Pore Depth Research Articles

Impaction durability of porous polyether-ether-ketone (PEEK) and titanium-coated PEEK interbody fusion devices

Background ContextVarious surface modifications, often incorporating roughened or porous surfaces, have recently been introduced to enhance osseointegration of interbody fusion devices. However, these topographical features can be vulnerable to damage during clinical impaction. Despite the potential negative impact of surface damage on clinical outcomes, current testing standards do not replicate clinically relevant impaction loading conditions. PurposeThe purpose of this study was to compare the impaction durability of conventional smooth polyether-ether-ketone (PEEK) cervical interbody fusion devices with two surface-modified PEEK devices that feature either a porous structure or plasma-sprayed titanium coating. Study Design/SettingA recently developed biomechanical test method was adapted to simulate clinically relevant impaction loading conditions during cervical interbody fusion procedures. MethodsThree cervical interbody fusion devices were used in this study: smooth PEEK, plasma-sprayed titanium-coated PEEK, and porous PEEK (n=6). Following Kienle et al., devices were impacted between two polyurethane blocks mimicking vertebral bodies under a constant 200 N preload. The posterior tip of the device was placed at the entrance between the polyurethane blocks, and a guided 1-lb weight was impacted upon the anterior face with a maximum speed of 2.6 m/s to represent the strike force of a surgical mallet. Impacts were repeated until the device was fully impacted. Porous PEEK durability was assessed using micro-computed tomography (µCT) pre- and postimpaction. Titanium-coating coverage pre- and postimpaction was assessed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy. Changes to the surface roughness of smooth and titanium-coated devices were also evaluated. ResultsPorous PEEK and smooth PEEK devices showed minimal macroscopic signs of surface damage, whereas the titanium-coated devices exhibited substantial visible coating loss. Quantification of the porous PEEK deformation demonstrated that the porous structure maintained a high porosity (>65%) following impaction that would be available for bone ingrowth, and exhibited minimal changes to pore size and depth. SEM and energy dispersive X-ray spectroscopy analysis of titanium-coated devices demonstrated substantial titanium coating loss after impaction that was corroborated with a decrease in surface roughness. Smooth PEEK showed minimal signs of damage using SEM, but demonstrated a decrease in surface roughness. ConclusionAlthough recent surface modifications to interbody fusion devices are beneficial for osseointegration, they may be susceptible to damage and wear during impaction. The current study found porous PEEK devices to show minimal damage during simulated cervical impaction, whereas titanium-coated PEEK devices lost substantial titanium coverage.

A flexible SERS-active film for studying the effect of non-metallic nanostructures on Raman enhancement.

Since the discovery of surface enhanced Raman scattering (SERS), the choice of SERS-active materials has been limited mainly to metals, especially gold and silver in the visible spectrum. Although non-metals can also be SERS-active by forming nanostructures or composite structures with SERS-active materials, the mechanism behind it is still unclear and there is no perfect technique to study it. In this work, by constructing a SERS structure on a flexible polydimethylsiloxane film, we provide a way to study the effect of non-metallic nanostructures on Raman enhancement by attaching the above film onto flat and nanostructured surfaces. It was found that a nanoporous silicon surface contributes to an additional, up to five times, Raman enhancement. The pore depth and pore size also influence the observed Raman enhancement. These findings will help us not only to understand the mechanism of SERS involving non-metallic nanostructures, but also to design more efficient SERS structures for various applications.

Silicon Structures with Variable Morphology of Pores Methods of Obtaining Physical and Optical Properties

This paper presents experimental results on the creation of porous silicon structures with variable pore morphology (GPS-var). At a pore depth of up to several hundred microns, the structures are characterized by the presence of a layer with nanoscale porous structures (hereinafter, nanoporous) on the surface. As the depth of etching increases, the pores smoothly transform into spongy, and then into a columnar structures with pore sizes of about a micron.

