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Shakeel Ahmed is an Assistant Professor at the Department of Chemistry, Government Degree College Mendhar, Jammu and Kashmir, India. He obtained his PhD in the area of biopolymers and bionanocomposites and has published several research publications in the area of green nanomaterials and biopolymers for various applications including biomedical, packaging, sensors, and water treatment. He has edited or co-edited 4 books for Wiley-Scrivener.
Preface xv
Part 1: Alginates-Introduction, Characterization and Properties 1
1 Alginates: General Introduction and Properties 3Rutika Sehgal, Akshita Mehta and Reena Gupta
1.1 Introduction 4
1.2 History 4
1.3 Structure 4
1.4 Alginates and Their Properties 6
1.4.1 Gel Formation 6
1.4.1.1 Ionic Alginate Gels 6
1.4.1.2 Alginic Acid Gels 8
1.4.2 Molecular Weight 8
1.4.3 Solubility and Viscosity 8
1.4.4 Ionic Cross-Linking 9
1.4.5 Chemical Properties 9
1.5 Sources 11
1.6 Biosynthesis of Bacterial Alginate 11
1.6.1 Precursor Synthesis 12
1.6.2 Polymerization and Cytoplasmic Membrane Transfer 13
1.6.3 Periplasmic Transfer and Modification 15
1.6.3.1 Transacetylases 15
1.6.3.2 Mannuronan C 5-Epimerases 16
1.6.3.3 Lyases 16
1.6.5 Export through the Outer Membrane 16
1.7 Conclusion 16
Acknowledgment 17
Conflict of Interests 17
References 17
2 Alginates Production, Characterization and Modification 21Pintu Pandit, T. N. Gayatri and Baburaj Regubalan
2.1 Introduction 22
2.2 Alginate: Production 24
2.2.1 Screening of Alginate-Producing Microbes 24
2.2.2 Production of Alginate by Bacteria 25
2.2.3 Production of Alginate by Pseudomonas 26
2.2.4 Production of Alginate by Azotobacter spp. 26
2.2.5 Influence of Medium Components 26
2.2.5.1 Effect of Nutrients on Bacterial Alginate Production 26
2.2.5.2 Effect of Phosphate on Bacterial Alginate Production 27
2.2.5.3 Effect of Dissolved Oxygen on Bacterial Alginate Production 27
2.2.5.4 Effect of Agitation in the Medium for the Production of Alginate 27
2.2.6 Commercial Production of Alginate 28
2.3 Characterization of Physicochemical Properties of Alginate 28
2.3.1 Composition of Alginate Polymer Chains 29
2.3.2 XRD, FTIR, and NMR Spectroscopy for Alginate Structure Analysis 31
2.3.3 Rheology and Mechanical Characterization of Alginate Gels and Solutions 32
2.4 Modification of Alginates 33
2.4.1 Chemical Modification 33
2.4.2 Oxidation 34
2.4.3 Sulfation 34
2.4.4 Phosphorylation 35
2.4.5 Graft Copolymerization 35
2.4.6 Esterification 35
2.4.7 Carbodiimide Coupling 36
2.4.8 Covalent Cross-Linking 36
2.5 Future Perspectives 38
2.6 Conclusions 39
References 39
3 Alginate: Recent Progress and Technological Prospects 45Tanvir Arfin and Kamini Sonawane
3.1 Introduction 45
3.2 Structure 46
3.3 Sources 47
3.4 Characteristics of Alginate Salts 48
3.5 Properties 48
3.6 Applications 50
3.7 Future Perspectives 53
3.8 Advantages 54
3.9 Disadvantages 54
3.10 Conclusion 54
Acknowledgments 55
References 55
4 Alginate Hydrogel and Aerogel 59Ajith James Jose, Kavya Mohan and Alice Vavachan
4.1 Introduction 59
4.2 Alginate Hydrogel 60
4.2.1 Preparation of Alginate Hydrogels 61
4.2.1.1 Ionic Cross-Linking 62
4.2.1.2 Covalent Cross-Linking 62
4.2.1.3 Thermal Gelation 62
4.2.1.4 Cell Cross-Linking 63
4.2.2 Biomedical Applications 63
4.2.2.1 Pharmaceutical Applications 63
4.2.3 Tissue Regeneration with Protein and Cell Delivery 68
4.2.3.1 Blood Vessels 68
4.2.3.2 Bones 69
4.2.3.3 Cartilage 69
4.2.3.4 Muscle, Nerve, Pancreas, and Liver 70
4.3 Alginate Aerogel 70
4.3.1 Properties of Alginate Aerogels 71
