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OpenDrop: An Integrated Do-It-Yourself Platform for Personal Use of Biochips

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Biochips, or digital labs-on-chip, are developed with the purpose of being used by laboratory technicians or biologists in laboratories or clinics. In this article, we expand this vision with the goal of enabling everyone, regardless of their expertise, to use biochips for their own personal purposes. We developed OPENDROP, an integrated electromicrofluidic platform that allows users to develop and program their own bio-applications. We address the main challenges that users may encounter: accessibility, bio-protocol design and interaction with microfluidics. OPENDROP consists of a do-it-yourself biochip, an automated software tool with visual interface and a detailed technique for at-home operations of microfluidics. We report on two years of use of OPENDROP, released as an open-source platform. Our platform attracted a highly diverse user base with participants originating from maker communities, academia and industry. Our findings show that 47% of attempts to replicate OPENDROP were successful, the main challenge remaining the assembly of the device. In terms of usability, the users managed to operate their platforms at home and are working on designing their own bio-applications. Our work provides a step towards a future in which everyone will be able to create microfluidic devices for their personal applications, thereby democratizing parts of health care.
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bioengineering
Article
OpenDrop: An Integrated Do-It-Yourself Platform for
Personal Use of Biochips
Mirela Alistar * and Urs Gaudenz
Gaudi Labs, Lucern 6003, Switzerland; info@gaudi.ch
*Correspondence: mirela.alistar@gmail.com; Tel.: +49-3315-5093-946
Academic Editor: Hyun Jung Kim
Received: 1 April 2017; Accepted: 11 May 2017; Published: 19 May 2017
Abstract:
Biochips, or digital labs-on-chip, are developed with the purpose of being used by
laboratory technicians or biologists in laboratories or clinics. In this article, we expand this vision with
the goal of enabling everyone, regardless of their expertise, to use biochips for their own personal
purposes. We developed OPENDROP, an integrated electromicrofluidic platform that allows users to
develop and program their own bio-applications. We address the main challenges that users may
encounter: accessibility, bio-protocol design and interaction with microfluidics. OPENDROP consists
of a do-it-yourself biochip, an automated software tool with visual interface and a detailed technique
for at-home operations of microfluidics. We report on two years of use of OPENDRO P, released as an
open-source platform. Our platform attracted a highly diverse user base with participants originating
from maker communities, academia and industry. Our findings show that 47% of attempts to replicate
OPENDROP were successful, the main challenge remaining the assembly of the device. In terms of
usability, the users managed to operate their platforms at home and are working on designing their
own bio-applications. Our work provides a step towards a future in which everyone will be able to
create microfluidic devices for their personal applications, thereby democratizing parts of health care.
Keywords:
droplet microfluidics; lab-on-a chip; electromicrofluidics; design automation; open source
hardware; do-it-yourself biology
1. Introduction
Microfluidics, the study and handling of small volumes of fluids, has the potential to
revolutionize the laboratory research with immediate applications in medical care (e.g., point-of-care
diagnostics [
1
3
] and drug discovery [
4
6
]). Such applications on biological materials, typically
including experimental procedures, recipes and data analyses, are commonly known as “bio-protocols”.
The explicit benefit of microfluidics for bio-protocols, stems from the miniaturization of fluids that
leads to reduced material consumption and faster time-to-result. However, microfluidics can further
benefit from automation and reconfigurability. That is why, in the past decade, microfluidics research
has become increasingly multidisciplinary, involving such varied fields as nanotechnology, electrical
engineering and computer science.
Microfluidic research is typically conducted in one of the following directions: (i) building the
microfluidic machines that reliably manipulate fluids [
7
13
]; (ii) designing new bio-protocols for
microfluidics [
1
6
]; or (iii) developing automation algorithms for the execution of bio-protocols on the
microfluidic machines [1418].
Recently, research trends have shifted towards integrated microfluidic platforms that provide a
complete workflow from bio-protocol specification to microfluidic operations.
Microfluidic platforms can be classified according to the liquid propulsion principle used for
operation, e.g., capillary, pressure driven, centrifugal, electrokinetic or acoustic.
Bioengineering 2017,4, 45; doi:10.3390/bioengineering4020045 www.mdpi.com/journal/bioengineering
Bioengineering 2017,4, 45 2 of 17
We are interested in digital microfluidic biochips, which manipulate the fluids as droplets on an
array of electrodes, using electrical voltage [
8
]. In Figure 1we show OPENDROP, the do-it-yourself
(DIY) biochip we developed for personal use.
Bioengineering 2017, 4, 45 2 of 16
We are interested in digital microfluidic biochips, which manipulate the fluids as droplets on an
array of electrodes, using electrical voltage [8]. In Figure 1 we show OPENDROP, the do-it-yourself
(DIY) biochip we developed for personal use.
Figure 1. O
PENDROP consists of an array of electrodes, with each electrode capable of holding a
droplet. To execute bio-applications (“bio-protocols”), OPENDROP moves the micro-droplets by means
of electrical voltage. OPENDROP is compact and portable as the electrode array can be actuated directly
from battery with no need for additional pressure or vacuum pumps.
Digital microfluidic biochips manipulate droplets by applying electrical voltage. The
phenomenon is called ‘electro-wetting on dielectric(EWoD) [8,9]. Electrical voltage unbalances the
force equilibrium at the solid-liquid-vapor interface, causing the droplets to move towards the
charged electrodes [10,11]. Using EWoD, biochips can create, transport, mix and split droplets [12].
As shown in Figure 1, OPENDROP inherits the advantages of a biochip, i.e., it is: (a) compact and
portable because the electrode array can be actuated directly from battery with no need for additional
pressure or vacuum pumps; (b) reconfigurable because the electrodes can be used interchangeably;
and (c) programmable because the droplet movement can be programmed directly from the
computer [14–18].
Due to their advantages, biochips have great potential of truly accomplishing the vision oflab-
on-a chip’, that is, a complete and automated wetlab in miniature [7,8].
2. Motivation and Vision
Biochips, such as Neoprep (Illumina, San Diego, CA, USA) or Dropbot [19], are developed with
the purpose of being used by lab technicians or biologists in laboratories or clinics [20,21]. In this
paper, we expand this vision, by exploring the possibility of developing an integrated platform for
personal use of biochips. Such a platform will enable interested users to develop and program their own
applications on biochips.
As mentioned, biochips have the advantage of “programmability”; thus, the users can define
their own application. When we expand the usability of biochips from biologists to a more general
user, the application area also enlarges from the intended bio-protocols to unexpected applications,
ranging from fragrance design to molecular gastronomy. Thus, in this paper we prefer to use the
Figure 1.
OPENDROP consists of an array of electrodes, with each electrode capable of holding a
droplet. To execute bio-applications (“bio-protocols”), OPENDROP moves the micro-droplets by means
of electrical voltage. OPENDROP is compact and portable as the electrode array can be actuated directly
from battery with no need for additional pressure or vacuum pumps.
Digital microfluidic biochips manipulate droplets by applying electrical voltage. The phenomenon
is called ‘electro-wetting on dielectric’ (EWoD) [
8
,
9
]. Electrical voltage unbalances the force equilibrium
at the solid-liquid-vapor interface, causing the droplets to move towards the charged electrodes [
10
,
11
].
Using EWoD, biochips can create, transport, mix and split droplets [12].
