Electrically Conductive Polymers and Polymer Composites E-Book
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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
A comprehensive and up-to-date overview of the latest research trends in conductive polymers and polymer hybrids, summarizing recent achievements.
The book begins by introducing conductive polymer materials and their classification, while subsequent chapters discuss the various syntheses, resulting properties and up-scaling as well as the important applications in biomedical and biotechnological fields, including biosensors and biodevices. The whole is rounded off by a look at future technological advances.
The result is a well-structured, essential reference for beginners as well as experienced researchers.
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Table of Contents
Cover
Title Page
Copyright
Dedication
About the Editors
Preface
Chapter 1: Bioinspired Polydopamine and Composites for Biomedical Applications
1.1 Introduction
1.2 Synthesis of Polydopamine
1.3 Properties of Polydopamine
1.4 Applications of Polydopamine
1.5 Conclusion and Future Prospectives
References
Chapter 2: Multifunctional Polymer-Dilute Magnetic Conductor and Bio-Devices
2.1 Introduction
2.2 Magnetic Semiconductor-Nanoparticle-Based Polymer Nanocomposites
2.3 Types of Magnetic Semiconductor Nanoparticles
2.4 Synthetic Strategies for Composite Materials
2.5 Biocompatibility of Polymer/Semiconductor-Particle-Based Nanocomposites and Their Products for Biomedical Applications
2.6 Biomedical Applications
References
Chapter 3: Polymer–Inorganic Nanocomposite and Biosensors
3.1 Introduction
3.2 Nanocomposite Synthesis
3.3 Properties of Polymer-Based Nanocomposites
3.4 Electrical Properties
3.5 Optical Properties
3.6 Magnetic Properties
3.7 Application of Polymer–Inorganic Nanocomposite in Biosensors
3.8 Conclusions
References
Chapter 4: Carbon Nanomaterial-Based Conducting Polymer Composites for Biosensing Applications
4.1 Introduction
4.2 Biosensor: Features, Principle, Types, and Its Need in Modern-Day Life
4.3 Common Carbon Nanomaterials and Conducting Polymers
4.4 Processability of CNTs and GN with Conducting Polymers, Chemical Interactions, and Mode of Detection for Biosensing
4.5 PANI Composites with CNT and GN for Biosensing Applications
4.6 PPy and PTh Composites with CNT and GN for Biosensing Applications
4.7 Conducting Polymer Composites with CNT and GN for the Detection of Organic Molecules
4.8 Conducting Polymer Composites with CNT and GN for Microbial Biosensing
4.9 Conclusion and Future Research
References
Chapter 5: Graphene and Graphene Oxide Polymer Composite for Biosensors Applications
5.1 Introduction
5.2 Polymer–Graphene Nanocomposites and Their Applications
5.3 Conclusions, Challenges, and Future Scope
References
Chapter 6: Polyaniline Nanocomposite Materials for Biosensor Designing
6.1 Introduction
6.2 Importance of PANI-Based Biosensors
6.3 Polyaniline-Based Glucose Biosensors
6.4 Polyaniline-Based Peroxide Biosensors
6.5 Polyaniline-Based Genetic Material Biosensors
6.6 Immunosensors
6.7 Biosensors of Phenolic Compounds
6.8 Polyaniline-Based Biosensor for Water Quality Assessment
6.9 Scientific Concerns and Future Prospects of Polyaniline-Based Biosensors
6.10 Conclusion
References
Chapter 7: Recent Advances in Chitosan-Based Films for Novel Biosensor
7.1 Introduction
7.2 Chitosan as Novel Biosensor
7.3 Application
7.4 Conclusion and Future Perspectives
Acknowledgment
References
Chapter 8: Self Healing Materials and Conductivity
8.1 Introduction
8.2 Classification of Self-Healing Materials
8.3 Conductivity in Self-Healing Materials
8.4 Current and Future Prospects
8.5 Conclusions
References
Chapter 9: Electrical Conductivity and Biological Efficacy of Ethyl Cellulose and Polyaniline-Based Composites
9.1 Introduction
9.2 Conductivity of EC Polymers
9.3 Conductivity of PANI Polymer
9.4 Biological Efficacy of EC and PANI-Based Composites
9.5 Summary and Conclusion
Acknowledgments
References
Chapter 10: Synthesis of Polyaniline-Based Nanocomposite Materials and Their Biomedical Applications
10.1 Introduction
10.2 Biomedical Applications of PANI-Supported Nanohybrid Materials
10.3 Conclusion
Acknowledgment
References
Chapter 11: Electrically Conductive Polymers and Composites for Biomedical Applications
11.1 Introduction
11.2 Conducting Polymers
11.3 Conductive Polymer Composite
11.4 Biomedical Applications of Conductive Polymers
11.5 Future Prospects
11.6 Conclusions
References
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 1: Bioinspired Polydopamine and Composites for Biomedical Applications
Figure 1.1 Formation mechanism of PDA in an alkali solution.
Figure 1.2 Graphical representation of the formation of PDA–laccase–MWCNT nanocomposite film on GCE for hydroquinone biosensing.
Figure 1.3 (a–e) Schematic representation of sub-micron size PDA particles and their morphological study.
Figure 1.4 (a) Graphical representation of PDA nanotube synthesis and its high-resolution TEM images.
Figure 1.5 (a) Melanin broadband optical absorbance spectrum (inset for log linear axes) and peaks below show individual absorbance peak chromophores.
Figure 1.6 Melanin photoconductivity versus time for four different hydration levels: (a) 8.6%, (b) 10.2%, (c) 13.4%, and (d) 16.2%, under dark, illuminated, and dark sequence each for 50 s.
Figure 1.7 (a) The μSR relaxation data obtained on hydrated melanin pellets. (b) A pH-dependent titration EPR study for colloidal suspensions of melanin.
Figure 1.8 Application of polydopamine in various emerging research fields.
Figure 1.9 (a) Digital image of SiO
2
scaffold before and after 6- and 24-h modification with PDA; (b) the proliferation of BMSCs on mesoporous silica (MS), PDA-modified silica (MSD), and dexamethasone (DEX)-loaded MSD (MSD-DEX) scaffolds. MSD shows improved proliferation of BMSCs.
Figure 1.10 FESEM images of the dopa-cotton/AgNPs fabrics (a) unwashed and (b) after 30 washes.
Figure 1.11 (a) Schematic illustration for the preparation of PDA-FONs and their application in cell imaging. (b) Normalized photoluminescence emission spectra of PDA-FON dispersion at different excitation wavelengths from 360 to 500 nm. (c) Fluorescence microscopy photograph of the PDA-FON dispersion excited by UV light (340–380 nm). (d) Effect of PDA-FONs on NIH-3T3 cells. (e–g) are confocal laser scanning microscopy images of cells imaged under bright field 405- and 458-nm excitations, respectively.
Figure 1.12 (a) Schematic of the PDA and its encapsulation and surface functionalization on yeast cells. Confocal micrographs of (b) native yeasts and (c) yeast@PDA. (d–g) TEM micrographs of PDA-encapsulated yeast cells. (h) Growth curve of native and PDA-coated yeast cells. (i) Survival of native and coated yeast cells in the presence of lyticase.
