Chips and Tips

Ali Hashmi, Jie Xu
Washington State University

Thomas Foster
University of Washington

Why is this useful?

Previously we presented a method for connecting inlets and outlets to an external source that involved tubing and needles [1]. However, the process involves the use of needles which could be a safety concern. The process is also somewhat time-consuming. We have now developed a more convenient and rapid method for fabricating inlets/outlets in a PDMS chip without the need for needles.

What do I need?

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• A puncher, for example, we use a Schmidt punch press (Syneo, LLC)
• Connectors with barbs and corresponding tubings, for example, we use elbow tube fitting with classic series barbs for 1/16” (1.6 mm) ID tubing (Valueplastic.com)

What do I do?

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1. When the PDMS device has been cured, punch inlets and outlets from the top of the device.

Figure 1: (a) Schmidt Press; (b) punching through holes at desired locations on the device; (c) device with a set of three punched holes.

2. After sealing the device, insert the connectors (“Elbow Tube Fitting with classic series Barbs, 1/16”, (1.6 mm) ID Tubing, White Nylon”) into the inlets and outlet.

3.Tubing can then be connected to the connectors at one end, and to a syringe pump at the other end.

What else should I know?

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The diameter of the punched holes is specific to the nominal cutting edge diameter of the punch. The punch, connectors, and tubing can be any size as long as they correspond to each other so that the connection does not leak. The connectors and tubing can be ordered from Value Plastics, INC.

The height of the Schmidt press can be adjusted according to the thickness of the PDMS device to ensure a through hole.

The maximum pressure we have tried with this type of connection is about 240 kPa, beyond which other parts of the chip fail (such as the PDMS/glass).

bonding.

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Reference

[1]  P. Li., W. Xue, and J. Xu, The fabrication of PDMS interconnecting interface assisted by tubing fixation, Lab Chip, Chips and Tips, 10 June 2011

Gabriele Pitingolo, Enza Torino and  Raffaele Vecchione
Center for Advanced Biomaterials for Healthcare, Istituto Italiano di tecnologia (IIT@CRIB), Largo Barsanti e Matteucci, 53, 80125  – Napoli  – Italy.

Why is this useful?

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Common systems to connect microfluidics devices with classic fluidic equipment (such as syringe  or peristaltic pumps) are based on the use of commercial connectors which are not always compatible with the device material.

Upchurch (Oak Harbor, WA, USA) NanoPorts™ assemblies are the first commercially available products to provide consistent fluid connectors for microfluidic chips. These products bond easily to some chip surfaces such as glass and polydimethylsiloxane (PDMS) with the provided preformed adhesive rings. All NanoPort™ components are made of inert, biocompatible PEEK™ polymer (nuts and ports) and Perlast® perfluoroelastomer (ferrules and gaskets). However, many microfluidic devices are made of polymethylmethacrilate (PMMA) and in this case the preformed adhesive rings are not suitable.

Here, we demonstrate an easy and effective way to bond NanoPorts to PMMA microdevices. Our approach is a hybrid system which glues the commercial nanoports with an alternative epoxy adhesive. Also remarkably this is a reusable system, in fact the Flat Bottom Port and the Flat Bottom Port Gasket may be removed and re bonded on another device as explained in the procedure.

What do I need?

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• Fully cured PMMA microchip with via holes to microchannels
• UPCHURCH® SCIENTIFIC NanoPort Assemblies [1]
• Loctite Super Attak Power Flex Gel (5g)
• Binder Clip Medium 1-1/4in
• FEP Tubing, 1/16’’ x 0.25 mm [2]
• Scalpel and tweezers
• Ethanol
• Hammer

What do I do?

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1. Prepare the PMMA surfaces (clean with water and dry with an absorbent cloth)  and NanoPort™ for bonding (Figure 1). The Inlet and Outlet holes must be of a diameter below the inner diameter of the Nanoport (around 2 mm) to guarantee no leakage at the Nanoport-PMMA interface.

