Using Cellulose Nanowhisker as a Cross-linker to Improve the Mechanical and Thermal Properties of Gelatin Hydrogels

Transcription

1 Using Cellulose Nanowhisker as a Cross-linker to Improve the Mechanical and Thermal Properties of Gelatin Hydrogels Rajalaxmi Dash and Arthur J. Ragauskas School of Chemistry & Biochemistry Institute of Paper Science and Technology Georgia Institute of Technology 10th April 2012

2 Outline Background Experimental methods Results and discussions Conclusions 2

3 BACKGROUND 3

4 Hydrogels Hydrogels are defined as a water insoluble polymer network which can absorb and retain large amount of water Natural Hydrogels Synthetic Physical Chemical Strong Weak Glassy nodules, lamellar microcrystals, double triple helices (elastomers/block copolymers, Gelatin) Condensation Polyester gel Hydrogen bonds, ionic and hydrophobic associations, agglomerations (xanthan, paint, polymer-polymer complexes, gum) Addition Kinetic growth, grafting (polydivinyl benzene, CMC-g-acrylic acid) Cross-linking End-linking, random cross-linking (polydimethyl siloxane, cis-polyisoprene) Gulrez, S. K.H and Al-Assaf, S and Phillips, G. O (2011) Hydrogels: Methods of Preparation, Characterization and Applications in Molecular and Environmental Bioengineering. Glyndŵr University Research Online 4

5 Applications of hydrogels Food packaging absorbing or delivering moisture for freshness and appearance Personal hygiene products- diapers, skin care, hair care Pharmaceutical and Biomedical contact lenses, wound dressings, plasma expander, hard or soft capsules, drug delivery, tissue engineering

6 Gelatin is a single strain protein obtained by denaturation of collagen Properties: High water content capacity Biocompatible Biodegradable Non-immunogenic Major Drawback Gelatin Heat(>35 O C) cool Helix formation in gel Random coil in solution To use cellulose nanowhiskers as cross-linkers in order to stabilize gelatin gels by establishing cross-links between the protein chains 6

7 Cellulose nanowhiskers (CNWs) Cellulose nanowhiskers are defined as crystalline rod-like nanoparticles which are obtained by acid hydrolysis of cellulose fibers Wood Plant cell Microfibril Acid hydrolysis G. Siqueira, J. Bras, A. Dufresne, Biomacromolecules 2009, 10, M. A. S. Azizi Samir, F. Alloin, A. Dufresne, Biomacromolecules 2005, 6, S. Beck-Candanedo, M. Roman, D. G. Gray, Biomacromolecules 2005, 6, M. M. de Souza Lima, R. Borsali, Macromol. Rapid Commun. 2004, 25,

8 Evolution of scientific papers on cellulose nanoparticles Motivation for using CNW Nano-dimension Hydrophilicity High surface area High mechanical property (152 GPa) Renewability Biodegradability Non-toxicity * Source: SciFinder literature research system (March 2012). ** Research based on Cellulose Whiskers and Cellulose Nanocrystals terminologies 8

9 Effect of reaction parameters on cellulose nanowhiskers properties from pulp Effect of reaction conditions on whisker properties (H 2 SO 4 hydrolysis, softwood pulp) Reaction conditions (reaction time (min), acid/pulp) Length (nm) Aspect ratio Sulfur content(%) Surface charge density (e/nm 2 ) 25, ± ± ± , ± ± ± , ± ±0.01 Sample Amounts of acidic groups on surface (mmol kg -1 ) Strong acid groups Weak acid groups H 2 SO HCl 0 <18 TEM images of (a) H 2 SO 4 (b) HCl hydrolyzed whiskers J. Araki et. al. Colloids Surfaces A, 1998, 142, J. Araki et. al. J. wood Sci. 1999, 45,

10 Cellulose nanowhiskers potential areas of application Nanocomposites Paper & Paperboard Biomedical Packaging, Adhesive Electronic displays, Foams Aerogels, Films Coatings / barriers Bioimaging nanodevice, drug delivery technology, skin care Arboranano* is a new Canadian Forest NanoProducts Network whose objective is to develop high value products from nanocrystalline cellulose. *Canada s Business-led Networks of Centers of Excellence program, FPInnovations and NanoQuébec. 10

11 EXPERIMENTAL 11

12 Synthesis of cellulose nanowhiskers Soft wood pulp 45 C Yield 20-30% 64% H 2 SO 4 Pre-heating for 45 min Stir Several Centrifugations 10,000 rpm, 10 min Several days of dialysis Sonication 6 min Centrifugation 10,000 rpm, 7min Cellulose whiskers in deionized water 12

13 Oxidation of cellulose nanowhiskers (CNWs) 45 o C, 45 min r=0.80 Cellulose fibers Cellulose nanowhiskers Cellulose nanowhiskers DACX X= 1, 2, 3, 4 =Weight ratio of NaIO 4 to cellulose = 0.1, 0.3, 0.5, 0.7 DAC= Dialdehyde cellulose whiskers

