Well construction of poly methyl methacrylate pmma based microfuidic device using carbon dioxide laser processing

Bachelor’s thesis

THAI NGUYEN UNIVERSITY
UNIVERSITY OF AGRICULTURE AND FORESTRY

DO XUAN BANG

TOPIC TITLE:

WELL CONSTRUCTION OF POLY (METHYL METHACRYLATE)
(PMMA) - BASED MICROFUIDIC DEVICE
USING CARBON DIOXIDE LASER PROCESSING

BACHELOR THESIS
Study Mode : Full-time
Major

: Environmental Science and Management.

Faculty

: Internatinonal Training and Development Center

Batch

: 2010-2015

Thai Nguyen, 23/01/ 2015


Bachelor’s thesis

THAI NGUYEN UNIVERSITY
UNIVERSITY OF AGRICULTURE AND FORESTRY

DO XUAN BANG
TOPIC TITLE:

WELL CONSTRUCTION OF POLY (METHYL METHACRYLATE)
(PMMA) - BASED MICROFUIDIC DEVICE USING CARBON DIOXIDE
LASER PROCESSING

BACHELOR THESIS
Study Mode : Full-time
Major

: Environmental Science and Management.

Faculty

: Internatinonal Training and Development Center

Batch

: 2010-2015

Superviors : Prof. Yuh-Chang Sun
MSc. Nguyen Huu Tho
Thai Nguyen, 23/01/2015

Bachelor’s thesis

DOCUMENTATION PAGE WITH ABSTRACT
Thai Nguyen University of Agriculture and Forestry

Degree Program

Bachelor of Environmental Science and Management

Student name

Do Xuan Bang

Atudent ID

DTN1053180011

Thesis Title

Well construction of Poly (Methyl methacrylate) (PMMA) –
based microfluidic device using carbon dioxide laser
processing

Supervisors

Prof. Yuh-Chang Sun
MSc. Nguyen Huu Tho
ABSTRACT

This study introduce about the topic: Well construction of Poly (Methyl

methacrylate) (PMMA) - Based microfluidic device using Carbon dioxide laser processing.
The study described a methodology of using a model of CO2 laser system to ablation in
PMMA based on the effects of laser power and processing speed on the depth and width of
microchannels manufactured from poly methyl methacrylate (PMMA).
Our result was like expectation, the study using high-resolution optical
microscope to inspect the microchip and then they showed and capture image of
microchops clearly to the desktop of computer. It is observed that the channel depth
varies linearly with an increase in laser power at a particular speed. For a prescribed
laser power, the channel depth decreased with an increase in laser speed for all the
grades of PMMA. The channel width increased with an increase in laser power but
decreased with an increase in speed. This results shows about what CO2laser can be
using for well construction of PMMA and the depth, width and aspect ratio of the
microchannels depend on the laser power and cutting speed and the profile of the
microchannels can be easily controlled by CO2 laser system.

Number of page

38

Date of submission

23/01/2015

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Bachelor’s thesis

ACKNOWLEDGEMENTS
To accomplish this thesis, I would like to say thank to my University: Thai

Nguyen University of Agriculture and Forestry, the Faculty of Environmental Science
and Management, the teachers in schools have to pass on to me the knowledge during
the time I study there.
I deeply thank to my Supervior Prof Yuh- Chang Sun at Department of
Biomedical Engineering and Environmental Science, Tsinghua University, Taiwan
who helped me, guided and accepted me to do this thesis. Who really friendly and
always care for his students. Without his support, I would like to say thanks to Assoc.
MSc Nguyen Huu Tho for his enthusiasm in guiding and correcting my report writing.
I would like to thank to my lab mates, Ph.D leader Shih Tsung-Ting and others
were enthusiastic to help me. Although I still do not remember your real name until
now, as well as the limitations of our language. All of you guys have shown me the
friendliness and culture of your country. And trying to teach the most basic one by
one. I felt really comfortable and with the help of you. Thank you so much.
Next one, from the depth of my heart, I would love to say thank for my parents
who always encourage me during the time I do my thesis.
During the internship I was trying my best to complete the requirements of The
internships, but by experience and knowledge is limited, my thesis inevitable
shortcomings and defects. I look forward to the teachers and students to contribute
additional ideas for my thesis to be excellent.

