Laser-induced Microbubbles Research Articles

Printing of liquid metal by laser-induced thermal bubble at the liquid–liquid interface

The dynamics of bubbles near a liquid–liquid interface represent a complex multiphase problem with numerous potential applications. This paper utilizes pulsed laser-induced microbubbles at the liquid–liquid interface to achieve the multi-orifice ejection of liquid metal microdroplets that are challenging to achieve with traditional inkjet printing. The study combines the expansion and collapse processes of thermal bubbles at the two-phase liquid interface with the ejection process of liquid metal droplets, unveiling the underlying mechanisms of liquid metal droplet ejection. In this work, the influence of laser parameters on the behavior of thermal bubbles at the liquid–liquid interface and the double-peak pressure effect was investigated. The impact of laser parameters on the ejection behavior of liquid metal droplets was also examined, which provides theoretical support for the wide applications of bubble dynamics at the liquid–liquid interface in the field of liquid metal inkjet printing.

Growth of Laser-Induced Microbubbles inside Capillary Tubes Affected by Gathered Light-Absorbing Particles.

Microbubbles have important applications in optofluidics. The generation and growth of microbubbles is a complicated process in microfluidic channels. In this paper, we use a laser to irradiate light-absorbing particles to generate microbubbles in capillary tubes and investigate the factors affecting microbubble size. The results show that the key factor is the total area of the light-absorbing particles gathered at the microbubble bottom. The larger the area of the particles at bottom, the larger the size of the microbubbles. Furthermore, the area is related to capillary tube diameter. The larger the diameter of the capillary tube, the more particles gathered at the bottom of the microbubbles. Numerical simulations show that the Marangoni convection is stronger in a capillary tube with a larger diameter, which can gather more particles than that in a capillary tube with a smaller diameter. The calculations show that the particles in contact with the microbubbles will be in a stable position due to the surface tension force.

Laser-induced optical breakdown effects of micro-lens arrays and diffractive optical elements on ex vivo porcine skin after 1064 nm picosecond laser irradiation.

The current study aims to investigate the effects of micro-lens arrays (MLA) and diffractive optical elements (DOE) on skin tissue via intra-dermal laser-induced optical breakdown (LIOB) after irradiation of 1064-nm picosecond laser light at high energy settings. Irradiation with MLA and DOE was tested on dimming paper, tissue-mimicking phantom, and dark pigmented porcine skin to quantitatively compare distributions of micro-beams, micro-bubbles, and laser-induced vacuoles in the skin. DOE yielded more uniform distributions of the micro-beams on the paper and laser-induced micro-bubbles in the phantom, compared to MLA. The ex vivo skin test confirmed that the DOE-assisted irradiation accompanied more homogeneous generation of the micro-beams on the tissue surface (deviation of ≤ 3%) and a high density of small laser-induced vacuoles (∼78 µm) in the dermis than the MLA-assisted irradiation (deviation of ∼26% and ∼163 µm). The DOE-assisted picosecond laser irradiation may help to achieve deep and uniformly-generated vacuolization under the basal membrane after intra-dermal LIOB for effective fractional skin treatment.

Photoacoustic identification of laser-induced microbubbles as light scattering centers for optical limiting in a liquid suspension of graphene nanosheets.

Liquid suspensions of carbon nanotubes, graphene and transition metal dichalcogenides have exhibited excellent performance in optical limiting. However, the underlying mechanism has remained elusive and is generally ascribed to their superior nonlinear optical properties such as nonlinear absorption or nonlinear scattering. Using graphene as an example, we show that photo-thermal microbubbles are responsible for optical limiting as strong light scattering centers: graphene sheets absorb incident light and become heated up above the boiling point of water, resulting in vapor and microbubble generation. This conclusion is based on the direct observation of bubbles above the laser beam as well as a strong correlation between laser-induced ultrasound and optical limiting. In situ Raman scattering of graphene further confirms that the temperature of graphene under laser pulses rises above the boiling point of water but still remains too low to vaporize graphene and create graphene plasma bubbles. Photo-thermal bubble scattering is not a nonlinear optical process and requires very low laser intensity. This understanding helps us to design more efficient optical limiting materials and understand the intrinsic nonlinear optical properties of nanomaterials.

