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  1. Article ; Online: Lithotripter shock wave interaction with a bubble near various biomaterials.

    Ohl, S W / Klaseboer, E / Szeri, A J / Khoo, B C

    Physics in medicine and biology

    2016  Volume 61, Issue 19, Page(s) 7031–7053

    Abstract: Following previous work on the dynamics of an oscillating bubble near a bio-material (Ohl et al 2009 Phys. Med. Biol. 54 6313-36) and the interaction of a bubble with a shockwave (Klaseboer et al 2007 J. Fluid Mech. 593 33-56), the present work concerns ... ...

    Abstract Following previous work on the dynamics of an oscillating bubble near a bio-material (Ohl et al 2009 Phys. Med. Biol. 54 6313-36) and the interaction of a bubble with a shockwave (Klaseboer et al 2007 J. Fluid Mech. 593 33-56), the present work concerns the interaction of a gas bubble with a traveling shock wave (such as from a lithotripter) in the vicinity of bio-materials such as fat, skin, muscle, cornea, cartilage, and bone. The bubble is situated in water (to represent a water-like biofluid). The bubble collapses are not spherically symmetric, but tend to feature a high speed jet. A few simulations are performed and compared with available experimental observations from Sankin and Zhong (2006 Phys. Rev. E 74 046304). The collapses of cavitation bubbles (created by laser in the experiment) near an elastic membrane when hit by a lithotripter shock wave are correctly captured by the simulation. This is followed by a more systematic study of the effects involved concerning shockwave bubble biomaterial interactions. If a subsequent rarefaction wave hits the collapsed bubble, it will re-expand to a very large size straining the bio-materials nearby before collapsing once again. It is noted that, for hard bio-material like bone, reflection of the shock wave at the bone-water interface can affect the bubble dynamics. Also the initial size of the bubble has a significant effect. Large bubbles (∼1 mm) will split into smaller bubbles, while small bubbles collapse with a high speed jet in the travel direction of the shock wave. The numerical model offers a computationally efficient way of understanding the complex phenomena involving the interplay of a bubble, a shock wave, and a nearby bio-material.
    Language English
    Publishing date 2016-10-07
    Publishing country England
    Document type Journal Article
    ZDB-ID 208857-5
    ISSN 1361-6560 ; 0031-9155
    ISSN (online) 1361-6560
    ISSN 0031-9155
    DOI 10.1088/0031-9155/61/19/7031
    Database MEDical Literature Analysis and Retrieval System OnLINE

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    In stock of ZB MED Cologne/Königswinter

    Zs.A 199: Show issues Location:
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  2. Article ; Online: The dynamics of a non-equilibrium bubble near bio-materials.

    Ohl, S W / Klaseboer, E / Khoo, B C

    Physics in medicine and biology

    2009  Volume 54, Issue 20, Page(s) 6313–6336

    Abstract: In many medical treatments oscillating (non-equilibrium) bubbles appear. They can be the result of high-intensity-focused ultrasound, laser treatments or shock wave lithotripsy for example. The physics of such oscillating bubbles is often not very well ... ...

    Abstract In many medical treatments oscillating (non-equilibrium) bubbles appear. They can be the result of high-intensity-focused ultrasound, laser treatments or shock wave lithotripsy for example. The physics of such oscillating bubbles is often not very well understood. This is especially so if the bubbles are oscillating near (soft) bio-materials. It is well known that bubbles oscillating near (hard) materials have a tendency to form a high speed jet directed towards the material during the collapse phase of the bubble. It is equally well studied that bubbles near a free interface (air) tend to collapse with a jet directed away from this interface. If the interface is neither 'free' nor 'hard', such as often occurs in bio-materials, the resulting flow physics can be very complex. Yet, in many bio-applications, it is crucial to know in which direction the jet will go (if there is a jet at all). Some applications require a jet towards the tissue, for example to destroy it. For other applications, damage due to impacting jets is to be prevented at all cost. This paper tries to address some of the physics involved in these treatments by using a numerical method, the boundary element method (BEM), to study the dynamics of such bubbles near several bio-materials. In the present work, the behaviour of a bubble placed in a water-like medium near various bio-materials (modelled as elastic fluids) is investigated. It is found that its behaviour depends on the material properties (Young's modulus, Poisson ratio and density) of the bio-material. For soft bio-materials (fat, skin, brain and muscle), the bubble tends to split into smaller bubbles. In certain cases, the resulting bubbles develop opposing jets. For hard bio-materials (cornea, cartilage and bone), the bubble collapses towards the interface with high speed jets (between 100 and about 250 m s(-1)). A summary graph is provided identifying the combined effects of the dimensionless elasticity (kappa) and density ratio (alpha) of the elastic materials which will result in a nearby oscillating bubble jetting towards, splitting or jetting away from the elastic material interface. Since the phenomenon of a bubble jetting away from an elastic material as it collapses has not been reported before in the literature, experiments were performed to validate the numerical observation. A bubble is created in a heavy fluid (hydrofluoroether (HFE)) using a laser pulse. The bubble collapses near the elastic material polydimethylsiloxane (PDMS). The experimental results obtained are compared with the corresponding simulation. The simulation provides spatial and temporal details about the bubble dynamics beyond experimental limits and can therefore be considered as a very useful tool to get a better understanding of the physics involved.
    MeSH term(s) Biocompatible Materials/chemistry ; Computer Simulation ; Elasticity ; Equipment Design ; Materials Testing ; Microfluidics/methods ; Models, Statistical ; Models, Theoretical ; Oscillometry ; Physics/methods ; Poisson Distribution ; Reproducibility of Results
    Chemical Substances Biocompatible Materials
    Language English
    Publishing date 2009-10-21
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 208857-5
    ISSN 1361-6560 ; 0031-9155
    ISSN (online) 1361-6560
    ISSN 0031-9155
    DOI 10.1088/0031-9155/54/20/019
    Database MEDical Literature Analysis and Retrieval System OnLINE

