Application of Three-Dimensional Printing for ...

3D Printing and Anaesthesia Education “The application of Three-Dimensional (3D) printing technology for Anaesthesia: A Narrative Review” Authors Ian Chao1,3, Jeremy Young2, Jasamine Coles-Black6,7, Laurence Weinberg3, Clive Rachbuch1, Jason Chuen4,5,6

1 Department of Anaesthesia, Box Hill Hospital, Eastern Health, Melbourne, Australia. 2 Department of Anaesthesia and Acute Pain Medicine, St Vincent’s Hospital, Melbourne, Australia. 3 Department of Anaesthesia, Austin Health, Melbourne, Australia 4 Department of Surgery, The University of Melbourne, Parkville, VIC Australia. 5 Department of Vascular Surgery, Department of Surgery, Austin Health, Melbourne, Australia 6 3D Medical Printing Laboratory, Austin Health, Melbourne, Australia 7 Research Platforms, The University of Melbourne, Parkville, VIC Australia Correspondence to: Dr Ian Chao ([email protected]) Short Title: 3D Printing and Anaesthesia Education Keywords: upper airway anatomy, L-spine: radiologic anatomy, Spinal anaesthetics: anatomy SUMMARY 3-Dimensional (3D) printing has in recent times rapidly become an easily accessible, innovative, and versatile technology with a vast range of applications across wide ranging industries. There has been a recent emergence in literature relating to its application across a multitude of fields within Medicine and Surgery, especially as the technology becomes more accessible to clinicians. However specific to Anaesthesia, this has yet to be formally explored. We therefore wish to briefly introduce this technology to the reader by discussing the background of the development of 3D printing technology and its application in other fields of medicine, identify what we see as a current paucity of literature specific to 3D printing and Anaesthesia, and pose the potential untapped possibilities of 3D printing specific to Anaesthesia and anaesthetic education.

3D Printing and Anaesthesia Education INTRODUCTION

3-Dimensional (3D) printing, also known as Additive Manufacturing, is a rapidly developing manufacturing process in which a three dimensional solid material object is created from a digital image. This can be done via a number of methods, utilising various print mediums. The most common and readily available technique is known as “Fused Deposition Modelling” (FDM), whereby a plastic polymer filament is extruded via a heated nozzle onto a print platform. Here, the plastic instantly cools down and solidifies, with further deposition of layer upon layer, thus building up a 3D object. Complex models are created by printing additional support structures within or around the planned object to form struts, which are easily removed once the plastic model has finished printing. The plastic mediums most commonly used include “thermoplastics” such as Acrylonite Butadiene Styrene (ABS) - the same polymer used to form LEGO® Bricks - and the biodegradable Polylactic Acid (PLA) as used in biodegradable plastic cups. Newer polymers with different flexibilities and hardness are currently exploding onto the market as consumers explore the potential uses of 3D printing - an example being flexible thermoplastic polyurethane (TPU) or Carbon Fiber Reinforced Filament. Other more costly, and complex means of 3D printing include Selective Laser Sintering (SLS) and Stereolithography (SLA). SLS utilises a laser to fuse materials such as powdered metal at defined points in space as dictated by the 3D print. SLA uses ultraviolet laser to solidify a liquid photopolymer resin. The focus of this paper will deal predominantly with FDM printers, more within the reach of everyday consumers. 3D printing has proven to be an exciting and revolutionary technology in industries outside of medicine, with applications in areas ranging from manufacturing, design, engineering, and art. Development of the technology since its inception in the early 1980’s has seen rapid innovation, and since the expiration of patents in 2009, what initially began as technology available only for multi-million dollar industry and commercial applications, has now led to affordable, desktop size, low cost printers for personal use. 3D printers that originally cost $20,000USD are now priced under $2000USD, thus welcoming the birth of the consumer 3D printer.

