Wearable Devices for Single-Cell Sensing and Transfection

Joule heating and electroosmotic flow in cellular micro/nano electroporation

Localized micro/nano-electroporation (MEP/NEP) shows tremendous potential in cell transfection with high cell viability, precise dose control, and good transfection efficacy. In MEP/NEP, micro or nanochannels are used to tailor the electric field distribution. Cells are positioned tightly by a micron or nanochannel, and the cargoes are delivered into the cell via the channel by electrophoresis (EP). Such confined geometries with micro and nanochannels are also widely used in sorting, isolation, and condensing of biomolecules and cells. Theoretical studies on the electrokinetic phenomena in these applications have been well established. However, for MEP/NEP applications, electrokinetic phenomena and their impact on the cell transfection efficiency and cell survival rate have not been studied comprehensively. In this work, we reveal the coupling between electric field, Joule heating, electroosmosis (EO), and EP in MEP/NEP at different channel sizes. A microfluidic biochip is used to investigate the electrokinetic phenomena in MEP/NEP on a single cell level. Bubble formation is observed at a threshold voltage due to Joule heating. The bubble is pushed to the cargo side due to EO and grows at the outlet of the nanochannel. As the voltage increases, the cargo transport efficiency decreases due to more intense EO, particularly for plasmid DNAs (3.5 kbp) with a low EP mobility. An 'electroporation zone' is defined for NEP/MEP systems with different channel sizes to avoid bubble formation and excessive EO velocity that may reduce the cargo delivery efficiency.

Recent Advances in Bioelectronics for Localized Drug Delivery

The last decade has witnessed remarkable advancements in bioelectronics, ushering in a new era of wearable and implantable devices for drug delivery. By utilizing miniaturized system design and/or flexible materials, bioelectronics illustrates ideal integration with target organs and tissues, making them ideal platforms for localized drug delivery. Furthermore, the development of electrically assisted drug delivery systems has enhanced the efficiency and safety of therapeutic administration, particularly for the macromolecules that encounter additional challenges in penetrating biological barriers. In this review, a concise overview of recent progress in bioelectronic devices for in vivo localized drug delivery, with highlights on the latest trends in device design, working principles, and their corresponding functionalities, is provided. The reported systems based on their targeted delivery locations as wearable systems, ingestible systems, and implantable systems are categorized. Each category is introduced in detail by highlighting the special requirements for devices and the corresponding solutions. The remaining challenges in this field and future directions are also discussed.

From Nanovesicles to Nanobubbles Based on Repeated Compression Method

Nanobubbles have been increasingly applied in biomedicine, which is attributed to their ability to work as ultrasound imaging contrast agents and powerful gene/drug carriers. Different production techniques or approaches have been developed to generate uniform and stable shelled nanobubbles. However, these shelled nanobubbles are usually prepared based on disordered shell materials, such as free phospholipids and polymers. In recent years, the continuous repeated compression method for a gas-liquid mixture has been developed to produce free and lipid-shelled nanobubbles. In this study, to explore the response of well-organized nanostructures to this method, the repeated compression method was used to treat preprepared liposomes and polymeric nanovesicles. Size distribution, morphologies, and ultrasound image contrast enhancement of these nanovesicles were determined before and after repeated compression. Results demonstrate that the presence of a phospholipid bilayer is vital to form liposome-based nanobubbles. And the low elastic modulus of the polymeric membrane is key to encapsulate gases into polymeric nanovesicles. Overall, it demonstrated the advantages of well-organized nanostructures to produce nanobubble structures, giving new insights into the preparation and understanding of nanobubbles.

