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The diffusion dynamics of polymer chains within a narrow slit formed by two patch-patterned surfaces is investigated utilizing Langevin dynamics simulations. These surfaces feature periodically arranged attractive patches of size L and period d , with a staggered configuration of (0.5 d , 0.5 d ) offsets along the x and y axes. When d is fixed, the polymer chain exhibits normal diffusion over long time scales, with the translational diffusion coefficient D xy gradually decreasing to zero as L increases. Notably, our findings reveal four distinct diffusion modes: free-diffusion mode for L ≤ L 1 , where the polymer chain is mainly in a desorption state; adsorption-desorption mode for L 1 < L ≤ L 2 , involving transitions from a single-patch adsorption state to a desorption state; exchange-patch mode for L 2 < L ≤ L 3 , where the polymer chain switches between a single-patch adsorption state and an upper-lower double-patch adsorption state by exchanging patches; and nondiffusion mode for L > L 3 , where the polymer chain is primarily in a pinned state. Furthermore, as the patch attraction strength ε ps increases, D xy decreases due to an increase in the adsorption time of the polymer chain. Simultaneously, critical patch size thresholds L 1 , L 2 , and L 3 , exhibit a decreasing trend. These observations highlight the significant influence of the confining slit and patch properties on the diffusion behavior of polymer chains.

Objective: Inflammation is recognized as a contributor in the development of pulmonary arterial hypertension (PAH), and the recruitment and functional capacity of immune cells are well-orchestrated by chemokines and their receptors. This study is aimed at identification of critical chemokines in the progression of PAH via transcriptomic analysis., Methods: Differentially expressed genes (DEGs) from lungs of PAH patients were achieved compared to controls based on Gene Expression Omnibus (GEO) database. Gene set enrichment analysis (GSEA) was applied for functional annotation and pathway enrichement. The abundance of immune cells was estimated by the xCell algorithm. Weighted correlation network analysis (WGCNA) was used to construct a gene expression network, based on which a diagnostic model was generated to determine its accuracy to distinguish PAH from control subjects. Target genes were then validated in lung of hypoxia-induce pulmonary hypertension (PH) mouse model., Results: ACKR4 (atypical chemokine receptor 4) was downregulated in PAH lung tissues in multiple datasets. PAH relevant biological functions and pathways were enriched in patients with low-ACKR4 level according to GSEA enrichment analysis. Immuno-infiltration analysis revealed a negative correlation of activated dendritic cells, Th1 and macrophage infiltration with ACKR4 expression. Three gene modules were associated with PAH via WGCNA analysis, and a model for PAH diagnosis was generated using CXCL12, COL18A1 and TSHZ2, all of which correlated with ACKR4. The ACKR4 expression was also downregulated in lung tissues of our experimental PH mice compared to that of controls., Conclusions: The reduction of ACKR4 in lung tissues of human PAH based on transcriptomic data is consistent with the alteration observed in our rodent PH. The correlation with immune cell infiltration and functional annotation indicated that ACKR4 might serve as a protective immune checkpoint for PAH., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Jiang, Wu, Liu, Feng, Ye, Huang, He, Shen, Zhu, Zhou, Jiang, Qi, Zhang and Yan.)

Mixed brushes consisting of flexible and semiflexible polymers of the same chain length exhibit a height-switching phenomenon because of rigidity-dependent critical adsorption [Yang et al. Macromolecules 2020, 53, 7369]. Semiflexible polymers stand higher at weak surface attraction (high temperature), but they close to the attractive surface at strong attraction (low temperature). In this work, the height-switching dynamics of the mixed polymer brushes is studied by Metropolis Monte Carlo simulation. The height-switching time is calculated by a sudden change in the surface attraction. Two surface attraction change modes, i.e., the weak-to-strong mode where the attraction is changed from weak to strong and the strong-to-weak mode where it is changed from strong to weak, are investigated. Simulation results show that the height-switching time is related to the grafting density, the polymer stiffness, and surface attraction change mode. We find that the height-switching time is significantly decreased for the strong-to-weak mode. And our results also show that the height switching in the mixed polymer brushes is reversible.

The effect of the size of nanoparticles, σ NP , on the glass transition temperature, T g , of polymer nanocomposites is studied by using molecular dynamics simulations. The variation of T g with σ NP shows two distinct behaviours for polymer nanocomposites at low and high volume fractions of nanoparticles ( f NP ). At a low f NP , T g decays almost exponentially with σ NP , whereas at a high f NP T g shows a complex behaviour: it initially increases and then decreases with increasing σ NP . The decrease in T g with σ NP is due to the significant decrease of adsorbed polymer monomers, while the increase in T g with σ NP is attributed to the slower diffusion of larger nanoparticles. We have also investigated the diffusion and relaxation of polymer chains at a temperature above T g for both low and high f NP s. The diffusion constant and relaxation time of polymer chains are highly consistent with the behaviour of T g .

The effect of the loading of nanoparticles on the glass transition temperature, Tg, of polymer nanocomposites is studied by using molecular dynamics simulations. Tg is estimated from the variation of system volume with temperature and the temperature-dependent diffusion of the polymer described by the Vogel-Fulcher-Tammann law. The estimated values of Tg from the two methods are consistent with each other. Results show that Tg can be regulated by changing the volume fraction of nanoparticles, fNP. A novel shift in Tg is observed, that is, Tg increases with fNP at fNP < , while it decreases with increasing fNP at fNP > . The basic mechanism behind the novel shift in Tg is the competition between the attraction of nanoparticles towards polymer chains and the fast diffusion of nanoparticles. The increase in Tg at low fNP is due to the attraction of nanoparticles, whereas the decrease in Tg at high fNP is attributed to the fast diffusion of nanoparticles. The diffusion of the polymer above Tg is also investigated. The diffusion of the polymer decreases with increasing fNP below and increases with fNP above , in agreement with the variation of Tg.

The critical adsorption and diffusion of a linear polymer chain on a heterogeneous surface with randomly distributed adsorption sites are studied using dynamic Monte Carlo simulations. Results show that the critical fraction of the adsorption sites at which critical adsorption takes place decreases exponentially with the increasing polymer-surface attraction strength and, at the same time, decreases with the increasing intra-polymer attraction strength. For adsorbed polymers with large intra-polymer attraction strength, we also find an adsorption-induced structural transition from a three-dimensional compact globule to a two-dimensional compacted pancake with an increasing fraction of adsorption sites. Anomalous sub-diffusion is observed for the adsorbed polymer diffusion on heterogeneous surfaces, in contrast to the normal diffusion on a homogeneous surface. The polymer on heterogeneous surfaces shows larger fluctuation in the total surface attraction energy and a longer waiting time.