2. Put a few drops of Loctite Super Attak Flex Power Gel (5g) on a surface, in our case we used a piece of PMMA (Figure 2). Take the UPCHURCH® SCIENTIFIC NanoPort, insert the gasket seal into the recess in the bottom of the port (Figure 3) and touch the port to the drop of Loctite Super Attak in order to deposit the right amount of glue on the bonding surface (Figure 4). Eliminate the excess glue with the aid of a scalpel and attach the flat bottom port gasket directly on the bottom of the port (Figure 5).

3. Take the complete Nanoport (flat bottom port and gasket) and touch the drop of Loctite super attack, eliminating the excess glue with the aid of a scalpel. Center and place the complete Nanoport on your final substrate surrounding the access hole (Figure 6).

4. Clamp the port to the substrate (Figure 7) for 3 hours.

5. Your well-bonded NanoPort interconnect to PMMA (Figure 8) is now ready to use.

6. It is possible to remove the Nanoport from the PMMA surface. Use ethanol to weaken the epoxy (Figure 9) and after 30 minutes punch with a hammer to separate the NanoPort™ from the PMMA device.

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References

[1] http://www.upchurch.com/PDF/I-Cards/N4.PDF

[2] http://www.idex-hs.com/product-families/5/Tubing-Upchurch-Scientific-Ismatec.aspx

Bretton Fletcher*, Miguel Z. Rosales and Bruno F.B. Silva
Department of Physics, Department of Materials, and Molecular, Cellular & Developmental Biology Department, University of California, Santa Barbara, California 93106, United States
*email: brettonfletcher[at]gmail.com  

Why is this useful? 

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Microfluidic chips are used for several different purposes in the lab. Experiments so diverse as nanoparticle synthesis; cell sorting; analytical determination of chemical and/or biological species; are all widely performed nowadays in many laboratories. Due to these so diverse applications, it is often hard to find parts (e.g. adaptors, tubing, etc) that fit the researcher’s needs for a particular project. Among these is the difficulty in finding suitable adapters to connect the microfluidic chip to tubing and syringes. A common difficulty is to connect small diameter tubing (inner diameter of 0.01 or 0.02”) to Luer adapters, which are normally designed to fit larger ID tubing sizes. A second common difficulty is the large dead volume normally associated with common Luer connectors. This can be a major setback when working with expensive and rare materials. 

Nanoports from Upchurch® are a valid solution for these two problems, but they are expensive, and somewhat long and bulky, which may restrict some experiments. For instance, if the connector is long, it may restrict access of a microscope lens to the area around it.
Here we show a suitable way of preparing customized Luer adapters that (i) fit a wide range of microfluidic tubing; (ii) have very low dead volume requirements, and (iii) are smaller than most of the market alternatives. 
  

What do I need? 

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• Natural Polypropylene Male Luer Coupler (Value Plastics, MLRLC-6). This design has the advantage of providing two custom connecters per original connecter (Figure 1). Other designs may be used, as long as one end has a Male Luer fitting. Other materials may also be used, provided that they bond with PDMS.
• Tygon Microbore Tubing, S-54-HL ID: .02in and ID: .04. Other sizes can be used.
• Polydimethylsiloxane (PDMS). We mix a 10 to 1 ration of silicone elastomer base and silicone elastomer curing agent.            
• Devcon 5 Minute Epoxy
• Petri Dish, Tape, & Scissors

  

What do I do? 

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1. Cut the cylindrical ends off either side of a Luer coupler to get two connector pieces (figure 1).
2. Push a few centimeters of tubing into the rough (cut) side of one connector and out of the clean side (figure 2).
3. Fix the connector and tubing vertically by attaching to a petri dish with tape so that the rough end faces up (figure 3).
4. Apply epoxy to the top of the connector so that it completely plugs the opening and fixes the tubing in place. Wait for it to dry (figure 4). One of the main purposes of the epoxy is to fix the tubing to the connector. Since it is very viscous and dries quickly, this is very suitable.
5. Once the epoxy dries, reattach the connector to the petri dish with the opposite end facing up, and fill the rest of the connector with PDMS. Be sure not to leave any air bubbles in the connector (figure 5).
6. Place connector and tubing on aluminum foil in an oven for two hours at 60°C. Be sure not to let the tubing touch hot surfaces in the oven. At this temperature the PDMS cures adequately and the Tygon tubing does not degrade.
7. Once the PDMS is completely hardened, cut off the excess tubing from the clean end of the connector for a smooth face (figure 6).