Figure 1.13 (a) Schematic representation of cell patterning with PDA as ink via micro-contact printing; (b) optical microscopic image of an imprinted PDA pattern on a gold substrate; (c) SEM images of PDA patterns on silicon; (d) SEM image of the cell-patterned substrate; (e) fluorescent microscopy image of the cell-patterned substrate after immobilization of fluorescein isothiocyanate conjugate – bovine serum albumin (FITC-BSA).
Figure 1.14 (a) Illustration of photothermal treatment (b) Time-dependent temperature change at different concentrations of PDA nanoparticle (NP) suspension. (c) The photothermal response of PDA NP suspension (200 µg mL
−1
) for 500 s with an NIR laser (808 nm, 2 W cm
−2
). (d–f) Digital photographs of the biocompatibility of PDA NPs with a tumor-bearing mouse for photothermal therapy. (g) A digital photograph of a 4T1 cell culture dish after incubation with PDA NPs and red circle shows the laser spot. (h–k) Confocal images of calcein acetoxymethyl (calcein AM) (green, live cells) and propidium iodide (red, dead cells) co-stained 4T1 cells after laser irradiation. (i) Cell viability of 4T1 cells after incubation with increasing concentrations of PDA NPs. (l) Cell viability of 4T1 cells treated with different concentrations of PDA NPs with laser irradiation (808 nm, 2 W cm
−2
, 5 min).
Figure 1.15 Schematic of the synthesis and application of PDAs@CP3-DOX. (a)
In vivo
T1, (c) T2; MR images of mice after intravenous injection of PDAs@CP3 at different time intervals, and its corresponding data analysis of T1 (b) and (d) T2-weighted MRI measurements.
Chapter 2: Multifunctional Polymer-Dilute Magnetic Conductor and Bio-Devices
Figure 2.1 Stability of the ferromagnetic state in (a) Mn-, (b) Fe-, (c) Co-, and (d) Ni-doped ZnO-based DMSs as a function of carrier concentration. A positive energy difference indicates that the ferromagnetic state is energetically more stable than the spin glass state.
Figure 2.2 (a) Magnetic semiconductor, (b) diluted magnetic semiconductor, and (c) nonmagnetic semiconductor.
Figure 2.3 Illustrative representation of the conducting nanocomposites prepared from pre-synthesized conducting polymers and magnetic nanoparticles (NPs).
Figure 2.4 Schematic description of interactions between polymers and inorganic materials (magnetic semiconductor) for the formation of PMNCs.
Figure 2.5 Schematic representation of the formation of semiconductor particle nanocomposites via
in situ
oxidative emulsion polymerization.
Chapter 3: Polymer–Inorganic Nanocomposite and Biosensors
Figure 3.1 Schematic representation of the main chemical routes for the synthesis of polymer–inorganic nanocomposites.
Figure 3.2 (A) Stress–strain curves for the PU/clay films with different clay contents and tensile properties: (a) 0, (b) 1, (c) 2, (d) 3, (e) 4, and (f) 5 wt%; (B) TEM microphotograph of the PU/clay nanocomposite with 5 wt% clay.
Figure 3.3 The thermal conductivity of composites containing hybrid filler.
Figure 3.4 The conductivity variation curve of PPy/SrFe
12
O
19
nanocomposite.
Figure 3.5 Transparencies of the (a) PC neat resin, (b) 1 wt% and (c) 2 wt% PC/alumina (SMA-coated), and (d) 2 wt% PC/alumina (untreated).
Figure 3.6 TEM of samples prepared with different pyrrole/SrFe
12
O
19
mass ratio: (a) 0; (b) 10 : 1; (c) 15 : 1; (d) 20 : 1.
Figure 3.7 The magnetic hysteresis loops at 300 K for PEDOT/PSS–Fe
3
O
4
nanocomposites with different Fe
3
O
4
content.
Figure 3.8 Schematic illustration of the electrochemical DNA sensor construction process.
Chapter 4: Carbon Nanomaterial-Based Conducting Polymer Composites for Biosensing Applications
Figure 4.1 Schematic diagram depicting the mode of action of biosensors.
Figure 4.2 Scope of biosensors in different fields.
Figure 4.3 Interaction of CNT/GN with PANI.
Figure 4.4 Immobilization of DNA strands synergistically by PANI and GN.
Figure 4.5 Immobilization of the enzyme (ascorbate oxidase) on Au-modified PANI–CNT electrode.
Figure 4.6 Zone of inhibition for
S. aureus
,
E. coli
and
C. albicans
by PANI–GN–ZnFe
2
O
4
composite.
Chapter 5: Graphene and Graphene Oxide Polymer Composite for Biosensors Applications
Figure 5.1 Synthesis of graphene and graphene oxide by Hummers’ method.
Figure 5.2 SEM of dry, as-produced TRGO powder. The sheets are very agglomerated, and the particles have a fleecy morphology [22].
Figure 5.3 Applications of graphene-based polymer composites.
Figure 5.4 (a) Polyaniline and (b) polypyrrole.
Figure 5.5 The enzymatic reaction among cholesterol and ChOx on G/PVP/PANI-modified-paper-based biosensor [39].
Figure 5.6 Schematic outline of the DNA recognition on various electrode modifications [45].
Figure 5.7 The assembly process of the electrode [46].
Figure 5.8 Schematic illustration of the electrochemical DNA sensor development process [45].
Figure 5.9 Schematic outline of the DNA biosensor [48].
Figure 5.10 Schematic portrayal of the immobilization and hybridization of DNA on the rGO/PANI/GCE [49].
Figure 5.11 Serotonin (5-HT) biosensor preparation scheme [50].
Figure 5.12 The reaction procedure used to set up the HP/PPy/GO nanosheets [54].
Figure 5.13 Preparation plan of rGO/PPy/AuNP biosensor for dopamine biosensing [56].
Figure 5.14 Illustration of the preparation of the Au–PPy–rGO-nanocomposite-based AChE biosensor [57].
Figure 5.15 Schematic portrayal of the development procedures of NiCo/PPy/rGO nanocomposites [62].
Figure 5.16 (a) The schematic diagram of glucose sensors in view of fiber organic electrochemical transistors with an active layer of PPy nanowires and rGO. (b) Reaction cycle involved in glucose sensing using GOx [63].
Chapter 6: Polyaniline Nanocomposite Materials for Biosensor Designing
Figure 6.1 Overview of the biosensor, showing antibody immobilization on PANI and specificity with selective molecules.
Figure 6.2 TEM images of PS latex beads (a), PS–PANI composite (b), PS–PANI–AuNPs (c), and SEM of PS–PANI–AuNPs (d). (Reproduced with permission from Liu
et al
. [53], American Chemical Society.)
Chapter 7: Recent Advances in Chitosan-Based Films for Novel Biosensor
Figure 7.1 Structure of chitosan.
Figure 7.2 Application of chitosan-based biosensor in environmental and biological field.
Chapter 9: Electrical Conductivity and Biological Efficacy of Ethyl Cellulose and Polyaniline-Based Composites
Figure 9.1 Powdered form of EC and its chemical structure.
