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Speed and Reliability in Medical Device Development Facilitated by Balancing Proper Design with Highly Functional Prototyping Materials

Wed, 06/23/2010 - 7:20am
Scott Castanon

This case study will focus 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.

Two words best encompass a challenge often faced by medical device designers and manufacturers: "speed" and "reliability.”

The Market Challenges

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.

The Product Challenge

 

The initial cartridge design
The initial cartridge design was 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.
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.

Our design assignment, in parallel with the 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.

For this product design project, Symbient Product Development needed to complete our 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

Our approach to meeting challenges of both the medical device marketplace and the individual product for which we were responsible, was based on a procedure almost identical to the accepted four-step plan for handling a medical emergency.

Step 1: Establish a Planning Team

Our first goal was to ensure that our vision and expertise aligned with our client's vision and expectations. This required input from our designers, engineers and administrators, but also the experience of professional resources such as DSM Somos, a world leader in high-performance stereolithography resins. We knew, from prior experience, that DSM's rapid prototyping materials would 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, we machined prototypes that were more than adequate given product specifications. However, in designing the Diagnostic Lateral Flow Cartridge, the hazard involved was that a machined prototype 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 the substantial cost of their production. Our analysis of such realities led us to determine 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”, 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 our design and developmental plan was the use of 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 is a fast-curing, low-viscosity resin, that produces clear, functional, accurate parts that simulate acrylic in appearance. It provides improved water resistance versus alternative resins.

Step 4: Implement the Plan

By 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. The implementation of our plan revolved around short prototyping cycles which were usually characterized by our ability to fabricate prototypes via stereolithography in a single day, followed by one to 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 we employed two types of engineering methods in a parallel path to complete the device. On one path we utilized industrial design, which 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 an appealing two-color design. The overall size and shape are intended to be ergonomic, easy to handle and clear to read. We made a variety of industrial design blanks, produced through stereolithography, for our customer to evaluate. Based on their feedback we would iterate the industrial design as necessary until we achieved a final industrial design.

On the parallel path, we developed the mechanical design that includes features that assemble the product and ensure that the device functions properly. Mechanical

The final design of the Diagnostic Lateral Flow Cartridge
The final design of the Diagnostic Lateral Flow
Cartridge, including both the industrial and
mechanical design aspects.
design requires a solid understanding of core concepts including fluid mechanics, and WaterShed XC 11122 prototyping material allowed us to visualize the flow through the strip as it ran during this mechanical design phase. Additionally, inside the cartridge we designed and built several features that engaged the strip in key areas. 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 we produced gave us the parts we needed and were as close to actual molded components as we could possibly get.

Once we had achieved our final industrial and mechanical designs they were merged into an integrated design that we then used to create a prototype mold. The fact that we were we able to use stereolithography for both mechanical design and also for a parallel industrial design was critical to our need for a rapid turnaround. WaterShed XC 11122 contributed significantly to making this possible. The material performed as promised and allowed us to achieve accuracy and repeatability with each prototyped iteration.

Conclusions

In order to appreciate how much the stereolithography process and WaterShed XC 11122contributed to the success of this project, it's important to note that some prototyping iterations required a tolerance of 0.002 inches.Therefore, reliability in accuracy and repeatability were paramount. This process and material enabled us to reach a desired result at a significant lower cost than possible with machined prototypes, and do so in four months. With this project, the challenges of speed and reliability were successfully met through a balance of proper design and highly functional prototyping materials.

 Scott Castanon is an Engineering Manager for Symbient Product Development

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