www.mae.ufl.edu

This illustration show the processing of a glass microfluidic device.
http://www.mae.ufl.edu/~zhf/Resear chInterests-ZHFan.htm
• Microfluidics
Introduction
• Biomicrofluidics
– Lab-on-a-chip
– Drug delivery and
Micro-dosage systems
•Materials
–For Microfluidics
–For valves
•Processes
–For Microfluidics
–For valves
•Future of Microfluidics

• The control of tiny amounts of gases or liquids in a miniaturized system of channels, pumps, valves, and sensors.
• The motivation stems from trying to be more efficient on a smaller scale (several tests on a single micro chip).
• Example in Nature: human body’s oxygen (blood) transport system
• mTAS: systems of channels, valves, pumps, detectors

• Macro scale = laminar, random, and turbulent flow
• Micro scale = laminar flow
• Laminar flow allows controlled mixing
• Low thermal mass
• Efficient mass transport
• Good (large) ratio of channel surface area: channel volume http://www.spie.org/web/oer/august/aug00/microfluidics.html

•Used for analyzing thousands of samples at once
•Can perform clinical diagnoses, scan DNA, run electrophoretic separations
•System: substrate with integrated microchannels and devices
•Experiment: uses fluid sample in picoliter range
•Advantage: conserve sample and time

•Also known as DNA chips or DNA microarrays
•Used for analyzing thousands of Genes at once
•DNA probes and DNA sample
•Can analyze cancerous cells
•Can determine which genes or turned on or off by a drug
•Advantage: accelerate the pace of genetic research

http://www.popcouncil.org/images/gene_chip.gif

•Needed in the medical field
•System: micropump and flowsensor
•High dosage approach used in the past
Insulin – wastage of insulin
Painkillers – possibility of addiction
•Insulin micropump: mimic action of pancreas http://www.yourmedicalsour
ce.com/images/pancreas.jpg
Microfluidics can make possible closed-loop system with glucose sensor
•Painkillers: deliver drug locally, not globally
Avoid addiction
Tested at Maternity Hospital in Dublin, Ireland

•Current research at Michigan
University on Neural Microfluidic
Devices for the intracerebral delivery of neuro-active compounds
•Challenge: Must get the drug to CNS, across blood-brain barrier and before drugs are degraded and metabolized
•High dosage approach can have detrimental effects on other parts of http://www.yourmedicalsource.com
/images/central_nervous_system_4
00.jpg
body
•Challenge can be faced with microfluidic technology

•Many micro-devices: valves, pumps, fluidic mixers, and sensors
•Device focus: Valves – needed to control flow of fluid
•Two types of Valves: Passive and Active

Passive Valves
No actuation required
Designed to give higher flow in one direction
Main application in mechanical micropumps
Flap is controlled by pressure difference across it
Active Valves: Slightly more complex
Need a form of actuation (thermal, electrical)
Actuation controls the flap

The type of material used depends on the structure or device
(mircochannel, pump, valve, etc…) being fabricated
-cost -compatibility
MATERIAL
POSITIVES
NEGATIVES
SILICON
Well understood
Highly available
Expensive
Not always bioinert
PLASTICS
Inexpensive
Disposable
Easily machined
Swelling
Pairing

-
-
-
PDMS – Polydimethylsiloxane
Used as a structural material for microchannels
Low interfacial free energy
Stable against humidity, temperature
Can be used as a stamp for processes such as microcontact printing, micromolding
Parylene
-
Can be used as a structural material or coating
Low permeability to moisture
High resistance to corrosion
Polyimide
Used for microchannels
Easy to deposit metals (sputter)

Conjugated polymers
•“Organic semiconductors”
•Doping level depends on the oxidation state of the polymer
•Volume change associated with oxidation state
•Volume change occurs as a result of ions moving into and out of the polymer
Large Immobile Anion: Small Mobile Cation:
P + (A ) + C + + e 
P

(AC) P + (A ) + C + + e 
P

+ A + C +

PEG (Polyethylene Glycol)
•Volume change associated with phase transition
Paraffin
•Volume change
Bimetallic Strips
•Expansion http://www.wam.umd.edu/~smela

• Overview
– Soft lithography
• Silicon is patterned with a negative photoresist
• Polymer is cast onto silicon mold
• Polymer is cured and removed from mold http://nanotron.ecn.pudue.edu

– micromachining
• Bulk micromachining
– Removes from bulk of material-etching
• Surface micromaching
– Adds to surface of material
» Deposistion
» Micro contact printing

• Diaphragm check valve http://touch.caltech.edu
http://gmwgroup.harvard.edu
• Begins with etching holes into silicon substrates from bottom

• Metal seals are deposited
• Photoresist and polymer are deposited
• Resist is removed with acetone and silicon membrane is etched http://touch.caltech.edu

• Automation of complex experimental procedures
• Transformation of macroscale lab tests to a device the size of a postage stamp, available to the individual, with the skill of the technician
• More rapid DNA sequencing and general biological procedures
• Key Factor: future fabrication techniques are compatible with current batch processing techniques
Small ridges along the channel walls can force mixing by a kneading motion, http://depts.washington.edu/bioe/shrunklab.pdf.