Figure 9.2 Comparison of the changes in the polymer conductivity as against the changes in the electrolyte type and concentration when tested for (a) EC–NiHPO
4
, (b) EC–MgHPO
4
, and (c) EC–SnHPO
4
composite.
Figure 9.3 Conductivity measurements for different composites of EC by the application of changes in temperature when tested for (a) EC–NiHPO
4
, (b) EC–MgHPO
4
, and (c) EC–SnHPO
4
.
Figure 9.4 Comparison of the activation energies for different composites of EC by the application of changes in electrolyte concentration for KCl and NaCl solutions when tested for (a) EC–NiHPO
4
, (b) EC–MgHPO
4
, and (c) EC–SnHPO
4
.
Figure 9.5 Comparison of electrode potentials as against the changes in solution pH for the three different EC-based composites, (a) EC–NiHPO
4
, (b) EC–MgHPO
4
, and (c) EC–SnHPO
4
.
Figure 9.6 Schematic representation of the formation of protonation and deprotonation of PANI in two different colors.
Figure 9.7 Comparison of PANI/MWCNTs and Co
3
O
4
/PANI/MWCNTs for (a) CV analysis and (b) specific capacitance as a function of potential sweep rate.
Figure 9.8 Comparison of the galvanostatic discharge curves between PANI/MWCNTs and Co
3
O
4
/PANI/MWCNTs (a), and (b) only Co
3
O
4
/PANI/MWCNTs composite at different current densities.
Figure 9.9 Comparison of the anticancer effects of different EC- and PANI-based composites when tested toward the MCF-7 breast carcinoma cell line over a concentration in the range of 0–250 µg mL
−1
for a 24 h period.
Chapter 10: Synthesis of Polyaniline-Based Nanocomposite Materials and Their Biomedical Applications
Figure 10.1 Different oxidized and reduced forms of PANI [13].
Figure 10.2 SEM images of adsorption of platelets on a native PANI surface (a), PANI–PEO film with a grafting density PANI of 3.3 (b) and 5.1 (c) [49].
Figure 10.3 Cultivation of NIH-3T3 fibroblasts on nanofiber scaffolds of PANI and PLCL and the electrical stimulation of (a) 20 mA and (b) 200 mA for 2 days [81].
Chapter 11: Electrically Conductive Polymers and Composites for Biomedical Applications
Figure 11.1 The use of conducting polymer and composites in biomedical applications.
Figure 11.2 Structures of the CPs (PPy, PANI, PTh, and PEDOT).
Figure 11.3 Solvent mixing method.
List of Tables
Chapter 2: Multifunctional Polymer-Dilute Magnetic Conductor and Bio-Devices
Table 2.1 Summarizes some of the most relevant magnetic-nanoparticle-based multifunctional polymer nanocomposites reported in the literature, with their respective properties and applications.
Chapter 3: Polymer–Inorganic Nanocomposite and Biosensors
Table 3.1 DNA sensors based on polymer nanocomposite (PNC)-modified electrodes.
Table 3.2 Immunosensors based on polymer nanocomposite (PNC)-modified electrodes.
Table 3.3 Aptamer sensors based on polymer nanocomposite (PNC)-modified electrodes.
Chapter 6: Polyaniline Nanocomposite Materials for Biosensor Designing
Table 6.1 PANI composite materials used for constructing biosensors.
Chapter 7: Recent Advances in Chitosan-Based Films for Novel Biosensor
Table 7.1 Chemical and biological properties of chitosan.
Table 7.2 Various types of chitosan-based biosensor for detection of analytes.
Chapter 8: Self Healing Materials and Conductivity
Table 8.1 Summary of healing performance of capsule-based self-healing materials.
Table 8.2 Summary of healing performance of vascular self-healing materials.
Table 8.3 Self-healing polymer systems under quasi-static fracture.
Chapter 9: Electrical Conductivity and Biological Efficacy of Ethyl Cellulose and Polyaniline-Based Composites
Table 9.1 Activation energies (eV) of conduction for different EC composites when tested in the presence of 0.5 M of 1 : 1 electrolytes at (25–50) ± 0.1 °C temperature.
Table 9.2 Comparison of the antimicrobial effects offered by the EC- and PANI-based composites when tested by means of ZoI at the corresponding MICs.
Chapter 10: Synthesis of Polyaniline-Based Nanocomposite Materials and Their Biomedical Applications
Table 10.1 Some reported PANI-supported polymer composite materials together with their electrical properties and applications in tissue engineering [14].
Table 10.2 PANI-supported nanocomposite and their biological applications in diverse fields.
Electrically Conductive Polymers and Polymer Composites
From Synthesis to Biomedical Applications
Edited by Anish Khan, Mohammad Jawaid, Aftab Aslam Parwaz Khan, and Abdullah M. Asiri
The Editors
Dr. Anish Khan
King Abdulaziz University
Center of Excellence for Advanced Materials Research, Chemistry Department
P.O. Box 80203
21589 Jeddah
Saudi Arabia
Dr. Mohammad Jawaid
Universiti Putra Malaysia
Biocomposite Technology Lab, INTROP
43400 Serdang
Selangor
Malaysia
Dr. Aftab Aslam Parwaz Khan
King Abdulaziz University
Center of Excellence for Advanced Materials Research
Chemistry Department
P.O. Box 80203
21589 Jeddah
Saudi Arabia
Prof. Abdullah M. Asiri
King Abdulaziz University
Center of Excellence for Advanced Materials Research
Chemistry Department
P.O. Box 80203
21589 Jeddah
Saudi Arabia
Cover
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The editors are honoured to dedicate this book to the “Indians to maintain harmony, peace, and brotherhood on all religious and sensitive issues.”
About the Editors
Anish Khan is currently working as Assistant Professor at the Chemistry Department, Centre of Excellence for Advanced Materials Research, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia. He completed his PhD from the Aligarh Muslim University, India in 2010. He has 13 years research experience working in the field of organic–inorganic electrically conducting nanocomposites and its applications in making chemical sensors. He completed his Postdoctoral from the School of Chemical Sciences, University Sains Malaysia (USM) in electroanalytical chemistry within 1 year. More than 100 research articles have been published in referred international journals. He has attended more than 10 international conferences/workshops and published two books and seven book chapters. He has also completed around 20 research projects. Managerial Editor of Chemical and Environmental Research (CER) Journal and Member of the American Nano Society, his field of specialization is polymer nanocomposite/cation exchangers/chemical sensors/microbiosensors/nanotechnology, applications of nanomaterials in electroanalytical chemistry, materials chemistry, ion-exchange chromatography, and electroanalytical chemistry, dealing with the synthesis, characterization (using different analytical techniques), and derivatization of inorganic ion exchanger by the incorporation of electrically conducting polymers. Preparation and characterization of hybrid nanocomposite materials and their applications, polymeric inorganic cation exchange materials, electrically conducting polymeric materials, composite material used as sensors, green chemistry by remediation of pollution, heavy metal ion-selective membrane electrodes, biosensors for neurotransmitters.
