Developing an injectable hydrogel system for nucleus pulposus replacement
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Developing an Injectable Hydrogel System for Nucleus Pulposus Replacement. Jeremy Griffin Mentor: Jennifer Vernengo Advisor: Dr. Tony Lowman Department of Chemical Engineering. The Issue. Over 5 million Americans suffer from lower back pain 1

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Developing an Injectable Hydrogel System for Nucleus Pulposus Replacement

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Developing an injectable hydrogel system for nucleus pulposus replacement

Developing an Injectable Hydrogel System for Nucleus Pulposus Replacement

Jeremy Griffin

Mentor: Jennifer Vernengo

Advisor: Dr. Tony Lowman

Department of Chemical Engineering


Developing an injectable hydrogel system for nucleus pulposus replacement

The Issue

  • Over 5 million Americans suffer from lower back pain1

  • At least four out of five adults will experience lower back pain2

  • Lower back pain is the leading cause of lost workdays in the US1

www.nohochiro.com

[1] MedPro Month, 1998. VIII(1).

[2] www.spine-health.com


Developing an injectable hydrogel system for nucleus pulposus replacement

The Issue

  • Lower back pain treatment and compensation costs:

    • $50 billion in the US

    • £12 billion in the United Kingdom2

  • 75% of lower back pain is due to intervertebral disc degeneration in the lumbar region of the spine1

www.lowbackpain.com

[1] MedPro Month, 1998. VIII(1).

[2] Bibby, S. R. S., D.A. Jones, R.B. Lee , J. Yu , J.P.G. Urban, The Pathophysiology of theIntervertebral Disc. Joint Bone Spine, 2001. 68: p. 537-542.


Developing an injectable hydrogel system for nucleus pulposus replacement

The Intervertebral Disc

www.lieberson.com

www.lieberson.com

http://www.nlm.nih.gov 

  • The disctransfers compressive loads to the annulus in tension by exerting hydrostatic pressure on its inner surface

  • The Intervertebral Disc:

    • - Annulus fibrosis

    • - Nucleus Pulposus [High water content (80%)]


Developing an injectable hydrogel system for nucleus pulposus replacement

Degenerative Disk Disease (DDD)

www.spinecenteronline.com

  • Caused by dehydration or damage of the nucleus pulposus

www.spineuniversity.com


Developing an injectable hydrogel system for nucleus pulposus replacement

The Damaged Intervertebral Disc

www.lieberson.com

www.lieberson.com

http://www.nlm.nih.gov 

www.neurosurgerytoday.org

  • No longer transfer loads to the annulus in tension

  • Compressive stress on annulus causes tears and cracks

  • Disc Herniation causes:

    • - Nerve impingement

    • - Inflammatory response


Developing an injectable hydrogel system for nucleus pulposus replacement

DDD Treatments

  • Conservative Treatments:

    • Pain Killers

    • Physical Therapy / Exercise

    • Bed Rest

www.brypix.com

www.rehabpub.com

fpb.cwru.edu


Developing an injectable hydrogel system for nucleus pulposus replacement

Major DDD Treatments

  • Surgical Interventions:

    • Discectomy

    • Complete disc replacement

    • Spinal Fusion

www.popsci.com

www.neurosurgerytoday.org


Developing an injectable hydrogel system for nucleus pulposus replacement

Problems with DDD Treatments

  • No resolve to the cause of the back pain

  • Additional stresses on the surrounding discs

    and vertebrae causing degeneration

  • Healthy biomechanics are not restored

  • Invasive

www.af.mil


Developing an injectable hydrogel system for nucleus pulposus replacement

Nucleus Pulposus Replacement

  • In early stages of disc degeneration the nucleus can be replaced with a synthetic material:

    • Less Invasive Procedure

    • Restores healthy biomechanical function

Nucleus

www.spineuniverse.com


Developing an injectable hydrogel system for nucleus pulposus replacement

Synthetic Nucleus Replacement

  • HYDROGELS

  • 3-D hydrated polymer network

  • Consistency similar to natural nucleus pulposus

  • Allow for the delivery of nutrition and removal of metabolism products


Developing an injectable hydrogel system for nucleus pulposus replacement

Injectable Nucleus Replacement

  • Synthetic material could be injected as a free flowing solution and solidify in situ

  • Advantages:

    • Potential to restore

      biomechanical function

    • Minimally invasive

    • Space filling


Developing an injectable hydrogel system for nucleus pulposus replacement

Thermo-responsive Polymers

Two phases

(polymer and solvent)

Temperature

Lower Critical Solution Temperature (LCST)

Single phase (polymer solution)

Concentration of polymer in solution


Developing an injectable hydrogel system for nucleus pulposus replacement

Poly (N-isopropylacrylamide)

  • PNIPAAm

    • Most widely studied thermo-responsive polymer because of the LCSTs proximity to the temperature of the human body

25oC

37oC

Polymer chains


Developing an injectable hydrogel system for nucleus pulposus replacement

Injectable Nucleus Replacement


Developing an injectable hydrogel system for nucleus pulposus replacement

Direction of this Research

  • PNIPAAm homopolymer:

    • Holds limited water at 37º C(hydrophobic)

    • Lacks elasticity

  • Tailor water content and mechanical properties of precipitated phase:

    • Create branched copolymers with hydrophilic component


Poly ethylene glycol dimethacrylate

Poly (ethylene glycol) Dimethacrylate

  • PEGDM

    • Copolymerization of NIPAAm and difunctional PEG yields branched copolymer

Branched PNIPAAm-PEGDM copolymer

+

NIPAAm

PEG

Dimethacrylate


Developing an injectable hydrogel system for nucleus pulposus replacement

Differential Scanning Calorimetry (DSC)

  • DSC defines the range of LCSTs

  • Hydrophilic component hinders dehydration and mobility of chains

  • LCST should increase with increasing PEGDM content


In vitro swelling study

In-Vitro Swelling Study

  • Monitor swelling ratio (Q) for up to 180 days in vitro

    • 37º C phosphate buffer solution (pH=7.4)

PEG rich copolymers

Swelling ratio, q

PNIPAAM homopolymer

Time (days)


Developing an injectable hydrogel system for nucleus pulposus replacement

Unconfined Compressive Modulus

  • Instron mechanical testing system (100 % / minute)

  • Maintain modulus in suitable range

  • More covalent bonds (PEG) between copolymer chains increases the stiffness

techunix.technion.ac.il


Developing an injectable hydrogel system for nucleus pulposus replacement

Acknowledgements

  • Jennifer Vernengo

  • Dr. Tony Lowman

  • All Members of the Biomaterials and Drug Delivery Lab


Questions

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