Authors: M. Boyce, M. Buehler, R. Cohen, C. Ortiz, M. Rubner and K. Van Vliet (MIT)

An interdisciplinary, inter-IRG team of researchers at the MIT MRSEC have developed arrays of surface-attached nanostructured polymer tubes. These polymer tube forests are “mechanomutable”– that is, they change their mechanical behavior reversibly in response to an external stimulus. By decreasing the pH, these polymer tubes exhibit dramatic changes in structure, geometry, and properties from a condensed to a swollen, nanoporous state, resulting in orders of magnitude changes in mechanical properties, such as stiffness. The team of researchers is exploring the use of mechanomutable materials for 2D dynamic substrates for cell biology studies, 3D locally tunable tissue engineered scaffolds, control of colloid transport in microfluidic devices and on 2D substrates, control of membrane morphology and wrinkling, and for tunable adhesives, lubricants, and penetration-resistant coatings.

IRG-II Highlight: Mechanomutable polymer tube forests IRG-II Highlight: Mechanomutable polymer tube forests

10-1

100

101

10-2

10-1

100

101

102

Indentation Rate (m/s)

Mo

du

lus

(MP

a) pH 5.5

pH 2.0

pH 2.0

pH 5.5

Tube Modulus

Effective Modulus (Thin Film)

Effective Modulus (Tube Forests)0

-0.8

Local Displacement (m)0 0.2 0.4 0.6 0.8

0

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1

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2

Indentation Depth (m)

Fo

rce

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)

pH 2.0

rate

rate

n ≥ 10(a)

loading

pH 5.5(b) (c)

K.-K. Chia, M.F. Rubner, R.E. Cohen. pH-Responsive reversibly swellable nanotube arrays. Langmuir 25, 14044 (2009).

The research was suported by the NSF MRSEC Program (award DMR-08-19762).

Figure: (a,b) Higher-magnification plan-view CLSM images of (PAH7.5/PAA3.5)20 nanotube arrays immersed in water at pH 5.5 and 1.8, respectively. Both images were scanned at half tube length. (c) Schematic of developed coarse-grain representation, allowing simulation of multilayer systems (or similar). (d) FEA simulations of loading indentation showing deformed contact area and stress distribution.

a b

c d