Characterization of Hydrogels for Nucleus Pulposus Replacement
Haley ThompsonMentor: Dr. Skip Rochefort, CBEE
Oregon State University8/20/2008
http://images.google.com/imgres?imgurl=http://www.3dscience.com/img/Products/3D_Models/Human_Anatomy/Skeletal/Human_Spine/3d_model_anat_spine_web1.jpg&imgrefurl=http://www.3dscience.com/3D_Models/Human_Anatomy/Skeletal/Human_Spine.php&h=300&w=300&sz=59&hl=en&start=9&tbnid=PAnjhO-ugBaxNM:&tbnh=116&tbnw=116&prev=/images%3Fq%3Dspine%26hl%3Den%26rlz%3D1T4GGLR_enUS235
Back Pain and Herniated Disks
Components of a spinal disk:
What happens when a disk is herniated? • Tear in annulus fibrosus•Nucleus pulposus squeezes out•Disk loses cushioning function
Bader, Rebecca. "Development and Characterization of Novel Hydrogels for Nucleus Pulposus Replacement." Oregon State University, Corvallis. 15 Dec. 2006.
Treatments•Discectomy• Spinal Fusion
Disadvantages: - short term solution - decreased mobility - not a spinal disk repair
http://brispine.com.au/images/posterior_fusion_x_ray.jpg
Disk Replacements
SB Charite Disk•Complete disk replacement
http://biomed.brown.edu/Courses/BI108/BI108_2002_Groups/discs/Charite.htm
PDN® Prosthetic Disc-Nucleus• Nucelus pulposus replacement
• Hydrogel encased in polyethylene jacket
DASCOR• Nucelus pulposus replacement• gel-inflated polyurethane balloon
Agar and Agarose Gels
Common electrophoresis gels that are:
•body-friendly•easy to produce•fairly cheap
"Gel Structure of Agarose." MBMB 451A Section One - Fall 2005. 1 Sept. 2005. Southern Illinois University School of Medicine. 30 June 2008 <http://web.siumed.edu/~bbartholomew/images/protein_methods/gel_structure_of_agarose.gif>.
FillersSodium Alginate BeadsDerived from seaweedFormed by chemical crosslinking of Sodium Alginate and Calcium ChlorideSodium Alginate FDA approved
Darlon FibersUsed in tying fliesThin thread similar to nylon
http://www.charliesflyboxinc.com/flybox//details.cfm?parentID=156
Gels and Filler Combinations
1% Agarose 1% Agar
Unfilled No filler No filler
Bead Filler1.0-1.3 mm diameter
33% filler by volume(low)
33% filler by volume(low)
50% filler by volume(high)
50% filler by volume(high)
Darlon Filler0.2in long
.02g per 6ml solution(low)
.02g per 6ml solution(low)
.04g per 6ml solution(med)
.04g per 6ml solution(med)
.06g per 6ml solution(high)
.06g per 6ml solution(high)
Using Rheometry to Characterize Gel
What is Rheometry?
The study of deformation and flow of materials
TA AR 2000EX
Test Procedure
Dynamic oscillation:
Frequency sweep• 0.1-10Hz•γ=1%Strain sweep•1-100% strain•ω=0.1Hz
sample
rotating plate
fixed plate sample
rotating plate
fixed plate
Parallel Plate Geometry
γω
Frequency Sweep
G’ is the elastic or ‘storage’ modulus
G’’ is the viscous or ‘loss’ modulus
G’
G’’
Agar and Agarose Comparison
Strain Sweep
Strain applied to the gel
Linear Region
Yielding region
Nonlinear Region
Agar and Agarose Comparison
Instron Extrusion Testing•Find a gel that is resistant to extrusion•Less likely to rupture again
Extrusion Tester
Side View
Top View
Sample of Results:1% Agarose 1g gel beads
First peak is initial break point
Sample G’ G’’ Rank by G’
Rank by G’’
Overall Rank
sheep NP 8,540 3,2100 0 0
1% agar med concentration .2in fibers 9,930 1,770
3 5 1
1% agar high concentration .2in fibers 8,430 1,730
1 6 2
1% agarose med concentration .2in fibers 10,160 1,860
4 4 3
1% agar low concentration .5gbeads 8,070 705
2 9 4
1% agarose low concentration .2in fibers 13,430 2,310
8 3 5
1% agar low concentration .2in fibers 6,600 1,035
5 8 6
1% agarose low concentration .5gbeads 13,730 1,570
10 7 7
1% agarose high concentration 1gbeads 16,210 2,775
11 2 8
1% agarose high concentration .2in fibers 17,360 3,540
12 1 9
1% Agarose 6,460 3506 11 10
1% agar high concentration 1gbeads 4,245 415
7 10 11
1% Agar 3,590 1809 12 12
Dynamic Oscillation Results
•Addition of fillers positively effects the moduli of the materials in the dynamic oscillatory test
Rheology Instron Rheology Instron
