<img height="1" width="1" style="display:none;" alt="" src="https://dc.ads.linkedin.com/collect/?pid=510762&amp;fmt=gif">
Skip to content
RheoSenseJanuary 30, 20243 min read

Viscosity & Protein Formulation

Injectable proteins have been a staple in the biopharma community for many years. Motivated by a common desire for fewer doctor visits and injections, subcutaneous injections of high concentration proteins have become one of the biggest trends in the industry. Now, protein concentrations exceed 100 mg/mL and new formulations are being tested above 200 mg/mL in certain cases. With the increase in protein concentrations, there is almost always an increase in viscosity. This must be accounted for to ensure that the final product meets viscosity limitations of injectability. Over 50 cP, solutions become too difficult or time-consuming to administer to patients. Most injectables must fall be between 20-25 cP. In order to properly formulate an injectable, viscosity studies must be performed regularly during development. Formulation scientists will alter pH, add various excipients, and vary temperature, to lower the viscosity of their protein formulations. They must find the appropriate combination and concentration of the excipients to lower the viscosity without negatively affecting the activity of the proteins by destabilizing the protein solution.

Excipients can alter the viscosity of proteins by various means:

1) Reducing the viscosity of concentrated protein dispersions

2) Suppress protein aggregation

3) Enhance solubility of specific biomaterials

4) Suppress liquid-liquid phase separation of proteins

5) Suppress hydrophobic interactions

6) Affecting protein-protein interactions

Some of the common excipients used in protein formulations: L-Arginine, L-Phenylalanine, Benzenesulfonic acid, and Pyridoxine hydrochloride. Common buffer types include phosphate or acetate.

Various excipients have been studied over the years for optimal formulation, but today we know that appropriate combinations of excipients can be beneficial for many reasons. The combination of various excipients with different charges can allow for lower concentrations of the excipients which helps maintain protein stability. Different excipients will affect different protein solutions in various ways mainly due to ionic charge and the corresponding effect on protein-protein interaction. To combat negative effects on stability, different buffer types can be used for more effective formulations.

After screening potential candidate formulations, there is a need to understand the degradative effects of the excipients and pH and their effect on the protein solutions. You will study the candidate at various storage conditions over specific periods of time to determine their shelf life. These tests can be done under refrigerated conditions (~4 degrees C), at room temperature (~25 degrees C) or both. The viscosity of the samples would be tested initially then after a set amount of days noting the change in viscosity until you see a significant reduction or increase in viscosity. An increase in viscosity could indicate protein agglomeration while a decrease could signify protein unfolding or destabilization. The RheoSense Initium one plus and m-VROC II both have the ability to test from 4 – 70 degrees C.

Most of these therapeutic proteins are limited in volume for testing during formulation. They are very expensive or difficult to manufacture so being able to test with extremely small volumes is essential.

Also, for proper formulation efforts, there will be various tests run on the different formulations such as temperature and stability studies. The need to test at various concentrations, pH, and with various excipients normally requires a great deal of time and effort to run all of the necessary testing. RheoSense can help with both of these requirements.

With RheoSense’s line of low-volume viscometers, you are able to gather nearly unlimited amounts of data with extremely small volumes of samples. If you need to test multiple excipient and solution combinations, the Initium one plus is the workhorse your formulation lab needs. After loading the vials and setting up the software, you can walk away and let the viscometer gather your data saving both time and money. If you are not ready to invest in your own automated viscometer, consider sending in your formulations to be tested by our experts.



RheoSense is a global high-tech company based in Silicon Valley. Our innovative m-VROC & microVISC instruments feature patented Viscometer/Rheometer-on-a-Chip (VROC) technology. Utilizing state-of-the-art MEMS and microfluidics breakthroughs that redefine the viscometry industry, our instruments offer the smallest sample volume per measurement coupled with exceptional ease-of-use and accuracy. We are the leader in biotechnology, pharmaceutical, and the emerging protein therapeutics industries. RheoSense instruments have been rigorously tested, approved, and adopted worldwide by Fortune Global 500 companies and leading research universities.