Porogen Content Research Articles

Microporous Graphite Composites of Tailorable Porosity, Surface Wettability, and Water Permeability for Fuel Cell Bipolar Plates

To address the water management problem in proton-exchange membrane fuel cells, porous graphite composites were prepared by incorporating sacrificial pore-forming agents in the blend of graphite and a phenolic resin formed into a flat plate using compression molding. Sucrose was found to be an effective porogen in the porous plate production process. The effects of relative amounts of graphite, polymer, and porogen in the composite were studied. Bipolar plate properties such as the water uptake by wicking and vacuum infusion, gas-breakthrough pressure across the water-infused pores, electrical conductivity, and flexural strength of the plates were measured and correlated with the plate composition. The plate porosity was evaluated by determining the masses of dry and water-infused plates in air and under water. The porosity, ε, showed a linear increase with an increase in the porogen concentration in the range of 0–10%. The permeabilities, K, of water through the graphite plates with different porosity values were calculated by measuring the water flux over a range of pressures. The water permeability increased with oxidation and hydrophilization of the pore surface. Dynamic water contact angle measurements were used to characterize the effect of chemical and thermal treatments on the water wettability of the plates. The gas-breakthrough pressure of the water-infused plates was found to be linearly correlated with the parameter, γcos⁡θ/K/ε, proportional to the capillary pressure of the gas–water interface of surface tension, γ, and contact angle, θ. Porous plates capable of a total water uptake greater than 25 wt %, with the gas-breakthrough pressure higher than 10 psi, through-plane electrical conductivity exceeding 100 S cm–1, and flexural strength exceeding 25 MPa were obtained.

Microporosity mediated proliferation of preosteoblast cells on 3D printed bone scaffolds

AbstractMicroporous structure plays a significant role in bone tissue engineering, to influence inductive bone formation and elevate bone ingrowth inside microporous scaffolds. We hereby fabricated microporous scaffolds by 3D printing with mixture of porogens and photopolymerizing resin. Our method can tune the microporosity of scaffolds from 0% to 36% by varying the porogen concentration in the inks from zero to 60 vol%. The microporosity and microspore size of scaffolds can affect in vitro expansion of preosteoblast cells. We evaluated the attachment, spreading and proliferation of MC3T3‐E1 mouse preosteoblast cells on the printed porous scaffolds. Our studies revealed that preosteoblast cells’ in vitro adhesion and proliferation were significantly mediated by the printed scaffolds. Cells proliferation on scaffolds with 20%–30% microporosity showed much higher rate than on other scaffolds. In this microporosity range, scaffolds also showed much better cell spreading and morphologies. At a low level of microporosity (< 7%), the cell proliferation rate was even lower than the solid scaffolds, which indicates that the microporous structure is “toxic” for cells at low microporosity range. A higher microporosity (> 35%) led to very poor cell attachment and is unfavorable for the proliferation of MC3T3‐E1 cells. Furthermore, the printed dual macro‐/micro‐porous scaffolds showed higher proliferation rate of MC3T3‐E1 cells as compared to mono‐pore sized scaffolds, either the macro‐porous or microporous structure.

Porous structure of bioceramics carbonated hydroxyapatite-based honeycomb scaffold for bone tissue engineering

In this work, bioceramic carbonated hydroxyapatite (CHA) was synthesized from abalone mussel shells (Halioitis asinina) using a co-precipitation method; CHA-based scaffolds were fabricated with honeycomb (HCB) as the porogen agent. The concentration of HCB porogen varied among 10, 20, 30, and 40 wt%. The Energy Dispersive X-Ray Spectroscopy (EDS) analysis revealed that the Ca/P molar ratio of CHA was 1.73, which was close to natural bone’s Ca/P molar ratio of 1.71. Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffractometer (XRD) tests revealed that the formed phase of the synthesized CHA was of the B-type. Analysis of the pores structure showed an increasing porogen concentration, pores size, and porosity of the scaffold. The addition of HCB porogen also decreased the crystallite size. This was very good for bone growth because the low crystallinity created dislocations, making it easier for cells to proliferate. Based on the results of cell viability assay on scaffold CHA + HCB 40 wt%, the growth of MC3T3E1 cells was inhibited beginning at a scaffold concentration of 500 μg/mL because the percentage of viability decreased to ∼ 115 % and the IC50 value of MC3T3E1 cells on the scaffold to 691830.97 μg/mL. Based on to the one-way ANOVA, those result reflected no statistically significant differences in the average of cell viability value in the five groups (p> 0.05). The cell metabolic activity and morphology of the CHA + HCB 40 wt% scaffold enable it to facilitate the attachment of MC3T3E1 cells on its surface. Thus, HCB 40 wt% was the best concentration to fabricate the scaffold based on the criteria for pores structure, crystallographic properties, chemical decomposition process and cell viability for biomedical applications.

