Marine Polysaccharides in Medicine Marine Polysaccharides in Medicine

About 70% of the Earth's surface is covered with seawater and 90% biosphere wraps maximum biodiversity that offers resourceful novel bio‐molecules. Marine species are enriched with organic compounds viz. terpenoids, polyethers/ketides, lipo‐glycopro‐ teins, peptides and polysaccharides that act as cell surface receptors and involve in cell development/differentiation, besides being antimicrobial agents. Algae, sponge and fish have various defense mechanisms developed via specific/potent natural molecules to survive under hostile, extreme conditions such as various degrees of salinity, pressure, temperature, darkness, besides microbial and viral attacks. Marine seaweeds and algae enriched with polysaccharides such as glycosaminoglycans, agar, alginate and chitin/ chitosan owing to their diversified significance have received growing attention among researchers. Currently, marine‐derived biomolecules cater 20% market drug load while other natural products bear 30% share. Chitins exhibit various biological and physico‐ chemical properties that can be exploited in biotechnology and medicine/drug, cosmetic, food and textile industries. This chapter focuses on chitin/chitosan production, its physicochemical characterization and biological activities and relationship between its chemical structure and bio‐activity, including chemical modification reactions such as acylation, substitution, sulfonation and other cross‐linking strategies applied to skeletal modification with the recently updated literature. and mollusks are a resource of chitin as well as arthropod, crustacean, yeasts, and squid pen exoskeletons. Comparatively, chitosan is a widely used in various industries,viz., biochemical, food, drugs, as dietary fiber, wastewater treatments, surgical threads, wound healing, immune response to allergy, plant immune inducer/defense against pathogens, and is also used in antimicrobial, anticholesterol, and antitumor activities. Chitosan alteration/designing via tissue engineering is also used in various areas such as bone scaffold, drug delivery, wound healing, and metal/dye absorbents. The marine crustacean shells are rich chitooligosaccharides with calcium carbonate (20–50%), proteins (20–40%), and chitin (15– 40%), contents that can be separated by using an integrated biorefinery with mechano/chemical processes for their distinct uses. This chapter presents a variety of chitooligosaccharides with specific characteristics, such as skeletal modifications, biocompatibility, and antimicrobial and antiinflammatory activities, in relation to possible solution properties.


Introduction
Nature is an ancient pharmacy known to human. Life originated over four billion years ago in oceans, besides sea aid ecosystems, and provides source of food for organism and man. Carbohydrates are abundant, essential natural polysaccharides consisting of carbon, hydrogen and oxygen atoms (H:O as 2:1 and empirical formula C m [H 2 O] n where m is different from n and usually varies from 200 to2500), having vast health benefits. Polysaccharides contain linear to high heterogeneity linkages of more than 10 monosaccharide/glycosides with slight repeating unit modifications (discrete from their monosaccharide) while oligosaccharides contain 3-10 monosaccharides. Amid carbohydrates, various polysaccharides are found in all marine organisms, which are accountable for an innate bio-active defense mechanism. Plant starch found as both amylose and amylopectin, which resemble cellulose (plant cell wall module), exhibit storage functions while chitin and glycogen in animals (same as starch/ cellulose except NH-substitution) afford structural component enhancement in arthropod exoskeleton and fungus cell wall. Chitins, fucoidan, carrageenan and alginate are few polysaccharides that control cell proliferation and modulate metabolism in marine organisms besides own pharmaceutics utility including antioxidative, antibacterial, antiviral, immunestimulatory, anticoagulant and anticancer activities poses novel ventures for harnessing potential of oceanic products.
Oceans occupy three-fourths of planet, which covers half of the global biodiversity envelope in certain marine species as the imperative resources for deriving novel bio-chemicals. Marine bacteria, macro/micro algae, sponges and fishes induce defensive actions via such biomolecules that enable organisms to survive in hostile environment such as different degrees of salinity, pressure, temperature and no/deem light [1], as well as microbial/viral attack. Naturally occurring bio-chemicals viz., terpenoids, polyethers, polyketides, lipo-glycoproteins, and polysaccharides display various functions in nature such as defense against predators, aiding in cell development/differentiation, acting as cell surface receptors and providing innate immunity. Carbohydrates exacted from terrestrial marine organisms/ sediments act as prospective feedstocks for medicine, fertilization, food storage, antioxidant, laxative, smooth/nonirritating hydrated bulk in the digestive tract, tablet ingredient and drug carrier agents, as shown in Figure 1.

Marine biotechnology
Marine biotechnology focuses the following goals: 1. Discovery of bioactive molecules from marine organisms to reveal their functions and actions.

2.
Study the environmental parameters, nutritional requirements and genetic factors that control the production of primary and secondary metabolites from marine species.

