3D printing is a promising new technology that has the potential to revolutionise medicine. Many non-invasive uses for 3D printing in urology have been explored ranging from surgical simulation (14–17), histopathological correlation (18, 19), augmented reality surgery (20, 21) and anatomical models (5, 6, 22–25). However, the next frontier in 3D printing research is the development of clinically useful 3D printed equipment, tools and implants. Oft-quoted low cost FDM 3D printers costing USD 300 suggest low barriers for this goal. To that end, some have begun exploring whether 3D printing could be used to create basic surgical equipment (8, 9). However, many clinicians are unaware of the limitations of low cost FDM 3D printing and the strengths of conventional manufacturing techniques.
Whilst FDM printing can be low cost and accessible to hospitals around the world, the quality of the parts produced may not be mechanically consistent enough, particularly in healthcare where standards of safety are high. To produce higher quality parts, the setup cost of a 3D printer or machine will be much higher such as the SLS printer used in this study which costs approximately USD 175,000. It is therefore unlikely that individual institutions will be able to use low cost FDM 3D printing to manufacture devices in-house at a quality that is clinically safe and reliable.
One of the difficulties in designing this study was the lack of data on what threshold of mechanical strength would be needed. Although the use of intermittent self-catheterisation to prevent stricture recurrence is established in the literature (26), most studies are focused on dilatation using long urethral catheters rather than the short meatal dilator in our study. In fact, the literature on meatal dilators is extremely limited (13). Therefore, our design aims to stress the dilator at its weakest point, although this may not occur in clinical practice. Based on clinical experience we are confident that the SLS dilator not breaking even at 5,000 g of force is sufficiently safe for clinical use. Even the horizontal ABS dilator which could take 500 g of weight and only failed at a 40 degree bend would likely be safe as a patient is unlikely to bend the dilator to that angle during use in the urethra. If a portion of the dilator did snap it would need to be retrieved via flexible cystoscopy by a urologist under local anaesthetic with overall minimal morbidity to the patient.
The strengths of 3D printing are in the creation of patient-specific parts, manufacturing complex parts which conventional methods cannot achieve, or prototyping. Despite the enormous potential of the technology, 3D printing should not be viewed yet as a replacement for conventional manufacturing techniques. This is especially true for parts needed in high quantities with simple geometry such as the dilator. For example, the quoted unit price of five machined steel dilators is around USD 98, but the unit price if ordering a quantity of 1000 becomes around USD 30. It is also worth noting that with modern machining parts with simple geometry such as the dilator can also be made to be patient-specific, particularly with the aid of computer numerical controlled (CNC) machining (27).
In the urological field, Park et al (28) used 3D printing to create a ureteric stent prototype which prevented reflux in vitro. This is a valid use of 3D printing to prototype a part in small quantities. However, if such a prototype entered mainstream use then 3D printing would not necessarily be the best method to continue production. Del Junco et al (29) tested 3D printed ureteric stents and laparoscopic trochars in porcine models and concluded it was feasible, despite the initial functional failures they described and with no discussion on cost.
3D printing in medicine has perhaps advanced the most in the field of orthopaedic surgery. 3D-printed acetabular cups demonstrate the strengths of 3D printing that we have discussed as they can be patient-specific but also they are highly porous to encourage bone ingrowth which conventional manufacturing cannot achieve (30), however the long term outcomes remain to be seen.
Our study is one of the first to examine the practicalities of using 3D printing techniques to produce low risk clinically applicable medical devices such as the urethral meatal dilator. Whilst many clinicians may be aware of how low cost 3D printing can be, we hope to show that there are limitations to this technology. 3D printing medical research should not seek to replace all conventional techniques in producing simple devices but instead capitalise on the advantages of 3D printing in creating complex geometries or patient-specific parts. To our knowledge, this is also the first project to investigate a method for mechanically testing the strength of urethral dilators.
In this study we have compared different materials as well as different manufacturing methods. This was necessary due to the practicalities of each method, for example low cost FDM printing cannot be used to 3D print in metals. We have performed relatively simple mechanical testing which would be suitable for a low risk device such as a meatal urethral dilator. However, higher risk devices that are required to be sterile would need more rigorous testing. Any discussion around cost is likely to change in the future as 3D printing technology continues to evolve and become cheaper and more accessible. Our quoted prices are from single commercial sources which should be taken as approximations only, valid at the present time (2019).