Solvent-Free Processing of Drug-Loaded Poly(ε-Caprolactone) Scaffolds with Tunable Macroporosity by Combination of Supercritical Foaming and Thermal Porogen Leaching.

Demand of scaffolds for hard tissue repair increases due to a higher incidence of fractures related to accidents and bone-diseases that are linked to the ageing of the population. Namely, scaffolds loaded with bioactive agents can facilitate the bone repair by favoring the bone integration and avoiding post-grafting complications. Supercritical (sc-)foaming technology emerges as a unique solvent-free approach for the processing of drug-loadenu7d scaffolds at high incorporation yields. In this work, medicated poly(ε-caprolactone) (PCL) scaffolds were prepared by sc-foaming coupled with a leaching process to overcome problems of pore size tuning of the sc-foaming technique. The removal of the solid porogen (BA, ammonium bicarbonate) was carried out by a thermal leaching taking place at 37 °C and in the absence of solvents for the first time. Macroporous scaffolds with dual porosity (50–100 µm and 200–400 µm ranges) were obtained and with a porous structure directly dependent on the porogen content used. The processing of ketoprofen-loaded scaffolds using BA porogen resulted in drug loading yields close to 100% and influenced its release profile from the PCL matrix to a relevant clinical scenario. A novel solvent-free strategy has been set to integrate the incorporation of solid porogens in the sc-foaming of medicated scaffolds.

Preparation and Characterization of Poly(L-lactide-co-glycolide-co-ε-caprolactone)/1,4-Butanediamine Modified Maleated Poly(D,L-lactide-co-glycolide) Blend Porous Films

Poly(L-lactide-co-glycolide-co-ε-caprolactone) (PLLGC) and 1,4-butanediamine modified maleated poly(D,L-lactide-co-glycolide) (BMPLGA) were both synthesized by ring-opening polymerization with stannous octoate as catalyst. Then PLLGC/BMPLGA blend porous films were prepared by using NaCl particles as a porogen through a solvent casting/particle leaching method. The PLLGC/BMPLGA blend porous films were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography and scanning electron microscopy. The tensile properties of the PLLGC/BMPLGA porous films were also studied. The results showed that the content and size of the NaCl porogens had significant effects on the porosity of the PLLGC/BMPLGA porous films. The tensile strength and elongation percentage of the porous films decreased with increasing porogen content. Thus, both the pore structure and mechanical properties of the porous PLLGC/BMPLGA blend films can be controlled by changing the amount and size of the porogen.

Uncovering the effects of PEG porogen molecular weight and concentration on ultrafiltration membrane properties and protein purification performance

Developing ultrafiltration (UF) membranes for protein purification requires a critical understanding of the pore engineering and active-layer morphological control. In this study, we systematically explored the use of polyethylene glycol (PEG) with molecular weights (MW, 600–6000 g⋅mol−1) and concentration (3–7.5 wt%) as a pore modifier to prepare polyvinyl difluoride (PVDF) membranes via the non-solvent phase-inversion process. The membranes demonstrated a high degree of control of the structure-property-performance relationship for improving the water flux, bovine serum albumin (BSA) rejection and antifouling properties. We found that the morphology of PEG-modified membranes showed the membrane surface crystal spherulite remarkably decreased, whilst surface pore size increased with increasing porogen MW. Similarly, the increase in membrane pore size correlated very well with porogen MW and concentration exponentially and linearly respectively. Furthermore, the PEG-MW membrane series showed a flux and rejection trade-off, whereas the PEG-concentration membrane series can produce a high BSA rejection and improve the flux owing to the presence of a dense active layer. Overall, the optimized membrane with the best protein separation properties was produced by using 6 wt% PEG with 600 g⋅mol−1, which reached a competitive permeate flux of ~60 LMH⋅bar−1, with excellent flux recovery rate of >90%, and a high BSA rejection rate of 90% at the end of the three test cycle. The results in this study have elucidated and advanced the fundamental knowledge of the interrelationship between porogen and membrane property-performance.

