Particle separation using ultrasound can radically reduce embolic load to brain after cardiac surgery

Application of therapeutic ultrasonic waves across the dialyzer membrane: A pilot study on the impact on dialyzer clearance and safety

INTRODUCTION

Progressive clogging of the dialyzer membrane during hemodialysis can compromise solute removal efficiency. Existing solutions fall short in addressing intradialytic reduction of dialyzer clearance. This pilot study aims to assess the impact and safety of applying therapeutic ultrasonic waves to dialyzers for mitigating intradialytic clogging.

METHODS

In this pilot study, 15 stable maintenance hemodialysis patients (12 males and 3 females) were enrolled. Each patient served as their own control. They underwent one session of hemodialysis with the application of therapeutic ultrasonic waves (Ultrasonic session) and were crossed-over to a second session without the use of ultrasonic waves (Control session). All the study sessions operated at a fixed dialysate flow rate of 500 mL/min and a blood flow rate of 250 or 300 mL/min. The adequacy of dialysis achieved during each session was monitored using Online Clearance Monitoring of the dialysis machines, and clearance K values, varying between 135 and 209 mL/min, were recorded, and plotted. A direct comparison between Control and Ultrasonic sessions was performed to assess the impact and safety of using ultrasonic waves during hemodialysis.

FINDINGS

The mean percentage decline in dialyzer clearance values was 4.41% for Ultrasonic sessions (SD: 5.3) and 12.69% for Control sessions (SD: 6.35) (p-value <0.001). This indicates that the application of ultrasonic waves reduced the decline in clearance values. The mean differences of the blood component parameters were comparable between both Ultrasonic sessions and Control sessions, suggesting the safety of utilizing ultrasonic waves during dialysis. Microscopic membrane analysis corroborated the safety.

DISCUSSION

Intradialytic clogging of dialyzer membranes is a significant problem that can cause dialysis inadequacy. Our study tackles this issue by introducing therapeutic ultrasonic waves to improve dialyzer clearance during hemodialysis sessions in patients.

Exploring operational boundaries for acoustic concentration of cell suspensions

The development of a standardized, generic method for concentrating suspensions in continuous flow is challenging. In this study, we developed and tested a device capable of concentrating suspensions with an already high cell concentration to meet diverse industrial requirements. To address typical multitasking needs, we concentrated suspensions with high solid content under a variety of conditions. Cells from Saccharomyces cerevisiae, Escherichia coli, and Chinese hamster ovary cells were effectively focused in the center of the main channel of a microfluidic device using acoustophoresis. The main channel bifurcates into three outlets, allowing cells to exit through the central outlet, while the liquid evenly exits through all outlets. Consequently, the treatment separates cells from two-thirds of the surrounding liquid. We investigated the complex interactions between parameters. Increasing the channel depth results in a decrease in process efficiency, attributed to a decline in acoustic energy density. The study also revealed that different cell strains exhibit distinct acoustic contrast factors, originating from differences in dimensions, compressibility, and density values. Finally, a combination of high solid content and flow rate leads to an increase in diffusion through a phenomenon known as shear-induced diffusion. KEY POINTS: • Acoustic focusing in a microchannel was used to concentrate cell suspensions • The parameters influencing focusing at high concentrations were studied • Three different cell strains were successfully concentrated.

Biomolecular actuators for genetically selective acoustic manipulation of cells

The ability to physically manipulate specific cells is critical for the fields of biomedicine, synthetic biology, and living materials. Ultrasound has the ability to manipulate cells with high spatiotemporal precision via acoustic radiation force (ARF). However, because most cells have similar acoustic properties, this capability is disconnected from cellular genetic programs. Here, we show that gas vesicles (GVs)-a unique class of gas-filled protein nanostructures-can serve as genetically encodable actuators for selective acoustic manipulation. Because of their lower density and higher compressibility relative to water, GVs experience strong ARF with opposite polarity to most other materials. When expressed inside cells, GVs invert the cells' acoustic contrast and amplify the magnitude of their ARF, allowing the cells to be selectively manipulated with sound waves based on their genotype. GVs provide a direct link between gene expression and acoustomechanical actuation, opening a paradigm for selective cellular control in a broad range of contexts.

Effect of microchannel protrusion on the bulk acoustic wave-induced acoustofluidics: numerical investigation