3.
Understand the genetics, biochemistry, physiology and ecology of marine organism/ mariculture.

4.
Develop diagnostic tools to improvehuman health.

5.
Explore bioremediation for waste processing/disposal, coastal clean-up and oil spilling.

Medical potential of marine products
About 20,000 metabolites yielded from marine bacteria, sponge, coral and starfish cater significant untapped promises and act as chemical library database in pharmaceutics due to their intrinsic features. MARPOL-73/78 an international organization is engaged in enzymatic up-gradation/modification of marine polysaccharides being substitute to oil-based polymers in utilizing renewable resource. MARPOL via enzyme technology-modified chitin, alginate, fucoidan, and laminaran from marine with enhanced inherent quality to cater sustainable industrial/pharmacy needs in the below targets (Figure 2): • To derive innovative bioactive chemicals from marine species.
• To increase value creation from biomass by refining/upgrading via enzymology.
• To generate cross-sectorial technology for enzyme evolution and biomaterial design.

Pharmacological uses of marine polysaccharides
Advance molecular biology has innovated methods for marine organisms to isolate assorted polyunsaturated fattyacids, polysaccharides, minerals, vitamins, enzymes, and peptides. These marine polysaccharides own health benefits besides feedstock for pharmaceutics, nutrition, and pharmaceutics besides cosmetic industries (Figure 3)   Agar and agarose have less sulfate content, but high uronic contents and corresponding beads are developed that exhibited better optical clarity with improved gel strength exploited in sustainable release of phenobarbital sodium hypnotic drug. Agars are effective for spatial infections such as poliovirus, herpes simplex, dengue viruses and also meats gelling, laxatives and flexible molds in dentistry and criminology. Chitin hydrogel provides cell signaling in vivo physiology [2,3] and hydroxylation enhances its biodegradability; while sulfonation generates heparin-like increased blood compatibility [4] besides amine quaternization imparts high solubility, muco-adhesiveness (via hydrogen bonding) responsible for elevated drug residence-time, inflammation reduction and antimicrobial activity). Nanochitosan-based drug delivery systems easily cross blood-brain barrier results in cell/tissue gap penetration to targeted spleen, spinal cord, liver, lungs, and lymphs.

Cosmetic applications
Polysaccharides formulated with vitamins, minerals, botanical extracts, and antioxidants can promote healthy skin, hair, and nails at a cellular level which areused as creams, lotions, ointments, liquids, and pills, as shown in Figures 2 and 3. The cosmetic industry and advance biotechnology are mainlyfocused on marine polysaccharides as compared to synthetic chemicals due to perceived inherent prominent effects such as reduce free radical provoked aging, inflammation, and skin degradation. Chitin shows resemblance with living tissues that aid to maintain cutaneous homeostasis, neutralize radical activity, and induces transcutaneous penetration of active drugs. Chitosan nanofibrils induce low TGF-β production results in skin protections by increasing the granular density of epithelial layers and fully compatible with skin cells besides complexing with vitamins, carotenoids, and collagens to facilitate transcutaneous penetration [5]. Chitosan without having amino/hydroxy groups. E.g., E-CE6 typ aid cationic pH-sensitive molds into various shapes such as bead, hydrogel, nanofiber and nanoparticle owning fascination for other biomolecules. Chitosan hydrogel's excellent water absorption property is exploited in making of some moisturizers; it also provides wound healing and exhibits antioxidant and antimicrobial activities against various bacteria, yeast and fungi and metalloproteinase.

Nutrition-pharmaceutics applications
Marine-derived products used as food/ingredients are developed in nutrition-pharmaceutics to prevent/treat diseases pertaining anticancer, antiinflammatory, antioxidant, and antimicrobial activities, as shown Figures 2-4. Ulva fasciata derive sulfated galactans and fucans possess good anticoagulant, gel stabilizers, preservative, and flavoring agents that reduce LDLcholesterol, plasma, and triacylglycerols [6]. Align emulsions are used as bio-flocculants in food formulation to obtain certain texture, mouth feel thickening effect, and stabilize suspended dispersed phases. Carrageenans-polyamide hydrocolloid with starch, locust bean gum, and carboxymethyl cellulose are used for milk protein stabilization [7]. Chitins are used in antidiabetic, hypocholesterolemic, adipogenesis inhibiter, food additives, and dietary supplements in nutrition-pharmaceutics which decrease body weight, serum lipids without digestions in GI tract (precipitates fat and reduces absorption via inhibiting pancreatic lipase actions). Cationic chitosan-fatty/bile acid combinations delay cholesterol and steroidal emulsifications via hydrophobic interaction, thus lessening intestinal absorptions.

