Deformation Of Biological Cells Research Articles

Hyper-elastic behavior of soft-tissue like microgels in two-phase converging microchannel flow

Deformation of biological cells, tissues, and similar soft materials is often considered linearly elastic; however, the assumption is only valid in a very limited stress range and often leads to significant errors in mechanical evaluation. We demonstrated the hyper-elastic behavior of ultra-soft poly(N-isopropyl acrylamide) (PNIPAm) microgels (USPNMs) in a converging channel flow, as a representation for biological tissues. The hyper-elasticity of USPNMs in response to a broad range of deformation was characterized at the centerline of the converging flow. We introduced a carrier fluid consisting of baby hydrogels (avg. diameter, 10 μm) and oil that carried the hydrophilic USPNM sample (avg. diameter, 100 μm) on the centerline of oil background fluid. By “baby hydrogel,” we mean small PNIPAm particles obtained during USPNM synthesis, using which, enabled settling-free flow, prevented wall contact, and enhanced carrier fluid viscosity for increased stresses at lower flowrates. Furthermore, drastic reduction of interfacial tension was observed in the converging area due to contact of baby gels with USPNM particles in the carrier fluid. The shear and elongational stresses were balanced with the elastic stress and interfacial Laplace pressure. As a result, we obtained a stress–strain curve from the microscopic images during flow. The non-linear stress–strain curve was characterized by conventional hyper-elastic models. The elastic modulus of the synthesized USPNM was 24 Pa, which is as low as animal brain tissue. This method holds great potential for implementing in similar hyper-elastic systems, enabling accurate mechanical evaluations in the field of soft materials, biology, and medicine.

Finite-difference and integral schemes for Maxwell viscous stress calculation in immersed boundary simulations of viscoelastic membranes.

The immersed boundary method (IBM) has been frequently utilized to simulate the motion and deformation of biological cells and capsules in various flow situations. Despite the convenience in dealing with flow-membrane interaction, direct implementation of membrane viscosity in IBM suffers severe numerical instability. It has been shown that adding an artificial elastic element in series to the viscous component in the membrane mechanics can efficiently improve the numerical stability in IBM membrane simulations. Recently Li and Zhang (Int J Numer Methods Biomed Eng 35:e3200, 2019) proposed a finite-difference method for calculating membrane viscous stress. In the present paper, two new schemes are developed based on the convolution integral expression of the Maxwell viscoelastic element. We then conduct several tests for the accuracy, stability, and efficiency performances of these three viscous stress schemes. By studying the behavior of a one-dimensional Maxwell element under sinusoidal deformation, we find that a good accuracy can be achieved by selecting an appropriate relaxation time. The twisting sphere tests confirm that, compared to the numerical errors induced by other components in capsule simulations, such as the finite element method for membrane discretization and IBM for flow-membrane interaction, the errors from the viscous stress calculation are negligible. Moreover, extensive simulations are conducted for the dynamic deformation of a spherical capsule in shear flow, using different numerical schemes and various combinations of the artificial spring constants and calculation frequency for the membrane viscous stress calculation. No difference is observed among the results from the three schemes; and these viscous stress schemes require very little extra computation time compared to other components in IBM simulations. The simulation results converge gradually with the increase in the artificial spring stiffness; however, a threshold value exists for the spring stiffness to maintain the numerical stability. The viscous stress calculation frequency has noapparent influence on the calculation results, but a large frequency number can cause the simulation to collapse. We therefore suggest to calculate the membrane viscous stress at each simulation time step, such that a better numerical stabilitycan be achieved. The three numerical schemes have nearly identical performances in all aspects, and they can all be utilized in future IBM simulations of viscoelastic membranes.