Acoustofluidics inside the microchannel has already found its wide applications recently. Acoustic streaming and radiation force are two underlying mechanisms that determine the trajectory of microparticles and cells in the manipulation. Critical particle size of viscous effects is found to be about 1.6 µm in the conventional rectangular microchannel (W × H = 380 m × 160 m) at the frequency of 2 MHz, below which the acoustic streaming dominants, and is independent of the driving voltage. In order to effectively adjust such a critical size, a approach is proposed and evaluated numerically to enhance the acoustic streaming by adding some protrusions (i.e., in the shape of a wedge, rod, half-ellipse) to the middle of the top or bottom wall. It is found that the resonant frequency and acoustic pressure will decrease and the acoustic streaming velocity will increase significantly, respectively, with the increase of protrusion height (up to 30 µm while keeping the width the same as 8 µm). Subsequently, trajectory motion patterns of microparticles have apparent changes in comparison to those inside the rectangular microchannel, and acoustic streaming can even dominate the motion of large microparticles (i.e., 10 µm). As a result, the critical particle size could be increased up to 72.5 µm. Furthermore, different protrusion shapes (i.e., wedge, rod, half-ellipse) on the top wall were compared. The sharpness of protrusion at its tip seems to determine the acoustic streaming velocity. The wedge attached to the bottom wall had higher resonant frequency and lower acoustic streaming velocity compared with the top wedge in the same dimension. The patterns of acoustic streaming and microparticle trajectory motion in the microchannel with dual wedges on the top and bottom walls are not the superposition of those of the top and bottom wedge individually. In summary, the geometry of the microchannel has a significant effect on the induced acoustofluidics by the bulk acoustic waves. A much larger acoustic streaming velocity is produced at the tip of the protrusion to change the critical size of microparticles between acoustic streaming and radiation force. It suggests that more applications of acoustofluidics (i.e., mixing and sonoporation) to microparticles and cells in various sizes are feasible by designing an appropriate geometry of the microchannel.

Scalable high-throughput acoustophoresis in arrayed plastic microchannels

Microfluidic acoustophoresis is a label-free technique that isolates a purified product from a complex mixture of cells. This technique is well-studied but thus far has lacked the throughput and device manufacturability needed for many medical and industrial uses. Scale-up of acoustofluidic devices can be more challenging than in other microfluidic systems because the channel walls are integral to the resonant behavior and coupling to neighboring channels can inhibit performance. Additionally, the increased device area needed for parallel channels becomes less practical in the silicon or glass materials usually used for acoustofluidic devices. Here, we report an acoustic separator with 12 parallel channels made entirely from polystyrene that achieves blood cell separation at a flow rate greater than 1 ml/min. We discuss the design and optimization of the device and the electrical drive parameters and compare the separation performance using channels of two different designs. To demonstrate the utility of the device, we test its ability to purify lymphocytes from apheresis product, a process that is critical to new immunotherapies used to treat blood cancers. We process a leukapheresis sample with a volume greater than 100 ml in less than 2 h in a single pass without interruption, achieving greater than 90% purity of lymphocytes, without any prepurification steps. These advances suggest that acoustophoresis could in the future aid in cell therapy bioprocessing and that further scale-up is possible.

The use of RemoweLL oxygenator-integrated device in the prevention of the complications related to aortic valve surgery in the elderly patient: Preliminary results

Background The effects of fat microembolization due to cardiopulmonary bypass are well known in cardiac surgery. Our aim is to evaluate the use of the RemoweLL device (Eurosets, Medolla, Italy) during elective aortic valve replacement in elderly patients (>70 years old) to rate its biochemical and clinical effects. The RemoweLL device is an oxygenator-integrated reservoir which combines two strategies for fat emboli and leucocytes removal: filtration and supernatant elimination. Methods Forty-four elderly patients were enrolled and assigned randomly to a Group A (standard device) and a Group B (RemoweLL). Biochemical effects were evaluated by blood samples, which were tested for white blood cells, neutrophils, protein SP-100 and interleukin 6 besides standard lab tests. Our clinical endpoints were any type of neurological, cardiac, respiratory, gastrointestinal or renal complications, and length of stay in the intensive care unit. Statistical analysis was carried out with chi square test for non-parametric data; t test and analysis of variance for repeated measures were used for parametric data. Results Group B showed lower levels of white blood cells, neutrophils, interleukin 6 and protein SP-100 immediately and 24 hours after the operation. Group B also showed a lower amount of neurocognitive type II dysfunction even if the length of stay in the ICU did not change. Conclusions The RemoweLL system is safe and effective in reducing inflammatory response to cardiopulmonary bypass and it could be a useful tool in minimizing negative effects of cardiopulmonary bypass; however, it does not seem to have any effect on elderly patients' hospital stay.

A Novel Macroscale Acoustic Device for Blood Filtration

Retransfusion of a patient's own shed blood during cardiac surgery is attractive since it reduces the need for allogeneic transfusion, minimizes cost, and decreases transfusion related morbidity. Evidence suggests that lipid micro-emboli associated with the retransfusion of the shed blood are the predominant causes of the neurocognitive disorders. We have developed a novel acoustophoretic filtration system that can remove lipids from blood at clinically relevant flow rates. Unlike other acoustophoretic separation systems, this ultrasound technology works at the macroscale, and is therefore able to process larger flow rates than typical micro-electromechanical system (MEMS) scale acoustophoretic separation devices. In this work, we have first demonstrated the systematic design of the acoustic device and its optimization, followed by examining the feasibility of the device to filter lipids from the system. Then, we demonstrate the effects of the acoustic waves on the shed blood; examining hemolysis using both haptoglobin formation and lactate dehydrogenase release, as well as the potential of platelet aggregation or inflammatory cascade activation. Finally, in a porcine surgical model, we determined the potential viability of acoustic trapping as a blood filtration technology, as the animal responded to redelivered blood by increasing both systemic and mean arterial blood pressure.

