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Vitamin D3, vitamin K2, and Mg (10%, 1.25%, and 5%, w/w, respectively)-loaded PLA (12%, w/v) (TCP (5%, w/v))/PCL (12%, w/v) 1:1 (v/v) composite nanofibers (DKMF) were produced by electrospinning method (ES) and their osteoinductive effects were investigated in cell culture test. Neither pure nanofibers nor DKMF caused a significant cytotoxic effect in fibroblasts. The induction of the stem cell differentiation into osteogenic cells was observed in the cell culture with both DKMF and pure nanofibers, separately. Vitamin D3, vitamin K2, and magnesium demonstrated to support the osteogenic differentiation of mesenchymal stem cells by expressing Runx2, BMP2, and osteopontin and suppressing PPAR-γ and Sox9. Therefore, the Wnt/β-catenin signaling pathway was activated by DKMF. DKMF promoted large axonal sprouting and needle-like elongation of osteoblast cells and enhanced cellular functions such as migration, infiltration, proliferation, and differentiation after seven days of incubation using confocal laser scanning microscopy. The results showed that DKMF demonstrated sustained drug release for 144 h, tougher and stronger structure, higher tensile strength, increased water up-take capacity, decreased degradation ratio, and slightly lower Tm and Tg values compared to pure nanofibers. Consequently, DKMF is a promising treatment approach in bone tissue engineering due to its osteoinductive effects.

When sessile nanofluid droplets evaporate, solid nanoparticles can be organized in a wide variety of patterns on the substrate. The composition of the nanofluid, internal flow type of droplet and the rate of drying affect drop geometry, and the final pattern. Using poly(lactic-co-glycolic acid)-block-poly(ethylene glycol)(PLGA-b-PEG) as the example, we produced micro-stripe patterning from nanoparticles by drying of sessile fluid droplets. We investigated the nanoparticle properties and flow dynamics to clarify their effects on the patterning. Nanoparticles were prepared by hydrodynamic flow focusing using a T-junction microfluidic device with high production efficiency and the ability to generate an extremely narrow size distribution. PLGA-b-PEG was prepared as oil phase in acetonitrile and water/oil flow rate was changed from 1 to 3 at constant oil phase flow rate (50 μL/min). Then, nanofluid was collected on the surface as sessile droplets within acetonitrile/water binary dispersed phase. Depending on size, charge and size-distribution, the nanoparticles deposited on the surface exhibited various patterns. Dynamic Light and X-ray Scattering measurements showed that, approximately 100 nm particles with relatively low PDI (0.04) were produced for the first time in surfactant free conditions in a microfluidic device and they generated self-assembled ordered patterns, which are regulated by the type of internal flow in the sessile nanofluid droplet during sequential evaporation of acetonitrile and water.

A one step approach to prepare hybrid nanoparticle embedded polymer fibres using pressurised gyration is presented. Two types of novel antimicrobial nanoparticles and poly(methylmethacrylate) polymer were used in this work. X-ray diffraction analysis of the nanoparticles revealed Ag, Cu and W are the main elements present in them. The concentration of the polymer solution and the nanoparticle concentration had a significant influence on the fibre diameter, pore size and morphology. Fibres with a diameter in the range of 6-20μm were spun using 20wt% polymer solutions containing 0.1, 0.25 and 0.5 wt% nanoparticles under 0.3MPa working pressure and a rotational speed of 36,000rpm. Continuous, bead-free fibre morphologies were obtained for each case. The pore size in the fibres varied between 36 and 300nm. Successful incorporation of the nanoparticles in polymer fibres was confirmed by energy dispersive x-ray analysis. The fibres were also gyrospun on to metallic discs to prepare filters which were tested for their antibacterial activity on a suspension of Pseudomonas aeruginosa. Nanoparticle loaded fibres showed higher antibacterial efficacy than pure poly(methylmethacrylate) fibres.

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.