As shown in Figure 1, OPENDROP inherits the advantages of a biochip, i.e., it is: (a) compact
and portable because the electrode array can be actuated directly from battery with no need for
additional pressure or vacuum pumps; (b) reconfigurable because the electrodes can be used
interchangeably; and (c) programmable because the droplet movement can be programmed directly
from the computer [1418].
Due to their advantages, biochips have great potential of truly accomplishing the vision of
‘lab-on-a chip’, that is, a complete and automated wetlab in miniature [7,8].
2. Motivation and Vision
Biochips, such as Neoprep (Illumina, San Diego, CA, USA) or Dropbot [
19
], are developed with
the purpose of being used by lab technicians or biologists in laboratories or clinics [
20
,
21
]. In this paper,
we expand this vision, by exploring the possibility of developing an integrated platform for personal use
of biochips. Such a platform will enable interested users to develop and program their own applications
on biochips.
As mentioned, biochips have the advantage of “programmability”; thus, the users can define their
own application. When we expand the usability of biochips from biologists to a more general user, the
application area also enlarges from the intended bio-protocols to unexpected applications, ranging
Bioengineering 2017,4, 45 3 of 17
from fragrance design to molecular gastronomy. Thus, in this paper we prefer to use the more general
term bio-applications instead of “bio-protocol”, to cover applications that deviate from the common
understanding of a bio-protocol.
In Figure 2, we schematically depict the envisioned interaction between a non-expert and a biochip.
First, the user designs a new bio-application on the computer. Next, the user loads the microfluidic
machine with the input fluids (i.e., samples, reagents, buffers) and connects the microfluidic machine
to the computer.
Bioengineering 2017, 4, 45 3 of 16
more general term “bio-applicationsinstead of “bio-protocol”, to cover applications that deviate from
the common understanding of a bio-protocol.
In Figure 2, we schematically depict the envisioned interaction between a non-expert and a
biochip. First, the user designs a new bio-application on the computer. Next, the user loads the
microfluidic machine with the input fluids (i.e., samples, reagents, buffers) and connects the
microfluidic machine to the computer.
On the computer, the dedicated software compiles the bio-application to automatically control
the movement of the fluids. When the bio-application finishes, the feedback from the sensors is
recorded by the computer and transformed into data to be further read and analyzed by the user.
Figure 2. System setup. The user actions are marked with dashed lines and the automated actions are
marked with solid lines. The user designs the application on the computer and then loads the
microfluidic machine with the input fluids (i.e., samples, reagents, buffers). On the computer, the
dedicated software compiles the application to automatically control the movement of the droplets.
When the application finishes, the feedback from the sensors is recorded by the computer and
transformed into data to be further read and analyzed by the user.
While we want to keep an open mind and not hinder the creativity of the users in any way, we
believe there is still a significant amount of users that have enough knowledge to adapt existing bio-
protocols for their own needs. Examples of bio-protocols that can be potentially customized by users
are: fast assay for blood grouping [22], semen monitoring [23], bacteria detection in water [24], etc. In
this paper, we focus on enabling these knowledgeable users to use biochips for developing
customized bio-protocols.
We believe our work is a first step towards personal laboratories: small portable devices that
people can own and use to develop customized bio-protocols, similar to today’s personal computers.
3. Our Contributions
Building a biochip for personal use encounters challenges in terms of (i) cost; (ii) accessibility;
and (iii) operability. In this paper, we introduce O
PEN
D
ROP
, a platform that addresses all these
challenges as follows.
Cost is the main concern for users. For that reason, we designed O
PEN
D
ROP
to be within the
affordable price range for consumers. We break down the costs of O
PEN
D
ROP
into (a) fabrication
costs: design, production and assembly costs; and (b) operation costs: the costs of the fluids used for
the targeted bio-application. (a) We minimize the design cost by publishing the design files
open-source, thus enabling everyone to use it directly, at no design cost. We also focused on reducing
the production costs, opting to use printed-circuit-board (PCB) for the electrode substrate. When
ordered online, the components of O
PEN
D
ROP
add up to a total of $300. The assembly takes in average
5 h and it requires previous experience in soldering surface-mount components; (b) Operation costs
are hard to estimate because they are highly specific to the bio-application: the reagents for gene
cloning cost $100, while fragrances cost less than $1. Our approach to reducing the volumes of
operational fluids is to keep the electrode size, and thus the droplet size, minimal.
Accessibility is a key feature for ensuring a high replicability of our platform. In general, users
have no access to the microfabrication facilities needed to produce a microfluidic chip. Moreover, the
services provided by some of the few specialized companies can easily get too expensive as they
charge for design, fabrication, transport and communication. We made the fabrication of O
PEN
D
ROP
Figure 2.
System setup. The user actions are marked with dashed lines and the automated actions
are marked with solid lines. The user designs the application on the computer and then loads the
microfluidic machine with the input fluids (i.e., samples, reagents, buffers). On the computer, the
dedicated software compiles the application to automatically control the movement of the droplets.
When the application finishes, the feedback from the sensors is recorded by the computer and
transformed into data to be further read and analyzed by the user.
On the computer, the dedicated software compiles the bio-application to automatically control the
movement of the fluids. When the bio-application finishes, the feedback from the sensors is recorded
by the computer and transformed into data to be further read and analyzed by the user.
While we want to keep an open mind and not hinder the creativity of the users in any way,
we believe there is still a significant amount of users that have enough knowledge to adapt existing
bio-protocols for their own needs. Examples of bio-protocols that can be potentially customized by
users are: fast assay for blood grouping [
22
], semen monitoring [
23
], bacteria detection in water [
24
],
etc. In this paper, we focus on enabling these knowledgeable users to use biochips for developing
customized bio-protocols.
We believe our work is a first step towards personal laboratories: small portable devices that people
can own and use to develop customized bio-protocols, similar to today’s personal computers.
3. Our Contributions
Building a biochip for personal use encounters challenges in terms of (i) cost; (ii) accessibility; and
(iii) operability. In this paper, we introduce OPENDRO P, a platform that addresses all these challenges
as follows.
Cost
is the main concern for users. For that reason, we designed OPENDROP to be within the
affordable price range for consumers. We break down the costs of OPENDROP into (a) fabrication costs:
design, production and assembly costs; and (b) operation costs: the costs of the fluids used for the
targeted bio-application. (a) We minimize the design cost by publishing the design files open-source,
thus enabling everyone to use it directly, at no design cost. We also focused on reducing the production
costs, opting to use printed-circuit-board (PCB) for the electrode substrate. When ordered online, the
components of OPENDR OP add up to a total of $300. The assembly takes in average 5 h and it requires
previous experience in soldering surface-mount components; (b) Operation costs are hard to estimate
because they are highly specific to the bio-application: the reagents for gene cloning cost $100, while
fragrances cost less than $1. Our approach to reducing the volumes of operational fluids is to keep the
electrode size, and thus the droplet size, minimal.
Bioengineering 2017,4, 45 4 of 17
Accessibility
is a key feature for ensuring a high replicability of our platform. In general, users
have no access to the microfabrication facilities needed to produce a microfluidic chip. Moreover,
the services provided by some of the few specialized companies can easily get too expensive as they
charge for design, fabrication, transport and communication. We made the fabrication of OPENDROP
highly accessible for users: our architecture is compatible with a widely spread fabrication technique:
printing circuit boards. Thus, anyone can order an OPENDROP online from a generic PCB fabrication
shop [25,26] at a fraction of the cost.
Moreover, we enabled customized fabrication by open-sourcing the OPENDROP design files under
the Creative Commons Attribution-ShareAlike license [27].