MicroBubble activated acoustic cell sorting

Acoustophoresis, the ability to acoustically manipulate particles and cells inside a microfluidic channel, is a critical enabling technology for cell-sorting applications. However, one of the major impediments for routine use of acoustophoresis at clinical laboratory has been the reliance on the inherent physical properties of cells for separation. Here, we present a microfluidic-based microBubble-Activated Acoustic Cell Sorting (BAACS) method that rely on the specific binding of target cells to microbubbles conjugated with specific antibodies on their surface for continuous cell separation using ultrasonic standing wave. In acoustophoresis, cells being positive acoustic contrast particles migrate to pressure nodes. On the contrary, air-filled polymer-shelled microbubbles being strong negative acoustic contrast particles migrate to pressure antinodes and can be used to selectively migrate target cells. As a proof of principle, we demonstrate the separation of cancer cell line in a suspension with better than 75% efficiency. Moreover, 100% of the microbubble-cell conjugates migrated to the anti-node. Hence a better upstream affinity-capture has the potential to provide higher sorting efficiency. The BAACS technique expands the acoustic cell manipulation possibilities and offers cell-sorting solutions suited for applications at point of care.

Safety of acoustic separation in plastic devices for extracorporeal blood processing

BACKGROUND

Acoustic cell separation uses ultrasound waves to separate cells from plasma to perform plasmapheresis. Although the fundamental process has been studied for decades, no acoustic cell separation has been studied in a disposable plastic format suitable for clinical applications.

STUDY DESIGN AND METHODS

We developed a disposable, rectangular, polystyrene microchannel acoustic cell-separation system and applied acoustic energy relevant for plasmapheresis. Fresh blood from healthy volunteers was exposed in vitro to acoustic energy in an open microfluidic circuit with and without ultrasound applied. Blood was tested for perturbations in red blood cells, platelets, and coagulation using clinical assays.

RESULTS

Red blood cell and platelet size parameters as well as coagulation activation all were within 3% of baseline values. P-selectin expression on platelets increased by an average of 10.9% relative to baseline. Hemolysis increased with flow through the microfluidic channel, but percentage hemolysis remained below 0.3%.

CONCLUSION

Blood parameters in a single-pass, microfluidic acoustic cell-separation apparatus remained within normal limits. In vivo animal studies that model continuous separation in a physiologic environment are warranted.

Affinity-Bead-Mediated Enrichment of CD8+ Lymphocytes from Peripheral Blood Progenitor Cell Products Using Acoustophoresis

Acoustophoresis is a technique that applies ultrasonic standing wave forces in a microchannel to sort cells depending on their physical properties in relation to the surrounding media. Cell handling and separation for research and clinical applications aims to efficiently separate specific cell populations. Here, we investigated the sorting of CD8 lymphocytes from peripheral blood progenitor cell (PBPC) products by affinity-bead-mediated acoustophoresis. PBPC samples were obtained from healthy donors (n = 4) and patients (n = 18). Mononuclear cells were labeled with anti-CD8-coated magnetic beads and sorted on an acoustophoretic microfluidic device and by standard magnetic cell sorting as a reference method. CD8 lymphocytes were acoustically sorted with a mean purity of 91% ± 8% and a median separation efficiency of 63% (range 15.1%⁻90.5%) as compared to magnetic sorting (purity 91% ± 14%, recovery 29% (range 5.1%⁻47.3%)). The viability as well as the proliferation capacity of sorted lymphocytes in the target fraction were unimpaired and, furthermore, hematopoietic progenitor cell assay revealed a preserved clonogenic capacity post-sorting. Bead-mediated acoustophoresis can, therefore, be utilized to efficiently sort less frequent CD8+ lymphocytes from PBPC products in a continuous flow mode while maintaining cell viability and functional capacity of both target and non-target fractions.

Acoustofluidic harvesting of microalgae on a single chip

We present an on-chip acoustofluidic platform for harvesting a target microalgal species from a heterogeneous population of cells and particles based on their size, density, and compressibility in a rapid, non-invasive, energy-efficient, continuously running, and automated manner. For our proof-of-principle demonstration, we use Euglena gracilis as a target species. Specifically, we show the simultaneous separation and enrichment of E. gracilis from a mixed population of E. gracilis in pond water (consisting of other microalgae and various kinds of particles as contaminants) on a single acoustofluidic chip with a recovery ratio of 92.6%, a target separation ratio of 90.1%, a concentration factor of 3.43, an enrichment factor of 12.76, and a cell viability rate of 98.3% at a high volume rate of 500 μl/min. Our results indicate that the on-chip acoustofluidic platform is an effective tool for harvesting target microalgae from mixed populations of microalgae and other contaminants.

