Probing the Nanomechanical Behavior of Cells and Cell Nuclei

Atomic force microscopy (AFM) is a nanoscale characterization technique that at its most basic level employs a nanometer-scale probe tip to physically trace a surface, generating a topographical map of the sample. However AFM has many applications beyond topography, including nanomechanical property analysis via cantilevered nanoindentation. In this project, tipless AFM probes functionalized with a 10 µm diameter glass bead have been used to measure the elastic modulus of live multipotent stromal stem cell nuclei before and after vibration treatments and/or structural component knockouts. The goal of these nanoindentation measurements of nuclear stiffness is to gain a better understanding of how mesenchymal stem cells respond to mechanical (in addition to chemical) signals in their environment to guide differentiation into osteoblasts, chondrocytes, or other cell types

Advanced Atomic Force Microscopy for BioMaterials Research

Optical microscopy uses the interactions between light and materials to provide images of the microscopic world. It is widely employed in science to study the behavior and properties of microscopic organisms and cells. Atomic force microscopy (AFM) is a technique for obtaining images of the surfaces of materials at the atomic to micrometer scales. AFM operates by rastering an ultra-sharp needle across a sample surface and recording the height of the needle at each position. While AFM can provide atomic resolution images of the contours (topography) of a surface, it can also perform extremely sensitive measurements of surface mechanical properties. By fabricating custom AFM probes, the mechanical properties of specific locations of living cells can be studied and manipulated. In addition, high-speed imaging of biological materials can provide images of changes to cellular surfaces in response to chemical or electrical signals. This poster will present examples and applications of advanced AFM capabilities for research in biomaterials available in the Boise State University Surface Science Laboratory

TiO2 Coatings Formed by Atomic Layer Deposition for Enhanced Corrosion Performance of Mg-biomaterials

Magnesium (Mg) alloys have experienced increased attention in the area of biomaterials due to Mg being considered a resorbable biomaterial. Mg alloy implants can potentially be designed to degrade in the body, thus an implant would not remain in the body for longer than is needed to perform its task. Mg and many of its alloys are considered to be biocompatible and non-toxic in the body; however, due to the high rate at which Mg degrades a negative host response is expected. A novel approach to inhibit corrosion rate using thin film coatings on a Mg alloy (AZ31B) via atomic layer deposition (ALD) is proposed. ALD is based on saturated surface reactions on the substrate unlike other thin film deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD). Sequentially-performed surface reactions between the substrate and precursor molecules water and titanium tetrachloride (H2O , TiCl4) result in thin film growth of amorphous titanium dioxide (TiO2). TiO2 is grown in an atomic layer-by-layer fashion during ALD allowing sub-nanometer thickness control of growth, with excellent coating uniformity and step coverage. TiO2 coatings and their impact on the corrosion resistance of AZ31B were characterized using atomic force microscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and linear polarization measurements

Electropolishing Valve Metals with a Sulfuric Acid-Methanol Electrolyte at Low Temperature

This study reports the electropolishing Ti and Nb metals using a fluoride-free electrolyte of sulfuric acid and methanol at low temperature (-70°C) without prior treatment. A fluoride-free electrolyte provides a less hazardous and more environmentally friendly option for electropolishing procedure. Experimental studies are presented on electropolishing with sulfuric acid electrolyte, which provides high quality macro- and micro-smoothing of the metal surfaces. Optimal conditions yielded leveling and brightening of the surface of Ti and Nb metals beyond that of the currently utilized electropolishing procedures with fluoride-containing electrolytes. The root mean squared roughness (Rq) from atomic force microscopy (AFM) analysis was 1.64 and 0.49 nm for Ti and Nb, respectively. Lower temperature experiments led to noticeable kinetic effects, indicated by a dramatic drop in current densities and the expansion of the steady-state current density plateau in anodic polarization curves. In addition, the voltage range of the current plateau expanded with increasing acid concentration. Surface characterization of Ti and Nb metals after polishing provided evidence of salt film formation. In addition, these metals were used as substrates in the formation of nanostructured metal oxides. The overall quality of the polishing led to a dramatic improvement in the uniformity of the nanostructures

Nuclear Response to Low Intensity Vibrations

The nucleus, central to all cellular activity, relies on both direct mechanical input as well as its molecular transducers to sense external stimuli and respond by regulating intra-nuclear organization that ultimately determines gene expression to control cell function and fate. It is long studied that signals propagate from extracellular environment to cytoskeleton and into the nucleus (outside-in signaling) to regulate cell behavior. Emerging evidence, however, has shown that both the cytoskeleton and nucleus have an inherent ability to sense and adapt to mechanical force independent of each other. This suggests mechano-signaling and cytoskeleton remodeling events in response to exercise mimetics, like low intensity vibration (LIV), may directly be sensed at the nucleus (inside-out signaling). Here we hypothesize that cell nuclei will directly adapt to dynamic accelerations in response to LIV. To answer this question directly, we isolated live nuclei from cells to test their mechanical responses to LIV. Isolated nuclei are introduced to a low intensity vibration (LIV, 0.7g, 90Hz) and their stiffness’ measured via AFM (Atomic force microscope) protocol. Findings from this study will allow evaluation of the mechanical role that the nucleus plays in the cell as an individual organelle

Developing Nucleus Specific Finite Element Models Using Confocal Microscopy Scans

