Anatomy of a glass vial

Hello everyone – I wanted to take some time with this post to cover basic terminology for the physical features of glass vials used as parenteral packaging.?This terminology is important because there are numerous performance characteristics that rely on specific dimensions and locations of a glass container.? I suspect that many of you reading this are already familiar with these terms, but let’s do a quick review to ensure that we’re speaking the same language.?I’ll also provide a non-exhaustive list of geometry-dependent performance characteristics as we walk through the anatomy of a glass vial.

Bottom

If you were to place a vial on a flat table, the bottom of the vial is a generally concave surface that is not directly in contact with the table.?The maximum distance between the vial’s bottom and the flat table, otherwise known as the “push-up”, is typically specified and varies depending upon the size of the vial.? Manufacturing defects such as a “concave bottom” occur when this maximum distance is exceeded and can lead to issues such as nozzle strikes (and subsequent glass breakage) during the vial filling process. ?While not frequently done, it’s also possible to manufacture vials with relatively flat bottoms to increase the contact area between the vial and the surface upon which it is placed.?This increased contact area can improve conductive heat transfer in applications such as lyophilization.

Footprint

The footprint could be regarded as that portion of the vial that is actually in contact with the surface upon which it is placed.?This sounds like a relatively straightforward concept, but the footprint can be difficult to define in practice.?For example, the vial manufacturing process can result in a footprint that intermittently contacts a surface.?Vials can become physically unstable given a certain distribution/amount of intermittent contact – this results in what is sometimes called a “wavy bottom” defect.?This instability can increase the likelihood of vials tipping over and lead to increased false rejects during in-process weight checks.?Issues can still arise even if the footprint exhibits 100% contact with a surface.

Heel

The heel could be considered a sort of transitional zone between the body and foot print of a vial.?In the case of converted tubular glass vials, the heel region is often associated with chemical heterogeneity on the interior surface that can increase the likelihood of glass delamination (see my prior post for more information on the origins of this heterogeneity).?The radius of the heel region can also have implications for mechanical reliability and machinability.?For example, a relatively small heel radius (i.e., a relatively sharp-cornered heel) can make a vial more prone to tipping over and to severe damage, cracking, etc. when the vial crosses transition points on a filling line.?Small heel radii can also lead to increased vial breakage (a so-called “lensing” failure) during processes such as lyophilization. ?A heel radius that is too large can also cause a “flared bottom” that creates vial handling issues if it balloons out past the radius of the vial body.

Body

The cylindrical section of the vial is called the body.?In the case of converted tubular vials, the body is dictated by the dimensions of the initial tubing.?The body should ideally be consistent in diameter with minimal ellipticity (i.e., the extent to which a cross-section of the body deviates from being a perfect circle) to enable consistent vial handling characteristics on fill-finish lines and inspection equipment.

Shoulder

The shoulder of the vial is another transitional zone from the body to the neck.?Improper forming of the shoulder can results in multiple defect types (e.g., flared shoulder, sunken neck, etc.) that impact machinability of the vial.?Consistent minor flaring of the shoulder region within a large population of vials can also lead to rings of abrasion damage around the upper circumference of the vial due to glass-on-glass contact (the same is true for the heel region).

Neck

Given its practical importance, one could argue that the vial neck is a somewhat underspecified feature.?Why do I say this??The inner diameter does have a specification (e.g., 7 mm ± 0.2 mm for 13 mm flange vials for the ISO converted tubular formats).?In addition, the ISO standard states that the inner diameter should be constant or perhaps a truncated cone if it meets certain requirements (larger diameter ideally at the top of the flange and not larger than the smallest diameter by 0.3 mm).?Care should always be taken to assess the dimensional stack-up of the inner neck feature with elastomer stoppers to ensure consistent stopper insertion and minimize the likelihood of stopper pop up.?The outer diameter of the neck only has a maximum specified value (10.5 mm for 13 mm flange vials), with no requirements for a constant diameter or taper.?As a result, I’ve seen quite a bit of variation in outer neck geometry amongst various sources – all within specification, mind you.?The external geometry of the neck can be important for multiple reasons, including but not limited to handling by grippers at the vial neck and consistent performance during the capping process.?Finally, the concentricity of the neck with the body of the vial (i.e., the extent to which the central axis of the neck and body coincide with each other) can also be important.?Significant deviation from concentricity can result in defects such as an offset finish that creates issues with vial handling (e.g., misalignment at hand-offs between format parts such as a star-wheel to a neck gripper) and processing steps such as washing or filling that require insertion of a nozzle.

