Quantification of Particle Filtration Using a Quartz Crystal Microbalance Embedded in a Microfluidic Channel.

To quantify colloidal filtration, a quartz crystal microbalance (QCM) with a silicon dioxide surface is embedded on the inner surface of a microfluidic channel to monitor the real-time particle deposition. Potassium chloride solution with micrometer-size polystyrene particles simulating bacterial strains flows down the channel. In the presence of intrinsic Derjaguin-Landau-Verwey-Overbeek (DLVO) intersurface forces, particles are trapped by the quartz surfaces, and the increased mass shifts the QCM resonance frequency.

In-Plane Rotation of Prolate Colloids Adhered to a Planar Substrate in the Presence of Flow.

Micron-size spherical polystyrene colloidal particles are mechanically stretched to a prolate geometry with desirable aspect ratios. The particles in an aqueous medium with specific ionic concentration are then introduced into a microchannel and allowed to settle on a glass substrate. In the presence of unidirectional flow, the loosely adhered particles in the secondary minimum of surface interaction potential are easily washed off, but the remnant in the strong primary minimum preferentially aligns with the flow direction and exercises in-plane rotation.

Sloshing Resonance of an Acoustically Levitated Air-in-Liquid Compound Drop.

An acoustically levitated air-in-liquid compound drop is set into an out-of-phase azimuthal sloshing resonance by a modulated frequency with modes = 4-9. Waveforms of the inner and outer liquid-air interfaces conform to the classical Saffren model. Resonance peaks and their harmonics in the frequency spectrum are found to be a function of drop dimension and resonance modes.

Influence of Relative Humidity on Interparticle Capillary Adhesion.

A homemade instrument is designed to directly characterize the adhesion between two rigid polymeric microspheres in the presence of moist air. The tensile load is measured as a function of approach distance at designated relative humidity (RH). The measurement is consistent with our model from the first approximation.

Encapsulation of metal nanoparticles at the surface of a prototypical layered material.

Encapsulation of metal nanoparticles just below the surface of a prototypical layered material, graphite, is a recently discovered phenomenon. These encapsulation architectures have potential for tuning the properties of two-dimensional or layered materials, and additional applications might exploit the properties of the encapsulated metal nanoclusters themselves. The encapsulation process produces novel surface nanostructures and can be achieved for a variety of metals.

Nanoparticle-Based Hybrid Scaffolds for Deciphering the Role of Multimodal Cues in Cardiac Tissue Engineering.

Myocardial microenvironment plays a decisive role in guiding the function and fate of cardiomyocytes, and engineering this extracellular niche holds great promise for cardiac tissue regeneration. Platforms utilizing hybrid hydrogels containing various types of conductive nanoparticles have been a critical tool for constructing engineered cardiac tissues with outstanding mechanical integrity and improved electrophysiological properties. However, there has been no attempt to directly compare the efficacy of these hybrid hydrogels and decipher the mechanisms behind how these platforms differentially regulate cardiomyocyte behavior.

Squeezed nanocrystals: equilibrium configuration of metal clusters embedded beneath the surface of a layered material.

Shapes of functional metallic nanocrystals, typically synthesized either free in solution or supported on surfaces, are key for controlling properties. Here, we consider a novel new class of metallic nanocrystals, copper clusters embedded near the surface of graphite, which can be considered a model system for metals embedded beneath surfaces of layered materials, or beneath supported membranes. We develop a continuum elasticity (CE) model for the equilibrium shape of these islands, and compare its predictions with experimental data.

Quantification of colloidal filtration of polystyrene micro-particles on glass substrate using a microfluidic device.

A microfluidic device was designed to investigate filtration of particles in an electrolyte in the presence of liquid flow. Polystyrene spheres in potassium chloride solution at concentrations of 3-100 mM were allowed to settle and adhere to a glass substrate. A particle free solution at the same concentration was then flushed through the microfluidic channel at 0.

Electrically Driven Microengineered Bioinspired Soft Robots.

