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The study of the effects of ultrasound-induced acoustic cavitation on biological structures is an active field in biomedical research. Of particular interest for therapeutic applications is the ability of oscillating microbubbles to promote both cellular and tissue membrane permeabilisation and to improve the distribution of therapeutic agents in tissue through extravasation and convective transport. The mechanisms that underpin the interaction between cavitating agents and tissues are, however, still poorly understood. One challenge is the practical difficulty involved in performing optical microscopy and acoustic emissions monitoring simultaneously in a biologically compatible environment. Here we present and characterise a microfluidic layered acoustic resonator (μLAR) developed for simultaneous ultrasound exposure, acoustic emissions monitoring, and microscopy of biological samples. The μLAR facilitates in vitro ultrasound experiments in which measurements of microbubble dynamics, microstreaming velocity fields, acoustic emissions, and cell-microbubble interactions can be performed simultaneously. The device and analyses presented provide a means of performing mechanistic in vitro studies that may benefit the design of predictable and effective cavitation-based ultrasound treatments.

The translation of continuous-flow microreactor technology to the industrial environment has been limited by cost and complexity of the fabrication procedures, and the requirement for specialised infrastructure. In the present study, we have developed a significantly cost-effective and easy-to-perform fabrication method for the generation of optically transparent, continuous-flow reactors. The method combines 3D printing of master moulds with sealing of the PDMS channels’ replica using a pressure-sensitive adhesive tape. Morphological characterisation of the 3D printed moulds was performed, and reactors were fabricated with an approximately square-shaped cross-section of 1 mm^2. Notably, they were tested for operation over a wide range of volumetric flow rates, up to 20 ml/min. Moreover, the fabrication time (i.e., from design to the finished product) was

In recent years, the development of nano- and micro-particles has attracted considerable interest from researchers and enterprises, because of the potential utility of such particles as drug delivery vehicles. Amongst the different techniques employed for the production of nanoparticles, microfluidic-based methods have proven to be the most effective for controlling particle size and dispersity, and for achieving high encapsulation efficiency of bioactive compounds. In this study, we specifically focus on the production of liposomes, spherical vesicles formed by a lipid bilayer encapsulating an aqueous core. The formation of liposomes in microfluidic devices is often governed by diffusive mass transfer of chemical species at the liquid interface between a solvent (i.e., alcohol) and a non-solvent (i.e., water). In this work, we developed a new approach for the analysis of mixing processes within microfluidic devices. The method relies on the use of a pH indicator, and we demonstrate its utility by characterizing the transfer of ethanol and water within two different microfluidic architectures. Our approach represents an effective route to experimentally characterize diffusion and advection processes governing the formation of vesicular/micellar systems in microfluidics, and can also be employed to validate the results of numerical modelling.

The aim of this study was to characterize the behaviour of superparamagnetic particles in magnetic drug targeting (MDT) schemes. A 3-dimensional mathematical model was developed, based on the analytical derivation of the trajectory of a magnetized particle suspended inside a fluid channel carrying laminar flow and in the vicinity of an external source of magnetic force. Semi-analytical expressions to quantify the proportion of captured particles, and their relative accumulation (concentration) as a function of distance along the wall of the channel were also derived. These were expressed in terms of a non-dimensional ratio of the relevant physical and physiological parameters corresponding to a given MDT protocol. The ability of the analytical model to assess magnetic targeting schemes was tested against numerical simulations of particle trajectories. The semi-analytical expressions were found to provide good first-order approximations for the performance of MDT systems in which the magnetic force is relatively constant over a large spatial range. The numerical model was then used to test the suitability of a range of different designs of permanent magnet assemblies for MDT. The results indicated that magnetic arrays that emit a strong magnetic force that varies rapidly over a confined spatial range are the most suitable for concentrating magnetic particles in a localized region. By comparison, commonly used magnet geometries such as button magnets and linear Halbach arrays result in distributions of accumulated particles that are less efficient for delivery. The trajectories predicted by the numerical model were verified experimentally by acoustically focusing magnetic microbeads flowing in a glass capillary channel, and optically tracking their path past a high field gradient Halbach array.

Introduction. An ideal stent would offer simple insertion and removal with no discomfort and/or migration, would have no biofilm formation or encrustation, and would also maintain patient's quality of life. Materials and methods. In this mini review we outline the engineering developments relating to stent material, design and coating. Results. There have been a wide variety of in-vitro, model based, animal based and clinical studies using a range of commercial and non-commercial stents. Ureteric stents have evolved since their first use with a wide range of stent design, material and coating available for laboratory and clinical use. Conclusions. While engineering innovations have led to the evolution of stents, more work needs to be done to address issues relating to stent encrustation and biofilm formation.

Therapeutic embolotherapy is the deliberate occlusion of a blood vessel within the body, which can be for the prevention of internal bleeding, stemming of flow through an arteriovenous malformation, or occlusion of blood vessels feeding a tumour. This is achieved using a wide selection of embolic devices such as; balloons, coils, gels, glues and particles.Particulate embolization is often favoured for blocking smaller vessels, particularly within hyper-vascularised tumours, as they are available in calibrated sizes and can be delivered distally via microcatheters for precise occlusion with associated locoregional drug delivery.Embolic performance has been traditionally evaluated using animal models, but with increasing interest in the 3R’s (Replacement, Reduction, Refinement), manufacturers, regulators and clinicians have shown interest in the development of more sophisticated in vitro methods for evaluation and prediction of in vivo performance. Herein we review the current progress in developing bespoke techniques incorporating; physical handling, fluid dynamics, occlusive behaviour and sustained drug elution kinetics within vascular systems.Whilst it is necessary to continue to validate the safety of such devices in vivo, great strides have been made in the development of bench tests that better predict the behaviour of these products aligned with the principles of the 3R’s.