  

  

 What else should I know? 

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This concept is very simple and can be extended to other types of tubing (material, diameter, etc) and connectors. By fixing one tube to one connector, we avoid all compatibility problems, and minimize possible leakage problems. The tubing and Luer connector become one single unit. With this comes the slight disadvantage that each connector will be associated permanently with one tube. We don’t find this discouraging. Since both tubing and connectors are relatively cheap, we prepare a whole range of connectors at a time that fit our needs. The total amount of work required is also not more than one hour, and does not require a high level of skill. 

One advantage of this method, compared to other nice solutions shown here in “Chips and Tips”, is the lack of needles in the connector, which decreases the chance of leakages and needle-related injuries. 

We have tested the connectors with water and protein solutions of intermediate viscosity at several flow rates and leaks from the Tygon tubing-connector junction were never detected. 

The main purpose of the epoxy resin is to fix the tubing to the connector. Since it is very viscous and dries quickly, this is very suitable. A second advantage is that indeed, epoxy creates a rigid and robust junction between the Tygon tubing and the polypropylene material, making it very robust. The PDMS is then poured on top of the epoxy. Since the epoxy is porous, it would not be suitable to have in contact with the liquids under study. By isolating it with PDMS we fix this problem.

Robert Henderson, Nick Selock and Dr. Govind Rao^*
Center for Advanced Sensor Technology, and Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
Email: grao[at]umbc.edu

Why is this useful?

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The use of HPLC fittings and tubing in microfluidics is becoming more commonplace as the use of microfluidics in the sciences increases. Even though acrylic or PMMA is one of the most common plastic substrates used in microfluidics, the ability to strongly and easily connect an HPLC fitting to a PMMA chip has until now been elusive. Although there are some commercially available HPLC-to-chip products from Idex, they require heating the microfluidic chip well above the glass transition temperature of PMMA to create a permanent epoxy bond between attachment and chip. For these reasons, we present a simple scheme to strongly connect a standard HPLC flat bottom nut to a PMMA microfluidic device through the creation and bonding of an easy-to-make ¼-28 PMMA microfluidic union, using common lab equipment.

What do I need?

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• Laser cutter or another implement to cut PMMA, such as a hacksaw or band saw
• An appropriate piece of equipment to anneal the PMMA (we use a convection toaster oven)
• 5.3mm thick acrylic sheet for the body of the PMMA microfluidic union
• A drill and drill bits
• Vise grips, or another way to hold the PMMA union in place while tapping
• A ¼-28 tap
• A few sheets of progressively finer sandpaper
• A 50-50% mixture of ethanol and water, along with an ultrasonic cleaner and lint-free wipes for cleaning purposes
• A strong solvent for acrylic, such as chloroform or methylene chloride
• A glass syringe with a blunt needle or needle blunted through filing

This connection scheme has been tested with good results when using the LT-115 and P-259 ¼-28 flat bottom HPLC nut and ferrule combination for 1/16″ OD tubing (Idex). This method was tested on microfluidic devices that were not bonded with the use of adhesives. This method is adaptable to other flat bottomed nuts as long as an appropriate tap and drill bit are used. Keep in mind that as the wall thickness of the PMMA union decreases, so does the strength of the connection between the HPLC nut and the device.

What do I do?