Influence of components of optical momentum and spin of evanescent waves on micro- and nanoobjects (Review)

Background: Mechanical properties of light are widely used in applied areas, such as optical trapping and manipulation, sorting, deformation of biological cells and molecules. In general, the evanescent field may exhibit three components of optical momentum and spin angular momentum (spin), which manifest themselves in the occurrence of corresponding components of optical force and torque. Such extraordinary properties of evanescent waves open up new possibilities for manipulating of micro- and nanoobjects, in comparing with classical optical tweezers and manipulators, which can be used for solving the applied problems, in particular, of biomedicine. Objectives: Aim of this work is to analyze and summarize recent studies regarding to the mechanical influence of evanescent field on micro- and nanoobjects, in particular, related to the influence of transverse components of optical momentum and spin. Materials and methods: Method of momenta allows one to distinguish in an evanescent field the action of optical forces and torques, associated with the components of optical momentum and angular momentum of different nature and action direction, depending on the polarization of the incident wave. Experimental methods of particle manipulation in the near field allow visualizing such an influence, which makes it possible for solving the applied problems. Results: Recent studies demonstrate the action on nano- and microobjects of such "extraordinary" optical momentum and spin components, as transverse spin momentum, transverse spin, transverse imaginary optical momentum component, and vertical spin. Using, in particular, the latter, to solve the applied problems of biomedicine is proposed, such as transporting of therapeutic agents to pathological areas or restoring vascular patency and tissue blood supply. Conclusions: Obtained results of theoretical and experimental investigation of the mechanical action of the optical momentum and spin components of evanescent field allow us to extend the approaches of optical manipulation of micro- and nanoobjects, with the possibility of applications, in particular, for the problems of biomedicine.

Reply to “Comment on ‘Deformation of biological cells in the acoustic field of an oscillating bubble’ ”

In the Comment by Choi [Phys. Rev. E 82, 013901 (2010)] on two our articles [Phys. Rev. E 72, 061907 (2005); Phys. Rev. E 79, 021910 (2009)], it is claimed that (a) there is more than one natural frequency associated with the quadruple mode and (b) the quadruple mode shows resonance more closely at the characteristic frequency ω(T)/2π than at ω(K)/2π. In this Reply we would like to provide evidence supporting the conclusions made in our original articles.

Comment on “Deformation of biological cells in the acoustic field of an oscillating bubble”

A recent paper by Zinin [Phys. Rev. E 79, 021910 (2009)] regarding the dynamics of biological cells in an acoustic field draws conclusions that we find open to debate. The present paper examines these conclusions and addresses some findings.

Mechanical Modeling of Biological Cells in Microinjection

Microinjection is an effective technique to introduce foreign materials into a biological cell. Although some semi-automatic and fully-automatic microinjection systems have been developed, a full understanding of the mechanical response of biological cells to injection operation remains deficient. In this paper, a new mechanical model based on membrane theory is proposed. This model establishes a relationship between the injection force and the deformation of biological cells with the quasi-static equilibrium equations, which are solved by the Runge-Kutta numerical method. Based on this model, other mechanical responses can also be inferred, such as the effect of the injector radius, the membrane stress and tension distribution, internal cell pressure, and the deformed cell shape. To verify the proposed model, experiments are performed on microinjection of zebrafish embryos at different developmental stages and medaka embryos at the blastula stage. It is demonstrated that the modeling results agree well with the experimental data, which shows that the proposed model can be used to estimate the mechanical properties of cell biomembranes. (In this paper, biomembrane refers to the membrane-like structures enveloping cells.)

Deformation of biological cells by electric fields: Theoretical prediction of the deformed shape

Abstract Biological cells, sickled human erythrocytes in particular, have been observed to undergo pronounced shape changes (deformation) when subjected to low frequency electrical fields. It has been suggested that the observed deformation is due to the mechanical stresses induced by the electrical field on the cell membrane. These mechanical stresses and their surface distribution can be calculated by means of the Maxwell Stress Tensor (MST). The cellular deformation due to the electric field is computed here by modelling a ‘typical’ cell as an ellipsoid with a thin shell. The cell membrane is assumed to be an incompressible material whose deformation is associated with both bending and shear energies. The principle of virtual work is then employed to compute the cellular shape and volume as a function of the external field strengths and the orientation of the cell with respect to the field.