Applications of stripe assay in the study of CXCL12-mediated neural progenitor cell migration and polarization

The polarization and migration of neural progenitor cells (NPCs) are critical for embryonic brain development and neurogenesis after brain injury. Although stromal-derived factor-1α (SDF-1α, CXCL12) and its receptor CXCR4 are well-known to mediate the migration of NPCs in the developing brain, the dynamic cellular processes and structure-related molecular events remain elusive. Transwell and microfluidic-based assays are classical assays to effectively study cellular migration. However, both of them have limitations in the analysis of a single cell. In this study, we modified the stripe assay and extended its applications in the study of NPC polarization and intracellular molecular events associated with CXCL12-mediated migration. In response to localized CXCL12, NPCs formed lamellipodia in the stripe assay. Furthermore, CXCR4 and Rac1 quickly re-distributed to the area of lamellipodia, indicating their roles in NPC polarization upon CXCL12 stimulation. Although the chemokine stripes in the assay provided concentration gradients that can be best used to study cellular polarization and migration through immunocytochemistry, they can also generate live imaging data with comparable quality. In conclusion, stripe assay is a visual, dynamic and economical tool to study cellular mobility and its related molecule mechanisms.     

Plasma-Induced Surface Modification of Polydimethylsiloxane Aimed at Reducing Salt and Protein Deposition

Polydimethylsiloxane (PDMS) is an elastomer that is widely used in construction and for biological and biomedical applications. The biocompatibility of PDMS was improved by different surface treatment methods, i.e., plasma treatment or a combination of plasma treatment with UV-irradiation or redox initiator, to minimize the effects of deposition of salts and proteins. In this work we used the vinyl monomers sulfobetaine and AMPS which have good biocompatible properties.     

Thermal,Mechanical, and Acoustic Properties of Polydimethylsiloxane Filled with Hollow Glass Microspheres

Polydimethylsiloxane (PDMS) is the most widely used silicon-based polymer due to its versatility and its various attractive properties. The fabrication of PDMS involves liquid phase cross-linking to obtain hydrophobic and mechanically flexible material in the final solid form. This allows to add various fillers to affect the properties of the resulting material. PDMS has a relatively low Thermal Conductivity (TC), in the order of 0.2 W/mK, which makes it attractive for thermal insulation applications such as sealing in construction. Although a further decrease in the TC of PDMS can be highly beneficial for such applications, most research on the thermal properties of PDMS composites have focused on fillers that increase the TC rather than decrease it. In the present work, we propose a simple and reliable method for making a PDMS-based composite material with significantly improved thermal insulation properties, by adding hollow glass microspheres (HGMs) to the mixture of the liquid base and the cross-linker (10:1 ratio), followed by degassing and heat-assisted crosslinking. We obtained a 31% reduction of thermal conductivity and a 60% increase in the elastic modulus of samples with HGM content of 17% by weight. At the same time, the sound insulation capacity of the PDMS-HGM composite is slightly decreased in comparison to pure PDMS, as a result of its lower density. Finally, the wettability of the samples had no dependence on HGM content.     

Mechanical tugging force regulates the size of cell–cell junctions

Actomyosin contractility affects cellular organization within tissues in part through the generation of mechanical forces at sites of cell–matrix and cell–cell contact. While increased mechanical loading at cell–matrix adhesions results in focal adhesion growth, whether forces drive changes in the size of cell–cell adhesions remains an open question. To investigate the responsiveness of adherens junctions (AJ) to force, we adapted a system of microfabricated force sensors to quantitatively report cell–cell tugging force and AJ size. We observed that AJ size was modulated by endothelial cell–cell tugging forces: AJs and tugging force grew or decayed with myosin activation or inhibition, respectively. Myosin-dependent regulation of AJs operated in concert with a Rac1, and this coordinated regulation was illustrated by showing that the effects of vascular permeability agents (S1P, thrombin) on junctional stability were reversed by changing the extent to which these agents coupled to the Rac and myosin-dependent pathways. Furthermore, direct application of mechanical tugging force, rather than myosin activity per se, was sufficient to trigger AJ growth. These findings demonstrate that the dynamic coordination of mechanical forces and cell–cell adhesive interactions likely is critical to the maintenance of multicellular integrity and highlight the need for new approaches to study tugging forces.     

A disposable lab-on-a-chip platform with embedded fluid actuators for active nanoliter liquid handling

In this work we present the development of a disposable liquid handling lab-on-a-chip (LOC) platform with embedded actuators for applications in analytical chemistry. The proposed platform for nanoliter liquid handling is based on a thermally responsive silicone elastomer composite, consisting of PDMS and expandable microspheres. In our LOC platform, we integrate active dosing, transportation and merging of nanoliter liquid volumes. The disposable platform successfully demonstrates precise sample volume control with smart microfluidic manipulation and on-chip active microfluidic components. It is entirely fabricated from low-cost materials using wafer-level processing. Moreover, an enzymatic reaction and real-time detection was successfully conducted to exemplify its applicability as an LOC.     

