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Materials, Volume 8, Issue 4 (April 2015), Pages 1369-2042

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Open AccessArticle Evaluation of Contact Heat Transfer Coefficient and Phase Transformation during Hot Stamping of a Hat-Type Part
Materials 2015, 8(4), 2030-2042; https://doi.org/10.3390/ma8042030
Received: 21 January 2015 / Revised: 16 April 2015 / Accepted: 17 April 2015 / Published: 22 April 2015
Cited by 3 | PDF Full-text (2227 KB) | HTML Full-text | XML Full-text
Abstract
Using an inverse analysis technique, the heat transfer coefficient on the die-workpiece contact surface of a hot stamping process was evaluated as a power law function of contact pressure. This evaluation was to determine whether the heat transfer coefficient on the contact surface
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Using an inverse analysis technique, the heat transfer coefficient on the die-workpiece contact surface of a hot stamping process was evaluated as a power law function of contact pressure. This evaluation was to determine whether the heat transfer coefficient on the contact surface could be used for finite element analysis of the entire hot stamping process. By comparing results of the finite element analysis and experimental measurements of the phase transformation, an evaluation was performed to determine whether the obtained heat transfer coefficient function could provide reasonable finite element prediction for workpiece properties affected by the hot stamping process. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessReview Misfit Layer Compounds and Ferecrystals: Model Systems for Thermoelectric Nanocomposites
Materials 2015, 8(4), 2000-2029; https://doi.org/10.3390/ma8042000
Received: 6 February 2015 / Revised: 3 April 2015 / Accepted: 7 April 2015 / Published: 22 April 2015
Cited by 19 | PDF Full-text (4023 KB) | HTML Full-text | XML Full-text
Abstract
A basic summary of thermoelectric principles is presented in a historical context, following the evolution of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by
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A basic summary of thermoelectric principles is presented in a historical context, following the evolution of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by the contradictory material requirements necessary for efficient thermal energy harvest. Misfit layer compounds are highlighted as an example of a highly ordered anisotropic nanocomposite system. Their layered structure provides the opportunity to use multiple constituents for improved thermoelectric performance, through both enhanced phonon scattering at interfaces and through electronic interactions between the constituents. Recently, a class of metastable, turbostratically-disordered misfit layer compounds has been synthesized using a kinetically controlled approach with low reaction temperatures. The kinetically stabilized structures can be prepared with a variety of constituent ratios and layering schemes, providing an avenue to systematically understand structure-function relationships not possible in the thermodynamic compounds. We summarize the work that has been done to date on these materials. The observed turbostratic disorder has been shown to result in extremely low cross plane thermal conductivity and in plane thermal conductivities that are also very small, suggesting the structural motif could be attractive as thermoelectric materials if the power factor could be improved. The first 10 compounds in the [(PbSe)1+δ]m(TiSe2)n family (m, n ≤ 3) are reported as a case study. As n increases, the magnitude of the Seebeck coefficient is significantly increased without a simultaneous decrease in the in-plane electrical conductivity, resulting in an improved thermoelectric power factor. Full article
(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)
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Open AccessArticle Crystal Quality and Light Output Power of GaN-Based LEDs Grown on Concave Patterned Sapphire Substrate
Materials 2015, 8(4), 1993-1999; https://doi.org/10.3390/ma8041993
Received: 17 February 2015 / Revised: 8 April 2015 / Accepted: 10 April 2015 / Published: 22 April 2015
Cited by 2 | PDF Full-text (2029 KB) | HTML Full-text | XML Full-text
Abstract
The crystal quality and light output power of GaN-based light-emitting diodes (LEDs) grown on concave patterned sapphire substrate (CPSS) were investigated. It was found that the crystal quality of GaN-based LEDs grown on CPSS improved with the decrease of the pattern space (percentage
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The crystal quality and light output power of GaN-based light-emitting diodes (LEDs) grown on concave patterned sapphire substrate (CPSS) were investigated. It was found that the crystal quality of GaN-based LEDs grown on CPSS improved with the decrease of the pattern space (percentage of c-plane). However, when the pattern space decreased to 0.41 μm (S0.41-GaN), the GaN crystallinity dropped. On the other hand, the light output power of GaN-based LEDs was increased with the decrease of the pattern space due to the change of the light extraction efficiency. Full article
(This article belongs to the Special Issue Luminescent Materials and Devices)
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Open AccessArticle Properties of Exchange Coupled All-garnet Magneto-Optic Thin Film Multilayer Structures
Materials 2015, 8(4), 1976-1992; https://doi.org/10.3390/ma8041976
Received: 3 February 2015 / Revised: 13 April 2015 / Accepted: 15 April 2015 / Published: 21 April 2015
Cited by 2 | PDF Full-text (2510 KB) | HTML Full-text | XML Full-text
Abstract
The effects of exchange coupling on magnetic switching properties of all-garnet multilayer thin film structures are investigated. All-garnet structures are fabricated by sandwiching a magneto-soft material of composition type Bi1.8Lu1.2Fe3.6Al1.4O12 or Bi3Fe
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The effects of exchange coupling on magnetic switching properties of all-garnet multilayer thin film structures are investigated. All-garnet structures are fabricated by sandwiching a magneto-soft material of composition type Bi1.8Lu1.2Fe3.6Al1.4O12 or Bi3Fe5O12:Dy2O3 in between two magneto-hard garnet material layers of composition type Bi2Dy1Fe4Ga1O12 or Bi2Dy1Fe4Ga1O12:Bi2O3. The fabricated RF magnetron sputtered exchange-coupled all-garnet multilayers demonstrate a very attractive combination of magnetic properties, and are of interest for emerging applications in optical sensors and isolators, ultrafast nanophotonics and magneto-plasmonics. An unconventional type of magnetic hysteresis behavior not observed previously in magnetic garnet thin films is reported and discussed. Full article
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Open AccessArticle Modification of pH Conferring Virucidal Activity on Dental Alginates
Materials 2015, 8(4), 1966-1975; https://doi.org/10.3390/ma8041966
Received: 13 February 2015 / Revised: 26 March 2015 / Accepted: 13 April 2015 / Published: 21 April 2015
Cited by 2 | PDF Full-text (602 KB) | HTML Full-text | XML Full-text
Abstract
To formulate an alginate dental impression material with virucidal properties, experimental alginate dental impression materials were developed and the formulations adjusted in order to study the effect on pH profiles during setting. Commercially available materials served as a comparison. Eight experimental materials were