Exploring retinal ganglion cells encoding to multi-modal stimulation using 3D microelectrodes arrays

Microelectrode arrays (MEA) are extensively utilized in encoding studies of retinal ganglion cells (RGCs) due to their capacity for simultaneous recording of neural activity across multiple channels. However, conventional planar MEAs face limitations in studying RGCs due to poor coupling between electrodes and RGCs, resulting in low signal-to-noise ratio (SNR) and limited recording sensitivity. To overcome these challenges, we employed photolithography, electroplating, and other processes to fabricate a 3D MEA based on the planar MEA platform. The 3D MEA exhibited several improvements compared to planar MEA, including lower impedance (8.73 ± 1.66 kΩ) and phase delay (-15.11° ± 1.27°), as well as higher charge storage capacity (CSC = 10.16 ± 0.81 mC/cm2), cathodic charge storage capacity (CSCc = 7.10 ± 0.55 mC/cm2), and SNR (SNR = 8.91 ± 0.57). Leveraging the advanced 3D MEA, we investigated the encoding characteristics of RGCs under multi-modal stimulation. Optical, electrical, and chemical stimulation were applied as sensory inputs, and distinct response patterns and response times of RGCs were detected, as well as variations in rate encoding and temporal encoding. Specifically, electrical stimulation elicited more effective RGC firing, while optical stimulation enhanced RGC synchrony. These findings hold promise for advancing the field of neural encoding.

Cell membrane damage and cargo delivery in nano-electroporation

Nanochannel electroporation (NEP) is a new technology for cell transfection, which provides superior gene delivery and cell viability to conventional bulk electroporation (BEP). In NEP, the cells laid on a porous substrate are subjected to an asymmetric electric field which induces asymmetric membrane poration. The cell membrane near the channel outlet ('transfection membrane') is porated intensely, allowing direct delivery of genetic materials, while the rest of the cell membrane ('non-transfection membrane') remains much less perturbed for low cellular damage. In this work, the transfection window of NEP for the delivery of different sized molecules is systematically investigated. The results show that small molecules (∼0.6 kDa) can be delivered into cells at a relatively lower voltage without significantly impacting the non-transfection membrane. To deliver larger molecules (∼6 kDa), a higher working voltage is required at the cost of cell viability due to more severe damage of the non-transfection membrane. Through numerical analysis of both transient transmembrane potential (t-TMP) and dynamic transmembrane potential (d-TMP), here we show that the membrane damage on both transfection and non-transfection sides of the cell membrane can be predicted. The agreement between experimental results and numerical analysis provides a comprehensive understanding of cell membrane damage and cargo delivery in NEP.

In vivo Visualization of Collagen Transdermal Absorption by Second-Harmonic Generation and Two-Photon Excited Fluorescence Microscopy

The transdermal administration of collagen is an important method used for wound healing and skin regeneration. However, due to the limitations of previous approaches, the process and degree of collagen transdermal absorption could only be quantitatively and qualitatively evaluated in vitro. In the present study, we introduced a novel approach that combines second-harmonic generation with two-photon excited fluorescence to visualize the dynamics of collagen transdermal absorption in vivo. High-resolution images showed that exogenous recombinant human collagen permeated the epidermis through hair follicles and sebaceous glands reached the dermis, and formed reticular structures in real time. We also validated these findings through traditional in vitro skin scanning and histological examination. Thus, our approach provides a reliable measurement for real-time evaluation of collagen absorption and treatment effects in vivo.

Semi-Implantable Bioelectronics

Developing techniques to effectively and real-time monitor and regulate the interior environment of biological objects is significantly important for many biomedical engineering and scientific applications, including drug delivery, electrophysiological recording and regulation of intracellular activities. Semi-implantable bioelectronics is currently a hot spot in biomedical engineering research area, because it not only meets the increasing technical demands for precise detection or regulation of biological activities, but also provides a desirable platform for externally incorporating complex functionalities and electronic integration. Although there is less definition and summary to distinguish it from the well-reviewed non-invasive bioelectronics and fully implantable bioelectronics, semi-implantable bioelectronics have emerged as highly unique technology to boost the development of biochips and smart wearable device. Here, we reviewed the recent progress in this field and raised the concept of "Semi-implantable bioelectronics", summarizing the principle and strategies of semi-implantable device for cell applications and in vivo applications, discussing the typical methodologies to access to intracellular environment or in vivo environment, biosafety aspects and typical applications. This review is meaningful for understanding in-depth the design principles, materials fabrication techniques, device integration processes, cell/tissue penetration methodologies, biosafety aspects, and applications strategies that are essential to the development of future minimally invasive bioelectronics.

