The authors acknowledge the financial support from NSERC and the Canada Research Chair in Smart Medical Devices, and are grateful for the various tools supplied by CMC Microsystems and ReSMiQ. Thanks are due to Laurent Mouden, for his contributions in this work.

1. Removable PDMS-based Interconnector for Low-pressure Microfluidic Applications15-16
<ol>
	<li>Preparation 
	This section describes different steps to prepare the glass and PDMS in order to produce the interconnector.
	<ol>
		<li>Prepare the PDMS: Mix the PDMS and curing agent with (10:1) ratio.</li>
		<li>Ensure that the oven temperature is stabilized at a constant temperature of 80 &#176;C. Depending on the oven, use a measurement device to sense the temperature of the oven and then manually monitor it.</li>
		<li>Thoroughly clean the Petri dish with ethanol.</li>
		<li>Clean the surface of the microfluidic access holes where the PDMS interconnector will be placed.</li>
	</ol>
	</li>
	<li>Fabrication 
	The interconnector described in this paper is essentially a compliant gasket. This gasket is formed from PDMS and contains holes into which microtubes may be inserted. It self-adheres to the surface of a microfluidic chip, to form a leak-proof seal between the microtube and access holes to microchannels in the chip. 
	Use the following steps to fabricate the interconnector.
	<ol>
		<li>Pour a thin layer (approximately 2 mm) of the PDMS (liquid) into a Petri dish.</li>
		<li>Let the PDMS slightly polymerize at a temperature of 80 &#176;C in the oven for 12-15 min. Place the microfluidic chip to which the connection will be made in the oven at the same time, so that it will be at the same temperature.</li>
		<li>When the PDMS starts to polymerize, remove it from the curing oven.</li>
		<li>Use a&#160;biopsy punch to form holes of the desired diameter in the microfluidic chip surface.</li>
		<li>Using the blade, cut the required piece of PDMS. 
		Note: It is recommended to initially cut out a larger piece of material than that will eventually be required. To avoid using multiple connectors, it is desirable that any given PDMS interconnector be cut to a square shape, and holes punched, so as to conform to the maximum possible number of holes on the user&#39;s chip.</li>
		<li>Keep the holes slightly smaller than the outside diameter of the microtube.</li>
		<li>Quickly remove the PDMS from the Petri dishes and place it onto the microfluidic chip.</li>
		<li>Ensure that there is no dust on either the PDMS or chip and ensure that the access holes on the microfluidic chip are aligned with those of PDMS.</li>
		<li>Using a micropositioner, insert tubes (e.g. Teflon tubes) through the PDMS interconnector. The tubes should be 110% of microfluidic access hole diameter to prevent liquid leakage. The same tubes can be connected to the liquid injection system depending on the user&#39;s application. 
		Note: Always place the tubes using a micropositioner, the PDMS layer is not very thick and can be detached if the tubes are twisted.</li>
		<li>If necessary, add epoxy between the tube and the PDMS for better adherence. 
		An example of the completed interconnector is shown in the figures and in Ghallab and Badawy2.</li>
	</ol>
	</li>
</ol>
2. Interconnecting Microtubes in Microfluidic Applications with Epoxy17&#160;
When fabricating an interconnector, ensure the edge of the microtube is correctly cut. Use a new sharp blade to cut the edge of the microtube straight and to ensure that the contact between microtubes and access hole is uniform.
<ol>
	<li>Using the micropositioner, carefully place the microtube in the access hole of the microfluidic chip.</li>
	<li>Apply a small pressure on the epoxy dispenser to deposit epoxy on the access holes or manually place it.</li>
	<li>Allow the epoxy to cure using the following steps:
	<ol>
		<li>UV curable Epoxy: Expose the UV epoxy to a UV source for 3-10 min, depending on the quantity of the epoxy used. For more details, refer to the epoxy specifications.</li>
		<li>Standard epoxy: If the microfluidic substrate is to be used only at RT, keep epoxy curing during 24 hr&#160;at RT. If the substrate is required to withstand high temperatures, rapidly solidify the epoxy by exposing it to 100 &#176;C using an oven or a heater, depending on the application. For more details, refer to the epoxy specifications.</li>
	</ol>
	</li>
</ol>
3. Assembly Technique for Reusable Microfluidic Chips with Electrical Interface17
<ol>
	<li>Assembling the Components 
	Figure 2 shows the links between the electrical connectors on the PCB and the electrical pads on the microfluidic chip. To assemble the PCB/microfluidic chip/Plexiglas components, follow these steps: 
	CAUTION: Avoid excessive compression pressure, which can break the microfluidic chip.
	<ol>
		<li>Solder the surface-mount multipin electrical connectors to the PCB.</li>
		<li>If there is surface contamination on the microfluidic chip&#39;s electrical pads, clean with plasma oxygen; otherwise clean the pads with ethanol.</li>
		<li>Use a sharp blade to cut the conductive tape into small pieces with the same dimensions as the microfluidic chip&#39;s electrical pads, as shown in Figures&#160;1 and 2.</li>
		<li>Using forceps, place the conductive tape on the PCB electrical pads.</li>
		<li>Align and then place the microfluidic chip onto the PCB. 
		Note: For placement precision, use an alignment machine.</li>
		<li>Place an insulation layer (such as paper) on the PCB to avoid short circuits before installing the metal brackets, depending on the location of the PCB traces.</li>
		<li>Attach the metal bracket using machine screws and nuts.</li>
	</ol>
	</li>
	<li>Disassembling
	<ol>
		<li>Remove the machine screws, nuts and the metal brackets.</li>
		<li>Gently separate the microfluidic chip and the PCB.</li>
		<li>Use ethanol to remove the conductive tape adhesive from the electrical pads on the PCB and microfluidic chip prior to reassembly.</li>
	</ol>
	</li>
</ol>