Preparations of chitin/chitosan
About10 gigatons/year of chitins are produced in biosphere which are soft and leathery, encrusted with CaCO 3 as the harden mass to obtain translucent, pliable, resilient as a tough exoskeleton of vertebrates, insects, and crustaceans. Chitin exhibited distinct characteristic against fungus pathogens resistance, autolytic, nutritional, and morphogenetic functions in plant, pathogenesis in virus and elicits lysozyme inductions, immunizations and parasitism in bacteria. Chitin is antidiabetic, hypocholesterolemic, adipogenesis inhibiters which decreases body weight/serum lipids without GI digestion prohibiting pancreatic lipase crucial for cholesterols emulsification to precipitate fat and fatty/bile acids [8].

Chitosan production
Chitin is feedstock for chitosan conversion via enzymatic as well chemical degradation ( Figure 5) because of its cheap and commercial production, as shown in Figure 6.

Chitosan copolymerization: acetylation, sulfonation, and other crosslink substitutions
Chitosan differs from concordant chitin, cellulose in fraction and distributions of their comonomers in respective of polymeric length/sequences and found as an alternate, block, and random fashion as shown in Figure 7. N-acetyl-glucosamine and N-glucosamine constitutional monomers in chitin and chitosan displayed varied, respectively, solution properties and impart slightly hydrophobic terminal in chitin and ionic character at acidic pH in chitosan. Skeletally different than others amplified in acetyl sequencing that owes vivid outcome in chain conformation and aggregation besides hydrophobic substituents is vital for selfassembling and crumpling as found in liposphere micelles. The modification in chitin/ chitosan's skeleton can be made by means of quaternization, glycosylation (via acetyl) and sulphonation (via sulphate groups) techniques that able grafting monomers at -NH2 linkages to yield terpolymer rather intricate matrix as shown in Figure 8. Chitosan compositions varied with the degree of acylation as determined by many methods such as titration, circular dichroism, FTIR, UV, NMR, and N-acetyl group hydrolysis [9,10]. Data from different techniques showed discrepancies in degree of acylation and solubility disparity as no technique points out appropriate clarification for solubility [11]. Differential scanning calorimetry study decomposition of amino/acetyls to provide sovereign composition and molecular weights 0-1 N-acylation degree cheaper than NMR but more accurate than FTIR. NMR easily recognizes O-acetyl groups that aid to obtain degree of acylation by integration/normalization of either anomeric proton or other ring protons.

Varied chemical modifications
Assorted chitosan matrix modifications at -NH 2 in C-2, at -OH in C-3/C-6 carbon are performed via etherification/etherification and amine quaternization [13]: 1. Carboxyalkylation at O-/N: Carboxyalkylation at O-/N of chitosan imparts the amphoteric polyelectrolyte nature needed in biomedical applications such as wound dressings, artificial bone and skin, bacteriostatic agents, and blood anticoagulants [14]. Carboxyl and amino chitosan functionality elicits special biophysical properties for controlled/sustained drug-delivery, e.g., water-soluble O-carboxy methylchitosan microspheres for control pazufloxacin mesilate: antibiotic drug release.

2.
Sulfonation: Chitosan sulfonation at amino/hydroxyl groups generates pharmaceutic heterogeneity (analogues to heparin: a natural blood anticoagulant) to pertain desired anticoagulant, antisclerotic, antitumor, and antiviral activities. Free NH 2 /OH sulfonation mostly disrupts chitosan crystanality by depleting inherent hydrogen bonding and amphilicity and imparted micelles can act as a drug carrier.

4.
Sugar-modified chitosan: Chitosan reductive N-alkylation by disaccharide or monosaccharide-aldehyde derivatives acts as a liver-specific drug carrier via specific binding at sialoglycoprotein receptors [15]. All these NH 2 -alkylated chitosan derivatives are soluble at neutral and basic pH conditions, whereas lactose, maltose, and cellobiose sugars imparted all pH range solubility. Galactosyled chitosan derivatives act as the synthetic extracellular matrix for hepatocyte attachment [14,15].

6.
Skeletal cross-linking: Cross-linking at chitosan yields hydrogel with adequate mechanical properties and high-drug-loading capability having potentials in controlled drug delivery systems [11,15]. Cross-linking by glutaraldehyde, genipin, ethylene glycol, diglycidyl ether, and diisocyanate at chitosan -NH 2 establishes speciality like nonionic/ ionic drug interactions and pH-sensitivity aids swelling in gastric conditions anticipated in site-specific drug release [11]. Chitosan cross-link microspheres are nontoxic, biodegradable oral drug agents [12,15] without potential deleterious impact. Tripolyphosphatechitosan ionic gels encapsulate plasmid DNA/dsDNA in vitro transfection, cellular uptake, and in vivo gene expressions via intratracheal administration imparting high physical stability without DNA release (even after heparin incubation). Confocal studies revealed endocytotic cellular nanoparticle uptake with subsequent cytoplasm fast releases, mediated in vivo intratracheal strong β-galactosidase expression. Chitosan-tripolyphosphate nanogel is used in nonviral gene delivery liable to cause steric stabilization and targeting [9,12]. Calcium sulfate-encapsulated alginate-N-succinylchitosan hydrogel pastes retained structural integrity and found to decrease resorption rate responsible for bone defect healing in bone regenerative techniques [11,15]. Hydrogels are beneficial due to easy handling, suitable molding, and instant hardening (water release from hydrogel and transform CaSO 4 hemihydrate by partial cross-link with alginate to exert cementing via egg-box effect aid in bone regeneration).