Acoustophoretic removal of proteins from blood components

This work presents the development of a miniaturized system for removing plasma proteins and other low-molecular-weight compounds from red blood cell (RBC) concentrate in a simple one-step-process using integrated ultrasound. The technology utilizes the principles of acoustophoresis to transfer the RBCs from the original plasma-containing solution into a protein-free SAG-M additive solution in a continuous flow process. The preparation of protein free RBC concentrate is important for blood transfusion to patients suffering from immunoglobulin A (IgA)-deficiency and developing antibodies against IgA. We show a nearly complete removal of both albumin and IgA from concentrated RBCs via this one-step-processes in samples obtained from RBC concentrate. The cell recovery of our technology is close to 97%, compared to just above 90% of the current procedure of repeated dilution and centrifugation steps. This work clearly shows the potential of integrated acoustophoresis in a miniaturized system for clinical applications.

Efficient purification of CD4+ lymphocytes from peripheral blood progenitor cell products using affinity bead acoustophoresis

Processing of peripheral blood progenitor cells (PBPC) for clinical transplantation or research applications aims to effectively isolate or deplete specific cell populations, utilizing primarily magnetic or fluorescence activated sorting methods. Here, we investigated the performance of microfluidic acoustophoresis for the separation of lymphocyte subsets from PBPC, and present a novel method for affinity-bead-mediated acoustic separation of cells which can otherwise not be acoustically discriminated. As the acoustic force on a particle depends on particle size, density and compressibility, targeting of cells by affinity specific beads will generate cell-bead complexes that exhibit distinct acoustic properties relative to nontargeted cells and are, thus, possible to isolate. To demonstrate this, PBPC samples (n = 22) were obtained from patients and healthy donors. Following density gradient centrifugation, cells were labeled with anti-CD4-coated magnetic beads (Dynal) and isolated by acoustophoresis and, for comparison, standard magnetic cell sorting technique in parallel. Targeted CD4+ lymphocytes were acoustically isolated with a mean (±SD) purity of 87 ± 12%, compared with 96 ± 3% for control magnetic sorting. Viability of sorted cells was 95 ± 4% (acoustic) and 97 ± 3% (magnetic), respectively. The mean acoustic separation efficiency of CD4+ lymphocytes to the target fraction was 65 ± 22%, compared with a mean CD4+ lymphocyte recovery of 56 ± 15% for magnetic sorting. Functional testing of targeted CD4+ lymphocytes demonstrated unimpaired mitogen-mediated proliferation capacity and cytokine production. Hematopoietic progenitor cell assays revealed a preserved colony forming ability of nontarget cells post sorting. We conclude that the acoustophoresis platform can be utilized to efficiently isolate bead-labeled CD4+ lymphocytes from PBPC samples in a continuous flow format, with preserved functional capacity of both target and nontarget cells. These results open up for simultaneous affinity-bead-mediated separation of multiple cell populations, something which is not possible with current standard magnetic cell separation technology. © 2014 International Society for Advancement of Cytometry.

Microchannel acoustophoresis does not impact survival or function of microglia, leukocytes or tumor cells

BACKGROUND

The use of acoustic forces to manipulate particles or cells at the microfluidic scale (i.e. acoustophoresis), enables non-contact, label-free separation based on intrinsic cell properties such as size, density and compressibility. Acoustophoresis holds great promise as a cell separation technique in several research and clinical areas. However, it has been suggested that the force acting upon cells undergoing acoustophoresis may impact cell viability, proliferation or cell function via subtle phenotypic changes. If this were the case, it would suggest that the acoustophoresis method would be a less useful tool for many cell analysis applications as well as for cell therapy.

METHODS

We investigate, for the first time, several key aspects of cellular changes following acoustophoretic processing. We used two settings of ultrasonic actuation, one that is used for cell sorting (10 Vpp operating voltage) and one that is close to the maximum of what the system can generate (20 Vpp). We used microglial cells and assessed cell viability and proliferation, as well as the inflammatory response that is indicative of more subtle changes in cellular phenotype. Furthermore, we adapted a similar methodology to monitor the response of human prostate cancer cells to acoustophoretic processing. Lastly, we analyzed the respiratory properties of human leukocytes and thrombocytes to explore if acoustophoretic processing has adverse effects.

RESULTS

BV2 microglia were unaltered after acoustophoretic processing as measured by apoptosis and cell turnover assays as well as inflammatory cytokine response up to 48 h following acoustophoresis. Similarly, we found that acoustophoretic processing neither affected the cell viability of prostate cancer cells nor altered their prostate-specific antigen secretion following androgen receptor activation. Finally, human thrombocytes and leukocytes displayed unaltered mitochondrial respiratory function and integrity after acoustophoretic processing.

CONCLUSION

We conclude that microchannel acoustophoresis can be used for effective continuous flow-based cell separation without affecting cell viability, proliferation, mitochondrial respiration or inflammatory status.