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Packag. 26, 242-247 (2003).</li><li>Lee, E., Howard, D., Liang, E., Collins, S., Smith, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Removable+tubing+interconnects+for+glass-based+micro-fluidic+systems+made+using+ECDM.">Removable tubing interconnects for glass-based micro-fluidic systems made using ECDM.</a> J. Micromech. Microeng. 14, 535-541 (2004).</li><li>Kua, C. H., Lam, Y. C., Yang, C., youcef-Toumi, K., Rodriguez, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+of+dielectrophoretic+force+for+moving+dielectrophoresis+electrodes.">Modeling of dielectrophoretic force for moving dielectrophoresis electrodes.</a> J. Electrostat. 66, 514-525 (2008).</li><li>Saarela, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Re-usable+multi-inlet+PDMS+fluidic+connector.">Re-usable multi-inlet PDMS fluidic connector.</a> J. Sens. Actuators B Chem. 114, 552-557 (2006).</li><li>Pattekar, A., Kothare, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+microfluidic+interconnectors+for+high+temperature+and+pressure+applications.">Novel microfluidic interconnectors for high temperature and pressure applications.</a> J. Micromech. Microeng. 13, 337-345 (2003).</li><li>Gray, B. 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There is nothing to disclose.

The PDMS interconnector is intended for low-pressure applications, liquid leakage into the chip access hole when the PDMS interconnector is subsequently placed on the access hole must be prevented. Therefore, the recommended thickness of PDMS is less than 2 mm. A greater thickness can induce a weak adhesion of the PDMS to the microfluidic chip surface and is not recommended. An unsuccessful trial was made using a thickness of 4 mm. This work focuses on the adherence of the PDMS interconnector to the glass while syringe pumps control the liquid injection. Solution leakage refers to the loss of adherence, which limits the maximum liquid flow rate. Thus, the solution leakage refers to the maximum liquid flow rate that can be used with the design PDMS interconnector.
The interconnector described in this method may not be ideal if, during the microfluidic chip or system prototyping phase, a removable interconnector is required. This interconnector is often single-use only, and once it is removed from the microfluidic chip it is difficult to be put back in place with the same initial adherence and must be replaced by a new one. However, in general, this interconnection technique is versatile and can also be adapted to any microfluidic chip and thus remain reusable. To place a permanent interconnector, the PDMS can also be bonded through a plasma-oxygen process. Although this is useful when the device is finalized, it is not useful when the system is for prototyping purposes and if changes and improvements are expected, which is usually the case with prototypes.
Attaching tubing is a challenging step in a system assembly when liquids are injected into MEMS, microfluidic or LoC devices. The complexity comes from the very limited space to connect tubes to access holes in this work. The smallest diameter of the currently commercially available connectors is in the range of 6 mm; however, the distance between the two access holes is 3 mm22&#8211;24.&#160;Therefore, we have proposed a tubing technique based on polydimethylsiloxane (PDMS) as shown in Figure&#160;4. This new tubing process is specially elaborated for the prototyping phase. In fact, owing to the chemical constraint, changing the connection tube after each usage is mandatory to avoid and minimize liquid leakage inside the microstructure. For these purposes, the described process in this paper is particularly employed for a fast prototyping design.
In the case of epoxy-based interconnectors, the biocompatibility was not considered in this work, however different types of biocompatible epoxy are available in the market and can be used with the proposed technique. In addition in-channel electrodes may need to be biocompatible depending on injected liquid25.

