Printing fixes

Materials World magazine
1 Aug 2018

In the coming years, we’ll see more prosthetics, implants, organs, and drugs become bespoke to individuals, and 3D printers are set to democratise healthcare across the world. But is this technology being over-promised? Anna Ploszajski investigates.

3D printing is a catch-all term for additive manufacturing techniques that build up a three-dimensional model under computer control. The majority of people will be most familiar with the fused deposition modelling method of 3D printing, where liquid material is extruded through a robot-guided nozzle to build up a 3D object layer-by-layer. However, many variants of 3D printing exist. The most common in biomedicine is the selective laser sintering (SLS) type, which selectively fuses a bed of powdered material using guided lasers, and inkjet printing, in which material is sprayed in a jet layer-by-layer to make up the pre-programmed shape. 

From aerospace to virtual reality, these techniques have already found application in a great number of sectors, and biomedicine is no exception. This boils down to one compelling reason, immortalised in Monty Python’s The Life of Brian – ‘We’re all individuals’. This is because 3D printing is especially good for making personalised, small runs of components. Assuming the computer modelling process of the desired object is well executed – a big assumption, particularly in the prototyping phase – it can be faster, cheaper, and generate less waste than alternative manufacturing methods. What’s more, doing away with having to re-shape standard-sized implants can reduce surgery times, ultimately increasing the standard of care for patients.

An open book

The other major benefit that 3D printing can bring to biomedicine is its ethos. The surrounding community is open and sharing, a philosophy brought to the table by its major followings in the hobbyist and maker movements. Open-source software and hardware form the backbone of the industry. Not only can doctors and researchers share knowledge and collaborate across geographical and institutional boundaries, but makers, engineers, crafters, and even garden shed enthusiasts can meaningfully contribute to emerging biomedical technologies. For example, MakerBot’s is a popular online design community, and features an open-source 3D printable umbilical cord clamp, which was reportedly used successfully in Haiti. 

However, open-source technology comes with its own challenges – government agencies have to act fast to keep up with regulation, intellectual property rights, quality assurance, and legal liability issues. Liability when 3D printing goes wrong is a rather grey area, and is considered on a case-by-case basis. 

Making the law more transparent with regards to 3D printing in biomedicine would certainly benefit its development.

Inside and out

The most successful area of 3D printing in biomedicine so far has been in implants and prosthetics. If you wear a hearing aid that sits inside the ear canal, the chances are it was 3D-printed, and similarly for the gumshield-type transparent orthodontic braces. These external components can be designed using simple 3D scanning technology. 

For internal components, routine imaging techniques such as MRI and CT scanning have allowed doctors to construct highly personalised pieces such as dental, hip, tracheal, and spinal implants. SLS printers can easily handle biocompatible metals like titanium, and bioactive substances like hydroxyapatite, such that porous bone implants may be produced that actively promote osteointegration to ensure the best mechanical and biological bond between implant and patient.

But these implants can be taken one step further. Today, there are around 6,400 people in the UK who are waiting for a potentially life-saving organ transplant, according to the NHS, and experts predict that 3D printers could reduce waiting times in the coming decades. By inkjet printing layers of living cells, or seeding stem cells onto 3D-printed scaffolds, organs, and tissues can be built up for transplant. So far, ears, spinal disks, and heart valves have been successfully grown. In future, a person’s stem cells could be harvested from their baby teeth and kept in a central repository to be accessed at any time during their life, should they require a new 3D-printed organ. 

It has also had a massive impact on surgery. 3D-printed replicas from scans of complex cases have allowed surgeons to practice before a procedure, and the same computer aided design files can be used indefinitely to benefit other surgeons and teaching practices all over the world. However, this does raise questions about rights to privacy of this very personal data.

In surgery itself, non-invasive 3D scans of burn victims could allow robots to map and then 3D-print healthy skin cells directly onto the patient – such a system is currently in pre-clinical trials. The debate over whether this is a good idea or not seems similar to that of driverless cars – safety could perhaps be improved by eliminating human error. 

The human body is, however, a complicated system that requires many intricate parts to function correctly. This can prove a problem for artificial organs and other implants.

The tricky stuff    

One barrier to printing more complex organs has been achieving adequate blood vessel networks. Without proper vasculature, the thickness of tissue that can be printed, and stay alive, is limited by the distance that oxygen can diffuse through to the living cells – about a millimetre. The challenge is to successfully mimic the multilayer composite structure of blood vessels, ensuring they have exactly matched mechanical and biological functions as the real thing, and also to print the required complex 3D structure. Work in this area is ongoing. 

This plays into one of the major difficulties in the field – managing unrealistic expectations from patients and practitioners on how far 3D printing technology can take us. There will always be limitations on the materials and geometries, which are possible using 3D printing 

techniques, but some are sceptical that we will ever be able to print organs as complex as a human heart. 

It raises moral and ethical questions, too. Researchers ask themselves, how would a 3D-printed heart know how to beat? Even if we could eventually print all parts of the body, would such an assembly of living tissues and organs actually be able to live? Would it be human? 

Aside from implants a transplants, less intrusive treatments such as pills can also benefit from the implementation of 3D printing.

Pills and systems

Advances in genomics are paving the way towards increasingly personalised drugs, and 3D printing can offer a complimentary technology to give doctors more control over their prescriptions. It can produce intricate structures down to micron resolution, and at these scales, the structure of pills or other drug delivery systems can be used to dictate the drug delivery profile.

What this means in practice, is this. Whereas a conventional pill may provide a spike in drug levels that falls exponentially over time, a printed pill could steadily provide just the right amount of drug over a more prolonged period. Alternatively, it could release a series of different active ingredients at pre-determined time intervals after swallowing, all depending on how the 3D-printed structure gets broken down by the body. 

3D printing may also have a part to play in the manufacture of drugs. Researchers at the University of Glasgow, UK, led by chemist Leroy Cronin, are developing so-called reactionware. This involves a series of 3D-printed reaction vessels that, by simply adding the correct starting compounds can synthesise a variety of drugs by processes such as filtration, evaporation, and mixing, which happen in pre-programmed succession. However, the implications of this technology for creating a generation of budding Walter Whites, who synthesised methamphetamine in TV drama Breaking Bad, are obvious.

Given the huge potential, yet very real limitations of this technology, what might the future of 3D printing in biomedicine look like? Many experts predict that it will become more commonplace in hospitals and pharmacies – North Manchester General Hospital already has its own 3D printing laboratory – and perhaps simple procedures could one day be carried out by domestic machines from the comfort of our own homes. But, with 3D printing already making waves in the fields of wearable tech and soft robotics, it could be a tool that increasingly blurs the line between humans and machines. For example, scientists at Princeton University, USA, have developed a 3D-printed bionic ear that can hear frequencies beyond the range of normal human hearing. 

Incorporating 3D printed components with electronics is already changing the lives of amputees for the better, but it could also change what it means to be human.