Progesterone-loaded poly(lactic) acid fibrous polymeric patches were produced using electrospinning and pressurized gyration for intra-vaginal application to prevent preterm birth. The patches were intravaginally inserted into rats in the final week of their pregnancy, equivalent to the third trimester of human pregnancy. Maintenance tocolysis with progesterone-loaded patches was elucidated by recording the contractile response of uterine smooth muscle to noradrenaline in pregnant rats. Both progesterone-loaded patches indicated similar results from release and thermal studies, however, patches obtained by electrospinning had smaller average diameters and more uniform dispersion compared to pressurized gyration. Patches obtained by pressurized gyration had better results in production yield and tensile strength than electrospinning; thereby pressurized gyration is better suited for scaled-up production. The patches did not affect cell attachment, viability, and proliferation on Vero cells negatively. Consequently, progesterone-loaded patches are a novel and successful treatment strategy for preventing preterm birth.

Bacterial cellulose (BC) is cellulose produced by a few limited species of bacteria in given conditions. BC has many remarkable properties such as its attractive mechanical properties, water uptake ability and biocompatibility which makes it a very desirable material to be used for wound healing. Inherently due to these important properties, the material is very resistant to easy processing and thus difficult to produce into useful entities. Additionally, being rate limited by the dependency on bacterial production, high yield is difficult to obtain and thus secondary material processing is sought after. In this review, BC is explained in terms of synthesis, structure and properties. These beneficial properties are directly related to the material's great potential in wound healing where it has also been trialled commercially but ultimately failed due to processing issues. However, more recently there has been increased frequency in scientific work relating to BC processing into hybrid polymeric fibres using common laboratory fibre forming techniques such as electrospinning and pressurised gyration. This paper summarises current progress in BC fibre manufacturing, its downfalls and also gives a future perspective on how the landscape should change to allow BC to be utilised in wound care in the current environment.

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.

Food grade polymeric nanoparticles have the potential to play a key role in the future of active component delivery which is an essential characteristic of functional foods. For this potential to be realized, it is important to study both the loading and release characteristics of the encapsulated material from the particle matrix as a function of particle size, material properties and processing conditions. In this study, ethylcellulose nanoparticles encapsulating ethylvanillin as a model active component were prepared by electrohydrodynamic processing. The mean particle size varied between 45 and 85 nm and the polydispersity index between 16 and 34%. The loading capacity and encapsulation efficiency ranged between 67 and 81% and 71 and 84%, respectively. It was found that the release rate was a function of both the nanoparticle size and structure, and hence of the composition and processing conditions. FT-IR analysis demonstrated that there was no degradation of the encapsulated material during processing or whilst encapsulated within the particle. It was therefore concluded that electrohydrodynamic processing was a suitable method for producing nanoparticles that can be readily tailored for the encapsulation and controlled release of specific active components to engineer the functional characteristics of food products.

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 encapsulation process has been studied to develop smart drug delivery systems for decades. In particular, micro-encapsulation and nano-encapsulation approaches have gained wide interest in the development of particulate drug delivery and achieved progress in specialties such as nano-medicine. Encapsulation technologies have evolved through various platforms including emulsion solvent evaporation, spray drying and polymer conjugation. Among current encapsulation methods, electrohydrodynamic and microfluidic processes stand out by enabling the making of formulations with uniform shape and nanoscale size. Pressurized gyration is a new method of combining rotation and controlled pressure to produce encapsulated structures of various morphologies. In this review we address key developments in electrohydrodynamic, microfluidic, their combined and new approaches as well as their potential to obtain combined therapies with desired drug release profiles.

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.

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 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.

This study investigates the effect of print head design on the electrohydrodynamic printed resolution of silk fibroin. Needles with large orifices measuring at 800 μm were used to build five different print heads. The print heads were manufactured, tested, and optimized using four different silk fibroin solution concentrations of 10 wt.%, 15 wt.%, 20 wt.%, and 22 wt.% at applied voltages that ranged from 10 to 20 kV with two different flow rates of 1.5 μl/min and 2.0 μl/min. Each print head design behaved in a unique manner in terms of printed line characteristics as the flow rate, voltage and concentration were varied. The highest printed resolution of the order of 1 μm was achieved using the pinhole reservoir print head. Possible explanations for each of the observed behaviors and design criteria for future print heads are discussed.

