Đồ án development of conductive alginate based hydrogels with excellent mechanical properties and conductivity via the reconstruction process

MINISTRY OF EDUCATION AND TRAINING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION
FACULTY FOR HIGH QUALITY TRAINING

CAPSTONE PROJECT
ELECTRONICS AND TELECOMMUNICATIONS
ENGINEERING TECHNOLOGY

DEVELOPMENT OF CONDUCTIVE ALGINATE-BASED
HYDROGELS WITH EXCELENT MECHANICAL
PROPERTIES AND CONDUCTIVITY VIA
THE RECONSTRUCTION PROCESS

LECTURER: PHD. TRAN VAN TRON
STUDENT: NGUYEN TRAM ANH
DOAN THAI BINH
NGUYEN LUU MINH THUAN

S K L 01 1 1 5 7

Ho Chi Minh City, 2023


MINISTRY OF EDUCATION AND TRAINING
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH-QUALITY TRAINING

GRADUATION PROJECT
Project: “Development of conductive alginate-based hydrogels
with excellent mechanical properties and conductivity

via the reconstruction process ”
Advisor:

PhD. TRAN VAN TRON

Students:

NGUYEN TRAM ANH
DOAN THAI BINH
NGUYEN LUU MINH THUAN

Student IDs:

18144003
18144008
18144054

Class:

18144CLA

Year:

2018-2022

Ho Chi Minh City, July 2023


HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION
FACULTY FOR HIGH-QUALITY TRAINING

Faculty: Mechanical Engineering

GRADUATION PROJECT
Project: “ Development of conductive alginate-based hydrogels
with excellent mechanical properties and conductivity
via the reconstruction process”
Advisor:

PhD. TRAN VAN TRON

Student:

NGUYEN TRAM ANH
DOAN THAI BINH
NGUYEN LUU MINH THUAN

Student ID:

18144003
18144008
18144054

Class:

18144CLA

Year:

2018-2022

Ho Chi Minh City, July 2022


UNIVERSITY OF TECHNOLOGY AND EDUCATION

THE SOCIALIST REPUBLIC OF VIETNAM

FACULTY OF HIGH-QUALITY TRAINING

Independence – Freedom– Happiness

GRADUATION PROJECT ASSIGNMENT
Semester 2/ Year 2022-2023
Advisor: PhD. Tran Van Tron
Student’s name: Nguyen Tram Anh

Student ID: 18144003

Phone no.: 0352267285

Student’s name: Doan Thai Binh

Student ID: 18144008

Phone no.: 0917991974

Student’s name: Nguyen Luu Minh Thuan

Student ID: 18144054

Phone no.: 0934862467

1. Graduation project
-

Project code: 22223DT83

-

Project title: “ Development of conductive alginate-based hydrogels with excellent
mechanical properties and conductivity via the reconstruction process”

2. Initial data and documents:
-

Molecular structure of sodium alginate;

-

Fabrication process of conductive alginate-based hydrogels via a diffusion method;

-

Evaluation of mechanical properties of hydrogels via tensile test;

-

Method of measuring conductivity;

3. Content of the project:
-

A survey on fabrications and applications of recently reported conductive hydrogels;

-

Synthesizing the initial conductive alginate-based hydrogels and developing the
reconstruction process for the gels;

-

Fabricating a series of conductive hydrogels via the developed reconstruction process;

-

Evaluating their mechanical properties and conductivity;

-

Preparing self-welding conductive hydrogels and determining their shear stress;

i


4. Final product:
-

Conductive alginate-based hydrogels;

-

Report of capstone project;

5. Project delivery date: 15/03/2023
6. Project submission date: 21/07/2023
7. Presentation language: Report:
Presentation:

English



Vietnamese 

English



Vietnamese 

HEAD OF MAJOR

ADVISOR

 Allowed to protect ............................................................

ii

LỜI CAM KẾT
-

Tên đề tài: “ Phát triển alginate hydrogels dẫn điện với cơ tính và độ dẫn điện vượt
trội thông qua quá trình tái cấu trúc”

-

GVHD: TS. Trần Văn Trọn

-

Họ tên sinh viên 1: Nguyễn Trâm Anh

-

MSSV: 18144003

-

Địa chỉ sinh viên 1: 50/1A, đường Xuyên Á (QL1A), KP Bình Đường 1, phường An
Bình, Thành phớ. Dĩ An, tỉnh Bình Dương.

-

Số điện thoại liên lạc 1: 0352267285

-

Email 1:

-

Họ tên sinh viên 2: Đoàn Thái Bình

-

MSSV: 18144008

-

Địa chỉ sinh viên 2: 189i/15 Tôn Thất Thuyết, phường 3, quận 4, Thành phố Hồ Chí
Minh.

