[SOLVED] Mechanical and Biomedical Engineering Worksheet – Engineering

by | Aug 5, 2022 | Engineering

BME 432
Lab on a Chip
Spring 2020
HW #3
Due Thursday, March 5
Name:
Answer the following questions on engineering paper. [40 pts]
1. SPROMs
[20 pts]
You are designing a microfluidic system using SPROMs. The general pattern for your design is shown
below.
100 μm
500 μm
A
R1
Vent
x
500 μm
B
R2
Given:
Surface tension of water-based solution, γ = 0.072 N/m
Contact angle, θ = 120°
Channel height is uniform throughout the design, h = 200 μm
a.) Calculate the pressure drop across R1 in units of Pa.
b.) Pick the width, x, of R2 to ensure the fluid fills Chamber A before it fills chamber B. Show your
work. (I recommend a factor of 1.5 difference in the pressure to ensure this will happen).
2. Pumps
[20 pts]
A thermopneumatic check-valve pump delivers a maximum flow rate of 34 μL/min and has a maximum
back pressure of 5 kPa. The heater that powers the pump has a resistance of 15 Ω, which is driven by a
symmetric square signal with a maximum voltage of 6V and a 50% duty cycle (i.e., it is on for half of the
time and off the other half). What is the pump efficiency?
Microfluidics
Components
(Pumps, mixers)
Western New England University
BME 432
© 2020 Michael J. Rust
Pumps
 Functions
 Transport of sample/reagents
 Delivery of pulsatile flow
 Generating pressure differences
 Moving cooling fluids
 Two major categories
 Mechanical pumps
 Non-mechanical pumps
Western New England University
BME 432
© 2020 Michael J. Rust
Example
 Centrifuge + microfluidic disk
Slide courtesy of J. Papu
Western New England University
BME 432
© 2020 Michael J. Rust
The centrifuge has failed!
Design a pump for a microfluidic system
that will function if the centrifuge fails
Must be suitable for low-resource
environment
Be creative!!
Western New England University
BME 432
© 2020 Michael J. Rust
Pumps
 Mechanical Pumps
 Integrated
• Pump integrated within microfluidic system
 External
• Pump located outside of microfluidic system
Integrated
Check-valve
Peristaltic
Valve-less rectification
Rotary
Ultrasonic
Western New England University
External
Centrifugal
Syringe
Capillary
BME 432
© 2020 Michael J. Rust
Pumps
 Non-mechanical pumps
 Add momentum to the fluid by converting another nonmechanical energy form into kinetic energy
• Electrical Potential Gradient
– Electro-osmosis
• Magnetic Potential
– Megnetohydrodynamic flow
• Surface tension driven
– Electrochemical
Western New England University
BME 432
© 2020 Michael J. Rust
Pumps
 Maximum flow rate
 Qmax
 Volume of liquid per unit time delivered by the pump at zero
back pressure
 Maximum back pressure
 Pmax
 Max pressure the pump can work against
 Power of pump
Ppump 
Pmax Qmax
2
 Efficiency

Western New England University
Ppump
Pactuator
x100%
BME 432
© 2020 Michael J. Rust
Mechanical Pumps
 Check-valve pump
 Membrane movement drives pump
Membrane
Actuator
Inlet valve
Stroke volume
Outlet valve
 Requires check-valves to control flow direction
 Membrane deflection determines stroke volume
Western New England University
BME 432
© 2020 Michael J. Rust
Mechanical Pumps
 Peristaltic Pump
 Synchronized movement of multiple membranes
Fig. 7.15 from N.-T. Nguyen, S. T. Wereley, Fundamentals and
Applications of Microfluidics, Artechouse, 2002, p. 304.
 Requires several controllable actuators
Western New England University
BME 432
© 2020 Michael J. Rust
Mechanical Pumps
 Valve-less rectification
Western New England University
Fig. 4.6 from O. Geschke, H. Klank, and P.Telleman, Microsystem
Engineering of Lab-on-a-Chip Devices, Wiley-VCH, 2008, p. 45
BME 432
© 2020 Michael J. Rust
Mechanical Pumps
 Rotary Pump
From G.T.A. Kovacs, Micromachined Transducers Sourcebook, p. 844.
