3D printed liver models for preoperative planning

3D printing a cost-effective, personalized liver model for preoperative planning

3D printing for preoperative planning offers great benefits in the medical field. However, due to the high costs of industrial-grade printers, not to mention difficult-to-obtain software, it isn’t widely used. Together with a team of researchers at Jagiellonian University, Jan Witowski has discovered how to create models of human livers for use before complex surgeries using a desktop 3D printer.

Preoperative models (or pre-surgical guides as they’re sometimes known) are particularly helpful in procedures requiring accurate anatomical visualization. They’re considered superior to standard imaging techniques, and offer several benefits, such as shorter operative and recovery time, reduced blood loss and better resection margins.

The challenges doctors face

When performing a laparoscopic resection on the liver, it’s important to be able to see where the tumor is and where nearby vessels are located. This reduces the risk of excessive blood loss during surgery.

It’s a minimally invasive procedure, and surgeons are keen to explore new ways to improve the preparation for the operation. However, based on the most recent literature review, there were only 10 incidences worldwide where doctors were using 3D printing as part of their preparation process. The big question is – what exactly is deterring them from using this technology?

Preoperative planning with 3D-printed liver models

As Witowski identified in his paper, traditionally, the main factor putting surgeons off from using 3D printing was cost. Industrial-grade printers cost over $200,000, and few medical facilities have staff with the expertise to use them. Additionally, software for segmentation costs thousands to use – and these are all costs that few practitioners are willing to take on. Until recently, most liver models were created using material jetting (Polyjet/Multijet), which cost up to $5,000 per model.

Another important factor deterring surgeons from embracing 3D print technology was time. It would take around four to seven days to develop a model using an industrial-grade 3D printer. Outsourcing took even longer.

Witowski also highlighted the fact that SLA and SLS weren’t suitable, as surgeons would lose the ability to visualize the parenchyma (the external shape of the liver). He made it his goal to offer an alternative, using an FDM printer and silicone – reducing manufacturing to a fraction of the price, while preserving all the details required to improve the surgical procedure.

Using Ultimaker 3D printers to create liver models

3D printing a liver model using a desktop 3D printer reduces the process to around 60-100 hours in total. It was also considerably lower in price. Witowski illustrates how it works using a case study.

The 52-year-old female patient in question first had a laparoscopic colorectal resection, then two years later, underwent a laparoscopic right hemihepatectomy (a second liver resection), after her follow-up CT scan showed a single metachronous metastasis.

Her CT scans were used to get a clear visualization of their anatomical structures, then virtual models were transformed into an STL file and 3D printed. For this, Witowski used Blender, Meshmixer and Ultimaker Cura and an Ultimaker 2+ 3D printer.

Cost-effective 3D-printed medical models

Model development phases

The model development consists of four key phases: object segmentation, 3D model computer processing in common view, slicing and printing, then finally, finishing and assembly with silicone curing.

The total printing time ranges from 60 to 100 hours, depending on the model size, number of parts, printing accuracy and type of printer used. In this instance, the print took 72 hours and was executed in six print jobs, due to interchanging material and build plate dimensions.

Post-processing was important, to maximize the smooth qualities of the silicone surface and prevent cloudiness. The model was sanded using 100-300 grit sandpaper, then washed with water and dried. It was then coated with XTC-3D, a self-leveling resin. Every part was coated, then left to cure for around three hours until the resin had dried, then the process was repeated to ensure the surface was smooth enough for silicone casting.

Multi-part structures were glued together using a common cyanoacrylate-based adhesive, then protected with insulating tape and plasticine in the connected areas. This prevents silicone leakage during the casting phase.

Results

Thanks to Ultimaker, Witowski was able to create a transparent, full-sized liver model, complete with visible vessels and colorectal metastasis, for under $150. This was achieved using a combination of 3D printed models and molds for silicone casting.

Desktop 3D printers like Ultimaker can be placed immediately in the hospital, and produce physical models of patient anatomy in a matter of hours or days. This allows surgeons to touch and feel the model, making the process of planning the surgery more realistic.

Jan concludes: “I chose Ultimaker because of its reliability. I need to have a printer that won’t fail me when I am printing several 20+ hour print jobs day after day. I truly believe that using low-cost printing is a huge step towards personalized medicine. I’ll definitely continue using Ultimaker, especially for high-impact projects where I need to be sure to provide results on time.”

3D printed liver model example
3D-printed visualisation aids

Costs and timing

Models created using traditional techniques were estimated as costing around $1,000 for a liver model and $500 for a kidney.

Fabrication methods
Cost comparison between fabrication methods

Labor costs and costs associated with 3D printer operation were neglected, as Witowski did not require extra staff (experts, technicians, computer graphics, etc.) for execution.

Using FDM methods, the model was created within five days. Surgeons were then able to explore the models visually and tactilely, helping them create an operative plan.

Wider implications

By adopting 3D printing across the departments of Vascular Surgery, Cardiac Surgery, and Urology, the Jagiellonian University hosts the largest 3D printing research center in Poland and consults doctors across the country. Jan and his team have demonstrated that 3D printing is not just a trend, but a real medical tool aid. The department is excited to work further with FDM technology while exploring the wider benefits. Surgery guidance, training for medical students, and demonstration models for patients provide doctors and patients alike with greater understanding and peace of mind.

I truly believe that using low-cost printing is a huge step towards personalized medicine.

Most recently Jan and his team have printed a model of pulmonary arteries for cardiologists in Otwock, Poland, used for balloon pulmonary angioplasty - a process to widen narrow or obstructed arteries or veins. Reports show that using these models reduced operative time, improved short-term outcomes, and assist with planning significantly.

It’s likely to be only a matter of time before medical practices start adopting desktop 3D printing technology more widely – and making the most of the benefits.

Disclaimer: Ultimaker 3D printers are designed and built for fused deposition modeling with Ultimaker engineering thermoplastics within a commercial/business environment. The mixture of precision and speed makes the Ultimaker 3D printers the perfect machine for concept models, functional prototypes and the production of small series. Although we achieved a very high standard in the reproduction of 3D models with the usage of Ultimaker Cura, the user remains responsible to qualify and validate the application of the printed object for its intended use, especially critical for applications in strictly regulated areas like medical devices and aeronautics.

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