Dr Mohammad Jawaid is currently working as Senior Fellow Researcher (Associate Professor), at Biocomposite Technology Laboratory, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Serdang, Selangor, Malaysia and is also Visiting Professor at the Department of Chemical Engineering, College of Engineering, King Saud University, Riyadh, Saudi Arabia since June 2013. He is also Visiting Scientist to TEMAG Laboratory, Faculty of Textile Technologies and Design at Istanbul Technical University, Turkey. Previously he worked as Visiting Lecturer, Faculty of Chemical Engineering, Universiti Teknologi Malaysia (UTM) and also worked as Expatriate Lecturer under the UNDP project with the Ministry of Education of Ethiopia at Adama University, Ethiopia. He received his Ph.D. from Universiti Sains Malaysia, Malaysia. He has more than 10 years of experience in teaching, research, and industries. His area of research interests includes hybrid reinforced/filled polymer composites, advance materials: graphene/nanoclay/fire retardant, lignocellulosic-reinforced/filled polymer composites, modification and treatment of lignocellulosic fibers and solid wood, nanocomposites, and nanocellulose fibers, polymer blends. So far he has published 13 books, 27 book chapters, and more than 195 international journal papers, and five published review papers under top 25 hot articles in ScienceDirect during 2013–2015. He is also the Deputy Editor-in-Chief of Malaysian Polymer Journal, Guest Editor of Special issue-Current Organic Synthesis, Current Analytical Chemistry, International Journal of Polymer Science, and Editorial board member-Journal of Asian Science Technology and Innovation. Beside that he is also reviewer of several high-impact ISI journals of Elsevier, Springer, Wiley, Saga, and so on. Presently he is supervising 20 PhD students and 8 Master’s students in the field of hybrid composites, green composites, nanocomposites, natural-fiber-reinforced composites, nanocellulose, and so on. Seven PhD and four Master students graduated under his supervision in 2015–2017. He has several research grants at the university, national and international level on polymer composites of around RM 3 million (USD 700 000). He also delivered the Plenary and Invited Talk in International Conferences related to composites in India, Turkey, Malaysia, Thailand, and China. Beside that he is also a member of the technical committee of several national and international conferences on composites and materials science.
Aftab Aslam Parwaz Khan is currently working as Assistant Professor, Chemistry Department, Centre of Excellence for Advanced Materials Research (CEAMR), Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia. He has a PhD from the Aligarh Muslim University, India, on the topic preparation and characterization of nanomaterials and their applications in drug delivery systems. Major fields are Materials Science, Medicinal Chemistry. He has published two books and more than 100 research papers. His research encompasses all aspects of polymer composites, homogenous catalysis, doped metal nanoparticle synthesis, and characterization as well as novel application in environmental studies, chemical sensing, drug delivery systems for mechanistic and interaction studies using a wide range of spectroscopic techniques and thermodynamic parameters.
Abdullah M. Asiri is Professor in the Chemistry Department, – Faculty of Science, King Abdulaziz University. A PhD (1995) from the University of Wales, College of Cardiff, UK on Tribochromic compounds and their applications. He has published more than 1000 research articles and 20 books. Currently the chairman of the Chemistry Department, King Abdulaziz University, he also serves as the director of the Center of Excellence for Advanced Materials Research. Director of Education Affairs Unit–Deanship of Community services. Member of Advisory committee for advancing materials, National Technology Plan (King Abdulaziz City of Science and Technology, Riyadh, Saudi Arabia). Color chemistry, Synthesis of novel photochromic, thermochromic systems, novel colorants, coloration of textiles, plastics, Molecular modeling, Applications of organic materials into optics such as OEDS, High-performance organic dyes and pigments. New applications of organic photochromic compounds in new novelty. Organic synthesis of heterocyclic compounds as precursor for dyes. Synthesis of polymers functionalized with organic dyes. Preparation of some coating formulations for different applications. Photodynamic thereby using Organic Dyes and Pigments Virtual Labs and Experimental Simulations. He is member of the Editorial board of Journal of Saudi Chemical Society, Journal of King Abdulaziz University, Pigment and Resin Technology Journal, Organic Chemistry Insights, Libertas Academica, Recent Patents on Materials Science, Bentham Science Publishers Ltd. Beside that he has professional membership of the International and National Society and professional bodies.
Preface
The current book deals about the conductive polymer nanocomposite about the device advancement. The current focus of the book is the preparation and applications of the polymer conductive nanocomposite for biological applicability. The conducting polymer composites are the material of current era and are in demand. The polymer conductive nanocomposites are the field of the multidisciplinary use in science and technology that’s why this composite are different from rest of the material currently in the market. The special characteristic of the book is that it presents a unified knowledge of conductive polymer composite on the basis of characterization, design, manufacture, and applications. This book has collective information about the conducting polymer nanocomposite special attention to the bio devices applications. This book benefits to the lecturers, students, researchers, and industrialist who are working in the field of material science with special attention to conducting polymer based composites. Present book on polymer conducting composite for electronic devices is a valuable reference book, hand book, and text book for teaching, learning, and research in both academic and industrial interest.
This book cover a wide range of the topics on the conducting polymer composite particularly multifunctional polymer-dilute magnetic conductor, polymer-inorganic nanocomposite, carbon nanomaterials based conducting polymer composites, synthesis of polyaniline-based nanocomposite, and self-healing conductive materials.
We are highly thankful to contributors of book chapters who provided us their valuable innovative ideas and knowledge in this edited book. We attempt to gather information related to conducting polymer composites bio-device application from diverse fields around the world (Malaysia, India, Korea, USA, Saudi Arabia, South Africa and so on) and finally complete this venture in a fruitful way. We greatly appreciate contributor’s commitment for their support to compile our ideas in reality. We are highly thankful to Wiley team for their generous cooperation at every stage of the book production.
30th Nov, 2017
Anish Khan, Aftab Aslam Parwaz Khan, and Abdullah M. Asiri Saudi Arabia Mohammad Jawaid Malaysia
Chapter 1Bioinspired Polydopamine and Composites for Biomedical Applications
Ziyauddin Khan1, Ravi Shanker1, Dooseung Um1, Amit Jaiswal2 and Hyunhyub Ko1
1Ulsan National Institute of Science and Technology (UNIST), School of Energy & Chemical Engineering, UNIST-gil 50, Ulsan, 44919, Republic of Korea
2BioX centre, School of Basic Sciences, Indian Institute of Technology Mandi, Kamand, Mandi, 175005, Himachal Pradesh, India
1.1 Introduction
Understanding the systems and functions existing in nature and mimicking them led researchers to discover novel materials and systems useful in all disciplines of science, whether it is chemistry, biology, electronics, or materials science [1, 2]. Numerous biopolymers (carbohydrates and proteins) such as cellulose, starch, collagen, casein, and so on, are naturally occurring polymers and have vast application in the biomedical research field. In recent years, PDA, a bioinspired polymer having a molecular structure similar to that of 3,4-dihydroxy-l-phenylalanine (DOPA), which is a naturally occurring chemical in mussels responsible for their strong adhesion to various substrates, has been regarded as a promising polymer, with applications in energy, electronics, and biomedical fields, due to its chemical, optical, electrical, and magnetic properties [3, 4]. For example, PDA can be easily deposited or coated with any substrate type of one’s choice, including superhydrophobic surfaces, making it a highly beneficial material for coating and strong adhesive applications [3]. PDA also has various functional groups such as amine, imine, and catechol in its structure, which opens up the possibility for it to be integrated covalently with different molecules and various transition metal ions, thus making it a prerequisite in many bio-related applications.