Small interfering RNA (siRNA) has significant therapeutic potential but its clinical translation has been severely inhibited by a lack of effective delivery strategies. Previous work has demonstrated that perfluorocarbon nanodroplets loaded with magnetic nanoparticles can facilitate the intracellular delivery of a conventional chemotherapeutic drug. The aim of this study is to determine whether a similar agent can provide a means of delivering siRNA, enabling efficient transfection without degradation of the molecule. Chitosan-deoxycholic acid nanoparticles containing perfluoropentane and iron oxide (d

Impaired fracture healing is a major financial burden for healthcare services; 5%–10% of bone fractures result in non-unions, and there is no clinically approved systemic therapy. This study characterises acoustically stimulated microbubbles (MBs) and nanodroplets (NDs) as non-invasive ultrasound responsive vehicles for the targeted delivery of osteogenic compounds. A microscope-compatible water-tank incorporating a passive cavitation detector was developed to study the acoustic behaviour of MBs and NDs within physical models of bone fractures (gap: 3.5–5.5 mm, angles: 0 deg and 90 deg). The device was designed using COMSOL Multiphysics (Burlington, MA) and tested in-vitro. The bone was simulated using a material with comparable acoustic impedance (Sawbones, WA). Numerical simulations showed that the developed experimental set-up generated a relatively uniform acoustic field at a target plane. It could be operated at either 1 or 2 MHz US frequency, at an acoustic pressure in the range 0–1 MPa. The inclusion of a fracture model caused perturbations to the acoustic field, which were dependent on the architecture of the fracture (i.e., relative to the incident US field). Ongoing studies are investigating how these perturbations affect ND/MB response in-vitro. Further studies will investigate the relationship between MB/ND acoustic response and the release of biologically active compounds.Impaired fracture healing is a major financial burden for healthcare services; 5%–10% of bone fractures result in non-unions, and there is no clinically approved systemic therapy. This study characterises acoustically stimulated microbubbles (MBs) and nanodroplets (NDs) as non-invasive ultrasound responsive vehicles for the targeted delivery of osteogenic compounds. A microscope-compatible water-tank incorporating a passive cavitation detector was developed to study the acoustic behaviour of MBs and NDs within physical models of bone fractures (gap: 3.5–5.5 mm, angles: 0 deg and 90 deg). The device was designed using COMSOL Multiphysics (Burlington, MA) and tested in-vitro. The bone was simulated using a material with comparable acoustic impedance (Sawbones, WA). Numerical simulations showed that the developed experimental set-up generated a relatively uniform acoustic field at a target plane. It could be operated at either 1 or 2 MHz US frequency, at an acoustic pressure in the range 0–1 MPa. The inclusi...

Ureteric stents are clinically deployed to retain ureteral patency in the presence of an obstruction of the ureter lumen. Despite the fact that multiple stent designs have been researched in recent years, encrustation and biofilm-associated infections remain significant complications of ureteral stenting, potentially leading to the functional failure of the stent. It has been suggested that “inactive” side-holes of stents may act as anchoring sites for encrusting crystals, as they are associated with low wall shear stress (WSS) levels. Obstruction of side-holes due to encrustation is particularly detrimental to the function of the stent, since holes provide a path for urine to by-pass the occlusion. Therefore, there is an unmet need to develop novel stents to reduce deposition of encrusting particles at side-holes. In this study, we employed a stent-on-chip microfluidic model of the stented and occluded ureter to investigate the effect of stent architecture on WSS distribution and encrustation over its surface. Variations in the stent geometry encompassed (i) the wall thickness and (ii) the shape of side-holes. Stent thickness was varied in the range 0.3-0.7 mm, while streamlined side-holes of triangular shape were evaluated (with a vertex angle in the range 45°-120°). Reducing the thickness of the stent increased WSS and thus reduced the encrustation rate at side-holes. A further improvement in performance was achieved by using side-holes with a triangular shape; notably, a 45° vertex angle showed superior performance compared to other angles investigated, resulting in a significant increase in WSS within “inactive” side-holes. In conclusion, combining the optimal stent thickness (0.3 mm) and hole vertex angle (45°) resulted in a ∼90% reduction in encrustation rate within side-holes, compared to a standard design. If translated to a full-scale ureteric stent, this optimised architecture has the potential for significantly increasing the stent lifetime while reducing clinical complications.Ureteric stents are clinically deployed to retain ureteral patency in the presence of an obstruction of the ureter lumen. Despite the fact that multiple stent designs have been researched in recent years, encrustation and biofilm-associated infections remain significant complications of ureteral stenting, potentially leading to the functional failure of the stent. It has been suggested that “inactive” side-holes of stents may act as anchoring sites for encrusting crystals, as they are associated with low wall shear stress (WSS) levels. Obstruction of side-holes due to encrustation is particularly detrimental to the function of the stent, since holes provide a path for urine to by-pass the occlusion. Therefore, there is an unmet need to develop novel stents to reduce deposition of encrusting particles at side-holes. In this study, we employed a stent-on-chip microfluidic model of the stented and occluded ureter to investigate the effect of stent architecture on WSS distribution and encrustation over its su...

In recent years, advancements in the fields of microfluidic and lab-on-a-chip technologies have provided unique opportunities for the implementation of nanomaterial production processes owing to the miniaturisation of the fluidic environment. It has been demonstrated that microfluidic reactors offer a range of advantages compared to conventional batch reactors, including improved controllability and uniformity of nanomaterial characteristics. In addition, the fast mixing achieved within microchannels, and the predictability of the laminar flow conditions, can be leveraged to investigate the nanomaterial formation dynamics. In this article recent developments in the field of microfluidic production of nanomaterials for drug delivery applications are reviewed. The features that make microfluidic reactors a suitable technological platform are discussed in terms of controllability of nanomaterials production. An overview of the various strategies developed for the production of organic nanoparticles and colloidal assemblies is presented, focusing on those nanomaterials that could have an impact on nanomedicine field such as drug nanoparticles, polymeric micelles, liposomes, polymersomes, polyplexes and hybrid nanoparticles. The effect of microfluidic environment on nanomaterials formation dynamics, as well as the use of microdevices as tools for nanomaterial investigation is also discussed.

