Study of the measurement for the diffusion coefficient by digital holographic interferometry

In the measurement of the diffusion coefficient by digital holographic interferometry, the conformity between the experiment and the ideal physical model is lacking analysis. Two data processing methods are put forward to overcome this problem. By these methods, it is found that there is obvious asymmetry in the experiment and the asymmetry is becoming smaller with time. Besides, the initial time for diffusion cannot be treated as a constant throughout the whole experiment. This means that there is a difference between the experiment and the physical model. With these methods, the diffusion coefficient of KCl in water at 0.33  mol/L and 25°C is measured. When the asymmetry is ignored, the result is 1.839×10(-9)  m2/s, which is in good agreement with the data in the literature. Because the asymmetry is becoming smaller with time, the experimental data in the latter time period conforms to the ideal physical model. With this idea, a more accurate diffusion coefficient is 2.003×10(-9)  m2/s, which is about 10% larger than the data in the literature.

Nanomechanical properties of human skin and introduction of a novel hair indenter

The mechanical resistance of the stratum corneum, the outermost layer of skin, to deformation has been evaluated at different length scales using Atomic Force Microscopy. Nanomechanical surface mapping was first conducted using a sharp silicon tip and revealed that Young׳s modulus of the stratum corneum varied over the surface with a mean value of about 0.4GPa. Force indentation measurements showed permanent deformation of the skin surface only at high applied loads (above 4µN). The latter effect was further demonstrated using nanomechanical imaging in which the obtained depth profiles clearly illustrate the effects of increased normal force on the elastic/plastic surface deformation. Force measurements utilizing the single hair fiber probe supported the nanoindentation results of the stratum corneum being highly elastic at the nanoscale, but revealed that the lateral scale of the deformation determines the effective elastic modulus.This result resolves the fact that the reported values in the literature vary greatly and will help to understand the biophysics of the interaction of razor cut hairs that curl back during growth and interact with the skin.

Static and dynamic fatigue behavior of topology designed and conventional 3D printed bioresorbable PCL cervical interbody fusion devices

Recently, as an alternative to metal spinal fusion cages, 3D printed bioresorbable materials have been explored; however, the static and fatigue properties of these novel cages are not well known. Unfortunately, current ASTM testing standards used to determine these properties were designed prior to the advent of bioresorbable materials for cages. Therefore, the applicability of these standards for bioresorbable materials is unknown. In this study, an image-based topology and a conventional 3D printed bioresorbable poly(ε)-caprolactone (PCL) cervical cage design were tested in compression, compression-shear, and torsion, to establish their static and fatigue properties. Difficulties were in fact identified in establishing failure criteria and in particular determining compressive failure load. Given these limitations, under static loads, both designs withstood loads of over 650 N in compression, 395 N in compression-shear, and 0.25 Nm in torsion, prior to yielding. Under dynamic testing, both designs withstood 5 million (5M) cycles of compression at 125% of their respective yield forces. Geometry significantly affected both the static and fatigue properties of the cages. The measured compressive yield loads fall within the reported physiological ranges; consequently, these PCL bioresorbable cages would likely require supplemental fixation. Most importantly, supplemental testing methods may be necessary beyond the current ASTM standards, to provide more accurate and reliable results, ultimately improving preclinical evaluation of these devices.

Quantification of the Contact Area at the Head-Stem Taper Interface of Modular Hip Prostheses

Corrosion of modular taper junctions of hip implants may be associated with clinical failure. Taper design parameters, as well as the intraoperatively applied assembly forces, have been proposed to affect corrosion. Fretting corrosion is related to relative interface shear motion and fluid ingress, which may vary with contact force and area. It was hypothesised in this study that assembly forces modify the extent and distribution of the surface contact area at the taper interface between a cobalt chrome head and titanium stem taper with a standard threaded surface profile. Local abrasion of a thin gold coating applied to the stem taper prior to assembly was used to determine the contact area after disassembly. Profilometry was then used to assess permanent deformation of the stem taper surface profile. With increasing assembly force (500 N, 2000 N, 4000 N and 8000 N) the number of stem taper surface profile ridges in contact with the head taper was found to increase (9.2±9.3%, 65.4±10.8%, 92.8±6.0% and 100%) and the overall taper area in contact was also found to increase (0.6±0.7%, 5.5±1.0%, 9.9±1.1% and 16.1±0.9%). Contact was inconsistently distributed over the length of the taper. An increase in plastic radial deformation of the surface ridges (-0.05±0.14 μm, 0.1±0.14 μm, 0.21±0.22 μm and 0.96±0.25 μm) was also observed with increasing assembly force. The limited contact of the taper surface ridges at lower assembly forces may influence corrosion rates, suggesting that the magnitude of the assembly force may affect clinical outcome. The method presented provides a simple and practical assessment of the contact area at the taper interface.

