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Characterization of Hydrogels for Nucleus Pulposus Replacement Haley Thompson Mentor: Dr. Skip Rochefort, CBEE Oregon State University 8/20/2008

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Presentation on theme: "Characterization of Hydrogels for Nucleus Pulposus Replacement Haley Thompson Mentor: Dr. Skip Rochefort, CBEE Oregon State University 8/20/2008"— Presentation transcript:

1 Characterization of Hydrogels for Nucleus Pulposus Replacement Haley Thompson Mentor: Dr. Skip Rochefort, CBEE Oregon State University 8/20/2008 ts/3D_Models/Human_Anatomy/Skeletal/Human_Spine/3d_model_anat_spine_ web1.jpg&imgrefurl=http://www.3dscience.com/3D_Models/Human_Anatomy/S keletal/Human_Spine.php&h=300&w=300&sz=59&hl=en&start=9&tbnid=PAnjh O- ugBaxNM:&tbnh=116&tbnw=116&prev=/images%3Fq%3Dspine%26hl%3Den% 26rlz%3D1T4GGLR_enUS235

2 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

3 Treatments Discectomy Spinal Fusion Disadvantages: - short term solution - decreased mobility - not a spinal disk repair y.jpg

4 Disk Replacements SB Charite Disk Complete disk replacement 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

5 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 Sept Southern Illinois University School of Medicine. 30 June 2008.

6 Fillers Sodium Alginate Beads  Derived from seaweed  Formed by chemical crosslinking of Sodium Alginate and Calcium Chloride  Sodium Alginate FDA approved Darlon Fibers  Used in tying flies  Thin thread similar to nylon parentID=156

7 Gels and Filler Combinations 1% Agarose1% Agar UnfilledNo filler Bead Filler mm diameter 33% filler by volume (low) 33% filler by volume (low) 50% filler by volume (high) 50% filler by volume (high) Darlon Filler 0.2in 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)

8 Using Rheometry to Characterize Gel What is Rheometry? The study of deformation and flow of materials TA AR 2000 EX

9 Test Procedure Dynamic oscillation: Frequency sweep Hz γ =1% Strain sweep 1-100% strain ω =0.1Hz Parallel Plate Geometry γ ω

10 Frequency Sweep G’ is the elastic or ‘storage’ modulus G’’ is the viscous or ‘loss’ modulus G’ G’’

11 Agar and Agarose Comparison

12 Strain Sweep Strain applied to the gel Linear Region Yielding region Nonlinear Region

13 Agar and Agarose Comparison

14 Instron Extrusion Testing Find a gel that is resistant to extrusion Less likely to rupture again Extrusion Tester Side View Top View

15 Sample of Results: 1% Agarose 1g gel beads First peak is initial break point

16 SampleG’G’’Rank by G’ Rank by G’’ Overall Rank sheep NP8,5403, % agar med concentration.2in fibers9,9301, % agar high concentration.2in fibers8,4301, % agarose med concentration.2in fibers10,1601, % agar low concentration.5gbeads8, % agarose low concentration.2in fibers13,4302, % agar low concentration.2in fibers6,6001, % agarose low concentration.5gbeads13,7301, % agarose high concentration 1gbeads16,2102, % agarose high concentration.2in fibers17,3603, % Agarose6, % agar high concentration 1gbeads4, % Agar3, Dynamic Oscillation Results Addition of fillers positively effects the moduli of the materials in the dynamic oscillatory test

17 Rheology Instron Rheology Instron stress at linearstrain max stressstrain stress at yieldstrain stress at linearstrainmax stressstrain stress at yieldstrain AGAR AGAROSE unfilled unfilled low beads low beads high beads high beads low fiber low fiber med fiber med fiber high fiber high fiber 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

18 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

19 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

20 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

21 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

22 Citations Bono, Christopher M., and Steven R. Garfin. "History and evolution of disc replacement." The Spine Journal 4 (2004): Nov ScienceDirect. Oregon State University, Corvallis. 1 July2008


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