Acoustic particle manipulation in a 40 kHz quarter-wavelength standing wave with an air boundary

An implementation of a quarter-wavelength standing wave separator that exploits an air drum to achieve the pressure node is presented and characterized experimentally. The air drum configuration was implemented and tested in a set-up with a 40 kHz transducer immersed in a water tank with the quarter-wavelength gap being approximately 9 mm wide. Injection of suspensions of 5 μm and 45 μm diameter polystyrene particles at flow rates of 30 ml/h and 60 ml/h was studied and particle deflection towards the pressure node at the air drum surface was observed for a range of acoustic pressures. Computational results on single particle trajectories show good agreement with the experimental findings for the 45 μm particles, but not for the 5 μm particles. These were considered to behave as aggregates of higher effective dimension, due to their much higher number density relative to the 45 μm particles in the suspensions used. The set-up developed in this study includes a robust method for achieving a pressure node in a quarter-wavelength system and can represent the first step toward the development of an alternative separator configuration in respect to small channel MHz range operated systems for the manipulation of particles streams.

Acoustofluidics 8: applications of acoustophoresis in continuous flow microsystems

This acoustofluidics tutorial focuses on continuous flow-based half wavelength resonator systems operated in the transversal mode, where the direction of the primary acoustic force acts in plane with the microchip. The transversal actuation mode facilitates integration with up- and downstream microchannel networks as well as visual control of the acoustic focusing experiment. Applications of particle enrichment in an acoustic half wavelength resonator are discussed as well as clarification of the carrier fluid from undesired particles. Binary separation of particle/vesicle/cell mixtures into two subpopulations is outlined based on the different polarities of the acoustic contrast factor. Furthermore, continuous flow separation of different particle/cell types is described where both Free Flow Acoustophoresis (FFA) and binary acoustophoresis are utilized. By capitalizing on the laminar flow regime, acoustophoresis has proven especially successful in performing bead/cell translations between different buffer systems. Likewise, the ability to controllably translate particulate matter across streamlines has opened a route to valving of cells/particles without any moving parts, where event triggered cell sorting is becoming an increasing area of activity. Recent developments now also enable measurements of fundamental cell properties such as density and compressibility by means of acoustophoresis. General aspects on working with live cells in acoustophoresis systems are discussed as well as available means to quantify the outcome of cell and particle separation experiments performed by acoustophoresis.

Acoustofluidics 7: The acoustic radiation force on small particles

In this paper, Part 7 of the thematic tutorial series "Acoustofluidics-exploiting ultrasonic standing waves, forces and acoustic streaming in microfluidic systems for cell and particle manipulation", we present the theory of the acoustic radiation force; a second-order, time-averaged effect responsible for the acoustophoretic motion of suspended, micrometre-sized particles in an ultrasound field.

Sheathless size-based acoustic particle separation

Particle separation is of great interest in many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In this paper, we present a microfluidic platform for sheathless particle separation using standing surface acoustic waves. In this platform, particles are first lined up at the center of the channel without introducing any external sheath flow. The particles are then entered into the second stage where particles are driven towards the off-center pressure nodes for size based separation. The larger particles are exposed to more lateral displacement in the channel due to the acoustic force differences. Consequently, different-size particles are separated into multiple collection outlets. The prominent feature of the present microfluidic platform is that the device does not require the use of the sheath flow for positioning and aligning of particles. Instead, the sheathless flow focusing and separation are integrated within a single microfluidic device and accomplished simultaneously. In this paper, we demonstrated two different particle size-resolution separations; (1) 3 μm and 10 μm and (2) 3 μm and 5 μm. Also, the effects of the input power, the flow rate, and particle concentration on the separation efficiency were investigated. These technologies have potential to impact broadly various areas including the essential microfluidic components for lab-on-a-chip system and integrated biological and biomedical applications.

Lipid emboli distribution in cardiac surgery is dependent on the state of emulsification

OBJECTIVE

Lipid embolizations from retransfused shed blood during cardiac surgery have been shown to enter the circulation and end up in different organs. The purpose of this investigation was to evaluate differences in the kinetics and deposition between emulsified and non-emulsified lipid emboli in a porcine model.

DESIGN

Twelve animals were anesthetized and put on cardiopulmonary bypass. A shed-blood phantom (6 animals given emulsified and 6 given non-emulsified lipids) was produced from arterial blood, saline, and tritium-labeled triolein. The phantom was infused into the cardiopulmonary bypass circuit. Arterial and venous blood samples were taken at short intervals. Tissue samples were taken post-mortem from examined organs and prepared for scintillation counting. Levels of radioactivity were used to measure lipid emboli content in blood and tissue.

RESULTS

Emulsified lipid emboli generated a 5-fold higher embolic load in the arterial and a 12-fold higher in the venous circulation, compared with non-emulsified lipid emboli. Emulsified lipid micro emboli resulted in a 2-15-fold higher tissue deposition in investigated organs compared with non-emulsified lipid micro emboli.

CONCLUSIONS

This study shows that the state of emulsion significantly alter the kinetics and tissue deposition of lipid emboli. Emulsified lipid emboli give higher embolic load in the arterial and venous circulation, and higher tissue deposition versus non-emulsified lipid emboli. In both groups, the embolic load was higher in the arterial circulation than on the venous side.

Emerging clinical applications of microchip-based acoustophoresis

Acoustophoresis is currently in a state of transition from the academic laboratories, moving into the biomedical laboratories and industries. Clear areas of interest are seen in clinical diagnostics and therapeutics, where new approaches to cell handling and purification are emphasized as highly potent areas. This article outlines some of the basic unit operations of acoustophoresis, where applications as cell washing, binary separation, free-flow acoustophoresis, and affinity acoustophoresis are highlighted. The most recent steps to move acoustophoresis into clinical and preclinical applications are also presented.

