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Micro- and multiscale material properties must be considered when manufacturing miniature devices, especially when considering utilizing multiscale sheet metal hydroforming processes. One of the critical considerations during the design process is the burst pressure for the sheet metal which is a limiting factor for potential hydroforming operations. In order to simplify determining tearing or rupture conditions, it is sometimes desired to use analytical methods for estimating material properties, including burst pressures, which occur shortly after material instability. Many researchers have developed approximate methods for predicting deformation during open die hydroforming based upon analytical approaches for biaxial conditions for circular and elliptical dies. Additionally, extracting material properties of sheet metal under biaxial conditions such as bulge hydroforming more closely matches forming conditions that the sheet metal will undergo for actual parts. The objective of the current research was to evaluate the analytically developed models’ ability to predict burst conditions and compare those burst results to those obtained from finite element models and experimentation. Stainless steel (annealed 0.2-mm thick AISI 304) was hydroformed in a circular open die with diameter of 11mm. Elliptical dies were also evaluated that had minor diameters of 11mm and aspect ratios down to 0.5. It was found that using the analytical method developed specifically for circular dies was a good predictor for the burst pressure while the more general analytical method for elliptical dies did not agree with either results from finite element analysis or experimental results.

Meso- and microscale sheet metal forming represents new and attractive solutions to many manufacturing problems for product miniaturization. Larger organizations are utilizing commercially available microscale digital image correlation systems to measure the strains on these scales. The cost of these systems is preventing smaller research and development organizations from entering this challenging area or they are sacrificing the ability to determine strains and evaluate material behavior at the microscale. However, microscale strain grid measurement has the advantage over digital image correlation when the researchers wish to avoid polishing and etching the surface of the sheet metal to make the grain structure visible for digital image correlation and where tooling interferes with obtaining images of the workpiece in real time. This article evaluates the strain measurement and strains resulting from multiscale sheet metal hydroforming operations for annealed 0.2-mm-thick ASTM 304 stainless steel using a simple method for producing microscale grids that has been previously described. The gridding methodology was shown to be accurate with high repeatability. In addition, a strain grid measurement method using an optical microscope and digital camera is described and an error analysis was performed. Provided reasonable care is taken, the inherent error in undeformed parts is 0.76% of true strain for samples with 127 µm grids using the strain measurement system described. The maximum variation in the mesoscale and microscale strain measurement static bulge testing was ±2.4% and more typically ±1.3% of true strain. With care, the errors were reduced to less than 1% of strain. Microscale strains from sheet bulge hydroforming experiments for 11, 5, and 1 mm diameter dies are used to show that the strains measured are reasonable and consistent.

This paper focuses on the microstructure and fracture surface morphology of neat and carbon nanofibers (CNF) modified asphalts and hot mix asphalt (HMA) mixtures using scanning electron microscopy (SEM). Asphalt binder was modified with 1.5 % of CNF by weight of binder. The modified asphalt was used to construct HMA mixtures at various CNF dosages, mixed with aggregate, using the Superpave Gyratory compactor. Small rectangular specimens extracted from the center of large HMA samples were tested under direct tension and the fracture surface was examined under SEM. The SEM analysis developed a fundamental understanding of the role that the CNF modification plays in the performance enhancement of asphalt and HMA mixtures. It was found that CNF not only possess good adhesion characteristics but also exhibits high connectivity and were evenly distribution throughout the binder. The fracture surface morphology also revealed that CNF exhibited crack bridging at micro/nano scale which may enhance the resistance to cracking due to repeated traffic loads.

From the perspective of osseointegration, nanograined/ultrafine-grained (NG/UFG) metals provide surfaces that are different from conventional coarse-grained (CG) polycrystalline metals because of the high fraction of grain boundaries. We describe here the interplay between the cellular response and grain boundary grooving as a potential approach to enhance osteoblast functions and facilitate the biomechanical interlocking and anchorage. This is accomplished by making a relative comparison of osteoblast response of NG/UFG grains electrochemically grooved to different depths to induce different degree of nanoscale roughness with planar NG/UFG surfaces, under identical biological environment. Electrochemically grooved NG/UFG structures indicated significant attachment and proliferation, and consequently enhanced modulation of cellular response that was significantly different from planar (non-grooved) NG/UFG substrate. Consistent with cell attachment and proliferation, immunofluorescence microscopy and computational analysis indicated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on electrochemically-grooved NG/UFG substrates. These observations are indicative of accelerated response of cell–substrate interaction and activity. The behavior is attributed to average nanoscale roughness and high surface hydrophilicity of the nanoengineered surface.

