how to design a microfluidic part 2 - think modularly · 2020. 1. 29. · how to design a...

ALine, Inc. 19500 S. Rancho Way, Ste 107 Rancho Dominguez, CA 90220 Tel: +1-877-707-8575 Fax: +1-770-818-5475 www.alineinc.com

How to Design a Microfluidic

Part 2 - “Think Modularly”

Leanna M. Levine, Ph.D., Founder and CEO, ALine, Inc.

The goal of this four-part series is to help non-microfluidics experts, and especially biologists and

biochemists who are interested in utilizing microfluidics to package their assay into a more user-friendly

or portable format, yet who are unsure how to plan a development effort and what to expect.

Whether the assay protocol is a sandwich immune assays, PCR, and cell-based assays, the same

considerations apply in the design development. The objective is to create a set of cartridge

specifications that will enable design for manufacture while delivering on the required limit of detection,

sensitivity within a limit of variability that ensures useful results are consistently provided. The

development process for microfluidics products is especially complex because the biological

components have been optimized to perform in standard lab ware, and will need to be re-optimized for

a microfluidic device. Part of the challenge is to organize the development in a logical sequence,

focusing on resolving big risk areas first, and part of it is looking at the problem from the desired end

result - what do you want this system to do and with what level of accuracy and precision? What's good

enough vs. what exactly mimics what is currently done in the lab with high quality analytical

instrumentation.

To help folks who are simply interested in becoming users of microfluidics, yet are in faced with

developing a protocol for a microfluidic cartridge, a four part series is presented here that captures the

things one should consider before picking up the phone and talking to any of a number of service

providers.

The content is broken down into the following outline:

1) Start at the end.

2) Think modularly.

3) How will I know if I'm getting good results?

4) The Integration Challenge

In Part 1 of this series, “Start at the End”, we discussed the need to reduce the development risk by starting

with the detection geometry, which often entails moving from a static, well-based assay to a flow-based

assay. Once the detection geometry, flow rates, and materials are understood, and routine measurements

are possible, it’s time to move further up the protocol, and consider the requirements for serial reagent

additions, mixing, metering, air bubble and dead volume management.

In Part 2, the development focus is to now consider more fully what assay modifications can reduce the

number of reagent additions. This has considerable impact on the overall cost of the consumable. Systems

with the need for more than one liquid reagent storage to execute the assay protocol have more than

double the complexity in the instrument and cartridge. More moving parts means more opportunities for

failure, whether it’s in cartridge manufacture and the need for more QA testing, or in the instrument

component complexity and service requirements.


Effort spent early to simplify the assay protocol, by combining reagents, and developing novel IP around

the reagents and protocol is far more valuable for the product than a novel microfluidic design. All of our

customers have IP around the assay and/or a unique biosensor. The microfluidics is just the package that

integrates the protocol into a convenient, low cost, portable fluid handling system. But simply porting an

assay that’s conveniently run using pipetting, whether its manually or robotically, into a microfluidic

system is to ignore the system integration complexity and its impact on the reliability, and the final cost

of manufacture and QA.

So, if you are considering an assay with two or more liquid reagent storage requirements, spend some

more time inventing ways to reduce the number of liquid reagent inputs. This is far more valuable to the

final product cost of manufacture, reduced risk, and market acceptance than anything else. Simplification

can be achieved by, for example, only storing a buffer for washes and reconstitution steps for reagents

that are dried into the cartridge.

At this point, it becomes apparent that parallel efforts to address reagent storage and assay integration

into the microfluidic are important for development planning.

Reagent Storage Options:

Liquid: Think of ways to come up with a single universal solution that can be amended with other

components that are dried into the cartridge.

Dried reagents: A number of processes exist for drying reagents into a device. A variety of vendors who

specialize in different dry reagent storage methods are available to support these activities. There are two

general strategies, lyophilization into a bead, or drying onto a surface. ALine works with several and can

offer guidance on what options to choose. This stage is a good time to design and build microfluidic

devices in which the dried reagents are reconstituted with a repeatable, semi-automated protocol which

will provide a robust process for optimizing the reconstitution process for testing in the already-developed

detection system. While you’re at it, set up your aging studies now to demonstrate the assay performance

over time under different storage conditions.


Discussion of the modular integration of these fluidic components and functions is in the section below.

Unfortunately, a lot of this upfront staging

work to support assay portability does not

produce the wow factor that investors like to

see. Blame it on all the folks who still think

about Star Trek and the tricorder every time

someone mentions a handheld diagnostic!

Yet, laying out this critical piece of the

product roadmap, in which the assay protocol

and reagent storage conditions are well

understood early on, gives the product

development effort a lot more flexibility in

latter development stages. Plus, most of the

value creation in the product resides in the

assay and reagents. Once you’ve got the

reagent compositions, the protocol and the

reagent storage well understood, the rest of it is a fluidic packaging problem. And like anything else in

engineering, there are multiple solutions for the fluidic engineering and integration piece.

Fluidic Integration with Engineered Components

The example assay protocol, shown above, calls for some standard mechanical components such as

valves, pumps, de-bubbling, metering, and mixing components with known performance characteristics.

Analogous to electro-mechanical components such as solenoid valves, and diaphragm pumps, ALine has

engineered and characterized off-the-shelf microfluidic components with known operational

characteristics. These components include valves, pumps, vents, and metering geometries with between

+/- 2% to 5% repeatable metering. They have been characterized and reported on in a series of technical

articles available by contacting us: [email protected]

WHAT IS YOUR MICROFLUIDIC DEVICE

BODY PLAN?

