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Christopher McKay - Rensselaer Polytechnic Institute - BMES 2014 Oral Presentation
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Transcript of Christopher McKay - Rensselaer Polytechnic Institute - BMES 2014 Oral Presentation
Presenter NameTitle/Date
Calcium Responsive Composite Hydrogels for Acute Spinal Cord
InjuryMechanical/Chemical Properties and Astrocytic Response
Christopher McKay, Christopher Johnson, Rebecca Pomrenke, Joshua McLane, Nicholas Schaub, Elise DeSimone, Lee Ligon, and Ryan Gilbert
BMES 2014
www.rpi.edu
SPINAL CORD INJURY AFFECTS OVER 1 MILLION PEOPLE 1
1
1 NCISC 2012
Fewer than 1% Recover
16 300 80
SCI
Lifetime Costs$1-4 Million1
Yearly Costs$10 Billion1
www.rpi.edu
FEWER THAN 1% EXPERIENCE COMPLETE FUNCTIONAL RECOVERY 1
Force
http://imgarcade.com/1/human-spine-anatomy/
Vertebra
Sp
inal C
ord
2
(1 NSCISC, 2012)
Contusion
www.rpi.edu
PROGRESSION OF SPINAL CORD INJURY
ACUTE (0-48hr)
SUB-ACUTE (48hr – 2 weeks)
CHRONIC (> 2 weeks )
• Inflammatory Response1
• Reactive Astrocyte Formation1
• Calcium Related Neuronal Death2
Ca++
Ca++
Ca++
Ca++
3 Liverman 2005
• Macroscopic Tissue Damage 1
• Disrupted Blood Brain Barrier
1
1 Tator 1998
• Formation of the Glial Scar3
3
= Reactive Astrocyte
2 Happel, 1981
www.rpi.edu
DESIGN CRITERIA
Conform to the irregular geometry of the contusion.
An injectable hydrogel is best suited to fill the contusion
The modulus should be near that of native tissue (200-1000Pa).
Hydrogels can be tuned to match the soft SC tissue
Sequester extracellular calcium. Alginate sequesters calcium during hydrogel formation
Facilitate astrocyte integration May improve material integration
4
www.rpi.edu
ALGINATE
• Biocompatible, low cytotoxicity1
• Crosslinks with Ca2+ ions2,3
• Negatively charged4
CHITOSAN
• Amine Groups shown to enhance cellular adhesion5
GENIPIN
• Natural crosslinking agent• Well suited for spinal cord
environments6-9
1 Wee and Gombotz 1998 2 Braccini and Perez 2001 3 Li et al 2007 4 Rowley et al 1999 5 Zuidema et al 20116 Yamazaki et al 2004 7 Koo et al 2006 8 Moura et al 2011 9 Yamazaki et al 2005
AN INJECTABLE HYDROGEL CAN FILL THE IRREGULAR GEOMETRY OF THE CONTUSION
5
www.rpi.edu
HYDROGEL STRUCTURE
6
www.rpi.edu
• Composition varied to control crosslinking behavior
INCREASE THE AMINE GROUPS IN THE SCAFFOLD TO IMPROVE ASTROCYTE
ATTACHMENT
• Internal crosslinking structural influences hydrogel charge
7
Amine Groups
Alginate
?
Chitosan
?
Genipin?
Facilitate astrocyte integration
www.rpi.edu
High Chitosan
Low Genipin
Low Ca2+
(1.4 mM)
INCREASED CALCIUM FROM IN-SITU CONDITIONS INCREASES THE HYDROGEL
STABILITY
In-situ gelation model
• 500 μL hydrogel injected into chamber slide
• 200 μL neurobasal media (1.4 or 6 mM Ca2+)
• Hydrogel incubated at 37°C. Media replaced daily
• Rheological assessment at 0, 2 and 5 days
High Chitosan
Low Genipin
High Ca2+
(6 mM)
8
www.rpi.edu
ASTROCYTE ATTACHMENT BEHAVIOR IS NOT DIRECTLY CORRELATED WITH THE AVAILABLE
AMINE GROUPS
Calcein-AM | Hoechst 33342 | 10X Magnification | Scale bar = 300 μm
Attachment Assay
• 500 μL of hydrogel was injected into a chamber slide well
• 200 μL of astrocyte media was added
• Stained with Calcein-AM and Hoechst 33342 after two daysNo Chitosan / No
GenipinLow Chitosan / High Genipin High Chitosan / Low
Genipin
0.5
% A
lgin
ate
9
www.rpi.edu
A A
B
CC
A
• Astrocyte attachment depends on composition
• Altered protein adsorption?
10
Hig
h A
lgin
ate
(0
.5%
)
Increasing NH4+
ASTROCYTE ATTACHMENT BEHAVIOR IS NOT DIRECTLY CORRELATED WITH THE AVAILABLE
AMINE GROUPS
www.rpi.edu
DESIGN CRITERIA Conform to the irregular geometry of the contusion.
Designed an injectable hydrogel with tunable mechanical properties
The modulus is near that of native tissue (200-1000Pa).
Hydrogels are responsive to calcium and can be tuned to match the soft SC tissue
Sequester extracellular calcium.
Alginate sequesters calcium during hydrogel formation
Facilitate astrocyte integration
Astrocytes attached to hydrogel surface in a composition dependent manner
11
www.rpi.edu
ACKNOWLEDGEMENTSAdvisor• Dr. Ryan GilbertGilbert Lab Dr. Christopher Rivet• Dr. Jonathan Zuidema• Nicholas SchaubDr. Deanna Thompson Lab• Dr. Linxia Zhang• Dr. Abby Koppes• Dr. Courtney Dumont• Chris Bertucci• Kathryn Kearns
This work was funded by support from the National Institutes of Health, National Insititute of Neurological Disorders and Stroke R21NS62392 and NSF CAREER Award 1150125 to R. Gilbert.
• Dr. Lee Ligon Lab• Dr. Lee Ligon• Joshua McLane
• Undergraduate Research Students• Rebecca Pomrenke• Elise DeSimone• Nicholas Zaccor• Greg Desmond
• High School Researchers• Addison Haxo• Austin Kim
• David Frey – Scanning Electron Microscopy
12
THANK YOU!THANK YOU!
For more information, see corresponding publication:
McKay C. A., R. D. Pomrenke, J. S. McLane, N. J. Schaub, E. K. DeSimone, L. A. Ligon, and R. J. Gilbert. “An Injectable, Calcium Responsive Composite Hydrogel for the Treatment of Acute Spinal Cord Injury.” ACS Applied Materials & Interfaces 6, no. 3 (February 12, 2014): 1424–38. doi:10.1021/am4027423.