At-home operation
of microfluidic machines is not trivial. In our case, to move droplets, the
electrodes of the biochip have to be coated with a thin hydrophobic layer. The common procedure is to
mix the insulator and hydrophobic chemicals and then apply them using either spin coating followed
by temperature curing (e.g., for Teflon) or vapor deposition (e.g., for Barium Strontium Titanite) [
12
,
28
].
To ensure OPENDROP is operable at home, we developed a coating technique based on thin film.
It can
be applied quickly, with no need for additional equipment or a clean room.
Lastly, we developed a software tool with a user-friendly interface that allows the user to interact
real-time with the droplets using hand-gestures on a touch screen. In Figure 3, we show the user
merging two droplets by dragging them to the same location. The software tool interprets the finger
drag, computes the electrode actuation sequence and automatically moves the droplets accordingly.
Bioengineering 2017, 4, 45 4 of 16
highly accessible for users: our architecture is compatible with a widely spread fabrication technique:
printing circuit boards. Thus, anyone can order an OPENDROP online from a generic PCB fabrication
shop [25,26] at a fraction of the cost.
Moreover, we enabled customized fabrication by open-sourcing the OPENDROP design files
under the Creative Commons Attribution-ShareAlike license [27].
At-home operation of microfluidic machines is not trivial. In our case, to move droplets, the
electrodes of the biochip have to be coated with a thin hydrophobic layer. The common procedure is
to mix the insulator and hydrophobic chemicals and then apply them using either spin coating
followed by temperature curing (e.g., for Teflon) or vapor deposition (e.g., for Barium Strontium
Titanite) [12,28]. To ensure OPENDROP is operable at home, we developed a coating technique based
on thin film. It can be applied quickly, with no need for additional equipment or a clean room.
Lastly, we developed a software tool with a user-friendly interface that allows the user to interact
real-time with the droplets using hand-gestures on a touch screen. In Figure 3, we show the user
merging two droplets by dragging them to the same location. The software tool interprets the finger
drag, computes the electrode actuation sequence and automatically moves the droplets accordingly.
Figure 3. Our proposed system consists of an OPENDROP machine, a personal computer (tablet, smart
phone) and the fluids needed for the target bio-application. The droplets are controlled real-time
through the software interface by using touch-based gestures, such as drag and drop.
4. Experimental Setup
Figure 1 presents OPENDROP, our cheap DIY biochip that can be operated at home by users using
a simplified interaction technique based on touch. A wetlab in miniature, O
PENDROP uses
micro-droplets to execute bio-applications (“bio-protocols”).
As shown in Figure 3, the system setup we propose consists of an OPENDROP machine, a personal
computer and the fluids needed for the target bio-application. After loading the OPENDROP reservoirs
with fluids, the user programs the movement of the droplets through the software that runs on the
computer. We designed the software to run through the internet browser, thus it is highly portable
and can also be run on laptops, tablets or even smart phones.
At system level, our proposed setup is minimal and ideal for home usage. As presented in
Section 6, we further propose several techniques to overcome the expertise needed for microfluidics.
In the next paragraphs, we present the experimental setup needed for microfluidics, emphasizing the
difficulties that users encounter.
As shown in Figure 4, OPENDROP consists of an array of electrodes, with each electrode capable
of holding a droplet. The electrodes are coated with a 310 µm lay er, with insulat ing an d hydropho bic
properties. Thus the droplets are not in direct contact with the electrodes.
Figure 3.
Our proposed system consists of an OPENDROP machine, a personal computer (tablet, smart
phone) and the fluids needed for the target bio-application. The droplets are controlled real-time
through the software interface by using touch-based gestures, such as drag and drop.
4. Experimental Setup
Figure 1presents OPENDROP, our cheap DIY biochip that can be operated at home by users
using a simplified interaction technique based on touch. A wetlab in miniature, OPENDRO P uses
micro-droplets to execute bio-applications (“bio-protocols”).
As shown in Figure 3, the system setup we propose consists of an OPENDROP machine, a personal
computer and the fluids needed for the target bio-application. After loading the OPENDROP reservoirs
with fluids, the user programs the movement of the droplets through the software that runs on the
computer. We designed the software to run through the internet browser, thus it is highly portable and
can also be run on laptops, tablets or even smart phones.
At system level, our proposed setup is minimal and ideal for home usage. As presented in
Section 6, we further propose several techniques to overcome the expertise needed for microfluidics.
Bioengineering 2017,4, 45 5 of 17
In the next paragraphs, we present the experimental setup needed for microfluidics, emphasizing the
difficulties that users encounter.
As shown in Figure 4, OPENDROP consists of an array of electrodes, with each electrode capable
of holding a droplet. The electrodes are coated with a 3–10
µ
m layer, with insulating and hydrophobic
properties. Thus the droplets are not in direct contact with the electrodes.
Bioengineering 2017, 4, 45 5 of 16
Figure 4. (a)
O
PEN
D
ROP has an array of 8 × 8 electrodes with four reservoirs; (b) The electrodes are
reconfigurable and thus they can be used interchangeably.
Depending on the properties of the droplet, a filler fluid, such as oil, may be required. Although more
difficult to achieve, it is preferred to move droplets in air, as oils can interfere with biological samples.
As mentioned, O
PEN
D
ROP
uses electrical voltage to turn ‘on’ the electrodes and thus, actuate the
droplets. For example in Figure 5, if the electrode on which the droplet is resting, is turned off
(Figure 5a), and the electrode on the right is activated by applying voltage (Figure 5b), the droplet
will move to the right (Figure 5c). In order to be actuated, the droplet has to be large enough to
overlap the gap between the neighboring electrodes. A droplet can move up, down, right, left and
diagonally on the electrode array.
Figure 5. EWoD explained. (a) The usual shape of a droplet in the absence of voltage. The electrode
underneath is coated with a hydrophobic layer, thus the droplet does not wet the surface; (b) Electrical
voltage unbalances the force equilibrium at the solid-liquid-vapor interface, causing the droplet to
wet the surface; (c) Consequently, the droplet moves towards the charged electrode.
To dispense droplets from a reservoir, O
PEN
D
ROP
charges several electrodes to form a ‘finger’
droplet that eventually pinches into a child droplet (Figure 6a) [12]. To split a larger droplet into
children droplets, O
PEN
D
ROP
charges concurrently two opposite electrodes to create opposite drag
forces that eventually split the droplet (Figure 6b). To mix two droplets, O
PEN
D
ROP
first brings them
together to merge (Figure 6c) and then transports them in a specific pattern (Figure 6d) [29–31].
The voltage values necessary to achieve EWoD depend on the targeted fluid, specifically on the
surface tension at the interface between the fluid and the filler medium. Some samples can be
impacted negatively by high voltage. In those cases, it is important to have a biochip that can actuate
droplets at low voltage. Otherwise, using higher voltage is preferred because it increases the speed
of droplets. We equipped O
PEN
D
ROP
with an adjustable power supply that can output between
50–260 V DC. Aqueous droplets can be moved with O
PEN
D
ROP
using 110 V. Similar results have been
reported for previous EWoD-based biochips [11].
Our software interprets the drag gestures of the user and decides on the ‘electrode actuation
sequence’ that specifies for each time step which electrodes have to turned off and on, in order to run
the target bio-application.
Figure 4.
(
a
) OPENDROP has an array of 8
×
8 electrodes with four reservoirs; (
b
) The electrodes are
reconfigurable and thus they can be used interchangeably.
