3D Printer

There are a large number of cheap and affordable FDM-type 3D printers on the market. Immediate investment in a high-tech professional 3D printer is not necessary; comparable results can be attained with affordable unbranded printers, though initial challenges may need to be overcome. Nevertheless, we recommend opting for a 3D printer that has available support, accessories, and spare parts as well as an active discussion forum. This ensures assistance with individual faults, errors, repairs, and settings. The Prusa printers (Prusa Research, Prague, Czech Republic), specifically the i3 MK3S + and MK4 models, have proven to be exceptionally successful in our context.

3D Filament

When using an FDM printer, the choice of printing material is crucial, as poor-quality material can lead to numerous printing issues. Also, the color that is added to the filament affects its physical properties such as the resulting strength, etc. We recommend using a quality-proven filament, in our case, we use Prusament, Aurapol, PM Filament, etc.

PLA (polylactic acid) is a new type of biodegradable material derived from starch extracted from renewable plant resources. Due to its good processability and biodegradability, PLA 3D printer filament has become one of the most commonly used 3D printing materials. However, rapid biodegradability is only possible in an industrial composter and this material cannot be recycled together with other plastic materials.

As an alternative option, PETG can be used. PETG filament, also known as Polyethylene Terephthalate Glycol, is a co-polyester recognized for its durability and ease of use. The G in PETG stands for glycol-modified, which makes the end product clear with glass-like visual properties.

The advantage is easy recycling with the possibility of repetition. However, preparing a printing sheet can be more intricate for beginners.

Another commonly employed material in the market is ABS, Acrylonitrile Butadiene Styrene. ABS is generally used for making inexpensive, sturdy mechanical parts (LEGO bricks, car parts, cellphone parts, etc.). The material is tenacious and temperature resistant - this makes it suitable for engineering applications. ABS printing requires specific conditions for successful results. It’s important to conduct the printing in a well-ventilated room due to the release of fumes and substances that may pose potential health risks. A big problem is the cracking of the model during cooling, which requires a higher stable temperature around the printed model.

Model Selection

For beginners, it is advisable to avoid starting with complex models that require several hours of print time. We recommend beginning with small models and toys unrelated to medicine that can be printed within minutes. This approach helps to prevent the frustration and demotivation that can occur if complications and glitches arise during a lengthy print job. Investing 20 h or more in a print that ultimately fails can be particularly discouraging.

Multi-Material Print

Certain printers offer the capability for multi-material printing, allowing for the use of multiple filaments of the same type but in different colors, as well as multiple materials. For example, supports can be printed using water-soluble material. While this may seem tempting, we consider this approach suitable for advanced users only due to its increased complexity, leading to a significantly higher error rate. Only after these initial setbacks have been mastered do we recommend moving forward with printing more complex models or experimenting with multi-material print.

Local Database

We highly advise cataloging and storing all copies in a local database from the outset, along with devising a method for labeling individual models. As the number of 3D models increases, it becomes exceedingly challenging to track down the source CT scans for each model.

Size of Printed Model

When printing a larger model, it is important to consider the size limitations of the specific 3D printer being used. For instance, the Prusa MK4 offers a print space of 250 × 210 × 210 mm. If a bone model exceeds these dimensions, there are a couple of options available. Firstly, the model can be divided into two parts using for example PrusaSlicer software, positioned side by side on the printing bed, and printed simultaneously. Subsequently, the parts can be joined together through post-processing by gluing. Alternatively, the model can be rotated diagonally instead of being printed horizontally. This approach can provide approximately 380 mm of printing height, allowing for larger models to be printed with transparency. Another option is to utilize a printer with a larger print area, such as the PrusaXL, which offers dimensions of 360 × 360 × 360 mm, or diagonally nearly 619 mm. However, it’s important to note that the cost of such a printer is approximately 2200 USD.

Most intra-articular fractures are less than 200 mm in length, however, for example, in the case of a complex fracture of the proximal and distal tibia, a length of more than 450 mm must be considered.

Time Requirements

The required time may vary depending on the complexity of the project; therefore, the following overview should be considered approximate:

1.

Primary model creation using 3D Slicer, Philips Intelispace, or other – 2 h.

2.

Invalid data processing in Meshmixer – 10 min.

3.

Connecting the parts and fragments of the model – 2 h.

4.

G-Code creation (depends on the CPU speed) – 10 min.

5.

Printing time (according to model complexity) – 15 to 50 h.

6.

Finishing the 3D model and removal of supports – 10 min.

The entire process involves approximately 5 h of design time, which can be shortened if a 3D model already exists or if a radiologist is willing to prepare one. However, the primary time investment lies in the printing phase. The choice of the specific printer and its print nozzle size, layer, and support settings becomes crucial. In our case, we conducted a comparison between an older model Prusa printer (i3 MK3S+) and a newer model (MK4). With the printer set to default specifications (nozzle 0.4 mm, layer size 0.2 mm, vertical shell perimeter 2), we achieved the following models with corresponding printing times and filament consumption:

Ankle Joint Model

i3 MK3S+, grid support: 28 h 01 min, 214 g / 72 m of filament.

i3 MK3S+, organic support: 27 h 26 min, 191 g / 64 m of filament.

MK4, grid support: 15 h 16 min, 213 g / 71 m of filament.

MK4, organic support: 15 h 26 min, 195 g / 65 m of filament.

Base of the Skull Model

i3 MK3S+, grid support: 59 h 38 min, 492 g / 165 m of filament.

i3 MK3S+, organic support: 56 h 8 min, 368 g / 123 m of filament.

MK4 grid support: 29 h 10 min, 454 g / 152 m of filament.

MK4 organic support: 31 h 00 min, 389 g / 130 m of filament.

While the filament consumption does not differ significantly, the newer printer was able to reduce the required time by almost half. The selected supports did not have a substantial effect on the printing time.

Since this methodology is primarily intended for physicians, it is understood that their primary responsibility is the standard treatment of patients. Creating 3D models, especially in the initial stages, falls outside their usual scope of work and consumes valuable time. Therefore, the time required for this process cannot be overlooked. However, if the task of processing images into 3D models is delegated to a technician, this time constraint is significantly reduced.

Cost-Effectiveness

While there are notable price differences among individual filaments, their selection, as mentioned above, is crucial. The cost for 1000 g of PLA filament typically falls within the range of 17–30 USD. For reference, an ankle joint model weighs about 200 g, and a skull base model weighs about 500 g.