Guang-Kui Xu

A physical model for the size-dependent cellular uptake of nanoparticles modified with cationic surfactants

Background The aim of this work was to improve oral bioavailability. The uptake of a series of quaternary ammonium salt didodecyl dimethylammonium bromide (DMAB)-modified nanoparticles (with uniform sizes ranging from 50 nm to 300 nm) into heterogeneous human epithelial colorectal adenocarcinoma cells (Caco-2) and human colon adenocarcinoma cells (HT-29) was investigated. Methods Coumarin-6 (C6) loaded poly (lactide-co-glycolide) (PLGA) nanoparticles were prepared with DMAB using the emulsion solvent diffusion method. The physicochemical properties and cellular uptake of these nanoparticles were studied. Deserno’s model was applied to explain the experimental observations. Results The results showed that the surface modification of PLGA nanoparticles with DMAB notably improved the cellular uptake. The cellular uptake was size-dependent and had an optimal particle size of 100 nm. The experimental data was integrated numerically, and was in agreement with the theoretical model. Conclusion These results indicated that the interactions between the charged nanoparticles and the cells resulted from various forces (eg, electrostatic forces, hydrophobic forces, bending and stretching forces, and limited receptor-mediated endocytosis), and the uptake of the nanoparticles occurred as a result of competition.

Mechanical properties and scaling laws of nanoporous gold

Nanoporous metals are a class of novel nanomaterials with potential applications in many fields such as sensing, catalysis, and fuel cells. The present paper is aimed to investigate atomic mechanisms associated with the uniaxial tensile deformation behavior of nanoporous gold. A phase field method is adopted to generate the bicontinuous open-cell porous microstructure of the material. Molecular dynamics simulations then reveal that the uniaxial tensile deformation in such porous materials is accompanied by an accumulation of stacking faults in ligaments along the loading direction and their junctions with neighboring ligaments, as well as the formation of Lomer–Cottrell locks at such junctions. The tensile strain leads to progressive necking and rupture of some ligaments, ultimately resulting in failure of the material. The simulation results also suggest scaling laws for the effective Youngs modulus, yield stress, and ultimate strength as functions of the relative mass density and average ligament size ...

Self-assembled nanostructures of homopolymer and diblock copolymer blends in a selective solvent.

Self-assembled nanostructures of amphiphilic block copolymers hold great promise for applications in nanomedicine. Blending polymers provides an effective way to produce multifunctional drug delivery vesicles at micro- and nanoscales. Here we investigate the self-assembly of homopolymer and diblock copolymer blends in a selective solvent by using the self-consistent field method. It is found that self-assembled nanostructures of different sizes and shapes (e.g., vesicles, circle- and line-like micelles, and their mixtures) can be obtained by varying the concentration and composition of the diblock copolymer. As the chain length or concentration of the homopolymer changes, morphological transitions may occur among the different nanostructures. On the basis of a number of simulations under various conditions, a phase diagram of aggregate morphologies is constructed with respect to the mixture ratio and the homopolymer chain length. The theoretical method presented here could be used to design novel nanomedicine carriers and to optimize their sizes and shapes for specific biomedical applications.

Highly Stable and Conductive Microcapsules for Enhancement of Joule Heating Performance

Nanocarbons show great promise for establishing the next generation of Joule heating systems, but suffer from the limited maximum temperature due to precociously convective heat dissipation from electrothermal system to surrounding environment. Here we introduce a strategy to eliminate such convective heat transfer by inserting highly stable and conductive microcapsules into the electrothermal structures. The microcapsule is composed of encapsulated long-chain alkanes and graphene oxide/carbon nanotube hybrids as core and shell material, respectively. Multiform carbon nanotubes in the microspheres stabilize the capsule shell to resist volume-change-induced rupture during repeated heating/cooling process, and meanwhile enhance the thermal conductance of encapsulated alkanes which facilitates an expeditious heat exchange. The resulting microcapsules can be homogeneously incorporated in the nanocarbon-based electrothermal structures. At a dopant of 5%, the working temperature can be enhanced by 30% even at a low voltage and moderate temperature, which indicates a great value in daily household applications. Therefore, the stable and conductive microcapsule may serve as a versatile and valuable dopant for varieties of heat generation systems.

Controlled release and assembly of drug nanoparticles via pH-responsive polymeric micelles: a theoretical study.

Tumor tissues often have a pH value lower than normal tissues, and this difference suggests a promising way of targeted cancer therapy by using pH-controlled drug delivery systems. On the basis of the mean-field theory, we present a theoretical methodology to predict the self-assembly and disassembly of pH-responsive polymers and nanoparticles in an ionic solution. It is found that vesicles, cylindrical, and spherical micelles can rapidly disassemble and release contained nanoparticles in a narrow pH range. The model is further used to study the controlled assembly of pH-sensitive drug with significantly improved encapsulation efficiency. This method is also applicable for the design of controlled delivery nanodevices for various biomedical applications.

