Literature Review:
Chitin and ChitosanChitin and Chitosan
From Nature to TechnologyFrom Nature to Technology
Po-Yu ChenMaterials Science & Engineering
University of California, San Diego
May 3rd ,2006
Outline
1. Introduction
2. Production of Chitin/Chitosan
3. Selected Applications
4. Chitin in Nature
5. Conclusions
Chitin: a brief history
1811 Chitin was first discovered by Professor Henri Braconnot, who isolated it from mushrooms and name it “Fungine”
1823 Antoine Odier found chitin while studying beetle cuticles and named “chitin” after Greek word “chiton” (tunic, envelope)
1838 Cellulose was discovered and noted
1859 Rought discovered chitosan, a derivative of chitin..
1920s Production of chitin fibers from different solvent systems
1930s Exploration of synthetic fibers
1950s The structure of chitin and chitosan was identified by X-ray diffraction, infrared spectra, and enzymatic analysis
1970s “Re-discovery” of the interest in chitin and chitosan
1977 1st international conference on chitin/chitosan
Henri Braconnot (1780-1856)http://en.wikipedia.org/wiki/Henri_Braconnot
Muzzarelli R. et al, Chitin in Nature and Technology. Plenum Press NY, 1985
21st Century: New era for chitin?
Survey of the scientific literature
The number of chitin scientific reports since 1990 as obtained from ScienceDirect®
The number of reports of 2006 is through April, 15 th
Number of US patents
Source: www.carmeda.com/eng/businessarea/
International conferencesInternational Conference on Chitin and Chitosan (ICCC)
International Conference of the European Chitin Society (EUCHIS)
International Conference “New achievements in study of chitin and chitosan”
Asia-Pacific Chitin Chitosan Symposium (APCCS)Source: www.sciencedirect.com/
Chitin: a promising material
Unique characteristics of chitin and chitosan:
Biocompatible
Biodegradable
Non-toxic
Remarkable affinity to proteins
Ability to be functionalized
Renewable
Abundant
Muzzarelli R. et al, Chitin in Nature and Technology. Plenum Press NY, 1985
What is chitin?
Chitin is a natural polysaccharide
The 2nd abundant organic source on earth
Structure similar to cellulose with hydroxyl group replaced by acetamido group
N-acetyl-glucosamine units in β-(1→4) linkage
Chitosan is the N-deacetylated derivative of chitin
N-glucosamine units in β-(1→4) linkage
N-deacetylation of chitin into chitosan is achieved by treating with 50% NaOH
Structure of Chitin, Chitosan, and Cellulose [1]
Images of Chitin molecules [2][1] Kohr E. Chitin: fulfilling a biomaterials promise. Elsevier Science, 2001
[2] http://invsee.asu.edu/Modules/yeast/structure.htm
12
3
45
64
6
32
1
5
Pure chitin does not exist in reality
Chitin and chitosan tend to form co-polymer
# of N-acetyl-glucosamine units > 50% => Chitin
# of N-glucosamine units > 50% => Chitosan
Degree of N-acetylation, DA = acetamido / (acetamido+amino)
Degree of N-deacetylation, DD = amino / (acetamido+amino)
In nature, chitin is commonly 70~90%
Structure of Chitin-Chitosan co-polymer
Kohr E. Chitin: fulfilling a biomaterials promise. Elsevier Science, 2001
Chitin is a Co-polymer
Chitin has 3 polymorphic forms:
α-chitin, β-chitin, γ-chitin
α-chitin: - the most abundant form - anti-parallel configuration - highly ordered crystalline structure - strong H-bonding (N-H····O=C) - rigid, intractable, insoluble
β-chitin:
- found in diatom spines and squid pens - parallel configuration - weak H-bonding - unstable, soluble in water
γ-chitin:
- mixture of α and β-chitin - intermediate properties
Crystalline structure
H-bonding in α-chitin H-bonding in β-chitin
[1] Muzzarelli R. Chitin. Pergamon Press, 1977
[2] Kohr E. Chitin: fulfilling a biomaterials promise. Elsevier Science, 2001
[1]
[2]
Estimates of Potential Chitin Sources
Resource Landings (MT)
Potential waste (MT)
Estimated waste (MT)
Dry waste (MT)
Chitin content (MT)
Shrimp 2,647,345 1,058,938 710,000 177,500 44,375
Squid 1,991,094 389,219 99,531 24,882 1,244
Crabs 1,348,323 943,826 482,744 144,823 28,964
Oyster
Clam2,547,287 1,783,100 304,948 274,453 12,350
Krill 232,700 93,080 93,080 23,270 1,629
Total 8,766,749 88,652
1. Shellfish Sources:
2. Fungi Sources:
I has been estimated that fungi can provide metric tons chitin annually and can be potentially limitless
4102.3
[1] Subasinghe S. The Development of crustacean and mollusk industries. Ampnag Press (1995) 27
[1]
Isolation of Chitin from Shellfish and Fungi
Kohr E. Chitin: fulfilling a biomaterials promise. Elsevier Science, 2001
Production of Chitin Fibers
Chitin and chitosan fibers are made by the wet-spinning process:
1. Dissolve raw chitin in a solvent
2. Extrude the polymer solution through fine holes into rollers
3. Chitin in filament form can be washed, drawn, and dried
Schematic presentation of typical wet-spinning production line
1. Dope tank; 2. metering pump; 3. spinneret; 4. coagulation bath; 5,6. take-up rollers; 7. washing bath; 8. orientation bath; 9,11. stretching rollers; 10. extraction bath; 12,14. advancing roller; 13. heater; 15. winder.