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1. Use a laser cutter to cut a circle with a diameter of 13mm out of the 5.3mm thick acrylic sheet. Make sure that you also either etch a center mark or make a small center hole using the laser cutter. If a laser cutter is not available, make a 13mm PMMA square using one of the other mentioned cutting implements. (Fig.1)
2. Using a small drill bit, drill a pilot hole for the larger drill bit to follow in the center of the circle that you cut out in Step 1.
3. Using the larger drill bit (a #3 or 0.213″ drill bit for the ¼-28 tap), drill the center hole in the cutout piece following the pilot hole drilled in Step 2.
4. Using the ¼-28 tap and appropriate technique, tap the hole you have been creating in Steps 1-3. Do not use oil to lubricate the plastic as it is unnecessary and difficult to clean.
5. After removing the plastic chips from the threads you just created, use progressively finer sandpaper to lap the surface that will make contact with your microfluidic device. Lapping the surface will ensure a very strong bond between the union and your device. We lap using a figure of eight motion to help guarantee a flat bonding surface. (Fig. 2)
6. Anneal both your created microfluidic union and your device in an appropriate fashion. Annealing will relieve the thermal stress present in the union due to laser cutting and the drilling/tapping steps. (We use a convection toaster oven, set at 85ºC for 90 minutes, 50ºC for 30 minutes and then off with the oven door closed for 30 minutes. We find it useful to put a smooth metal plate below and above the piece to be annealed, to prevent uneven heating in the oven.)
7. Thoroughly clean both the union and the microfluidic device to be bonded using a 50-50% mixture of ethanol and water. Clean only the union in an ultrasonic cleaner for 10 minutes. This mixture will not cause the union or the device to crack if they are both appropriately annealed beforehand and if the cleaning is performed within a few days of annealing.
8. Place the union, lapped side down, onto the microfluidic device’s surface where the connection is desired. It is essential to center the union over the hole which receives the fluid or gas from the HPLC tubing. We use a small jig composed of two different sized plastic dowels to help us in this step (the black object in the bottom right corner of Fig.3).
9. Pull some solvent into the glass syringe.While holding the union in place using your jig, gently drip some solvent from the glass syringe at the interface between the union and your microfluidic device (start with a single drop). The solvent will creep into the joint between the union you created and your microfluidic device due to capillary action. Add enough solvent to fill the gap between the union and your device, but be careful not to get any solvent into the fluid passages within your device.
10. Being careful not to disturb the union’s position, gently apply pressure on the union until the surfaces become lightly bonded using your gloved fingers (Fig. 3). Light bond is usually achieved in less than a minute. In this step, also attempt to add enough pressure to force out any bubbles at the interface.
11. Remove the alignment jig and add more solvent around the interface between the union and your device. This step reinforces the union’s connection to the microfluidic device.
12. Put a small mass directly on top of the union, and leave the bonding union overnight to achieve the strongest connection between the union and your device.
13. After the piece has dried overnight, remove the mass and then use the connection as you would any other flat bottom HPLC union. (Figure 4)

Notes

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The following YouTube video ‘Power Tools & Carpentry Skills : How to Use a Tap & Die Set’ by Expert Village helps explain the use of taps (Step 4): http://www.youtube.com/watch?v=6DDhw191MLo

Acknowledgements

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The authors would like to acknowledge the work of Dr. Yordan Kostov, Mike Tolosa and Mike Frizzell.

Boyang Zhang¹, Milica Radisic¹, Shashi Murthy^2
1Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON, Canada
²Department of Chemical Engineering, Northeastern University, Boston, MA, USA

Background

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The operation of microfluidic systems often requires sequential injection of more than one type of solution with a syringe pump. For instance, many adhesion-based cell-separation devices require additional injection of washing buffer or/and cell-releasing buffer after cell injection [1, 2]. Minimal flow disturbance to the system during switching to the next solution is critical for proper operation of such devices. Switching syringes during pumping will inevitably stop the flow and risk introducing bubbles to the device. Simple four-way valves are traditionally used in such cases [3]. However, many commercially available four-way valves have large dead volumes and long residence times that make them incompatible with microfluidic systems.

Why is this useful?

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Here we present a simple, three-chamber microfluidic system with interconnected tubings (Figure 1) as an alternative to the traditional 4-way valve used for switching between solutions during experiments. For microfluidics applications, our system has the advantages of (1) allowing for switching between two solutions with minimal disturbance to the flow, (2) greatly reduced risk of introduction of unwanted air bubbles into the system, and (3) greatly reduced dead volume. The total volume of our system is two orders of magnitude less than a typical, commercially available 4-way valve (~1 µL as compared to ~1 mL) [5]. Our valve system is simple and cost-effective, as it utilizes clamps (binder clips) to block selected tubings. We have also shown that the tubings are strong enough to withstand several iterations of clamping and release. Lastly, this method can be scaled up to control the flow of more than two types of solutions, simply by adding more chambers and clamps.