Herein, this chapter describes the general synthetic route, polymerization mechanism, key properties, and biomedical applications of PDA. PDA can be synthesized by oxidation and self-polymerization of dopamine under ambient conditions; however, it can also be synthesized by enzymatic oxidation and electropolymerization processes, which are discussed in detail. Furthermore, this chapter also gives a brief idea about the characteristic properties of PDA such as optical, electrical, adhesive, and so on, followed by an extensive discussion of its applications in drug delivery, bioimaging, tissue engineering, cell adhesion and proliferation, and so on, with a special focus on its conductivity.
1.2 Synthesis of Polydopamine
1.2.1 Polymerization of Polydopamine
In the general synthesis of PDA, the dopamine monomer undergoes oxidation and self-polymerization in an alkaline medium (pH > 7.5) with air as an oxygen source for oxidation. This self-polymerization of the oxidative product of dopamine reaction is extremely facile and does not require any complicated steps. Although the polymerization of dopamine looks simple, the synthesis mechanism has not yet been investigated comprehensively [3, 5]. As shown in Figure 1.1, it is believed that in an alkaline solution dopamine is first oxidized by oxygen to dopamine quinone, followed by intramolecular cyclization to leucodopaminechrome through Michael addition. The formed intermediate leucodopaminechrome undergoes further oxidation and rearrangement to form 5,6-dihydroxyindole, which may yield 5,6-indolequinone by further oxidation [6]. Both these indole derivatives can undergo branching reactions at a different position (2, 3, 4, and 7), which can yield various isomers of dimers and finally higher oligomers. These oligomers can self-assemble by dismutation reaction between catechol and o-quinone to form a cross-linked polymer [3, 6]. Furthermore, there have been various other reports in which the authors have tried to investigate the exact mechanism of PDA formation, but this aspect is still unclear [7–10].
Figure 1.1 Formation mechanism of PDA in an alkali solution.
(Reprinted with permission from Refs [5] and [3] Copyright 2011 and 2014 American Chemical Society.)
Along with the oxidation and self-polymerization of dopamine in an alkali solution, PDA can also be synthesized by enzymatic oxidation and electropolymerization processes [11–13]. Enzymatic polymerization has attracted considerable interest owing to its environment-friendly characteristics. Inspired by the formation of melanin in a living organism, dopamine has been enzymatically polymerized using laccase enzyme into PDA at pH 6 (Figure 1.2) [1]. In laccase-catalyzed polymerization, laccase gets entrapped into the PDA matrix, which offers great advantages in biosensing and biofuel cell applications. In contrast to the enzymatic process, dopamine can also be electropolymerized and deposited on the substrate at a given potential in a deoxygenated solution. However, the electropolymerization process requires highly conductive materials, which is one of the main disadvantages of this process of dopamine polymerization.
Figure 1.2 Graphical representation of the formation of PDA–laccase–MWCNT nanocomposite film on GCE for hydroquinone biosensing.
(Reprinted with permission from Ref. [1] Copyright 2010 American Chemical Society.)
1.2.2 Synthesis of Polydopamine Nanostructures
A great deal of attention has been paid of late toward the synthesis of monodisperse PDA nanoparticles and PDAs with different morphologies, which can be used for other applications such as chemical sensors, energy storage, and so on. The size of the PDA particles can be tuned using a different ratio of solvents and base [14, 15]. Usually, after the self-polymerization reaction, PDA tends to form uniform spherical particles after prolonged reaction up to 30 h. Ai et al. have demonstrated that the size of PDA spheres can be controlled by varying the ratio of ammonia to dopamine and thereby synthesize various sizes of PDA nanoparticles (Figure 1.3a–e) [14]. In another study, Jiang et al. reported that varying the amount of ethanol and ammonia can also tune the size of PDA particles (Figure 1.3f) [15].
Figure 1.3 (a–e) Schematic representation of sub-micron size PDA particles and their morphological study.
(Redrawn and reprinted with permission from Ref. [14] Copyright 2013 Wiley-VCH.) (f) Study of EtOH and ammonia concentration on PDA morphology.
(Redrawn and reprinted with permission from Ref. [15] Copyright 2014 Nature Publishing Group.)
Recently, PDA with some unique morphology, for example, PDA nanotubes, have also been reported using a template-based method. Yan et al. coated a PDA layer on ZnO nanorods as a template by self-polymerization reaction of dopamine; and later the ZnO nanorod template was etched by ammonium chloride solution, leaving behind hollow PDA nanotubes (Figure 1.4a) [16]. Xue et al. reported the scalable synthesis of PDA nanotubes using curcumin crystal as a template [17], as shown in Figure 1.4b. These PDA nanotubes are several tens of micrometers long with 40-nm wall thickness and 200- to 400-nm tube diameter, which can be tuned by stirring rate and curcumin crystal size. Further to nanotubes, freestanding films of PDA and hybrid PDA films have also been prepared for their use in structural color, by layer-by-layer assembly [18–20]. In one of the reports, Yang et al. have reported composite freestanding films of PDA with polyethyleneimine (PEI), which was grown on air/water interface [20]. The prepared film was a freestanding transparent film, more than 1 cm in diameter, 80 nm in thickness, and without any visual defects on the film surface as proved by field emission scanning electron microscopy (FESEM). The film size can be tuned by the container which holds the dopamine and PEI solution.
Figure 1.4 (a) Graphical representation of PDA nanotube synthesis and its high-resolution TEM images.
(Reprinted with permission from Ref. [16] Copyright 2016 Royal Society of Chemistry.) (b) PDA nanotube synthesis by curcumin crystals and its morphology.
(Reprinted with permission from Ref. [17] Copyright 2016 American Chemical Society.)
Although there has been excellent progress in preparing different shapes and sizes of PDA nanoparticles, producing monodisperse nanoparticles is still a challenge, which is an essential parameter in biological science to ensure consistency in experiments. In the near future we can expect that this field will make further progress in producing highly monodisperse nanoparticles.
1.3 Properties of Polydopamine
1.3.1 General Properties of Polydopamine
PDA is an analog of eumelanin (a type of natural melanin) due to the similarity in chemical structure/component, which leads to the resemblance in physical properties [3, 21, 22]. Therefore, PDA has been regarded as a natural biopolymer, which has been utilized as a coating material in various applications. PDA is most commonly known for its inherent adhesive property; but functionalities of PDA have not been limited to adhesion as it possesses various properties, which are listed and discussed here.
1.
Optical properties
: PDA shows broadband absorption ranging from ultraviolet (UV) to visible region, which increases exponentially toward the UV spectrum as in the case of the naturally occurring analog eumelanin. The absorption in the UV region originates from oxidation of dopamine to dopachrome and dopaindole; however, the absorption in the visible and near-infrared (NIR) region is due to the subsequent self-polymerization process [23, 24].
2.
