Porous Underlayer Research Articles

Impact of porous silicon thickness on thermoelectric properties of silicon-germanium alloy films produced by electrochemical deposition of germanium into porous silicon matrices followed by rapid thermal annealing

Silicon-germanium alloy films were formed by electrochemical deposition of germanium into porous silicon matrices with thicknesses varying from 1.5 to 10 μm followed by subsequent rapid thermal processing at 950 °C in an inert atmosphere. Study of the fabricated structures using SEM and Raman spectroscopy, as well as measurements of their electrical conductivity and thermoelectric properties revealed that the highest Seebeck coefficient (−505 μV/K at 450 K) and Power Factor (1950 μW/(m·K2) at 400 K) values were obtained when a 5 μm-thick porous silicon was used as a structural matrix. Under such conditions, an optimal balance between electrical conductivity, structural disorder and electrical insulation from the substrate is achieved due to the presence of a residual porous underlayer, making it possible to maximize the film's thermoelectric performance. The obtained silicon-germanium alloy films are deemed suitable for the fabrication of both discrete and integrated thermoelectric devices based on monocrystalline silicon substrates.

3D nanostructured nickel film supported to a conducting polymer as an electrocatalyst with exceptional properties for hydrogen evolution reaction

A two-layer system was applied to a nickel substrate for use as the electrocatalyst of the hydrogen evolution reaction (HER) in a phosphate buffer solution. It was comprised of a three-dimensional (3D) porous underlayer of nickel nanoparticles with a size of less than 35 nm, followed by an electrodeposited top layer of poly (aniline-co-pyrrole). The underlayer and top coating were both synthesized by applying a constant potential to a three-electrode system. The catalyst characterization was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectrometry. The electrocatalytic activity of the fabricated electrodes was measured by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. The electrode exhibited an overpotential of 520 mV at a current density of 10 mA cm−2, comparable to 530 mV of platinum. Furthermore, the Tafel slope of the electrode was 90 mV dec−1, almost equal to that of platinum. This exceptional performance was explained by the synergistic interaction between 3D-Ni and poly (aniline-co-pyrrole) layers. Such a synergism was demonstrated by the fact that the resulting electrode lacked substantial catalytic activity when each of these two layers was deposited on the substrate alone. The Nyquist diagrams revealed that the 3D-Ni film resulted in minimal charge transfer resistance, allowing fast kinetics of HER. The coupling of this property with the ability of the polymer to adsorb H+ ions led to the high electrocatalytic activity of the proposed electrode. This electrode performed better than platinum, which was a promising result. This indicated that a lower voltage input was required to generate hydrogen gas using the prepared electrode.

Homoepitaxial Growth of InP on Electrochemical Etched Porous InP Surface

Single crystal indium phosphide (InP) layers were epitaxially grown on porous (001) InP surfaces with controlled porosities. Changes in the underlying porous layer structure, and hence its stability, during epitaxial growth at elevated temperatures were observed. The same change in the porous structure was achieved by only annealing under the same growth conditions. A 100%-layer transfer rate is demonstrated for annealed dual porous InP layers. Plan-view transmission electron microscopy (TEM) images of the epitaxial layer show that the layer is continuous over the porous underlayer and had a dislocation density lower than 3 × 106 cm−2. The high crystallinity of the epitaxy layer was verified by high resolution X-ray diffraction (HRXRD) rocking curve scans. These high quality epitaxial layers grown on porous InP show promise for active layers in thin, flexible high-performance devices, which are readily transferred from the growth substrate by fracture at the epitaxial-porous layer interface.

Biocompatible slippery fluid-infused films composed of chitosan and alginate via layer-by-layer self-assembly and their antithrombogenicity.

Antifouling super-repellent surfaces inspired by Nepenthes, the pitcher plant, were designed and named slippery liquid-infused porous surfaces (SLIPS). These surfaces repel various simple and complex liquids including water and blood by maintaining a low sliding angle. Previous studies have reported the development of fluorinated SLIPS that are not biocompatible. Here, we fabricated fluid-infused films composed of biodegradable materials and a biocompatible lubricant liquid. The film was constructed using a combination of electrostatic interactions between chitosan and alginate and hydrogen-bonding between alginate and polyvinylpyrrolidone (PVPON) via the layer-by-layer self-assembly method. After chitosan and alginate were cross-linked, the PVPON was removed by increasing the pH to generate porosity from the deconstruction of the hydrogen-bonding. The porous underlayer was hydrophobized and covered by biocompatible almond oil. Blood easily flowed over this biodegradable and biocompatible SLIPS without leaving stains on the surface, and the material is environmentally durable, has a high transmittance of about 90%, and is antithrombogenic. The results of this study suggest that this SLIPS may facilitate the creation of nonfouling medical devices through a low-cost, eco-friendly, and simple process.

Self-assembly of diverse alumina architectures and their morphology-dependent wettability

This work reports the fabrication of diverse nanostructured alumina films under high-field anodization in oxalic-acid electrolytes. Different surface morphologies of these alumina films can be obtained by adjusting reaction parameters, which was ascribed to the anisotropic chemical etching induced by the reaction heat and the concentration gradient of the oxalic-acid solution along the nanopore channels during the high-field anodization process. These alumina surfaces without coating low energy materials show remarkable morphology-dependent wettability. Specially, the alumina surface consisting of porous underlayer and nanowire pyramids with no chemical modification reveals excellent super water-repellent behavior for the first time. This study could provide a new approach for designing functional surfaces with tunable wettability.

