Programmable/Water
Actuatable Shape Memory Polymer
W. M. Huang, B. Yang, and C. Li
CMMS, School of MPE
Nanyang Technological
University, Singapore
Contact Dr WM Huang:
Telephone: (65) 67904859; Fax: (65) 67911859; E-mail: Mwmhuang@ntu.edu.sg.
Background
In
recent years, shape memory polymers attract great interest for their enormous
potential applications, in particular, in medical devices [1,2]. The most
recent invention of biodegradable shape memory polymers opens a window for some
more advanced ones [3]. The shape memory phenomenon in some polymers is a
result of two structural features, one determining the permanent shape and the
other having a thermal transition within a certain temperature range [4,5].
However,
it is difficult to fabricate functionally gradient shape memory polymers, which
have different properties, e.g. variable transformation temperature, from one
segment to another. The main advantage of functionally gradient shape memory
polymer, for instance with variable transformation temperature, is that the
recovery of the polymer can be in a programmable manner instead of
simultaneously everywhere. In addition, as shape memory polymers are
non-conductive in nature, their actuation has to be triggered by external heat.
Although conductive shape memory polymers can be produced by blending with
conductive particles (one existing patent), the properties of shape memory
polymers (i.e., bio-compatibility) may be changed.
It
is a significant advantage if shape memory polymers are functionally gradient
(i.e. with variable transformation temperature) and can be actuated by some
other convenient means.
Novelty
of the invention
We
propose a novel way to fabricate functionally gradient shape memory polymers,
which can be actuated by water. This technique provides an approach for
recovery of shape memory polymers inside, e.g., human body, without any heating
system and in a programmable manner following a prescribed sequence.
Advantages
and improvements over existing methods, devices or materials
The
proposed approach is convenient in fabrication and application. To the best of our knowledge, this has not
yet been mentioned anywhere else. It is based on our recent findings.
Technical
description of the invention
The
fundamental reason is the effect of moisture on the transformation temperature
of shape memory polymers.
Water actuated SMP
Recovery of SMP in a programmable manner
Water actuated functionally gradient SMP
Commercial
applications
The
application of this invention should be enormous, in particular in medical
devices as shape memory polymers are bio-compatible, very cheap and easy in
fabrication as compared with others, e.g. shape memory alloys.
Retractable
stent and self-tightened suture are potential ones at present.
References
[1] Wache, H.M., Tartakowska, D.J., Hentrich,
A., Wagner, M.H., J. Mater. Sci: Mater. Medicine., 12, 2003, 109-112
[2] Metcalfe, A., Desfaits, A.-C., Salazkin,
I., Yahia, L., Sokolowski, W.M., Raymond, J., Biomaterials, 24, 2003, 491-497
[3]
Lendlein, A. Langer, R., Science, 296, 2002, 1673-1676
[4]
Lee, B.S., Chun, B.C., Chung, Y.-C. Sul, K.I, Cho, J.W., Macromolecules, 34,
2001, 6431-6437
[5]
Lendlein, A., Schmidt, A. M., Langer, R., PNAS, 98(3), 2001, 842-847