The role of surface wettability and surface charge of electrosprayed nanoapatites on the behaviour of osteoblasts.

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.

Deposition of nano-hydroxyapatite particles utilising direct and transitional electrohydrodynamic processes.

Electrohydrodynamic spraying is a well established process used to deposit, coat, analyse and synthesise materials within the biomedical remit. Recently, electrohydrodynamic printing has been developed to afford structures for potential applications in the biomedical and medical engineering fields. Both of these processes rely on the formation of an electrically-induced jet, however the resulting products can be made strikingly different and offer potential in broader applications. Here we show how spraying and printing are linked by elucidating the ease of transition between the processes. Changes in the deposition distance can result in either spray (>10 mm) or print formation (<3 mm), with an overlap of the two in between this range. For the optimal printing distance of 0.5 mm, gradual changes in the applied voltage (0-4.5 kV) encounters transitional printing modes (dripping, micro-dripping, rapid micro-dripping, unstable and stable jetting) which can be utilised for patterning. The results indicate the robustness of the electrohydrodynamic route in the nano-materials processing arena, with emphasis on biomedical materials.

Influence of nanohydroxyapatite patterns deposited by electrohydrodynamic spraying on osteoblast response.

Electrohydrodynamic spraying has been used to produce patterns of line width up to 100 microm in size on glass discs, using nanohydroxyapatite (nHA). A human osteoblast (HOB)-like cell model was then used to study the interaction between the HOB cells and nHA patterns in vitro. Growth of the cells was significantly increased (p < 0.05) on the nHA surfaces. In addition, HOBs attached and spread well, secreting extracellular matrix. It was found that a confluent, aligned cell layer was achieved on nHA patterns by day 9. Immunofluorescent staining indicated that these cells showed elongated nuclei, enhanced adhesion (vinculin adhesion plaques) and a well-aligned cytoskeleton (actin stress fibres). This work suggests that this type of spraying may provide a route for the production of nanoscale features on implants for biomedical applications.

Bio-electrosprays: the development of a promising tool for regenerative and therapeutic medicine.

Regenerative and therapeutic medicine are two fields of research to which engineering sciences are increasingly contributing. One such case in which physical sciences have been greatly involved is in the generation of tissues by directly processing living cells. In this article we focus on the current status of cell or tissue engineering approaches by way of jets, particularly focusing on bio-electrosprays.

Submerged electrosprays: a versatile approach for microencapsulation.

The unearthing of fundamental science and technology associated with microencapsulation is an ongoing exciting scientific endeavour focused on by several scientists. Encapsulated structures (containing either a gas, molecules or materials) previously have been shown as having widespread applications across the physical and life sciences. In particular, such methodologies used for forming encapsulations in medical-related studies have shown great promise from diagnostics and imaging, to gene therapy and drug delivery which are only a few amongst several other applications. At present there are numerous 'jet-based' manifestations available for microencapsulation, these primarily root from either capillary or channel-based techniques. The driving mechanisms employed in these approaches exploit aerodynamic/pressure gradients to piezoelectricity. In this paper submerged electrosprays a multipurpose electric field driven jet-based technique is explored for forming near mono-dispersed encapsulations sized in the micrometer range. Our studies elucidate the ability to form microencapsulations containing either a gas or a micro/nanoparticulate-based material suspension as capsules sized in the ranges approximately 65-80 microm, approximately 8-25 microm to approximately 3-14 microm, respectively. We believe this technique can significantly contribute to the microencapsulation field of research based on both the size of the generated encapsulations to the containment of immiscible high viscosity particulate-based suspensions. Furthermore our investigations show the ability to control the production of these encapsulations in terms of both their size and rate of generation with ease; hence demonstrating this electrospray-assisted microencapsulation route as having a wide range of applications. It should be noted that in its present form this technique could be explored for generating emulsions with a variety of materials especially with living organisms for applications in the clinical and biomedical areas of research.

Aerodynamically assisted jet processing of viscous single- and multi-phase media.

This paper reports a robust approach for jet-processing viscous media in both the single- and multi-phase. The multi-phase medium (a nanosuspension) has nanosized SiO (5 nm) particulate material at a loading of ∼10 wt% in suspension. Aerodynamically assisted jetting has previously not been applied to the processing of particulate-based high viscosity nanosuspensions. Our investigations demonstrate that it is possible to generate jets, from which droplets are initiated by jet fragmentation, to the drawing of continuous threads in the micrometer range from the processing of particulate suspensions. The study presents an operational guide of applied pressure-flow rate; demarcations identify regions within the map where droplets and threads are generated, together with their respective operational parameters. The effect of applied pressure and flow rate on the jetting process to the generation of droplets to threads together with transmission electron micrographs of the droplet residues forms the discussion in this paper. These investigations into this jetting approach both elucidate and welcome aerodynamically assisted jetting into the micro- and nano-fabrication arena.

Stable electric-field driven cone-jetting of concentrated biosuspensions.

