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