Volumetric graphics using laser-induced microbubbles in glycerin containing gold nanorods

Volumetric graphics using laser-induced microbubbles in glycerin containing gold nanorods

Volumetric graphics using laser-induced microbubbles in glycerin containing gold nanorods

Volumetric graphics using laser-induced microbubbles in glycerin containing gold nanorods

Differential detachment of intact and viable cells of different sizes using laser-induced microbubbles.

Single cell isolation is a prerequisite for the analysis of rare or small cell subtypes. Here, we selectively detach single cells in a heterogeneous population comprised of different morphological subtypes whose sizes vary in body and extension. Such a cellular environment is first accommodated for by a photomechanical method in which pulsed laser irradiation produces microbubbles from a polymer substrate, thus pushing out and detaching cultured cells in an intact, viable, and spatially tailored way. While this has previously only bene used at a very low cell density with lack of quantitative characterization, we determine optimal detachment conditions for different cell sizes in terms of an optical fluence and the number of laser pulses. Importantly, our approach is employed to isolate cancer cells with inherent size variation and elucidate cellular heterogeneity in drug sensitivity: i.e., higher resistance for larger cell size. For cells detached by laser-induced microbubbles, morphology, proliferation, and viability are compared with those of conventional trypsin-treated cells detached without any spatial selectivity. These results support the suitability of our photomechanical method for biochemical screen and secondary analysis of cells with unusual responses.

Dynamics of laser-induced microbubbles in an absorbing liquid

The generation and subsequent dynamics of a microbubble in a liquid are investigated, both experimentally and theoretically. When a laser beam is focused into an absorbing liquid comprising colloidal red dye particles in isopropanol alcohol inside a thick quartz cuvette, microbubbles can be generated at around the focus due to nucleation and thermal cavitation. It is experimentally shown that in some cases, the generated microbubble that initially moves away from the focus due to the longitudinal optical gradient force is later attracted to the focus due to the longitudinal thermocapillary force. In our previous work, the thermocapillary force acting on a microbubble is studied two dimensionally. The thermocapillary force acting on the microbubble is determined by directly solving the three-dimensional (3-D) heat equation by 3-D Fourier transform methods. When developing the complete force model in microbubble dynamics, the thermo-capillary force, optical force, buoyancy force, gravity, and the viscous force have been considered.

All-fiber impurity collector based on laser-induced microbubble

Microbubbles have attracted interests in polluted water treatment industry. We proposed and constructed an all-fiber impurity collector based on the laser-induced microbubbles characteristics for polluted water treatment. Without any special pretreatment, such as metallically coating or carbon materials doping, the proposed impurity collector performed microbubbles generation and impurities extraction and collection. We employed the graphite oxide nanoplatelets in an aqueous solution to construct the polluted water environment to show the performance of the all-fiber impurity collector. With the optimal incident laser power of 11 mW, we performed the collection efficiency as high as 16.3×104 /s. The optimal microbubbles diameter was in the range of 80–120 μm. The proposed all-fiber impurity collector extends the potential applications of fiber-based optical manipulation for polluted water treatment.

The Generation and Assembly of Laser-Induced Microbubbles

Microbubbles have broad applications for optofluidic devices, optical manipulation, and sensing. Here we report a series of experimental observations, demonstrating the controllable generation and assembly of microbubbles by using an optical fiber-coupled laser. The microbubbles can be photothermally generated with high efficiency in deionized water, without adding light-absorbing nanomaterials. The temporal evolution and assembled pattern, quantified by diameter, number and density of the microbubbles, can be flexibly controlled by the surface area of liquid, the insertion depth of fiber, and the laser power for heating. Good repeatability is confirmed for the microbubble generation. This kind of microbubble may have the potential for sensing, microstructure formation, etc.

Localized Single-Cell Lysis and Manipulation Using Optothermally-Induced Bubbles.

Localized single cells can be lysed precisely and selectively using microbubbles optothermally generated by microsecond laser pulses. The shear stress from the microstreaming surrounding laser-induced microbubbles and direct contact with the surface of expanding bubbles cause the rupture of targeted cell membranes. High-resolution single-cell lysis is demonstrated: cells adjacent to targeted cells are not lysed. It is also shown that only a portion of the cell membrane can be punctured using this method. Both suspension and adherent cell types can be lysed in this system, and cell manipulation can be integrated for cell–cell interaction studies.

