2007/12/8 1

www.drummondsci.com/ products/oo_03a.html

Volume Microdispenser designed for DNA sequencing operations

www.elmat.lth.se/.../ Microdispenser.html

Microdispenser interfaces a capillary based separation system, dispensing picoliter fractions onto a chip based high density nano titre () plate.

7.5 Microdispensers

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(1) Closed-loop controlled dispensers(i) A fluidic actuator (ii) A flow sensor For continuous flow systems.

Classification scheme of microdispensers: Microdispenser

Close-loop controlled dispenser

Pump and flow sensorValve and flow sensor

Open-loop controlled dispenser

Droplet dispenser In-channel dispenser

ThermopneumaticElectrochemicalThermomechanicElectrostaticPiezoelectric

PneumaticThermopneumaticElectrokinetic

(2) Open-loop controlled dispensersTwo types:(i) Droplet dispensers: generating external droplet with constant volume.(ii) In-channel dispensers: preparing the fixed volume in the channel for further analysis on the same chip.

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7.5.1 Design consideration7.5.1.1 Droplet dispensers

Advantage: Small energy stored in the drop.

The total energy of a droplet:

d s kU U U= +Us: surface energy; Uk: kinetic energy

2s oU d=

do: droplet diameter; : surface tension 2 3 21 1

2 12k oU mv d v= =

: density of the liquid; v: droplet speed

Us/Uk increases with miniaturization. The surface energy dominates in the microscale.

2

12sk o

UU d v

=

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Nozzle: The most important part of a droplet microdispenser. To minimize the front surface effect (affecting the direction of dispensed droplets):

Making a ring-shaped nozzle with minimum front surface area.Coating the outer surface with a hydrophilic layer.

(a)(i) wet etching (ii) boron-doping (iii) blanket etching from the front(iv) selective wet etching from the front

2.

1.

3.

4.

(a)

Si Doped Si

(b)

SiO2Si

(b)(i) wet etching (ii) (ii) DRIE from the front(iii) selective oxidation to

form the nozzle shape(iv) selective dry etching

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Actuators:At ultrasonic driving frequencies:

13

2

80.34( )od f

=

f: frequency

At slow frequency or at a single droplet: o nozzled d=

Example 7-6: Thermal efficiency of a thermopneumaticdroplet dispenserGiven: A thermopneumatic droplet dispenser with:

(1)A heater resistance of 57 .(2)The ejection of a droplet following a voltage pulse

of 15 V and 0.8 s.(3)The droplet having a volume of 3.210-12 L and a

initial velocity of 9.6 m/s.Find: The thermal efficiency of this dispenser.Sol:(1) The total electrical energy of the heater:

2 26 615 0.8 10 3.16 10

57inVq t JR

= = =

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(2) The diameter of a spherical droplet:

2 3 21 12 12k o

U mv d v= = 316d o

V d= (volume of the droplet) 1 1153 36 6 3.2 10( ) ( ) 18.28 mdo

Vd

= = =

(3) The energy of droplet: 3 2

2 102.23 10 J12

od o

d vU d = + =

(4) The thermal efficiency:

0.007 %din

Uq

= =

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7.5.1.2 In-channel dispensersTwo steps in a measuring process:(1) Measuring the fluid amount needed.

The fluid amount is bordered by a stopper on one end and by outlet of delivering actuator on the other end.

(2) Pushing the measured amount to desired position using a common actuating principle.

Stopper structure: (A one-way valve)The surface tension can be adopted to realize such a passive valve. Pressure generated by surface tension:

2pr

= r: radius of curvature

and r can be used to manipulate the pressure of the stopper.

www.familyhealthmedia.com/VLU.htm

2007/12/8 8

(a) With hydrophoblic valve(b) With capillary valve(c) With electro-osmotic flow

Measuring Dispensing

Hydrophobic patch Dispensed liquid

Bubble delivered by an actuator

Capillary valve Dispensed liquid

Bubble delivered by an actuator

Electroosomotic flow

Electroosomotic flow

Dispensed liquid+

+

-

-

(a)

(b)

(c)

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Design Example: Mass Spectrometry Electro-Spray Tip

Mass Spectrometry

www.mhhe.com/.../carey/student/olc/ch13ms.html

2007/12/8 10

A mass spectrometer measures the mass of molecules and atoms. Mass spectrometers separate ions according to their mass-to-charge

ratio. Because most of the ions have a charge of +1, we can consider the mass spectrometer to separate ions with different masses.

Ions moving at high speeds through the mass spectrometer will travel along different trajectories from which their masses can be determined.