We investigate tooth wear in the context of removing dental plaque biofilms from tooth surfaces using high velocity water droplets. A laboratory model system was designed using a dextran gel as a biofilm surrogate and a typodont model was used to reproduce the geometry of the mouth. Using uni-axial compression, the elastic modulus of Streptococcus mutans biofilms was 0.280 kPa (±0.350; n=30), and the relaxation time was 11 s (±12; n=10). The type of surface, concentration of sugar, chelation and osmotic pressure all had significant effects on biofilm stiffness. However, there was no direct relationship between biofilm stiffness and surface hydrophobicity or roughness. The elastic modulus of the gel was 17 kPa (±12; n=3), and the relaxation time was 15 s (±12; n=3) which was in the reported viscoelastic range of real bacterial biofilms. High velocity 115 μL water drops travelling with an exit velocity of 60 m/s were generated using a prototype interdental cleaning device (Sonicare AirFloss). High-speed imaging showed that the gel was removed within approximately 6 ms of impact by adhesive failure from the tooth surface and within approximately 26 ms of impact by cohesive failure.

The corrosion properties of the nickel–aluminium bronze (NAB) in aqueous chloride media were investigated at different pHs by using linear potential sweep voltammetry and scanning electron microscopy. The NAB electrochemical behaviour was dependent on the solution pH, due to the different stabilities of the phases present within its microstructure. In particular, at solution pHs higher than 4.0 the NAB oxidation was driven by the dissolution of the copper-rich ?-phase, whereas at pH values lower than 4.0 its anodic behaviour was controlled by the oxidation of the iron-, nickel- and aluminium-rich ?I-, ?II- and ?IV-phases. Furthermore, a kinetic model for the NAB oxidation, in neutral chloride solutions, was developed on the basis of the observed behaviour, i.e., order of reactions of NAB with respect to protons and chloride. Finally, considering the high affinity of benzotriazole for copper, the corrosion performance of NAB was studied in the presence of the inhibitor in neutral (pH of 6.2) and acidic (pH of 3.5) chloride solutions, where NAB exhibited different anodic behaviours.

The microcirculation plays a key role in the delivery of essential substrates for oxidative processes in cells, the removal of products of cell metabolism, and the regulation of peripheral blood flow distribution. The functional properties of microvascular networks strongly depend on the rheological properties of blood and on the heterogeneity of their architecture. However, studying blood flow behaviour through in vivo microvascular systems is limited by ethical, economical and technical issues. Such limitations have opened the way to in vitro models, such as straight microcapillaries or network- like microchannel constructs, but current in vitro models present simplifications in the architecture design which result in the impossibility of faithfully reproducing key features of the in vivo microvascular haemodynamics. In the present study we report the development of a microfluidic-based in vitro model of the human arteriolar system, characterised by circular channel cross-section, network asymmetry and the presence of both bifurcation- and side-branches. The developed microdevice allows for the quantification of the velocity fields, cell-depletion layer thickness and haematocrit distribution within biomimetic microchannel networks. Results show the potential of our in vitro model in reproducing key features of blood flow behaviour which have been detected for microvascular systems in vivo, including the relationships between cell-depletion layer thickness, haematocrit and vessel diameter. The developed microdevices can find extensive applications in biological and biophysical research, where the mimicking of flow dynamics at the microcirculatory level is required

The transfer of material from phospholipid-coated microbubbles to cell membranes has been hypothesized to play a role in ultrasound-mediated drug delivery. In this study, we employed quantitative fluorescence microscopy techniques to investigate this phenomenon in both artificial and biological membrane bilayers in an acoustofluidic system. The results of the present study provide strong evidence for the transfer of material from microbubble coatings into cell membranes. Our results indicate that transfer of phospholipids alters the organization of molecules in cell membranes, specifically the lipid ordering or packing, which is known to be a key determinant of membrane mechanical properties, protein dynamics, and permeability. We further show that polyethylene-glycol, used in many clinical microbubble formulations, also has a major impact on both membrane lipid ordering and the extent of lipid transfer, and that this occurs even in the absence of ultrasound exposure.

This paper provides an analysis of microfluidic techniques for the production of nanoscale lipid-based vesicular systems. In particular we focus on the key issues associated with the microfluidic production of liposomes. These include, but are not limited to, the role of lipid formulation, lipid concentration, residual amount of solvent, production method (including microchannel architecture), and drug loading in determining liposome characteristics. Furthermore, we propose microfluidic architectures for the mass production of liposomes with a view to potential industrial translation of this technology.