High pressure assessment of bilayered electrospun vascular grafts by means of an Electroforce Biodynamic System®

INTRODUCTION

Tissue engineering offers the possibility of developing a biological substitute material in vitro with the inherent properties required in vivo. However, the inadequate performance in vascular replacement of small diameter vascular grafts (VG) reduces considerably the current alternatives in this field. In this study, a bilayered tubular VG was produced, where its mechanical response was tested at high pressure ranges and compared to a native femoral artery.

MATERIALS AND METHOD

The VG was obtained using sequential electrospinning technique, by means of two blends of Poly(L-lactic acid) and segmented poly(ester urethane). Mechanical testing was performed in a biodynamic system and the pressure-strain relationship was used to determine the elastic modulus.

RESULTS

Elastic modulus assessed value of femoral artery at a high pressure range (33.02×106 dyn/cm(2)) was founded to be 36% the magnitude of VG modulus (91.47×106 dyn/cm(2)) at the same interval.

CONCLUSION

A new circulating mock in combination with scan laser micrometry have been employed for the mechanical evaluation of bioresorbable bilayered VGs. At same pressure levels, graft elasticity showed a purely "collagenic" behavior with respect to a femoral artery response.

Contractile cell forces deform macroscopic cantilevers and quantify biomaterial performance

Cells require adhesion to survive, proliferate and migrate, as well as for wound healing and many other functions. The strength of contractile cell forces on an underlying surface is a highly relevant quantity to measure the affinity of cells to a rigid surface with and without coating. Here we show with experimental and theoretical studies that these forces create surface stresses that are sufficient to induce measurable bending of macroscopic cantilevers. Since contractile forces are linked to the formation of focal contacts, results give information on adhesion promoting qualities and allow a comparison of very diverse materials. In exemplary studies, in vitro fibroblast adhesion on the magnetic shape memory alloy Fe-Pd and on the l-lysine derived plasma-functionalized polymer PPLL was determined. We show that cells on Fe-Pd are able to induce surface stresses three times as high as on pure titanium cantilevers. A further increase was observed for PPLL, where the contractile forces are four times higher than on the titanium reference. In addition, we performed finite element simulations on the beam bending to back up the calculation of contractile forces from cantilever bending under non-homogenous surface stress. Our findings consolidate the role of contractile forces as a meaningful measure of biomaterial performance.

Green chromatography determination of fatty acid methyl esters in biodiesel

This work proposes a green, simple and rapid chromatographic methodology for separation and determination of a group of 13 fatty acids methyl esters (FAMEs) by using a capillary gas chromatography with a flame ionization detector. The method was successfully applied for the determination of FAMEs in biodiesel samples from commercial and waste cooking oils, synthesized by homogeneous catalysis. Detection and quantification limits were in the μg L(-1) level. Direct injection of sample solution was compared with solid-phase extraction and solid-phase microextraction procedures, giving similar results. The lower analysis time represent considerable improvement compared with other papers. The described methodology is especially suitable for process control applications. The samples analysed showed total contents of FAMEs higher than 96.5%, which verifies the European regulations.

