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Renewable polymers with excellent stretchability and self-healing ability are interesting for a wide range of applications. A novel type of wholly biobased, self-healing, polyamide-based thermoplastic elastomer was synthesized using a fatty dimer acid and a fatty dimer amine, both containing multiple alkyl chains, through facile one-pot condensation polymerization under different polymerization times. The resulting elastomer shows superior stretchability (up to 2286%), high toughness, and excellent shape recovery after being stretched to different strains. This elastomer also displays high room-temperature autonomous self-healing efficiency after fracture and zero water uptake during water immersion. The highly entangled main chain, the multiple dangling chains, the abundant reversible physical bonds, the intermolecular diffusion, and the low ratio of amide to methylene group within the elastomer are responsible for these extraordinary properties. The polymerization time influences the properties of the elastomer. The use of the optimal self-healing thermoplastic elastomer in anticorrosion coating, piezoresistive sensing, and highly stretchable fibers is also demonstrated. The elastomer coating prevents stainless-steel products from corrosion in a salty environment due to its superhydrophobicity. The elastomer serves as a robust flexible substrate for creating self-healing piezoresistive sensors with excellent repeatability and self-healing efficiency. The elastomer fiber yarn can be stretched to 950% of its original length confirming its outstanding stretchability.

Forming polymeric core–sheath nanofibers is gaining prominence owing to their numerous potential applications, most notably in functional scenarios such as antiviral filtration, which is attracting significant attention due to the current COVID pandemic. This study has successfully designed and constructed a novel pressurized gyration vessel to fabricate core–sheath polymer nanofibers. Several water-soluble and water-insoluble polymer combinations are investigated. Both polyethylene oxide and polyvinyl alcohol were used as the core while both poly(lactic acid) (PLA) and poly(caprolactone) (PCL) were used as the sheath; PLA and PCL were used as core and sheath, in different instances; respectively. The fluid behavior of the core–sheath within the vessel was studied with and without applied pressure using computational fluid dynamics to simulate the core–sheath flow within the chamber. A high-speed camera was used to observe the behavior of jetted solutions at core–sheath openings, and the best scenario was achieved using 6000 rpm spinning speed with 0.2 MPa (twice atmospheric) applied pressure. The surface morphology of core–sheath fibers was studied using a scanning electron microscope, and focused ion beam milling assisted scanning electron microscopy was used to investigate the cross-sectional features of the produced fibers. Laser confocal scanning microscopy was also used to verify the core–sheath structure of the fibers, which were further characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. Thus, using a variety of polymer combinations, we show, both theoretically and experimentally, how core–sheath fibers evolve in a vessel that can serve as a scalable manufacturing pressurized gyration production process.

Suspensions containing 8 and 10 wt% polyacrylonitrile (PAN) and 1, 2, 3, 5, 7 and 10 wt% graphene oxide (GO) were prepared using a special mixing routine and fibres were generated from these mixtures by pressurised gyration. The combination of pressure and gyration speed was effective in controlling the fibre morphology and fibre diameter which ranged from 1 to 20 μm. Fibres were pyrolysed to remove the polymer and only the 10 wt% PAN fibres survived. The microstructure of the pre- and post-pyrolysis products were characterised by scanning electron microscopy, both with and without focussed ion beam etching, Fourier-transformed infrared and Raman spectroscopies. Pyrolysed fibre electrical conductivities were measured and only those containing 1 and 2 wt% GO were conductive.

The ability to generate core&ndash, sheath bicomponent polymer nanofibers in a single-step with scale-up possibilities is demonstrated using pressurised gyration manufacturing. This is the first time that nanofiber containing more than one polymer having a core&ndash, sheath configuration has been generated in this way. Water-soluble polymers polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) are used as the core and sheath layers, respectively. Core&ndash, sheath nanofibers with a diameter in the range of 331 to 998 nm were spun using 15 wt % PEO and 15 wt % PVP polymer solutions. The forming parameters, working pressure and rotating speed, had a significant influence on the size, size distribution and the surface morphology of the nanofibers generated. Overall, fibre size decreased with increasing working pressure and rotating speed. The fibre size was normally distributed in all cases, with 0.2 MPa working pressure in particular showing narrower distribution. The fibre size distributions for 0.1 and 0.3 MPa working pressure were broader and a mean fibre size of 331 nm was obtained in the latter case. The fibre size was evenly distributed and narrower for rotating speeds of 2000 and 4000 RPMs. The distribution was broader for rotating speed of 6000 RPM with a mean value obtained at 430 nm. Continuous, smooth and bead-free fibre morphologies were obtained in each case. The fibre cross-section analysis using a focused ion beam machine showed a solid core surrounded by a sheath layer. Our findings demonstrate that the pressurised gyration could be used to produce core&ndash, sheath polymer nanofibers reliably and cost-effectively with scale-up possibilities (~4 kg h&minus, 1).

Several new spinning methods have been developed recently to mass produce polymeric fibers. Pressure-coupled infusion gyration is one of them. Because the fiber diameter plays a pivotal role for the mechanical, electrical, and optical properties of the produced fiber mats, in this work, polyethylene oxide is used as a model polymer, and the processing parameters including polymer concentration, infusion (flow) rate, working pressure, and rotational speed are chosen as variables to control fiber diameters spanning the micro- to nanoscale. The experimental process is modeled using response surface methodology, both in linear and nonlinear fitting formats, to allow optimization of processing parameters. The successes of the fitted models are evaluated using adjusted R2 and Akaike information criterion. A systematic description of the experimental process could be obtained according to the model in this study. From the analysis of variance, it is concluded that the polymer concentration of the solution and the working pressure affected the fiber diameters more strongly than other parameters.

