Microfluidics Design & Chip
Application
Reporter: AGNES Purwidyantri
Student ID no: D0228005
Biomedical Engineering Dept.
Microfluidics
• Microfluidics refers to the behavior
and control of liquids constrained to
volumes near the μL range.
• Behavior of liquids in the micro
domain differs greatly from
macroscopic fluids.
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Surface tension.
Laminar flow.
Fast thermal relaxation.
Diffusion.
• Microfluidics was developed in the
1980s, mainly for use in inkjet
printers.
• Microfluidics is an multidisciplinary
field with a wide variety of
applications.
Micro-channels
Nano-tubes
Microfluidic Technologies
Micro-scale
Handling System
Small Volume
Transport
Sample Loading
And Injection
Microfluidic
Device
Subatmospheric
Pressure
Chamber
Electro-Osmotic
Pump
Electro-Pneumatic
Distributor
The objectives of micro-fluidic
systems
• Micro-Total-Analysis-Systems
(mTAS)
▫ One system to provide all of the
possible required analyses for a
given type problem
▫ All processing steps are
performed on the chip
▫ No user interaction required
except for initialization
▫ Portable bedside systems
possible
• Lab-on-a-chip
• Microarray
• Micro-fluidics in nature
▫ Aveoli (Lung bubbles)
Micro-fluidics is Interdisciplinary
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Micro-Fabrication
Chemistry
Biology
Mechanics
Control Systems
Micro-Scale Physics and Thermal/Fluidic Transport
Numerical Modeling
▫ Simulation of micro-flows
• Material Science
• Electronics
• …
The fluids in micro-fluidic system
• Simple fluids
Injection of a droplet into a micro-channel.
▫ liquids and gases
• Complex fluids
▫ immersed structures,
surfactants, polymers,
DNA …
Cells in a microchannel.
Polymer flow in a micro-channel
Typical fluidic components
Channel-circuit
• Micro-channels and channelcircuit
• Functional structures
▫ Micro-pump and switches
▫ Mixing and separating
devices
Typical functional structre
Electroosmotic
Pumping
Length scales in micro-fluidic systems
1mm
Typical size of a chip
100mm
Extended lenght of DNA
Micro-channel
10mm
Microstructure and micro-drops
Cellular scale
1mm
100nm
Colloid and polymer molecular size
10nm
Radius of Gyration of DNA
Other flow features for micro-fluidics
• Low Reynolds number flow
▫ Large viscous force
• Low Capillary number flow
▫ Large surface force
• High Peclet number flow
▫ Disperse and diffusion
▫ Slow diffusion effects
• Special transport mechanism
▫ Mixing: chaotic mixing
▫ Separation: particle, polymer and DNA
Low Reynolds number flow (Stokes flow)
• Reynolds number (Re) is the ratio between
inertial force to viscous force
• Scaling between intertial force and viscous force
in NS equation
u
1
▫ Length scale L
▫ Velocity scale U
t
 u  u  

p  2u
• Flow classification based on Re
http://www.youtube.com/watch?v=gbDscDSUAg4&feature=channel_page
http://www.youtube.com/watch?v=2ghBUcQG1lQ&feature=channel_page
Low Reynolds number flow (Stokes flow)
• In micro-fluidics, Re<1
▫ Laminar flow
▫ the viscous force dominant the inertial force
▫ Inertial irrelevance
Purcell 1977
http://www.youtube.com/user/Swimmers1
Low Capillary number flow
• Capillary number (Ca) is the ratio between
viscous force to surface force Ca  mU

• What is surface tension?
▫ Stretch force along the material interface
Low Capillary number flow
• In micro-fluidics, Ca <<1
▫ Surface force dominant
flow
▫ Wetting effects
Micro-fluidic pin-ball: routing
Separation in micro-fluidics
• External force used to
move the solute
• Separating particle on
different mobility
▫ Large mass, small velocity
▫ Dielectric properties
Driving Forces in Microfluidics
Systems
Surface Tension
• Molecules in any medium experience an attractive
force with other molecules.
▫ Mainly hydrogen bonds for polar molecules
▫ Van der Waals forces for other molecules
• Imbalance of this attractive
force at an interface leads to
surface tension
Surface Tension
Let U be the average total cohesive energy of a
molecule, and δ be a characteristic dimension of a
molecule such that δ2 represents the effective surface
area of a molecule, then surface tension is
approximately
Surface tension has units of J/m2 = N/m, and is usually
given in mN/m. If S is the total surface are of an
interface and γ is the surface tension, then the total
energy stored in the interface is
Surface Tension Example
Surface tension can be treated in two ways: as stored
energy per unit area (J/m2) or as a tangential force per
unit length (N/m)
Contact Angle: Young’s Law
The contact angle at a triple point (intersection of three
interfaces) is entirely determined by balancing the
surface tensions of each interface.
A more rigorous derivation from minimization of free
energy yields the same result as a geometric argument.
Capillary Action
• Capillary action refers to the movement of liquid
through thin tubes, not a specific force.
• Several effects can contribute to capillary action, all
of which relate to surface tension
▫ Minimization of surface energy
▫ Young-Laplace equation: pressure difference due to
curvature of interface.
Minimization of Surface Energy
Like any type of energy stored in a system, surface
energy wants to be minimized.
Examples include
• Soap films on wire frames form minimal surfaces.
• Water in capillary tubes rises above or falls below the
surrounding water level.
Capillary Rise
Capillary rise is a balance of
surface energy and gravitational
potential energy:
For a contact angle less than 90o,
the liquid will rise in the tube,
but the liquid can also fall if the
contact angle is greater than 90o.
If the liquid is water, solids with
a contact angle less than 90o are
called hydrophilic, the opposite
is hydrophobic.
Electrowetting
Applications of Microfluidics: Biology (LOC)
Fast PCR using nanodroplets
Kim, H. et al. “Nanodroplet real-time PCR system with laser
assisted heating.” Optics Express Vol. 17 No. 1. 5 Jan 2009
Lab on a Chip (LOC) for
bacterial culturing and testing.
Orenstein, D. “’Microfluidic’ chips may accelerate
biomedical research.” Stanford Report, 18 Jan 2009.
http://news-service.stanford.edu
Lab-on-a-Robot
Wireless mobile unit carrying an
electrochemical detection unit and HVPS.
After choosing a location, onboard GPS
navigates the robot to the test site. At test site,
a MEMS device diffuses a gas sample through
50 μL of buffer solution. A small sample of
this solution is injected into a microfluidic
device that electrophoretically separates the
components of the gas. A detector sends realtime sampling data back to the base computer
running a LabVIEW program, which can be
used to relay new commands to the robot and
analyze the data transmitted from the robot.
Berg, C. et al. “Lab-on-a-robot: Integrated
microchip CE, power supply, electrochemical
detector, wireless unit, and mobile platform.”
Electrophoresis Vol. 29, 2008.
Microfluidic Flow Cytometers
Wlodkowic, D &Darzynkiewics, Z. 2011.
Methods Cell Biol. 102: 105–125.
Thank
you