Bio-transport and Design

of BioMEMS Devices(Bios 10 lecture)

James Gilchrist

Department of Chemical Engineering

September 30, 2009

an engineer

What is chemical engineering?

Chemical engineers design processes that perform

molecular transformations of raw materials

into products.

Intersection of Math, Physics, Chemistry, Biology

Math

PhysBio

Chembut

Math + Physics + Chemistry + Biology ≠ ChE

Industries relevant to chemical engineering

and biology:

• Agriculture

• Chemical

• Cosmetic

• Food/beverage

• Energy/Petroleum/Biofuels

• Pharmaceutical

• Medical devices/drug delivery

• other…

What is chemical engineering?

(and why might biologists care)?

Core areas of chemical engineering:

• Reactor engineering:

Most biological processes are highly

efficient and selective

• Transport processes:

Organelles, cells, and organs are structured to

control transport rate of chemicals

• All of chemical engineering is rooted in

Material and Energy Balances

Cells that do not transport

material and energy

cannot survive.

Images from wiki

Transport processes across scales (distance and time)

Two primary modes of material transport:

• Diffusive

• molecular → cellular scale

• random motion of macromolecules discovered by

botanist Robert Brown in 1827

– explained by Albert Einstein in 1905)

• collisional diffusion

• Convective (flow)

• cellular → system scale

Péclet number (Pe): diffusion time-scale / flow time-scale

Pe << 1 – processes depend on diffusion

Pe >> 1 – processes depend on convection

Examples of diffusion:

A single blood cell in a

droplet of water will take

over 2 years to interact with

a 40x40 micron sensor by

diffusion alone.

Most molecules

within a cell diffuse

in microseconds.

Example: blood transport

Increasing scale

Echocardiogram

of flow in heartLaminar to

turbulent flow

Developing Labs on a chip: why BioMEMS?

(MEMS – micro-electro-mechanical systems)

Why miniaturize?

“Better, faster, cheaper”

• Smaller scales optimize transport properties related to

macromolecular and cellular processes

• Faster and more accurate/reproducible analyses

Also

• Smaller sample size

• Less waste of reagents and lower fabrication costs

Developing Labs on a chip: why BioMEMS?

(MEMS – micro-electro-mechanical systems)

Two considerations:

• How do suspensions of macromolecules or cells

flow, mix, and segregate in these systems?

• How can we design microscale capture-and-release

platforms for disease detection?

• How can we use microscale processes to

„filter‟ out disease?

Blood flow in microchannels – Fahraeus-Lindqvist effect

?

In flow in a microchannel, the flow is fastest near the center and slowest

near the wall

water and other „normal‟ or Newtonian fluids develop a parabolic velocity

profile.

Blood has shear-dependent viscosity (Fahraeus-Lindqvist effect):

Less shear – higher viscosity

More shear – lower viscosity

„Separates‟ into cell-rich and cell-lean streams

Mixing at small scales

meters10010-110-210-310-410-510-610-710-810-9(mm)(mm)(nm)

Smaller scales produce both quantitative and

qualitative differences.

No turbulence.

Pe >> 1, diffusion is slow.

Surface forces are significant.

Incorporation of conventional approaches to

manipulation difficult.

Only recently has design of the

channels begun to overcome limitations

in mixing by introducing chaotic

advection via breaking symmetries.

Geometric modulation

Time-periodic forcing

Even with chaotic advection, invariant

manifolds often exist, inhibiting mixing.

Invariant surfaces

Ottino, 1989

Strook and Whitesides, Science, 2001

Liu et al, Mic. Mech.

Sys., 2000

Therriault et al, Nature

Mat., 2003

Straight Channel (1D Flow), ~30 mm from entrance

No

Image

40 mm

f = 0.1

f = 0.2

f = 0.3

Re ~ 0.04

Pe ~ 600

Re ~ 0.22

Pe ~ 3000

Re ~ 0.44

Pe ~ 6000

Re ~ 1.1

Pe ~ 15,000

Herringbone Channel (2D Flow)

2D Concentration contours across the channels

Re = 8.2x10-7 Pe = 5,100 C. Gao, B, Xu and J. F. Gilchrist, PRE, 2009

tracking3D Confocal Imaging – 2D channels, instability near entrance

0 10 20 30 40 50 60 70 800

5

10

15

20

25

0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12

0 10 20 30 40 50 60 700

5

10

15

20

25

0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12

0 10 20 30 40 50 60 70 800

5

10

15

20

25

0.02 0.04 0.06 0.08 0.1 0.12 0.14

trackingConfocal Imaging – Blood flow in 2D channels (elastic particles)

Developing Labs on a chip: why BioMEMS?

(MEMS – micro-electro-mechanical systems)

Two considerations:

• How do suspensions of macromolecules or cells

flow, mix, and segregate in these systems?

• How can we design microscale capture-and-release

platforms for disease detection?

• How can we use microscale processes to

„filter‟ out disease?

