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Properties of polysaccharides in sol and gel states.
M.Rinaudo Biomaterials Applications
Grenoble (France)
Guadalajara, Mexico, 2-4 May 2017
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3- Ionic gelation
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Test proposed to determine the ability to gelation of alginate or pectins.
Ionic selectivity
Structure of a pectin
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Gelation of pectin.
Ionic Selectivity:
Ba>Sr>Ca
In dilute solution:
dimer formation
with Ba, Sr, Ca.
No specific interaction with Mg,
no dimer formation & no
gelation
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Gel point of Pectin. Role of the
distribution of –COO- sites (DE=30%).
PE PH
PE=enzymic hydrolysis, blockwise distribution
PH=NaOH hydrolysis, random distribution
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Theory and
oligomannuronic acid
Oligo-guluronic
&galacturonic
Alginate.
Influence of polymer
concentration on the
osmotic coefficient of
Ca counterion.
Dimer
Multimer
Alginates & pectins.
Influence of DP on activity
coefficient of Ca counterion
for different polyuronates.
R.Kohn (Slovakia)
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ManA ManAGulAGulAGulA ManAOH
OOH
HO
HOOCO
OH
O
OH
HOOC
O OH
OH
HOOC
O
O
HOOC
HO
OOH
O
OH
HOOC
O
OOH
O
HOOC
HO
O
O
OOH
HO
HOOCO
OH
O
OH
HOOC
O OH
OH
HOOC
O
O
HOOC
HO
OOH
O
OH
HOOC
O
OOH
O
HOOC
HO
O
O
MGGGGGGMMMMMMMMGMGMGMGMMMMMM
G-block M-block MG-block M-block
OH
OH
HO
HOOCOHO
OH
OH
HO
HOOCOHO
OH
HO
OH
OHHOOC O
OH
HO
OH
OHHOOC O
GulAManA polyanion
Alginate structure: fibers, beads in presence of calcium
Ionic gelation in alginate/pectins
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Elastic modulus of alginate.
Role of M/G ratio.
With X4 M/G=0.28 ; X2 M/G=0.56 ; X5 M/G= 1.98. G units favour gelation.
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Ionic selectivity for alginate in presence of
divalent salts (q= [COO-]/[Me]
Ionic selectivity Ba+2> Sr+2> Ca+2 -with Mg+2,no dimer
formation and no gelation.
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Role of DP on cooperative ionic interaction on oligo-uronic acid based on dimer formation Existence of a critical DP depending on sugar configuration
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Mechanism of gelation
First step of dimerisation Blockwise gelation
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0.1000 1.000 10.00frequency (Hz)
1000
10000
1.000E5
1.000E6G'
(Pa)
1000
10000
1.000E5
1.000E6
G'' (Pa)
AG acidic form
AG calcium form
Acidic and calcium alginate gel formed at 20g/L and 25°C
-Cooperative junction based on specific Ca fixation for the Ca salt form
-Cooperative H-bonds junction based on –COOH/-OH interaction
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Mechanism of Ionotropic Gelation of Poly(HEMAm-g-GulA20) (side chain mechanism)
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Biohybrid glycopolymers.
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- Obtention of purified guluronic and mannuronic oligomers with well defined DP (by controlled hydrolysis of alginates and SEC)
- -Preparation of oligoalginate-derived monomers (AlgiMERs) in two
steps without the need for protective group chemistry: glycosamine or oligoglycuronan-derived 1-amino-1-deoxy alditols react with 2-isocayanatoethyl methacrylate macromonomers (ManA16MAm and GulA20MAm) or ManA10Am (acrylamide derivative) (all reactions in water at exclusion of RAFT)
- Copolymerization studies of AlgiMERs (acrylamide,
methacrylamide) with N-(2-hydroxyethyl) methacrylamide (HEMAm) (radical polymerization or RAFT) give high molecular weight polymers
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Biohybrid glycopolymers. Strategy
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alginate
=
=
β-D-mannuronic acid
α-L-guluronic acid
OOH
OH-OOCO
O
HO
OH-OOC
O
functionalization
vinyl glycomonomers
O O
(AlgiMERs)
depolymerization separation
R
Controlled polymerization
A schematic representation for the transformation of alginate into a biohybrid polymer with defined and tailored physico-chemical properties.