Objective To compare foam bubble size and bubble size distribution, stability, and degradation rate of commercially available polidocanol endovenous microfoam (Varithena®) and physician-compounded foams using a number of laboratory tests. Methods Foam properties of polidocanol endovenous microfoam and physician-compounded foams were measured and compared using a glass-plate method and a Sympatec QICPIC image analysis method to measure bubble size and bubble size distribution, Turbiscan™ LAB for foam half time and drainage and a novel biomimetic vein model to measure foam stability. Physician-compounded foams composed of polidocanol and room air, CO2, or mixtures of oxygen and carbon dioxide (O2:CO2) were generated by different methods. Results Polidocanol endovenous microfoam was found to have a narrow bubble size distribution with no large (>500 µm) bubbles. Physician-compounded foams made with the Tessari method had broader bubble size distribution and large bubbles, which have an impact on foam stability. Polidocanol endovenous microfoam had a lower degradation rate than any physician-compounded foams, including foams made using room air (p 2 foams were the least stable and different O2:CO2 mixtures had intermediate performance. In the biomimetic vein model, polidocanol endovenous microfoam had the slowest degradation rate and longest calculated dwell time, which represents the length of time the foam is in contact with the vein, almost twice that of physician-compounded foams using room air and eight times better than physician-compounded foams prepared using equivalent gas mixes. Conclusion Bubble size, bubble size distribution and stability of various sclerosing foam formulations show that polidocanol endovenous microfoam results in better overall performance compared with physician-compounded foams. Polidocanol endovenous microfoam offers better stability and cohesive properties in a biomimetic vein model compared to physician-compounded foams. Polidocanol endovenous microfoam, which is indicated in the United States for treatment of great saphenous vein system incompetence, provides clinicians with a consistent product with enhanced handling properties.

We describe a cost-effective and simple method to fabricate PDMS-based microfluidic devices by combining micromilling with replica moulding technology. It relies on the following steps: (i) microchannels are milled in a block of acrylic; (ii) low-cost epoxy adhesive resin is poured over the milled acrylic block and allowed to cure; (iii) the solidified resin layer is peeled off the acrylic block and used as a mould for transferring the microchannel architecture onto a PDMS layer; finally (iv) the PDMS layer is plasma bonded to a glass surface. With this method, microscale architectures can be fabricated without the need for advanced technological equipment or laborious and time-consuming intermediate procedures. In this manuscript, we describe and validate the microfabrication procedure, and we illustrate its applicability to emulsion and microbubble production. Electronic supplementary material The online version of this article (doi:10.1007/s10544-015-0027-x) contains supplementary material, which is available to authorized users.

We report the development of a microfluidic-based process for the production of polymeric micelles (PMs) in continuous-flow microreactors where Pluronic® tri-block copolymer is used as model polymeric biomaterial relating to drug delivery applications. A flow focusing configuration is used enabling a controllable, and fast mixing process to assist the formation of polymeric micelles through nanoprecipitation which is triggered by a solvent exchange process when organic solutions of the polymer mixed with a non-solvent. We experientially investigate the effect of polymer concentration, flow rate ratio and microreactor dimension on the PMs size characteristics. The mixing process within the microfluidic reactors is further analyzed by computational modeling in order to understand the hydrodynamic process and its implication for the polymeric micelles formation process. The results obtained show that besides the effect of the flow rate ratio, the chemical environment in which the aggregation takes place plays an important role in determining the dimensional characteristics of the produced polymeric micelles. It is demonstrated that microfluidic reactors provide a useful platform for the continuous-flow production of polymeric micelles with improved controllability, reproducibility, and homogeneity of the size characteristics.

Acoustically-responsive microbubbles have been widely researched as agents for both diagnostic and therapeutic applications of ultrasound. Recently, there has also been considerable interest in magnetically functionalised microbubbles as multi-modality imaging agents and carriers for magnetically targeted drug delivery. The latter application in particular requires simultaneous application of magnetic and acoustic fields to a target region. This can present a significant practical challenge, especially in vivo where access is typically limited. In this paper, we present a design for an integrated device capable of generating co-aligned magnetic and acoustic fields in order to accumulate microbubbles at a specific location and then to activate them acoustically. For the purposes of this proof of concept study, the magnetic component of the device was designed to concentrate microbubbles at a distance of 10 mm from the probe’s surface, commensurate with relevant tissue depths in preclinical small animal models. The ultrasound transducer was designed to maximise the acoustic intensity in the same region in order to induce cavitation of the magnetically captured microbubbles. Previous studies have indicated that both microbubble concentration and duration of cavitation activity are positively correlated with therapeutic effect. The ability of the device to trap and activate microbubbles was therefore assessed by a series of in vitro tests in a tissue mimicking phantom containing a single vessel of 1.2 mm diameter. At a flow rate of 4.2 mm/s magnetic trapping produced an increase in intensity under B-mode ultrasound imaging consistent with the predicted accumulation profile. When the microbubbles were exposed to the ultrasound field from the probe, the resulting cavitation activity was sustained for a period more than 4 times longer than that achieved with an identical acoustic field but in the absence of a magnet. The feasibility of developing a larger scale device for human applications is discussed.

A two-pool simulator of fluid and mass transfer among patient body compartments during hemodialysis (HD) was developed to characterize commercial dialyzers taking into account dynamic mass transfer effects.

A key challenge in the development of magnetic drug targeting (MDT) as a clinically relevant technique is designing systems that can apply sufficient magnetic force to actuate magnetic drug carriers at useful tissue depths. In this study an optimisation routine was developed to generate designs of Halbach arrays consisting of multiple layers of high grade, cubic, permanent magnet elements, configured to deliver the maximum pull or push force at a position of interest between 5 and 50 mm from the array, resulting in arrays capable of delivering useful magnetic forces to depths past 20 mm. The optimisation routine utilises a numerical model of the magnetic field and force generated by an arbitrary configuration of magnetic elements. Simulated field and force profiles of optimised arrays were evaluated, also taking into account the forces required for assembling the array in practice. The resultant selection for the array, consisting of two layers, was then constructed and characterised to verify the simulations. Finally the array was utilised in a set of in vitro experiments to demonstrate its capacity to separate and retain microbubbles loaded with magnetic nanoparticles against a constant flow. The optimised designs are presented as light-weight, inexpensive options for applying high-gradient, external magnetic fields in MDT applications.

