Template-assisted electrohydrodynamic atomization of polycaprolactone for orthopedic patterning applications

This paper presents the development of the novel deposition of biodegradable polycaprolactone (PCL) polymer patterns on a metallic substrate using a jet spraying technique, template-assisted electrohydrodynamic atomization (TAEA), at ambient temperature. The structure of patterns was controlled by systematically varying the polymer concentration (2–15 wt.%) and the flow rate (1–25 μl min^? 1). Polymer deposition was carried out in the stable cone-jet mode to precisely control the surface structure and morphology. The patterns were studied by optical microscopy, scanning electron microscopy and profilometry, and a high degree of control over the pattern geometry and thickness was achieved by varying the spraying time. The hardness and the effective elastic modulus of the polymer patterns were estimated using nanoindentation. The effect of load, loading rate and the holding time on the hardness and effective elastic modulus was derived. Optimal results were obtained with 5 wt.% PCL in DMAC solution sprayed within the stable cone-jet mode operating window at a flow rate of 15 μl min^? 1 for 300 s at 11.1 kV with a working distance of 60 mm. Hexagonal patterns were well-defined and repeatable with thickness of ~ 34 μm. The hardness is 1.6 MPa at a loading rate of 0.1 μN/s and nearly halved when the load rate was increased to 1 μN/s. The effective elastic modulus of ~ 12 MPa is obtained for a load rate of 0.1 μN/s.     

Mechanical properties of conventional and nanostructured plasma sprayed alumina coatings

The hardness and the elastic modulus measured by microindentation of three different types of plasma sprayed alumina coatings have been compared. Usually, such coatings present porosity and heterogeneity which affect the measurement of the mechanical properties. To take such effects into account along with the indentation size effect which is relevant to all hardness studies, the Proportional Specimen Resistance model is applied. The three alumina coatings show closely similar mechanical properties at indentation loads exceeding 1 N, i.e., macrohardness around 5.7 GPa, indentation size effect parameter around 5.5 MPa mm and elastic modulus around 160 GPa. For loads below 1 N, the extrapolated values of the macrohardness of crushed and agglomerated alumina coatings increased to 8.5 GPa, while the indentation size effect parameter has the same value, and the elastic modulus increased to 320 GPa. However, no significant change in the measured values of hardness and the elastic modulus of the nanostructured alumina coating has been observed. This result is attributed to porosity and the bimodal microstructure of the nanostructured coating where a semimolten phase coexists along with the fully molten phases.     

Nanocomposite protective coatings based on Ti–N–Cr/Ni–Cr–B–Si–Fe,their structure and properties

The first results of manufacturing and investigations of a new type of nanocomposite protective coatings are presented. They were manufactured using a combination of two technologies: plasma-detonation coating deposition with the help of plasma jets and thin coating vacuum-arc deposition. We investigated structure, morphology, physical and mechanical properties of the coatings of 80–90 μm thickness, as well as defined the hardness, elastic Young modulus and their corrosion resistance in different media. Grain dimensions of the nanocomposite coatings on Ti–N–Cr base varied from 2.8 to 4 nm. The following phases and compounds formed as a result of plasma interaction with the thick coating surface were found in the coatings: Ti–N–Cr (200), (220), γ-Ni₃–Fe, a hexagonal Cr₂–Ti, Fe₃–Ni, (Fe, Ni)N and the following Ti–Ni compounds: Ti₂Ni, Ni₃Ti, Ni₄Ti, etc. We also found that the nanocomposite coating microhardness increased to H = 31.6 ± 1.1 GPa. The Young elastic modulus was determined to be E = 319 ± 27 GPa – it was derived from the loading–unloading curves. The protective coating demonstrated the increased corrosion resistance in acidic and alkaline media in comparison with that of the stainless steel substrate.     