-

Số điện thoại liên lạc 2: 0917991974

-

Email 2:

-

Họ tên sinh viên 3: Nguyễn Lưu Minh Thuận

-

MSSV: 18144054

-

Địa chỉ sinh viên 3: 226/1 đường Nguyễn Văn Lượng, phường 17, quận Gò Vấp, Thành
phố Hồ Chí Minh

-

Số điện thoại liên lạc 3: 0934862467

-

Email 3:

-

Ngày nộp khóa luận tốt nghiệp (ĐATN):

-

Lời cam kết: “Chúng tơi xin cam đoan khố luận tốt nghiệp (ĐATN) này là cơng trình
do chính chúng tôi nghiên cứu và thực hiện. Chúng tôi không sao chép từ bất kỳ một
bài viết nào đã được công bố mà khơng trích dẫn nguồn gốc. Nếu có bất kỳ một sự vi
phạm nào, chúng tơi xin chịu hồn tồn trách nhiệm”.
Tp. Hờ Chí Minh, ngày ... tháng … năm 2023
Ký tên
iii


COMMITMENT
-

Project’s title:“ Development of conductive alginate-based hydrogels with excellent
mechanical properties and conductivity via the reconstruction process”

-

Advisor: PhD. Tran Van Tron

-

Name of student 1: Nguyen Tram Anh

-

ID number of student 1: 18144003

-

Address of student 1: 50/1A, Xuyen A (QL1A) Street, Binh Duong 1 Town, An Binh
Ward, Di An City, Binh Dương Province.

-

Phone number of student 1: 0352267285

-

Email of student 1:

-

Name of student 2: Doan Thai Binh

-

ID number of student 2: 18144008

-

Address of student 2: 189i/15 Ton That Thuyet Street, Ward 3, District 4, Ho Chi Minh
City.

-

Phone number of student 2: 0917991974

-

Email of student 2:

-

Name of student 3: Nguyen Luu Minh Thuan

-

ID number of student 3: 18144054

-

Address of student 3: 226/1 Nguyen Van Luong Street, Ward 17, Go Vap District, Ho
Chi Minh City

-

Phone number of student 3: 0934862467

-

Email of student 3:

-

The deadline for submitting the graduation thesis (ĐATN):

-

Commitment: “ We hereby solemnly declare that this graduation thesis is the result of
our research and implementation. We have not copied from any previously published
articles without proper citation. In case of any violation, we take full responsibility.”
Tp. Hồ Chí Minh, ngày ... tháng … năm 2023
Ký tên

iv


LỜI CẢM ƠN
Chúng tơi xin bày tỏ lịng biết ơn chân thành đến Tiến sĩ Trần Văn Trọn vì sự hỗ
trợ śt q trình thực hiện và hoàn thành đề tài luận văn tốt nghiệp của chúng tôi. Sự hướng
dẫn và hỗ trợ từ thầy, cùng việc cung cấp kiến thức cần thiết và trang thiết bị vật lý, đã đóng

vai trị quan trọng trong thành cơng của dự án của chúng tôi. Nhờ sự hướng dẫn của thầy,
chúng tôi đã hoàn thành dự án với kết quả mong muốn.
Chúng tơi cũng ḿn bày tỏ lịng biết ơn đến các giảng viên làm việc ở phòng Thí
nghiệm Vật liệu đã tạo điều kiện thuận lợi để nhóm chúng tơi tiến hành các thí nghiệm. Sự
hỗ trợ từ các thầy/ cơ đã giúp chúng tôi tiếp cận với thiết bị và vật liệu cần thiết để tiến hành
thí nghiệm và nghiên cứu.
Ći cùng, chúng tơi ḿn bày tỏ lịng biết ơn đến bạn Lê Hồng Trà và các thành
viên khác trong nhóm vì sự hỗ trợ và sự đờng hành trong śt q trình dự án. Sự giúp đỡ của
các bạn đã giúp chúng tôi vượt qua những thách thức và đạt được kết quả cuối cùng.
Một lần nữa, chúng tôi xin bày tỏ lòng biết ơn chân thành tới Tiến sĩ Trần Văn
Trọn, tất cả các giảng viên và các thành viên trong nhóm vì những đóng góp đáng kể vào
thành cơng của nhóm chúng tơi. Sự giúp đỡ và hỗ trợ của các bạn đã là nguồn động lực to lớn
giúp chúng tơi hồn thành dự án.
Trân trọng,
Ngũn Trâm Anh
Đoàn Thái Bình
Nguyễn Lưu Minh Thuận

v


EXPRESSIONS OF GRATITUDE
We would like to express our gratitude to Dr Tran Van Tron for assisting us
throughout the process of conducting and completing our graduation project. The guidance
and support provided by Dr Tran Van Tron, as well as the provision of essential knowledge
and physical equipment, have been instrumental in our project's success. We appreciate Dr
Tran Van Tron's willingness to answer our questions and support us during the research and
implementation phases. Thanks to his guidance, we have successfully completed our project
with the desired outcomes.
We would also like to extend our appreciation to the supervisors in the Materials