Thank you very much!
Thai Nguyen, Jan 15th 2015
Signature of Student

Do Xuan Bang
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Bachelor’s thesis

TABLE OF CONTENTS
PART I. INTRODUCTION ...................................................................................... 6
1.1. Research rationale ........................................................................................ 6
1.2. Research’s objectives ................................................................................... 6
1.3. Research questions and hypothesis ............................................................... 6
1.4. Limitations ................................................................................................... 7
1.5. Definitions .................................................................................................... 7
PART II. LITERATURE REVIEW ......................................................................... 8
2.1. Fabrication of microfluidic device ................................................................ 8
2.1.1. Microfluidic device .................................................................................. 8
2.1.2. Microfluidic chip ....................................................................................... 9
2.2. Birth of Microfluidics: a bit of History ......................................................... 9
2.3. Application of microfluidic device ............................................................. 12
2.3.1. The Microfluidic technology has found many applications mainly .......... 12
2.3.2. Pros and cons about microfluidic device compared with traditional ways.
.......................................................................................................................... 13
2.4. The common materials for microfluidic chip fabrication ......................... 13
2.4.1. Inorganic Materials .................................................................................. 14
2.4.2. Elastomers and Plastics............................................................................ 15
2.4.3. Elastomers ............................................................................................... 16
2.4.4. Thermosets. ............................................................................................. 16
2.4.5. Thermoplastics ........................................................................................ 18
2.4.6. Hydrogels ................................................................................................ 18

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Bachelor’s thesis
2.4.7. Paper ....................................................................................................... 19
2.5. Mechanism of CO2 laser processing in PMMA........................................... 21

2.6. Experiment design and setup ...................................................................... 22
2.6.1. CO2laser system ...................................................................................... 22
2.6.2. Experimental determination of threshold fluence ..................................... 23
2.6.3. PMMA channel depth .............................................................................. 24
2.6.4. PMMA channel profile ............................................................................ 25
2.6.5. Channel micromachining ......................................................................... 26
PART III. METHODS ............................................................................................ 27
3.1. Reagent and Materials ............................................................................... 27
3.2. Apparatus and Instrumentation ................................................................... 27
3.3. Methods ..................................................................................................... 27
3.3.1. Draw microchannels on software for PMMA using AutoCAD ................ 27
3.3.2. Setting and control for CO2 laser on AutoCAD........................................ 28
3.3.3. Control of CO2 Laser machine ................................................................. 29
3.3.4. Inspection of the channel ......................................................................... 30
3.3.5 Using Power Image Analysis (PIA) systems for analyzing microchannels 31
PART IV. RESULTS ............................................................................................... 33
4.1. Fabrication microchannels on PMMA ........................................................ 33
4.2. Effect of Speed and Power of CO2 laser on microchannels of PMMA ........ 33
PART V. DISCUSSION AND CONCLUSION ...................................................... 38
5.1. Discussion .................................................................................................. 38
5.2. Conslusion.................................................................................................. 39
REFERENCES ........................................................................................................ 40
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Bachelor’s thesis

LIST OF FIGURE
Figure 2.1. The first transistor ................................................................................... 10
Figure 2.2. Glass microfluidic chip ........................................................................... 11