Porogen Effect on Structural and Physical Properties of β-TCP Scaffolds for Bone Tissue Regeneration

Scaffolds for bone tissue applications have been an outstanding alternative to repair and regenerate bone tissue defects caused by traumas or illness. There are many methods available to fabricate porous scaffold such as solvent casting, gas bubble, phase separation, electrospinning, particle-leaching, among others. The particle-leaching technique has shown advantages in bone tissue regeneration applications, the main benefit of this technique is related to the porogen particle size and the porogen content in the manufacture of scaffolds. Tricalcium phosphate is one calcium phosphate that presented appropriated characteristic to be used for bone tissue engineering due to the chemical properties similar to the human bones. Scaffolds of tricalcium phosphate β phase were made using sugar particles. The porogen was varied in amounts of 50, 60 and 70 wt.% of two commercial sugars with the remainder of the composition made up of tricalcium phosphate powders. The pore sizes in all the scaffolds were in the range of 90 to 600 μm with an irregular pore morphology and the porosity was in the range of 63 to 77%.

Salt leaching using powder (SLUP) process for glass/chitosan scaffold elaboration for biomaterial applications

Tissue engineering has emerged as an alternative approach to create bone tissue by growing cells on 3D scaffolding. The aim of this study was to synthesize a composite glass/chitosan (BG-CH) by using new salt leaching using powder (SLUP) process in order to control the porosity rate and then the chemical reactivity of the final product. SLUP process consists on the cavity creation with desired pore sizes. It does not require heat treatment. This process is based on washing out the NaCl particles used for that. It is due to its high solubility in aqueous media. This work focuses on the elaboration, physicochemical, and chemical reactivity studies of pure bioactive glass and bioactive glass associated with chitosan. A range of composite scaffolds with different bioactive glass/chitosan contents has been synthesized. NaCl with a distinct range size was used with the aim of optimizing the pore network. Obtained results show that the specific surface area and pore volume increase with increasing of chitosan and porogen content. The same observations for pore volume were registered. The obtained scaffolds had high porosity (90%) with good pore connectivity. SEM images revealed strong dependence of sizes and shapes of pores on the salt/composite ratios.

Combined Porogen Leaching and Emulsion Templating to produce Bone Tissue Engineering Scaffolds.

Bone has a hierarchy of porosity that is often overlooked when creating tissue engineering scaffolds where pore sizes are typically confined to a single order of magnitude. High internal phase emulsion (HIPE) templating produces polymerized HIPEs (polyHIPEs): highly interconnected porous polymers which have two length scales of porosity covering the 1–100 μm range. However, additional larger scales of porosity cannot be introduced in the standard emulsion formulation. Researchers have previously overcome this by additively manufacturing emulsions; fabricating highly microporous struts into complex macroporous geometries. This is time consuming and expensive; therefore, here we assessed the feasibility of combining porogen leaching with emulsion templating to introduce additional macroporosity. Alginate beads between 275 and 780 μm were incorporated into the emulsion at 0, 50, and 100 wt%. Once polymerized, alginate was dissolved leaving highly porous polyHIPE scaffolds with added macroporosity. The compressive modulus of the scaffolds decreased as alginate porogen content increased. Cellular performance was assessed using MLO-A5 post-osteoblasts. Seeding efficiency was significantly higher and mineralized matrix deposition was more uniformly deposited throughout porogen leached scaffolds compared to plain polyHIPEs. Deep cell infiltration only occurred in porogen leached scaffolds as detected by histology and lightsheet microscopy. This study reveals a quick, low cost and simple method of producing multiscale porosity scaffolds for tissue engineering.