Mechanical and wear behaviours of nano and microfilled polymeric composite: Effect of filler fraction and size

The addition of ceramic reinforced material, SiC particles, to resin matrices, results in the improvement of the overall performance of the composite, allowing the application of these materials as tribo-materials in industries such as: automotive, aeronautical and medical. Particle-reinforced polymeric composites are widely used as biomaterials, for example as dental filler materials and bone cements. These reinforced composites have improved mechanical and tribological performance and have higher values of elastic modulus and hardness, and also reduce the shrinkage during the polymerisation compared with resin matrices. However, the effect of the filler level in mechanical and tribological behaviour is not quite understood.The aim of this work is to determine the influence of the particle volume fraction and particle size in the wear loss of the composites and their antagonists. Reciprocating wear tests were conducted using a glass sphere against resin polyester silica reinforced composite in a controlled medium, with an abrasive slurry or distilled water. For 6 μm average particle dimension, seven particles contents were studied ranging from 0% to 46% of filler volume fraction (FVF). Afterwards, filler volume fractions of 10% and 30% were selected; and, for these percentages, 7 and 4 average particle dimensions were tested and were evaluated regarding their wear behaviour, respectively. The reinforcement particle dimensions used ranged from 0.1 μm to 22 μm with the 10% filler fraction, and for 30% of filler content the range extended from 3 μm to 22 μm. The results allow us to conclude that in an abrasive slurry medium the composite abrasion resistance decreases with the increase of the particle volume fraction, in spite of the accompanying rise in hardness and elastic modulus. With constant FVF, and abrasive slurry, the composite wear resistance increases with increasing average particle dimension. In a distilled water medium and with several FVF values, the minimum wear was registered for a median particle content of 24%. In this medium and with constant FVF the highest wear resistance occurred for average reinforcement particles of 6 μm. The removal mechanisms involved in the wear process are discussed, taking into account the systematic SEM observations to evaluate the wear mechanisms.     

Effect of cryo-induced microcracks on microindentation of hydrated cortical bone tissue

Microcracks accumulate in cortical bone tissue as a consequence of everyday cyclic loading. However, it remains unclear to what extent microdamage accumulation contributes to an increase in fracture risk. A cryo-preparation technique was applied to induce microcracks in cortical bone tissue. Microcracks with lengths up to approximately 20 μm, which were initiated mainly on the boundaries of haversian canals, were observed with cryo-scanning electron microscopy. A microindentation technique was applied to study the mechanical loading effect on the microcracked hydrated bone tissue. The microindentation patterns were section-scanned using confocal laser scanning microscopy to understand the deformation and bone damage mechanisms made by mechanical loading. The results show that there was no significant difference with respect to microhardness between the original and microcracked hydrated cortical bone tissues (ANOVA, p > 0.05). The cryo-induced microcracks in the bone tissue were not propagated further under the mechanical loads applied. The deformation mechanism of the microcracked cortical bone tissue was plastic deformation, not brittle fracture.     

Effects of sintering temperature on morphology and mechanical characteristics of 3D printed porous titanium used as dental implant

Porous titanium samples were manufactured using the 3D printing and sintering method in order to determine the effects of final sintering temperature on morphology and mechanical properties. Cylindrical samples were printed and split into groups according to a final sintering temperature (FST). Irregular geometry samples were also printed and split into groups according to their FST. The cylindrical samples were used to determine part shrinkage, in compressive tests to provide stress-strain data, in microCT scans to provide internal morphology data and for optical microscopy to determine surface morphology. All of the samples were used in microhardness testing to establish the hardness. Below 1100 °C FST, shrinkage was in the region of 20% but increased to approximately 30% by a FST of 1300 °C. Porosity varied from a maximum of approximately 65% at the surface to the region of 30% internally. Between 97 and 99% of the internal porosity is interconnected. Average pore size varied between 24 μm at the surface and 19 μm internally. Sample hardness increased to in excess of 300 HV0.05 with increasing FST while samples with an FST of below 1250 °C produced an elastic–brittle stress/strain curve and samples above this displayed elastic–plastic behaviour. Yield strength increased significantly through the range of sintering temperatures while the Young's modulus remained fairly consistent.     

