Here, we present a protocol to demonstrate 3D printing in the construction of deep brain stimulation implants.
3D printing has been widely applied in the medical field since the 1980s, especially in surgery, such as preoperative simulation, anatomical learning and surgical training. This raises the possibility of using 3D printing to construct a neurosurgical implant. Our previous works took the construction of the burr hole ring as an example, described the process of using softwares like computer aided design (CAD), Pro/Engineer (Pro/E) and 3D printer to construct physical products. That is, a total of three steps are required, the drawing of 2D-image, the construction of 3D-image of burr hole ring, and using a 3D printer to print the physical model of burr hole ring. This protocol shows that the burr hole ring made of carbon fiber can be rapidly and accurately molded by 3D printing. It indicated that both CAD and Pro/E softwares can be used to construct the burr hole ring via integrating with the clinical imaging data and further applied 3D printing to make the individual consumables.
3D printing has been applied in the medical field since the 1980s, especially in surgery for preoperative simulation, anatomical learning and surgical training1. For example, in cerebrovascular operations, preoperative simulation can be conducted by using 3D printed vascular models2. With the development of 3D printing, the texture, temperature, structure and weight of cerebral blood vessels can be simulated to the greatest extent of clinical scenarios. Trainees can perform surgical operations such as cutting and clamping on such models. This training is very important for the surgeons3,4,5. Currently, titanium patches formed by 3D printing have also gradually been applied6, since the skull prostheses developed by 3D printing after imaging and reconstruction are highly conformal. However, the development and application of 3D printing in neurosurgery is still limited.
The burr hole ring, as a part of the lead fixation device, has been widely used in deep brain stimulation (DBS)7,8,9,10. However, current burr hole rings are made by medical device manufacturers according to the unified specifications and dimensions. This standard burr hole ring is not always suitable for all conditions, such as skull malformation and scalp atrophy. It may increase the uncertainties of operation and reduce the acurracy. The emergence of 3D printing makes it possible to develop individualized burr hole rings for patients in clinical scenarios5. At the same time, the burr hole ring, which is not easy to obtain, is not conducive to extensive preoperative demonstration and surgical training1.
To address the problems mentioned above, we proposed to construct a burr hole ring with 3D printing. A previous study in our lab described an innovative burr hole ring for DBS11. In this study, this innovative burr hole ring will be regarded as an excellent example to exhibit the detailed production process. Therefore, the purpose of this study is to provide a modeling process and a detailed technical process of building a solid burr hole ring using 3D printing.
1. Drawing a two dimensional (2D)-image of a burr hole ring
2. Construction of a 3D-image of the burr hole ring
3. Using 3D printer to print the physical model of burr hole ring
4. Measurement of absolute error
Three views of 2D images were built through commercial CAD software (see the Table of Materials). In these images, practical size and technical requirements have also been added (Figure 1). Further, three-dimensional data were constructed in (Figure 2) and saved in STL format (Figure 3). As presented in Figure 4, solid parts were built on the platform of the printer. Choosing five groups of these parts, absolute error and error range was calculated (Figure 6a,b). The result showed that, in outer ring, the maximum absolute error and minimum absolute error were found in the outside diameter of the waist and in the thickness of the top respectively. In the inner ring, the maximum absolute error and the minimum absolute error were found in the inside diameter and thickness of the top respectively. The total error range was [0.00, 0.59] (Figure 6a,b).
The STL file is further be converted to Gcode file in the slicing solfware. After that, the Gcode file is transmitted into the 3D printer using an SD card. In the 3D printer, carbon fiber was fed through feeding port. A temperature control unit was used to control the melting of the carbon fiber and the nozzle was used to control the release of printing material and construct the solid model.
Figure 1: 2D image of burr hole ring. (a–c) 2D views (front view, left view and top view, respectively) of the outer ring. (d–f) 2D views (front view, left view and top, view respectively) of the inner ring. Unit: mm. Please click here to view a larger version of this figure.
Figure 2: 3D image of the burr hole ring. (a–c) 3D views (front view, left view and top view, respectively) of the outer ring. (d–f) 3D views (front view, left view and top view, respectively) of the inner ring. Please click here to view a larger version of this figure.
Figure 3: The flowchart for constructing a burr hole ring via 3D printing. Please click here to view a larger version of this figure.
Figure 4: The process of slicing the burr hole ring by slicing solfware. In the slicing solfware, the STL model was sliced into 0.1 mm thick layers (the black solid arrows). Parameters such as speed and temperature were set (red box) as follows: printing speed at 30 mm/s, printing temperature at 210 °C and bed temperature at 80 °C. Finally, we pressed Save toolpath, and the STL file was converted into Gcode files for 3D printing directly. Please click here to view a larger version of this figure.
Figure 5: The example of constructing burr hole ring via 3D printing. (a)The solid arrow on the left indicated the nozzle and the solid arrow on the right side showed the touching buildplate, which was used to host the solid model. (b) The outer ring (the solid arrow) was constructed on the touching buildplate. (c) The inner ring was built on the touching builplate (the solid arrow). (d) The inner ring was built on the right side of the bed (the solid arrow). (e-f) Example of inner ring and the outer ring (the solid arrow) after polishing. Please click here to view a larger version of this figure.
Figure 6: Measurement of absolute error. (a) Absolute error and error range of outer rings (AE = | MV – SV |; main structures: (1) outer diameter of the top; (2) outer diameter of the waist; (3) thickness of main body; (4) thickness of the top; (5) width of the hook; (6) inner diameter of the top). (b) Absolute error and error range of inner rings (AE = | MV – SV |; main structures: (1) outside diameter of the top; (2) outer diameter of the bottom; (3) inner diameter; (4) total height; (5) thickness of the bottom; (6) thickness of the top. P = part, MV = measured values, SV = standard values, AE = absolute error, ER = error range. Accuracy = 0.02 mm; Unit = mm. Please click here to view a larger version of this figure.
