Unusual 3D printing materials: from pureed food to bio-ink and body parts
Image credit: Loughborough University
Living tissue, food, even moon dust – research is currently underway to 3D print everything from your dinner to replacement body parts or building components for use in space.
These days, it’s tough to imagine a world without 3D printing. The process has changed the face of countless sectors including design, manufacturing, medicine, aerospace and construction, to name just a few.
Although the very first 3D-printing processes were developed back in 1980s, growth in the sector really took off in 2009 when industrial patents for common 3D-printing techniques, such as fused deposition modelling, started to expire.
This has led to 3D printing becoming accessible and affordable to a much wider audience.
It’s not just the hardware that’s evolving. Across academia, researchers are experimenting with alternative printing media. The innovative products developed from these projects have the potential to transform items in our kitchen cupboard, our hospitals and even drive future space exploration and colonisation efforts.
At the University of Bristol, researchers from the School of Cellular and Molecular Medicine have developed a new type of bio-ink containing stem cells that allows the 3D printing of living tissue.
Traditional tissue engineering takes a top-down approach where a natural synthetic scaffold is seeded with cells and subjected to a cocktail of growth factors. In this new method, living cells are assembled layer-by-layer by delivering them in a specially developed bio-ink extruded from a retrofitted bench-top 3D printer.
“Designing a bio-ink is extremely challenging,” says lead researcher Adam Perriman. “It needs to be cytocompatible, able to be extruded and to undergo a phase transition (from liquid-solid) to provide a structure with high fidelity.
“We developed a hybrid bio-ink containing two different polymers. The first, a synthetic polymer, transforms the bio-ink from a liquid to a gel when it reaches 37°C.”
Cross-linked with calcium, the second component, alginate – a natural polymer from seaweed - provides structural support when introducing cell nutrients.
The team has been able to use its bio-ink to engineer 3D-printed living structures, including a full-sized tracheal cartridge ring. As cartilage is avascular, the complexity in the system is greatly reduced, but the team is taking on the challenge of bioprinting more complex organ structures.
“In the body, most cells are within 100-200 microns from a source of blood, as oxygen diffusion is inherently low,” explains Perriman. “Accordingly, if larger more complex tissue structures are to be printed, vasculature will need to be integrated. Fortunately, as more high resolution bioprinting approaches come online, so too will tissue models with functional vasculature.”
In Australia, a team from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) has been developing methods for 3D printing food with the aim of assisting those that suffer from dysphagia; a difficulty in swallowing food or liquids. This is a growing concern in the country due to its rapidly ageing population – by 2045 an estimated quarter of those living in Australia will be over 65 years old.
How does 3D printing help? Well, it can produce foods that are soft enough to not require chewing, but which look very similar to ‘normal’ food. Normal methods of food processing for dysphagia generally involved food being minced or pureed, which not only looks unappealing but also causes issues for patients with dementia, who often refuse food that they don’t recognise.
By 3D printing pureed food to look more like it ‘should’, meals appear more visually appealing while staying soft enough for those who struggle to chew. One example from CSIRO has been a 3D-printed meal shaped like a tuna fish, using 3D-printed tuna, beetroot and pumpkin purees.
In addition to helping dysphagia suffers directly, 3D printing food also has the potential to save hospitals and care establishments time and money, negating the need to either process meals in-house or pay suppliers for pre-pureed products.
CSIRO is also investigating ways that 3D printing can help personalise nutrition, allowing the printed meals to be boosted with vitamins or minerals such as iron and calcium to address any deficiencies present.
Experiments with unusual 3D printing materials aren’t just confined to this planet. At Loughborough University, research associate Thanos Goulas has been investigating the feasibility of using lunar regolith (aka moon dust) as a way to make physical assets, such as nuts and bolts, on the moon itself, rather than relying on traditional Earth-based supply methods.
This concept, known as in-situ resource utilisation, would help move towards completely autonomous, self-sustaining off-world colonies and allow the manufacture of parts on-demand without having to launch them from Earth using rockets. The process could also potentially be adapted for other planetary bodies such as Mars.
The main challenge in developing this application is the material itself.
“Unlike most 3D printing applications, we cannot tailor the material to the manufacturing process but instead we must tailor the process to the material,” notes Goulas. “The lunar regolith is a non-traditional material to be used as a feedstock for 3D printing; it is highly complex and multicomponent in nature and poses a significant challenge for current 3D printing techniques.”
To overcome this issue, a number of process parameters and material investigation techniques, including differential scanning calorimetry, scanning electron microscopy and particle size analysis have been employed to create an understanding of the best way to control the use of the material.
“The next major step is to test the material and process in a reduced gravity vacuum situation to better simulate the lunar environment,” says Goulas. “We would also look to increase the range of material mixes we have used to make the technique more adaptable to any variations in the lunar material make-up, and also improve the applicability to other world environments; such as Mars.”