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Method Article
Design and fabrication of a three-dimensionally (3-D) printed microfluidic cross-flow filtration system is demonstrated. The system is used to test performance and observe fouling of ultrafiltration and nanofiltration (thin film composite) membranes.
Minimization and management of membrane fouling is a formidable challenge in diverse industrial processes and other practices that utilize membrane technology. Understanding the fouling process could lead to optimization and higher efficiency of membrane based filtration. Here we show the design and fabrication of an automated three-dimensionally (3-D) printed microfluidic cross-flow filtration system that can test up to 4 membranes in parallel. The microfluidic cells were printed using multi-material photopolymer 3-D printing technology, which used a transparent hard polymer for the microfluidic cell body and incorporated a thin rubber-like polymer layer, which prevents leakages during operation. The performance of ultrafiltration (UF), and nanofiltration (NF) membranes were tested and membrane fouling could be observed with a model foulant bovine serum albumin (BSA). Feed solutions containing BSA showed flux decline of the membrane. This protocol may be extended to measure fouling or biofouling with many other organic, inorganic or microbial containing solutions. The microfluidic design is especially advantageous for testing materials that are costly or only available in small quantities, for example polysaccharides, proteins, or lipids due to the small surface area of the membrane being tested. This modular system may also be easily expanded for high throughput testing of membranes.
Membrane technology is integral to industrial and other processes requiring the separation of solutes from a bulk solution, however, membrane fouling is a major ongoing challenge.1 Common examples where membrane fouling occurs include the use of ultrafiltration membranes for the size based separation of wastewater,2 and thin film composite membranes for the separation of ions and larger solutes from brackish or seawater.3 Characteristic indications of fouling include an increase in transmembrane pressure and a decline in flux. This decreases the productivity of the membrane and shortens its lifetime due to chemical or other cleaning protocols. Therefore membrane performance is a good indicator to assess fouling and to understand the mechanisms and effects of fouling, biofouling and biofilm formation on membranes. Also, performance assessment is important in the design or modification of new membranes.
Interest in the use of membranes in microfluidic devices has been growing over the last decade.4 Recently, we studied the effect of microbial components lipopolysaccharide, and glycosphingolipid on fouling the surface of a nanofiltration membrane, and the subsequent susceptibility of the conditioned surface to microbial attachment.5 A microfluidic cross-flow device was used to assess the performance of nanofiltration membranes. This allowed the use of special non-commercial lipid components only available in small quantities for membrane surface fouling because the membrane surface area was small. The system size allowed efficient use of membrane materials and low volumes of solutions. In this protocol, we describe the design and fabrication of the microfluidic device for membrane performance testing, and outline the incorporation of the device into a pressure flow system. Demonstration of the device is shown by testing the performance of ultrafiltration membranes and nanofiltration membranes using a model foulant, BSA.6,7
1. Design and Fabrication of the Microfluidic Test System
2. Prepare Membranes to Be Tested
3. Prepare Solutions to Be Tested with Nanofiltration Membranes
4. Perform a Nanofiltration Fouling Experiment
Note: Perform the experiment at RT (ca. 24 °C). First configure the system for measuring a single membrane by closing valves to flow cells not connected to the flow-meter.
5. Calculate Salt Rejection of Nanofiltration Membranes
6. Prepare Solution to Be Tested with Ultrafiltration Membranes
7. Perform an Ultrafiltration Fouling Experiment
Note: Perform an experiment at RT (ca. 24 °C). First configure the system to measure 4 membranes in parallel by opening all valves to flow cells.
The microfluidic flow cells were designed using a CAD program and printed using a multi-material photopolymer three-dimensional (3-D) printer. This cell was designed in two parts, so that membranes could be easily inserted and removed from the device (Figure 1). Each part was 1 cm thick, printed from a hard, clear polymer for structural integrity, and the sides facing the membrane were overcoated with a very thin 50 µm layer of rubber-like polymer. The overcoating was performed to provide the cell w...
This protocol describes the design of a three-dimensionally printed microfluidic cross-flow device for testing of nanofiltration and ultrafiltration membranes. Recently, we have shown the success of a variation of this protocol with nanofiltration membrane conditioning and fouling with glycosphingolipids and lipopolysaccharides and membrane performance differences with subsequent bacterial culture injection.5 Future applications employing this technique could be used to evaluate membrane performance changes wi...
The authors have nothing to disclose.
The authors thank Stratasys (Rehovot, Israel) for three-dimensional printing of the device. We are grateful to Microdyne-Nadir (Germany) for the membrane samples. This research was supported by The Israel Science Foundation (Grant 1474-13) to C.J.A.
Name | Company | Catalog Number | Comments |
BSA | SIGMA-ALDRICH | A6003 | |
NaCl | DAEJUNG | 7548-4100 | |
MgSO4 | EMSURE | 1058861000 | |
NF Membrane | Filmtec | NF200 | |
30 kDa UF Membrane | MICRODYN NADIR | UH030 | |
50 kDa UF Membrane | MICRODYN NADIR | UH050 | |
Pressure Transducer | Midas | 43006711 | |
Ball Valves | AV-RF | Q91SA-PN6.4 | |
3-way Valve | iLife Medical Devices | 902.071 | |
Pressure Regulator | Swagelok | KCB1G0A2A5P20000 | |
Flow-meter | Bronkhorst | L01-AGD-99-0-70S | |
Balances | MRC | BBA-1200 | |
Pump | Cole-Parmer | EW-00354-JI | |
1/8" Tubing | Cole-Parmer | EW-06605-27 | |
1/16" Tubing | Cole-Parmer | EW-06407-41 | |
1/16" Fittings | Cole-Parmer | EW-30486-70 | |
1/8" Fittings | Kiowa | QSM-B-M5-3-20 | |
Microcontroller | Adafruit | 50 | Arduino UNO R3 |
Continuous Rotation Servo | Adafruit | 154 | |
Standard Servo | Adafruit | 1142 | |
Power Supply | Adafruit | 658 | |
Servo Shield | SainSmart | 20-011-905 | |
Switches | Parts Express | 060-376 | |
0.45 Micron Filters | EMD Millipore | SLHV033RS | |
Potentiostat | Gamry | PCI4 | |
Sonicator | MRC | DC-150H | |
Connex 3D Printer | Stratasys | Objet Connex | |
Veroclear | Stratasys | RGD810 | transparent polymer for printing flow cell |
Tangoblack-plus | Stratasys | FLX980 | soft rubbery polymer for gasket layers on flow cell |
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