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    In stock of ZB MED Cologne/Königswinter

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  3. Article ; Online: A low-voltage spark-discharge method for generation of consistent oscillating bubbles.

    Goh, B H T / Oh, Y D A / Klaseboer, E / Ohl, S W / Khoo, B C

    The Review of scientific instruments

    2013  Volume 84, Issue 1, Page(s) 14705

    Abstract: Underwater spark-discharge methods have been widely utilized for experimental studies in many fields such as material processing, water treatment, and cavitation bubble dynamics. However, the precise control of bubble size using this method has been ... ...

    Abstract Underwater spark-discharge methods have been widely utilized for experimental studies in many fields such as material processing, water treatment, and cavitation bubble dynamics. However, the precise control of bubble size using this method has been difficult. This poses challenges to better understand the complex interactions of non-spherical cavitation bubble growth and collapse, which require fine and careful control of bubble size. A novel low-voltage (60.0 V) underwater spark-discharge method using a metal-oxide-semiconductor field effect transistor is presented here. We are able to repeatedly generate oscillating bubbles of consistent maximum radius, a. The dependency of the total circuit resistance to spark-generated bubble size in this method is discussed.
    Language English
    Publishing date 2013-01
    Publishing country United States
    Document type Journal Article
    ZDB-ID 209865-9
    ISSN 1089-7623 ; 0034-6748
    ISSN (online) 1089-7623
    ISSN 0034-6748
    DOI 10.1063/1.4776187
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Scaling law for bubbles induced by different external sources: theoretical and experimental study.

    Gong, S W / Ohl, S W / Klaseboer, E / Khoo, B C

    Physical review. E, Statistical, nonlinear, and soft matter physics

    2010  Volume 81, Issue 5 Pt 2, Page(s) 56317

    Abstract: The scaling relations for bubbles induced by different external sources are investigated based on a modified Rayleigh model and experimental observations. The equations derived from the modified Rayleigh model are presented to describe the collapse of ... ...

    Abstract The scaling relations for bubbles induced by different external sources are investigated based on a modified Rayleigh model and experimental observations. The equations derived from the modified Rayleigh model are presented to describe the collapse of bubbles induced by the different external sources such as electrical spark, laser, and underwater explosion. A scaling law is then formulated to establish the scaling relations between the different types of bubbles. The scaling law reveals the fact that the characteristic length scale factor differs from the characteristic time scale factor for the different types of bubbles. It is then validated by our experimental observations of the spark- and laser-generated bubbles as well as the bubbles induced by underwater explosions from previous published reports. With the present scaling law, studies on spark- or laser-generated bubbles as well as their applications (for example, in industrial or biomedical related applications) can benefit from the experiences and information built up over the years in underwater explosion bubbles. Conversely, it is possible to substitute a spark- or laser-generated bubble for an underwater explosion bubble in the study of a large-scale and complex physical problem.
    Language English
    Publishing date 2010-05
    Publishing country United States
    Document type Journal Article
    ISSN 1550-2376
    ISSN (online) 1550-2376
    DOI 10.1103/PhysRevE.81.056317
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article: Characterizing bubble dynamics created by high-intensity focused ultrasound for the delivery of antibacterial nanoparticles into a dental hard tissue.

    Ohl, S W / Shrestha, A / Khoo, B C / Kishen, A

    Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine

    2010  Volume 224, Issue 11, Page(s) 1285–1296

    Abstract: Hig hintensity focused ultrasound (HIFU) has been applied for drug delivery in various disease conditions. Delivery of antibacterial-nanoparticles into dental hard tissues may open up new avenues in the treatment of dental infections. However, the basic ... ...