Agboh O.C. and Qin Y. Chitin and chitosan fibers. Polymers for Advanced Technologies, 8 (1996) 355-365
Applications of chitin and chitosan
[1] Goosen M. in Applications of Chitinand Chitosan. Technomic Publishing Inc, PA. 1997
Table. Applications of chitin, chitosan and their derivatives [1]
Chitosan soap, lotion, shampoo http://www.conybio.com.my/galleries.html
ChitoSan® fibers and chitin sockshttp://cd.tradehelper.or.kr/
Crini G. Progress in Polymer Science, 30 (2005) 38
Fungicide seed coating http://www.une.edu.au/agronomy/pastures/research/pastureresearc.htm
http://matsyafed.org/img/chi.jpg
Biomedical Applications
Wound dressings are used to protect wound skin form insult, contamination and infection
Chitin-based wound dressings - Increase dermal regeneration - Accelerate wound healing - Prevent bacteria infiltration - Avoid water lossChitin surgical threads - strong, flexible, decompose
after the heals
Chitosan wound dressings
[1] Kohr E. Chitin: fulfilling a biomaterials promise. Elsevier Science, 2001
[2] Khor E. Lee Y.L. Implantable applications of chitin and chtosan. Biomaterials 24 (2003) 2339
[1]
Cell culture compatibility ranking of wound dressing materials
[2]
Wound Dressing
Anticoagulation
Anticoagulation is essential for open-heart surgery and kidney dialysis
Preventing blood from clotting during the surgery
Sulfated chitin derivatives have good anticoagulant activity
Tissue engineering research is based on the seeding of cells onto porous biodegradable matrix
Chitosan can be prepared in porous forms permitting cell growth into complete tissue
Biomedical Applications
Tissue Engineering
Orthopedic Applications
Bone is a composite of soft collagen and hard hydroxyapatite (HA)
Chitin-based materials are suitable candidate for collagen replacement (chitin-HA composite)
Mechanically flexible, enhanced bone formation
Temporary artificial ligaments for the knee joint
[1] Sundararajan V. et al. Porous chitosan scaffolds for tissue engineering Biomaterials 20 (1999) 1133
Ratner B.D. Biomaterials Science 2nd edition. Elsevier Science, 2004, chapter 7
Porous character of chitosan scaffold [1]
50μm
Biomedical Applications: Drug Delivery Hydrogels Hydrogels are highly swollen, hydrophilic polymer networks
that can absorb large amounts of water
pH-sensitive hydrogels have potential use in site-specific drug delivery to gastrointestinal tract (GI)
Chitosan hydrogels are promising in drug delivery system
Tablets Chitin and chitosan have been reported to be useful
diluents in pharmaceutical preparations
Microcapsules
Microcapsule is defined as a spherical empty particle with size varying from 50 nm to 2 mm
Chitosan-based microcapsules are suitable for controlled drug release
Mechanism for pH-sensitive hydrogels
[1]
Schematic structure of chitosan microcapsules coated with anionic polysaccharide and lipid
[2]