Supplemental File 1: Outer Burr Hole Ring. Please click here to view this file. (Right-click to download.)
Supplemental File 2: Inner Burr Hole Ring. Please click here to view this file. (Right-click to download.)
These results showed that the software used were practicable to build 3D models of burr hole rings (Figure 1 and Figure 2), and 3D printing can be used to build solid models with designated materials (Figure 4). In terms of the size of the solid model, there was an absolute error from 0 to 0.59 mm determined through the measurement made by Vernier calipers (Figure 6). To some extent, the error is unavoidable since such absolute error comes from many factors, such as the quality of the printing instrument. Industrial printers can have better precision. In addition, when building smaller and more precise parts, the absolute error is more obvious. In general, as shown in Figure 3, the process that constructed the model and further formed the solid model by 3D printing is effective and feasible. Although there is an absolute error, such error can be reduced by improving the quality of the printers and accurately adjusting the printing parameters.
An innovative burr hole ring for DBS was published previously11. In this study, the same model was applied as an example to further demonstrate the systematic process of making the related implants. Currently, in the limited clinical application of 3D printing, model building generally adopts two methods: Firstly, CAD modeling has been used to generate 3D models for further 3D printing operations12. Secondly, imaging data (like in the format of DICOM) has been used to reconstruct the bone structure of patients in three dimensional models according to CT and MRI data. After rendering, the data could be further converted into editable STL files, and then the highly simulated anatomical structure can be produced by 3D printing12,13,14. Similarly, patching or implanting materials that are highly suitable for morphology can be designed according to the anatomical structure of three dimensional reconstruction15,16,17. This method has been applied in cranioplasty. A previous study showed titanium skull patches constructed by 3D printing technology6. Although using 3D printing technology to construct burr hole rings through credible flow visualization in this study in possible, this modeling method has certain limitations in practice.
Being different from the traditional production of burr hole rings, this study proposed to use 3D printing to construct these implantable parts. In fact, traditional products are mostly uniform in size, which does not apply to some patients with skull shape variation and scalp atrophy. The application of 3D printing would potentially provide the implants customized for different patients. Previous studies have proposed and implemented the application of 3D printing to produce skull fragments for skull defect repairment, and has showed its permanent effect6. The efficacy of DBS for functional neurosurgical diseases has been widely recognized (such as Parkinson's disease, dyskinesia)18,19,20, but the popularity of this treatment is limited, which may be the result of economic burden caused by high consumable costs. Products made by 3D printing have the advantages of high production efficiency, low cost and customization, which makes 3D printing of great potential in the field. The development and application of this technology may provide more patients with an opportunity to receive DBS surgery. However, there are few reports on the use of 3D printing to produce consumables for DBS in the literature.
Moreover, the burr hole ring constructed by 3D printing can have other advantages. This rapid prototyping product can be used for preoperative demonstration, which will better inform patients and their families about the procedure of electrode implantation and enhance doctor-patient communication effectively. Clinicians can carry out preoperative simulation and surgical training through 3D printed products to maximize the simulation of DBS surgery, which will effectively improve their surgical skills. In the surgical treatment of cerebrovascular tumors and cranioplasty, 3D printed products have been applied to surgical training2,5.
This study used carbon fiber, which has good strength and toughness, as the printing material to show the production process of 3D printing. In practice, many factors of implant material should be considered. Firstly, whether the implant has excellent disinfection performance and can keep its properties unchanged under ethylene oxide and hot steam for a long time12. Secondly, implants need to have good biocompatibility and can be placed for a long time without rejectiong by the body. Thirdly, implants need to have excellent mechanical strength, toughness and chemical resistance.
In this study, the construction of a burr hole ring as an example was demonstrated to systematically describe the process from modeling to 3D printing. This is a complete process example. In the future, the use of CAD software, imaging data (e.g., DICOM) and 3D printing to construct the burr hole ring should be encouraged. As mentioned above, 3D reconstruction of DICOM data obtained by imaging can be further converted into STL files that can be used for 3D printing. This is also the mainstream modeling method in clinical scenarios12,13. This method has not been applied in the DBS surgery.
The authors have nothing to disclose.
This work is supported by grants from Natural Science Fund of Guangdong Province (No. 2017A030313597) and Southern Medical University (No. LX2016N006, No. KJ20161102).
Adobe Photoshop Version 14.0 | Adobe System,US | _ | Only available with a paid subscription. |
Allcct 3D printer | Allcct technology co., LTD, WuHan, China | 201807A794124CN | |
Allcct_YinKe_V1.1 | Allcct technology co., LTD, WuHan, China | The software is provided by the 3D printer manufacturer and there is no Catalog number associated with it | |
AutoCAD 2004 | Autodesk co., LTD,US | 666-12345678 | Software for 2D models |
Carbon Fibre | Allcct technology co., LTD, WuHan, China | PLA175Ø5181Ø3ØB | The material is provided by the 3D printer manufacturer |
Netfabb Studio Basic 4.9 | Autodesk co., LTD,US | – | The software is provided by a 3D printer manufacturer and is open to access |
Pro/E 2001 | Parametric Technology Corporation, PTC, US | _ | Software for 3D models; Only available with a paid subscription. |
Vernier caliper | Beijing Blue Light Machinery Electricity Instrument Co,. LTD, China | GB/T 1214.1-1996 |