Figure 2.3. Microfluidic chip made of PDMS on glass .............................................. 11
Figure 2.4. Inorganic Materials ................................................................................. 15
Figure 2.5. Elastomers .............................................................................................. 16
Figure 2.6. Thermosets ............................................................................................. 17
Figure 2.7. Hydrogels ............................................................................................... 19
Figure 2.8. Paper based microfluidic chips. ............................................................... 20
Figure 2.9. Molecular’ structure of PMMA ............................................................... 21
Figure 2.10. Experiment system for laser micromachining of PMMA. ...................... 22
Figure 2.11. Burn patterns in PMMA (the scale bar is 100 m). ............................... 23
Figure 2.12. Channel depth as a function of laser power at different scanning speeds. ........ 24
Figure 2.13. Comparisons of selected experimental channel profiles and their
corresponding theoretical models ............................................................................... 25
Figure 2.14. Experimental sample design for laser micromachining measurements... 26
Figure 3.15. Schematic illustration of the channel. .................................................... 27
Figure 3.16. Setting for CO2 laser ........................................................................... 28
Figure 3.17. PMMA substrate ................................................................................... 29
Figure 3.18. Machining ............................................................................................. 29
Figure 3.19. High-resolution optical microscope ....................................................... 30
Figure 3.20. Breaking PMMA................................................................................... 30
Figure 3.21. Microchannel under Video input and measurement of PIA 16............... 30
Figure 3.22. SS-50 lens on High-resolution optical microscope ................................ 31
Figure 3.24. Size of Microchannel ............................................................................ 32

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Bachelor’s thesis
Figure 4.25. Schematic diagram of the photothermal ablation process of CO2 laser on
PMMA substrate........................................................................................................ 33
Figure 4.26. Microchips on PMMA .......................................................................... 33

Figure 4.27. Effect of the laser power on depth ......................................................... 34
and width at a constant speed of 50% for PMMA ...................................................... 34
Figure 4.28. Effect of the laser beam speed in the depth and width of the microchannel
at a laser power of 50% for PMMA ........................................................................... 35
Figure 4.29. Photo of microchannels on PMMA took by PIA ................................... 36
with a constant power 50% and increases speed......................................................... 36
Figure 4.30. Photo of microchannels on PMMA took by PIA with a constant speed
50% and increases power. .......................................................................................... 37
Figure 4.31. Micrograph of a typical channel cross-section in PMMA at a laser power
of 50% and speed of 25%. ......................................................................................... 38

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LIST OF ABBREVIATIONS

PMMA

: Poly methyl methacrylate

PDMS

: Poly dimethyl siloxane

PIA

: Power Image Analysis

MMA

: Methyl methacrylate

HAZ

: Heat affected zones

SD

: Standard deviations

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Bachelor’s thesis

PART I. INTRODUCTION
1.1. Research rationale
The laser ablation mechanism is usually a combination of photochemical and
photothermal processes, in which some chemical bonds of the substance are broken
directly due to photon absorption while others are thermally broken by the released
heat from those excited molecules that do not break up photochemically. A CO2 laser
emits infrared radiation at a wavelength of 10.6 lm, which is not capable of directly
breaking the chemical bonds, so that it is a totally photothermal mechanism for the
CO2 laser ablation process, CO2 laser systems have been widely used for rapid
production of microfluidic systems with polymers such as PMMA.
1.2. Research’s objectives
This study investigated a low cost direct writing laser ablation process to
fabricate microchannel in PMMA using CO2 laser processing based on the effects of

laser power and processing speed on the depth and width of microchannels
manufactured from poly methyl methacrylate (PMMA). From the strong of position in
low cost, fast speed and stable, it will open the door to development for well
construction of Poly (Methyl Methacrylate) (PMMA)-based microfluidic device using
CO2 laser processing.
1.3. Research questions and hypothesis
i) Will the possibility of using CO2 processing for fabricate microchannel in
PMMA become real?
ii) What is the effect of laser power and processing speed on the depth and
width of microchannels from Poly methyl methacrylate (PMMA) for determining their
percentage for setting CO2 laser processing?
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Bachelor’s thesis
1.4. Limitations
The possibility assessment of using CO2 laser for fabrication microchannel in
PMMA is firstly focused on lab-scaled experiment due to low financial and narrowed
capacity of micro-analytical laboratory at department of biomedical engineering and
environmental science, national Tsing Hua University, Taiwan. However CO2 laser
systems will be widely using for rapid production of microfluidic systems with
polymers such as PMMA if successfully conducted.
1.5. Definitions
During recent years, microfluidics has emerged as an advanced technique for
analytical, biological, diagnostics and biomedical research. As a subcategory of
microfluidics, droplet microfluidics is very attractive for its potential to generate and
manipulate discrete droplets in continuous flow, thus allowing for independent control
of each droplet to act as microreactors that can be individually transported, mixed and
analyzed.
Compared with conventional materials like silicon and glass, polymers have

become more and more attractive to fabricate microfluidic devices because of their
many advantages, such as low cost and ease of fabrication. Many kinds of polymers
have been used to fabricate microfluidic devices, such as Poly (methyl methacrylate)
(PMMA).

