Enhanced performance of Fe2O3 doped yttria stabilized zirconia hollow fiber membranes for water treatment

Fe₂O₃ powders were introduced as sintering aid to fabricate yttria-stabilized zirconia (YSZ) hollow fiber membranes using a combined wet-spinning and post-sintering method. The obtained Fe₂O₃-YSZ hollow fiber membranes show enhanced performance for water treatment with fine crystal structure in terms of bending strength and pure water permeability. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and thermogravimetric analysis (TGA) along with mechanical tests were employed to investigate the structural evolution in the sintering process and the effect of Fe₂O₃. It is suggested that the Fe₂O₃ dopants dissolve into YSZ at elevated temperatures, providing defect sites and vacancies for fast ion migration, favoring for densification and grain growth of the YSZ, which yields dense microstructures of fine crystallites at relatively low sintering temperature. The Fe₂O₃-YSZ hollow fiber membranes sintered at 1150 °C show a 3-fold increase of the permeate flux of pure water (F) (743 L m⁻² h⁻¹) along with comparable bending strength (152 MPa) compared to pure YSZ membranes. This modified method can reduce sintering costs and therefore fabrication costs which should pave the way for scale-up production for ceramic hollow fiber membranes.     

The observation of elongation dependent macrovoid evolution in single- and dual-layer asymmetric hollow fiber membranes

We have reported, for the first time, that macrovoids in asymmetric hollow fiber membranes may be completely eliminated at high elongational draws. The evolution of macrovoids vs. elongational draw was observed for both single- and dual-layer hollow fiber membranes. The number of macrovoids and the number of macrovoid layer decrease with an increase in elongational draw ratio, while the dimension of macrovoids varies with increasing elongational draw ratio until the macrovoids are fully eliminated. This study indicates that the elongational stress may play a much more important role than our original thoughts on hollow fiber membrane morphology.     

Development and characterization of niobium-releasing silicate bioactive glasses for tissue engineering applications

Novel niobium-containing bioactive glass formulations (Nb-BGs) were designed, produced and used to fabricate sintered glass-ceramic granules to examine their in vitro bioactivity and angiogenic potential. Nb-BGs were prepared by melting and quenching. Afterwards, the glasses were crushed and milled into fine powders. These powders were used to make aqueous slurries which were poured into molds, dried and sintered to produce pellets, from which granules of 0.5–0.85 mm in size were obtained. In vitro bioactivity was tested by immersing the granules in simulated body fluid for up to 14 days. Cell biology tests were carried out by indirect culture of bone marrow stromal cells (ST-2) with supernatants resulting from incubation of BG granules in cell culture medium. The effect of dissolution products from Nb-BGs on the secretion of vascular endothelial growth factor (VEGF) was assessed to characterize the angiogenic potential of the new Nb-containing BG compositions.     

Smart membranes for biomedical applications

Smart membranes with tunable permeability and selectivity have drawn widespread attention because of their unique biomimetic characteristics. Constructed by incorporating various stimuli-responsive materials into membrane substrates, smart membranes could self-adjust their physical/chemical properties(such as pore size and surface properties) in response to environmental signals such as temperature,pH, light, magnetic field, electric field, redox and specific ions/molecules. Such smart membranes...     

Fabrication and characterization of silk/forsterite composites for tissue engineering applications

In this research, novel composite scaffolds consisting of silk fibroin and forsterite powder were prepared by a freeze-drying method. In addition, the effects of forsterite powder contents on the structure of the scaffolds were investigated to provide an appropriate composite for bone tissue engineering applications. The morphology studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques showed that the forsterite ceramic was well distributed throughout the structures of SF/forsterite scaffolds. Furthermore, the forsterite powder (up to 40 wt%) was homogenously distributed within the silk fibroin as a matrix.     

High-flux CO2-stable oxygen transport hollow fiber membranes through surface engineering

The influences of bulk diffusion and surface exchange on oxygen transport of (La_0.6Ca_0.4)(Co_0.8Fe_0.2)O_3-δ (LCCF) hollow fiber membranes were investigated. As an outcome, two strategies for increasing the oxygen permeation were pursued. First, porous LCCF hollow fibers as support were coated with a 22 μm dense LCCF separation layer through dip coating and co-sintering. The oxygen permeation of the porous fiber with dense layer reached up to 5.10 mL min^?1 cm^-2 at 1000 °C in a 50 % CO₂ atmosphere. Second, surface etching of dense LCCF hollow fibers with H₂SO₄ was applied. The surface etching of both inner and outer surfaces leads to a permeation improvement up to 86.0 %. This finding implies that the surface exchange reaction plays a key role in oxygen transport through LCCF hollow fibers. A good long-term (>250 h) stability of the asymmetric hollow fiber in a 50 % CO₂ atmosphere was found at 900 °C.     

