3D Printing Prototypes for Healthcare Professionals: Creating a Reciprocating Syringe

Background

Commercially available 3D printing allows for rapid prototyping of novel ideas to solve problems in the field of medicine in an extremely cost-effective manner [1–5]. Resources, where users of varying skill levels can utilize 3D printing, are widely available. The goal of this case study is to detail the creation of a product using 3D printing technology. It is particularly useful for healthcare professionals as they would not need an in-depth knowledge of product engineering to contribute to the prototyping process.

There are two aspects of device design that one needs to keep in perspective to come up with a successful product: first is identification of a problem. However, devices do not exist in a vacuum and need to be useful in an ecosystem of healthcare professionals, which is where the second aspect of device design comes into play, a thorough understanding of the environment in which the device will be utilized.

The only way to truly understand the problems associated with any profession is through immersing oneself in it. Physicians have a nuanced understanding of where their equipment is failing them, or ways in which the equipment can be enhanced to make the process of using it more streamlined to serve the needs of the user. The product can be designed knowing exactly how it would be used in real life settings. The flaw in the current design and innovation process is that only a fraction of healthcare professionals play an active and integrated role in device prototyping, and engineers only have a limited understanding of the way the device is actually going to be used in the hands of medical professionals.

This case study will review the problems observed in the current image-guided aspiration technique. During ultrasound-guided aspiration of solid organ masses or fluid, it is difficult to generate a vacuum while maintaining syringe control (Fig. 1). The process involves holding the syringe while pulling the plunger simultaneously. Often, in order to generate an adequate level of vacuum, two hands are needed, which in turn, implies that an assistant is required to position the ultrasound probe for image guidance. Multiple needle passes might be needed due to repeat sampling or needle control.

Having identified the issue, we have designed a multi-lumen reciprocating syringe which aims at increasing the efficiency of the technique. There on, we have outlined our design process to aid any healthcare professional looking for a guideline to exploring 3D printing technology to create innovative healthcare solutions.

Methods

In order to solve the problem of generating adequate force during ultrasound-guided aspiration, a rapid prototype was created using 3D printing. First, multiple hand-drawn solutions were drafted, and feedback was obtained from several colleagues to refine the design. The draft of the initial design was made on MS PowerPoint 2010 (Microsoft Corp., Redmond, WA), which is easily accessible and familiar to healthcare professionals. A background literature search was conducted along with an informal patent search using Google Patents (Google, Mountain View, CA) to analyze the current body of work in this space.

Due to lack of experience using 3D modeling software and product design on CAD, the design was submitted to a freelance CAD designer from Fiverr^TM, who generated a file suitable for 3D printing using the sketch in Fig. 2. The approximate cost of this service is $20. Additional public resources available to the lay public are summarized in Table 1 [6]. The initial syringe design (Fig. 3) was manufactured by a third party 3D printing company SD3D. Additional parts, including washers and plunger, were purchased from a local hardware store to complete the prototype.

The first iteration of the prototype gave insight into the manufacturing and design process. The second generation model is refined from the first iteration to increase functionality while using existing resources. For convenience, the inner lumen of the syringe was sized to fit the same plunger as a 20-cm³ syringe. This allowed for the utilization of the rubber stoppers that fit the existing syringes, streamlining the process of manufacturing by removing an unnecessary step. Then, the second design (Fig. 4) was printed by the University of Maryland Department of Radiology 3D printing lab with an Ultimaker 2 fused deposition modeling (FDM) printer.

Results

The final design (Fig. 3 and Fig. 4) created contains two concentric cylinders. Fluid flows from the needle tip through an outer lumen into the inner lumen, which is outfitted with a plunger. These two chambers are connected at the proximal end of the syringe. The inner lumen is outfitted with concentric rubber washers to create an airtight seal ensuring the effectiveness of the plunger. A metal dowel rod that fit the aperture size of the rubber washers serves as the plunger. On the most distal end of the plunger, another set of concentric washers creates a second airtight seal. As the plunger is depressed, the negative pressure generated in the inner lumen is transferred to the outer lumen via the proximal connection. This allows fluid to be drawn into the needle as the plunger is depressed.

