Glass Alchemy: Decoding the Types and Properties of Pharma Glass

There's a lot more to pharmaceutical glass than meets the eye. Understanding the properties of glass and how they relate to different glass types is key to choosing an appropriate vial for a pharmaceutical product. It also helps with troubleshooting when things go wrong.

The types and properties of glass can impact the form, fit, and function of pharmaceutical packaging, but why is that? Here, we'll explore the varieties of glass used for pharmaceutical packaging as well as the properties of pharma glass.

Pharmaceutical glass is classified according to its hydrolytic resistance (its ability to resist corrosion when in contact with water under certain circumstances), which is influenced by the chemical composition of the glass and by any surface treatments. The following types are listed from lowest to highest hydrolytic resistance.

Type III glass is soda-lime silicate glass, which contains little or no boron.

Type II glass is treated soda-lime silicate glass, which begins as Type III glass and undergoes a surface treatment to increase its hydrolytic resistance.

Type I glass has the highest hydrolytic resistance. Under the updated USP <660>, the following compositions can qualify as Type I:

• Borosilicate glass contains boron and silicon, along with smaller quantities of other components like aluminum oxide. Varying the proportions of these components leads to borosilicate glass with different thermal expansion properties, such as 33 expansion, 51 expansion, and 70 expansion borosilicates.
• Aluminosilicate glass is similar to borosilicate glass but with no boron and a relatively high proportion of aluminum oxide.
• Fused quartz is made of nearly pure SiO2 (silicon dioxide).

Type I glass is considered generally suitable for packaging parenteral products, while Types II and III are less suitable for this purpose due to their potential to negatively impact drug safety, efficacy, and quality. The preference to use Type I glass for parenteral drugs is primarily due to chemical resistance, although Types II and III glass still have common uses in the pharmaceutical industry for oral drugs such as solid tablets, liquid suspensions, and syrups. However, the use of Type I glass does not automatically guarantee compatibility with a given drug product. Additional drug stability studies must be conducted to verify compatibility.

Glass is often a good option for pharma packaging due to the following properties:

Permeability describes the extent to which a material allows other substances to pass through it. The low permeability of glass means it can maintain hermeticity (i.e., an airtight state). This is a valuable property in parenteral drug product packaging for two reasons: it keeps the product sterile and it prevents the exchange of gases (carbon dioxide, oxygen, and water) that could react with and degrade the drug product. In general, plastic vials have greater permeability than glass vials and often need to be used with an additional barrier material such as a coating or impermeable secondary packaging.

Based on their compositions and manufacturing processes, different glasses have different chemical resistance properties, which are determined by the chemicals and conditions they successfully resist. The chemical durability of a glass vial is evaluated using various tests that measure the extent to which inorganic elements are dissolved into a given liquid. For example, the test methods described in USP <660> are used to determine whether a vial qualifies as Type I, II, or III. However, compatibility with a particular drug product must still be tested under actual storage conditions.

Corning^® Valor^® glass is a highly chemically durable, breakage-resistant pharmaceutical glass based on a revolutionary formulation and manufacturing process. The boron-free formulation of Valor glass products eliminates the risk of delamination, a long-standing problem in pharmaceutical packaging, and reduces the formation of glass particulates and cracks.

The strength of glass is its resistance to breakage when a load is applied. The theoretical strength of glass is greater than steel. The practical strength of pharma glass is still quite good (particularly in compression), although it is limited by damage introduced at various points during the product life cycle, including but not limited to initial manufacturing, shipping, and handling on pharma fill-finish lines. Glass surface flaws can concentrate applied tensile stresses and increase the chance of cracking and breakage. In practical terms, the strength of a glass vial has potentially significant implications for:

1. The safety, efficacy, and quality of drug products if a stable crack forms in the vial.
2. The efficiency of pharma fill-finish operations impacted by glass breakage leading to downtime and product loss.
3. Drug recalls initiated by the mechanical failure of distributed vials.
4. The safety of pharma manufacturing staff, healthcare providers, and patients.

Adding to the intrinsic strength of glass, some manufacturers use coatings to protect glass containers from the introduction of strength-limiting damage that can occur during shipping and handling. Corning's pharmaceutical glass vials, including Corning Velocity^®, Valor, and Viridian^® vials, are enhanced by the application of a proprietary, low coefficient of friction external coating which has been shown to reduce glass particulates up to 96% and improve fill line efficiency by 20-50%. In the case of Viridian vials, the external coating still offers the same benefits to support improved handling and efficiency even though the vials are manufactured with 20% less glass.

Another useful property of glass is that it can be optically clear. This feature enables vials filled with drug product to be visually inspected by human inspectors and/or automated inspection machines. We can also impart color to glass to achieve specific functionality such as protecting drugs from UV light. Amber glass, which contains added iron, sulfur, and titanium to provide UV-protective properties, is commonly used to protect UV-sensitive drug products.

A key feature of glass is its temperature-dependent viscosity properties. The viscosity of glass can be adjusted by changing the temperature, allowing glass to flow and be shaped into relatively complex objects when it is heated to the appropriate temperatures.

In addition to vials, Corning pharmaceutical glass tubing is shaped into many other packaging products for the pharmaceutical industry, including syringes, ampoules, and glass cartridges. The manufacture of pharma-grade glass tubing and the subsequent conversion of glass tubing into individual vials or other packaging products that are dimensionally consistent relies on manipulating glass viscosity. This dimensional consistency is important for ensuring that vials are compatible with pharma fill-finish equipment and other primary packaging components such as elastomeric stoppers and aluminum seals. Finally, while the viscosity of glass is dependent on temperature, glasses that are suitable for parenteral packaging are still thermally stable during standard pharma fill-finish processes such as depyrogenation and terminal sterilization.

Corning Pharmaceutical Technologies supplies the pharmaceutical industry with high-quality glass tubing and vials for reliable and efficient pharmaceutical packaging.

Browse our website to learn more about our pharmaceutical glass offerings and recent innovations. Or, get in touch with our pharmaceutical glass experts today.