14 Preparation of hydrogels Gelatin in water 40 O C Oxidized whisker suspension in H 2 O at 40 O C casting Hydrogel formulation Gelatin (90 wt%) + Dialdehyde nanowhisker (10 wt %) 40 O C 30min Gelatin Dialdehyde cellulose nanowhiskers Gelatin cross-linked with nanowhiskers 14

15 RESULTS AND DISCUSSIONS 15

16 Characterization of dialdehyde cellulose nanowhiskers Samples NaIO 4 /CNWs (w/w) CNWs DAC DAC Carbonyl content (mmols g -1 ) DAC3 DAC FT-IR spectra of (a) nanowhisker (b)dac1 (c) DAC2 (c) DAC3 (d) DAC4 Estimation of aldehyde content of dialdehyde cellulose nanowhiskers by copper number titration 16

17 FT-IR spectra of hydrogels - Gelatinnanowhiskers Gelatin C=O Dialdehyde cellulose nanowhiskers Evidence of chemical interaction between gelatin and cellulose nanowhisker! 17

18 Cross-linking density of hydrogels Cross-linking density was determined by UV spectrometer following a Ninhydrin assay measuring the free amine groups Degree of cross-linking (%) = {1- (Absorbance of cross-linked gel/absorbance of non crosslinked gel)} 100 Degree of cross-linking increases with the level of oxidation! 18

19 Relative rigid and mobile components of the hydrogels Determined by 1 H spin-spin relaxation (T 2 ) NMR experiments - T 2 relaxation decay intensity is sensitive to the local chain dynamics - The faster the T 2 the more rigid components the sample has Degree of chemical cross-linking (%) % Ridge % Mobile Relatively higher chain rigidity of the cross-linked hydrogels! 19

20 Equilibrium swelling ratio of hydrogels Hydrogels were swelled in water for 2 days Equilibrium fluid content (%) = {1- (weight of dry gel/weight of swollen gel)} 100 Decrease in swelling ratio with increase in cross-linking! 20

21 Viscoelastic properties of the gelatin gels G : Elastic modulus G : Loss modulus G >>G Hydrogels showing elastic network! 21

22 Effect of chemical cross-linking on the storage modulus of the gelatin gels Cross-linking significantly increases storage modulus! 22

23 Effect of temperature on dynamic rheological behavior of the physical gelatin gels Temperature ramp of 27 to 50 C Heating rate of 1.5 C/min Frequency 1 Hz Shear rate of 0.05 Gelatin hydrogel becomes liquid like after 35 O C! 23

24 Effect of temperature on storage modulus of chemically cross-linked gelatin gels Temperature ramp 27 to 50 C Heating rate of 1.5 C/min Frequency 1 Hz Shear rate of 0.05 Cross-linked hydrogels become stable well above 35 O C (melting point)! 24

25 Cross-sectional morphologies of hydrogels a Swollen samples were quickly frozen in liquid nitrogen and then freeze dried. b c Morphological changes: d e Increase in compactness Pores become more regular Decrease in pore size (a) gelatin and (b) 7%, (c) 21%, (d) 25%, (e) 33% cross-linked gels (scale bar 20 μm) 25

26 Conclusions First successful study on the synthesis of gelatin hydrogels chemically cross-linked by dialdehyde cellulose nanowhiskers. The increase in aldehyde groups resulted in an increase in degree of cross-linking leading to the formation of a rigid dense network. The rigid network reduced water uptake ability of the hydrogels. Further, the increase in degree of cross-linking improved the mechanical properties of hydrogels by 150% and increased the thermal stability of the gels as the gels did not degrade until 50 o C. These findings on this work would broaden the biomedical applications of the chemically cross-linked gelatin hydrogels in wound dressing, tissue engineering and sustained release applications. 26

27 Acknowledgements Dr. Arthur J. Ragauskas Marcus Foston Shaobo Pan Department of Energy for providing support for this study 27

28 Characterization of cellulose nanowhiskers O-H stretching FTIR C-H stretching O-H bending S=O XPS S (At %) 0.83 L: nm D: 4-8 nm Birefringence TEM image 200nm 28

29 29

30 Shear modulus(g') KPa Thermal properties of cross-linked hydrogels Temp ( C) Gelatin DAC1-gelatin DAC2-gelatin DAC3-gelatin Hydrogels are stable until 50 o C! 30

31 Cellulose nanowhiskers The geometric dimensions depend on the source of the cellulosic material and hydrolysis conditions. Cotton Ramie Wood Tunicate L/D=11.8 L/D=28.6 L/D=25.0 Dimensions: Length: nm; Diameter: 4 50 nm. L/D=67.0 Habibi, Y.; Goffin, A.-L.; Schiltz, N.; Duquesne, E.; Dubois, P.; Dufresne, A. J. Mater. Chem. 2008, 18, Azizi Samir, M. A. S.; Alloin, F.; Paillet, M.; Dufresne, A. Macromolecules 2004, 37, Roohani, M.; Habibi, Y.; Belgacem, N. M.; Ebrahim, G.; Karimi, A. N.; Dufresne, A. Eur. Polym. J. 2008, 44, 2489.Favier, V.; Canova, G. R.; Cavaille, J. Y.; Chanzy, H.; Dufresne, A.; Gauthier, C. Polym. AdV. Technol. 1995, 6,