Western New England University
BME 432
© 2020 Michael J. Rust
Mechanical Pumps
 Ultrasonic pump
 Uses mechanical traveling wave to create acoustic
streaming
 No moving parts, heat, or electric field required
 Wave induced by interdigitated piezoelectric transducers
• Requires integrated electrodes
Western New England University
BME 432
© 2020 Michael J. Rust
Mechanical Pumps
 Centrifugal pump
 Uses external actuator to drive centrifugal force
http://mmadou.eng.uci.edu/Research/CD.htm
Western New England University
BME 432
© 2020 Michael J. Rust
Mechanical Pumps
 Syringe Pump
 e.g. – New Era NE-1000
http://syringepump.com/NE-1000.htm
 Features
• Infusion and/or withdrawal
• Max pressure ~200 kPa
• Flow rate: 1.7 nL/min – 35 µL/min
Western New England University
BME 432
© 2020 Michael J. Rust
Design an alternative to syringe
pump
Interfaces with syringe
Eliminates need for electricity
Western New England University
BME 432
© 2020 Michael J. Rust
Mechanical Pumps
 Capillary pump
 e.g. – Springfusor (Go Medical Industries)
http://www.gomedical.com.au/products/springfusor.php
 Features
• Spring-driven
• Re-usable, low-cost, compact, no power
• Flow rate: 2 µL/min – 2 mL/min
Western New England University
BME 432
© 2020 Michael J. Rust
Non-Mechanical Pumps
 Electro-osmosis
 Uses electric field to provide pumping
1
100 mm
3
4
2
 Simple integration (just requires electrical interconnects)
 Uniform flow velocity (plug-like)
 Requires conductive fluid, dielectric materials (E-field)
 Flow dependent on chemistry
Western New England University
BME 432
© 2020 Michael J. Rust
Non-Mechanical Pumps
 Magnetohydrodynamic pump
 Uses applied magnetic field
_
+
B
F I
 Requires conductive solution to generate current
 Requires electrodes on channel walls and interconnects
Western New England University
BME 432
© 2020 Michael J. Rust
Non-Mechanical Pumps
 Electrochemical pump
 Uses pressure of gas bubbles generated by electrolysis of
water
C. Lui, Lab Chip, 2010, 10, 74-79
Western New England University
BME 432
© 2020 Michael J. Rust
Pump Design Considerations
 Integrated vs External
 Does our pump need to be on-chip?
 Is portability an important design consideration?
 What about power?
 Will our pump selection affect materials we can use for
fabrication?
 Will it affect the complexity of the system?
Western New England University
BME 432
© 2020 Michael J. Rust
Pump Design Considerations
 Mechanical vs. Non-mechanical
 Mechanical pumps have traditionally been used in macroscale fluidic systems
 Non-mechanical pumps show advantages in microscale
• High viscous forces and small dimensions lead to high fluidic
resistance
– Thus very high pressures needed, which consumes power
1 µL/min
10 µL/min
100 µL/min 1 mL/min
New pumps
Electrokinetic
Magnetohydrodynamic
Ultrasonic
Western New England University
BME 432
10 mL/min
Mechanical pumps
Check-valve
Peristaltic
Valve-less rectification
© 2020 Michael J. Rust
Microfluidics
Components
(Channels, valves)
Western New England University
BME 432
© 2020 Michael J. Rust
Microfluidic Components
 Major components of microfluidic systems
 Microchannels
 Valves
 Pumps
 Mixers
J.S. Shim, et al., Proc. SPIE, vol. 6465. From G.T.A. Kovacs, Micromachined Transducers Sourcebook, p. 824, 844.
Western New England University
BME 432
T.M. Squires, Rev. Mod. Phys., vol. 77, July
2005., 977-1026.
