The present and future role of 3D printing in medicine

By Samara Macrae

Published 11:23 EST, Weds October 13th, 2021

Introduction:

3D printing, also known as additive manufacturing, is a process that holds enormous potential – and is not only currently used in medicine, but it will undoubtedly continue to revolutionise this field in the future. The process of 3D printing began in the 1980s, and this technology has been implemented into various areas of medicine – for example, medical imaging apparatus can often be fed into a 3D printer to form a physical model of the digital image. In 2016, the use of 3D printing in medicine was valued at $713.3 million, but this is predicted to rise to $3.5 billion by only 2025¹.  Within the field of medicine, 3D printing can additionally be used to produce implants as well as in bio-printing. Other major applications of 3D printing in medicine include producing artificial human organs for transplants and making surgical procedures faster and more efficient.

How does 3D printing work?

To begin with, before a physical 3D model can be created, a graphic model has to first be designed. This can be done using programs such as TinkerCAD and Fusion360. This digital model then needs to be ‘sliced’ in order for the printer to process the designs for the many layers – as it cannot fully conceptualize a 3D model in its entirety. This process is called ‘slicing’². Once divided into layers, the design for each individual layer is fed into the printer, typically via a USB stick or can be done wirelessly. This is an example of an additive process, which is where a 3D object is created through placing many layers of material on top of one another. Each layer is a cross-section of the 3D object that has been created. 3D printing began as creating prototypes but has escalated into large-scale manufacturing due to how rapid the process is compared to other forms of industrial production.³ Manufacturing using a 3D printer can also be cheaper, as iterations are easier and there is no need for expensive tools nor high labour costs to manage the machines. 3D printing is utilized extensively in the car manufacturing industry, in order to produce individual vehicle parts on demand and en-masse. 3D printing is used in a multitude of other industries, including aviation and consumer products, such as eyewear and footwear.

Bioprinting and organ transplantation:

Bioprinting is a process similar to 3D printing, as it is an additive manufacturing process through which cells and other biomaterials are ‘printed’ to create biological structures in which living cells are able to divide and multiply⁴. The cells used to create complex bodily structures – such as skin, bones, and other organs – can be extracted directly from a patient. Adult stem cells can also be used, and they are cultivated into a bioink; this is a material used to produce artificial living tissue via 3D printing. Bioink can consist solely of the cells but can also contain a carrier material – typically a biopolymer gel. This will provide a 3D framework which the cells are able to attach to and spread out as they multiply⁵. The result of this scaffolding being in place means that the cells can be moulded into the desired shape. 

Bioprinting is a technique that is being researched currently, and Swansea University in the UK, has recently developed a bioprinting process⁶ by which bone matrix can be artificially produced using a regenerative biomaterial. This material is comprised of calcium phosphate, polycaprolactone, gelatine, agarose, and collagen alginate. This can potentially be used to correct severe and complex bone fractures, where otherwise the missing or damaged bones would be replaced with synthetic materials. This is part of the surgical procedure known as ‘bone grafting’. If the 3D-printed bone matrix is used instead, over time it will fuse with the patient’s bones and result in greater strength, compared to when synthetic materials would have been used instead.

In addition, the prospects of bioprinting extend further: for instance, the development of artificial corneas. Globally, there were approximately 12.7 million people in 2013 awaiting a corneal transplant, with 7 million of these individuals in India alone⁷. ⁸ In South Korea, in 2019, there were approximately 2000 people requiring a cornea donation – and the average wait time for surgery there is 6 years. This is due to the lack of cornea donations in the country as well as the problems associated with the current synthetic corneas available. These synthetic corneas are made from recombinant collagen or other chemical substances, like synthetic polymers, and one predominant problem with them is the fact that they are not always transparent after being implanted. This is due to the present inability to synthetically replicate the natural structure of the cornea being that of a lattice of collagen fibrils, which affects its transparency.

⁸However, a research team at the Pohang University of Science and Technology in South Korea, in conjunction with researchers at the Kyungpook National University School of Medicine also in South Korea, have worked to 3D print a cornea. This was done using a tissue-derived bioink, and this meant it is biocompatible with an individual’s eye. Bioprinting was utilised to create this artificial cornea in such a way that its transparency is akin to that of a natural human cornea. The joint research teams noticed, while working to develop a 3D printed cornea, that the collagen fibrils which were produced by the process of 3D bioprinting were similar to the lattice pattern found in human corneas.

⁹In other areas of bioprinting, the accomplishment of developing artificial organs suitable for transplantation remains a more futuristic hope. An example of this is a research project using 3D bioprinting of stem cells in order to create artificial, biocompatible kidney tissue. This research was led by the Murdoch Children’s Research Institute (MCRI) in Australia, alongside the American biotech company, Organovo. A 3D bioprinting process was used, in which a bioink created from stem cells was formed, and this produced an artificial kidney approximately the size of a human fingernail. Despite the small size, these bio-printed kidneys did contain very similar structures to human kidneys – including having nephrons and the division between the cortex and medulla being identifiable. While the research needs to continue to create artificial kidneys suitable for human transplantations, these kidneys are still functional for drug testing, predominantly for toxicity, instead of animal testing. Professor Melissa Little from the MCRI stated: “The pathway to renal replacement therapy using stem cell-derived kidney tissue will need a massive increase in the number of nephron structures present in the tissue to be transplanted.” This shows that the research is auspicious but requires considerably more time and effort.