Science Department for creating favourable conditions for our team to conduct experiments.
The support from the supervisors has enabled us to have access to the necessary equipment
and materials for conducting experiments and research.
Lastly, we would like to express our gratitude to Ms Le Hong Tra and our fellow
team members for their support and companionship throughout the project. Your assistance
has helped us overcome challenges and achieve the final results.
Once again, we would like to express our sincere appreciation to Dr Tran Van
Tron, all the supervisors, and our team members for their significant contributions to the
success of our group. Your help and support have been a tremendous source of motivation for
us to complete the project.
Sincerely,
Nguyen Tram Anh
Doan Thai Binh
Nguyen Luu Minh Thuan

vi


ABSTRACT
Development of conductive alginate-based hydrogels with excellent mechanical
properties and conductivity via the reconstruction process
Hydrogel alginate, as an electrically conductive material, represents a promising
and rapidly developing field in materials science and engineering. Research and development
on hydrogel alginate can lead to significant discoveries regarding its properties and
applications, opening up new opportunities for technological advancements and future
applications. Therefore, our team has decided to undertake a project on the development of
alginate-based hydrogels with electrical conductivity.
The focus of this thesis is on the development of alginate-based hydrogels, a type
of polymer derived from seaweed, which exhibits both electrical conductivity and favourable
mechanical properties through a restructuring process. The research team has conducted

detailed studies and achieved impressive results. Through experimental investigations and
based on the obtained results, the optimal composition and mixing ratios have been
determined to create hydrogels with superior electrical conductivity and mechanical
properties. Importantly, the alginate hydrogel exhibits the ability to self-restructure after
deformation, ensuring reliability and durability in practical applications.
The chosen application for development is the fabrication of electrical circuits.
Thanks to its good electrical conductivity and the ability to form interconnections between
hydrogel joints through self-welding methods, alginate hydrogels can be used to create
flexible and stretchable electrical circuits. This opens up numerous opportunities for
applications in medical fields, electronic technologies, biological monitoring, and
measurement devices.
In summary, this thesis focuses on the development of electrically conductive
alginate hydrogels with superior mechanical properties and electrical conductivity through
the restructuring process. The main application of these hydrogels within the scope of this
project is in the fabrication of flexible electrical circuits, offering great potential for
applications in the medical and electronic industries. The research outcomes hope to
contribute to the development and wide-ranging applications of electrically conductive
alginate hydrogels. Further research can concentrate on process optimization, fine-tuning the
properties of the hydrogels, and exploring their diverse applications in the industrial and
medical fields.

vii


TÓM TẮT ĐỀ TÀI
Phát triển alginate hydrogel dẫn điện với tính chất cơ học và độ dẫn điện vượt trội
thơng qua quá trình tái cấu trúc
Alginate hydrogel dẫn điện đại diện cho một lĩnh vực nghiên cứu mới đang phát
triển mạnh mẽ trong ngành vật liệu và kỹ thuật. Việc nghiên cứu và phát triển hydrogel
alginate có thể mang lại những khám phá quan trọng về tính chất và ứng dụng của vật liệu

này, mở ra nhiều cơ hội mới cho sự phát triển công nghệ và ứng dụng trong tương lai. Vì thế,
nhóm chúng tôi quyết định thực hiện đề tài về phát triển hydrogel dựa trên alginate dẫn điện.
Đồ án tốt nghiệp tập trung vào phát triển hydrogel dựa trên alginate, mợt loại
polymer từ rong biển, có khả năng dẫn điện và các tính chất cơ học tớt thơng qua q trình tái
cấu trúc. Nhóm nghiên cứu đã tiến hành các nghiên cứu chi tiết và đạt được những kết quả ấn
tượng. Thông qua việc tiến hành thí nghiệm và dựa trên kết quả thực nghiệm, đã xác định
được thành phần tối ưu và tỷ lệ pha trộn để tạo ra hydrogel với đợ dẫn điện và tính chất cơ
học vượt trợi. Đặc biệt, hydrogel alginate có khả năng tái cấu trúc sau khi bị biến dạng, tạo
nên sự đáng tin cậy và bền vững trong các ứng dụng thực tế.
Ứng dụng chính mà nhóm nghiên cứu chọn để phát triển là trong chế tạo mạch
điện. Nhờ tính chất dẫn điện tốt và khả năng liên kết giữa các mối nối hydrogel thông qua
phương pháp self- welding, hydrogel alginate có thể được sử dụng để tạo ra các mạch điện
linh hoạt và có khả năng đàn hời. Điều này mở ra nhiều cơ hội ứng dụng trong các lĩnh vực y
tế, công nghệ điện tử, các thiết bị đo lường và giám sát sinh học.
Tóm lại, đờ án tốt nghiệp này tập trung vào phát triển hydrogel alginate dẫn điện
với tính chất cơ học và đợ dẫn điện vượt trợi thơng qua q trình tái cấu trúc. Ứng dụng chính
của hydrogel trong phạm vi đề tài này là trong chế tạo mạch điện linh hoạt, mang lại tiềm
năng lớn cho việc áp dụng trong lĩnh vực y tế và công nghệ điện tử. Kết quả nghiên cứu này
hi vọng sẽ đóng góp một phần nhỏ cho sự phát triển và ứng dụng rộng rãi của hydrogel
alginate dẫn điện. Các nghiên cứu tiếp theo có thể tập trung vào tới ưu hóa quy trình sản x́t,
điều chỉnh tính chất của hydrogel, và khả năng ứng dụng trong các lĩnh vực công nghiệp và y
tế đa dạng.
Nguyễn Trâm Anh
Đoàn Thái Bình
Nguyễn Lưu Minh Thuận