What do I need?

• Clamps (Binder Clips)
• Tygon tubing (any size)
• PDMS silicone elastomer base and curing agent (Sylgard 184, Dow Corning)
• Glass slides, pre-cleaned (Fisher Scientific, 75mm x 50mm x 1mm, Cat. No. 12-550-C)
• Scotch tape (3M Scotch® Transparent Tape 600)

What do I do?

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(1)  Fabricate the master for the device. The device includes three triangular shaped chambers. The exact dimensions of these chambers are not critical and should be tailored to the specific experiment. In this case, triangular shaped channel with height of 40 μm and edge-width of 3 mm is used for flow rate up to 80 μl/min. The master can be fabricated with scotch tape which would greatly speed up the fabrication step especially for design with only large features [4].

(1)  Pour PDMS over the master and cure to create a PDMS-based device.

(2)  Drill holes as indicated in Figure 1 and bond the device to a glass slide.

(3)  Insert the tubing into the holes, again following Figure 1.

(4)  Fill the device with selected solution and clamp shut the selected tubing.

(5)  To switch solutions during an experiment, simply switch the position of the clamps as shown in Figure 1.

Figure 1. Device schematic: (A) Microfluidic 4 way valve with color dyes to demonstrate the function of the clamps to stop and re-route flows. (B) Schematic of the device in operation. (C) Traditional concept of 4 way valves.

References

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1. B. D. Plouffe, M. A. Brown, R. K. Iyer, M. Radisic and S. K. Murthy, Controlled capture and release of cardiac fibroblasts using peptide-functionalized alginate gels in microfluidic channels, Lab Chip, 2009, 9, 1507-10.
2. B. D. Plouffe, M. Radisic and S. K. Murthy, Microfluidic depletion of endothelial cells, smooth muscle cells, and fibroblasts from heterogeneous suspensions, Lab Chip, 2008, 8, 462-72.
3. L. Kim, M. D. Vahey, H.-Y. Lee and J. Voldman, Microfluidic arrays for logarithmically perfused embryonic stem cell culture, Lab Chip, 2006, 6, 394-406.
4.  A. B. Shrirao and R. Perez-Castillejos, Simple Fabrication of Microfluidic Devices by Replicating Scotch-tape Masters, Chips & Tips (Lab on a Chip), 17 May 2010.
5. 4 WAY ACTUATION VALVES, Parker Hannifin Corp, 04 October 2011.

Sopan M. Phapal, Tuhina Vijay and P. Sunthar
Chemical Engineering Department, Indian Institute of Technology Bombay, Powai-400 076, India.

Why is this useful?

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There are several ways to connect macro to micro interfaces (e.g., from syringe pump to microfluidic chip) in the miniaturization field. The ideal connector should withstand very high pressure and not leak. Commercially available Nanoports are often used as connectors but they are expensive, sometimes become clogged when glue is used, and cannot be reused. In this tip we present an easy and inexpensive way to produce a macro to micro interface connector which can withstand high pressure and is glue free.

What do I need?

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•    2.5 ml plastic BD syringe with Luer-Lok (Luer tip ID at back 2.33 mm/0.095”; front ID 1.75 mm/0.07”)
•    16G SS needles (OD= 1.65  mm/0.065”)
•    Grinder with hard abrasive disk to cut/ blunt the needles
•    16G PTFE tubing, Hamilton, Cat No.20916 ; OD=1.9 mm/0.075”; ID=1.2 mm/0.047”[1]
•    Surgical knife/cutter to cut the Luer part of the syringe
•    Glue (Araldite).

A syringe contains a male Luer part and the needle head is its counter female Luer part. There are two types of Luer fittings, one Luer-slip which when pressed together, fits in each other by friction; and the other is Luer-Lok which has threads in the male part and the female part (needle head) screws in to it (Figure 1). We used both Luer-slip and Luer-Lok syringe tips, but the Luer-Lok is better for high pressure application.

What do I do?

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1. Make the needles blunt with the help of grinder (Fig. 2A & B). Cut the Luer-Lok tip of the plastic syringe with a sharp blade/cutter (Fig. 2C).