The average longevity of hip replacement devices is approximately 10–15 years, which generally depends on many factors. But for younger generation patients this would mean that revisions may be required at some stage in order to maintain functional activity. Therefore, research is required to increase the longevity to around 25–30 years; a target that was initially set by John Charnley. The main issues related to metal-on-metal (MoM) hip replacement devices are the high wear rates when malpositioned and the release of metallic ions into the blood stream and surrounding tissues. Work is required to reduce the wear rates and limit the amount of metallic ions being leached out of the current MoM materials, to be able to produce an ideal hip replacement material. The most commonly used MoM material is the cobalt-based alloys, more specifically ASTM F75, due to their excellent wear and corrosion resistance. They are either fabricated using the cast or wrought method, however powder processing of these alloys has been shown to improve the properties. One powder processing technique used is spark plasma sintering, which utilises electric current Joule heating to produce high heating rates to sinter powders to form an alloy. Two conventionally manufactured alloys (ASTM F75 and ASTM F1537) and a spark plasma sintered (SPS) alloy were evaluated for their microstructure, hardness, tribological performance and the release of metallic content. The SPS alloy with oxides and not carbides in its microstructure had the higher hardness, which resulted in the lowest wear and friction coefficient, with lower amounts of chromium and molybdenum detected from the wear debris compared to the ASTM F75 and ASTM F1537. In addition the wear debris size and size distribution of the SPS alloy generated were considerably small, indicating a material that exhibits excellent performance and more favourable compared to the current conventional cobalt based alloys used in orthopaedics.

Microparticles were fabricated for pharmaceutical purposes using electrospraying with the aim to determine the effect of the solvent(s) used. Particles of poly(lactic-co-glycolic acid) (PLGA) and the drug Celecoxib were prepared from acetone, acetonitrile and acetone:methanol with different polymer and drug concentrations. The solvent power, evaporation rate and electrical conductivity of the solvents all had a significant effect on the particle formation process as well as the particle characteristics and drug release profile. Particles were near-spherical and between 2 and 7 μm in diameter with smooth or corrugated surfaces. The drug release rate was mainly dependent on particle size, with larger particles showing slower release. The solvent in which PLGA was poorly soluble resulted in small grainy particles that disintegrated instantaneously with full drug release. It may be concluded that the selection of an appropriate solvent may be a useful way to control particle characteristics and drug release profiles when using electrospraying. © 2012 Elsevier Ltd. All rights reserved.

Micro- and nanoparticle formulations are widely used to improve the bioavailability of low solubility drugs. In this study, electrospraying is introduced as a method for producing drug-loaded microspheres at ambient conditions. PLGA microspheres containing celecoxib, a low solubility drug, were prepared with the objective of producing near-monodisperse microspheres with the drug in a stable amorphous form. We found that it is possible to produce near-monodisperse celecoxib-loaded PLGA microspheres at different polymer:drug ratios. The microspheres produced were in the size range 1-5 μm depending on the polymer:drug ratio and had smooth surfaces. Thermal analysis further indicates that celecoxib is present in an amorphous form inside the microspheres. Drug dissolution studies showed an initial burst release followed by a period of sustained release with the dissolution curve depending on the polymer:drug ratio. Electrospraying is thus a promising method for producing amorphous microspheres of low solubility drugs such as celecoxib. The microsphere properties may be further optimized to achieve an appropriate dissolution profile with the aim of increasing oral bioavailability of low solubility drugs.

Submicrometre size spheres prepared from biocompatible polymers are becoming increasingly popular in drug and gene delivery. This paper describes the preparation of polymeric spheres with a mean diameter of 0.4 μm with a polydispersivity index of 8%, using coaxial electrohydrodynamic atomization (CEHDA) microbubbling. An 18 wt.% solution of polymethylsilsesquioxane, a hydrophobic biocompatible polymer, was subjected to CEHDA microbubbling by passing air through the inner needle and polymer solution through the outer needle of a twin needle co-axial device, under the influence of an electric field. A parametric plot of the flow rate of air and the flow rate of polymer solution was constructed and used for systematic process control to reduce the diameter of the microspheres from micrometre size to submicrometre size. CEHDA is an excellent method for obtaining polymer microspheres. By studying the process in detail and mapping it, we can now demonstrate it can also be used to prepare submicrometre sized particles with the ability to control size and polydispersivity.

