In the above article [1], the authors regret that there was a mistake in calculating the mol% of the microbubble coating composition. For all experiments, the unit in mg/mL was utilized and the conversion mistake only came when converting to mol% in order to define the ratio between the coating formulation components. The correct molecular weight of PEG-40 stearate is 2046.54 g/mol [2], [3], not 328.53 g/mol. On page 1661, paragraph II-A, it should read 'The coating was composed of DSPC (84.8 mol%; P 6517; Sigma-Aldrich, Zwijndrecht, The Netherlands);PEG-40 stearate (8.2 mol%; P 3440; Sigma-Aldrich); DSPE-PEG(2000) (5.9 mol%; 880125 P; Avanti Polar Lipids, Alabaster, AL, USA); and DSPE-PEG(2000)-biotin (1.1 mol%; 880129 C; Avanti Polar Lipids)'.

The authors regret that there was a mistake in reporting the mol% of the microbubble coating composition used. For all experiments, the unit in mg/mL was used and the conversion mistake occurred only when converting to mol% to define the ratio between the coating formulation components. The correct molecular weight of PEG-40 stearate is 2046.54 g/mol (Shen et al. 2008; Kilic and Bolukcu 2018), not 328.53 g/mol. On page 1433, the sentence should read “The lipid coating was composed of 84.8 mol% DSPC (P6517, Sigma-Aldrich, Zwijndrecht, Netherlands) or DPPC (850355, Avanti Polar Lipids, Alabaster, AL, USA); 8.2 mol% polyoxyethylene-40-stearate (PEG40 stearate, P3440, Sigma-Aldrich); 5.9 mol% 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[carboxy(polyethylene glycol)2000 (DSPE-PEG2000, 880125, Avanti Polar Lipids); and 1.1 mol% 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[biotinyl(polyethylene glycol)-2000] (DSPE-PEG2000-biotin) (880129, Avanti Polar Lipids).” This correction does not change the conclusions published in this work. The authors apologize for any inconvenience caused.

In vivo cell tracking of therapeutic, tumor, and endothelial cells is an emerging field and a promising technique for imaging cardiovascular disease and cancer development. Site-specific labeling of endothelial cells with the MRI contrast agent superparamagnetic iron oxide (SPIO) in the absence of toxic agents is challenging. Therefore, the aim of this in vitro study was to find optimal parameters for efficient and safe SPIO-labeling of endothelial cells using ultrasound-activated CD31-targeted microbubbles for future MRI tracking. Ultrasound at a frequency of 1 MHz (10,000 cycles, repetition rate of 20 Hz) was used for varying applied peak negative pressures (10–160 kPa, i.e. low mechanical index (MI) of 0.01–0.16), treatment durations (0–30 s), time of SPIO addition (-5 min– 15 min with respect to the start of the ultrasound), and incubation time after SPIO addition (5 min– 3 h). Iron specific Prussian Blue staining in combination with calcein-AM based cell viability assays were applied to define the most efficient and safe conditions for SPIO-labeling. Optimal SPIO labeling was observed when the ultrasound parameters were 40 kPa peak negative pressure (MI 0.04), applied for 30 s just before SPIO addition (0 min). Compared to the control, this resulted in an approximate 12 times increase of SPIO uptake in endothelial cells in vitro with 85% cell viability. Therefore, ultrasound-activated targeted ultrasound contrast agents show great potential for effective and safe labeling of endothelial cells with SPIO.

In this study we present a combined optical sizing and acoustical characterization technique for the study of the dynamics of single freely-floating ultrasound contrast agent microbubbles exposed to long burst ultrasound excitations up to the milliseconds range. A co-axial flow device was used to position individual microbubbles on a streamline within the confocal region of three ultrasound transducers and a high-resolution microscope objective. Bright-field images of microbubbles passing through the confocal region were captured using a high-speed camera synchronized to the acoustical data acquisition to assess the microbubble response to a 1-MHz ultrasound burst. Nonlinear bubble vibrations were identified at a driving pressure as low as 50 kPa. The results demonstrate good agreement with numerical simulations based on the shell-buckling model proposed by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499-3505 (2005)]. The system demonstrates the potential for a high-throughput in vitro characterization of individual microbubbles.

Microbubbles (MBs) have been shown to create transient or lethal pores in cell membranes under the influence of ultrasound, known as ultrasound-mediated sonoporation. Several studies have reported enhanced drug delivery or local cell death induced by MBs that are either targeted to a specific biomarker (targeted microbubbles, tMBs) or that are not targeted (non-targeted microbubbles, ntMBs). However, both the exact mechanism and the optimal acoustic settings for sonoporation are still unknown. In this study we used real-time uptake patterns of propidium iodide, a fluorescent cell impermeable model drug, as a measure for sonoporation. Combined with high-speed optical recordings of MB displacement and ultra-high-speed recordings of MB oscillation, we aimed to identify differences in MB behavior responsible for either viable sonoporation or cell death. We compared ntMBs and tMBs with identical shell compositions exposed to long acoustic pulses (500–50,000 cycles) at various pressures (150–500 kPa). Propidium iodide uptake highly correlated with cell viability; when the fluorescence intensity still increased 120 s after opening of the pore, this resulted in cell death. Higher acoustic pressures and longer cycles resulted in more displacing MBs and enhanced sonoporation. Non-displacing MBs were found to be the main contributor to cell death, while displacement of tMBs enhanced reversible sonoporation and preserved cell viability. Consequently, each therapeutic application requires different settings: non-displacing ntMBs or tMBs are advantageous for therapies requiring cell death, especially at 500 kPa and 50,000 cycles, whereas short acoustic pulses causing limited displacement should be used for drug delivery.

The Brandaris 128 ultra-high-speed imaging facility has been updated over the last 10 years through modifications made to the camera’s hardware and software. At its introduction the camera was able to record 6 sequences of 128 images (500×292 pixels) at a maximum frame rate of 25 Mfps. The segmented mode of the camera was revised to allow for subdivision of the 128 image sensors intoarbitrary segments (1–128) with an inter-segment time of 17 μs. Furthermore, a region of interest can be selected to increase the number of recordings within a single run of the camera from 6 up to 125.By extending the imaging system with a laser-induced fluorescence setup, time-resolved ultra-highspeed fluorescence imaging of microscopic objects has been enabled. Minor updates to the systemare also reported here. © 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4758783]