Miniaturizing Non-Spill

Accurate handling of fluids is essential in analytical and in-vitro diagnostic tools, and leaks of any kind can have critical implications. In hospitals or analytical labs, the risks are even higher, where leakage in test equipment can lead to potentially harmful chemicals entering the environment, not only affecting analysis results, but also compromising the safety of staff or patients. While technicians may not always be aware of the technologies working behind the scenes, a variety of different solutions are currently employed to manage fluid transfer and reduce the likelihood of spills – from traditional products, such as luer-lock and hose-barb fittings, to the more advanced lines of innovative, non-spill connectors.

Non-spill connectors developed by companies such as Colder Products Co. have been an integral component of flow-management applications for decades. Colder’s non-spill connectors allow users to connect and disconnect tubing without even a drip of liquid escaping the fluid system. This is especially important when handling potentially bio-hazardous waste materials, such as those found in molecular diagnostic waste receptacles. Non-spill connectors are ideal for systems that require zero air inclusion for accurate test results, or in areas where buffers, diluents, or reagents are frequently connected and disconnected.

However, industry requirements continue to change, with the trend moving to smaller, more compact solutions. Recently, designers at Colder faced the need to create a new non-spill connector that was one-quarter the size of their smallest existing technology. Miniaturizing components to create a non-spill connecter within the overall size constraints while providing an easy-to-use connector with high-flow characteristics brought about a unique set of challenges that required engineers to combine Colder’s expertise in connector design, material innovation, and tooling to create the NS1 – the smallest plastic non-spill connector available to date.

Evolution of the Non-Spill Connector
Non-spill solutions, such as Colder’s line of NS connectors, include fixed and moving components in both the insert and the body of the connector. A rigid stem inside the connector body depresses a valve on the insert, which itself holds open the outer sleeve on the body. Only when these two circumstances are met is the flow channel opened – otherwise it remains closed and leak-free by default, making the connectors highly suitable for transferring fluids that are toxic, biological, expensive, or simply messy.

Colder began developing its line of non-spill connectors more than a decade ago with the introduction of a 3/8" flow connector designated NS6 (standing for 6/16" inner diameter aperture). The NS4 (1/4" flow) followed shortly after and has proven to be one of Colder’s flagship technologies. Featuring an intuitive interface, with an audible “click” for technicians to recognize when the connection is secure and a simple thumb-latch for easy release, the NS4 is found in a wide range of applications where a reliable connect/disconnect is needed – from advanced therapy hypothermia devices to cleaning-chemical systems and fluid collection. A further addition came with the introduction of the NS2 1/8" flow connector, which departed from the original form-factor by eliminating the thumb latch and replacing it with a twist-to-connect mechanism to meet the need for smaller, more cost-effective medical couplings.

While the NS2 found wide acceptance, it raised awareness for the benefits that a small, reliable non-spill coupling can bring to a device or machine. Customer feedback for new applications with even smaller geometries showed the need to reduce the size further. It also became clear that some applications were looking to create closed systems with small profile non-spill connectors in order to reduce operational risks. With in-vitro diagnostic tools, even a small volume of air introduced into the system is enough to invalidate the test results, thus requiring a re-test of the sample. In some cases, the need came about because an existing technology was shrinking in size and required a new generation of connector. In others, because a target application was simply too small to accept existing technologies.

Medical Laboratories
In-vitro diagnostic equipment manufacturers are making their instruments smaller so that they can be used in an office or clinical environment where space is at a premium. This new requirement highlighted the need for a smaller non-spill connector, but the company also saw the opportunity to expand into new applications where the original NS series – and its sister PMC line – were not the perfect fit.

High-volume testing applications in hospital labs require frequent connection and disconnection of test equipment, reagents containers, and chemical bottles within confined spaces. This equipment frequently uses semi-rigid microbore tubing either attached to luer fittings or secured to bottles directly, often with multiple lines being affixed to a single container. Design engineers recognized that these applications would benefit from a non-spill connector that could prevent chemicals from evaporating, which reduces the concentration and can ultimately affect test results. At the same time, existing connectors like the company’s PMC12 were too bulky to allow for four to five connectors to merge on one container lid or cap, and the application called instead for a solution with a markedly smaller footprint. If a smaller, sleeker design was available, equipment design engineers would no longer need to hide the unsightly reagent bottle connections – typically hidden under or behind the analytical equipment – and get their reagent bottles closer to the machine, thus reducing the amount of tubing required to connect to the equipment.

From initial discussions with existing medical customers, Colder engineers determined that an entirely new connector needed to be designed – one that was half the flow size of the NS2 but that still incorporated the familiar thumb latch that made the NS4 and NS6 so easy to use.

The concept appeared simple – miniaturize the NS4 design for a 1/16" flow connector, to be designated NS1.

Overcoming the Challenges
There are currently few non-spill connectors available on the market at the 1/16" flow specification, and these are typically made of either brass or stainless steel, the latter of which comes at a high price point while the former has low chemical compatibility, making it unsuitable for many applications. Plastics, which are typically both more cost-effective and chemically resistant would, therefore, seem to be the optimal materials for a new connector design.

