Viscosity Testing
Viscosity testing measures a fluid’s resistance to flow and is used to characterize how a liquid behaves when force or shear is applied. It helps determine whether a solution flows smoothly or resists movement under processing conditions[1]. Viscosity testing plays a key role in buffer manufacturing, especially in the bioprocessing, diagnostic, and pharmaceutical sectors.
History of Viscosity Testing
The concept of viscosity, how "thick" or "thin" a fluid is, has been studied since the 17th century. Early scientists like Isaac Newton helped define how fluids resist flow, giving rise to the term “Newtonian” fluids (those with constant viscosity)[2]. Fluids generally fall into two categories: Newtonian fluids, such as water or saline, maintain a constant viscosity regardless of the applied shear rate. In contrast, non-Newtonian fluids, like polymeric buffers or protein solutions, exhibit viscosity that changes depending on the shear rate (becoming either thinner or thicker under different flow conditions). Understanding this behavior is essential for ensuring consistent performance in manufacturing processes.
Traditional viscometers relied on falling balls or spinning cylinders. Today, with the development of microfluidics and chip-based technologies, viscosity testing can be conducted rapidly and accurately using just microliter-scale samples. This makes it ideal for modern reagent manufacturing and quality control.
Importance of Viscosity in Buffers and Reagents
In biotech and pharmaceutical workflows, viscosity plays a critical role in how solutions behave in real-world processes. Whether a buffer is being mixed in a bioreactor, pumped through a chromatography column, or filtered into a final container, its viscosity affects:
- Flow rate and pump performance
- Mixing and blending efficiency
- Filtration throughput and pressure
- Equipment wears and scale-up predictability
Variations in viscosity can also indicate problems like incorrect concentration, incomplete mixing, or precipitation. For buffers containing sugars, polymers, or high salt concentrations, routine viscosity checks help ensure every batch meets expected physical properties.
Viscosity Testing at Boston BioProducts
To ensure quality, we perform viscosity testing using the RheoSense microVISC™ system, a state-of-the-art chip-based viscometer powered by VROC® (Viscometer-Rheometer on a Chip) technology. This method measures viscosity from the pressure drop while a test liquid flows through the rectangular slit[3].
This method offers several key advantages:
- Requires only samples as small as 100 µl
- Measures both Newtonian and non-Newtonian fluids
- Capable of shear-rate sweeps for advanced profiling
- Complies with USP <914>
Every result is documented and reviewed for consistency with historical data, product specifications, and processing requirements.
Considerations and Limitations of Filter Integrity |
|
|---|---|
| Temperature sensitivity | Viscosity is highly temperature dependent. Even small changes can affect measurements, so testing is done under controlled or specified conditions. |
| Particulate matter | Suspensions or precipitates can skew results. Testing is ideally performed on clear, homogeneous solutions |
| Sample limitations | Extremely high-viscosity samples (>20,000 cP) may require alternate methods. |
| Non-Newtonian behavior | Some formulations exhibit shear-thinning or thickening behavior, which may require additional profiling at multiple shear rates. |
Despite these considerations, routine viscosity testing is a fast, reproducible, and high-value checkpoint for ensuring the quality and performance of process-critical reagents.
Our Commitment to Quality
At Boston BioProducts, Viscosity testing is one more way we ensure that our products meet the performance expectations of scientists and manufacturers in the world’s most demanding biotech and pharma environments.
Whether you're optimizing upstream process solutions or ensuring the flow of downstream buffers, our commitment to viscosity control helps you move forward, with confidence.
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References:
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- Bhattad, A. Review on viscosity measurement: devices, methods and models. J Therm Anal Calorim2023, 148, 6527–6543 (2023).
- Walters, K. and Jones, W. M., Measurement of Viscosity, Instrumentation Reference Book (Third Edition); 2003, 45-52.
- Walters, K. Non-Newtonian Fluids : Rheometry, Chapman and Hall, London, 1975