3D printed polylactic acid nanocomposite scaffolds for tissue engineering applications

In this study, biodegradable polylactic acid (PLA) and PLA nanocomposite scaffolds reinforced with magnetic and conductive fillers, were processed via fused filament fabrication additive manufacturing and their bioactivity and biodegradation characteristics were examined. Porous 3D architectures with 50% bulk porosity were 3D printed, and their physicochemical properties were evaluated. Thermal analysis confirmed the presence of ~18 wt% of carbon nanostructures (CNF and GNP; nowonwards CNF) and ~37 wt% of magnetic iron oxide (Fe₂O₃) particles in the filaments. The in vitro degradation tests of scaffolds showed porous and fractured struts after 2 and 4 weeks of immersion in DMEM respectively, although a negligible weight loss is observed. Greater extent of degradation is observed in PLA with magnetic fillers followed by PLA with conductive fillers and neat PLA. In vitro bioactivity study of scaffolds indicate enhancement from ~2.9% (PLA) to ~5.32% (PLA/CNF) and ~ 3.12% (PLA/Fe₂O₃). Stiffness calculated from the compression tests showed decrease from ~680 MPa (PLA) to 533 MPa and 425 MPa for PLA/CNF and PLA/Fe₂O₃ respectively. Enhanced bioactivity and faster biodegradation response of PLA nanocomposites with conductive fillers make them a potential candidate for tissue engineering applications such as scaffold bone replacement and regeneration.     

Microanalysis of hybrid characterization of PLA/cHA polymer scaffolds for bone regeneration

Tissue engineering uses some engineering strategies for the reconstruction and repair of the compromised tissues, among which the use of biomaterials as an alternative to conventional transplants is significant. However, not many research has been developed on the use of biopolymer nanostructure microanalysis and calcium phosphate composites of carbon apatite in PLA as scaffolds for tissue regeneration. In this work, poly (lactic acid) filaments with 5% and 20%, carbon apatite (cHA) were microanalysis to produce a 3D printing scaffold. The scaffolds were characterised by the Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray (EDX) techniques, thereby making it possible to notice a good load dispersion. The microstructural analysis of the scaffolds was carried out by computerised micro-tomography to determine the roughness, morphological parameters of pore size distribution, porosity, as well as better visualisation of the distribution of particles. A computational in vitro and microanalysis tests to assess the biocompatibility viability of the PLA/cHA structure with a variation of scaffold geometry to evaluate their effects on morphological, physicochemical and mechanical properties were also carried out. The characterisation of Ca and P release assays were observed for longer incubation times and the dynamic condition control to simulate the stresses suffered by the biomaterial exerted by the flow of fluids was achieved. The results obtained indicated that the micrographs of the cross-sections of the scaffolds showed a flatness in the loaded material when compared to the 100/0 PLA. Furthermore, the apparent porosity of 5% and 20% of cHA scaffolds gave a porosity percentage of approximately 62% and 41% respectively. The reduced summit height, reduced valley depth and the percentage upper and lower bearing area difference of the samples are 16.33 nm, 9.62 nm and 75.07% respectively. The morphological characterisation surface roughness analysis and tolerance insertion gave a favourable reduced porosity result for the composite scaffolds with 5% of cHA. Hence, this work will assist biomaterial industries in the development of biomaterials which have been engineered with biological systems to meet medical purposes.     

