The research on shock-wave induced bio-effects is expanding rapidly where an emerging field is the so-called cell transformation, i.e., the uptake of deoxyribonucleic acid (DNA) from the surrounding. ‘Competent bacteria’ are those which are capable of being transformed. The standard method to identify transformed cells uses plasmids (DNA molecules that replicate independently of the chromosomal DNA) containing a gene that increases bacteria resistance to the antibiotic they are normally sensitive to. After plating the bacteria on a medium containing the antibiotic, only the transformed cells proliferate. Chilling the cells in CaCl
, shocking them with an electric field to create holes in the membrane, and ultrasound are physical methods to increase bacteria competence . Nevertheless, there is still a lack of efficient methods for DNA delivery. Cell transformation by ultrasound is based on cavitation-induced membrane permeability . Shock wave-induced sonoporation has also been associated with cavitation, i.e. growth and collapse of microbubbles [3-5]. In most studies clinical shock wave generators have been adapted to apply up to several hundredths of shock waves to a vial containing cells in suspension. After passage of each shock wave, a cloud of bubbles forms inside the vial. These bubbles expand and collapse violently after approximately
s, emitting high speed microjets that are supposed to be responsible for cell transformation . Microjet emission can be intensified if a second shock wave (Fig. 1) arrives shortly before the bubbles start to collapse. This phenomenon has been used to improve kidney stone fragmentation [7-8]. Temperature is another factor affecting cell transformation. Increased membrane permeability due to a temperature reduction has been reported ; however, if temperature reduction enhances microjet emission and thus contributes to cell transformation is unknown. To analyze this issue, the dynamics of a bubble immersed in water was simulated by using a well-known numerical model. The object of this study is to enhance shock wave-induced transfer of plasmids into
using tandem shock waves and to analyze the influence of the temperature on bubble dynamics and cell transformation.