2. Prepare the male Luer part. Insert the PTFE tube (OD= 1.9mm) into Luer-Lok tip (back ID= 2.3 mm and front ID is 1.75 mm) as shown in Fig. 3A. Now heat the 16G SS blunt needle and insert it into the PTFE tube up to some mm and remove it (Fig. 3B). Because of this, the tip of the tube becomes wider than Luer-Lok ID, fitting tight mechanically. Pull the Luer-Lok up to the wide tip of PTFE tube and place a drop of araldite at the back side of it (Fig. 3C). This will cause a tight fit of the Luer-Lok tip with the PTFE tube.

3. Preparation of the female Luer part. Heat the 16G SS blunt needle (OD= 1.65 mm) and insert it into 16G PTFE tube (ID=1.2mm), as shown in Fig. 4. As the needle OD is bigger than tube ID, it will permanently fit into the PTFE tube upon cooling.

4. Examples of connecting the male Luer part of tubing into a needle head (female Luer part) which is acting as an inlet of micro channel assembly (Fig. 5). Example of the use of macro to micro interface tubing to connect a syringe to a microchip: screw fit the needle head (female Luer) into the male Luer part on the syringe placed on syringe pump and the male Luer-Lok part will screw fit into the inlet needle (counter fitting female part) of microfluidic chip (Fig. 6).

References

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[1]. http://www.hamiltoncompany.com

Acknowledgements

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We would like to acknowledge a grant provided by the Department of Science and Technology, Government of India (07-DS-032).

Myra T. Koesdjojo*, Jintana Nammoonnoy, and Vincent T. Remcho

Department of Chemistry, Oregon State University, Corvallis, OR 97331
*Corresponding author: Myra T. Koesdjojo
Fax: (541) 737-2062
Email: koesdjom[at]onid.orst.edu

Why is this useful?

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Microfluidic systems, also referred to lab-on-a-chip or micro total analysis systems (μTAS) have been developing at a rapid pace in the last decade and offers promising analytical tools that may transform routine chemical analysis in the future. Microfluidic devices typically require multiple interconnects.¹ Consequently, reliable microfluidic interconnections have become one of the basic necessities in integrated fluidic and on-chip systems. The lack of an efficient interface or interconnect between microfluidic devices and the macroscale world has historically been a major challenge and one of the greatest limiters on acceptability and the application of μTAS into the broad world market. Clearly, there is a need for a low-cost, flexible interconnects for microfluidic devices to be successful in the long term.² There are a variety of current products available and techniques that have been used to provide interfacing between microchannels to external devices.^3-6 The most common and simplest approach is the direct integration of tubing or a syringe needle into the microchip inlet using epoxy glue. The drawback is it often leads to clogging of the microchannels and these types of interconnections are impractical to remove and are not reusable. This tip presents a simple method to making reusable quick release magnetic-based fluidic connectors. It is an alternative approach that provides a simple, cost effective universal interconnects in the microfluidic applications. The magnetic-based connectors was developed using two permanent magnets that form a compression seal against the tubing line and the surface of the microfluidic device. The magnetic connector also allow for standard tubing to be interfaced with the microchips. With this approach, interconnects can be easily assembled and reconfigured numerous times without causing damage to the microfluidic device. And since connection is established though a magnetic based approach, clogging of microchannels from adhesive or epoxy can be avoided.

What do I need?

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• Permanent magnets (design and dimension shown in Figure 2)
• Magnetic base
• Elastic such as PDMS compression seals or vacuum cup
• PEEK or Teflon tubing (not limited to the materials of the tubing)

What do I do?

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1. Custom made permanent magnet shown in Figure 2. The first component was a permanent magnet that allowed for a standard tubing to be attached to a microfluidic device via a flexible compression seal. It was manufactured with the dimensions shown below to provide a tight fitting to the flexible seal when sandwiched between two magnets, which in turns compressing the tubing inside. The magnets are Neodymium magnets which are over ten times stronger than the ceramic magnets. These magnets are ideal for use as interconnects since they provide much greater holding forces. They can be purchased from Indigo Instruments or K&J Magnetics.

