Microneedle Array Electrode Research Articles

Microneedle Array Electrode With Ag-PPS Modification for Superior Bio-Signal Recording on Skin

Microneedle Array Electrode With Ag-PPS Modification for Superior Bio-Signal Recording on Skin

A PDMS-based microneedle array electrode for long-term ECG recording.

To acquire high-quality electrocardiogram (ECG) signals, traditional Ag/AgCl wet electrodes used together with conductive gel can effectively reduce electrode-skin interface impedance (EII) in a short term. However, their weaknesses of poor flexibility and instability can no longer meet the long-term monitoring requirements of intelligent wearable devices. Owing to the flexible dry electrode without conductive gel, it is a good choice to solve the critical problem on drying-out of conductive gel. Therefore, we develop a flexible microneedle array electrode (FMAE) based on polydimethylsiloxane (PDMS) substrate, which obtains reliable bioelectrical signals by way of penetrating into the stratum corneum (SC) of the skin. The fabrication process, including silicon mold, twice PDMS shape-transferring and encapsulation, has advantages of low cost, repeatable production and good biocompatibility. Afterwards, by comparing the performance with different electrodes, impedance test results indicate that the impedance of FMAE are smaller and more stable, and ECG tests in long term and at resting/jogging states also verify that FMAE can obtain durable, stable and reliable signals. In conclusion, FMAE is promising in long-term ECG monitoring.

Fabrication and characterization of a microneedle array electrode with flexible backing for biosignal monitoring.

The conventional wet electrode for recording biosignals poses many inconveniences, as it requires an electrolytic gel that dries over time changing its electrical characteristics. The skin typically needs to be abraded when the electrode is applied to record high-quality signals, requiring assistance of trained personnel for the placement of the wet electrode. Alternative electrode designs to overcome these challenges often have difficulties recording small amplitude signals or their fabrication methods are complex and expensive. This research proposes a novel design and a simple fabrication method for a dry microneedle electrode for biosignal monitoring. The electrode can record electroencephalogram and electrocardiogram signals from a human subject without electrolytic gel and it does not require skin preparation such as abrasion, making it suitable for long term measurements as opposed to the wet electrode. When applied to the skin of a human subject with an impact inserter, the electrode has a lower impedance at the skin-electrode interface yielding better signal recording compared to application by hand. The selected electrode materials provides microneedles stiff enough to cross the outmost layer of the skin, while the flexible backing of the electrode has been designed to improve the conformation of the electrode to the rounded shape of the body. The proposed fabrication method for the electrode is based on a simple mold casting process that enables batch production while also reducing the time spent in a cleanroom and the use of expensive machinery.

Miura-ori structured flexible microneedle array electrode for biosignal recording

Highly reliable signal recording with low electrode-skin impedance makes the microneedle array electrode (MAE) a promising candidate for biosignal sensing. However, when used in long-term health monitoring for some incidental diseases, flexible microneedles with perfectly skin-tight fit substrates lead to sweat accumulation inside, which will not only affect the signal output but also trigger some skin allergic reactions. In this paper, a flexible MAE on a Miura-ori structured substrate is proposed and fabricated with two-directional in-plane bendability. The results from the comparison tests show enhanced performance in terms of (1) the device reliability by resisting peeling off of the metal layer from the substrate during the operation and (2) air ventilation, achieved from the air-circulating channels, to remove sweat. Bio-signal recordings of electrocardiography (ECG), as well as electromyography (EMG) of the biceps brachii, in both static and dynamic states, are successfully demonstrated with superior accuracy and long-term stability, demonstrating the great potential in health monitoring applications.

Microneedle array sensor for monitoring glucose in single cell using glucose oxidase-bonded polyterthiophene coated on AuZn oxide layer

A monomer precursor of conducting polymer, 2,2´:5´,5″-terthiophene-3´-carboxylic acid, (TCA) was electropolymerized on the raspberry-like AuZn oxide (AuZnOx) layer coated on microneedle array electrode (μ-NAE) at single and multi-cell analysis. The AuZnOx was used to elevate the catalytic effect of H2O2 oxidation and to prevent the passivation of the Au surface by chloride ion in biological samples. After optimizing the experimental variables affecting the analytical signal, in terms of monomer and GOx concentrations, electropolymerization cycles, pH, applied potential, and temperature. The sensor was responded with in 1 s, and showed the two dynamic ranges of 0.01–5.0 and 5.0–50.0 mM with detection limit of 1.2 (± 0.026) μM. The sensor performance and reliability were examined by measuring glucose in cells of different cancer types (PC-12, MG-62, HeLa, A549, and Saos-2), comparing with normal (Vero) cells. In addition, the effect of K+ ion on the glucose level was also investigated for a single cell. The sensor confirmed the higher concentration of glucose in cancer cells than the normal cells, where the intracellular glucose level was 2.2 folds higher as compared to the extracellular levels in PC-12 cells.