Depending on the properties of the droplet, a filler fluid, such as oil, may be required.
Although more difficult to achieve, it is preferred to move droplets in air, as oils can interfere with
biological samples.
As mentioned, OPENDROP uses electrical voltage to turn ‘on’ the electrodes and thus, actuate
the droplets. For example in Figure 5, if the electrode on which the droplet is resting, is turned off
(Figure 5a), and the electrode on the right is activated by applying voltage (Figure 5b), the droplet will
move to the right (Figure 5c). In order to be actuated, the droplet has to be large enough to overlap the
gap between the neighboring electrodes. A droplet can move up, down, right, left and diagonally on
the electrode array.
Bioengineering 2017, 4, 45 5 of 16
Figure 4. (a)
O
PEN
D
ROP has an array of 8 × 8 electrodes with four reservoirs; (b) The electrodes are
reconfigurable and thus they can be used interchangeably.
Depending on the properties of the droplet, a filler fluid, such as oil, may be required. Although more
difficult to achieve, it is preferred to move droplets in air, as oils can interfere with biological samples.
As mentioned, O
PEN
D
ROP
uses electrical voltage to turn ‘on’ the electrodes and thus, actuate the
droplets. For example in Figure 5, if the electrode on which the droplet is resting, is turned off
(Figure 5a), and the electrode on the right is activated by applying voltage (Figure 5b), the droplet
will move to the right (Figure 5c). In order to be actuated, the droplet has to be large enough to
overlap the gap between the neighboring electrodes. A droplet can move up, down, right, left and
diagonally on the electrode array.
Figure 5. EWoD explained. (a) The usual shape of a droplet in the absence of voltage. The electrode
underneath is coated with a hydrophobic layer, thus the droplet does not wet the surface; (b) Electrical
voltage unbalances the force equilibrium at the solid-liquid-vapor interface, causing the droplet to
wet the surface; (c) Consequently, the droplet moves towards the charged electrode.
To dispense droplets from a reservoir, O
PEN
D
ROP
charges several electrodes to form a ‘finger’
droplet that eventually pinches into a child droplet (Figure 6a) [12]. To split a larger droplet into
children droplets, O
PEN
D
ROP
charges concurrently two opposite electrodes to create opposite drag
forces that eventually split the droplet (Figure 6b). To mix two droplets, O
PEN
D
ROP
first brings them
together to merge (Figure 6c) and then transports them in a specific pattern (Figure 6d) [29–31].
The voltage values necessary to achieve EWoD depend on the targeted fluid, specifically on the
surface tension at the interface between the fluid and the filler medium. Some samples can be
impacted negatively by high voltage. In those cases, it is important to have a biochip that can actuate
droplets at low voltage. Otherwise, using higher voltage is preferred because it increases the speed
of droplets. We equipped O
PEN
D
ROP
with an adjustable power supply that can output between
50–260 V DC. Aqueous droplets can be moved with O
PEN
D
ROP
using 110 V. Similar results have been
reported for previous EWoD-based biochips [11].
Our software interprets the drag gestures of the user and decides on the ‘electrode actuation
sequence’ that specifies for each time step which electrodes have to turned off and on, in order to run
the target bio-application.
Figure 5.
EWoD explained. (
a
) The usual shape of a droplet in the absence of voltage. The electrode
underneath is coated with a hydrophobic layer, thus the droplet does not wet the surface; (
b
) Electrical
voltage unbalances the force equilibrium at the solid-liquid-vapor interface, causing the droplet to wet
the surface; (c) Consequently, the droplet moves towards the charged electrode.
To dispense droplets from a reservoir, OPENDROP charges several electrodes to form a ‘finger
droplet that eventually pinches into a child droplet (Figure 6a) [
12
]. To split a larger droplet into
children droplets, OPENDROP charges concurrently two opposite electrodes to create opposite drag
forces that eventually split the droplet (Figure 6b). To mix two droplets, OPENDROP first brings them
together to merge (Figure 6c) and then transports them in a specific pattern (Figure 6d) [2931].
The voltage values necessary to achieve EWoD depend on the targeted fluid, specifically on the
surface tension at the interface between the fluid and the filler medium. Some samples can be impacted
negatively by high voltage. In those cases, it is important to have a biochip that can actuate droplets at
Bioengineering 2017,4, 45 6 of 17
low voltage. Otherwise, using higher voltage is preferred because it increases the speed of droplets.
We equipped OPENDRO P with an adjustable power supply that can output between 50–260 V DC.
Aqueous droplets can be moved with OPENDR OP using 110 V. Similar results have been reported for
previous EWoD-based biochips [11].
Our software interprets the drag gestures of the user and decides on the ‘electrode actuation
sequence’ that specifies for each time step which electrodes have to turned off and on, in order to run
the target bio-application.
Bioengineering 2017, 4, 45 6 of 16
Figure 6. The microfluidic operations that can run on O
PEN
D
ROP
.
The droplets are: (a) dispensed from
reservoirs; (b) split; (c) merged and (d) mixed.
5. Materials and Methods
We designed O
PEN
D
ROP
for easy DIY fabrication. Figure 7a shows O
PEN
D
ROP
as a modular
machine compatible with the Arduino, an accessible microcontroller currently having more than
400,000 users [32]. We used a double layer PCB, with electrodes on one side (Figure 7b) and the power
supply and control on the other side (Figure 7c). The electrodes are gold-coated and connected
through-hole to the control circuit.
Figure 7. (a) We designed O
PEN
D
ROP
as a modular device that can be easily dis-assembled; (b) The
front side of the PCB contains the electrode array and the high-voltage switch and regulator; (c) The
back side of the PCB embeds the control circuit and the step-up voltage converter.
To satisfy the voltage requirements for electromicrofluidics, we integrated a DC to DC power
converter that steps up the voltage from 12 V to 260 V. The power converter was initially designed
for Nixie tubes [33] and we adapted it to allow an adjustable voltage between 50 and 260 V DC
(see Figure 8a). Thus, O
PEN
D
ROP
has integrated high-voltage control and can be operated directly
from the common wall socket. The user has the option to adjust the voltage according to the type of
fluid used by simply rotating the potentiometer using a screwdriver, as shown in Figure 8b.
Electrical lines transport the high voltage from the power converter to the electrodes, as shown
in Figure 9. The electrodes are switched on and off by high-voltage surface-mount transistors (BSS131,
Infineon SIPMOS, Logic-Level, PG-SOT-23). To keep O
PEN
D
ROP
as a two-layer PCB (thus much
cheaper than a multi-layer version) we connected the source pins of the transistors to the electrodes
through small wires, see Figure 9.
Figure 6.
The microfluidic operations that can run on OPENDROP. The droplets are: (
a
) dispensed
from reservoirs; (b) split; (c) merged and (d) mixed.
5. Materials and Methods
We designed OPENDRO P for easy DIY fabrication. Figure 7a shows OPENDROP as a modular
machine compatible with the Arduino, an accessible microcontroller currently having more than
400,000 users [
32
]. We used a double layer PCB, with electrodes on one side (Figure 7b) and the
power supply and control on the other side (Figure 7c). The electrodes are gold-coated and connected
through-hole to the control circuit.
Bioengineering 2017, 4, 45 6 of 16
Figure 6. The microfluidic operations that can run on O
PEN
D
ROP
.
The droplets are: (a) dispensed from
reservoirs; (b) split; (c) merged and (d) mixed.