Nanometre hydroxyapatite (nHA) coated metallic materials have been successfully used for bone tissue implantation for several decades now due to its sound biological and mechanical properties. The microstructure and surface topography of the implant material are well-known to play a crucial role in influencing cellular responses to implants and bone tissue regeneration ultimately. Recently, a novel jet-based patterning technique, template-assisted electrohydrodynamic atomisation (TAEA) spraying, has been devised to prepare depositions with defined surface topography for guiding the cellular response. In this study, an improvement investigation of this patterning process was carried out to precisely control the nHA surface structure in terms of geographies and dimensions via an angular needle jetting during the patterning process. More importantly, the mechanism of such improvement of the TAEA patterning technique was also discussed and uncovered. A range of diverse nHA surface structures with high-resolution was therefore achieved, which paves the way for the research of the new generation implant materials with defined cellular response.

The biological performance of orthopaedic and oral metallic implants can be enhanced significantly by the application of bioactive coatings. In this work, a cost-efficient alternative to the traditional technique to produce a hydroxyapatite (HA) coating with a nanostructured feature onto a metallic implant surface at room temperature via electrospray deposition, is presented. To evaluate the bioactive capacity of these nanoHA (nHA) coatings in vitro, an acellular simulated body fluid soaking experiment and a human osteoblast (HOB) cell culture work were conducted. Under these physiological conditions, the accelerated apatite precipitation process occurred on the nHA-coated titanium surfaces as compared to the uncoated titanium surfaces. HOB cells developed mature cytoskeletons with distinct evidence of actin stress fibres and vinculin adhesion plaques, on these nHA coatings. Hence, this deposition technique holds great potential in producing high quality nHA coatings for biomedical applications. (C) 2010 Elsevier B.V. All rights reserved.

Porous alginate films were prepared using a novel route in which alginate solutions of similar surface tensions but different viscosities were bubbled using a T-junction device to generate the films. The relationship between bubble size and bubbling conditions such as solution flow rate and air pressure was systematically investigated. The films obtained were characterized by optical microscopy, combined focused ion beam/scanning electron microscopy, and ultrasound reflection measurements. It is concluded that in a film, the thickness can be varied from 1-40 μm, where the minimum and maximum represent bubble-free and bubble-containing areas, respectively. Based on the characterization results obtained, a possible structure for the bubbles in the films is hypothesized. © 2010 Elsevier Ltd. All rights reserved.

The selection of a desirable solvent or solvent system as the carrier of a particular polymer is fundamental for the optimisation of electrospinning. Solvent selection is pivotal in determining the critical minimum solution concentration to allow the transition from electrospraying to electrospinning, thereby significantly affecting solution spinnability and the morphology of the electrospun fibres. 28 solvents diversely positioned on the Teas graph were studied for their solubility and electrospinnability for making polymethylsilsesquioxane (PMSQ) solutions. The results are combined and mapped on the Teas graph using different colour codes. Based on this new spinnability–solubility map, various solvent systems for PMSQ are methodically developed. Solvents are selected to produce binary solvent systems that have solvent parameters close to a good single solvent for electrospinning of the polymer solution. This work shows that solvents of high solubility do not necessarily produce solutions good for electrospinning. Polymethylsilsesquioxane solutions of the same concentration in solvents of partial solubility showed better spinnability than solutions in solvents of high solubility. A methanol–propanol binary solvent system produced electrospun fibres with high surface porosity, showing that high volatility and high vapour pressure difference among solvents mixed can induce phase separation in electrospinning. It is noteworthy that the binary solvent system mixing 2-nitropropane (high solubility) and dimethylsulphoxide (non-solvent), neither of which exhibited high volatility, also produced highly porous electrospun fibres. This demonstrates that phase separation can be induced by solubility difference in the electrospun polymer solution.

A new deposition method is presented, based on electrospraying, that can build bioceramic structures with desirable surface properties. This technology allows nanoapatite crystals, including hydroxyapatite (nHA), carbonate-substituted HA (nCHA) and silicon-substituted HA (nSiHA), to be electrosprayed on glass substrates. Human osteoblast cells cultured on nSiHA showed enhanced cell attachment, proliferation and protein expression, namely alkaline phosphatase, type 1 collagen and osteocalcin, as compared to nHA and nCHA. The modification of nanoapatite by the addition of silicon into the HA lattice structure renders the electrosprayed surface more hydrophilic and electronegatively charged.

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.

