Medical Device Link.

FEATURE

Image: OLIVER MEDICAL

The ultimate defence

As the last line of defence between the medical device and bacteria, sterile barrier packaging plays an important role in patient safety. As such, failures in medical packaging materials present serious issues for medical device manufacturers. Measures can and should be taken to avoid them. A breach in the sterile barrier system can be associated with a pinhole or crack in one of the package materials or a leak in the seal. If a failure is observed in the field, the result can be as costly as a product recall and can include a damaged reputation in the market place. This article examines how device design, materials choice, package design, sealing/forming process, and package distribution and handling can affect the potential for package material failures, and the measures that can be taken to avoid them.

Medical device design

Figure 1: Round rather than square edges reduce the potential for pin holing.

When possible, a packaging professional should provide input during the design and development of the medical device. Because many medical device components are formed by an injection moulding process, it is important to ensure that mould flash is minimised. A part that exhibits excessive flash can easily puncture the film of a pouch or thermoform-fill-seal (TFFS) package and cause a breach in sterility. For injection moulded components, corners and edges should be round instead of square to reduce the potential for pin holing of the packaging materials (Figure 1). When designing new device components, sharp edges should be avoided by making radii as large as possible. This will reduce future expense when packaging materials are chosen and validated. If a device is designed with the minimal number of sharp components, lower cost films can be used, thus lowering costs for medical device manufacturers on an annualised basis.

Packaging materials and components

Choosing the right supplier is just as important as choosing the right packaging materials. Device manufacturers must ensure that the supplier has a strong quality system in place. Material defects such as gels, thin spots and seal failures often originate in the supplier’s manufacturing process. Manufacturers should make certain that the supplier has robust process validations in place to support the production of defect-free materials. Attention should be paid to how the supplier handles materials internally and how they are shipped to the manufacturer. Is adequate protection provided during transit to prevent damaged rolls of film, such as the use of core protectors, protective bags corrugated shippers? Are premade pouches packed in bags to protect against particulate, and in appropriate sized cartons to prevent folding or bending that can result in delamination or flex cracking?

Package design

Figure 2: Pressure on the seal of the package causes seal creep. (click image to enlarge)

When designing a sterile barrier package for a medical device, the size, shape and weight of the device should be considered. If the device is exerting pressure on the seal of a package, seal creep can occur during ethylene oxide sterilisation (Figure 2). The depth of a TFFS package is also critical. If the package is too deep, the film thickness will need to be increased to maintain sufficient strength. If the package is not deep enough, there is the risk of the product putting pressure on the lid of the package. If the size of the device is close to the volume limit of the TFFS cavity, tubing or other components of the device can be pushed into the seal as the machine is indexed. Both scenarios can result in a breach of the sterile barrier and problems are often not detected until the end user attempts to use the device.

Figure 3 : The corner radii of the formed cavity should be maximised. (click image to enlarge)

When designing a TFFS package, the corner radii of the formed cavity should be maximised (Figure 3). This will allow for better forming of the bottom film into the corners of the cavity. The corners and sidewalls are typically the thinnest and weakest areas of a TFFS package. Maintaining the thickness of the bottom film in the corners and sidewalls will result in better resistance of the package to puncture and flex cracking.

Device manufacturers should be sure to design pouches, trays and TFFS packages with sufficient seal widths. Narrow seal widths are less able to withstand a rigorous sterilisation and distribution environment. Another point to consider when choosing films and lidding for the unit package is the type of materials that are acceptable for the application. For example, sharp bulky products may require tougher films such as nylon. Manufacturers should utilise packaging suppliers’ expertise when selecting materials for their applications.

Sealing process

Figure 4 : Undersealing produces weak or light seals. (click image to enlarge)

Defects in the seal can often be traced back to problems in the sealing process. When troubleshooting a seal defect, it is important to consider the state of the sealing equipment. Are gauges calibrated? Are preventative maintenance procedures in place and followed to ensure seal gaskets and tooling are in good working order? Are the parameters of temperature, pressure and dwell in control? Undersealing, which produces weak or light seals and potential channels, is typically caused by having too little heat or dwell time when creating the seal (Figure 4). Oversealing, which produces transparent looking seals and/or tearing and delamination when peeling open the package is typically caused by too much heat, pressure and dwell time (Figure 5). When defining the minimum seal strength requirements, it is important to verify that sterilisation and distribution environments can be withstood.

Distribution and handling

Figure 5 : Oversealing produces tearing and delamination. (click image to enlarge)

Product distribution and handling environments are commonly overlooked, but they are responsible for a large number of the medical packaging defects seen in the field. When reviewing package handling inside the manufacturer’s facility, it is important to consider how the unit package is transferred from the sealing operation to its final shipping carton. Belted conveyor systems and transfer chutes should not put the unit package in contact with sharp objects such as staples and bolt heads. In addition, the conveying system should not expose the package to large free-fall drops that can create punctures in the sterile barrier. When human interaction is required to handle packages, operators should be trained to minimise the potential for damage that can be created by dragging packages across rough or abraded surfaces.

When reviewing package handling external to the device manufacturer’s facility, it is important to consider how the master shipping cartons are distributed to the end user. The method of packing and shipping, by pallet load or individual case, will affect the level of shock and vibration that the package will endure. Individually shipped cartons are more likely to experience extremes in shock and vibration; this should be taken into account when designing the packaging system to avoid defects. Will the package be exposed to altitude via air shipment or truck shipment in moutainous regions? If so, package materials must be porous or incorporate high seal strength to avoid prematurely opened seals caused by pressure differentials. Will the product be exposed to high temperature and humidity? Seals must be able to withstand the heat they will be exposed to in the distribution cycle.

Conduct a review

Sterile barrier packaging plays a critical role in patient safety by keeping bacteria from the medical device. A simple review of the areas mentioned in this article can greatly reduce the risk of failure of the medical device sterile barrier system. Using a rigorous validation plan for both the package sealing/forming process and the package system will further help to reduce the risk of failure. The areas reviewed in this article should be accounted for in a comprehensive validation plan. A proper review of all areas of risk and mitigation of those risks will help ensure a robust sterile barrier system is produced that is free from defects. This will provide a medical device that is sterile to the point of end use.

Kevin Zacharias is an Engineering Programme Manager at Oliver Medical, 445 Sixth Street, NW, Grand Rapids, Michigan 49504, USA, tel. +1 616 456 7711, e-mail: kzacharias@olivermedical.com, www.olivermedical.com.