Phosphoester modified poly(ethylenimine) as efficient and low cytotoxic genevectors

Cyclic phosphoester monomer ethyl ethylene phosphate (EEP) modified poly(ethylenimine) (PEI),denoted as PEI-EEP,was developed for gene delivery.Three PEI-EEP polymers were synthesized and their structures were characterized by 1H and 31P NMR methods.All the PEI-EEP polymers could condense DNA efficiently at N/P ratios higher than 0.5/1.The physiochemical characteristics of PEI-EEP/DNA complexes were analyzed by particle size and zeta potential measurements.The particle sizes of complexes were around 160–250 nm,and their zeta potentials were around 30–45 mV at the N/P ratios ranging from 10/1 to 50/1.In vitro cell viability and transfection ability were evaluated in HEK293 and HeLa cells using PEI as the control.The cytotoxicity of PEI-EEP and PEI-EEP/DNA complexes was lower than that of PEI and its complexes with DNA.The transfection efficiency of PEI-EEP/DNA complexes was correlated to modification degrees with phosphoester.When the modification of phosphoester to PEI was moderate,the PEI-EEP1/DNA and PEI-EEP2/DNA complexes exhibited comparable or even higher transfection ability than PEI/DNA complex at its optimal N/P ratio in the absence of serum.However,transfection efficiency of PEI-EEP3 reduced dramatically.More importantly,the PEI-EEP exhibited higher transfection efficiency in the presence of 10% serum than that without serum.Therefore,PEI-EEP polymers may be attractive vectors for non-viral gene therapy.

A flexible various-scale approach for soil-structure interaction and its application in seismic damage analysis of the underground structure of nuclear power plants

In simulations of geotechnical engineering, interface elements are versatile tools and are widely used in the modeling of the relative displacements between soils and structures. To consider the case of a local failure adjacent to a soil-structure interaction region, a partial mesh refinement should be performed. In this study, a three-dimensional(3 D) interface element with an arbitrary number of nodes is developed as a new technique to reduce the complexity and difficulty of managing the various scales between soil and structure. An asymmetric number of nodes is permissible on the two sliding surfaces. In this manner, soil and structure can be discretized independently, and the various-scale model is established conveniently and rapidly. The accuracy of the proposed method is demonstrated through numerical examples. The various-scale approach is employed in an elasto-plastic seismic damage analysis of a buried concrete drainage culvert of a nuclear power plant. The results indicate that by applying the proposed method, the number of elements decreased by 72.5%, and the computational efficiency improved by 59% with little influence on accuracy. The proposed method is powerful for local damage evolution analyses of both soil and structure and possesses great practical significance and the potential for further application, especially for nonlinear analysis of large-scale geotechnical engineering.