Recent progresses in microfabrication have led to more complex microfluidic devices including a large number of electrodes and different types of control algorithms. However, these advances highlighted new challenges in packaging. Furthermore, Lab-on-Chip (LoC) is a multidisciplinary concept where microfluidic devices, microelectromechanical systems (MEMS), microelectronic chips among other parts are connected together. Consequently it is impossible to develop a packaging process without considering different constraints of LoC components such as microelectronics circuitry sensitivity and protection, tubing, and mechanical aspects. In addition, packaging the components of a given LoC is closely related to the application1,2. As an example, in optical applications, the transparence of the device is crucial, especially for testing purposes. Thus, it is important to monitor system behavior by keeping the device observable. In applications related to cell or particle manipulations, using low-voltage techniques is more attractive, with the emergence of new microfabrication technologies which facilitate reduced electrode dimensions (from few a micrometers to submicron scale3-5) but considerably increase the number of electrodes to 100 or more.
On the other hand, LoCs dedicated for chemical and biological analysis require long-term observation. Thus, the system packaging and test bench must avoid biological contamination as well as any failure in the electronic devices of LoC in addition to keeping the system observable.
In recently published papers, microfluidic and MEMS are the main parts of a LoC, but other modules may be used for the monitoring of the system. Consequently, testing and validating microfluidic architectures became a challenging issue with the new microfabrication approaches and the high complexity and throughput architectures. Up to now there are no standard testing platforms or supports for microfluidic system, as it is the case for microelectronics dies.
Researchers proposed different packaging techniques for specific uses, such as Xie et al.6&#160;who designed a bio-microfluidic packaging including a microelectronics chip to control DNA separation in microfluidic channels. Beebe et al.7&#160;designed a microfluidic channel with integrated fluid reservoirs and stimuli-responsive hydrogel valves to manipulate fluid samples. Other systems propose the use of electrolytic bubble-based flow sensors to detect pressures through an electrical field to generate air bubbles and measure corresponding pressure8.&#160;The sensing system measures the impedance of the bubble and then determines the pressure, which requires special packaging designed to avoid introducing any interference into the measurements. In another work, a room temperature microfluidic packaging method was introduced based on sequential plasma activation process9. Despite the fact that this process could lead to a strongly assembled device, it has limitations when it is used for prototyping purpose or when the device is used several times. The latter may imply frequent replacement of some parts of the system. Moreover, Lee et al. introduced a new packaging technique, called Biolab-on-IC, based on using magnetic fields for individual magnetic bead manipulation, where the microfluidic architecture is designed on the top of the integrated circuit10. In addition, the reliability of packaging and integration of microfluidic systems, considering the system size, optical aspects, and connection parts, are critical issues as detailed by Han and Frazier11. This latter work reflects a typical approach for LoC systems, where several parameters must be precisely fixed and measured during the packaging.
Consequently, microfluidic packaging is a challenging issue for new a generation of microfluidic devices. Packaging includes heterogeneous parts such as tubing, electrical connections and microfluidic support. For tubing, the main issue is the very limited space available to connect the tubes to access the microfluidic holes. The diameter of the current commercially available connectors is in the range of 6 mm; however, the distance between the two access holes is becoming smaller with the reduction of overall system dimensions12-13. Therefore, we have proposed a tubing technique based on PDMS. This tubing process is specially elaborated for the prototyping phase. In fact, owing to the chemical constraint, changing the connection tube after each usage is mandatory to avoid and minimize liquid leakage inside the microstructure and to clean the microchannels. For these purposes, the described process in this paper is particularly applicable for a fast prototyping design.
On the other hand, electrical connections are critical for microfluidic devices that utilize direct or indirect electrical manipulation or measurement. Due to the wide range of microfluidic applications, device dimensions, shape, and number of electrical contacts may vary considerably. Therefore, a versatile method is required, which can be used for different applications. Kaler&#160;et al.&#160;reported results from their microfluidic rapid prototyping platform, which is based on zero insertion force (ZIF) connectors14. Instead of these later connectors, the presented methods use an anisotropic adhesive conductive film, which can be easily adapted to any shape.
Many researchers do not take into consideration the testing constraints when designing their microfluidic device. In microelectronics, there is many supports used for prototyping purpose and testing, which are called IC holders. These are mainly designed to reduce prototyping and testing times, and offer researchers and engineers an easy way to replace devices in case of failure. Similar to microelectronics, we are also proposing a new testing package for microfluidic devices limited to a 45 mm x 90 mm device size.
Our proposed techniques are targeting to cover a large number of microfluidic devices and applications. These methods can be adapted, extended and upgraded to other applications. We aim to provide one of the first versatile packaging methods for microfluidic devices that are optimized for microfluidic manipulations. For example, one end application for devices packaged with these techniques is separation of polystyrene and carboxyl modified microspheres with artificial cerebrospinal fluid. Nevertheless, they can be used in other applications with different solutions.
In the remainder of this article, three different tubing techniques, 2 electrical connection methods and one microfluidic packaging method are presented and compared.

<table><tbody><tr><td>Epoxy 731</td><td>Epotek</td><td>731</td><td></td></tr><tr><td>PDMS</td><td>Dow Corning</td><td>SYLGARD 184</td><td></td></tr><tr><td>UV Epoxy</td><td>Epotek</td><td>OG159</td><td></td></tr><tr><td>Micropump</td><td>Harvard Apparatus</td><td>PHD Ultra</td><td></td></tr><tr><td>PCB</td><td>Advanced Circuits</td><td></td><td></td></tr><tr><td>Plexiglass</td><td>Ecole Polytechnique</td><td></td><td></td></tr><tr><td>Adhesive conductive film</td><td>3M</td><td>9703</td><td></td></tr></tbody></table>