Chitosan characterization
Chitosan quality like variable appearance, turbidity, molecular weight, and mechanical stability depends on chitin resource, isolation method [9,16], and deacetylation degree as manifested in Figure 6. Degree of deacetylation >0.5 imparts in aqueous acids soluble to chitosan but not in alkaline/physiological pH as uneven acetyl distribution lowers solubility due to aggregation as determined by FTIR 1 H/ 13 C-NMR (liquid state, solid state) and potentiometric titration. Average molecular weight of chitosan is obtained from stearic exclusion chromatography-viscometer, light scattering detector, matrix-assisted laser desorption, and MS spectrometry as mentioned in Table 1 Chitosan is the only cationic polysaccharide that is nontoxic and biodegradable in body, thus exploited by tissue engineering for wound dressings, drug delivery, and bone graft alternative in orthopaedic beside scaffolds for cartilage, intervertebral disc, and bone tissue. The relevant physicochemical and biological properties of chitosan are presented in Table 2.

Crystallographic studies of chitosan
X-ray diffraction and crystallography of chitin revealed two polymorphs, namely, hydrated/ tendon and anhydrous/annealed conformers. Crystalline chitosan own ant parallel chains in two-fold helix, zigzag pattern with almost constant pitches of 10.34 A 0 for hydrate and 10.34 A 0 anhydrous forms (similar to cellulose). Chitosan conformations of two-fold extension with moderate flexibility due to salt formation/protonation of free -NH 2 with acids imparting tunablehypocholesterolemic and fungicidal activity and metal chelation besides chromatographic uses and gel production [9].

Critical physico-chemical properties of chitosan
Understanding of relation structure-properties in chitosan become a matter of great interest encountered by regulatory agencies in approving chitosan uses. The critical examination of literature results in correlation between properties of nanoconstructs with component structures as advantageous due to modulating. Thus, chitosan nanoparticles are exploited in modern pharmaceutics/biomedicals by alteration of acylation, molecular weight/its distribution, nature, and fraction of substituents. In general, applications its need to examine molecular characteristics interplay with supramolecular interactions to provide size, shape, and surfaceactive nanomaterials [12].

Chitosan properties and bio-activity from gel to nanobead in drug delivery
Chitin/chitosan own wide pharmaceutical utility due to excellent biocompatibility, biodegradability, nontoxicity, and adsorption properties which fuels global research interests, e.g., 1150 articles in 1981-1990, about 5700 reviews in 1991-2000, and 23,100 publications in 6 years [9,15]. Among all natural polysaccharides, chitin/chitosan's outstanding benefited industrial and pharmaceutics significance are depicted in Figure 1. Chitin/chitosan is the only high molecular weight cationic polyelectrolyte, while other polysaccharides are either neutral or anionic in nature. Moreover, chitosan owns some undesired features like large variable chemical composition differences in its resultant polymeric chain-size and assorted acetylation degree appropriately classified as "ugly,"frustrating research applicability. Nevertheless, chitosan skeletal optimization yields biomaterials with therapeutic and biological profiles useful in drug delivery formulations and as functional excipients. Chitosan interactions with some cosolutes/biostructures revealed subtle effects in classical solution thermodynamics and in biological utility like interactions with endotoxins.

Chitosan as antiinflammatory/immunomodulatory agents
Chitoneous administration through vascular system enhances cytokines release by macrophage, and upregulates Th1-immunity and downregulates Th2-immune activity [12]. Chitosan cross-linked resin and chitosan poly-γ-glutamic acid nanoparticles are use as alternative vehicles for oral delivery of NSAID aceclofenac and diclofenac drugs, respectively, which inhibits prostaglandin E2 production to stifle ultimate local inflammatory responses.

Chitosan as anticoagulants
Sulfation at N-2 and O-3 link of chitin increases thrombin level and activates partial thromboplastin-thrombin time [12] and at C-2, C-3, and C-6 position showed anticoagulant activity at par with therapeutic heparin (mere heparin use infects animal proteins to own antiplatelet activity responsible for abnormal bleeding). Sulfated chitins anticoagulant action inhibits FXamediated antithrombin-III activity via N-sulfo/N-acetyls complexation with antithrombin-III, which prolongs thrombin-clotting time. Coagulation interfering factors in fibrin polymerization are assay via antithrombin activity andprothrombin-atroxin time assessment (Tables 1  and 2).