A molecular mechanisms-based biophysical model for two-phase cell spreading

Cell spreading on an extracellular matrix is crucial for many biological functions and processes. By accounting for the molecular mechanisms of actin polymerization and integrin binding between the cell and the extracellular matrix, we here propose a biophysical model to predict the time-dependent growth rate of cell spreading. A general power-law is derived to predict the increasing contact radius of the cell with time and it is valid for almost all types of cells. With focus on the geometrical and biological characteristics, the results of this model agree well with relevant experimental measurements.

A Tensegrity Model of Cell Reorientation on Cyclically Stretched Substrates.

Deciphering the mechanisms underlying the high sensitivity of cells to mechanical microenvironments is crucial for understanding many physiological and pathological processes, e.g., stem cell differentiation and cancer cell metastasis. Here, a cytoskeletal tensegrity model is proposed to study the reorientation of polarized cells on a substrate under biaxial cyclic deformation. The model consists of four bars, representing the longitudinal stress fibers and lateral actin network, and eight strings, denoting the microfilaments. It is found that the lateral bars in the tensegrity, which have been neglected in most of the existing models, can play a vital role in regulating the cellular orientation. The steady orientation of cells can be quantitatively determined by the geometric dimensions and elastic properties of the tensegrity elements, as well as the frequency and biaxial ratio of the cyclic stretches. It is shown that this tensegrity model can reproduce all available experimental observations. For example, the dynamics of cell reorientation is captured by an exponential scaling law with a characteristic time that is independent of the loading frequency at high frequencies and scales inversely with the square of the strain amplitude. This study suggests that tensegrity type models may be further developed to understand cellular responses to mechanical microenvironments and provide guidance for engineering delicate cellular mechanosensing systems.

Integrin activation and internalization mediated by extracellular matrix elasticity: A biomechanical model

Cells sense and respond to the elasticity of extracellular matrix (ECM) via integrin-mediated adhesion. As a class of well-documented mechanosenors in cells, integrins switch among inactive, bound, and dissociated states, depending upon the variation of forces acting on them. However, it remains unclear how the ECM elasticity directs and affects the states of integrins and, in turn, their cellular functions. On the basis of our recent experiments, a biomechanical model is proposed to reveal the role of ECM elasticity in the state-switching of integrins. It is demonstrated that a soft ECM can increase the activation level of integrins while a stiff ECM has a tendency to prevent the dissociation and internalization of bound integrins. In addition, it is found that more stable focal adhesions can form on stiffer and thinner ECMs. The theoretical results agree well with relevant experiments and shed light on the ECM elasticity-sensing mechanisms of cells.

Self-assembled lipid nanostructures encapsulating nanoparticles in aqueous solution

Liposomes and nanoparticles, as well as their composite nanostructures, have great promise for potential applications in the nanobiotechnology of drug delivery and cancer therapy. Here, we use the self-consistent field method to investigate the interaction between lipid molecules and nanoparticles in an aqueous solution. It is shown that lipid molecules can self-assemble into monolayered or bilayered structures encapsulating nanoparticles. By varying the concentration of lipid molecules as well as the surface charge density and size of particles, several novel self-assembled nanostructures have been found. This method could be used to predict and design novel nanovehicles and nanomedicine carries for various biomedical applications, and the obtained results are helpful for gaining a deeper understanding of lipid-nanoparticle interactions.

Microencapsulated Phase Change Materials in Solar-Thermal Conversion Systems: Understanding Geometry-Dependent Heating Efficiency and System Reliability

The performance of solar-thermal conversion systems can be improved by incorporation of nanocarbon-stabilized microencapsulated phase change materials (MPCMs). The geometry of MPCMs in the microcapsules plays an important role for improving their heating efficiency and reliability. Yet few efforts have been made to critically examine the formation mechanism of different geometries and their effect on MPCMs-shell interaction. Herein, through changing the cooling rate of original emulsions, we acquire MPCMs within the nanocarbon microcapsules with a hollow structure of MPCMs (h-MPCMs) or solid PCM core particles (s-MPCMs). X-ray photoelectron spectroscopy and atomic force microscopy reveals that the capsule shell of the h-MPCMs is enriched with nanocarbons and has a greater MPCMs-shell interaction compared to s-MPCMs. This results in the h-MPCMs being more stable and having greater heat diffusivity within and above the phase transition range than the s-MPCMs do. The geometry-dependent heating efficiency and system stability may have important and general implications for the fundamental understanding of microencapsulation and wider breadth of heating generating systems.