4.3.1.1 Bulk Density and Pore Volume 71
4.3.1.2 Specific Surface Area 71
4.3.1.3 Compressibility 71
4.3.1.4 Thermal Conductivity and Absorption 72
4.3.2 Preparative Methods 72
4.4 Future Perspectives 73
References 73
Part 2: Alginates in Biomedical Applications 79
5 Alginate in Biomedical Applications 81Luiz Pereira da Costa
5.1 Introduction 81
5.2 Chemical Structure and Properties of Alginate 83
5.3 Types of Interaction of Alginate 84
5.4 Biomedical Application of Alginates 87
5.5 Future Perspective of the Use and Biomedical Applications 90
References 90
6 Alginates in Pharmaceutical and Biomedical Application: A Critique 95Vivek Dave, Kajal Tak, Chavi Gupta, Kanika Verma and Swapnil Sharma
6.1 Introduction 95
6.2 Structure of Alginate 96
6.3 Different Types of Alginates Used in Pharmaceutical Industries 97
6.4 Properties of Alginate 98
6.5 Pathway for the Biosynthesis of Alginate 98
6.6 Regulatory Consideration of Alginate 100
6.7 Applications 100
6.7.1 Other Applications 113
6.8 Conclusion 114
References 115
7 Alginates in Evolution of Restorative Dentistry 125S.C. Onwubu, P.S. Mdluli, S. Singh and Y. Ngombane
7.1 Introduction 125
7.2 Method of Alginate Extraction 126
7.3 Evolution of Alginate in Restorative Dentistry 128
7.3.1 Problems with Conventional Alginate 129
7.3.2 Current Trends and Modification of Alginate 129
7.3.2.1 Extended Pour Time Alginate 130
7.3.2.2 Dust-Free Alginates 130
7.3.2.3 Infection-Free Alginates 132
7.3.2.4 High Viscosity Alginates 132
7.3.2.5 Alginates in Two Pastes Form 133
7.3.2.6 Tray Adhesive Alginates 133
7.4 The Art of Impression Taking Using Alginates 133
7.4.1 Selection of Impression Trays 134
7.4.2 Mixing and Loading Alginates 135
7.4.3 Preparation of the Oral Cavity before Impression Taking 135
7.4.4 Impression Taking Using Alginate Material 136
7.4.5 Removal and Inspection of Alginate Material 137
7.4.6 Effects of Cast Production Techniques 137
7.5 Conclusions 138
References 138
8 Alginates in Drug Delivery 141Srijita Basumallick
8.1 Introduction 141
8.2 Chemistry of Alginates 142
8.2.1 Hydrogel Formation by Alginates 143
8.2.1.1 Preparation of Hydrogel 143
8.3 Pharmaceutical and Biomedical Chemistry of Alginates 144
8.3.1 Factors Governing Drug Encapsulation and Drug Delivery Processes 145
8.3.1.1 Delivery and Encapsulation of Small Drugs 145
8.3.1.2 Macromolecular Drug Delivery by Alginates 148
8.4 Conclusions 149
Acknowledgments 149
References 149
9 Alginate in Wound Care 153Satyaranjan Bairagi and S. Wazed Ali
9.1 Introduction 154
9.2 Sources and Synthesis of Alginate 154
9.3 Physicochemical Properties of the Alginate Biopolymer 156
9.4 Biomedical Applications of Alginate 157
9.4.1 Alginate in Wound Care 158
9.4.1.1 Pure Alginate Polymer-Based Wound Dressing 160
9.4.1.2 Intercellular Mediators Incorporated Alginate Polymer-Based Wound Dressing 160
9.4.1.3 Zinc/Alginate- and Silver/Alginate-Based Wound Dressing 161
9.4.1.4 Chitosan/Alginate- and Collagen/Alginate-Based Wound Dressing 163
9.4.1.5 Alginate Fiber-Based Wound Dressing 163
9.4.1.6 Alginate Hydrogel-Based Wound Dressing 167
9.5 Opportunities and Future Thrust 172
References 173
10 Alginate-Based Biomaterials for Bio-Medical Applications 179Reena Antil, Ritu Hooda, Minakshi Sharm and Pushpa Dahiya
10.1 Introduction 180
10.2 Alginate: General Properties 180
10.2.1 Chemical Properties, Structure, and Characterization 181
10.3 Extraction and Preparation 182
10.3.1 Gelation and Cross-Linking of Alginate 183
10.3.2 Ionic Cross-Linking 184
10.3.3 External Gelation 184