[1] Park S.B. et al. A novel pH-sensitive membrane from chitosan — TEOS IPN. Biomaterials 22 (2001) 323
[2] Majeti N.V. Kumar R. A review of chitin and chitosan applications. Reactive & Functional Polymers 46 (2000) 1-27
What’s next: Biotechnology
Gene Delivery [2] Viral gene delivery / Non-Viral gene delivery
Viral: high transfection efficiency, dangerous
Non-Viral: low transfection efficiency, safer
Chitosan-DNA complexes can be optimized to enhance the transfection efficiency
[1] Krajewska B. Application of chitin and chitosan-based materials for enzyme immobilizations Enzyme and Microbial Technology 35 (2004) 126[2] Shi C. et al Therapeutic potential of chitosan and Its derivatives in regenerative medicine.Journal of Surgical Research (2006) In press
http://ghr.nlm.nih.gov/dynamicImages/understandGenetics/gene_therapy/gene_therapy.jpg
Enzyme immobilization [1]
Purves W.K. et al Life: The Science of Biology 6 th edition. Sinauer Associates Inc. (2001)
Specific, efficient, operate at mild conditions
Unstable, sensitive after isolation and purification
Chitin and chitosan-based materials are suitable enzyme immobilizers
- Biocompatible
- Biodegradable
- High affinity to protein
- Reactive functional group
Limitations
1. High Isolation CostsDependent on NaOH price fluctuations
2. Consistent Raw Material SupplyPoor storage propertiesDrying reduces activity Easily contaminated by pathogens, exotoxins
3. High Requirements for Biomedical ApplicationsHigh product purityNon-toxicGood Manufacturing Practices (GMP)
4. Synthesis and Production
Chitosan: $ 600/Kg (Fisher Scientific)
Chitin: $ 169/Kg
Ultra-pure grade chitosan: $ 40,000/Kg !!
[1] Kohr E. Chitin: fulfilling a biomaterials promise. Elsevier Science, 2001
Flowchart for biomedical grade chitin products [1]
Chitin in Nature
Exoskeletons of arthropods
Spines of diatoms Cell walls of fungi, mold, yeast
Shells of mollusks
Other invertebrate animals
What are fungi? [1]
Fungi have the following characteristics:
Their main body is in the form of thin strands called mycelium
Can not produce their own food through photosynthesis
The major decomposer of organic matter
Their cell walls are made mostly of chitin
Chitin in Fungi Cell Walls
Chitin in fungi
Fungal chitin occurs as randomly oriented microfibrils typically 10-25 nm in diameter and 2~3 μm long
Chitin is covalently linked to other polysaccharides, such as glucans, and forms chitin-glucan complex
The chitin content in fungi varies from 0.5% in yeast to 50% on filamentous fungi species
http://www.anselm.edu/homepage/jpitocch/genbios/31-01-FungalMycelia-L.jpg
SEM micrograph of chitin microfibrils (Poterioochromonas stipitata) [2][1] Purves W.K. et al Life: The Science of Biology 6th edition. Sinauer Associates Inc. (2001)
[2] Herth W. Zugenmaier P. Microbiology Letters, (1986) 263
Muzzarelli R. et al, Chitin in Nature and Technology. Plenum Press NY, 1985
0.1 μm
The fascinating mollusk shells!