Apatite nanocrystals, which mimic the dimensions of natural bone mineral, were electrosprayed on glass substrates, as a suitable synthetic biomedical material for osteoblast outgrowth was explored. A variety of topographic patterns were deposited and the influence of these designs on osteoblast alignment and cell differentiation was investigated. Patterned cell growth and enhanced cell differentiation were seen. Osteoblasts were also cultured on apatite nanocrystals chemically modified with either carbonate or silicon ions. Enhanced cell proliferation and early formation of mineral nodules were observed on apatite nanocrystals with silicon addition. This work highlights the importance of the combined effects of surface topography and surface chemistry in the guidance of cell behaviour.

Fabricating artificial vascularised tissue would involve tissue-engineering techniques, but current technology limits this as cultured cells depend on growth media in vitro and on diffusion in vivo. Therefore, there is a need to construct a synthetic microvascular network, which would sustain these cultured cells in a similar manner to normal tissue. This is again hampered by the poor patency rates of current microvascular grafts. Based on our previous work on polyhedral oligomeric silsesquioxane-polyurethane nanocomposites, which have shown the unique ability to repel coagulant proteins whilst still allowing endothelialisation, we have now developed a new generation of microvascular prosthesis using this polymer. Using these dip-coated nanocomposite microvessels, we have shown that it is possible to mimic the hydraulic conductivity and pressure-responsive radial compliance characteristics of biological microvessels. This would allow nutrient exchange across its walls as well as minimise compliance mismatch throughout the physiological pressure range thus reducing intimal hyperplasia in the long term. This microvessel would have the following implications: (1) as a microvascular substitute to vein grafts and (2) in the future as a component of a microvascular network.

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.

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.

An alumina suspension, containing ∼20 vol.% of powder was pumped through a needle held at a high voltage, with respect to a point-like ground electrode, and subjected to electrostatic atomisation. The flow rate and voltage was varied between 10−9 and 10−8 m3 s−1, and 5 and 12 kV, respectively and the mode of atomisation observed was recorded to construct mode selection (M-S) maps. In the stable cone-jet mode, the jet diameter was measured as a function of flow rate and applied voltage. Alumina relics obtained in the stable cone-jet mode regime were collected and studied by optical microscopy to establish the conditions which generated the finest relics.

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.

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.

Water, glycerol and their mixtures having viscosities in the range 1– 1340 mPa s were subjected to electrostatic atomization at a constant applied voltage and flow rate. The conductivity of the liquids were kept approximately equal by adding citric acid and their density, relative permittivity and surface tension values were measured. The electrospray was deposited on silicone release paper and the size of the relics produced were measured. Results show that the increase in viscosity had a significant effect on the mode of atomization and increased the size and size distribution of relics obtained.

An investigation has been carried out into the production of tungsten oxide coatings from tungstic chloride and tungstic acid precursors, via a sol–gel type process, using various combinations of ethanediol and block co-polymers as stabilising additives to achieve microstructural control. The products were characterised by scanning electron microscopy, X-ray diffraction, FTIR spectroscopy and thermal analysis, with colour changes investigated by UV/Vis spectroscopy. Strongly photochromic transparent coatings were successfully prepared by the reaction of tungstic acid under basic conditions in the presence of ethanediol.

The juxtaposition of direct ceramic ink-jet printing with high throughput screening, data-mining and interpretation methods using artificial neural networks is bringing to the ceramics community a capability for combinatorial analysis presently enjoyed mainly by the pharmaceutical industry. This paper attempts to set out the potential and scope for high speed, high resolution sample preparation, high throughput screening and informatics-driven local optimisation methods. It describes the distinct philosophical basis for this approach to discovery and identifies it as primarily Baconian. It examines in detail the aspirating-dispensing systems being used for ceramic sample preparation from powder suspensions, explores their likely strengths and limitations and how these may be mitigated through the application of sophisticated computational methods.

A polysilane solution used as a silicon carbide (SiC) precursor was mixed with different amounts of titanium carbide (TiC) powder and open cell polyurethane (PU) foams were dipped in these suspensions. The resulting pre-foams were pyrolyzed at 900°C in nitrogen and then heated further at various temperature between 1100 and 1600°C in the same atmosphere to produce SiC–TiC composite foams. The evolution of the composite foams has been studied using thermogravimetry and X-ray diffraction. The PU foam, pre-foams and the SiC–TiC composite foams were characterized by optical and scanning electron microscopy. These studies show that the pre-foams retained their shape well during pyrolysis and the composite foams produced consist of an open cell structure and hole-free solid struts. Prevention of cracking in the foams were dependent on the TiC content. The shrinkage observed during the conversion of the pre-foams to the composite ceramic foams can be controlled by varying the TiC content and the sintering temperature.

