Viability of yeast cells in well controlled propagating and standing ultrasonic plane waves

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.

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.

Acoustic tweezing of microparticles in microchannels with sinusoidal cross sections

Acoustic tweezing of bioparticles has distinct advantages over other manipulation methods such as electrophoresis or magnetophoresis in biotechnological applications. This manipulation method guarantees the viability of the bio-particles during and after the process. In this paper, the effects of sinusoidal boundaries of a microchannel on acoustophoretic manipulation of microparticles are studied. Our results show that while top and bottom walls are vertically actuated at the horizontal half-wave resonance frequency, a large mono-vortex appears, which is never achievable in a rectangular geometry with flat walls and one-dimensional oscillations. The drag force caused by such a vortex in combination with the tilted acoustic radiation force leads to trapping and micromixing of microparticles with diameters larger and smaller than the critical size, respectively. Simulation results in this paper show that efficient particle trapping occurs at the intermediate sinusoidal boundary amplitudes. It is also indicated that in a square-sinusoidal geometry there are two strong vortices, instead of one vortex. Sub-micrometer particles tend to be trapped dramatically faster in such a geometry than in the rectangular-sinusoidal ones.

Effects of Ultrasound on Fermentation of Glucose to Ethanol by Saccharomyces cerevisiae

Previous studies have shown that pretreatment of corn slurries using ultrasound improves starch release and ethanol yield during biofuel production. However, studies on its effects on the mass transfer of substrates and products during fermentation have shown that it can have both beneficial and inhibitory effects. In this study, the effects of ultrasound on mass transfer limitations during fermentation were examined. Calculation of the external and intraparticle observable moduli under a range of conditions indicate that no external or intraparticle mass transfer limitations should exist for the mass transfer of glucose, ethanol, or carbon dioxide. Fermentations of glucose to ethanol using Saccharomyces cerevisiae were conducted at different ultrasound intensities to examine its effects on glucose uptake, ethanol production, and yeast population and viability. Four treatments were compared: direct ultrasound at intensities of 23 and 32 W/L, indirect ultrasound (1.4 W/L), and no-ultrasound. Direct and indirect ultrasound had negative effects on yeast performance and viability, and reduced the rates of glucose uptake and ethanol production. These results indicate that ultrasound during fermentation, at the levels applied, is inhibitory and not expected to improve mass transfer limitations.

Generation of functional hepatocyte 3D discoids in an acoustofluidic bioreactor

Ultrasonic standing wave systems have previously been used for the generation of 3D constructs for a range of cell types. In the present study, we cultured cells from the human hepatoma Huh7 cell line in a Bulk Acoustic Wave field and studied their viability, their functions, and their response to the anti-cancer drug, 5 Fluorouracil (5FU). We found that cells grown in the acoustofluidic bioreactor (AFB) expressed no reduction in viability up to 6 h of exposure compared to those cultured in a conventional 2D system. In addition, constructs created in the AFB and subsequently cultured outside of it had improved functionality including higher albumin and urea production than 2D or pellet cultures. The viability of Huh7 cells grown in the ultrasound field to 5FU anti-cancer drug was comparable to that of cells cultured in the 2D system, showing rapid diffusion into the aggregate core. We have shown that AFB formed 3D cell constructs have improved functionality over the conventional 2D monolayer and could be a promising model for anti-cancer drug testing.

Surface-Acoustic-Wave (SAW)-Driven Device for Dynamic Cell Cultures

In the last few decades, new types of cell cultures have been introduced to provide better cell survival and development, with micro- and nanoenvironmental physicochemical conditions aimed at mimicking those present in vivo. However, despite the efforts made, the systems available to date are often difficult to replicate and use. Here, an easy-to-use surface-acoustic-wave (SAW)-based platform is presented for realizing dynamic cell cultures that is compatible with standard optical microscopes, incubators, and cell-culture dishes. The SAW chip is coupled to a standard Petri dish via a polydimethylsiloxane (PDMS) disc and consists of a lithium niobate (LN) substrate on which gold interdigital transducers (IDTs) are patterned to generate the SAWs and induce acoustic streaming in the dish. SAW excitation is verified and characterized by laser Doppler vibrometry, and the fluid dynamics is studied by microparticle image velocimetry (μPIV). Heating is measured by an infrared (IR) thermal camera. We finally tested this device with the U-937 monocyte cell line for viability and proliferation and cell-morphological analysis. The data demonstrate that it is possible to induce significant fluid recirculation within the Petri dish while maintaining negligible heating. Remarkably, cell proliferation in this condition was enhanced by 36 ± 12% with respect to those of standard static cultures. Finally, we show that cell death does not increase and that cell morphology is not altered in the presence of SAWs. This device is the first demonstration that SAW-induced streaming can mechanically improve cell proliferation and further supports the great versatility and biocompatibility of the SAW technology for cell manipulation.

