title: Investigation of the electrical properties of agarose gel: characterization of concentration using nyquist plot phase angle and the implications of a more comprehensive in vitro model of the brain.
abstract: BACKGROUND
  The electrical properties of agarose gel, namely impedance and capacitance, are relatively unexplored. Agarose gels are used as in vitro models in studies across numerous disciplines, including imaging, radiotherapy, infusion, and neurosurgery.
  
  
  OBJECTIVE
  In this study, we seek to characterize the impedance response of low concentration agarose gels by relating the gel concentrations to Nyquist Plot phase in order to establish a baseline with which to modify the response of the gel to simulate that of in vivo brain tissue. This information is relevant to areas such as deep brain stimulation, and could have a significant impact on in vitro model design for such studies in the future.
  
  
  METHODS
  Ten agarose gels spanning four different concentrations were subjected to impedance spectroscopy using a Model 3387 DBS electrode. Phase angles were calculated and Cartesian Nyquist plots generated from the data.
  
  
  RESULTS
  Results suggest that an inverse relationship exists between agarose gel concentration and phase angle. In addition, the results indicate that agarose gel reasonably emulates a constant phase element, which portrays the electrode-electrolyte interface impedance of some equivalent circuit models of brain tissue.
  
  
  CONCLUSIONS
  The data shows that agarose gel is a suitable substrate for a deep brain stimulation in vitro model, but requires modification. In the future, we plan to utilize this data to determine the modifications necessary in the current agarose gel model to make it scientifically applicable to studies of both deep brain stimulation and infusion due to their overlapping variables.
authors.affiliation: Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Roland
authors.initials: R
authors.lastname: Pomfret
authors.affiliation: Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Karl
authors.initials: K
authors.lastname: Sillay
authors.affiliation: Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Gurwattan
authors.initials: G
authors.lastname: Miranpuri
keywords: Agarose gel; Brain infusion; Deep Brain Stimulation; Electrode; Impedance; In vitro model; Nyquist Plot; Phase angle; Reactance; Resistance