The detector of the mass spectrometer measures how many ions travel through the curved trajectory without colliding into the walls of the instrument. MagnetCurrent

regulator

Collector slit

Detector

Molecules in

Accelerator

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The mass spectrum for Boron

1. It indicates that out of 100 atoms of Boron there will be 81.7 atoms of Boron10 and 18.7 atoms of Boron11.

2.The average isotopic mass of Boron: (10 81.3/100) + (11 18.7/100) = 10.8

www.teachmetuition.co.uk/.../atomic1.htm

F (E v B)q= + F am=( / )a (E v B)m q = +

(Lorentz force law)

(Newton's second law of motion)

F is the force applied to the ion.m is the mass of the ion.a is the acceleration.q is the ionic charge.E is the electric field.v x B is the vector cross product of theion velocity and the magnetic field.

2007/12/8 12

www.sisweb.com/lc/ electrospray-tip.htm

www.nrc-cnrc.gc.ca/.../ nrc-imb_mass_spec-lr.jpg

electrospray needle

www.chemistry.nmsu.edu/.../ Image44.gif

touch.caltech.edu/.../ amish/trans97/nozzle.jpg

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Design Example: Mass Spectrometry Electrospray Tip

High performance High performance Taylor coneTaylor cone tiptip

Dead volume free tipDead volume free tip

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www.unige.ch/.../ PerretC/these_body.html www.soton.ac.uk/ ~lbrg/esims.htm

Gas and heat cause the droplets to evaporate prior to entering the instrument. As the solvent evaporates, the electric field density increases, hence the mutual repulsion between individual species becomes so great that it exceeds the surface tension and ions leave the droplet through what is known as a 'Taylor cone' .

Principle of the high performance Taylor cone tip

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1. Inside the micro channel (from the sample wall to the outlet of the spray-tip as indicated by d1)

2. From the micro channel outlet to the spray tip-head d23. From the spray tip-head to the mass spectrometry d34. Entering the the mass spectrometry

H

h'

MassspectrometerV=V1+V2+V3

S

d1 d2 d3

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Inside the micro channel d1

212

P Z constant + + =

1 12 1

2 2 2a aa aZ gZ gZ

= = =2 12b bgZ =

2p gH =(No electric field)

26p

ggH E Er

= + +

(Applied electric field)

Z a

Z b

h

H

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From the micro channel outlet to the spray tip-head d2

2 22

1 ( )2p p p T p

q V m gh m + =

sin cosea g >ea g

sin ( sin cos ) sin sin ( )sinp e p e p ea g t a t a t + + = +

cos ( cos sin ) cos cos ( )cosp e p e p ea g t a t a t + + + = +

Micro channel

sinea

cosea

ae

gsing cosg

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For

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Entering the the mass spectrometry ()

pMS

MS p

mm kq q

=

2 23

1 1 ( )2

MSMS p

MS

mV Kq k

= +T p

Due to colliding with the air molecular, the mass of the charged ions reduced.

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Mass Spectrometry Electrospray Tip Design

Design conceptSharp tip to form Taylor conePrevent the droplets from collecting at the tip

The spray-tip dimensions=20304560

7 cm 2 cm 0.024 cm

5cm

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Tip materialThe spray-tip is made of polymer PET with good hydrophobic characteristics.

Mass Spectrometry Electrospray Tip FabricationFabrication processes of the proposed spray-tip

PET film

bonding

Micromachining

cutting attaching

samplewall

Micromachining

PET film

PET film

(i) Prepare 3 pieces of 80 m thick PET film.

(ii) Clamp one of the three films using a specific fixture.

(iii) Micromachine the micro slot on the PET laminated film by a 100 m flat mill.

(iv) Bond the micro machined film with the two other pieces of film to make a micro channel

(v) Micro machine the incline with a larger flat mill.

(vi) Micro machine the tip into sharp point with the help of a CCD camera.

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Spray tip bonding

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Fixture

Micro CNC & Micro channel

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Temperature controllable roller 105~110 C

Micro machine the incline

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Micro machine the tip into sharp point with the help of a CCD camera

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High performance Taylor cone tipIincluded angle =20

Iincluded angle =30

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Iincluded angle =45

Iincluded angle =60

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Experimental Design

Sample preparation A 1 g/mL amphetamine and methamphetamine with 50% methanol containing 1% acetic acid () was selected as the sample solutions for these experiments. The molecular weights are 135 and 149, respectively.

Mass spectrometry LCQ ion-trap mass spectrometry (Finnigan MAT, San Jose, CA)

Experimental Verification

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Results

Charged liquid getting together at the tip

Taylor cone being formed

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The flat-head tip can only generate scattering Taylor cones around the outlet of the micro channel.

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Mass spectrograph of the proposed spray-tips with incline 60

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Mass spectrograph of the proposed spray-tips with incline 45

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Mass spectrograph of the proposed spray-tips with incline 30

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Mass spectrograph of the proposed spray-tips with incline 20

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Mass spectrograph of the conventional spray-tips with incline 90

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Dead Volume Free Tip

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Design of the dead volume free spray-chip

Design conceptTo embed a tiny needle penetrating the micro-channel of the spray-chip such that there is no connecting joint inside the micro channel; therefore, the dead volume problem can be avoided.