Chitoneousanticancer agents
Chitosan is trusted due to nontoxicity, biodegradability, efficient drug delivery, best cellpermeability, and antiproliferativity against adenocarcinoma HT-29 and caco-2, colon carcinoma HCT-116 in kinase protein of intestinal epithelial cells, which colorectaly inhibits NF-κB transcription and NF-κB-mediated inflammations. Caffeic acid and doxorubicin individually doped chitosan composites revealed strong fluorescence intensity used to vehicle anticancer drugs [17]. Curcumin-coated chitosan nanoparticles possess significant cytotoxicity and reduce human oral cancer cell line.

Chitosan vehicle drugs delivery systems
Distinctly doped glutamine,methionine, and tryptophan in chitosan matrix exerted protection to C-8166 cells against cytolyticity of HIV-1RF strain and restrain HIV-induced syncytium formation with HIV-1 reverse transcriptase/protease enzymes by suppressing HIV-infected C8166 cells. Similarly, sulfated chitosaccharide-III found to suppress HIV-1 replications,syncytium formation, lytic action, p24 antigen production, and thwarted viral entry/cell fusion by intrusive HIV-1-gp-120 bound CD4-cell receptors (unsulfated chitosan lack such actions). Polyethylated-chitosan vehicle lamivudine curbs HIV-replication more powerfully than lamivudine/no chitosan carrier. Thioglycolic acid-conjugated chitosan carrying tenofovir disoproxil fumarate exhibited high mucoadhesion via intravaginal microspheres stabilization without vagina epithelial cells cytotoxicity and lactobacillus crispatus compared to native nanochitosan. Drug encapsulation and mucoadhesion are profound for chitosan-O-isopropyl-5'-O-d4T-monophosphate vehicle zidovudine since it reduces the diameter to stop HIV transmission. Nanochitosan carrying saquinavir drug imparted excellent antiHIV potential and high cell target efficiency to yield efficient HIV proliferation control [18,19]. Poly-d,llactide-co-glycolide nanochitosan vehicle anti-HIV acyclic nucleoside and phosphonate aids cellular uptakes in target macrophage cells. Broad bioactivity pattern of chitosan vehicle drugs are summarize in Table 3.

Targets Chitosan composites (antibiotic stock solution minimal inhibitory concentration in ppm)
Gram-negative   Pharmaceutically, chitosan delivered tablets, microspheres, micelles, vaccines, nucleic acids, hydrogels, nanoparticles, and conjugates via implantable, injectable oral, nasal, and ocular routes. Chitosan facilitates transmucosal absorption vital in delivery of peptides and in protein vaccination [9,12,20] besides an excipient in oral tablet formulation. High molecularweight chitosan is more viscous to impart delayed ingredient release/drug duration activities which improve therapeutic efficiency by lessening side effects of oral tablets [12]. Chitosan-tripolyphosphate/alginates microspheres can control or protect proteins, drugs, and vaccines absorption in the digestive tract via paracellular route on epithelial layer release in oral and nasal administrations [9]. Hydrophilic chitosan imparts low surface activity that gets improved by glucosidic modifications, hydrophobic substitutions, and by providing hydrophilic shield at hydrophobic centers [12] to protect hydrophobic drugs with improved solubility and bioavailability [20]. Chitosan 3-D hydrogels are structured via diffusion, entrapment, and tethering with hydrophilic polymers to hold up thousands times more fluids than its dry weights is best utilized in drug delivery. Thermosensitive chitosan solution when injected into the body at phisiological conditions forms hydrogels which aids protection of drugs from degradation besides its prolonged-steady release [21]. Biocompatible chitosan drug carriers yield via ionotropic gelation, emulsion, cross-linking, solvent extraction, diffusion/droplet coalescence, reverse microemulsion, and self-assembly techniques. But ionotropic gelation is preferred due to mildness and less time involved in spontaneous aggregation. Chitosan-aided delivery systems protect drugs from chemical/enzymatic degradation in digestive system due to strong mucus binding that enhance drug adsorption in intestinal epithelial cells [20]. Chitosan-glycol nanogel uptakes endocytosis mediated by flotillin-1 with Cdc42 and macropinocytosis attended by actin cytoskeleton participation and internalization mechanisms by folate receptor are useful in drug delivery vectors for targeting different intracellular compartments [9]. Glipizide chitosan-xanthan beads exhibited control-drug release, mucoadhesion, pH-based swell kinetics, good bioadhesiveness, and comparable floating capacity in gastric fluids [22]. Insulin-chitosan-tris-buffer (pH 6.5) nano emulsions showed physical and chemical stability in a reverse micelle system and potent hypoglycemic activity in diabetic rat [20,22]. Colon prolongs progesterone absorption for much first-pass metabolism with low oral bioavailability, but zinc-pectinate-chitosan vehicle increases drugs oral bioavailability with more residence time in plasma for colonic-specific delivery. Glutaraldehyde-Boswellia-resin doped chitosan composites (phosphate buffer pH 6.8) releases 70% drug load in 7 hours with augmented drug entrapment [9,12,20]. Chitosan-catechol carrier imparts higher retention for mussel adhesive proteins found in GI track via irreversible catechol-mucin cross-links aids in mucosal drug delivery [9]. Fish oil-based N-stearoyl O-butylglyceryl-chitosan microcapsules own desirable capacity and carrier encapsulation efficiency for sustained release of fish oil besides higher thermostability [9].