5. Materials and Methods
We designed O
PEN
D
ROP
for easy DIY fabrication. Figure 7a shows O
PEN
D
ROP
as a modular
machine compatible with the Arduino, an accessible microcontroller currently having more than
400,000 users [32]. We used a double layer PCB, with electrodes on one side (Figure 7b) and the power
supply and control on the other side (Figure 7c). The electrodes are gold-coated and connected
through-hole to the control circuit.
Figure 7. (a) We designed O
PEN
D
ROP
as a modular device that can be easily dis-assembled; (b) The
front side of the PCB contains the electrode array and the high-voltage switch and regulator; (c) The
back side of the PCB embeds the control circuit and the step-up voltage converter.
To satisfy the voltage requirements for electromicrofluidics, we integrated a DC to DC power
converter that steps up the voltage from 12 V to 260 V. The power converter was initially designed
for Nixie tubes [33] and we adapted it to allow an adjustable voltage between 50 and 260 V DC
(see Figure 8a). Thus, O
PEN
D
ROP
has integrated high-voltage control and can be operated directly
from the common wall socket. The user has the option to adjust the voltage according to the type of
fluid used by simply rotating the potentiometer using a screwdriver, as shown in Figure 8b.
Electrical lines transport the high voltage from the power converter to the electrodes, as shown
in Figure 9. The electrodes are switched on and off by high-voltage surface-mount transistors (BSS131,
Infineon SIPMOS, Logic-Level, PG-SOT-23). To keep O
PEN
D
ROP
as a two-layer PCB (thus much
cheaper than a multi-layer version) we connected the source pins of the transistors to the electrodes
through small wires, see Figure 9.
Figure 7.
(
a
) We designed O PENDROP as a modular device that can be easily dis-assembled; (
b
) The
front side of the PCB contains the electrode array and the high-voltage switch and regulator; (
c
) The
back side of the PCB embeds the control circuit and the step-up voltage converter.
To satisfy the voltage requirements for electromicrofluidics, we integrated a DC to DC power
converter that steps up the voltage from 12 V to 260 V. The power converter was initially designed
for Nixie tubes [
33
] and we adapted it to allow an adjustable voltage between 50 and 260 V DC (see
Figure 8a). Thus, OPENDR OP has integrated high-voltage control and can be operated directly from
Bioengineering 2017,4, 45 7 of 17
the common wall socket. The user has the option to adjust the voltage according to the type of fluid
used by simply rotating the potentiometer using a screwdriver, as shown in Figure 8b.
Figure 8.
(
a
) Integrated power supply that steps up the voltage from 12 V to 260 V DC; (
b
) The user
adjusts the voltage to fit the EWoD requirements for the targeted fluid.
Electrical lines transport the high voltage from the power converter to the electrodes, as shown in
Figure 9. The electrodes are switched on and off by high-voltage surface-mount transistors (BSS131,
Infineon SIPMOS, Logic-Level, PG-SOT-23). To keep OPENDROP as a two-layer PCB (thus much
cheaper than a multi-layer version) we connected the source pins of the transistors to the electrodes
through small wires, see Figure 9.
Bioengineering 2017, 4, 45 7 of 16
Figure 8. (a) Integrated power supply that steps up the voltage from 12 V to 260 V DC; (b) The user
adjusts the voltage to fit the EWoD requirements for the targeted fluid.
Figure 9. High Voltage Transistors used: BSS131, Infineon SIPMOS, Logic-Level, PG-SOT-23. Each
transistor is connected to the corresponding electrode through a small through-hole wire, soldered
manually. Electrical lines are transporting the high voltage from the power converter to the electrodes.
For the coating, we acquired the materials as follows: Parafilm from Scienova GmbH [34], ETFE
thin film 13 µm from Fluoroplasts GmbH [35], RainX from Conrad Electronic [36], Silicone oil 5 cst
from QUAX GmbH [37], Cytop and Fluoropel from Cytonix LLC [38].
6. Interaction Techniques
The user experiences two major types of interactions with the O
PEN
D
ROP
system: at fluidic level
and at software level.
6.1. Interaction with Fluids
At fluidic level, the user has to prepare the surface of the electrode array for electrowetting by
applying a uniform coating. Considering the voltage limit of O
PEN
D
ROP
(250 V DC), the droplet must
have a minimum contact angle of 120°, ideally 18 to be actuated [15]. Moreover, the coating has to
be as thin as possible (in the range of 1–10 µm), and have a dielectric constant of 200–300 [12]. All
these values are determined for the case when we move the fluids in air. Moving fluids in oil is less
challenging in terms of coating. The goal of our work is to move the droplets in air.
6.1.1. Adapting the Laboratory Coating Procedure
The traditional laboratory procedure consists of spin coating Teflon AF 1600, DuPont, 200-nm thick,
or using vapor deposition of a mix of Parylene C and Cytop, then baking at 170° for 30 min [28]. We
adapted this procedure in the context of running experiments on O
PEN
D
ROP
at home.
Since Teflon exceeded the targeted budget ($10/run), we used Fluoropel and spin-coated it over
ITO glass [39]. A spin-coater is a relatively expensive machine (2000 to 5000 USD) that uses
Figure 9.
High Voltage Transistors used: BSS131, Infineon SIPMOS, Logic-Level, PG-SOT-23. Each
transistor is connected to the corresponding electrode through a small through-hole wire, soldered
manually. Electrical lines are transporting the high voltage from the power converter to the electrodes.
For the coating, we acquired the materials as follows: Parafilm from Scienova GmbH [
34
], ETFE
thin film 13
µ
m from Fluoroplasts GmbH [
35
], RainX from Conrad Electronic [
36
], Silicone oil 5 cst
from QUAX GmbH [37], Cytop and Fluoropel from Cytonix LLC [38].
6. Interaction Techniques
The user experiences two major types of interactions with the OPENDROP system: at fluidic level
and at software level.
6.1. Interaction with Fluids
At fluidic level, the user has to prepare the surface of the electrode array for electrowetting by
applying a uniform coating. Considering the voltage limit of OPENDROP (250 V DC), the droplet
must have a minimum contact angle of 120
, ideally 180
to be actuated [
15
]. Moreover, the coating
Bioengineering 2017,4, 45 8 of 17
has to be as thin as possible (in the range of 1–10
µ
m), and have a dielectric constant of 200–300 [
12
].
All these values are determined for the case when we move the fluids in air. Moving fluids in oil is less
challenging in terms of coating. The goal of our work is to move the droplets in air.
6.1.1. Adapting the Laboratory Coating Procedure
The traditional laboratory procedure consists of spin coating Teflon AF 1600, DuPont, 200-nm
thick, or using vapor deposition of a mix of Parylene C and Cytop, then baking at 170
for 30 min [
28
].
We adapted this procedure in the context of running experiments on OPENDR OP at home.
Since Teflon exceeded the targeted budget ($10/run), we used Fluoropel and spin-coated it over
ITO glass [
39
]. A spin-coater is a relatively expensive machine (2000 to 5000 USD) that uses high-speed
rotation to spin and spread a droplet of coating material into a thin layer. The viscosity of the material,
the frequency and duration of the spinning determine the final thickness of the coating layer. The DIY
version of a spin coater can be built for a fraction of the price [40].
Our DIY spin-coating technique worked reliably, but it has the following disadvantages:
It requires a total of 4 h of work and a clean space (specks of dust can alter the quality of the
coating and thus prevent electrowetting).
It requires additional equipment such as a spin coater and an oven.
The coating wears off in 24 h.