Potential of Microneedle Systems for COVID-19 Vaccination: Current Trends and Challenges

To prevent the coronavirus disease 2019 (COVID-19) pandemic and aid restoration to prepandemic normality, global mass vaccination is urgently needed. Inducing herd immunity through mass vaccination has proven to be a highly effective strategy for preventing the spread of many infectious diseases, which protects the most vulnerable population groups that are unable to develop immunity, such as people with immunodeficiencies or weakened immune systems due to underlying medical or debilitating conditions. In achieving global outreach, the maintenance of the vaccine potency, transportation, and needle waste generation become major issues. Moreover, needle phobia and vaccine hesitancy act as hurdles to successful mass vaccination. The use of dissolvable microneedles for COVID-19 vaccination could act as a major paradigm shift in attaining the desired goal to vaccinate billions in the shortest time possible. In addressing these points, we discuss the potential of the use of dissolvable microneedles for COVID-19 vaccination based on the current literature.

Wearable Bioelectronics for Chronic Wound Management

Chronic wounds are a major healthcare issue and can adversely affect the lives of millions of patients around the world. The current wound management strategies have limited clinical efficacy due to labor-intensive lab analysis requirements, need for clinicians' experiences, long-term and frequent interventions, limiting therapeutic efficiency and applicability. The growing field of flexible bioelectronics enables a great potential for personalized wound care owing to its advantages such as wearability, low-cost, and rapid and simple application. Herein, recent advances in the development of wearable bioelectronics for monitoring and management of chronic wounds are comprehensively reviewed. First, the design principles and the key features of bioelectronics that can adapt to the unique wound milieu features are introduced. Next, the current state of wound biosensors and on-demand therapeutic systems are summarized and highlighted. Furthermore, we discuss the design criteria of the integrated closed loop devices. Finally, the future perspectives and challenges in wearable bioelectronics for wound care are discussed.

Cellular nanointerface of vertical nanostructure arrays and its applications

Vertically standing nanostructures with various morphologies have been developed with the emergence of the micro-/nanofabrication technology. When cells are cultured on them, various bio-nano interfaces between cells and vertical nanostructures would impact the cellular activities, depending on the shape, density, and height of nanostructures. Many cellular pathway activation processes involving a series of intracellular molecules (proteins, RNA, DNA, enzymes, etc.) would be triggered by the cell morphological changes induced by nanostructures, affecting the cell proliferation, apoptosis, differentiation, immune activation, cell adhesion, cell migration, and other behaviors. In addition, the highly localized cellular nanointerface enhances coupled stimulation on cells. Therefore, understanding the mechanism of the cellular nanointerface can not only provide innovative tools for regulating specific cell functions but also offers new aspects to understand the fundamental cellular activities that could facilitate the precise monitoring and treatment of diseases in the future. This review mainly describes the fabrication technology of vertical nanostructures, analyzing the formation of cellular nanointerfaces and the effects of cellular nanointerfaces on cells' fates and functions. At last, the applications of cellular nanointerfaces based on various nanostructures are summarized.