We have recently reported on the development of a biomimetic vein model to measure the performance of sclerosing foams. In this study we employed the model to compare the commercially-available Varithena® (polidocanol injectable foam) 1 % varicose vein treatment (referred to as polidocanol endovenous microfoam, or PEM) with physician compounded foams (PCFs) made using different foam generation methods (Double Syringe System and Tessari methods) and different foam formulations [liquid to gas ratios of 1:3 or 1:7; gas mixtures composed of 100 % CO2, various CO2:O2 mixtures and room air (RA)]. PCFs produced using the DSS method had longer dwell times (DTs) (range 0.54–2.21 s/cm in the 4 mm diameter vein model) than those of the corresponding PCFs produced by the Tessari technique (range 0.29–0.94 s/cm). PEM had the longest DT indicating the best cohesive stability of any of the foams produced (2.92 s/cm). Other biomimetic model variables investigated included effect of vessel size, delayed injection and rate of plug formation (injection speed). When comparing the 4 and 10 mm vessel diameters, the DTs seen in the 10 mm vessel were higher than those observed for the 4 mm vessel, as the vein angle had been reduced to 5° to allow for foam plug formation. PCF foam performance was in the order RA > CO2:O2 (35:65) ≅ CO2:O2 (65:35) > CO2; PEM had a longer DT than all PCFs (22.10 s/cm) except that for RA made by DSS which was similar but more variable. The effect of delayed injection was also investigated and the DT for PEM remained the longest of all foams with the lowest percentage deviation with respect to the mean values, indicating a consistent foam performance. When considering rate of plug formation, PEM consistently produced the longest DTs and this was possible even at low plug expansion rates (mean 29.5 mm/s, minimum 20.9 mm/s). The developed vein model has therefore demonstrated that PEM consistently displays higher foam stability and cohesiveness when compared to PCFs, over a range of clinically-relevant operational variables. Electronic supplementary material The online version of this article (doi:10.1007/s10856-015-5587-z) contains supplementary material, which is available to authorized users.

Anticancer treatment using embolic drug-eluting beads (DEBs) has shown multifarious advantages compared to systemic chemotherapy. However, there is a growing need for a better understanding of the physical parameters governing drug-elution from embolic devices under physiologically relevant fluidic conditions. In the present study, we investigated the spatiotemporal dynamics of doxorubicin hydrochloride elution from drug-loaded hydrogel embolic beads within a microfluidic device consisting of a network of interconnected microchannels which replicates the architectural properties of microvascular systems. Drug-elution has been investigated experimentally at a single-bead level, using in-house developed microscopy- and spectrofluorimetry-based methods. Results demonstrated that the kinetics of drug-elution and the amount of eluted drug strongly depended on the location of the embolic event within the embolised channel (e.g. fractional amount of eluted drug after 3 h was equal to ~ 0.2 and ~ 0.6 for completely-confined and partially-confined bead, respectively). Drug-elution from partially-confined bead showed a counterintuitive dependence on the local Reynolds number (and thus on the mean fluid velocity), as a result of dynamic changes in bead compressibility causing the displacement of the bead from the primary embolic site. Conversely, the kinetics of drug-elution from fully-confined bead was less affected by the local Reynolds number and bead displayed faster elution from the surface area exposed to the systemic flow, which was associated with the formation of fluid eddies nearby the bead post embolisation.

We demonstrate an imaging flow cytometer that uses acoustic levitation to assemble cells and other particles into a sheet structure. This technique enables a high resolution, low noise CMOS camera to capture images of thousands of cells with each frame. While ultrasonic focussing has previously been demonstrated for 1D cytometry systems, extending the technology to a planar, much higher throughput format and integrating imaging is non-trivial, and represents a significant jump forward in capability, leading to diagnostic possibilities not achievable with current systems. A galvo mirror is used to track the images of the moving cells permitting exposure times of 10 ms at frame rates of 50 fps with motion blur of only a few pixels. At 80 fps, we demonstrate a throughput of 208 000 beads per second. We investigate the factors affecting motion blur and throughput, and demonstrate the system with fluorescent beads, leukaemia cells and a chondrocyte cell line. Cells require more time to reach the acoustic focus than beads, resulting in lower throughputs; however a longer device would remove this constraint.

Ultrasound (US), in combination with microbubbles, has been found to be a potential alternative to viral therapies for transfecting biological cells. The translation of this technique to the clinical environment, however, requires robust and systematic optimization of the acoustic parameters needed to achieve a desired therapeutic effect. Currently, a variety of different devices have been developed to transfect cells in vitro, resulting in a lack of standardized experimental conditions and difficulty in comparing results from different laboratories. To overcome this limitation, we propose an easy-to-fabricate and cost-effective device for application in US-mediated delivery of therapeutic compounds. It comprises a commercially available cell culture dish coupled with a silicon-based "lid" developed in-house that enables the device to be immersed in a water bath for US exposure. Described here are the design of the device, characterization of the sound field and fluid dynamics inside the chamber and an example protocol for a therapeutic delivery experiment.

The flow field and local hydrodynamics of high-velocity water microdrops impacting the interproximal (IP) space of typodont teeth were studied experimentally and computationally. Fourteen-day old Streptococcus mutans biofilms in the IP space were treated by a prototype AirFloss delivering 115 µL of water at a maximum exit-velocity of 60 ms(-1) in a 33-ms burst. Using high-speed imaging, footage was generated showing the details of the burst, and demonstrating the removal mechanism of the biofilms. Footage was also generated to characterize the viscoelastic behavior of the biofilms when impacted by an air-only burst, which was compared to the water burst. Image analysis demonstrated the importance of fluid forces on the removal pattern of interdental biofilms. X-ray micro-Computed Tomography (µ-CT) was used to obtain 3D images of the typodont and the IP spaces. Computational Fluid Dynamics (CFD) simulations were performed to study the effect of changing the nozzle position and design on the hydrodynamics within the IP space. Results confirmed our previous data regarding the wall shear stress generated by high-velocity water drops which dictated the efficacy of biofilm detachment. Finally, we showed how CFD models could be used to optimize water drop or burst design towards a more effective biofilm removal performance.

