Tensile Strength Of Thin Film Research Articles

Pharmaceutical polymer-based hydrogel formulations as prospective bioinks for 3D bioprinting applications: A step towards clean bioprinting

BackgroundThree-dimensional (3D) bioprinting has emerged as a game-changer technology in tissue engineering. Bioink is a crucial component in the 3D bioprinting process and is consists of biomaterials, cells, and growth factors. Current research on bioink formulations primarily uses animal-derived biomaterials for 3D bioprinting operations and soft tissue engineering, which possess challenges of batch-to-batch variability, immunogenicity, and microbial growth with aging. ObjectiveIn this study we aimed to investigate pharmaceutical polymers as biomaterials for hydrogel formulations and examine them for prospective bioink qualities. MethodsHydrogel formulations containing partially pregelatinized starch, sodium alginate along with either of hydroxypropyl methylcellulose or polyvinyl alcohol-polyethylene glycol graft co-polymer or sodium carboxymethyl cellulose were assessed for tensile strength of thin films; the viscosity of hydrogels, the structural integrity of crosslinked scaffolds, and effects of moist heat sterilization on physical properties, chemical properties and microbial contaminations. ResultsWe found that thin films made out of hydrogels found to have tensile strength suitable for soft tissue engineering. Viscosity results meet workable ranges for extrusion-based bioprinting. Structural integrity revealed crosslinked scaffolds were able to withstand in culture medias for few days and then started to disintegrate demonstrated biodegradation patterns of diffrent formulations. The moist heat sterilization process eliminated microbial contaminations effectively without altering the physicochemical properties of the hydrogels. ConclusionWe proved pharmaceutical polymers as biomaterials in hydrogel formulations that could be used as bioinks in future. These hydrogels has appropriate qualities for 3D bioprinting and soft tissue engineering. This study paves the way for clean bioprinting, with the possibility of formulating bioinks free from animal derived biomaterials.

Hierarchical reinforcement of randomly-oriented carbon nanotube mats by ion irradiation

Because of their outstanding mechanical properties, carbon nanotubes (CNTs) are attractive 1-D nanoscale building blocks for lightweight composites that could potentially outperform naturally occurring materials. A still unsolved challenge for fully exploiting CNT superior mechanical properties for reinforcement of macroscopic systems is control of the interfacial interaction across multiple length scales to favor load transfer. Toward overcoming this challenge, we investigate here the effect of high-energy He+ ion irradiation on the elastic modulus and tensile strength of thin films of randomly oriented double-walled nanotube (DWCNT) mats and DWCNT-epoxy composites. We correlate irradiation-induced reinforcement with the formation of cross-links at different hierarchical levels of the DWCNT network. Our measurements reveal a rapidly increasing reinforcement at low ion doses, attributed to intra-bundle CNT cross-links, followed by a slow mechanical reinforcement at higher doses, associated to inter-bundle cross-links. At the highest ion irradiation dose of this study, the strength and elastic modulus of DWCNT-epoxy composites approach ∼900 MPa and 25 GPa, respectively, which is among the best mechanical performances reported for randomly-oriented CNT mats. We also develop a model accounting for radiation-induced hierarchical reinforcement of DWCNT films. The model is in good agreement with the experimental results across the entire dose range.

Surface-induced size-dependent ultimate tensile strength of thin films

The surface eigenstress model was further developed to study the surface-induced size-dependent ultimate biaxial tensile strength of thin films. First-principles calculations and molecular dynamics (MD) simulations were conducted on Au and Si thin films with different thicknesses. The atomistic calculations show that the ultimate biaxial tensile strength of Au thin films increases when the film thickness decreases, a typical the thinner the stronger phenomenon, while the Si thin films exhibit the thinner the weaker behavior. Nevertheless, both behaviors were perfectly predicted by a nonlinear scaling law developed from the surface eigenstress model. Moreover, the first-principles calculations put insight into the surface induced strengthening or weakening mechanism.