Comparison between transcranial Doppler and Coulter counter for detection of lipid micro embolization from mediastinal shed blood reinfusion during cardiac surgery

INTRODUCTION

Lipid micro embolization (LME) from re-transfused shed blood has been postulated to be a potential reason for short- and long-term cognitive dysfunction after cardiac surgery. The purpose of this investigation was to evaluate if transcranial Doppler (TCD) has the capacity to detect LME.

METHODS

Thirteen patients undergoing cardiopulmonary bypass surgery were investigated. Each patient's cerebral circulation was monitored with transcranial Doppler during the first two minutes after re-transfusion of shed blood and blood was simultaneously sampled and characterised by a Coulter counter.

RESULTS

Strong correlation was found between embolic loads, as measured by transcranial Doppler and Coulter counter (r=0.79, P<0.005).

CONCLUSIONS

This pilot study shows that non-invasive monitoring by transcranial Doppler could be a potential tool to monitor LME during cardiopulmonary bypass surgery.

Efficient removal of platelets from peripheral blood progenitor cell products using a novel micro-chip based acoustophoretic platform

Background

Excessive collection of platelets is an unwanted side effect in current centrifugation-based peripheral blood progenitor cell (PBPC) apheresis. We investigated a novel microchip-based acoustophoresis technique, utilizing ultrasonic standing wave forces for the removal of platelets from PBPC products. By applying an acoustic standing wave field onto a continuously flowing cell suspension in a micro channel, cells can be separated from the surrounding media depending on their physical properties.

Study Design and Methods

PBPC samples were obtained from patients (n = 15) and healthy donors (n = 6) and sorted on an acoustophoresis-chip. The acoustic force was set to separate leukocytes from platelets into a target fraction and a waste fraction, respectively. The PBPC samples, the target and the waste fractions were analysed for cell recovery, purity and functionality.

Results

The median separation efficiency of leukocytes to the target fraction was 98% whereas platelets were effectively depleted by 89%. PBPC samples and corresponding target fractions were similar in the percentage of CD34+ hematopoetic progenitor/stem cells as well as leukocyte/lymphocyte subset distributions. Median viability was 98%, 98% and 97% in the PBPC samples, the target and the waste fractions, respectively. Results from hematopoietic progenitor cell assays indicated a preserved colony-forming ability post-sorting. Evaluation of platelet activation by P-selectin (CD62P) expression revealed a significant increase of CD62P+ platelets in the target (19%) and waste fractions (20%), respectively, compared to the PBPC input samples (9%). However, activation was lower when compared to stored blood bank platelet concentrates (48%).

Conclusion

Acoustophoresis can be utilized to efficiently deplete PBPC samples of platelets, whilst preserving the target stem/progenitor cell and leukocyte cell populations, cell viability and progenitor cell colony-forming ability. Acoustophoresis is, thus, an interesting technology to improve current cell processing methods.

Newtonian viscous effects in ultrasonic emboli removal from blood

We have modeled the removal of emboli from cardiopulmonary bypass circuits via acoustic radiation force. Unless removed, emboli can result in cognitive deficit for those undergoing heart surgery with the use of extracorporeal circuits. There are a variety of mathematical formulations in the literature describing acoustic radiation force, but a lingering question that remains is how important viscosity of the blood and/or embolus is to the process. We implemented both inviscid and viscous models for acoustic radiation force on a sphere immersed in a fluid. We found that for this specific application, the inviscid model seems to be sufficient for predicting acoustic force upon emboli when compared with the chosen viscous model. Thus, the much simpler inviscid model could be used to optimize experimental techniques for ultrasonic emboli removal.

A label-free cell separation using surface acoustic waves

We present two-stage microfluidic platform for a continuous label-free cell separation using surface acoustic waves. In the proposed platform, cells are first lined up at the center of the channel by using standing surface acoustic waves without introducing any external sheath flow. After focused at the center of the channel, the cells are then entered to the actual cell separation stage where the larger cell are exposed to more lateral displacement in the channel towards the pressure node due to the acoustic force differences. Consequently, different size cells are separated into multiple collection outlets. The focusing and separation of the cells can be accomplished simultaneously in the present two-stage microfluidic device. The device doesn't require the use of the sheath flow for positioning or aligning of cells. In this study, we demonstrated the separation of two different size particle streams (3 μm and 10 μm) with this microfluidic platform without introducing any external sheath flow.

Efficacy of a New Oxygenator-Integrated Fat and Leukocyte Removal Device

We evaluated the effectiveness of a new oxygenator-integrated device for removing lipid particles and leukocytes from shed mediastinal blood in 20 patients undergoing elective cardiac surgery under cardiopulmonary bypass. Another 20 patients undergoing cardiac surgery without the device served as controls. After filtration with the RemoveLL device, lipid particles, leukocytes, and fats were significantly reduced compared to preoperative levels. In the control group, blood fats and lipid particles at the end of cardiopulmonary bypass were significantly increased compared to preoperative levels. Leukocyte counts at the end of bypass were significantly lower in patients who had the filtration device compared to the control group. Platelets counts and hematocrit changes were not significantly different between the 2 groups.

