Biodegradable iron-silicon implants produced by additive manufacturing.

Due to many negative and undesirable side effects from the use of permanent implants, the development of temporary implants based on biocompatible and biodegradable materials is a promising area of modern medicine. In the presented study, we have investigated complex-shaped iron-silicon (Fe-Si) scaffolds that can be used as potential biodegradable framework structures for solid implants for bone grafting. Since iron and silicon are biocompatible materials, and their alloy should also have biocompatibility. It has been demonstrated that cells, mesenchymal stromal cells derived from the human umbilical cord (UC-MSC) and 3T3, were attached to, spread, and proliferated on the Fe-Si scaffolds' surface. Most of UC-MSC and 3T3 remained viable, only single dead cells were observed. According to the results of biological testing, the scaffolds have shown that deposition of calcium phosphate particles occurs on day one in the scaffold at the defect site that can be used as a primary marker of osteodifferentiation. These results demonstrate that the 3D-printed porous iron-silicon (Fe-Si) alloy scaffolds are promising structures for bone grafting and regeneration.

Role of Nitrogen and Oxygen in Capacitance Formation of Carbon Nanowalls.

Supercapacitors based on carbon nanomaterials are attracting much attention because of their high capacitance enabled by large specific surface area. The introduction of heteroatoms such as N or O enhances the specific capacitance of these materials. However, the mechanisms that lead to the increase in the specific capacitance are not yet well-studied. In this Letter, we demonstrate an effective method for modification of the surface of carbon nanowalls (CNWs) using DC plasma in atmospheres of O2, N2, and their mixture. Processing in the plasma leads to the incorporation of ∼4 atom % nitrogen and ∼10 atom % oxygen atoms. Electrochemical measurements reveal that CNWs functionalized with oxygen groups are characterized by higher capacitance. The specific capacitance for samples with oxygen reaches 8.9 F cm-3 at a scan rate of 20 mV s-1. In contrast, the nitrogen-doped samples demonstrate a specific capacitance of 4.4 F cm-3 at the same scan rate. The mechanism of heteroatom incorporation into the carbon lattice is explained using density functional theory calculations.

Model of graphene nanobubble: Combining classical density functional and elasticity theories.

A graphene nanobubble consists of a graphene sheet, an atomically flat substrate, and a substance enclosed between them. Unlike conventional confinement with rigid walls and a fixed volume, the graphene nanobubble has one stretchable wall, which is the graphene sheet, and its volume can be adjusted by changing the shape. In this study, we developed a model of a graphene nanobubble based on classical density functional theory and the elastic theory of membranes. The proposed model takes into account the inhomogeneity of the enclosed substance, the nonrigidity of the wall, and the alternating volume. As an example application, we utilize the developed model to investigate fluid argon inside graphene nanobubbles at room temperature. We observed a constant height-to-radius ratio over the whole range of radii considered, which is in agreement with the results from experiments and molecular dynamics simulations. The developed model provides a theoretical tool to study both the inner structure of the confined substance and the shape of the graphene nanobubble. The model can be easily extended to other types of nonrigid confinement.

Bubble cluster dynamics in an acoustic field.

A mathematical model describing dynamics of the cluster of gas bubbles in an acoustic field is presented. According to this model a cluster is considered as a large drop with microbubbles inside. The proposed model is used as a basis (1) for an analytical study of small bubble oscillations in mono- and polydisperse clusters and (2) for numerical investigations of nonlinear bubble oscillations and of the diffusion stability of gas bubbles in the cluster. A synchronization of the collapse phases of bubbles with different radii and collapse intensification for bubbles of one size in the presence of bubbles of other size is found. These effects are explained by the interaction between the bubbles of different radii in the cluster. For the cluster with one radius bubbles the numerical values are obtained for the initial gas concentrations in the liquid at which the bubbles tend to one of two equilibrium states because of rectified diffusion. It is found that the cluster with the bubbles of two different radii tends to become a cluster with the bubbles of one radius due to rectified diffusion.

Model of a liquid nanofilm on a solid substrate based on the van der Waals concept of capillarity.

Van der Waals attractive forces drastically change the material properties of thin liquid layers several nanometers when in contact with a solid. At this scale, the fluid is no longer homogeneous. Moreover, it has properties which are analogous to those of solids. In particular, in equilibrium the stress tensor is no longer spherical. For such fluids, we use a long-wave approximation to derive the evolution of a liquid nanofilm on a substrate. We establish that the driving pressure in the nanofilm should be associated with the mean value of the component of the pressure tensor tangential to the liquid interface (along the substrate). Finally, we derive the equation for nanofilm dynamics by using a mass conservation formulation. This is not a conventional, conservative equation for the position of the free surface normally used in the theory of thick films where the density is homogeneous, but rather a conservative equation for the liquid mass. The equation turns out to be a nonlinear parabolic equation with a diffusion coefficient of a "good" sign.