Chitosan in tissue engineering
Flexible mechanical and structural features of chitin is explored in tissue engineering to procure materials which impart improved bio-functions to be used to repair tissues like bone, cartilage, blood vessels, bladder, skin, and muscles. Tissue engineering induces varied dimensional/shape/size chitin forms like fiber, filament, film, sponge, and gel to provide instant mechanical support and compatibility to bio-fluids/tissues via cell, scaffold, and cell scaffold interaction as shown in Figure 9. The 3-D chitosan scaffold act as an artificial extracellular matrix as reabsorbed by body with time till new tissue forms to aid to integrate new tissues [20]. Chitosan interacts with cellular glycosaminoglycans to enhance cell attachment and proliferation results for cell growth via mechanical enhancement which resembles replaceable hard/soft tissue like bones, cartilage, muscles, and blood vessels. Medical textiles or healthcare textiles is arapidly expanding technical textile market to prepare materials for medical and healthcare products like simple gauzes, bandages, tissue culturing scaffolds, and prostheses for permanent body implants [23]. Chitosan acquire basic requirements of textile material for medical applications like biocompatible, resistance to alkali, acids, and microorganisms, high-dimensional stability, elasticity, free from contaminates/impurities, absorption/repellence, and air permeability [24].

Chitosan in wound healing
Low immunogenicity characteristics of chitosan aids to provide 3-D tissue growth matrix with profound activities such as enhancing macrophage activity, stimulating cell proliferation to heal wound and facilitating polymorphonuclear leukocytes, macrophages besides fibroblasts induced granulation responsible for tissue repairs [25]. N-acetyl-β-d-chitosan degradation imparts peculiarity like fibroblast proliferation, collagen deposition, and hyaluronic acid stimulation at wound to accelerate healing without scar formation [26]. Nanochitosan adhesive mats own high porosity, tensile strength, surface area, and ideal H 2 O vapour-O 2 transmission rate compatible with adipose-derived stem cells accountable for wound dressing (Figure 10(A-D)). Nanochitosan surgical dressing provides fast wound healing through adhesiveness with strong sealing strength without sutures/staples and prohibits blood vessel bleeding and air leakage in lung surgery [26]. Clinically, chitosan-based nanofibers, composites, films, and sponges used for wound healing in plastic surgery [9,25], skin grafting [9,27], and endoscopic sinus surgery [26,27]. HemCon® hemostatic latex-free bandages derived from chitosan-coatings acts as extreme adherent on blood contact to seal wound and controls bleeding (via affinity to red blood cells) and effectively reduces hemostasis span. ChiGel, Chitopack-C®, Trauma-Stat™, Tegasorb™ and Tegaderm™ Guarda-Care®, Chito-Flex®, and Chito-Gauze® are chitosanbased products used for dressings in surgical protective thickness, dermal, limb trauma, ulcers, injury, abrasions, and burns where chitosan swells with exudates to gel inaid healings. Celox™ granules/flakes are hemostatic gauze that controls emergency bleeding via swelling to gel-clot on contact with blood and induce hemostasis in penetrating limb trauma in contrast to conventional pressure bandages [9]. Topical chitosan-coated pads promote vascular hemostasis percutaneous catheters/tubes interventionally put on puncture site found to aggregate red blood cells and platelets, thus shortening the clot formation-5. Carboxypolyvinylalcohol-chitosan hydrogel film improved swelling ratio to maintain moisture over wound besides sustaining drug release and effective suppression of bacterial proliferations [27]. Curcuminbioglass-encapsulated chitosan found many uses like wound healing dressing, quenchingactivity of DPPH and superoxide, inhibit Staphylococcus aureus bacteria, and reduce tumor necrosis [9,27]. Varied ionic cross-linkers aid in chitosan drug delivery as shown in Table 4.

