13 Dash R Hydrogels

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

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Outline

Background Experimental methods Results and discussions Conclusions

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BACKGROUND

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Hydrogels

Hydrogels are defined as a water insoluble polymer network which can absorb and retain large amount of water

Hydrogels

Physical Chemical

Glassy nodules, lamellar microcrystals, double triple helices (elastomers/block copolymers, Gelatin) Hydrogen bonds,

ionic and hydrophobic associations, agglomerations (xanthan, paint, polymer-polymer complexes, gum)

Strong Weak

Condensation

Polyester gel

Addition

Kinetic growth, grafting (polydivinyl benzene,

CMC-g-acrylic acid)

Cross-linking

End-linking, random cross-linking (polydimethyl siloxane,

cis-polyisoprene)

Natural

Synthetic

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

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http://www.datlof.com/8Axamal/docs/Marketing/jhu/JE/index.htm www.nano.org.uk www.medline.com

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

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Heat(>35 OC)

cool

Random coil in solution Helix formation in gel

Gelatin is a single strain protein obtained by denaturation of collagen

Gelatin

Properties: High water content capacity Biocompatible Biodegradable Non-immunogenic

Major Drawback

To use cellulose nanowhiskers as cross-linkers in order to stabilize gelatin gels by establishing cross-links between the protein chains

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Cellulose nanowhiskers (CNWs)

Cellulose nanowhiskers are defined as crystalline rod-like nanoparticles which are obtained by acid hydrolysis of cellulose fibers

G. Siqueira, J. Bras, A. Dufresne, Biomacromolecules 2009, 10, 425-432. M. A. S. Azizi Samir, F. Alloin, A. Dufresne, Biomacromolecules 2005, 6, 612-626. S. Beck-Candanedo, M. Roman, D. G. Gray, Biomacromolecules 2005, 6, 1048-1054. M. M. de Souza Lima, R. Borsali, Macromol. Rapid Commun. 2004, 25, 771-787.

Microfibril

Plant cell

Acid hydrolysis

Wood

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Evolution of scientific papers on cellulose nanoparticles

* Source: SciFinder literature research system (March 2012). ** Research based on Cellulose Whiskers and Cellulose Nanocrystals terminologies

Motivation for using CNW

Nano-dimension Hydrophilicity High surface area High mechanical property (152 GPa) Renewability Biodegradability Non-toxicity 0

50

100

150

200

250

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

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Effect of reaction parameters on cellulose nanowhiskers properties from pulp

J. Araki et. al. Colloids Surfaces A, 1998, 142, 75 – 82. J. Araki et. al. J. wood Sci. 1999, 45, 258 - 261

Sample

Amounts of acidic groups on surface (mmol kg-1)

Strong acid groups

Weak acid groups

H2SO4 84 26

HCl 0 <18 TEM images of (a) H2SO4 (b) HCl hydrolyzed whiskers

Reaction conditions

(reaction time (min), acid/pulp)

Length

(nm)

Aspect ratio

Sulfur

content(%)

Surface charge density (e/nm2)

25, 8.75 141±6 28.2 0.89±0.06 0.33±0.02

45, 8.75 120±5 24.5 1.06±0.02 0.38±0.01

45, 17.5 105±4 23.3 1.26±0.01

Effect of reaction conditions on whisker properties (H2SO4 hydrolysis, softwood pulp)

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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.

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EXPERIMENTAL

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Synthesis of cellulose nanowhiskers

64% H2SO4

Pre-heating

45°C

for 45 min Stir

Several Centrifugations 10,000 rpm, 10 min

Several days of dialysis

Sonication 6 min

Centrifugation 10,000 rpm, 7min

Yield 20-30%

Soft wood pulp

Cellulose

whiskers in de-

ionized water

Oxidation of cellulose nanowhiskers (CNWs)