Polyurethane fibrous membranes tailored by rotary jet spinning for tissue engineering applications

Polymeric membranes have gained popularity as fibrous structures for tissue regeneration. This research focuses on the rotary jet spinning (RJS) process combined with a polymer as a strategy for designing membranes. To this end, RJS-polyurethane (RJS-PU) membranes with different microstructures were produced. Considering the effects of solution properties on fiber production, the viscosity of PU solutions was evaluated. Membrane morphology was studied based on scanning electron microscopy and 2D fast Fourier transform analysis. The chemical and thermal properties were characterized by Fourier-transform infrared spectroscopy and thermogravimetric analysis, respectively. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and Live/Dead cell assays were performed to determine the material cytotoxicity by assessment of the profile of proliferation and cell viability. The results indicated that the combination of PU and RJS was an effective one for the production of fibrous structures for tissue engineering applications, demonstrating good compatibility with the cultured osteoblastic cell line. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48455.     

Enhanced forward osmosis from chemically modified polybenzimidazole (PBI) nanofiltration hollow fiber membranes with a thin wall

To develop high-flux and high-rejection forward osmosis (FO) membranes for water reuses and seawater desalination, we have fabricated polybenzimidazole (PBI) nanofiltration (NF) hollow fiber membranes with a thin wall and a desired pore size via non-solvent induced phase inversion and chemically cross-linking modification. The cross-linking by p-xylylene dichloride can finely tune the mean pore size and enhance the salt selectivity. High water permeation flux and improved salt selectivity for water reuses were achieved by using the 2-h modified PBI NF membrane which has a narrow pore size distribution. Cross-linking at a longer time produces even a lower salt permeation flux potentially suitable for desalination but at the expense of permeation flux due to tightened pore sizes. It is found that draw solution concentration and membrane orientations are main factors determining the water permeation flux. In addition, effects of membrane morphology and operation conditions on water and salt transport through membrane have been investigated.     

Polymeric materials as anion-exchange membranes for alkaline fuel cells

After summarizing the different fuel cells systems, including advantages and drawbacks, this review focuses on the preparation of copolymers and polymeric materials as starting materials for solid alkaline fuel cells membranes. The requirements for such membranes are also summarized. Then, different strategies are given to synthesize anion-exchange polymeric materials containing cationic (especially ammonium) groups. The first pathway focuses on heterogeneous membranes that consist in: (i) polymer blends and composites based on poly(alkene oxide)s and hydroxide salts or polybenzimidazole doped with potassium hydroxide, (ii) organic–inorganic hybrid membranes especially those synthesized via a sol–gel process, and (iii) (semi)interpenetrated networks based on poly(epichlorhydrine), poly(acrylonitrile) and polyvinyl alcohol for example, that have led to new polymeric materials for anion-exchange membranes. The second and main part concerns the homogeneous membranes divided into three categories. The first one consists in materials synthesized from (co)polymers obtained via direct (co)polymerization, for example membranes based on poly(diallyldimethylammonium chloride). The second pathway concerns the modification of polymeric materials via radiografting or chemical reactions. These polymeric materials can be hydrogenated or halogenated. The radiografting of membranes means the irradiation via various sources – electron beam, X and γ rays, ⁶⁰Co and ¹³⁷Cs that lead to trapped radicals or macromolecular peroxides or hydroperoxides, followed by the radical graft polymerization of specific monomers such as chloromethyl styrene. The third route deals with the chemical modifications of commercially available hydrogenated aliphatic and aromatic (co)polymers, and the syntheses of fluorinated (co)polymers such as carboxylic and sulfonic perfluoropolymers. In addition, several approaches for the crosslinking of above-mentioned polymeric materials are also reported as this process enhances the properties of the resulting membranes. Moreover, electrochemical and thermal properties of various above ionomers are given and discussed.     

