Two words best encompass a challenge often faced by medical device designers and manufacturers: speed and reliability.
The Marketplace Challenge
Intense competitive pressures, combined with demands from the medical community for solutions to combat the spread of disease, have created a marketplace in which even months can be too long for companies to react and produce relevant products. And yet, speed-to-market must be achieved without compromising the critical need for medical products to perform as required in accordance with highly technical specifications, many of which are predicated upon accuracy and durability.
Symbient Product Development strives to achieve both speed and reliability by blending current science and engineering theory with solid design principles for the creation of medical device and diagnostic products. In that process, our ability to evaluate a design and anticipate product performance is often highly dependent upon the quality and comprehensiveness of prototyping technology. This case study focuses on the vital role played by WaterShed® XC 11122, a rapid prototyping resin from DSM Somos, which helps to ensure a remarkably fast turnaround coupled with the ability to replicate actual performance attributes of production-grade engineered thermoplastics.
The Product Challenge
Symbient Product Development was given the opportunity to participate in a fast-timeline project to develop a Diagnostic Lateral Flow Cartridge. This device uses a lateral flow test strip to evaluate, within a matter of minutes at the point-of-care, whether or not a patient is infected with a virus. In conducting such a test, a fluid sample is collected from the patient and mixed with a buffer, after which several drops of the combined sample and buffer are added to a sample well. The sample is applied, test strips run, and a clinician then places the Diagnostic Lateral Flow Cartridge into an instrument that reads the test result.
Shown here, the initial cartridge design intended to allow rapid prototyping iteration and development of the critical internal features that interface with the test strip and are fabricated and iterated to maximize medical assay performance.
The design assignment, in parallel with development of the internal cartridge features, was to develop an exterior industrial design that includes the user interface, features to aid in handling and insertion into the instrument, and aesthetic factors intended to give the product a unique appearance.
In accepting the project, Symbient committed to complete its responsibilities within four months --- an extremely fast turnaround --- without sacrificing the quality of prototyping evaluations that would assure the end-user that the Diagnostic Lateral Flow Cartridge would perform as required.
Solving the Challenges
Symbient’s approach was based on a procedure almost identical to the accepted 4-step plan for handling a medical emergency:
Step 1 -- Establish a Planning Team
The first goal was to ensure that Symbient’s vision and expertise aligned with the client's vision and expectations. This required input from designers, engineers and administrators, but also the experience of professional resources such as DSM Somos, a world leader in high-performance stereolithography resins. Symbient knew, from prior experience, that DSM's rapid prototyping materials would provide the ability to shorten development time and facilitate the production of functional Diagnostic Lateral Flow Cartridge models.
Step 2 -- Analyze Capabilities and Hazards
In previous medical design projects the company had been able to machine prototypes that were more than adequate given product specifications. Although they had the capability of doing so in designing the Diagnostic Lateral Flow Cartridge, the hazard involved was that a machined prototype, although providing suitable accuracy, would require too much time. In this application, testing demanded confirmation of proper device function using actual biological samples. Specifically: the sample is spiked with various quantities of a designated virus in order to evaluate the detection ability of the assay. The chemistry of the assay is then revised and evolved as necessary in order to achieve the required sensitivity.
An additional downside to machined prototypes is that they would require substantial cost to produce. The company’s analysis of such realities led to the determination that working prototypes would best be produced through stereolithography, a process that permits rapid creation of 3-dimensional prototypes utilizing a computer-controlled laser that polymerizes light-sensitive resins. Stereolithography is highly precise and constructs the object in a series of additive layers, providing the advantage of producing highly complex forms that would be expensive and very time consuming to fabricate by machining or traditional molding techniques.
Step 3 -- Develop the Plan
At the heart of the design and developmental plan was the determination to use WaterShed® XC 11122, an optically clear rapid prototyping resin developed by DSM Somos to provide ABS-like properties and good temperature resistance. WaterShed® XC 11122, a fast-curing, low-viscosity resin, produces clear, functional, accurate parts that simulate acrylic in appearance, and provides improved water resistance vs alternative resins.
Step 4 -- Implement the Plan
Using stereolithography, Symbient Product Development produced several iterations of the Diagnostic Lateral Flow Cartridge design while fine-tuning the geometry necessary to optimize medical assay performance. These iterations were quickly but accurately evaluated to establish precise parameters for the final design. Implementation of the plan revolved around short prototyping cycles, which were usually characterized by an ability to fabricate prototypes via stereolithography in a single day, followed by one or two days of testing, leading to the design and fabrication of the next iteration on the fourth day.
This design project was unique in that two types of engineering methods were employed in a parallel path to complete the device. One path utilized industrial design, the aspect of design that makes the product appealing to the user and includes human factors, branding, and ergonomics. In this case, industrial design involved the grip features at the end of the device that enable a user to hold it in a specific way for proper insertion into the instrument that reads the test result. The pointed end is another industrial design cue that points the user to install the device in the correct orientation.
The industrial design also involved a 2-color design so that it is visually appealing to users. The overall size and shape are intended to be ergonomic, easy to handle, and clear to read. Symbient made a variety of industrial design blanks, produced through stereolithography, for the customer to evaluate. Based on customer feedback, the industrial design was iterated as necessary until a final industrial design was achieved.
On a parallel path, the mechanical design was developed, including features that assemble the product and ensure that the device functions properly. Mechanical design requires a solid understanding of core concepts including fluid mechanics, and WaterShed® XC 11122 prototyping material allowed developers to visualize the flow through the strip as it ran during this mechanical design phase.
Additionally, inside the cartridge several features that engaged the strip in key areas were designed and built. The degree of compression was critical for proper strip function, therefore accuracy and repeatability of the internal cartridge features was extremely important. Hence, the mechanical stereolithography models produced yielded the parts needed and were as close to actual molded components as the designers could possibly get.
Once the final industrial and mechanical designs were achieved, they were merged into an integrated design that was used to create a prototype mold. The fact that Symbient was able to use stereolithography for both mechanical design and also for a parallel industrial design was critical to the need for a rapid turnaround. WaterShed® XC 11122 contributed significantly to making this possible. The material performed as promised and gave a proven ability to achieve accuracy and repeatability with each prototyped iteration.
Shown above, final design of the Diagnostic Lateral Flow Cartridge, including both industrial and mechanical design aspects.
Conclusions
In order to appreciate how much the stereolithography process and WaterShed® XC 11122 contributed to the success of this project, it's important to note that some prototyping iterations required a tolerance of 0.002 in.Therefore, reliability in accuracy and repeatability were paramount. Moreover, this process and material enabled Symbient to reach a desired result at a significantly lower cost than possible with machined prototypes. And they were able to meet their obligation to complete the project in less than four months!
Speed and reliability --- two challenges successfully met through a balance of proper design and highly functional prototyping materials.