Electrical conductivity
: In 1974, McGinness
et al
. observed the electrical switching properties of eumelanin, and since then it was assumed that eumelanin has organic semiconductive properties [25, 26]. It was suggested that highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) levels of eumelanin act as valence and conduction bands as in the case of the semiconductor. Eumelanin is an aromatic compound that results in HOMO and LUMO levels composed of π-system and the charges move through this π-system, leading to the electrical conductivity of eumelanin. See the electrical properties (
Section 1.3.2
) for a detailed description.
3.
Adhesive property
: PDA displays a strong adhesive property to all kinds of surfaces and it is believed that this property arises due to the presence of the catechol group. However, it is not well understood yet how PDA diffuses to a different kind of surface, but based on literature it can be stated that PDA interacts with the substrate by a covalent or noncovalent binding mechanism [27, 28].
4.
Biocompatibility and biodegradation property
: Biocompatibility and biodegradation are the key parameters for any material to have an application in the biomedical field. PDA, a major component of melanin, shows exceptional biocompatibility even at high doses when its cytotoxicity was studied with mouse 4T1 breast cancer cells and human cervical cancer cells (HeLa cells) [29]. However, melanin can be degraded
in vitro
in the presence of oxidizing agents such as hydrogen peroxide, which is also the case for PDA [30]. The color fading was observed in PDA when incubated with hydrogen peroxide, which suggests its degradation [29]. Bettinger
et al
. in an
in vivo
study also suggests complete degradation of implanted PDA in 8 weeks [31].
1.3.2 Electrical Properties of Polydopamine
Organic semiconductors possess structural similarity to biological compounds, which opens up the possibility of their use in biomedical science [32]. A few of the most used organic semiconductors in biomedical science are poly(3,4-ethylenedioxythiophene):poly(4-styrenesulphonate) (PEDOT:PSS) and poly(3-hexylthiophene) (P3HT) due their excellent ion and electron mobility, and higher tissue integration ability [33, 34]. PEDOT:PSS is one of the first and widely used active channels in biomedical devices such as organic electrochemical transistors (OECTs) [33]. The performance of these devices can be improved by making a thinner film of the active channel below 100 nm [35, 36]. However, past literatures for such devices are mainly based on four transducing materials: P3HT, polypyrrole, PEDOT:PSS, and polyaniline [37]. This opens up the possibility of searching for alternative materials to be used in bioelectronic devices, in particular for edible electronics.
Interest in melanin, both natural and synthetic, has bloomed since the seminal study by McGinness et al. [25]. In recent years, PDA, also called synthetic melanin similar to natural melanin, has emerged as an additional candidate to be used in bioelectronics for transduction purposes. Since major research work in the context of the conductivity studies has been done on natural melanin, from hereon we use the word melanin as PDA’s properties are essentially similar to those of melanin. Melanin has some very interesting properties for biomedical application, such as broad monotonic optical absorption [38, 39], free radical population state [24, 40], and the possibility of making thin films less than 100 nm, thus offering device integration with neurons [4, 24, 41], hydration-dependent electrical and photoconductivity ranging from 10−8 to 10−4 S cm−1, depending on the hydrated state [39, 42], and the ability to link electronic and protonic/ionic signals in a common mechanism through comproportionation reaction (CRR) [43].
To describe each point is beyond the scope of this chapter, so we have mainly focused on its charge transport/electrical properties based on two different charge transport models available in the literature. Of the two models available to explain melanin charge transport properties, the first is based on an amorphous semiconductor model (ASM) and the other is hydration-dependent muon spin resonance (μSR) described by a CRR.
1.3.2.1 Amorphous Semiconductor Model (ASM) of Melanin Conductivity
This model is based on the four observations and considers melanin to be an amorphous semiconductor because it shows the following:
Semiconductor-type Arrhenius temperature dependence on its conductivity [42, 44]
Bistable switching behavior [25, 45]
Broadband optical absorbance [39]
Stable free radical: unpaired electrons at the Fermi energy level [46].
However, there are a few shortcomings in this model, the first one being its broad absorbance (Figure 1.5a), which can also be described by the oligomer structure, that is, the spectrum is made up of multiple individual chemical chromophores [39, 49]. It cannot describe the delocalized electronic state for which large 2D sheet-type structures are required; this is not true for oligomers, which are fairly small. The second is that only wet melanin samples display hydration-dependent switching behavior.
Figure 1.5 (a) Melanin broadband optical absorbance spectrum (inset for log linear axes) and peaks below show individual absorbance peak chromophores.
(Reprinted with permission from Ref. [39] Copyright 2005 Royal Society of Chemistry.) (b) Equilibrium adsorption isotherm for melanin in the presence of water vapor.
(Reprinted with permission from Ref. [47] Copyright 2010 American Chemical Society.) (c) Melanin dark conductivity versus water content in sandwich geometry. (d) Melanin dark conductivity versus water in van der Pauw geometry.
((c and d) Reprinted with permission from Ref. [48] Copyright 2012, AIP Publishing LLC.)
To observe the conductivity of hydration-dependent melanin, Mostert et al. measured the water–melanin adsorption isotherm on melanin pallet samples and the result is shown in Figure 1.5b, which exhibits the significant presence of water in melanin [47]. Mostert et al. also measured the hydration-dependent conductivity using two different contact geometries, that is, sandwich and van der Pauw, and the results are shown in Figure 1.5c,d [48].
It can be seen from Figure 1.5c that the conductivity increases by orders of magnitude in a sub-exponential manner. However, the specimen was found to be at nonequilibrium in sandwich geometry due to low exposure of the surface area by the presence of the contacts. Therefore, an open-contact arrangement, van der Pauw geometry (Figure 1.5d inset), has been used where ~71% of surface area can be exposed than to ~37% in sandwich geometry; and the result is shown in Figure 1.5d [48]. Interestingly, these data were found not to be in agreement with previous literature and also could not be explained by the existing ASM theory [42, 50].
This argument was also supported with controlled photoconductivity experiments, which are shown in Figure 1.6a–d and have a simple explanation: as heating increases, water desorption takes place and produces a negative conductivity, whereas as per ASM it is due to the trap states in the photo bandgap of melanin [48]. This study also shows strong evidence that water plays a crucial role in the basic charge transport mechanism and ASM cannot be applied to melanin.
Figure 1.6 Melanin photoconductivity versus time for four different hydration levels: (a) 8.6%, (b) 10.2%, (c) 13.4%, and (d) 16.2%, under dark, illuminated, and dark sequence each for 50 s.
(Reprinted with permission from Ref. [48] Copyright 2012, AIP Publishing LLC.)
1.3.2.2 Spin Muon Resonance Model (SMRM) of Melanin Conductivity
To further elucidate the charge transport mechanism of melanin, an alternative technique – magnetic resonance (μSR) – has been used because it can discount electrical effects, probe the material’s local environment and mobility behavior of protons in the specimen [51], and estimate the number density of the free radicals [52, 53]. μSR demonstrates that in melanin, charge transport is determined by an equilibrium reaction. The controlled, water-dependent μSR carried out as a function of hydration is shown in Figure 1.7. It can be seen from Figure 1.7a that muon hopping rate ν does not change throughout the hydration range of melanin, meaning that proton mobility remains the same. However, muon relaxation ∆ and spin–lattice relaxation rate λ show qualitative changes and exhibit a response similar to the conductivity data in Figure 1.5d because λ is directly related to free-radical density in a sample; thus, the unpaired electrons present in melanin increase with hydration, along with the conductivity. Mostert et al. suggested that a CRR, which is essentially an equilibrium reaction, can only explain the conductivity and μSR results [55].
