Although nanoparticles have tremendous potential for a host of applications, their adverse effects on living cells have raised serious concerns recently for their use in the healthcare and consumer sectors. As regards the central nervous system (CNS), research data on nanoparticle interaction with neurons has provided evidence of both negative and positive effects. Maximal application dosage of nanoparticles in materials to provide applications such as antibacterial and antiviral functions is approximately 0.1 -1.0 wt%. This concentration can be converted into a liquid phase release rate (leaching rate) depending upon the host or base materials used. For example, nanoparticulate silver (Ag) or copper oxide (CuO)-filled epoxy resin demonstrates much reduced release of the metal ions (Ag þ or Cu 2þ ) into their surrounding environment unless they are mechanically removed or aggravated. Subsequent to leaching effects and entry into living systems, nanoparticles can also cross through many other barriers, such as skin and the blood-brain barrier (BBB), and may also reach bodily organs. In such cases, their concentration or dosage in body fluids is considered to be well below the maximum drug toxicity test limit (10 25 g ml 21) as determined in artificial cerebrospinal solution. As this is a rapidly evolving area and the use of such materials will continue to mature, so will their exposure to members of society. Hence, neurologists have equal interests in nanoparticle effects (positive functionality and negative toxicity) on human neuronal cells within the CNS, where the current research in this field will be highlighted and reviewed.

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The objective of this work was to produce drug-loaded nanometre-and micrometre-scale particles using a single-step process that provides control over particle size and size distribution. Co-axial electrohydrodynamic processing was used, at ambient temperature and pressure, with poly(lactic-co-glycolic acid) as the polymeric coating material and oestradiol as the encapsulated drug. The particle diameter was varied from less than 120 nm to a few micrometres, by simple methodical adjustments in the processing parameters ( polymer concentration and applied voltage). In vitro studies were performed to determine the drug release profile from the particles during unassisted and ultrasound-stimulated degradation in simulated body fluid. An encapsulation efficiency of approximately 70% was achieved and release of the drug was sustained for a period of over 20 days. Exposing the particles to ultrasound (22.5 kHz) increased the rate of release by approximately 8 per cent. This processing method offers several advantages over conventional emulsification techniques for the preparation of drug-loaded particles. Most significantly, process efficiency and the drug's functionality are preserved, as complex multistep processing involving harsh solvents, other additives and elevated temperatures or pressures are avoided. Production rates of 10 12 particles min 21 can be achieved with a single pair of co-axial needles and the process is amenable to being scaled up by using multiple sets.

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In this short communication, we describe the scope and flexibility of using a novel device containing three coaxially arranged needles to form a variety of novel morphologies. Different combinations of materials are subjected to controlled flow through the device under the influence of an applied electric field. The resulting electrohydrodynamic flow allows us to prepare doublelayered bubbles, porous encapsulated threads and nanocapsules containing three layers. The ability to process such multilayered structures is very significant for biomedical engineering applications, for example, generating capsules for drug delivery, which can provide multistage controlled release.

Drug administration via the transdermal route is an evolving field that provides an alternative to oral and parenteral routes of therapy. Several microneedle (MN) based approaches have been developed. Among these, coated MNs (typically where drug is deposited on MN tips) are a minimally invasive method to deliver drugs and vaccines through the skin. In this review, we describe several processes to coat MNs. These include dip coating, gas jet drying, spray coating, electrohydrodynamic atomisation (EHDA) based processes and piezoelectric inkjet printing. Examples of process mechanisms, conditions and tested formulations are provided. As these processes are independent techniques, modifications to facilitate MN coatings are elucidated. In summary, the outcomes and potential value for each technique provides opportunities to overcome formulation or dosage form limitations. While there are significant developments in solid degradable MNs, coated MNs (through the various techniques described) have potential to be utilized in personalized drug delivery via controlled deposition onto MN templates.

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