viii


TABLE OF CONTENTS

GRADUATION PROJECT ASSIGNMENT ....................................................................... i
LỜI CAM KẾT .....................................................................................................................iii
COMMITMENT ................................................................................................................... iv
LỜI CẢM ƠN ......................................................................................................................... v
EXPRESSIONS OF GRATITUDE ..................................................................................... vi
TÓM TẮT ĐỀ TÀI .............................................................................................................viii
ABSTRACT .......................................................................................................................... vii
TABLE OF CONTENTS ..................................................................................................... ix
LIST OF TABLES ............................................................................................................... xii
LIST OF DIAGRAMS, ILLUSTRATIONS .....................................................................xiii
LIST OF ABBREVIATIONS ............................................................................................. xv
CHAPTER 1: INTRODUCTION......................................................................................... 1
1.1.

General introduction of hydrogels .......................................................................... 1

1.2.

Topic importance ...................................................................................................... 2

1.3.

Aim of this capstone project .................................................................................... 2

1.4.

Research limitations ................................................................................................. 2

1.5.

Approaching methods .............................................................................................. 2

1.5.1.

Approaching methods .............................................................................................. 2

1.5.2.

Available documents ................................................................................................ 3

1.6.

Structure of the report ............................................................................................. 3

CHAPTER 2: FABRICATING ALGINATE HYDROGELS ........................................... 4
2.1.

Fundamental of hydrogels fabrication ................................................................... 4

2.2.

Alginate- based hydrogels ........................................................................................ 7

2.2.1.

Alginate resources .................................................................................................... 7

2.2.2.

Alginate chemical structure..................................................................................... 8

2.2.3.

General properties of alginate ................................................................................. 9

2.2.4.

Gelation of alginate .................................................................................................. 9
ix


2.3.

Conductive hydrogels and their applications ...................................................... 10

2.3.1.

Conductive hydrogels ............................................................................................. 10

2.3.2.

Conductive hydrogel applications......................................................................... 12

CHAPTER 3: MATERIALS AND METHODS ............................................................... 16
3.1.

Materials and types of equipment......................................................................... 16

3.1.1.

Materials.................................................................................................................. 16

3.1.2.

Initial measurement instrument ........................................................................... 17

3.1.3.

Conductivity measurement.................................................................................... 18

3.1.4.

Mechanical properties measurement ................................................................... 19

3.1.5.

Water content measurement ................................................................................. 21

3.2.

Hydrogels making processes ................................................................................. 21

3.2.1.

Initial gels ................................................................................................................ 22

3.2.2.

Procedure A ............................................................................................................ 24

3.2.3.

Procedure B............................................................................................................. 26

CHAPTER 4: EXPERIMENT AND RESULTS .............................................................. 29
4.1.

Experiment, comparison, and evaluation ............................................................ 29

4.1.1.

The comparison of the results from the initial gel fabrication........................... 30

4.1.2.

Discussion of the results of process A ................................................................... 34

4.1.3.

Discussion of the results of process B ................................................................... 38

4.1.4.

The comparison of the results between procedure A and B............................... 42

4.1.5.

Comparing experimental results when varying the concentration of Cu2+ ...... 46

4.2.

Summary ................................................................................................................. 50

CHAPTER 5: SELF-WELDING AND APPLICATIONS .............................................. 52
5.1.

Self- welding ............................................................................................................ 52

5.1.1.

The process of manufacturing a self-welding joint ............................................. 52

5.1.2.

Analysis, evaluation, and results ........................................................................... 53

5.2.

Applications ............................................................................................................ 56

5.2.1.

Preparation and design .......................................................................................... 56
x


5.2.2.

Fabricating flexible electrical circuits .................................................................. 57

5.2.3.

Results and conclusions ......................................................................................... 59

CHAPTER 6: CONCLUSIONS ......................................................................................... 61
6.1.

Summary ................................................................................................................. 61

6.2.

Dicussions ................................................................................................................ 61

6.3.