45oC, 45 min

Cellulose fibers Cellulose nanowhiskers

Cellulose nanowhiskers DACX

X= 1, 2, 3, 4 =Weight ratio of NaIO4 to cellulose = 0.1, 0.3, 0.5, 0.7 DAC= Dialdehyde cellulose whiskers

r=0.80

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Gelatin in water 40 OC

Oxidized whisker suspension in H2O at

40 OC

casting

Gelatin Gelatin cross-linked with nanowhiskers

Dialdehyde cellulose nanowhiskers

40 OC

30min

Hydrogel formulation Gelatin (90 wt%) + Dialdehyde nanowhisker (10 wt %)

Preparation of hydrogels

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RESULTS AND DISCUSSIONS

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Samples NaIO4/CNWs (w/w)

Carbonyl content (mmols g-1)

CNWs 0.00 0.006

DAC1 0.10 0.060

DAC2 0.30 0.114

DAC3

DAC4

0.50

0.70

0.150

0.231

Characterization of dialdehyde cellulose nanowhiskers

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

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FT-IR spectra of hydrogels

Evidence of chemical interaction between gelatin and cellulose nanowhisker!

Dialdehyde cellulose nanowhiskers

Gelatin

Gelatin-nanowhiskers

-

C=O

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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 cross-linked gel)} × 100

Degree of cross-linking increases with the level of oxidation!

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Degree of chemical cross-linking (%) % Ridge % Mobile

0 35 65

7 44 56

21 42 58 25 50 50 33 50 50

Relative rigid and mobile components of the hydrogels

Determined by 1H spin-spin relaxation (T2) NMR experiments - T2 relaxation decay intensity is sensitive to the local chain dynamics

- The faster the T2 the more rigid components the sample has

Relatively higher chain rigidity of the cross-linked hydrogels!

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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!

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Viscoelastic properties of the gelatin gels

G’: Elastic modulus G”: Loss modulus

G’>>G”

Hydrogels showing elastic network!

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Effect of chemical cross-linking on the storage modulus of the gelatin gels

Cross-linking significantly increases storage modulus!

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Effect of temperature on dynamic rheological behavior of the physical gelatin gels

Gelatin hydrogel becomes liquid like after 35 OC!

Temperature ramp of 27 to 50 °C Heating rate of 1.5 °C/min Frequency 1 Hz Shear rate of 0.05

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Effect of temperature on storage modulus of chemically cross-linked gelatin gels

Cross-linked hydrogels become stable well above 35 OC (melting point)!

Temperature ramp 27 to 50 °C Heating rate of 1.5 °C/min Frequency 1 Hz Shear rate of 0.05

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a

b c

d e

Cross-sectional morphologies of hydrogels

(a) gelatin and (b) 7%, (c) 21%, (d) 25%, (e) 33% cross-linked gels (scale bar 20 μm)

Swollen samples were quickly frozen in liquid nitrogen and then freeze dried.

Morphological changes: Increase in compactness Pores become more regular Decrease in pore size

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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 oC.

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.

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Acknowledgements

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

28 TEM image Birefringence

S=O

Characterization of cellulose nanowhiskers

C-H stretching

O-H stretching

O-H bending

L: 150-300 nm D: 4-8 nm

XPS

S (At %) 0.83

FTIR

200nm

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Thermal properties of cross-linked hydrogels

0

3000

6000

9000

12000

15000

18000

25 30 35 40 45 50

Temp (°C)

Sh

ea

r m

od

ulu

s(G

')

KP

a

Gelatin

DAC1-gelatin

DAC2-gelatin

DAC3-gelatin

Hydrogels are stable until 50oC!

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Cellulose nanowhiskers

The geometric dimensions depend on the source of the cellulosic material and hydrolysis conditions.

Dimensions: Length: 100 – 1000 nm; Diameter: 4 – 50 nm.

L/D=67.0

L/D=25.0

Habibi, Y.; Goffin, A.-L.; Schiltz, N.; Duquesne, E.; Dubois, P.; Dufresne, A. J. Mater. Chem. 2008, 18, 5002. Azizi Samir, M. A. S.; Alloin, F.; Paillet, M.; Dufresne, A. Macromolecules 2004, 37, 4313. 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, 351.

L/D=11.8 L/D=28.6

Cotton Ramie Wood Tunicate