As they approached the process of designing the NS1, Colder’s engineers already had experience in shrinking the NS series. However, while the NS2 had featured a different connection, it was essentially a downscaled NS4. For the NS1 it quickly became apparent that this scale of miniaturization would be considerably more demanding.

Creating the NS2 had largely been a matter of reducing each component’s size – a challenge in and of itself. The designers were not able to follow a similar route for the NS1 because of one significant hurdle. While the individual parts of the connector had to be essentially one quarter of the size of the corresponding NS4 pieces, the tolerance and performance had to remain the same as in the larger connectors.

In addition, while some components could be minimized easily, Colder engineers found that others would not perform in the same way when shrunk beyond a certain point. Reduced thickness of the plastics, for example, meant that components could not tolerate the same stress as the larger fittings and would instead begin to warp. In some cases, the non-spill valve itself was compromised – the stem on the body being too thin to remain rigid through repeated use, buckling under the pressure rather than pushing open the valve. Even elements as comparatively simple as the thumb latch proved a challenge with test users complaining that they could not easily disconnect the connector because the latch was too small to depress comfortably.

It was apparent that the only way to succeed with the NS1 would be to individually examine and review every component of the NS4 – and every process used to manufacture it – in order to understand where adjustments needed to be made and to evaluate alternative approaches.

It was determined that the visual and functional design of the connector would remain unchanged, with one noticeable exception – the thumb latch. As Colder engineers had found, a connector that was one quarter the size of the NS4 in all respects simply was not as easily manipulated in the palm of the hand. Moreover, when users attempted to use the correspondingly small latch, it was uncomfortable to push it hard enough to open. Counterintuitively, Colder engineers opted instead to create what would proportionally be an over-sized latch – the one component that would be comparatively bigger than the rest of the connector in order for it to be simple and intuitive to use. Through numerous tests and multiple rounds of customer feedback, researchers determined that a new latch approximately half as big as the NS4’s would remain comfortable to depress without dramatically increasing the connector’s form factor.

Material selection was equally important. The NS4 line was predominantly made of polypropylene, but Colder engineers had already found that this material became too soft and pliable at reduced thickness, leading to early models quickly warping and buckling. Instead, engineers reverted to a prototype for the NS1 that used an alternative material – polyether ether ketone, or PEEK – which offered the necessary sturdy mechanical and chemical properties to meet high design tolerances in a small form factor. While an NS1 made entirely out of PEEK would prove cost-prohibitive, Colder engineers recognized that the stronger, more rigid plastic would be perfect for the thumb latch and valve stem, both of which were most prone to warping.

New materials alone would not solve every challenge, however. While PEEK could be used to replace certain parts, the rest of the connector would still be made out of polypropylene, in particular the two halves of the body within which the individual components are fitted. These halves would then need to be bonded together using spin-welding – a method whereby one half is held rigid while the other is affixed and then spun at high speeds, creating friction that melts the plastic sufficiently to bond the pieces together. The existing equipment used was not suitable as the NS1 parts were so small that the machine could not grip them properly and instead rotated freely without spinning the body halves. This necessitated a full redesign of the process.

Even a component as simple as the O-ring, which is designed to be seated in a groove and compressed during connection to create a tight seal at the interface, needed to be reviewed and addressed. Miniaturization of this O-ring necessitated a much smaller cross-section, which in turn meant that the material was much less forgiving. While on the NS4, the O-ring could be stretched over the lip of the insert, whereupon it would then snap to size within its groove. When engineers attempted to mimic this on the NS1, the O-ring either snapped due to over-stretching or would not shrink back to size once past the lip. Adjustments to the equipment design finally overcame this challenge, and the connector is now assembled with a new manufacturing process with new equipment developed to minimize the force on the small-sized O-rings.

Introducing the NS1
From early ideation and through a complex creative process, the NS1 underwent a number of radical shifts in design and development prior to its launch in the summer of 2013.

The end-user experience was critical, and the final design features an enlarged thumb latch with a spring to provide a responsive “click” that is intuitive to use and reassures technicians that a positive link has been made – and is a mark of the reliable Colder connection. Composed of standard and glass-filled polypropylene with a PEEK thumb latch and an EPDM O-ring, the NS1 features the tightest inner diameter tolerances ever on a connector and, as standard at Colder, has been tested to perform reliably for the life of the product.

At the same time, the NS1 continues to meet the high standards that Colder demands of all its non-spill connectors in response to customers’ requirements. The rotating design allows tubing to move freely or relax without kinking or leaking, creating a closed system for drip-free disconnect with ultra-low air inclusion, which minimizes contaminants and eliminates the need to purge air bubbles from the system. Currently available with both hose-barb and 1/4-28 thread terminations, the NS1 is suited for high performance across a broad range of demanding applications, from analytical lab instrumentation to in-vitro diagnostic equipment.

Refined and perfected over the course of several years, the NS1 from Colder Products Co. is today one of the most advanced and smallest plastic non-spill connectors currently available.

Colder Products Co.
St. Paul, Minn.
www.colder.com

About the author: Jim Brown is business unit manager for medical markets at Colder Products Co., and has been customizing fluid connections for more than 20 years. He can be reached at jim.brown@colder.com.