Inter-wafer bonding strength characterization by laser-induced shock waves

A previously developed laser spallation experiment to measure the tensile strength of thin film interfaces is extended to quantify the intrinsic tensile strength of bonded wafers. In this experiment, a laser generated compressive stress wave on the back surface of one wafer reflects into a tensile wave after reflecting from the free surface of the second wafer to separate the inter-wafer bond. Optical interferometery is used in conjunction with a wave mechanics simulation to quantify the bond strength. The technique was used to study the dependence of the inter-wafer bond strength on the annealing temperature which varied between 200 °C and 1100 °C. A peak bond strength value of 3.91 GPa is reported at 1100 °C. We show that the measured bond strength values compares well with the bonding energies measured by alternate methods.

Thickness effects in polycrystalline thin films: Surface constraint versus interior constraint

The uniaxial tension behavior of polycrystalline thin films, in which all grain boundaries (GBs) are penetrable by dislocations, is investigated by two-dimensional discrete dislocation dynamics (DDD) method with a penetrable dislocation-GB interaction model. In order to study thickness effect on the tensile strength of thin films with and without surface treatment, three types of thin films are comparatively considered, including the thin films without surface treatment, with surface passivation layers (SPLs) of nanometer thickness and with surface grain refinement zones (SGRZs) consisting of nano-sized grains. Our results show that thickness effects and their underlying dislocation mechanisms are quite distinct among different types of thin films. The thicker thin films without surface treatment are stronger than the thinner ones; however, opposite thickness effects are captured in the thin films with SPLs or SGRZs. Moreover, the underlying dislocation mechanisms of the same thickness effects of thin films with SPLs and SGRZs are different. In the thin films with SPLs, the thickness effect is caused by the sharp increase of dislocation density near the film-passivation interface, while it is mainly due to the sharp decrease of dislocation density within the refined surface grains of the thin films with SGRZs. No matter in what type of thin films, thickness effect gradually disappears when the number of grains in the thickness direction is large enough. Our analysis reveals that general mechanism of those thickness effects lies in the competition between the exterior surface-constraint and interior GB-constraint on gliding dislocations.

An Understanding of the Mechanism That Promotes Adhesion Between Roughened Titanium Implants and Mineralized Tissue

A previously developed laser spallation technique to determine the tensile strength of thin film interfaces was successfully adopted to study the effect of microsurface roughness of titanium disks on the adhesion strength of mineralized bone tissue. The study demonstrated that mineralized tissue has about 25% higher interfacial strength when it is cultured on the acid-etched titanium surface than on its machined counterpart. Specifically, interfacial tensile strength of 179+/-4.4 MPa and 224+/-2.6 MPa were measured when the mineralized tissue was processed on the machined titanium and acid-etched titanium surfaces, respectively. Since in the laser spallation experiment, the mineralized tissue is pulled normal to the interface, this increase is attributed to the stronger interfacial bonding on account of higher surface energy associated with the acid-etched surface. This enhanced local chemical bonding further enhances the roughness-related mechanical interlocking effect. These two effects at very different length scales--atomic (enhanced bonding) versus continuum (roughness-related interlocking)-act synergistically and explain the widely observed clinical success of roughened dental implants.

Measurement of the tensile strength of cell–biomaterial interface using the laser spallation technique

A previously developed laser spallation technique to determine the tensile strength of thin film interfaces was successfully adopted to determine the tensile strength of interfaces between three different live mammalian cells (osteoblast, chondrocyte and fibroblast) and polystyrene (untreated and fibronectin coated) and titanium surfaces. No noticeable differences in the interfacial tensile strength values were found across the three cell types on the same substrate although osteoblasts showed slightly lower adhesion strength when cultured on untreated polystyrene surfaces. Significant differences were, however, measured for cells treated on different surfaces. Use of fibronectin increased the interfacial tensile strength for all cell types, and cells bonded much better to titanium than to untreated polystyrene surfaces. Cell interfacial strength was higher when cultured with serum than in a serum-free environment. The results demonstrate the remarkable sensitivity of the laser spallation experiment in determining the effects of local interfacial microstructure and chemistry on cell adhesion.