Figure 1.7 (a) The μSR relaxation data obtained on hydrated melanin pellets. (b) A pH-dependent titration EPR study for colloidal suspensions of melanin.
(Reprinted with permission from Ref. [54] Copyright 2012, PNAS.)
In CRR, two different oxidative state chemical units of melanin form semiquinones, which are hydronium and free radicals on the introduction of water (Eq. (1.1)) [54]. With the increase of hydration, an imbalance occurs between the reactant and product; and to counterbalance this, the unevenness reaction starts producing more products in accordance with Le Chatelier’s principle [54, 55]. In addition, it was also explained by electron paramagnetic resonance (EPR) measurement, as shown in Figure 1.6b, that when the base is added (the same effect as adding water), the titration curve displays a response similar to both the μSR and conductivity [54]. Therefore, it was proposed that the conductivity increase in charge carrier density, both protonic as well as electronic, is due to the link between two charge entities and which makes melanin a potential transducing material for biomedical devices.
1.4 Applications of Polydopamine
As mentioned, PDA has a range of intriguing properties and is a potential candidate in a variety of important applications, from biomedical science to energy, as shown in Figure 1.8. For example, in energy and environment applications, heterogeneous photocatalysis, which is known as a cost-effective approach for dye degradation and solar water splitting under light irradiation [56–60], PDA can be coupled with photocatalytic materials which help the photocatalytic materials improve their performance synergistically by π–π* electronic transition [61]. Feng et al. synthesized core–shell AgNPs@PDA and used it for photocatalytic degradation of neutral red dye. They reported that the AgNPs@PDA catalyst showed improved performance than bare Ag NPs and PDA under UV irradiation. PDA can produce holes under UV illumination, which extends the duration of the recombination rate of photogenerated charge carrier and results in enhancement in the lifetime of electron pairs due to the existence of π–π* electronic transition. In addition, it also offers extra surface for dye adsorption. Recently, Mao et al. synthesized TiO2@PDA photocatalyst and used it for the degradation of rhodamine B (RhB) under visible light illumination [62]. TiO2 is a well-known UV-light-driven photocatalyst; however, PDA shows strong absorption in the visible region, and coupling of these two can form a catalyst which can have visible light activity, as investigated by Mao et al. The authors have coated different thickness PDA on TiO2 nanoparticles and found that 1 nm coated PDA on TiO2 showed highly improved performance for RhB degradation. The reason for such an enhancement is still not clear, but it was proposed theoretically by Persson and coworkers that there is a one-step charge transfer from dopamine to the conduction band of TiO2, which can improve the catalytic performance of the composite material. Besides, PDA can be utilized for various energy-related applications such as batteries, supercapacitors, and dye-sensitized solar cells [63–65]. However, as per the demand of the chapter, we mainly focus on its biomedical applications.
Figure 1.8 Application of polydopamine in various emerging research fields.
1.4.1 Biomedical Applications of Polydopamine
PDA, a major component of naturally occurring melanin, has vast biomedical application due to its exceptional biocompatibility, hydrophilicity, and thermal and adhesive properties. It can also undergo further reaction with various molecules/materials and produce hybrid materials with applications in diverse research fields. This section deals with the various biomedical applications of PDA and PDA-derived materials.
1.4.1.1 Drug Delivery
PDA capsules have been considered fascinating material for drug delivery owing to their high water solubility, exceptional biocompatibility, and biodegradation ability. The interest in the synthesis of PDA capsules with well-defined structures has increased tremendously for drug delivery because drugs can easily be encapsulated in the capsule’s cavities. Various soft and hard template-based methods have been used to synthesize PDA capsules. However, the hard template method is least favored due to its requirement of harsh conditions for removal, which can hinder its application in the biomedical field [66–69]. The drug loading behavior of PDA capsules depends on the size of the capsules, as bigger capsule size increases the interior volume which leads to higher drug loading. Furthermore, the pH of the solution and the charge state of the loading molecules also greatly affect the drug loading behavior [66, 70]. PDA have different functional groups and therefore display zwitterionic property. At low pH (pH ~ 3), the PDA capsule walls were positively charged; however, if the loading molecule is methyl orange (MO), which is in a neutral state at this pH, the presence of the sulfonate group gives it an anionic character. Thus, there exists strong ionic interaction between the positively charged PDA capsule and the negatively charged MO dye, which leads to higher loading of a dye molecule in PDA capsules. However, if the loading molecule is rhodamine 6G, then there is almost negligible loading of the dye molecule to PDA capsules because of strong electrostatic repulsion between the positively charged PDA and the positively charged rhodamine 6G at this pH [66]. Regardless of the high loading of the desired drug, these systems suffer from poor drug delivery in aqueous media which needs to be overcome [3].
1.4.1.2 Tissue Engineering
Tissue engineering has been considered an effective technique to replace damaged or diseased body parts with man-made artificial tissues or organs without any transmission disease. The research, in tissue engineering, is mainly focused on the development of effective scaffolds for cells and tissue growth [71]. Typically, in extracellular matrix cell attachment, proliferation and differentiation take place for natural tissues; and, therefore, it would be a prerequisite for effective tissue engineering that artificial scaffolds should be chemically and physically analogous to the extracellular matrix. Mesoporous SiO2 has been used as scaffolds for tissue engineering because the big pores are beneficial to cell growth, while the mesoporous structure can also help transport drugs that stimulate bone-forming cells. However, mesoporous SiO2 suffers from poor cytocompatibility and mineralization rate [72]. Wu et al. took advantage of the adhesive and hydrophilic properties of PDA and used it as a surface modifier for mesoporous SiO2 to study the mineralization and cytocompatibility for drug delivery and bone tissue engineering [72]. Investigation into the in vitro mineralization and proliferation of bone marrow stem cells (BMSCs) revealed that the PDA-modified SiO2 scaffold displayed noteworthy apatite mineralization and also that attachment of BMSCs on PDA-modified SiO2 had been increased (Figure 1.9a,b). It would be worthwhile to mention here that despite these efforts, the SiO2-based scaffold suffers from in vivo degradation.
Figure 1.9 (a) Digital image of SiO2 scaffold before and after 6- and 24-h modification with PDA; (b) the proliferation of BMSCs on mesoporous silica (MS), PDA-modified silica (MSD), and dexamethasone (DEX)-loaded MSD (MSD-DEX) scaffolds. MSD shows improved proliferation of BMSCs.
(Reprinted with permission from Ref. [72], Copyright 2011 Royal Society of Chemistry.) (c) Cell adhesion graphics on PDA-coated polycaprolactone nanofibers (PCL NFs); (d) SEM image of fibers; (e) hydrophilicity measurement by contact angle analysis. (f) A number of live cells, and fold-increase of cell viability for HUVECs grown on unmodified, gelatin-coated, and PDA-coated PCL NFs.
