3D printer uses gel matrix to tie the knot

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Complex 3D patterns can be ‘written’ in a gel that switches between solid and liquid states

<cite>T Bhattacharjee, K Schulze, W G Sawyer and T E Angelini, University of Florida</cite>Cross-linked structures like these 'jellyfish' can be removed from the gel without damage</div>And the gel is compatible with many ink materials, as it shares a common solvent. ‘Polymeric inks having a huge range of viscosity can be printed, colloids can be printed, living cells can be printed – all with almost no modification of the granular gel medium,’ says Angelini. If cross-linked polymers are used, they solidify and separate from the gel, whereas softer materials like cells can stay put indefinitely, supported by the matrix.The team demonstrated their technique by writing several intricate designs into the gel, including nesting Russian dolls that are contained within one another, a detailed model of a jellyfish and a knotted tube that would otherwise be impossible to create using traditional 3D printing methods. ‘In the case of the knot, the hanging parts of the loop are created and then later connected to the rest of the knot. Without the trapping action of the granular gel medium, these parts of the knot would just fall downward as they are printed,’ explains Angelini.<h3>Practice organs</h3>The technique’s potential applications are varied, and include building components for flexible electronics and engineering smart materials. But Angelini and colleagues are particularly interested in its potential to improve the field of tissue engineering. One day, similar approaches could be used to create complex tissues and organs for use in medicine, Angelini says, although this is still a long way off. The use of granular gels could, however, have a more immediate impact in research, helping to create surrogate organs and other structures that could be used as training aids for medics to practice on. ‘We are currently building the 3D printing machines for our surgeons here at the University of Florida. We have already 3D printed a quarter-scale model of a whole brain out of hydrogel,’ Angelini says.<a href="http://www.manchester.ac.uk/research/Brian.derby/">Brian Derby</a>, a materials scientist at the University of Manchester, UK, says the technique was clever, but ‘unlikely to be earth shattering’. ‘The idea of writing something inside a fluid to give it support has been done before,’ he says. ‘The way they’re doing it using a highly shear-rate sensitive gel is new … there will be some specific examples that [the technique] is particularly good for. But it’s very niche, it would be difficult to do it fast.’Derby also points out that printing objects inside a gel matrix can sometimes make it difficult to retrieve them. Angelini agrees that separating 3D models from the gel is an area that could be improved, and says his team are currently developing new granular gels that allow easy separation.