Echogenic particles, such as microbubbles and volatile liquid micro/nano droplets, have shown considerable potential in a variety of clinical diagnostic and therapeutic applications. The accurate prediction of their response to ultrasound excitation is however extremely challenging, and this has hindered the optimisation of techniques such as quantitative ultrasound imaging and targeted drug delivery. Existing characterisation techniques, such as ultra-high speed microscopy provide important insights, but suffer from a number of limitations; most significantly difficulty in obtaining large data sets suitable for statistical analysis and the need to physically constrain the particles, thereby altering their dynamics. Here a microfluidic system is presented that overcomes these challenges to enable the measurement of single echogenic particle response to ultrasound excitation. A co-axial flow focusing device is used to direct a continuous stream of unconstrained particles through the combined focal region of an ultrasound transducer and a laser. Both the optical and acoustic scatter from individual particles are then simultaneously recorded. Calibration of the device and example results for different types of echogenic particle are presented, demonstrating a high throughput of up to 20 particles per second and the ability to resolve changes in particle radius down to 0.1 μm with an uncertainty of less than 3%.

Ultrasound-based external manipulation of biological bodies in microfluidics has emerged as a contactless way of manipulating cells and particles for a range of applications, including sample enrichment, filtration, and sorting. Furthermore, it has been recently utilized to drive cells to form multi-cellular architectures, including clusters and planar sheets, by appropriately designing the resonant ultrasound field within the acoustofluidic device. In this presentation, we demonstrate the development of ultrasonic bioreactors for generating 3D, scaffold-free tissue constructs. We apply this technology to the generation of neocartilage grafts and examine their potential for repair chondral defects, and to the generation of co-culture models of the mucosal airway. Furthermore, we illustrate how the ultrasonic standing wave field can be designed to generate and modulate different stress regimes on suspended cells, for activating mechanotransductive pathways or for enhancing intracellular delivery of bioacti...

Ultrasound-based external forcing of biological bodies in microfluidics has emerged as a contactless way of manipulating cells and particles for a range of applications, including sample enrichment, filtration, and sorting. Recently, acoustic radiation forces have shown potential for manipulating pathogenic organisms in biological assays. In this presentation, we demonstrate the development of acoustofluidic systems designed for high-throughput manipulation and capturing of biological bodies in applications ranging from medical to environmental diagnosis. Specifically, we apply our acoustofluidic systems to the detection of (i) cancer and immune cells in the early-stage diagnosis of blood malignancies and allergies, and (ii) bacterial microorganisms, spores, and planktonic cells for screening of environmental and industrial samples.

The influence of the impact of a high-velocity water microdrop on the detachment of Streptococcus mutans UA159 biofilms from the interproximal (IP) space of teeth in a training typodont was studied experimentally and computationally. Twelve-day-old S. mutans biofilms in the IP space were exposed to a prototype AirFloss delivering 115 µL water at a maximum exit velocity of 60 m/sec in a 30-msec burst. Using confocal microscopy and image analysis, we obtained quantitative measurements of the percentage removal of biofilms from different locations in the IP space. The 3D geometry of the typodont and the IP spaces was obtained by micro-computed tomography ( µ-CT) imaging. We performed computational fluid dynamics (CFD) simulations to calculate the wall shear stress ( τw) distribution caused by the drops on the tooth surface. A qualitative agreement and a quantitative relationship between experiments and simulations were achieved. The wall shear stress ( τw) generated by the prototype AirFloss and its spatial distribution on the teeth surface played a key role in dictating the efficacy of biofilm removal in the IP space.

Background: In ultrasonic micro-devices, contrast agent micro-bubbles are known to initiate cavitation and streaming local to cells, potentially compromising cell viability. Here we investigate the effects of US alone by omitting contrast agent and monitoring cell viability under moderate-to-extreme ultrasound-related stimuli.Results: Suspended H9c2 cardiac myoblasts were exposed to ultrasonic fields within a glass micro-capillary and their viability monitored under different US-related stimuli. An optimal injection flow rate of 2.6 mL/h was identified in which, high viability was maintained (~95%) and no mechanical stress towards cells was evident. This flow rate also allowed sufficient exposure of cells to US in order to induce bioeffects (~5 sec), whilst providing economical sample collection and processing times. Although the transducer temperature increased from ambient 23 [degree sign]C to 54[degree sign]C at the maximum experimental voltage (29 Vpp), computational fluid dynamic simulations and controls (absence of US) revealed that the cell medium temperature did not exceed 34[degree sign]C in the pressure nodal plane. Cells exposed to US amplitudes ranging from 0--29 Vpp, at a fixed frequency sweep period (tsw = 0.05 sec), revealed that viability was minimally affected up to ~15 Vpp. There was a ~17% reduction in viability at 21 Vpp, corresponding to the onset of Rayleigh-like streaming and a ~60% reduction at 29 Vpp, corresponding to increased streaming velocity or the potential onset of cavitation. At a fixed amplitude (29 Vpp) but with varying frequency sweep period (tsw = 0.02-0.50 sec), cell viability remained relatively constant at tsw >= 0.08 sec, whilst viability reduced at tsw < 0.08 sec and minimum viability recorded at tsw = 0.05 sec.Conclusion: The absence of CA has enabled us to investigate the effect of US alone on cell viability. Moderate-to-extreme US-related stimuli of cells have allowed us to discriminate between stimuli that maintain high viability and stimuli that significantly reduce cell viability. Results from this study may be of potential interest to researchers in the field of US-induced intracellular drug delivery and ultrasonic manipulation of biological cells.