Trapping of nanoparticles in a liquid by laser-induced microbubbles

Nanoparticles a few nanometers in diameter contained in a colloidal solution can be captured by the surface of a microbubble produced by a well-focused beam of a continuous wave visible laser. The concentration of the nanoparticles on the surface of the microbubble is found to gradually increase during the course of irradiation. The mechanism of such a trapping is associated with the laser-induced Marangoni convection developing in the vicinity of the microbubble as a result of the temperature gradient obtained at its surface.

Fast temperature measurement following single laser-induced cavitation inside a microfluidic gap.

Single transient laser-induced microbubbles have been used in microfluidic chips for fast actuation of the liquid (pumping and mixing), to interact with biological materials (selective cell destruction, membrane permeabilization and rheology) and more recenty for medical diagnosis. However, the expected heating following the collapse of a microbubble (maximum radius ~ 10–35 µm) has not been measured due to insufficient temporal resolution. Here, we extend the limits of non-invasive fluorescence thermometry using high speed video recording at up to 90,000 frames per second to measure the evolution of the spatial temperature profile imaged with a fluorescence microscope. We found that the temperature rises are moderate (< 12.8°C), localized (< 15 µm) and short lived (< 1.3 ms). However, there are significant differences between experiments done in a microfluidic gap and a container unbounded at the top, which are explained by jetting and bubble migration. The results allow to safe-guard some of the current applications involving laser pulses and photothermal bubbles interacting with biological material in different liquid environments.

The Mechanical Properties of Ex Vivo Bovine and Porcine Crystalline Lenses: Age-Related Changes and Location-Dependent Variations

The mechanical properties of ex vivo animal lenses from three groups were evaluated: old bovine (25–30 mo old, n = 4), young bovine (6 mo old, n = 4) and young porcine (6 mo old, n = 4) eye globes. We measured the dynamics of laser-induced microbubbles created at different locations within the crystalline lenses. An impulsive acoustic radiation force was applied to the microbubble, and the microbubble displacements were measured using a custom-built high pulse repetition frequency ultrasound system. Based on the measured dynamics of the microbubbles, Young's moduli of bovine and porcine lens tissue in the vicinity of the microbubbles were reconstructed. Age-related changes and location-dependent variations in the Young's modulus of the lenses were observed. Near the center, the old bovine lenses had a Young's modulus approximately fivefold higher than that of young bovine and porcine lenses. The gradient of Young's modulus with respect to radial distance was observed in the lenses from three groups.

A high pulse repetition frequency ultrasound system for the ex vivo measurement of mechanical properties of crystalline lenses with laser-induced microbubbles interrogated by acoustic radiation force

A high pulse repetition frequency ultrasound system for an ex vivo measurement of mechanical properties of an animal crystalline lens was developed and validated. We measured the bulk displacement of laser-induced microbubbles created at different positions within the lens using nanosecond laser pulses. An impulsive acoustic radiation force was applied to the microbubble, and spatio-temporal measurements of the microbubble displacement were assessed using a custom-made high pulse repetition frequency ultrasound system consisting of two 25 MHz focused ultrasound transducers. One of these transducers was used to emit a train of ultrasound pulses and another transducer was used to receive the ultrasound echoes reflected from the microbubble. The developed system was operating at 1 MHz pulse repetition frequency. Based on the measured motion of the microbubble, Young’s moduli of surrounding tissue were reconstructed and the values were compared with those measured using the indentation test. Measured values of Young’s moduli of four bovine lenses ranged from 2.6 ± 0.1 to 26 ± 1.4 kPa, and there was good agreement between the two methods. Therefore, our studies, utilizing the high pulse repetition frequency ultrasound system, suggest that the developed approach can be used to assess the mechanical properties of ex vivo crystalline lenses. Furthermore, the potential of the presented approach for in vivo measurements is discussed.

