Properties of polysaccharides in sol and gel states.

Transcription

1 Properties of polysaccharides in sol and gel states. M.Rinaudo Biomaterials Applications Grenoble (France) Guadalajara, Mexico, 2-4 May

2 3- Ionic gelation

3 Test proposed to determine the ability to gelation of alginate or pectins. Ionic selectivity Structure of a pectin 3

4 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

5 Gel point of Pectin. Role of the distribution of C - sites (DE=30%). PE PH PE=enzymic hydrolysis, blockwise distribution PH=NaH hydrolysis, random distribution

6 Dimer Alginate. Influence of polymer concentration on the osmotic coefficient of Ca counterion. Multimer Alginates & pectins. Influence of DP on activity coefficient of Ca counterion for different polyuronates. Theory and oligomannuronic acid ligo-guluronic &galacturonic R.Kohn (Slovakia)

7 Ionic gelation in alginate/pectins HC H H H H HC H H H ManA H GulA polyanion HC H H HC GulA GulA H H HC H H ManA H HC H ManA HC H H GulA H HC H ManA MGGGGGGMMMMMMMMGMGMGMGMMMMMM G-block M-block MG-block M-block Alginate structure: fibers, beads in presence of calcium 7

8 Elastic modulus of alginate. Role of M/G ratio. With X4 M/G=0.28 ; X2 M/G=0.56 ; X5 M/G= G units favour gelation.

9 Ionic selectivity for alginate in presence of divalent salts (q= [C-]/[Me] Ionic selectivity Ba +2 > Sr +2 > Ca +2 -with Mg +2,no dimer formation and no gelation.

10 Role of DP on cooperative ionic interaction on oligo-uronic acid based on dimer formation Existence of a critical DP depending on sugar configuration 10

11 Mechanism of gelation First step of dimerisation Blockwise gelation 11

12 Acidic and calcium alginate gel formed at 20g/L and 25 C 1.000E E6 AG acidic form AG calcium form 1.000E E5 G' (Pa) G'' (Pa) frequency (Hz) -Cooperative junction based on specific Ca fixation for the Ca salt form -Cooperative H-bonds junction based 12 on CH/-H interaction

13 Biohybrid glycopolymers. Mechanism of Ionotropic Gelation of Poly(HEMAm-g-GulA20) (side chain mechanism) 13

14 Biohybrid glycopolymers. Strategy - btention 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 (ManA 16 MAm and GulA 20 MAm) or ManA 10 Am (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 14

15 alginate depolymerization separation = - C H H α-l-guluronic acid R functionalization = - C H H β-d-mannuronic acid Controlled polymerization vinyl glycomonomers (AlgiMERs) A schematic representation for the transformation of alginate into a biohybrid polymer with defined and tailored physico-chemical properties. 15

16 H H HC H HC i) NH H 4 Ac, NaBH 3 CN ii) Methacryloyl chloride H H HC H H H H NH H HC H X-1 X-1 CH 3 (1-4)- -L-guluronan GulA X MAm X = 10, 20 H 3 C HN GulAx + HN Azo-initiator D 2, 60 C HN n co HN m GulA X MAm H GulAx H HEMA m Poly(HEMA m -co-gula X ) Shematic representation of the synthesis of poly(hemam-g-gulax) via conventional radical copolymerization (random grafting) 16

17 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 alginateextracted oligosaccharides and aqueous radical polymerization can be combined for the flexible design of biohybrid glycopolymers capable of ionotropic gelation under very mild conditions. 17

18 (a) Formation of gel beads when an aqueous solution of poly(hemam-g- GulA 20 MAm) (c= 71 g. L- 1 ) was dripped into 0.5 mol /L CaCl 2. Note the progressive gelation from the outside to the inside of the polymer (b) Dynamic rheological characterization of the gel in oscillatory mode. 18

19 poly(hemam-g-mana 16 ) poly(hemam-g-gula 20 ) Hydrogels of poly(hemam-g-mana 16 ) (left, laying on the dialysis membrane) and poly(hemam-g-gula 20 ) (right) obtained by dialysis against with CaCl 2...ManA16 with 4% grafting.gula 20 with 2.7% grafting 19

20 At C= 1.5 C* 20

21 Gelation involving two polysaccharides Synergistic mixtures: Xanthan/glucomannan or Xanthan/galactomannan galactomannan xanthan 21

22 Cooling and heating curves for G on 1 g/l deacetylated Xanthan g/l galactomannan nin 22 5mM NaCl; DSC exotherm on the same solution.

