Internal Pressurization Seal Testing for Medical Device Packaging

Internal pressurization seal testing is a proven method for evaluating the seal strength and overall integrity of medical device packaging by introducing pressurized air into a sealed sterile barrier system. By driving packages to burst, creep, or bubble-emission endpoints, manufacturers can validate sealing processes, detect gross leaks, and demonstrate compliance with ISO 11607 and related standards. This article explains the principle, applicable samples, test items, methods, and practical applications of the internal pressure method for medical packaging seal testing.

Technical Overview

The internal pressure method is a destructive or semi-destructive test technique used to assess the hermetic quality of seals in medical device packaging. Pressurized air is introduced into a sealed package through a puncture probe, needle, or specialized fixture, and the package is then subjected to a controlled pressure profile until a defined endpoint is reached, such as seal rupture, sustained pressure hold, or the visual observation of bubble emission in a water bath.

This method serves two complementary purposes: it quantifies the mechanical strength of the seal (how much internal pressure the seal can withstand before failing) and it verifies gross leak resistance (whether the package maintains integrity under internal pressure without losing air). The approach is directly referenced in several internationally recognized standards, including ASTM F2054/F2054M (burst testing of flexible package seals by internal air pressurization), ASTM F1140/F1140M (resistance of unconstrained and constrained packages to internal pressurization), and ASTM F2096 (detection of gross leaks by internal pressurization and bubble emission). These techniques support compliance with ISO 11607-1 and ISO 11607-2, as well as their Chinese counterparts GB/T 19633.1 and GB/T 19633.2, which govern sterile barrier systems for terminally sterilized medical devices.

Testing can be performed in either an unconstrained configuration, where the package is free to expand, or a constrained configuration, where the package is held within a rigid restraining fixture that simulates product support and directs stress toward the seals rather than the package walls. The choice of configuration significantly influences the measured failure pressure and must be defined in the test protocol.

Testing Samples

Flexible Pouches and Bags

The most common test articles include sterile barrier pouches made from porous materials such as medical-grade paper or Tyvek-type flash-spun polyolefin laminated to plastic films, as well as header bags, gusseted pouches, and roll-stock packages sealed on three or four sides. Flexible packages are typically tested in the unconstrained configuration unless product simulation is required.

Thermoformed Trays with Lidding Films

Rigid or semi-rigid thermoformed trays sealed with lidding films, including blister trays for syringes, catheters, implants, and surgical instruments, are frequently evaluated using the constrained method. The restraining fixture prevents tray deformation and focuses the internal pressure on the peripheral seal, which is usually the weakest and most critical interface.

Various Sealing Formats and Materials

Samples produced by heat sealing, adhesive sealing, or ultrasonic welding across different material combinations can be compared using this method. It is equally applicable to validation lots, production samples, packages subjected to simulated distribution hazards, and aged samples from stability studies.

Testing Items

Internal pressurization seal testing typically covers the following measurable outputs:

• Burst pressure: the maximum internal pressure a package seal withstands before failure, reported in kPa or psi.
• Creep resistance: the ability of a seal to sustain a specified pressure (commonly a percentage of the burst pressure) for a defined hold period without failure.
• Creep-to-failure time: the elapsed time until seal failure occurs at a constant applied pressure.
• Gross leak detection: identification of continuous air escape, observed as a steady stream of bubbles when the pressurized package is submerged underwater.
• Failure mode and location: documentation of which seal or seal segment fails first, valuable for process diagnosis and design improvement.

Testing Methods

Burst Test Method

In the burst test, the package is mounted on a pressurization fixture and air is introduced at a controlled, steady ramp rate, commonly around 10 kPa per second or as specified in the product standard. Pressure increases until the seal fails, and the peak pressure at failure is recorded. Burst testing under ASTM F2054/F2054M and ASTM F1140/F1140M provides a quantitative index of overall seal strength and is widely used for sealing process validation and comparative material evaluation.

