Reproducing biological tissue structures in a laboratory is becoming increasingly commonplace. Recent research has already shown that complex heart structures, such as branching artery patterns, can be 3D printed using biological “ink.” Now, a new study in the journal Advanced Healthcare Materials has revealed that cotton candy machines, of all things, may hold the key to creating functional, artificial capillary networks.
While that may sound like a strange choice, these machines spin out incredibly fine sugary fabrics with remarkable efficiency. That's why lead researcher Leon Bellan, assistant professor of mechanical engineering at Vanderbilt University in Tennessee, thought it wouldn’t be too difficult to get them to produce capillaries, which are relatively simple structures. The difficulty lay in finding a material that could mimic the structure of capillaries, while also being resilient enough not to easily fracture – this is where hydrogels come in.
Hydrogels, networks of large, chained molecules that absorb and contain water, have been used before by engineers trying to replicate biological structures. They are malleable, can be rapidly solidified, and allow dissolved solutions – including vital cell nutrients – to diffuse through them. Hydrogels effectively replicate the natural, extracellular matrix that surrounds cells within the human body, and this makes them an excellent scaffold for artificial capillaries.
The network of dissolvable microfibers produced by the cotton candy machine. Bellan Lab/Vanderbilt University
In order to form capillary-like networks using the cotton candy machine, the hydrogel first needed to be coated on an underlying “sacrificial” material. This material had to be able to form extremely thin strands that would dissolve away when the hydrogel layer was applied, leaving behind hollow tubes.
After experimenting with a few types, the researchers settled on PNIPAM, a non-harmful compound that's soluble at around room temperature, but insoluble above 32°C (89.6°F). Using this material, the team stretched out and formed microfiber structures with their cotton candy machine, creating structures that were physically comparable to a natural capillary system. These microfibers were then coated in a gelatin hydrogel mixture – infused with living cells from natural capillaries – within a warm incubator.
After the hydrogel set, the structures were moved into a room-temperature environment, and the embedded PNIPAM threads dissolved. This left behind thin channels made of hydrogels, which averaged in diameter at around 35 micrometers, roughly the size of a natural capillary.
“No one’s been able to produce this size of biological structure using 3D printing – that’s impossible,” Bellan told IFLScience. “In fact, by partly relinquishing control of the construction process, this technique is in many ways the inverse of 3D printing. I would also argue that in this case, it’s cheaper and faster.”
Artificial organs, packed with living cells, require the transfer of oxygen, nutrients, and waste throughout their internal architecture. To accomplish this, a network of artificial capillaries have to be created, and it appears hydrogel networks, spun using cotton candy machines, provide a near-perfect construction method.
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