INTRODUCTION
Traditionally, bone fractures have been treated by some type of orthopedic cast in order to immobilize the area and facilitate healing. Typically, fiberglass and plaster casts have been used; however there are quite a few issues with them. Discussing the challenges of 3D casting, breathability, irritation, patient discomfort and satisfaction, and patient-customized.
Additive manufacturing technology can be used to manufacture any shape, parts, tools for end-use. Additive manufacturing builds up material upon the existing material to create the end use part. Since first publication in 1984’, the medical field has taken a part of interest in additive manufacturing recently. We will focus on 3D printed orthopedic casts where it’s personalized to individual patient anatomy providing biocompatible, more comfort, breathable, washable and quicker to develop than other marketed 3D-printed casts.
We will work on a scale version of the orthopedic cast which we would later scale to a larger size. Also, we desire to use a material which is biocompatible for surface contact with the tissue of the arm and prevent any irritation. We also believe that post-processing will be required to smooth prints, improve product appearance, and improve patient comfort.
Methodology
Traditional methods utilized for stabilization of the hand for medical purposes whether bone fracture, ligament surgeries are plaster cast or fiberglass cast. Both stabilization methods have pros and cons. However, there is intensive research presented that 3D printed materials were shown to have higher tensile strength and flexural strength than traditional methods. With the benefits of AM printed material to have thinner breathable (open structure) without destruction of tensile strength, flexural strength, and being water-resistant.
Several measures had been taken in order to develop the required customized hand cast by 3D print technology with minimal printing time. Starting from data acquisition, data analyzing, modeling, designing, printing methods and fabrication.
Data acquisition gathered from 3D scanning at the UW- Madison Makerspace, one member of the project team volunteered to undergo a data acquisition of his arm for the purpose of printing hand cast. Initial scan was obtained using the Creaform Academia 50 scanner and using Creaform’s VX-Elements software to post-processing to create STL file. The scanning process requires 15-30 minutes for the vertical hand position, which is relatively quick and for sure requires more higher care on medical care in terms of degrees of freedom to minimize size error.
Next step for data analyzing. using softwares packages Fusion360 and meshmixer to model the initial scanned hand. These softwares provide at a precision higher than (1.0e-6) six decimal points-nanometer.
Modeling and designing of unique hand casts has various steps. Interpolation of the spline curve simplifies the starting point for hand splint cast which is unique for individual anatomy. Fusion350 package was used to model and modify the STL for surface reconstruction, offset the cast over arm size and thumb to create a clean surface model. After a clean surface model, a solid model body was created to measure size errors and trimming unnecessary length of the cast.
The solid model was taken to a meshmixer to check offsets size between scanned model and solid model of hand cast. with modification to split hand cast for smooth use and ligature zip-tie. Final model steps are to select breathable pattern shape and extruded required thickness.
Figures
Figure 1. Scanning Arm by Creaform Academia 50 scanner.
Figure 2. Creaform’s VX-Elements software to mesh post-processing.
Figure 3. Patient Scanned STL file
Figure 4. combined initial scan and hand cast.
Figure 5. Conversion of the solid model into a perforated model.
MATERIALS
Various designs of the cast include pattern and thickness and colors significance impact printing duration and section analysis. One material will be used for this project: Polylactic Acid (PLA). Material Selection Criteria are biocompatibility, safety for prolonged skin contacts and mechanical properties such as flexibility and durability.
Printing Process
The STL file was sliced using the UltiMaker Cura software and printed using Ultimaker S5. The STL file when sliced with the default settings at 0.15 mm layer thickness and 30% infill in the vertical orientation takes about 40 hours to print with regular supports. It uses 292 grams of PLA resulting in a part cost of $14.6. The support structures are attached to the inner surfaces of the cast which will be in contact with the patient’s skin. This is not desirable as a smooth surface finish cannot be achieved without post-processing to prevent discomfort. The STL file was sliced again in the same orientation with 0.3 mm layer thickness, 30% infill, and tree support structures. This resulted in significantly less print time of 13 hours and 49 minutes. The print consumes 192 grams of PLA filament resulting in a part cost of $9.6. The support structures were also attached primarily on the external surfaces which also makes the post-processing easier. The sliced file was exported as G-code to the Ultimaker S5 printer to be printed with PLA.
Results
The final printed cast parts are shown in Figures 6 and 7 respectively. Post processing of the part mainly involved removal of supports followed by sanding to remove any rough edges. The post–processing took about 20 minutes to complete. The final cast is shown in Figure 8.
Figure 6. Forearm cast with supports attached (Radial half cast)
Figure 7. Forearm cast with supports attached (Ulnar half cast)
Figure 8. Forearm cast after post processing with radial and ulnar halves together
Conclusions & Outlook
Given the inherent challenges faced with traditional orthopedic casts impact patients’ hygiene, care, and treatment outlook, 3D-printing these has become a commercially available method of alleviating a number of these issues.
Although 3D-printed orthopedic casts have the benefit of being breathable, lightweight, customizable, and hygienic, it still presents disadvantages that must be overcome in order to increase their adoption in the market. These disadvantages include the slow-print times and need for 3D-printing technology. Our team was mostly concerned with the long processing times associated with developing a customized 3D-printed cast, which can take several days to produce one cast.
Our team was able to acquire necessary data, research relevant design requirements, design human-centered orthopedic arm cast models, and print prototypes in a manner that met our initial goal. We were capable of fully 3D-printing a cast in approximately 14 hours, yet we still believe that our process can be further optimized for even quicker production of parts.
Overall, we believe that the time our team took to work on this complex project was well-spent, and could be further optimized in order to reach potential scalability. Our team believes that further optimization of design and processing of on the market 3D-printed orthopedic casts will improve their ability to be widely accepted by hospital systems, clinics, and general consumers.