The use of 3D printing in surgery:

3D printing is currently in use for many surgical procedures, and this will continue to increase as this technology develops. An example of this is using 3D printing to create patient-specific implants (PSIs) which are the exact complementary shape for the patient. For example, ¹⁰craniomaxillofacial reconstruction implants, which are used predominantly in head and neck surgery. These implants have to be bent into shape during surgery, which is time-consuming and is likely to place unnecessary stress on the implant as it has to be bent multiple times. In an article published in ScienceDirect entitled ‘A Systematic Approach for Making 3D-Printed Patient-Specific Implants for Craniomaxillofacial Reconstruction’¹⁰, the researchers discuss how they have devised an approach to this form of surgery, which has resulted in 41 successful surgeries using patient-specific implants which have been 3D-printed. This approach begins with using SolidWorks software to create a graphic design model to then print. The 3D-printed product undergoes a series of treatments – including heat and tension treatments – before being sterilised. The implant is then used in the surgery, and this article furthermore states that the use of these 3D-printed patient specific implants “reduces surgery time and shortens patient recovery time”.

A specific example of the use of 3D printing patient specific implants is a lower jaw implant, which was created for a child in China in 2018¹¹. This child had a mandibular tumour in his lower jaw which, if removed, would cause a severe facial malformation. However, this child needed to have this tumour removed as he struggled greatly with tasks such as talking, eating, and even opening his mouth. This led to him undergoing a surgery in which the tumour was removed, and the part of his lower jaw which was also removed was replaced using a titanium alloy implant. This implant had been 3D printed, using models of the child’s jaw, in order to create a patient-specific implant for him.

A further example is the use of a 3D printed patient-specific implant of an ossicle, in 2019. This implant was made, again, of titanium, and replaced the ossicles of the patient – as they had been damaged during a car accident and led to the patient losing their hearing. The medical team carrying this innovative surgical procedure was led by Professor Mashudu Tshifularo, a professor at the University of Pretoria in South Africa. As a result of this work, the patient’s hearing was restored¹¹. This 3D-printed middle-ear replacement surgery was the first in the world, and according to the news platform ‘Good Things Guy’, Professor Mashudu Tshifularo said: “By replacing only the ossicles that aren’t functioning properly, the procedure carries significantly less risk that known prostheses and their associated surgical procedures”¹².

Conclusion:

To conclude, while the technology of 3D printing in medicine can certainly progress in the future, it is still in use and being researched further currently. The promising nature of this process means that surgical procedures can continue to develop, becoming safer and more time-efficient, and there are the hopes of artificially creating biocompatible tissues and organs. This could revolutionise organ transplantation – not only reducing waiting times but additionally decreasing the risks of rejection. Furthermore, this technology could mean that implants are a better fit for the patient – as hip and knee replacements are some of the most common surgical procedures performed worldwide. The research for this technology is boundless and is one of many examples of computer technology merging with, and arguably, dominating the field of medicine in order to improve every aspect of it.

Samara Macrae Youth Medical Journal 2021

References:

1. Medical Device Network: “3D printing in the medical field: four major applications revolutionising the industry” – https://www.medicaldevice-network.com/features/3d-printing-in-the-medical-field-applications/
2. Interesting Engineering: “How Exactly Does 3D Printing Work?” – https://interestingengineering.com/how-exactly-does-3d-printing-work
3. 3DPrinting.COM: “What is 3D Printing?” – https://3dprinting.com/what-is-3d-printing/
4. Cellink: “Bioprinting Explained” – https://www.cellink.com/blog/bioprinting-explained-simply/#:~:text=Bioprinting%20is%20an%20additive%20manufacturing,that%20let%20living%20cells%20multiply.
5. All3DP: “What Exactly is Bioink?” – https://all3dp.com/2/for-ricardo-what-is-bioink-simply-explained/#:~:text=Bioink%20is%20the%20material%20used,as%20a%203D%20molecular%20scaffold.
6. Medical device Network: “The future of bioprinting: A new frontier in regenerative healthcare” – https://www.medicaldevice-network.com/features/future-of-3d-bioprinting/?utm_source=Army%20Technology&utm_medium=website&utm_campaign=Must%20Read&utm_content=Headline
7. JAMA Network: “Global Survey of Corneal Transplantation and Eye Banking – https://jamanetwork.com/journals/jamaophthalmology/fullarticle/2474372
8. Medical Device Network: “3D-printed artificial corneas could replace donor transplants” – https://www.medicaldevice-network.com/news/3d-printed-corneas/
9. XINHUANET: “Aussie research on bioprinting mini kidney raises hope for lab-grown transplantation – http://www.xinhuanet.com/english/2020-11/24/c_139540203.htm
10. ScienceDirect: “A Systematic Approach for Making 3D-Printed Patient-Specific Implants for Craniomaxillofacial Reconstruction” – https://www.sciencedirect.com/science/article/pii/S2095809920302794#:~:text=Patient%2Dspecific%20craniomaxillofacial%20reconstruction%20implants%20are%20made%20using%20a%20selective,quality%2Dcontrol%20procedure%20is%20needed.
11. 3Dnatives: “Top 12 3D Printed Implants” – https://www.3dnatives.com/en/best-3d-printed-implants-230720195/#!
12. AFROTECH: “Mashudu Tshifularo Makes History By Performing World’s First 3D-Printed Middle-Ear Transplant” – https://afrotech.com/mashudu-tshifularo-makes-history-by-performing-worlds-first-3d-printed-middle-ear-transplant

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