Injectability is one of the screening criteria in determining the candidacy of protein therapeutics. It is determined by the required force during injection. For a fixed syringe geometry and delivery rate, the required injection force is solely determined by the viscosity of the therapeutics. (see Higher shear viscosity measurement and injectability application note). Therefore, candidate protein therapeutics are scrutinized if their viscosity is higher than the pre-set threshold.
The cut-off viscosity generally ranges from 20 to 40 mPa-s depending on the device. However, this type of generalization without specifying the shear rate could potentially lead to a false negative determination of an otherwise excellent therapeutic resulting in a significant financial loss during development.
Learn how to avoid this pitfall with the sequel to our most popular application note, Injectability at High Shear Rates
When you download the application note, you will be able to see that we use nylon 66 in formic acid and our preparation time is by rotating for a minimum of 2 hours. According to ASTM D789, it is recommended to shake for a minimum of 1 hour. There are many users who even rotate for 2 weeks.
Overall, nylon 66 and formic acid are not immediately miscible. It takes quite a long time for the two solutions to interact and often results in a cloudy solution which is the key indicator that the the two are just not miscible. However, after 2 hours or even 2 weeks of rotation, the solution becomes a lot more homogenous enabling a more smooth solution to work with.
Slow rotation also helps with preventing bubble formation which is another reason to use the rotator for a given period of time.