NER: NANO-GRATING FORCE SENSOR FOR MEASUREMENT OF NEURON MEMBRANE CHARACTERISTICS UNDER GROWTH AND CELLULAR DIFFERENTIATION

1
NER NANO-GRATING FORCE SENSOR FOR MEASUREMENT OF
NEURON MEMBRANE CHARACTERISTICS
UNDER GROWTH AND CELLULAR DIFFERENTIATION
Ashwini Gopal1, Zhiquan Luo2, Karthik Kumar1, Jae
Young Lee3, Kazunori Hoshino1, Bin Li2, Christine
Schmidt1, 3, Paul S. Ho2, and Xiaojing Zhang1
Departments of Biomedical Engineering1,
Mechanical Engineering2, Chemical Engineering3The
University of Texas at Austin,Texas, USA
Motivation
Device Design
Fabrication Sequence
Results

• Cell experiences stress and strain
• Physical/Chemical cues (growth)
• Environmental perturbation (robustness)
• Neuronal shape depend on both progressive and
  regressive processes such as axonal elongation
  and axonal elimination 2-3
• Mechanical tension is a direct stimulus for
  neurite initiation and elongation from peripheral
  neurons
• Classical concepts fail to explain
  mechano-transduction4
• Size-dependant mechanical properties have not
  been characterized
• PC12-a cell line derived from rat
  pheochromocytoma
• Serve as good models of neuron cells
• Easily be induced to extend neurites with NGF
• Significance
• guided nerve regeneration
• wound healing
• cell based drug delivery

Cell Structure 1

• Probing causes motion of grating
• Change in diffraction spot
• Determines the amount of force applied. (Fkx)

Suspension Stiffness

• Two symmetric nanogratings provide mechanical
  balance and maximal optical surface area.
• Nanogratings consist of flexure folding beams
  suspended between two parallel cantilevers of
  known stiffness7.

Flexure Stiffness
PC12 Cells 5
SEM Images
Simulation Results

• Experiment was conducted on 10-15 cells
• Time for testing cells-30mins
• An average force of 228µN caused the neurite
  length to contract up to 6µm

Basic structure of neuron 6
Principle of Operation

• Probe displacement, therefore the force, can be
  measured through the spatial frequency of
  far-field diffraction pattern.

Conclusions

• Opto-mechanical sensing interface to study cell
  mechanics
• Design, simulation, and fabrication of
  nanograting displacement-force sensor
• Displacement range of 10µm force sensitivity
  8?N/?m
• Eigen modes vs. optical detection
• Localized, quantitative interactions in
  microenvironment
• Neuron(PC12) mechanics characterization
• Neurite contraction under mechanical stimulation
• Elastic modulus of neuron membrane 42530 Pa
• Platform to study mechano-transduction in other
  cell lines
• Hippocampal cells, spinal cord motor neuron

m is diffraction order,? is wavelength, p is
grating pitch, a is illumination angle, and ? is
diffraction angle.
Absence of stress across the gratings and stress
concentrated on the flexure beams

• Sensitivity of the device can be greatly improved
  by reducing the critical feature size, p, of the
  grating to the nanometer regime to match the
  illumination wavelength.

Experimental Setup
Reference 1 See http//www.uic.edu/classes/b
ios/bios100/lecturesf04am/cytoskeleton.jpg 2
Cowan, W.M, Fawcett, J. W, O'Leary, D. D. M, and
Stanfield, B. B Regressive events in
neumgenesis. Science. 225, p1258-1265, 1984. 3
Purves, D, and Lichtman, J. W, Elimination of
synapses in the developing nervous system.,
Science, 210, p153-157, 1980. 4 McKintosh F C,
Kas J and Janmey P A 1995 Phys. Rev. Lett. 75
4425 5 See http//scienceblogs.com/purepedantry
/2006/07/background_to_the_20_year_coma.php 6
See http//www.med.osaka-u.ac.jp/pub/molonc/www/E
signal.html 7 Stephen D. Sentura Microsystem
Design,2001

• Nanograting sensor is attached to a
  piezoelectric actuator
• Placed in a liquid media (serum containing F12K
  media) to probe the PC12 cells (Neurons)
• Illuminated with a 635 nm He-Ne laser diode
• Spot size covering the grating area of 120µm x
  120µm.

Eigen modes under mechanical vibration were
simulated using CoventorWare .
Acknowledgement NSF Nanoscale Exploratory
Research Award (NER), ECS-0609413, the Welch
Foundation and the Strategic Partnership for
Research in Nanotechnology (SPRING), and NSF
NNIN Facilities at UT Austin and Stanford Center
for Integrated Systems (Grant 0335765 and
9731293 respectively)