Expandable Temperature-Responsive
Polymeric Nanotubes
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Abstract
Materials with the ability of dimensional changes on
demand exhibit
many potential applications ranging from adaptive composites that
mimic biological functions under extreme conditions to microfluidics
or neural implants to stimulate components of the nervous systems.
These studies show the synthesis of temperature-induced reversibly
expandable nanotubes that were prepared by polymerization of <i>N</i>-isopropylacrylamide (NIPAAM) in the presence of biologically
active 1,2-bis(tricosa-10,12-diynoyl)-<i>sn</i>-glycero-3-phosphocholine
(DC<sub>8,9</sub>PC) diacetylenic phospholipids (PL). As a result,
thermally responsive poly-NIPAM-phospholipid nanotubes (PNNTs) were
prepared. Polymerization reactions occur within hydrophilic regions
of PL bilayers, whereas PL hydrophobic zones facilitate transport
and supply of the monomer for polymerization. The unique feature of
PNNTs is that, above 37 °C, the outer diameter (OD) as well as
the wall thickness (WT) shrink by 20 and 55%, respectively, whereas
the inner diameter (ID) increases by ∼16%. This behavior is
attributed to the PNIPAM backbone buckling induced by local rearrangements
within PL bilayered morphologies. The presence of acetylenic moieties
along the PL bilayers in PNNTs provides an opportunity for irreversible
“locking” of designable dimensions, which is facilitated
by the formation of cross-linked PNNTs (CL-PNNTs)