OxyArm: Engineering a Medical First with Durability Testing

This is part three of a multi-part series covering how medical device firm Southmedic used virtual simulation technology to bring OxyArm, the first open oxygen delivery system, to market. In part one, we covered how flow simulation was used to determine optimal airflow and real world performance. Part two focused on material selection based on manufacturability and environmental impact. In the part three of the series, we’ll discuss durability and make a final decision on the best material for the job.

Our durability test is used to analyze field use. This type of design review focuses on how the device will stand up to regular wear and tear. Here we use Simulation to discover how the OxyArm will react to real-world use…or in abuse in this case.

We’ve all had clumsy moments holding a product in our hands. Almost everyone has dropped their cell phone once or twice (hopefully not in the bathroom). We can safely assume that a user wearing an OxyArm will be subject to a case of the dropsies. Having the product shatter after one drop would be troublesome. The OxyArm needs to the comfortable enough to wear, but strong enough to take a hit.

In this study we’re testing to understand how the OxyArm will react to a four foot drop on a surface without give, like cement. The test will evaluate how our four plastics, ABS (acrylonitrile butadiene styrene), HDPE (high density polyethylene), PC (polycarbonate) and PP (polypropylene), will withstand a drop and allow us to see the stresses placed upon each material.

Here we gather insight into the transient sensor, which shows maximum stress experienced at the point where the device first hits the cement. This is the OxyArm’s most vulnerable point where failure is most likely to occur. This test assumes that the OxyArm is dropping straight down. However, we can add complexity by dropping it at an angle or making the device spin while falling. Since the device can be dropped in a number of ways, Simulation allows for testing multiple angles and drops to ensure all contingencies are accounted for.

The PSI determined in the drop test influences the OxyArm design’s thickness. We’ve identified HDPE and PP as the best material candidates. The drop test adds the final level of understanding to make a material selection.

Based on the drop test results, we can strengthen the design by making it thicker, but keep in mind that adjusting thickness also changes manufacturability control. For example, using a larger plastic requires a longer cooling time. It also affects cost. The thickness study found that optimal size pushed the price of an HDPE OxyArm to skyrocket from $1,795 to $8,404, meaning it is not the best choice to meet our complete manufacturability costing goals and that PP is the best option to bring the OxyArm to life.

During this series, we’ve uncovered how integrated Simulation testing directly influences design. Concurrent testing is not just a secondary application. When analysis is part of your regular design workflow, you’re equipped with knowledge to adapt your products for optimal manufacturability, cost, durability, and environmental impact before considering a physical prototype. Taking a concurrent approach to design and analysis will save you time, money and frustration because you understand all scenarios before you even have a chance to drop a physical product on cement.