Characterization of a setup to test the impact of high-amplitude pressure waves on living cells

In vitro effect of Er: YAG laser irradiation in caries cavity preparation on biobehaviors of adjacent human dental pulp cells in the pulp chamber

The erbium-doped yttrium aluminum garnet (Er: YAG) laser has been successfully applied in caries removal; however, little is known about proper parameters of Er: YAG laser on different conditions of caries removal, especially the influence of Er: YAG irradiation on human dental pulp cells (hDPCs). Here, we tested the effects of Er: YAG laser at different output energy levels (100, 200, 300, 400, and 500 mJ) on biobehaviors of hDPCs. To simulate clinical deep caries conditions, hDPCs were cultured on the pulpal side of 500-μm-thick dentin disks in an in vitro pulp chamber model. Temperature change, structural change, and ablation depth of dentin disk were also recorded. The findings suggested that the biological behaviors of hDPCs are strongly correlated with the energy output of the Er: YAG laser. Er: YAG laser irradiation at 100 mJ may be proper and safe for deep caries removal since it would not cause any adverse effect on hDPCs biobehaviors.

Molecular dynamics simulation of cancer cell membrane perforated by shockwave induced bubble collapse

It has been widely accepted that cancer cells are softer than their normal counterparts. This motivates us to propose, as a proof-of-concept, a method for the efficient delivery of therapeutic agents into cancer cells, while normal cells are less affected. The basic idea of this method is to use a water jet generated by the collapse of the bubble under shockwaves to perforate pores in the cell membrane. Given a combination of shockwave and bubble parameters, the cancer membrane is more susceptible to bending, stretching, and perforating than the normal membrane because the bending modulus of the cancer cell membrane is smaller than that of the normal cell membrane. Therefore, the therapeutic agent delivery into cancer cells is easier than in normal cells. Adopting two well-studied models of the normal and cancer membranes, we perform shockwave induced bubble collapse molecular dynamics simulations to investigate the difference in the response of two membranes over a range of shockwave impulse 15-30 mPa s and bubble diameter 4-10 nm. The simulation shows that the presence of bubbles is essential for generating a water jet, which is required for perforation; otherwise, pores are not formed. Given a set of shockwave impulse and bubble parameters, the pore area in the cancer membrane is always larger than that in the normal membrane. However, a too strong shockwave and/or too large bubble results in too fast disruption of membranes, and pore areas are similar between two membrane types. The pore closure time in the cancer membrane is slower than that in the normal membrane. The implications of our results for applications in real cells are discussed in some details. Our simulation may be useful for encouraging future experimental work on novel approaches for cancer treatment.

Evolution of Shock-Induced Pressure in Laser Bioprinting

Laser bioprinting with gel microdroplets that contain living cells is a promising method for use in microbiology, biotechnology, and medicine. Laser engineering of microbial systems (LEMS) technology by laser-induced forward transfer (LIFT) is highly effective in isolating difficult-to-cultivate and uncultured microorganisms, which are essential for modern bioscience. In LEMS the transfer of a microdroplet of a gel substrate containing living cell occurs due to the rapid heating under the tight focusing of a nanosecond infrared laser pulse onto thin metal film with the substrate layer. During laser transfer, living organisms are affected by temperature and pressure jumps, high dynamic loads, and several others. The study of these factors’ role is important both for improving laser printing technology itself and from a purely theoretical point of view in relation to understanding the mechanisms of LEMS action. This article presents the results of an experimental study of bubbles, gel jets, and shock waves arising in liquid media during nanosecond laser heating of a Ti film obtained using time-resolving shadow microscopy. Estimates of the pressure jumps experienced by microorganisms in the process of laser transfer are performed: in the operating range of laser energies for bioprinting LEMS technology, pressure jumps near the absorbing film of the donor plate is about 30 MPa. The efficiency of laser pulse energy conversion to mechanical post-effects is about 10%. The estimates obtained are of great importance for microbiology, biotechnology, and medicine, particularly for improving the technologies related to laser bioprinting and the laser engineering of microbial systems.

Shock wave impact on the viability of MDA-MB-231 cells

Shock waves are gaining interests in biological and medical applications. In this work, we investigated the mechanical characteristics of shock waves that affect cell viability. In vitro testing was conducted using the metastatic breast epithelial cell line MDA-MB-231. Shock waves were generated using a high-power pulse laser. Two different coating materials and different laser energy levels were used to vary the peak pressure, decay time, and the strength of subsequent peaks of the shock waves. Within the testing capability of the current study, it is shown that shock waves with a higher impulse led to lower cell viability, a higher detached cell ratio, and a higher cell death ratio, while shock waves with the same peak pressure could lead to different levels of cell damage. The results also showed that the detached cells had a higher cell death ratio compared to the attached cells. Moreover, a critical shock impulse of 5 Pa·s was found to cause the cell death ratio of the detached cells to exceed 50%. This work has demonstrated that, within the testing range shown here, the impulse, rather than the peak pressure, is the governing shock wave parameter for the damage of MDA-MB-231 breast cancer cells. The result suggests that a lower-pressure shock wave with a longer duration, or multiple sequential low amplitude shock waves can be applied over a duration shorter than the fundamental response period of the cells to achieve the same impact as shock waves with a high peak pressure but a short duration. The finding that cell viability is better correlated with shock impulse rather than peak pressure has potential significant implications on how shock waves should be tailored for cancer treatments, enhanced drug delivery, and diagnostic techniques to maximize efficacy while minimizing potential side effects.