Emerging evidence suggests that nucleus have an inherent ability to adapt to mechanical force. Current approaches, however, are unable to quantify native forces generated in on cell nuclei without inserting sensors that affect cell function. Our goal in this research therefore is to use Finite Element Modeling in combination with confocal microscopy to generate mechanical models of nuclei. To build nuclear Finite element models chromatin of mesenchymal stem cell nuclei were imaged with a Zeiss 810 confocal microscope at 120nm planar resolution at every 360nm. These images were developed into hexahedral based models. To calibrate the model, isolated live cell nuclei stiffness were deduced using an Atomic force microscope (AFM). Establishing this process will enable the creation of nucleus specific models that allow further research into how the mechanical stiffness of a nucleus is regulated

High-Performance Flexible Bismuth Telluride Thin Film from Solution Processed Colloidal Nanoplates

Thermoelectric generators are an environmentally friendly and reliable solid‐state energy conversion technology. Flexible and low‐cost thermoelectric generators are especially suited to power flexible electronics and sensors using body heat or other ambient heat sources. Bismuth telluride (Bi2Te3) based thermoelectric materials exhibit their best performance near room temperature making them an ideal candidate to power wearable electronics and sensors using body heat. In this report, Bi2Te3 thin films are deposited on a flexible polyimide substrate using low‐cost and scalable manufacturing methods. The synthesized Bi2Te3 nanocrystals have a thickness of 35 ± 15 nm and a lateral dimension of 692 ± 186 nm. Thin films fabricated from these nanocrystals exhibit a peak power factor of 0.35 mW m−1·K−2 at 433 K, which is among the highest reported values for flexible thermoelectric films. In order to evaluate the flexibility of the thin films, static and dynamic bending tests are performed while monitoring the change in electrical resistivity. After 1000 bending cycles over a 50 mm radius of curvature, the change in electrical resistance of the film is 23%. Using Bi2Te3 solutions, the ability to print thermoelectric thin films with an aerosol jet printer is demonstrated, highlighting the potential of additive manufacturing techniques for fabricating flexible thermoelectric generators

Thin‐Film Ferroelectrics

Over the last 30 years, the study of ferroelectric oxides has been revolutionized by the implementation of epitaxial-thin-film-based studies, which have driven many advances in the understanding of ferroelectric physics and the realization of novel polar structures and functionalities. New questions have motivated the development of advanced synthesis, characterization, and simulations of epitaxial thin films and, in turn, have provided new insights and applications across the micro-, meso-, and macroscopic length scales. This review traces the evolution of ferroelectric thin-film research through the early days developing understanding of the roles of size and strain on ferroelectrics to the present day, where such understanding is used to create complex hierarchical domain structures, novel polar topologies, and controlled chemical and defect profiles. The extension of epitaxial techniques, coupled with advances in high-throughput simulations, now stands to accelerate the discovery and study of new ferroelectric materials. Coming hand-in-hand with these new materials is new understanding and control of ferroelectric functionalities. Today, researchers are actively working to apply these lessons in a number of applications, including novel memory and logic architectures, as well as a host of energy conversion devices

Electropolishing Valve Metals with Sulfuric Acid-Methanol Electrolyte

To develop uniform oxide nano-structures on the surface of valve metals, via anodization, it is desirable to start with a polished surface. Electropolishing is a common method to produce highly polished surfaces. However, common procedures utilize toxic, fluoride containing electrolytes. This study reports on a novel method for electropolishing titanium and niobium, in a sulfuric acid/methanol electrolyte, at low temperature (-70 oC). Electropolishing at low temperature has a significant effect on reaction kinetics. Experiments show an expansion of the steady-state current density plateau of anodic polarization curves. Additionally, increasing the sulfuric acid concentration led to broadening of the current density plateau. Optimization of conditions produced a root mean squared roughness of 1.64 nm and 0.49 nm for titanium and niobium, respectively. An improvement over results obtained with fluorine-containing electrolytes. We believe it is possible to apply this method to other valve metals, like zirconium and tantalum. Preliminary experiments with zirconium have shown a brightening and smoothing of the surface. However, there is further work required to optimize results with this metal. Additionally, we show that polished valve metal surfaces produce more uniform nano-structures, formed via anodization

Isolated nuclei stiffen in response to low intensity vibration

The nucleus, central to all cellular activity, relies on both direct mechanical input and its molecular transducers to sense and respond to external stimuli. While it has been shown that isolated nuclei can adapt to applied force ex vivo, the mechanisms governing nuclear mechanoadaptation in response to physiologic forces in vivo remain unclear. To investigate nuclear mechanoadaptation in cells, we developed an atomic force microscopy (AFM) based procedure to probe live nuclei isolated from mesenchymal stem cells (MSCs) following the application of low intensity vibration (LIV) to determine whether nuclear stiffness increases as a result of LIV. Results indicated that isolated nuclei were, on average, 30% softer than nuclei tested within intact MSCs prior to LIV. When the nucleus was isolated following LIV (0.7 g, 90 Hz, 20 min) applied four times (4×) separated by 1 h intervals, stiffness of isolated nuclei increased 75% compared to non-LIV controls. LIV-induced nuclear stiffening required functional Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, but was not accompanied by increased levels of the nuclear envelope proteins LaminA/C or Sun-2. While depleting LaminA/C or Sun-1&2 resulted in either a 47% or 39% increased heterochromatin to nuclear area ratio in isolated nuclei, the heterochromatin to nuclear area ratio was decreased by 25% in LIV-treated nuclei compared to controls, indicating LIV-induced changes in the heterochromatin structure. Overall, our findings indicate that increased apparent cell stiffness in response to exogenous mechanical challenge of MSCs in the form of LIV is in part retained by increased nuclear stiffness and changes in heterochromatin structure