Room-Temperature Fabrication of p-Type SnO Semiconductors Using Ion-Beam-Assisted Deposition.

Over the past decade, SnO has been considered a promising p-type oxide semiconductor. However, achieving high mobility in the fabrication of p-type SnO films is still highly dependent on the post-annealing procedure, which is often used to make SnO, due to its metastable nature, readily convertible to SnO2 and/or intermediate phases. This paper demonstrates a fully room-temperature fabrication of p-type SnOx thin films using ion-beam-assisted deposition. This technique offers independent control between ion density, via the ion-gun anode current and oxygen flow rate, and ion energy, via the ion-gun anode voltage, thus being able to optimize the optical band gap and the hole mobility of the SnO films to reach 2.70 eV and 7.89 cm2 V-1 s-1, respectively, without the need for annealing. Remarkably, this is the highest mobility reported for p-type SnO films whose fabrication was carried out entirely at room temperature. Using first-principles calculations, we rationalize that the high mobility is associated with the fine-tuning of the Sn-rich-related defects and lattice densification, obtained by controlling the density and energy of the oxygen ions, both of which optimize the spatial overlap of the valence bands to form a continuous conduction path for the holes. Moreover, due to the absence of the annealing process, the Raman spectra reveal no significant signatures of microcrystal formation in the films. This behavior contrasts with the case involving the air-annealing procedure, where a complex interaction occurs between the formation of SnO microcrystals and the formation of SnOx intermediate phases. This interplay results in variations in grain texture within the film, leading to a lower optimum Hall mobility of only 5.17 cm2 V-1 s-1. Finally, we demonstrate the rectification characteristics of all-fabricated-at-room-temperature SnOx-based p-n devices to confirm the viability of the p-type SnOx films.

Enhanced Plasmonic Biosensor Utilizing Paired Antibody and Label-Free Fe3O4 Nanoparticles for Highly Sensitive and Selective Detection of Parkinson's α-Synuclein in Serum.

Parkinson's disease (PD) is an acute and progressive neurodegenerative disorder, and diagnosis of the disease at its earliest stage is of paramount importance to improve the life expectancy of patients. α-Synuclein (α-syn) is a potential biomarker for the early diagnosis of PD, and there is a great need to develop a biosensing platform that precisely detects α-syn in human body fluids. Herein, we developed a surface plasmon resonance (SPR) biosensor based on the label-free iron oxide nanoparticles (Fe3O4 NPs) and paired antibody for the highly sensitive and selective detection of α-syn in serum samples. The sensitivity of the SPR platform is enhanced significantly by directly depositing Fe3O4 NPs on the Au surface at a high density to increase the decay length of the evanescent field on the Au film. Moreover, the utilization of rabbit-type monoclonal antibody (α-syn-RmAb) immobilized on Au films allows the SPR platform to have a high affinity-selectivity binding performance compared to mouse-type monoclonal antibodies as a common bioreceptor for capturing α-syn molecules. As a result, the current platform has a detection limit of 5.6 fg/mL, which is 20,000-fold lower than that of commercial ELISA. The improved sensor chip can also be easily regenerated to repeat the α-syn measurement with the same sensitivity. Furthermore, the SPR sensor was applied to the direct analysis of α-syn in serum samples. By using a format of paired α-syn-RmAb, the SPR sensor provides a recovery rate in the range from 94.5% to 104.3% to detect the α-syn in diluted serum samples precisely. This work demonstrates a highly sensitive and selective quantification approach to detect α-syn in human biofluids and paves the way for the future development in the early diagnosis of PD.

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. The model is further extended to include a rough surface. Capillary adhesion force is shown to be monotonically increasing with RH for smooth surfaces but becomes more pronounced at low RH for rough surfaces. Moisture has a profound influence on interparticle adhesion, which has significant impacts on a wide range of industrial applications.

Soft Polymer-Based Technique for Cellular Force Sensing.