Production and characterization of elastomeric cardiac tissue-like patches for Myocardial Tissue Engineering

Cardiovascular disease remains the leading cause of death. Damaged heart muscle is the etiology of heart failure. Heart failure is the most frequent cause of hospital and emergency room admissions. As a differentiated organ, current therapeutics and techniques can not repair or replace the damaged myocardial tissue. Myocardial tissue engineering is one of the promising treatment modalities for repairing damaged heart tissue in patients with heart failure. In this work, random Polylactic acid (PLA), Polylactic acid/Polyethylene glycol (PLA/PEG) and random and aligned Polylactic acid/Polyethylene glycol/Collagen (PLA/PEG/COL) nanofiber patches were successfully produced by the electrospinning technique. In vitro cytotoxic test (MTT), morphological (SEM), molecular interactions between the components (FT-IR), thermal analysis (DSC), tensile strength and physical analysis were carried out after production. The resulting nanofiber patches exhibited beadless and smooth structures. When the fiber diameters were examined, it was observed that the collagen doped random nanofiber patches had the lowest fiber diameter value (755 nm). Mechanical characterization results showed that aligned nanofiber patches had maximum tensile strength (5.90 MPa) values compared to PLA, PLA/PEG, and PLA/PEG/COL (random). In vitro degradation test reported that aligned patch had the highest degradation ratio. The produced patches displayed good alignment with tissue on cardiomyocyte cell morphology studies. In conclusion, newly produced patches have noticeable potential as a tissue-like cardiac patch for regeneration efforts after myocardial infarction.     

New approach on the development of plasticized polylactide (PLA): Grafting of poly(ethylene glycol) (PEG) via reactive extrusion

In this work, new ways of plasticizing polylactide (PLA) with low molecular poly(ethylene glycol) (PEG) were developed to improve the ductility of PLA while maintaining the plasticizer content at maximum 20 wt.% PLA. To this end, a reactive blending of anhydride-grafted PLA (MAG-PLA) copolymer with PEG, with chains terminated with hydroxyl groups, was performed. During the melt-processing, a fraction of PEG was grafted into the anhydride-functionalized PLA chains. The role of the grafted fraction was to improve the compatibility between PLA and PEG. Reactive extrusion and melt-blending of neat and modified PLA with PEG did not induce any dramatic drop of PLA molecular weight. The in situ reactive grafting of PEG into the modified PLA in PLA/PEG blends showed a clear effect on the thermal properties of PLA. It was demonstrated by DSC that the mobility gained by PLA chains in the plasticized blends yielded crystallization. The grafting of a fraction of PEG into PLA did not affect this process. However, DSC results obtained after the second heating showed an interesting effect on the T_g when 20 wt.% PEG were melt blended with neat PLA or 10 wt.% MAG-PLA. In the latter case, the T_g displayed by the reactive blend was shifted to even lower temperatures at around 14 °C, while the T_g of neat PLA and PLA blended with 20 wt.% PEG was around 60 and 23 °C, respectively. Regarding viscoelastic and viscoplastic properties, the presence of MAG-PLA does not significantly influence the behavior of plasticized PLA. Indeed, with or without MAG-PLA, elastic modulus and yield stress decrease, while ultimate strain increases with the addition of PEG into PLA.     

Tough crystalline blends of polylactide with block copolymers of ethylene glycol and propylene glycol

The effect of crystallinity of polylactide (PLA) on the structure and properties of tough PLA blends with PEG-b-PPG-b-PEG block copolymers was studied. PLA was melt blended with a set of the copolymers with varying ratio of the hydrophilic (PEG) and hydrophobic (PPG) blocks. Although the blend phase structure depended on the copolymer molar mass and PEG content, as well as on the copolymer concentration in the blend, crystallinity also played an important role, increasing the copolymer content in the amorphous phase and enhancing phase separation. The influence of crystallinity on the thermal and mechanical properties of the blends depended on the copolymer used and its content. The blends, with PLA crystallinity of 25 ÷ 34 wt%, exhibited relatively high glass transition temperature ranging from 45 to 52 °C, and melting beginning above 120 °C. Although with a few exceptions crystallinity worsened the drawability and toughness, these properties were improved with respect to neat crystalline PLA in the case of partially miscible blends, in which fine liquid inclusions of the modifier were dispersed in PLA rich matrix. About 20-fold increase of the elongation at break and about 4-fold increase of the tensile impact strength were reached at a small content (10 wt%) of the modifier. Moreover, crystallinity decreased oxygen and water vapor transmission rates through neat PLA and the blend, and the barrier property for oxygen of the latter was better than that of neat polymer.     

