Getting Different Results from External Laboratories?
It’s more common than you might think. Many customers have reported receiving different viscosity values from vendors, product datasheets, and even their own clients. So, what should you do when this happens?
Every situation is unique, but here’s an example: one customer was initially told their monoclonal antibody was non-Newtonian and exhibited shear thickening. However, when they later tested the same sample using a VROC viscometer, the data indicated that it behaved as a Newtonian fluid over the same shear rate range previously tested.
If your sample is a protein or monoclonal antibody (mAb), Newtonian behavior may only occur within a specific shear rate range; so it’s important to note the shear rate ranges being reported. Monoclonal antibodies are non-Newtonian shear thinning. When you are told that your protein sample is showing shear thickening, or you are asked to compare data,, ask a few open-ended questions:
- How was the data you're comparing gathered?
- Are the tools used properly calibrated and accurate?
- Was the viscosity measurement taken with an open system or a closed system?
- Are there particulates in the samples?
After you have addressed questions (1) and (2), focusing on (3): When working with proteins in open systems, molecules can migrate toward the air–liquid interface. This can cause artificial shear thinning, or even shear thickening, due to evaporation. Open systems are prone to evaporation, which can artificially increase viscosity.
VROC® powered viscometers, listed in the U.S. Pharmacopeia Chapter 914 under rectangular slit methods, are closed systems. This eliminates evaporation and minimizes interface effects.
For question (4):
Samples containing large particles, such as suspensions, may occasionally show shear thickening. This is usually due to particle sedimentation or aggregation at high shear rates, which increases viscosity. True shear thickening is rare and not typically observed in most samples.
Working with mAbs?
In our in-house testing of monoclonal antibodies, we typically use a combination of B05 and E02 chips with m-VROC II viscometer and VROC initium 1++.
- B05 – Suitable for lower shear rates (up to ~22,000 s⁻¹ with a 100 µL syringe)
- E02 – Designed for higher shear rates, capturing the onset of shear thinning (up to ~150,000 s⁻¹ with a 100 µL syringe)
Note: B05 and E05 chips share the same channel depth (50 µm) and therefore have the same maximum shear rate (~22,000 s⁻¹ with a 100 µL syringe). The E02 chip, with its smaller channel depth (20 µm), achieves much higher shear rates with the same sample volume (<100 µL). If more volume is available and you want to fully characterize high-shear behavior (e.g., for injection force studies), you can use the E05 with a 2.5 mL syringe, which can reach ~500,000 s⁻¹. Keep in mind this configuration requires more sample volume (about 1.5 mL loaded into the syringe).
