Enhancing Patient Safety through the Use of a Pharmaceutical Glass Designed To Prevent Cracked Containers

Cross-sectional schematic of a glass article under uniform applied tension, showing low level stress (grey shading) throughout the part and high stress concentration (dark grey shading) near the flaw tip.

Vial schematic labeled with common locations. The highlighted regions (Body, Heel, & Footprint) show where more than 90% of cracks are introduced.

Photograph of a borosilicate vial returned from the field with a bump check crack that extends through the glass wall that was formed during shipping to the health care facility.

Mechanical testing equipment designed to replicate the features of a bump check crack by loading a vial heel with a sacrificial borosilicate glass ball.

Optical microscopy comparison between a field return bump check crack and the laboratory replication, showing key fractographic features: frictive material transfer, crescent-shaped initial crack, and fracture propagating away from the origin creating “wing-shaped” features. The replication of these features demonstrates that the mechanical testing equipment is able to generate bump check cracks in borosilicate vials.

Schematic of two-step process of creating lens cracks. At left, the borosilicate glass vial is pressed into silicon carbide fixed abrasive paper (textured surface contacting vial footprint) with a 10N load, creating initial surface damage in the footprint region. At right, the center bottom is then lightly struck with a low-pressure pneumatic actuator putting the footprint in tension and propagating the initial damage to a lensing crack.

a) Field-returned borosilicate vials that experienced a lensing crack that propagated up the sidewall from additional applied stress but did not break the vial. b) Optical microscopy image of two vials from controlled lab experiments that replicated these lensing cracks.

a) At left, seal crimping equipment configured to shape aluminum caps on vials. When operating, the crimping wheel (at lower left of image) is displaced a fixed distance toward the neck OD (at lower right), bending the aluminum cap under the flange. The vial being processed has larger neck OD, causing the crimping wheel to damage the glass surface in the vial neck. b) At right, rotary disc blade cutting into vial neck mimicking the location of damage from seal crimping equipment contact. Cutting through the vial neck with the rotary disc without the vial breaking demonstrates the stable nature of cracks in conventional glass vials. However, if the vial breaks before the disc can completely penetrate through the neck, that vial is not at risk to cause patient harm through the injection of contaminated drug product.

Positive control population for semi-quantitative comparison of dye ingress tests. The vial set shows (from left to right) a process blank (no methylene blue) and serial dilutions of methylene blue dye from 0.000049% to 0.1%.

Illustration of the engineered stress profile resulting from ion-exchange of a thin-walled glass article, where the abscissa is the wall thickness (t, radial direction) and stress is the ordinate. High compressive stress (CS) is installed at the surfaces, and it decreases to the depth of the compressive stress layer (DOL). The compressive strain energy induced by this ion-exchange process is balanced by tensile strain energy, measurable as central tension (CT).

Percent of containers exhibiting stable cracks from damage introduction, as a function of increasing central tension. The response shows a clear “threshold” response, above which damage (severe enough to cause cracks) causes obvious breaking into fewer pieces with clean edges, facilitating detection.

a) At left, an image of a conventional borosilicate vial neck showing rotary disc damage going through the neck thickness without flange separating from the neck. b) At right, an image of a strengthened aluminosilicate vial neck after a rotary disc damage demonstrating that the disc penetrated less than 75% of the way through the thickness before central tension from the engineered stress profile (ESP) initiated the glass fracture and separated the flange from the neck. This response prevents the vial from being at risk of containing a contaminated drug product that could be administered to a patient.