Morphological characteristics and properties of TPS/PLA/cassava pulp biocomposites

The effect of cassava pulp (CP) on morphological, tensile, and thermal properties of a thermoplastic cassava starch (TPS)/poly (lactic acid) (PLA) blend was investigated. TPS/PLA/CP biocomposites were manufactured by melt extrusion and then converted into specimens using an injection molding. The weight fraction of PLA to TPS/CP was fixed at 40:60, whereas the final CP concentration in the composites was varied in the range of 4.4–22.1 wt%. CP could act as a reinforcement for TPS/PLA blend to enhance its tensile strength up to 354% and Young's modulus up to 722% when 22.1 wt% of CP was loaded and a nucleating agent for PLA as confirmed from the reduced T_cc. In addition, TPS/PLA/CP composites showed a discrete phase structure (i.e., droplets in matrix) when CP with lower concentration (i.e., 4.4 wt%, 8.8 wt%, and 13.3 wt%) was incorporated and a bicontinuous phase structure (i.e., co-continuous) when higher concentration of CP (i.e., 17.7 wt% and 22.1 wt%) was employed. The results suggest that TPS/PLA/CP biocomposites have potential to be used in the manufacturing of injection-molded articles, particularly when biodegradability and renewability of the material are required.     

Microstructure and mechanical properties of bacterial cellulose/chitosan porous scaffold

A family of polysaccharide based scaffold materials, bacterial cellulose/chitosan (BC/CTS) porous scaffolds with various weight ratios (from 20/80 to 60/40 w/w%) were prepared by freezing (−30 and −80 °C) and lyophilization of a mixture of microfibrillated BC suspension and chitosan solution. The microfibrillated BC (MFC) was subjected to 2,2,6,6-tetramethylpyperidine-1-oxyl radical (TEMPO)-mediated oxidation to introduce surface carboxyl groups before mixing. The integration of MFC within chitosan matrix was performed by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC)-mediated cross-linking. The covalent amide bond formation was determined by ATR-FTIR. Because of this covalent coupling, the scaffolds retain their original shapes during autoclave sterilization. The composite scaffolds are three-dimensional open pore microstructure with pore size ranging from 120 to 280 μm. The freezing temperature and mean pore size take less effect on scaffold mechanical properties. The compressive modulus and strength increased with increase in MFC content. The results show that the scaffolds of higher MFC content contribute to overall better mechanical properties.     

Mechanical,aging, optical and rheological properties of toughening polylactide by melt blending with poly(ethylene glycol) based copolymers

Two novel biodegradable copolymers, including poly(ethylene glycol)-succinate copolymer (PES) and poly(ethylene glycol)-succinate-l-lactide copolymer (PESL), have been successfully synthesized via melt polycondensation using SnCl₂ as a catalyst. The copolymers were used to toughen PLA by melt blending. The DSC and SEM results indicated that the two copolymers were compatible well with PLA, and the compatibility of PESL was superior to that of PES. The results of tensile testing showed that the extensibility of PLA was largely improved by blending with PES or PESL. At same blending ratios, the elongation at break of PLA/PESL blends was far higher than that of PLA/PES ones. The elongation maintained stable through aging for 3 months. The moisture absorption of the blends enhanced due to the strong moisture absorption of PEG segments in PES or PESL molecules, which did not directly lead to enhance the hydrolytic degradation rate of the PLA. The PLA blends containing 20–30 wt% PES or PESL were high transparent materials with high light scattering. The toughening PLA materials could potentially be used as a soft biodegradable packaging material or a special optical material.     