high throughput microfluidic rapid and low cost prototyping packaging methods

In this work, 3 different packaging and assembly techniques are presented. They can be classified into two categories: one-time use and reusable packaging techniques.
The one-time use packaging technique employs UV-based and temperature curing epoxies to connect microtubes to access holes, wire-bonding for integrated circuit connections, and silver epoxy for electrical connections. This method is based on a robust assembly technique that can support relatively high pressure close to 1 psi and does not need any support to strengthen the microfluidic architecture.
Reusable packaging techniques consist of PDMS-based microtube interconnectors and anisotropic adhesive films for electrical connections. These devices are more sensitive and fragile. Consequently, Plexiglas support is added to the microfluidic structure to improve the electrical contact when anisotropic adhesive films are used, and also to strengthen the microfluidic architecture. In addition, a micromanipulator is needed to maintain tubes while using a thin PDMS layer to connect them to the access holes. Different PDMS layer thicknesses, ranging from 0.45-3 mm, are tested to compare the best adherence versus injection rates. Applied injection rates are varied from 50-300 &#956;l/hr for 0.45-3 mm PDMS layers, respectively. These techniques are mainly applicable for low-pressure applications. However, they can be extended for high-pressure ones through plasma-oxygen process to permanently seal the PDMS to glass substrates. The main advantage of this technique, besides the fact that it is reusable, consists of keeping the device observable when the microchannel length is very short (in the range of 3 mm or lower).

Figure 3 illustrates a detailed schematic of the proposed packaging technique. The packaging solution was tested with several PDMS thicknesses and sizes to characterize a transparent and efficient packaging process for hybrid microelectronics/microfluidic microsystems as shown in Figures 4 and 5. The dimensions of the designed PDMS interconnector layer are 6 mm x 6 mm and it is used to connect two access holes. However, with major commercially available connectors, it is not possible to connect more than one hole within these dimensions if space between access holes is 5 mm or less. Thus epoxy and PDMS are the best choices for tubing in this case. Different thicknesses of the PDMS interconnector are tested such as 0.45 mm, 1 mm, and 1.75 mm. The best adherence is achieved with thin PDMS layers (0.45 mm). Finally, the fabrication of the PDMS-based interconnector requires approximately 20 min.
The liquid flow speed is monitored through a microsyringe pump. Both the 0.45 mm and 1 mm PDMS layers are tested with 50 &#956;m channel depth on a glass substrate. The PDMS adherence to glass is broken when the injection speed is 30 ml/hr and 150 ml/hr for the 0.45 mm and 1 mm PDMS layers, respectively. Table 1 is a comparison with recently published results. In Saarela et al.22 the PDMS layer is glued to the glass chip. To overcome this inconvenience, a new approach is proposed, which is based on control of the thickness of the PDMS layer interconnector.
Table 1. Main interconnector comparisons.
<table border="1">
	<tbody>
		<tr>
			<th></th>
			<th>Gray24</th>
			<th>Lee20</th>
			<th>Kua21</th>
			<th>This work1</th>
			<th>This work2</th>
		</tr>
		<tr>
			<td>P. (psi)</td>
			<td>315</td>
			<td>57</td>
			<td>30</td>
			<td>0.073</td>
			<td>0.213</td>
		</tr>
		<tr>
			<td>V. R. (ml/hr)</td>
			<td>N.A</td>
			<td>N.A</td>
			<td>N.A</td>
			<td>304</td>
			<td>1504</td>
		</tr>
		<tr>
			<td>Features</td>
			<td>H.P</td>
			<td>N.R</td>
			<td>C.F.P</td>
			<td>R</td>
			<td>R</td>
		</tr>
	</tbody>
</table>
P.: Pressure, V.R.: Volume rate, N.A: Non Applicable, H.P.: High Pressure, C.F.P.: Custom Fabrication Process, R: Reusable, N.R: Non Reusable 
1 0.45 mm PDMS thickness 
2 1 mm PDMS thickness 
3 Simulation results 
4 Experimental results
This method allowed achieving good results for low-pressure liquid injection, which is why in previous works19,20 the comparison was based on the pressure, but in this case, it was based on volume rate and pressure.
Table 2 presents a comparison between different tubing techniques detailed in this work. This comparison helps the designer to choose a suitable technique for their design, according to its use and the application of the system:
Table 2. Assembling technique comparison.
<table border="1">
	<tbody>
		<tr>
			<th>
			