Integrated phenotypic-genotypic approach to understand the influence of ultrasound on metabolic response of Lactobacillus sakei

The lethal effects of soundwaves on a range of microorganisms have been known for almost a century whereas, the use of ultrasound to promote or control their activity is much more recent. Moreover, the fundamental molecular mechanism influencing the behaviour of microorganisms subjected to ultrasonic waves is not well established. In this study, we investigated the influence of ultrasonic frequencies of 20, 45, 130 and 950 kHz on growth kinetics of Lactobacillus sakei. A significant increase in the growth rate of L. sakei was observed following ultrasound treatment at 20 kHz despite the treatment yielding a significant reduction of ca. 3 log cfu/mL in cells count. Scanning electron microscopy showed that ultrasound caused significant changes on the cell surface of L. sakei culture with the formation of pores "sonoporation". Phenotypic microarrays showed that all ultrasound treated L. sakei after exposure to various carbon, nitrogen, phosphorus and sulphur sources had significant variations in nutrient utilisation. Integration of this phenotypic data with the genome of L. sakei revealed that various metabolic pathways were being influenced by the ultrasound treatments. Results presented in this study showed that the physiological response of L. sakei in response to US is frequency dependent and that it can influence metabolic pathways. Hence, ultrasound treatments can be employed to modulate microbial activity for specialised applications.

Advances in Mid-Infrared Spectroscopy for Chemical Analysis

Infrared spectroscopy in the 3-20 μm spectral window has evolved from a routine laboratory technique into a state-of-the-art spectroscopy and sensing tool by benefitting from recent progress in increasingly sophisticated spectra acquisition techniques and advanced materials for generating, guiding, and detecting mid-infrared (MIR) radiation. Today, MIR spectroscopy provides molecular information with trace to ultratrace sensitivity, fast data acquisition rates, and high spectral resolution catering to demanding applications in bioanalytics, for example, and to improved routine analysis. In addition to advances in miniaturized device technology without sacrificing analytical performance, selected innovative applications for MIR spectroscopy ranging from process analysis to biotechnology and medical diagnostics are highlighted in this review.

Ultrasound-assisted bioalcohol synthesis: review and analysis

The present article highlights the efficacy of ultrasound in the intensification of all the steps of bioalcohol synthesis with a critical analysis of the literature.

Ultrasound-assisted bioethanol production from waste newspaper

The present work deals with intensification of bioethanol production from waste newspaper using Saccharomyces cerevisiae using ultrasonic irradiations. The effect of different process parameters such as application of ultrasonic irradiation at different growth phases, irradiation time, ultrasonic power and duty cycle on the bioethanol production has been investigated. The favorable conditions for the maximum yield were established as application of ultrasonic irradiation (duration of 10 min) to fermentation broth at 12 h of growth phase with 25 kHz frequency, 160 W power and 20% duty cycle. The bioethanol productivity was increased by 1.8 times from 7.8 to 14.1 g/L compared with the non-sonicated control fermentation. Decrease in glucose concentration from 0.63% to 0.2% w/v in ultrasound-assisted fermentation confirmed the improved substrate uptake of the microbial cell due to the application of ultrasound. ESEM analysis also confirmed the changes in the cell morphology leading to improved cell permeability. Results were fitted to an unstructured kinetic model comprising of the kinetic and physiological parameters. Overall, the work has demonstrated an intensified approach for the bioethanol production based on the use of ultrasound.

