Microfluidics-based assay on the effects of microenvironmental geometry and aqueous flow on bacterial adhesion behaviors

Abstract A new microfluidic system with four different microchambers （a circle and three equilateral concave polygons） was designed and fabricated using poly（dimethylsiloxane） （PDMS） and the soft lithography method. Using this microfluidic device at six flow rates （5, 10, 20, 30, 40, and 50 μL/h）, the effects of microenvironmental geometry and aqueous flow on bacterial adhesion behaviors were investigated. Escherichia coli HB101 pGLO, which could produce a green fluorescent protein induced by L-arabinose, was utilized as the model bacteria. The results demonstrated that bacterial adhesion was significantly related to culture time, microenvironment geometry, and aqueous flow rates. Adhered bacterial density increased with the culture time. Initially, the adhesion occurred at the microchamber sides, and then the entire chamber was gradually covered with increased culture time. Adhesion densities in the side zones were larger than those in the center zones because of the lower shearing force in the side zone. Also, the adhesion densities in the complex chambers were larger than those in the simple chambers. At low flow rates, the orientation of adhered bacteria was random and disorderly. At high flow rates, bacterial orientation became close to the streamline and oriented toward the flow direction; All these results implied that bacterial adhesion tended to occur in complicated aqueous flow areas.The present study provided an on-chip flow system for physiological behavior of biological cells, as well as provided a strategic cue for the prevention of bacterial infection and biofilm formation.

Biophysical Regulation of Cell Behavior-Cross Talk between Substrate Stiffness and Nanotopography

The stiffness and nanotopographical characteristics of the extracellular matrix （ECM） influence numerous developmental, physiological, and pathological processes in vivo. These biophysical cues have therefore been applied to modulate almost all aspects of cell behavior, from cell adhesion and spreading to proliferation and differentiation. Delineation of the biophysical modulation of cell behavior is critical to the rational design of new biomaterials, implants, and medical devices. The effects of stiffness and topographical cues on cell behavior have previously been reviewed, respectively; however, the interwoven effects of stiffness and nanotopographical cues on cell behavior have not been well described, despite similarities in phenotypic manifestations. Herein, we first review the effects of substrate stiffness and nanotopography on cell behavior, and then focus on intracellular transmission of the biophysical signals from integrins to nucleus. Attempts are made to connect extracellular regulation of cell behavior with the biophysical cues. We then discuss the challenges in dissecting the biophysical regulation of cell behavior and in translating the mechanistic understanding of these cues to tissue engineering and regenerative medicine.

A review on adhesion behavior of chip seal pavement and aggregate

Chip seal is widely used for preventive maintenance to mitigate pavement deterioration,but it is prone to aggregate loss during pavement service.To further promote the development and application of chip seals in road engineering in China,the research progress of the adhesion behavior of aggregate and binder in chip seals was reviewed in this paper,focusing on the adhesion mechanism of emulsified asphalt and alkaline aggregate.The Influencing factors and evaluation methodology of chip seals'aggregate adhesion behavior were also discussed.The results demonstrate that the adhesion process between emulsified asphalt and alkaline aggregate is divided into three processes including infiltration,demulsification,and cluster,which is more complicated when compared to hot asphalt.When designing a chip seal,not only the characteristics of single material should be paid attention to,but also the combination of binder and aggregate matters a lot.To form good adhesion between aggregate and asphalt binder,various influencing factors such as material selection,design method,and construction technical index should be considered comprehensively in the whole design,construction,and operation process.Three methods for evaluating adhesion behavior are summarized,including macroscopic adhesion performance tests,image analysis technology,and model prediction.It is not objective to evaluate the aggregate adhesion behavior of chip seal only by a single evaluation method.A comprehensive evaluation based on the micro-macro multi-scale method should be considered in the future.

Deposition Behavior at Different Substrate Temperatures by Using Supersonic Laser Deposition

The supersonic laser deposition （SLD） is a new fabrication process which combines the supersonic powder stream found in cold spray with laser heating of the deposition zone. Because of the instantaneity of particles impact, the deformation behaviors and the adhesion behaviors of particles impacted on the substrate by SI.D cannot be well investigated through experiments. Therefore, a finite elemen! model was developed to solve the problems above. Meanwhile, the heat effect of the substrate heated by laser was discussed. The effective plastic strain and the effec- tive stress between the particle and substrate at different laser preheal temperatures were studied. The results show that laser depositing temperatures of 1 000 and 1 100 ℃ on substrate would be the optimized for the bonding of parti- cles and substrate. In addition, the simulation results conformed to experimental results.

FTIR-ATR study for adsorption of trypsin in aqueous environment on bare and TiO2 coated ZnSe surfaces

Undesired adsorption of proteins brings big troubles to marine structures.The settled proteins change the physical and chemical properties of the surfaces,which allow marine fouling organisms to settle down on the structures.Therefore,to understand the adsorption mechanism of proteins is very helpful to find an environment-friendly solution against biofouling.Many approaches have been developed to study protein adsorption,but most of them are insufficient to give the chemical interaction information between proteins and surfaces.Fourier transform infrared spectroscopy with attenuated total reflection(FTIR-ATR)is an efficient,fast and non-destructive method for in situ surface measurement,which greatly minimizes the interference of water to infra red spectra,because of the very small depth of penetration of the evanescent wave.In this paper,an in situ FTIR-ATR technology was used to investigate the adsorption process of trypsin on a bare ZnSe surface and on a TiO2 coated ZnSe surface,and the effect of calcium cation strength and ultraviolet light irradiation on the secondary structure of trypsin were also evaluated.FTIR spectra of trypsin showed that Amide I band red shift and AmideⅡband blue shift in aqueous environment on both surfaces compared with the dry trypsin powder,and the addition of calcium cations further changed the Amide bands position,which indicated that the change of the secondary structure could be interfered by the environment.The hydrogen bond formation between water and trypsin,the interaction between surface and trypsin,the interaction between hydrated calcium cations and trypsin,are major facto rs to change the secondary structure of trypsin,and UV light irradiation also showed its influence for the secondary structure.