Incorporation of inorganic bioceramics into electrospun scaffolds for tissue engineering applications: A review

Today, the integration of medical and engineering principles for producing biological replacements has attracted much attention. Tissue engineering is an interdisciplinary field introduced for recovery, preservation, and improvement of tissues' function. During the process of reproduction, scaffolds with the support of cells and biological materials and growth factors underlie the effective regeneration of the target tissue. Among the numerous methods, the electrospinning method has the great ability to mimic the extracellular matrix by creating a network of polymer fibers with a high surface area at the nanoscale in order to provide more binding sites for cells. Considering the capabilities and limitations of different polymers, the use of ceramics as a reinforcement phase is a promising approach. Over the past few decades, electrospun scaffolds have been developed by adding different ceramics in terms of their nature, bioinert, bioactive, and biodegradable properties. The main results are related to enhancing the mechanical properties and biological behavior of the polymeric scaffolds after the incorporation of ceramics. Enhanced hydrophilicity, antibacterial and antioxidant properties are other aspects caused by chemical interactions of ceramics and polymers. In this review, the effect of adding inorganic ceramic structures incorporated into polymeric electrospun scaffolds is discussed by highlighting the most recent studies in tissue engineering applications.     

Generation of chitosan nanoporous structures for tissue engineering applications using a supercritical fluid assisted process

In recent years, considerable attention has been given to chitosan-based materials and their applications in the field of tissue engineering. However, the techniques proposed until now for the formation of chitosan scaffolds present some limitations such as: they are very time-consuming, use organic solvents, have difficulties in the obtainment and preservation of various levels of porosity and the 3-D structure. In this work, a new SC-CO₂ assisted process for the production of chitosan scaffolds is proposed; it consists of three steps: formation of a chitosan hydrogel by thermally induced phase separation; substitution of water with a suitable solvent; drying of the gel using SC-CO₂. Using this process, we produced chitosan nanostructured networks with filaments diameters around 50 nm, without any collapse of the gel nanostructure, characterized by a high porosity (>91%) and high compressive modulus (150 kPa).     

Preparation and properties of high performance gelatin-based hydrogels with chitosan or hydroxyethyl cellulose for tissue engineering applications

High performance gelatin-based biocompatible hybrid hydrogels are developed using functionalized polyethylene glycol as a cross-linker in presence of chitosan or hydroxyethyl cellulose. Tensile test shows robust and tunable mechanical properties and reveals non-linear and J-shaped stress-strain curves similar to those found for native extracellular matrix. Degradation study demonstrates that the mass loss and change in mechanical properties are dependent on hydrogel composition and cross-linking density. Structural features of the hydrogels are confirmed by infrared spectroscopy. A preliminary biological evaluation is carried out using rat myoblasts and human fibroblasts cell lines. The results show that all hydrogels allow cell adhesion and proliferation during four days culture, hence, they might have a great potential for use in the biomedical applications.     

Review on polyphosphazenes-based materials for bone and skeleton tissue engineering

The skeleton performs motley of functions. Defected bones and metameric loss of bone are often resulted due to innate abnormalities and accidental injuries. An assessment is made on the diversity of chemistry of phosphazene with an inflection on new developments and their importance in tissue engineering. Tissue engineering mostly uses polymers that can biodegrade in porous/permeable scaffolds form for treating damaged tissues and skeleton. Demand of these polymers is increasing as timely substrates for tissue regeneration in contrast to the mostly used polyethylene terephalate, polyorthoesters, and poly(α-amino acids). Polyphosphazenes as biodegradable polymers have great potential for applications of tissue engineering. Due to biodegradability of P–N backbone, vast diversity of structure and high functional density polyphosphazenes provides many advantages for the formation of biologically compatible macromolecules. However, the nature of the side group determines the degradation ability of such polymers. These biodegradable polymers (polyphosphazenes) provide harmless and pH neutral substances because phosphates and ammonia have high buffer capacity. This review article focuses on the biocompatible polyphosphazenes and their utilization as regeneration of tissues, skeleton, and bones with a particular focus on materials that contains only polyphosphazenes, blends of polyphosphazene, and composites made from polyphosphazene.     