Highly stretchable and highly resilient polymer-clay nanocomposite hydrogels were synthesized by in situ polymerization of acrylamide in the presence of pristine montmorillonite (MMT) or chitosan-treated MMT nanoplatelets at an elevated temperature. Both nanocomposite hydrogels can be stretched to a strain of no less than 1290%. The treatment of clay with chitosan improves the tensile strength, elongation at break, and energy at break of the nanocomposite hydrogel by 237%, 102%, and 389%, respectively, due to the strong chitosan-MMT electrostatic interaction and the grafting of polyacrylamide onto chitosan chains. Both hydrogels display excellent resilience with low hysteresis; with a maximum tensile strain of 50%, ultralow hysteresis is found, while, with a maximum strain of 500%, both hydrogels fully recover their original state in just 1 min. The superb resilience of the nanocomposite hydrogels is attributed to the strong interactions within the hydrogels brought by chain branching, multiple hydrogen bonding, covalent bonding, and/or electrostatic force. The hydrogels can be fabricated into different shapes and forms, including microfibers spun using pressurized gyration, which may find a variety of potential applications in particular in healthcare.

Pressure-coupled infusion gyration (PCIG) is a novel promising technique for economical and effective mass production of nanofibres with desirable geometrical characteristics. The average diameter of spun fibres significantly influences the structural, mechanical and physical properties of the produced fibre mats. Having a comprehensive understanding of the significant effects of PCIG experimental variables on the spun fibres is beneficial. In this work, response surface methodology was used to explore the interaction effects and the optimal PCIG experimental variables for achieving the desired morphological characteristics of fibres. The effect of experimental variables, namely solution concentration, infusion (flow) rate, applied pressure and rotational speed, was studied on the average fibre diameter and standard deviations. A numerical model for the interactional influences of experimental variables was developed and optimized with a nonlinear interior point method that can be used as a framework for selecting the optimal conditions to obtain poly-ethylene oxide fibres with desired morphology (targeted average diameter and narrow standard deviation). The adequacy of the models was verified by a set of validation experiments. The results proved that the predicted optimal conditions were able to achieve the average diameter that matched the pre-set desired value with less than 10% of difference.

This work focuses on forming bead on string poly(caprolactone) (PCL) by using gyration under pressure. The fibre morphology of bead on string is an interesting feature that falls between bead-free fibres and droplets, and it could be effectively controlled by the rheological properties of spinning dopes and the major processing parameters of the pressurised gyration system which are working pressure and rotating speed. Bead products were not always spherical in shape and tended to be more elliptical, therefore both their width and length were measured. The average bead width and length produced spanned a range 145-660μm and 140-1060μm, respectively. The average distance between two adjacent beads (i.e. inter-bead distance) and the bead size (width and length) are shown to be a function of processing parameters and polymer concentration. An interesting morphology i.e. beads with short fibre was observed when using a high polymer concentration. Bead on string structure agglomeration was promoted by a low polymer concentration. Formation of droplets or agglomerated bead on string is promoted below 5wt% polymer concentration, and beads with short fibre were present in the microstructure beyond a polymer concentration of 20wt%.

A simple and effective process combining pressure and gyration has been developed and used to jet-out composite fibres containing graphene nanoplatelets. Thermoplastic polyurethane and phenolic resin polymers were used as matrices. Processing parameters such as rotation speed, pressure and polymer concentration had a marked influence on the composite fibre diameter. Focussed ion beam milling and etching verified the effective incorporation of the graphene nanoplatelets into the composite fibres. Morphological, rheological, physico-chemical and thermal properties of the composite fibres were evaluated to identify possible applications for them.

A novel fabrication of polymer composite fibers using polycaprolactone (PCL), montmorillonite nanoclay (MMT-Clay), and nano-hydroxyapatite-clay (HAP MMT-Clay) is reported for bone tissue engineering applications. Using a pressurized gyration (PG) setup, polycaprolactone (PCL) fibers incorporated with in situ mineralized HAP MMT-Clay and MMT-Clay were investigated. Using the novel fabrication method, we were able to successfully manufacture HAP-nanoclay-PCL fibers. Further, 3D scaffolds made using the prepared fibers were able to enhance bone growth, cell viability, and proliferation. The results demonstrated that the polymer fiber scaffolds are biocompatible, and the cells were able to thrive and differentiate on the fiber scaffolds. A significant increase in cell viability, osteogenic differentiation, ECM formation, and collagen formation was observed with PCL HAP MMT-Clay fibers scaffolds compared to the behaviors in PCL fibers. Further, the intracellular ALP levels increased with PCL HAP MMT-Clay fiber scaffold, indicating enhanced osteogenic differentiation of MSCs. This work shows a promising outlook for the future of manufacturable composite nanoclay polymer fibers incorporated as scaffolds for bone tissue engineering applications.