Recommendations .................................................................................................. 61

REFERENCES ..................................................................................................................... 62

xi


LIST OF TABLES
Table 4.1: Comparison of properties of initial gels, procedure A and procedure B ............. 42

xii


LIST OF DIAGRAMS, ILLUSTRATIONS
Figure 2.1: Picture showing a comparison of a polyrotaxane gel in as-prepared, dried, and

fully swollen (equilibrium) states of TP gel ......................................................................... 5
Figure 2.2: Schematic showing of covalent crosslinking of alginate using adipic acid
dihydrazide as cross-linker ................................................................................................... 6
Figure 2.3: Schematic showing of construction of cell crosslinked hydrogel of ligandmodified alginate ................................................................................................................... 7
Figure 2.4: Schematic showing of chemical perspective of alginate..................................... 7
Figure 2.5: Schematic showing a typical process for the extraction of sodium alginate from
brown algae ........................................................................................................................... 8
Figure 2.6: Schematic showing alginate monomers (M versus G); the macromolecular
conformation of the alginate polymer; chain sequences ....................................................... 9
Figure 2.7: Schematic showing alginate gelation occurs due to the interaction between
alginate and divalent cations (Ca2+), which results in an egg-box structure ......................... 10
Figure 2.8: Schematic showing conductive hydrogels ......................................................... 11
Figure 2.9: Schematic showing ColHA hydrogel prepared via HRP-catalyzed crosslinking of
collagen and HA modified with phenol groups .................................................................... 13
Figure 2.10: Pictures showing the use of a conductive hydrogel to create a flexible and
stretchable neural electrode array ......................................................................................... 14
Figure 2.11: Pictures showing the use of synthetic hydrogels in ophthalmology ................ 15
Figure 3.1: Picture showing sodium chloride (NaCl) bottle ................................................. 16
Figure 3.2: Picture showing calcium chloride (CaCl2) bottle ............................................... 16
Figure 3.3: Picture showing copper (II) chloride dihydrate (CuCl2 + 2H20) bottle ............. 16
Figure 3.4: Picture showing charcoal (steam activated) ....................................................... 16
Figure 3.5: Picture showing alginate 80Cp ~ 120Cp bottle ................................................... 17
Figure 3.6: Picture showing glycerol 99% bottle ................................................................. 17
Figure 3.7: Picture showing distilled water can .................................................................... 17
Figure 3.8: Picture showing electronic scale ......................................................................... 17
Figure 3.9: Picture showing Atorn electronic calliper .......................................................... 18
Figure 3.10: Picture showing dedicated resistance tester CD800A ...................................... 19
xiii

Figure 3.11: Pictures showing specific tensile strength tester PT-1699vdo ......................... 20
Figure 3.12: Pictures showing heating apparatus ................................................................. 21
Figure 3.13: Schematic showing initial Ca-alginate with 4 wt% of C making process ....... 22
Figure 3.14: Schematic showing free-dried hydrogels obtained through Procedure A ........ 24
Figure 3.15: Schematic showing free-dried hydrogels obtained through Procedure B ........ 26
Figure 4.1: Picture showing sample test ............................................................................... 29
Figure 4.2: Graphs showing stress-strain curves of initial gels ............................................ 30
Figure 4.3: Graphs showing properties of initial gels ........................................................... 31
Figure 4.4: Graphs showing stress-strain curves of procedure A ........................................ 34
Figure 4.5: Graphs showing properties of procedure A ....................................................... 35
Figure 4.6: Graphs showing stress-strain curves of procedure B ......................................... 38
Figure 4.7: Graphs showing properties of procedure B ........................................................ 39
Figure 4.8: Graphs showing comparison stress-strain curves of two procedures A-B.......... 43
Figure 4.9: Graphs showing comparison properties of two procedures A-B ........................ 44
Figure 4.10: Graphs showing stress-strain curves of 5 wt%Alg, 4 wt%C Dried RT/Na/Ca/Cu
x M ....................................................................................................................................... 47
Figure 4.11: Graphs showing properties of 5 wt% Alg, 4 wt% C Dried RT/Na/Ca/Cu x M 48
Figure 5.1: Schematic showing a manufacturing process of self- welding joint .................. 52
Figure 5.2: Pictures showing the quality testing process for the self-welded joint .............. 54
Figure 5.3: Graph showing mechanical properties of the self-welding of sample ............... 55
Figure 5.4: Wiring diagram of flexible circuit ...................................................................... 56
Figure 5.5: Pictures showing the base plate before and after performing self-welding to create
an electrical circuit ................................................................................................................ 57
Figure 5.6: Picture showing the circuit after being immersed in the Ca2+ ions solution ...... 57
Figure 5.7: Picture showing the circuit after being immersed CuCl2 solution ...................... 58
Figure 5.8: Picture showing the circuit after the electronic components have been installed 58
Figure 5.9: Picture showing the circuit after being powered up ........................................... 59

xiv

LIST OF ABBREVIATIONS
EGDMA

Ethylene Glycol Dimethacrylate

HEMA

2- Hydroxyethyl Methacrylate

NVP

N-Vinyl-2-pyrrolidone

PNIPAAm

Poly(N-isopropyl acrylamide)

PEG

Polyethylene Glycol

RGD

Arginine-Glycine-Aspartic Acid

HRP

Horseradish Peroxidase

HA

Hyaluronic Acid

UV

Ultraviolet

TRIS

Trimethylolpropane Tris(3-(methacryloyloxy)propyl) Ether

Wt%

Weight percentage

DriedRT

Dried at Room Temperature

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CHAPTER 1
CHAPTER 1: INTRODUCTION
1.1.

