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specific patient. Surgical teams can and do speak with patients, read medical histories and plan operations with the help of radiologists and an array of scans, but there’s a certain something missing from even the best 2D image or virtual 3D projection.


“Surgery is a tactile thing,” explains Richard Arm, Flexural Composites Research Fellow at Nottingham Trent University. “When a surgeon looks at a scan, he’s not seeing the same thing the radiologist sees. He knows what he’s looking at in terms of the anatomy, of course, but he’s more familiar with it in three dimensions, covered in blood and lots of colour. On the scan, it’s very clinical – it’s black and white. You can pick out the tissues and see, for instance, where a tumour is, but actually understanding how that tumour interacts with the surrounding soft tissue is something only a surgeon can really know – and only through being able to feel it. He can feel how the tumour is embodied by the organ, how much he needs to cut out, and where he needs to make his incision.” Throughout the history of surgery, that knowledge has only become available in the operating theatre. Helpfully, then, Arm and medical textiles expert Arash Moghaddassian Shahidi have developed a method for 3D printing scan data into startlingly lifelike patient-specific liver models, which surgeons can use to simulate procedures. The extra practice means they can save as much blood and healthy liver tissue as possible when it comes to the live operation, which they might also be able to perform faster. At minimum, this should translate to shorter recovery times and lower the risk of infection, but in abnormal cases, it can be the difference between life and death. “It’s about improving outcomes for patients,” Arm explains. “You can try surgeries where the surgeon would previously have looked at the scan and thought, ‘No, we can’t do that’. It just opens up more options, more possibilities and greater survival rates for more people. The surgeons are not only able to do the procedure with confidence and greater proficiency, and to teach it with greater proficiency, but also to actually offer the physical patient – that unique, one patient with that particular tumour in that particular place – a greater chance of survival.”


Silicone prostates Perhaps most importantly, unlike other mooted life- saving applications for 3D printing, these organ models are ready for use today. In fact, replicating human tissue to help train and prepare surgeons might be the closest thing Mike McAlpine, associate professor of mechanical engineering at the University of Minnesota, has found to a ‘killer app’ for 3D printing. Since 2018, when McAlpine’s team published a paper on the topic, visitors to his lab have been able to palpate anatomically exact models of the prostates of


Medical Device Developments / www.nsmedicaldevices.com


three former University of Minnesota Hospital patients. Moreover, anyone squeezing one of these models can do so in the knowledge that it was tuned to specifically match the mechanical properties of its original, each of which was whisked off to a testing lab straight after it was surgically removed. “It’s not just a random ‘general human’,” McAlpine stresses. “These were actually three humans with three different prostates. We performed the mechanical tests on their prostate tissue samples and we then tuned our silicone inks to match. That’s the level of resolution that you can get.” Those prostates also incorporate sensors that record the force with which they interact with surgery tools, enabling surgeons to “fine-tune their limit space” and determine how to perform a procedure without causing a bleed. “It not only provides a platform for surgical rehearsal, because you have a soft model that you can suture into now, but also a feedback mechanism so that the practice surgery actually gives you quantitative feedback on how you’re performing”, McAlpine says. “It’s like a game of Operation – the sensors respond to the feedback.” More recently, the team worked with Medtronic to produce patient-specific aortic root models with embedded sensor arrays that can be used by surgeons and medical device manufacturers to both determine the optimum dimensions for a transcatheter aortic valve replacement and practice inserting it correctly.


>250,000


Deaths caused by medical error in the US, the third- leading cause. BMJ


“It’s about improving outcomes for patients. You can try surgeries where the surgeon would previously have looked at the scan and thought, ‘No, we can’t do that’. It just opens up more options, more possibilities and greater survival rates for more people.”


Richard Arm


“As a medical device, this resonates with people because you don’t have to ask them to imagine printing it on to their wrist or whatever in 20 years’ time,” says McAlpine. “It’s a low-hanging fruit for 3D printing. It’s not implantable, so you don’t have to worry about getting all the approvals, and we’re not trying to print biological material, so we don’t have to keep cells alive. It’s an aid that can be printed pretty much on the fly now for anyone to use. That’s the advantage. This is something that you can put right in the hands of doctors now.” McAlpine’s next goal is to trial some of his team’s models in a large-scale patient study and see precisely how they impact outcomes, but their relevance to surgical practice is already clear. Just recalling the first time one of his team’s liver models was put in front of a surgeon, Arm’s voice


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