Electrospraying, or electrohydrodynamic jetting, is one of several jet-based technologies being explored to process living biological organisms. One of the key advantages of electrospraying is its ability to deposit advanced materials with high resolution that cannot be obtained with other competing technologies, such as ink-jet printing. However, to generate a controlled droplet size distribution in the micrometre range necessary for precision drop and placement of materials requires jetting in stable cone-jet mode. In this paper, we describe the experimental set-up and conditions by which electrospray jetting in stable cone-jet is achieved and use this methodology to process a highly concentrated biological suspension having 10(7) cells ml(-1), the highest cellular loading processed to this day by a jetting approach in this jet based category. The areas of study to which this technology may be applied span the physical and the life sciences.

Electrohydrodynamic atomization: an approach to growing continuous self-supporting polymeric fibers.

The investigation presented in this paper illustrates a technique for growing in-situ polymerized networks, forming scaffold-like structures usually formed by means of electrospinning. The technique of jet atomization employing electrohydrodynamics is a manifestation of electrospinning. However, we show for the first time that using this technique where individual droplets are generated, a continuous self-supporting submicrometer web-like structure can be grown whereby fragments of the structure are delivered in the droplets and polymerize on the surface of the growing structure via polycondensation. The development of these growing fibers into web structures is a direct result of the processing route together with the excellent tailor-made cross-linking nature of the resin. An operational map is generated to identify a parametric space in which the stable cone-jet mode of electrohydrodynamic atomization prevails for generating the finest droplets. A statistical analysis on the formed fibers for a given time and electrospray condition is presented together with optical micrographs of the structure, which concludes the discussion in this paper.

Novel deposition of nano-sized silicon substituted hydroxyapatite by electrostatic spraying.

Suspensions containing nano-sized silicon substituted hydroxyaptite (nSiHA) particles were produced and processed for electrostatic spray deposition. No secondary phases were detected by X-ray diffraction, which indicated that the nSiHA was phase pure. Electrostatic spraying of nSiHA in cone-jet mode was achieved at flow rate of 10(-9) m3s(-1) with an applied voltage between the needle and the ring-shaped ground electrode set at 6 to 8 kV. Micrometer- and submicrometer-scaled islands of nSiHA have been deposited on glass and titanium substrates. The surface roughness of such nHA and nSiHA islands was in the range 60 to 80 nm, as measured from atomic force microscopy in tapping mode. The growth of primary human osteoblast (HOB) cells on the nSiHA deposited substrates increased with time during the 4 days of culture, and the increase was related with the Si content in substituted HA, indicating that nSiHA was able to promote and support the growth of HOB cells. Scanning electron microscopy (SEM) revealed that extracellular matrix (ECM) produced by the HOB cells on these nSiHA deposits was well organized. In addition, the presence of Ca and P containing nodules in the ECM were also confirmed by Energy Dispersive X-ray (EDX) analysis, indicating early signs of calcification fronts. The results showed that nSiHA produced by electrostatic spray deposition was able to promote the attachment and the growth of HOB cells. Therefore, electrostatic spray deposition offers great potential for the creation of bioactive surfaces to provide improved interfacial bonding with host tissues.

Electrohydrodynamic atomization of protein (bovine serum albumin).

Bovine serum albumin (BSA) was chosen as a model protein. Three solutions of different concentrations of 5, 20 and 50 mg/ml were prepared, characterised and subjected to electrohydrodynamic atomization (EHDA). The 5 and 20 mg/ml solutions were atomized successfully and mode selection (M-S) maps were drawn for both concentrations to find out regions of stable cone-jet mode atomizaton. Droplet relics of these two solutions were investigated by electron microscopy. Samples were investigated by UV spectroscopy and circular dichroism (CD) spectroscopy before and after electrohydrodynamic atomization. We conclude that, particularly at the higher concentration of protein, EHDA does not result in significant structural change of BSA, and therefore is a processing route that can be considered for encapsulating drugs in proteins.

Jet break-up in nano-suspensions during electrohydrodynamic atomization in the stable cone-jet mode.

This paper reports jet break-up phenomena, which occurs during the electrohydrodynamic atomization (EHDA) of nano-suspensions. We investigated three ethylene glycol-based near-monodisperse suspensions, containing 30 wt% of SiO2 particles sized at 20, 80 and 120 nm. These suspensions were subjected to electrohydrodynamic atomization in the stable cone-jet mode and the jet break-up in each is discussed and compared with those of liquids reported in the literature.

In vitro assessment of the biological response to nano-sized hydroxyapatite.

Nano-sized, rod-like hydroxyapatite (nHA) crystals were produced and shown to be phasepure by X-ray diffraction analysis, as no secondary phases were observed. The nHA suspension was electrosprayed onto glass substrates using a novel processing routine to maintain nanocrystals of hydroxyapatite. The biocompatibility of nHAwas determined using human monocyte-derived macrophages and human osteoblast-like (HOB) cell models. The release of lactate dehydrogenase (LDH) from human monocyte-derived macrophages was measured as an indicator of cytotoxicity. The release of the inflammatory cytokine, tumour necrosis factor alpha (TNF-alpha) from cells in the presence of nHA crystallites was used as a measure of the inflammatory response. Although there was some evidence of LDH release from human monocyte-derived macrophages when in contact with high concentrations of nHA crystals, there was no significant release of TNF-alpha. Moreover, nHA-sprayed substrates were able to support the attachment and the growth of HOB cells. These results indicate that nHA crystals may be suitable for intraosseous implantation and offers the potential to formulate enhanced composites for biomedical applications.