Analysis of Cerebrospinal Fluid Rheology using Shear and Extensional Techniques

Understanding the rheological behavior of cerebrospinal fluid (CSF) will be critical in the development of head-brain system biomechanical models as well as surgical and medical devices and techniques directed at alleviating intracranial pressure or altering CSF flow. CSF serves many functions in the head-brain system including cushioning the brain against impact, providing nutrient transport, and clearing waste via the glymphatic system. It is derived from blood plasma and is often considered a protein free Newtonian fluid, since typical CSF protein content is found to be between 25-60 mg/100g. However, it has been shown that the protein content of CSF can be different depending on the location (e.g. lumbar vs ventricular shunt) as well as condition of the patient (e.g. shunt infection, hemorrhage, or obstruction) from whom it has been extracted. In this study, we have performed a comprehensive rheological analysis of CSF specimens extracted from neurosurgical patients at the UCLA hospital. These specimens were tested using a conventional shear rheometer as well as a recently developed micro-extensional technique, which has been shown to be much more sensitive to protein content of dilute solutions. Preliminary tests show weak extensional behavior consistent with the protein concentration of CSF. The results of this study have shown that CSF exhibits quantifiable non-Newtonian behavior, and that this behavior may be influenced by the medical condition of the patient. Though the non-Newtonian contribution is relatively small, this characterization of CSF may have significant impacts on the development of brain models and medical technologies.