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The challenge of pinpointing reagent blister seal strength specifications

The mechanical forces specified to access reagents packaged in on-board microfluidic blisters used in point-of-care diagnostic products is essential to their clinical use. But designers of these products must consider how these activation forces relate to risks inherent to the blister manufacturing process that could manifest in later clinical use.

Identifying the ideal blister pack seal strength is arguably the most important consideration. Some practical challenges must be addressed to ensure a blister development and manufacturing program is viable for mass production.

What is reagent blister seal strength?

A reagent blister is manufactured from polymer-lined foils that are cold-formed into shape and then heat-welded to create a perimeter seal around the blister that keeps the liquid from leaking out.

Typically, a reagent blister is activated by a mechanism within the diagnostic instrument that applies pressure to the top of the blister while a piercing mechanism punctures the bottom of the blister, enabling the reagent to flow from the blister to the microfluidic consumable. The force required to pierce and extract the reagent from the blister is termed the “activation force.”

Seal strength differs from activation force in that it is the maximum force that the blister can withstand without leaking. Seal strength refers to the strength of the bond made by heat welding the perimeter of the blister foils, which contain plastic laminate layers that bond to each other under heat and pressure. Material characteristics, blister geometry and heat seal process temperature combine to determine the strength of that bond.

In addition, the chemistry of the reagents may cause the seal to weaken over time, so it is crucial that product developers and manufacturers choose materials wisely.

Seal strength is a critical risk management metric

In general, microfluidic-based diagnostic test developers favor higher seal strengths to prevent blisters from leaking. Higher seal forces prevent blisters from leaking their reagents onto delicate test instruments, which can risk severely damaging the sensitive electronic equipment contained inside. It’s a costly problem that also invalidates the diagnostic tests the equipment is designed to perform.

However, there are costs and technical limitations to the seal strengths that can be achieved. Reliability, or process capability, is essential. Developers should partner with manufacturers during program development to conduct compressive force testing to identify the ideal design and manufacturing specs that will result in the most reliable high-volume manufacturing of these critical products.

Manufacturers must manage tradeoffs

There is a tradeoff relationship between the blister activation force and the burst force that causes the perimeter seal to fail. If the force required to activate the blister is greater than the blister’s perimeter seal strength, the blister will leak. Likewise, even if the activation force is less than the seal strength, a malfunction of the piercing mechanism can cause a buildup of forces within the blister that also exceeds its seal strength. This will also cause a leak.

One of the ways product designers have historically addressed the risk of blister leaks has been to specify very high seal strengths. Likewise, designers tend to specify strong activation mechanisms to minimize the chance the blister fails to activate.

But sometimes these specifications do not account for limitations imposed by the blister materials, manufacturing process parameters and reagent chemical properties that react with the seal. There will be a unique limit to the maximum seal force that can be achieved depending on how those variables interact.

For one example, the upper limit of seal strength differs depending on foil and polymer coatings materials. Some materials might not be able to achieve a specified seal strength regardless of how manufacturing parameters are tweaked.

For another, temperature-sensitive reagents cannot tolerate prolonged exposure to high-temperature tooling responsible for welding blister material layers together.

How a device manufacturer can help

Partnership with a medical device manufacturer closes the circle for product developers by delivering a comprehensive understanding of manufacturing considerations to product development challenges.

J-Pac Medical was among the industry’s first to provide reliable manufacturing of reagent blister products. Our engineers’ expertise has been essential to identifying the fastest, most reliable and most cost-effective pathways to market for some of the most commercially successful diagnostic reagent blister products.

It’s helpful to show as well as tell, so we invite you to order a sample blister kit as you consider working with a manufacturing provider. And if you want to make our team part of your own, let’s get in touch.