Microbubble-Assisted Ultrasound for Drug Delivery to the Retina in an Ex Vivo Eye Model

Efficacy and safety of ultrasound combined with microbubbles for treating retinal artery occlusion in rats

Retinal artery occlusion (RAO) is an eye emergency that results in severe and permanent visual impairment. The effectiveness of conventional treatment on retinal artery recanalization and vision improvement is uncertain. Ultrasound combined with microbubbles (USMB) technology is a minimally invasive transvascular drug delivery technique that has been used to investigate the treatment of stroke, myocardial infarction ，and obstructive vascular disease. The aim of this study was to investigate the efficacy and safety of USMB in the treatment of RAO. RAO model was induced by photochemical thrombosis. Normal rat eyes were treated with ultrasound at different mechanical index (MI) of 0.2,0.4 and 0.8, to explore its safety. RAO rats were randomly divided into RAO group, RAO + USMB group and RAO + US (Ultrasound) group to explore the effectiveness of the USMB in the treatment of RAO. A set of relevant ophthalmic in vivo imaging techniques was used to explore the natural history of RAO model rats while assessing tolerance and efficacy to USMB treatment. We found that blocked retinal arteries recanalized within 4-24 h in the RAO model. Retinal edema peaks within 4-24 h and resolves within 3-7 days. Blood flow density (BFD) began to recover 4 h after model induction. USMB did not cause irreversible retinal damage when the MI was below 0.4. Treatment with USMB at an MI of 0.2 significantly reduced retinal edema in RAO rats 1 day after model induction and prevented further retinal atrophy. In addition, USMB significantly increased BFD in RAO rats within 4 h and promoted the recovery of visual function. USMB can be a safe and effective treatment for RAO with protective effects on the neuroretina.

From concept to early clinical trials: 30 years of microbubble-based ultrasound-mediated drug delivery research

Ultrasound mediated drug delivery, a promising therapeutic modality, has evolved remarkably over the past three decades. Initially designed to enhance contrast in ultrasound imaging, microbubbles have emerged as a main vector for drug delivery, offering targeted therapy with minimized side effects. This review addresses the historical progression of this technology, emphasizing the pivotal role microbubbles play in augmenting drug extravasation and targeted delivery. We explore the complex mechanisms behind this technology, from stable and inertial cavitation to diverse acoustic phenomena, and their applications in medical fields. While the potential of ultrasound mediated drug delivery is undeniable, there are still challenges to overcome. Balancing therapeutic efficacy and safety and establishing standardized procedures are essential areas requiring attention. A multidisciplinary approach, gathering collaborations between researchers, engineers, and clinicians, is important for exploiting the full potential of this technology. In summary, this review highlights the potential of using ultrasound mediated drug delivery in improving patient care across various medical conditions.

Ultrasound-Mediated Ocular Drug Delivery: From Physics and Instrumentation to Future Directions

Drug delivery to the anterior and posterior segments of the eye is impeded by anatomical and physiological barriers. Increasingly, the bioeffects produced by ultrasound are being proven effective for mitigating the impact of these barriers on ocular drug delivery, though there does not appear to be a consensus on the most appropriate system configuration and operating parameters for this application. In this review, the fundamental aspects of ultrasound physics most pertinent to drug delivery are presented; the primary phenomena responsible for increased drug delivery efficacy under ultrasound sonication are discussed; an overview of common ocular drug administration routes and the associated ocular barriers is also given before reviewing the current state of the art of ultrasound-mediated ocular drug delivery and its potential future directions.

Efficacy and Safety of Low-Intensity Pulsed Ultrasound-Induced Blood-Retinal Barrier Opening in Mice

Systemic drugs can treat various retinal pathologies such as retinal cancers; however, their ocular diffusion may be limited by the blood-retina barrier (BRB). Sonication corresponds to the use of ultrasound (US) to increase the permeability of cell barriers including in the BRB. The objective was to study the efficacy and safety of sonication using microbubble-assisted low-intensity pulsed US in inducing a transient opening of the BRB. The eyes of C57/BL6J mice were sonicated at different acoustic pressures (0.10 to 0.50 MPa). Efficacy analyses consisted of fluorescein angiography (FA) performed at different timepoints and the size of the leaked molecules was assessed using FITC-marked dextrans. Tolerance was assessed by fundus photographs, optical coherence tomography, immunohistochemistry, RT-qPCR, and electroretinograms. Sonication at 0.15 MPa was the most suitable pressure for transient BRB permeabilization without altering the morphology or function of the retina. It did not increase the expression of inflammation or apoptosis markers in the retina, retinal pigment epithelium, or choroid. The dextran assay suggested that drugs up to 150 kDa in size can cross the BRB. Microbubble-assisted sonication at an optimized acoustic pressure of 0.15 MPa provides a non-invasive method to transiently open the BRB, increasing the retinal diffusion of systemic drugs without inducing any noticeable side-effect.