Electrospun hyperbranched polylactic acid–modified cellulose nanocrystals/polylactic acid for shape memory membranes with high mechanical properties

The polylactic acid (PLA) nanofiber membranes reinforced with hyperbranched PLA‐modified cellulose nanocrystals (H‐PLA‐CNCs) were prepared by electrospinning. The H‐PLA‐CNCs and the nanofiber membranes were researched by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The outcomes embodied that the cellulose nanocrystals (CNCs) could be successfully improved by the hyperbranched PLA, which would offer powerful CNCs/matrix interfacial adhesion. Thus, the mechanical and shape memory properties of PLA can be improved by adding the H‐PLA‐CNCs. In particular, when the addition of H‐PLA‐CNCs was 7 wt%, the tensile strength and an ultimate strain of PLA composite nanofiber membranes was 15.56 MPa and 25%, which was 228% and 72.4% higher than that of neat PLA, respectively. In addition, the shape recovery rate of the PLA/5 wt% H‐PLA‐CNCs composite nanofiber membrane was 93%, which was 37% higher than that of neat PLA. We expected that this present study would provide unremitting efforts for the development of more effective approaches to prepare biology basic shape memory membranes with high mechanical properties.     

Tri(3-alkoxyl-3-oxopropyl) phosphine oxides derived from PH3 tail gas as a novel phosphorus-containing plasticizer for polylactide

Preparing a polylactide (PLA)/plasticizer system has been regarded as an effective solution to improve the ductility of brittle PLA. In this reach, a novel type of alkyl phosphine oxides consisting of three aliphatic ester substituents was prepared from PH₃ tail gas, and its potential to be employed as a PLA plasticizer was studied. Differential scanning calorimeter tests confirmed that the newly-prepared plasticizer decreased the T_g of PLA (28 wt% plasticizer) from 52°C (neat PLA) to 11°C, and increased the elongation at break from 11% (neat PLA) to 271% (plasticized PLA). X-ray diffraction results showed that the crystallization degree of PLA (28 wt% plasticizer) increased from 0.12% of neat PLA to 14.04%, while Young's modulus of PLA remained as high as 121.3 MPa, which was much higher than that of the PLA/citrate ester systems with same plasticizer content. These novel phosphorus-containing plasticizers exhibited excellent thermal stability and a weight-loss of the system no more than 2.5% at 180°C; therefore, no unpleasant volatiles were released during processing. In contrast, the weight loss of the PLA/citrate system was as high as 10.8% at 180°C, forming heavy fog with an unpleasant smell during thermal mixing. Scanning electron microscopy was employed to observe the microstructure of the PLA/plasticizer systems, which indicated that the carboxylic butyl ester-containing phosphine oxides was compatible with PLA matrix.     

Effect of polyethylene glycol on the crystallization and impact properties of polylactide‐based blends

Polylactide (PLA) was plasticized by polyethylene glycols (PEGs) with five different molecular weights (M_w = 200–20,000 g/mol). The effects of content and molecular weight of PEG on the crystallization and impact properties of PLA were studied by wide‐angle X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, and V‐notched impact tests, respectively. The results revealed that PEG‐10,000 could significantly improve the crystallization capacity and impact toughness of PLA. When the PEG‐10,000 content ranged from 0 to 20 wt%, the increases in both V‐notched Izod and Charpy impact strengths of PLA/PEG‐10,000 blends were 206.10% and 137.25%, respectively. Meanwhile, the crystallinity of PLA/PEG‐10,000 blends increased from 3.95% to 43.42%. For 10 wt% PEG content, the crystallization and impact properties of PLA/PEG blends mainly depended upon PEG molecular weight. With increasing the M_w of PEG, the crystallinity and impact strength of PLA/PEG blends first decreased and then increased. The introduction of PEG reduced the intermolecular force and enhanced the mobility of PLA chains, thus improving the crystallization capacity and flexibility of PLA. Copyright © 2015 John Wiley & Sons, Ltd.     