			</th>
			<th>
			PDMS
			</th>
			<th>
			UV epoxy
			</th>
			<td>
			Standard epoxy
			</td>
		</tr>
		<tr>
			<td>
			Removable
			</td>
			<td>
			Yes
			</td>
			<td>
			No
			</td>
			<td>
			No
			</td>
		</tr>
		<tr>
			<td>
			Preparation temperature
			</td>
			<td>
			80 &#176;C
			</td>
			<td>
			UV
			</td>
			<td>
			24 &#176;C~100 &#176;C*
			</td>
		</tr>
		<tr>
			<td>
			Preparation time
			</td>
			<td>
			20 min
			</td>
			<td>
			3 min~10 min
			</td>
			<td>
			30 min~24 hr
			</td>
		</tr>
		<tr>
			<td>
			Pressure
			</td>
			<td>
			&#60;0.5 psi
			</td>
			<td>
			high pressure 
			&#62;1 psi
			</td>
			<td>
			high pressure 
			&#62;1 psi
			</td>
		</tr>
		<tr>
			<td>
			Adherence
			</td>
			<td>
			Good
			</td>
			<td>
			Very good
			</td>
			<td>
			Very good
			</td>
		</tr>
		<tr>
			<td>
			Need support system for microtubes
			</td>
			<td>
			Yes
			</td>
			<td>
			No**
			</td>
			<td>
			No**
			</td>
		</tr>
		<tr>
			<td>
			Risk of microchannel obstruction
			</td>
			<td>
			No
			</td>
			<td>
			Yes***
			</td>
			<td>
			Yes***
			</td>
		</tr>
		<tr>
			<td>
			Transparency
			</td>
			<td>
			Yes
			</td>
			<td>
			No
			</td>
			<td>
			No
			</td>
		</tr>
		<tr>
			<td>
			Accuracy
			</td>
			<td>
			Good
			</td>
			<td>
			Very high
			</td>
			<td>
			Good
			</td>
		</tr>
		<tr>
			<td>
			Alignment
			</td>
			<td>
			Yes
			</td>
			<td>
			No
			</td>
			<td>
			No
			</td>
		</tr>
	</tbody>
</table>
Notes:
PDMS is suggested for use with low-pressure applications when the microfluidic design must be uncovered and requires fast prototyping. If it is necessary to fix the PDMS interconnector permanently to the microfluidic design; this can be achieved by using a plasma oxygen process.
Standard epoxy provides a strong interconnection technique that can be used for both low- and high-pressure applications, but it is not recommended for prototyping because it cannot be removed from the microfluidic chip. Furthermore, it is not suitable for designs where the distance between the access holes is less than 5 mm because during the fabrication, the epoxy may spread over the chip surface.
UV epoxy has the same properties as standard epoxy but has the advantage of solidifying in just a few minutes depending on the UV light.
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/50735/50735fig1highres.jpg" src="/files/ftp_upload/50735/50735fig1.jpg" /> 
Figure 1. Microfluidic-PCB connection. (a) No established connection, (b) Microfluidic-PCB connection with good alignment and (c) bad alignment.
<img alt="Figure 2" fo:content-width="5in" fo:src="/files/ftp_upload/50735/50735fig2highres.jpg" src="/files/ftp_upload/50735/50735fig2.jpg" /> 
Figure 2. Example of assembled device using ACF.
<img alt="Figure 3" fo:content-width="5in" fo:src="/files/ftp_upload/50735/50735fig3highres.jpg" src="/files/ftp_upload/50735/50735fig3.jpg" /> 
Figure 3. Fast prototyping assembly. (a) global device architecture (b) microfluidic architecture and (c) microfluidic-PCB contacts.
<img alt="Figure 4" fo:content-width="5in" fo:src="/files/ftp_upload/50735/50735fig4highres.jpg" src="/files/ftp_upload/50735/50735fig4.jpg" /> 
Figure 4. PDMS interconnector. (a) only one access hole is covered by a PDMS interconnector, (b) both access holes are covered.
<img alt="Figure 5" fo:content-width="5in" fo:src="/files/ftp_upload/50735/50735fig5highres.jpg" src="/files/ftp_upload/50735/50735fig5.jpg" /> 
Figure 5. Fast Prototyping Platform for microfluidic devices.

Watch this Scientific Journal Video about High Throughput Microfluidic Rapid and Low Cost Prototyping Packaging Methods at JoVE.com

High Throughput Microfluidic Rapid and Low Cost Prototyping Packaging Methods

In this article we describe different techniques for microfluidic rapid prototyping platforms. The proposed techniques are based on ultraviolet (UV) sensitive and temperature curing epoxies, polydimethylsiloxane (PDMS) based tubing, wire-bonding, and anisotropic adhesive films. The assembling procedures presented are developed for both one-time use devices as well as reusable microfluidic systems.

In this work, 3 different packaging and assembly techniques are presented. They can be classified into two categories: one-time use and reusable packaging ...

high-throughput-microfluidic-rapid-low-cost-prototyping-packaging

Nanyang Technological University

Research

JoVE Journal

Bioengineering

7.3K 次观看.  Polytechnique Montreal. In this article we describe different techniques for microfluidic rapid prototyping platforms. The proposed techniques are based on ultraviolet (UV) sensitive and temperature curing epoxies, polydimethylsiloxane (PDMS) based tubing, wire-bonding, and anisotropic adhesive films. The assembling procedures presented are developed for both one-time use devices as well as reusable microfluidic systems.

视频: High Throughput Microfluidic Rapid and Low Cost Prototyping Packaging Methods

Microfluidic Chips Controlled with Elastomeric Microvalve Arrays

Miniaturized microfluidic systems provide simple and effective solutions for low-cost point-of-care diagnostics and high-throughput biomedical assays. Robust flow control and precise fluidic volumes are two critical requirements for these applications. We have developed microfluidic chips featuring elastomeric polydimethylsiloxane (PDMS) microvalve arrays that: 1) need no extra energy source to close the fluidic path, hence the loaded device is highly portable; and 2) allow for microfabricating deep (up to 1 mm) channels with vertical sidewalls and resulting in very precise features.