Quantitative and Qualitative Analyses of Genus Pyrus L. (Pear Tree) in West Azerbaijan Province, Iran

Pollen morphology of Pyrus L. spp. genus from West Azerbaijan Province of Iran using light microscope and scanning electron microscope was studied. The species under study included Pyrus syriaca, Pyrus amygdaliformis, Pyrus salicifolia, and Pyrus communis. The measured characteristics were longitudinal axis, transverse axis, length-to-width ratio, depth of groove or pore, shapes, and decorations of wall, and size and type of pollen grain (number of tracks). The images and details of the internal structure of all these four pollen species are provided comprehensively. The results showed that the depth of groove or pore was in the range of 1.0–3.12. The pollen species were small or medium-sized and the most common type among them was type III. The pollen grains of these species were symmetrical with three tracks and their wall decorations were striate and striate and micro-reticulate.

Graphene Nanocomposites: Sandwich‐Type Nanocomposite of Reduced Graphene Oxide and Periodic Mesoporous Silica with Vertically Aligned Mesochannels of Tunable Pore Depth and Size (Adv. Funct. Mater. 47/2017)

Graphene Nanocomposites: Sandwich‐Type Nanocomposite of Reduced Graphene Oxide and Periodic Mesoporous Silica with Vertically Aligned Mesochannels of Tunable Pore Depth and Size (Adv. Funct. Mater. 47/2017)

New insights into the oxidation rate and formation of porous structures on silicon

The rate of oxide formation on silicon was investigated by in situ I–V measurements, one after the other within 300 s, and as a result the current or I–V gap was used to compare the relative oxidation rate during pore formation at different anodizing currents. The study was based on the electrochemical etching of p-type silicon using HF electrolyte treated with surfactant to obtain pores with straight walls. The study showed that the rate of oxidation during the formation of macropores, which have straight walls and relatively deep structures, decreases as the pores grow down with time, where it shows that the etching rate decreases as the pores grow deep. However, electropolishing resulted in a relatively high and constant rate of oxide formation with time. These observed properties are related to the expected diffusion limitation of oxide-forming (OH−) molecules, which reach the electrolyte-pore tip while etching occurs. Anodic oxide formation rate at the electrolyte-pore tip, which was created under complex kinetic conditions, depends on the pore structure, pore depth, diffusion rate of oxide-forming species, and anodizing current. The fast I–V method is an advanced approach and can be used to study pore formation mechanisms in different semiconductor materials.

Controllable Switching Filaments Prepared via Tunable and Well-Defined Single Truncated Conical Nanopore Structures for Fast and Scalable SiOx Memory.

The controllability of switching conductive filaments is one of the central issues in the development of reliable metal-oxide resistive memory because the random dynamic nature and formation of the filaments pose an obstacle to desirable switching performance. Here, we introduce a simple and novel approach to control and form a single silicon nanocrystal (Si-NC) filament for use in SiOx memory devices. The filament is formed with a confined vertical nanoscale gap by using a well-defined single vertical truncated conical nanopore (StcNP) structure. The physical dimensions of the Si-NC filaments such as number, size, and length, which have a significant influence on the switching properties, can be simply engineered by the breakdown of an Au wire through different StcNP structures. In particular, we demonstrate that the designed SiOx memory junction with a StcNP of pore depth of ∼75 nm and a bottom diameter of ∼10 nm exhibited a switching speed of up to 6 ns for both set and reset process, significantly faster than reported SiOx memory devices. The device also exhibited a high ON-OFF ratio, multistate storage ability, acceptable endurance, and retention stability. The influence of the physical dimensions of the StcNP on the switching features is discussed based on the simulated temperature profiles of the Au wire and the nanogap size generated inside the StcNP structure during electromigration.

Effect of Char Particle Size on NO Release during Coal Char Combustion

In this study, the effect of particle size on the release of NO during the char combustion under particle packed-layer conditions was investigated at combustion temperatures of 900 °C~1400 °C. The results show that after pyrolysis, the small size char favored more pores and specific surface area. No significant variations of the intrinsic reactivity of O2 and NO with char particle size were measured. By increasing char particle size, more NO conversion from nitrogen in char (char-N) was found regardless of the combustion temperature and bulk oxygen concentration. This can be explained as follows. By increasing char particle size, less O2 penetrated into the pores and more NO formed because of a less accessible pore surface area and a decreased NO reduction time. The effects of reaction temperature and bulk oxygen concentration were also discussed. A quantified description using a first-order reaction model shows that the char particle size will finally influence the accessible pore surface area and depth ...

Anatomical and diffusional determinants inside leaves explain the difference in photosynthetic capacity between Cypripedium and Paphiopedilum, Orchidaceae.