Producing fuel cells bipolar plates and other devices such as microscale heat exchangers for electronics requires both macroscale and microscale forming processes. At the macroscale, typically, mechanical properties of sheet metal are determined by performing tensile tests. In addition, it has long been recognized that bi-axial tension tests, dome tests, and hydroforming or viscous bulge tests provide the basis for improved understanding of the mechanics of sheet metal forming. At the microscale strain gauges are too large for measuring strains in small regions and membrane theory is only valid at the poles of the bulge. Continuum mechanics models are useful but require tedious thickness measurements for multiple work pieces, requiring extensive sample preparation and analysis. In this paper experimental results from hydroforming tests for 0.2-mm thick annealed ASTM 304 stainless steel sheet in 11 mm, 5 mm, and 1 mm diameter open dies at various pressures were evaluated. The height of the bulge at the pole and strains based upon measurements of 127 micron strain grids were determined. These dies represent the transition from a small macroscale process to a microscale forming process. Two methods were used to estimate material properties: an analytical model and an iterative method which compared experimental strain results with the strains from a finite element model where the Holloman constitutive properties of the sheet were varied. The problems estimating material properties based upon grid strain measurement, membrane theory, and the iterative finite element approaches were investigated and the results were compared. This study indicates that membrane theory will provide adequate predictions for Holloman constructive properties provided the assumptions for membrane theory are not violated. However, using measured microscale grid deformation strains does not produce very good agreement estimates of the Holloman constitutive model when comparing experimental results with FEA strains. It is believed that while the grid strain measurement method used results in strain measurement errors of less than 1.5% of strain, this error is sufficient to result in enough uncertainty to produce results that are inconsistent with other methods.

In the context of osseointegration of metallic implants, while nanostructuring the surface favorably modulates cellular response, the disinfective attributes required during the healing process are not available. Thus, in the present study, we demonstrate that nanocrystalline titania provides cumulative benefit of enhancing osteoblasts functions to promote the efficacy of metal implants together with the disinfective attributes. To this end, the primary objective here is to examine the select functions of bone forming cells (osteoblasts) on electrocrystallized nanonodular titania-coated nanograined/ultrafine grained (NG/UFG) austenitic stainless steel. The accompanying objective is to study the disinfective/antimicrobial activity. To the best of our understanding this is the first study of nanophase titania on a non-titanium substrate. The osteoblasts functions were investigated in terms of cell attachment, proliferation, and quantitative analysis of proteins, actin and vinculin. In comparison to the bare NG/UFG substrate, the nanophase titania-coated substrate exhibited higher degree of cell attachment and proliferation which are regulated via cellular and molecular interactions with proteins, actin and vinculin. The enhanced functions of osteoblasts suggest that nanophase titania adsorbs extracellular matrix proteins, fibronectin and vitronectin from serum enhancing protein, with subsequent binding of integrins and osteoblasts precursor to titania. The antimicrobial attributes assessed in terms of degradation of methyl orange and effectiveness in killing E. coli supports the viewpoint that large surface area of titania would be instrumental in reducing the detrimental effect of biologically reactive oxygen species produced by macrophages in the vicinity of the metal bone/implant interface. In summary, the study provides some new insights concerning nanostructuring of metallic substrates with specific physical and surface properties for medical devices with significantly improved cellular response.