23 Complex forms with disordered xanthan conformation Role of the conformation of xanthan on the gel formation: in acidic conditions, xanthan is helical but disordered after 23 neutralisation.

24 «Complex» formed better when deacetylated xanthan and galactomannan are mixed. 24

25 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) 25

26 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 26

27 Hyaluronan, viscoelastic fluid used for viscosupplementation (arthrosis) Walk corresponds to low frequency deformation and viscous character. 27

28 Hyaluronan, viscoelastic fluid. Running corresponds to larger frequency & elastic character. 28

29 Bacterial HA is used for viscosupplementation (in physiological conditions) steoarthritis with C and MW of HA decrease Synovial fluid f 0 =0.22 cycle/s (or Hz). Walking frequency 0.5 Hz Running frequency 2.5 Hz 29

30 HA in acidic medium H-bond network gelation (thermoreversible gelation) 50 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 40 and/or NH 3+ /-C - interaction ph -This gelation allows to produce good films after drying (medical application, with slow release). ther polysaccharides give gel under -CH form (alginate, pectin ) 30

31 Hyaluronan: biocompatible, hydrating polymer. Application for cosmetics.

32 Chitin transformation & applications SEM microphotograph: (a) nonwoven chitin* fabric; (b) sponge chitin sheet. *Very low solubility in usual solvents (DMAc/LiCl is often used) 32

33 Agriculture Water & waste treatment Food &beverages Cosmetics & toiletries Biopharmaceutics Defensive mechanism in plants Stimulation of growth Seed coating, Frost protection Time release of fertilizers, nutrients into the soil Floculant to clarify water (drinking water,pools) Removal of metal ions Ecological polymer (eliminate synthetic polymers) Reduce odors Not digestible by human (dietary fiber) Bind lipids (reduce cholesterol) preservative Thickener & stabilizer for sauces Protective, fungi static, antibacterial coating for fruits Maintain skin moisture Treat acne Improve suppleness of hair Reduce static electricity in hair Tone skin ral care (toothpaste, chewing gum) Immunologic, Antitumoral Hemostatic and anticoagulant 33 Cicatrisant, Bacteriostatic Applications of chitosan

34 Main properties of chitin and chitosan* in biomedical applications**. Biodegradability Biocompatibility Bioadhesivity Polycationic substance Antifungal Antibacterial Immunoadjuvant Antithrombogenic Film forming Hydrating agent Renewable Absorption promoters Non toxicity Non allergenic Anticholesteremic agent *chitosan is obtained by deacetylation of chitin ** they are processed under different forms: bead, microsphere,fiber,film,sponge,solution, gel, tablet, capsule 34

35 How Electrospinning Work? ( Michigan Technological University. Used with permission 35

36 Morphologies of the nanostructures Chitosan/PE Chitosan/PE 70/30 (w/w)% 60/40 (w/w)% Chit 5% MW~100,000 + PE powder MW=

37 Perspectives: Biomedical applications Tissue engineering Nanofibers Wound healing.. Casted film SEM image; Nanofibrous structure (left) promoted the attachment of human osteoblasts and chondrocytes and maintained characteristic cell morphology. Bhattarai et al. (2005) Electrospun chitosan-based nanofibers and their cellular compatibility

38 Alginate application Production of gel beads (Na-alginate drops into CaCl 2 ) Use of these particles for bacteria or fungi encapsulation 38

39 Encapsulation of microorganisms in gels for metabolite production (alginate, agar, carrageenan) 39

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41 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)

42 Application of methylcellulose which forms a gel when temperature increases.

43 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) DNA-CHITSAN ELECTRSTATIC CMPLEX CMPLEX FRMATIN: STICHIMETRY AND AND CNFRMATIN - 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 43

44 * 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 44

45 Thank you for your attention 45

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