RNA-based therapies have shown promise in a wide range of applications, from cancer therapy, treatment of inherited diseases to vaccination. Encapsulation of RNA into ionizable lipid (IL) containing lipid nanoparticles (LNPs) has enabled its safe and targeted delivery. We present here the simulations of the self-assembly process of pH-sensitive RNA-carrying LNPs and their internal morphology. At low pH, the simulations confirm a lipid core encapsulating RNA in the hexagonal phase. Our all-atom and coarse-grained simulations show that an RNA molecule inside an LNP is protected from interactions with ions by being enveloped in the charged ILs. At neutral pH, representing the environment after LNP administration into human tissues, LNPs expelled most of the encapsulated RNA and water and formed separate bulk IL-rich and ordered the helper-lipid-rich phase. Helper lipids arranged themselves to be in contact with RNA or water. The presented models provide atomistic understanding of the LNP structure and open a way to investigate them in silico, varying the LNP composition or interacting with other biostructures aiming at increasing the efficiency of RNA-based medicine.

The computational procedure for investigation vibration stability of a flexible rotor consisting of an asymmetric shaft, one disc, and supported by ball bearings is developed in this work. Lagrange equations of the second kind were used for derivation of the motion equation. The vibration response stability of the Jeffcott-like rotor was studied by means of eigenvalues of a transition matrix. Three different methods for approximation of the transition matrix have been investigated. The presented simulations are focused on studying the influence of parametric excitation produced by the shaft asymmetry and self-excitation vibration caused by the shaft material damping. The numerical results proved the applicability of the developed procedure, which has been verified by the direct integration of the motion equation.

The frequency response of the console, discretized by three-dimensional finite elements, excited by a pulsating surface distributed load and mounted on a bilateral nonlinear elastic foundation, reaction forces of which are described by the third-degree polynomial, was investigated. The solution was performed in a program library for solving the problems of steady-state vibration of nonlinear dynamic systems, which is being developed in the MATLAB software. To describe the frequency response curve, the Crisfield's continuous arc length method with the secant predictor was applied. The harmonic balance method using the Alternating Frequency-Time scheme was used to evaluate the non-linear forces in each iteration of the solution to solve the steady-state vibration response in every continuation increment.