Flange

The flange of the vial (also referred to as the finish, crown, lip, or collar) is generally the most important feature from a “critical to quality” perspective.?The top of the vial flange interacts with a compressed elastomer stopper to form what is called the “land seal” – i.e., the seal that is primarily responsible for maintaining sterility of the drug product.?Much like the neck, it is important to assess the dimensional stack-up of all the components being used (vial, stopper, and seal) to ensure compatibility under appropriate capping conditions.?In particular, the height of the flange is often thought to be the most important dimension to consider, although I’ve heard others mention that the radii of the flange corners can also play a role.?Defects that can affect the integrity of the flange sealing surface (e.g., chips and knots) must also be carefully monitored.

Blowback

The illustration that appeared at the very beginning of this post is missing one last feature that I want to briefly discuss.?Vials may or may not include a blowback, as illustrated below in Figure 1.?As previously discussed in the section concerning necks, a vial with no blowback should have a cylindrical opening (or perhaps a truncated cone).?The European style blowback is a protrusion that creates an undercut, while the American style blowback is a groove.?Blowbacks are used in theory to prevent stopper pop up and facilitate sealing between the stopper and vial.?I frequently get asked: “Which is better? Blowback or no blowback??European or American style?”?Given the evidence available to me, the only clear guidance I can provide is that any of these options can be made to work, provided that proper attention is given to overall compatibility of the primary packaging components and optimization of the stoppering and capping steps.?However, should someone choose to use a vial with a blowback, the European style is generally the more popular option for new products.?

Finally, I expanded upon this post last year by asking my readers for some assistance.? Anyone who has worked in this industry for a while knows that vial specifications don’t recognize borders.? On any given day, I might have to review documents provided by a pharma customer in the US, Brazil, Japan, France, etc., and there’s no guarantee that it will be in English (actually – the one from the US is probably in English, but I digress).? I assumed that others might be having the same experience as me (i.e., stumbling their way through translating specifications not in their native language), and so I decided to start a glossary in other languages as an easily accessible online resource.

Table 1 includes everything that I have so far.? A few comments:

·?????? This compilation is by no means complete.? There are obviously many other languages not captured here, and so I’m hoping this initial post will encourage others to make further contributions, thereby expanding this resource intended for the global packaging community.

·?????? Some of these terms are best efforts at an educated guess.? In other cases, no obvious equivalent was available.? For example, I had more than one person say they didn’t have a term for “Footprint”.? Please let me know if you have alternate suggestions or can fill in what is currently blank in Table 1.

·?????? The unexpected learnings were interesting.? For example, the French terms for the neck of a vial include “Bague”, "Cou", and “Col”.? “Col” is apparently an older term.? I’m assuming for now that “Col” shares etymological roots with the English term “Collar” – more research is required.? Refer to the Footnotes section for additional items of interest.

·?????? I’d like to thank everyone who generously helped me with this translation effort.? Please let me know if you can contribute to improving and/or expanding Table 1.?

Questions or comments? – please leave them below or feel free to directly contact me.

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Footnotes

1.?????? “Col” is an older French term for the neck of a vial. It's not clear to me how prevalent its usage is relative to "Bague" and "Cou".

2.?????? My understanding is that “Moletage” and “Barrettes” refer to different footprint shapes found in molded glass vials.? Equivalent English translations might be “Knurling” and “Strip”, respectively.

3.?????? The Serbian term “Grli?” is used to describe the combination of the Flange and Neck regions.

4.?????? The Turkish terms “Flan?”, “Birl?me”, and “Noktasi” are used to describe the combination of the Flange and Neck regions.

5.?????? The Turkish terms “Etiket Alan?”, “üst G?vde”, and “Alt G?vde” are also used to more specifically describe the “Label Area”, “Upper Body”, and “Lower Body” of a vial, respectively.