Soft polymers have emerged as a vital type of material adopted in biomedical engineering to perform various biomechanical characterisations such as sensing cellular forces. Distinct advantages of these materials used in cellular force sensing include maintaining normal functions of cells, resembling in vivo mechanical characteristics, and adapting to the customised functionality demanded in individual applications. A wide range of techniques has been developed with various designs and fabrication processes for the desired soft polymeric structures, as well as measurement methodologies in sensing cellular forces. This review highlights the merits and demerits of these soft polymer-based techniques for measuring cellular contraction force with emphasis on their quantitativeness and cell-friendliness. Moreover, how the viscoelastic properties of soft polymers influence the force measurement is addressed. More importantly, the future trends and advancements of soft polymer-based techniques, such as new designs and fabrication processes for cellular force sensing, are also addressed in this review.

Ageing modulates human dermal fibroblast contractility: Quantification using nano-biomechanical testing.

Dermal fibroblasts play a key role in maintaining homoeostasis and functionality of the skin. Their contractility plays a role in changes observed during ageing, especially in processes such as wound healing, inflammation, wrinkling and scar tissue formation as well as structural changes on extracellular matrix. Although alternations in skin physiology and morphology have been previously described, there remains a paucity of information about the influence of chronological ageing on dermal fibroblast contractility. In this study, we applied a novel nano-biomechanical technique on cell-embedded collagen hydrogels in combination with mathematical modelling and numerical simulation to measure contraction forces of normal human dermal fibroblasts (NHDF). We achieved quantitative differentiation of the contractility of cells derived from 'young' (< 30 years old) and 'aged' (> 60 years old) donors. Transforming growth factor ß1 (TGF-ß1) was used to stimulate the fibroblasts to assess their contractile potential. NHDF from aged donors exhibited a greater basal contractile force, while in contrast, NHDF from young donors have shown a significantly larger contractile force in response to TGF-ß1 treatment. These findings validate our nano-biomechanical measurement technique and provide new insights for considering NHDF contractility in regenerative medicine and as a biomarker of dermal ageing processes.

Vascular Adhesion Protein-1 Determines the Cellular Properties of Endometrial Pericytes.

Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible adhesion molecule and a primary amine oxidase involved in immune cell trafficking. Leukocyte extravasation into tissues is mediated by adhesion molecules expressed on endothelial cells and pericytes. Pericytes play a major role in the angiogenesis and vascularization of cycling endometrium. However, the functional properties of pericytes in the human endometrium are not known. Here we show that pericytes surrounding the spiral arterioles in midluteal human endometrium constitutively express VAP-1. We first characterize these pericytes and demonstrate that knockdown of VAP-1 perturbed their biophysical properties and compromised their contractile, migratory, adhesive and clonogenic capacities. Furthermore, we show that loss of VAP-1 disrupts pericyte-uterine natural killer cell interactions in vitro. Taken together, the data not only reveal that endometrial pericytes represent a cell population with distinct biophysical and functional properties but also suggest a pivotal role for VAP-1 in regulating the recruitment of innate immune cells in human endometrium. We posit that VAP-1 could serve as a potential biomarker for pregnancy pathologies caused by a compromised perivascular environment prior to conception.

Examining Cell-Cell Interactions in the Kidney Using AFM Single-Cell Force Spectroscopy.

The ability of individual cells to synchronize activity is a basic feature of efficient and appropriate tissue function. Central to this is the physicochemical binding between cells through multiprotein complexes that functionally mediate adhesion. Importantly, the direct connection of physical properties and intercellular signaling is of great importance to certain pathologies including diabetes. Atomic force microscopy (AFM) single-cell force spectroscopy (SCFS) is a high-resolution technique that provides a statistically reliable measurement of the minute forces involved in cell tethering and membrane dynamics. Detection of altered nanoscale forces underlying the loss of adhesion in early tubular injury is pivotal for the development of novel therapeutic strategies for diabetic nephropathy. Here we describe the step-by-step use of an integrated AFM-SCFS system designed to measure functional force-displacement in separating renal tubular epithelial cells. Parameters such as unbinding forces, detachment energy, and distance to complete separation can be obtained from force-displacement (F-d) curves and are critical in assessing how physical changes of cellular adhesion contribute to cell contact, coupling, and communication in the diabetic kidney.

Quantifying cellular mechanics and adhesion in renal tubular injury using single cell force spectroscopy.