2007/12/8 38

3cm6cm75

m

0.1c

m

30o

Sample wall

Embedded needle

700 m

550 m

Micro needles with different inclined angles

10 cm 500

m

The spray-tip dimensions

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A stable and effective Taylor cone can be anticipated.

Tip materialOptical glass is selected to be the material of the spray-chip. To improve its hydrophoblic property, the micro channel surface is coated with hydrophoblic reagent. Material of the embedding needle is the high speed stainless steel (HSS).

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Samplewall

Dicing sawcutting

Opticalglass

UV-filmsticking

UVfilm

++

++

+

HSS needle LinearEDM

Fabrication of the dead volume free spray-chip

Fabricate the micro-channel on a 1mm thick optical glass by conducting dicing saw U-groove cutting.Cut out the side portions.Stick the UV-film to the front part of the already machined glass to seal the micro-channel.Sharp the high-speed stainless steel (HSS) tiny needle by linear EDM.Plug the sharpened needle into the micro-channel.Attach the sample wall to complete the dead volume free spray-chip

2007/12/8 41

Micro machined dead volume free chip

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Charged particles gather at the spray-tip and emit to the MS

Experimental Verification

2007/12/8 43

Mass spectrograph of the proposed spray-chip with needle angle =20

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Mass spectrograph of the proposed spray-chip with needle angle =30

2007/12/8 45

7.6 Microseparators

www.marstechusa.com/ tsk150.html

www.mpi-magdeburg.mpg.de/. ../1056/1071/microsep

2007/12/8 46

7.6.1 Design considerationTypes of microseparators:(1) Gas chromatography; (2) Liquid chromatography (); (3) Electrophoresis:

(i) Capillary electrophoresis (ii) Gel electrophoresis (iii) Free flow electrophoresis

Chromatography: Separation technique, which is based on the affinity differences between a stationary phase and the components of a mobile phase.

The stationary phase: Solid or liquid that interacts with the components in the mobile phase and causes their different flow velocities.

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The mobile phase: Consisting of the sample and a carrier medium.

(1)Gas chromatography: The carrier medium is a gas.

(2)Liquid chromatography: The carrier medium is a buffer solution.

Chromatogram: The time diagram of the concentration of different species in the sample. Each peak in the chromatography represents a component.

Analysis time: The time the slowest component needs to reach the sensor at the end of the separation channel.

slowest

Ltv

= L: channel length

2007/12/8 48

Separation speed:

The number of theoretical plates (N): 2

2

LN =

2: The variance contribution of longitudinal diffusion that represents the broadening of the peaks.

The smaller the signal peak compared to channel length, the higher is N and the better the separation.

The plate height (H): 2LH

N L

= =

The diffusion should be avoided to gain a better separation.

Recall 2xt

D=

The relation between the separation time and the dimension of the separation channels x.

2

1N Dt x

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Baseline resolution:The resolution between two close peak:

1 20.5( )xR

w w

=+

x: the distance between the peaksw1, w2: the widths of the peaksWhen R=1.5, the baseline resolution is reached.

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7.7 Cell Seeding of the Microvessel Scaffold

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Static Seeding

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(a) Initial stage (b) 24 hours in seeding

Cells died out due to the lack of metabolic nutrient and air.

(c) 36 hours in seeding (d) 48 hours in seeding

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Dynamic Seeding

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Major problems for long term cultivation:Aging and crack of the connection pipes and over evaporation of the cultivation medium.

(a) Initial stage (b) 12 hours in seeding

(c) 48 hours in seeding (d) 4 days in seeding

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Semi-dynamic Seeding

The cultivation medium is effected by periodically injecting fresh medium into, and sucking old medium out of, the scaffold.

Circulation frequency: 2-3 times daily.

The cultivation medium can be exchanged periodically and thus reduces the probability of virus infection.

Cultivation conditions: 37C, 5% CO2, relative humidity of 95%

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(a) 7 days in seeding

(b) 10 days in seeding

(c) 14 days in seeding

Cells can survive in the scaffold up to 4 weeks.

2007/12/8 57

PLGA Scaffold

The initial stage of seeding

24 hours of seedingThe PLGA scaffold becomes completely milky and opaque .

2007/12/8 58

Calcein-AM labeling

Fluorescence microscopy images after 7 days of seeding

Calcein-AM is the most suitable fluorescent probe for staining viable cells.

The cells are well adhered to and have grown in an orderly fashion along the circular microchannels.

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Quantum dots labeling

Fluorescence microscopy images after 96 hours of seeding

Scattered cells (dead) being leaked out during injection are observed.