The effects of fatigue and residual strain on the mechanical behavior of poly(ethylene terephthalate) unreinforced and nanocomposite fibers

Poly(ethylene terephthalate) (PET) control fibers (nominal diameter ～24 ± 3 μm) and PET fibers with embedded vapor-grown carbon nanofibers (PET-VGCNF) (nominal diameter ～25 ± 2 μm) were exposed to cyclic loading and monotonic tensile tests. The control fibers were processed through a typical melt-blending technique and the PET-VGCNF samples were processed with approximately 5 wt.% carbon nanofibers present in the sample. Under uniaxial fatigue conditions, the fibers were subjected to a maximum stress that was approximately 60% of the fracture stress of the sample at an elongation rate of 10 mm/min in uniaxial tension. The fibers were subjected to a frequency of 5 Hz. Subsequent to non-fracture fatigue conditions, the fibers were tested under uniaxial stress conditions for observation of the change in mechanical properties to assess the effects of fatigue loading. The elastic modulus, hardening modulus, fracture strength, work done, and yield strain of both PET control and PET-VGCNF samples in uniaxial tension subsequent to fatigue were shown to be dependent on the residual fatigue strains. Relative mechanical properties were used to quantify the difference in PET and PET-VGCNF samples as a function of residual strain. In most cases, the results indicated a strengthening mechanism (strain hardening effect) in the low residual strain limit for fatigued PET samples and not for fatigued PET-VGCNF samples. In comparison with the unreinforced PET sample, the PET-VGCNF fibers showed greater degradation of mechanical properties as a function of residual strain due to fatigue when cycled at 60% of the fracture stress. The effects of the fatigue process on the change in mechanical properties have been quantified and supported through existing qualitative, quantitative, and scanning electron microscopy (SEM) techniques.     

Carbon nanotube reinforced small diameter polyacrylonitrile based carbon fiber

Polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) composite (99/1) based carbon fibers with an effective diameter of about 1 μm have been processed using island-in-a-sea bi-component cross-sectional geometry and gel spinning. PAN/CNT (99/1) based carbon fibers processed using this approach exhibited a tensile strength of 4.5 GPa (2.5 N/tex) and tensile modulus of 463 GPa (257 N/tex), while these values for the control PAN-based carbon fiber processed under the similar conditions were 3.2 GPa (1.8 N/tex) and 337 GPa (187 N/tex), respectively. Properties of these 1 μm diameter carbon fibers have been compared to the properties of the larger diameter (>6 μm) PAN and PAN/CNT based carbon fibers.     

Resistance of blended cement pastes subjected to organic acids: Quantification of anhydrous and hydrated phases

Concrete for agricultural construction is often subject to aggressive environmental conditions. Ground granulated blast furnace slag (GGBFS) or metakaolin (MK) largely improve the chemical resistance of the binder. Anhydrous particles seem particularly resistant to the acid solution. The purpose of this study is to quantify anhydrous particles in blended cement pastes as a function of acid exposition time in order to evaluate their acid resistance.Cement pastes were moist cured for 28 days and then immersed in an acetic acid solution for 2 months. The quantification of the anhydrous phases was carried out using ²⁹Si MAS NMR, selective dissolution and back-scattered electron (BSE) images analysis, while the hydrated phases content was evaluated by TGA. After 28 days of hydration, 60% of OPC, 44% of GGBFS and 76% of MK particles were hydrated. The amount of anhydrous particles drops for all materials during acid immersion. After 2 months of immersion, the amount of anhydrous particles drops by 49%, 23% and 15% for OPC, GGBFS, and MK respectively. This study confirms that GGBFS and MK anhydrous and hydrates phases present higher acid resistance than OPC.     

Processing and mechanical properties of porous Ti–7.5Mo alloy

Titanium (Ti) and its alloys continue to be utilized extensively for skeletal repair and dental implants. Most metallic implant materials including pure Ti and Ti alloys used today are in their solid forms and are often much stiffer than human bone. However, the elastic modulus of Ti and Ti alloys can be reduced through the introduction of a porous structure, which may also provide new bone tissue integration and vascularization abilities. In the present study, porous Ti–7.5Mo alloy scaffolds made from ball-milled alloy particles and sintered at 1100 °C for 10, 15 and 20 h respectively were successfully prepared through a space-holder sintering method. In the sintered Ti–7.5Mo, no obvious diffraction peaks of elemental Mo remained after the sintering, and a duplex α + β microstructure was confirmed from the XRD pattern. The samples made from BM15 (the alloy particles ball-milled for 15 h) had higher relative density, compressive strength and elastic modulus performance than those from BM3 and BM30 (the alloy particles ball-milled for 3 and 30 h, respectively) when they were sintered under the same conditions. Moreover, the longer sintering time lead to the higher relative density and the greater compressive strength and modulus of the sample. In this work, the strength and modulus of the sintered porous Ti–7.5Mo conforms to the basic mechanical property requirement of cancellous bones.     