Tubulointerstitial fibrosis represents the major underlying pathology of diabetic nephropathy where loss of cell-to-cell adhesion is a critical step. To date, research has predominantly focussed on the loss of cell surface molecular binding events that include altered protein ligation. In the current study, atomic force microscopy single cell force spectroscopy (AFM-SCFS) was used to quantify changes in cellular stiffness and cell adhesion in TGF-ß1 treated kidney cells of the human proximal tubule (HK2). AFM indentation of TGF-ß1 treated HK2 cells showed a significant increase (42%) in the elastic modulus (stiffness) compared to control. Fluorescence microscopy confirmed that increased cell stiffness is accompanied by reorganization of the cytoskeleton. The corresponding changes in stiffness, due to F-actin rearrangement, affected the work of detachment by changing the separation distance between two adherent cells. Overall, our novel data quantitatively demonstrate a correlation between cellular elasticity, adhesion and early morphologic/phenotypic changes associated with tubular injury. FROM THE CLINICAL EDITOR: Diabetes affects many patients worldwide. One of the long term problems is diabetic nephropathy. Here, the authors utilized atomic force microscopy single cell force spectroscopy (AFM- SCFS) to study cellular stiffness and cell adhesion after TGF1 treatment in human proximal tubule kidney cells. The findings would help further understand the overall disease mechanism in diabetic patients.

Cell mechanics in biomedical cavitation.

Studies on the deformation behaviours of cellular entities, such as coated microbubbles and liposomes subject to a cavitation flow, become increasingly important for the advancement of ultrasonic imaging and drug delivery. Numerical simulations for bubble dynamics of ultrasound contrast agents based on the boundary integral method are presented in this work. The effects of the encapsulating shell are estimated by adapting Hoff's model used for thin-shell contrast agents. The viscosity effects are estimated by including the normal viscous stress in the boundary condition. In parallel, mechanical models of cell membranes and liposomes as well as state-of-the-art techniques for quantitative measurement of viscoelasticity for a single cell or coated microbubbles are reviewed. The future developments regarding modelling and measurement of the material properties of the cellular entities for cutting-edge biomedical applications are also discussed.

A novel collagen gel-based measurement technique for quantitation of cell contraction force.

Cell contraction force plays an important role in wound healing, inflammation,angiogenesis and metastasis. This study describes a novel method to quantify single cell contraction force in vitro using human aortic adventitial fibroblasts embedded in a collagen gel. The technique is based on a depth sensing nano-indentation tester to measure the thickness and elasticity of collagen gels containing stimulated fibroblasts and a microscopy imaging system to estimate the gel area. In parallel, a simple theoretical model has been developed to calculate cell contraction force based on the measured parameters. Histamine (100 mM) was used to stimulate fibroblast contraction while the myosin light chain kinase inhibitor ML-7 (25 mM) was used to inhibit cell contraction. The collagen matrix used in the model provides a physiological environment for fibroblast contraction studies. Measurement of changes in collagen gel elasticity and thickness arising from histamine treatments provides a novel convenient technique to measure cell contraction force within a collagen matrix. This study demonstrates that histamine can elicit a significant increase in contraction force of fibroblasts embedded in collagen,while the Young's modulus of the gel decreases due to the gel degradation.

Quantitative investigation of calcimimetic R568 on beta cell adhesion and mechanics using AFM single-cell force spectroscopy.

In this study we use a novel approach to quantitatively investigate mechanical and interfacial properties of clonal ß-cells using AFM-Single Cell Force Spectroscopy (SCFS). MIN6 cells were incubated for 48 h with 0.5 mM Ca(2+) ± the calcimimetic R568 (1 µM). AFM-SCFS adhesion and indentation experiments were performed by using modified tipless cantilevers. Hertz contact model was applied to analyse force-displacement (F-d) curves for determining elastic or Young's modulus (E). Our results show CaSR-evoked increases in cell-to-cell adhesion parameters and E modulus of single cells, demonstrating that cytomechanics have profound effects on cell adhesion characterization.

Calcium-sensing receptor activation increases cell-cell adhesion and ß-cell function.

