Mimicking Glues From Shellfishto Develop Underwater, Renewable,and Pressure Sensitive Adhesives
Jon WilkerPurdue University
The Heroes of Our Story
• Reduce turbulence
• Deter predators
• Reproductive efficiency
Marine Biological Adhesives
• sea stars • cucumbers • soft coral
• giant clams • sea squirts • kelp
Protein Cross-Linking in Marine Bioadhesives
-Work of Kei Kamino, David Kaplan, Dan Rittschof, Herb Waite, our lab
Our Lab: Marine Biological Materials
Characterization Synthetic mimics Applications
H3C NH CH NH CH NH CH NH CH NH2
O O O O OCH2 CH2HCH2
CH2
OHOH
CH2
NH
NH2
ONH2
H2N+
+
• live animals
• whole protein
• model peptides
HN
HO OH
NH
NH O O
O OHDOPA
OHOH
HO
HO OHHO
CH CH2 CH CH2
OHxyOH
• antifouling surfaces
• biomedical adhesives• biomimetic polymers
Polymer Mimics of Mussel Adhesive
• Wilker Lab
• Macromol., 2007, 40, p. 3960
• Deming Lab
• Macromol., 1998, 31, p. 4739
• Messersmith Lab
• Biomacromol., 2002, 3, p. 397
• Stewart Lab
• ACS Appl. Mat. & Interfaces 2011, 3, p. 941
CH CH2 CH CH2
OHxyOH
CH CNHO
HOOH
CH CNHO
NH3+
x y
CH C
OH
NH
OH
O
RHN CH2CH2O CH2CH2 NH CH NHR
OHOH
C
O
x
CCH2O
CH3
HOOH
HN
CCH2O
CH3
PO3-
O
x
y
• Other Chung- Polyacrylatesbulk Kuroda- Polyacrylatesadhesives: Liu- Polypeptides
Patton- Thiol-enesWashburn- Polyacrylates
• Coatings: Jiang- PolyacrylatesLee- PolycaprolactonesLee- PolydopamineZurcher- Polypeptides
Reductionist Approach to New Materials
HN
HO OH
NH
NH O O
O OHDOPA
• Complex protein
• DOPA cross-linkable sidechains
• Simple polymer backbone
• Catechol groups
OHOH
HO
HO OHHO
Polystyrenes
HN
HOOH
O
DOPA simplified:
polystyrene:
target random copolymers:
CH CH2
x
CH CH2 CH CH2
OHxyOH
CH CH2
OHyOH
-similar structure-easy synthesis-no adhesion
Synthesis
CH CH2 CH CH2
OCH3xyOCH3
OCH3OCH3
+x y
1. BBr3, CH2Cl2
1. n-BuLi, toluene
CH CH2 CH CH2
OHxyOH
2. HCl, H2O
2. MeOH
• 2 step synthesis• Can make ~2-5 grams
Adhesive Testing
0
100
200
300
400
500
600
700
0 0.5 1 1.5
forc
e (N
)extension (mm)
• polymer composition (x and y)
• polymer molecular weight
• cross-linker choice
• cross-linker:polymer ratio• cure time
• cure temperature
• cure humidity
• concentration/viscosity
• solvent
• fillers• substrate
• surface preparation
0
1
2
3
4
5
6
7
8
0 10 20 30 40
adhe
sion
str
engt
h (M
Pa)
percent catechol monomer (%)
Polymer Composition and Adhesion
CH CH2 CH CH2
OHxyOH
polymer alone
(IO4)- cross-linked
Mn ≈ 32,000 - 57,000Mw ≈ 38,000 - 84,000
Gorilla Glue, urethane 3.3 ( 0.8) MPa
Elmer s white PVA glue: 3.8 ( 0.6) MPa
Super Glue, cyanoacrylate 5.0 ( 0.7) MPa
Epoxy glue, Loctite Quick Set 18 ( 2) MPa
Our biomimetic copolymers: 11.0 ( 0.5) MPa
Adhesive Strengths on Etched Aluminum
Underwater Adhesion Testing
Bond Configurations (on Polished Aluminum)
lap shear
1 day cure
butt tensile
3 day cure
• Joint geometry influences performance
• Bonding stronger than many commercial adhesives
Performance Versus Commercials & on Substrates
Gorilla Glue 0.7 0.1 0.4 0.2 0.5 0.1 0 3.0 0.6 0(urethane)
Mr. Sticky s 1.0 0.3 0.2 0.1 0.4 0.1 0 3.0 0.6 0.10 0.08(epoxy)
North Sea Resin 0.3 0.1 0 0.2 0.1 0 0 0(acrylic)
Marine Loctite 0.6 0.3 0 0.2 0.1 0 2.0 0.5 0(epoxy)
3M Marine 0.2 0.1 0.4 0.2 0.5 0.1 0 3.0 0.6 0(urethane)
biomimetic polymer 3.0 0.4 0.2 0.1 0.10 0.02 0.2 0.1 0.4 0.1 0.3 0.1stronger same weaker stronger weaker stronger
polishedaluminum
etchedaluminum
sandedsteel
redoak
PVC Teflon
• High performance versus commercial products
Adhesives from Renewable Resources
• Current high strength adhesives are all made from petroleum
• Toxic formaldehyde is in 4 of 9 billion kg of glues/year (e.g., wood)
• Permanent nature of glues prevents recycling of cars, furniture, electronics
• Combine polylactic acid and mussel adhesion
• The resulting materials may be sustainable, degradable, and biocompatible
• Entry into removable adhesives
O C
CH3
C
OH
x
O C C
O
OH
OH
H
y
Where We Were Last Year: Renewable Glues
• Tried many routes (open dilactides, make acid chlorides, etc.)