Comparing with other angiosperms, most members within the family Orchidaceae have lower photosynthetic capacities. However, the underlying mechanisms remain unclear. Cypripedium and Paphiopedilum are closely related phylogenetically in Orchidaceae, but their photosynthetic performances are different. We explored the roles of internal anatomy and diffusional conductance in determining photosynthesis in three Cypripedium and three Paphiopedilum species, and quantitatively analyzed their diffusional and biochemical limitations to photosynthesis. Paphiopedilum species showed lower light-saturated photosynthetic rate (A N), stomatal conductance (g s), and mesophyll conductance (g m) than Cypripedium species. A N was positively correlated with g s and g m. And yet, in both species A N was more strongly limited by g m than by biochemical factors or g s. The greater g s of Cypripedium was mainly affected by larger stomatal apparatus area and smaller pore depth, while the less g m of Paphiopedilum was determined by the reduced surface area of mesophyll cells and chloroplasts exposed to intercellular airspace per unit of leaf area, and much thicker cell wall thickness. These results suggest that leaf anatomical structure is the key factor affecting g m, which is largely responsible for the difference in photosynthetic capacity between those two genera. Our findings provide new insight into the photosynthetic physiology and functional diversification of orchids.

Epidermal morphology and leaflet anatomy of Dioon (Zamiaceae) with comments on climate and environment

Anatomical descriptions can be effective for solving systematic issues, but these studies are relatively scarce for cycads. Therefore, we present here a leaflet and cuticle anatomical study on the genus Dioon, to provide a set of epidermal traits that clarify species delimitation and relationships between species and their habitats. We used standard micro-technique for leaflet sectioning, and cuticular peel preparation for light microscopy. Also, we used the chromium trioxide method for scanning electron microscope observations on cuticles. Measurements were taken on 10 randomly chosen replicates of each cell or tissue type, for each of the leaflets sampled per taxon. Micromorphological variation among species was calculated for each trait. Finally, we reconstructed the ancestral states of the observed epidermal fibre-like cell and pore shapes, by tracing the characters on the species phylogenetic tree of Dioon. We were able to describe the leaflet anatomy, cuticles, and epidermal features for 14 Dioon species. The quantitative analysis was useful to reveal five geographically structured species groups. Character tracing on the phylogenetic tree of Dioon has amplified our current understanding on species relationships with respect to habitats. The presence/absence data suggest that the evolutionary acquisition-deletion of structural shapes is phylogenetically independent, thus climate seems to play a very important role in the variation of cuticular and stomatal traits. Many epidermal traits, especially adaxial cuticle thickness and epistomatal pore width and depth, might be adaptations resulting from a long-term influence of climate, since they appear to have correlation with climatic conditions in relation to their biogeography. We conclude that the variation of all traits are mostly sustained and intrinsic to the species, and are of promising taxonomic value. The combination of the epidermal traits with other characters has potential for taxonomic resolution at species level.

In-situ stress, stress-dependent permeability, pore pressure and gas-bearing system in multiple coal seams in the Panguan area, western Guizhou, China

Independent superposed coalbed methane (CBM)-bearing systems are widely distributed in coal-bearing strata with multiple coal seams in western Guizhou province, which is liable to cause interference among systems in the multilayer combination production process. Therefore, precisely defining the independent superposed CBM-bearing systems is important for CBM development in this area. However, the recognition of gas-bearing system at present was mostly based on the sedimentary cycle and the sequence stratigraphic framework, of which ignored the control of in-situ stress on physical properties of coal-bearing strata. In this work, the distribution characteristics of in-situ stress and its control on coal permeability was analyzed systematically based on well test parameters of 22-layer coal seams measured within depths from 352 to 1245 m in the Panguan area. Within depths shallower than 500 m, σH and σh tend to decrease with an increasing depth, and the stress field gradually transforms from σH>σh>σv to σv>σH>σh. For immediately coal seams (500–750 m), the σv>σH>σh type is dominant, revealing a normal faulting stress type. For coal seams with depth >750 m, σH and σh increases rapidly instead of continuously decreasing, and the stress field transformed into the type of σH> σv> σh when being deeper than 1000 m. Coal permeability shows a low→ high → low→ extremely low trend with the increase of depth, and it was verified with well test permeability measured in other areas of western Guizhou, the essence of which is the compression and deformation of the pore-fracture system under the control of in-situ stress. The correlation between pore pressure and depth was also illustrated, which showed five linear relationships in depth of <200, 200–500, 500–750 m, 750–1000 m and >1000 m, separately. Those five depth ranges represent five independent pressure systems, and the depth boundary point between different pressure systems is precisely the conversion depth of stress fields and coal permeability. Within the same pressure system, the gas content increases as the buried depth increases. For CBM development in western Guizhou province, commingling production need carry out in the same pressure system to avoid interlayer interference, and it is recommended that middle CBM systems (500–750 m) with lower stress and higher permeability should be a priority for CBM development. At depths >750 m, CBM development conditions tend to deteriorate.

