Investigation of Optimized Treatment Conditions for Acoustic-Transfection Technique for Intracellular Delivery of Macromolecules

Medical Ultrasound Application Beyond Diagnosis: Insights From Ultrasound Sensing and Biological Response

Ultrasound (US) can easily penetrate media with excellent spatial precision corresponding to its wavelength. Naturally, US plays a pivotal role in the echolocation abilities of certain mammals such as bats and dolphins. In addition, medical US generated by transducers interact with tissues via delivering ultrasonic energy in the modes of heat generation, exertion of acoustic radiation force (ARF), and acoustic cavitation. Based on the principle of echolocation, various assistive devices for visual impairment people have been developed. High-Intensity Focused Ultrasound (HIFU) are developed for targeted ablation and tissue destruction. Besides thermal ablation, histotripsy with US is designed to damage tissue purely via mechanical effect without thermal coagulation. Low-Intensity Focused Ultrasound (LIFU) has been proven to be an effective stimulation method for neuromodulation. Furthermore, US has been reported to transiently increase the permeability of biological membranes, enabling acoustic transfection and blood-brain barrier open. All of these advances in US are changing the clinic. This review mainly introduces the advances in these aspects, focusing on the physical and biological principles, challenges, and future direction.

Genetically Encoded Trensor Circuits Report HeLa Cell Treatment with Polyplexed Plasmid DNA and Small-Molecule Transfection Modulators

HeLa cell transfection with plasmid DNA (pDNA) is widely used to materialize biologicals and as a preclinical test of nucleic acid-based vaccine efficacy. We sought to genetically encode mammalian transfection sensor (Trensor) circuits and test their utility in HeLa cells for detecting molecules and methods for their propensity to influence transfection. We intended these Trensor circuits to be triggered if their host cell was treated with polyplexed pDNA or certain small-molecule modulators of transfection. We prioritized three promoters, implicated by others in feedback responses as cells import and process foreign material and stably integrated each into the genomes of three different cell lines, each upstream of a green fluorescent protein (GFP) open reading frame within a transgene. All three Trensor circuits showed an increase in their GFP expression when their host HeLa cells were incubated with pDNA and the degraded polyamidoamine dendrimer reagent, SuperFect. We next experimentally demonstrated the modulation of PEI-mediated HeLa cell transient transfection by four different small molecules, with Trichostatin A (TSA) showing the greatest propensity to boost transgene expression. The Trensor circuit based on the TRA2B promoter (Trensor-T) was triggered by incubation with TSA alone and not the other three small molecules. These data suggest that mammalian reporter circuits could enable low-cost, high-throughput screening to identify novel transfection methods and reagents without the need to perform actual transfections requiring costly plasmids or expensive fluorescent labels.

Recent Advancements in High-Frequency Ultrasound Applications from Imaging to Microbeam Stimulation

Ultrasound is a versatile and well-established technique using sound waves with frequencies higher than the upper limit of human hearing. Typically, therapeutic and diagnosis ultrasound operate in the frequency range of 500 kHz to 15 MHz with greater depth of penetration into the body. However, to achieve improved spatial resolution, high-frequency ultrasound (>15 MHz) was recently introduced and has shown promise in various fields such as high-resolution imaging for the morphological features of the eye and skin as well as small animal imaging for drug and gene therapy. In addition, high-frequency ultrasound microbeam stimulation has been demonstrated to manipulate single cells or microparticles for the elucidation of physical and functional characteristics of cells with minimal effect on normal cell physiology and activity. Furthermore, integrating machine learning with high-frequency ultrasound enhances diagnostics, including cell classification, cell deformability estimation, and the diagnosis of diabetes and dysnatremia using convolutional neural networks (CNNs). In this paper, current efforts in the use of high-frequency ultrasound from imaging to stimulation as well as the integration of deep learning are reviewed, and potential biomedical and cellular applications are discussed.

Low-intensity transcranial focused ultrasound suppresses pain by modulating pain-processing brain circuits