© 2020 Michael J. Rust
Microchannels
 Uses
 Connection between components
 Reactant delivery
 Reaction zone
 Separation
 Types
 Bulk
 Near-surface
 Surface
Western New England University
BME 432
© 2020 Michael J. Rust
Microchannels
 Bulk Microchannels
 Channel is formed directly in substrate material
 Bonding
• Achieved with flat coverslip
Western New England University
BME 432
© 2020 Michael J. Rust
Microchannels
 Bulk Microchannels
 Advantages
•
•
•
•
Simplicity
Possibility of coating channel walls
Robust channels
Large channel cross-section
 Disadvantages
• Microvoids possible
• Bonding required
• Poor access
 By far the most common type of microchannel
Western New England University
BME 432
© 2020 Michael J. Rust
Microchannels
 Near-Surface Microchannels
 Similar to bulk channels, but typically shallower
 Sealing achieved by deposition of thin film
Western New England University
BME 432
© 2020 Michael J. Rust
Microchannels
 Near-Surface Microchannels
 Advantages
•
•
•
•
Close to substrate surface
Clear walls
Some control over channel depth
No bonding
 Disadvantages
• Poor control over channel dimensions and shape
• Fragile
Western New England University
BME 432
© 2020 Michael J. Rust
Microchannels
 Surface Microchannels
 Channels built on top of substrate using sacrificial layer
 Sacrificial layer removed to form channel
Western New England University
BME 432
© 2020 Michael J. Rust
Microchannels
 Surface Microchannels
 Advantages
• Precise control of channel dimensions
• Simple access
 Disadvantages
• Fragile walls
• Small cross-sectional areas
• Long clearance times for removal of sacrificial layer
Western New England University
BME 432
© 2020 Michael J. Rust
Microfluidic Valves
 Valves are critical components of microfluidic
systems
 Function
 Used to shut off or otherwise modify the flow of a fluid that
passes through it
 Types
 Passive valves
• No energy needed for operation
• Can use energy from flow
 Active valves
• Require external energy to function
Western New England University
BME 432
© 2020 Michael J. Rust
What are the desired
characteristics of valves?
Western New England University
BME 432
© 2020 Michael J. Rust
Microfluidic Valves
 Desired characteristics
 No leakage
 Minimal power consumption
 No dead volume
 Large closing force (pressure range)
 Maximum capacity
 Zero response time
 Linear operation
 Insensitivity to particulate contamination
 Compatible with wide range of fluids
 Other important characteristics to consider
 Normally open or closed
 Proportional or digital
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 Check Valve
 Allows flow in forward direction
From G.T.A. Kovacs, Micromachined Transducers Sourcebook, p. 823.
 Advantage
 Disadvantage
Western New England University
fast response time, simple response
leaky
BME 432
© 2020 Michael J. Rust
Passive Valves
 Biological example
http://www.sjm.com/assets/popups/valvereplace.gif
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 Biomimetic hydrogel
 Hydrogels
• materials that can change some physical parameter (typically
volume) based on some physical or chemical stimulus
• pH sensitive hydrogel swells or stays in shrunken state
– Swells = blocks channel
– Shrunken = flow continuous
Fig. 4.2 from O. Geschke, H. Klank, and P.Telleman, Microsystem
Engineering of Lab-on-a-Chip Devices, Wiley-VCH, 2008, p. 41.
 Advantages
 Disadvantages
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responds to sample pH
difficult to integrate
BME 432
© 2020 Michael J. Rust
Passive Valves
 Geometric restriction
 Use geometry of channels to control flow
 Requirements
• Hydrophobic surfaces
• Abrupt changes in channel geometries
w2
w1
 Operation
•
•
•
•
Fluid arrives at interface between large and small channels
Significant pressure is required to overcome surface tension
Fluid stops until higher pressure is achieved
Flow continues
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 SPROMs
 Structurally Programmable Microfluidic Systems
 Series of microfluidic channels with passive valves located at
strategic locations
• Fill channels in specific sequence
C.H. Ahn, et al., Proc. IEEE, vol. 92, no. 1, 2004, pp. 154-173.
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 SPROMs
 Structurally Programmable Microfluidic Systems
 Series of microfluidic channels with passive valves located at
strategic locations
• Fill channels in specific sequence
(a)
C.H. Ahn, et al., Proc. IEEE, vol. 92, no. 1, 2004, pp. 154-173.
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 SPROMs
 Structurally Programmable Microfluidic Systems
 Series of microfluidic channels with passive valves located at
strategic locations
• Fill channels in specific sequence
(b)
C.H. Ahn, et al., Proc. IEEE, vol. 92, no. 1, 2004, pp. 154-173.
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 SPROMs
 Structurally Programmable Microfluidic Systems
 Series of microfluidic channels with passive valves located at
strategic locations
• Fill channels in specific sequence
(c)
C.H. Ahn, et al., Proc. IEEE, vol. 92, no. 1, 2004, pp. 154-173.
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 SPROMs
 Structurally Programmable Microfluidic Systems
 Series of microfluidic channels with passive valves located at
strategic locations
• Fill channels in specific sequence
(d)
C.H. Ahn, et al., Proc. IEEE, vol. 92, no. 1, 2004, pp. 154-173.
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 SPROMs
 Structurally Programmable Microfluidic Systems
 Series of microfluidic channels with passive valves located at
strategic locations
• Fill channels in specific sequence
(e)
C.H. Ahn, et al., Proc. IEEE, vol. 92, no. 1, 2004, pp. 154-173.