Specific to medicine, certain subspecialties have begun to embrace 3D printing. Surgery tops the list of applications for use of 3D printing.1,2 Uses include preoperative surgical planning in maxillofacial surgery3-6, neurosurgery7, orthopaedics8, plastics and reconstructive surgery9,10, general surgery specifically hepatobiliary resection,11,12 and cardiothoracic surgery13,14 Other uses include the printing of orthopaedics prosthesis,15,16 teaching through use of 3D printed anatomical models,18-21 and for patient education purposes22,23. As the

3D Printing and Anaesthesia Education technology becomes more accessible and affordable, the ability to tinker with the technology is now within reach for most hospital departments. There has yet to be any formal literature review on 3D printing directly related to the field of Anaesthesia. We therefore performed a narrative review of the current literature, and further investigate potential future applications of uses of 3D printing within the field of Anaesthesia. METHOD We performed a literature search for pertinent articles using the Medline, PubMed, Embase, CINAHL, and Google Scholar databases. Minimal search limitations were included to ensure capture of all potentially relevant articles, though only included publications in English, availability of an abstract, and search period between 1990 and June 2016. Initial search containing variations of combinations of the terms “Printing, three-dimensional; 3Dimensional Print/printing; 3D/3-D Printing; Rapid Prototyping; and Fused Deposition Modelling” combined with variations of the terms “anaesthesia; anesthesia; anaesthetics; anesthetics; or anaesthesiology” identified a possible 34 articles from the 5 databases once duplications were excluded. Of these, each abstract was independently screened by each investigator to identify relevant studies, with many spurious results quickly dismissed. Many articles dealt with intraoperative use, and 3D printed anatomical models for medical student and trainee education. If there was no direct relevance to anaesthesia, they too were excluded.

RESULTS

Of closest direct relevance regarding 3D printing in the field of anaesthesia, merely 8 articles were identified24-31, which will be discussed in detail. In 2015, Wilson et al describe a situation where 3D printing was used to produce a representation of a paediatric patient’s airway, to assist in preoperative sizing and practice in inserting airway devices to achieve one lung ventilation prior to surgery.24 The model was printed on a SLA printer, in a clear, rigid resin, and allowed trial to find the most suitable size and method of placing side by side tracheal and bronchial tubes prior to the patient’s operation. Han et al experimented with 3D printing an airway representation of a patient following total laryngectomy for use in preanaesthesia planning, using a desktop FDM printer, with a final airway model in ABS plastic.25 Both cases employed the use of the commercial software Mimics (Materialise, Leuven, Belgium). Both noted that their models were of hard plastic which may not represent

3D Printing and Anaesthesia Education the flexibility of human tissue, but felt was adequate to achieve their desired results. Zopf et al described the successful use of a commercial SLS 3D printed bioresorbable airway splint.26 The design was engineered specifically for a premature infant born with localised tracheobronchomalacia. Emergency FDA approval for use was obtained and the stent was deployed to maintain patency in the collapsed bronchus. At one year follow up, the bronchus remained patent, and the stent was estimated to be fully absorbed within 3 years. This case required the use of specialised commercial 3D printing software, hardware and print medium. Likewise, Cheng et al presented a similar approach in adults whereby 3D printing was used to create moulds sized from patient CT scans, upon which silicone based implantable airway stents were produced for treatment of tracheobronchial stenosis.27 In terms of uses for education and training, West et al developed an 3D printed spinal column for the purpose of using it as an ultrasound teaching phantom.28 The creation involved utilising commercially available software program to recreate the 3D model based on patient CT scans, and then printing on a FDM printer. They then immersed the model in a gelatinous medium to produce their trainer. Side by side comparisons with real time ultrasound of human lumbar regions showed similar sonographic images. Bustamante and Shravan published a short piece discussing the theoretical possibility of printing bronchial tree anatomy for the purpose of double lumen tube placement for both teaching, and surgical pre-planning, and had suggested this could potentially be achieved in under 20 hours with the right software and 3D printing hardware.29 This concept was based on a prior publication by Bustamante et al where a bronchial tree replica model was produced with an SLA printer.30 The cost of their model was quoted at $250USD. Byrne et al similarly created a bronchoscopy trainer by modelling a normal adult airway up to tertiary bronchioles using a desktop FDM printer which showed good fidelity for the purpose of teaching bronchoscopy to Respiratory Physician trainees.31 Both West and Byrne with their FDM printers discussed lower costs in developing their 3D printed models.

DISCUSSION

We were surprised at the scarcity of anaesthesia specific literature pertaining to 3D printing, given its presence in other medical subspecialties. Currently here in Melbourne, Australia, we have formed a multidisciplinary working group of clinicians with interests in 3D printing technology to explore ways whereby this technology could be beneficially utilised. Specifically, in the field of anaesthesia, our working group felt that there existed a multitude

3D Printing and Anaesthesia Education of potential applications for 3D printing. Prominently, the role of this technology to be used for education, became the forefront idea. As mock anatomical models are used commonly in the anaesthesia training, we studied the potential for 3D printing as a means of developing anatomical training models. Some of the benefits we potentially perceived over current educational models on the market are listed in Table 1.