((c–f) Reprinted with permission from Ref. [73], Copyright 2010 Elsevier Ltd.)
Ku and Park utilized nanofibers of biodegradable polymer polycaprolactone and deposited a thin layer of PDA on top to improve the cell affinity with polymeric nanofibers [73]. It was observed that the cell can attach, spread, and survive effectively on PDA-modified fibers. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay suggests that human umbilical vein endothelial cells (HUVECs) displayed fivefold enhancement in viability on PDA-modified nanofibers (Figure 1.9c–f). These investigations suggest that PDA can play a vital role in the design of artificial scaffolds in future in the tissue engineering area.
1.4.1.3 Antimicrobial Applications
The robust adhesion of PDA on various substrates makes it viable for fabrication of antimicrobial surfaces [74–76]. Xu et al. fabricated antibacterial cotton by coating a PDA layer on top of cotton fabrics, followed by in situ deposition of silver nanoparticles (Figure 1.10a) [74]. The prepared antibacterial cotton completely killed the bacteria. Even after 30 washes, the cotton fabrics were able to reduce 99.99% Escherichia coli, suggesting reusability and durability of cotton fabrics after coating with PDA (Figure 1.10b). Later, Sileika et al. utilized the adhesive property of PDA to make an antimicrobial surface by coating PDA on a polycarbonate substrate, followed by silver nanoparticle deposition as an antibacterial agent and in situ implanting of poly(ethylene glycol) (PEG) as an antifouling agent, as shown in Figure 1.10c [75]. The resulting substrate killed both gram-negative and gram-positive bacteria strains and resisted their attachment on the substrate. These outstanding studies reveal that PDA can provide a new avenue to fabricate an antibacterial substrate for use in practical applications.
Figure 1.10 FESEM images of the dopa-cotton/AgNPs fabrics (a) unwashed and (b) after 30 washes.
(Reprinted with permission from Ref. [74], Copyright 2011 Elsevier Ltd.) (c) Synthesis protocol of silver deposited (directly deposited silver (DDS)) and PDA-mediated antimicrobial coatings on a polycarbonate substrate.
(Reprinted with permission from Ref. [75], Copyright 2011 American Chemical Society.)
1.4.1.4 Bioimaging
Fluorescence-based bioimaging of samples or cells has attracted tremendous attention in the past few decades with advances in nanotechnology and become the most widespread method in biomedical science due to its key properties, including high sensitivity, cost-effectiveness, and facile detection. Various kinds of nanoparticles have been developed and are widely used as fluorescent probes for bioimaging of cells and tissues. An excellent review by Wolfbeis covers different nanoparticles widely used in probes for bioimaging such as doped silica, hydrogels, noble metal nanoparticles, quantum dots, carbon dots, upconversion nanoparticles, and so on [77, 78]. However, their cytotoxicity is still a debatable issue, as discussed by Zhang et al. [79]. As a recent addition to nanoparticle-based bioimaging, PDA has emerged as a new class of biocompatible organic fluorescent material. In a study, Wei and coworkers synthesized polydopamine fluorescent organic nanoparticles (PDA-FONs) and reported excitation-wavelength-dependent emission reaching maximum at 440 nm excitation with excellent photostability [80]. These PDA-FONs offer a simple fabrication method in contrast to the conventional method of complex organic synthesis of FONs (Figure 1.11). In addition, PDA has also been used as a coating material to enhance optical signals of fluorescent materials such as graphene quantum dots, and so on [81, 82]. Despite excellent biocompatibility, the fluorescence intensity is a rather weak point to overcome. Therefore, the future work will be on the design of novel PDA-based multifunctional fluorescent nanoparticles with tunable size, morphology, and fluorescent properties.
Figure 1.11 (a) Schematic illustration for the preparation of PDA-FONs and their application in cell imaging. (b) Normalized photoluminescence emission spectra of PDA-FON dispersion at different excitation wavelengths from 360 to 500 nm. (c) Fluorescence microscopy photograph of the PDA-FON dispersion excited by UV light (340–380 nm). (d) Effect of PDA-FONs on NIH-3T3 cells. (e–g) are confocal laser scanning microscopy images of cells imaged under bright field 405- and 458-nm excitations, respectively.
(Reprinted with permission from Ref. [80] Copyright 2012 Royal Society of Chemistry.)
1.4.1.5 Cell Adhesion and Proliferation
Currently, interest in immobilization of cells by new synthetic materials is crucial to promote cell adhesion. PDA has emerged as a simple, versatile, and biocompatible material for such applications, which show excellent cellular response and strong affinity of cells to PDA coatings. PDA shows potential to enhance cell immobilization on various kinds of substrates. In a study, Yang et al. have shown that using PDA coating on living yeast cell can control and preserve cell division (Figure 1.12) [83]. Lee et al. observed PDA coating cytocompatibility is cell dependent and reported fibroblast and megakaryocytes cell adhesion to PDA-coated surfaces [4]. Park and coworkers reported excellent adhesion in vitro cytocompatibility of HUVECs on PDA-coated polycaprolactone nanofibers [73]. PDA coating also offers a key method to make bioactive surfaces including non-wetting and 3D porous scaffolds [84–86].
Figure 1.12 (a) Schematic of the PDA and its encapsulation and surface functionalization on yeast cells. Confocal micrographs of (b) native yeasts and (c) yeast@PDA. (d–g) TEM micrographs of PDA-encapsulated yeast cells. (h) Growth curve of native and PDA-coated yeast cells. (i) Survival of native and coated yeast cells in the presence of lyticase.
Reprinted with permission from Ref. [83] Copyright 2011 American Chemical Society.)
In addition to the excellent binding abilities, PDA-treated surfaces overcome the challenges of adhesive proteins for cellular patterning and can be deposited using different deposition methods such as microfluidic, micro-contact printing, and lithography (Figure 1.13 shows cell pattering using PDA ink) [4, 83, 87, 88]. In addition, combined studies on submicron topography and surface chemistry effect on cells have shown synergic enhancement in cell adhesion and proliferation [89, 90]. The possible mechanism of cell adhesion is also reported and is likely due to higher immobilization and/or adsorption of adhesive proteins [84, 85]. Recent studies suggest a new mechanism that the quinone group of PDA induced a larger amount of protein adsorption, and thus promoted endothelial attachment and proliferation [91–93].
Figure 1.13 (a) Schematic representation of cell patterning with PDA as ink via micro-contact printing; (b) optical microscopic image of an imprinted PDA pattern on a gold substrate; (c) SEM images of PDA patterns on silicon; (d) SEM image of the cell-patterned substrate; (e) fluorescent microscopy image of the cell-patterned substrate after immobilization of fluorescein isothiocyanate conjugate – bovine serum albumin (FITC-BSA).
Reprinted with permission from Ref. [87] Copyright 2012 American Chemical Society.)
1.4.1.6 Cancer Therapy
Photothermal therapy (PTT) is a minimally invasive treatment in which NIR light radiation is used for the treatment of many medical conditions such as
