Properties of Self Healing Films in a Stretched StateNiederecker, R.W., Islam, M., Lyon, L.A.

Lyon Group

Chapman University, Orange, CA

IntroductionMicrogel are colloidally stable hydrogel particles.

Micorgel have been in use a number of applications

including drug delivery and regenerative medicine.[1] In

this study we used microgel composed of N-

Isopropylacrylamide (NIPAm). The chemistry and the

properties of microgels can be very easily manipulated

to make it responsive to a wide variety of stimuli.

Additionally p-NIPAm has been used to construct thin

films that express self-healing properties when in the

presence of water.[2]

Figure 1. a) Image of koosh ball, very similar structure to that of

microgel b)10x10µm atomic force microscopy (AFM) image of 68%

NIPAm, 2% BIS, and 30% AAc microgel

Figure 2. Organic line bond structure of NIPAm, BIS, and Aac.

MethodsMicrogel Synthesis

Two NIPAm based microgels were synthesized

with the composition of 10% AAc, 2% BIS, 88%

NIPAm, and 30% Aac, 2% BIS, 68% NIPAm. Both

were synthesized by using aqueous free radical

precipitation polymerization in a N2 rich environment

at 70 C. The reaction was initiated using ammonium

persulfate (APS). The Sample was then purified and

lyophilized.

Figure 3. A. cycle of layering process for thin film construction. 1st

microgel was added to substrate, 2nd substrate was washed, 3rd

PDADMAC was added to substrate, 4th substrate was washed, then

repeat for desired layers. B. Animation of anionic and cationic layering

process.

Figure 4. 10x10µm and 20x20µm AFM images of 8-layer microgel before deformation, after deformation and after the healing steps.

Figure 5. AFM images across bend gradient on control and

experimental 10% AAc films.

ResultsThe 30% AAc and 10% AAc micogels were

synthesized and shown to have a radius of 600nm and

1,200nm by dynamic light scattering (DLS) and AFM.

Ten percent AAc 8-layer microgel thin films were

constructed and shown to have self-healing properties

in the presence of water. To test the hypothesis

Discussion and ConclusionWe were able to fabricate self-healable microgel

thin films. No observable difference was found when

the film was soaked in 30% AAc microgel solution in a

stretched state.

Future research could be performed by varying

the particle size and the chemistry of microgel.

AcknowledgementsI would like to acknowledge the Saddleback

faculty and Chapman Schmid mentors Dr. Islam

and Dean Lyon for the opportunity and funding to

make this research project possible.

References

[1] Clarke, K. C., Douglas, A. M., Brown, A. C., Barker, T. H., & Lyon, L.

A. (2013, October). Colloid-matrix assemblies in

regenerative medicine. Current Opinion in Colloid & Interface Science,

18(5), 393-405.[2] Jones, C. D., & Lyon, L. A. (2000, October). Synthesis and

Characterization of Multiresponsive Core- Shell Microgel.

Macromolecules, 33, 8301-8306.[3] South, Antoinette B. and Lyon, L. Andrew. (2010), Autonomic Self-

Healing of Hydrogel Thin Films. Angewandte Chemie, 122: 779–783.

a 10% AAc thin film was bent in the presence of

0.1mg/mL 30% AAc microgel solution while a control

was bent in the presence of nanopure water. Both

films were observed across a gradient of bend angles

with AFM microscopy and found to have no difference

in surface morphology as shown in figure 6.NIPAm BIS AAc

a. b.

HypothesisTo check whether the bending of multilayer

microgel film can create a charge gradient by

exposing the PDADMAC under layer by adsorbing

smaller microgel particles.

Film ConstructionFilms were constructed on Poly(dimethylsiloxane)

(PDMS) substrate. The PDMS substrate was

fabricated using 1:10 weight ratio of curing agent and

elastomeric base, mixed thoroughly and allowed to

cure at 50 C for 24 hours. The PDMS was cut,

cleaned, and functionalized in 1% ethanollic APTMS.

Films were then built by adding the microgel by

active deposition followed by soaking the films in 0.14

monoM PDADMAC solution and repeated similar to

that shown in figure 3.

Deformation and Healing of filmsFilms were bent 180 for 10 minutes to deform

the surface. The films were then dipped in water to

heal. Film formation, deformation, and healing were

monitored using AFM imaging techniques.

Experimental Film

Control Film