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To formulate an alginate dental impression material with virucidal properties, experimental alginate dental impression materials were developed and the formulations adjusted in order to study the effect on pH profiles during setting. Commercially available materials served as a comparison. Eight experimental materials were tested for antiviral activity against Herpes Simplex Virus type 1 (HSV-1). Changing the amount of magnesium oxide (MgO) used in the experimental formulations had a marked effect on pH. Increasing MgO concentration corresponded with increased pH values. All experimental materials brought about viral log reductions ranging between 0.5 and 4.0 over a period of 4 h. The material with the lowest pH was the most effective. The current work highlights the very important role of MgO in controlling pH profiles. This knowledge has been applied to the formulation of experimental alginates; where materials with pH values of approximately 4.2–4.4 are able to achieve a significant log reduction when assayed against HSV-1. Full article
(This article belongs to the Special Issue Dental Materials)
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Open AccessArticle Gas Permeation Properties of Soluble Aromatic Polyimides Based on 4-Fluoro-4,4'-Diaminotriphenylmethane
Materials 2015, 8(4), 1951-1965; https://doi.org/10.3390/ma8041951
Received: 26 January 2015 / Revised: 26 March 2015 / Accepted: 9 April 2015 / Published: 21 April 2015
Cited by 6 | PDF Full-text (415 KB) | HTML Full-text | XML Full-text
Abstract
A series of new organic polyimides were synthesized from 4-fluoro-4'4"-diaminotriphenylmethane and four different aromatic dianhydrides through a one-step, high-temperature, direct polycondensation in m-cresol at 180–200 °C, resulting in the formation of high-molecular-weight polyimides (inherent viscosities ~ 1.0–1.3 dL/g). All the resulting polyimides exhibited
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A series of new organic polyimides were synthesized from 4-fluoro-4'4"-diaminotriphenylmethane and four different aromatic dianhydrides through a one-step, high-temperature, direct polycondensation in m-cresol at 180–200 °C, resulting in the formation of high-molecular-weight polyimides (inherent viscosities ~ 1.0–1.3 dL/g). All the resulting polyimides exhibited good thermal stability with initial decomposition temperatures above 434 °C, glass-transition temperatures between 285 and 316 °C, and good solubility in polar aprotic solvents. Wide-angle X-ray scattering data indicated that the polyimides were amorphous. Dense membranes were prepared by solution casting and solvent evaporation to evaluate their gas transport properties (permeability, diffusivity, and solubility coefficients) toward pure hydrogen, helium, oxygen, nitrogen, methane, and carbon dioxide gases. In general, the gas permeability was increased as both the fractional free volume and d-spacing were also increased. A good combination of permeability and selectivity was promoted efficiently by the bulky hexafluoroisopropylidene and 4-fluoro-phenyl groups introduced into the polyimides. The results indicate that the gas transport properties of these films depend on both the structure of the anhydride moiety, which controls the intrinsic intramolecular rigidity, and the 4-fluoro-phenyl pendant group, which disrupts the intermolecular packing. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle Flexural Behavior of HPFRCC Members with Inhomogeneous Material Properties
Materials 2015, 8(4), 1934-1950; https://doi.org/10.3390/ma8041934
Received: 30 January 2015 / Revised: 10 April 2015 / Accepted: 13 April 2015 / Published: 21 April 2015
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Abstract
In this paper, the flexural behavior of High-performance Fiber-Reinforced Cementitious Composite (HPFRCC) has been investigated, especially focusing on the localization of cracks, which significantly governs the flexural behavior of HPFRCC members. From four points bending tests with HPFRCC members, it was observed that
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In this paper, the flexural behavior of High-performance Fiber-Reinforced Cementitious Composite (HPFRCC) has been investigated, especially focusing on the localization of cracks, which significantly governs the flexural behavior of HPFRCC members. From four points bending tests with HPFRCC members, it was observed that almost evenly distributed cracks formed gradually, followed by a localized crack that determined the failure of the members. In order to investigate the effect of a localized crack on the flexural behavior of HPFRCC members, an analytical procedure has been developed with the consideration of intrinsic inhomogeneous material properties of HPFRCC such as cracking and ultimate tensile strengths. From the comparison, while the predictions with homogeneous material properties overestimated flexural strength and ductility of HPFRCC members, it was found that the analysis results considering localization effect with inhomogeneous material properties showed good agreement with the test results, not only the flexural strength and ductility but also the crack widths. The test results and the developed analysis procedure presented in this paper can be usefully applied for the prediction of flexural behaviors of HPFRCC members by considering the effect of localized cracking behavior. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Three-Dimensional Imaging of Dislocations in a Ti–35mass%Nb Alloy by Electron Tomography
Materials 2015, 8(4), 1924-1933; https://doi.org/10.3390/ma8041924
Received: 5 January 2015 / Revised: 9 April 2015 / Accepted: 13 April 2015 / Published: 21 April 2015
Cited by 2 | PDF Full-text (6857 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We have studied three-dimensional (3D) configurations of dislocations in the β phase of a Ti–35mass%Nb alloy by means of single-axis tilt tomography using bright-field scanning transmission electron microscopy (BF-STEM). To visualize dislocations, the hh0 systematic reflections were excited throughout tilt-series acquisition with
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We have studied three-dimensional (3D) configurations of dislocations in the β phase of a Ti–35mass%Nb alloy by means of single-axis tilt tomography using bright-field scanning transmission electron microscopy (BF-STEM). To visualize dislocations, the hh0 systematic reflections were excited throughout tilt-series acquisition with the maximum tilt angle of 70°. Dislocations in the β grains were clearly reconstructed by the weighted back-projection algorithm. The slip planes of the dislocations were deduced by rotating the reconstructed volumes with the aid of selected area electron diffraction patterns. It was found that BF-STEM images with relatively low contrasts, taken along low-order zone axes, are capable to reproduce and preserve the quality of reconstructed image of dislocations. We also found that tilt angles as low as 40° are practically acceptable to visualize 3D configurations of dislocations, while there exists limitation in resolution due to the existence of a large missing wedge. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Setup of Extruded Cementitious Hollow Tubes as Containing/Releasing Devices in Self-Healing Systems