Effect of plasma CVD operating temperature on nanomechanical properties of TiC nanostructured coating investigated by atomic force microscopy

The structure, composition, and mechanical properties of nanostructured titanium carbide (TiC) coatings deposited on H₁₁ hot-working tool steel by pulsed-DC plasma assisted chemical vapor deposition at three different temperatures are investigated. Nanoindentation and nanoscratch tests are carried out by atomic force microscopy to determine the mechanical properties such as hardness, elastic modulus, surface roughness, and friction coefficient. The nanostructured TiC coatings prepared at 490 °C exhibit lower friction coefficient (0.23) than the ones deposited at 470 and 510 °C. Increasing the deposition temperature reduces the Young's modulus and hardness. The overall superior mechanical properties such as higher hardness and lower friction coefficient render the coatings deposited at 490 °C suitable for wear resistant applications.     

Microindentation creep of monophasic calcium–silicate–hydrates

Microindentation creep results for monophasic synthetic C–S–H (C/S = 0.6–1.5), 1.4 nm tobermorite, jennite and calcium hydroxide at 11%RH are reported. Creep results for well hydrated cement paste and C₃S ‘composite’ systems are also described. The significance of the co-linear behavior of creep modulus functions of indentation modulus and indentation hardness for C–S–H obtained by microindentation and nanoindentation methods is discussed. The porosity dependence of creep modulus and the general equivalence of density values determined by helium pycnometry and by calculations employing unit cell dimensions (obtained using X-ray crystallography techniques) are also discussed in terms of postulates for the existence of two types of C–S–H. Comment on the compatibility of the creep modulus data for 1.4 nm tobermorite and jennite with models of C–S–H present in cement paste is provided.     

Porous and strong bioactive glass (13–93) scaffolds fabricated by freeze extrusion technique

Scaffolds fabricated by current methods often lack the combination of high strength and high porosity for skeletal substitution of load-bearing bones. In this work, freeze extrusion fabrication (FEF), a solid freeform fabrication technique, was investigated for the creation of porous and strong bioactive glass (13–93) scaffolds for potential applications in the repair of loaded bone. The process parameters for forming three-dimensional (3D) scaffolds with a pre-designed, grid-like microstructure by FEF were determined. Following thermal treatment of the as-formed constructs at temperatures up to 700 °C, scaffolds consisting of dense glass struts and interconnecting pores (porosity ≈ 50%; pore width ≈ 300 μm) were obtained. These scaffolds showed an elastic mechanical response in compression, with a compressive strength of 140 ± 70 MPa and an elastic modulus of 5.5 ± 0.5 GPa, comparable to the values for human cortical bone. The scaffolds supported the proliferation of osteogenic cells in vitro, showing their biocompatibility. These results indicate that 13–93 bioactive glass scaffolds created by the FEF method could have potential application in the repair and regeneration of load-bearing bones.     

Investigation of structural,optical and micro-mechanical properties of (NdyTi1 − y)Ox thin films deposited by magnetron sputtering

TiO₂ and (Nd_yTi_1 − y)O_x thin films were deposited by reactive magnetron sputtering process from mosaic Ti–Nd targets and characterised by X-ray diffraction (XRD), Raman optical spectroscopy and nanoindentation technique. XRD measurements revealed that as-prepared titanium dioxide and TiO₂ thin films with 4 and 7 at.% of Nd had nanocrystalline rutile structure, while coatings with larger amount of Nd were amorphous. Raman spectroscopy investigations showed that the increase of the neodymium concentration caused amorphisation of the coatings and hindered their crystal growth. All as-prepared coatings were transparent in the visible wavelength range with a transmittance of approximately 80%. The refractive index and extinction coefficient of the thin films gradually decreased with the increase of the neodymium concentration. Micro-mechanical properties, i.e. hardness and elastic modulus, were determined using traditional load-controlled nanoindentation testing and continuous stiffness measurements. The highest hardness and elastic modulus values were obtained for thin films with 7 at.% of Nd and were approximately 14.8 GPa and 166.3 GPa, respectively.     