CFD modeling of an ultrasonic separator for the removal of lipid particles from pericardial suction blood

A computational fluid dynamics (CFD) model is presented to simulate the removal of lipid particles from blood using a novel ultrasonic quarter-wavelength separator. The Lagrangian-Eulerian CFD model accounts for conservation of mass and momentum, for the presence of lipid particles of a range of diameters, for the acoustic force as experienced by the particles in the blood, as well as for gravity and other particle-fluid interaction forces. In the separator, the liquid flows radially inward within a fluid chamber formed between a disc-shaped transducer and a disc-shaped reflector. Following separation of the lipid particles, blood exits the separator axially through a central opening on the disc-shaped reflector. Separator diameters studied varied between 12 and 18 cm, and gap sizes between the discs of 600 μm, 800 μm and 1 mm were considered. Results show a strong effect of residence time of the particles within the chamber on the separation performance. Different separator configurations were identified, which could give a lipid removal performance of 95% or higher when processing 62.5 cm (3)/min of blood. The developed model provides a design method for the selection of geometric and operating parameters for the ultrasonic separator.

Acoustic whole blood plasmapheresis chip for prostate specific antigen microarray diagnostics

The generation of high quality plasma from whole blood is of major interest for many biomedical analyses and clinical diagnostic methods. However, it has proven to be a major challenge to make use of microfluidic separation devices to process fluids with high cell content, such as whole blood. Here, we report on an acoustophoresis based separation chip that prepares diagnostic plasma from whole blood linked to a clinical application. This acoustic separator has the capacity to sequentially remove enriched blood cells in multiple steps to yield high quality plasma of low cellular content. The generated plasma fulfills the standard requirements (<6.0 x 10(9) erythrocytes/L) recommended by the Council of Europe. Further, we successfully linked the plasmapheresis microchip to our previously developed porous silicon sandwich antibody microarray chip for prostate specific antigen (PSA) detection. PSA was detected by good linearity (R(2) > 0.99) in the generated plasma via fluorescence readout without any signal amplification at clinically relevant levels (0.19-21.8 ng/mL).

Harmonic microchip acoustophoresis: a route to online raw milk sample precondition in protein and lipid content quality control

A microfluidic approach for raw milk sample preconditioning prior to protein and lipid content analysis has been developed. The system utilizes microchip acoustophoresis and is a further extension of our previously reported multiple node ultrasonic standing wave focusing platform (Grenvall, C., Augustsson, P., Matsuoka, H. and Laurell, T. Proc. Micro Total Anal. Syst. 2008, 1, 161-163). The microfluidic approach offers a method for rapid raw milk quality control using Fourier transform infrared spectroscopy (FT-IR). Two acoustophoresis modes are explored, 2 lambda/2 and 3 lambda/2, offering lipid content enrichment or depletion, respectively. Lipid content depletion above 90% was accomplished. FT-IR data on microchip-processed raw milk samples, enabling direct lipid and protein content analysis, are reported. Most importantly, the harmonic operational modes bypass the problem of lipid aggregation and subsequent clogging, inherent in lambda/2 acoustophoresis systems.

Continuous separation of cells and particles in microfluidic systems

The progress in microfabrication and lab-on-a-chip technologies has been a major area of development for new approaches to bioanalytics and integrated concepts for cell biology. Fundamental advances in the development of elastomer based microfluidics have been driving factors for making microfluidic technology available to a larger scientific community in the past years. In line with this, microfluidic separation of cells and particles is currently developing rapidly where key areas of interest are found in designing lab-on-a-chip systems that offer controlled microenvironments for studies of fundamental cell biology. More recently industrial interests are seen in the development of micro chip based flow cytometry technology both for preclinical research and clinical diagnostics. This critical review outlines the most recent developments in microfluidic technology for cell and particle separation in continuous flow based systems. (130 references).

Acoustic resonances in straight micro channels: beyond the 1D-approximation

Acoustic actuation can be used to perform several tasks in microfluidic systems. In this paper, we investigate an acoustic separator through micro-PIV analysis in stop-flow mode and numerical simulations, and a good agreement between the two is found. Moreover, we demonstrate that it is not sufficient only to characterize devices in flow-through mode, since in these systems much different resonant patterns can result in similarly looking band formations. Furthermore, we conclude that extended 1D approximations of the acoustic radiation force are inadvisable, and instead, a 2D model is preferred. The results presented here provide valuable insight into the nature and functionality of acoustic microdevices, and should be useful in the interpretation and understanding of the same.