Ultrasound-enhanced attenuated total reflection mid-infrared spectroscopy in-line probe: acquisition of cell spectra in a bioreactor

This article presents a novel method for selective acquisition of Fourier transform infrared (FT-IR) spectra of microorganisms in-line during fermentation, using Saccharomyces cerevisiae as an example. The position of the cells relative to the sensitive region of the attenuated total reflection (ATR) FT-IR probe was controlled by combing a commercially available ATR in-line probe with contact-free, gentle particle manipulation by ultrasonic standing waves. A prototype probe was successfully constructed, assembled, and tested in-line during fed-batch fermentations of S. cerevisiae. Control over the position of the cells was achieved by tuning the ultrasound frequency: 2.41 MHz was used for acquisition of spectra of the cells (pushing frequency f(p)) and 1.87 MHz, for retracting the cells from the ATR element, therefore allowing spectra of the medium to be acquired. Accumulation of storage carbohydrates (trehalose and glycogen) inside the cells was induced by a lack of a nitrogen source in the feed medium. These changes in biochemical composition were visible in the spectra of the cells recorded in-line during the application of f(p) and could be verified by reference spectra of dried cell samples recorded off-line with a FT-IR microscope. Comparison of the cell spectra with spectra of trehalose, glycogen, glucose, and mannan, i.e., the major carbohydrates present in S. cerevisiae, and principal components analysis revealed that the changes observed in the cell spectra correlated well with the bands specific for trehalose and glycogen. This proves the applicability and capability of ultrasound-enhanced in-line ATR mid-IR spectroscopy as a real-time PAT method for the in situ monitoring of cellular biochemistry during fermentation.

Focusing of sub-micrometer particles and bacteria enabled by two-dimensional acoustophoresis

Handling of sub-micrometer bioparticles such as bacteria are becoming increasingly important in the biomedical field and in environmental and food analysis. As a result, there is an increased need for less labor-intensive and time-consuming handling methods. Here, an acoustophoresis-based microfluidic chip that uses ultrasound to focus sub-micrometer particles and bacteria, is presented. The ability to focus sub-micrometer bioparticles in a standing one-dimensional acoustic wave is generally limited by the acoustic-streaming-induced drag force, which becomes increasingly significant the smaller the particles are. By using two-dimensional acoustic focusing, i.e. focusing of the sub-micrometer particles both horizontally and vertically in the cross section of a microchannel, the acoustic streaming velocity field can be altered to allow focusing. Here, the focusability of E. coli and polystyrene particles as small as 0.5 μm in diameter in microchannels of square or rectangular cross sections, is demonstrated. Numerical analysis was used to determine generic transverse particle trajectories in the channels, which revealed spiral-shaped trajectories of the sub-micrometer particles towards the center of the microchannel; this was also confirmed by experimental observations. The ability to focus and enrich bacteria and other sub-micrometer bioparticles using acoustophoresis opens the research field to new microbiological applications.

Ultrasound stimulated production of a fibrinolytic enzyme

The present study is aimed at enhanced production of a fibrinolytic enzyme from Bacillus sphaericus MTCC 3672 under ultrasonic stimulation. Various process parameters viz; irradiation at different growth phases, ultrasonication power, irradiation duration, duty cycle and multiple irradiation were studied for enhancement of fibrinolytic enzyme productivity. The optimum conditions were found as follows, irradiation of ultrasonic waves to fermentation broth at 12 h of growth phase with 25 kHz frequency, 160 W ultrasound power, 20% duty cycle for 5 min. The productivity of fibrinolytic enzyme was increased 1.82-fold from 110 to 201 U/mL compared with the non sonicated control fermentation. Drop in glucose concentration from 0.41% to 0.12% w/v in ultrasonicated batch implies that, ultrasonication increases the cell permeability, improves substrate intake and progresses metabolism of microbial cell. Microscopic images before and after ultrasonic stimulation clearly signifies the impact of duty cycle on decreasing biomass concentration. However, environmental scanning electron micrograph does not show any cell lysis at optimum ultrasonic irradiation. Offshoots of our results will contribute to fulfill the demand of enhancement of microbial therapeutic enzyme productivity, through ultrasonication stimulation.

