Bionic ears may be more at home in a 1970s TV drama, but have actually been created by bioengineers at Princeton University in the US. They managed to build an ear that can hear radio frequencies far beyond the range of normal human capability. Importantly, they created it in a laboratory, using a 3D printer they’d bought off the Internet.

Making body parts is just one of a multitude of applications of 3D printing being trialled in healthcare today. So far, many kinds of tissues have been printed, and so-called bio printing is of huge interest to healthcare professionals says Dr Ali Khademhosseini, director of the Biomaterials Innovation Research Center at Brigham and Women's Hospital in Boston. “Basically, the application of bioprinting is for regenerative medicine – to make transplantable tissues – but also making tissues outside the body that you can use for drug testing or other kinds of applications,” he said.

3D printers have produced bone, lung tissue and cartilage used to build ears. They have been used to engineer hard-tissue scaffolds such as knee menisci and intervertebral discs, and living skin to help treat and heal severe burns and chronic ulcers, as well as for cosmetic testing. One US company Organovo, is even printing liver and kidney tissue to test new drugs before they are tested in humans.

Dramatic growth

Beyond tissues, 3D printers have been used to create everything from pills to 3D-printed casts. Incorporate pulsed ultrasound to reduce bone healing times is just one example. “3D printing is getting bigger and bigger,” said Dr Khademhosseini. “If you look at hospitals, more and more of them are having 3D printers at the hospital. Particularly over the past five years it’s taken off.”

No surprise then, that the 3D printing market has grown dramatically. Pete Basiliere, research vice president at research firm Gartner said worldwide shipments of 3D printers reached 455,772 units in 2016 – more than double those shipped in 2015. He estimates 6.7 million units will be shipped in 2020.

Once a niche market, 3D printing has continued its rapid transformation into a broad-based mainstream technology embraced by consumers and enterprises around the world, Dr Khademhosseini said. It involves creating a 3D object by building successive layers of raw material. Objects are produced from a digital 3D file, such as a computer-aided design (CAD) drawing or a body scan, such as one produced through magnetic resonance image (MRI). The ink used is anything from biopolymers, such as polycaprolactone, to rubber and even human cells.

The driving force

The gradual layering from a digital file means 3D structures are highly accurate in size and colour. And, importantly, those digital files ensure that the implant is exactly the right size for the body it was intended. So, while much of the 3D printing industry creates identical copies of the same device – like car parts – 3D printers are being used to create devices unique to specific patients. It’s a customisable manufacturing process and that’s the key to success.

Customisation is what has driven 3D printing technology, which was only just emerging in the 80s and 90s said Khademhosseini. “There is the possibility of making devices that are the same dimensions that you need for the patient or can be more functional because they have better way of interfacing with the body,” he added.

Certainly, many hospitals are printing prototype medical devices and implants, which can be altered until they are perfect, at lower cost than other methods. Take bioengineers and surgeons at the University of Michigan in the US and its affiliated CS Mott Children's Hospital, who have been investigating all sorts of 3D-printed devices.

They ended up collaborating to design and make a tiny splint for a baby who could not breathe. He was born without the necessary cartilage to keep his airways open – a very rare condition called severe tracheobronchomalacia. The idea was that the splint would expand the bronchus and give it a skeleton to aid proper growth. Crucially, this tiny implant was created using a scan of the baby, so that it fitted exactly the size of the tiny windpipe, and was made with a 3D printer. And, because it could be made using special materials, it was designed to be gradually reabsorbed by the child’s body so that no further surgery would be needed. His breathing was much better after surgery, said the hospital.

The importance of personalised medicine

Customisation may lead to personalised medicine. 3D-printing pills, for example, enable different pill shapes to be created. Each shape completely alters the drugs’ release rates, research has found. And some researchers are even working on combinations of drugs within the same pill. Precise amounts of individual components could be tailored to individual patients, depending on their needs, they say.

Importantly, customisation is absolutely vital for implants and prosthetics. That’s why 3D printing has been used in everything from cranial plates and hip joints to dentistry. Examples of 3D implants include dental restorative and prosthetic devices such as direct filling resins, dental cements, denture resins, orthodontic retainers, night guards, crowns, bridges, inlays, and inlays.

And, customisation explains why so many hospitals have been buying their own 3D printers from a range of providers including Stratasys, 3D Systems and Formlabs (General Electric Co. and Johnson & Johnson are new entrants too). 3D printers have been used everywhere from the Mayo Clinic in the US to the maxillofacial wing of Queen Elizabeth Hospital in Birmingham, UK, from Italy to India. 

Surgical planning and templates

By far the most widespread use of 3D printing at the moment, however, is surgical planning and templates. Surgeons are effectively customising their surgical procedures to individual patients by using 3D printing to help plan and practice complex interventions. This is not an application for trainees, but for experienced surgeons too, says Professor Shi-Joon Yoo, a cardiac radiologist at Toronto’s Hospital for Sick Children, also known as SickKids, and the department of Diagnostic Imaging, University of Toronto, Canada.

3D printing has become vital in this area because most significant congenital heart diseases require surgical treatment during infancy or childhood. It’s technically demanding because of the wide variation and complexity of pathological anatomy, relative rarity of the individual lesions, and the small size of the heart and vessels, said Professor Yoo.

