36 research outputs found
Dissipation and detonation of shock waves in lipid monolayers
Lipid interfaces not only compartmentalize but also connect different
reaction centers within a cell architecture. These interfaces have well defined
specific heats and compressibilities, hence energy can propagate along them
analogous to sound waves. Lipid monolayers prepared at the air-water interface
of a Langmuir trough present an excellent model system to study such
propagations. Here we propose that recent observations of two-dimensional shock
waves observed in lipid monolayers also provide the evidence for the detonation
of shock waves at such interfaces, i.e. chemical energy stored in the interface
can be absorbed by a propagating shock front reinforcing it in the process. To
this end, we apply the classical theory in shock waves and detonation in the
context of a lipid interface and its thermodynamic state. Based on these
insights it is claimed that the observed self-sustaining waves in lipid
monolayers represent a detonation like phenomena that utilizes the latent heat
of phase transition of the lipids. However, the general nature of these
equations allows that other possible sources of chemical energy can contribute
to the propagating shock wave in a similar manner. Consequently, the
understanding is applied to the nerve pulse propagation that is believed to
represent a similar phenomenon, to obtain a qualitative understanding of the
pressure and temperature dependence of amplitude and threshold for action
potentials. While we mainly discuss the case of a stable detonation, the
problem of initiation of detonation at interfaces and corresponding heat
exchange is briefly discussed, which also suggests a role for thunder like
phenomena in pulse initiation.Comment: 6 Figure
Non-linear solitary sound waves in lipid membranes and their possible role in biological signaling.
Thesis (Ph. D.)--Boston UniversityBiological macromolecules self-assemble under entropic forces to form a
dynamic 20 interfacial medium where the elastic properties arise from the curvature of
the entropic potential of the interface. Elastic interfaces should be capable of propagating localized perturbations analogous to sound waves. However, (1) the existence and (2) the possible role of such waves in affecting biological functions remain unexplored. Both these aspects of "sound' as a signaling mechanism in biology are explored
experimentally on mixed monolayers of lipids-fluorophores-proteins at the air/water
interface as a model biological interface.
This study shows - for the first time - that the nonlinear susceptibility near a
thermodynamic transition in a lipid monolayer results in nonlinear solitary sound waves
that are of 'all or none ' nature. The state dependence of the nonlinear propagation is
characterized by studying the velocity-amplitude relationship and results on distance
dependence, effect of geometry and collision of solitary waves are presented. Given that
the lipid bilayers and real biological membranes have such nonlinearities in their
susceptibility diagrams, similar solitary phenomenon should be expected in biological
membranes. In fact the observed characteristics of solitary sound waves such as, their all
or none nature, a biphasic pulse shape with a long tail and optp-mechano-electro-thermal
coupling etc. are strikingly similar to the phenomenon of nerve pulse propagation as
observed in single nerve fibers.
Finally given the strong correlation between the activity of membrane bound
enzymes and the susceptibility and the fact that the later varies within a single solitary
pulse, a new thermodynamic basis for biological signaling is proposed. The state of the
interface controls both the nature of sound propagation and its impact on incorporated
enzymes and proteins. The proof of concept is demonstrated for acetylcholine esterase
embedded in a lipid monolayer, where the enzyme is spatiotemporally "knocked out" by a
propagating sound wave
On measuring the acoustic state changes in lipid membranes using fluorescent probes
Ultrasound is increasingly being used to modulate the properties of
biological membranes for applications in drug delivery and neuromodulation.
While various studies have investigated the mechanical aspect of the
interaction such as acoustic absorption and membrane deformation, it is not
clear how these effects transduce into biological functions, for example,
changes in the permeability or the enzymatic activity of the membrane. A
critical aspect of the activity of an enzyme is the thermal fluctuations of its
solvation or hydration shell. Thermal fluctuations are also known to be
directly related to membrane permeability. Here solvation shell changes of
lipid membranes subject to an acoustic impulse were investigated using a
fluorescence probe, Laurdan. Laurdan was embedded in multi-lamellar lipid
vesicles in water, which were exposed to broadband pressure impulses of the
order of 1MPa peak amplitude and 10{\mu}s pulse duration. An instrument was
developed to monitor changes in the emission spectrum of the dye at two
wavelengths with sub-microsecond temporal resolution. The experiments show that
changes in the emission spectrum, and hence the fluctuations of the solvation
shell, are related to the changes in the thermodynamic state of the membrane
and correlated with the compression and rarefaction of the incident sound wave.
The results suggest that acoustic fields affect the state of a lipid membrane
and therefore can potentially modulate the kinetics of channels and proteins
embedded in the membrane
Optimization of a Hydrodynamic Computational Reservoir through Evolution
As demand for computational resources reaches unprecedented levels, research
is expanding into the use of complex material substrates for computing. In this
study, we interface with a model of a hydrodynamic system, under development by
a startup, as a computational reservoir and optimize its properties using an
evolution in materio approach. Input data are encoded as waves applied to our
shallow water reservoir, and the readout wave height is obtained at a fixed
detection point. We optimized the readout times and how inputs are mapped to
the wave amplitude or frequency using an evolutionary search algorithm, with
the objective of maximizing the system's ability to linearly separate
observations in the training data by maximizing the readout matrix determinant.
Applying evolutionary methods to this reservoir system substantially improved
separability on an XNOR task, in comparison to implementations with
hand-selected parameters. We also applied our approach to a regression task and
show that our approach improves out-of-sample accuracy. Results from this study
will inform how we interface with the physical reservoir in future work, and we
will use these methods to continue to optimize other aspects of the physical
implementation of this system as a computational reservoir.Comment: Accepted at the 2023 Genetic and Evolutionary Computation Conference
(GECCO 2023). 9 pages, 8 figure
The thermodynamic theory of action potential propagation: A sound basis for unification of the physics of nerve impulses
The thermodynamic theory of action potential propagation challenges the conventional understanding of the nerve signal as an exclusively electrical phenomenon. Often misunderstood as to its basic tenets and predictions, the thermodynamic theory is virtually ignored in mainstream neuroscience. Addressing a broad audience of neuroscientists, we here attempt to stimulate interest in the theory. We do this by providing a concise overview of its background, discussion of its intimate connection to Albert Einstein's treatment of the thermodynamics of interfaces and outlining its potential contribution to the building of a physical brain theory firmly grounded in first principles and the biophysical reality of individual nerve cells. As such, the paper does not attempt to advocate the superiority of the thermodynamic theory over any other approach to model the nerve impulse, but is meant as an open invitation to the neuroscience community to experimentally test the assumptions and predictions of the theory on their validity