Chitosan in water treatment
Chitosan acts as a natural adsorbent due to free amino and hydroxyl groups responsible for adsorptive interactions with water pollutants like dyes [29], metals [30][31][32][33], and organic compounds, etc. Functionality of chitosan is facile for modifications, viz., cross-linking and grafting so as to enhance its inherent absorption efficiency and specificity. Cross-linking of chitosan's functionality improved its sorption efficiency at low pH while grafting with sulfur/ nitrogen improves specificity and capacity for heavy metals [30][31][32][33]. Dye adsorption by unmodified chitosan is good; but its low stability prompted researchers to modify/graft at amino, carboxyl, sulfur, and alkyl groups. Chitosan can be cross-linked with epichlorohydrin, ethylene glycol diglycidyl ether, glutaraldehyde, and tripolyphosphate to improve its sorption efficiency besides mechanical and physical properties. Chitosan alteration is best for adsorption of dyes, phenols, polycyclic aromatic, pesticide, herbicides, and metal ions. Metal cations are chelated specifically at protonated amines in acidic conditions whereas anions by electrostatic interactions. Chitoneous adsorptive interaction includes partition, diffusion, chelation, trapping, scavenging, cation exchange, hydrogen bonding, Van der waals force, dipole-dipole, and electrostatic interactions [29][30][31][32][33]. Quaternary tetra-alkylammoniumchitosans own permanent +ve charge at -OH/NH 2 to boost antimicrobial activity (at wide pH) in orthopedic, wound dressing in surgery, anion exchange cartridge, dental implants, colorimetric analysis, and perchlorate removal of water [9,20]. Fe-chelated-chitosan granules found to promote selective fluoride sorption over chloride from water in defluoridation technique. Protonated polyamidoamine-grafted chitosan-Zr (IV) beads selectively removed fluoride than other ions in spontaneous and endothermic way [34]. Magnetic hydroxypropyl-chitosan multiwalledcarbon nanotubes adsorbs lead (II) from water. Chitosan-glutaraldehydenanofibers exhibited double adsorption capacity (than chitosan) forCr (VI) removal from water. Chitosan-polyphenol-oxidase quinine nanobeads rapidly eliminate bisphenols from water [33]. Chitosanpyruvic acid composites are found to adsorb Cd (II) from wastewater. Chitosan-modified soil cyanobacterial breakdowns harmful algae blooms and microcystins via flocculation and inhibiting algal cells and sequester liberate toxins to promote biodegradation [9]. Chitosandoped sodium tripolyphosphate nanorods mitigate toxic Cr +6 from water via multilayer adsorption and consequent oxidation to ambient Cr +3 ions [34]. These chitosan-based commercialized viable adsorbents own peculiar characters like high specific surface area, low internal diffusion resistance, biodegradability, quantum size effect, ecofriendliness, versatility, low cost, and high adsorption capability and selectivity.

Chitosan in regenerative medicines
N-methacryloyl chitosan possessesdesirable features like hydro-solubility, UV-cross-linkability, and injectability facilitating cell-loaded microhydrogels and quick transdermal curing in vivo needed in localizing/sustaining protein delivery [20]. Chitosan-α-tricalcium phosphate exhibited histocompatibility for Beagle mesenchymal stem cells without effecting cellular growth and proliferation, further manifesting efficacy by enhancing osteogenesis and vascularization to repair bone defects in conjunction with mesenchymal stem cells [12,20]. Silk reinforced chitosan promotes redifferentiation of caprine chondrocytes and retained more glycosaminoglycan to improve aggregate modulus construction, whichresembles with native tissues. Bone morphogenic protein-chitosan scaffolds burst sustainable drug release and biocompatibility which is necessary for cartilage tissue [9,20]. Chitosan hollow tubes regenerates repair sciatic and damage phrenic nerves via improved diaphragm movement besides slow phrenic nerve transfer by granulation in beagle-dogs [12]. Cell encapsulated chitosan gels/porous chitosan fibrous matrix with biocompatible materials like CaPO 4 , gelatin modifying biomechanical stiffness, and cell-matrixinteraction properties. These chitosan adaptations optimize cell/tissue differentiation and tailor transplantation to different clinical cell delivery by improving adherent ability for seeding cells to allow encapsulations.

Chitosan in obesity treatment
Chitosan dietary supplement/nutraceutical lowers serum cholesterol besides controlling obesity imparted to no digestion in our gastrointestinal tract. Chitosan gets swelled up to feel satiety by physically filling the stomach [9,20] and inhibition of pancreatic lipase enzyme chitosan reduces dietary fat absorption in intestines. Chitosan precipitates fat in intestines via anionic binding with carboxyls of fatty/bile acids and hinder neutral cholesterol/sterol emulsification through hydrophobic interaction, thus it remains reduced/unabsorbed in GI tract for obesity and hypercholesterolemia treatments [35].