The effect of ultrasound-related stimuli on cell viability in microfluidic channels

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°C to 54°C at the maximum experimental voltage (29 V_pp), computational fluid dynamic simulations and controls (absence of US) revealed that the cell medium temperature did not exceed 34°C in the pressure nodal plane. Cells exposed to US amplitudes ranging from 0–29 V_pp, at a fixed frequency sweep period (t_sw = 0.05 sec), revealed that viability was minimally affected up to ~15 V_pp. There was a ~17% reduction in viability at 21 V_pp, corresponding to the onset of Rayleigh-like streaming and a ~60% reduction at 29 V_pp, corresponding to increased streaming velocity or the potential onset of cavitation. At a fixed amplitude (29 V_pp) but with varying frequency sweep period (t_sw = 0.02-0.50 sec), cell viability remained relatively constant at t_sw ≥ 0.08 sec, whilst viability reduced at t_sw < 0.08 sec and minimum viability recorded at t_sw = 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.

Ultrasonic manipulation of yeast cells in suspension for absorption spectroscopy with an immersible mid-infrared fiberoptic probe

Recent advances in combining ultrasonic particle manipulation with attenuated total reflection infrared spectroscopy of yeast suspensions are presented. Infrared spectroscopy provides highly specific molecular information about the sample. It has not been applicable to in-line monitoring of cells during fermentation, however, because positioning cells in the micron-thin measurement region of the attenuated total reflection probe was not possible. Ultrasonic radiation forces exerted on suspended particles by an ultrasonic standing wave can result in the buildup of agglomerates in the nodal planes, hence enabling the manipulation of suspended cells on the microscopic scale. When a chamber setup and a prototype in-line applicable probe were used, successful control over the position of the yeast cells relative to the attenuated total reflection sensor surface could be proven. Both rate of increase and maximum mid-infrared absorption of yeast-specific bands during application of a pushing frequency (chamber setup: 1.863 MHz, in-line probe: 1.990 MHz) were found to correlate with yeast cell concentration.

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.

Acoustofluidics 22: multi-wavelength resonators, applications and considerations

One important niche for multi-wavelength resonators is the filtration of suspensions containing very high particle concentration. For some applications, multi-wavelength ultrasound enhanced sedimentation filters are second only to the centrifuge in efficiency but, unlike the centrifuge they are easily adapted for continuous flow. Multi-wavelength resonators are also an obvious consideration when half-wavelength chambers are too small for a specific application. Unfortunately the formula, bigger = higher-throughput, does not scale linearly. Here we describe the relationships between chamber size and throughput for acoustic, electrical, flow and thermal convection actions, allowing the user to define initial parameters for their specific applications with some confidence. We start with a review of some of the many forms of multi-wavelength particle manipulation systems.

Microfluidic, label-free enrichment of prostate cancer cells in blood based on acoustophoresis

Circulating tumor cells (CTC) are shed in peripheral blood at advanced metastatic stages of solid cancers. Surface-marker-based detection of CTC predicts recurrence and survival in colorectal, breast, and prostate cancer. However, scarcity and variation in size, morphology, expression profile, and antigen exposure impairs reliable detection and characterization of CTC. We have developed a noncontact, label-free microfluidic acoustophoresis method to separate prostate cancer cells from white blood cells (WBC) through forces generated by ultrasonic resonances in microfluidic channels. Implementation of cell prealignment in a temperature-stabilized (±0.5 °C) acoustophoresis microchannel dramatically enhanced the discriminatory capacity and enabled the separation of 5 μm microspheres from 7 μm microspheres with 99% purity. Next, we determined the feasibility of employing label-free microfluidic acoustophoresis to discriminate and divert tumor cells from WBCs using erythrocyte-lysed blood from healthy volunteers spiked with tumor cells from three prostate cancer cell-lines (DU145, PC3, LNCaP). For cells fixed with paraformaldehyde, cancer cell recovery ranged from 93.6% to 97.9% with purity ranging from 97.4% to 98.4%. There was no detectable loss of cell viability or cell proliferation subsequent to the exposure of viable tumor cells to acoustophoresis. For nonfixed, viable cells, tumor cell recovery ranged from 72.5% to 93.9% with purity ranging from 79.6% to 99.7%. These data contribute proof-in-principle that label-free microfluidic acoustophoresis can be used to enrich both viable and fixed cancer cells from WBCs with very high recovery and purity.