Elasticity Imaging and Sensing Using Targeted Motion: From Macro to Nano

The methods used to estimate tissue elasticity based on the motion of local inhomogeneities such as laser-induced gas microbubbles, magnetic nanoparticles and other targets under an externally applied force are reviewed. The theoretical bases of the motion of a target in a viscoelastic medium are described. Given various targets differing in size, these methods allow for elasticity measurements at different levels of spatial resolution. Short acoustic radiation force and magnetic field pulses were used to initiate the motion of various test objects (solid spheres, laser-induced microbubbles and magnetic nanoparticles) with sizes ranging from several millimeters to tens of nanometers. The induced motion was monitored by conventional pulse-echo ultrasound systems adapted for these measurements. The elasticity of the medium was evaluated based on a theoretical model describing the motion of a particle in a viscoelastic medium. Shear elasticity, evaluated using the developed approach, agrees well with independent measurements of mechanical properties of the medium. In this paper we review our recent theoretical and experimental results and discuss the applications of elasticity imaging and sensing using targeted motion, i.e., motion induced via the external forces acting on local inhomogeneities.

Estimation of mechanical properties of a viscoelastic medium using a laser-induced microbubble interrogated by an acoustic radiation force

An approach to assess the mechanical properties of a viscoelastic medium using laser-induced microbubbles is presented. To measure mechanical properties of the medium, dynamics of a laser-induced cavitation microbubble in viscoelastic medium under acoustic radiation force was investigated. An objective lens with a 1.13 numerical aperture and an 8.0 mm working distance was designed to focus a 532 nm wavelength nanosecond pulsed laser beam and to create a microbubble at the desired location. A 3.5 MHz ultrasound transducer was used to generate acoustic radiation force to excite a laser-induced microbubble. Motion of the microbubble was tracked using a 25 MHz imaging transducer. Agreement between a theoretical model of bubble motion in a viscoelastic medium and experimental measurements was demonstrated. Young's modulii reconstructed using the laser-induced microbubble approach were compared with those measured using a direct uniaxial method over the range from 0.8 to 13 kPa. The results indicate good agreement between methods. Thus, the proposed approach can be used to assess the mechanical properties of a viscoelastic medium.

Young's modulus estimation of bovine lens ex-vivo using a laser-induced microbubble under impulsive acoustic radiation force

According to the most widely accepted theory of presbyopia, the age-related loss of accommodation is attributed to Young's modulus changes in the lens. Previously, we have developed an approach to measure the mechanical properties of viscoelastic medium using microbubbles and acoustic radiation force. In this study, we tested this technique to assess the mechanical properties of bovine lenses ex-vivo. An impulsive acoustic radiation force was applied to laser-induced microbubbles created with nanosecond laser pulses at different locations in the lens. An acoustic radiation force with typical duration less than 150 μs was generated by a 3.5 MHz transducer. For accurate spatio-temporal measurements of the microbubble's displacement, a custom-made ultrasound system consisting of two 25 MHz transducers was built. The first transducer emitted a train of pulses and the other transducer received the train of echoes reflected from the microbubble. The developed system was operating at 400 kHz pulse repetition frequency. The results show good agreement between experimental measurements and the theoretical model of microbubble dynamics. Evaluation of the spatial distribution of elasticity demonstrates that the Young's modulus of the nucleus is higher than that of the cortex for bovine eye lenses of mature animals. [Work supported by NIH Grant EY018081.]

Dynamics and flow field produced by coupled oscillation of tandem microbubble.

Coupled oscillations of two adjacent laser-induced microbubbles have been shown to produce unique asymmetric bubble deformation and microjet formation. The resultant microstreaming and shear stress can cause localized cell membrane poration with potential application in targeted drug and gene delivery. In this study, we investigate the bubble dynamics and flow field produced by laser-generated tandem microbubble in a microfluidic device. Flow field around the tandem microbubble is analyzed with respect to phase delay, inter-bubble distance, and size ratio between the two microbubbles. In addition, micropatterning technique is used to control the adhesion site and growth pattern of HeLa cells in relation to the tandem microbubble. Flow vorticity is observed to be a key parameter that correlates with the strength of tandem microbubble oscillation and resultant macromolecule uptake efficiency. [Work supported by NIH Grant Nos. R01DK052985, R21CA135221, and S10RR016802].

Ultrasound measurements of cavitation bubble radius for femtosecond laser-induced breakdown in water.

A recently developed ultrasound technique is evaluated by measuring the behavior of a cavitation bubble that is induced in water by a femtosecond laser pulse. The passive acoustic emission during optical breakdown is used to estimate the location of the cavitation bubble's origin. In turn, the position of the bubble wall is defined based on the active ultrasonic pulse-echo signal. The results suggest that the developed ultrasound technique can be used for quantitative measurements of femtosecond laser-induced microbubbles.