General introduction of hydrogels

Gels are solid substances that maintain their shape without flowing when

undisturbed [1]. Hydrogels, a specific type of gel, consist of three-dimensional structures
composed of hydrophilic polymer chains, meaning they have an affinity for and retain water
without dissolving in it [1]. The integrity of hydrogels relies on cross-linking, which can be
either physical, such as chain entanglements, ionic bonds, or hydrogen bonds, or chemical,
such as covalent bonds [8]. Hydrogels can be classified based on the source of the polymer
or their constituents, as well as the method of their fabrication. Notably, hydrogels exhibit a
high water content, typically exceeding 99.9% [1]. One intriguing property of hydrogels is
their responsiveness to specific stimuli, including changes in pH, temperature, or light [8].
Additionally, they are biocompatible and biodegradable, making them valuable in biological
and environmental applications, such as implants or materials for pollutant removal [2].
Moreover, certain hydrogels possess electrical conductivity, enabling their utilization in the
development of supercapacitors, which play a crucial role in advancing electronics [2].
Brown seaweed serves as a natural source of alginate, which is harnessed for its
versatile properties [3]. Alginate is a copolymer consisting of α-l-guluronic acid [G] and ß-dmannuronic acid [M] units, linked together in a linear binary structure [8]. The arrangement
and composition of these copolymers exhibit significant and non-random variations [4]. The
copolymers adopt block-like structures, with α-l-guluronic acid [G] blocks playing a crucial
role in ion binding, thereby contributing to the gel-forming characteristics of alginate [4].
Furthermore, the [G] blocks readily form Ca-alginate hydrogels by interacting with
multivalent cations such as Ca2+ [4]. Hence, we have opted for alginate as the polymer for
hydrogel formulation due to its environmental sustainability, biocompatibility,
biodegradability, and its inherent rheological properties.
Conductive hydrogels represent a unique class of hybrid materials that combine
the characteristics of hydrogels, which are gel-like substances capable of retaining water, with
the conductive properties of certain materials [8]. Unlike traditional hydrogels, these
conductive hydrogels exhibit electrical conductivity in addition to their inherent hydrogel
properties [8]. Recent advancements in this field have demonstrated the successful integration
of metal nanoparticles into the hydrogel matrix, leading to the development of conductive
hydrogels with enhanced properties and stimuli-responsive behaviour [5]. These innovative
materials have found widespread applications in diverse fields, including artificial muscles,
switches, memory devices, catalysts, and photographic materials. By leveraging the

synergistic effects of conductivity and hydrogel characteristics, conductive hydrogels offer
exciting opportunities for the development of advanced functional materials.
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CHAPTER 1
In 2020, Zhao and colleagues developed a conductive hydrogel network using a
process called in situ polymerization [8]. They used quaternate chitosan, which is a type of
modified chitosan, and oxidized dextran as a dynamic Schiff crosslinker to create the
hydrogel. The resulting conductive hydrogel not only exhibited antibacterial properties but
also had a conductivity of 0.43 mS/cm [6]. Importantly, it maintained cell viability and even
promoted cell proliferation, making it suitable for biomedical applications.
1.2.

Topic importance

Conductive hydrogels have attracted considerable attention in recent years due to
their unique combination of mechanical and electrical properties [7]. In this context, a survey
was conducted on the fabrications and applications of recently reported conductive hydrogels.
Therefore, an initial alginate-based conductive hydrogel was synthesized, and a
reconstruction process was developed to enhance the gels’ properties. Using the developed
process, a series of conductive hydrogels were fabricated and evaluated for their mechanical
properties and conductivity. Additionally, self-welding conductive hydrogels were prepared,
and their shear stress was determined. These findings provide valuable insights into the
synthesis and properties of conductive alginate-based hydrogels for general applications.
1.3.

Aim of this capstone project
In this project, we will develop conductive alginate-based hydrogels with excellent

mechanical properties and electrical conductivity using a reconstruction process. The
mechanical properties of the developed hydrogels have been determined using the tensile test.
By incorporating conductive materials into the alginate matrix and subjecting it to a
reconstruction process, the resulting hydrogel exhibits superior tensile strength and
conductivity compared to traditional hydrogels.
1.4.