Array-controlled ultrasonic manipulation of particles in planar acoustic resonator

Ultrasonic particle manipulation tools have many promising applications in life sciences, expanding on the capabilities of current manipulation technologies. In this paper, the ultrasonic manipulation of particles and cells along a microfluidic channel with a piezoelectric array is demonstrated. An array integrated into a planar multilayer resonator structure drives particles toward the pressure nodal plane along the centerline of the channel, then toward the acoustic velocity maximum centered above the subset of elements that are active. Switching the active elements along the array moves trapped particles along the microfluidic channel. A 12-element 1-D array coupled to a rectangular capillary has been modeled and fabricated for experimental testing. The device has a 300-μm-thick channel for a half-wavelength resonance near 2.5 MHz, with 500 μm element pitch. Simulation and experiment confirm the expected trapping of particles at the center of the channel and above the set of active elements. Experiments demonstrated the feasibility of controlling the position of particles along the length of the channel by switching the active array elements.

Acoustofluidics 12: Biocompatibility and cell viability in microfluidic acoustic resonators

Manipulation of biological cells by acoustic radiation forces is often motivated by its improved biocompatibility relative to alternative available methods. On the other hand, it is well known that acoustic exposure is capable of causing damage to tissue or cells, primarily due to heating or cavitation effects. Therefore, it is important to define safety guidelines for the design and operation of the utilized devices. This tutorial discusses the biocompatibility of devices designed for acoustic manipulation of mammalian cells, and different methods for quantifying the cell viability in such devices.

Acoustophoretic microfluidic chip for sequential elution of surface bound molecules from beads or cells

An acoustophoresis-based microfluidic flow-chip is presented as a novel platform to facilitate analysis of proteins and peptides loosely bound to the surface of beads or cells. The chip allows for direct removal of the background surrounding the beads or cells, followed by sequential treatment and collection of a sequence of up to five different buffer conditions. During this treatment, the beads/cells are retained in a single flow by acoustic radiation force. Eluted peptides are collected from the outlets and subsequently purified by miniaturized solid-phase extraction and analyzed with matrix assisted laser desorption mass spectrometry. Fundamental parameters such as the system fluidics and dispersion are presented. The device was successfully applied for wash and sequential elution of peptides bound to the surface of microbeads and human spermatozoa, respectively.

Stable cavitation induces increased cytoplasmic calcium in L929 fibroblasts exposed to 1-MHz pulsed ultrasound

An increase in cytoplasmic calcium (Ca(2+) increase) is a second messenger that is often observed under ultrasound irradiation. We hypothesize that cavitation is a physical mechanism that underlies the increase in Ca(2+) in these experiments. To control the presence of cavitation, the wave type was controlled in a sonication chamber. One wave type largely contained a traveling wave (wave type A) while the other wave type largely contained a standing wave (wave type B). Fast Fourier transform (FFT) analysis of a sound field produced by the wave types ascertained that stable cavitation was present only under wave type A ultrasound irradiation. Under the two controlled wave types, the increase in Ca(2+) in L929 fibroblasts was observed with fluorescence imaging. Under wave type A ultrasound irradiation, an increase in Ca(2+) was observed; however, no increase in Ca(2+) was observed under wave type B ultrasound irradiation. We conclude that stable cavitation is involved in the increase of Ca(2+) in cells subjected to pulsed ultrasound.

Wastewater disinfection by combination of ultrasound and ultraviolet irradiation

Reclamation and reuse of wastewater is one of the most effective ways to alleviate water resource scarcity. In many countries very stringent limit for chlorination by-products such as trihalomethanes has been set for wastewater reuse. Accordingly, the use of alternative oxidation/disinfection systems should be evaluated as possible alternative to chlorine. Recently ultrasound (US) was found to be effective as pre-treatment for wastewater disinfection by UV irradiation. The aim of this work is to investigate the wastewater advanced treatment by simultaneous combination of UV and US in terms of bacteria inactivation (Total coliform and Escherichia coli) at pilot-scale. The pilot plant was composed of two reactors: US-UV reactor and UV reactor. The influence of different reaction times, respective US and UV dose and synergistic effect was tested and discussed for two different kinds of municipal wastewater. An important enhancement of UV disinfection ability has been observed in presence of US, especially with wastewater characterized by low transmittance. In particular the inactivation was greater for T. coliform than for E. coli. Furthermore, the results obtained showed also that the fouling formation on the lamps was slower in US-UV reactor than in UV reactor both with and without solar radiation.