Western New England University
BME 432
© 2020 Michael J. Rust
Passive Valves
 SPROMs
 Structurally Programmable Microfluidic Systems
 Series of microfluidic channels with passive valves located at
strategic locations
• Fill channels in specific sequence
(f)
C.H. Ahn, et al., Proc. IEEE, vol. 92, no. 1, 2004, pp. 154-173.
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Operation
 Working state is determined by closure of element (valve seat)
 Actuator provides mechanical action to control position of valve
seat
 Types
 Digital operation
• Normally open
– Requires energy to close and remain closed
• Normally closed
– Requires energy to open and remain open
• Bistable
– Can be open or closed
– Requires energy for the transition between states
 Analog operation
• Proportional operation
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Actuation principles
 Pneumatic
 Thermopneumatic
 Thermomechanic
 Piezoelectric
 Electrostatic
 Electromagnetic
 Electrochemical
 Evaluation criteria
 Operating force (pressure range)
 Response time
 Power requirement
 Integration
 Stroke displacement
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Pneumatic
 Uses compressed gas
T.M. Squires, Rev. Mod. Phys., vol. 77, July 2005., 977-1026.
 Simplest actuation concept
 Requires external pressure source and interconnects
• Not suitable for compact designs
 Large pressure range
 Slow response time
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Pneumatic
T.M. Squires, Rev. Mod. Phys., vol. 77, July 2005., 977-1026.
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Pneumatic
Silicone
membrane
Fluid inlet
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Fluid outlet
BME 432
© 2020 Michael J. Rust
Active Valves
 Pneumatic
Applied Pressure
Silicone
membrane
Fluid inlet
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Fluid outlet
BME 432
© 2020 Michael J. Rust
Active Valves
 Thermopneumatic
 Using heated fluids
Fig. 4.3 from O. Geschke, H. Klank, and P.Telleman, Microsystem Engineering of Lab-on-a-Chip Devices,
Wiley-VCH, 2008, p. 42.
 Large pressure range
 Relatively slow response time
 High power consumption
 May heat sample
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Thermomechanic
 Convert thermal energy directly into mechanical stress
• e.g. bimetallic valves
heat
heat
 High pressure range
 Relatively slow response
 High power consumption
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Thermomechanic
 Convert thermal energy directly into mechanical stress
• e.g. shape-memory alloys
Fig. 6.17c from N.-T. Nguyen, S. T. Wereley, Fundamentals and
Applications of Microfluidics, Artechouse, 2002, p. 270.
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Piezoelectric
 Material expands due to applied voltage
Fig. 4.4 from O. Geschke, H. Klank, and P.Telleman, Microsystem Engineering of Lab-on-a-Chip Devices,
Wiley-VCH, 2008, p. 42.
 High pressure range
 Low displacements
 Large power consumption
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Electrostatic
 Uses electrical attraction/repulsion
Fig. 6.21a from N.-T. Nguyen, S. T. Wereley, Fundamentals and
Applications of Microfluidics, Artechouse, 2002, p. 280.
 Non-linear forces
 Large movements
 Very fast response time
 Low power (but high voltages)
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Electromagnetic
 Uses applied magnetic field
Fig. 6.22c from N.-T. Nguyen, S. T. Wereley, Fundamentals and
Applications of Microfluidics, Artechouse, 2002, p. 282.
 Large movements
 Low power
 Fast response time
 Have to integrate magnetic materials
Western New England University
BME 432
© 2020 Michael J. Rust
Active Valves
 Electrochemical
 Uses gas bubbles generated by the electrolysis of water
Fig. 6.23a from N.-T. Nguyen, S. T. Wereley, Fundamentals and
Applications of Microfluidics, Artechouse, 2002, p. 285.
 Low pressure
 Slow response time
 High power consumption
Western New England University
BME 432
© 2020 Michael J. Rust
Passive vs. Active Valves
 Passive
 Advantages
• No power
• Simple design
• Relatively simple integration
 Disadvantages
• Cannot modify operation
• Leaky
 Active
 Advantages
• Can modify operation
 Disadvantages
• Power required
• Complex design/integration
Western New England University
BME 432
© 2020 Michael J. Rust
Valve Design Considerations
 There is no optimum valve for all applications
 Important questions
 What kind of fluids will come into contact with the valves?
 How often do we need the valves to operate?
• Many times per minute
• A few times total
 Can we afford to exhaust energy on actuating the valves?
 Will an off-chip method be better?
Western New England University
BME 432
© 2020 Michael J. Rust

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