Evaluation of laser spallation as a technique for measurement of cell adhesion strength

Cell adhesion to material surfaces is one of the fundamental phenomena of cellular response to implanted devices. Controlling the strength, dynamics, and mechanics of cell adhesion offer opportunities for designing novel biomaterials for tissue engineering and biotechnology. Many techniques have been developed for the purpose of quantifying various types of cell-biomaterial interaction. One method to evaluate cell affinity for a biomaterial is to measure the stress required to remove adherent cells from the material. This study investigates the possibility of using laser spallation, a technique previously developed for measuring the tensile strength of thin film interfaces, for evaluation of initial cell attachment strength. MC3T3-E1 preosteoblasts were cultured on fibronectin-coated polystyrene, a surface known to engage cells in receptor mediated adhesion, and untreated polystyrene, which elicit nonspecific adhesion mechanisms during early stages of cell attachment. The laser spallation technique effectively detached cells from polymer substrates and also distinguished relative cell adhesion strengths to surfaces with known differences in cell binding affinities. Scanning electron micrographs determined that cell detachment resulting from laser spallation left a cleaner surface than jet impingement, possibly suggesting a more complete detachment mechanism. Absolute values of adhesion strengths determined by laser spallation were significantly higher than those found using jet impingement, a previously reported hydrodynamic technique.

Effect of Ar Gas Pressure on Mechanical Properties of Sputtered Ti Thin Films

The effect of sputtering gas (Ar gas) pressure on the mechanical properties of free-standing Ti thin film membranes of 300-400 nm thickness, microfabricated by magnetron sputtering, has been studied by using a novel tensile testing machine. These free-standing thin film membranes are extremely difficult to handle because they are fragile. Therefore, the thin film test specimens were fabricated in Si frames to protect them. Sputtering gas pressure was varied from 1.5 to 15 mT. The stress and strain of the thin films was measured continuously from elastic deformation to fracture. Both the tensile strength and the strain at fracture of the thin films were affected by the sputtering gas pressure. The tensile strength of thin films increased with decreasing gas pressure. However, there was no obvious trend between the sputtering gas pressure and Young's modulus of the thin films. The experimental results confirmed that the Ti thin film membranes are more reliable with decreasing the gas pressure.

Poly(ether imide)s derived from phthalazinone‐containing dianhydrides

AbstractAn unsymmetrical and noncoplanar heterocyclic dianhydride was synthesized from a bisphenol‐like phthalazinone, 4‐(4‐hydroxylphenyl)‐2,3‐phthalazin‐1‐one, and a series of novel poly(ether imide)s based on it, with intrinsic viscosities of 0.67–1.42 dL/g, were obtained by one‐step solution polymerization in m‐cresol at 200 °C for 20 h. The polymers were readily soluble in N‐methyl‐2‐pyrrolidinone and m‐cresol. The poly(ether imide)s derived from 4,4′‐oxydianiline and 4,4′‐methylenedianiline were also very soluble in chloroform, 1,1′,2,2′‐tetrachloroethane, and N,N‐dimethylacetamide. The glass‐transition temperatures were 289–326 °C, as determined by differential scanning calorimetry. All the degradation temperatures for 5% weight loss occurred above 482 °C in nitrogen. The tensile strength of thin films of some of the polymers varied from 103.1 to 121.4 MPa. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6089–6097, 2004

