Hydrogels

Hydrogels
A
hydrogel is a gel in which water is the dispersed
media
 Hydrogel is typically a 3D network of hydrophilic
polymer molecules that attract water molecules
 Many applications, including
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Soft materials for tissue repair
Contact lenses
Slow or smart drug release implants
Diaper absorbent
Toys (slime)
food
http://www.gcsescience.com/hydrogel-hydrogen-bonding.gif
Hydration
http://www.gcsescience.com/hydrogel-salt.gif
Hydration - effect of salt
Hydrogel
Valves
Many hydrogels are dynamic
Classes of Hydrogels
 Thermal
– raise/lower Temperature to gel
– Gelatin
– Agar
 Ionic
– add ions to gel
– Agarose
 Cryogel
– freeze/thaw cycles create gel
– Polyvinyl alcohol
 Covalent
– chemical bonding of polymers
– Polyvinyl alcohol/glutaraldehyde
A Cooper Union Connection
 Glue
Factory
 1845 Patent
 Instant gelatin in
small packages
 Competing product:
gelatin sheets
Tissue Engineered Blood Vessels
State of art
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1.
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3.
Internal mammary a.
Sapphenous vien
Artificial materials
(>6mm ID; NVG)
What is needed?
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Suture and healing
Withstand 400 mmHg
No thrombosis
No hyperplasia
Similar compliance
Adjust diameter
Tissue Engineering Approaches
Layer-by layer assembly
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Cells (fibroblasts) make collagen layers
Roll into multilayer tube
Culture under flow and strain
Add endothelium
Implant
Resorbable polymer scaffold seeding
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Surface treat, seed with smooth muscle cells
Culture under flow and strain
Add endothelium
Implant
Human Cell TE Blood Vessel
L’Heureux et al.
Human Cell TE Blood Vessel
Niklason et al
What makes them work?
 History
prior to L’Heureux, Niklason
– Burst strengths of 10 to 20 mmHg
– Importance of stress/strain during culture
 New
approaches
– Used high-ascorbate growth medium
» Boosts collagen synthesis
– Included stress/strain
– Multistage culture process
– Burst pressures over 1000 mmHg
 Outcome
differences
– Elastin observed in L’Heureux’s method
Where are we now?
 Discovery
was 9 years ago
 In vivo testing is difficult
– Immunological rejection
– How to prove safety?
– Will artery degrade in vivo?
 Are
they arteries?
– Wall was thicker relative to lumen
– Less compliant
– Higher burst pressure
Tissue Engineering Manufacturing
 How
to make tissues more efficiently?
 How to improve control of tissue
constructs?
 Use
modern manufacturing methods
Electrospinning
http://www.centropede.com/UKSB2006/ePoster/images/background/ElectrospinFigure.jpg
Salt Leaching
Agrawal CM et al, eds, Synthetic Bioabsorbable Polymers for Implants, STP 1396, ASTM, 2000
Freeze Drying
Phase Separation
Bulk methods summary
 Relatively
fast batch processing
 Often low investment required
 Non optimal structures (due to
randomness):
– High porosity required for connectedness
– Permeability often low (especially foams)
– Strength is low (eg too low to replace bone)
CAD-based Porogen Method
Mondrinos M et al, Biomaterials 27 (2006) 4399–4408
Photopatterning Surface Chem.
Microcontact and Microfluidic Printing
Micromachining, Soft Lithography
Soft
Lithography
3D Printing
Spread powder layer
Print powder binder
Solid Freeform Fabrication
 Make
arbitrary shapes
 Limited resolution
 Incrementally build
http://www.msoe.edu/rpc/graphics/fdm_process.gif
– Layer by layer
– Fuse Layers to get 3D part
 Several
processes including
– Fused deposition
– Drop on demand
– Laser sintering
http://www-ferp.ucsd.edu/LIB/REPORT/
CONF/SOFE99/waganer/fig-2.gif
Current Research on Scaffolds
 Senior
Project/Research Project Opportunity
– Electrowetting-based tissue manufacturing technology
– Print:
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Hydrogel
Crosslinker
Cells
Growth Factors
Dead
Live
Biomedical Engineering
 Very
broad field
– Imaging, biosensors, clinical engineering, surgical
robotics, and more
– Strong research orientation
– Some agreement about 4 year degree contents
– Growth of acceptance and recruiting
 Biomedical
Applications of ME, ChE, EE, OR,
provide countless opportunities
 Biomedical engineer understands living systems
(and creates models) to design, optimize, and test
biomedical devices, diagnostic tools, implants, …
Biomedical Engineering at Cooper Union
 Centers
– Kanbar Center
– Center for Signal Processing, Communications
and Computer Engineering Research
(S*ProCom2)
 People:
Wootton, Ben-Avi, Duncan,
Fontaine, Sidebotham, Delagrammatikas,
Ahmad, Ahmed, Cumberbatch, Uglesich,
Savizky, Wei, and others
Biomedical Engineering at Cooper Union

Research and Project Activities include
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Orthopedic biomechanics
Tissue engineering manufacturing
Obstructive Sleep Apnea biomechanics and research
Operating room safety and thermal management
Neural processing of visual data
Novel MRI hardware/software development
Magnetic resonance elastography
Hemostasis and Thrombosis
Infrared imaging diagnostics
Knee simulator
Trans-bronchial needle aspiration tracking system
Magnetic muscle activation
Novel gait force sensors for free subject studies