1. Anatomical models based on real patient anatomy, as sourced from real patient DICOM medical imaging files to improve fidelity 2. Long term economic benefit of producing cheap in-house models, compared to purchasing expensive high-end commercial models 3. Ease of replacement of models when damaged 4. Ability to modify models and customise towards the trainer’s needs and expertise 5. Ability to replicate and “mass produce” training models on demand 6. Ability to freely share .stl files for printing pre-designed models 7. Benefits of plastic compared to animal or cadaveric models including issues surrounding ethical use, sourcing, storage, disposal, contamination and infection, reusability, and unpleasantness to use 8. The ability to produce cheap and rapid prototypes for problem solving or as potential inventions Table 1. List of potential benefits of 3D printing for anaesthesia education

Setting up the ability to 3D print was rather straightforward. Consumer Desktop 3D Printers range in price from anywhere as little as under $1,000AUD, to over $10,000AUD depending on the degree of print “resolution” required. At the Austin Hospital, Melbourne, we decided to purchase two mid-range consumer printers (Makerbot Replicator 5th Gen) for circa $5000AUD per printer (Fig 1). The use of taking medical imaging file standards, in Digital Imaging and Communications in Medicine, or DICOM files, and then converting them into a virtual 3D model, known as Stereolithography, or STL file as a blueprint for 3D printing has been well described online, using readily available computer software. Numerous software packages exist on the market, including those that require commercial licences, along with several Open Source (aka freeware) software. To minimise costs, we embraced two Open Source software packages 3D Slicer (version 4.5; Harvard, US, 2015),32 and Meshmaker

3D Printing and Anaesthesia Education (version 3.0, Autodesk, California, US, 2015)33 both freely downloadable from the internet. 3D Slicer allowed good functionality in terms of converting our CT and MRI files from their standard DICOM format into 3D virtual models (Fig 2). These were then further rendered and refined using Meshmixer, a user friendly Computer-aided Design (CAD) software (Fig 3a&3b). To date, we have not been limited by the functionalities of these free programs, and have found benefit of online support forums where guidance and support were readily available. Within a few months of experimenting with the technology, our group has managed to convert real patient CT scans into reproducible prototype models as discussed below.

Fig 1. Our FDM 3D printer: Makerbot™ Replicator 2X

3D Printing and Anaesthesia Education

Fig 2. Screenshot of 3D Slicer (version 4.5; Harvard, US, 2015) demonstrating production of a 3D model (.STL) of a trachea from patient CT imaging (DICOM)

Fig 3a. Finalised .STL image of printable adult trachea in Meshmaker

3D Printing and Anaesthesia Education

Fig 3b. Finalised .STL image of printable Thoracic Spine segment in Meshmaker

Currently we are developing the following prototypes:

1. NEURAXIAL NEEDLING TRAINER Similar to West et al28, we applied our technique of converting CT images of human anatomy, to print segments of thoracic and lumbar spines. Immersing the model within a stable, translucent medium allows for a realistic neuraxial trainer for registrar teaching. The translucency of the medium allows visualisation of the angle and depth of the needle to assist trainees in understanding the need for correct their site and angle of needle insertion, as well as help understanding alternative techniques to a midline approach, such as paramedian insertions.

3D Printing and Anaesthesia Education

Fig 4a. 3D printed Thoracic Spine Segment in ABS

Fig 4b. Neuroaxial Needling Trainer

3D Printing and Anaesthesia Education

Fig 4c. 18G Tuohy with Loss of Resistance to Saline on Neuroaxial Needling Trainer

Financially, the models cost was under $25AUD to produce including all consumables (excluding cost of printer). We are unaware of any similar trainers of equivalent fidelity for a similar price tag.

As with West et al’s model, our model showed similar abilities to be used to teach ultrasound, along with for needling technique.

