Stanford Cornea Project
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Laura Hartman, Dale Waters, Rachel ParkeHouben,
Curtis W. Frank
Stayce Beck, Luo Luo Zheng, Yuhua Hu
Jennifer Cochran
Resmi Charalel, Phil Huie, Vijay Vanchinathan
Roopa Dalal, Michael Carrasco, Jaan Noolandi
Christopher N. Ta
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Who needs an artificial cornea?
trachoma
trachoma
corneal ulcer
corneal ulcer
• In the United States, over 33,000 corneal
transplants are performed each year
• Worldwide, 10 million people are blind due
to corneal disease. Most of these people do
not have access to corneal transplants and
remain blind due to a lack of donor tissue
supply and distribution.
Current available keratoprosthesis
Osteo-odonto keratoprosthesis
Boston keratoprosthesis (PMMA)
≈1,200 devices implanted to date
(still requires donor corneas)
AlphaCor device (PHEMA)
•224 devices implanted with
surprisingly high success rates.
≈ 300 devices implanted to date; limited use
•requires complex surgery and is
only performed by a select few
surgeons throughout the world
Falcinelli, G., et al. Arch Ophthalmol,
2005. 123(10): p. 1319-29.
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Properties of an Artificial Cornea
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Biocompatible
Optically clear centrally
Nutrient permeable
Mechanically strong
Surface epithelialization
Peripheral tissue integration
CAD model acknowledgement: L. Kourtis, Stanford Dept. of Mechanical Engineering
The Stanford Approach
1.
high diffusion + stable, optically clear
hydrogel
 “invisible” material
2.
protein modification
(Collagen and EGF)
 Epithelium grows back
Epithelium
Stroma
hydrogel
hydrogel
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Material
Single Network
Double Network
• no chemical linkage
• two interpenetrating networks (IPNs)
• highly improved mechanical properties
Single Network
Double Network
polymerization
of 2nd network
1st network swollen in
monomeric building blocks of
2nd network
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J.P. Gong, et al., Advanced Materials 2003
Mechanical Stability
1st network: Poly(ethylene glycol) (PEG)
2nd network: Poly(acrylic acid) (PAA)
water content: ~90%
IPN
88
77
tunable material
IPN
Maximum Tensile Stress (MPa)
66
• mechanical stability
(contact lens vs. inlay)
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PEG 3.4K PAA
DN
(PEG 3.4K-PAA)
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PEG 8.0K PAA
DN
(PEG 8.0K-PAA)
PEG 14K PAA
IPN
PEG (14kDa)
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PAA
22
PEG (8kDa)
33
PAA
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PEG (4.6kDa)
55
PAA
Maximum Tensile Stress [MPa]
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• pore size: diffusion
(nutrient vs. drug delivery)
• longterm stability
(implant vs. tissue scaffold)
DN
(PEG 14K-PAA)
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Diffusion
• A high rate of small molecule diffusion
through the hydrogel is required to
maintain a healthy epithelium
glucose
urea
lactic acid
ascorbic acid
Epithelium
Hydrogel (~100 μm)
Flap edge
Stroma
amino acids
sodium bicarbonate
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Protein Tethering: Cell Re-Growth
• no de-swelling of the gel
• washing in buffer possible
• no denaturation of proteins
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Protein Tethering: Qualitative
BINDING OF COLLAGEN
• Using fluorescently-labeled collagen, we have shown that this tethering
method supports a stable binding of ECM protein.
Control (adsorption)
PEG Diacrylamide Hydrogel
NHS/EDC (covalent linkage)
PEG Diacrylamide Hydrogel
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Protein Tethering: Cell Re-Growth
Corneal Fibroblast Cells Attach to ECM-Tethered Hydrogels
A) control
B
D
C
D
E
Phalloidin (red) and Nuclear (DAPI(blue)) staining of primary rabbit corneal
fibroblast cells grown on PEGacrylate/PAA Hydrogel tethered with A)Control, B) Collagen,
C)Fibronectin, D)Laminin and E) 1:1 mixture of collagen and Fibronectin.
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In vivo experiments
rabbit # 2 - post-op 50 days
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Future Work
MATERIAL
• Determine diffusion coefficients for other proteins through human cornea
• Apply principles to development of artificial cornea
• Modify refractive index for inlay application (presbyopia)
DEVICE
Protein tethering
• Optimize the ECM content tethered to the hydrogel
• Use time-lapse microscopy to study cell migration on the hydrogel
• Addition of enhanced growth factor (EGF) to the protein layer
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Tissue Integration
Fine-tuning is still needed to reduce the pore diameter to 50 – 100 μm
Confocal fluorescence microscopy will be used to demonstrate that the channels are
interconnected
Tether proteins to the channel walls and test for fibroblast growth
IN VIVO EXPERIMENTS
• Implant hydrogel-onlays/inlays
• Implant artificial cornea
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Funding
• National Institutes of Health / National Eye Institute
– R01 EY016987
– NIH Grant 5T90 DK070103-03.
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Singapore Eye Research Institute (SERI)
BioX
Stanford Office of Technology Licensing
Stanford MedScholar Program
Fight for Sight
Visx
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