Internal three-dimensional strains in human intervertebral discs under axial compression quantified noninvasively by magnetic resonance imaging and image registration

Study objectives were to develop, validate, and apply a method to measure three-dimensional (3D) internal strains in intact human discs under axial compression. A custom-built loading device applied compression and permitted load-relaxation outside of the magnet while also maintaining compression and hydration during imaging. Strain was measured through registration of 300 μm isotropic resolution images. Excellent registration accuracy was achieved, with 94% and 65% overlap of disc volume and lamellae compared to manual segmentation, and an average Hausdorff, a measure of distance error, of 0.03 and 0.12 mm for disc volume and lamellae boundaries, respectively. Strain maps enabled qualitative visualization and quantitative regional annulus fibrosus (AF) strain analysis. Axial and circumferential strains were highest in the lateral AF and lowest in the anterior and posterior AF. Radial strains were lowest in the lateral AF, but highly variable. Overall, this study provided new methods that will be valuable in the design and evaluation surgical procedures and therapeutic interventions.

Circularly polarized near-field optical mapping of spin-resolved quantum Hall chiral edge states

We have successfully developed a circularly polarized near-field scanning optical microscope (NSOM) that enables us to irradiate circularly polarized light with spatial resolution below the diffraction limit. As a demonstration, we perform real-space mapping of the quantum Hall chiral edge states near the edge of a Hall-bar structure by injecting spin polarized electrons optically at low temperature. The obtained real-space mappings show that spin-polarized electrons are injected optically to the two-dimensional electron layer. Our general method to locally inject spins using a circularly polarized NSOM should be broadly applicable to characterize a variety of nanomaterials and nanostructures.

Fatigue performance of medical Ti6Al4V alloy after mechanical surface treatments

Mechanical surface treatments have a long history in traditional engineering disciplines, such as the automotive or aerospace industries. Today, they are widely applied to metal components to increase the mechanical performance of these. However, their application in the medical field is rather rare. The present study aims to compare the potential of relevant mechanical surface treatments on the high cycle fatigue (R = 0.1 for a maximum of 10 million cycles) performance of a Ti6Al4V standard alloy for orthopedic, spinal, dental and trauma surgical implants: shot peening, deep rolling, ultrasonic shot peening and laser shock peening. Hour-glass shaped Ti6Al4V specimens were treated and analyzed with regard to the material’s microstructure, microhardness, residual stress depth profiles and the mechanical behavior during fatigue testing. All treatments introduced substantial compressive residual stresses and exhibited considerable potential for increasing fatigue performance from 10% to 17.2% after laser shock peening compared to non-treated samples. It is assumed that final mechanical surface treatments may also increase fretting wear resistance in the modular connection of total hip and knee replacements.

Comparison of Hybrid-III and postmortem human surrogate response to simulated underbody blast loading

Response of the human body to high-rate vertical loading, such as military vehicle underbody blast (UBB), is not well understood because of the chaotic nature of such events. The purpose of this research was to compare the response of postmortem human surrogates (PMHS) and the Hybrid-III anthropomorphic test device (ATD) to simulated UBB loading ranging from 100 to 860 g seat and floor acceleration. Data from 13 whole body PMHS tests were used to create response corridors for vertical loading conditions for the pelvis, T1, head, femur, and tibia; these responses were compared to Hybrid-III responses under matched loading conditions.

Effect of potting technique on the measurement of six degree-of-freedom viscoelastic properties of human lumbar spine segments

Polymethyl methacrylate (PMMA) and Wood's Metal are fixation media for biomechanical testing; however, the effect of each potting medium on the measured six degree-of-freedom (DOF) mechanical properties of human lumbar intervertebral discs is unknown. The first aim of this study was to compare the measured 6DOF elastic and viscoelastic properties of the disc when embedded in PMMA compared to repotting in Wood's Metal. The second aim was to compare the surface temperature of the disc when potted with PMMA and Wood's Metal. Six human lumbar functional spinal units (FSUs) were first potted in PMMA, and subjected to overnight preload in a saline bath at 37 °C followed by five haversine loading cycles at 0.1 Hz in each of 6DOF loading directions (compression, left/right lateral bending, flexion, extension, left/right axial rotation, anterior/posterior, and lateral shear). Each specimen was then repotted in Wood's Metal and subjected to a 2-h re-equilibrating preload followed by repeating the same 6DOF tests. Outcome measures of stiffness and phase angle were calculated from the final loading cycle in each DOF and were expressed as normalized percentages relative to PMMA (100%). Disc surface temperatures (anterior, left/right lateral) were measured during potting. Paired t-tests (with alpha adjusted for multiple DOF) were conducted to compare the differences in each outcome parameter between PMMA and Wood's Metal. No significant differences in stiffness or phase angle were found between PMMA and Wood's Metal. On average, the largest trending differences were found in the shear DOFs for both stiffness (approximately 35% greater for Wood's Metal compared to PMMA) and phase angle (approximately 15% greater for Wood's Metal). A significant difference in disc temperature was found at the anterior surface after potting with Wood's Metal compared to PMMA, which did not exceed 26 °C. Wood's Metal is linear elastic, stiffer than PMMA and may reduce measurement artifact of potting medium, particularly in the shear directions. Furthermore, it is easier to remove than PMMA, reuseable, and cost effective.