Optimized material properties due to its micro- and nano-scale laminate composite structure
Chitin is demonstrated in the shells of mollusk species (105 species so far)
Chitin forms cross-linked chitin-protein complex and distributes mainly in the hinge and edges of the shell
Bivalve mollusks deposit and orient the chitin in a very defined manner
The major role of chitin:
- mechanical strength
- integrate the flexible region
- coordinating switch during shell formation
Chitin in Mollusks Shells
The bivalve mollusk Mytilus galloprovincialshttp://digilander.libero.it/conchiglieveneziane/bivalvi/immagini/MytilusGalloprovincialis1.jpg
Confocal laser scanning microscopy (LSM) image reveals a cross-linked fibrous chitin-protein matrix. The samples are labeled with chitin-binding GFP with decalcification and fixation. [1]
[1] Weiss I.M. Schonitzer V. The distribution of chitin in larval shells Journal of structural biology,153 (2006) 264
Muzzarelli R. et al, Proceedings of the 1st International Conference on Chitin and Chitosan. MIT Sea Grant Program (1977)
Chitin in Arthropods Cuticles
What are arthropods? [1]
The arthropods constitute over 90% of the animal kindom
Exoskeleton composed mainly of chitin
Distinct parts of the body
Jointed legs and appendages
Bilateral symmetry
Classification of arthropods [2]
Trilobites are a group of ancient marine animals
Myriapods comprise millipedes and centipedes
Chelicerates include spiders, mites, scorpions
Hexapods comprise insects
Crustaceans include crabs, lobsters, shrimps and barnacles
[1] http://en.wikipedia.org/wiki/Arthropod/ [2] http://insected.arizona.edu/arthroinfo.htm
http://evolution.berkeley.edu/evolibrary/images/arthropodphylogeny7.gif
Arthropod cuticle: multifunctional composite
Epicuticle covered by a layer of wax, waterproofing barriers
Exocuticle & endocuticle
Main structural components of the cuticle
Resist mechanical loads
Multilayered chitin-protein composite embedded with minerals
Exocuticle
Dense, stiffer, chemically inert, and relatively dehydrated
Endocuticle
Sparse, softer, hydrated, and readily soluble
Membrane layer
Pore canals
Transport mineral ions, wax, nutrition during growth
Soft, ductile, can be highly deformed
seta
pore canals
exocuticle
endocuticle
epicuticle
SEM micrograph of lobster cuticle [2]
Typical structure of arthropod cuticle [1]
[1] Neville A. C. Biology of the Arthropod Cuticle. Springer-Verlag NY (1975) 8
[2] Rabbe D. et al. Journal of Crystal Growth 283 (2005) 1-7
The Hierarchical Structure of Cuticles
chitin molecules
α-chitin chains nanofibrils
proteins
fibrils
bundlesBouligand structure
Rabbe D. et al. The crustacean exoskeleton as an example of a structurally and mechanically graded biological nanocomposite material Acta Materialia 53 (2005) 4281
American lobster claw
The Bouligand (Twisted Plywood ) Structure
A diagram shows the parabolic patterns on the oblique surface [1]
Simplified Schematic presentation of Bouligand patterns [2]
SEM photograph of chitin-protein matrix showing parabolic patterns [3]
Collagen network observed in optical polarized light microscopy [3]
Primary, secondary, tertiary walls of typical wood hierarchy [4]
[1] Bouligand Y. Tissue & Cell 4 (1972) 189
[2] Rabbe D. et al. Acta Materialia 53 (2005) 4281
[3] Giraud-Guille M.M. Current Opinion in Soilid State and Materials Science 3 (1998) 221
[4] Vincent J.F.V Structural Biomaterials. Priceton University Press (1991) 155
40μm1 μm
Twisted plywood structure in nature
Crab cuticles Collagen Wood
Each layer corresponds to periodic 180º rotation of stacking sequence [2]
Brittle v.s. Ductile
The flat fracture surfaces of chitin bundles reveal the brittle mechanical property
High density of ‘tubules’ in z-direction fail in ductile mode under tensile tractions
SEM micrograph of sheep crab Loxorhynchu grandis
Strengthening Mechanism
Insects The most advanced development of
insects is the ability to fly
Insect cuticles contain mainly chitin and protein with very low mineral content
The stiffening mechanism of insect cuticle is called “tanning”
Tanning is due to cross-linking between proteins
Crustaceans Crustacean cuticles consist of chitin,
protein, and minerals, mainly CaCO3
The deposition of minerals resides in the epidermis beneath the membrane layer
The mineral ions transport through pore canals and deposit in chitin-protein matrix
Before molting, calcium ions can be dissolved to the environment or stored within the body (Gastrolith disk in stomach)