Bilayered biodegradable poly(ethylene glycol)/poly(butylene terephthalate) copolymer (Polyactive) as substrate for human fibroblasts and keratinocytes.

The purpose of this study was to find an optimal polymer matrix and to optimize the culture conditions for human keratinocytes and fibroblasts for the development of a human skin substitute. For this purpose porous, dense bilayers made of a block copolymer of poly(ethylene glycol terephthalate) (PEGT) and poly(butylene terephthalate) (PBT; Polyactivetrade mark) with a PEGT/PBT weight ratio of 55/45 and a PEG molecular weight (MW) of 300, 600, 1000, or 4000 Da were used. The best performance was achieved with PEGT/PBT copolymer with MW of PEG 300 D (300PEG55PBT45). When fibroblasts were seeded into the porous underlayer and cultured for 3 weeks in medium supplemented with 100 microg/mL ascorbic acid, all pores were filled with fibroblasts and with extracellular matrix, which was judged from the presence of collagen types I, III, and IV, and laminin. When seeded onto the dense top layer of the bilayered (cell free or fibroblast populated) copolymer matrix, human keratinocytes grew out into confluent sheets. After subsequent lifting to the air-liquid interface, a multilayered epithelium with a morphology corresponding to that of the native epidermis was formed. Some differences could still be observed: the expression and localization of some differentiation specific proteins was different and close to that seen in hyperproliferative epidermis; a basal lamina and anchoring zone were absent.

Preventing postoperative intraperitoneal adhesion formation with Polyactive™, a degradable copolymer acting as a barrier

In this study a degradable barrier, composed of a poly(ethyleneglycol) and poly(butyleneterephthalate) copolymer (1000 Polyactive™ 55/45), was investigated for the prevention of postoperative adhesion formation. Three different designs of polymer films were used in a standardized rat adhesion model in order to investigate which barrier form would be most efficacious in reducing adhesion formation. Neither non-porous nor porous film reduced the adhesion formation as compared with control experiments. A bilayered film, however, composed of a porous underlayer and a non-porous toplayer, reduced the adhesion formation significantly compared with control animals without a barrier. In the case of adhesion formation with this bilayered film the adhesions were limited to areas that were macroscopically not covered, either due to fractures in or detachment of the barrier. Subsequently a more malleable porous/dense film was designed which did not fracture and reduced the adhesion formation significantly compared with animals treated with Interceed™, even though some barriers detached as in the first experiment. The porous/dense Polyactive™ barrier seems to be a promising adjuvant in the reduction of postoperative adhesion formation, although further research is needed to accomplish better attachment of the barrier.

Degradative behaviour of polymeric matrices in (sub)dermal and muscle tissue of the rat: a quantitative study

Bilayered matrices, made of synthetic degradable polymers, are developed for use as a dermal regeneration template in large surface area full-thickness skin defects. The porous underlayer is designed to allow ingrowth of dermal components and the dense top layer will serve as a substrate for keratinocytes. Considering the importance of the degradation kinetics of tissue regeneration templates, quantification of matrix degradation up to 1 yr post-implantation, and histological and ultrastructural examination of the implants was performed. In this study a moderate foreign body reaction was observed at both the intramuscular and subcutaneous implantation sites, including the presence of mono- and multinucleated phagocytes. Poly( l-lactic acid) underlayers tended to elicit a stronger cellular infiltrate than co-polymeric ones. In the course of the implantation periods this inflammatory response subsided and neovascular ingrowth and the formation of fibrous tissue in the pores was observed. Matrix degradation was demonstrated, starting with the fragmentation of the constituent polymers into increasingly smaller particles. During the implantation period, fragments showed progressive surface erosion. Poly( l-lactic acid) fragments had a more rounded off appearance as compared to co-polymeric ones. Implant surface area had decreased to less than 20%, 1 yr post-implantation. At both implantation sites and with all matrices, polymer particles were observed inside phagocytic cells. Degradation kinetics were similar with the different matrices. Implants fragmented more rapidly at the subcutaneous implantation site as compared to the intramuscular one. Although the data suggest biomaterial degradation, remnants of matrices could still be retrieved 1 yr post-implantation.

Biocompatibility of a biodegradable matrix used as a skin substitute: an in vivo evaluation.

Synthetic biodegradable polymeric matrices, with a dense top layer and porous under-layer, made of a (poly)ether/(poly)ester (PEO:PBT) copolymer called Polyactive, and also of poly-L-lactide (PLLA), are under investigation as part of a cell-seeded skin substitute for third-degree, large-scale skin defects. The biocompatibility of subcutaneously implanted matrices representing large body surface areas, were studied at 2, 4, 13, 26, and 52 weeks in rats. To investigate local or systemic effects, the weight development of the complete animal and of their hearts, kidneys, lungs, livers, and spleens, as well as the macroscopic and histologic appearance of the implants and organs, were monitored. Early inflammatory response was associated with surgical implantation trauma. All matrices showed neovascular and fibrous tissue ingrowth into the porous underlayer within 2-4 weeks after implantation. Copolymeric and PLLA matrices increasingly fragmented and liquified. After 1 year, small polymeric fragments embedded in fibrous, vascularized tissue could be retrieved at the implantation site. No systemic effects of the implants on the organs or on the animal as a whole were observed. These results and earlier studies on (skin) cell substrate properties and physicochemical characteristics of the matrices indicate the suitability of the matrices as part of a cell-seeded skin substitute.