F-Actin reassembly during focal adhesion impacts single cell mechanics and nanoscale membrane structure

Elucidating structure–function relationships governing the interfacial response of human mesenchymal stem cells to polydopamine coatings

Deposition of mussel-inspired polydopamine (PDA) has rapidly emerged as a simple yet effective strategy to functionalize the surface of biomaterials.

Regulation of the migration of endothelial cells by a gradient density of vascular endothelial growth factor

To investigate the effect of the surface gradient density of growth factor on the migration of endothelial cells (ECs), an approach to fabricate a gradient density of vascular endothelial growth factor (VEGF) onto silicon slides has been developed in this study. Our approach involves gradual injection of 3-glycidoxypropyltrimeth oxysilane (GPTMS) and then back filling with 3-triethoxysilylpropyl succinicanhydride (TESPSA) to produce a gradient density of carboxyl groups (-COOH) onto the silicon slides. The -COOH moieties were then activated for the immobilization of VEGF, which leading to a surface gradient density of VEGF. The successful formation of both carboxyl and VEGF gradient densities were confirmed by contact angle measurement, confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS), respectively. The treated silicon slide displayed a gradient density of VEGF from 54 to 132 ng/cm2 with a slope of 7.8 ng/cm2/mm. ECs cultured on the surface gradient density of VEGF demonstrated preferential orientation and an enhanced directional migration behavior. Up to 72% of cells migrated towards the region with high surface density of VEGF. However, the gradient density of VEGF had no significant effect on the cell migration rate. The study provides an alternative to explore chemical-directing cells migration, which is essentially important for understanding cell migration/in-growth behavior for angiogenesis involved in implant technology.

A density gradient of basic fibroblast growth factor guides directional migration of vascular smooth muscle cells

The migration of vascular smooth muscle cells (VSMCs) is an important process in many physiological events. It is of paramount importance to control the migration rate and direction of VSMCs by biomaterials. In this paper, a density gradient of basic fibroblast growth factor (bFGF) was fabricated using an injection method and the bio-conjugation between heparin and bFGF. The density of bFGF gradually increased with a slope of 17 ng/cm(2)/mm. Adhesion and migration of VSMCs were studied on the bFGF gradient. The VSMCs exhibited preferential orientation and an enhanced directional migration behavior on the gradient surface. Up to 70% cells migrated towards the region with a higher density of bFGF on the gradient. However, the bFGF gradient had no effect on the cell migration rate.

New approach to investigate the cytotoxicity of nanomaterials using single cell mechanics

Current in vitro methods to assess nanomaterial cytotoxicity involve various assays to monitor specific cellular dysfunction, such as metabolic imbalance or inflammation. Although high throughput, fast, and animal-free, these in vitro methods suffer from unreliability and lack of relevance to in vivo situations. New approaches, especially with the potential to reliably relate to in vivo studies directly, are in critical need. This work introduces a new approach, single cell mechanics, derived from atomic force microscopy-based single cell compression. The single cell based approach is intrinsically advantageous in terms of being able to directly correlate to in vivo investigations. Its reliability and potential to measure cytotoxicity is evaluated using known systems: zinc oxide (ZnO) and silicon dioxide (SiO2) nanoparticles (NP) on human aortic endothelial cells (HAECs). This investigation clearly indicates the reliability of single cell compression. For example, ZnO NPs cause significant changes in force vs relative deformation profiles, whereas SiO2 NPs do not. New insights into NPs-cell interactions pertaining to cytotoxicity are also revealed from this single cell mechanics approach, in addition to a qualitative cytotoxicity conclusion. The advantages and disadvantages of this approach are also compared with conventional cytotoxicity assays.

Resiliency of the plasma membrane and actin cortex to large-scale deformation

The tight coupling between the plasma membrane and actin cortex allows cells to rapidly change shape in response to mechanical cues and during physiological processes. Mechanical properties of the membrane are critical for organizing the actin cortex, which ultimately governs the conversion of mechanical information into signaling. The cortex has been shown to rapidly remodel on timescales of seconds to minutes, facilitating localized deformations and bundling dynamics that arise during the exertion of mechanical forces and cellular deformations. Here, we directly visualized and quantified the time-dependent deformation and recovery of the membrane and actin cortex of HeLa cells in response to externally applied loads both on- and off-nucleus using simultaneous confocal and atomic force microscopy. The local creep-like deformation of the membrane and actin cortex depends on both load magnitude and duration and does not appear to depend on cell confluency. The membrane and actin cortex rapidly recover their initial shape after prolonged loading (up to 10 min) with large forces (up to 20 nN) and high aspect ratio deformations. Cytoplasmic regions surrounding the nucleus are shown to be more resistant to long-term creep than nuclear regions. These dynamics are highly regulated by actomyosin contractility and an intact actin cytoskeleton. Results suggest that in response to local deformations, the nucleus does not appear to provide significant resistance or play a major role in cell shape recovery. The membrane and actin cortex clearly possess remarkable mechanical stability, critical for the transduction of mechanical deformation into long term biochemical signals and cellular remodeling.