stress at linear strain
max stress strain
stress at yield strain
stress at linear strain max stress strain
stress at yield strain
AGAR AGAROSE
unfilled 280 12 580 53.5 84750 2.8 unfilled 380 9 700 38 345500 4.8low beads 390 9 725 37 70100 1.4 low beads 745 10 1180 53.5 139250 1.25
high beads 245 10.5 605 85.5 44625 1.3 high beads 865 11 1520 51.5 86700 1.4
low fiber 340 10 560 68 62150 1.2 low fiber 800 11 1400 70 170300 1.5
med fiber 600 11.5 1055 90 60700 1.1 med fiber 600 11 1040 67 152000 1.4
high fiber 430 11 710 78 62800 0.85 high fiber 890 10 1580 87.5 157950 1.6
Strain Comparison Results
• In dynamic oscillatory shear experiments fillers increase the modulus as evidenced by the increase in the maximum yield stress
•In Instron compression tests the modulus of the unfilled material is always higher than filled materials
•Relative moduli of individual gels (max stress at yield) correlates well with the magnitudes of the gel stiffness in the compression test
•Although dynamic oscillatory shear tests are useful for general screening of materials, compression tests are important for real world applications
Summary of Research
• Got a new rheological instrument on line.
•Designed strain sweep test
•Developed techniques to make gels and forms
• Added fibers and gel beads to gels
• Tested in Instron apparatus
•Determined areas for focus of future research
Conclusions• Addition of fillers increases the strength and the resiliency of the gels
• Fillers did not have the anticipated effect on the performance in the instron test
• While the dynamic oscillatory strain sweep is good for screening gels, the compression test is important because it more closely mimics the true conditions in the back • Instron test indicates that bonding between gels and matrix are the ‘weak link’
• Syneresis of Agarose affects performance in the Instron test
Future Work
• Address issues with syneresis of the Agarose gels
• Try to enhance interstitial strength of the filler and the gel matrix
• Continue to test a variety of concentrations of new and existing fillers
Acknowledgements
• HHMI Thank you for funding this internship and supporting research for undergraduates.
• Dr. Kevin Ahern Thank you for heading this program and helping at every step.
• Dr. Skip Rochefort Thank you for giving me the opportunity to work in your lab and gain valuable experience.
• Nikki Buck, Jessica McKiernan, Coralie Backlund for being valuable friends and research partners
• Will Beattie and Rebecca Bader for sharing their research on the subject
Citations
Bono, Christopher M., and Steven R. Garfin. "History and evolution of disc replacement." The Spine Journal 4 (2004): 145-50. 12 Nov. 2004. ScienceDirect. Oregon State University, Corvallis. 1 July2008<http://www.science direct.com/science?_ob =ArticleURL&_udi=B6W7P4DSGJ9014&_user=576687&_coverDate=11%2F01% 2F2004&_rdoc=3&_fmt=high&_orig=browse&_srch=docinfo(%23toc%236632%232004%23999959993.8998%23567049%23FLA%23display%23Volume)&_cdi=6632&_sort=
Cloyd, Jordan M., Neil R. Malhotra, Lihui Weng, Weiliam Chen, Robert L. Mauck, and Dawn M. Elliot. "Material properties in unconfined compression of human nucleus." European Spine Journal 16 (2007): 1892-898. 28 July 2007.
Springer-verlag. Oregon State University, Corvallis. 14 July 2008 <http://www.springerlink.com/content/4734757161711440/fulltext.pdf>.
Deyo, Richard A. Scientific American vol. 279, issue 2, (1998): 49-49. EBSCO. Oregon State University, Corvallis. 20 June 2008 <http://0web.ebscohost.com.oasis.oregonstate.edu/ehost/detail?vid=1&hid=103&sid=42fb68ce-d1bf-4ae0-
ac9f-b84ddd59b470%40sessionmgr107>.
Thomas, Jonathan, Anthony Lowman, and Michele Marcolongo. "Novel Associated Hydrogels for Nucleus Pulposus Replacement.“ Journal of Biomedical Materials Research Part A 67 (2003): 1329-337. 2003. InterScience. Oregon State University, Corvallis. 23 June 2008 <http://www3.interscience.wiley.com/cgibin/fulltext/106563998/htmlstart>.