Micro Electromechanical Systems (MEMS) Based Microfluidic Devices for Biomedical Applications

Micro Electromechanical Systems (MEMS) based microfluidic devices have gained popularity in biomedicine field over the last few years. In this paper, a comprehensive overview of microfluidic devices such as micropumps and microneedles has been presented for biomedical applications. The aim of this paper is to present the major features and issues related to micropumps and microneedles, e.g., working principles, actuation methods, fabrication techniques, construction, performance parameters, failure analysis, testing, safety issues, applications, commercialization issues and future prospects. Based on the actuation mechanisms, the micropumps are classified into two main types, i.e., mechanical and non-mechanical micropumps. Microneedles can be categorized according to their structure, fabrication process, material, overall shape, tip shape, size, array density and application. The presented literature review on micropumps and microneedles will provide comprehensive information for researchers working on design and development of microfluidic devices for biomedical applications

Madden, Julia; O'Mahony, Conor; Thompson, Michael; O'Riordan, Alan; Galvin, Paul

This article explores recent advances in the development of electrochemical biosensors on microneedle platforms towards on-device sensing of biomarkers present in dermal interstitial fluid. The integration of a biosensor with a microneedle platform opens the possibility for minimally invasive bio-chemical detection or continuous monitoring within the dermal interstitial fluid. An introduction to interstitial fluid is provided placing emphasis on sampling methods that have been employed to extract and/or sample tissue fluid for analysis. We look briefly at microneedle technologies used to extract dermal interstitial fluid for subsequent analysis. Successive content will focus on microneedle technologies which have been integrated with electrochemical biosensors for the quantification of various metabolites, electrolytes and other miscellaneous entities known to be present in the dermal interstitial fluid. The review concludes with some of the key challenges and opportunities faced by this next-generation wearable sensing technology

Microneedle based electrochemical (bio)sensing: towards decentralized and continuous health status monitoring

Microneedle (MN) based electrochemical (bio)sensing has become a growing field within the discipline of analytical chemistry as a result of its unique capacity for continuous, decentralized health status monitoring. There are two significant advantages to this exclusive feature: i) the ability to directly analyze interstitial fluid (ISF), a body fluid with a similar enough composition to plasma (and blood) to be considered a plentiful source of information related to biologically relevant molecules and biomarkers; and ii) the capacity to overcome some of the major limitations of blood analysis including painful extraction, high interferant concentrations, and incompatibility with diagnosis of infants (and especially newborns). Recent publications have demonstrated important advancements in electrochemical MN sensor technology, among which are included new MN fabrication methods and various modification strategies, providing different architectures and allowing for the integration of electronics. This versatility highlights the undeniable need for interdisciplinary efforts towards tangible progress in the field. In a context evidently dominated by glucose sensing, which is slowly being expanded towards other analytes, the following crucial questions arise: to what extent are electrochemical MN (bio)sensors a reliable analytical tool for continuous ISF monitoring? Which is the best calibration protocol to be followed for in vivo assays? Which strategies can be employed to protect the sensing element during skin penetration? Is there an appropriate validation methodology to assess the accuracy of electrochemical MN (bio)sensors? How significant is the distinction between successful achievements in the laboratory and the real commercial feasibility of products? This paper aims to reflect on those previous questions while reviewing the progress of electrochemical MN (bio)sensors in the last decade with a focus on the analytical aspects. Overall, we describe the current state of electrochemical MN (bio)sensors, the benefits and challenges associated to ISF monitoring, as well as key features (and bottlenecks) regarding its implementation for in vivo assays

Microneedle array sensors based on carbon nanoparticle composites: interfacial chemistry and electroanalytical properties

Conductive microneedle patches consisting of carbon nanoparticles embedded in a polystyrene matrix have been prepared using micro-moulding techniques. The interfacial properties of the structures before and after electrochemical etching have been characterised using X-ray photoelectron spectroscopy and contact angle. Anodisation of the needles leads to a significant increase in oxygen functionality and is shown to dramatically improve the electroanalytical capabilities of the microneedle array. The detection of uric acid in horse blood was used as a model system through which to assess the performance of the system. The composite approach is shown to lead to viable carbon-based sensors and can offer a rapid prototype option for the development of tailored microneedle systems