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Bachelor’s thesis

PART II. LITERATURE REVIEW
2.1. Fabrication of microfluidic device
A definition of microfluidics
Microfluidics is the science that deals with the flow of liquid inside channels of
micrometer size. At least one dimension of the channel is of the order of a micrometer
or tens of micrometers in order to consider it microfluidics. Microfluidics can be
considered both as a science and a technology. Generally, when researchers speak of
microfluidics, they refer to man-made channels. Fluid flows in natural microchannels
as blood vessels or plants capillaries are mostly excluded from microfluidics.
2.1.1. Microfluidic device
Microfluidics is a multidisciplinary field intersecting engineering, physics,
chemistry, biochemistry, nanotechnology, and biotechnology, with practical
applications to the design of systems in which small volumes of fluids will be
handled. Microfluidics emerged in the beginning of the 1980s and is used in the
development of inkjet print heads, DNA chips, lab-on-a-chip technology, micropropulsion, and micro-thermal technologies. It deals with the behavior, precise
control and manipulation of fluids that are geometrically constrained to a small,
typically sub-millimeter, and scale. Typically, micro means one of the following
features: small volumes (

; NL, pL, fL),small size, low energy consumption,

effects of the micro domain,
Typically fluids are moved, mixed, separated or otherwise processed.
Numerous applications employ passive fluid control techniques like capillary forces.
In some applications external actuation means are additionally used for a directed

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Bachelor’s thesis
transport of the media. Examples are rotary drives applying centrifugal forces for the
fluid transport on the passive chips. Active microfluidics refers to the defined
manipulation of the working fluid by active components as micro pumps or micro
valves. Micro pumps supply fluids in a continuous manner or are used for dosing.
Micro valves determine the flow direction or the mode of movement of pumped
liquids. Often processes which are normally carried out in a lab are miniaturized on a
single chip in order to enhance efficiency and mobility as well as reducing sample and
reagent volumes.
2.1.2. Microfluidic chip
A microfluidic chip is a set of micro-channels etched or molded into a material
(glass, silicon or polymer such as PDMS, PMMA). The micro-channels forming the
microfluidic chip are connected together in order to achieve a desired function (mix,
pump, redirect and/or allow chemical reactions in a cell).
This network of microchannels trapped in the microfluidic chip is connected to
the outside by inputs and outputs pierced through the chip, as an interface between the
macro- and micro-world.
It is through these holes that the liquids (or gas) are injected and removed from
the microfluidic chip (through tubing, syringe adapters or even free holes in the chip).
2.2. Birth of Microfluidics: a bit of History
As reminded before, the technologies developed to miniaturize transistors and

manufacture microprocessors have enabled to produce microscopic channels and
integrate them on chips. Thus, the history of microfluidics will take us to the first lunar
expedition, from our printer heads to our hospitals.

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Bachelor’s thesis
The 50′s saw the invention and development of the first transistors. (Figure 2.1).
Made in blocks of semiconductors, they have gradually replaced the lamps previously
used in the manufacture of electronic devices (radio, computer …)

Figure 2.1.The first transistor
In the 90′s, many researchers investigated the applications of MEMS in
biology, chemistry and biomedical fields. These applications needed to control the
movement of liquids in micro-channels and have significantly contributed to the
development of microfluidics.
A major research effort was made to develop laboratories on a chip to enable
the integration of almost all diagnostic operations performed in a hospital on a single
microfluidic chip.
At that time the majority of microfluidic devices were still made of silicon or
glass, and thus, required the heavy infrastructure of the microelectronics industry.