ABSTRACT

There is an urgent and unmet clinical need to develop nonpharmacological interventions for chronic pain management because of the critical side effects of opioids. Low-intensity transcranial focused ultrasound (tFUS) is an emerging noninvasive neuromodulation technology with high spatial specificity and deep brain penetration. Here, we developed a tightly focused 128-element ultrasound transducer to specifically target small mouse brains using dynamic focus steering. We demonstrate that tFUS stimulation at pain-processing brain circuits can significantly alter pain-associated behaviors in mouse models in vivo. Our findings indicate that a single-session focused ultrasound stimulation to the primary somatosensory cortex (S1) significantly attenuates heat pain sensitivity in wild-type mice and modulates heat and mechanical hyperalgesia in a humanized mouse model of chronic pain in sickle cell disease. Results further revealed a sustained behavioral change associated with heat hypersensitivity by targeting deeper cortical structures (eg, insula) and multisession focused ultrasound stimulation to S1 and insula. Analyses of brain electrical rhythms through electroencephalography demonstrated a significant change in noxious heat hypersensitivity-related and chronic hyperalgesia-associated neural signals after focused ultrasound treatment. Validation of efficacy was carried out through control experiments, tuning ultrasound parameters, adjusting interexperiment intervals, and investigating effects on age, sex, and genotype in a head-fixed awake model. Importantly, tFUS was found to be safe, causing no adverse effects on motor function or the brain's neuropathology. In conclusion, the validated proof-of-principle experimental evidence demonstrates the translational potential of novel focused ultrasound neuromodulation for next-generation pain treatment without adverse effects.

Landscape of Cellular Bioeffects Triggered by Ultrasound-Induced Sonoporation

Sonoporation is the process of transient pore formation in the cell membrane triggered by ultrasound (US). Numerous studies have provided us with firm evidence that sonoporation may assist cancer treatment through effective drug and gene delivery. However, there is a massive gap in the body of literature on the issue of understanding the complexity of biophysical and biochemical sonoporation-induced cellular effects. This study provides a detailed explanation of the US-triggered bioeffects, in particular, cell compartments and the internal environment of the cell, as well as the further consequences on cell reproduction and growth. Moreover, a detailed biophysical insight into US-provoked pore formation is presented. This study is expected to review the knowledge of cellular effects initiated by US-induced sonoporation and summarize the attempts at clinical implementation.

Sonoporation: Past, Present, and Future

A surge of research in intracellular delivery technologies is underway with the increased innovations in cell-based therapies and cell reprogramming. Particularly, physical cell membrane permeabilization techniques are highlighted as the leading technologies because of their unique features, including versatility, independence of cargo properties, and high-throughput delivery that is critical for providing the desired cell quantity for cell-based therapies. Amongst the physical permeabilization methods, sonoporation holds great promise and has been demonstrated for delivering a variety of functional cargos, such as biomolecular drugs, proteins, and plasmids, to various cells including cancer, immune, and stem cells. However, traditional bubble-based sonoporation methods usually require special contrast agents. Bubble-based sonoporation methods also have high chances of inducing irreversible damage to critical cell components, lowering the cell viability, and reducing the effectiveness of delivered cargos. To overcome these limitations, several novel non-bubble-based sonoporation mechanisms are under development. This review will cover both the bubble-based and non-bubble-based sonoporation mechanisms being employed for intracellular delivery, the technologies being investigated to overcome the limitations of traditional platforms, as well as perspectives on the future sonoporation mechanisms, technologies, and applications.

Investigation of displacement of intracranial electrode induced by focused ultrasound stimulation

Transcranial focused ultrasound (tFUS) is an emerging neuromodulation technique to modulate brain activity non-invasively with high spatial specificity and focality. Given the influence of tFUS on brain activity, combining tFUS with multi-channel intracranial electrophysiological recordings enables monitoring of the activity of large populations of neurons with high temporal resolution. However, the physical interactions between tFUS and the electrode may affect a reliable assessment of neuronal activity, which remains poorly understood. In this paper, high-frequency ultrasound (HFUS) system was developed and integrated into tFUS neuromodulation system. The performance of the HFUS-based displacement tracking and analysis was evaluated by the theoretical analysis in the literature. The effects of various pressure levels on the displacements of the silicon-based microelectrode array in ex vivo brain tissue were investigated. The developed approach was capable of tracking and measuring the motion of a solid sphere in a tissue-mimicking phantom and measured displacements were comparable to theoretical predictions. The significant changes in the averaged peak displacements of the microelectrode array in ex vivo brain were observed with a pulse duration of 200 μs and a peak-to-peak pressure from 131 kPa at a center frequency of 500 kHz compared with the values from the negative control group. The present results demonstrate the relationship between several pressure levels and displacements of the microelectrode array in ex vivo brain through the developed approach. This approach can be used to determine a vibration-free threshold of ultrasound parameters in multi-channel intracranial recordings for a reliable assessment of electrophysiological activities of living neurons.