Co-axial electrospraying and electrospinning are versatile electrohydrodynamic (EHD) techniques that can be used to encapsulate a variety of materials in the form of polymeric particles and fibres via a one step process. The successful production of uniform encapsulated products in co-axial EHD (CEHD) processing depends on multiple parameters including solution concentration, applied voltage and needle capillary diameter. Although many studies have been conducted to investigate the effects of these parameters, there has been very limited research on how the axial displacement between the two needle tips affects the final products formed. Hence the purpose of this study was to adjust the positioning of the inner needle such that its tip extends beyond, is level with or resides inside that of the outer needle and to thus determine the most effective arrangement for controlling product size, uniformity and/or yield. Core–shell particles were prepared using two polymers, poly(lactic-co-glycolic)acid (PLGA) as the shell and polymethylsilsesquioxane (PMSQ) as the core and core–shell fibres using PMSQ as the shell and a volatile liquid, perfluorohexane (PFH) as the core. The products formed were analyzed by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After analysis, it was concluded that the most effective arrangement for generating both particles and fibres with the optimal combination of size, uniformity and yield was to have the inner needle 2 mm inside the outer needle. This allows for formation of a stable cone–jet and successful encapsulation of the inner liquid within the outer liquid, before the outer stable cone–jet forms. The corresponding collected product diameter and percentage of products in which material was successfully encapsulated were found to be 0.6 ± 0.1 μm and 85 ± 3% respectively for particles and 9 ± 1 μm and 92 ± 2% for fibres.

This paper reports for the very first time a facile and simple method, consisting of simultaneous centrifugal spinning and solution blowing, to mass produce ceramic fibres from preceramic polymers. Solutions of two different commercially available silicone resins and a mixture of a silicone resin and graphene were used, and a polymer (polyvynilpyrolidone) was added to aid the fibre generation process. The fibre diameter and the morphology of the spun and the pyrolysed fibres were shown to be influenced by rotating speed, working pressure and the polymer concentration. Non-porous fibres were obtained using a low volatility binary solvent system and, after pyrolysis at high temperature, dense SiOC ceramic fibre bundles were produced. This fabrication method based on pressurised gyration shows great promise in the mass production of ceramic fibre bundles.

Honeycomb-like 3D polymeric structures are useful to grow cells inside pores or in between nanofibres in cellular containment but their generation and morphology control involves different processing and forming procedures. In this work, using high speed camera footage, we show the dramatic effect of relative humidity (RH) has on the deposition of honeycomb structures using a hydrophilic water-soluble polymer. Approximately 35 mm diameter deposits were generated under several conditions of humidity while all other process parameters were kept constant. The morphology of the structures, i.e., their porosity and nanofibres, were studied and are related to the jet behaviour characteristics to explain why 3D honeycomb structures are obtained under selected optimum humidity conditions. 3D honeycomb structures were obtained only at an optimised 73% RH.

The ability to generate nanofibres useful for biomedical applications at bench and at a larger scale is a significant manufacturing challenge. In this study, we demonstrate that it is possible to generate nanofibre meshes of poly(N-vinylpyrrolidone) (PVP) using pressurised gyration. The effects of altering polymer molecular weight and concentration on fibre morphology and size have been investigated, with identification of minimum values for both parameters for successful fibre fabrication. In addition, we note that changing the molecular weight may result in changes to the Fourier Transform Infrared (FTIR) spectra associated with changes in fibre intramolecular bond strength and arrangement. Overall the study has demonstrated that pressure gyration represents a feasible means of producing nanofibres (470–970 nm) on a scale commensurate with commercial viability and have identified key parameters that influence mesh structure.

The fabrication of polymeric micro/nanofibers is gaining attention due to their use in an array of applications including tissue engineering scaffolds, nanosensors, and fiber-reinforced composites. Despite their versatile nature, polymeric fibers are widely underutilized due to the lack of reliable, large-scale production techniques. Upon the discovery of centrifugal spinning and, recently, pressurized gyration techniques, new research directions have emerged. Here, we report a comprehensive study detailing the optimal conditions to significantly improve the morphology, homogeneity, and yield of fibers of varying diameters. A series of polymeric fibers was created using a 21 wt.% solution of polyethylene oxide in distilled water and the fluid behavior was monitored inside a transparent reservoir using a high-speed camera. Fabrication of the fibers took less than 1 s. Using centrifugal spinning, we studied the formation of the fibers at three different rotational speeds, and for pressurized gyration, one rotational speed was studied with three different nitrogen gas pressures. Using the pressurized gyration technique at a gas pressure of 0.3 MPa, there was significant improvement in the production yield of the fibers. We found a strong correlation between the variation of pressure and the rate of the solution leaving the reservoir with the improved morphology of the fibers. The use of reduced power techniques, like centrifugal spinning and pressured gyration, to yield high-quality nonwoven nanofibers and microfibers in large quantities is important due to their use in rapidly expanding markets. (C) 2019 Author(s).

Core-sheath fibres of two polymers were generated using a novel set-up where rotating speed and pressure can be varied at ambient temperature. The specially designed spinneret consists of inner and outer chambers which can accommodate two polymers and other additives. The new methodology was demonstrated using poly(ethylene oxide) and poly(methylmethacrylate) (PMMA). Dyes were used as colouring agents for the polymers to verify core-sheath formation, and optical, scanning and fluorescent microscopy of the formed fibres confirmed the presence of a core-sheath combination. The core diameter obtained was in the range 5–10 μm and the sheath fibre diameter was 20–30 μm. The core/sheath diameter can be pre-set by selecting the forming conditions. To show the flexibility of the new method, nanoparticle containing PMMA fibres were also produced using the new device and incorporation of the nanoparticles in the sheath and core of the fibres was verified by electron microscopy and energy-dispersive X-ray spectroscopy analysis. A high yield of fibre was obtained and with more severe forming conditions the size of core-sheath fibres generated can be reduced to the nanoscale. Thus, the new process has a real capability of manufacturing a wide variety of novel functional materials and structures in a single scalable set-up. Keywords: Core-sheath, Polymer, Gyration, Pressure, Fibre, Device