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Bachelor’s thesis

Figure 2.2.Glass microfluidic chip
Starting 2000, technologies based on molding microchannels in polymers such

as PDMS (Poly Dimethyl Siloxane) experienced strong growth. Reducing the cost and
production time of these devices enabled a large number of laboratories to conduct
researches in microfluidics.
Today, thousands of researchers are working in microfluidics to extend its
application fields especially via on-chip laboratories for hospitals.

Figure 2.3.Microfluidic chip made of PDMS on glass

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Bachelor’s thesis
2.3. Application of microfluidic device
2.3.1. The Microfluidic technology has found many applications mainly
-In medicine with the laboratories on a chip because they allow the integration
of many medical tests on a single chip.
-In cell biology researches because the micro-channels have the same
characteristic size as the cells and allow such manipulation of single cells and rapid
change of drugs.
-In protein crystallization because microfluidic devices allow the generation
on a single chip of a large number of crystallization conditions (temperature, pH,
humidity…) and also many other areas: drug screening, sugar testers, chemical
microreactor, microprocessor cooling (just reward) or micro fuel cells.
Microfluidic structures include micropneumatic systems, i.e. microsystems for
the handling of off chip fluids (liquid pumps, gas valves, etc.), and microfluidic
structures for the on chip handling of Nano and politer volumes (Wereley, 2006). To
date, the most successful commercial application of microfluidics is the inkjet print
head. Significant research has also been applied to microfluidic synthesis and production
of various biofunctionalized nanoparticles including quantum dots (QDs) and metallic
nanoparticles (DeMello, 2006) and other industrially relevant materials (e.g., polymer

particles). (Wei et al., 2009) Additionally, advances in microfluidic manufacturing allow
the devices to produce in low-cost plastics (Ryan et al., 2013) and part quality may be
verified automatically.
Advances in microfluidics technology are revolutionizing molecular biology procedures
for enzymatic analysis (e.g., glucose and lactate assays), DNA analysis (e.g., polymerase
chain reaction and high-throughput sequencing), and proteomics. The basic idea of

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Bachelor’s thesis
microfluidic biochips is to integrate assay operations such as detection, as well as sample
pretreatment and sample preparation on one chip (Herold et al., 2009 ; Rasooly et al., 2009).
An emerging application area for biochips is clinical pathology, especially the
immediate point of care diagnosis of diseases. In addition, microfluidics-based
devices, capable of continuous sampling and real-time testing of air/water samples for
biochemical toxins and other dangerous pathogens, can serve as an always
on biosmokealarm" for early warning.
2.3.2. Pros and cons about microfluidic device compared with traditional ways.
In recent years, microfluidics has emerged as an advanced technology for
analytical, biological, diagnostics and biomedical research. For the fabrication of
microfluidic devices, polymers have become more and more important compared
with conventional materials such as silicon and glass due to a number of
advantages such as low cost, ease of fabrication and bulk material properties. A
large number of polymer microfabrication technologies have been established.
These technologies can be divided into two main groups: replication techniques
(Narasimhan and Papautsky, 2004; Pfleging et al., 2002), in which a master
structure is replicated onto the polymer material, and the direct technique (Yao et
al., 2005; Li et al., 2004) in which each single device is manufactured separately.
For a small number of devices, replication methods such a hot embossing and

injection molding are not only complex but also expensive compared with a direct
technique such as laser ablation.
2.4. The common materials for microfluidic chip fabrication
Through manipulating fluids using microfabricated channel and chamber
structures, microfluidics is a powerful tool to realize high sensitive, high speed,