The PDMS microvalves-based devices consist of three layers: a fluidic layer containing fluidic paths and microchambers of various sizes, a control layer containing the microchannels necessary to actuate the fluidic path with microvalves, and a middle thin PDMS membrane that is bound to the control layer. Fluidic layer and control layers are made by replica molding of PDMS from SU-8 photoresist masters, and the thin PDMS membrane is made by spinning PDMS at specified heights. The control layer is bonded to the thin PDMS membrane after oxygen activation of both, and then assembled with the fluidic layer. The microvalves are closed at rest and can be opened by applying negative pressure (e.g., house vacuum). Microvalve closure and opening are automated via solenoid valves controlled by computer software.

Here, we demonstrate two microvalve-based microfluidic chips for two different applications. The first chip allows for storing and mixing precise sub-nanoliter volumes of aqueous solutions at various mixing ratios. The second chip allows for computer-controlled perfusion of microfluidic cell cultures.

The devices are easy to fabricate and simple to control. Due to the biocompatibility of PDMS, these microchips could have broad applications in miniaturized diagnostic assays as well as basic cell biology studies.

We demonstrate protocols for manufacturing and automating elastomeric polydimethylsiloxane (PDMS)-based microvalve arrays that need no extra energy to close and feature photolithographically defined precise volumes. A parallel subnanoliter-volume mixer and an integrated microfluidic perfusion system are presented.

微流控芯片控制，弹性微阀阵列

Miniaturized microfluidic systems provide simple and effective solutions for low-cost point-of-care diagnostics and high-throughput biomedical assays.  ...

科研

生物学

High-throughput Protein Expression Generator Using a Microfluidic Platform

Rapidly increasing fields, such as systems biology, require the development and implementation of new technologies, enabling high-throughput and high-fidelity measurements of large systems. Microfluidics promises to fulfill many of these requirements, such as performing high-throughput screening experiments on-chip, encompassing biochemical, biophysical, and cell-based assays1. Since the early days of microfluidics devices, this field has drastically evolved, leading to the development of microfluidic large-scale integration2,3. This technology allows for the integration of thousands of micromechanical valves on a single device with a postage-sized footprint (Figure 1). We have developed a high-throughput microfluidic platform for generating in vitro expression of protein arrays (Figure 2) named PING (Protein Interaction Network Generator). These arrays can serve as a template for many experiments such as protein-protein 4, protein-RNA5 or protein-DNA6 interactions.
The device consist of thousands of reaction chambers, which are individually programmed using a microarrayer. Aligning of these printed microarrays to microfluidics devices programs each chamber with a single spot eliminating potential contamination or cross-reactivity Moreover, generating microarrays using standard microarray spotting techniques is also very modular, allowing for the arraying of proteins7, DNA8, small molecules, and even colloidal suspensions. The potential impact of microfluidics on biological sciences is significant. A number of microfluidics based assays have already provided novel insights into the structure and function of biological systems, and the field of microfluidics will continue to impact biology.

We present a microfluidic approach for the expression of protein arrays. The device consists of thousands of reaction chambers controlled by micro-mechanical valves. The microfluidic device is mated to a microarray-printed gene library. These genes are then transcribed and translated on-chip, resulting in a protein array ready for experimental use.

利用微流控平台的高通量蛋白质表达发生器

Rapidly increasing fields, such as systems biology, require the development and implementation of new technologies, enabling high-throughput and ...

生物工程

A Microfluidic Device for Studying Multiple Distinct Strains

The study of cell responses to environmental changes poses many experimental challenges: cells need to be imaged under changing conditions, often in a comparative manner. Multiwell plates are routinely used to compare many different strains or cell lines, but allow limited control over the environment dynamics. Microfluidic devices, on the other hand, allow exquisite dynamic control over the surrounding conditions, but it is challenging to image and distinguish more than a few strains in them. Here we describe a method to easily and rapidly manufacture a microfluidic device capable of applying dynamically changing conditions to multiple distinct yeast strains in one channel. The device is designed and manufactured by simple means without the need for soft lithography. It is composed of a Y-shaped flow channel attached to a second layer harboring microwells. The strains are placed in separate microwells, and imaged under the exact same dynamic conditions. We demonstrate the use of the device for measuring protein localization responses to pulses of nutrient changes in different yeast strains.

We present a simple method to produce microfluidic devices capable of applying similar dynamic conditions to multiple distinct strains, without the need for a clean room or soft lithography.

一种微流体装置研究多个不同的菌株

The study of cell responses to environmental changes poses many experimental challenges: cells need to be imaged under changing conditions, often in a ...

Rapid and Low-cost Prototyping of Medical Devices Using 3D Printed Molds for Liquid Injection Molding

Biologically inert elastomers such as silicone are favorable materials for medical device fabrication, but forming and curing these elastomers using traditional liquid injection molding processes can be an expensive process due to tooling and equipment costs. As a result, it has traditionally been impractical to use liquid injection molding for low-cost, rapid prototyping applications. We have devised a method for rapid and low-cost production of liquid elastomer injection molded devices that utilizes fused deposition modeling 3D printers for mold design and a modified desiccator as an injection system. Low costs and rapid turnaround time in this technique lower the barrier to iteratively designing and prototyping complex elastomer devices. Furthermore, CAD models developed in this process can be later adapted for metal mold tooling design, enabling an easy transition to a traditional injection molding process. We have used this technique to manufacture intravaginal probes involving complex geometries, as well as overmolding over metal parts, using tools commonly available within an academic research laboratory. However, this technique can be easily adapted to create liquid injection molded devices for many other applications.