3D Printing and Anaesthesia Education

Fig 4d. Ultrasounding the Spinous Process of the Neuroaxial Needling Trainer

Apart from use as a neuraxial trainer, we have also considered the potential for 3D printing technology as a means for preoperative planning. Potentially, a patient’s spinal column could be 3D printed in select patients where neuraxial anaesthesia may be presumed difficult. Such examples include patients with advanced degenerative arthritis, previous surgery or metalware such as Harrington Rods, or anatomical abnormalities such as kyphoscoliosis or ankylosing spondylitis. An anaesthetist could therefore theoretically predetermine and plan the most successful insertion site and angle of attack in which to perform a neuraxial procedure, or deem that physically there would be no viable path to accessing the neuraxial space, and therefore decide not to even consider attempting neuraxial blockade. As with surgical planning, the model could be referred to in real time whilst performing the procedure to best understand reasons for difficulty with insertion. This concept has never before been suggested in the literature. 2. SURGICAL AIRWAY TRAINER

3D Printing and Anaesthesia Education Currently for surgical airway training, many institutes including our own, have adopted the use of animal parts to closely replicate the feel of performing procedures on live human tracheas. In terms of fidelity and experience, so far, it appears to be the closest surrogate to live human tissue, and avoids the complexities of accessing human cadaveric specimens. However, even animal parts have problems of sourcing, storage, disposal, contamination, risk of disease transmission, and being unpleasant to use for some participants. They are also labour intensive in terms of acquiring, and cleaning up the specimen for teaching purposes.

We have therefore created 3D printed tracheas based on human CT Neck scans, which we refined initially with ABS Plastic. To more closely mimic the tactile properties of human tissue, we have been exploring printing with flexible TPU medium, and have designed a robust working prototype. Subjectively, we believe this has a similar feel in terms of compressibility and deformity as compared with animal tracheas when penetrated with a needle or scalpel. We are currently completing more in-depth research into how closely this mimics our animal trainers.

Figure 5. 3D printed Tracheas using flexible filament

Again suspending in a gelatinous medium to replicate subcutaneous tissue, will help improve fidelity. Economically, these print for as little as $5USD per model. To compare, our current commercial “Can’t Intubate, Can’t Oxygenate” (CICO) training models cost above $500USD.

3D Printing and Anaesthesia Education Applications not only relate to teaching CICO scenarios within Anaesthesia circles, but also for teaching Critical Care and surgical communities within their own particular workshops.

Because of the ease of customisation with 3D printing, with the ability to refine and mould with our computer modelling programs, we see a potential for these airways to be manipulated for different needs. An example would be to print models of varying adult sizes, as well as to develop paediatric airways to produce paediatric surgical airway teaching models - something currently missing from the market. Our airway models could further potentially be used as a teaching tool for insertion and management of tracheostomies for intensivists, respiratory physicians, and allied health staff involved in care of patients requiring tracheostomies.

By immersing in our gelatinous medium, we can alter the depth of the supposed subcutaneous tissue, therefore further developing “bariatric necks”. A thin layer of our printed plastic polymer provides a realistic flexible layer on top to provide the sensation of skin. Again, the use of ultrasound can be applied in airway training.

3. Tracheostomy, Bronchoscopy and Lung Isolation Trainers

3D Printing and Anaesthesia Education

Figure 6. 3D printed Tracheobronchial tree in ABS

As with Byrne et al, we have printed a bronchial tree from ABS to further corroborate the ease and feasibility put forth of printing anatomical models from CT scans. As bronchoscopy trainers, these have wide reaching implications for trainees of not only anaesthesia and respiratory medicine, but also intensive care, ENT, and thoracic surgery trainees. We are however also exploring the use of our flexible polymer medium to see if this further improves realism. Not mentioned in Byrne’s publication is what we see as a benefit of 3D printing, is that of the ability to model a multitude of differing patient pathologies such as tracheal stenosis or tumours, thereby creating a bank of varying pathologies for teaching purposes. Furthermore, our 3D printed airway models could be used to practice insertion of advanced lung isolation techniques as theoretically proposed by Bustamante, though FDM does have the added advantage of cost, as our models printed for under $1USD, as compared with the higher resolution but more expensive option of SLA printing. Additionally, just as described by Wilson’s24 and Han’s25 group, the idea to pre-plan airway devices in patients with

3D Printing and Anaesthesia Education advanced airway pathologies such as tracheal tumours or stenosis should further be explored.