First-principles calculations of mechanical and thermodynamic properties of YAlO3

First-principles calculations are performed to investigate the crystal structure, electronic properties, the elastic properties, hardness and thermodynamic properties of YAlO₃. The calculated ground-state quantities such as lattice parameter, bulk modulus and its pressure derivative, the band structure and densities of states were in favorable agreement with previous works and the existing experimental data. The elastic constants C_ij, the aggregate elastic moduli (B, G, E), the Poisson’s ratio, and the elastic anisotropy have been investigated. YAlO₃ exhibits a slight elastic anisotropy according to the universal elastic anisotropy index A^U = 0.24. The estimated hardness for YAlO₃ is consistent with the experimental value, and Al–O bond in AlO₆ octahedra plays an important role in the high hardness. The Y–O bonds in YO₁₂ polyhedra exhibit different characteristic. Using the quasi-harmonic Debye model considering the phonon effects, the temperature and pressure dependencies of bulk modulus, heat capacity and thermal expansion coefficient are investigated systematically in the ranges of 0–20 GPa and 0–1300 K.     

Nanoscale characterization of bone–implant interface and biomechanical modulation of bone ingrowth

Bone–implant interface is characterized by an array of cells and macromolecules. This study investigated the nanomechancial properties of bone–implant interface using atomic force microscopy in vitro, and the mechanical modulation of implant bone ingrowth in vivo using bone histomorphometry. Upon harvest of screw-type titanium implants placed in vivo in the rabbit maxilla and proximal femur for 4 weeks, nanoindentation was performed in the bone–implant interface at 60-μm intervals radially from the implant surface. The average Young's Moduli (E) of the maxillary bone–implant interface was 1.13 ± 0.27 MPa, lacking significant differences at all intervals. In contrast, an increasing gradient of E was observed radially from the femur bone–implant interface: 0.87 ± 0.25 MPa to 2.24 ± 0.69 MPa, representing significant differences among several 60-μm intervals. In a separate experiment, bone healing was allowed for 6 weeks for proximal femur implants. The right femoral implant received axial cyclic loading at 200 mN and 1 Hz for 10 min/d over 12 days, whereas the left femoral implant served as control. Cyclic loading induced significantly higher bone volume, osteoblast numbers per endocortical bone surface, mineral apposition rate, and bone formation rate than controls. These data demonstrate nanoscale and microscale characterizations of bone–implant interface, and mechanical modulation of bone ingrowth surrounding titanium implants.     

Stress analysis in bone tissue around single implants with different diameters and veneering materials: A 3-D finite element study

The aim of this study was to evaluate the stress distribution on bone tissue with a single prosthesis supported by implants of large and conventional diameter and presenting different veneering materials using the 3-D finite element method. Sixteen models were fabricated to reproduce a bone block with implants, using two diameters (3.75 × 10 mm and 5.00 × 10 mm), four different veneering materials (composite resin, acrylic resin, porcelain, and NiCr crown), and two loads (axial (200 N) and oblique (100 N)). For data analysis, the maximum principal stress and von Mises criterion were used. For the axial load, the cortical bone in all models did not exhibit significant differences, and the trabecular bone presented higher tensile stress with reduced implant diameter. For the oblique load, the cortical bone presented a significant increase in tensile stress on the same side as the loading for smaller implant diameters. The trabecular bone showed a similar but more discreet trend. There was no difference in bone tissue with different veneering materials. The veneering material did not influence the stress distribution in the supporting tissues of single implant-supported prostheses. The large-diameter implants improved the transference of occlusal loads to bone tissue and decreased stress mainly under oblique loads. Oblique loading was more detrimental to distribution stresses than axial loading.     

