Mechanical and contact guidance properties of live cortical neurons in vitro measured via atomic force and fluorescent microscopy
Abstract: Neurons are highly specialized cells that are the main building
blocks of the nervous system. Neurons work together in complex networks to send, receive,
store, and communicate information electrically and biochemically. In the developing
vertebrate, neurons form connections with other neurons and cells to build the nervous
system. They do this by extending processes called neurites.... read moreAt the distal end of a neurite
is a sensing structure called the growth cone, which has the ability to sense and respond
to chemical, mechanical, and topographic cues, a process called neuron guidance. In this
thesis we explore the mechanism of neuronal guidance by performing atomic force and
fluorescence measurements. Specifically, we study the angular growth of neurites over time
on three different types of polydimethylsiloxane surfaces imprinted with parallel ridges
with ~ 0.8μm, ~ 1.6μm, and ~ 3.3μm spaced parallel ridges and stud. We observe maximum
parallel alignment with surface features with surface 1, followed by surface 2, and surface
3, and maximum perpendicular alignment with surface 1, followed by surface 2, and surface
3. Additionally, the stiffness of cells can be an indicator of cell health, function, and
biopolymer arrangements. Most cells have a protective polymer brush layer that shields the
cell from mechanical damage and allows other cells to adhere it. We perform the first
mechanical measurements of the neuronal polymer brush layer using atomic force microscopy
(AFM) indentation techniques, and delineate its properties from the underlying soma. Our
measurements reveal the cell body is an elastic material, 3-4 times stiffer than previously
reported, and surrounded by a viscoelastic polymer brush layer. We show this brush layer is
much softer than the cell body, and accounts for the previously reported viscoelastic
properties of neurons. We also use AFM to measure mechanical and topographical properties
of novel biomaterials that can be used as substrates for neuronal growth. Understanding the
mechanical properties of neurons and their contact guidance properties is of great
fundamental importance, and can also lead to better cellular modeling, new regenerative
therapies and devices for nerve and brain regeneration, and safer and more effective
surgeries and recoveries.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Physics.
Advisor: Cristian Staii.
Committee: Roger Tobin, Peggy Cebe, and Austin Napier.
Keyword: Physics.read less