    Abstract Hig hintensity focused ultrasound (HIFU) has been applied for drug delivery in various disease conditions. Delivery of antibacterial-nanoparticles into dental hard tissues may open up new avenues in the treatment of dental infections. However, the basic mechanism of bubble dynamics, its characterization, and working parameters for effective delivery of nanoparticles, warrants further understanding. This study was conducted to highlight the basic concept of HIFU and the associated bubble dynamics for the delivery of nanoparticles. Characterization experiments to deliver micro-scale particles into simulated tubular channels, activity of ultrasonic bubbles, and pressure measurement inside the HIFU system were conducted. Subsequently, experiments were carried out to test the ability of HIFU to deliver nanoparticles into human dentine using field emission scanning electron micrographs (FESEM) and elemental dispersive X-ray analysis (EDX). The characterization experiments showed that the bubbles collapsing at the opening of tubular channels were able to propel particles along their whole length. The pressure measured showed sufficient negative and positive pressure suggesting that the bubble grew to a certain size before collapsing, thus enabling the particles to be pushed. The FESEM and EDX analysis highlighted the ability of HIFU to deliver nanoparticles deep within the dentinal tubules. This study highlighted the characteristics and the mechanism involved of the bubbles generated by the HIFU and their capability to deliver nanoparticles.
    MeSH term(s) Animals ; Anti-Bacterial Agents/administration & dosage ; Dentin/chemistry ; Drug Delivery Systems/methods ; Humans ; Microbubbles/therapeutic use ; Microscopy, Electron, Scanning ; Nanoparticles/chemistry ; Nanoparticles/therapeutic use ; Spectrometry, X-Ray Emission ; Tooth/anatomy & histology ; Ultrasonography/methods
    Chemical Substances Anti-Bacterial Agents
    Language English
    Publishing date 2010-11
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1065942-0
    ISSN 2041-3033 ; 0954-4119 ; 0046-2039
    ISSN (online) 2041-3033
    ISSN 0954-4119 ; 0046-2039
    DOI 10.1243/09544119JEIM762
    Database MEDical Literature Analysis and Retrieval System OnLINE

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    Zs.A 2652: Show issues Location:
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  6. Article ; Online: Interaction of a spark-generated bubble with a rubber beam: numerical and experimental study.

    Gong, S W / Goh, B H T / Ohl, S W / Khoo, B C

    Physical review. E, Statistical, nonlinear, and soft matter physics

    2012  Volume 86, Issue 2 Pt 2, Page(s) 26307

    Abstract: In this paper, the physical behaviors of the interaction between a spark-generated bubble and a rubber beam are studied. Both numerical and experimental approaches are employed to investigate the bubble collapse near the rubber beam (which acts as a ... ...

    Abstract In this paper, the physical behaviors of the interaction between a spark-generated bubble and a rubber beam are studied. Both numerical and experimental approaches are employed to investigate the bubble collapse near the rubber beam (which acts as a flexible boundary) and the corresponding large deformation of the beam. Good agreement between the numerical simulations and experimental observations is achieved. The analysis reveals that the ratio of the bubble-beam distance to the maximum bubble radius influences the bubble evolution (from expansion to collapse) and the beam deformation. The stiffness of the beam plays an important role in the elastic beam response to bubble expansion and collapse. The effect of the vapor pressure on both bubble collapses and beam deflections is also examined. The results from this paper may provide physical insight into the complex physics of the bubble-rubber interaction. The understanding is possibly applicable in biomedicine for drug delivery to tissue, which is a soft material. It is also probably useful in the marine industry where ultrasonic bubbles are generated for the defouling of ship surfaces, which has been coated with an elastic material. There is also potential interest in underwater explosions near elastic structures.
    MeSH term(s) Algorithms ; Computer Simulation ; Elasticity ; Equipment Design ; Gases/chemistry ; Models, Theoretical ; Physics/methods ; Rubber/chemistry ; Time Factors ; Ultrasonics
    Chemical Substances Gases ; Rubber (9006-04-6)
    Language English
    Publishing date 2012-08
    Publishing country United States
    Document type Journal Article
    ISSN 1550-2376
    ISSN (online) 1550-2376
    DOI 10.1103/PhysRevE.86.026307
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Article: Interaction of a spark-generated bubble with a rubber beam: Numerical and experimental study

    Gong, S. W. / Goh, B. H. T. / Ohl, S. W. / Khoo, Boo Cheong

    Abstract: In this paper, the physical behaviors of the interaction between a spark-generated bubble and a rubber beam are studied. Both numerical and experimental approaches are employed to investigate the bubble collapse near the rubber beam (which acts as a ... ...

    Abstract In this paper, the physical behaviors of the interaction between a spark-generated bubble and a rubber beam are studied. Both numerical and experimental approaches are employed to investigate the bubble collapse near the rubber beam (which acts as a flexible boundary) and the corresponding large deformation of the beam. Good agreement between the numerical simulations and experimental observations is achieved. The analysis reveals that the ratio of the bubble-beam distance to the maximum bubble radius influences the bubble evolution (from expansion to collapse) and the beam deformation. The stiffness of the beam plays an important role in the elastic beam response to bubble expansion and collapse. The effect of the vapor pressure on both bubble collapses and beam deflections is also examined. The results from this paper may provide physical insight into the complex physics of the bubble-rubber interaction. The understanding is possibly applicable in biomedicine for drug delivery to tissue, which is a soft material. It is also probably useful in the marine industry where ultrasonic bubbles are generated for the defouling of ship surfaces, which has been coated with an elastic material. There is also potential interest in underwater explosions near elastic structures.
    Language en_us
    Document type Article
    Database AGRIS - International Information System for the Agricultural Sciences and Technology

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