Materials 2015, 8(4), 1897-1923; https://doi.org/10.3390/ma8041897
Received: 27 February 2015 / Revised: 6 April 2015 / Accepted: 14 April 2015 / Published: 21 April 2015
Cited by 7 | PDF Full-text (3611 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this research is to produce self-healing cementitious composites based on the use of cylindrical capsules containing a repairing agent. Cementitious hollow tubes (CHT) having two different internal diameters (of 2 mm and 7.5 mm) were produced by extrusion and used
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The aim of this research is to produce self-healing cementitious composites based on the use of cylindrical capsules containing a repairing agent. Cementitious hollow tubes (CHT) having two different internal diameters (of 2 mm and 7.5 mm) were produced by extrusion and used as containers and releasing devices for cement paste/mortar healing agents. Based on the results of preliminary mechanical tests, sodium silicate was selected as the healing agent. The morphological features of several mix designs used to manufacture the extruded hollow tubes, as well as the coatings applied to increase the durability of both core and shell materials are discussed. Three-point bending tests were performed on samples produced with the addition of the above-mentioned cementitious hollow tubes to verify the self-healing effectiveness of the proposed solution. Promising results were achieved, in particular when tubes with a bigger diameter were used. In this case, a substantial strength and stiffness recovery was observed, even in specimens presenting large cracks (>1 mm). The method is inexpensive and simple to scale up; however, further research is needed in view of a final optimization. Full article
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Open AccessArticle Additively Manufactured Open-Cell Porous Biomaterials Made from Six Different Space-Filling Unit Cells: The Mechanical and Morphological Properties
Materials 2015, 8(4), 1871-1896; https://doi.org/10.3390/ma8041871
Received: 18 January 2015 / Revised: 8 April 2015 / Accepted: 14 April 2015 / Published: 21 April 2015
Cited by 64 | PDF Full-text (3621 KB) | HTML Full-text | XML Full-text
Abstract
It is known that the mechanical properties of bone-mimicking porous biomaterials are a function of the morphological properties of the porous structure, including the configuration and size of the repeating unit cell from which they are made. However, the literature on this topic
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It is known that the mechanical properties of bone-mimicking porous biomaterials are a function of the morphological properties of the porous structure, including the configuration and size of the repeating unit cell from which they are made. However, the literature on this topic is limited, primarily because of the challenge in fabricating porous biomaterials with arbitrarily complex morphological designs. In the present work, we studied the relationship between relative density (RD) of porous Ti6Al4V EFI alloy and five compressive properties of the material, namely elastic gradient or modulus (Es20–70), first maximum stress, plateau stress, yield stress, and energy absorption. Porous structures with different RD and six different unit cell configurations (cubic (C), diamond (D), truncated cube (TC), truncated cuboctahedron (TCO), rhombic dodecahedron (RD), and rhombicuboctahedron (RCO)) were fabricated using selective laser melting. Each of the compressive properties increased with increase in RD, the relationship being of a power law type. Clear trends were seen in the influence of unit cell configuration and porosity on each of the compressive properties. For example, in terms of Es20–70, the structures may be divided into two groups: those that are stiff (comprising those made using C, TC, TCO, and RCO unit cell) and those that are compliant (comprising those made using D and RD unit cell). Full article
(This article belongs to the Special Issue Mechanics of Biomaterials) Printed Edition available
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Open AccessArticle Impact of Different Surface Ligands on the Optical Properties of PbS Quantum Dot Solids
Materials 2015, 8(4), 1858-1870; https://doi.org/10.3390/ma8041858
Received: 12 February 2015 / Revised: 7 April 2015 / Accepted: 9 April 2015 / Published: 21 April 2015
Cited by 22 | PDF Full-text (2858 KB) | HTML Full-text | XML Full-text
Abstract
The engineering of quantum dot solids with low defect concentrations and efficient carrier transport through a ligand strategy is crucial to achieve efficient quantum dot (QD) optoelectronic devices. Here, we study the consequences of various surface ligand treatments on the light emission properties
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The engineering of quantum dot solids with low defect concentrations and efficient carrier transport through a ligand strategy is crucial to achieve efficient quantum dot (QD) optoelectronic devices. Here, we study the consequences of various surface ligand treatments on the light emission properties of PbS quantum dot films using 1,3-benzenedithiol (1,3-BDT), 1,2-ethanedithiol (EDT), mercaptocarboxylic acids (MPA) and ammonium sulfide ((NH4)2S). We first investigate the influence of different ligand treatments on the inter-dot separation, which mainly determines the conductivity of the QD films. Then, through a combination of photoluminescence and transient photoluminescence characterization, we demonstrate that the radiative and non-radiative recombination mechanisms in the quantum dot films depend critically on the length and chemical structure of the surface ligands. Full article
(This article belongs to the Special Issue Luminescent Materials and Devices)
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Open AccessArticle Collagen Fibrils in Skin Orient in the Direction of Applied Uniaxial Load in Proportion to Stress while Exhibiting Differential Strains around Hair Follicles
Materials 2015, 8(4), 1841-1857; https://doi.org/10.3390/ma8041841
Received: 4 March 2015 / Revised: 9 April 2015 / Accepted: 14 April 2015 / Published: 20 April 2015
Cited by 10 | PDF Full-text (1185 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We determined inhomogeneity of strains around discontinuities as well as changes in orientation of collagen fibrils under applied load in skin. Second Harmonic Generation (SHG) images of collagen fibrils were obtained at different strain magnitudes. Changes in collagen orientation were analyzed using Fast