Optimization of microbubble-based DNA vaccination with low-frequency ultrasound for enhanced cancer immunotherapy

Immunotherapy is an important cancer treatment strategy; nevertheless, the lack of robust immune cell infiltration in the tumor microenvironment remains a factor in limiting patient response rates. In vivo gene delivery protocols can amplify immune responses and sensitize tumors to immunotherapies, yet non-viral transfection methods often sacrifice transduction efficiency for improved safety tolerance. To improve transduction efficiency, we optimized a strategy employing low ultrasound transmission frequency-induced bubble oscillation to introduce plasmids into tumor cells. Differential centrifugation isolated size-specific microbubbles. The diameter of the small microbubble population was 1.27 ± 0.89 μm and that of larger population was 4.23 ± 2.27 μm. Upon in vitro insonation with the larger microbubble population, 29.7% of cancer cells were transfected with DNA plasmids, higher than that with smaller microbubbles (18.9%, P <0.05) or positive control treatments with a commercial transfection reagent (12%, P < 0.01). After 48 h, gene expression increased more than two-fold in tumors treated with large, as compared with small, microbubbles. Furthermore, the immune response, including tumor infiltration of CD8⁺ T cells and F4/80⁺ macrophages, was enhanced. We believe that this safe and efficacious method can improve preclinical procedures and outcomes for DNA vaccines in cancer immunotherapy in the future.

Measurements of acoustic radiation force of ultrahigh frequency ultrasonic transducers using model-based approach

Even though ultrahigh frequency ultrasonic transducers over 60 MHz have been used for single-cell-level manipulation such as intracellular delivery, acoustic tweezers, and stimulation to investigate cell phenotype and cell mechanics, no techniques have been available to measure the actual acoustic radiation force (ARF) applied to target cells. Therefore, we have developed an approach to measure the ARF of ultrahigh frequency ultrasonic transducers using a theoretical model of the dynamics of a solid sphere in a gelatin phantom. To estimate ARF at the focus of a 130 MHz transducer, we matched measured maximum displacements of a solid sphere with theoretical calculations. We selected appropriate ranges of input voltages and pulse durations for single-cell applications, and the estimated ARF was in the range of tens of μN. To gauge the influence of pulse duration, an impulse of different pulse durations was estimated. Fluorescence resonance energy transfer live cell imaging was demonstrated to visualize calcium transport between cells after a target single cell was stimulated by the developed ultrasonic transducer.

An Ultrasonic Tweezer With Multiple Manipulation Functions Based on the Double-Parabolic-Reflector Wave-Guided High-Power Ultrasonic Transducer

The development of ultrasonic tweezers with multiple manipulation functions is challenging. In this work, multiple advanced manipulation functions are implemented for a single-probe-type ultrasonic tweezer with the double-parabolic-reflector wave-guided high-power ultrasonic transducer (DPLUS). Due to strong high-frequency (1.49 MHz) linear vibration at the manipulation probe's tip, which is excited by the DPLUS, the ultrasonic tweezer can capture microobjects in a noncontact mode and transport them freely above the substrate. The captured microobjects that adhere to the probe's tip in the low-frequency (154.4 kHz) working mode can be released by tuning the working frequency. The results of the finite-element method analyses indicate that the manipulations are caused by the acoustic radiation force.

High-Performance Ultrasonic Tweezers for Manipulation of Motile and Still Single Cells in a Droplet

The manipulation of motile and still single cells with the simultaneous features of selective trapping, 3-D path free transport, position-controllable release and little heat damage has been a significant challenge. We developed an ultrasonic method for capturing motile and still single cells with the aforementioned features in a droplet. During manipulation, a micromanipulation probe (MMP), which vibrated linearly with a trajectory parallel to a silicon substrate, was immersed in the droplet and was not in contact with the substrate. Motile and still single cells, such as Chattonella marina with a length of 30-50 μm and yeast cells with a diameter of 3-10 μm, at the interface between the droplet and substrate were selectively sucked onto the vibrating MMP and transported via a 3-D route inside the droplet by moving the MMP (or the device). The MMP and captured single cells were in contact, making the release position controllable. The measured temperature rise of the MMP was <0.1°C; thus, it is competitive for the manipulation of biological samples. Finite-element analyses revealed that the contact-type capture was due to acoustic radiation force generated by the ultrasonic field around the vibrating MMP. The dependence of the capture capability and working frequency bandwidth on the working conditions was investigated experimentally.

Advances in mechanism studies on ultrasonic gene delivery at cellular level

Ultrasound provides a means for intracellular gene delivery, contributing to a noninvasive and spatiotemporally controllable strategy suitable for clinical applications. Many studies have been done to provide mechanisms of ultrasound-mediated gene delivery at the cellular level. This review summarizes the studies on the important aspects of the mechanisms, providing an overview of recent progress in cellular experiment of ultrasound-mediated gene delivery.