astronauts get are fractures and jammed fi ngers.”

Replicate, reuse, recycle

To develop devices suitable for space, Zuniga and his team collaborate heavily with industry. There is a 3D-printing facility in the ISS, where researchers can get their devices manufactured.

“We design them here with the anthropometric measures of the astronauts,” explains Zuniga.

“This goes by email to the ISS, the astronauts push a button, it gets manufactured with this antimicrobial material, and then the astronauts use it and then we recycle it. So, we melt it down and put it in the machine again, so we can print something else.”

At the moment, this technology is at the proof-of-concept stage but nevertheless offers huge value, as it means that astronauts can have their health needs met in a quick and sustainable way.

The environmental impact of space missions is a major issue. “You have no idea how much garbage they have up there; it is crazy,” says Zuniga. “You send things up there, they are used and they have to come down. So, high volumes are always going up and down, because you can’t really put garbage into space, as they have plenty of that already.”

Sustainability is something taken very seriously by Nasa, which is funding much of the research in this area. “They want to have something that they can recycle, something that’s ecofriendly and something that’s versatile,” says Zuniga.

3D printing can be used to manufacture products made from a range of materials, but some are more suitable for space than others. Zuniga and his team have been using copper, which has several useful properties.

“You can take the particles of copper and reduce them to nanometres,” explains Zuniga. “We’ve known for many years that copper has an antimicrobial behaviour. The free radicals that are produced by copper disrupt the bilayered phospholipid of the cells. So, when a bacteria gets in contact with a cyst, it will attract the free radicals of the nanoparticles of the copper, and they go into the membrane and disrupt the membrane until it dies.”

Copper can also help to combat viruses through a different mechanism. “In a virus, it goes all the way – it goes into the membrane, all the way to the DNA level, and changes the configuration of amino acids that are part of the DNA configuration of the virus,” explains Zuniga. “In theory, what it does is it deactivate viruses, such as HIV-1 or herpes.”

A process called thermal forming is used to change the properties of the material. “When you manufacture them, you can expose them to heat a little bit like a hairdryer or something like that, and you can change the configuration – so you can adjust them as you need it,” says Zuniga.

Unsurprisingly, this work comes with challenges. “For Nasa to allow new material to go into space, you have to go through a board of specialists that supervise all the new materials that go to space,” explains Zuniga. “First, we have to establish that the material is not inflammable, that the material is biocompatible, that it does not produce irritation for the skin, is not toxic, and all those things.”

Challenges still to solve

Ensuring that the material can be physically transported to space can be difficult. “You have to find a way to minimise the volume to be able to send the material,” says Zuniga. “We found a way to do rolls, like the typical rolls you put in 3D printing – we call them spools – so we send them like that. Once we get it up there, we can recycle the actual spool that is allowing the material to be around it.”

This process also relies on cooperation from astronauts themselves. “Once it goes up there, then we have to hire an astronaut that has skills in handling such tools and they have to print it in space. Then they try it out, recycle it and print again, and then – finally – some of those medical devices and instruments are being manufactured in space,” explains Zuniga. “Then the products have to come down because we have to do an evaluation, we have to see if the antimicrobial nature of the material has changed, we have to test the strength, durability and ageing, if radiation may have an effect on the device. As you can imagine, this is extremely expensive and, as a result, we are trying to use just one material.”

Looking to the future, Zuniga is excited about what is set to come. “If you are not related to Nasa, if you do not go to the conference or understand the mission of Nasa, it’s really hard to understand what I am about to explain, but all this work we are doing is to allow habitation on Mars,” says Zuniga. “What we are doing now in the ISS will allow us to eventually find a sustainable and practical way to build infrastructure. We are anticipating a lot of problems with the delay of communication, you know, because right now if you try to communicate with the ISS, it is relatively fast. However, on Mars, it’s not going to be as fast.”

There are many uncertainties that need to be addressed for this to be successful. “We can’t possibly take all the surgical instruments you will need in an operating room to the ISS,” says Zuniga. “I mean, it’s ridiculous, it’s too much for all the potential interventions, such as surgeries. There is some potential for astronauts manufacturing their own surgical instruments, as you can recycle and use them again and again. We’re trying to see if it actually will work that way or not.”

It’s not just space missions that stand to benefit from these efforts. “The applications on earth are very significant,” explains Zuniga. “You can apply the same technology we are applying in the ISS to rural parts on earth.”

The future of antimicrobial 3D printing

The use of antimicrobial 3D printing materials, such as emerging thermoplastic polyurethane-based flexible materials, will play a major role in in the development of tissue-engineered scaffolds and other soft tissues, including blood vessels and cardiac walls. Their applications will not be limited to astronauts in the ISS but can also be used for military personnel in the battlefield for prevention of infections associated with combat-related injuries.

Sterilisation and biocidal technology in combat support hospitals and emergency humanitarian relief settings must be capable of providing a wide range of ‘on-demand’ medical devices. Currently, the sterilisation of medical devices depends on large-chamber stream sterilisers introducing a significant logistical burden. The treatment of battlefield trauma presents the unique logistical challenge of providing sterile medical devices to medical personnel. Transport and supply constraints limit the quantity and variety of medical devices available in the field, and sterilisation equipment is often not available to support the instruments required.

There is a critical need to develop a raw material for the development of a variety of antimicrobial medical devices, in order to address the current supply chain problems involving the medical care in austere medical environments. Antimicrobial 3D-printing materials will provide an attractive solution to solve these real-world problems, especially in austere environments.

Source: Journal of 3D Printing in Medicine