BACKGROUND/AIMS: The extracellular calcium-sensing receptor (CaR) is expressed in pancreatic ß-cells where it is thought to facilitate cell-to-cell communication and augment insulin secretion. However, it is unknown how CaR activation improves ß-cell function. METHODS: Immunocytochemistry and western blotting confirmed the expression of CaR in MIN6 ß-cell line. The calcimimetic R568 (1µM) was used to increase the affinity of the CaR and specifically activate the receptor at a physiologically appropriate extracellular calcium concentration. Incorporation of 5-bromo-2'-deoxyuridine (BrdU) was used to measure cell proliferation, whilst changes in non-nutrient-evoked cytosolic calcium were assessed using fura-2-microfluorimetry. AFM-single-cell-force spectroscopy related CaR-evoked changes in epithelial (E)-cadherin expression to improved functional tethering between coupled cells. RESULTS: Activation of the CaR over 48hr doubled the expression of E-cadherin (206±41%) and increased L-type voltage-dependent calcium channel expression by 70% compared to control. These changes produced a 30% increase in cell-cell tethering and elevated the basal-to-peak amplitude of ATP (50µM) and tolbutamide (100µM)-evoked changes in cytosolic calcium. Activation of the receptor also increased PD98059 (1-100µM) and SU1498 (1-100µM)-dependent ß-cell proliferation. CONCLUSION: Our data suggest that activation of the CaR increases E-cadherin mediated functional tethering between ß-cells and increases expression of L-type VDCC and secretagogue-evoked changes in [Ca(2+)](i). These findings could explain how local changes in calcium, co-released with insulin, activate the CaR on neighbouring cells to help ensure efficient and appropriate secretory function.

Gene expression of single human mesenchymal stem cell in response to fluid shear.

Stem cell therapy may rely on delivery and homing through the vascular system to reach the target tissue. An optical tweezer model has been employed to exert different levels of shear stress on a single non-adherent human bone marrow-derived mesenchymal stem cell to simulate physiological flow conditions. A single-cell quantitative polymerase chain reaction analysis showed that collagen type 1, alpha 2 (COL1A2), heat shock 70-kDa protein 1A (HSPA1A) and osteopontin (OPN) are expressed to a detectable level in most of the cells. After exposure to varying levels of shear stress, there were significant variations in gene transcription levels across human mesenchymal stem cells derived from four individual donors. Significant trend towards upregulation of COL1A2 and OPN gene expression following shear was observed in some donors with corresponding variations in HSPA1A gene expression. The results indicate that shear stress associated with vascular flow may have the potential to significantly direct non-adherent stem cell expression towards osteogenic phenotypic expression. However, our results demonstrate that these results are influenced by the selection process and donor variability.

Biomimetic three-dimensional microenvironment for controlling stem cell fate.

Stem cell therapy is an emerging technique which is being translated into treatment of degenerated tissues. However, the success of translation relies on the stem cell lineage commitment in the degenerated regions of interest. This commitment is precisely controlled by the stem cell microenvironment. Engineering a biomimetic three-dimensional microenvironment enables a thorough understanding of the mechanisms of governing stem cell fate. We review the individual microenvironment components, including soluble factors, extracellular matrix, cell-cell interaction and mechanical stimulation. The perspectives in creating the biomimetic microenvironments are discussed with emerging techniques.

Influence of cell and collagen concentration on the cell-matrix mechanical relationship in a corneal stroma wound healing model.

The effect of different collagen and cell concentrations on the mechanical and remodeling behaviors of corneal stroma wound healing models consisting of collagen hydrogels seeded with human corneal fibroblasts during a 25 day culture period were examined. Human corneal fibroblasts were seeded at 1 × 10(5), 3 × 10(5) or 5 × 10(5) cells per hydrogel, and collagen concentrations of 2.5 mg/ml, 3.5 mg/ml or 4.5 mg/ml were examined. Two non-destructive techniques, spherical indentation and optical coherence tomography, were used to measure the elastic modulus and dimensional changes respectively at several time-points over the culture period. The elastic modulus of the hydrogels increased continuously over 25 days. Hydrogels with higher initial cell seeding densities and lower initial collagen concentrations were found to increase in elastic modulus faster and possessed a higher elastic modulus by the end of the culture period when compared to the other hydrogels. A mathematical equation was applied to accurately fit the change in elastic modulus over time. This study demonstrates a robust in vitro technique able to monitor the effect of different parameters on the cell-matrix mechanical relationship in a corneal stroma model during prolonged culture periods and enhances our understanding on corneal wound healing processes.