Sandwich‐Type Nanocomposite of Reduced Graphene Oxide and Periodic Mesoporous Silica with Vertically Aligned Mesochannels of Tunable Pore Depth and Size

AbstractSandwich‐type nanocomposites of graphene oxide (GO) and periodic mesoporous silica (PMS) with vertically aligned mesochannels of different pore depth and size are synthesized and characterized, and their formation modes are examined. The existence of mesoscale ordered structure in the mixture of GO and surfactant solutions is confirmed for the first time by in situ small angle X‐ray scattering measurement using synchrotron radiation. The mesochannel depth and pore wall ripening of PMS in the nanocomposites are controlled by the reaction time of the hydrolysis of tetraethyl orthosilicate. The pore size of PMS in the nanocomposites can be varied in the range of 1–5 nm by varying the chain length of alkyltrimethylammonium (CnTA+) template and high specific surface area (≈1000 m2 g−1) is achieved for all samples. Nanocomposites with vertically aligned PMS mesochannels can be synthesized by applying CnTA+ templates of n ≥ 12, whereas with CnTA+ of n ≤ 10, either PMS nanoparticle deposited GO structure or the structure with incomplete coverage of GO surface with imperfect PMS is found. The aggregation behaviors of surfactant molecules on GO depend on surfactant concentration relative to critical micelle concentration and reaction temperature, and result in the peculiar nanocomposites of different structural styles.

Quantitative Analysis of Weld-Pore Size and Depth and Effect on Fatigue Life of Ti-6Al-2Zr-1Mo-1V Alloy Weldments

Titanium-alloy weldments have been extensively used in engineering structures, and accurate estimation of the fatigue life is beneficial for avoiding catastrophic failures in titanium-alloy structures. The weld pore is a common defect in these weldments that significantly influences the fatigue process. In this study, the weld-pore size and depth and its effect on the fatigue life of Ti-6Al-2Zr-1Mo-1V (TA15) alloy weldments are investigated by adopting fatigue tests and fracture observations. The results show that fatigue crack initiations occurred at the weld pores for all specimens. The diameter and depth of all weld pores on fracture surfaces were then measured, and an indicator, P, was proposed, defined as a combination of pore diameter and depth. It was found that all the fatigue cracks initiated from the pore have the smallest P indicator, which suggests that P can be used to judge the location of crack initiation in an individual sample. Moreover, a model was developed based on P to estimate the fatigue life of weldments, considering the effects of weld-pore size and depth. Finally, analogous fatigue tests were carried out for model verification, and results show that the proposed model has a higher accuracy compared with several typical models. The findings of this study can be helpful in estimating the fatigue life and fatigue design of titanium-alloy weldments.

Effect of ablative laser on in vitro transungual delivery

Topical therapy of nail psoriasis using methotrexate has not been realized due to the high molecular weight and low permeability of the compound. In this study, we used a 2940nm fractional ablative laser to disrupt the nail barrier to enhance the in vitro transungual delivery of methotrexate. Bovine hoof membrane―an in vitro model of the human nail―was treated by the laser at different energy levels and pore densities. A successful microporation was characterized by mechanical properties, scanning electron microscopy, Fourier transform infrared spectrophotometer, dye binding, histology, pore uniformity, confocal laser microscopy, nail integrity measurement, and permeation studies. No significant difference in the pore dimension was found in different treatment groups (p>0.05). Increases in pore depth corresponded with increases in the laser energy. Laser ablation was found to affect the mechanical properties of the hoof membrane. In in vitro permeation studies, laser ablation resulted in a significant increase in the drug cumulative delivery, flux, and permeability coefficient as compared to the untreated group (n=3, p<0.05). A change in the laser energy and pore density was found to alter the drug permeability. Thus, transungual methotrexate delivery was enhanced by the fractional laser ablation.