Preparation and characterization of alumina hollow fiber membranes

With the rapid development of membrane technology in water treatment, there is a growing demand for membrane products with high performance. The inorganic hollow fiber membranes are of great interest due to their high resistance to abrasion, chemical/thermal degradation, and higher surface area/volume ratio therefore they can be utilized in the fields of water treatment. In this study, the alumina (Al₂O₃) hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The organic binder solution (dope) containing suspended Al₂O₃ powders was spun to a hollow fiber precursor, which was then sintered at elevated temperatures in order to obtain the Al₂O₃ hollow fiber membrane. The dope solution consisted of polyethersulfone (PES), Nmethyl-2-pyrrolidone (NMP) and polyvinylpyrrolidone (PVP), which were used as polymer binder, solvent and additive, respectively. The prepared Al₂O₃ hollow fiber membranes were characterized by a scanning electron microscope (SEM) and thermal gravimetric analysis (TG). The effects of the sintering temperature and Al₂O₃/PES ratios on the morphological structure, pure water flux, pore size and porosity of the membranes were also investigated extensively. The results showed that the pure water flux, maximum pore size and porosity of the prepared membranes decreased with the increase in Al₂O₃/PES ratios and sintering temperature. When the Al₂O₃/PES ratio reached 9, the pure water flux and maximum pore size were at 2547 L/m²·h and 1.4 μm, respectively. Under 1600dgC of sintering temperature, the pure water flux and maximum pore size reached 2398 L/(m²·h) and 2.3 μm, respectively. The results showed that the alumina hollow fiber membranes we prepared were suitable for the microfiltration process. The morphology investigation also revealed that the prepared Al₂O₃ hollow fiber membrane retained its’asymmetric structure even after the sintering process.     

Polymers for medical and tissue engineering applications

Recent decades have seen great advancements in medical research into materials, both natural and synthetic, that facilitate the repair and regeneration of compromised tissues through the delivery and support of cells and/or biomolecules. Biocompatible polymeric materials have become the most heavily investigated materials used for such purposes. Naturally‐occurring and synthetic polymers, including their various composites and blends, have been successful in a range of medical applications, proving to be particularly suitable for tissue engineering (TE) approaches. The increasing advances in polymeric biomaterial research combined with the developments in manufacturing techniques have expanded capabilities in tissue engineering and other medical applications of these materials. This review will present an overview of the major classes of polymeric biomaterials, highlight their key properties, advantages, limitations and discuss their applications. © 2014 Society of Chemical Industry     

Preparation and characterization of polyvinylidene fluoride hollow fiber membranes for ultrafiltration

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared using the solvent spinning method. N,N-dimethylacetamide was the solvent and ethylene glycol was employed as non-solvent additive. The effect of the concentration of ethylene glycol in the PVDF spinning solution as well as the effect of ethanol either in the internal or the external coagulant on the morphology of the hollow fibers was investigated. The prepared membranes were characterized in terms of the liquid entry pressure of water measurements, the gas permeation tests, the scanning electron microscopy, the atomic force microscopy, and the solute transport experiments. Ultrafiltration experiments were conducted using polyethylene glycol and polyethylene oxides of different molecular weights cut-off as solutes. A comparative analysis was made between the membrane characteristic parameters obtained from the different characterization techniques.     

Ultra-thin skin carbon hollow fiber membranes for sustainable molecular separations

A transformative platform is reported to derive ultra-thin carbon molecular sieve (CMS) hollow fiber membranes from dual-layer precursor hollow fibers with independently tuned skin layer and substrate properties. These ultra-thin CMS hollow fiber membranes show attractive CO₂/CH₄ separation factors and excellent CO₂ permeances up to ~1,400% higher than state-of-the-art asymmetric CMS hollow fiber membranes. They provide a unique combination of permeance and selectivity competitive with zeolite membranes, but with much higher membrane packing density and potentially much lower costs.     

Preparation and characterization of microporous polyethylene hollow fiber membranes

Microporous polyethylene (PE) hollow fiber membrane with a porosity of 43% and N₂ permeation of 4.96 cm³ (STP)/cm² s cmHg was prepared by melt‐spinning and cold‐stretching method. It was found that PE with a density higher than 0.96 g/cm³ should be used for the preparation of microporous PE hollow fiber membranes. By increasing the spin–draw ratio, both the porosity and the N₂ permeation of the hollow fiber membranes increased. Annealing the nascent hollow fiber at 115°C for 2 h was suitable for attaining membranes with good performance. By straining the hollow fiber to higher extensions, the amount and size of the micropores in the hollow fiber wall increased, and the N₂ permeation of the membranes increased accordingly. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 203–210, 2002; DOI 10.1002/app.10305