Electrochemical Cell-based Biosensors for Biomedical Applications

Abstract:

Electrochemical cell-based biosensors have been showing increasing interest within the last 15 years, with a large number of reports generally dealing with the sensors’ sensitivity, selectivity, stability, signal-to-noise ratio, spatiotemporal resolution, etc. However, only a few of them are now available as commercial products on the market. In this review, technological advances, current challenges and opportunities of electrochemical cell-based biosensors are presented. The article encompasses emerging studies, mainly focusing on the last five years (from 2016 to mid 2021), towards cell-based biological field-effect devices, cell-based impedimetric sensors and cell-based microelectrode arrays. In addition, special attention lies on recent progress in recording at the single-cellular level, including intracellular monitoring with high spatiotemporal resolution as well as integration into microfluidics for lab-on-a-chip applications. Moreover, a comprehensive discussion on challenges and future perspectives will address the future potential of electrochemical cell-based biosensors.

Nanostructured Carbons: towards Soft-Bioelectronics, Biosensing and Theraputic Applications

Recently, nanostructured carbon-based soft bioelectronics and biosensors have received tremendous attention due to their outstanding physical and chemical properties. The ultrahigh specific surface area, high flexibility, lightweight, high electrical conductivity, and biocompatibility of 1D and 2D nanocarbons, such as carbon nanotubes (CNT) and graphene, are advantageous for bioelectronics applications. These materials improve human life by delivering therapeutic advancements in gene, tumor, chemo, photothermal, immune, radio, and precision therapies. They are also utilized in biosensing platforms, including optical and electrochemical biosensors to detect cholesterol, glucose, pathogenic bacteria (e. g., coronavirus), and avian leucosis virus. This review summarizes the most recent advancements in bioelectronics and biosensors by exploiting the outstanding characteristics of nanocarbon materials. The synthesis and biocompatibility of nanocarbon materials are briefly discussed. In the following sections, applications of graphene and CNTs for different therapies and biosensing are elaborated. Finally, the key challenges and future perspectives of nanocarbon materials for biomedical applications are highlighted.

A finger-driven disposable micro-platform based on isothermal amplification for the application of multiplexed and point-of-care diagnosis of tuberculosis

Tuberculosis (TB) remains the high-risk infectious pathogen that caused global pandemic and high mortality, particularly in the areas lack in health resources. Clinical TB screening and diagnosis are so far mainly conducted on limited types of commercial platforms, which are expensive and require skilled personnel. In this work, we introduced a low-cost and portable finger-driven microfluidic chip (named Fd-MC) based on recombinase polymerase amplification (RPA) for rapid on-site detection of TB. After injection of the pre-treated sample solution, the pre-packaged buffer was driven by the pressure generated by the finger-actuated operation to accomplish sequential processes of diagnosis in a fully isolated microchannel. An in-situ fluorescence strategy based on FAM-probe was implemented for on-chip results read-out though a hand-held UV lamp. Hence, the Fd-MC proved unique advantageous for avoiding the risk of infection or environmental contamination. In addition, the Fd-MC was designed for multiplexed detection, which is able to not only identify TB/non-TB infection, but also differentiate between human Mycobacterium tuberculosis and Mycobacterium bovis. The platform was verified in 37 clinical samples, statistically with 100% specificity and 95.2% sensitivity as compared to commercial real-time RPA. Overall, the proposed platform eliminates the need on external pumps and skilled personnel, holding promise to POC testing in the resource-limited area.

Microfluidic platforms for single neuron analysis

Single-neuron actions are the basis of brain function, as clinical sequelae, neuronal dysfunction or failure for most of the central nervous system (CNS) diseases and injuries can be identified via tracing single-neurons. The bulk analysis methods tend to miscue critical information by assessing the population-averaged outcomes. However, its primary requisite in neuroscience to analyze single-neurons and to understand dynamic interplay of neurons and their environment. Microfluidic systems enable precise control over nano-to femto-liter volumes via adjusting device geometry, surface characteristics, and flow-dynamics, thus facilitating a well-defined micro-environment with spatio-temporal control for single-neuron analysis. The microfluidic platform not only offers a comprehensive landscape to study brain cell diversity at the level of transcriptome, genome, and/or epigenome of individual cells but also has a substantial role in deciphering complex dynamics of brain development and brain-related disorders. In this review, we highlight recent advances of microfluidic devices for single-neuron analysis, i.e., single-neuron trapping, single-neuron dynamics, single-neuron proteomics, single-neuron transcriptomics, drug delivery at the single-neuron level, single axon guidance, and single-neuron differentiation. Moreover, we also emphasize limitations and future challenges of single-neuron analysis by focusing on key performances of throughput and multiparametric activity analysis on microfluidic platforms.

