Single-use Disposable Technology
There is an increasing trend in the industry toward single-use disposable technology in process development and both clinical and commercial production. Monitoring pressure in disposable manufacturing requires optimal process solutions.
If silicone or other tubing is being used, stainless steel pressure transmitters can also be used. However, tubing adapters, gaskets, clamps, and a sanitary tee may be required with this traditional set-up. Parts cleaning, tracking, sanitization, and possible re-sterilization are also needed. If the process is sterile, a stainless steel transmitter is frequently sterilized by moist heat.
Some pressure transmitters are compatible with steam-in-place and only the product contact surface is exposed to steam, and some can be placed in an autoclave where the entire unit is exposed to steam. Many single-use process components, however, are not compatible with moist-heat sterilization temperatures and are gamma radiated before delivery to the end user. In this case, separate sterilization of the stainless steel pressure transmitter device is required, along with a potentially nonoptimal connection to the previously gamma-radiated disposable assembly.
A more ideal solution for the end user would be to have a single-use pressure sensor that arrives integrated to the single-use process assembly and gamma-radiated with the process assembly.
Disposable pressure sensors with a narrow flow-through path with luer fittings on the inlet/out, commonly used in the medical field, have been used for process R&D and small-scale production by some companies. They can be delivered to the end user as part of a disposable assembly or presterilized and individually packaged for aseptic connection to a process assembly.
For small-scale processes, the medical sensors can be used with flexible tubing in a flow-through mode with the use of hose barb to luer adapters. When working with small ID tubing, these disposable pressure sensors are useful because it may be difficult to connect traditional pressure-measurement devices to the process stream. For wider flow paths, a hose barb fitting with a luer port can be used (Figure 1).
To better determine the applicability of MEMS disposable pressure sensors, like those used in medical applications, for use in bioprocess applications, testing was done. Micro Electro Mechanical System (MEMS) is the integration of micromachined mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology—a system on a chip.
The MEMS pressure sensor is manufactured using a silicone micromachined piezoresistive sensing element in a Wheatstone bridge circuit where applied pressure to the circuit gives a proportional output voltage. Testing of the pressure sensors yielded positive results with the accuracy, repeatability, and robustness required for bioprocess applications.