Analysis of heat-treated bovine cortical bone by thermal gravimetric and nanoindentation

Xenograft bone has been widely used as a bone grafting material because it gains advantages in biological and mechanical properties as compare with the use of an allograft bone. Heat-treatment of bone is recognized as one of the simple and practical methods to lower the human immunodeficiency virus (HIV) infection and overcome the risks of rejection and disease transfer during the bone transplantation. Therefore, understanding the change of bone’s organic matrix after heat treatment has become a significant topic. In this study, thermal gravimetric analysis (TGA) was used to investigate the condition of organic constituents of a bovine cortical bone. In order to well characterize the microstructural and mechanical property of the bone after heat treatment, nanoindention technique was also employed to measure the localized elastic modulus (E) and hardness (H) of its interstitial lamellae and osteons lamellae at the temperatures of 23 °C (RT), 37 °C, 90 °C, 120 °C and 160 °C, respectively.The TGA results demonstrated that heat-treated bones had three stages of weight loss. The first stage was the loss of water, which started from RT to 160 °C. Follow by a weight loss of organic constituents starting from 200 °C to 600 °C. Upon reaching 600 °C, the organic constituents were decomposed and mineral phase loss started taking place until 850 °C. From the nanoindentation results, it showed the values of E and H measured for the interstitial lamellae were higher than that of the osteons lamellae. This phenomenon indicates that the interstitial lamellae are stiffer and easy to be mineralized than osteons lamellae. For a specimen heat-treated at 90 °C, the values of E and H of interstitial lamellae and osteons lamellae were similar to a non-heat-treated specimen. For a specimen heat-treated at 120 °C, its interstitial lamellae had higher E and H values than osteons lamellae. When a specimen was heat-treated at 160 °C, both interstitial lamellae and osteons lamellae demonstrated a slight decrease of their E and H values. An ANOVA statistical analysis was used to analyze the difference in elastic properties and hardness in various temperature ranges.     

Crystallization and hardening of Zr-40 at.% Cu thin film metallic glass: Effects of isothermal annealing

Effects of isothermal annealing on structural relaxation, crystallization and mechanical behavior of Zr-40 at.% Cu thin film metallic glass (TFMG) are reported. Two annealing temperatures have been chosen in the supercooled liquid region (ΔT) and one below the glass transition temperature (T_g). During annealing the free volume decreased and nanocrystals nucleated into the matrix. Results show that the nanocrystalline CuZr₂ intermetallic phase precipitates in the glassy matrix with respect to the annealing temperature and duration. When annealed below T_g, the structural relaxation induces a slight improvement of the mechanical properties with a hardness and Young's modulus variation of about 2.5% and 9.0% compared with the as-deposited values. At higher temperatures, it is shown that hardness increases of about 5.5% and 25.0% after a heat treatment of 60 min at 350 °C and 380 °C, respectively. The elastic modulus follows a time dependent increase from ~ 100 GPa (as-deposited) up to ~ 105 GPa after a one-hour annealing at 350 °C and ~ 125 GPa at 380 °C, respectively.     

Co-electrospun blends of PU and PEG as potential biocompatible scaffolds for small-diameter vascular tissue engineering

A small-diameter vascular graft (inner diameter 4 mm) was fabricated from polyurethane (PU) and poly(ethylene glycol) (PEG) solutions by blend electrospinning technology. The fiber diameter decreased from 1023 ± 185 nm to 394 ± 106 nm with the increasing content of PEG in electrospinning solutions. The hybrid PU/PEG scaffolds showed randomly nanofibrous morphology, high porosity and well-interconnected porous structure. The hydrophilicity of these scaffolds had been improved significantly with the increasing contents of PEG. The mechanical properties of electrospun hybrid PU/PEG scaffolds were obviously different from that of PU scaffold, which was caused by plasticizing or hardening effect imparted by PEG composition. Under hydrated state, the hybrid PU/PEG scaffolds demonstrated low mechanical performance due to the hydrophilic property of materials. Compared with dry PU/PEG scaffolds with the same content of PEG, the tensile strength and elastic modulus of hydrated PU/PEG scaffolds decreased significantly, while the elongation at break increased. The hybrid PU/PEG scaffolds demonstrated a lower possibility of thrombi formation than blank PU scaffold in platelet adhesion test. The hemolysis assay illustrated that all scaffolds could act as blood contacting materials. To investigate further in vitro cytocompatibility, HUVECs were seeded on the scaffolds and cultured over 14 days. The cells could attach and proliferate well on the hybrid scaffolds than blank PU scaffold, and form a cell monolayer fully covering on the PU/PEG (80/20) hybrid scaffold surface. The results demonstrated that the electrospun hybrid PU/PEG tubular scaffolds possessed the special capacity with excellent hemocompatibility while simultaneously supporting extensive endothelialization with the 20 and 30% content of PEG in hybrid scaffolds.