Surgeons are effectively customising their surgical procedures to individual patients by using 3D printing to help plan and practice complex interventions

But scarily, mortality and morbidity are greatly affected by the congenital heart surgeon’s technical proficiency, as well as the number of surgical cases they’ve been given. The problem is, there also is limited training in such complex cases. “Learning surgical procedures has mostly been based on experience on patients,” explained Professor Yoo. “The major limitations include limited opportunities, patient's risk and limited time available. 3D-print models allow ample opportunity for exploration, repeated rehearsals and modification without the patient's health at risk. So, using 3D image data from CT or MRI, we make a cast and wall models of the heart.” The models help doctors with surgical management decisions and planning. In complex cases, they have an opportunity for surgical practice before beginning work on a patient.

That’s why 3D printers have been used within SickKids for around nine years. Professor Yoo believes this so-called hands-on surgical training (HOST) is necessary and will be a part of the Hospital’s standard training programme for surgeons, and hopefully, will be integrated elsewhere too. And, says Yoo, the hospital benefits in a number of ways. “There are more appropriate surgical decisions, reduced anaesthesia and surgery time, more precise surgical procedures. Although it is not easy to prove what is listed, all add up to better surgical outcomes,” he said.

It’s thought that these surgical planning tools can actually save money. Stefan Edmondson, consultant maxillofacial prosthetist at Queen Elizabeth Hospital in Birmingham, UK, said the ability to produce life-like medical models in-house on a 3D Printer translates to up to £20,000 per surgery in savings, with a reduction in surgical planning time of 93 per cent. He uses such tools for cancer patients who have had a surgical procedure to remove a tumour or bone fragment, and are often left with a space that must be bridged with another piece of bone or material.

Usually, prosthetic plates or bone replacements are routinely used but getting them to the right size can be quite tricky; surgeons often have to make several alterations while the patient is on the operating table. Using 3D printers, however, a precise cutting template of the space can be made in advance. That can be used to create a more precise bone replacement. Edmondson says it cuts down surgery time and risk to the patient too.

Surgical planning is finding applications in cosmetic surgery, too. One company, MirrorMe3D, that was launched by plastic surgeons fed up with working from 2D X-rays, creates 3D models that can be used as surgical guides in advance of surgery. There’s an added benefit, the company says, that patients can see what they might look like after surgery.

Because 3D printing is an additive technology, meaning it is built up molecule by molecule, it is cheaper than traditional creative methods, which involve getting a larger piece of material and chipping, slicing or cutting away – and therefore create a great deal more material wastage.

3D-printed prosthetics

3D printing has proved to be life-changing for many patients requiring prosthetics, because they can be made more cheaply. Take facial prostheses that are usually made for eye cancer patients that have hollow sockets resulting from eye surgery following cancer or congenital deformities. They are created by an ocularist, an artisan who makes a mould of the face, casts it using rubber and then adds the final touches such as skin colour and individual eyelashes. Such prostheses cost up to US$15,000 and take weeks to produce (and are not covered by most medical insurance packages).

But researchers at the University of Miami, US, say they can do the same job on a 3D printer in a fraction of the time and cost. The undamaged side of the face is scanned, software creates a mirror image, and the final image is sent to a 3D printer, which creates an injection-moulded rubber suffused with coloured pigments matching the patient's skin tone.

The next step … is being able to bio-print entire organs such as livers, kidneys and hearts. That would revolutionise, and shorten, organ transplantation lists

The price differential that can be achieved is driving numerous applications. Field Ready prints surgical instruments – from tweezers to scalpels – in rural areas during humanitarian crises, such as after the earthquake in Nepal. And some organisations are attempting to create cheaper limbs for children, who often need many different sized limbs as they grow. Some individual devices can cost as much as $4,000 according to Dr Jorge Zuniga, assistant professor of Biomechanics at the University of Nebraska, US. He has designed a 3D-printed prosthetic hand named Cyborg Beast, complete with movable fingers and he reckons the cost of materials was about $50.

Achievingvascularisation

Similarly, Nia Technologies, a Canadian social enterprise, is working with clinical partners at four sites to create prosthetics for patients in low and middle-income countries – Cambodia, Tanzania, and Uganda so far. Essentially, a residual limb is scanned, creating a 3D model. Nia believes a 3D model prosthetic can be printed from a digital scan in about six hours. Instead of plaster casting, the printer creates a leg from a plastic polymer called polypropylene.

But while these 3D innovations proliferate, so has the focus of regulatory bodies, such as the US’s Federal Drug Administration (FDA). Many have started to approve certain 3D-printed items – from pills to implants – for critical processes and issued guidance to ensure these new inventions are both effective and safe.  

The next step, then, is being able to bio-print entire organs such as livers, kidneys and hearts. That would revolutionise, and shorten, organ transplantation lists says Khademhosseini, whose work centres on these much more complex structures that incorporate matrices of tiny blood vessels and nerve cells. This complexity, called vascularisation, will enable organs to be printed for implantation in humans. But nobody has managed to achieve this goal yet. This is the future, he says, but still many years off. “For simpler ones, like bone and skin-related structures, people are more at the clinical or close to pre-clinical stage. But for some of the most complex structures, this is definitely preclinical,” he said.