A Mini Review of Microneedle Array Electrode for Bio-Signal Recording: A Review

Bio-signal recording is vital for human condition monitoring and early disease diagnosis. An electrode is a biosensor for bio-signal collection. The conventional wet electrode is not suitable for long-term bio-signal recording owing to the gradual drying of the electrolytic gel and increase in the electrode-skin interface impedance. Microneedle array electrode is a dry electrode that can painlessly pierce skin, form a contact interface between the microneedles and skin tissue, eliminate the high impedance of stratum corneum, weaken the motion artifact, and accurately record bio-signals without skin preparation and application of electrolytic gel. This review focuses on the recently developed fabrication techniques, the mechanical performance, and bio-signal recording performance of microneedle array electrode. The microneedle array electrode is a potential electrode for long-term bio-signal recording, although progress is required in terms of safety and scaled-up manufacture.

Fabrication of Flexible Microneedle Array Electrodes for Wearable Bio-Signal Recording.

Laser-direct writing (LDW) and magneto-rheological drawing lithography (MRDL) have been proposed for the fabrication of a flexible microneedle array electrode (MAE) for wearable bio-signal monitoring. Conductive patterns were directly written onto the flexible polyethylene terephthalate (PET) substrate by LDW. The microneedle array was rapidly drawn and formed from the droplets of curable magnetorheological fluid with the assistance of an external magnetic field by MRDL. A flexible MAE can maintain a stable contact interface with curved human skin due to the flexibility of the PET substrate. Compared with Ag/AgCl electrodes and flexible dry electrodes (FDE), the electrode–skin interface impedance of flexible MAE was the minimum even after a 50-cycle bending test. Flexible MAE can record electromyography (EMG), electroencephalography (EEG) and static electrocardiography (ECG) signals with good fidelity. The main features of the dynamic ECG signal recorded by flexible MAE are the most distinguishable with the least moving artifacts. Flexible MAE is an attractive candidate electrode for wearable bio-signal monitoring.

Fabrication of Composite Microneedle Array Electrode for Temperature and Bio-Signal Monitoring.

Body temperature and bio-signals are important health indicators that reflect the human health condition. However, monitoring these indexes is inconvenient and time-consuming, requires various instruments, and needs professional skill. In this study, a composite microneedle array electrode (CMAE) was designed and fabricated. It simultaneously detects body temperature and bio-signals. The CMAE consists of a 6 × 6 microneedles array with a height of 500 μm and a base diameter of 200 μm. Multiple insertion experiments indicate that the CMAE possesses excellent mechanical properties. The CMAE can pierce porcine skin 100 times without breaking or bending. A linear calibration relationship between temperature and voltage are experimentally obtained. Armpit temperature (35.8 °C) and forearm temperature (35.3 °C) are detected with the CMAE, and the measurements agree well with the data acquired with a clinical thermometer. Bio-signals including EII, ECG, and EMG are recorded and compared with those obtained by a commercial Ag/AgCl electrode. The CMAE continuously monitors bio-signals and is more convenient to apply because it does not require skin preparation and gel usage. The CMAE exhibits good potential for continuous and repetitive monitoring of body temperature and bio-signals.

Flexible microneedle array electrode using magnetorheological drawing lithography for bio-signal monitoring

Monitoring and timely intervention are extremely important in the continuous home care. Microneedle array electrode (MAE) have been employed for the long-term bio-signal monitoring without skin preparation. We developed a novel magneto-rheological drawing lithography (MRDL) method to cost-effectively fabricate a flexible micro-needle array electrode (FMAE) for the wearable bio-signal monitoring. Flexible substrate may match closely with curved skin and maintain a stable interface between skin and electrode. The formation mechanism of microneedle array (MA) by MRDL and bio-signal recording performance of FMAE were investigated. MA can be one-step drawn from the droplet array of curable magnetorheological fluid under the assist of external magnetic field. Ti/Au film was coated on the surface of solidified MA to insure the conductivity and compatibility of FMAE. 36-FMAE consists of 6×6 micro-needles with an average height of 600μm and an average tip radius of 12μm. FMAE with 36 needles (36-FMAE) shows a better bio-signal monitoring performance in some specific situations compared with flexible dry electrode (FDE) and commercial Ag/AgCl electrode. Electrode-skin interface impedance (EII) measured by 36-FMAE is the lowest at a given low input frequency and the amplitude of electrocardiography (ECG) and electroencephalography (EEG) signals recorded by 36-FMAE is the largest. 36-FMAE can collect more distinguishable features and weaken the effect of motion artifact during the dynamical ECG recording. Therefore, 36-FMAE is a promising sensor for the wearable bio-signal monitoring in home care.

Evaluation of a minimally invasive glucose biosensor for continuous tissue monitoring.