Fabrication of Biodegradable Polymeric Microspheres with Controllable Porous Structure for Cell Delivery

Porous microspheres fabricated by biodegradable polymers show great potential as carriers for cell cultivation in tissue engineering. We have attempted to prepare porous microspheres using various biodegradable polymers, and the polymer used is biodegradable Poly(D,L-lactide-co-glycolide) (PLGA), chitosan, hyaluronic acid, gelatin. The influence of fabrication parameters, such as the concentration of crosslinker and polymer, concentration and type of porogen, as well as the post-hydrolysis treatment and thawing time of the porous structure of the microspheres are discussed. an active spread of Hep3B-GFP cells on the microspheres is observed, which indicates that the biodegradable polymeric microsphere with controllable porous structure are of great potential as cell delivery carriers for tissue engineering.

Quantification of porogen effect on the drug release from single- and multi-layered ethylcellulose coated pellets containing single or combined drugs

The aim of this work was to develop a mathematical model to estimate the drug release from a conventional single-compartment reservoir pellet and extend its applicability to multi-compartment reservoir pellets. Conventional pellets were prepared by layering the drug onto starter-core then applying various ethylcellulose/HPC coatings for drug release control. Multi-layered pellets comprised a first drug layer of propranolol HCl (D1) followed by a first controlled release coating (C1) and consecutively a second drug layer of carbamazepine or caffeine (D2) and then a second controlled-release coating (C2). Drug release from single- and multi-compartment pellets generally increased with an increase of the water-soluble HPC in the coatings. The response described a sigmoidal curve, which agreed with a cumulative normal distribution function. The developed mathematical model facilitated quantification of the drug release of pellets as a function of the porogen content and the coating level. Additionally, the model was applied successfully in multi-compartment pellets to calculate theses effects on the release of drugs with a broad range of aqueous solubility.

KOH-doped Porous Polybenzimidazole Membranes for Solid Alkaline Fuel Cells

In this study the preparation and properties of potassium hydroxide-doped meta-polybenzimidazole membranes with 20–30 μm thickness are reported as anion conducting polymer electrolyte for application in fuel cells. Dibutyl phthalate as porogen forms an asymmetrically porous structure of membranes along thickness direction. One side of the membranes has a dense skin layer surface with 1.5–15 μm and the other side of the membranes has a porous one. It demonstrated that ion conductivity of the potassium hydroxide-doped porous membrane with the porogen content of 47 wt.% (0.090 S cm−1), is 1.4 times higher than the potassium hydroxide-doped dense membrane (0.065 S cm−1). This is because the porous membrane allows 1.4 times higher potassium hydroxide uptake than dense membranes. Tensile strength and elongation studies confirm that doping by simply immersing membranes in potassium hydroxide solutions was sufficient to fill in the inner pores. The membrane-electrode assembly using the asymmetrically porous membrane with 1.4 times higher ionic conductivity than the dense non-doped polybenzimidazole (mPBI) membrane showed 1.25 times higher peak power density.

Synthesis of Acrylonitrile Based High Internal Phase Emulsion Monoliths and their Application in Recovery of Heavy Metal Ions

Polymeric monoliths based on acrylonitrile-divinyl benzene were synthesized successfully by high internal phase emulsion (HIPE) polymerization. Highly porous polyHIPEs were prepared by variation in oil to water ratio as well as type and concentration of porogens. The porogens evaluated were toluene, chlorobenzene, heptane and chloroform. The effect of oil to water ratio and porogen type and concentrations on morphology and surface area of polyHIPEs were investigated. The polyHIPEs were modified to amidoxime functionality by treating base catalyzed reaction with hydroxylamine hydrochloride in presence of base. The treated and modified polymeric monoliths were characterized by FT-IR, SEM and surface area analysis. The modified porous polyHIPEs were tested for adsorption of Cr(VI) metal ions at various pH.

Fabricating Fibers of a Porous-Polystyrene Shell and Particle-Loaded Core.