Method

Convective force /- Spin Coat

Jiang et. al., Appl. Phys. Lett 89., 2006

200- 8,000 rpm

Optical force /- Optical Tweezers

Vossen et al., Mat. Res. Soc. Symp. Proc 705., 2002

Furst, Curr. Opin. Coll. Surf. Sci., 10., 2005

Background - Fabrication of Colloidal Crystals

Electrical force /- Elec. field induction

Lumsdon et al., Appl. Phys. Lett. 82., 2003

Gravitational force /- Epitaxy

Lee et al., Langmuir 20., 2004

Method-Convec

)1(605.0

)(

kd

Jlvv ek

w C

Continuous

Convective Assembly

Dimitrov and Nagayama

Langmuir, 12, 1996

Dekov et al., Nature, 361,1993

Lazarov et al., J. Chem. Soc. Faraday Trans, 90, 1994

Capillary Force / Convective Evaporation

Background - Fabrication of 2D Colloidal Crystals

Prevo and Velev, Langmuir, 20, 2004

Fluid mechanics

neglected in

most previous studies

Fcap

Enhancement of Light Extraction Efficiency

Membranes for HIV

Separations/Sensing

Example Applications Varying Surface Morphology

Dye-sensitized Solar Cells

Transparent

conductors

Electrolyte (-)

Dye-coated

Nano/Mesoporous TiO2

+

–

Cell Capture and Release Substrates

with N. Tansu (Lehigh)

with M. Snyder (Lehigh) & G. Willing (U. Louisville)

with X. Cheng (Lehigh)

Ee et al., Applied Physics Letters 2007.

Kumnorkaew et al., Langmuir 2008.

Ee et al., IEEE J. Selected Topics in Quantum Electronics, 2009.

Ee et al., Optics Express, 2009.

Staggered Herringbone Channel (Chaotic Flow)

f = 0.3

Re ~ 0.44

Pe ~ 600020 mm

cycle = 25 25 ½ 26

Multiple local maxima in

concentration profile.

Center dense region

“roping” through

channel.

Final concentration

profile is steady

W

Undergraduate Students:

Colleen Curley, Abbe Lefkowitz, Kristen

Mason, and D’Andre Watson

Graduate Students:

Pisist Kumnorkaew, Bu Wang, and Alex

Weldon

Professors:

Xuanhong Cheng and James F. Gilchrist

2009 HHMI - BDSI summer research

Our Microchips

We want to build devices that reversibly

capture cells

There are currently no effective methods for

the isolation and release of specific cells

Releasing cells from the device allows

for research on targeted infected cells

Objectives Deposit a well-ordered

monolayer of SiO2 magnetic

beads on a glass substrate

Functionalize magnetic beads

with antibodies and build

microfluidic channels over the

monolayer

Capture Jurkat and THP1

cells in the microfluidic

channels

Controllably release captured

cells by magnetic force

Convective Deposition

Process by which a meniscus of suspension is drawn across a substrate to deposit a thin film.

Used to obtain a well-ordered monolayer of polystyrene nanoparticles and SiO2 magnetic bead microspheres Helps quantify the amount of magnetic

beads in a given area

Gives high surface coverage which prevents cells from binding to substrate

Each concentration of suspension (Φnano , Φmicro) has its optimum condition (angle, speed, temperature, humidity)

.

1 µm

5 µm

Magnetic Bead Layers

Depending on deposition and surface conditions,

we obtain monolayers of magnetic beads

Challenges arise due to non-uniform particle size

Sub-monolayerMonolayer

(Optimum) Multilayer

ResultsIdeal monolayer deposited with 20% SiO2, 6%

Polystyrene, and 30 µm/s deposition speed

Op

tim

izin

g

nan

op

art

icle

co

ncen

trati

on

Op

tim

izin

g

dep

os

itio

n s

peed

Magnetic Bead Liftoff:

Surface Chemistry Binding force between beads and

substrates must be optimized

Must be strong enough for beads to endure

fluid flow through the microchannels

Must be weak enough so that the beads can lift

off from the surface when magnetic force is

applied

Surface Chemistry When deposited on the untreated substrate, magnetic

beads bind too strongly

Silane treatment alters substrate surface chemistry to

weaken binding between the magnetic beads and the

substrate

Silanes change liquid contact angle and particle affinity for

the substrate

○ Hydroxymethyl triethoxysilane (H-treated)

○ 2-[Methoxy(polyethyleneoxy)propyl] trimethoxysilane (P-treated)

○ 2-Cyanoethyl triethoxysilane(C-treated)

Untreated Substrate

<10ºH Silane

47º

P Silane

41.5º

C Silane

37º

Suspension Droplet Contact Angles

Surface Chemistry We measured deposition speed

necessary to obtain a monolayer

of magnetic beads on slides

treated with each silane

Silane Treatment Optimum Speed for a Monolayer

Clean Glass 12.5 µm/s

H 12.5 µm/s

P 13.3 µm/s

C 11.7 µm/s

All other parameters held constant

Lift-off Experiments

We aim to quantify when beads irreversibly bind to the

substrate and when they can be controllably released

under flow and magnetic forces

Experimental conditions:

• Silane treatment, polystyrene removal in a toluene bath,

and drying under nitrogen flow and in air

• Solvent replacement and DI water wash experiments to

remove unknown stock solution

Treated slides rinsed under various flow rates to

simulate microchannel conditions

Results Toluene baths preceding DI water baths promoted

uncontrollable liftoff (in DI water baths)