Bacterial cellulose/poly(ethylene glycol) composite: characterization and first evaluation of biocompatibility

Bacterial cellulose (BC)/poly(ethylene glycol) (PEG) composite was prepared by immersing wet BC pellicle in PEG aqueous solution followed by freeze-drying process. The product looks like a foam structure. The morphology of BC/PEG composite was examined by scanning electron microscope (SEM) and compared with pristine BC. SEM images showed that PEG molecules was not only coated on the BC fibrils surface but also penetrated into BC fiber networks. It has very well interconnected porous network structure and large aspect surface. The composite was also characterized by Fourier transform infrared spectrum, X-ray diffraction, thermogravimetric analysis (TGA) and tensile test. It was found that the presence of PEG affected the preferential orientation of the (1[`1]0 1\bar{1}0 ) plane during the drying process of BC pellicle, which in turn decrease the crystallinity of dried BC. The TGA result showed that the thermal stability was improved from 263 to 293 °C, which might be associated with strong interaction between BC and PEG. Tensile test results indicate that the Young’s modulus and tensile strength tend to decrease. Biocompatibility of composite was preliminarily evaluated by cell adhesion studies using 3T3 fibroblast cells. The cells incubated with BC/PEG scaffolds for 48 h were capable of forming cell adhesion and proliferation, which showed much better biocompatibility than the pure BC. The prepared BC/PEG scaffolds can be used for wound dressing or tissue-engineering scaffolds.     

In vitro degradation and release behavior of porous poly(lactic acid) scaffolds containing chitosan microspheres as a carrier for BMP-2-derived synthetic peptide

To develop a novel tissue engineering scaffold with the capability of controlled releasing BMP-2-derived synthetic peptide, porous poly(lactic acid)/chitosan microspheres (PLA/CMs) composites containing different quantities of chitosan microspheres were prepared by a thermally induced phase separation method. FTIR analysis revealed that there were strong hydrogen bond interactions between the PLA and chitosan component. Introduction of less than 30% CMs (on PLA weight basis) did not remarkably affect the morphology and porosity of the PLA/CMs scaffolds. The compressive strength of the composite scaffolds increased from 0.48 to 0.66 MPa, while the compressive modulus increased from 7.29 to 8.23 MPa as the microspheres' contents increased from 0% to 50%. In vitro degradability investigation indicated that the dissolution of chitosan component was preferential than PLA matrix and the inclusion of CMs could neutralize the acidity of PLA degradation products. Compared with the rapid release from CMs, the synthetic peptide was released from PLA/CMs scaffolds in a temporally controlled manner, mainly depending on the degradation of PLA matrix. The promising microspheres based scaffold release system can be used to deliver bioactive factors for a variety of non-loaded bone regeneration and tissue engineering application.     

Effects of poly(ethylene glycol) on the morphology and properties of biocomposites based on polylactide and cellulose nanofibers

Polylactide (PLA)/cellulose nanofiber (CNF) biocomposites were prepared via solution casting and direct melt mixing. To improve the compatibility, a masterbatch of CNFs and poly(ethylene glycol) (PEG) (1:2) was also prepared. The effects of PEG on the morphology and properties of the biocomposites were investigated. The dispersion/distribution of nanofibers in PLA was improved when the masterbatch was used and the composites were prepared in solution. Substantial effects on the rheological properties of solution-prepared PLA/CNF/PEG composites were observed compared to composites containing no PEG, whereas for melt-prepared composites no significant changes were detected. Increased crystalline content and crystallization temperature were observed for the composites prepared via the masterbatch and solvent casting. The storage modulus of PLA was increased by 42 and 553% at 25 and at 80 °C, respectively, for the solution-based PEG-compatibilized composite containing 2 wt% nanofibers. Also, a better light transmittance was measured for the PLA/CNF/PEG composites prepared in solution.     