Polystyrene (PS) polymers have broad applications in protective packaging for food shipping, containers, lids, bottles, trays, tumblers, disposable cutlery and the making of models. Currently, most PS products, such as foams, are not accepted for recycling due to a low density in the porous structure. This poses a challenge for logistics as well as creating a lack of incentive to invest in high-value products. This study, however, demonstrated the use of a dry-jet wet-spinning technique to manufacture continuous PS fibers enabled by an in-house designed and developed spinning apparatus. The manufactured fibers showed porosity in the shell and the capability to load particles in their core, a structure with high potential use in environmentally relevant applications such as water treatment or CO2 collections. A two-phase liquid-state microstructure was first achieved via a co-axial spinneret. Following coagulation procedures and heat treatment, phase-separation-based selective dissolution successfully generated the porous-shell/particle-core fibers. The pore size and density were controlled by the porogen (i.e., PEG) concentrations and examined using scanning electron microscopy (SEM). Fiber formation dynamics were studied via rheology tests and gelation measurements. The shell components were characterized by tensile tests, thermogravimetric analysis, and differential scanning calorimetry for mechanical durability and thermal stability analyses.

Properties of Porous Polyimide Films Based on Melamine Template

In this paper, melamine was used as porogen to prepare porous polyimide film by in-situ polymerization. The mechanical properties, thermal properties, dielectric properties, oil content and friction and wear properties of polyimide films with different porosity were investigated. The tensile strength of porous films decreases obviously with increase of melamine content. It shows the lower thermal decomposition temperature and the faster decomposition speed compared with the non-porous film, indicating higher heat exchange rate due to holes in porous films. As the porogen content increases, the dielectric constant decreases significantly, and the film with melamine content of 20 wt.% has the lowest dielectric constant of 2.43. The holes lead to good oil storage performance and the wear rate and the friction coefficient decrease with the increase of porosity. Keywords: polyimide; porous; melamine; dielectric; friction

Development of porous fabric‐hydrogel composite membranes with enhanced ion permeability for microalgal cultivation in the ocean

ABSTRACTThis article presents a strategy to develop the porous fabric‐hydrogel composite membranes (PFHCMs) with high nitrate ion (NO3−, a source of a main nutrient, nitrogen) permeability and sufficient mechanical strength required for microalgal cultivation in the ocean. The porous structure in the PFHCMs is generated by using three different types of porogens: water‐soluble macromolecules, surfactant micelles, and CaCO3 microparticles. Various PFHCMs, composed mainly of poly(hydroxyethyl methacrylate) hydrogels and cotton fabric, are prepared with varying the content of monomer, initiator, and crosslinker and the type and content of porogen. Their morphological, physical, and mechanical properties are characterized for variables. Among three porogens, the surfactant micelles with a large enough amount produce the optimal PFHCMs with NO3− ion permeability coefficient (5.49 × 10−8 m2 min−1, approximately 5 and 20 times higher than those of the fabric‐hydrogel composite membranes, synthesized without any porogen in a previous work, and the commercial cellulose acetate membranes, respectively). Their mechanical strength (i.e., the ultimate stress is 9.37 MPa) is high enough for practical uses. Therefore, these PFHCMs are good candidate membranes in microalgal cultivation for biorefinery and other biomedical applications, including wound dressings. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48324.

Vancomycin- and Poly(simvastatin)-Loaded Scaffolds with Time-Dependent Development of Porosity

Biodegradable scaffolds are widely use in drug delivery and tissue engineering applications. The scaffolds can be modified to provide the necessary mechanical support for tissue formation and to deliver one or more drugs to stimulate tissue formation or for the treatment of a specific condition. In the current study, we developed biodegradable scaffolds that have the potential for dual drug delivery. The scaffolds consisted of simvastatin-containing prodrug, poly(simvastatin) entrapped in poly(β-amino ester) (PBAE) porogen particles and vancomycin encapsulated in poly(lactic-co-glycolic acid) (PLGA) microspheres, which were fused together around the PBAE porogens to create a slow-degrading matrix. Upon hydrolysis, poly(simvastatin) releases simvastatin acid, which has angiogenic and osteogenic properties, while the PLGA microspheres release vancomycin as an antibacterial agent. Degradation of PBAE porogens through hydrolysis of ester linkages led to the development of porosity in a controlled manner and led to water penetration that facilitated hydrolysis of PLGA. Higher porogen loading (~60% by weight) gave rise to ~70% interconnected porosity with pore spacing of ~180 μm. This open volume facilitated simvastatin acid release upon hydrolysis and entrapped vancomycin release via diffusion through and degradation of PLGA. During the study, ~162 μg of simvastatin acid and ~18 mg vancomycin were released from the highest porosity scaffolds. Bioactivity studies showed that released simvastatin acid stimulated preosteoblastic activity, indicating that scaffold fabrication did not damage the polymeric prodrug. Regarding mechanical properties, compressive modulus, failure strain, and failure stress decreased with increasing PBAE porogen content. These dual drug releasing scaffolds with controlled development of microarchitecture can be useful in bone tissue engineering applications.