Digital printing of selective and reversible ion optodes on fabrics: toward smart clothes for epidermal chemical sensing

While wearable chemical sensors often rely on electrochemical techniques, optical chemical sensors coupled with a smartphone or a miniaturized camera represent an attractive approach to the monitoring of sweat composition. In this paper, we modify real sports fabrics such as polyester-spandex fabrics with rational combinations of sensing chemicals including a pH indicator, an ion exchanger, and an ionophore via one-step inkjet printing. Highly selective and fully reversible pH optodes as well as Na⁺- and K⁺-selective optodes are obtained only when the most hydrophobic sensing chemicals are used (e.g., sodium ionophore VIII vs. sodium ionophore VI). These sensors exhibit large color-based responses that can be readily identified by naked eye or analyzed via an iPhone app. Their dynamic ranges well cover the physiological sweat concentrations of the analytes. Compared to most other sensors created on garments, our fabric-based optodes are cost-effective, mass-reproducible by the digital printing technology currently used in the textile industry, and do not significantly compromise the essential properties of fabrics such as flexibility, stretchability, wickability, and breathability.

Microscopic impedance cytometry for quantifying single cell shape

In this work, we investigated the ability of impedance flow cytometry to measure the shape of single cells/particles. We found that the impedance pulses triggered by micro-objects that are asymmetric in morphology show a tilting trend, and there is no such a tilting trend for symmetric ones. Therefore, we proposed a new metric, tilt index, to quantify the tilt level of the impedance pulses. Through simulation, we found that the value of tilt index tends to be zero for perfectly symmetrical objects, while the value is greater than zero for asymmetrical ones. Also, this metric was found to be independent on the trajectories (i.e., lateral, and z-direction shift) of the target micro-object. In experiments, we adopted a home-made lock-in amplifier and performed experiments on 10 μm polystyrene beads and Euglena gracilis (E. gracilis) cells with varying shapes. The experimental results coincided with the simulation results and demonstrated that the new metric (tilt index) enables the impedance cytometry to characterize the shape single cells/particles without microscopy or other optical setups.

A Single-Neuron: Current Trends and Future Prospects

The brain is an intricate network with complex organizational principles facilitating a concerted communication between single-neurons, distinct neuron populations, and remote brain areas. The communication, technically referred to as connectivity, between single-neurons, is the center of many investigations aimed at elucidating pathophysiology, anatomical differences, and structural and functional features. In comparison with bulk analysis, single-neuron analysis can provide precise information about neurons or even sub-neuron level electrophysiology, anatomical differences, pathophysiology, structural and functional features, in addition to their communications with other neurons, and can promote essential information to understand the brain and its activity. This review highlights various single-neuron models and their behaviors, followed by different analysis methods. Again, to elucidate cellular dynamics in terms of electrophysiology at the single-neuron level, we emphasize in detail the role of single-neuron mapping and electrophysiological recording. We also elaborate on the recent development of single-neuron isolation, manipulation, and therapeutic progress using advanced micro/nanofluidic devices, as well as microinjection, electroporation, microelectrode array, optical transfection, optogenetic techniques. Further, the development in the field of artificial intelligence in relation to single-neurons is highlighted. The review concludes with between limitations and future prospects of single-neuron analyses.

pH-Modulated memristive behavior based on an edible garlic-constructed bio-electronic device

A new type of memristive memory device with an edible garlic-constructed Ag/garlic/fluorine-doped SnO₂(FTO) structure for analog neuromorphic sensor applications was designed.