Polylactide/poly(butylene adipate‐co‐terephthalate)/rare earth complexes as biodegradable light conversion agricultural films

Rare earth europium(III) complex with α‐thenoyltrifluoroacetone and triphenylphosphine oxide (Eu (TTA)₃(TPPO)₂, shortened as EuTT) was synthesized in this paper, then blended with polylactide (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) to prepare the biodegradable agricultural films. Through the optical performance, mechanical properties, and other research, the results showed that the rare earth complex could convert the sun's ultraviolet light to red light when doped polymer. Moreover, the relative intensity ratio of ⁵D₀/⁷F₂ to ⁵D₀/⁷F₁ of PLA/PBAT/EuTT film could reach 3.79, which implied that the film had strong fluorescence intensity and high color purity. The highest tensile strength of the film could reach 36.7/25.2 MPa, and the elongation at break was 462.8/483.0% in the machine and in the transverse direction when the added amount of Eu (TTA)₃(TPPO)₂ was 0.1 wt%. The tensile strength of the film was 33.3/20.1 MPa, and the elongation at break could reach 535.8/413.6% when the added amount of Eu (TTA)₃(TPPO)₂ was increased up to 0.3 wt%. Gel permeation chromatography showed that the Eu (TTA)₃(TPPO)₂ could cause depolymerization of polylactide, resulting in a decrease in the molecular weight of PLA. Furthermore, the crystallization ability of PLA was also improved. In this paper, the biodegradable films exhibited excellent ultraviolet light conversion ability and mechanical properties.     

Properties of Calcium Phosphate Scaffolds Produced by Freeze-Casting

The pore structure of three-dimensional scaffolds applied in tissue engineering may influence the mechanical properties and cellular activity. As the optimal pore size is dependent on the specifics of the biomaterial or tissue engineering application, the ability to alter the pore size over a wide range is necessary for several scaffolds in order to meets the requirements of the applications. The aim of this study is to develop methodologies to produce calcium phosphate scaffolds with acceptable pore size and defined pore-channel interconnectivity. The pore size of calcium phosphate scaffolds is established during the freeze-drying fabrication process. In this process, material suspension is simply frozen and then dried by freeze-drier, which able to produce material with unique porous architectures, where the porosity is almost a direct replica of the frozen solvent crystals. There are two different method of freeze-casting carried out in order to study the effect of freezing temperature by which in the first method; sample being soaked with liquid nitrogen (-196 °C) for about 10 minutes before been place inside a freezer (-40 °C). In the second method, the sample was directly placed inside a freezer for casting at temperature of -40 ̊C. The results show that the pore size of the scaffolds decreased as the freezing temperature was reduced. Taken together, these results demonstrate that the methodologies applied in this study can be used to produce a range of calcium phosphate scaffolds exhibiting better compressive strength, approximately 665-875 KPa for 54-64.3% of porosity with mean pore size from 102-113 μm. The methods developed in this study provide a basis for the investigation on the effects of different freezing temperature in freeze-casting process on the porosity, morphology, and compressive properties of the calcium phosphate scaffolds.     

Preparation and In Vitro Bioactivity Study of a Novel Hollow Mesoporous Bioactive Glass Nanofiber Scaffold

In this study, a novel three-dimensional hollow mesoporous bioactive glass nanofiber scaffold has been synthesized with a template-assisted sol-gel method using bacterial cellulose (BC) as a template and nonionic triblock copolymer (P123) as a pore-directing agent, ethyl orthosilicate (TEOS), calcium nitrate tetrahydrate (CN), and triethyl phosphate (TEP) as glass precursors. Scanning and transmission electron microscopies, X-ray diffraction, nitrogen adsorption-desorption, and nuclear magnetic resonance method were applied to characterize the morphology, crystal structure, and chemical structure of the mesoporous bioactive glass nanofiber scaffold. Furthermore, the in vitro bioactivity and biocompatibility were also explored. The obtained scaffold depicted nanofiber-like morphology and interconnected three-dimensional network structure that replicated the BC template. The scaffold showed a large specific surface area (230.0 cm² g⁻¹) and pore volume (0.2 m³ g⁻¹). More importantly, the scaffold exhibited excellent apatite-forming ability and cellular biocompatibility. We believe that the hollow mesoporous bioactive glass nanofiber scaffold has great potential application in bone tissue regeneration.     