Butterfly molting pupal casehttp://sps.k12.ar.us/massengale/arthropod_notes_b1.htm
The molting process of blue crabshttp://www.serc.si.edu/education/resources/bluecrab/molting.jsp
Vincent J.F.V. Arthropod Structure & Development 33 (2004) 187Simkiss K. Wilbur K.M. Biomineralization. Academic Press Inc. (1989)
Warner G.F. The Biology of Crabs. Van Nostrand Reihold. (1977)
Typical Stress-Strain Curve for Chitin
• The chitin samples were obtained after removing protein and inorganic mineral components
• Specimens were made in dumb-bell shape and tested in hydrated and dehydrated conditions
• Dry chitin shows a defined failure point immediately beyond the UTS; wet chitin has extensive plastic deformation beyond the UTS
• Dry chitin is stiff and brittle; wet chitin is more ductile
• The presence of water has remarkably effects on mechanical properties
Source UTS (MPa) E (MPa) ε (%)
Crab Wet
Dry
20 330 6.1
36 1095 3.4
Prawn Wet
Dry
13 475 2.8
21 1220 1.8
Beetle Wet
Dry
26 630 2.0
80 2900 0.6
Mechanical properties of chitin taken from different sources
[1][1]
[2]
[3]
Typical tensile stress-train curves for wet and dry isolated crab chitin
[1] Hepburn H. R. et al Comparative Biochemistry and Physiology A 50 (1975) 551
[2] Joffe I. et al Comparative Biochemistry and Physiology A 50 (1975) 545
[3] Hepburn H. R. Ball A. Journal of Materials Science 8 (1973) 618
Typical Stress-Strain Curve for Crustacean Cuticle
• A typical tensile stress-strain curve for whole crustacean cuticle shows a discontinuity in the low strain region
• This discontinuity is associated with the brittle failure of the inorganic mineral phase of the cuticle
• Brittle failure of the mineral phase occurs at low strain, leaving the chitin and protein phases to bear the load
Source UTS (MPa) E (MPa) ε (%)
Crab Wet
Dry
23.01 ± 3.8 481 ± 75 6.3
30.14 ± 5.0 640 ± 89 3.9
Prawn Wet
Dry
28 ± 3.8 549 ± 48 6.9
29 ± 4.1 682 ± 110 4.9
Mechanical properties of crustacean cuticle
[1]
[2]
[1] Hepburn H. R. et al Comparative Biochemistry and Physiology A 50 (1975) 551
[2] Joffe I. et al Comparative Biochemistry and Physiology A 50 (1975) 545
Typical tensile stress-train curves for wet and dry whole crab cuticle show low strain discontinuities
[1]
Mechanical Effects of Dark Pigment in Crab Cuticle
• The stone crab exhibits a dark color on tips of claw and walking legs, which are exposed to higher stress and abrasive wear
• Vicker hardness test and three-point bending test were performed on dark and light specimens
• The hardness and fracture toughness for the darkened cuticle are greater than those for the light-colored cuticle
• The darkened cuticle has lower porosity level than light-colored cuticle
• Tanning (cross-linking between proteins) is the primary reason for the increased mechanical properties
Hardness (GPa) σf (MPa) KІC (MPa·m1/2)
Dark 1.33 ± 0.06 108.9 ± 22.6 2.3 ± 0.4
Light 0.48 ± 0.04 32.4 ± 23.6 1.0 ± 0.4
Dark specimen Light specimen Size of specimen: 12mm x 2mm
Hardness, Fracture strength (σf), and toughness (KIC) measurements
SEM photograph showing level of porosity in yellow cuticle (left) and dark cuticle (right)
Melnick C. A. Chen Z. Mecholsky J. J. Journal of Materials Research 11 (1996) 2903
The stone crab Menippe mercenaria
The Through-thickness Mechanical Properties of the Lobster Cuticle
Microindentation testing was conducted through the thickness of the lobster cuticle
Both the hardness and the redueced stiffness show a strong discontinuity at the interface between the exocuticle and the endocuticle
The exocuticle is harder and stiffer than the endocuticle
exocuticle
endocuticle
epicuticle
The hardness and reduced stiffness through the thickness of the dry exoskeleton of lobster H. americanus
SEM micrograph shows the exocuticle has higher stacking density than the endocuticle
The American lobster H. americanus
Rabbe D. Sachs C. Romano P. Acta Materialia 53 (2005) 4281
The most advanced development of insects is the ability to fly
Insect cuticles contain mainly chitin and protein with very low mineral content
Two stiffening mechanism of insect cuticle: “tanning” and “dehydration”
Tanning is due to cross-linking between proteins
Dehydration induces sufficient secondary bonds to account for the stiffness and insolubility of cuticle
Strengthening Mechanism of Insect Cuticles
E (Wet) (MPa) E (Dry) (MPa)
Before tanning 74.3 ± 1.08 2200 ± 0.41
