Carbon Nanotube Syringes

1
Carbon Nanotube Syringes

• Joe Yeager

2
Introduction

• Major obstacle in drug delivery how to get
  specific drugs across the cell membrane?
• If membrane is not permeable to the drug, it may
  not achieve the desired effect
• With better permeability, lower concentrations of
  drugs would be necessary, limiting side effects
  greatly
• Better targeting to specific areas of the body

3
The Cell Membrane

• Fluid mosaic flexible and varied structure
• Consists of phospholipids (DMPC)
• Hydrophilic head
• Hydrophobic tail

4
Transport Across A Membrane

• Cell membranes must have a way to allow certain
  molecules to pass through
• Generally accomplished by proteins
• Allow metal cations (i.e. Ca2, Na, K), anions
  (i.e. Cl-) as well as other molecules to permeate
  the membrane
• Proteins specifically designed to transport
  particular molecules

5
Carbon Nanotubes

• Sheets of graphite (hexagonal lattice) rolled
  into tubes
• Exceedingly strong
• Properties vary greatly with length, diameter,
  and configuration (especially twist)
• Identified in 1991 by S. Iijima when passing
  fullerenes through an electric arc
• Can be capped at end
• Can be single-walled or multiple-walled
• Can have one of three different structures
  depending on how graphite sheet is rolled

6
Nanosyringe Design

• Carbon nanotube created with particular size and
  properties to accommodate a certain molecule
• Nanotube body is nonpolar
• Ends affixed with polar caps
• Chaperone lipids used to help the nanosyringe
  move into position in the membrane

7
Molecular Dynamics

• Computer simulation of molecules
• Can accurately predict interactions even between
  very large molecules
• Unfortunately, takes a great deal of time
• Takes into account mechanics, thermodynamics,
  electrical charges and polarity, and even quantum
  mechanical factors
• Often used to understand folding of proteins

8
Nanosyringe Simulation

• A basic nonpolar nanotube
• B nanotube with polar ends
• C molecular model of membrane phospholipid
• D simplified MD model of membrane phospholipid

9
Nanosyringe Findings

• Nanotubes with polar caps will insert themselves
  into a phospholipid bilayer membrane
• Once in place, nanotube can conduct molecules
  (i.e. water) across the membrane
• In order for the nanotube to stay in place, polar
  caps must be present on the nonpolar body
• Otherwise the tube rotates and lipid tails enter
  the openings of the tube
• This prevents conduction across the membrane

10
Nanotube Self-Alignment

• Nanosyringe begins near cell membrane

11
Nanotube Self-Alignment

• Nanotube is absorbed into membrane

12
Nanotube Self-Alignment

• Polar-polar and nonpolar-nonpolar sections of
  membrane and nanotube start to align

13
Nanotube Self-Alignment

• Nanotube fully aligns with cell membrane

14
Chaperone Lipids

• (Marked in Orange above)
• Attach to one end of the nanosyringe from the
  near phospholipid layer
• Move along with one end of nanosyringe to help
  guide it through the phospholipid bilayer
• Once movement is complete, chaperone lipids are
  integrated into far phospholipid layer

15
Future Directions

• Bacterial membranes are negatively charged, while
  human membranes are neutral
• Nanosyringes could selectively target bacteria,
  leaving human cells alone
• Different types of nanotubes with varying
  attached groups could selectively transport
  molecules across a membrane
• Nanosyringes could operate like enzymes, with a
  very specific template for molecules to be
  transported

16
Sources

• Adams, Thomas A. Physical Properties of Carbon
  Nanotubes. http//www.pa.msu.edu/cmp/csc/ntproper
  ties/
• Dalton, Mark. Cell Membranes.
  http//www.cbc.umn.edu/mwd/cell_www/chapter2/memb
  rane.html
• Lopez, Carlos F., Nielsen, Steve O., Moore,
  Preston B., and Klein, Michael L. Understanding
  Natures Design for a Nanosyringe.
  http//www.pnas.org/cgi/content/full/101/13/4431
• Travis, J. New Antibiotics Take Poke at
  Bacteria. Science News http//wilsontxt.hwwilson.
  com/pdfhtml/00744/P16QI/ZS4.htm