This work investigates the generation of monodisperse microbubbles using a microfluidic setup combined with electrohydrodynamic processing. A basic T-junction microfluidic device was modified by applying an electrical potential difference across the outlet channel. A model glycerol air system was selected for the experiments. In order to investigate the influence of the electric field strength on bubble formation, the applied voltage was increased systematically up to 21 kV. The effect of solution viscosity and electrical conductivity was also investigated. It was found that with increasing electrical potential difference, the size of the microbubbles reduced to ~25% of the capillary diameter whilst their size distribution remained narrow (polydispersity index ~1%). A critical value of 12 kV was found above which no further significant reduction in the size of the microbubbles was observed. The findings suggest that the size of the bubbles formed in the T-junction (i.e. in the absence of the electric field) is strongly influenced by the viscosity of the solution. The eventual size of bubbles produced by the composite device, however, was only weakly dependent upon viscosity. Further experiments, in which the solution electrical conductivity was varied by the addition of a salt indicated that this had a much stronger influence upon bubble size.

This paper presents the development of the novel deposition of biodegradable polycaprolactone (PCL) polymer patterns on a metallic substrate using a jet spraying technique, template-assisted electrohydrodynamic atomization (TAEA), at ambient temperature. The structure of patterns was controlled by systematically varying the polymer concentration (2-15 wt.%) and the flow rate (1-25 μl min(-1)). Polymer deposition was carried out in the stable cone-jet mode to precisely control the surface structure and morphology. The patterns were studied by optical microscopy, scanning electron microscopy and profilometry, and a high degree of control over the pattern geometry and thickness was achieved by varying the spraying time. The hardness and the effective elastic modulus of the polymer patterns were estimated using nanoindentation. The effect of load, loading rate and the holding time on the hardness and effective elastic modulus was derived. Optimal results were obtained with 5 wt.% PCL in DMAC solution sprayed within the stable cone-jet mode operating window at a flow rate of 15 μl min(-1) for 300 s at 11.1 kV with a working distance of 60mm. Hexagonal patterns were well-defined and repeatable with thickness of ~34 μm. The hardness is 1.6 MPa at a loading rate of 0.1 μN/s and nearly halved when the load rate was increased to 1 μN/s. The effective elastic modulus of ~12 MPa is obtained for a load rate of 0.1 μN/s.

Conventional fabrication techniques and structures employed in the design of silk fibroin (SF) based porous materials provide only limited control over pore size and require several processing stages. In this study, it is shown that, by utilizing electrohydrodynamic bubbling, not only can new hollow spherical structures of SF be formed in a single step by means of bubbles, but the resulting bubbles can serve as pore generators when dehydrated. The bubble characteristics can be controlled through simple adjustments to the processing parameters. Bubbles with diameters in the range of 240-1000 μm were fabricated in controlled fashion. FT-IR characterization confirmed that the rate of air infused during processing enhanced β-sheet packing in SF at higher flow rates. Dynamic mechanical analysis also demonstrated a correlation between air flow rate and film tensile strength. Results indicate that electrohydrodynamically generated SF and their composite bubbles can be employed as new tools to generate porous structures in a controlled manner with a range of potential applications in biocoatings and tissue engineering scaffolds.

Ultra fine short fibres have a variety of applications. Short aligned fibres or a mixture of short and long fibres can reinforce brittle materials, alter the appearance, texture and durability of synthetic fibres, and adjust the strength, toughness and stiffness of a composite material. Among electrospun products, short fibres are usually produced by secondary processing of continuous as-spun fibres. However, this is not entirely straightforward or cost-effective due to the efficiency of the secondary process and the relatively low tensile strength of the electrospun ultrafine fibres. Besides, sub-micrometre size fibres with an average aspect ratio (AR) 3000 under the same spinning conditions.

A method for generating poly(lactic-co-glycolic acid) and polycaprolactone biodegradable particles of different size and shape using a jet generated in an electric field is elucidated. These particles are suitable for use as drug carriers and the method can be developed into a mass production route. The effect of different parameters such as applied voltage, collecting distance, flow rate and polymer concentration on inducing size and shape differences in these particles was studied. It was found that the flow rate, polymer concentration and collecting distance have a significant impact on the size of the generated particles and by changing the collecting distance a systematic reduction in the particle size by at least an order of magnitude (10microm-100nm) can be achieved. By using a high polymer concentration (30 wt. %) the shape and surface morphology of these particles can also be controlled from spherical to fibrous, and smooth to irregular, respectively, which presently is an interesting strategy and concept in drug delivery. This method is very useful as a one-step generator of different sizes of drug carriers with morphological variations.

Porous polymeric near-spherical capsules, ~ 3.6 mm in diameter, were prepared using an electrodydrodynamic process. These capsules were pyrolysed to porous ceramics, ~ 3 mm in diameter. The ceramic capsules had interconnected pores of ~ 1.3 μm in size, and large cells with a mean size of 28 μm. The larger pores resemble the cells in a typical ceramic foam and were evenly distributed throughout the structure. A large proportion of the ceramic capsules contained 65-70% porosity, and their compressive strength was 0.2-0.4 MPa. © 2008 Elsevier B.V. All rights reserved.