Effect of Electric Field Strength on Barrier Layer Thickness and Anion Incorporation of Anodic Porous Alumina

Anodic porous alumina films having a closely packed hexagonal array of cells have attracted much attention as a starting material in the fabrication of nano-devices because of the high controllability of porous structures (e.g., cell size, pore size, pore interval, and pore depth) on dimensions ranging from the submicron to nanometer range. In recent years, the mechanism of self-ordering of cell arrangement of anodic porous alumina has been intensely studied. We proposed anodizing under high electric field strength as a key factor for self-ordering of cell arrangement [1, 2]. However, only a few reports are found on the irregularities of barrier layer thickness and morphology of each cell of anodic porous alumina. In this study, we evaluated the influence of electrolytic factors (e.g., current density, applied voltage, and anodizing time) on cell morphology of anodic porous alumina. Especially, we focused on the effect of the electric field strength on the barrier layer thickness and anion incorporation behavior. High purity aluminum sheets were anodized in typical electrolytes of sulfuric acid, oxalic acid, and phosphoric acid at different voltage. After detachment of the porous alumina films from the substrate in saturated mercuric chloride solution, the specimens were immersed in phosphoric acid to dissolve the barrier layer from the backside. By SEM observation of structural change of the cells during chemical etching, the homogeneity of the barrier layer thickness could be evaluated. Although the thickness of the barrier layer of porous alumina formed at constant voltage has been believed to be uniform, we confirmed that the thickness of the barrier layer of each cell was not uniform; the thickness of the barrier layer of the smaller cells was thinner than that of the larger cells. Concerning anion incorporation behavior, we evaluated the depth of anion incorporation into the cell wall by the difference in the strength of contrast of the SEM image of rear surface of porous alumina films because the dissolution rate of the anion-free layer was slower than that of the anion-incorporated layer. The details of the thickness inhomogeneity of the barrier layer and anion incorporation behavior will be discussed from a standpoint of the high field theory.

Preparation and characterization of microporous cellulose acetate films using breath figure method by spin coating technique

This work reports the preparation and characterization of microporous cellulose triacetate films. Cellulose triacetates were obtained from homogeneous acetylation of cellulose extracted from wood by an effective method totally free of chlorine. The microporous films were produced by breath figure method by spin coating technique. In the breath figure method, the formation of the pores in the polymer films involves the phenomenon of condensation of water vapor on a polymer solution surface, so that the condensed water droplets act as a template for formation pores. The porous films were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films showed pores with rounded morphology and the pore diameter ranged from 0.1 to 0.5 µm. The effects of the solvent, concentration of the polymer solution and polymer molecular weight were investigated on the formation, morphology and size of the pores. Large porous structures are observed when lower polymer concentrations and higher molecular weight are used. Higher pore densities were observed when dichloromethane was used as solvent. The films produced could be used as biomaterials such as cell culture substrate or in sensing devices. From the results obtained in this work it is possible to predict the pore depth, size and density in cellulose triacetate films, allowing the manipulation of these parameters for future desired applications.

Long term performance of porous platinum coated neural electrodes.

Over the last several years, there has been a growing interest in neural implants for the study and diagnostics of neurological disorders as well as for the symptomatic treatment of central nervous system related diseases. One of the major challenges is the trade-off between small electrode sizes for high selectivity between single neurons and large electrode-tissue interface areas for excellent stimulation and recording properties. This paper presents an approach of increasing the real surface area of the electrodes by creating a surface microstructure. Two major novelties let this work stand out from existing approaches which mainly make use of porous coatings such as platinum black or iridium oxide, or Poly(3,4-ethylenedioxythiophene) (PEDOT). Roughening is carried out by a dry etching process on the silicon electrode core before being coated by a sputtered platinum layer, eliminating complicated deposition processes as for the materials described above. The technology is compatible with any commonly used coating material. In addition, the surface roughening is compatible with high aspect ratio penetrating electrode arrays such as the well-established Utah electrode array, whose unique geometry presents a challenge in the surface modification of active electrode sites. The dry etching process is well characterized and yields a high controllability of pore size and depth. This paper confirms the superior electrochemical properties including impedance, charge injection capacity, and charge storage capacity of surface engineered electrode arrays compared to conventional arrays over a period of 12weeks. Furthermore, mechanical stability of the modified electrodes was tested by implantation in the brain of a recently deceased rat. In conclusion, the larger interface surface of the electrodes does not only decrease the impedance which should lead to enhanced Signal to noise ratio (SNR) for recording purposes, but also yields higher charge injection capacities, which improve the stimulation characteristics of the implants.