Dynamic nature of particle motion in blood flow is an important determinant of embolization based cancer therapy. Yet, the manner in which the presence of high volume fraction of red blood cells influences the particle dynamics remains unknown. Here, by investigating the motions of embolic microspheres in pressure-driven flows of red blood cell suspensions through capillaries, we illustrate unique oscillatory trends in particle trajectories, which are not observable in Newtonian fluid flows. Our investigation reveals that such oscillatory behavior essentially manifests when three simultaneous conditions, namely, the Reynolds number beyond a threshold limit, degree of confinement beyond a critical limit, and high hematocrit level, are fulfilled simultaneously. Given that these conditions are extremely relevant to fluid dynamics of blood or polymer flow, the observations reported here bear significant implications on embolization based cancer treatment as well as for complex multiphase fluidics involving particles.

For effective cancer therapy, therapeutic agents must extravasate from the blood stream into the tumour mass, then overcome the elevated intratumoural pressure and dense extracellular matrix to reach each and every cancer cell. Several recent studies have suggested that inertial cavitation in the absence or presence of artificial cavitation nuclei can significantly enhance the delivery, penetration, and distribution of small-molecule or nanoparticulate therapeutic agents into tumors. We first present a comparison of the reported enhancements in delivery achieved for a range of frequencies and therapeutic sizes without or with pre-seeding of cavitation, with particular emphasis on the potential role of cavitation persistence and spatial distribution. With microstreaming hypothesized to be the dominant transport mechanism for drug delivery, the likely benefit of using sub-micron cavitation nucleation agents capable of extravasating alongside the therapeutic, rather than microbubbles confined to the blood po...

The biophysical mechanisms that underpin the interaction between microbubbles and cells in the context of ultrasound-mediated drug delivery are still poorly understood. To aid the identification of these mechanisms, giant unilamellar vesicles (GUVs) were used as cell models to quantify changes in membrane properties as a result of the interaction with ultrasound (1 MHz, 150 kPa, and 60 s continuous wave) and phospholipid-shelled microbubbles (DSPC-PEG40S 9:1 molar ratio), either alone or in combination. The spatial quantification of the vesicle lipid order was performed via spectral microscope imaging, by measuring the contours of generalized polarisation (GP) from the emission spectrum of c-Laurdan, a polarity-sensitive dye. Preliminary data show synergistic mechanical and chemical effects on membranes: ultrasound exposure and shear flow alone generally decrease the vesicle lipid packing, while exposures involving microbubbles reveal contrasting effects depending on the initial vesicle composition and ac...

The response of microbubbles to a given sound field is determined by their size and coating. These, in turn, depend on their chemical formulation and the production technique. Sonication is the most commonly employed method and can generate high concentrations of microbubbles rapidly but with a broad size distribution and poor reproducibility. Microfluidic devices provide excellent control over size, but the small-scale architectures required are often challenging to manufacture, offer low production rates, and are prone to clogging. Microbubbles may also have inferior surface characteristics and stability compared to those produced by sonication. In this study we investigate a hybrid technique in which monodisperse microbubbles of ~200μm diameter are produced at high flow rates in a simple T-junction and then undergo controlled fragmentation by exposure to ultrasound via an integrated transducer operating between 71-73kHz. Microbubbles were prepared using the device or a standard sonication protocol and ...

A novel analysis system for the quantification of sclerosing foam properties under clinically relevant conditions was developed with the purpose of establishing a robust methodology for comparative characterisation of different foam formulations and production strategies. The developed biomimetic-inspired model comprised of 4 or 10 mm inner diameter polytetrafluoroethylene tubing, filled with a blood substitute and fixed to a platform with an adjustable inclination angle. Sclerosing foams were produced by mixing polidocanol with either atmospheric air or 100 % CO2, using a double-syringe system method. Individual foams were injected into the tube, while videos were captured simultaneously. Videos were then transferred to an in-house computational foam analysis system (CFAS) which performed a sequence of semi-automated operations, allowing quantitative characterisation of sclerosing foam dynamic behaviour. Using CFAS, degradation rates of different foams were measured and the effect of gas composition, liquid sclerosant concentration and time delay between foam production and injection were evaluated.

Microreactors have been shown to be a powerful tool for the production of nanoparticles (NPs); however, there is still a lack of understanding of the role that the microfluidic environment plays in directing the nanoprecipitation process. Here we investigate the mechanism of nanoprecipitation of block copolymer stabilized organic NPs using a microfluidic-based reactor in combination with computational fluid dynamics (CFD) modelling of the microfluidic implementation. The latter also accounts for the complex interplay between molecular and hydrodynamic phenomena during the nanoprecipitation process, in order to understand the hydrodynamics and its influence on the NP formation process. It is demonstrated that the competitive reactions result in the formation of two types of NPs, i.e., either with or without loading organic actives. The obtained results are interpreted by taking into consideration a new parameter representing the mismatching between the aggregations of the polymers and actives, which plays a decisive role in determining the size and polydispersity of the prepared hybrid NPs. These results expand the current understanding of the co-nanoprecipitation mechanism of active and block copolymer stabilizer, and on the role exerted by the microfluidic environment, giving information that could be translated to the emerging fields of microfluidic formation of NPs and nanomedicine.