10.3.4 Internal Gelation 185
10.3.5 Covalent Cross-Linking 185
10.3.6 Large Bead Preparation 186
10.3.7 Microbead Preparation 186
10.4 Alginate Hydrogels 187
10.5 Photocross-Linking 188
10.6 Shape-Memory Alginate Scaffolds 188
10.7 Biodegradation of Alginate 189
10.8 Biomedical Application of Alginates 190
10.8.1 Controlled Chemical and Protein Drug Delivery 190
10.8.2 Wound/Injury Dressings 193
10.8.3 Cell Culture 194
10.8.4 Tissue Regeneration 195
References 196
Part 3: Alginates in Food Industry 205
11 Alginates for Food Packaging Applications 207Radhika Theagarajan, Sayantani Dutta, J.A. Moses and C. Anandharamakrishnan
11.1 Introduction 207
11.2 Biopolymer in Food Industry 208
11.3 Alginates in Food Packaging 209
11.4 Biosynthesis of Alginate 213
11.5 Application of Alginate in Formation of Biofilm 215
11.5.1 Preparation of Packaging Films 215
11.5.2 Role of Alginate in Biofilm Formation 215
11.6 Packaging Properties of Alginate 217
11.6.1 Thermostability of Alginate Packaging 218
11.6.2 Water Solubility 218
11.6.3 Water Vapor Permeability 218
11.6.4 Tensile Strength 218
11.6.5 Oxygen Permeability 219
11.6.6 Barrier Property 219
11.6.7 Antimicrobial Activity 219
11.7 Effect of Alginate on the Quality of Food 222
11.8 Interaction between Food and Alginates 223
11.9 Environmental Effects on Alginate Packaging 224
11.10 Market Outlook 224
11.11 Conclusion 225
References 226
12 Potential Application of Alginates in the Beverage Industry 233S. Vijayalakshmi, S.K. Sivakamasundari, J.A. Moses and C. Anandharamakrishnan
12.1 Introduction 233
12.2 Alginate Source 234
12.3 Extraction of Alginates 235
12.4 Physical, Chemical and Functional Properties of Alginate 236
12.5 Uses as a Food Additive/Ingredient 241
12.6 Alginate as Stabilizer 245
12.7 As Encapsulating Wall Material 247
12.7.1 Immobilization of Biocatalysts 249
12.7.2 Probiotics 250
12.7.3 Improvement of the Alginate Encapsulation: Prebiotics Addition 253
12.8 Conclusion 254
References 254
13 Alginates in Comestibles 263Ashwini Ravi, S. Vijayanand, Velu Rajeshkannan, S. Aisverya, K. Sangeetha, P.N. Sudha and J. Hemapriya
13.1 Introduction 264
13.2 Alginates in Agricultural Marketing 265
13.3 Use of Alginates in Food Industry 266
13.3.1 Thickeners and Gelling Agents 267
13.3.2 Stabilizers and Emulsifiers 268
13.3.3 Texturizers 269
13.3.4 Encapsulation 269
13.3.5 Food Coating 270
13.4 Use of Alginates for Pets 271
13.5 Effect of Dietary Alginates 271
13.6 Alginate Safety 272
13.7 Conclusion 272
References 272
Part 4: Alginates Future Prospects 281
14 Alginates: Current Uses and Future Perspective 283Ashwini Ravi, S. Vijayanand, G. Ramya, A. Shyamala, Velu Rajeshkannan, S. Aisverya, P.N. Sudha and J. Hemapriya
14.1 Introduction 284
14.2 Sources of Alginate Synthesis 285
14.2.1 Brown Seaweeds 285
14.2.2 Bacteria 287
14.3 Synthesis of Alginate 288
14.3.1 Alginate Biosynthesis Gene 289
14.4 Properties of Alginates 290
14.4.1 Molecular Weight 290
14.4.2 Solubility 291
14.4.3 Stability 291
14.4.4 Ionic Binding Property 292
14.4.5 Gel Formation Ability 293
14.4.6 Biological Properties 293
14.5 Application of Alginates 294
14.6 Future Perspectives of Alginates 295
14.6.1 3D-Based Cell Culture Systems 295
14.6.2 Impressions 296
14.6.3 Cell-Based Microparticles 296
14.6.4 Alginate Oligosaccharides 298
14.6.5 Drug Targeting 299
14.6.6 Nanoparticulate Systems 300
14.7 Conclusion 300
References 300
Index 313
Rutika Sehgal1, Akshita Mehta1 and Reena Gupta1*
1Department of Biotechnology, Himachal Pradesh University, Summerhill, Shimla, India
