Keyun Chen's research while affiliated with Sun Yat-Sen University and other places

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 600 μm and an average tip radius of 12 μm. 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.

Micro-needle electrodes (MEs) have attracted more and more attention for monitoring physiological electrical signals, including electrode-skin interface impedance (EII), electromyography (EMG) and electrocardiography (ECG) recording. A magnetization-induced self-assembling method (MSM) was developed to fabricate a microneedle array (MA). A MA coated with Ti/Au film was assembled as a ME. The fracture and insertion properties of ME were tested by experiments. The bio-signal recording performance of the ME was measured and compared with a typical commercial wet electrode (Ag/AgCl electrode). The results show that the MA self-assembled from the magnetic droplet array under the sum of gravitational surface tension and magnetic potential energies. The ME had good toughness and could easily pierce rabbit skin without being broken or buckling. When the compression force applied on the ME was larger than 2 N, ME could stably record EII, which was a lower value than that measured by Ag/AgCl electrodes. EMG signals collected by ME varied along with the contraction of biceps brachii muscle. ME could record static ECG signals with a larger amplitude and dynamic ECG signals with more distinguishable features in comparison with a Ag/AgCl electrode, therefore, ME is an alternative electrode for bio-signal monitoring in some specific situations.

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.

Worker honeybee pierces animal or human skin with its ultra-sharp stinger and injects venom to defend itself. The insertion behavior is a painless transdermal drug delivery process. In this study, Apis cerana cerana worker honeybee was chosen as the research object. The geometry and structure of the stinger were observed by the Scanning Electron Microscope (SEM). High-speed video imaging technique was adopted to observe the stinger insertion and pull behavior of honeybee. The skin insertion, pull-out, in-plane buckling and out-of-plane bending forces of honeybee stinger were tested by a self-developed mechanical loading equipment. Results showed that the honeybee stinger pierces directly into skin without frequent vibration. The pull-out force (average 136.04 mN) was two orders of magnitude higher than the penetration force (average 1.34mN). Compared with the penetration force, the in-plane buckling force (average 6.72 mN) was in the same order of magnitude. The result of out-of-plane bending test showed that the stinger was elastic and it could recover after bending. The excellent geometry and structure of honeybee stinger will provide an inspiration for the further improved design of microneedle-based transdermal drug delivery system.

Magnetization-induced self-assembly method (MSM) was proposed to fabricate micro-needle array (MA). Curable magnetic fluid droplet array was extruded from the holes of perforated mask and meanwhile drawn to form the MA shape by magnetic force. MA was heated and cross linking solidified. The formation mechanism of magnetization-induced self-assembly micro-needle was analyzed and its process was divided into three stages: powders magnetizing, chain and aggregation, formation of micro-needle tip, and formation of micro-needle. The formation process was observed by high-speed camera. It was found that the formation process was consistent with the theoretical analysis. The effects of mask-hole diameter, powder-to-volume ratio and magnetic field intensity on MA fabrication were investigated by experiments. The results showed that the sharpness of micro-needle decreased with the decrement of mask-hole diameter and the increment of magnetic field intensity. The height of micro-needle increased with magnetic field intensity and powder-to-volume ratio. We anticipate that MSM will be suitable to fabricate MA-substrate for biomedical engineering fields such as biosensor, bio-electrode and transdermal drug delivery.