Chitosan in cardiovascular treatment
Chitooligosaccharides entry in gastric gavages of mice in the treatment of apo-lipoprotein-E deficiency along with high-fat diet feeding showed peculiar changes like lowered triglycerides and cholesterols, undermined atherosclerosis, increased atherosclerotic plaque stability, unregulated hepatic expression of low density lipoprotein receptor, macrophage scavenger receptor BI, and ATP binding cassette transporter-A1. But in wild mice with low density lipoprotein receptors deficiency and high cholesterol absorption found no change in plasma lipid levels of LDL-R. Chitooligosaccharides aid in hypercholesterolemia, i.e., remove lowdensity lipoprotein (LDL) oxidized products: cholesterol which causes coronary atherosclerosis as toxic for endothelial cells. Chitosan increase binding of LDL to endothelium and smooth muscle by mediating inflammation such as TNF-α, IL-1, and macrophage colonystimulating factors. Hypocholesterolemic effect lowers lipid and media-milled chitosan treatments found to decrease serum triacylglycerol, total, and LDL cholesterol which is highest than pure chitosan. The elevated serum cholesterol causing cardiovascular diseases, since 10% blood cholesterol reduction using chitosan consumptions reduces the risk of coronary heart disease by 30%.

Chitosan in aging treatments
Degenerative aging diseases like cardio-/cerebrovascular, diabetes, osteoporosis, and cancer are common in old people that are diet-affected [9]. Old people showdeficiency of Zn, Fe, Se, Cu-metals, Vit-A, B, C, and E, which impacts immune responses or impair immunity. But chitosan-ascorbate can compensate such deficit and thrust neutrophils, NK/NKT/dendritic cell, monocyte/macrophage, and mediate initial pathogen interactions link to compromise signal transduction T cells pathway and gut microbiota homeostatic regulation to reduce lowgrade inflammation in age-related diseases via triggering intestinal activity. Chitosanoligosaccharides used as functional food and aging disease therapy/treatment, pathophysiology via affecting oxidative stress, low-density lipoprotein oxidation, enhance tissue stiffness, govern protein conformational changes, and chronic inflammations [9,20,35].

Chitosan in mucosal immunity enhancer
Chitosan -C48/80 nanoparticle carried Bacillus anthracis protective antigen in mice have produced elevated serum titers of antibodies against protective antigen and a more balanced Th1/Th2 pattern then mere C48/80 solution and nanochitosan/alginate -C48/80 composite. C48/80 within chitosan found to promote a stronger mucosal immunity than other adjuvant groups indicating action in concert with a mast cell activator to affect nasal immunity [9,20].

Chitosan in dry mouth syndrome therapy
Chitosan-thioglycolic-mercaptonicotinamide conjugates are nontoxic andare useful against Caco-2 cells that remarkably improved swelling and cohesive characteristics that are promising for dry mouth syndrome therapy where lubrication and mucoadhesiveness of mucosa is needed [9,12,20] than that of unmodified chitosan. About 10% of older people have dry mouth syndrome/xerostomia, i.e., not enough saliva/spit in the mouth. Treatment of dry mouth syndrome includes chitin-based products that moisten themouth, e.g., electrospun chitosan fibers decrease microorganisms, molds, yeast, to yield lighter appearance, and less muscle denaturation in comparison with traditional dryageing. Test disks were compressed out of unmodified chitosan-TGA (thiomers) and/or TGA-MNA conjugates to investigate cohesive properties, cytotoxicity assays, and mucoadhesion studies. Immobilized-MNA achieved higher swelling and cohesion for chitosan-TGA-MNA conjugates compared to unmodified chitosan. Preactivated chitosan thiomer exhibited higher stability among all conjugates and nontoxic against Caco-2 cells.

Chitosan in gene silencing in disease vector mosquito larvae
The vector mosquitoes inflict diseases in humans, such as malaria, dengue, and yellow fever, which cause death of more than one million people per year compared to any other living organism. RNA interference mediated gene silencing/targeting the interested/responsible gene for disease using chitosan nanoparticles combined with food and ingested by larvae. Thus, a technically straightforward, high-throughput, and cheap methodology is compatible for mosquitoes, insects, agricultural pests, and nonmodel organisms deals with long doublestranded/small interfering RNA. Chitosan nanofibers can potentially inhibit gene functions in disease vector mosquitoes ingested by larvae when mixed with food [12,20]. Chitosan/siRNA nanoparticles used to target semaphorin-1-a during olfactory system development in dengue and yellow fevers arise by vector Aedesaegypti mosquitos. Chitosan/AgCHS-dsRNAbasenanocrystals own repression of AgCHS-1 and AgCHS-2 chitin synthase genes via feeding larval in Anopheles gambiae.

Conclusion
Chitinorchitosan hasdistinctive biological/physicochemical properties and are researchedin the fields of biotechnology, medicine, cosmetics, food technology, and textiles. Marine crabs,