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Bachelor’s thesis
high throughput, and low cost analysis. In addition, the method can establish a well
controlled microenvironment for manipulating fluids and particles. It also has rapid
growing implementations in both sophisticated chemical/biological analysis and
low-cost point of care assays. Some unique phenomena emerge at the micrometer
scale. For example, reactions are completed in a shorter amount of time as the
travel distances of mass and heat are relatively small, the flows are usually laminar;
and the capillary effect becomes dominant owing to large surface to volume ratios.
In the mean-time, the surface properties of the device material are greatly amplified,
which can lead to either unique functions or problems that we would not encounter
at the macroscale. Also, each material inherently corresponds with specific
microfabrication strategies and certain native properties of the device. Therefore,
the material for making the device plays dominating role in microfluidic
technologies. In this Account, we address the evolution of materials used for
fabricating microfluidic chips, and discuss the application-oriented pros and cons of
different materials.
2.4.1. Inorganic Materials
Before the concept of microfluidic was introduced, microchannels had already
been used, for example, glass or quartz capillaries for gas chromatography and
capillary electrophoresis (CE), and flow reactors micromachined in metal; they
contributed to the incubation of microfluidics. Sparked by the microfabrication

technologies in the semiconductor industry, the first-generation microfluidic chips
were prepared in silica or glass. (Reyes et al., 2002; Whitesides, 2006)

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Bachelor’s thesis

Figure 2.4. Inorganic Materials
(A) Fabrication of glass microchips using wet-etching and fusion bonding
methods. (B) Rapid separation on glass microfluidicchip with CE. (C) Hightemperature reaction in microdroplets on a glass chip. (D) In-situ metal etching and
deposition on a glass substrate using laminar flow.
2.4.2. Elastomers and Plastics
Polymer-based chips were introduced several years later after silicon/glass
chips. The vast variety of polymers offers great flexibility in choosing suitable
material with specific properties (Sollier et al., 2011; Becker et al., 2007). Compared
with inorganic materials, polymers are easy to access and inexpensive, and there fore
have become the most-commonly used microchip materials. Ac-cording to their
physical properties, polymers can be classified into three groups: elastomers,
thermosets, and thermoplastics.

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Bachelor’s thesis
2.4.3. Elastomers
Elastomers consist of cross-linked polymer chains that are normally entangled;
they can stretch or compress when external force is exerted, and return to the original
shape when the external force is withdrawn.

Figure 2.5. Elastomers
(A) Fabrication of 3D microchannels in PDMS. (B) Microsized pneumatic
valves in PDMS for manipulating fluids and particles. (C) Complicated manipulation
of picoliterfluidsona PDMS device. (D) Application of PDMS3D structure and
deformation of PDMS structure to mimic the function of lungs.
2.4.4. Thermosets.
Before their introduction into microfluidics, thermosets (e.g., SU-8 photoresist and
polyimide) have already served as negative photoresists; later they were adapted for the
fabrication of microchannel structures (Jackman et al., 2001). When heated or radiated,
the thermosetting molecules cross-link to form a rigid network that cannot soften before
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Bachelor’s thesis
decomposition. That is, thermosets cannot be reshaped once cured. Normally, these
materials are stable even at high temperatures, resistant to most solvents, and optically
transparent. With proper bonding methods, microfluidic chips can be fabricated entirely in
thermosets (Becker et al., 2007). One major advantage of thermosets is for true 3D
microfabrication using photo polymerization (Figure 2.6A) (Sato et al., 2006). Another
advantage is their high strength, which allows the fabrication of high-aspect ratio and freestanding structures (Figure 2.6B). (Zheng et al., 2010) Because of their high stiffness,
thermosets are improper for the fabrication of the diaphragm valve mentioned above; also
with their high cost, their applications in microfluidics are limited.

Figure 2.6. Thermosets
(A) Microchannel made entirely with SU-8, with in situ fabricated 3D fine
structures.

(B)

3D

microfluidic

channel

fabricated

in

thermoset

NOA.

