Heat Sealing Process Validation: Consider More than Time, Temperature, and Pressure

By Ray Johnson, Product Manager, and Mark Larson, Sales Engineer
Bosch Packaging Technology Inc.

Packaging plays a vital role in ensuring the sterility of medical devices and instruments from manufacture to point of use. Effectively heat sealing the packaging of terminally sterilized medical devices is arguably the most critical step to ensure the aseptic presentation of a product. No matter how robust the sterilization or disinfection process, if the packaging and seal closures of a medical pouch are compromised, there is significant risk of product contamination during shipping and storage that could pose serious danger to the end user.

Image of a band break detector courtesy Bosch Packaging Technology.

Validating the heat-sealing process is thus critical both to comply with regulatory oversight and to be confident in the overall quality of the final product. All components of the sealing process that influence package integrity must be monitored, measured, and controlled. Moreover, equipment must perform heat sealing in a repeatable, invariable manner such that final product quality is consistent with predetermined standards.

The relevant regulatory standard for validation of the heat-sealing process for medical applications is ISO 11607, Part 2. It specifies the validation requirements for the forming, sealing, and assembly process for the packaging of terminally sterilized medical devices. As laid out in the standard, the objective of seal process validation is to document the sequence of events in which the process is established to produce effective seals that maintain sterility to the point of use and do so in a repeatable, reliable way.

It is important to emphasize that the ultimate purpose of a packaging system for medical devices is the maintenance of sterility. Validation of packaging processes is crucial to guaranteeing the integrity of the final product.

ISO 11607 characterizes heat sealing as achievable with a bar sealer, impulse sealer, or a continuous feed sealer (rotary band sealer) and defines the critical sealing parameters as temperature, pressure, and dwell time. The standard dictates that critical process parameters should be controlled, monitored, and documented. In the event that critical process parameters exceed predetermined tolerances, alarms, warning systems, or machine stops should be initiated. Additionally, the standard indicates that critical process instruments and sensors must be calibrated.

Therefore, process control validation for heat sealing has typically dealt with three specific variables: dwell time, temperature, and sealing pressure. However, while consistency in these three variables is crucial for an effective seal, it is possible to thoroughly validate a packaging process for these three and still produce faulty seals that could ultimately imperil patient safety.

Example of a validatable continuous band sealer for medical applications courtesy Bosch Packaging Technology.

Any component of a sealing process is theoretically validatable. Process steps that can have negative effects on seal quality should be heavily scrutinized and be incorporated into validation. A few salient examples include wrinkle detection, band breakage, and label application.

Wrinkles can occur throughout the seal even if temperature, pressure, and dwell time are all operating within accepted parameters. An effective validation tool for wrinkle detection can sense a wrinkled seal, trigger an alarm, and cause the machine stop. If specified, an alarm can prompt a bag direction reversal and reject a bag back to the operator and then reverse back to normal operating direction once the defective bag has cleared the machine.

Likewise, band integrity is a critical factor not captured through traditional validation procedures (applicable for band sealers only). If all of the process variables are functioning within the effective ranges, but the sealer doesn’t have sealing bands installed, or they are worn, the creation of an adequate seal is not possible. A continuous sealer must monitor band integrity and be integrated into the PLC system to display current status and trigger alarms and stops when a band breaks or is missing.

Optical detection should be used for monitoring and ensuring accurate label application. A camera can capture the image of a finished package and compare it to a preprogrammed image in which the correct label has been accurately applied. Deviation from that standard image will result in a reject or alarm.

Though critical, these relatively prominent process parameters fall out of the traditional scope of medical heat sealing validation. However, validation should not be limited only to what has been mentioned here. It is important to be able to engineer in validatability in a flexible manner, such that, for a given requirement, a process step can be easily incorporated into the validation procedure. Naturally, the demands of the market drive product development. Today’s new requirement is tomorrow’s standard feature.

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