ECONOMIC VIABILITY

A potential barrier to clinicians exploring 3D printing may be the perceived idea of costs associated with this technology. Certainly, a commercial market exists, and several wellknown professional 3D printing businesses offer to print for medical services. The products are extremely high end, as often they employ SLS and SLA printers outside the reach of most institutes, barring those with affiliations to universities who may have access to such machines. Unfortunately, with these, comes a price tag. We therefore see this option as being out of the reach of most departments in terms of costs involved, with prices ranging from hundreds to thousands of dollars for such printed models, similar to that of currently available traditional plastic moulded training sets. We therefore have focussed our research on desktop FDM printers. Setup as explained includes initial purchase price of the printer, a functional computer to run software, the software itself, and ongoing print medium. FDM printers are reasonably affordable for most, has minimal ongoing costs, minimal maintenance, and extremely cheap consumables with 1kg spools of polymer able to create a large number of models. Though SLA printers are slowing coming down in price, entry level SLA printers still cost around double that of the higher end FDM printers. Furthermore, a standard unit of ultraviolet resin costs up to 10 times as much as that of FDM printers, and produces far less end product. Open Source software again avoids costs with acquiring computer programs, though some may justify the cost of licencing of the commercially available software, with the added benefit of providing customer support. We clearly identify this technology to be an exciting and economically viable option for departments to consider when deciding on how best to provide realistic skills lab training models. We also offer that being based on real patient imaging, our models potentially offer more realism and fidelity than commercial trainers, which often simply teach dexterity and steps of the procedure, at the cost of realism.

CONCLUSION We believe this is the first time to date that the idea of 3D printing directly relating to anaesthesia purposes has been published in the literature. We hope that this inspires others to consider this form of technology as a viable and creative means to provide high quality, high fidelity training phantoms for clinicians and trainees to learn, improve, and maintain

3D Printing and Anaesthesia Education procedural skills at minimal cost. We invite hearing thoughts from other anaesthetists, or critical care specialists having had experience, or interest in exploring 3D printing further in the realm of education, and invite further discussion on the use of this technology. Our ultimate hopes in writing this editorial piece is to help develop this technology so that one day, we are able to provide a bank of freely available, ready to print, downloadable 3D blueprints with accompanying easy to follow instructions so that any teaching department in the world, large or small, has the ability to economically 3D print training models for their trainees, so long as they have access to a computer and a 3D printer. This technology is already within reach to all, and we expect an explosion in interest and ideas in the coming years as this technology rapidly progresses and 3D printers become even cheaper than they already are.

WORD COUNT: 3001 ACKNOWLEDGEMENT

We would like to acknowledge the following people. The Department of Vascular Surgery at The Austin Hospital, Melbourne, for spearheading the creation of the 3D Printing Working Group, for which provided the initial inspiration for developing its use in Anaesthesia.

The team at Research Platforms Services, The University of Melbourne, for training, guidance and troubleshooting with 3D Slicer and Meshmixer software programs, and providing access to the University’s shell terminal to remote run 3D Slicer with greater processing power.

We also acknowledge the developers of 3D Slicer and Meshmixer for their generous provision of their product as Open Source to consumers, and for developing what we feel is a high end product which was central to our ability to create our models

Dr Colin Marsland, Dr Andrew Heard, Dr Louise Ellard, Dr Jon Graham, and Dr Timothy McIver for their advice, expertise, and guidance in developing our airway model prototype, and providing access to the Austin Hospital’s Surgical Airway workshop, animal models, and materials, and Eastern Health’s Simulation Lab.

3D Printing and Anaesthesia Education No conflict of interest has been declared. We have no affiliations with any of the 3D printer manufacturers, suppliers of print mediums, nor software used. Appendix 1. #

Search Statement

Results

1 exp Printing, Three-Dimensional/

754

2 exp Anesthesia/

176053

3 exp Anesthetics/

224614

4 exp Anesthesiology/

29132

5 exp Perioperative Care/

134182

6 exp Perioperative Period/

66596

7 exp Postoperative Complications/

466731

8 2 or 3 or 4 or 5 or 6 or 7

930528

9 1 and 8

36

10 limit 9 to (english language and yr="1990 -Current")

32

11 exp airway management/ or exp injections/ or injections, spinal/ 362745 12 1 and 11

4

Appendix 1. Search string for Embase and Medline. Similar approach for other databases applied.

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