To create life-like movements, living muscle actuator technologies have borrowed inspiration from biomimetic concepts in developing bioinspired robots. Here, the development of a bioinspired soft robotics system, with integrated self-actuating cardiac muscles on a hierarchically structured scaffold with flexible gold microelectrodes is reported. Inspired by the movement of living organisms, a batoid-fish-shaped substrate is designed and reported, which is composed of two micropatterned hydrogel layers.

Measuring Interfacial Adhesion of Carbon Nanotube Bundles and Electrospun Polymer Fibers.

Adhesion at the dissimilar interface of single wall carbon nanotube (SWCNT) bundles and electrospun polymer nanofibers (Espun) was directly measured using a nano cheese cutter. A sample fiber suspended at the tip of an atomic force microscope cantilever and another freestanding fiber on a mica substrate were arranged in a cross-cylinder configuration and allowed to adhere. External tensile load led to spontaneous detachment or "pull-off".

Reduced Graphene Oxide-GelMA Hybrid Hydrogels as Scaffolds for Cardiac Tissue Engineering.

Biomaterials currently used in cardiac tissue engineering have certain limitations, such as lack of electrical conductivity and appropriate mechanical properties, which are two parameters playing a key role in regulating cardiac cell behavior. Here, the myocardial tissue constructs are engineered based on reduced graphene oxide (rGO)-incorporated gelatin methacryloyl (GelMA) hybrid hydrogels. The incorporation of rGO into the GelMA matrix significantly enhances the electrical conductivity and mechanical properties of the material.

Printing Highly Controlled Suspended Carbon Nanotube Network on Micro-patterned Superhydrophobic Flexible Surface.

Suspended single-walled carbon nanotubes (SWCNTs) offer unique functionalities for electronic and electromechanical systems. Due to their outstanding flexible nature, suspended SWCNT architectures have great potential for integration into flexible electronic systems. However, current techniques for integrating SWCNT architectures with flexible substrates are largely absent, especially in a manner that is both scalable and well controlled.

Universal quantifier derived from AFM analysis links cellular mechanical properties and cell-surface integration forces with microbial deposition and transport behavior.

In this study, we employed AFM analysis combined with mathematical modeling for quantifying cell-surface contact mechanics and magnitude and range of cell-surface interaction forces for seven bacterial strains with a wide range of cell morphology, dimension, and surface characteristics. Comprehensive cell-surface characterization including surface charge, extracellular polymeric substance content, hydrophobicity, and cell-cell aggregation analyses were performed. Flow-through column tests were employed to determine the attachment efficiency and deposition-transport behavior of these bacterial strains.

Microfluidics-assisted fabrication of gelatin-silica core-shell microgels for injectable tissue constructs.

Microfabrication technology provides a highly versatile platform for engineering hydrogels used in biomedical applications with high-resolution control and injectability. Herein, we present a strategy of microfluidics-assisted fabrication photo-cross-linkable gelatin microgels, coupled with providing protective silica hydrogel layer on the microgel surface to ultimately generate gelatin-silica core-shell microgels for applications as in vitro cell culture platform and injectable tissue constructs. A microfluidic device having flow-focusing channel geometry was utilized to generate droplets containing methacrylated gelatin (GelMA), followed by a photo-cross-linking step to synthesize GelMA microgels.

Mechanical performance of hydrogel contact lenses with a range of power under parallel plate compression and central load.

When a contact lens is compressed between two parallel plates (PPC) or under a central load (CLC), the constitutive relation depends not only on the mechanical properties such as elastic modulus, E, of the hydrogel materials, but also the lens power, d, or thickness variation, h(ϕ0), along the meridional direction ϕ0. Hyperopic lenses (d>0) are thicker at the apex along the optical axis and thin out gradually along the meridian, while myopic lenses (d<0) are thinnest at the apex. Mechanical deformation is quantified by the inter-relationship between applied force, F, vertical displacement of the external load, w0, contact or dimple radius, a, and the deformed profile, w(r).

Carbon-nanotube-embedded hydrogel sheets for engineering cardiac constructs and bioactuators.

