characterization of composite hydrogels for nucleus pulposus replacement rheological property...

Characterization of Composite Hydrogels for Nucleus Pulposus Replacement

Rheological Property Analysis

Acknowledgements

Jenny Lauder, Stacy Long, Fan Yang, and Sandra BakerSchool of Chemical, Biological and Environmental Engineering

Agarose

Polymer extracted from red algaeForms a gel network in waterInexpensive and biocompatible

1.5% Agarose-gel composites were created with 0.2% and 0.4% polystyrene, more carboxylated, less carboxylated and sulfated microshperesThe 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.

http://brispine.com.au/images/

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

http://www.usc.edu/schools/medicine/

Current Approaches

Recommendations

Formulations

Rheology: the study of material flow. Looked at dynamic shear modulusG’= Storage (Elastic) ModulusG’’= Loss (Viscous) Modulus

The spine experiences mostly torsional forces, various frequency were tested to mimic what the human spine experiencesAdding microspheres to 1.5% agarose did help simulate the G’ or G’’ values for the nucleus pulposusNo numerical trends could be developed due to insufficient data which was a result of limited resources.

Choose a less brittle hydrogel for future researchOptimize the mechanical and rheological properties of the new hydrogel matrix by varying the microsphere filler loading levelTest pegalated microspheres to determine if they have greater interfacial interaction, increasing mechanical strengthDesign a device for hydrogel injection into the annulus fibrosus

ConclusionsThe rheological properties of 1.5% agarose is not significantly changed by adding various fillersThe compressive modulus of 1.5% agarose increase by adding microsphere fillers but still much lower than the actual nucleus pulposus dataAgarose 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 plateMicrospheres were added to the agarose solution with a syringeThe mixture is quickly poured into molds to prevent filler settling

Synthesis

ObjectiveTo 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.http://www.cryolife.com/about/research/emerging/biodisc

Gel

Parallel Plate

http://design4health.org/spine.jpg

MicrospheresPoloymer spheres with various surface groupsIncrease the mechanical strength of gel

http://www.alrise.de/images/great-microspheres.jpg

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.

www.porcpotlas.hu/en/porckorongserv

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.www.pivotalwellness.com

http://catalog.nucleusinc.com/imagescooked/9122W.jpg

Spinal problems that can arise include bulging discs, thinned or degenerated discs, and herniated discs.

Mechanical Property Analysis/

/ o

F AK

h h

Compression Modulus, KF = applied forceA = initial cross-sectional area∆h = change in heightho = initial height

Compression testing at a strain rate of 5 mm/minData shows no substantial difference in compressive modulus while varying microsphere fillersComposite moduli are all well below the human nucleus pulposus, therefore are unable to withstand forces existing in the spineLow 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 matrixFigure 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