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?