Influence of microbubble size on postexcitation collapse thresholds for single ultrasound contrast agents using double passive cavitation detection

Antibacterial Sonodynamic Therapy: Current Status and Future Perspectives

Multidrug-resistant bacteria have emerged in both community and hospital settings, partly due to the misuse of antibiotics. The inventory of viable antibiotics is rapidly declining, and efforts toward discovering newer antibiotics are not yielding the desired outcomes. Therefore, alternate antibacterial therapies based on physical mechanisms such as light and ultrasound are being explored. Sonodynamic therapy (SDT) is an emerging therapeutic approach that involves exposing target tissues to a nontoxic sensitizing chemical and low-intensity ultrasound. SDT can enable site-specific cytotoxicity by producing reactive oxygen species (ROS) in response to ultrasound, which can be harnessed for treating bacterial infections. This approach can potentially be used for both superficial and deep-seated microbial infections. The majority of the sonosensitizers reported are nonpolar, exhibiting limited bioavailability and a high clearance rate in the body. Therefore, targeted delivery agents such as nanoparticle composites, liposomes, and microbubbles are being investigated. This article reviews recent developments in antibacterial sonodynamic therapy, emphasizing biophysical and chemical mechanisms, novel delivery agents, ultrasound exposure and image guidance strategies, and the challenges in the pathway to clinical translation.

Design of Albumin-Coated Microbubbles Loaded With Polylactide Nanoparticles

OBJECTIVES

A protocol was designed to produce albumin-coated microbubbles (MBs) loaded with functionalized polylactide (PLA) nanoparticles (NPs) for future drug delivery studies.

METHODS

Microbubbles resulted from the sonication of 5% bovine serum albumin and 15% dextrose solution. Functionalized NPs were produced by mixing fluorescent PLA and PLA-polyethylene glycol-carboxylate conjugates. Nanoparticle-loaded MBs resulted from the covalent conjugation of functionalized NPs and MBs. Three NP/MB volume ratios (1/1, 1/10, and 1/100) and unloaded MBs were produced and compared. Statistical evaluations were based on quantitative analysis of 3 parameters at 4 time points (1, 4, 5, and 6 days post MB fabrication): MB diameter using a circle detection routine based on the Hough transform, MB number density using a hemocytometer, and NP-loading yield based on MB counts from fluorescence and light microscopic images. Loading capacity of the albumin-coated MBs was evaluated by fluorescence.

RESULTS

Loaded MB sizes were stable over 6 days after production and were not significantly different from that of time-matched unloaded MBs. Number density evaluation showed that only 1/1 NP/MB volume ratio and unloaded MB number densities were stable over time, and that the 1/1 MB number density evaluated at each time point was not significantly different from that of unloaded MBs. The 1/10 and 1/100 NP/MB volume ratios had unstable number densities that were significantly different from that of unloaded MBs (P < .05). Fluorescence evaluation suggested that 1/1 MBs had a higher NP-loading yield than 1/10 and 1/100 MBs. Quantitative loading evaluation suggested that the 1/1 MBs had a loading capacity of 3700 NPs/MB.

CONCLUSIONS

A protocol was developed to load albumin MBs with functionalized PLA NPs for further drug delivery studies. The 1/1 NP/MB volume ratio appeared to be the most efficient to produce stable loaded MBs with a loading capacity of 3700 NPs/MB.

Non-invasive delivery of stealth, brain-penetrating nanoparticles across the blood-brain barrier using MRI-guided focused ultrasound

The blood-brain barrier (BBB) presents a significant obstacle for the treatment of many central nervous system (CNS) disorders, including invasive brain tumors, Alzheimer's, Parkinson's and stroke. Therapeutics must be capable of bypassing the BBB and also penetrate the brain parenchyma to achieve a desired effect within the brain. In this study, we test the unique combination of a non-invasive approach to BBB permeabilization with a therapeutically relevant polymeric nanoparticle platform capable of rapidly penetrating within the brain microenvironment. MR-guided focused ultrasound (FUS) with intravascular microbubbles (MBs) is able to locally and reversibly disrupt the BBB with submillimeter spatial accuracy. Densely poly(ethylene-co-glycol) (PEG) coated, brain-penetrating nanoparticles (BPNs) are long-circulating and diffuse 10-fold slower in normal rat brain tissue compared to diffusion in water. Following intravenous administration of model and biodegradable BPNs in normal healthy rats, we demonstrate safe, pressure-dependent delivery of 60nm BPNs to the brain parenchyma in regions where the BBB is disrupted by FUS and MBs. Delivery of BPNs with MR-guided FUS has the potential to improve efficacy of treatments for many CNS diseases, while reducing systemic side effects by providing sustained, well-dispersed drug delivery into select regions of the brain.