We have devised a method for low-cost and rapid prototyping of liquid elastomer rubber injection molded devices by using fused deposition modeling 3D printers for mold design and a modified desiccator as a liquid injection system.

医疗器械的使用3D印刷模具的液体注射成型快速，低成本原型

Biologically inert elastomers such as silicone are favorable materials for medical device fabrication, but forming and curing these elastomers using ...

High Speed Droplet-based Delivery System for Passive Pumping in Microfluidic Devices

A novel microfluidic system has been developed that uses the phenomenon of passive pumping along with a user controlled droplet based fluid delivery system. Passive pumping is the phenomenon by which surface tension induced pressure differences drive fluid movement in closed channels. The automated fluid delivery system consists of a set of voltage controlled valves with micro-nozzles connected to a fluid reservoir and a control system. These voltage controlled valves offer a volumetrically precise way to deliver fluid droplets to the inlet of a microfluidic device in a high frequency manner. Based on the  dimensions demonstrated in the current study example, the system is capable of flowing 4 milliliters per minute (through a 2.2mm by 260um cross-sectional channel). Based on these same channel dimensions, fluid exchange of a point inside the channel can be achieved in as little as eight milliseconds. It is observed that there is interplay between momentum of the system (imparted by a combination of the droplets created by the valves and the fluid velocity in the channel), and the surface tension of the liquid. Where momentum provides velocity to the fluid flow (or vice-versa), equilibration of surface tension at the inlet provides a sudden stop to any flow. This sudden stop allows the user to control the flow characteristics of the channel and opens the door for a variety of biological applications, ranging anywhere from reagent delivery to drug-cell studies. It is also observed that when nozzles are aimed at the inlet at shallow angles, the droplet momentum can cause additional interesting fluid phenomena, such as mixing of multiple droplets in the inlet.

A novel microfluidic system has been developed using the phenomenon of passive pumping and a user controlled fluid delivery system. This microfluidic system has the potential to be used in a wide variety of biological applications given its low cost, ease of use, volumetric precision, high speed, repeatability and automation.

基于液滴在微流体装置的被动抽水高速输送系统

A novel microfluidic system has been developed that uses the phenomenon of passive pumping along with a user controlled droplet based fluid delivery ...

Multi-step Variable Height Photolithography for Valved Multilayer Microfluidic Devices

Microfluidic systems have enabled powerful new approaches to high-throughput biochemical and biological analysis. However, there remains a barrier to entry for non-specialists who would benefit greatly from the ability to develop their own microfluidic devices to address research questions. Particularly lacking has been the open dissemination of protocols related to photolithography, a key step in the development of a replica mold for the manufacture of polydimethylsiloxane (PDMS) devices. While the fabrication of single height silicon masters has been explored extensively in literature, fabrication steps for more complicated photolithography features necessary for many interesting device functionalities (such as feature rounding to make valve structures, multi-height single-mold patterning, or high aspect ratio definition) are often not explicitly outlined. 
Here, we provide a complete protocol for making multilayer microfluidic devices with valves and complex multi-height geometries, tunable for any application. These fabrication procedures are presented in the context of a microfluidic hydrogel bead synthesizer and demonstrate the production of droplets containing polyethylene glycol (PEG diacrylate) and a photoinitiator that can be polymerized into solid beads. This protocol and accompanying discussion provide a foundation of design principles and fabrication methods that enables development of a wide variety of microfluidic devices. The details included here should allow non-specialists to design and fabricate novel devices, thereby bringing a host of recently developed technologies to their most exciting applications in biological laboratories.

Multilayer microfluidic devices often involve the fabrication of master molds with complex geometries for functionality. This article presents a complete protocol for multi-step photolithography with valves and variable height features tunable to any application. As a demonstration, we fabricate a microfluidic droplet generator capable of producing hydrogel beads.

多级可变高度的光刻多层带瓣微流体装置

Microfluidic systems have enabled powerful new approaches to high-throughput biochemical and biological analysis. However, there remains a barrier to ...

Computer Numerical Control Micromilling of a Microfluidic Acrylic Device with a Staggered Restriction for Magnetic Nanoparticle-Based Immunoassays

Microfluidic systems have greatly improved immunoassay techniques. However, many microfabrication techniques require specialized, expensive, or complicated equipment, making fabrication costly and incompatible with mass production, which is one of the most important preconditions for point-of-care tests (POCT) to be adopted in low-resource settings. This work describes the fabrication process of an acrylic (polymethylmethacrylate, PMMA) device for nanoparticle-conjugated enzymatic immunoassay testing using the computer numerical control (CNC) micromilling technique. The functioning of the microfluidic device is shown by performing an immunoassay to detect a commercial antibody using lysozyme as a model antigen conjugated to 100 nm magnetic nanoparticles. This device integrates a physical staggered restriction of only 5 &#181;m in height, used to capture magnetic microparticles that make up a magnetic trap by placing an external magnet. In this way, the magnetic force on the immunosupport of conjugated nanoparticles is enough to capture them and resist flow drag. This microfluidic device is particularly suitable for low-cost mass production without the loss of precision for immunoassay performance.