VERTICAL OR HORIZONTAL?

GRAVITY IS YOUR FRIEND, AND A FREE FORCE THAT

YOU CAN USE TO ACT ON YOUR FLUIDICS.

IN MANY CASES, GRAVITY CAN SIMPLIFY AIR

BUBBLE CONTROL AND REDUCE THE NEED FOR

ACTIVE VALVES.

DON’T GET STUCK IN THE INTEGRATED CIRCUIT

PARADIGM!


These ALine product components are pneumatically controlled and integrate into the device to enable

the desired protocol. In the workflow shown above, there is a need for metering, mixing, and the ability

to select between two different fluid paths, one for sample and reagent, and one for wash. Mixing is

achieved using the pumping module, which can be run forward and back to create turbulence to effect

mixing. Downstream of the detection chamber, there is a waste container. Each blue box represents

amodule that will be optimized and/or integrated to achieve the workflow in the device. The next step is

to demonstrate the functionality in the sub-components, typically in this order: Sub component 1, the

detection, which was discussed in Part 1; Subcomponent 2, to ensure the front-end sample management

meets the requirements, followed by integration of subcomponent 3 and 4 with the well-defined

geometries and layout for components 1 and 2.

Once all the functions are combined in a single device, with a well-designed layout for the operations and

channels to minimize the number of solenoid valves, reduce the dead volume, and to simplify the

microfluidic device/instrument interface, an instrument control actuation routine is created to run the

entire protocol. This system is then delivered with an option for training support by ALine engineers either

at your facility or at ALine.

But what about the blister packs or other liquid reagent storage mechanisms, when do we engineer

those in? Or what about the sample introduction geometry and any plasma separation from whole blood?

Following the same principle of start at the end, we will continue to move toward a completely integrated

design once we show the assay can achieve the limit of detection and selectivity with spiked samples, or


with patient samples that are prepared off chip.

The liquid reagent storage is more about finding the

space than about the integration. If you have 1mL

of buffer, and you need three or four of them,

you’ve got space constraints.

We’ll discuss these final integration aspects in the

last installment, “The Integration Challenge”.

The next installment, “How will I know if I’m getting

good data” will address optimization of the assay

protocol using instrumented control to enable a

rapid SPEC-design-build-test cycle. The emphasis

shifts now to the set of SPECifications for the

components of the system; reagents, cartridge,

instrument. As all components of the system now

work together and data collection is enabled, it’s

now time for parametric specifications for the

system performance. This will guide the next phase

of the development which focuses on knowing

when you are getting data that meets your acceptance criteria and with fewer than 5% failures in the

entire protocol. And that information drives the mechanical specifications that are part of the package for

regulatory submission.

About ALine:

Founded on the need for high quality custom microfluidics with a rapid prototyping process that supports a rapid design-build-test cycle, ALine has grown and matured to enable us to support our client’s development programs with microfluidics expertise in biology and engineering. Our microfluidics experts had direct experience with integrating assays into microfluidic devices.

Contact us at [email protected] or call 877-707-8575 to discuss your microfluidic requirements.

From our beginnings in rapid prototyping 14 years ago, ALine has created a set of engineered fluid-handling components, such as pneumatically–controlled on-board valves and pumps, design rules and material sets that work for a variety of assays, including PCR and cell culture. Our development instrumentation is delivered to our customers with the actuation protocol already developed. With our on-site support, we deliver integration of an assay protocol into a microfluidic system in less than four months. This means our clients are busy collecting data and optimizing the assay through a systems integration approach early in the program. Optimization of the assay, microfluidic device design, and the actuation protocol that runs the assay are all developed together in a tight series of design-build-test cycles. The result is a device design and instrument interface that is de-risked for commercialization.

Our Team:

Dr. Leanna M. Levine, Ph.D. CEO and Founder: [email protected] Dr. Stefano Begolo, Ph.D. Director of Engineering: [email protected] Mr. Said Ehrlich, M.S.E.E., Lead Engineer: [email protected] Mr. Justin Podcerviensky, B.S., Production Manager: [email protected] Ms. Francesca Yu, B.S., Quality Specialist: [email protected]

THERE’S A SERPENTINE COMPONENT IN MY

MICROFLUIDIC DEVICE!

WHICH OF THE FOLLOWING ARE TRUE:

1. A SERPENTINE CHANNEL WILL MIX TWO FLUID STREAMS.

2. A SERPENTINE CHANNEL IS EASY TO INJECTION MOLD

WITH GOOD PRECISION.

3. A SERPENTINE CHANNEL IS EASY TO MAKE IN PDMS PARTS

USED IN THE LAB.

4. A SERPENTINE CHANNEL IS USEFUL FOR CREATING

CONTROLLED PRESSURE DROPS IN A FLUID CIRCUIT.

5. A SERPENTINE CHANNEL CAN BE USED TO INCREASE THE

RESIDENCE TIME OF A SOLUTION IN A CONTANT FLOW

SYSTEM.

6. A SERPENTINE CHANNEL IS LIKE A COIL OF TUBING.

7. SERPENTINE CHANNELS LOOK COOL, AND EVERYONE

RECOGNIZES THEM AS MICROFLUIDIC COMPONENTS.

ANSWER: 3-7. WHEN IT COMES TO SERPENTINE CHANNELS,

DON’T, UNLESS 4 IS REQUIRED.

mailto:[email protected]

how to design a microfluidic part 2 - think modularly · 2020. 1. 29. · how to design a...

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