The dynamics of surface acoustic wave-driven scaffold cell seeding

Flow visualization using fluorescent microparticles and cell viability investigations are carried out to examine the mechanisms by which cells are seeded into scaffolds driven by surface acoustic waves. The former consists of observing both the external flow prior to the entry of the suspension into the scaffold and the internal flow within the scaffold pores. The latter involves micro-CT (computed tomography) scans of the particle distributions within the seeded scaffolds and visual and quantitative methods to examine the morphology and proliferation ability of the irradiated cells. The results of these investigations elucidate the mechanisms by which particles are seeded, and hence provide valuable information that form the basis for optimizing this recently discovered method for rapid, efficient, and uniform scaffold cell seeding. Yeast cells are observed to maintain their size and morphology as well as their proliferation ability over 14 days after they are irradiated. The mammalian primary osteoblast cells tested also show little difference in their viability when exposed to the surface acoustic wave irradiation compared to a control set. Together, these provide initial feasibility results that demonstrate the surface acoustic wave technology as a viable seeding method without risk of denaturing the cells.

A scaffold cell seeding method driven by surface acoustic waves

Surface acoustic waves (SAW) have been employed to drive a particle suspension into a porous scaffold as a means for cell seeding. Straight, simple interdigital electrode structures were fabricated on lithium niobate to permit the generation of Rayleigh SAW radiation. Fluorescent microscopy was used to investigate the seeding process; the SAW-driven seeding process occurred in approximately 10s, much quicker than if the scaffold were to be seeded by gravity-driven diffusional processes alone (>30min). Analysis of high-speed micrographic images demonstrated that the SAW method could also drive particles deeper into the scaffold, thereby significantly improving the uniformity of the particle distribution. The proposed SAW technique therefore offers a promising technology to dramatically improve the speed and uniformity of cell seeding in scaffolds, which might contribute to rapid and uniform tissue regeneration.

Ultrasonic Trapping of Microparticles in Suspension and Reaction Monitoring Using Raman Microspectroscopy

An ultrasonic standing wave around 2 MHz has been used for trapping and concentration of suspended micrometer-size particles in a flow cell, whereas Raman microspectroscopy was used as a nondestructive technique to provide molecular information about the trapped particles. With this approach, detection and discrimination of different polymer microparticles based on their characteristic Raman spectra was performed. Dextran, poly(vinyl alcohol), and melamine resin-based beads, with and without functionalization, were used for this purpose. Furthermore, taking advantage of the flow-through characteristics of the cell and the versatility of the employed flow system, full control over the media surrounding the trapped particles was achieved. This allowed us to perform chemical reactions on the trapped particles and to monitor spectral changes in real time. Here retention of cation-exchanger beads loaded with silver ions and subsequent reduction of the silver ions was demonstrated. In this way, surface-enhanced Raman (SER) active beads were prepared and retained in the focus of the Raman microscope by means of the ultrasonic field. Injection of analytes in the flow system thus allowed recording of their SER spectra. Using 9-aminoacridine, a linear dependence of the found SER signal in the range from 1 to 10 microM has been achieved. The repeatability in the recorded SER intensities was on the order of 4-5%. This included bead retention, surface-enhanced Raman layer synthesis, and analyte detection.

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.

Nonviral transfection of suspension cells in ultrasound standing wave fields

Ultrasound-induced cavitation has been widely used for delivering DNA vectors into cells. However, this approach may seriously disrupt cell membranes and cause lethal damage when cells are exposed to the inertial cavitation field. In this study, instead of using sonoporation, ultrasound standing wave fields (USWF) were explored for nonviral transfection of suspension cells. Acoustic resonance in a tubular chamber was generated from the interference of waves emitted from a piezoelectric transducer and consequently reflected from a borosilicate glass coverslip. The suspended K562 erythroleukemia cells were transfected by polyethyleneimine (PEI)/DNA complexes with and without exposure to 1-MHz USWF for 5 min. During USWF exposure, K562 cells moved to the pressure nodal planes first and formed cell bands by the primary radiation force. Nanometer-sized PEI/DNA complexes, circulated between nodal planes by acoustic microstreaming, then used the cell agglomerates as the nucleating sites on which to attach. After incubation at 37 degrees C for 48 h, the efficiency of nonviral transfection based on EGFP transgene expression was determined by fluorescent microscopy and fluorometry. Both studies showed that USWF brought suspended K562 cells and PEI/DNA complexes into close contact at the pressure nodal planes, yielding an approximately 10-fold increment of EGFP transgene expression compared with the group without ultrasonic treatment.

