Oleksandr Shpak's research while affiliated with University of Twente and other places

... Among these methods, ultrasound (US) is a promising delivery method for several therapeutic molecules (e.g., chemotherapeutic drugs, immunotherapeutic agents, nucleic acids, and sensitizing agents) in various kinds of tumors. Depending on acoustic parameters, ultrasound can generate both thermal and mechanical stimuli, which may be exploited (i) to trigger the release of drugs from particles (e.g., liposomes, polymer particles, micelles, microbubbles, etc.), (ii) to excite sensitizers, and (iii) to induce the reversible permeabilization of biological barriers (e.g., endothelial barriers, plasma membrane, etc.), thus improving the accumulation of drugs in tumor cells [16][17][18][19][20][21][22][23][24][25]. These US strategies, including mild hyperthermia, sonodynamic therapy, microbubble-assisted US, and US on its own, improve the efficacy of anticancer therapies in a safe and noninvasive way [26][27][28][29]. ...

... Both molecular and polymeric F-surfactants ( Table 2) allow production of stable NEs, MBs, reverse water-in-PFC emulsions, multiple emulsions or high internal phase ratio gel-emulsions. While use of F-surfactants is no longer needed for stable NE production, they are often used for preparing P-SNEs from volatile PFCs [76][77][78], and have so far been systematically used for reverse PFC emulsion preparation. F-surfactants are also relevant to colloid preparation through microfluidic procedures. ...

... Earlier studies showed that ADV begins with the formation of a single vapor nucleus within the droplet [10][11][12][13]. The nucleation site, resulting from pressure amplification due to the superharmonic focusing effect [14], depended on the ratio of droplet size to the incoming wavelength. ADV physics and the effect of critical parameters have been reviewed in prior articles [15][16][17]. ...

... Due to the low surface tension and high vapor pressure of the perfluorocarbon core in phase-shift droplets, ultrasound can trigger a phase transition without substantial generation of heat when the liquid is under tension during the peak rarefactional half cycle of the ultrasound pulse. Earlier studies showed that ADV begins with the formation of a single vapor nucleus within the droplet [10][11][12][13]. The nucleation site, resulting from pressure amplification due to the superharmonic focusing effect [14], depended on the ratio of droplet size to the incoming wavelength. ...

... The nanodroplets likely coalesced together during the repeated vaporization, eventually forming stable microbubbles. A similar behavior has been described with ADV of PFP nanodroplets, where repeated vaporization is needed to result in the formation of stable microbubbles [49]. Meanwhile, nanodroplets in water did not exhibit this behavior. ...

... It is shown that an increase in the initial droplet size leads to a stronger growth of the vapor bubble, as well as to an increase in the amplitude of its oscillations. Experimental data on the evaporation of a droplet of dodecafluoropentane in water are presented in [9], and a mathematical model of a vapor bubble is also considered, taking into account gas diffusion in an infinite perfluorocarbon liquid. It is noted that, without taking into account gas diffusion, the vapor bubble collapses after the first acoustic cycle. ...