Differential Depth Sensing Reduces Cancer Cell Proliferation via Rho-Rac-Regulated Invadopodia.

Bone, which is composed of a porous matrix, is one of the principal secondary locations for cancer. However, little is known about the effect of this porous microenvironment in regulating cancer cell proliferation. Here, we examine how the depth of the pores can transduce a mechanical signal and reduce the proliferation of noncancer breast epithelial cells (MCF-10A) and malignant breast cancer cells (MDA-MB-231 and MCF-7) using micrometer-scale topographic features. Interestingly, cells extend actin-rich protrusions, such as invadopodia, to sense the depth of the matrix pore and activate actomyosin contractility to decrease MCF-10A proliferation. However, in MDA-MB-231, depth sensing inactivates Rho-Rac-regulated actomyosin contractility and phospho-ERK signaling. Inhibiting contractility on this porous matrix using blebbistatin further reduces MDA-MB-231 proliferation. Our findings support the notion of mechanically induced dormancy through depth sensing, where invadopodia-mediated depth sensing can inhibit the proliferation of noncancer and malignant breast cancer cells through differential regulation of actomyosin contractility.

In situ regulating of surface morphologies, anti-corrosion and tribological properties of epoxy resin coatings by heat treatment

A simple and in situ formation method through controlling curing temperature was used to regulate the surface morphology of epoxy resin (EP) coating. Multi-functional tribology test equipment and an electrochemistry workstation were used to evaluate the tribological and anti-corrosion properties of the EP coating cured with diethylenetriamine at room temperature, 80 °C, 100 °C and 120 °C, respectively. The results indicated that the diameter and depth of pores or pits existing on the surface of EP coatings decreased significantly with the increase of curing temperature. The EP coating cured at 120 °C exhibited the best tribological performance, the friction coefficient and wear trace area were 0.56 and 0.003 02 mm2 under dry conditions, 0.18 and 1.873 × 10−5 mm2 under seawater conditions, respectively. The excellent tribological performance could be attributed to the surface morphologies and high hardness of EP coatings. The EP coating cured at 80 °C exhibited the best anti-corrosion performance that the impedance modulus at 0.01 Hz was close to 5.0 KΩ cm2 even after being immersed in 3.5 wt% NaCl solution for 24 h, which was closely related to its hydrophobic behavior and surface morphology.

Influence of HF concentration and current density on characteristic morphological features of mesoporous silicon

This report explores the variations in morphological features of electrochemically fabricated mesoporous silicon as a function of two important fabrication parameters, HF concentration and current density. Four set of samples corresponding to four different HF concentrations (15%, 25%, 35% and 45% HF) were prepared with systematically varied current density (10, 20, 30, 60 and 100 mA/cm2). The effect of these parameters on many significant features like mean pore diameter, mean neighbor distance, pore count per unit area, surface roughness, surface area etc. of resulting mesoporous structure have been determined by very sophisticated UHV SPM (Omicron VT AFM XA) in contact mode. The analysis has been performed using Scanning Probe Image Processor (SPIP Version 6.0.9). The AFM analysis is supported by the results of FESEM JSM 7600F and DXR Raman Microscope. The comparative study shows that some features are more sensitive to HF concentration while others seem to depend more on current density. Pore diameter varies mainly with HF concentration while pore depth varies largely with current density. Exceptionally high pore count (450pores/100 nm2) is found at 45% HF while samples have higher average roughness (3.5 nm) at 15% HF. Sponge like layer is formed at lower current density while well aligned very straight channels are formed at higher current density. Some very interesting regimes found at high current density conditions, recorded by FESEM have also been discussed to develop more understanding of porous silicon formation mechanism.