Characterization of Salt Templated Hyaluronic Acid Hydrogels for Nerve Regeneration

Richelle C. Thomas, Christine E. SchmidtUniversity of Texas at Austin

Motivation: Peripheral Neuropathy

Over 20 million Americans suffer from some form of peripheral neuropathy

The Neuropathy Association <http://www.neuropathy.org/site/PageServer?pagename=About_Facts>

Motivation: Peripheral Neuropathy

InjuryDisease

Disease

Motivation: Diabetes

Global Prevalence 60-70% of diabetics have

mild to severe nervous system damage

Diabetic foot ~80% of non-traumatic amputations

Largest diabetic population:▪ India, China, US

Largest cause of PN in west US Prevalence

10.7% US aged 20 & older 23.1% US aged 60 &older

Cost US $174 B in 2007

National Institute of Diabetes and Digestive and Kidney Diseases. National Diabetes Statistics, 2007 fact sheet. Bethesda, MD: U.S. Department of Health and Human Services, National Institutes of Health, 2008.

Injury

Motivation: Peripheral Neuropathy

Easy to injure Trauma

1.5-2.8% incidence rate

War 35% troops

extremities wounded in combat

Journal of Craniofacial Surgery. 21(4):998-1001, July 2010.

Nerve Repair Options

End-to-End Suturing

BridgingGraftingConduit/Implant

Ciardelli G, Chiono V. 2006. Materials for Peripheral Nerve Regeneration. Macromol. Biosci. 6:13-26

Communication between nerve stumps

Physical guidance to regenerating axons

Biomaterials for PN requires proper integration of stimuli

Chemical Contact Electrical

Lee et al. (2002) Gomez et al. (2006) Huang et al. (2008)

For more information on stimuli integration see Forciniti et al. ABME. (2008).

Motivation: Peripheral Neuropathy

Soft tissue scaffold Focus on injury Supports wound healing Reduces inflammation Promotes tissue reorganization

Properties of an Ideal Scaffold

Hudson TW, Evans GR, Schmidt CE. 1999. Engineering strategies for peripheral nerve repair. Clin. Plast. Surg. 26:617–28

Properties of an Ideal Scaffold

Artif Organs V 30 No 7 2006

Degradation rateComparable to new tissue formation

BiocompatibleInflammatory Response

Mechanically soundNot collapse

BiodegradabilityRoom for tissue growthNo need for 2nd surgery

Naturally Derived Polymer Hydrogels

PBS Swollen

Hyaluronic Acid

Extracellular matrix component

Polyanionic Hydrophillic Involved in

mediating wound repair

Non-cell adhesive

Photocrosslinkable Hydrogels

ModulateSwellingDegradationMechanical Properties

AdvantagesBiocompatibleNon-cell adhesiveControl local chemical

propertiesOptically transparent

High Swelling HA Hydrogels

1 min 20 min 2 min 5 min 10 min

UV Exposure

Motivation

Hyaluronic Acid gels beneficial for wound healing applications

Problem: Hydrogels are amorphous and do not provide any significant physical contact guidance to infiltrating cells beyond their inherent porosity

Role of Physical vs. Chemical Cues

Physical cues are preferred over chemical cues for axon initiation

(polarization)

70 % Physical Cues (microchannels) 30 % Chemical Cues (NGF or Laminin)

Microchannels vs. Laminin

25 mm

12 mm

Gomez, Chen, Schmidt (2007). J. R. Soc Interface. 4(13): 223-233.

Gomez, N., Schmidt, C.E. (2007) Biomaterials. 28 (2): 271-284

Combined Chemical & Physical Cues

Neurons extended longer and more oriented axons on surfaces with combinatorial cues.

Gomez, N., Schmidt, C.E. (2007) Biomaterials. 28 (2): 271-284

Hippocampal cells on PDMSMicrochannels w/immobilized NGF (0.11 ng/mm2)Scale bars=10 μm

Motivation

Hyaluronic Acid gels beneficial for wound healing applications

Problem: Hydrogels are amorphous and do not provide any significant physical contact guidance to infiltrating cells beyond their inherent porosity

Goal

Develop natural polymer hydrogels that have 3D internal architecture

Extend internally patterned films into 3D hydrogel constructs

Methods

32% Methacrylated Hyaluronic Acid50 mg/ml GMHA0.1-1% Photoinitiator

Photocrosslinkable Hydrogels

High Swelling HA Hydrogels

1 min 20 min ModulateSwellingDegradationMechanical Properties

AdvantagesBiocompatibleNon-cell adhesiveControl local chemical

propertiesOptically transparent

2 min 5 min 10 min

UV Exposure

Modulate Enzymatic Degradation

UV Exposure & Photoinitiator Concentration Effect on Swelling

Storage/Loss Modului over Frequency Range

2D Porous Structure

• connectivity among the pores of the scaffold• protein diffusion was restricted to the pores • tightly crosslinked, low-permeability hydrogel

Scale bar: 10 lm.

Zawko, S.A. , et al. (2010. “Crystal templating dendritic pore networks and fibrillar microstructure into hydrogels.” Acta Biomaterialia 6(7): 2415-2421

TRITC- labeled Green fluorescent albumin–FITC

Conclusions

Degradation rate, swelling dependent on UV exposure & PI concentration

Storage moduli consistent over frequency range

Tunability of mechanical properties makes system for variety of applications Drug delivery Vascularization

Future Work

Peripheral Nerve Regeneration Determine swollen pore size of 3D

hydrogels with confocal microscopy Render porous network cell-adhesive

and evaluate cell mobility within hydrogel.

Other applications Incorporate anti-inflammatory agents

into hydrogel matrix to evaluate ability to provide sustained drug release over time

Acknowledgements

Dr. Christine E. Schmidt Labmates

Leandro Forciniti, Sarah Mayes, John Hardy

Undergraduate Researchers Shan Modi, Paul Chung

Questions?