Encapsulation of materials in fibres with a well-controlled size distribution is an important application of the electrospinning technique. This study investigates the effect of key parameters of the coaxial electrospinning process including flow rate, applied voltage and polymer concentration on the efficient encapsulation and size distribution of perfluorohexane (PFH) in polymethylsilsesquioxane (PMSQ) microfibres. Perfluorohexane can be exchanged for a drug via a simple diffusion-controlled process. By altering the polymer concentration and processing parameters, PMSQ microfibres with different diameters, PFH core size and core-to-core distance were obtained. It was found that PFH-encapsulated fibres with a diameter between 8 and 15 μm can be prepared when the PMSQ concentration is kept between 55–70 wt%. The PFH regions (cores) encapsulated in the fibre are uniformly distributed and of size 5–14 μm. The core-to-core distance significantly increased from 4 μm to 22 μm when the applied voltage was increased from 8 kV to 11 kV. These results indicate a potential strategy for controlling fibre diameter, core size and core-to-core distance by using coaxial electrospinning as the forming procedure and thus this work will help to advance biomedical engineering applications, for example, drug delivery, scaffolding for tissue engineering and wound dressing.

A recently developed electrohydrodynamic printing method is described that can be used to create ordered structures and complex patterns using coarse processing needles and two polymeric materials. The results highlight the method's potential for direct 3D writing of biomedical polymers and composites for a variety of biomedical applications.

A novel nanocomposite polymer with a polycarbonate soft segment (PCU) and polyhedral oligomeric silsesquioxanes (POSS) nanoparticle (POSS-PCU) has been selected for a synthetic heart valve due to its superior biocompatibility and in vivo biostability. However, the development of synthetic heart valves from polymeric materials requires an understanding of the basic mechanical and surface properties of the polymer. In this study, the mechanical properties of POSS-PCU, including tensile strength, tear strength and hardness, were tested and compared to control (PCU). The surface property was analyzed using contact angle measurement and the resistance to platelet adhesion was also investigated. POSS-PCU (hardness 84+/-0.8 Shore A) demonstrated significantly higher tensile strength 53.6+/-3.4 and 55.9+/-3.9Nmm(-2) at 25 and 37 degrees C, respectively) than PCU (33.8+/-2.1 and 28.8+/-3.4Nmm(-2) at 25 and 37 degrees C, respectively). Tensile strength and elongation at break of POSS-PCU was significantly higher than PCU at both 25 and 37 degrees C (P0.001). POSS-PCU showed a relatively low Young's modulus (25.9+/-1.9 and 26.2+/-2.0Nmm(-2)) which was significantly greater in comparison with control PCU (9.1+/-0.9 and 8.4+/-0.5Nmm(-2)) at 25 and 37 degrees C, respectively, with 100mum thickness. There was no significant difference (P0.05) in tear strength between POSS-PCU and PCU at 25 degrees C. However, tear strength increased significantly (P0.001) (at 37 degrees C) as the thickness increased from 100microm (51.0+/-3.3Nmm(-1)) to 200microm (63+/-1.5Nmm(-1)). The surface of POSS-PCU was significantly less hydrophilic than that of PCU.

The present study is focused on the processing of columnar lead zirconate titanate (PZT) structures on Ti/Pt-coated silicon substrates using electrohydrodynamic deposition. It was found that the as-deposited PZT structure is highly dependent on the concentration of the sprayed precursor, which is believed to be the characteristic of electrohydrodynamic deposition. 0.01, 0.03, 0.06, 0.12, 0.3 and 0.6 M PZT sols were used to prepare as-deposited structures. Columnar PZT structures, which are important for the processing of 1-3 composites, were obtained with the 0.6 M sol. As-deposited and heat-treated columnar PZT structures were investigated using scanning electron microscopy and X-ray diffraction. The development of the PZT columns was studied by observing the cross-section of the structures deposited over different time sprays, revealing a three-stage growth process for these structures. The affect of substrate temperature on the columnar structure was also analysed by studying the density of the columns. Finally, a 1-3 composite was produced by infiltrating photoresists into the columnar PZT structures and the relative permittivity and dissipation factor of such composite were measured as 105 and 0.021. Modelling the structures as a PZT and a polymer capacitor connected in parallel in the PZT/polymer composite suggests that the relative permittivity of PZT columnar material is approximately 154.

In this work, electrohydrodynamic atomization was used to spray deposit lead zirconate titanate (PZT) thick films using a PZT composite sol–gel slurry. During atomization splats and clusters were generated from jet break-up. The influence of atomization–substrate distance on the characteristics of splats and clusters was analysed. At a greater distance dried clusters were predominant, which led to the formation of porous films; conversely, at a smaller distance wet splats dominated, which generated dense films. A distance of 10 mm was found to be the optimum deposition distance for this slurry to produce dense films. 28 μm thick PZT crack-free films were produced by depositing 60 layers of slurry using this technique. The resulting films had a homogenous microstructure and exhibited a relative permittivity of ∼ 220 and d33, f of ∼71 pC N−1.

In this paper, we investigate in detail the electrohydrodynamic spraying of a nonbiodegradable nanocomposite polyhedral oligomeric silsesquioxane polymer developed in our laboratories and currently being explored for coating metallic stent materials. Different concentrations of the polymer have been dissolved to prepare, characterise, and electrohydrodynamically deposit the polymer on stainless steel. From the experiments, the solution containing 15 wt% polymer was selected for further investigation. The variation of film/ coating thickness as a function of spraying time was studied and the structural features of the film were assessed using microscopy. Films were also tensile tested. This study has identified a process and conditions which can be used in our stent coating research.

