The problem of intracellular delivery is not only about permeating the outer membrane but also about mixing with the inner ones; when the state matters and when it doesn't.

A cartoon of the cell highlighting the crowded membranous intracellular environment from the textbook by Prof. Sackmann

Following is an excerpt from an email exchange on the topic of why measuring the thermodynamic state is important in violent hydrodynamic forcing (through processes like micro jets ) of drugs into cells and bacteria.

When we use the word “state” we mean knowing the location of the system on scalar function S(x) (a hyperplane), which is at least known locally on (x), where x is a vector with a basis…

A scientific and impact summary of the paper titled “Thermodynamic state of the interface during acoustic cavitation in lipid suspension” Phys. Rev. Materials 3, 055602 — Published 9 May 2019

The main significance of this paper

This paper shows that it is much easier to rupture (cavitate) water if it contains lipids that are about to “melt”; water with lipids in a frozen or liquid state is harder to cavitate. Second; the paper shows that when a cavitation bubble expands the lipids at the surface of the bubble can condense and “freeze”.

Medical Applications of Acoustic Cavitation

Acoustic cavitation has a number of medical application. In diagnostic ultrasound imaging, when visualisation of blood flow is important then small microbubbles of gas are injected into the bloodstream (and yes it is safe to inject small microbubbles of gas) and the response of…

A cartoon describing the study

Summary for our article published in American Chemical Society Materials & Interfaces

Just like the rays of sunlight focussed through a lens can easily cause a burn, sound waves can also be concentrated deep inside the human body to produce a physical effect. The “destructive” power of acoustic waves has had remarkable success in treating many ailments that require micro-ablation or incisions, as I covered in a previous post. State of the art now allows precise control and delivery of acoustic energy into various internal organs of the human body where the energy can be focussed to form controlled…

In our latest publication, we show that the width of the emission spectrum of fluorescent dyes embedded in lipid membranes is related to (1) the heat capacity of the dye-membrane system and (2) the acoustic response of a lipid membrane. Thus it is shown that fluorescence emission wavelengths should be treated as a thermodynamic state variable of the system and not just the dye. The work is based on a top-down approach to thermodynamics, in particular, we drew inspiration from its application to the phenomenon of blackbody radiation, critical opalescence and specific heat of solids.

The state dependence of fluorescence…

A membrane pulse represented as a propagating perturbation in a thermodynamic manifold

The article summarises our approach to the physics of action potential and addresses some of the criticism and misconception related to its application to nerves, in particular, how it addresses the dissipation and temperature dependence of action potentials.

Recently, Scientific American and Spektrum magazines highlighted our alternative perspective on how signals in neurons propagate physically. Our approach has been presented as a mechanical one as opposed to an electrical one, which I believe creates a false dichotomy that needs to be addressed. For this blog entry, I didn’t want to list the limitations of the Hodgkin and Huxley based equations…

The following is a list of my key papers on electromechanical waves in pure lipid monolayers, essentially a negative control for Hodgkin and Huxley based description of Action Potentials (AP) (without channel, pumps and chemical gradient). (posted previously as tweets)1/18

The observed electromechanical waves propagate as sound and not via ions and behave exactly like action potentials near a nonlinearity in the state diagram of the monolayer, e.g. due to a phase transition. 2/18

Also, some key control experiments from my colleagues related to channel and synapse activity are included that show how all these phenomena are related by the…

Cartoon depicts the vision of a sound-wave propagating in a neuron as an action potential.

Sound waves in lipid films can annihilate each other upon collision, just like action potentials in neurons

Nerve impulses, also known as action potentials, are believed to propagate in a manner similar to the conduction of current in an electrical cable. However, for as long as the electrical theory has been around, scientists have also been measuring various other physical signals that are equally characteristic of a nerve impulse, such as changes in the mechanical and optical properties that propagate in sync with the electrical signal. Furthermore, several studies have reported reversible temperature changes that accompany a nerve impulse, which…

The black and white image of a developing fetus, also known as Sonogram, is a familiar sight for most of us and the imagery already has an iconic status in the story of humanity. From prenatal sonograms and real-time images of various other parts of human anatomy to advanced applications in monitoring blood flow and elastography, ultrasound (US) imaging or sonography is central to our medical diagnostic capabilities. But can the same technology be used for therapeutic purposes as well?

Ultrasound image sequence from a study of valves in a patient’s heart. Generated by Kieran Maher using OsiriX and ImageJ (

The diagnostic US has been around for clinical use since the 1950s. It uses high-frequency sound waves, inaudible to human…

with Prof. Mishra and Chaitanya after graduation May 2008

I have heard people say, “it hasn’t sunk in yet”. I think today for the first time I know what do they mean by that. I came to know about Prof. Mishra’s demise this morning. I went about my day, as usual, I guess it was still sinking in. Now its evening and I am just reading our email conversations over the years and I think it has sunk in. It hurts that I was planning on writing an email to him one of these days but never did. Don’t know what I was waiting for but it made me…

Einstein’s approach to statistical physics

Applying Einstein’s Scientific Philosophy to Biological Physics: A revolution waiting to happen

The recent discovery of gravitational waves has yet again put Albert Einstein back in the limelight, as his genius continues to shake our world even a century later. Einstein possessed a keen interest and a deep understanding of physics that spanned a wide range of phenomena. It would be interesting to know how Einstein would have approached developing underlying theories of physical processes that have biological significance. …

Shamit Shrivastava

Biophysics of sound in membranes and its applications. Post Doctoral Researcher, Engineering Sciences, University of Oxford, UK

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