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O
OH
OH
HOOC
OH
O
OH
OH
HOOC
O
OH
O
OH
OH
HOOC
OH
OH
OH
OH
HOOC
O
NH
O
CH3
X-1 X-1
(1-4)--L-guluronan
i) NH4OAc, NaBH
3CN
ii) Methacryloyl chloride
GulAXMAm X = 10, 20
NH
O
OH
NH
O
CH3
GulAx
+
Azo-initiator
D2O, 60°C
GulAXMAm
HEMAm
n
co
ONH
GulAx
ONH
OH
m
Poly(HEMAm-co-GulA
X)
Shematic representation of the synthesis of poly(HEMAm-g-GulAx) via conventional radical copolymerization (random grafting)
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They were then copolymerized with 2-hydroxyethylmethacrylamide in aqueous solution to yield high molar mass biohybrid glycopolymers containing between 25 and 52% by mass of oligosaccharide grafted chains.
In this study, it was demonstrated that alginate-extracted oligosaccharides and aqueous radical polymerization can be combined for the flexible design of biohybrid glycopolymers capable of ionotropic gelation under very mild conditions.
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(a) Formation of gel beads when an aqueous solution of poly(HEMAm-g- GulA20MAm) (c= 71 g. L-1) was dripped into 0.5 mol /L CaCl2. Note the progressive gelation from the outside to the inside of the polymer (b) Dynamic rheological characterization of the gel in oscillatory mode.
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poly(HEMAm-g-ManA16) poly(HEMAm-g-GulA20)
Hydrogels of poly(HEMAm-g-ManA16) (left, laying on the dialysis membrane) and poly(HEMAm-g-GulA20) (right) obtained by dialysis against with CaCl2. …..ManA16 with 4% grafting ….GulA 20 with 2.7% grafting
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At C= 1.5 C*
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Synergistic mixtures: Xanthan/glucomannan or Xanthan/galactomannan
galactomannan
xanthan
Gelation involving two polysaccharides
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Cooling and heating curves for G’ on 1 g/L deacetylated Xanthan + 4.2 g/L galactomannan nin 5mM NaCl; DSC exotherm on the same solution.
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Role of the conformation of xanthan on the gel formation: in acidic conditions, xanthan is helical but disordered after neutralisation.
Complex forms with disordered xanthan conformation
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« Complex » formed better when deacetylated xanthan and galactomannan are mixed.
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Conclusions
- Physical gels are often obtained with stereoregular or blockwise structured polysaccharides involving different mechanisms but based on junction zones
- The gelation is directly related to the nature of counterions, and thermodynamics conditions (temperature, ionic concentration, pH)
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Sixth part
Specific applications of some polysaccharides: -HA -chitosan -alginates,pectins - methylcelluloses
General applications as thickeners, gelling agents, stabilisers for emulsion or solid particles suspension… but also as good film and fiber forming systems
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Hyaluronan, viscoelastic fluid used for visco-supplementation (arthrosis)
Walk corresponds to low frequency deformation and viscous character. 27
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Hyaluronan, viscoelastic fluid.
Running corresponds to larger frequency & elastic character.
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Bacterial HA is used for viscosupplementation
(in physiological conditions)
Synovial fluid f0=0.22 cycle/s (or Hz).
Walking frequency 0.5 Hz
Running frequency 2.5 Hz
Osteoarthritis with C and MW of HA decrease
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0
10
20
30
40
50
1 2 3 4 5 6 7pH
Test of the influence of pH on the viscosity of HA at 10g/L. Gel-like at pH~2.5 based on H-bond network
and/or –NH3+/-COO- interaction
-This gelation allows to produce
good films after drying
(medical application, with slow release).