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We determined inhomogeneity of strains around discontinuities as well as changes in orientation of collagen fibrils under applied load in skin. Second Harmonic Generation (SHG) images of collagen fibrils were obtained at different strain magnitudes. Changes in collagen orientation were analyzed using Fast Fourier Transforms (FFT) while strain inhomogeneity was determined at different distances from hair follicles using Digital Image Correlation (DIC). A parameter, defined as the Collagen Orientation Index (COI), is introduced that accounts for the increasingly ellipsoidal nature of the FFT amplitude images upon loading. We show that the COI demonstrates two distinct mechanical regimes, one at low strains (0%, 2.5%, 5% strain) in which randomly oriented collagen fibrils align in the direction of applied deformation. In the second regime, beginning at 5% strain, collagen fibrils elongate in response to applied deformation. Furthermore, the COI is also found to be linearly correlated with the applied stress indicating that collagen fibrils orient to take the applied load. DIC results indicated that major principal strains were found to increase with increased load at all locations. In contrast, minimum principal strain was dependent on distance from hair follicles. These findings are significant because global and local changes in collagen deformations are expected to be changed by disease, and could affect stem cell populations surrounding hair follicles, including mesenchymal stem cells within the outer root sheath. Full article
(This article belongs to the Special Issue Mechanics of Biomaterials) Printed Edition available
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Open AccessArticle The Microstructural Evolution and Mechanical Properties of Zr-Based Metallic Glass under Different Strain Rate Compressions
Materials 2015, 8(4), 1831-1840; https://doi.org/10.3390/ma8041831
Received: 30 January 2015 / Revised: 23 March 2015 / Accepted: 10 April 2015 / Published: 16 April 2015
Cited by 7 | PDF Full-text (1425 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was
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In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD) and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10−3 to 5.1 × 103 s−1 and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB) and an MTS tester. An in situ transmission electron microscope (TEM) nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles. Full article
(This article belongs to the Special Issue Selected Papers from ICETI2014)
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Open AccessArticle Conductive Polymer Porous Film with Tunable Wettability and Adhesion
Materials 2015, 8(4), 1817-1830; https://doi.org/10.3390/ma8041817
Received: 7 January 2015 / Revised: 25 March 2015 / Accepted: 1 April 2015 / Published: 16 April 2015
Cited by 9 | PDF Full-text (2171 KB) | HTML Full-text | XML Full-text
Abstract
A conductive polymer porous film with tunable wettability and adhesion was fabricated by the chloroform solution of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacid-methyl-ester (PCBM) via the freeze drying method. The porous film could be obtained from the solution of 0.8 wt%, whose pore diameters ranged
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A conductive polymer porous film with tunable wettability and adhesion was fabricated by the chloroform solution of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacid-methyl-ester (PCBM) via the freeze drying method. The porous film could be obtained from the solution of 0.8 wt%, whose pore diameters ranged from 50 nm to 500 nm. The hydrophobic porous surface with a water contact angle (CA) of 144.7° could be transferred into a hydrophilic surface with CA of 25° by applying a voltage. The water adhesive force on the porous film increased with the increase of the external voltage. The electro-controllable wettability and adhesion of the porous film have potential application in manipulating liquid collection and transportation. Full article
(This article belongs to the Special Issue Mechanics of Biomaterials) Printed Edition available
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Open AccessReview Bone Regeneration Using Bone Morphogenetic Proteins and Various Biomaterial Carriers
Materials 2015, 8(4), 1778-1816; https://doi.org/10.3390/ma8041778
Received: 20 January 2015 / Revised: 24 March 2015 / Accepted: 27 March 2015 / Published: 15 April 2015
Cited by 14 | PDF Full-text (871 KB) | HTML Full-text | XML Full-text
Abstract
Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily
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Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily of proteins and are very promising and intensively studied for in the enhancement of bone healing. More than 20 types of BMPs have been identified but only a subset of BMPs can induce de novo bone formation. Many research groups have shown that BMPs can induce differentiation of mesenchymal stem cells and stem cells into osteogenic cells which are capable of producing bone. This review introduces BMPs and discusses current advances in preclinical and clinical application of utilizing various biomaterial carriers for local delivery of BMPs to enhance bone regeneration. Full article
(This article belongs to the Special Issue Dental Materials)
Open AccessArticle Effect of Heat Treatment on the Physical Properties of Provisional Crowns during Polymerization: An in Vitro Study
Materials 2015, 8(4), 1766-1777; https://doi.org/10.3390/ma8041766
Received: 12 December 2014 / Revised: 2 April 2015 / Accepted: 7 April 2015 / Published: 15 April 2015
Cited by 1 | PDF Full-text (1980 KB) | HTML Full-text | XML Full-text
Abstract
This study concerned the effect of heat treatment during setting on the physical properties of four resin-based provisional restorative materials: Duralay (polymethyl methacrylate), Trim II (polyethyl methacrylate), Luxatemp (bis-acrylic composite), and Protemp 4 (bis-acrylic composite). Specimens were prepared at 23, 37, or 60
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This study concerned the effect of heat treatment during setting on the physical properties of four resin-based provisional restorative materials: Duralay (polymethyl methacrylate), Trim II (polyethyl methacrylate), Luxatemp (bis-acrylic composite), and Protemp 4 (bis-acrylic composite). Specimens were prepared at 23, 37, or 60 °C for evaluation of flexural strength, surface roughness, color change and marginal discrepancy. Flexural strength was determined by a three-point bending test. Surface profile was studied using atomic force microscopy. Color change was evaluated by comparing the color of the materials before and after placement in coffee. A travelling microscope helped prepare standardized crowns for assessment of marginal discrepancy. Flexural strength of all tested materials cured at 23 °C or 37 °C did not significantly change. The surface roughness and marginal discrepancy of the materials increased at 60 °C curing temperature. Marginal discrepancies, color stability, and other physical properties of materials cured at 23 °C or 37 °C did not significantly change. Flexural strength of certain provisional materials cured at 60 °C increased, but there was also an increase in surface roughness and marginal discrepancy. Full article
(This article belongs to the Special Issue Dental Materials)
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Open AccessArticle Spherical V-Fe-MCM-48: The Synthesis, Characterization and Hydrothermal Stability
Materials 2015, 8(4), 1752-1765; https://doi.org/10.3390/ma8041752
Received: 14 February 2015 / Revised: 30 March 2015 / Accepted: 31 March 2015 / Published: 14 April 2015
Cited by 7 | PDF Full-text (3981 KB) | HTML Full-text | XML Full-text
Abstract
Spherical MCM-48 mesoporous sieve co-doped with vanadium and iron was successfully synthesized via one-step hydrothermal method. The material was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, inductively coupled plasma (ICP), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV-vis spectra,
[...] Read more.