Design of a pulsatile flow facility to evaluate thrombogenic potential of implantable cardiac devices

Due to expensive nature of clinical trials, implantable cardiac devices should first be extensively characterized in vitro. Prosthetic heart valves (PHVs), an important class of these devices, have been shown to be associated with thromboembolic complications. Although various in vitro systems have been designed to quantify blood-cell damage and platelet activation caused by nonphysiological hemodynamic shear stresses in these PHVs, very few systems attempt to characterize both blood damage and fluid dynamics aspects of PHVs in the same test system. Various numerical modeling methodologies are also evolving to simulate the structural mechanics, fluid mechanics, and blood damage aspects of these devices. This article presents a completely hemocompatible small-volume test-platform that can be used for thrombogenicity studies and experimental fluid mechanics characterization. Using a programmable piston pump to drive freshly drawn human blood inside a cylindrical column, the presented system can simulate various physiological and pathophysiological conditions in testing PHVs. The system includes a modular device-mounting chamber, and in this presented case, a 23 mm St. Jude Medical (SJM) Regents® mechanical heart valve (MHV) in aortic position was used as the test device. The system was validated for its capability to quantify blood damage by measuring blood damage induced by the tester itself (using freshly drawn whole human blood). Blood damage levels were ascertained through clinically relevant assays on human blood while fluid dynamics were characterized using time-resolved particle image velocimetry (PIV) using a blood-mimicking fluid. Blood damage induced by the tester itself, assessed through Thrombin-anti-Thrombin (TAT), Prothrombin factor 1.2 (PF1.2), and hemolysis (Drabkins assay), was within clinically accepted levels. The hydrodynamic performance of the tester showed consistent, repeatable physiological pressure and flow conditions. In addition, the system contains proximity sensors to accurately capture leaflet motion during the entire cardiac cycle. The PIV results showed skewing of the leakage jet, caused by the asymmetric closing of the two leaflets. All these results are critical to characterizing the blood damage and fluid dynamics characteristics of the SJM Regents® MHV, proving the utility of this tester as a precise system for assessing the hemodynamics and thrombogenicity for various PHVs.

Assessment of Carbon- and Metal-Based Nanoparticle DNA Damage with Microfluidic Electrophoretic Separation Technology

In this study, we examined the feasibility of extracting DNA from whole cell lysates exposed to nanoparticles using two different methodologies for evaluation of fragmentation with microfluidic electrophoretic separation. Human lung macrophages were exposed to five different carbon- and metal-based nanoparticles at two different time points (2 h, 24 h) and two different doses (5 µg/ml, 100 µg/ml). The primary difference in the banding patterns after 2 h of nanoparticle exposure is more DNA fragmentation at the higher NP concentration when examining cells exposed to nanoparticles of the same composition. However, higher doses of carbon and silver nanoparticles at both short and long dosing periods can contribute to erroneous or incomplete data with this technique. Also comparing DNA isolation methodologies, we recommend the centrifugation extraction technique, which provides more consistent banding patterns in the control samples compared to the spooling technique. Here we demonstrate that multi-walled carbon nanotubes, 15 nm silver nanoparticles and the positive control cadmium oxide cause similar DNA fragmentation at the short time point of 2 h with the centrifugation extraction technique. Therefore, the results of these studies contribute to elucidating the relationship between nanoparticle physicochemical properties and DNA fragmentation results while providing the pros and cons of altering the DNA isolation methodology. Overall, this technique provides a high throughput way to analyze subcellular alterations in DNA profiles of cells exposed to nanomaterials to aid in understanding the consequences of exposure and mechanistic effects. Future studies in microfluidic electrophoretic separation technologies should be investigated to determine the utility of protein or other assays applicable to cellular systems exposed to nanoparticles.

