Introduction - Towards Autonomous Soft Matter Systems - page 3

Investigations on biological systems and their organization are naturally being
inspired by physics based approaches and have followed two broad paths: (1) the
application of techniques andmethods developed for soft matter and non-equilibrium
science to biology [ 6 ] and (2) to construct suitable minimal, biomimetic model sys-
tems from biological and soft components to test if they are capable of imitating
biological function [ 13 ].
In the present work, we take the approach of constructing minimal biomimetic
systems and the main concerns are investigations on membranes and active emul-
sions, aspects of both soft matter and non-equilibrium phenomena. We demonstrate
that these minimal reconstitutions are already capable of a range of complex behav-
iour such as nonlinear electric responses, chemical communication and locomotion.
The topic is organized in two broad parts and the first part, comprising three chap-
ters is about membranes. Demonstrations of soft functional devices based on bilayer
membranes in microfluidic channels are described in Chap. 2 . The reconstitution of
Ca 2 + triggered membrane fusion in vitro and the electrostatic interactions of the
SNARE complex of proteins and lipids are discussed in Chap. 3 . An x-ray phase
contrast technique for the direct imaging of lipid membranes is then presented in
Chap. 4 .
The second part is comprised of Chaps. 5 - 7 , on non-equilibrium processes in
active emulsions. Chapter 5 is about chemical micro-oscillator droplets and their
coupling. An artificial microscopic swimmer and its hydrodynamic flow fields are
described in Chap. 6 . This is followed by Chap. 8 discussing the various interactions
of swimmers that lead to collective dynamics and bound states.
1.1 Membranes
We explore lipid bilayers in the first part. Lipid bilayers are nanoscopic structures that
play a very important role in the hierarchical assembly of living systems. Apart from
compartmentalising cellular matter, cell membranes are the sites of intense activ-
ity concerning the communication between intra- and extra-cellular environments.
Transport across the membrane is regulated in multiple ways and can be either pas-
sive, i.e, occurring without the input of cellular energy, or active, requiring the cell to
expend energy in transportation. The process of photosynthesis exemplifies both pas-
sive and active transport in cells, (upper panel of Fig. 1.2 ) in which single molecules
passively transfer photo generated electrons across lipid bilayers while hydrogen ion
gradients are generated by ion pumps that operate by the consumption of adenosine
triphosphate (ATP) [ 14 ].
These processes are reminiscent of micro and nanotechnological elements, partic-
ular electronic devices that have motored the advancement of science and technology
in the past few decades. While nature has evolved these systems to be self-assembled
and very robust, serious limitations to the present top-down approach of man-made
devices are rapidly becoming obvious as downscaling continues [ 15 ]. This has led to
some intriguing biomimetic approaches (Fig. 1.3 ) to building self assembled systems