We engineered functional cardiac patches by seeding neonatal rat cardiomyocytes onto carbon nanotube (CNT)-incorporated photo-cross-linkable gelatin methacrylate (GelMA) hydrogels. The resulting cardiac constructs showed excellent mechanical integrity and advanced electrophysiological functions. Specifically, myocardial tissues cultured on 50 μm thick CNT-GelMA showed 3 times higher spontaneous synchronous beating rates and 85% lower excitation threshold, compared to those cultured on pristine GelMA hydrogels.

Small-angle light scattering to detect strain-directed collagen degradation in native tissue.

It has been demonstrated that there is a mechanochemical relationship between collagen and collagenolytic enzymes such that increased tensile mechanical strain reduces the enzymatic cutting rate. This mechanochemical relationship has the potential to permit directed remodelling of tissue-engineered constructs in vitro and to shed light on the generation of load-adapted collagen-based connective tissue. In this investigation, we demonstrate that small-angle light scattering (SALS) has the sensitivity to dynamically detect the preferential enzymatic degradation of a subset of unloaded collagen fibrils within differentially loaded native tissue.

Elastic and viscoelastic characterization of mouse oocytes using micropipette indentation.

This paper reports the first quantitative comparison study of elastic and viscoelastic properties of oocytes from young and aged mice. A force measurement technique, including a poly(dimethylsiloxane) (PDMS) cell holding device and a sub-pixel computer vision tracking algorithm, is utilized for measuring forces applied to an oocyte and resultant cell deformations in real time during oocyte manipulation. To characterize elastic and viscoelastic properties of the oocytes, a stress-relaxation indentation test is performed.

Measurement of adhesion work of electrospun polymer membrane by shaft-loaded blister test.

The work of adhesion at the interface of electrospun membrane and rigid substrate is measured by a shaft-loaded blister test (SLBT). Poly(vinylidene fluoride) (PVDF) were electrospun with an average fiber diameter of 333 ± 59 nm. Commercial cardboard with inorganic coating was used to provide a model substrate for adhesion tests.

Correlation of macroscopic aggregation behavior and microscopic adhesion properties of bacteria strains using a dimensionless Tabor's parameter.

Macroscopic adhesion-aggregation, floc formation, and subsequent transportation of microorganisms in porous media are closely related to the microscopic behavior and properties of individual cells. The classical Tabor's parameter in colloidal science is modified to correlate the macroscopic aggregation and microscopic adhesion properties of microorganisms. Seven bacterial strains relevant to wastewater treatment and bioremediation were characterized in terms of their macroscopic aggregation index (AI) using an optical method, and their microscopic coupled adhesion and deformation properties using atomic force microscopy (AFM).

Do electrospun polymer fibers stick?

Adhesion between electrospun polycaprolactone (PCL) fibers was directly measured in a cross-cylinder geometry using a nanoforce tensile tester. The surface roughness of fibers was determined by an atomic force microscope (AFM), and the structural factors were characterized by differential scanning calorimeter (DSC) and wide-angle X-ray diffraction (WAXD). "Pull-off" force was found to be in the order of 10(-6) N, and the adhesion energy was 190 +/- 7 mJ/m(2).

Mechanical property characterization of mouse zona pellucida.

Previous intracytoplasmic sperm injection (ICSI) studies have indicated significant variation in ICSI success rates among different species. In mouse ICSI, the zona pellucida (ZP) undergoes a "hardening" process at fertilization in order to prevent subsequent sperm from penetrating. There have been few studies investigating changes in the mechanical properties of mouse ZP post fertilization.

Effect of acyl chain mismatch on the contact mechanics of two-component phospholipid vesicle during main phase transition.

It has been recently demonstrated that acyl chain mismatch of phospholipid bilayer composed of a binary lipid mixture induces component formation on the lateral plane of the bilayer [Biophys. J. 83 (2002) 1820-1883].

Thermal induced modification of the contact mechanics of adhering liposomes on cationic substrate.

The correlation between the mechanical property and the thermotropic transition of the phospholipid bilayer has been recently demonstrated (Chem. Phys. Lipids 110 (2001) 27).