posted on 2019-12-11, 22:43authored bySpyridon Varlas, Robert Keogh, Yujie Xie, Sarah L. Horswell, Jeffrey C. Foster, Rachel K. O’Reilly
The dynamic interactions of membranes, particularly their
fusion
and fission, are critical for the transmission of chemical information
between cells. Fusion is primarily driven by membrane tension built
up through membrane deformation. For artificial polymersomes, fusion
is commonly induced via the external application of a force field.
Herein, fusion-promoted development of anisotropic tubular polymersomes
(tubesomes) was achieved in the absence of an external force by exploiting
the unique features of aqueous ring-opening metathesis polymerization-induced
self-assembly (ROMPISA). The out-of-equilibrium tubesome morphology
was found to arise spontaneously during polymerization, and the composition
of each tubesome sample (purity and length distribution) could be
manipulated simply by targeting different core-block degrees of polymerization
(DPs). The evolution of tubesomes was shown to occur via fusion of
“monomeric” spherical polymersomes, evidenced most notably
by a step-growth-like relationship between the fraction of tubular
to spherical nano-objects and the average number of fused particles
per tubesome (analogous to monomer conversion and DP, respectively).
Fusion was also confirmed by Förster resonance energy transfer
(FRET) studies to show membrane blending and confocal microscopy imaging
to show mixing of the polymersome lumens. We term this unique phenomenon
polymerization-induced polymersome fusion, which operates via the
buildup of membrane tension exerted by the growing polymer chains.
Given the growing body of evidence demonstrating the importance of
nanoparticle shape on biological activity, our methodology provides
a facile route to reproducibly obtain samples containing mixtures
of spherical and tubular polymersomes, or pure samples of tubesomes,
of programmed length. Moreover, the capability to mix the interior
aqueous compartments of polymersomes during polymerization-induced
fusion also presents opportunities for its application in catalysis,
small molecule trafficking, and drug delivery.