Spherical MCM-48 mesoporous sieve co-doped with vanadium and iron was successfully synthesized via one-step hydrothermal method. The material was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, inductively coupled plasma (ICP), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV-vis spectra, and X-ray photoelectron spectra (XPS) techniques. Results indicated that the V-Fe-MCM-48 showed an ordered 3D cubic mesostructure with spherical morphology, narrow pore size distribution and high specific surface area. Most of vanadium and iron atoms existing as tetrahedral V4+ and Fe3+ species were co-doped into the silicate framework. The particle sizes of V-Fe-MCM-48 were smaller and the specific area was much higher than those of of V-MCM-48. Additionally, the synthesized V-Fe-MCM-48 exhibited improved hydrothermal stability compared with the pure MCM-48. Full article
(This article belongs to the Special Issue Advances in Mesoporous Material 2015)
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Open AccessArticle Preparation and Tribological Study of Biodegradable Lubrication Films on Si Substrate
Materials 2015, 8(4), 1738-1751; https://doi.org/10.3390/ma8041738
Received: 30 January 2015 / Revised: 23 March 2015 / Accepted: 7 April 2015 / Published: 14 April 2015
Cited by 10 | PDF Full-text (3797 KB) | HTML Full-text | XML Full-text
Abstract
A novel method for preparing eco-biodegradable lubricant based on hydroxypropyl methylcellulose (HPMC) via hydration process is demonstrated. The smooth and homogeneous HPMC coating has a uniform thickness (~35 μm). It has been demonstrated that the preparation parameters play a critical role in controlling
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A novel method for preparing eco-biodegradable lubricant based on hydroxypropyl methylcellulose (HPMC) via hydration process is demonstrated. The smooth and homogeneous HPMC coating has a uniform thickness (~35 μm). It has been demonstrated that the preparation parameters play a critical role in controlling the lubricating behavior of the coating; in addition, excess HPMC and water concentration suppress the tribology properties. Nevertheless, a remarkable friction-reduction and anti-wear performance has been obtained. Impressively, the preparation parameter of 5% HPMC + 30 mL water significantly improves lubricant performance and durability. A simple approach for the water-degradability evaluation of HPMC is proposed. Full article
(This article belongs to the Special Issue Selected Papers from ICETI2014)
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Open AccessArticle Direct Ink Writing of Three-Dimensional (K, Na)NbO3-Based Piezoelectric Ceramics
Materials 2015, 8(4), 1729-1737; https://doi.org/10.3390/ma8041729
Received: 11 March 2015 / Revised: 31 March 2015 / Accepted: 8 April 2015 / Published: 14 April 2015
Cited by 4 | PDF Full-text (1244 KB) | HTML Full-text | XML Full-text
Abstract
A kind of piezoelectric ink was prepared with Li, Ta, Sb co-doped (K, Na)NbO3 (KNN) powders. Piezoelectric scaffolds with diameters at micrometer scale were constructed from this ink by using direct ink writing method. According to the micro-morphology and density test, the
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A kind of piezoelectric ink was prepared with Li, Ta, Sb co-doped (K, Na)NbO3 (KNN) powders. Piezoelectric scaffolds with diameters at micrometer scale were constructed from this ink by using direct ink writing method. According to the micro-morphology and density test, the samples sintered at 1100 °C for 2 h have formed ceramics completely with a high relative density of 98%. X-ray diffraction (XRD) test shows that the main phase of sintered samples is orthogonal (Na0.52K0.4425Li0.0375)(Nb0.87Sb0.07Ta0.06)O3. The piezoelectric constant d33 of 280 pC/N, dielectric constant ε of 1775, remanent polarization Pr of 18.8 μC/cm2 and coercive field Ec of 8.5 kV/cm prove that the sintered samples exhibit good electrical properties. The direct ink writing method allows one to design and rapidly fabricate piezoelectric structures in complex three-dimensional (3D) shapes without the need for any dies or lithographic masks, which will simplify the process of material preparation and offer new ideas for the design and application of piezoelectric devices. Full article
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Open AccessArticle High Throughput Screening of Valganciclovir in Acidic Microenvironments of Polyester Thin Films
Materials 2015, 8(4), 1714-1728; https://doi.org/10.3390/ma8041714
Received: 1 December 2014 / Revised: 19 March 2015 / Accepted: 30 March 2015 / Published: 13 April 2015
Cited by 3 | PDF Full-text (635 KB) | HTML Full-text | XML Full-text
Abstract
Ganciclovir and valganciclor are antiviral agents used for the treatment of cytomegalovirus retinitis. The conventional method for administering ganciclovir in cytomegalovirus retinitis patients is repeated intravitreal injections. In order to obviate the possible detrimental effects of repeated intraocular injections, to improve compliance and
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Ganciclovir and valganciclor are antiviral agents used for the treatment of cytomegalovirus retinitis. The conventional method for administering ganciclovir in cytomegalovirus retinitis patients is repeated intravitreal injections. In order to obviate the possible detrimental effects of repeated intraocular injections, to improve compliance and to eliminate systemic side-effects, we investigated the tuning of the ganciclovir pro-drug valganciclovir and the release from thin films of poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), or mixtures of both, as a step towards prototyping periocular valganciclovir implants. To investigate the drug release, we established and evaluated a high throughput fluorescence-based quantification screening assay for the detection of valganciclovir. Our protocol allows quantifying as little as 20 ng of valganciclovir in 96-well polypropylene plates and a 50× faster analysis compared to traditional HPLC measurements. This improvement can hence be extrapolated to other polyester matrix thin film formulations using a high-throughput approach. The acidic microenvironment within the polyester matrix was found to protect valganciclovir from degradation with resultant increases in the half-life of the drug in the periocular implant to 100 days. Linear release profiles were obtained using the pure polyester polymers for 10 days and 60 days formulations; however, gross phase separations of PCL and acid-terminated PLGA prevented tuning within these timeframes due to the phase separation of the polymer, valganciclovir, or both. Full article
