Foil has traditionally been used in pharmaceutical packaging because of its high barrier properties in the face of extreme environmental conditions, including extremes of temperature and humidity. Paying particular attention to pack design can optimise these benefits by using advanced options rather than traditional solutions
An innovative foil ploughing mechanism produced highly consistent opening of small (3mm wide) sensor pockets
Dr Jez Clements, Partner and Senior Mechanical Engineer at Cambridge Design Partnership, describes key criteria in the design of innovative foil packaging for pharmaceuticals and argues that remaining conservative in design is not always the best approach.
Foil packaging is a competitive and complex industry, and one that benefits from considerable specialism in design and engineering. Designers involved in the production of foil solutions must employ a process of constant and considered innovation to ensure that they meet the strictly regulated and often complex design briefs of the pharmaceutical and medical device industries.
The most important challenge in many packaging designs is to understand the barrier properties required and how, exactly, these can be incorporated in the design. For example, the brief might include the requirement to minimise gas or moisture transportation across the seal and through the materials. Furthermore, a barrier needs to retain its extraordinarily high integrity right up to the point that it is used, stand up to several rounds of testing and provide a shelf life of up to five years.
It has to achieve this in the face of varied, unpredictable and aggressive environmental conditions, including high temperature and extremes of humidity. While various grades of plastics can provide some protection, only foil can deliver this total barrier solution.
Often large suppliers will employ specialist foils only when high order volumes are involved; otherwise they will try to steer customers into using existing foil types. While this can save development time, it can also result in inappropriate solutions.
Large suppliers also tend to insist on 3mm seal lands, which are unworkable in many projects: if a company needed a blister pack with 50 compartments, for example, the design could not afford to adhere to 3mm seal land constraints without dramatically increasing the size of the product.
The best way to avoid a design becoming hampered by conservative manufacturing criteria is to seek out options that keep the design of the product at the heart of the manufacturing process. Good packaging designers will push foil processes to their limits instead of following the solutions presented to them, minimising costs while adhering to a vigorous process of testing and measurement.
Even the most robust foil seal tends to need a laminate structure at its base, providing a potential weak point through which moisture can travel
The varying approaches to foil packaging seals can provide a good illustration of the difference between ‘conservative’ and ‘innovative’ design. Most foil packaging in the market applies polymer-to-polymer heat sealing, meaning that even the most robust foil seal tends to need a laminate structure at its base. These laminates provide a potential weak point through which moisture can travel.
However, more advanced options exist. Heat sealing can be combined with a process of folding and otherwise manipulating 2D foil sheets to produce 3D geometric seals. With this, a design can allow one sheet of foil to seal several sides of a complex structure. Ultrasonic sealing, on the other hand, provides a total aluminium barrier that can dramatically extend a product’s longevity.
A moisture sensor packaged within a humidity controlled environment
Designers must also take into account the various properties required of foil packaging as it moves through the supply chain. Testing needs to be rigorous enough to account for the dramatic changes in atmospheric pressure that can occur during freighting. This can cause seals to swell, weaken or burst, resulting in a damaged and unuseable product. Very thinly rolled foil can develop hard-to-detect pinholes (around the 5µm level). Testing needs to account for this, as well as any unusual or innovative structures employed.
Completely wet or completely dry environments are, of course, reasonably simple to maintain. Medical sensors and certain drugs, for example, can be extremely sensitive to a rise in moisture, so it is sometimes simpler to include desiccants that will take a multiple of the shelf life to saturate, thus ensuring equilibrium in the humidity levels for quite some time. Similarly, products such as contact lenses can simply be suspended in water.
Certain products require that the relative humidity within the blister be controlled for the duration of the product’s life. Thankfully moisture transport can be almost eliminated with foil, and compounds inside the packaging can be used to absorb and desorb substances to achieve a stable relative humidity. This maintains the optimum chemical structure of pharmaceuticals or, in the case of medical devices, helps to maintain properties such as ‘ability to flow’.
However, external temperatures change the ability of gases to support moisture changes as well. This results in changes to the atmosphere within the packaging. As the temperature of the air inside rises, it is able to carry more moisture. Once it cools it has reduced ability, and so the relative humidity changes, eventually resulting in condensation. Cambridge Design Partnership has found an innovative solution using materials that can be preconditioned to stabilise a known quantity of air for a known temperature range.
The opening of the product can also pose many dangers to the contents. How will the shape of the product, or the nature of its contents, or the condition it aims to treat, be affected by the way it might be opened? Also, an understanding of how cracks and tears propagate through the design is vital.
Small flakes of material could be lethal if they got into an inhaler
The properties of foil packaging, and in particular the manner of opening it, can be manipulated to fit with the product, but the criteria must be carefully considered as the stakes can be high. For example, small flakes of material could be lethal if they got into an inhaler.
Similarly, where particularly damage-sensitive drugs or devices sit close to the surface of the foil special piercing tools or ‘sardine can’ formats may be required. Alternatively, frangible seals might be considered, whereby permanent seals are used around most of the cell, with a different sealing method at one point creating a point of weakness that can easily be broken.
Innovative multi surface 3D heat seal enabling reduced manufacturing processes
In a heavily regulated sector such as pharmaceuticals, the key consideration with any product is to make sure that all aspects of the design cycle have been considered and regulations have been complied with. Foils need to pass a myriad of tests ranging from sterilisation, barrier forming, fragmentation and ultimate source traceability of the aluminium.
For these reasons it is vital to have a dedicated team of consultants familiar with foil who can provide all-industry expertise with a user-centred view, and create innovative bespoke solutions rather than simply design products to fit around existing technologies.