Proliferation and viability of adherent cells manipulated by standing-wave ultrasound in a microfluidic chip

Ultrasonic-standing-wave (USW) technology has potential to become a standard method for gentle and contactless cell handling in microfluidic chips. We investigate the viability of adherent cells exposed to USWs by studying the proliferation rate of recultured cells following ultrasonic trapping and aggregation of low cell numbers in a microfluidic chip. The cells form 2-D aggregates inside the chip and the aggregates are held against a continuous flow of cell culture medium perpendicular to the propagation direction of the standing wave. No deviations in the doubling time from expected values (24 to 48 h) were observed for COS-7 cells held in the trap at acoustic pressure amplitudes up to 0.85 MPa and for times ranging between 30 and 75 min. Thus, the results demonstrate the potential of ultrasonic standing waves as a tool for gentle manipulation of low cell numbers in microfluidic systems.

Surface free energy effect on bacterial retention

Bacterial infection is one of the most frequent and severe complications in the long-term effectiveness of medical implants and devices, greatly increasing treatment cost and inconvenience to the patient. Surface physical and chemical properties are known to influence the extent and form of bacterial infection, although the exact correlation with specific properties is difficult due to the complexity of the system. One approach in the attempt to reduce the bacterial colonisation is to modify the surface energy and chemistry, so as to influence the interactions between the surface and the bacteria that come into contact with it. Five types of coatings were investigated in this study, together with silicone, and polished and non-polished stainless steel 316L. Surfaces were tested for retention of Pseudomonas aeruginosa AK1 after 1h. A good correlation (>90%) was found between P. aeruginosa AK1 retention and total surface free energy, as well as its polar and dispersive components. The minimum level of P. aeruginosa AK1 retention was found for a range of total surface free energy in the range 20-27 mN/m.

A new immobilisation method to arrange particles in a gel matrix by ultrasound standing waves

Ultrasonic forces may be used to manipulate particles in suspension. For example, a standing wave ultrasound (US) field applied to a suspension moves the particles toward areas of minimal acoustic pressure, where they are orderly retained creating a predictable heterogeneous distribution. This principle of ultrasonic retention of particles or cells has been applied in numerous biotechnological applications, such as mammalian cell filtering and red blood cell sedimentation. Here, a new US-based cell immobilisation technique is described that allows manipulation and positioning of cells/particles within various nontoxic gel matrices before polymerisation. Specifically, gel immobilisation was used to directly demonstrate that the viability of yeast cells arranged by an US standing wave is maintained up to 4 days after treatment. The versatility of this immobilisation method was validated using a wide range of acoustic devices. Finally, the potential biotechnological advantages of this US-controlled particle positioning method combined with gel immobilisation/encapsulation technology are discussed.

Inactivation of Saccharomyces cerevisiae by ultrasonic irradiation

We have investigated the inactivation of Saccharomyces cerevisiae (yeast cells) by ultrasonic irradiation. The amplitude on the vibration face contacting the sample solution was used as an indication of the ultrasonic power intensity. The effects of the amplitude on the vibration face and the initial cell numbers on the sonolytic inactivation of yeast cells have been investigated using a horn-type sonicator (27.5 kHz). The inactivation of the yeast cells by ultrasonic irradiation shows pseudo first-order behavior. The inactivation rate constant varied from 0.0007 to 0.145 s(-1) when the amplitude on the vibration face was in the range of 1-7 microm(p-p). The change in the inactivation rate constant as a function of the amplitude on the vibration face was similar to that of the OH radical formation rate under the same conditions. The threshold of this sonicator was 3 microm(p-p) with the amplitude on the vibration face. The initial cell numbers (from 10(2) to 10(5) mL(-1)) had an influence on the inactivation of the yeast cells by ultrasonic irradiation. The inactivation rate constants varied from 0.023 to 6.4 x 10(-3) s(-1), and the inactivation by ultrasonic irradiation was fastest at the lowest initial cell numbers. In a squeeze-film-type sonicator (26.6 kHz), 90% inactivation of the yeast cells was achieved by ultrasonic irradiation for 60 min.