X-ray elastic constants of chromium nitride films deposited by arc-ion plating

Thin films have been successfully utilized to improve the property of mechanical components. However, it is generally known that mechanical properties, such as elastic constants and tensile strength of thin films, are different from those of bulk material, and they are not known in the present state. In many times, x-ray stress measurement revealed a very high compressive residual stress state in the film when bulk elastic constants were used in the stress calculation. The purpose of this research is to investigate the elastic constants of chromium nitride (CrN) films. The film was deposited on austenitic stainless steel (JIS: SUS304) substrates by the arc-ion-plating (AIP) method under the following conditions: the pressure of nitrogen atmosphere was maintained at 2.63 Pa, the substrate temperature of about 573 K, the arc discharge current of 100 A, the bias voltage between −300 and −100 V, and the substrate rotating rate at 3 rpm. The lattice strain of CrN films was measured by x-ray method at various loading stages and the x-ray elastic constants of CrN films were evaluated.

In-Situ Intrinsic Interface Strength Measurement at Elevated Temperatures and its Relationship to Interfacial Structure

A previously developed laser spallation technique has been modified to measure the tensile strength of thin film interfaces in-situ at temperatures up to 1100°C. Tensile strengths of Nb/A-plane sapphire, FeCrAl/A-plane sapphire and FeCrAlY/A-plane sapphire were measured up to 950°C. The measured strengths at high temperatures were substantially lower compared with their corresponding strengths at ambient temperature. For example, at 850°C, the interface tensile strength for the Nb/sapphire (151 ± 17 MPa), FeCrAl/sapphire (62 ± 8 MPa) and FeCrAlY/sapphire (82 ± 11 MPa) interface systems were lower by factors of approximately, 3, 5, and 8, respectively, over their corresponding ambient values. These results underscore the importance of using such in-situ measured values under operating conditions as the failure criterion in any life prediction or reliability models of such coated systems where local interface temperature excursions are expected. The results on alloy film interfaces also demonstrate that the presence of Y increases the strength of FeCrAl/Al2O3 interfaces.

Method for Instability Analysis of Atomic Structure and its Application to Ideal Strength of Thin Film.

In order to derive the instability criterion of atomic structures, such as thin film and nano-tube, an analytical method is proposed on the basis of the energy balance against the deformation. Taking into account all degree of freedom for atoms in system, the criterion is given as the positiveness of determinant consisted of the second derivation of energy against the infinitesimal displacement. This method is available for any deformation mode of any atomic structure as well as for any form of interatomic potential. As an application of this method, the ideal tensile strength of thin film is analyzed in order to understand the effect of surface on the instability. Critical stress is successfully extracted by the proposed method combining with the molecular statics simulation. Ideal strength eminently decreases for the films with the thickness of less than 10 nm.

Measurement of the interface tensile strength at elevated temperatures

A new experimental procedure to measure the tensile strength of thin film interfaces. in iii, at elevated temperatures is presented. In this experiment, the substrate with coating of interest is placed inside a quartz furnace tube evacuated to 10 -3 torr and heated under a continuous flow of argon. A Nd:YAG laser pulse is then focussed on the back surface of the substrate, which due to surface melting and rapid cooling generates a compressive stress wave directed towards the test coating interface. The compressive stress wave reflects as a tensile wave from the free surface of the coating and leads to its spallation (complete removal) at a sufficiently high wave amplitude The coating's free surface velocity during interface decohesion is measured using an optical interferometer and used to calculate the peak interfacial tensile stress. The technique is quite general and applicable to interlaces between polymeric metallic and ceramic coatings and engineering substrates. Here, it is demonstrated on a model Nb/sapphire interface system, for which an average tensile strength of 400 MPa at 1100°C was obtained. This value is remarkably different than the value of 1.9 GPa obtained under ambient conditions. This large difference suggests the importance of this research because interfaces in tribology, multilayer devices. and composite materials undergo local temperature excursion during service and their design should consider the possibility of such strength degradations.

On the connection between the strength and conditions of preparation of copper and aluminum vacuum condensates

A method of measuring the microhardness and tensile strength of thin films has been devised, and this has been used to investigate copper and aluminum films obtained by condensation in vacuum. The connection between the strength of the films and the condensation conditions has been studied.