Ohl SW et al, 2016: Lithotripter shock wave interaction with a bubble near various biomaterials.
Ohl SW, Klaseboer E, Szeri AJ, Khoo BC.
Institute of High Performance Computing, 1 Fusionopolis Way #16-16 Connexis, 138632, Singapore.
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.
Phys Med Biol. 2016 Oct 7;61(19):7031-7053. Epub 2016 Sep 20.
Cavitation bubbles are considered playing an important role in shockwave lithotripsy. In vitro experiments show that bubbles collapsing near interfaces (stone surface etc.) develop tiny waterjets with a velocity of several hundred m/s, pointing straight to the surface. Those jets may puncture surface areas of stones as well as small vessels. Micro damages on stone surfaces may be a significant mechanism of fragmentation by accelerating fatigue and fracture growth.
The authors calculate bubble interaction with various bio-materials such as bone, fat, skin, muscle cartilage and find only small variations. The mechanism of bubble dynamics is analysed, however according improvement for shock wave lithotripsy is not clear. In particular, possible means of utilization in clinical routine are missing.