An ultra-thin PDMS membrane as a bio/micro–nano interface: fabrication and characterization

We report a method for making ultra-thin PDMS membrane devices. Freely suspended membranes as thin as 70 nm have been fabricated. Bulging tests were performed with a custom built fluidic cell to characterize large circular membranes. The fluidic cell allows the media (such as air or water) to wet one side of the membrane while maintaining the other side dry. Pressure was applied to the membrane via a liquid manometer through the fluidic cell. The resulting load-deflection curves show membranes that are extremely flexible, and they can be reproducibly loaded and unloaded. Such devices may potentially be used as mechanical and chemical sensors, and as a bio-nano/micro interface to study cellular mechanics in both static and dynamic environments.     

Influences of Dispersions’ Shapes and Processing in Magnetic Field on Thermal Conductibility of PDMS–Fe3O4 Composites

Composites of magnetite (Fe₃O₄) nanoparticles dispersed in a polydimethylsiloxane (PDMS) matrix were prepared by a molding process. Two types of samples were obtained by free polymerization with randomly dispersed particles and by polymerization in an applied magnetic field. The magnetite nanoparticles were obtained from magnetic micrograins of acicular goethite (α-FeOOH) and spherical hematite (α-Fe₂O₃), as demonstrated by XRD measurements. The evaluation of morphological and compositional properties of the PDMS:Fe₃O₄ composites, performed by SEM and EDX, showed that the magnetic particles were uniformly distributed in the polymer matrix. Addition of magnetic dispersions promotes an increase of thermal conductivity compared with pristine PDMS, while further orienting the powders in a magnetic field during the polymerization process induces a decrease of the thermal conductivity compared with the un-oriented samples. The shape of the magnetic dispersions is an important factor, acicular dispersions providing a higher value for thermal conductivity compared with classic commercial powders with almost spherical shapes.     

Mechanical Properties Evaluation of Polymer-Binding C-S-H Structure from Nanoscale to Macroscale: Hydroxyl-Terminated Polydimethylsiloxane (PDMS) Modified C-S-H

Exploring and modifying the C-S-H structure at a micro–nano level is an effective solution to improve the performance of Portland cement. Compared with organics inserting C-S-H, the research on the performance of a polymer-binding C-S-H structure from nanoscale to macroscale is limited. In this work, the mechanical properties of a modified C-S-H, using hydroxyl-terminated polydimethylsiloxane (PDMS) as the binders, are evaluated. The PDMS-modified C-S-H structures are introduced into macro-defect-free cement to obtain stress–strain curves changes at a macro scale. The AFM–FM was adopted to measure the morphology and elastic modulus of C-S-H at a nano scale. The molecular dynamics (MD) simulation was performed to assess the toughness, tensile properties, and failure mechanism. The results show that the PDMS-modified C-S-H powders change the break process and enhance ductility of MDF cement. The elastic modulus of PDMS-modified C-S-H is lower than pure C-S-H. When PDMS molecules are located between the stacking crystal units, it can enhance the toughness of C-S-H aggregates. The PDMS-modified C-S-H stacking structure has better plasticity, and its tensile strains are higher than the pure C-S-H. PDMS molecules hinder the initial crack expansion, leading to the branching of the initial crack. In addition, the measurement of AFM–FM can identify and obtain the mechanical properties of basic units of C-S-H. This paper enhances the understanding of cement strength sources and modification methods.     

Friction Property of Hierarchical Micro/Nanopatterned PDMS

Polydimethylsiloxane (PDMS) has many advantages, but the friction coefficient generated by contact with the counter material is high. The purpose of this study is to reduce the friction coefficient by forming hierarchical micro/nanopatterns on the PDMS surface using the imprinting method. In addition, the optimum conditions for reducing the friction coefficient by controlling the sliding speed and normal load were determined. After contacting flat bare PDMS and hierarchical micro/nanostructured PDMS with a counter tip made of polyurethane (PU), the change in friction with sliding speed and vertical load was evaluated. Under normal load conditions, the average friction coefficient of the bare PDMS decreased as the sliding speed increased, and that of the patterned PDMS slightly increased. Regardless of the sliding speed, the friction coefficient decreased as the normal load increased for both specimens. At a sliding speed of 4 mm/s under a load of 10 mN, the friction reduction effect of the pattern structure was the largest at 79%. Overall, the greatest friction reduction effect (84%) was confirmed in patterned PDMS with the lowest friction coefficient under the conditions of 4 mm/s, 50 mN, compared to bare PDMS with the highest friction coefficient under the conditions of 4 mm/s, 10 mN.     

Synthesis of Silicone‐Methacrylate Copolymers by ATRP Using a Nickel‐Based Supported Catalyst

Summary: A nickel (II) bromide catalyst immobilized onto crosslinked diphenylphosphinopolystyrene (PS‐PPh₃/NiBr₂) was used for the synthesis of silicone‐methacrylate copolymers by atom transfer radical polymerization (ATRP) of various methacrylate monomers using ω‐bromide silicone chains as macroinitiator. The polymerization proved to be very well‐controlled when a sufficient amount of soluble ligand, i.e., triphenylphosphine (PPh₃), was added to the polymerization medium. Under these conditions, this technique efficiently led to the production of different copolymers with controlled compositions and molecular weights as well as narrow polydispersity indices ( < 1.5). The recovered copolymers proved to be almost free of catalyst residues. Indeed, inductively coupled plasma (ICP) analysis revealed a metal content lower than 100 ppm, representing only a few percent of the initial metal content in the polymerization medium.

Synthesis of PDMS block copolymer in toluene catalyzed by PS‐PPh₃/NiBr₂ in the presence of soluble PPh₃ at 90 °C.