STRAIN GAGE SENSORS HELP TO IMPROVE VIALS FOR COVID-19 VACCINES.

We never imagined in VPG that there would be a need for our strain gages, temperature sensors and Data Acquisition System (DAS) to help find a solution for ending a pandemic.

A lot of science, including stress analysis, go into making quality glass to protect our most valuable liquids.

Why glass? Easily cast into useful shapes, easily sanitized, long-term safe storage, and relatively inexpensive are all attributes that make glass a good choice for holding precious contents like vaccines.

At its most basic phase, generic glass is the liquefied form of sand (silicon dioxide), heated and poured into a shape.

Typical glass can be strengthened using methods like tempering, the way a swordsmith would temper a sword, and by adding various metals and minerals during manufacturing.

With the worldwide COVID-19 vaccine search taking place over the past year, one question that has emerged is whether there are enough safe glass vials available. We have all heard stories about glass vials breaking or cracking when being filled. What causes these breakages? There are several possible causes, but temperature and pressure extremes certainly contribute to increased chances for breakage.

We are all in a race to develop vials that can protect their contents under extreme temperatures and will not chemically react with the a potential vaccine solution.

Glass weakens at extreme temperatures and becomes dangerously brittle at extremely low temperatures. Biotech and pharmaceutical companies have depended on vials made of borosilicate glass for decades. The properties of borosilicate glass allow vials made from this material to safely store drugs and vaccines by preventing contamination. Although the most common borosilicate vials have been significantly improved and strengthened over the years to resist temperature and mechanical induced stresses, they are still susceptible to failures at extreme temperatures.

Borosilicate glass originated with the German chemist and glassmaker Friedrich Otto Schott, who invented it in 1897. Borosilicate glass has a very low coefficient of thermal expansion. But at temperatures below zero degrees Celsius (as is required for some of the new Covid-19 vaccines), manufacturers start seeing an increase in the amount of breakage during filling. Several tests have indicated that freeze-thaw cycles, where the glass vial is repeatedly cooled and heated, can also increase the breakage rate.

Micro-Measurements strain gages and temperature sensors were chosen for testing glass vials used for storing/transporting COVID-19 vaccines. In this article we present a quick look at the unique processes used to test a glass vial with a temperature coefficient near 6 ppm/°C.

Glass vials are the preferred packaging for most biologics, including Coronavirus (COVID-19) vaccines, they are used in pharma because they provide the best container closure integrity (CCI).

As the COVID-19 virus and it’s variants continue to spread around the world, the supply chain of a vaccine remains a critical path toward global immunity and an end to the pandemic.

Standard medical vials made of borosilicate can easily crack or break at the filling temperatures required for certain COVID-19 vaccines. Developing and testing better vial solutions will help global pharmaceutical companies deliver vaccines safely and efficiently. These new solutions must be capable of withstanding significant stresses caused by extreme temperatures. Remember that just one damaged vial can ruin a batch of vaccine doses and halt a production line.

We never imagined in VPG that there would be a need for our strain gages, temperature sensors and Data Acquisition System to help find a solution for ending a pandemic.

Vial testing used bonded Micro-Measurements strain gage T-rosettes for axial and hoop strain values and Micro-Measurements temperature sensor to precisely measure the temperature on surface of the glass. The goal was to test and measure the vials ability to handle increased mechanical stress.

Test programs and Vishay Precision Group (VPG) products used:

• (4) installed SK-06-062TT-350 strain gages and one ETG-50B/E temperature sensor, all bonded using AE-10 adhesive. Solder about 10’ of Teflon lead wires to the sensor solder tabs. Each vial has sensing capability for axial & circumferential strain and temperature = three input channels. The strain gages are used to test how strong the glass is under stress tests in the lab. The stress analysis is performed on small containers for vaccines that should meet extremely high safety standards, including resistant to unusual temperatures.

• (1) Installed ETG-50B/E temperature sensor with AE-10 adhesive. Solder about 10’ of Teflon lead wires to the sensor solder tabs. This vial has temperature only sensing = one input channel. Resistance of the vial to extreme temperature is useful because pharmaceutical companies wash vials and heat them to sterilize them before filling them with liquid.

Loading racks of 100 (10X10) vials into cryo cooler @ -75C. Each vial contains “liquid material”.  Some vials would break and waste the entire batch.  They needed to do temperature versus strain on vials to determine which vial manufacturers were acceptable. Needed to at least establish a baseline since there was no existing data. 

The laboratory testing of  glass vials required a versatile data acquisition system (DAQ) for making many measurements, including in-house material tests and on-site design validation testing. A simple interface, quick setup and reconfiguration, and easy maintenance were essential. The choice was a Micro-Measurements System 8000, a portable, flexible, capable DAQ  to record and do multiple vial configurations arranged in the rack to determine if certain locations within the rack were worse than others (edge, center, …?).

Compact, versatile and incredibly successful, System 8000 was and is still well received across all industries and applications, especially due to the 8 programmable channels which can accept common strain gauge inputs and resistances, thermocouples and voltages. This compact unit can be carried in a laptop bag and can be expanded up to 16 units for 128 channels.

Winning the race against the COVID-19 virus requires safe, effective vaccines that can be safely and reliably delivered around the world. The required number of vials to satisfy demand will reach into the billions. Problematic broken vials only slow the supply pace and puts more people at risk of the virus. VPG Micro-Measurements is proud that its products – strain gages, temperature sensors and instrumentation – could be used to gather important data, eventually leading to safe storage and transport of COVID-19 vaccines.

Vishay Precision Group and the Micro-Measurements brand are where the world go to find products for making precision measurements.