6.1.2. Special Coating Technique at-Home Operation
We investigated coating techniques that are more suitable for users. We looked for techniques
that can be applied fast (in less than 10 min), on the go (portable) and are accessible (using materials
that can be acquired in a shop, not requiring authorization for specialized chemicals).
In the following paragraphs, we present such three different techniques.
Saran wrap and RainX
are two products highly available on the market. Saran wrap, also known
as cling wrap has a thickness of 10
µ
m and it constitutes a good insulator and dielectric material.
RainX [
36
] is a product developed for car drivers to coat the windscreens against rain. We first tense
the Saran wrap over a frame until there are no wrinkles left. Then we coat the wrap with RainX as
instructed on the label (pour a generous amount, wait for one minute, rinse out with cold running
water). We cut the wrap to the desired size, tape it on the OPENDROP carrier and apply it on the
electrodes. To ensure a better adherence to the electrode surface, we spread a thin layer of kitchen oil
on the electrodes, before applying the wrap. This coating does not last more than 2 h, and it needs
access to a tap or running water.
Parafilm and Silicone oil
are also easily accessible for users through online shops. Parafilm is an
extensible film used in biological laboratories to seal Petri dishes. Similarly to the Saran wrap, we
tense the parafilm to the maximum and apply it directly on the surface of the electrodes. We coat the
top of the electrodes with a thin layer of silicone oil of viscosity cst 5.
ETFE film and Silicone oil.
The ETFE thin film is not stretchable and comes in different thicknesses.
We experimented with films from various companies and found that ETFE 13
µ
m works the best. As
shown in Figure 10b, a thin layer of silicone oil cst 5 is manually applied on top of the ETFE foil [
41
]. If
the exposure to dust is minimized, this coating can last up to two-three days. For that, we recommend
storing the coated ETFE film in a petri dish, or directly on the device, but covered with a glass top.
Bioengineering 2017,4, 45 9 of 17
Bioengineering 2017, 4, 45 8 of 16
high-speed rotation to spin and spread a droplet of coating material into a thin layer. The viscosity
of the material, the frequency and duration of the spinning determine the final thickness of the
coating layer. The DIY version of a spin coater can be built for a fraction of the price [40].
Our DIY spin-coating technique worked reliably, but it has the following disadvantages:
It requires a total of 4 h of work and a clean space (specks of dust can alter the quality of the
coating and thus prevent electrowetting).
It requires additional equipment such as a spin coater and an oven.
The coating wears off in 24 h.
6.1.2. Special Coating Technique at-Home Operation
We investigated coating techniques that are more suitable for users. We looked for techniques
that can be applied fast (in less than 10 min), on the go (portable) and are accessible (using materials
that can be acquired in a shop, not requiring authorization for specialized chemicals).
In the following paragraphs, we present such three different techniques.
Saran wrap and RainX are two products highly available on the market. Saran wrap, also known
as cling wrap has a thickness of 10 µm and it constitutes a good insulator and dielectric material.
RainX [36] is a product developed for car drivers to coat the windscreens against rain. We first tense
the Saran wrap over a frame until there are no wrinkles left. Then we coat the wrap with RainX as
instructed on the label (pour a generous amount, wait for one minute, rinse out with cold running
water). We cut the wrap to the desired size, tape it on the O
PEN
D
ROP
carrier and apply it on the
electrodes. To ensure a better adherence to the electrode surface, we spread a thin layer of kitchen oil
on the electrodes, before applying the wrap. This coating does not last more than 2 h, and it needs
access to a tap or running water.
Parafilm and Silicone oil are also easily accessible for users through online shops. Parafilm is an
extensible film used in biological laboratories to seal Petri dishes. Similarly to the Saran wrap, we
tense the parafilm to the maximum and apply it directly on the surface of the electrodes. We coat the
top of the electrodes with a thin layer of silicone oil of viscosity cst 5.
ETFE film and Silicone oil. The ETFE thin film is not stretchable and comes in different
thicknesses. We experimented with films from various companies and found that ETFE 13 µm works
the best. As shown in Figure 10b, a thin layer of silicone oil cst 5 is manually applied on top of the
ETFE foil [41]. If the exposure to dust is minimized, this coating can last up to two-three days. For
that, we recommend storing the coated ETFE film in a petri dish, or directly on the device, but covered
with a glass top.
Figure 10. The simplest coating technique uses ETFE film and silicone oil. (a) The first step is to glue
the ETFE film on the cartridge using double sided tape; (b) Next, the user applies a thin layer of
silicone oil; (c) Finally, the cartridge is mounted on top of O
PEN
D
ROP
.
Figure 10.
The simplest coating technique uses ETFE film and silicone oil. (
a
) The first step is to glue
the ETFE film on the cartridge using double sided tape; (
b
) Next, the user applies a thin layer of silicone
oil; (c) Finally, the cartridge is mounted on top of OPENDROP.
As mentioned, we envisioned our system to be used at home by everyone, so we assumed the
user is not in possession of a specialized goniometer to measure the contact angle. Alternatively,
we propose the experimental approach: after coating, the user turns on the device and checks whether
the droplet moves or not. Our findings show that, without any theoretical knowledge about the contact
angle, the users develop an intuitive feeling on whether the coating is hydrophobic enough to actuate
the droplets. Thus, after several days working with OPENDROP, the users were able to visually inspect
the droplet and estimate the contact angle.
6.2. Interaction with the Software
Our visual interface allows the user to select the size of the electrode array and then visually
actuate the droplets to the desired locations. We implemented this feature through drag and drop. On
the virtual electrode array, the user creates a new droplet (double click) and then drags it to the desired
location (Figure 11).
Bioengineering 2017, 4, 45 9 of 16
As mentioned, we envisioned our system to be used at home by everyone, so we assumed the
user is not in possession of a specialized goniometer to measure the contact angle. Alternatively, we
propose the experimental approach: after coating, the user turns on the device and checks whether
the droplet moves or not. Our findings show that, without any theoretical knowledge about the
contact angle, the users develop an intuitive feeling on whether the coating is hydrophobic enough
to actuate the droplets. Thus, after several days working with O
PEN
D
ROP
,
the users were able to
visually inspect the droplet and estimate the contact angle.
6.2. Interaction with the Software
Our visual interface allows the user to select the size of the electrode array and then visually
actuate the droplets to the desired locations. We implemented this feature through drag and drop.
On the virtual electrode array, the user creates a new droplet (double click) and then drags it to the
desired location (Figure 11).
Figure 11. Through the software the user interacts with the droplets. (a) A new droplet is created by
double tap on an empty electrode; (b) The user has the option to give a descriptive name to the
droplet; (c) When using finger drag, the user decides on the route of the droplet that can be
backtracked; (d) by looking at the traces.
The user has the option to simulate the movement of the droplets before actually executing it on
O
PEN
D
ROP
. As shown in Figure 12, traces are visible at any time to indicate the droplet routes and
allow the user to visually predict an eventual undesired merge even before simulation. When two
droplets meet, either vertically, horizontally or diagonally, they merge into a larger droplet that can
be split afterwards by using two-finger drag gesture.
Figure 12. (a) When two droplets meet, they instantly merge together and (b) the user can manipulate
them as a single entity using finger drag; (c) The merged droplets follow the drag as a unit; (d) In
delete mode, with a single tap, the user can (e) delete droplets.
7. Results
The goal of our work is to investigate whether users can fabricate and use a biochip. As
presented in the previous sections, we made O
PEN
D
ROP
accessible through design and operability
techniques. In the next paragraphs we present our results obtained in two years after O
PEN
D
ROP
was
released.