Research limitations

In this study, we used alginate (5 wt%) and activated carbon in terms of 0 wt%, 2
wt%, 4 wt% and 8 wt% to create the initial conductive hydrogels. To get the hydrogels in dry
form, we will apply two different methods, the first way we let them dry either naturally at
room temperature or 75°C in a laboratory furnace.
1.5. Approaching methods
1.5.1. Approaching methods
-

Surveyed the recent developments and applications of conductive hydrogels.

-

Synthesized an initial set of conductive alginate-based hydrogels and developed a
reconstruction process for them.
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CHAPTER 1
-

Used the developed reconstruction process to fabricate a series of conductive

hydrogels.

-

Evaluated the mechanical properties and conductivity of the fabricated conductive
hydrogels.

-

Prepared applications of the conductive hydrogels.

1.5.2. Available documents
-

Describing the molecular structure of sodium alginate;

-

Outlining a process for creating conductive hydrogels based on alginate using a
diffusion method;

-

Testing the mechanical properties of the hydrogels by conducting a tensile test;

-

Explaining the method used for measuring the conductivity of the hydrogels.

1.6.

Structure of the report

The thesis consists of six chapters. Specifically, chapter 2 of the thesis covers
concepts, definitions, and relevant background knowledge. It summarizes previous research,
identifies gaps, and outlines the unique contributions of the proposed work. Chapter 3 will
present the materials and equipment required for the project. Additionally, it will outline the
proposed approaches to address the project's challenges and provide theoretical explanations
for these alternatives. In Chapter 4, experimental results will be discussed, comparisons
between the obtained outcomes will be made, and conclusions will be drawn. Chapter 5 will
focus on the self-welding method and the application of conductive hydrogels through selfwelding. Finally, Chapter 6 will serve as a synthesis of the project's findings, lessons learned,
and future development directions.

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CHAPTER 2
CHAPTER 2: FABRICATING ALGINATE HYDROGELS
2.1.

Fundamental of hydrogels fabrication

A commonly used method for creating hydrogels involves linking together
multiple types of monomers using a multifunctional co-monomer as a cross-linking agent [9].
To create hydrogels, it is necessary to select monomers and their corresponding linear
polymers that can dissolve in water [9]. Polymerization can occur through different methods,
such as bulk, solution, or suspension, and can be initiated using chemical, photo, thermal,
redox, gamma ray, or microwave methods [9].
The second approach to forming hydrogels includes cross-linking of pre-formed
linear polymers with the help of irradiation or chemical compounds [10]. An example of this

is the reaction between α,ω-hydroxyl poly (ethylene glycol) and a diisocyanate in the presence
of a triol as a cross-linker, which results in the creation of hydrophilic polyurethanes that are
cross-linked [10]. The ionic polymer network is formed by using monomers that have either
an ionizable group, a group that can be ionized, or a group that can undergo a substitution
reaction after the polymerization process is finished [9]. Therefore, hydrogels that are
synthesized may contain weakly acidic groups such as carboxylic acids, weakly basic groups
like substituted amines, or strong acidic and basic groups like sulfonic acids and quaternary
ammonium [9]. Commonly used cross-linking agents such as divinyl benzene, EGDMA, and
others are often utilized in hydrogel synthesis [11]. The monomers frequently utilized for this
process include acrylic acid, methacrylic acid, acrylamide, HEMA, maleic anhydride,
glycidyl methacrylate, N, N- dimethyl acrylamide, N- [3- (dimethylamino) propyl]
methacrylamide, N-isopropyl acrylamide, NVP, and 2- acrylamide- 2 -methyl propane
sulfonic acid [11]. By selecting appropriate monomers and cross-linking agents, hydrogels
can be synthesized with specific properties such as biodegradability, mechanical strength, and
chemical and biological responsiveness to external stimuli. This enables the design and
production of hydrogels with tailored characteristics for diverse applications [9]. A different
strategy involves transforming the hydroxyl terminal groups of poly (ethylene glycol) into
methacrylate, which can subsequently be cross-linked via radical polymerization with the
help of co-monomers and a cross-linking agent [9]. Despite that, the process of synthesizing
biodegradable hydrogels typically involves the addition of biodegradable organic components
to the hydrogel. This can be done by modifying an already biodegradable polymer or by
adding biodegradable components to the hydrogel's backbone or as pendant groups. The
selection of appropriate monomers and synthetic strategies is crucial in achieving this [12].
In addition, Tanaka, Gong, and Osada reviewed new methods for enhancing the
mechanical properties of hydrogels [13]. These methods include the use of sliding crosslinking agents, double networks, and nano clay-filling to prepare hydrogels with improved
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CHAPTER 2
mechanical properties [13]. Figure 2.1 shows a comparison of a polyrotaxane gel in asprepared, dried, and fully swollen (equilibrium) states of TP gel. A ‘topological (TP) gel’ is

a gel mentioned in Tanaka’s, Gong’s, and Osada’s research paper. After improvement, the
gel swells to about 500 times of its original (as-prepared) weight and can be stretched to about
20 times its original length. [13]