Inactivation of Escherichia coli by ultrasonic irradiation

Ultrasonic inactivation of Escherichia coli XL1-Blue has been investigated by high-intensity ultrasonic waves from horn type sonicator (27.5 kHz) utilizing the "squeeze-film effect". The amplitude of the vibration face contacting the sample solution was used as an indication of the ultrasonic power intensity. The inactivation of the E. coli cells by ultrasonic irradiation shows pseudo first-order behavior. The inactivation rate constant gradually increased with increasing amplitude of the vibration face and showed rapid increase above 3 microm (p-p). In contrast, the H2O2 formation was not observed below 3 microm (p-p), indicating that the ultrasonic shock wave might be more important than indirect effect of OH radicals formed by ultrasonic cavitation in this system. The optimal thickness of the squeeze film was determined as 2 mm for the E. coli inactivation. More than 99% of E. coli cells was inactivated within 180-s sonication at the amplitude of 3 microm (p-p) and 2 mm of the thickness of the squeeze film.

Sonication effect on cellular material in sedimentation and gravitational field flow fractionation

Sonication procedures are generally used prior to field flow fractionation (FFF) separation in order to produce suspensions without aggregates. Yeast cells manufactured in active dry wine yeast (ADWY) were placed in an ultrasound water bath in order to disrupt possible clumps and to obtain a single-cell suspension to be used in optimal conditions during fermentation processes. In order to determine whether this sample preparation procedure meets absolute needs, different yeast samples before and after sonication were analysed by two field flow fractionation techniques. It is shown that 2 min of sonication in the sample preparation process is sufficient to obtain an optimal dispersion of the yeast cells, that is, without critical percentage of aggregates. To demonstrate this effect, photographs of the yeast cell suspensions were performed with non-sonicated and sonicated yeast sample dispersion. The resulting data are compared with the elution profiles obtained from the two different FFF techniques. It is demonstrated that fractogram profiles prove the effectiveness of sonication methodologies.

Sonobioreactors: using ultrasound for enhanced microbial productivity

Enhanced metabolic productivity of microbial, plant and animal cells in bioreactors can greatly improve the economics of biotechnology processes. Ultrasound is one method of intensifying the performance of live biocatalysts. Ultrasonication is generally associated with damage to cells but evidence is emerging for beneficial effects of controlled sonication on conversions catalyzed by live cells. This review focuses on the productivity enhancing effects of ultrasound on live biological systems and the design considerations for sonobioreactors required for ultrasound-enhanced biocatalysis.

Ultrasound-induced physiological changes in cultured cells of Petunia hybrida

Petunia hybrida cell suspension cultures were exposed to ultrasonic standing wave fields at 2.43 MHz for 40 min with mean sound pressures (within homogenous sound fields) varying from 0 (control) to ca. 1.1 MPa. Mean (+/- s.d.; n =6-9) cell viability was reduced to 87+/-10% at 0.6 MPa and to 59 +/- 23% at 1.1 MPa, compared to an initial control value of 92 +/- 6% (P <0.05). Mean (n = 3) cell alkaline phosphatase concentration increased linearly with sound pressure from a control value of 0.006+/-0.001 to 0.02+/-0.01 Sigma-Units microg(-1) protein at 1.1 MPa (P<0.05). Similarly, mean cell catalase activity increased from a control value of 0.020 +/- 0.003 to 0.026 +/- 0.008 arbitrary units at 1.1 MPa. In contrast, mean cellular lactate dehydrogenase concentration was unchanged. These observations indicate that cellular repair processes associated with increased alkaline phosphatase activity might be triggered by physical cell damage caused by ultrasound. The observed increase in catalase activity suggests increasing production of free radicals and other sonochemicals, which warrants further study. The absence of changes in lactate dehydrogenase indicates that there was no major damage to respiratory pathways or to overall cellular integrity.