Microfluidics

Question 1

Microfluidics advantages

Answer 1

compact

faster and more efficient

multifunctional

mass production

less materials

safer handling

disposable

Question 2

Microfluidics Disadvantages

Answer 2

complex

things work differently at smaller scales

harder to detect

no defined standards

things don’t scale linearly

Question 3

Reynolds Number

Answer 3

measures if laminar or turbulent

> 4000 turbulent

< 2000 laminar

Question 4

Transport mechanisms

Answer 4

1. diffusion

entropy driven molecular movement

2. convection/direction

controlled by a force

bulk fluid motion

Question 5

Peclets Number

Answer 5

Measure if diffusion or directed dominates

> 1: convection dominates

< 1: diffusion dominates

Question 6

Directed Convection Transport kinds

Answer 6

1. Hydrodynamic

parabolic flow profile

2. Electroosmotic Flow

uniform flow profile

Question 7

Flow Rate

Answer 7

proportional to pressure difference/drop

smaller dimensions = slower flow

Question 8

How to mix in microchannel

Answer 8

1. Diffusion

increase length

2. Flow focussing

flow directed in to continuous flow

3. Microstructures in microchannel

creates secondary flows that mix

Question 9

Materials

Answer 9

Silicon and Glass

Elastomers and plastics

hydrogels

paper

Question 10

Silicon/glass advantages

Answer 10

organic solvents

metal depositing

high thermo conductivity

stable electroosmotic flow

Question 11

silicon/glass disadvantages

Answer 11

expensive

dangerous fabrication

difficult to bond layers

can’t do valves

not gas permaeble

Question 12

Elastomers Plastics advantages

Answer 12

Inexpensive

easy fabrication

non toxic

high resolution

reversibly or irreversibly bonded

multilayer

can make valves

gas permeable

Question 13

elastomers plastics disadvantages

Answer 13

no organic solvents

interact with analytes limiting quantification

Question 14

Hydrogel benefits

Answer 14

3D networks of hydrophilic polymer

highly porous

permeability

good for cell culture

Question 15

Paper pros

Answer 15

highly porous

easy to fabricate

wiking of ligands

no pump/power needed

low cost

filters particles

Question 16

paper cons

Answer 16

not transparent

poor detection sensitivity

evaporation from open channels

Question 17

Fabrication Methods

Answer 17

Photolithography

chemical Etching

Physical etching

deposition

replication/moulds

3D printing

micromilling

Question 18

Photoresist kinds

Answer 18

positive:

regions exposed become soluble

negative:

regions not exposed become soluble

Question 19

Etching details

Answer 19

subtractive process

wet etching with chemicals

dry etching with plasma

isotropic - spherical front, undercuts mask

ansiotropic - directed, straight edges

Question 20

Physical etching pros and cons

Answer 20

pros

faster

no clean room

cons

surface roughness

lower accuracy

Question 21

physical etching methods

Answer 21

powder blasting

electron discharge machining

laser abalation

Question 22

Replication Techniques

Answer 22

create high precision mold

1. micro moulding

apply pdms to mould and bake

2. injection moulding

inject molten plastic in mould

3. hot embossing

master pressed into soft plastic

Question 23

Bonding layers

Answer 23

silicon to silicon - fusion bonding

silicon to glass - anodic bonding

pdms - reversible by contact, irreversible by oxygen plasma

Question 24

3D printing

Answer 24

layer by layer fabrication

fast prototyping

from 3D model

Question 25

micromilling

Answer 25

subtractive process rapid prototyping

Question 26

Paper fabrication methods

Answer 26

1. photolithography 2. paper cutting 3. wax printing 4. oragami 3D structures 5. hydrogel driven

Question 27

paper photolithography process

Answer 27

1. soak in resist 2. prebake 3. mask 4. expose to UV 5. post bake 6. wash away resist 7. plasma oxidise residual hydrophobic polymer creates channels

Question 28

Paper cutting

Answer 28

cut out channels arrange and set between two layers of plastic

Question 29

wax printing

Answer 29

draw hydrophobic wax channels on paper

Question 30

Hydrogel driven devices

Answer 30

release fluid with stimulus e.g. temp hence can control fluid flow

Question 31

Digital Droplet based devices

Answer 31

generate and manipulate drops of fluids in immiscible continuous phase

Question 32

digital droplet advantages

Answer 32

high control over droplet size, frequency with uniform higher surface area to volume means faster transfer and reaction times each droplet can be individually transported, mixed, reacted and analysed allows for parallel processing high through put much greater control/uniformity than traditional agitation

Question 33

Droplet formation factors

Answer 33

flow rate flow angle controls size and frequency

Question 34

Droplet formation methods

Answer 34

1. T junction 2. flow/shear focussing 3. Dielectrophoresis (DEP) 4. Electrowetting (EWOD) 5. Pneumatic valve pump

Question 35

Concentrating Sample

Answer 35

1. Electrophoretic - stacking - isotachophoresis - isoelectric focussing - temperature gradient focussing 2. support based - solid phase extraction

Question 36

why microfluidics good for biology

Answer 36

- channels and chambers are same size as cells - study cell interactions in controlled environment - single cell handling - real time observations - continuous flow systems - can sort cells e.g. DEP

Question 37

biological applications

Answer 37

1. mimick biological functions/organs create microstructures for trapping cells and reducing shear stress 2. bioreactor chemical processes using arranged cells 3. cell cultivation trap cells in microstructures 4. cell assays create chemical gradients 5. 3D hydrogel cell cultivation contains water and forms 3D structures

Question 38

Digital Droplet applications

Answer 38

cell encapsulation mixing drug delivery

Question 39

T junction

Answer 39

cell size depends on flow rates and channel size

Question 40

flow shear focussing

Answer 40

increasing dispersed phase flow creates smaller droplets at higher frequency

Question 41

DEP details

Answer 41

polarisable fluid at higher dielectric permittivity apply nnon-uniform elecric field generating droplets magnitude of voltage and frequency determines size

Question 42

electrowetting details

Answer 42

electric field reduces interfacial energy/contact angle causes wetting of surface when voltage turned off surface becomes hydrophobic again creating droplets size dependent on field strength, frequency and channel size higher frequency produces smaller droplets

Question 43

Flow rate minimisation

Answer 43

rate decreases as fluidic resistance higher in microchannels same time but lower reagent consumption

Question 44

Analytical Applications

Answer 44

Isotachophoresis preconcentration solid phase extraction purification of DNA for pcr analysis isoelectric focussing

Question 45

Biological Applications

Answer 45

Replicating biological functions e.g. lung on a chip Bioreactor Cell cultures

Question 46

PDMS soft lithography process

Answer 46

1. coat silicon wafer with photoresist 2. soft bake 3. apply photo mask 4. expose to uv 5. post bake 6. develop photoresist 7. apply pdms over mould and bake to cure 8. remove PDMS layer 9. permanenly seal by oxygen plasma

Question 47

Why Biological

Answer 47

Microchannels match cell size study cell-cell/cell-matrix trap cells in microstructures can form complex cell structures/environments gradients sort cells real time obserations

Question 48

shear stress minimisation

Answer 48

microstructures reduce shear stress improves cell growth and survivability