Figure 2.1. A comparison of a polyrotaxane gel in as-prepared (a), dried (b), and fully swollen
(equilibrium) states (c) of TP gel.
In summary, to effectively regenerate hydrogels, it is necessary to know the
principles of selecting suitable monomers as well as designing reasonable cross-linkers. From
there, the researcher will adjust and improve the mechanical and chemical factors to suit the
purpose of the research.
For the scope of this study, the type of hydrogel to be regenerated is alginate
hydrogels. Alginate hydrogels are typically prepared using divalent ions such as Ca2+ and
Mg2+ as ionic crosslinking agents, which interact with the branches of the G-block to form an
egg-box structure. However, the use of CaCl2, the most common cross-linker, can result in an
uncontrollably high gelation rate, negatively impacting the homogeneity and mechanical
properties of the hydrogel. To control the gelation rate, other methods such as using more
soluble crosslinkers like CaSO4 or CaCO3 can be used. Alginate concentration, the
concentration of crosslinked ions, the experimental method, and temperature can also be
modified to tune the mechanical properties of the hydrogel. In case, increasing the alginate or
crosslinked ion concentration can result in denser and stiffer hydrogels, while decreasing
these factors can lead to softer and more porous hydrogels. By adjusting these parameters,
researchers can modulate the mechanical properties of alginate hydrogels to suit their specific
research needs.
One method for making alginate hydrogel can be thought of as thermoresponsive
hydrogel formed by alginate. Specifically, sodium alginate is an appropriate choice to
combine with PNIPAAm for the production of thermoresponsive hydrogels due to its
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CHAPTER 2

biocompatibility, biodegradability, non-toxicity, charitable property, and the possibility of
chemical modification [14]. Alginate is a type of water-soluble polysaccharide found in
brown seaweed [14]. It is a copolymer made up of α-L-guluronic acid (G) and β-Dmannuronic acid (M) linked by 1-4 bonds [14]. Two G-block aligned areas can create a
diamond-shaped cavity, which is suitable for the cooperative binding of divalent cations like
calcium ions, resulting in physically crosslinked hydrogels [14].
In addition, covalent crosslinking is also a method of making alginate hydrogel
that can be thought of. The process of covalent crosslinking involves using a crosslinking
agent to join two polymer chains [15]. The functional groups (-OH, −COOH, and -NH2) in
natural and synthetic polymers react with crosslinkers such as glutaraldehyde, adipic acid
dihydrazide, and poly (ethylene glycol)-diamine to form a crosslinked hydrogel [15]. As
Figure 2.2 illustrates, alginate gels with covalent crosslinking are formed by the reaction of
carboxylic groups in different alginate branches with a crosslinking molecule containing
primary diamines [15]. The mechanical properties and swelling degrees of alginate hydrogels
can be significantly affected by the type of crosslinking molecules and controllable
crosslinking density [15]. Increasing crosslinking density enhances the mechanical properties,
while the type of crosslinking molecules significantly affects swelling properties [15]. Using
hydrophilic crosslinking molecules like PEG compensates for the reduction of hydrophilic
character during crosslinking, making it useful in biomedical applications [15]. The approach
allows for the control of hydrogel properties by adjusting crosslinking density and types of
crosslinking molecules [15].

Figure 2.2. Schematic showing of covalent crosslinking of alginate using adipic acid
dihydrazide as cross-linker [38].
There are various physical and chemical methods to create alginate gels; however,
it is important to acknowledge the potential for cells to participate in the gel formation process
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CHAPTER 2
[15] (Figure 2.3). If polymer chains have specific ligands that can bind to receptors on the

surface of cells, then the cells can crosslink with the polymers to form gels [15]. Alginate
chains lack bioactive ligands for cell anchoring, but when modified with cell adhesion
peptides like Arg-Gly-Asp (RGD), cells can bind to the chains and form a polymer network
through specific receptor-ligand interactions [15]. The addition of cells to RGD-modified
alginate solutions results in a uniform dispersion of cells within the solution, leading to the
formation of a polymer network even in the absence of chemical crosslinking agents [15].
The resulting gels exhibit high biocompatibility and mechanical strength [15].

Figure 2.3. Schematic showing of construction of cell crosslinked hydrogel of ligandmodified alginate [15].
2.2. Alginate- based hydrogels
2.2.1. Alginate resources
Alginates are naturally occurring polymers found in the cell wall and intercellular
matrix of brown seaweeds [16]. They provide seaweed with the necessary mechanical
strength and flexibility to survive in the ocean [16]. Alginates naturally bond with various
salts present in seawater, including calcium, sodium, magnesium, strontium, and barium ions
[16]. Chemically, alginate consists of unbranched binary copolymers composed of monomers
of (1-4)-linked β-dmannuronic acid (M) and α-l-guluronic acid (G) residues, which can form
M-, G-, and MG- sequential block structures [16] (Figure 2.4).

Figure 2.4. Schematic showing of chemical perspective of Alginate [16].
7