Sonoporation is a useful biophysical mechanism for facilitating the transmembrane delivery of therapeutic agents from the extracellular to the intracellular milieu. Conventionally, sonoporation is carried out in the presence of ultrasound contrast agents, which are known to greatly enhance transient poration of biological cell membranes. However, in vivo contrast agents have been observed to induce capillary rupture and haemorrhage due to endothelial cell damage and to greatly increase the potential for cell lysis in vitro. Here, we demonstrate sonoporation of cardiac myoblasts in the absence of contrast agent (CA-free sonoporation) using a low-cost ultrasound-microfluidic device. Within this device an ultrasonic standing wave was generated, allowing control over the position of the cells and the strength of the acoustic radiation forces. Real-time single-cell analysis and retrospective post-sonication analysis of insonated cardiac myoblasts showed that CA-free sonoporation induced transmembrane transfer of fluorescent probes (CMFDA and FITC-dextran) and that different mechanisms potentially contribute to membrane poration in the presence of an ultrasonic wave. Additionally, to the best of our knowledge, we have shown for the first time that sonoporation induces increased cell cytotoxicity as a consequence of CA-free ultrasound-facilitated uptake of pharmaceutical agents (doxorubicin, luteolin, and apigenin). The US-microfluidic device designed here provides an in vitro alternative to expensive and controversial in vivo models used for early stage drug discovery, and drug delivery programs and toxicity measurements.

A microfluidic based device has been developed for the characterisation of embolisation behaviour with polyvinyl alcohol (PVA) hydrogel beads within a microchannel network with bifurcations which mimic the blood vessel network. Both distal and proximal embolisations were achieved within the PMMA-made microdevice exhibiting comparable embolisation characteristics with those observed in vivo. Results showed that small beads allowed more distal embolisations with a reduced control of the spatial location of occlusion sites. In contrast, large beads generated effective proximal embolisations with an improved reproducibility of embolisation performance. Embolic bead hydrodynamics, partitioning at bifurcations, penetration through microchannels and embolisation locations across the channel network were characterised by quantifying the effects of embolic bead size, bead concentration, channel geometry and fluidic conditions. This development provided further insights into the physical principles governing embolisation performances within the constructed microdevices allowing the improvement of the predictability and controllability of the clinical process outcomes. Furthermore, it can potentially provide a useful platform for preclinical research as an alternative to animal models, with an ultimate goal to reduce the amount of animal testing.

This study outlines the relationship between polymer concentration, flow rate ratio and microreactor dimension and the size of polymeric micelles produced in continuous flow microreactors. The general production strategy is based on a nanoprecipitation process within the microfluidic environment which improves control, reproducibility, and homogeneity of the size of the produced polymeric micelles.

Ultrasound and microbubbles have been widely demonstrated to accelerate the breakdown of blood clots, but the mechanisms of treatment require further investigation. In particular, there is a need to clarify the effect on the fibrin matrix—the insoluble polymer mesh that determines a clot’s integrity and mechanical properties. The objective of this in vitro study was to observe in real-time the mechanisms of microbubble-enhanced sonothrombolysis at the microscale. Fluorescently labeled porcine plasma clots were prepared on a glass coverslip and exposed to different types of microbubbles with or without the fibrinolytic agent recombinant tissue plasminogen activator. A 1 mm thick piezoelectric element was coupled with the glass substrate and driven at the resonant frequency of the system (1.9 MHz), with a duty cycle of 5% and a 0.1 Hz pulse repetition frequency. The acoustic field within the clot was characterized using a fiber optic hydrophone. Changes in the fiber network were monitored for 30 min by confocal microscopy.

Double-J stenting is the most common clinical method employed to restore the upper urinary tract drainage, in the presence of a ureteric obstruction. After implant, stents provide an immediate pain relief by decreasing the pressure in the renal pelvis (P). However, their long-term usage can cause infections and encrustations, due to bacterial colonization and crystal deposition on the stent surface, respectively. The performance of double-J stents - and in general of all ureteric stents - is thought to depend significantly on urine flow field within the stented ureter. However very little fundamental research about the role played by fluid dynamic parameters on stent functionality has been conducted so far. These parameters are often difficult to assess in-vivo, requiring the implementation of laborious and expensive experimental protocols. The aim of the present work was therefore to develop an artificial model of the ureter (i.e. ureter model, UM) to mimic the fluid dynamic environment in a stented ureter. The UM was designed to reflect the geometry of pig ureters, and to investigate the values of fluid dynamic viscosity (mu), volumetric flow rate (Q) and severity of ureteric obstruction (OB%) which may cause critical pressures in the renal pelvis. The distributed obstruction derived by the sole stent insertion was also quantified. In addition, flow visualisation experiments and computational simulations were performed in order to further characterise the flow field in the UM. Unique characteristics of the flow dynamics in the obstructed and stented ureter have been revealed with using the developed UM.

In the current study, we have developed and fabricated a novel lab-on-a-chip device for the investigation of biofilm responses, such as attachment kinetics and initial biofilm formation, to different hydrodynamic conditions. The microfluidic flow channels are designed using computational fluid dynamic simulations so as to have a pre-defined, homogeneous wall shear stress in the channels, ranging from 0.03 to 4.30 Pa, which are relevant to in-service conditions on a ship hull, as well as other man-made marine platforms. Temporal variations of biofilm formation in the microfluidic device were assessed using time-lapse microscopy, nucleic acid staining, and confocal laser scanning microscopy (CLSM). Differences in attachment kinetics were observed with increasing shear stress, i.e., with increasing shear stress there appeared to be a delay in bacterial attachment, i.e., at 55, 120, 150, and 155 min for 0.03, 0.60, 2.15, and 4.30 Pa, respectively. CLSM confirmed marked variations in colony architecture, i.e.,: (i) lower shear stresses resulted in biofilms with distinctive morphologies mainly characterised by mushroom-like structures, interstitial channels, and internal voids, and (ii) for the higher shear stresses compact clusters with large interspaces between them were formed. The key advantage of the developed microfluidic device is the combination of three architectural features in one device, i.e., an open-system design, channel replication, and multiple fully developed shear stresses.