Figure 11.
Through the software the user interacts with the droplets. (
a
) A new droplet is created by
double tap on an empty electrode; (
b
) The user has the option to give a descriptive name to the droplet;
(
c
) When using finger drag, the user decides on the route of the droplet that can be backtracked; (
d
) by
looking at the traces.
The user has the option to simulate the movement of the droplets before actually executing it on
OPENDROP. As shown in Figure 12, traces are visible at any time to indicate the droplet routes and
allow the user to visually predict an eventual undesired merge even before simulation. When two
droplets meet, either vertically, horizontally or diagonally, they merge into a larger droplet that can be
split afterwards by using two-finger drag gesture.
Bioengineering 2017,4, 45 10 of 17
Bioengineering 2017, 4, 45 9 of 16
As mentioned, we envisioned our system to be used at home by everyone, so we assumed the
user is not in possession of a specialized goniometer to measure the contact angle. Alternatively, we
propose the experimental approach: after coating, the user turns on the device and checks whether
the droplet moves or not. Our findings show that, without any theoretical knowledge about the
contact angle, the users develop an intuitive feeling on whether the coating is hydrophobic enough
to actuate the droplets. Thus, after several days working with O
PEN
D
ROP
,
the users were able to
visually inspect the droplet and estimate the contact angle.
6.2. Interaction with the Software
Our visual interface allows the user to select the size of the electrode array and then visually
actuate the droplets to the desired locations. We implemented this feature through drag and drop.
On the virtual electrode array, the user creates a new droplet (double click) and then drags it to the
desired location (Figure 11).
Figure 11. Through the software the user interacts with the droplets. (a) A new droplet is created by
double tap on an empty electrode; (b) The user has the option to give a descriptive name to the
droplet; (c) When using finger drag, the user decides on the route of the droplet that can be
backtracked; (d) by looking at the traces.
The user has the option to simulate the movement of the droplets before actually executing it on
O
PEN
D
ROP
. As shown in Figure 12, traces are visible at any time to indicate the droplet routes and
allow the user to visually predict an eventual undesired merge even before simulation. When two
droplets meet, either vertically, horizontally or diagonally, they merge into a larger droplet that can
be split afterwards by using two-finger drag gesture.
Figure 12. (a) When two droplets meet, they instantly merge together and (b) the user can manipulate
them as a single entity using finger drag; (c) The merged droplets follow the drag as a unit; (d) In
delete mode, with a single tap, the user can (e) delete droplets.
7. Results
The goal of our work is to investigate whether users can fabricate and use a biochip. As
presented in the previous sections, we made O
PEN
D
ROP
accessible through design and operability
techniques. In the next paragraphs we present our results obtained in two years after O
PEN
D
ROP
was
released.
Figure 12.
(
a
) When two droplets meet, they instantly merge together and (
b
) the user can manipulate
them as a single entity using finger drag; (
c
) The merged droplets follow the drag as a unit; (
d
) In delete
mode, with a single tap, the user can (e) delete droplets.
7. Results
The goal of our work is to investigate whether users can fabricate and use a biochip. As presented
in the previous sections, we made OPENDROP accessible through design and operability techniques.
In the next paragraphs we present our results obtained in two years after OPENDROP was released.
7.1. Replicability Study
To make OPENDRO P accessible to as many people as possible, we used the following strategy:
1.
We provided the design files as open source resources on github [
42
] and personal websites [
43
].
That way, anyone has the possibility to download, customize and make their own biochips.
2.
We made a significant effort to document the fabrication, operation and various applications of
OPENDROP. Proper documentation is a key element to ensure replicability. We maintained the
documentation periodically. Apart from written documentation, we posted video tutorials on
accessible channels, such as YouTube and Vimeo.
3.
We initiated and developed a community of users by offering them technical support when
needed. We implemented this step by hosting forums and organizing international meetings. We
emphasized the educational aspect by giving lectures, course and weekly online seminars.
Figure 13 shows the distribution of our user base over different occupational sectors. We are
aware of 100 users that have expressed their interest in owning an OPENDRO P, out of which 72 users
are in regular contact forming our total user base (39% academia, 27% companies, 21% hacker spaces
and 13% individuals). Almost half of our total user base, that is 34 users, tried to replicate OPENDRO P
(Figure 13b). Although both industry and academia showed a similar interest in replicating our
platform, the users from academia were by far the most successful (Figure 13c).
Geographically, most interest was concentrated in North America and Europe, but lately a few
Asian and South American research labs have expressed their interest in replicating and using an
OPENDROP.
As mentioned, we observed the biggest interest in the academic sector. Researchers from technical
domains (such as computer science or electrical engineering) used OPENDROP as an easy and
cheap way to develop customized bio-applications [
44
46
]. Larger companies, such as Autocad
and Novozymes, as well as start-ups [
47
,
48
] were also interested in replicating OPENDRO P. A limited
amount of OPENDR OPs found their home in various hacker spaces [49,50] or with individuals [51].
The interest of the users varied from using OPENDROP for educational purposes to adapting and
customizing the design for specific applications. DROPIO project from the Tangible Media Lab [
45
],
MIT adapted OPENDR OP to have a much larger array of electrodes. Their purpose is to have a
microfluidic-based display that allows the study of various interaction techniques. The Computer
Architecture Group from Bremen [
44
] increased the modularity of OPENDR OP to support several layers
Bioengineering 2017,4, 45 11 of 17
that can be stacked on top of each other. Trojok et al. developed an adaptor that makes OPENDR OP
compatible with paper microfluidics [52].
Bioengineering 2017, 4, 45 10 of 16
7.1. Replicability Study
To make O
PEN
D
ROP
accessible to as many people as possible, we used the following strategy:
1. We provided the design files as open source resources on github [42] and personal websites [43].
That way, anyone has the possibility to download, customize and make their own biochips.
2. We made a significant effort to document the fabrication, operation and various applications of
O
PEN
D
ROP
. Proper documentation is a key element to ensure replicability. We maintained the
documentation periodically. Apart from written documentation, we posted video tutorials on
accessible channels, such as YouTube and Vimeo.
3. We initiated and developed a community of users by offering them technical support when
needed. We implemented this step by hosting forums and organizing international meetings.
We emphasized the educational aspect by giving lectures, course and weekly online seminars.
Figure 13 shows the distribution of our user base over different occupational sectors. We are
aware of 100 users that have expressed their interest in owning an O
PEN
D
ROP
,
out of which 72 users
are in regular contact forming our total user base (39% academia, 27% companies, 21% hacker spaces
and 13% individuals). Almost half of our total user base, that is 34 users, tried to replicate O
PEN
D
ROP
(Figure 13b). Although both industry and academia showed a similar interest in replicating our
platform, the users from academia were by far the most successful (Figure 13c).
Geographically, most interest was concentrated in North America and Europe, but lately a few
Asian and South American research labs have expressed their interest in replicating and using an
O
PEN
D
ROP
.
Figure 13. Our user base has 72 members, out of which 34 have tried to replicate O
PEN
D
ROP
.
A total
of 15 users (47%) succeeded to replicate our platform. We show the distribution of users by occupation
for (a) the total user base; (b) the number of users that attempted to replicate O
PEN
D
ROP
; and (c) the
users that succeeded to replicate O
PEN
D
ROP
.