Microfluidic in situ mechanical testing of photopolymerized gels

Gels are a functional template for micro-particle fabrication and microbiology experiments. The control and knowledge of their mechanical properties is critical in a number of applications, but no simple in situ method exists to determine these properties. We propose a novel microfluidic based method that directly measures the mechanical properties of the gel upon its fabrication. We measure the deformation of a gel beam under a controlled flow forcing, which gives us a direct access to the Young's modulus of the material itself. We then use this method to determine the mechanical properties of poly(ethylene glycol) diacrylate (PEGDA) under various experimental conditions. The mechanical properties of the gel can be highly tuned, yielding two order of magnitude in the Young's modulus. The method can be easily implemented to allow for an in situ direct measurement and control of Young's moduli under various experimental conditions.

Recent developments in testing techniques for elastic mechanical properties of 1-D nanomaterials

One-dimensional (1-D) nanomaterials exhibit great potentials in their applications to functional materials, nano-devices and systems owing to their excellent properties. In the past decade, considerable studies have been done, with new patents being developed, on these 1-D building blocks for for their mechanical properties, especially elastic properties, which provide a solid foundation for the design of nanoelectromechanical systems (NEMS) and predictions of reliability and longevity for their devices. This paper reviews some of the recent investigations on techniques as well as patents available for the quantitative characterization of the elastic behaviors of various 1-D nanomaterials, with particular focus on on-chip testing system. The review begins with an overview of major testing methods for 1-D nanostructures' elastic properties, including nanoindentation testing, AFM (atomic force microscopy) testing, in situ SEM (scanning electron microscopy) testing, in situ TEM (transmission electron microscopy) testing and the testing system on the basis of MEMS (micro-electro-mechanical systems) technology, followed by advantages and challenges of each testing approach. This review also focuses on the MEMS-based testing apparatus, which can be actuated and measured inside SEM and TEM with ease, allowing users to highly magnify the continuous images of the specimen while measuring load electronically and independently. The combination of on-chip technologies and the in situ electron microscopy is expected to be a potential testing technique for nanomechanics. Finally, details are presented on the key challenges and possible solutions in the implementation of the testing techniques referred above.

An instrumented pendulum system for measuring energy absorption during fracture insult to large animal joints in vivo

For systematic laboratory studies of bone fractures in general and intra-articular fractures in particular, it is often necessary to control for injury severity. Quantitatively, a parameter of primary interest in that regard is the energy absorbed during the injury event. For this purpose, a novel technique has been developed to measure energy absorption in experimental impaction. The specific application is for fracture insult to porcine hock (tibiotalar) joints in vivo, for which illustrative intra-operative data are reported. The instrumentation allowed for the measurement of the delivered kinetic energy and of the energy passed through the specimen during impaction. The energy absorbed by the specimen was calculated as the difference between those two values. A foam specimen validation study was first performed to compare the energy absorption measurements from the pendulum instrumentation versus the work of indentation performed by an MTS machine. Following validation, the pendulum apparatus was used to measure the energy absorbed during intra-articular fractures created in 14 minipig hock joints in vivo. The foam validation study showed close correspondence between the pendulum-measured energy absorption and MTS-performed work of indentation. In the survival animal series, the energy delivered ranged from 31.5 to 48.3 Js (41.3±4.0, mean±s.d.) and the proportion of energy absorbed to energy delivered ranged from 44.2% to 64.7% (53.6%±4.5%). The foam validation results support the reliability of the energy absorption measure provided by the instrumented pendulum system. Given that a very substantial proportion of delivered energy passed--unabsorbed--through the specimens, the energy absorption measure provided by this novel technique arguably provides better characterization of injury severity than is provided simply by energy delivery.