We describe here the structure―property―process relationship of two sets of chitosan-based scaffolds as potential materials for hard tissue bioengineering applications. The first set of scaffolds was designed to study the effect of degree of deacetylation (%DD) of chitosan at 85 and 95% DD with identical molecular weight. The second set of scaffolds were synthesized to enhance the bioactivity and mechanical properties of 95% DD chitosan scaffold by the addition of 1, 3, and 5 wt% nanohydroxyapatite (nHA). Both sets of scaffolds were processed using freezing and lyophilization and their in vitro biological response was examined using pre-osteoblast (MC 3T3-E1) cells. The pure chitosan and chitosan―nHA nanocomposite scaffolds were characterized by a three-dimensional porous structure with pore size in the range of (≈50―120 μm), irrespective of %DD and nHA content. The compression modulus of hydrated 95% DD chitosan scaffolds increased from 6.0 kPa in pure chitosan to 9.2 kPa in chitosan-5 wt% nHA. The water uptake ability of 95% DD chitosan scaffolds was lower than 85% DD chitosan scaffolds, and decreased with the addition of nHA. On the other hand the water retention ability of 95% DD chitosan scaffolds was greater than 85% DD chitosan scaffolds but did not increase much with the addition of nHA. Chitosan degrades mainly by lysozyme present in physiological fluid. After 28 days of in vitro biodegradation test with physiological fluid, the 95% DD chitosan exhibited slightly lower degradation rate as compared to 85% DD and the degradation decreased with increase in nHA content in chitosan scaffold. Pre-osteoblasts (MC3T3-E1) grown on nHA scaffolds showed improved cell attachment, more proliferation, and a more extended cellular morphology. In vitro experimental observations suggest chitosan-nHA nanocomposite scaffolds as potential biomaterials for hard tissue bioengineering (bone regeneration) or as a template for cell attachment and proliferation in the repair of osseous and chondral defects.

Given the need to develop high strength/weight ratio bioimplants with enhanced cellular response, we describe here a study focused on the processing–structure–functional property relationship in austenitic stainless steel that was processed using an ingenious phase reversion approach to obtain an nanograined/ultrafine-grained (NG/UFG) structure. The cellular activity between fibroblast and NG/UFG substrate is compared with the coarse-grained (CG) substrate. A comparative investigation of NG/UFG and CG structures illustrated that cell attachment, proliferation, viability, morphology and spread are favorably modulated and significantly different from the conventional CG structure. These observations were further confirmed by expression levels of vinculin and associated actin cytoskeleton. Immunofluorescence studies demonstrated increased vinculin concentrations associated with actin stress fibers in the outer regions of the cells and cellular extensions on NG/UFG substrate. These observations suggest enhanced cell–substrate interaction and activity. The cellular attachment response on NG/UFG substrate is attributed to grain size and hydrophilicity and is related to more open lattice in the positions of high-angle grain boundaries.

The objective of this study was to develop a reliable method for the measurement of pipe surface roughness. Roughness of coated pipe was measured with two linear surface profilers, a Dektak3ST® and a Hommel T 1000, and a Dimension 3000® atomic force microscope (AFM). Arithmetic roughness (Ra), root mean square roughness (Rq), and mean peak-to-valley height (RZD) were statistically analyzed. Each instrument yielded reliable results, but there were significant differences between the AFM and the other two instruments. The ability of RZD to ignore intermediate height data while focusing on extreme height data made it a useful parameter for detecting differences in height that would be the most likely to affect fluid flow in pipes.

The objectives of this study were to determine: the type of coating that minimized pipe surface roughness and how the choice of metrological instrument could influence pipe surface roughness data. The internal surface of pipe was coated with either phenolic, modified novalac, epoxy, or nylon material. Roughness of coated pipe was assessed with two linear surface profilers, a Dektak3ST® and a Hommel T1000, and a Dimension 3000® atomic force microscope (AFM). Arithmetic roughness (Ra), root mean square roughness (Rq), and mean peak‐to‐valley height (RZD), were statistically analyzed. The ability of RZD to focus on the extremes of height and depth on the surface made it a significant parameter for detecting features that would affect fluid flow in pipes.

Cotton (Gossypium hirsutum cv. MD51) fiber cell walls were analyzed with an atomic force microscope to determine the effect of chemical treatments on cell wall organization and topography. Analysis of fibers in either air or water and without any staining or coating produced high-resolution images of cell wall microstructure which could be used for detailed quantitative analysis. Treatment of fibers with 1% H2O2 had little effect on surface morphology. Alkali removed much of the cuticle, some primary wall components, and revealed mostly thin-diameter microfibrils. Acidic Updegraff reagent fragmented the fibers, removed much of the cuticle, and revealed mostly thick microfibrils. The surface roughness of fibers treated sequentially with alkali and acid was quantitatively distinguishable from all other fiber types based on the standard deviation of the height data, amplification of surface area, and integration of the scan line data. Analysis of the fractal dimension enabled untreated and peroxide-treated fibers to be clearly distinguished from the other fiber types. Segmentation of the fractal data revealed specific portions of the fractal dimension which were especially useful for defining the size of structures that differentiated fiber types. Areas containing microfibrils could be quantitatively differentiated from non-microfibrillar areas. In water, some alkali-treated fibers had microfibrils that were relatively small in diameter while others appeared to consist of crystalline arrays of smaller fibrils.