As mentioned, we observed the biggest interest in the academic sector. Researchers from
technical domains (such as computer science or electrical engineering) used O
PEN
D
ROP
as an easy
and cheap way to develop customized bio-applications [44–46]. Larger companies, such as Autocad
and Novozymes, as well as start-ups [47,48] were also interested in replicating O
PEN
D
ROP
. A limited
amount of O
PEN
D
ROP
s found their home in various hacker spaces [49,50] or with individuals [51].
The interest of the users varied from using O
PEN
D
ROP
for educational purposes to adapting and
customizing the design for specific applications. D
ROP
IO project from the Tangible Media Lab [45],
MIT adapted O
PEN
D
ROP
to have a much larger array of electrodes. Their purpose is to have a
microfluidic-based display that allows the study of various interaction techniques. The Computer
Architecture Group from Bremen [44] increased the modularity of O
PEN
D
ROP
to support several
layers that can be stacked on top of each other. Trojok et al. developed an adaptor that makes
O
PEN
D
ROP
compatible with paper microfluidics [52].
Figure 13.
Our user base has 72 members, out of which 34 have tried to replicate OPENDR OP. A total
of 15 users (47%) succeeded to replicate our platform. We show the distribution of users by occupation
for (
a
) the total user base; (
b
) the number of users that attempted to replicate OPENDR OP; and (
c
) the
users that succeeded to replicate OPENDROP.
7.2. Bio-Applications
Developing a new bio-application in general takes about 1.5 years of research. Thus our users are
just in the incipient stage of bio-application development.
Currently, we are aware of work-in-progress for several applications as follows.
Tissue printing
: Using OPENDROP to move and arrange droplets containing cells. Similar to
the recent work of Chiang et al. [
53
], researchers at the Center for Regenerative Medicine Munich,
Germany are working on integrating OPENDR OP with a DIY bioprinter they built by modifying a 3D
printer. While the bioprinter can arrange the cells in space, it cannot determine a temporal arrangement
as the cells are printed sequentially. OPENDROP can overcome this issue by actuating cells in microgels
in parallel and at programmed time intervals. Thus the cells will arrive at their specific location at the
right time to communicate with each other and form a tissue.
Synthetic biology
: Using OPENDROP to transform bacteria cells. Recently, researchers have
proven that E. coli can be transformed on an electromicrofluidic platform by using magnetic beads [
54
].
We are aware of several research laboratories that are pushing the boundaries further as in trying
to adapt the existing DIY kits for CRISPR/CAS9. The kit developed by Odeon for home use is an
ideal candidate for OPENDROP. If successful, this project will enable users to genetically transform
organisms in a much more accessible way, through an automatic touch-based interactive software.
Phage therapy
: Using OPENDROP to generate new phages by altering genetically existing phages.
As the antibiotic crises is becoming more and more life-threatening, phages seem the best solution
so far for critical infections. However, phages cannot be administrated the same way at antibiotics,
based on ‘one size fits all’ principle. Phages need to be administrated in a personalized cocktail for the
specific patient and they cannot be stored for long time. This project [
47
] aims at using OPENDROP as a
computational machine to explore the solution space of new phage cocktails. The envisioned scenario
is the following: in case of infection, the user isolates the targeted bacteria, then loads OPENDROP with
the closest phage known so far for the targeted bacteria. OPENDROP iteratively inserts mutations in
the phage to design new organisms. The new phages are placed with the targeted bacteria and their
action is monitored. In case of success, the user orders the phage cocktail from a synthesis company
and takes it as a cure. From a broader perspective, the success of this project is a first step towards
enabling everyone to ‘print’ their own medical cure.
Interactive displays
: Using OPENDROP to mix colors in a controlled and precise range.
Electrowetting on dielectric (the physics phenomenon that actuates the droplets on OPENDROP)
Bioengineering 2017,4, 45 12 of 17
was used for screens and displays. Thus, coming back, 50 years later, to the same area of application is
not a surprise. Currently, researchers in human computer interaction [
45
] are interested in studying
various ways of interacting with a display in a real-time manner. For that purpose, they have extended
OPENDROP to a much large array of electrodes, in the range of thousands. Every droplet becomes a
pixel that can be manipulated in real-time by the user to have the desired position and color.
Perfume making
: Using OPENDROP to design new fragrances for real-time scenarios. Fragrance
design is still a cumbersome manual task executed by specialized perfumers. OPENDRO P could
explore the perfume design space in a much faster and automated way, making it possible for users
to design personalized perfumes. With additional equipment that connects the droplet outlets to the
user’s nose, OPENDROP can also be used for augmented reality. In this scenario, the olfactory sense of
the user is augmented by adding a programmed real-time fragrance.
Currently, OPENDR OP is limited to bio-applications based on sequences of dispensing, splitting,
merging, and mixing droplets. With the aid of various sensors (in the future, integrated) and additional
equipment (e.g., temperature and magnetic bars, spectrophotometer), OPENDROP will be able to
monitor, incubate and separate (chemically) the fluids.
8. Related Work
The only comparable work so far is the Dropbot [
19
], developed at Toronto University, Canada.
In Table 1we draw a schematic comparison between the major features of the two devices.
Table 1. Comparison between Dropbot and OPENDROP.
Dropbot OP ENDROP
Electrode substrate Chromium (vapor deposition, $500) Golden PCB (etching, $10)
Coating technique Nanocoating Thin film and oil
Power supply AC DC
Community Centralized, academic Decentralized, makers
Dropbot uses a chromium substrate for electrodes, fabricated by vapor-deposition. These
electrodes are much more reliable than the PCB version, however, they cost 50% more than the
cost of fabricating the entire OPENDR OP. To actuate droplets, Dropbot uses AC voltage with an
additional power supply at much larger size than the machine itself. In terms of coating, Dropbot uses
an advanced nanocoating, at a high price range ($500) suitable for academic laboratories. In Figure 14,
we show a side-by-side comparison of the Dropbot and OPENDR OP.
In a more centralized way than our approach, the Dropbot design files were released open source
and a forum run by the Dropbot authors was setup for common discussions and support. This
approach ensured the quality of the information and support. Since our targeted users could basically
be anyone, we chose an approach that would maximize the spread of our platform. In a de-centralized
manner, we encouraged anyone to post the OPENDROP design files on their own websites and also
host a discussion around its use.
Generally, Dropbot wins in terms of reliability and robustness, but pays the price of costs that
cannot be afforded by makers or technology enthusiasts. Recently, we have established a collaboration
with Fobel et al., together working on a hybrid platform that combines the advantages from both
Dropbot and OPENDR OP.
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Table 1. Comparison between Dropbot and OPENDROP.
Dropbot OPENDROP
Electrode substrate Chromium (vapor deposition, $500) Golden PCB (etching, $10)
Coating technique Nanocoating Thin film and oil
Power supply AC DC
Community Centralized, academic Decentralized, makers
Dropbot uses a chromium substrate for electrodes, fabricated by vapor-deposition. These
electrodes are much more reliable than the PCB version, however, they cost 50% more than the cost
of fabricating the entire OPENDROP. To actuate droplets, Dropbot uses AC voltage with an additional
power supply at much larger size than the machine itself. In terms of coating, Dropbot uses an
advanced nanocoating, at a high price range ($500) suitable for academic laboratories. In Figure 14,
we show a side-by-side comparison of the Dropbot and OPENDROP.
Figure 14. Dropbot (left) and OPENDROP (right) picture by Ryan Fobel.
In a more centralized way than our approach, the Dropbot design files were released open
source and a forum run by the Dropbot authors was setup for common discussions and support. This