Characterization of Composite Hydrogels for Nucleus Pulposus Replacement Rheological Property Analysis Acknowledgements Dr. Skip Rochefort - Project Sponsor Will Beattie Dr. Phil Harding DN Foster Rose Felber Kelsey Yee Dr. Christine Kelly Dr. Devon Quick Jenny Lauder, Stacy Long, Fan Yang, and Sandra Baker School of Chemical, Biological and Environmental Engineering Agarose Polymer extracted from red algae Forms a gel network in water Inexpensive and biocompatible 1.5% Agarose-gel composites were created with 0.2% and 0.4% polystyrene, more carboxylated, less carboxylated and sulfated microshperes The rheological and compressive properties for each gel were tested Trends were analyzed to predict the effect of microsphere fillers on gel compression strength and rheological properties Most approaches to address back problems require extremely invasive surgeries. Current Approaches: Total Disc Replacement: Completely replaces spinal disc to restore very limited functions Lumbar Spinal Fusion: Screws immobilize spinal vertebrae to reduce pain related to movement Lumbar Laminectomy: Relieves pressure on nerve root Lumbar Discectomy: Nucleus pulposus removal to relieve pressure on spinal chord Current Approaches Recommendations Formulations Rheology: the study of material flow. Looked at dynamic shear modulus G’= Storage (Elastic) Modulus G’’= Loss (Viscous) Modulus The spine experiences mostly torsional forces, various frequency were tested to mimic what the human spine experiences Adding microspheres to 1.5% agarose did help simulate the G’ or G’’ values for the nucleus pulposus No numerical trends could be developed due to insufficient data which was a result of limited resources. Choose a less brittle hydrogel for future research Optimize the mechanical and rheological properties of the new hydrogel matrix by varying the microsphere filler loading level Test pegalated microspheres to determine if they have greater interfacial interaction, increasing mechanical strength Design a device for hydrogel injection into the annulus fibrosus Conclusions The rheological properties of 1.5% agarose is not significantly changed by adding various fillers The compressive modulus of 1.5% agarose increase by adding microsphere fillers but still much lower than the actual nucleus pulposus data Agarose is brittle and at high risk for dehydration and thus is not suitable for in vivo application Agarose is dissolved in water and heated on a hot plate Microspheres were added to the agarose solution with a syringe The mixture is quickly poured into molds to prevent filler settling Synthesis Objective To evaluate the rheological and compressive properties of various microsphere fillers in a 1.5% agarose hydrogel matrix to be used as a non- invasive, injectable nucleus pulposus replacement. Gel Parallel Plate Microspheres Poloymer spheres with various surface groups Increase the mechanical strength of gel Spinal Discs Parts of a Spinal Disc: Annulus Fibrosus: Acts as a container for the nucleus pulposus. Nucleus Pulposus: Inner jelly-like material that acts to distribute forces the body experiences. The spine is a column of vertebrae separated by spinal discs. Newman, Donald Spinal discs act as shock absorbers that allow the spine to obtain a diverse range of movements. A 2002 National Health Survey reported that 34 million Americans over 18 have lower back pain, and that 80% of people will have some form of back pain in their lives. Problems Disc Herniation: When the annulus fibrosus ruptures and the nucleus pulposus extrudes out, placing pressure on the spinal nerve. W.jpg Spinal problems that can arise include bulging discs, thinned or degenerated discs, and herniated discs. Mechanical Property Analysis Compression Modulus, K F = applied force A = initial cross-sectional area ∆h = change in height h o = initial height Compression testing at a strain rate of 5 mm/min Data shows no substantial difference in compressive modulus while varying microsphere fillers Composite moduli are all well below the human nucleus pulposus, therefore are unable to withstand forces existing in the spine Low compressive modulus values due to the agarose matrix strength Image Source: Rose Felber 2010 Gel Compressive Weight Instron Rheometer Special thanks to: Figure 2: Results for 0.4% filler in 1.5% agarose matrix Figure 1: Results for 0.2% filler in 1.5% agarose matrix Frequencies Experienced by Spine Breathing 0.1 Hz Walking 1-3 Hz Driving 4-6 Hz