Biomimetic Cilia as a Model Ependymal Cilia System

Abstract

Cilia are ubiquitous throughout the human body and serve a variety of functions. Human lung cilia in particular have been widely studied due to the prevalence of ciliary diseases such as cystic fibrosis. Less-well-studied are ependymal cilia, which are responsible for transporting cerebrospinal fluid throughout the ventricular system; however, their response to increased viscous loading during infection may be critical in understanding the pathology and treatment of meningitis and other inflammatory diseases. While ependymal cilia and human lung cilia are morphologically homologous, it has been shown in ex vivo studies that they respond very differently to increased viscous loading: lung cilia maintain a constant beat frequency but show decreased beat amplitude, while ependymal cilia maintain amplitude but decrease frequency. This difference may have dramatic implications in the clearance of viscoelastic fluids. However, the physical mechanisms behind this clearance are not well understood. We present therefore an artificial, biomimetic system which replicates the features of ependymal cilia as a tool for understanding the biological system. These biomimetic cilia are constructed of a material which is a composite of magnetic nanoparticles and silicone polymer. The composite has a high magnetic content (up to 50% wt.) and is homogenous at length scales below 100 nm, making it ideally suited to the fabrication of micro-scale magnetic actuators. The cilia are templated in a porous polycarbonate track-etched membrane which is subsequently dissolved with chloroform. The resulting cilia are 25 microns tall by 1 micron in diameter and may be actuated with an external magnetic field. A large array of cilia can be implemented in a microfluidic geometry for analysis of tracer particle movement to elucidate the interaction of cilia with a viscoelastic fluid.