The gradation of porosity in a biomaterial can be very useful for a variety of medical engineering applications such as filtration, bone replacement and implant development. However, the preparation of such structures is not a technologically trivial task and replication methods do not offer an easy solution. In this work, we elucidate the preparation of structures having a graded porosity by electrohydrodynamic spraying, using zirconia (ZrO 2 ), which is widely used in biomedical and other applications. The processes are generic and can be achieved using other bioactive ceramics with similar particle characteristics. The pores on the sprayed surface, the innermost surface and lengthwise cross sections have been analysed in addition to the change in depth of penetration as a function of spraying time. Control of porosity, pore size and depth of penetration has been obtained by varying parameters such as the spraying time, sintering temperature and the sacrificial template. It has been possible to obtain structures with interconnected pore networks of pore size greater than 100 μm as well as scattered pores smaller than 10 μm in size.

Porous scaffolds are considered a key strategy in the concept of bone tissue engineering. Hydroxyapatite, which is a bioceramic has been used as a popular scaffold material due to its bioactive and osteoconductive properties. A combination of slurry-dipping and electrospraying has been used as a new foam fabrication method to produce porous and interconnected foam structures. The combined method has shown to overcome the shortcomings of the individual methods and it has produced open pores in the desired range of 100-350 microm. The porosity which was determined by calculation and microtomography was between 84% and 88%. Reduced cracks and thicker struts were observed in the microstructure, pointing to improved mechanical properties.

Polymeric nanofibres with smooth, rough and porous surfaces were prepared by pressurised gyration, which is a novel method for producing nanofibres, utilising the combination of centrifugal spinning and solution blowing. A series of fibres were prepared by using polyacrylonitrile (Pan), poly(methyl methacrylate) (PMMA) and 50:50 Pan–PMMA polymer solutions without pressure and with 0·2 MPa working pressure. The surface morphology of the nanofibres was analysed by scanning electron microscopy, and their thermal properties were studied by thermogravimetry and hot-stage microscopy. Nanofibres with a smooth surface were generated at 0·2 MPa working pressure, and those with a rough surface were generated without any working pressure. Porous Pan nanofibres were prepared by using PMMA as a sacrificial polymer. The 50:50 Pan–PMMA blend fibres were subjected to heat treatment to obtain porous fibres. The less thermally stable PMMA decomposes when heated, generating pores on the surface of the Pan fibres. The porous nanofibres have a higher surface area-to-volume ratio compared to smooth fibres, and these fibres could be useful in a variety of applications, such as tissue engineering, filtering and purification.

Electrohydrodynamic atomisation (EHDA) spraying of a hydroxyapatite (HA) suspension consisting of nano-particles (nHA) has been used to produce a HA coating comprising of nanostructured surface topography. In EHDA the suspension is jetted from a needle under an electric field. Obtaining the stable cone-jet mode of EHDA is critical to improve the quality and optimise the morphology of HA coatings, therefore a systematic investigation of the effects of several key processing parameters, such as suspension flow rate, applied voltage and distance between the needle and substrate, and needle size was carried out in this work. The HA coatings processed under different spraying parameters were compared and then scored according to uniformity and microstructural integrity. It was found that all of these parameters had a very significant influence on the morphology of nHA coating prepared. Under an optimised processing condition, where a needle orifice diameter of 300 microm, kept at a distance of 20 mm from the substrate, a flow rate of 20 microL/min, and the applied voltage kept within 4.3 kV and 5.2 kV, a uniform nHA coating was obtained. This is a crucial step forward in obtaining advanced nano-hydroxyapatite coatings of high quality for biomedical applications by using EHDA spraying.

An electrically charged jet of polymer solution is used to encapsulate silver particles contained in a suspension using co-axial dual needle jetting. The polymer solution flowing through the outer needle undergoes electrospinning while the silver suspension is simultaneously subjected to electrohydrodynamic atomization in the inner needle. The pattern and uniformity of encapsulation in the core is mainly determined by the speed of jetting in the inner needle. We demonstrate that this process could be utilized as a commercial freeform fabrication method of encapsulating metal particles within a polymeric sheath and this development could have numerous advanced technological applications.

Bioceramic fibres, scaffolds and mats are important structures in biomedical applications. Electrohydrodynamic routes are relatively new for processing advanced materials and in this paper we use electrospinning to prepare zirconia fibres diameter down to 200nm and hydroxyapatite (HA) fibres down to 1$m. Zirconia-polymer and nHA-polymer composite scaffolds structures (mats) with 400-1000 $m windows were also prepared.

