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Pharmaceutical Manufacturing and Packing Sourcer

Blistering Pace

A new whitepaper by a leading packaging expert into the integrity of pharmaceutical packaging has established that existing methods for testing the seal integrity of blister packs are not as accurate as newer, technology-based test equipment – such as non-destructive laser testing, which offers a credible alternative to conventional blue dye leak methods

The expert, Dr Dorian Dixon at the University of Ulster, discovered that a non-destructive laser test device was capable of detecting 15 per cent more product defects than the traditional blue dye test methods used by the majority of the pharmaceutical market (1). In a global market valued at over $40 billion per annum, where quality control is of paramount importance, a 15 per cent difference in the ability to detect if a blisterpack is correctly sealed or not is significant.

Study Design A preliminary study was conducted to determine the ability of a laser test device to identify defects in a wide range of blister pack designs. A design of experiment was used that would investigate the effect of pocket dimensions, foil thickness, pack material and defect size on detection rates by both the laser test device and blue dye testing. This study found that the laser test device test method found 100 per cent of 15 μm sized holes while only 85 per cent of such defects were picked up by blue dye testing.

In his whitepaper study, Dixon compared the ability of both the laser test device and the blue dye to detect defective pockets in blister packs. Thirty cavity PVC thermoformed packs sealed with a 25 μm foil laminate were used, with 12 μm or 20 μm holes laser-drilled into the packs to create defective samples. Ninety pockets were tested for each of the three sample types investigated (defect free, 12 μm or 20 μm holes). The defects were made approximately in the centre of the foil laminate covering each pocket and the dimensions of the holes were confirmed to a tolerance level of +/-2 μm using an electron microscope.



Blue Dye Test

The current industry standard for testing blister pack integrity is blue dye testing, which consists of placing a selection of packs into blue stained water, subjecting the packs to a vacuum of typically 400 to 600 mBar for several minutes and then removing this vacuum, which allows any defective pockets to take up the dye. The packs are manually deblistered and inspected for dye ingress. This technique relies on human subjectivity, and Dixon states that it is unlikely that the accuracy he achieved in his laboratory tests could be reproduced during routine factory quality control procedures.




Laser Test Device

A laser test device is a dry, non-destructive technique which uses a laser to measure changes in the pack profile that result from applying a vacuum.The lidding material of defective pockets will respond in a different manner to a perfectly sealed pocket when a vacuum is applied. Dixon states that the approach is preferable to systems that rely on contacting the lid material with a probe in order to measure pressure or displacement.

Laser test device testing consists of initially scanning the surface of each pocket in order to provide a datum value for subsequent deflection measurements. A vacuum level of 500 mBar is then applied and held for 10 seconds and the pack re-measured.Deflection refers to the difference in average height when the vacuum is applied compared to the datum value.The vacuum level is then reduced to 400 mBar and held for a further 30 seconds before the pack is scanned again.The variation in average height at the full and reduced vacuum levels is referred to as ‘collapse’.

Figure 1 illustrates the typical difference in deflection behaviour measured by the laser test device between a defect-free pocket (left) and one containing a 30 μm sized defect (right).The black dotted line is the profile of the foil surface before the vacuum is applied. It can be seen that a variation in profile exists between packs.The profiles after the full and reduced vacuum is applied are shown by the green and purple lines respectively. The solid blue line denotes the deflection, which is the difference between the profiles before and after the vacuum is applied, while the red line illustrates collapse (the difference between profiles at full and reduced vacuum). It can be seen from Figure 1 that the pack with a 30 μm hole does not deflect significantly from the initial profile when the vacuum is applied.The defect-free pocket however displays a large deflection and adopts a domed profile as a result of the applied vacuum. In this case, a deflection of 410 μm was recorded for the defect-free pack compared to only 4 μm for the pack containing the 30 μm hole. A large hole greater than 20 μm allows the pressure inside the pocket to equalise to the applied vacuum, inhibiting foil movement. Small holes manifest as a greater than normal collapse when the vacuum level is reduced.This occurs as the air slowly escapes through a small defect allowing the pressure inside the pocket to equalise with the applied vacuum.

Once the packs had been tested by the laser test device they were then subjected to the blue dye test.The packs which were submerged in methylene blue stained water and a vacuum of 500 mBar was applied.This vacuum level was maintained for a soak time of one minute.The vacuum was then released with the packs remaining in the dye for a further period of one minute to allow the dye to penetrate any defective pockets.The pockets were then opened and the contents visually inspected for signs of dye ingress.



Conclusion

Building on Dixon’s initial study, where all of the 15 μm holes were detected, the laser test device went on to detect 100 per cent of the 20 μm holes and 99 per cent of the 12 μm holes in the final whitepaper study. Conversely blue dye testing was only capable of detecting 85 per cent of the 15 μm holes, 90 per cent of the 12 μm holes and 99 per cent of the 20 μm holes.

Commenting on the results of the whitepaper,Dixon said,“Laser test device testing is a rapid non-destructive test method which can detect the presence of 12 μm, 15 μm and 20 μm sized defects in pharmaceutical blister packaging with a higher degree of reliability than conventional blue dye testing.” Dixon went on to conclude that “The nonsubjective nature of laser test device testing removes the possibility of human error and reliance on operator judgement, which a key element in the correct identification of small holes using traditional blue dye testing.”

As manufacturers seek to improve their levels of quality control and drive costs down, laser test device testing represents a significant improvement over traditional blue dye testing in terms of both accuracy and cost reduction.

References
  1. www.sepha.com/en/downloads/ new-sepha-white-paper
  2. Pilchik R, Pharmaceutical Blister Packaging, Pharmaceutical Technology: p68, December 2000
  3. Wright JM et al, Evaluation of the Use of Calendar Blister Packaging on Patient Compliance, Sexually Transmitted Diseases 26(10): p556, 1999
  4. Tablet Blister Testing, Lippke VC1360, www.lippke.com, accessed February 2011
  5. Kossinna J and Meyer A, Helium Leak Testing of Packages for Oral Drug Products, European Journal of Pharmaceutics and Biopharmaceutics 75(2): p297, 2010
  6. Wolf H et al, Vacuum Decay Container Integrity Testing, PDA Journal of Pharmaceutical Science and Technology 63(5): p489, 2009
  7. Stauffer O and Wolf H, Blister Pack Leak Detection, Pharmaceutical Solutions Update, Autumn 2007



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Phil Stevenson is Product Manager at Sepha and holds an MEng in Mechanical Engineering from Loughborough University. Prior to Sepha, Phil spent three years with Optimal Industrial Automation where he worked with a number of large pharmaceutical companies, advising on product, technical and production issues. Since joining Sepha, Phil as been instrumental in developing the Sepha non-destructive leak test device range. This range of innovative, accurate and objective leak measurement products can test across a wide spectrum of pharmaceutical delivery methods from blisterpacks to medical devices. Email: marketing@sepha.com
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