2. Rubber cup compression seals The second component was a flexible rubber cup or compression seals. The dimension should be optimized so that the inner diameter of the seal should provide a tight fitting for a tubing (a in Figure 3b) and the outer diameter (b) is slightly larger than the magnets core so when it is sandwiched in between the two magnets, the tubing is tightly held. The last parameter is the diameter of the lip base (c), which should be larger than the magnet’s core so it can be compressed to the magnetic base and tightly secured against the microchip surface to prevent leaking. A variety selection of compression seal (vacuum cup) with different sizes can be purchased from McMaster-Carr.

3. A magnetic base was used which applied pressure between the microfluidic chip and the interconnects (Figure 4). The base is particularly useful for microchip and devices having different dimensions and port locations, as the interconnects could easily be relocated.

4. The magnetic interconnects were placed on each of the reservoir holes of the microchip to test for leaking.

References

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[1] T. Das, D. Chakraborty and S. Chakraborty, Interfacing of microfluidic devices, Chips & Tips (Lab on a Chip), 27 February 2009.
[2] IEEE Trans. On Adv. Packaging., 2003, 26 (3), 242-247.
[3] J. Greener, W. Li, D. Voicu and E. Kumacheva, Reusable, robust NanoPort connections to PDMS chips, Chips & Tips (Lab on a Chip), 8 October 2008.
[4] http://www.upchurch.com/
[5] www.labsmith.com/microfluidicsinterconnects.html
[6] J. Micromech. Microeng., 2005, 15, 928-934.

Lorenzo Capretto¹, Stefania Mazzitelli², Stefano Focaroli² and Claudio Nastruzzi^2
1 School of Engineering Sciences, University of Southampton, UK
² Department of Chemistry and Technology of Drugs, University of Perugia, Perugia, Italy

Why is this useful?

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Common ways to link microdevices with standard fluidic equipments (such as syringe or peristaltic pumps) are based on the use of nanoports, created by: hand screwing a tube in the substrate material, gluing the tube fitting directly on the microfluidic device or commercial nanoports.
However, when such types of connection are used, there might be a series of potential issues, including: possible leakage of liquid from the connections, especially when high pressure inlet are required, possible clog of the port when glue is used or the high cost of the commercial devices.
Here, we demonstrate an easy and effective way for the creation of cheap and tight microfluidic connection ports for a varied range of substrate material including glass, silicon and polymers. Our approach solves the issues reported above with the creation of and inexpensive, well tight and glue-free port based on a “wall plug inspired” effect.

What do I need?

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• Plastic tube (ETEF, FEP or PTFE) 1/16″ OD, 0.75 mm ID [1]

• 21 gauge hypodermic needle [2]

• Drilling bit 1.5 mm [3]

• A Proxxon, table top, micro miller [3] or any other handheld power tool

• A cutting disc made of a hard abrasive [3] or any other tool for cutting the needle

Fig. 1.  Tubing used for the production of “wall plug inspired” connectors for macro to microfluidic interfacing: FEP (fluorinated ethylene-propylene) tube (A) and hypodermic needle with Luer-Lock (21 gauge) (B).

Fig. 2. Stereo photomicrographs of the FEP tube (A), the hypodermic needle (B), the hypodermic needle inserted into the FEP tube (C) and the bit used for drilling the microfluidic chips (D). Note the different (crucial) sizes as determined by photomicrograph analysis. External diameter of the FEP tube: 1.58 mm (red arrow); internal diameter of the FEP tube: 0.76 mm (magenta arrow); external diameter of the 21 gauge needle: 0.82 mm (yellow arrow); external diameter of the FEP tube after insertion of the hypodermic needle: 1.66 mm and finally, diameter of the bit used for drilling the microchips: 1.5 mm (white arrow).

What do I do?

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1. First drill the hole on the microfluidic device you wish to connect.

Fig. 3. Drilling process on different materials, namely: commercial TOPAS® COC (A) and custom made poly(methyl methacrylate) (PMMA) (B) or epoxy resin (C) chips.

2. Cut the needle and pre-insert it in the plastic tube.

Fig. 4.  Assembly of the”wall plug inspired” connectors. Cutting (A), sanding (B) and insertion (C) of the needle into the FEP tube.