The influence of matrix crystallinity,filler grain size and modification on properties of PLA/calcium carbonate composites

Thermal and mechanical properties of polylactide (PLA) composites with different grades of calcium carbonate, 40 nm and 90 nm nanoparticles, and also with submicron particles, unmodified and modified with calcium stearate or stearic acid, obtained by melt mixing, were compared. Films with amorphous and crystalline matrices were prepared and examined.T_g of PLA in the composites remained unaffected whereas its cold crystallization was enhanced by the fillers and predominantly depended on filler content. Filling decreased thermal stability of the materials but their 5% weight loss temperatures well exceeded 250 °C, evidencing stability in the temperature range of PLA processing. The amorphous nanocomposites with modified nanoparticles exhibited improved drawability and toughness without a significant decrease of tensile strength; nearly two-fold increase of the elongation at break and tensile toughness was achieved at 5 wt% content of the modified nanofiller. Lack of surface modification of the filler, larger grain size with an average of 0.9 μm, and matrix crystallinity had a detrimental effect on the drawability. However, the presence of nanofillers and crystallinity improved tensile modulus of the materials by up to 15% compared to neat amorphous PLA.     

Effects of dip coating parameters on the morphology and transport properties of cellulose acetate–ceramic composite membranes

This work presents the fabrication of cellulose acetate (CA)–ceramic composite membranes using dip coating technique. Ceramic supports used in this work were prepared from kaolin with an average pore size of 560 nm and total porosity of 33%. The dip coating parameters studied experimentally were the concentration of CA solution (varying from 2 wt% to 8 wt%) in acetone and dipping time (varying from 30 s to 150 s). The fabricated composite membranes were characterized using scanning electron microscope, gas permeation, pure water flux and ultrafiltration (UF) experiments using bovine serum albumin (BSA). It was observed that the membrane prepared with 2 wt% and 4 wt% CA were suitable for microfiltration applications and those with 6 wt% and 8 wt% were for ultrafiltration applications. Theoretical investigation was conducted to know the macroporous and mesoporous structure of the prepared membranes using Knudsen and viscous permeability analysis of air. A resistance in series model was applied to identify different resistances responsible for the flux decline. Phenomenological models were proposed to illustrate the dependency of hydraulic resistance of membrane on the structural parameters such as average pore size, effective porosity as well as dip coating parameters like dipping time and concentration of CA. It was found that, the growth rate of CA film on the ceramic support followed exponential growth law with respect to dipping time. The total hydraulic resistance of the membrane was evaluated to be inversely proportional to the ratio of pore sizes of top layer and ceramic support. The resistance due to the CA film was found to be depended to the order of 1.73 with respect to concentration of CA. An increase in the concentration of CA was found to be more effective than dipping time to reduce the membrane pore size.     

The formation of ultrafine polyamide 6 nanofiber membranes with needleless electrospinning for air filtration

Particulate matter (PM) is a major air pollutant, which has a significant impact on public health. Filtration of PM through filters is a common method to protect the environment. However, the effective removal of PM with conventional filters still remains a challenge because of its small sizes. Here, we reported the formation of ultrafine polyamide 6 (PA‐6) nanofiber membranes formed with needleless electrospinning, in which both relative humidity condition and electrode type were included in the discussion. The PA‐6S nanofibers formed by using spiral electrode as a spinneret at 60% RH had the diameter of 33 nm, while the PA‐6C nanofibers formed by using cylindrical electrode had the diameter of 120 nm. With the integration of fine diameter, small pore size, and high porosity, the resultant PA‐6S nanofiber membrane exhibits high filtration efficiency of 99.42% and low pressure drop of 85.5 Pa under a face velocity of 85 L/min. Besides, it took only 10 minutes to reduce the concentration of PM_2.5 from 999 to 34.1 μg/m³ when used to filter real PM particles.