Other polysaccharides give gel under
-COOH form (alginate, pectin…)
HA in acidic medium H-bond network gelation (thermoreversible gelation)
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Hyaluronan: biocompatible, hydrating polymer.
Application for cosmetics.
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SEM microphotograph: (a) nonwoven chitin* fabric; (b) sponge chitin sheet.
*Very low solubility in usual solvents (DMAc/LiCl is often used)
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Chitin transformation & applications
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Applications of chitosan
Agriculture Defensive mechanism in plants Stimulation of growth Seed coating, Frost protection Time release of fertilizers, nutrients …into the soil
Water & waste treatment Floculant to clarify water (drinking water ,pools) Removal of metal ions Ecological polymer (eliminate synthetic polymers) Reduce odors
Food &beverages Not digestible by human (dietary fiber) Bind lipids (reduce cholesterol) preservative Thickener & stabilizer for sauces Protective, fungi static, antibacterial coating for fruits
Cosmetics & toiletries Maintain skin moisture Treat acne Improve suppleness of hair Reduce static electricity in hair Tone skin Oral care (toothpaste, chewing gum)
Biopharmaceutics Immunologic, Antitumoral Hemostatic and anticoagulant Cicatrisant, Bacteriostatic 33
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Main properties of chitin and chitosan* in biomedical applications**.
Biodegradability Film forming
Biocompatibility Hydrating agent
Bioadhesivity Renewable
Polycationic substance
Absorption promoters
Antifungal Non toxicity
Antibacterial Non allergenic
Immunoadjuvant Anticholesteremic agent
Antithrombogenic
*chitosan is obtained by deacetylation of chitin
** they are processed under different forms: bead, microsphere,fiber,film,sponge,solution, gel, tablet, capsule
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How Electrospinning Work?
(http://nano.mtu.edu) 2005. Michigan Technological University. Used with permission
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Chit 5% MW~100,000 + PEO powder MW=106
70/30 (w/w)%
Chitosan/PEO 60/40 (w/w)%
Chitosan/PEO
Morphologies of the nanostructures
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Perspectives: Biomedical applications
Tissue engineering Wound healing …..
SEM image; Nanofibrous structure (left) promoted the attachment of human osteoblasts and chondrocytes and maintained characteristic cell morphology.
Nanofibers Casted film
Bhattarai et al. (2005) Electrospun chitosan-based nanofibers and their cellular compatibility
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Production of gel beads
(Na-alginate drops into CaCl2)
Use of these particles for bacteria or fungi encapsulation
Alginate application
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Encapsulation of microorganisms in gels for metabolite production (alginate, agar, carrageenan)
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Pectins is a gelling polysaccharide
The mechanism of gelation depends on the degree of esterification (DE)
-high DE, gelification in acidic medium in the presence of sucrose
-DE< 50%, gelification in the presence of calcium (same model as for alginate)
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Application of methylcellulose which forms a gel when temperature increases.
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DNA-CHITOSAN ELECTROSTATIC
COMPLEX FORMATION:
STOICHIOMETRY AND CONFORMATION
DNA-CHITOSAN ELECTROSTATIC COMPLEX
FORMATION:
STOICHIOMETRY AND CONFORMATION
Conclusions
-Due to their original chemical structure (nature of repeat unit, functionnality allowing easy chemical modification) -To their macromolecular characteristics ( stereoregular conformation, blockwise or random repetition of sugar units) - To their biological properties (antimicrobial and biocompatible properties) Polysaccharides have a large potential of developments and new applications But in carefull conditions of preparation & purification
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* Polysaccharides are hydrophilic polymers with many applications in:
- Food, cosmetics, pharmaceutical and biomedical domains - Some of them are biocompatible and biodegradable (mainly chitosan, HA) * They are easy to process under film, powder, bead, fiber, capsule…
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Thank you for your attention
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