Metallic biomedical devices with nanometer-sized grains (NGs) provide surfaces that are different from their coarse-grained (CG) (tens of micrometer) counterparts in terms of increased fraction of grain boundaries (NG>50%; CG

The objective of the study is to elucidate the interplay between fibronectin-metal hybrid surfaces and osteoblast function. The practical relevance is that a significant initial step in the process of prosthetic integration within a physiological system is the rapid adsorption of proteins, including fibronectin, on the surface of biomedical device. Here, we compare and contrast the cell–substrate interactions on bare and protein-modified surfaces. The protein adsorption on the surface was beneficial in favorably modulating biological functions including cell attachment, proliferation, and viability. Additionally, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on protein-adsorbed surfaces. These results support the hypothesis that protein adsorption on artificial biomedical devices can promote bioactivity and regulate biological functions. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A:3157–3166, 2012.

The rapid adsorption of proteins is the starting and primary biological response that occurs when a biomedical device is implanted in the physiological system. The biological response, however, depends on the surface characteristics of the device. Considering the significant interest in nano-/ultrafine surfaces and nanostructured coatings, we describe here, the interplay between grain structure and protein adsorption (bovine serum albumin: BSA) on osteoblasts functions by comparing nanograined/ultrafine-grained (NG/UFG) and coarse-grained (CG: grain size in the micrometer range) substrates by investigating cell-substrate interactions. The protein adsorption on NG/UFG surface was beneficial in favorably modulating biological functions including cell attachment, proliferation, and viability, whereas the effect was less pronounced on protein adsorbed CG surface. Additionally, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on protein adsorbed NG/UFG surface. The functional response followed the sequence: NG/UFG(BSA) > NG/UFG > CG(BSA) > CG. The differences in the cellular response on bare and protein adsorbed NG/UFG and CG surfaces are attributed to cumulative contribution of grain structure and degree of hydrophilicity. The study underscores the potential advantages of protein adsorption on artificial biomedical devices to enhance the bioactivity and regulate biological functions.

Metallic materials with submicron- to nanometer-sized grains provide surfaces that are different from conventional polycrystalline materials because of the large proportion of grain boundaries with high free energy. In the study described here, the combination of cellular and molecular biology, materials science and engineering advances our understanding of cell-substrate interactions, especially the cellular activity between preosteoblasts and nanostructured metallic surfaces. Experiments on the effect of nano-/ultrafine grains have shown that cell attachment, proliferation, viability, morphology and spread are favorably modulated and significantly different from conventional coarse-grained structures. Additionally, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on nanograined/ultrafine-grained substrate. These observations suggest enhanced cell-substrate interaction and activity. The differences in the cellular response on nanograined/ultrafine-grained and coarse-grained substrates are attributed to grain size and degree of hydrophilicity. The outcomes of the study are expected to reduce challenges to engineer bulk nanostructured materials with specific physical and surface properties for medical devices with improved cellular attachment and response. The data lay the foundation for a new branch of nanostructured materials for biomedical applications.

Investigations of the longitudinal distribution of the extensibility of staminal filaments of the common thistle (Cirsium horridulum Michx.) showed that the base of the filaments (attachment to corolla) is almost twice as elastic as the apical portion (next to anthers). Boiling leads to a more uniform distribution of extensibility. Using a stress-strain analyzer we investigated the elastic properties of fresh, water-boiled, partially hydrolyzed (acid-boiled), and dehydrated filaments. Stress-strain curves of sinusoidally stretched sets of filaments revealed complex, non-linear behavior with an average modulus of elasticity of 5 MPa·m−2. The phase angle varied from approximately 18 degrees for 0.01-Hz deformations to 84 degrees at 2 Hz, indicating strong viscoelastic components. The viscoelasticity of the filaments indicates that the cell walls have a high ratio of pectin to cellulose. Boiling does not affect Young's modulus, but dehydration does. The technique of applying sinusoidal loads and the analysis of the stress-strain curves proves useful for the assessment of mechanical properties of cell walls, especially for non-growing or contractile tissues.