*Corresponding author: reenagupta_2001@yahoo.com
Alginates (ALGs) are a group of naturally occurring anionic polysaccharides derived from brown seaweeds. They are linear biopolymers of 1,4-linked ß-D-mannuronic acid (M) and 1,4 a-L-guluronic acid (G) residues that are arranged in homogenous (poly-G, poly-M) or heterogenous (MG) block-like patterns. The physiological and chemical characteristics of ALGs depend on this arrangement of residues. Alginates are primarily used as thermally stable cold-setting gelling agents, which are formed in presence of divalent cations. They are more efficient gelling agents than gelatin and can gel at far lower concentrations as compared to other agents. This ability to create a chemically set, irreversible gel has proved to be useful in many food applications. Among various ALGs, sodium ALG is most widely studied in the pharmaceutical and biomedical field. Its various properties favor its use for viscosity enhancement, encapsulation polymer, matrixing agent, stabilizer, bioadhesive, and film former in transdermal and transmucosal drug delivery. With well-established uses in dentistry, the ALGs also offer interesting possibilities in the field of medicine and cosmetics as a skin care ingredient. This chapter will include general introduction, understanding of structure and properties of ALGs, and different forms of ALGs used in industries.
Keywords: Alginates, biopolymer, polysaccharide, medicines, cosmetics
Alginates (ALGs) are naturally occurring anionic polysaccharides that are present as a structural component in cell walls of brown algae, mainly from Macrocystis pyrifera, Ascophyllum nodosum, and Laminaria hyperborea and as a capsular polysaccharide in bacterial strains like Azotobacter and Pseudomonas. It is present in the cell wall of brown algae as the calcium, magnesium, and sodium salts; therefore, it is usually referred to as "alginic acid and its salts." Alginates are available commercially as sodium, potassium, or ammonium salts in filamentous, granular, or powdered forms. Their color ranges from white to yellowish-brown. The molecular weight of ALG generally ranges from 60,000 to 700,000 Da depending on the application [1]. The size (diameter) of ALG gel particles can be macro (greater than 1 mm), micro (from 0.2 to 1,000 mm), or nano (less than 0.2 mm). These gel particles have high water holding capacity to form a viscous gum and have adjustable chemical and mechanical properties that are dependent on the type of cross-linking agent used. As a natural ingredient, ALG gel particles are attractive for various biological applications because they are biocompatible, nontoxic, biodegradable, and relatively cheap [2, 3]. Alginate is also a significant component of the biofilms produced by the bacterium Pseudomonas aeruginosa, the major pathogen in cystic fibrosis, that confers it a high resistance to antibiotics and killing by macrophages.
Alginate was discovered in the late 19th century by a British Pharmacist, E.C.C. Stanford, who called it "algin," which was a viscous solution obtained initially from Laminariaceae. Since its discovery in 1883, it has become an important industrial product that is commercially obtained from coastal brown seaweeds. Later its extracts were termed as "alginic acid." Its commercial production started in 1929. It has been estimated that algal ALGs are produced nearly 38,000 tons worldwide annually, and their major part contributes to food and pharmaceutical industries because of their increased demand [4].