• Samples dried between toluene and DI water baths

showed no liftoff

Increased time between deposition and rinse

strengthens binding between beads and substrate

Liftoff on P-treated substrates was difficult to tune

Solvent-replaced suspensions deposited on

H-treated substrates left at room temperature

to equilibrate showed most controllable

release

• Optimum silane equilibration time is 1 hour

Results

Liftoff No Liftoff

Cell Capture and Culture Objective

Our eventual goal is to capture infected cells

using a microfluidic channel and keep them

viable for analysis

Preliminary Model

Used cells that simulate white blood cells

Fabricated and flowed cells through microchannels

Analyzed cell capture using fluorescence microscopy

Deposition vs. Plain Glass Microchannels made on slides with monolayer depositions

Cells pumped through channels at 2-5 µl/minute for 5

minutes

Cells (~7 µm diameter) fixed and stained to fluoresce green

Devices analyzed using fluorescence microscopy

Plain glass and defect areas captured more cells than areas

of monolayer deposition

Deposition

Clean Glass

100 µm

Geometric Factor in Cell Capture The idea: smaller beads will result in more

contact area. Therefore will make cell capture

more efficient.

Small beads: more contact area

Big beads: less contact area

The test:

0.5 um silica beads 1um silica beads

Number of Cells

Captured on Deposition

47 14

5 µm

Ongoing Work

Refine and optimize deposition, surface

treatment, and cell capture

Continue parametric studies on magnetic

bead liftoff and cell capture

Optimize cell release in microfluidic channels

Modeling forces involved for release

Proof of Concept

Transition to capturing rare instead of model cells

Acknowledgements

We gratefully acknowledge funding from the

Howard Hughes Medical Institute as well as

those in connection with the Biosystems

Dynamics Summer Institute

Acknowledgements

FABRICATION OF NANOPOROUS MEMBRANES FOR

BIO-NANO-PARTICLE FILTRATION

Sherwood Benavides

Colleen Curley

Jonathan Cursi

Meaghan Phipps

OBJECTIVES

Deposit monolayers of binary suspensions to be used in membrane fabrication

Fabricate membrane 6-10 microns in thickness and functionalize its surface with antibodies

Develop platform to test efficacy of nanoporous membrane in microfluidic device

Model filtration and sensitivity analysis

Purification Concentration

Detection

OBJECTIVES

Deposit monolayers of binary suspensions to be used in membrane fabrication

Fabricate membrane 6-10 microns in thickness and functionalize its surface with antibodies

Develop platform to test efficacy of nanoporous membrane in microfluidic device

Model filtration and sensitivity analysis

MEMBRANE TEMPLATING VIA SELF-ASSEMBLY

Convective deposition was used to obtain a well-ordered monolayer

A meniscus of suspension drawn across a substrate deposits a thinfilm

Binary suspensions of polystyrene nanoparticles or PEG pre-polymer were deposited with silica microspheres

MEMBRANE TEMPLATE VIA SELF-ASSEMBLY

20% SiO2 and 8% polystyreneUnmelted

20% SiO2 and 8% polystyreneMelted

MEMBRANE TEMPLATE VIA SELF-ASSEMBLY

10% PEG6% PEG 15% PEG 20% PEG

30% PEG 50% PEG

MEMBRANE FABRICATION

1/6 Vmono

MEMBRANE FABRICATION

To form the pores of the membrane, silica spheres were removed by etching with HF and KOH

Once etched, the membrane will be functionalized with antibodies to selectively capture viral particles

Etched with HF Etched with KOH

ETCHING WITH KOH

½ Vmono – 3 layers80 degrees Celsius

7 hours

ETCHING WITH KOH

½ Vmono – 3 layers90 degrees Celsius

17 hours

ETCHING WITH KOH

½ Vmono – 3 layers90 degrees Celsius24+ hours Etching

ETCHING WITH KOH

½ Vmono – 3 layers90 degrees Celsius24+ hours Etching

PLATFORM DEVELOPMENT

Flow liquid through the device at a constant pressure and flow rate will be measured at the outlet

As more viral particles are captured on the membrane, the flow rate will decrease

The number of particles captured in the devices, and ultimately in the patient’s blood, can be calculated

MODELING: BEGINNING STAGES

p0 = 1.1e5 Pa; T_in = 298K

Velocity Field Pressure Field

Pf = 1.0e5 Pa

MODEL SENSITIVITY AND FILTRATION ANALYSIS

SiO2 microspheres randomly arrange into square close packed and hexagonally close packed (HCP) structures during convective deposition

The HCP arrangement maximizes crystal array density

Polystyrene/PEG particles fill the interstices between SiO2 particles and remain after etching in order to form a membrane

Hexagonally close packed

unit cell

Etched HCP unit cell

MODEL SENSITIVITY AND FILTRATION ANALYSIS

Velocity field data for fluid flow through a single HCP-based pore for a pressure drop of 1.5 psi:

Surface Plot Cross Section Higher Value

Lower Value