Acoustophoresis in wet-etched glass chips

Acoustophoresis in microfluidic structures has primarily been reported in silicon microfabricated devices. This paper demonstrates, for the first time, acoustophoresis performed in isotropically etched glass chips providing a performance that matches that of the corresponding silicon microdevices. The resonance mode characteristics of the glass chip were equal to those of the silicon chip at its fundamental resonance. At higher order resonance modes the glass chip displays resonances at lower frequencies than the silicon chip. The cross-sectional profiles of acoustically focused particle streams are also reported for the first time, displaying particles confined in a vertical band in the channel center for both glass and silicon chips. A particle extraction efficiency of 98% at flow rates up to 200 microL/min (2% particle concentration) is reported for the glass chip at the fundamental resonance. The glass and silicon chips displayed equal particle extraction performance when tested for increasing particle concentrations of 2-15%, at a flow velocity of 12.9 cm/s for the glass chip and 14.8 cm/s for the silicon chip.

Acoustic resonances in microfluidic chips: full-image micro-PIV experiments and numerical simulations

We show that full-image micro-PIV analysis in combination with images of transient particle motion is a powerful tool for experimental studies of acoustic radiation forces and acoustic streaming in microfluidic chambers under piezo-actuation in the MHz range. The measured steady-state motion of both large 5 microm and small 1 microm particles can be understood in terms of the acoustic eigenmodes or standing ultra-sound waves in the given experimental microsystems. This interpretation is supported by numerical solutions of the corresponding acoustic wave equation.

Free Flow Acoustophoresis: Microfluidic-Based Mode of Particle and Cell Separation

A novel method, free flow acoustophoresis (FFA), capable of continuous separation of mixed particle suspensions into multiple outlet fractions is presented. Acoustic forces are utilized to separate particles based on their size and density. The method is shown to be suitable for both biological and nonbiological suspended particles. The microfluidic separation chips were fabricated using conventional microfabrication methods. Particle separation was accomplished by combining laminar flow with the axial acoustic primary radiation force in an ultrasonic standing wave field. Dissimilar suspended particles flowing through the 350-microm-wide channel were thereby laterally translated to different regions of the laminar flow profile, which was split into multiple outlets for continuous fraction collection. Using four outlets, a mixture of 2-, 5-, 8-, and 10-microm polystyrene particles was separated with between 62 and 94% of each particle size ending up in separate fractions. Using three outlets and three particle sizes (3, 7, and 10 microm) the corresponding results ranged between 76 and 96%. It was also proven possible to separate normally acoustically inseparable particle types by manipulating the density of the suspending medium with cesium chloride. The medium manipulation, in combination with FFA, was further used to enable the fractionation of red cells, platelets, and leukocytes. The results show that free flow acoustophoresis can be used to perform complex separation tasks, thereby offering an alternative to expensive and time-consuming methods currently in use.

Chip integrated strategies for acoustic separation and manipulation of cells and particles

Acoustic standing wave technology combined with microtechnology opens up new areas for the development of advanced particle and cell separating microfluidic systems. This tutorial review outlines the fundamental work performed on continuous flow acoustic standing wave separation of particles in macro scale systems. The transition to the microchip format is further surveyed, where both fabrication and design issues are discussed. The acoustic technology offers attractive features, such as reasonable throughput and ability to separate particles in a size domain of about tenths of micrometers to tens of micrometers. Examples of different particle separation modes enabled in microfluidic chips, utilizing standing wave technology, are described along a discussion of several potential applications in life science research and in the medical clinic. Chip integrated acoustic standing wave separation technology is still in its infancy and it can be anticipated that new laboratory standards very well may emerge from the current research.

Particle separation using ultrasound can be used with human shed mediastinal blood

BACKGROUND

Shed mediastinal blood collected by cardiotomy suction has been shown to be a large contributor to lipid microemboli ending up in different organs. The aim of this study was to test the separation efficiency on human shed blood of a new separation method developed to meet this demand.

METHODS

Shed mediastinal blood collected from the pericardial cavity of 13 patients undergoing cardiac surgery with cardiopulmonary bypass was collected. The blood was processed in an eight-channel parallel PARSUS separator, and separation efficiency was determined.

RESULTS

Erythrocyte recovery, in terms of a separation ratio, varied between 68% and 91%. Minor electrolyte changes took place, where levels of sodium increased and levels of potassium and calcium decreased.

CONCLUSION

This study demonstrates that PARSUS technology can be used on human shed mediastinal blood with good separation efficiency. The technology is, thereby, suggested to have future clinical relevance.

Carrier Medium Exchange through Ultrasonic Particle Switching in Microfluidic Channels

This paper describes a method, utilizing acoustic force manipulation of suspended particles, in which particles in a laminar flow microchannel are continuously translated from one medium to another with virtually no mixing of the two media. During the study, 5-microm polyamide spheres suspended in distilled water, spiked (contaminated) with Evans blue, were switched over to clean distilled water. More than 95% of the polyamide spheres could be collected in the clean medium while removing up to 95% of the contaminant. Preliminary experiments to use this method to wash blood were performed. Red blood cells were switched from blood, spiked with Evans blue, to clean blood plasma. At least 95% of the red blood cells (bovine blood) could be collected in clean blood plasma while up to 98% of the contaminant was removed. The obtained results indicate that the presented method can be used as a generic method for particle washing and, more specifically, be applied for both intraoperative and postoperative blood washing.