Shock Wave-Induced Damage of a Protein by Void Collapse

In this study, we report on a series of molecular dynamics simulations that were used to examine the effects of shock waves on a membrane-bound ion channel. A planar shock wave was found to compress the ion channel upon impact, but the protein geometry resembles the crystal structure as soon as the solvent density begins to dissipate. When a void was placed in close proximity to the membrane, the shock wave proved to be more destructive to the protein due to formation of a nanojet that results from the asymmetric collapse of the void. The nanojet was able to cause significant structural changes to the protein even at low piston velocities that are not able to directly cause poration of the membrane.

Dose-dependent and cell type-specific cell death and proliferation following in vitro exposure to radial extracorporeal shock waves

Radial extracorporeal shock wave (rESW) therapy is widely used in musculoskeletal disorders and wound repair. However, the mechanisms of action are still largely unknown. The current study compared the effects of rESWs on two cell types. Human fetal foreskin fibroblasts (HFFF2) and human placental choriocarcinoma cell line JEG-3 were exposed to 0, 100, 200, 500 or 5000 rESWs generated with a Swiss DolorClast device (2.5 bar, 1 Hz). FACS analysis immediately after rESW exposure showed that initially, rESWs rather induced mechanical cell destruction than regulated or programmed cell death. Cell damage was nearly negated by reducing cavitation. Furthermore, cell viability decreased progressively with higher numbers of rESWs. Exposure to rESWs had no impact on growth potential of JEG-3 cells, but dose-dependently increased growth potential of HFFF2 cells. Cultivation of cells that were initially exposed to sham-rESWs in conditioned media increased the growth potential of HFFF2 cells, nevertheless, an even stronger effect was achieved by direct exposure to rESWs. Additionally, cell cycle distribution analysis demonstrated a shift in proportion from G0/G1 to G2/M phase in HFFF2 cells, but not in JEG-3 cells. These data demonstrate that rESWs leads to initial and subsequent dose-dependent and cell type-specific effects in vitro.

On the dynamics of molecular self-assembly and the structural analysis of bilayer membranes using coarse-grained molecular dynamics simulations

We present a molecular dynamics simulation study of the self-assembly of coarse-grained lipid molecules from unbiased random initial configurations. Our lipid model is based on a well-tried CG polymer model with an additional potential that mimics the hydrophobic properties of lipid tails. We find that several stages of self-organization of lipid clusters are involved in the dynamics of bilayer formation and that the resulting equilibrium structures sensitively depend on the strength of hydrophobic interactions hc of the lipid tails and on temperature T. The obtained stable lipid membranes are quantitatively analyzed with respect to their local structure and their degree of order. At equilibrium, we obtain self-stabilizing bilayer membrane structures that exhibit a bending stiffness κB and compression modulus KC comparable to experimental measurements under physiological conditions. We present a phase diagram of our lipid model which covers a sol-gel transition, a liquid (or gel-like) phase including stable bilayer structures and vesicle formation, as well as a quasi-crystalline phase. We also determine the exact conditions for temperature T and degree of hydrophobicity hc for stable bilayer formation including closed vesicles.

Destruction of cancer cells by laser-induced shock waves: recent developments in experimental treatments and multiscale computer simulations

In this emerging area article we review recent progress in the mechanical destruction of cancer cells using laser-induced shock waves. The pure mechanical damaging and destruction of cancer cells associated with this technique possibly opens up a new route to tumor treatments and the corresponding therapies. At the same time progress in multiscale simulation techniques makes it possible to simulate mechanical properties of soft biological matter such as membranes, cytoskeletal networks and even whole cells and tissue. In this way an interdisciplinary approach to understanding key mechanisms in shock wave interactions with biological matter has become accessible. Mechanical properties of biological materials are also critical for many physiological processes and cover length scales ranging from the atomistic to the macroscopic scale. We argue that the latest developments and progress in experimentation enable the investigation of the shock wave interaction with cancer cells on multiple time- and length-scales. In this way the integrated use of experiment and simulation can address key challenges in this field. The exploration of the biological effects of laser-generated shock waves on a fundamental level constitutes an emerging multidisciplinary research area combining scientific methods from the areas of physics, biology, medicine and computer science.