Sample-averaged biexciton quantum yield measured by solution-phase photon correlation

The brightness of nanoscale optical materials such as semiconductor nanocrystals is currently limited in high excitation flux applications by inefficient multiexciton fluorescence. We have devised a solution-phase photon correlation measurement that can conveniently and reliably measure the average biexciton-to-exciton quantum yield ratio of an entire sample without user selection bias. This technique can be used to investigate the multiexciton recombination dynamics of a broad scope of synthetically underdeveloped materials, including those with low exciton quantum yields and poor fluorescence stability. Here, we have applied this method to measure weak biexciton fluorescence in samples of visible-emitting InP/ZnS and InAs/ZnS core/shell nanocrystals, and to demonstrate that a rapid CdS shell growth procedure can markedly increase the biexciton fluorescence of CdSe nanocrystals.

Simultaneous measurement of polymerization stress and curing kinetics for photo-polymerized composites with high filler contents

OBJECTIVES

Photopolymerized composites are used in a broad range of applications with their performance largely directed by reaction kinetics and contraction accompanying polymerization. The present study was to demonstrate an instrument capable of simultaneously collecting multiple kinetics parameters for a wide range of photopolymerizable systems: degree of conversion (DC), reaction exotherm, and polymerization stress (PS).

METHODS

Our system consisted of a cantilever beam-based instrument (tensometer) that has been optimized to capture a large range of stress generated by lightly-filled to highly-filled composites. The sample configuration allows the tensometer to be coupled to a fast near infrared (NIR) spectrometer collecting spectra in transmission mode.

RESULTS

Using our instrument design, simultaneous measurements of PS and DC are performed, for the first time, on a commercial composite with ≈80% (by mass) silica particle fillers. The in situ NIR spectrometer collects more than 10 spectra per second, allowing for thorough characterization of reaction kinetics. With increased instrument sensitivity coupled with the ability to collect real time reaction kinetics information, we show that the external constraint imposed by the cantilever beam during polymerization could affect the rate of cure and final degree of polymerization.

SIGNIFICANCE

The present simultaneous measurement technique is expected to provide new insights into kinetics and property relationships for photopolymerized composites with high filler content such as dental restorative composites.

From basic physics to mechanisms of toxicity: the "liquid drop" approach applied to develop predictive classification models for toxicity of metal oxide nanoparticles

Many metal oxide nanoparticles are able to cause persistent stress to live organisms, including humans, when discharged to the environment. To understand the mechanism of metal oxide nanoparticles' toxicity and reduce the number of experiments, the development of predictive toxicity models is important. In this study, performed on a series of nanoparticles, the comparative quantitative-structure activity relationship (nano-QSAR) analyses of their toxicity towards E. coli and HaCaT cells were established. A new approach for representation of nanoparticles' structure is presented. For description of the supramolecular structure of nanoparticles the "liquid drop" model was applied. It is expected that a novel, proposed approach could be of general use for predictions related to nanomaterials. In addition, in our study fragmental simplex descriptors and several ligand-metal binding characteristics were calculated. The developed nano-QSAR models were validated and reliably predict the toxicity of all studied metal oxide nanoparticles. Based on the comparative analysis of contributed properties in both models the LDM-based descriptors were revealed to have an almost similar level of contribution to toxicity in both cases, while other parameters (van der Waals interactions, electronegativity and metal-ligand binding characteristics) have unequal contribution levels. In addition, the models developed here suggest different mechanisms of nanotoxicity for these two types of cells.

Breathing simulator of workers for respirator performance test

Breathing machines are widely used to evaluate respirator performance but they are capable of generating only limited air flow patterns, such as, sine, triangular and square waves. In order to evaluate the respirator performance in practical use, it is desirable to test the respirator using the actual breathing patterns of wearers. However, it has been a difficult task for a breathing machine to generate such complicated flow patterns, since the human respiratory volume changes depending on the human activities and workload. In this study, we have developed an electromechanical breathing simulator and a respiration sampling device to record and reproduce worker's respiration. It is capable of generating various flow patterns by inputting breathing pattern signals recorded by a computer, as well as the fixed air flow patterns. The device is equipped with a self-control program to compensate the difference in inhalation and exhalation volume and the measurement errors on the breathing flow rate. The system was successfully applied to record the breathing patterns of workers engaging in welding and reproduced the breathing patterns.

