A Healthy Environment for Medical Device Development
24th April 2006
Innovations in mini-environments continue to cut costs and shorten development cycles for medical device manufacturers. A new generation of multi-chamber cabinets with multiplexed control systems enhances a broad range of biocompatibility testing, accelerated life studies and similar experiments.
Although heralded for years as a major breakthrough in critical environment manufacturing, mini-environments are hardly a one-design-fits-all solution to contamination control.
The term itself encompasses many distinct enclosures with very different applications. The designation "mini-environment" gained popularity as a particle-controlled enclosure designed to achieve clean conditions around electronics and semiconductor processing tools. Semiconductor mini-environments often include a robotic interface, thereby eliminating human-generated particulates from the manufacturing process.
In the life sciences, the term has been used in conjunction with containment chambers, isolation chambers, glove boxes (which can be configured for containment, isolation, or both), and even biological safety cabinets. Each of these enclosures plays an important role in medical device manufacturing, but each is generally limited by a single-enclosure design. Multiple operations must be performed sequentially, and exposure studies performed under differing environmental conditions require time-consuming adjustment and calibration of control systems.
An alternative to this single-chamber mini-environment extends desiccator technologies that have developed in parallel with those of the mini-environment. Originally designed as a dry storage chamber, often based on a renewable desiccant medium, desiccators have developed in sophistication, now incorporating automated monitor/control systems that regulate a flow of dry gas to maintain low-moisture chamber conditions. Like other mini-environments, they can also perform additional contamination control functions, including static elimination, low and high temperature cycling, and particulate filtration.
By controlling these conditions in multiple chambers, a multi-chamber mini-environment (MCM) provides a new range of benefits to medical device manufacturers.
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PDA-style computers can be configured to enter set point data and display environmental conditions
Chamber-by-Chamber Control Cuts Recovery Time to Seconds
Because many medical devices incorporate microelectronic components, their manufacture involves critical moisture exposure requirements common in the electronics and semiconductor industries. MCMs improve on the performance of conventional desiccators or other storage cabinets by providing humidity stability and uniformity throughout the cabinet, whether access doors are open or closed.
A separate high-accuracy, miniaturized humidity module in each chamber provides independent monitor/control capability. Each module can be programmed locally or remotely to maintain a humidity set point down to 0% RH. The purge controller directs dry process gas (generally nitrogen) only to the chamber where it is needed to keep the %RH level below the critical set point.
This highly efficient feedback/control system eliminates prolonged humidity spikes, which otherwise result when a chamber door is opened and which degrade sensitive medical device electronics. Compared to a flow-meter-controlled desiccator, an MCM cuts this recovery time by over 400% and saves over 75% in nitrogen expenses. More importantly, it ensures a zero-tolerance low-moisture environment.
Nitrogen Consumption |
Recovery Time |
| Fig. 1: 110 cu. ft. |
Fig. 1: 40 minutes |
| Fig. 2: 55 cu. ft. |
Fig. 2: 20 minutes |
| Fig. 3: 15 cu. ft. |
Fig. 3: 10 minutes |
To eliminate accidental moisture exposure, an MCM can be configured to activate safety alarms if a chamber door is left open or ajar.
Multiplexed Control for Differential Exposure Studies
Multiplexed monitoring and control also allow the user to specify a different set point for humidity, temperature or other environmental variables (depending on sensors used) for each chamber. Measured %RH or temperature levels can be displayed, and set point data entered, directly on chamber humidity modules as well as on a remote hand-held computer.
This flexibility has several important application benefits. It allows a single cabinet to store parts with varying exposure sensitivities. It also allows accelerated life or biocompatibility testing under varying humidity or temperature levels. Multiple environmental set points in a single cabinet also facilitate evaluation of packaging materials, encapsulants, and similar materials under many different conditions simultaneously.
Substituting other environmental sensors expands this operational versatility, further blurring the line between a dry box and an environmental test chamber. Specialized sensors installed inside a chamber can be used to monitor the concentration of specific biological agents, such as spores, gas or aerosols. In these scenarios, the same control system that regulates the purge of dry gas in a desiccator maintains a specific concentration of test substance in each chamber. This capability accelerates material exposure studies performed on medical implants, inhalation studies performed on laboratory animals, or out gassing studies performed in various process gas environments.
Cabinet designs can be optimized for the particular tests being performed. Like other environmental test chambers, multi-chamber mini-environments are available in a wide range of application-sensitive materials, including 316L stainless steel, anti-microbial steel, and plastics that resist disinfectants, dissipative static charges or shield against UV light. Thermal insulation can be specified for high/low temperature studies, as well as germicidal or fluorescence detecting UV lighting. Process-compatible materials include bio-inert seals and gaskets.
Author : Alan Waterman-Smith - C.Eng. M.I.E.E. Managing Director Sirus Microtech Ltd.
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