We describe here a minimally invasive glucose biosensor based on a microneedle array electrode fabricated from an epoxy-based negative photoresist (SU8 50) and designed for continuous measurement in the dermal compartment with minimal pain. These minimally invasive, continuous monitoring sensor devices (MICoMS) were produced by casting the structures in SU8 50, crosslinking and then metallising them with platinum or silver to obtain the working and reference electrodes, respectively. The metallised microneedle array electrodes were subsequently functionalised by entrapping glucose oxidase in electropolymerised polyphenol (PP) film. Sensor performance in vitro showed that glucose concentrations down to 0.5 mM could be measured with a response times (T90) of 15 s. The effect of sterilisation by Co60 irradiation was evaluated. In preparation for further clinical studies, these sensors were tested in vivo in a healthy volunteer for a period of 3–6 h. The sensor currents were compared against point measurements obtained with a commercial capillary blood glucometer. The epoxy MICoMS devices showed currents values that could be correlated with these. Graphical Microneedle arrays for continuous glucose monitoring in dermal interstitial fluid

Fabrication of a Micro-Needle Array Electrode by Thermal Drawing for Bio-Signals Monitoring.

A novel micro-needle array electrode (MAE) fabricated by thermal drawing and coated with Ti/Au film was proposed for bio-signals monitoring. A simple and effective setup was employed to form glassy-state poly (lactic-co-glycolic acid) (PLGA) into a micro-needle array (MA) by the thermal drawing method. The MA was composed of 6 × 6 micro-needles with an average height of about 500 μm. Electrode-skin interface impedance (EII) was recorded as the insertion force was applied on the MAE. The insertion process of the MAE was also simulated by the finite element method. Results showed that MAE could insert into skin with a relatively low compression force and maintain stable contact impedance between the MAE and skin. Bio-signals, including electromyography (EMG), electrocardiography (ECG), and electroencephalograph (EEG) were also collected. Test results showed that the MAE could record EMG, ECG, and EEG signals with good fidelity in shape and amplitude in comparison with the commercial Ag/AgCl electrodes, which proves that MAE is an alternative electrode for bio-signals monitoring.

Curved Microneedle Array-Based sEMG Electrode for Robust Long-Term Measurements and High Selectivity.

Surface electromyography is widely used in many fields to infer human intention. However, conventional electrodes are not appropriate for long-term measurements and are easily influenced by the environment, so the range of applications of sEMG is limited. In this paper, we propose a flexible band-integrated, curved microneedle array electrode for robust long-term measurements, high selectivity, and easy applicability. Signal quality, in terms of long-term usability and sensitivity to perspiration, was investigated. Its motion-discriminating performance was also evaluated. The results show that the proposed electrode is robust to perspiration and can maintain a high-quality measuring ability for over 8 h. The proposed electrode also has high selectivity for motion compared with a commercial wet electrode and dry electrode.

Characterization of skin penetration efficacy by Au-coated Si microneedle array electrode

Investigation of skin penetration efficacy by a silicon microneedle array is presented. Experiments were performed on porcine and chicken skin samples in vitro and on human skin in vivo. Solid microneedle arrays (13×13mm2), each consisting of 100 microneedles, were designed and fabricated by deep reactive ion etching process. To evaluate the penetration efficacy through the mechanically and electrically resistant upper skin layer of stratum corneum, the electrical skin impedance change with applied force was measured by using Au-coated Si microneedle array as working electrode in 2 and 3 electrode configurations. Skin impedance changes between 2 and 8% were measured when applying incremental force, increased from 1 to 10N on a Au metalized microneedle array electrode. When impact assisted penetration of microneedle array was applied instead of incremental increase of applied force, a significant impedance reduction of up to 50% on animal skin and 95% on human skin was obtained, which is a strong evidence of successful skin penetration. Furthermore, the microneedle array electrode showed consistently lower interface impedance compared to the flat electrode for the samples involved. Analyses of Si microneedle mechanical properties revealed that by proper use a satisfactory safety margin (>60) can be achieved.

A flexible microneedle array as low-voltage electroporation electrodes for in vivo DNA and siRNA delivery.

In vivo electroporation is an appealing method to deliver nucleic acid into living tissues, but the clinical application of such a method was limited due to severe tissue damage and poor coverage of the tissue surface. Here we present the validation of a novel flexible microneedle array electrode (MNAE) chip, in which the microneedle array and the flexible substrate are integrated together to simultaneously facilitate low-voltage electroporation and accomplish good coverage of the tissue surface. The efficient delivery of both DNA and siRNA was demonstrated on mice. Upon penetrating the high-resistance stratum corneum, the electroporation voltage was reduced to about 35 V, which was generally recognized safe for humans. Also, a pathological analysis of the microneedle-electroporated tissues was carried out to thoroughly assess the skin damage, which is an important consideration in pre-clinical studies of electroporation devices. This MNAE constitutes a novel way of in vivo delivery of siRNA and DNA to certain tissues or organs with satisfactory efficiency and good adaptation to the tissue surface profile as well as minimum tissue damage, thus avoiding the disadvantages of existing electroporation methods.