Three-Dimensionally Printed Microfluidic Cross-flow System for Ultrafiltration/Nanofiltration Membrane Performance Testing

Summary

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.

Abstract

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. 

Introduction

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 othe....

Protocol

1. Design and Fabrication of the Microfluidic Test System

1. Design microfluidic device as two separate parts: a top part and bottom part (Figure 1) in a CAD program.
2. Start making the bottom part by using the rectangle tool to draw a 40 mm by 60 mm rectangle.
3. At one corner with the circle tool create a 6.2 mm diameter circle centered 10 mm from edges. With the linear pattern tool replicate the holes across the rectangle with 20 mm spacing for a total of 6 holes.
4. Using the fillet tool fillet the rectangles with a radius of 1 mm.
5. Extrude the part 10 mm with the extrude tool.
6. In the center of the....

Results

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 with a.......

Discussion

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.......

Materials

List of materials used in this article

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