richelle c. thomas, christine e. schmidt university of texas at austin
TRANSCRIPT
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?