Ptosis describes a low position of the upper eyelid. When this condition is due to poor function of the levator palpebrae superioris muscle, responsible for raising the lid, "brow-suspension" ptosis correction is usually performed, which involves internally attaching the malpositioned eyelid to the forehead musculature using brow-suspension materials. In service, such materials are exposed to both rapid tensile loading and unloading sequences during blinking, and a more sustained tensile strain during extended periods of closure. In this study, various mechanical tests were conducted to characterise and compare some of commonly-used synthetic brow-suspension materials (Prolene(®), Supramid Extra(®) II, Silicone rods (Visitec(®) Seiff frontalis suspension set) and Mersilene(®) mesh) for their time-dependent response. At a given constant tensile strain or load, all of the brow-suspension materials exhibited stress-relaxation or creep, with Prolene(®) having a statistically different relaxation or creep ratio as compared with those of others. Uniaxial tensile cyclic tests through preconditioning and fatigue tests demonstrated drastically different time-dependent response amongst the various materials. Although the tests generated hysteresis force-strain loops for all materials, the mechanical properties such as the number of cycles required to reach the steady-state, the reduction in the peak force, and the cyclic energy dissipation varied considerably. To reach the steady-state, Prolene(®) and the silicone rod required the greatest and the least number of cycles, respectively. Furthermore, the fatigue tests at physiologically relevant conditions (15% strain controlled at 6.5 Hz) demonstrated that the reduction in the peak force during 100,000 cycles ranged from 15% to 58%, with Prolene(®) and the silicone rod exhibiting the greatest and the least value, respectively. Many factors need to be considered to select the most suitable brow-suspension material for ptosis correction. These novel data on the mechanical time-dependent performance could therefore help to guide clinicians in their decision-making process for optimal surgical outcome.

Two monodisperse nano-suspensions, which contain 20-nm and 120-nm silica particles (30 wt.%), were electrohydrodynamically jetted simultaneously in coaxial needles. Irrespective of which suspension was in the inner or outer needle, the cone-jet mode was obtained and the droplets resulting from jet break-up were used to direct write ∼80 µm lines. Turbulent flow in the cones ensured that the suspensions were subjected to intense mixing and therefore the microstructure contains a random mixture of the two types of nanoparticles of unchanged morphology.

The behaviour of three high viscosity (4875, 12 125 and 58 560 mPa s), dielectric liquids was investigated at flow rates of 10 −10 , 10 −12 and 10 −14 m 3 s −1 and the applied voltage range 6–15 kV. In these experiments, due to the low electrical conductivity of the liquids (10 −13 S m −1 ) and therefore the ensuing high electrical relaxation time, classical electrohydrodynamic atomization conditions are not satisfied. Only dripping and unstable jetting were observed at 4875 mPa s. A transition from no jetting to stable microthreading was observed for the 12 125 and 58 560 mPa s samples. The relics accompanying the transition were found to change from discrete droplets to a continuous filament. Stable microthreading, which generates uniform filaments, was obtained for the 12 125 mPa s sample at flow rates 10 −10 and 10 −12 m 3 s −1 and in the case of the 58 560 mPa s sample at all the flow rates investigated. The high viscosity assisted stable microthreading with the filament diameter decreasing with increasing applied voltage and more dramatically decreasing with reducing flow rate.

A zirconia suspension containing 5–10 nm size zirconia particles was modified by adding different amounts of polymer solution to enable electrospinning of zirconia fibers from a range of compositions. The electrospun fibers were heat treated at 600° and 1200°C, and analysis of size distribution reveals that zirconia fibers down to about 200 nm in diameter can be prepared in this way, in contrast to other spinning processes, which are able to produce zirconia fibers having diameters ≥3000 nm.

A novel process, namely replication combined with electrospraying, was used to fabricate bioceramic (zirconia) scaffolds with the intention of improving the mechanical function of hard tissue engineering scaffolds. A comparative study was carried out on the microstructure and mechanical properties of zirconia foams prepared by this new process or by the conventional slurry-dip coating method. After forming the green bodies, they were subjected to a sintering heat treatment at 1450°C for 5 h. It was found that the number and size of microcracks and micropores can be reduced in foams prepared by electrospraying in comparison with those prepared by slurry-dip coating. The values of compressive mechanical strength and Young's modulus were found to be collectively higher for scaffolds prepared by electrospraying than for those prepared by slurry-dip coating. Moreover, the mechanical reliability was improved in foams produced by the electrospraying technique. The improvement is attributable to the reduction in the population and size of microcracks and micropores.

In this work, maize starch was used to demonstrate a novel method which enables the preparation of starch films and coatings with good thickness control. 5% starch in de-ionized water (w/v) was gelatinized at 120 °C for 30 min, subsequently small quantities of dispersant and ethanol were added and subjected to ultrasonic disruption to make a stable modified starch solution. Electrohydrodynamic behavior of this solution was studied and optimum conditions for film preparation were determined. The solution was then electrosprayed in the cone-jet mode and films were collected on a rotating plate. Film thickness was investigated by electron microscopy. Films of varying thickness were prepared by varying the electrospraying time and their characteristics are compared with solvent-cast films.

In this work we demonstrate a novel method of preparing composite ceramic microstructures, using alumina–zirconia as an example. Suspensions of these two ceramics, containing a similar solids content, were simultaneously subjected to electrohydrodynamic atomization (EHDA) in the stable cone-jet mode and the resulting relics were analyzed by microscopical techniques before and after partial sintering at 1200°C. We show that the new method, coaxial EHDA (CEHDA), is capable of forming different annular microstructures, which are mainly controlled by the speed of the jetting.

The deposition of a propanol-based lead zirconate titanate (PZT) sol using electrohydrodynamic atomization (EHDA) in the stable cone-jet mode was investigated. The droplets generated were deposited onto a copper substrate as a film, which was investigated using X-ray diffraction and scanning electron microscopy. The PZT film was shown to contain uniform nano-particles of PZT, which maintained their shape on sintering (650 degrees C, 1 hour) while forming the perovskite phase of PZT.