Alginates are linear biopolymers of 1,4-linked ß-D-mannuronic acid (M) and 1,4 a-L-guluronic acid (G) residues (Figure 1.1) organized in homogenous (poly-G, poly-M) or heterogenous (MG) block patterns. The G and M block pattern and sequence may be different in commercial ALG depending on the source of seaweed used, harvesting season, and geographical location of the seaweed source [5]. The random sequence of M and G block chains (Figure 1.2) are composed of regions of alternating MG blocks whose monad, diad, and triad frequencies are determined. Rigid six-membered sugar rings and restricted rotation around the glycosidic linkage make ALG molecules stiff. The rigidity of the chains further is due to electrostatic repulsion between the charged groups on the polymer chain and on ALG composition. It increases in the order MG < MM < GG; therefore, G-rich ALGs generally form hard and brittle gels, while soft and elastic gels are produced by M-rich samples. Hence, the physicochemical properties and degree of polymerization of the ALG depend on the arrangement of these blocks [5].
Figure 1.1 Structure of ALG monomers (L-guluronic acid and D-mannuronic acid).
Figure 1.2 (a) Homopolymeric blocks of poly-ß-1,4-D-mannuronic acid (MM blocks); (b) homopolymeric blocks of poly-a-1,4-L-guluronic acid (GG blocks); (c) heteropolymeric blocks of MG monomers in random pattern [6].
Alginate can form gel independent of temperature as compared to other polysaccharides such as gelatin or agar. The ALG gels can either be ionic gels (formed by cationic cross-linking) or acidic gels (formed by acid precipitation).
The ability of ALG to form ionic gel in the presence of multivalent cations is mostly desired in food industries. The process of binding of ALG to divalent cation is very specific, and the affinity of ALG toward cations is in the order Mn < Zn, Ni, Co < Fe < Ca < Sr < Ba < Cd < Cu < Pb [7, 8], and it depends on the number of G blocks present in the structure [9]. The cooperative binding of G block and divalent cations results in gelation of ALGs. The use of highly toxic cations such as Pb, Cu, and Cd is limited for practical applications, but less toxic cations like Sr and Ba have been reported to be used in cell immobilization applications at limited concentrations [10]. Calcium being nontoxic is widely accepted to form ionic ALG gels. Calcium-ALG gel is the most commonly used ALG gel. Interactions between Ca ions and G residues result in gelation of ALG, which leads to chain-chain association and to the formation of junction zones. The two G chains bind on opposite sides with the addition of Ca ions to the ALG polymer, which results in a diamond-shaped structure with a hydrophilic cavity. The oxygen atoms from the carboxyl groups form multicoordination with the Ca ions in the hydrophilic cavity. This tightly bound complex forms a junction zone that is shaped like an "egg box" (Figure 1.3). In this egg box, a 3-D network is formed by the binding of each cation with four G residues [11]. In case of Ca ALG gels, there should be 8 to 20 adjacent G residues in order to form a stable junction [12]. Although it is generally observed that most divalent cations form ALG gels by the "egg-box" formation, it is still not known if other divalent cations follow the same mechanism for gel formation [13-16]. Binding of Ca ion enhances with increasing content of G residues in the chains, while poly-M blocks and alternating MG blocks have lower affinity toward the ion. Generally, by raising the ALG G block content or molecular weight, more strong and brittle ALG gels may be achieved [4]. The affinity of ALG toward Ca ions increases with increasing content of the ion in the gel due to an autocooperative zipper mechanism. This first stage of dimerization is followed by a second stage of lateral association of the dimers at higher Ca2+ concentrations. Isolated and purified G blocks have been shown to act as gel modulators, forming higher-order junction zones composed of two or more chains.
Figure 1.3 Egg-box structure formation during the ionic gelation of sodium ALG [17].
Studies have shown previously that there could be different block sequence than G blocks to which cations can bind in ALG. For example, binding studies have recognized that Ca is able to bind to G and MG blocks, Ba can bind to G and M blocks, and Sr can bind to G blocks only [8, 12]. Trivalent cations such as Al3+ and Fe3+ can also be used to gel ALG. In fact, they generally have an increased affinity of binding with ALGs as compared to divalent cations. They form a more compact gel network by binding in a 3-D structure due to their ability to bind with three carboxyl groups from different ALG biopolymers at the same time [18].
The ionic gels are widely used in various industries; like in the food industry, these are used in encapsulation of bioactives, in pharmaceuticals for making drugs, and in the biotechnology industry for cell immobilization.
Alginic acid gels are formed when pH less than the dissociation constant (pKa) of the polymer is used for making the solution [12]. Alginate is negatively charged across a wide range of pH because M and G residues have pKa of 3.38 and 3.65, respectively [19, 20]. Alginate solution is affected in two ways by the rate of...
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