• Synthetic route to poly(catechol-lactic acid) developed
• Initial adhesion shown
• Polymers could be degraded in water
• Synthesis improved since last year (better Mw control)
HO C CO
OH
OO
O C CO
OO
H H
~3-4
heat
O CCH3
COH
~1100
O CCH3
COH
~120
O C CO
OHOH
H
~20
1. Sn(oct)2, H+
2. H+
Comparisons to Commercials
• Dry bonding looks good versus commercial products
dry adhesion (MPa)
Elmer’s Glue (acetate) 3 1
Gorilla Glue (urethane) 2.8 0.7
starch glue 2.4 0.4
hide glue 0.8 0.1
poly(lactic acid) 0.21 0.6
poly(catechol-lactic acid) + (IO4)- 2.6 0.4
Debonding
water
substrate
adhesive
substrate
air• Polyesters can hydrolyze
• Bond dry
• Submerge under water
• Monitor adhesion kinetics
• Adhesives can be debonded
• Debonding times can be tuned with cross-linking
PLA-catechol
PLA-catechol + (IO4)-
PLA(no catechol)
0% PEG 72% PEG
Flexibility of Adhesive Polymers
• PEG reduces polymer modulus
• Implications for bonding soft versus hard tissues
Adhesion and Stress Buildup
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2
forc
e (N
)
extension (mm)
high glue strength,low ductility,
high adhesion force,low adhesion energy
low glue strength,high ductility,
low adhesion force,high adhesion energy
• Which scenario is preferred depends upon the situation
• Data here are first systematic investigation of adhesion versus ductility
• Ductility versus material strength remains an issue
brittle:stress concentrates at edges
ductile:stress distributes throughout bond
pullapart
pullapart
Adhesion Strengths and Energies
• Identified the strongest adhesive: 45% PEG
• Found where material strength and ductility are in balance
force versus extensionduring testing
adhesion versus PEG%after testing
• Examine adhesion strength (peak maximum) versus adhesion energy (area under curve) on aluminum
Conclusions
• Developing new biomimetic, cross-linking polymers
• Strong adhesion achieved, comparable to super glues
• High strength underwater adhesion found
• Making adhesives from renewable resources and degradable
• Polymer flexibility influences performance
• Flexibility provides entry to pressure sensitive adhesives
Acknowledgments
Jessie Román
Natalie Hamada
Erik AlbertsCori Jenkins
Michael North
Chelsey Del GrossoJenna DeSousa
Gwendolyn Snyder
Andrés Tibabuzo
Heather Siebert
Taylor Jones
Heather Meredith
Aarushi Ghandi
National Science Foundation
Office of Naval ResearchDan Barlow & Kathy Wahl, NRLJanie Brennan & Julie Liu, Purdue UTara Essock-Burns & Dan Rittshof, DukeNeeraj Gohad & Andy Mount, ClemsonChia Ping Huang & Debby Sherman,
PurdueKaren Hudson, VIMS
Paul Kenny, Baruch Marine LabChuan Leng, Yuwei Liu, Zhan Chen,
U of MichiganEmily Ralston & Geoff Swain, FITErik Soderblom & Arthur Moseley, DukeSergey Suslov, Purdue