Effect of the porogen content and the sintering temperature on the aperture of porous copper materials

Copper porous materials had been manufactured by adding methylcellulose as the porogen. The effect of weight percentage of methylcellulose and sintering temperature on the microstructure and porosity of porous copper materials were investigated. The results show that the pyrolysis of methylcellulose leads to the pores in copper matrix. The porosity of copper porous materials enhances along with the increase of methylcellulose content. The permeability of them increases firstly and then decreases along with the porogen content, because excessive methylcellulose brings about the apparent uneven distribution of pores. The sintering mechanism changes from surface diffusion to volume diffusion with the rise of sintering temperature, which influences the porosity and pore structure of materials. With the rising of sintering temperature, the porosity of porous materials increases firstly under the lower sintering temperature and then decreases under the higher sintering temperature. The number of micropores increases obviously at high sintering temperature.

Porous structure engineering of bioceramic hydroxyapatite-based scaffolds using PVA, PVP, and PEO as polymeric porogens

ABSTRACTNanobioceramic hydroxyapatite (HAp) was synthesized from golden apple snail (Pomacea canaliculata) shell and used to fabricate HAp-based scaffolds with polyvinyl alcohol (PVA), polyethylene oxide (PEO), or polyvinylpyrrolidone (PVP) as the porogen agent. The porogen was removed during the HAp sintering process. The SEM results showed increased agglomeration of HAp particles with increases in concentration of polymeric porogen used in the scaffold fabrication process. The XRD pattern showed the scaffolds to be HAp/β-TCP composites. Thermal analysis of the porogen weight loss at a sintering rate of 32°C/min showed that all the porogen had leached out before the sample attained the maximum sintering temperature. Fourier transform infrared (FTIR) spectra confirmed the absence of porogen functional groups within the scaffold after sintering. The weight concentration of the porogen plays an important role in establishing the homogeneity and interconnectivity of the pores, as well as the mechanical strength of the scaffold.

Next generation in vitro liver model design: Combining a permeable polystyrene membrane with a transdifferentiated cell line

Herein we describe the manufacture and characterisation of biocompatible, porous polystyrene membranes, suitable for cell culture. Though widely used in traditional cell culture, polystyrene has not been used as a hollow fibre membrane due to its hydrophobicity and non-porous structure.Here, we use microcrystalline sodium chloride (4.7 ± 1.3 µm) to control the porosity of polystyrene membranes and oxygen plasma surface treatment to reduce hydrophobicity. Increased porogen concentration correlates to increased surface pore density, macrovoid formation, gas permeability and mean pore size, but a decrease in mechanical strength. For tissue engineering applications, membranes spun from casting solutions containing 40% (w/w) sodium chloride represent a compromise between strength and permeability, having surface pore density of 208.2 ± 29.7 pores/mm2, mean surface pore size of 2.3 ± 0.7 µm, and Young's modulus of 115.0 ± 8.2 MPa.We demonstrate the biocompatibility of the material with an exciting cell line-media combination: transdifferentiation of the AR42J-B13 pancreatic cell line to hepatocyte-like cells. Treatment of AR42J-B13 with dexamethasone/oncostatin-M over 14 days induces transdifferentiation towards a hepatic phenotype. There was a distinct loss of the pancreatic phenotype, shown through loss of expression of the pancreatic marker amylase, and gain of the hepatic phenotype, shown through induction of expression of the hepatic markers transferrin, carbamoylphosphate synthetase and glutamine synthetase.The combination of this membrane fabrication method and demonstration of biocompatibility of the transdifferentiated hepatocytes provides a novel, superior, alternative design for in vitro liver models and bioartificial liver devices.