3. Assemble the port and tighten it in the previously drilled hole by inserting the needle in the tube. The needle must be inserted deeper than the interface between tube and hole in order to leverage the wall plug effect.

Fig. 5.  Insertion of the finished “spit inspired nanoport” into different chip type, namely: commercial TOPAS® COC (A) and custom made epoxy resin (B) or polydimethylsiloxane (PDMS) (C) chips

Fig. 6. Schematic representation of the assembling of “wall plug inspired” microfluidic ports.

References

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[1] http://www.upchurch.com
[2] http://www.artsana.com
[3] http://www.proxxon.com

Gregory A Cooksey¹ and Glynis Mattheisen²

¹ Biochemical Science Division, National Institute of Standards and Technology, Gaithersburg, MD
² Louisiana State University, Baton Rouge, LA

Why is this useful?

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Luer adapters are convenient tools to rapidly and reversibly connect tubing from fluid reservoirs to microfluidic devices. One problem associated with the use of these adapters is that they trap considerable dead volume (approx 100 µl), which dramatically increases the time required to rinse away one fluid when another fluid is to be delivered down the same line. Another common shortcoming of leur adapters is that they are only available for 1.59 mm (1/16″) and larger inner diameter (ID) tubing. We demonstrate how to modify luer adapters to fit almost any size tubing while dramatically reducing the dead fluid volume trapped inside the connector.

What do I need?

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• 25 mm or longer needle or stainless steel tubing.  We use blunt 25 gauge needles (McMasterCarr # 75165A761). Use extreme care with exposed needles!
• Polypropylene 1/16 in. barbed male luer adapter (Cole Parmer #R-45503-07)

• Silicone tubing with large enough ID to slip over needle but small enough outer diameter (OD) to fit inside luer adapter.  We use 0.8 mm ID silicone tubing (Cole Parmer #R-06411-60)
• Poly(dimethylsiloxane) (PDMS) (Sylgard 184, Dow Corning)
• Tubing to attach to the connectors.  We use 0.51 mm ID tygon microbore tubing for 25 gauge needles (Cole Parmer #R-06418-02)
• Dremel 300 (Dremel) or similar tool with cutoff wheel (Dremel #409)

How do I do it?

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1. Insert the needle into the barbed end of the 1/16 in. barbed male luer adapter.
2. Thread about 15 mm of silicone tubing onto the needle and push the tubing to the base of the adapter using tweezers.  This keeps the needle centered in the adapter, and the silicone tubing bonds well to the PDMS.  The tubing should stick out of the adapter about 3mm, which accounts for extra dead space that exists in needle hubs and other female luer adapters.
3. Place the hubs of the needles you’ve made onto a dish standing upright.  Double-sided tape on the bottom of the dish will help keep the needles upright.
4. Fill the inside of the luer adapters with PDMS.  We find it helpful to use a syringe (with an 18 G needle) to inject PDMS into the adapters.  At this point it is recommended to de-gas the PDMS by placing it in a vacuum jar for several minutes.
5. Place the dish in an oven at 70ºC to cure for at least 2 hours.  Check after about an hour to make sure the luer hubs stayed filled with PDMS.  You may have to add some additional PDMS if some has leaked out the barbed end.
6. Remove the needle from the dish and clear away excess PDMS from the base of the needle and the outside of the adapter.
7. Push the adapter to the tip of the needle.
8. Cut away the needle luer hub.  A wire cutter can be used, but we prefer using a Dremel tool fitted with a cutting wheel.  It is less likely to compress the tubing closed.  Polishing the end of the needle with the cutting wheel is also recommended.
9. Insert the needle extending from the barbed end of the adapter into 0.51 mm ID Tygon tubing.

What else should I know?

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“Quick connects” for the same or different ID tubing can be made by plugging the connector into the luer hub of a blunt needle that fits tightly inside the desired tubing.

We have also tried filling the luer hubs with PDMS and curing them prior to inserting needles or stainless steel tubing.  Because the needles are flexible, we find it difficult to keep the needles straight through the center of PDMS core.  This method also typically plugs the needle, so a new needle would be necessary to replace the coring needle.

Disclaimer: Certain commercial equipment, instruments or materials are identified in this report to specify adequately the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.