How We Used Design for Assembly to Optimize IVD Product

Preventing Leakage and Enhancing User Experience with Design for Assembly 

An engineer’s core duty includes the seamless integration of design, manufacturing, and utilization. This includes a frequently overlooked yet critical step during the Design for Manufacturing process: Design for Assembly. As organizations expand, sometimes there’s a tendency to separate responsibilities ─ dividing design, manufacturing, and testing into distinct areas. However, engineers who invest time and effort to understand the entire production process and the end-user experience gain a distinct advantage.

This is one of the reasons why the Wright Brothers beat the Smithsonian and achieved the first powered flight, despite the Smithsonian Institution having a decade-long head start and seventy times the budget! While the Smithsonian divided tasks among separate groups for design, construction, and testing, the Wright Brothers took on all three roles themselves, improving their development process with faster and richer feedback. Applied in the world of plastics design and manufacturing, engineers who not only design components, but also develop manufacturing processes and rigorously test component performance are better equipped to achieved optimized part designs and processes.

This is why Design for Manufacturing and Assembly (DFMA) is so crucial. Although it may initially increase development cycle costs, it substantially reduces the number of cycles required and the time per cycle, ultimately cutting overall project costs. The experiences of our engineers offer a recent example that demonstrates this concept.

Application

The Client: A client with an In-Vitro Diagnostic (IVD) application came to Natech needing an updated design for injection molding.

The Product: The application featured onboard reagents, which includes a collector for patient blood samples. The collector first collects the sample via capillary tube, then directs the sample, followed by a buffer reagent, onto a test strip.

Operator holding a plastic molded IVD component

The critical requirement is that, once the sample is collected and before releasing the sample and buffer, the system must remain a closed, sealed system to:

  • Direct the flow of the sample and buffer onto the assay
  • Prevent any sample or buffer from escaping the system during this process.

The engineering challenge lies in overcoming the holding force of a parked groove when pressure is applied, allowing the collector to move into the mating component to release the buffer.

Issue

Natech Engineers spent time with the client to understand the broader system functionality and the collector’s role within the system. Thanks to this, they had an understanding that went beyond the defined requirements and identified a functional risk.

During assembly, when the collector joined with the mating component in the parked position, the collector would wiggle in place, potentially creating a leak path. This occurred because, in the parked position, only one of the three radial seals made contact with the mating surface. The consequences were clear: any escaped sample or buffer could jeopardize the integrity of the assay or pose health risks to the user.

IVD component assembly part drawing

Additionally, the assembly process offered no direct feedback for the insertion of the collector into the mating component. This lack of feedback meant that the people inserting the collector wouldn’t really know when they had reached the correct insertion point. This could lead to under-insertion, resulting in disassembly during transport, or over-insertion, and potentially puncture the buffer container and make the unit totally unusable.

Solution

Don’t worry, we’re in a good spot now. Identifying risks can be the most challenging part of problem-solving, so actually solving the issues becomes much more straightforward.

For the radial seal issue, adding of extra seals ensured that at least two seals engaged with the mating component in the parked position. These added seals acted like o-rings and created a hydraulic lock that prevented fluid from escaping the system.

IVD plastic part updated assembly design

To address the lack of assembly position feedback, our engineers designed an increased diameter at the bottom end and created a mating feature to establish a firm snap when the component reached the proper parked position. This groove significantly reduced the risks of unintentional part removal and premature release of the buffer reagent.

Results

Thanks to the introduction of o-ring grooves, the collector remained securely in place, leaving no room for the buffer to escape except along the intended flow path. The park groove aligned flat against the surface and provided a tactile snap into place, show that it’s in the correct position. Despite the potentially more intricate appearance of the finished component, the manufacturing process was simplified with reduced operational risks. 

Problem-solving is an important skill for DFMA success. Identifying risks and developing solutions becomes easy when your team combines knowledge across various engineering disciplines. An engineer who has expertise in design, manufacturing, and practical use is better equipped to tackle the surprise challenges that come up during the product development process.