Flexible neural probes: a review of the current advantages, drawbacks, and future demands

Brain diseases affect millions of people and have a huge social and economic impact. The use of neural probes for studies in animals has been the main approach to increasing knowledge about neural network functioning. Ultimately, neuroscientists are trying to develop new and more effective therapeutic approaches to treating neurological disorders. The implementation of neural probes with multifunctionalities (electrical, optical, and fluidic interactions) has been increasing in the last few years, leading to the creation of devices with high temporal and spatial resolution. Increasing the applicability of, and elements integrated into, neural probes has also led to the necessity to create flexible interfaces, reducing neural tissue damage during probe implantation and increasing the quality of neural acquisition data. In this paper, we review the fabrication, characterization, and validation of several types of flexible neural probes, exploring the main advantages and drawbacks of these devices. Finally, future developments and applications are covered. Overall, this review aims to present the currently available flexible devices and future appropriate avenues for development as possible guidance for future engineered devices.This work was supported by the CMEMS-UMinho Strategic Project (Nos. UIDB/04436/2020 and UIDP/04436/2020) and the MPhotonBiopsy (No. PTDC/FIS-OTI/1259/2020; https:// doi.org/10.54499/PTDC/FIS-OTI/1259/2020). João R. FREITAS thanks Fundação para a Ciência e a Tecnologia (FCT) for the Ph.D. grant (No. 2020.07708.BD). Sara PIMENTA thanks FCT for the grant (No. 2022.00101.CEECIND/CP1718/CT0008; https:// doi.org/10.54499/2022.00101.CEECIND/CP1718/CT0008)

Using microneedle array electrodes for non-invasive electrophysiological signal acquisition and sensory feedback evoking

Introduction: Bidirectional transmission of information is needed to realize a closed-loop human-machine interaction (HMI), where electrophysiological signals are recorded for man-machine control and electrical stimulations are used for machine-man feedback. As a neural interface (NI) connecting man and machine, electrodes play an important role in HMI and their characteristics are critical for information transmission.Methods: In this work, we fabricated a kind of microneedle array electrodes (MAEs) by using a magnetization-induced self-assembly method, where microneedles with a length of 500–600 μm and a tip diameter of ∼20 μm were constructed on flexible substrates. Part of the needle length could penetrate through the subjects’ stratum corneum and reach the epidermis, but not touch the dermis, establishing a safe and direct communication pathway between external electrical circuit and internal peripheral nervous system.Results: The MAEs showed significantly lower and more stable electrode-skin interface impedance than the metal-based flat array electrodes (FAEs) in various testing scenarios, demonstrating their promising impedance characteristics. With the stable microneedle structure, MAEs exhibited an average SNR of EMG that is more than 30% higher than FAEs, and a motion-intention classification accuracy that is 10% higher than FAEs. The successful sensation evoking demonstrated the feasibility of the MAE-based electrical stimulation for sensory feedback, where a variety of natural and intuitive feelings were generated in the subjects and thereafter objectively verified through EEG analysis.Discussion: This work confirms the application potential of MAEs working as an effective NI, in both electrophysiological recording and electrical stimulation, which may provide a technique support for the development of HMI

Smart responsive microneedles for controlled drug delivery

As an emerging technology, microneedles offer advantages such as painless administration, good biocompatibility, and ease of self-administration, so as to effectively treat various diseases, such as diabetes, wound repair, tumor treatment and so on. How to regulate the release behavior of loaded drugs in polymer microneedles is the core element of transdermal drug delivery. As an emerging on-demand drug-delivery technology, intelligent responsive microneedles can achieve local accurate release of drugs according to external stimuli or internal physiological environment changes. This review focuses on the research efforts in smart responsive polymer microneedles at home and abroad in recent years. It summarizes the response mechanisms based on various stimuli and their respective application scenarios. Utilizing innovative, responsive microneedle systems offers a convenient and precise targeted drug delivery method, holding significant research implications in transdermal drug administration. Safety and efficacy will remain the key areas of continuous efforts for research scholars in the future.This research was funded by College Nature Science Research Project of Jiangsu Province, China (Grant No. 20KJA540002) and Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (Grant No. KYCX23-3257