(This article belongs to the Special Issue Materials for Drug Delivery)
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Open AccessArticle Teflon/SiO2 Bilayer Passivation for Improving the Electrical Reliability of Oxide TFTs Fabricated Using a New Two-Photomask Self-Alignment Process
Materials 2015, 8(4), 1704-1713; https://doi.org/10.3390/ma8041704
Received: 7 January 2015 / Revised: 13 March 2015 / Accepted: 26 March 2015 / Published: 13 April 2015
Cited by 6 | PDF Full-text (895 KB) | HTML Full-text | XML Full-text
Abstract
This study proposes a two-photomask process for fabricating amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) that exhibit a self-aligned structure. The fabricated TFTs, which lack etching-stop (ES) layers, have undamaged a-IGZO active layers that facilitate superior performance. In addition, we demonstrate a bilayer
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This study proposes a two-photomask process for fabricating amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) that exhibit a self-aligned structure. The fabricated TFTs, which lack etching-stop (ES) layers, have undamaged a-IGZO active layers that facilitate superior performance. In addition, we demonstrate a bilayer passivation method that uses a polytetrafluoroethylene (Teflon) and SiO2 combination layer for improving the electrical reliability of the fabricated TFTs. Teflon was deposited as a buffer layer through thermal evaporation. The Teflon layer exhibited favorable compatibility with the underlying IGZO channel layer and effectively protected the a-IGZO TFTs from plasma damage during SiO2 deposition, resulting in a negligible initial performance drop in the a-IGZO TFTs. Compared with passivation-free a-IGZO TFTs, passivated TFTs exhibited superior stability even after 168 h of aging under ambient air at 95% relative humidity. Full article
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Open AccessReview Nanophotonics: Energy Transfer towards Enhanced Luminescent Chemosensing
Materials 2015, 8(4), 1682-1703; https://doi.org/10.3390/ma8041682
Received: 9 January 2015 / Revised: 24 March 2015 / Accepted: 30 March 2015 / Published: 13 April 2015
Cited by 1 | PDF Full-text (1844 KB) | HTML Full-text | XML Full-text
Abstract
We discuss a recently proposed novel photonic approach for enhancing the fluorescence of extremely thin chemosensing polymer layers. We present theoretical and experimental results demonstrating the concept of gain-assisted waveguided energy transfer (G-WET) on a very thin polymer nanolayer spincoated on an active
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We discuss a recently proposed novel photonic approach for enhancing the fluorescence of extremely thin chemosensing polymer layers. We present theoretical and experimental results demonstrating the concept of gain-assisted waveguided energy transfer (G-WET) on a very thin polymer nanolayer spincoated on an active ZnO thin film. The G-WET approach is shown to result in an 8-fold increase in polymer fluorescence. We then extend the G-WET concept to nanostructured media. The benefits of using active nanostructured substrates on the sensitivity and fluorescence of chemosensing polymers are discussed. Preliminary theoretical results on enlarged sensing surface and photonic band-gap are presented. Full article
(This article belongs to the Special Issue Luminescent Materials and Devices)
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Open AccessArticle A Thin C-Band Polarization and Incidence Angle-Insensitive Metamaterial Perfect Absorber
Materials 2015, 8(4), 1666-1681; https://doi.org/10.3390/ma8041666
Received: 30 January 2015 / Revised: 16 March 2015 / Accepted: 2 April 2015 / Published: 13 April 2015
Cited by 11 | PDF Full-text (1789 KB) | HTML Full-text | XML Full-text
Abstract
A novel metamaterial absorber design able to operate in the C frequency band is presented, along with an analysis and a method to improve both its bandwidth and its angular stability. Simulation results for a FR4-based design are shown for comparison with existing
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A novel metamaterial absorber design able to operate in the C frequency band is presented, along with an analysis and a method to improve both its bandwidth and its angular stability. Simulation results for a FR4-based design are shown for comparison with existing designs. In addition, a simplified equivalent circuit is provided for a better understanding of the great angular stability and wide bandwidth exhibited by the proposed structure. Moreover, simulations, manufacturing and measurements of a thinner and more flexible metamaterial absorber, keeping the angular stability of the former one, while providing a wide bandwidth, are presented. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Tuning the Pore Geometry of Ordered Mesoporous Carbons for Enhanced Adsorption of Bisphenol-A
Materials 2015, 8(4), 1652-1665; https://doi.org/10.3390/ma8041652
Received: 25 February 2015 / Revised: 26 March 2015 / Accepted: 31 March 2015 / Published: 10 April 2015
Cited by 9 | PDF Full-text (1002 KB) | HTML Full-text | XML Full-text
Abstract
Mesoporous carbons were synthesized via both soft and hard template methods and compared to a commercial powder activated carbon (PAC) for the adsorption ability of bisphenol-A (BPA) from an aqueous solution. The commercial PAC had a BET-surface of 1027 m2/g with
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Mesoporous carbons were synthesized via both soft and hard template methods and compared to a commercial powder activated carbon (PAC) for the adsorption ability of bisphenol-A (BPA) from an aqueous solution. The commercial PAC had a BET-surface of 1027 m2/g with fine pores of 3 nm and less. The hard templated carbon (CMK-3) material had an even higher BET-surface of 1420 m2/g with an average pore size of 4 nm. The soft templated carbon (SMC) reached a BET-surface of 476 m2/g and a pore size of 7 nm. The maximum observed adsorption capacity (qmax) of CMK-3 was the highest with 474 mg/g, compared to 290 mg/g for PAC and 154 mg/g for SMC. The difference in adsorption capacities was attributed to the specific surface area and hydrophobicity of the adsorbent. The microporous PAC showed the slowest adsorption, while the ordered mesopores of SMC and CMK-3 enhanced the BPA diffusion into the adsorbent. This difference in adsorption kinetics is caused by the increase in pore diameter. However, CMK-3 with an open geometry consisting of interlinked nanorods allows for even faster intraparticle diffusion. Full article
