Valves are critical components of many disposable medical devices. They are responsible for controlling the movement of fluid, which could be a pharmaceutical or nutritional product, saline solution, blood, or other fluid. Almost all liquids must pass through a valve before reaching their destination.
These small, seemingly simple components are actually quite sophisticated. Engineers have many valve designs from which to choose. Selection usually starts with the basic specifications: connection port types, flow rate, opening pressure, and back pressure are among the most common.
However, it’s imperative to step beyond the specifications and examine a broad scope of user requirements to make sure the valve will function as expected over the device’s entire life cycle—from manufacturing through clinical use. There are several of the user requirements that are often unshared unless the valve supplier and the device engineer communicate fully.
Material compatibility is often viewed in terms of how the fluid going through the valve will impart stress to the valve. Certainly, that’s essential to know. Some drugs and fluids are corrosive: lipids, chemotherapy agents, and other caustic substances could require the use of one material over another. But material compatibility assessment also needs to extend into the manufacturing process. For instance, how will the valve interact with any tubing attached to it as well as the solvent used to bond the tubing to the valve? In addition, the valve might be attached to another rigid component. The torque required to attach the valve during assembly could cause cracking. Completely sharing what the valve will be assembled to, and how it will be assembled, will lower the chance of incompatibility.
Further, stresses are cumulative. One must consider the combination of all potential mechanical stresses and chemical stresses on the valve. Under a low mechanical stress (low pressure situations, for example), a certain chemical stress could be acceptable. But a high mechanical stress combined with multiple chemical stresses could result in malfunction. (See Figure 1)
Some valves do not permit passage of fluid until a specified pressure is applied, for example, by aspirating or injecting with a syringe. By their nature, they’re sealed. When both ends of a valve are open, it can be ethylene oxide (EtO) sterilized. However, a closed attachment on either end of the valve could act as a barrier to flow. The device may have to be designed to incorporate a venting mechanism so EtO can reach the entire valve. Other options could be gamma sterilization or pre-sterilization of the valve before assembly. Understanding how a valve will be incorporated into a final device, as well as the intended sterilization method, will ensure that potential issues are identified and mitigated early in the design cycle.
Criticality of Function
One of the things that should be discussed when dealing with an off-the-shelf valve is criticality of function for the given application. The risk assessment of the final device should include the valve criticality. What impact would a valve failure have on the ability of the device to function properly? And how would it affect the patient? Like any product, valves can be designed and tested to meet extremely rigorous demands. The criticality will influence the valve’s design and manufacturing methods to ensure it meets the requirements of the given application.
Length of Use and Shelf Life
One disposable device might be in use for an hour, another for three days. Anticipated length of use is crucial information. Valve manufacturers test their valves to a certain number of cycles based on patient contact and duration of use. Anything beyond the existing test limit will require additional testing and validation. The same holds true with shelf life. While many valves have a five-year shelf life, some have shorter ones. Additional age testing may be required to extend the labeled shelf life and ensure proper function.
Quantity over Time
Certainly, knowing the order quantity is mandatory when any valve is requested. But it’s especially influential when purchasing valves for disposable medical devices. Accurate projections of long-term volumes can impact decisions about tooling and assembly that could lower costs, improve efficiency, and ensure capacity over time. (See Figure 2)
While many manufacturers offer dozens of valves of various specifications for disposable medical devices, a host of additional variables should be considered before a valve is selected. Specifications are a great place to start a discussion with a valve vendor. But they are certainly not the only criteria to discuss. Communicating openly and fully with the valve supplier can help overcome unexpected problems and ensure that a valve functions as required.
This article was written by Ken Raines, Director of Intellectual Property, and Joel Bartholomew, Innovation Manager, B. Braun Medical, Inc., Allentown, PA. For more information, visit http://info.hotims.com/45605-162.