Design and Fabrication of Concentration-
Gradient Generators with Two and Three
Inlets in Microfluidic Chips
A simple and low-cost method for designing and fabricating concentration-
gradient generators with two and three inlets is proposed which can generate dif-
ferent concentration gradients at varying flow velocities. The microchannel struc-
ture was designed in S-shape and left-right symmetry. The concentration-gradient
generator was simulated based on the finite element method. The microchannels
were processed on a computer numerical control (CNC) engraving and milling
machine on poly(methylmethacrylate) substrate, and then two concentration-
gradient generators were fabricated by hot bonding technology. The results of
experiment and simulation were compared to prove the feasibility of the method.
Flow velocity was an important factor for generating different concentration gra-
dients. The concentration-gradient profiles of the generators with two and three
inlets present approximately linear and quadratic curves.
Keywords: Concentration-gradient generator, Finite element method, Flow velocity
Received: May 25, 2017; revised: June 29, 2017; accepted: November 13, 2017
In recent years, microfluidic chips have been widely used in
biochemical engineering fields having a huge potential as an
emerging technology. Hansen et al. analyzed the microfluidic
devices and methods facilitating growth and analysis of crystal-
lized materials such as proteins . Liu et al. demonstrated a
robust and reliable approach to fabricate multicompartment
particles for cell co-culture studies . Chen et al. reported on
a novel continuous-flow polymerase chain reaction chip .
Huang et al. successfully synthesized nanoporous materials
with organic frameworks in the microchannel through solvo-
thermal polymerization of divinylbenzene and methacrylic acid
in the presence of tetrahydrofuran .
In research systems of microfluidic chips, the concentration-
gradient generator is one of the most important parts. This
generator can create a concentration gradient at the outlet of
microchannels with different samples, thus demonstrating the
trend study of cells and molecules in biochemical engineering.
Saddi et al. studied the neutrophil trends in concentration gra-
dient of interleukin-8 . Takayama et al. successfully
researched the cells using the classic Y-microfluidic network
. Many scientists obtained various concentration gradients
in differently shaped microchannels, such as comet shape 
and nonlinear shape . Dertinger et al. designed a classic
‘‘Christmas-tree’’ microfluidic network for studying the con-
centration gradient generator .
Xu et al. revealed the possible factors that cause significant
errors in the gradients generated by a conventional universal
microfluidic-gradient generator with numerically simulating
the flow behavior . Orsi et al. developed a new 3D concen-
tration gradient maker able to generate 3D concentration gra-
dients of soluble species which could be used for differential
perfusion of scaffolds. The same device can be applied to build
hydrogel matrixes with a 3D gradient of mechanical properties
The COMSOL Multiphysics software has been used for
design and forecast of a numerical simulation of concentra-
tion-gradient generators . In addition, many researchers
have made a series of concentration-gradient generators on dif-
ferent materials. The feasibility of using micromachining tech-
niques to fabricate microchannels on single quartz, glass, or
poly(methylmethacrylate) (PMMA), poly(dimethylsiloxane)
(PDMS) substrates was studied. By comparison, PMMA is the
easiest to process in all materials . The effective control of
partially mixed samples is critical in the design of a concentra-
tion gradient generator. In recent years, we have carried out a
series of studies on design , simulation [15, 16], optimiza-
tion [17, 18], and fabrication  of micromixers.
This work introduces a highly efficient and low-cost method
for designing and fabricating the microfluidic chips which gen-
Chem. Eng. Technol. 2018, 41, No. 3, 489–495 ª 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com
Zengliang Hu, Dr. Xueye Chen
Liaoning University of Technology, Faculty of Mechanical Engineer-
ing and Automation, Shiying Street, 121001 Jinzhou, China.
Dalian University of Technology, School of Mechanical Engineering,
Linggong Road, 116024 Dalian, China.