In vivo high-content evaluation of three-dimensional scaffolds biocompatibility

While developing tissue engineering strategies, inflammatory response caused by biomaterials is an unavoidable aspect to be taken into consideration, as it may be an early limiting step of tissue regeneration approaches. We demonstrate the application of flat and flexible films exhibiting patterned high-contrast wettability regions as implantable platforms for the high-content in vivo study of inflammatory response caused by biomaterials. Screening biomaterials by using high-throughput platforms is a powerful method to detect hit spots with promising properties and to exclude uninteresting conditions for targeted applications. High-content analysis of biomaterials has been mostly restricted to in vitro tests where crucial information is lost, as in vivo environment is highly complex. Conventional biomaterials implantation requires the use of high numbers of animals, leading to ethical questions and costly experimentation. Inflammatory response of biomaterials has also been highly neglected in high-throughput studies. We designed an array of 36 combinations of biomaterials based on an initial library of four polysaccharides. Biomaterials were dispensed onto biomimetic superhydrophobic platforms with wettable regions and processed as freeze-dried three-dimensional scaffolds with a high control of the array configuration. These chips were afterward implanted subcutaneously in Wistar rats. Lymphocyte recruitment and activated macrophages were studied on-chip, by performing immunocytochemistry in the miniaturized biomaterials after 24 h and 7 days of implantation. Histological cuts of the surrounding tissue of the implants were also analyzed. Localized and independent inflammatory responses were detected. The integration of these data with control data proved that these chips are robust platforms for the rapid screening of early-stage in vivo biomaterials' response.

A low cycle fatigue test device for micro-cantilevers based on self-excited vibration principle

This paper reports a low-cycle fatigue test device for micro-cantilevers, which are widely used in micro scale structures. The working principle of the device is based on the phenomenon that a micro-cantilever can be set into self-excited vibration between two electrodes under DC voltage. Compared with previous devices, this simple device can produce large strain amplitude on non-notched specimens, and allows a batch of specimens to be tested simultaneously. Forty-two micro-cantilever specimens were tested and their fatigue fracture surfaces exhibit typical low cycle fatigue characteristics. As such, the device is very attractive for future fatigue investigation for micro scale structures.

Diffraction phase microscopy: monitoring nanoscale dynamics in materials science [invited]

Quantitative phase imaging (QPI) utilizes the fact that the phase of an imaging field is much more sensitive than its amplitude. As fields from the source interact with the specimen, local variations in the phase front are produced, which provide structural information about the sample and can be used to reconstruct its topography with nanometer accuracy. QPI techniques do not require staining or coating of the specimen and are therefore nondestructive. Diffraction phase microscopy (DPM) combines many of the best attributes of current QPI methods; its compact configuration uses a common-path off-axis geometry which realizes the benefits of both low noise and single-shot imaging. This unique collection of features enables the DPM system to monitor, at the nanoscale, a wide variety of phenomena in their natural environments. Over the past decade, QPI techniques have become ubiquitous in biological studies and a recent effort has been made to extend QPI to materials science applications. We briefly review several recent studies which include real-time monitoring of wet etching, photochemical etching, surface wetting and evaporation, dissolution of biodegradable electronic materials, and the expansion and deformation of thin-films. We also discuss recent advances in semiconductor wafer defect detection using QPI.

Determination of thin hydrodynamic lubricating film thickness using dichromatic interferometry

This paper introduces the application of dichromatic interferometry for the study of hydrodynamic lubrication. In conventional methods, two beams with different colors are projected consecutively on a static object. By contrast, the current method deals with hydrodynamic lubricated contacts under running conditions and two lasers with different colors are projected simultaneously to form interference images. Dichromatic interferometry incorporates the advantages of monochromatic and chromatic interferometry, which are widely used in lubrication research. This new approach was evaluated statically and dynamically by measuring the inclination of static wedge films and the thickness of the hydrodynamic lubricating film under running conditions, respectively. Results show that dichromatic interferometry can facilitate real-time determination of lubricating film thickness and is well suited for the study of transient or dynamic lubricating problems.