(This article belongs to the Special Issue Advances in Mesoporous Material 2015)
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Open AccessArticle Characterization of Fibrin and Collagen Gels for Engineering Wound Healing Models
Materials 2015, 8(4), 1636-1651; https://doi.org/10.3390/ma8041636
Received: 27 February 2015 / Revised: 27 March 2015 / Accepted: 2 April 2015 / Published: 10 April 2015
Cited by 19 | PDF Full-text (3343 KB) | HTML Full-text | XML Full-text
Abstract
Hydrogels are used for 3D in vitro assays and tissue engineering and regeneration purposes. For a thorough interpretation of this technology, an integral biomechanical characterization of the materials is required. In this work, we characterize the mechanical and functional behavior of two specific
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Hydrogels are used for 3D in vitro assays and tissue engineering and regeneration purposes. For a thorough interpretation of this technology, an integral biomechanical characterization of the materials is required. In this work, we characterize the mechanical and functional behavior of two specific hydrogels that play critical roles in wound healing, collagen and fibrin. A coherent and complementary characterization was performed using a generalized and standard composition of each hydrogel and a combination of techniques. Microstructural analysis was performed by scanning electron microscopy and confocal reflection imaging. Permeability was measured using a microfluidic-based experimental set-up, and mechanical responses were analyzed by rheology. We measured a pore size of 2.84 and 1.69 μm for collagen and fibrin, respectively. Correspondingly, the permeability of the gels was 1.00·10−12 and 5.73·10−13 m2. The shear modulus in the linear viscoelastic regime was 15 Pa for collagen and 300 Pa for fibrin. The gels exhibited strain-hardening behavior at ca. 10% and 50% strain for fibrin and collagen, respectively. This consistent biomechanical characterization provides a detailed and robust starting point for different 3D in vitro bioapplications, such as collagen and/or fibrin gels. These features may have major implications for 3D cellular behavior by inducing divergent microenvironmental cues. Full article
(This article belongs to the Special Issue Mechanics of Biomaterials) Printed Edition available
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Open AccessArticle Preparation of High Density Polyethylene/Waste Polyurethane Blends Compatibilized with Polyethylene-Graft-Maleic Anhydride by Radiation
Materials 2015, 8(4), 1626-1635; https://doi.org/10.3390/ma8041626
Received: 20 January 2015 / Revised: 13 March 2015 / Accepted: 30 March 2015 / Published: 8 April 2015
Cited by 6 | PDF Full-text (1890 KB) | HTML Full-text | XML Full-text
Abstract
Polyurethane (PU) is a very popular polymer that is used in a variety of applications due to its good mechanical, thermal, and chemical properties. However, PU recycling has received significant attention due to environmental issues. In this study, we developed a recycling method
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Polyurethane (PU) is a very popular polymer that is used in a variety of applications due to its good mechanical, thermal, and chemical properties. However, PU recycling has received significant attention due to environmental issues. In this study, we developed a recycling method for waste PU that utilizes the radiation grafting technique. Grafting of waste PU was carried out using a radiation technique with polyethylene-graft-maleic anhydride (PE-g-MA). The PE-g-MA-grafted PU/high density polyethylene (HDPE) composite was prepared by melt-blending at various concentrations (0–10 phr) of PE-g-MA-grafted PU. The composites were characterized using fourier transform infrared spectroscopy (FT-IR), and their surface morphology and thermal/mechanical properties are reported. For 1 phr PU, the PU could be easily introduced to the HDPE during the melt processing in the blender after the radiation-induced grafting of PU with PE-g-MA. PE-g-MA was easily reacted with PU according to the increasing radiation dose and was located at the interface between the PU and the HDPE during the melt processing in the blender, which improved the interfacial interactions and the mechanical properties of the resultant composites. However, the elongation at break for a PU content >2 phr was drastically decreased. Full article
(This article belongs to the Special Issue Smart Materials)
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Open AccessArticle Effect of Alkali-Acid-Heat Chemical Surface Treatment on Electron Beam Melted Porous Titanium and Its Apatite Forming Ability
Materials 2015, 8(4), 1612-1625; https://doi.org/10.3390/ma8041612
Received: 28 January 2015 / Revised: 23 March 2015 / Accepted: 30 March 2015 / Published: 8 April 2015
Cited by 9 | PDF Full-text (607 KB) | HTML Full-text | XML Full-text
Abstract
Advanced additive manufacturing techniques such as electron beam melting (EBM), can produce highly porous structures that resemble the mechanical properties and structure of native bone. However, for orthopaedic applications, such as joint prostheses or bone substitution, the surface must also be bio-functionalized to
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Advanced additive manufacturing techniques such as electron beam melting (EBM), can produce highly porous structures that resemble the mechanical properties and structure of native bone. However, for orthopaedic applications, such as joint prostheses or bone substitution, the surface must also be bio-functionalized to promote bone growth. In the current work, EBM porous Ti6Al4V alloy was exposed to an alkali acid heat (AlAcH) treatment to bio-functionalize the surface of the porous structure. Various molar concentrations (3, 5, 10M) and immersion times (6, 24 h) of the alkali treatment were used to determine optimal parameters. The apatite forming ability of the samples was evaluated using simulated body fluid (SBF) immersion testing. The micro-topography and surface chemistry of AlAcH treated samples were evaluated before and after SBF testing using scanning electron microscopy and energy dispersive X-ray spectroscopy. The AlAcH treatment successfully modified the topographical and chemical characteristics of EBM porous titanium surface creating nano-topographical features ranging from 200–300 nm in size with a titania layer ideal for apatite formation. After 1 and 3 week immersion in SBF, there was no Ca or P present on the surface of as manufactured porous titanium while both elements were present on all AlAcH treated samples except those exposed to 3M, 6 h alkali treatment. An increase in molar concentration and/or immersion time of alkali treatment resulted in an increase in the number of nano-topographical features per unit area as well as the amount of titania on the surface. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Effect of Different Luting Agents on the Retention of Lithium Disilicate Ceramic Crowns