Naturally tanned 245 ± 0.15 3050 ± 0.49
Stiffness of cuticle taken before tanning from the white puparium stage, and naturally tanned
Stress-train curves for wet larval cuticles tanned in various concentrations of catechol for 1.5 hour
Dry cuticle is significantly stiffer than wet , wet tanned cuticle is significantly stiffer than untanned, but there is no much difference in stiffness between dry cuticles
Butterfly molting pupal casehttp://sps.k12.ar.us/massengale/arthropod_notes_b1.htm
Vincent J.F.V. Hillerton J. E. Journal of Insect Physiology 25 (1979) 653
Mechanical Hysteresis of Insect Cuticles
• Insect cuticles of comparably low relative stiffness are capable of work-hardening on hysteresis cycles
• The hysteresis is related to the arrangement of chitin fibrils with respect to the direction of the applied load
• Cyclic-hardening provides a fine control for instar larval growth
Average tensile hysteresis behavior of eight different cuticle samples. Curves for which all points are greater than 1 exhibit cyclic-hardening; The intersegmental membrane exhibits stress-softening. [1]
5th stage instar larva, Epiphyas postvittana
Typical tensile hysteresis curves for fresh silkworm cuticle showing a progressive increase in stress with additional cycles [1]
[1]Hepburn H. R Chandler H. D. Journal of Insect Physiology 22 (1976) 221
Comparison of Cuticle with other Natural Materials
Wide range of mechanical performance of arthropod cuticle 0.3 ~ 20 GPa
Wegst U.G.K Ashby M. The mechanical efficiency of natural materials Philosophical Magazine vol84 (2004) 2167
The mantis shrimp use their limbs to smash hard-shelled prey
The energy of a strike is about 50J
They make hundreds of strikes per day, the dactyl is rarely damaged
The dactyl shows an increased hardness towards outer surface
The increased hardness of dactyl is due to:
- Increased mineralization of cuticle
- The replacement of calcium carbonate by calcium phosphate
The Hammer of the Shrimp
The smashing limb of stomatopod consists of merus, propodite, and the dactyl
The knee of the dactyl has a thick, heavily calcified region towards the right
Currey J.D. Nash A. Bonfield W. Journal of materials science 17 (1982) 1939
Heavily Calcified Region
Chitin Fibrous
Soft Tissue
Dactyl
Propodide
Values for Reichardt microhardness, and values for P:Ca (multiplied by 1000). Note the high values for both variables in the outermost regions of the dactyl.
◄P:Ca►
Relationship between microhardness and the ratio of phosphorus to calcium
Photonic Structures in Nature
Blue Morpho butterfly (Morpho menelaus)
The brilliant blue butterfly can be found in the rainforests of South America (Brasil & Guyana)
Underside of wings.When the Morpho lands, it closes its wings showing the brown sides, which eludes their main predators, birds.
Why are their top wings blue?o Blue color is caused by “interference”o Blue light has a wavelength about 400 nm,
and is interfered constructively by the slits of the morpho, which range 200 nm apart
Why are their underside wings brown?o The underside scales do not cause interferenceo Brown color are produced by pigment, which is
called chemical color
Hierarchical structure of the wing ( wing > scales > veins > ridges)
Vukusic P. Sambles J.R.Photonic structures in biology Nature 424 (2003) 852
Kertesz K. et al. Photonic crystal strucutres if biological origin Current Applied Physics 6 (2006) 252-258 Source: http://webexhibits.org/causesofcolor/15.html
Hierarchy in Biology
Characteristics:
Recurrent use of elementary units
Controlled orientation
Combination of hard and soft materials
Sensitivity to the presence of water
Multifunction
Fatigue resistance
Capacity for self-repair
Applications: Self-assembly
Functionally Gradient Materials (FGM)
3-D fibrous materials (Z-Fiber® )
Aerospace Engineering
Novel composite materials
Tirrell D.A. et al Hierarchical Structures in Biology as a Guide for New Materials Technology. National Academy Press. Washington D.C. (1994)
Z-Fiber® is composed of hundreds of structural rods inserted through the thickness of an uncured composite structure (AZTEX Inc. http://www.zfiber.com/z-fiber.php)
Conclusions
Chitin and chitosan remain underutilized natural polymers
Chitin and chitosan are promising materials for diverse applications
Isolation and production need to be improved
Hierarchical structures in nature are highly sophisticated, multifunctional, with unique properties
Thank you!
Questions?