A general equation applicable to a sphere, an infinite plate, and an infinite cylinder is used to calculate the transient diffusion of degradation product in a ceramic molding during pyrolysis. The solution includes the concentration-dependent diffusion coefficient for diffusion of monomer in its parent polymer which forms the continuous phase in the ceramic in the as-molded state. In the early stages of pyrolysis, before continuous porosity has developed, the model searches for the critical heating rate above which defects are produced. Reasonable agreement is obtained with experimentally measured critical heating rates for 3-mm-thick plates.

Electrospraying of nano-sized hydroxyapatite (HA) has been used as a technique to modify the surface of alumina in order to achieve the goal of improving bone integration. A porous HA coating on alumina was produced by heat treating electrsprayed HA. Preliminary in vitro studies shown that this porous HA coating provided a favourable surface for attachment and growth of HOB cells. The results indicate that electrospraying is a very promising technique to create thin HA coatings on a range of biomedical implants to improve interfacial bonding with the host tissue.

Different amounts (0.5-10.0 wt%) of an oligomeric dispersant were added to a ceramic ink containing 30 vol% of zirconia in butyl acetate, The sediment packing densities of the resulting suspensions were measured. The viscosities of the suspensions were determined using a syringe that was adapted as a capillary viscometer suitable for the measurement of the low viscosities encountered (up to 400 mPa . s). The highest sediment-packing density coincided with the lowest viscosity and occurred when 1-2 wt% of dispersant, based on the ceramic, was added. Investigation of the supernatant of the suspensions by thermogravimetric analysis indicated that this amount corresponded to the highest level of adsorption of the dispersant on the ceramic. The sediment from this suspension yielded a high density on subsequent sintering.

This paper describes the preparation of ceramic inks for forming ceramic components by multilayer printing using a continuous-ink-jet printer. The selection of appropriate binders and dispersants combined with high shear and ultrasonic mixing has enabled zirconia-containing inks to be printed successfully to produce 2.5 mm thick bars. Printing trials show that the method of dispersion of the ceramic powder in the ink is decisive for accurate ink droplet positioning. The quality of the vertical walls and the top surface of the bars are related closely to the rate of drying of each printed layer. Inks with higher ceramic volume loadings (up to 10%) were also studied and produced useful information for further investigations.

A family of silicone oils, of similar density, surface tension, relative permittivity and electrical conductivity but having viscosities in the range 970– 58200 mPa s were used to elucidate the role of very high viscosity on the electrically driven flow of liquids. The electrical conductivities of the oils are very low (∼10 −9 mS m −1 ) and in effect the behaviour of these dielectric liquids is indicative of the viscosities and electrical conductivities encountered in the processing of concentrated suspensions containing inorganic powders. We show that these oils do not undergo electrostatic atomization in the applied voltage-flow rate regime we have investigated. Nevertheless, electrically forced stable jets are produced from some of the oils and in such instances the jet diameter, size of relics and droplets obtained have been estimated. We show that in the range 103– 10 4 mPa s , a stable ball cone jet prevails, however at >10 4 mPa s the liquids produce micro-threads.

This paper describes the methodology for simulating a reprographic ink with a ceramic ink based on a commercially available zirconia powder for direct ceramic ink-jet printing. Of over-riding importance was matching viscosity and this was tested systematically by using a mineral oil–hexane binary system. Of secondary importance was adjustment of the pressure defect behind the nozzle to compensate for small differences in surface tension. The inks tested in the wide array print-head were based on low electrical conductivity liquids to avoid damage to the electroding system. The organic binder for the zirconia ink was paraffin wax and the dispersant was a hydroxystearic acid based polyester.

Polymeric fibers are prepared by using electric field driven fiber production technology-electrospinning and pressure driven fiber production technology-pressurized gyration. Fibers of four different polymers: polyvinylidene fluoride (PVDF), poly(methyl methacrylate (PMMA), poly(N-isopropylacrylamide), and polyvinylpyridine (PVP), are spun by both techniques and differences are analyzed for their suitability as drug carriers. The diameters of electrospun fibers are larger in some cases (PVDF and PMMA), producing fibers with lower surface area. Pressurized gyration allows for a higher rate of fiber production. Additionally, drug-loaded PVP fibers are prepared by using two poorly water-soluble drugs (Amphotericin B and Itraconazole). In vitro dissolution studies show differences in release rate between the two types of fibers. Drug-loaded gyrospun fibers release the drugs faster within 15 min compared to the drug-loaded electrospun fibers. The findings suggest pressurized gyration is a promising and scalable approach to rapid fiber production for drug delivery when compared to electrospinning.

Ceramic ink droplets have been deposited on two fundamentally different types of substrate and the evolution of contact angle, width of the ink–substrate interface and droplet height was measured as a function of time from digital images of the droplet captured on video. On substrate type I, with a lower surface free energy than the surface tension of the ceramic ink, after reaching stability in a few seconds, the contact angle decreased and the width of the ink–substrate interface remained stationary. Subsequently, the contact angle stayed constant and thereafter reduced again, while the width of the ink–substrate interface decreased and remained constant thereafter. On substrate type II, with a higher surface free energy than the surface tension of the ceramic ink, stability was achieved instantaneously and the contact angle decreased rapidly, while the width of the ink–substrate interface increased initially but thereafter remained constant. The corresponding variation of droplet height due to spreading and evaporation, and volume shrinkage rate were also found to be much faster on the type–II substrate.