(C)Microfabrication of thermoplastics with high temperature transfer molding
method. (D)Microfluidic chip fabricated entirely using Teflon PFA

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Bachelor’s thesis
2.4.5. Thermoplastics
Different from thermosets, thermo-plastics can be reshaped after being
cured. Because of their wide use in industry, plentiful experience has been
accumulated with thermoplastics. Thermoplastics distinctly soften at glass
transition temperature (Tg), making them processable around this temperature. They
can be reshaped multiple times by reheating, which is important for the
convenience of their molding and bonding. Typical thermoplastics for microchips
are PMMA, PC, polystyrene (PS), polyethylene terephthalate (PET), and
polyvinylchloride (PVC). (Becker et al., 2007) In general, they show a slightly
better solvent compatibility than PDMS; fair resistance to alcohols, but

incompatible with most other organic solvents such as ketones and hydrocarbons.
Because they are barely permeable togas, their sealed microchannels and micro
chambers are unsuitable for long-term cell study. Additionally, diaphragm valves
are difficult to realize in these materials because of their rigidity.
2.4.6. Hydrogels
With its explosive advancement, microfluidics has been increasingly involved in
biological/medical research and biomimicking. (Ghaemmaghami et al., 2012)
Hydrogels, resembling the extra cellular matrix, have been widely used to embed cells
for various applications; microchannels can be built in the hydrogels for delivering of
solutions, cells, and other substances. (Ghaemmaghami et al., 2012; Domachuk et al.,
2010). Hydrogels are 3D networks of hydrophilic polymer chains that span in aqueous
medium, of which over 99% content can be water. They are highly porous with
controllable pore sizes, allowing small molecules or even bioparticles to diffuse through.
The combination of aqueous nature and high permeability makes hydrogels perfect for
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Bachelor’s thesis
encapsulating cells for 3D culture. (Ghaemmaghami et al., 2012) However, the diffusion
of nutrition and oxygen through bulk gel is not yet adequate to support thick layer cell
culture; the cells may behave differently along the gradient, and typically, necrosis starts
to occur at the depth of several hundred micrometers. (Griffith et al., 2006) The
introduction of microfluidic channels into the bulk gel matrix could realize rapid mass
transfer through the bulk, offering similar function as the natural bifurcating
vasculatures, thereby allowing bulk 3D culture of cells (Figure 2.7). (Choi et al., 2007).

Figure 2.7. Hydrogels
(A) Microfluidic device fabricated in alginate gel with embedded cells for
culture. (B) Diffusion of molecules through channel wall into alginate gel.
2.4.7. Paper

Before the introduction of paper-based devices, most micro-fluidic devices
were prepared with sealed channels. However, channels do not have to be sealed;

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Bachelor’s thesis
a paper-based device is a good example (Figure 2.8). (Martinez et al., 2007)
Paper is a highly porous matrix made of cellulose, excellent in wicking liquids.
When certain areas of a paper are modified hydrophobic ally, aqueous solution
applied to the paper will be precisely guided through the hydrophilic region by the
capillary effect. Paper-based microfluidic devices are promising in portable and
low-cost analysis, especially for bioassay-based personalized medical care.
(Martinez et al., 2007).

Figure 2.8. Paper based microfluidic chips.
(A) Bioassay on a paper-chip. (B) Multilayer channel fabrication.
The evolution of chip materials reflects the two major trends of the
microfluidic technology: powerful microscale research platforms and low-cost,
portable analyses. For laboratory research, choosing materials generally needs to
compromise the ease in prototyping and the performance of device, while in
commercialization the major concerns are the cost of production and the ease and

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Bachelor’s thesis
reliability in use. Such difference leads to varied preference in materials for device
fabrication. Current trends seem to be that glass/silicon and PDMS are commonly
used in research laboratories while plastics and paper are more promising for

commercial devices. Each material has its pros and cons.
2.5. Mechanism of CO2 laser processing in PMMA

Figure 2.9. Molecular’ structure of PMMA
A strong rise in temperature occurs due to the high power density of the focused
incident laser beam radiation. The material will first melt and then decompose, leaving
a void. PMMA, whose structure is shown in (Figure 2.9), is a fast burning
thermoplastic. Below 115 °C, it remains in glassy state. When the temperature
increases beyond 115 °C, PMMA reaches a rubbery state. At higher temperatures
between 170 and 210 °C, long range deformations of chains of molecules occur. The
thermal decomposition process of PMMA is comparatively straightforward. Because
of the very large zip length of PMMA, the overwhelmingly dominant product released
from the bulk phase is the monomer methyl methacrylate (MMA). The main part of

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