Shock and Ultrasound waves through membranes

Every year, more than 8 million people around the globe die from cancer and more than 12 million are diagnosed for the first time, making cancer one of the leading causes of death in the western world. Therefore, efforts across the scientific community have been devoted to establishing new methods as well as improving the potency and efficacy of existing ones. The treatment of cancerous tissue with high-intensity focused ultrasound (HIFU) relies on destruction of cells through conversion of mechanical energy into heat (coagulative necrosis) and through mechanical damage induced by acoustic cavitation (formation and implosion of microscopic gas bubbles that generate liquid jets toward the cell membrane). The latter could be utilized not only to eliminate localized cancer tumor cells but also in conjunction with chemotherapy in order to temporally increase the chemotherapeutic agents absorption across the membrane . The basic composition and structure of a biological membrane is often described by the fluid mosaic model, where the membrane is considered as a two-dimensional fluid along the cell surface composed mainly of a phospholipid bilayer with embedded protein channels that allow the drug to actively penetrate into the cell. As the shock wave, following Ganzenmullers definition impacts the membrane, the lateral diffusion of the lipids and protein channels is enhanced and, hence, the probability of the drug to be trapped by these channels is consequently increased. Using molecular dynamics (MD) we have investigated the response of a DPPC membrane in crystalline phase subjected to ultrasonic shocks and examine whether there is a critical impulse value for which the membrane can no longer recover, in view of the ultrasound cancer treatment. In order to study long timescales of diffusion phenomena, a method that allows to expand the total simulation time has been developed.

The example above shows a biological membrane and how the interaction of a shock wave with the membrane changes the center of mass, consequently having effects on the diffusion through the membrane (click on pictures to watch the movies)

The example above shows a biological membrane and how the interaction of a shock wave with the membrane changes the center of mass, consequently having effects on the diffusion through the membrane. Findings from this research are pertinent to cancer chemotherapy using shock and ultrasound waves.

Effects of the ensemble on the deuterium order parameters, SCD. Validation of the present MD model (NVE and NPT curves) has been obtained against nuclear magnetic resonance (experiments 1 & 2) and other numerical results (Klauda, Andoh); see [1] for more details.

References

  • S. Espinosa, N. Asproulis, and D. Drikakis, Chemotherapy efficiency increase via shock wave interaction with biological membranes: a molecular dynamics study, Microfluidics and Nanofluidics, 1-10, 2014
  • D. Drikakis, J. Lechuga, S. Pal, Effects of Shock Waves on Biological Membranes: A Molecular Dynamics Study, Journal of Computational and Theoretical Nanoscience, Vol.6, 1-6, 2009
  • J. Lechuga, D. Drikakis, S. Pal, Molecular dynamics study of the interaction of a shock wave with a biological membrane, International Journal for Numerical Methods in Fluids, 57, 677-692, 2008.