Microfluidics is a powerful tool for the development of diagnostic tests. However, expensive equipment and materials, as well as laborious fabrication and handling techniques, are often required. Here, we detail the fabrication protocol of an acrylic microfluidic device for magnetic micro- and nanoparticle-based immunoassays in a low-cost and simple-to-use setting.

基于磁性纳米颗粒免疫分析的交错限制微流控亚克力装置的计算机数控微铣削

Microfluidic systems have greatly improved immunoassay techniques. However, many microfabrication techniques require specialized, expensive, or ...

工程学

Rapid Fabrication of Custom Microfluidic Devices for Research and Educational Applications

Microfluidic devices allow for the manipulation of fluids, particles, cells, micro-sized organs or organisms in channels ranging from the nano to submillimeter scales. A rapid increase in the use of this technology in the biological sciences has prompted a need for methods that are accessible to a wide range of research groups. Current fabrication standards, such as PDMS bonding, require expensive and time consuming lithographic and bonding techniques. A viable alternative is the use of equipment and materials that are easily affordable, require minimal expertise and allow for the rapid iteration of designs. In this work we describe a protocol for designing and producing PET-laminates (PETLs), microfluidic devices that are inexpensive, easy to fabricate, and consume significantly less time to generate than other approaches to microfluidics technology. They consist of thermally bonded film sheets, in which channels and other features are defined using a craft cutter. PETLs solve field-specific technical challenges while dramatically reducing obstacles to adoption. This approach facilitates the accessibility of microfluidics devices in both research and educational settings, providing a reliable platform for new methods of inquiry.

Here we present a protocol to design and fabricate custom microfluidic devices with minimal financial and time investment. The aim is to facilitate the adoption of microfluidic technologies in biomedical research laboratories and educational settings.

用于研究和教育应用的定制微流体器件的快速制造

Microfluidic devices allow for the manipulation of fluids, particles, cells, micro-sized organs or organisms in channels ranging from the nano to ...

Generation of Dynamical Environmental Conditions using a High-Throughput Microfluidic Device

Mimicking in vivo environmental conditions is crucial for in vitro studies on complex life machinery. However, current techniques targeting live cells and organs are either highly expensive, like robotics, or lack nanoliter volume and millisecond time accuracy in liquid manipulation. We herein present the design and fabrication of a microfluidic system, which consists of 1,500 culture units, an array of enhanced peristaltic pumps and an on-site mixing modulus. To demonstrate the capacities of the microfluidic device, neural stem cell (NSC) spheres are maintained in the proposed system. We observed that when the NSC sphere is exposed to CXCL in day 1 and EGF in day 2, the round-shaped conformation is well maintained. Variation in the input order of 6 drugs causes morphological changes to the NSC sphere and the expression level representative marker for NSC stemness (i.e., Hes5 and Dcx). These results indicate that dynamic and complex environmental conditions have great effects on NSC differentiation and self-renewal, and the proposed microfluidic device is a suitable platform for high throughput studies on the complex life machinery.

We present a microfluidic system for high throughput studies on complex life machinery, which consists of 1500 culture units, an array of enhanced peristaltic pumps and an on-site mixing modulus. The microfluidic chip allows for the analysis of the highly complex and dynamic micro-environmental conditions in vivo.

使用高通量微流体设备生成动态环境条件

Mimicking in vivo environmental conditions is crucial for in vitro studies on complex life machinery. However, current techniques targeting live cells and ...

用于组合插头生产的微流体装置的设置

Bilayer Microfluidic Device for Combinatorial Plug Production

Droplet microfluidics is a versatile tool that allows the execution of a large number of reactions in chemically distinct nanoliter compartments. Such systems have been used to encapsulate a variety of biochemical reactions - from incubation of single cells to implementation of PCR reactions, from genomics to chemical synthesis. Coupling the microfluidic channels with regulatory valves allows control over their opening and closing, thereby enabling the rapid production of large-scale combinatorial libraries consisting of a population of droplets with unique compositions. In this paper, protocols for the fabrication and operation of a pressure-driven, PDMS-based bilayer microfluidic device that can be utilized to generate combinatorial libraries of water-in-oil emulsions called plugs are presented. By incorporating software programs and microfluidic hardware, the flow of desired fluids in the device can be controlled and manipulated to generate combinatorial plug libraries and to control the composition and quantity of constituent plug populations. These protocols will expedite the process of generating combinatorial screens, particularly to study drug response in cells from cancer patient biopsies.

作者聚焦：在精准肿瘤学中整合计算和实验方法

The fabrication of a polydimethylsiloxane (PDMS)-based bilayer device for the production of combinatorial libraries in water-in-oil emulsions (plugs) is presented here. The necessary hardware and software required to automate plug production are detailed in the protocol, and the production of a quantitative library of fluorescent plugs is also demonstrated.

用于组合塞生产的双层微流控装置

Droplet microfluidics is a versatile tool that allows the execution of a large number of reactions in chemically distinct nanoliter compartments. Such ...