Creep Test Method

The creep test applies a constant internal pressure, typically set at a defined fraction of the previously determined burst pressure, and holds it for a specified duration, such as 15 to 60 seconds or longer. The package either passes by maintaining the pressure without seal failure or fails by creep rupture. Because it applies sustained stress similar to real-world pressure exposure during sterilization, transport, or altitude changes, the creep test reveals slow-seal weaknesses that a rapid burst test may miss.

Bubble Emission Gross Leak Test Method

Following ASTM F2096, the package is pressurized while fully submerged in a water bath. A continuous, steady stream of bubbles from any seal area or package surface indicates a gross leak, while isolated bubbles caused by entrained air in porous materials are disregarded. This method is particularly useful for porous packages, such as paper or Tyvek-type pouches, where vacuum-based leak methods are difficult to apply, and it confirms the absence of unsealed channels, seal defects, and material breaches.

Constrained Versus Unconstrained Configuration

In the unconstrained configuration, the package inflates freely and failure often initiates at the most stressed seal region. In the constrained configuration, the package is enclosed in a rigid fixture sized to the actual product, limiting wall expansion and directing the pressure load onto the seals in a manner that better simulates in-use conditions. Test reports must clearly state which configuration was used, because failure pressures from the two modes are not directly comparable.

Applications

Internal pressurization seal testing supports multiple stages of the medical device packaging lifecycle:

• Sealing process validation: establishing optimal heat-sealing parameters of temperature, dwell time, and pressure during installation, operational, and performance qualification.
• Routine quality control: periodic verification of seal consistency in production, including evaluation of lot-to-lot uniformity.
• Package design and material selection: comparing candidate films, coatings, and tray geometries during development.
• Distribution and stability studies: confirming that seals retain adequate strength after simulated transport hazards, sterilization cycles, and accelerated or real-time aging.
• Regulatory compliance: generating objective evidence of sterile barrier system performance for technical files and submissions aligned with ISO 11607 requirements.
• Failure analysis: locating the weakest seal segment and diagnosing process drift or tooling defects when complaints or deviations occur.

Many manufacturers partner with accredited third-party laboratories to perform these tests under ISO/IEC 17025-accredited conditions, ensuring that results are recognized by regulatory authorities and global customers.

FAQ

What is internal pressurization seal testing for medical device packaging?

It is a family of test methods in which air is introduced into a sealed package to evaluate seal strength and leak resistance. Depending on the protocol, the package is pressurized to burst, held at a constant pressure for a creep test, or submerged and observed for bubble emission to reveal gross leaks.

Which standards govern the internal pressure method?

The principal standards are ASTM F2054/F2054M for burst testing, ASTM F1140/F1140M for constrained and unconstrained package testing, and ASTM F2096 for gross leak detection by bubble emission. These methods support the performance requirements of ISO 11607-1 and ISO 11607-2, adopted in China as GB/T 19633.1 and GB/T 19633.2.

What is the difference between a burst test and a creep test?

A burst test raises pressure continuously until the seal fails and reports the maximum pressure achieved, reflecting overall seal strength. A creep test holds a constant pressure for a set time and reports pass or fail, reflecting the seal's ability to resist sustained stress over time.

When should the constrained method be used?

The constrained method is recommended for thermoformed trays and packages with a rigid product inside, because the restraining fixture mimics the support provided by the product and applies stress primarily to the seal area, yielding results more representative of actual distribution conditions.

Can this method detect very small leaks or pinholes in the packaging film?

The bubble emission variant is designed for detecting gross leaks, such as unsealed areas and channel defects, rather than micro-leaks. For fine leak detection, complementary methods such as helium leak testing or other high-sensitivity techniques should be considered based on the package design and risk assessment.

How many samples should be tested?

Sample size depends on the purpose of the study, the statistical justification in the validation protocol, and the applicable acceptance criteria. Process validation typically requires a statistically significant number of specimens drawn from multiple production runs, while routine monitoring may use smaller periodic sample groups defined in the quality plan.