Pharma glass defects - 34. Scuff
Welcome to Part 34 of an ongoing series about visual defects that may be observed in pharmaceutical glass vials. Today we’ll be discussing the “Scuff” defect, which is defined by PDA TR 43 as a “cluster of several fine external surface abrasions”. This definition helps to set the Scuff defect apart from the Scratch defect, which is a single line of damage that will often be longer/wider than one of the individual lines of abrasion within a Scuff.
Figure 1 shows a magnified view of a Scuff defect on the exterior surface of a vial. These Scuff marks were created using a simple demo that I perform to demonstrate the effects of friction between glass containers. I take three vials (held in contact with each other by an appropriately sized rubber band) and rub them together between the palms of my hands. In addition to producing a sound that induces instant teeth clenching, you can readily observe the surface damage to the vials. This speaks to the basic mechanism for creating Scuff defects – i.e., glass-to-glass contact and/or contact between glass and other surfaces during vial manufacturing, shipping, or handling during the fill-finish process.
A Scuff defect is considered Minor if the cluster of fine abrasions covers ≥15% of the surface area of the vial body (see Footnote 1). Assessing the coverage requires a suitable measuring device such as an eye loupe with graduations to measure distance, a caliper, etc. Otherwise, a Scuff is classified as an Acceptable Imperfection.
PDA TR 43 states that a Scuff defect can affect the aesthetics of the container, meaning a negative impact on visual inspection and possible product yield. However, I would point out that what seems like relatively minor damage associated with a Scuff can still reduce the strength and mechanical reliability of a glass container. Why is this the case? In brief, flaws on a glass surface can act as “stress concentrators” – i.e. the flaws essentially act as micro-scale levers that can amplify applied tensile stresses to a point that induces fracture of the glass. You can review my prior post on the strength of glass for more information.
Questions or comments? – please leave them below or feel free to directly contact me.
Footnotes
1. The criticality threshold for a Scuff is based on assessing the size of the defect relative to the vial body surface area. That sounds straightforward enough, but I wonder about how consistently the term “body” is being defined amongst suppliers and users. I’d be curious to hear from readers who have direct experience with this topic.
About the Author
Matthew Hall is Technical Affairs Director for Corning Pharmaceutical Technologies , a manufacturer of primary glass packaging for parenteral drug products. Based in upstate New York, Dr. Hall serves as a technical expert supporting business operations, sales, and marketing and educating customers on pharmaceutical glass packaging. He is a member of the Parenteral Drug Association and the International Society of Pharmaceutical Engineering.