Mohan Edirisinghe

Novel microbubble preparation technologies

Gas microbubbles, stabilised by a surfactant or polymer coating, have become well established over the past 20–30 years as the most effective type of contrast agent available for ultrasound radiography. More recently, their potential for use in therapeutic applications including targeted drug delivery, gene therapy, thrombolysis and focused ultrasound surgery has also been investigated. Developments in both diagnostic and therapeutic applications have greatly increased the need for more advanced preparation technologies which provide a high degree of control over microbubble size, composition, stability and uniformity. Conventional processing techniques such as sonication and high shear emulsification offer high yield and low cost production but poor control over microbubble size and uniformity. This is being addressed by the development of new technologies, such as membrane emulsification, inkjet printing, electrohydrodynamic atomisation and microfluidic processing which offer significant improvements in terms of control over microbubble characteristics. The aim of this paper is to review the range of techniques available for microbubble preparation and how these have evolved to keep pace with advances in clinical practice.

Review: Fabrication of engineering ceramics by injection moulding. I. Materials selection

Abstract The present article, Part I, reviews the literature on ceramic powders and organic polymers used to compound ceramic injection moulding mixtures. The intention is to distil, from a somewhat diverse literature, guidelines for the proper selection of materials, with the aim of facilitating the development of the defect-free moulding of ceramic components. Part II will examine mixing methods, moulding techniques and procedures for removal of the organic vehicle prior to sintering.

Forming of Polymer Nanofibers by a Pressurised Gyration Process

A new route consisting of simultaneous centrifugal spinning and solution blowing to form polymer nanofibers is reported. The fiber diameter (60-1000 nm) is shown to be a function of polymer concentration, rotational speed, and working pressure of the processing system. The fiber length is dependent on the rotational speed. The process can deliver 6 kg of fiber per hour and therefore offers mass production capabilities compared with other established polymer nanofiber generation methods such as electrospinning, centrifugal spinning, and blowing.

Effect of viscosity on the size of relics produced by electrostatic atomization

Water, glycerol and their mixtures having viscosities in the range 1-1340 mPas 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

A novel nanocomposite polymer for development of synthetic heart valve leaflets.

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 (P<0.001). POSS-PCU showed a relatively low Youngs 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 (P>0.05) in tear strength between POSS-PCU and PCU at 25 degrees C. However, tear strength increased significantly (P<0.001) (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.

Generation of multilayered structures for biomedical applications using a novel tri-needle coaxial device and electrohydrodynamic flow

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 double-layered 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.

A new method for the preparation of monoporous hollow microspheres.

The feasibility of producing a hollow microsphere with a single hole in its shell by coaxial electrohydrodynamic atomization (CEHDA) is demonstrated. Polymethylsilsesquioxane (PMSQ) was used as a model shell material encapsulating a core of a volatile liquid, perfluorohexane (PFH), which was subsequently evaporated to produce the hollow microspheres. The diameters of the microspheres and of the single surface pore were controlled by varying the flow rate of the components, the concentration of the PMSQ solution, and the applied voltage in the CEHDA process. The particles were characterized by scanning electron microscopy, and the ranges obtained were 275-860 nm for the microsphere diameter and 35-135 nm for the pore size. The process overcomes several of the key problems associated with existing methods of monoporous microsphere formation including removing the need for elevated temperatures, multiple processing steps, and the use of surfactants and other additives.

One-step electrohydrodynamic production of drug-loaded micro- and nanoparticles

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 drugs functionality are preserved, as complex multistep processing involving harsh solvents, other additives and elevated temperatures or pressures are avoided. Production rates of 1012 particles min−1 can be achieved with a single pair of co-axial needles and the process is amenable to being scaled up by using multiple sets.

Review: Fabrication of engineering ceramics by injection moulding. II. Techniques

Abstract The development of injection moulding techniques and their applicationto ceramic suspensions is described, with particular attention being paid to the mixing of suspensions prior to moulding and to the origin of moulding defects. Methods for the removal of the organic component of the injection moulding blend are reviewed.

A novel method for the preparation of biodegradable microspheres for protein drug delivery

Microspheres are potential candidates for the protein drug delivery. In this work, we prepared polymer-coated starch/bovine serum albumin (BSA) microspheres using co-axial electrohydrodynamic atomization (CEHDA). First, starch solution in dimethyl sulphoxide (DMSO) was prepared and then an aqueous solution of BSA was added to it to make a starch–BSA solution. Subsequently, this solution was made to flow through the inner capillary, while the polymer, polydimethylsiloxane (PDMS), flowed through the outer capillary. On collection, filtration and subsequent drying, near-monodisperse microspheres of 5–6 μm in size were obtained. The microspheres were characterized by Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscopy. Cumulative BSA release was investigated by UV spectroscopy. BSA structure and activity was preserved in the microspheres and its release in 0.01 M phosphate buffered saline (PBS) was studied over a period of 8 days. There was an initial burst with 32 wt% of total BSA released in 2 h. Overall 75 wt% of BSA was released over a 7 day period.