Discussion

3D printing uses additive processes in which successive layers of material are assembled on top of one another to build the desired object [3, 7]. This process means that items can be assembled directly from a digital model. Since the process is based on addition rather than extraction of excess material, less raw material is wasted. Due to the recent advances in technology, 3D printing is relatively cost-effective to produce small-scale customized solutions [7, 8]. Although there are a variety of methods, the general steps involved to manufacture a product using 3D printing are

1. Identify a problem that can be solved by a customized 3D printed solution

2. List the resources available to translate the idea into a printable model

3. Print and test the prototype

4. Reiterate and perfect the prototype based on the feedback collected in the previous step

The design process is outlined in Fig. 5. In order to print a prototype, the blueprint of the object is first converted into a CAD file. The most commonly used file format is Standard Tessellation Language (.stl) or .stl formatted file. It is a file that encodes 3D designs as a collection of triangles, which are called facets. These facets interlock together like a jigsaw puzzle to make the 3D design [3]. Other 3D printing formats include Additive Manufacturing File Format (AMF), Virtual Reality Modeling Language (.wrl), and Form1 (.form). After a file is created, a slicing software is used to create the 3D design into sequential slices. The type of slicing program used will depend on the type of printing hardware one plans to use. Resources required for creating and slicing a CAD file, as well as for printing a design, are described below.

Resource Identification

With the advent of affordable 3D printers, it is certainly possible to invest in one but it is not entirely necessary. It is not practical for novices to purchase a 3D printer or realistically become quickly proficient with 3D modeling software. Therefore, we have identified multiple affordable publically available resources and outlined ways to discover the resources available within one’s network. It is helpful to identify available resources prior to creating a CAD file for 3D printing so that the entire process can be completed smoothly.

3D Printing Hardware Review

An understanding of the available 3D printing hardware is crucial before one creates a CAD file for the prototype design. The decision of which printer to use is influenced by several factors like availability, cost, color capabilities, sterilization capabilities, and materials [3]. A thorough understanding of the software and hardware available would streamline the process of prototype generation and would ensure that it remains cost-effective. The International Organization for Standardization (ISO) and the American Society for Testing and Materials (ASTM) have developed a standard nomenclature that defines seven 3D printing technologies [9]. These seven technologies fall into four categories and are summarized in Table 2 [3, 10].

Sterilization Considerations

Throughout the process of prototyping, sterilization should be considered depending on the application. If the goal is to create 3D printed surgical equipment, or other devices in which direct contact with a patient or animal is made, a sterilization plan is necessary. The four most common sterilization techniques are autoclave, ethylene oxide gas, hydrogen peroxide gas plasma, and gamma radiation. The standards and definitions of sterility and sterilization, as well as descriptions for each technique, can be found on the CDC website [11]. Recent tests have shown that most 3D printed material can withstand ethylene oxide gas, hydrogen peroxide gas plasma, and gamma radiation sterilization techniques; however, certain materials may be damaged when sterilized with autoclave methods [12]. If one plans to use autoclave as the method of sterilization, it is best to consider heat-resistant printing materials.

Conclusion

The advent of commercially available 3D printers greatly decreases the barrier to entry for healthcare providers. The process of prototype generation and design is no longer cost intensive and can be accomplished with the help of readily available resources. The purpose of this study is to demonstrate through an example, the process of designing and generating a device prototype in a way that is cost-effective and does not require special expertise.

One can come up with possible solutions to everyday problems in medicine and customize these solutions to fit the existing healthcare ecosystem. Inexpensive 3D printing would also encourage rapid prototyping to have a closed feedback in the iterative process. Working prototypes can be assembled and tested using 3D printers commercially available to the public or within one’s institution. The democratization of the process of prototype creation by 3D printers is remarkable. This approach can aid creative device design collaborations by encouraging healthcare professionals to lead the process of creating the next generation of medical innovations.