Materials 2015, 8(4), 1604-1611; https://doi.org/10.3390/ma8041604
Received: 17 January 2015 / Revised: 28 March 2015 / Accepted: 31 March 2015 / Published: 7 April 2015
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Abstract
No studies are available that evaluate the retention of disilicate crowns according to different cementation procedures. The purpose of this study was to measure the retention of lithium disilicate crowns cemented using two different cementation systems. Twenty extracted mandibular premolars were prepared. Anatomic
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No studies are available that evaluate the retention of disilicate crowns according to different cementation procedures. The purpose of this study was to measure the retention of lithium disilicate crowns cemented using two different cementation systems. Twenty extracted mandibular premolars were prepared. Anatomic crowns were waxed and hot pressed using lithium disilicate ceramic. Teeth were divided into two groups (n = 10): (1) self-curing luting composite and (2) glass-ionomer cement (GIC). After cementation, the crowns were embedded in acrylic resin block with a screw base. Each specimen was pulled along the path of insertion in Universal Testing Machine. Failure load in Newtons (N) and failure mode were recorded for each specimen. Failure mode was classified as decementation or fracture. Failure load data were analyzed using one-way analysis of variance (ANOVA). Failure modes were compared using Pearson’s Chi-square test. Mean failure load was 306.6(±193.8) N for composite group and 94.7(±48.2) N for GIC group (p = 0.004). Disilicate crown cemented with luting composite most often failed by fracture; otherwise, crown cemented with glass-ionomer cement most often failed by decementation (p = 0.02). Disilicate full crown cemented with luting composite showed higher failure load compared with conventional cementation with glass-ionomer cement. Full article
(This article belongs to the Special Issue Dental Materials)
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Open AccessArticle A Six-Fold Symmetric Metamaterial Absorber
Materials 2015, 8(4), 1590-1603; https://doi.org/10.3390/ma8041590
Received: 12 January 2015 / Revised: 24 March 2015 / Accepted: 30 March 2015 / Published: 3 April 2015
Cited by 13 | PDF Full-text (984 KB) | HTML Full-text | XML Full-text
Abstract
A novel microwave metamaterial absorber design is introduced along with its manufacturing and characterization. Significant results considering both bandwidth and angular stability are achieved. Parametric analysis and simplified equivalent circuit are provided to give an insight on the key elements influencing the absorber
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A novel microwave metamaterial absorber design is introduced along with its manufacturing and characterization. Significant results considering both bandwidth and angular stability are achieved. Parametric analysis and simplified equivalent circuit are provided to give an insight on the key elements influencing the absorber performance. In addition, the constitutive parameters of the effective medium model are obtained and related to the absorber resonant behavior. Moreover, a new thinner and more flexible absorber version, preserving broad bandwidth and angular insensitive performance, is simulated, and an 8 × 8 unit-cells prototype is manufactured and measured for a limited angular margin in an anechoic chamber. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle All-Ceramic Single Crown Restauration of Zirconia Oral Implants and Its Influence on Fracture Resistance: An Investigation in the Artificial Mouth
Materials 2015, 8(4), 1577-1589; https://doi.org/10.3390/ma8041577
Received: 23 February 2015 / Revised: 20 March 2015 / Accepted: 27 March 2015 / Published: 1 April 2015
Cited by 5 | PDF Full-text (1032 KB) | HTML Full-text | XML Full-text
Abstract
The aim of the current investigation was to evaluate the fracture resistance of one-piece zirconia oral implants with and without all-ceramic incisor crowns after long-term thermomechanical cycling. A total of 48 implants were evaluated. The groups with crowns (C, 24 samples) and without
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The aim of the current investigation was to evaluate the fracture resistance of one-piece zirconia oral implants with and without all-ceramic incisor crowns after long-term thermomechanical cycling. A total of 48 implants were evaluated. The groups with crowns (C, 24 samples) and without crowns (N, 24 samples) were subdivided according to the loading protocol, resulting in three groups of 8 samples each: Group “0” was not exposed to cyclic loading, whereas groups “5” and “10” were loaded with 5 and 10 million chewing cycles, respectively. This resulted in 6 different groups: C0/N0, C5/N5 and C10/N10. Subsequently, all 48 implants were statically loaded to fracture and bending moments were calculated. All implants survived the artificial aging. For the static loading the following average bending moments were calculated: C0: 326 Ncm; C5: 339 Ncm; C10: 369 Ncm; N0: 339 Ncm; N5: 398 Ncm and N10: 355 Ncm. To a certain extent, thermomechanical cycling resulted in an increase of fracture resistance which did not prove to be statistically significant. Regarding its fracture resistance, the evaluated ceramic implant system made of Y-TZP seems to be able to resist physiological chewing forces long-term. Restauration with all-ceramic single crowns showed no negative influence on fracture resistance. Full article
(This article belongs to the Special Issue Dental Materials)
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