Microfluidic systems for biosensing.

In the past two decades, Micro Fluidic Systems (MFS) have emerged as a powerful tool for biosensing, particularly in enriching and purifying molecules and cells in biological samples. Compared with conventional sensing techniques, distinctive advantages of using MFS for biomedicine include ultra-high sensitivity, higher throughput, in-situ monitoring and lower cost. This review aims to summarize the recent advancements in two major types of micro fluidic systems, continuous and discrete MFS, as well as their biomedical applications. The state-of-the-art of active and passive mechanisms of fluid manipulation for mixing, separation, purification and concentration will also be elaborated. Future trends of using MFS in detection at molecular or cellular level, especially in stem cell therapy, tissue engineering and regenerative medicine, are also prospected.

Online monitoring of the mechanical behavior of collagen hydrogels: influence of corneal fibroblasts on elastic modulus.

Collagen hydrogels have been widely used to model biological systems and examine cell behavior in vitro. Of increasing interest is how cells affect the mechanical characteristics of their surrounding matrix and vice versa over long culture periods. In this study, the change in mechanical properties of collagen hydrogels embedded with human corneal fibroblasts was examined over a 6-week culture period using a novel online spherical indentation system. The elastic modulus of the hydrogels was found to increase during the first 2 weeks of culture and decrease after 4 weeks in culture. The effects of actin polymerization and matrix metalloproteinase inhibitors were also examined, which verified some mechanisms involved in the alteration of the mechanical properties such as cell tensile forces and other potential factors. This online monitoring technique demonstrates the ability to examine the mechanical properties of cell-seeded constructs in response to the culture environments--in particular, the response to the addition of drugs or chemical reagents--which will provide a useful tool in studying the mechano-feedback loop between cells and their surrounding matrix.

An optical-manipulation technique for cells in physiological flows.

We have developed a technique to manipulate human red blood cells (RBCs) in hydrodynamic flows. This method applies optical tweezers to trap and move microbead-attached RBCs in a liquid medium at various speeds, while it significantly minimizes laser heating and photon-induced stress for normal operation with laser-trapped cells. Computational fluid dynamics is applied to simulate flow-induced shear stress over the cell membrane and to correlate quantitatively the forces with the cell deformations. RBCs can be manipulated under physiological conditions by this approach, which may open an avenue to design principles for the next generation of cell sorting and delivery.

Mechanical characterization of biomimetic membranes by micro-shaft poking.

The popularity of biomimetic membranes has recently increased due to their biomedical applications such as tissue engineering/regenerative medicine and biosensors. Characterization of the viscoelastic properties of these membranes is important in developing functional membranes. A new micro-shaft poking technique has been developed, which is free from the complication of substrate backing, and which is normally an intractable problem in conventional indentation testing of membrane materials. A tailored indentation apparatus with a spherical indenter and a force resolution and displacement of 1 microN and 1 mum was constructed. Alginate and agarose were used to fabricate biomimetic membranes. Chicken epidermis was examined to represent a real biological tissue. The results show that the elastic modulus increased with concentration in hydrogels. Epidermis moduli appeared to increase with increased strain. Stress relaxation tests have also been conducted to examine the time-dependent behaviours of various hydrogels and a viscoelastic model has been correspondingly developed and applied to describe the experimental results. Potential applications of this new instrument to other membranes, both artificial and biological, have also been addressed.

Optical tweezers for single cells.

Optical tweezers (OT) have emerged as an essential tool for manipulating single biological cells and performing sophisticated biophysical/biomechanical characterizations. Distinct advantages of using tweezers for these characterizations include non-contact force for cell manipulation, force resolution as accurate as 100aN and amiability to liquid medium environments. Their wide range of applications, such as transporting foreign materials into single cells, delivering cells to specific locations and sorting cells in microfluidic systems, are reviewed in this article. Recent developments of OT for nanomechanical characterization of various biological cells are discussed in terms of both their theoretical and experimental advancements. The future trends of employing OT in single cells, especially in stem cell delivery, tissue engineering and regenerative medicine, are prospected. More importantly, current limitations and future challenges of OT for these new paradigms are also highlighted in this review.