A new method of forming silicon carbide–silicon nitride composite foams is presented. These are prepared by immersing a polyurethane foam in a polysilane precursor solution mixed with Si3N4 powder to form a pre-foam followed by heating it in nitrogen at >900°C. X-ray diffraction patterns indicate that a SiC–Si3N4 composite was formed after sintering the ceramic foam at >1500°C. Micrographs show that most of these foams have well-defined open-cell structures and macro-defect free struts. The shrinkage is reduced considerably due to the addition of Si3N4 particles.

Three strategies for the synthesis of silicon carbide–silicon nitride composites from organosilicon preceramic polymers were investigated. Firstly, polymeric precursors with reactive groups for silicon carbide and silicon nitride were synthesized, blended and pyrolyzed. Secondly, a polymeric precursor for silicon carbide was mixed with silicon powder which acts as a reactive filler and the resulting mixtures were pyrolyzed. Thirdly, a co-polycyclodisilazane–silane single polymeric precursor was synthesized and pyrolyzed. The precursors and the various stages of processing were studied using gel permeation chromatography, Fourier transform-infrared spectroscopy, thermo-mechanical analysis, thermogravimetry and X-ray diffraction. In each instance silicon carbide–silicon nitride composites were prepared successfully.

Polycarbosilane was synthesised directly from chloromethyltrichlorosilane and specimens were heat treated at 200, 300 and 400°C in nitrogen. The as-synthesised polymer and heat treated specimens were characterised using infra-red and Fourier transform infra-red spectroscopy, solid-state nuclear magnetic resonance and differential scanning calorimetry and were also subjected to thermogravimetric analysis in nitrogen. All types of specimens were pyrolysed in nitrogen at 1500°C. The ceramic residue obtained from thermogravimetric and pyrolysis experiments was characterised using X-ray diffraction and scanning electron microscopy. Heating the polymer before pyrolysis improved significantly the yield of the ceramic but the gain beyond 200°C was minimal. It was shown that the heat treatment initially caused the as-synthesised polymer to lose volatile oligomers and subsequently to cross-link. Pyrolysis at 900°C and subsequent crystallisation by further heating to 1500°C of the cross-linked polymer produced homogeneous and fine grained silicon carbide.

Some microstructural elements, such as microtwins in tetragonal ZrO 2 grains (t-ZrO 2 ), were identified in a plasma-sprayed ZrO 2 -Y 2 O 3 -TiO 2 coating by using transmission electron microscopy. These elements are similar to those described in plasma-sprayed ZrO 2 -Y 2 O 3 coatings and are characteristic of nontransformable t-ZrO 2 . This microstructure could promote some toughening mechanisms. The monoclinic ZrO 2 phase (m - ZrO 2 ), produced by a martensitic transformation of the metastable t-ZrO 2 phase, also was observed. The variation in the concentration of Ti in the ZrO 2 -Y 2 O 3 -TiO 2 coating body was found to be appreciable. The energy-dispersive spectroscopic analyses showed that a high concentration of Ti was associated with t-ZrO 2 whereas a relatively lower content of Ti was found in m-ZrO 2 . ZrO 2 -Y 2 O 3 -TiO 2 thermally treated at 1400 and 1600°C showed signs of grain growth. A higher incidence of m- and t-ZrO 2 twins indicated higher constraints of the polycrystalline structure as a result of the grain growth and rapid cooling rate.

Several polysilanes, including two groups of copolymers and a group of ter-polymers, with overall functionalities ranging between 2 and 3 were prepared using the alkali metal dechlorination reaction. The yields of the soluble solid fractions of these polymers (the potential ceramic precursor) were in the range 40–70% wt and decreased with increasing overall functionalities in both cases of co- and terpolymers. The molecular weights and FT-IR spectra of the precursors have been determined and the ceramic in the residue after pyrolysis has been identified as silicon carbide. The pyrolytic yield can be increased by using a polymeric precursor of higher overall functionality. The reasons for this are discussed with reference to pyrolysis mechanisms. In particular, some of the ter-polymeric precursors synthesised with a high yield also give a high yield on pyrolysis due to the presence of branched structures and potential cross-linking sites.