Editorial

2 pages, 151 KiB

Open AccessEditorial

Editorial for the Special Issue on Implantable Microdevices

by Wen Li and Zhen Qiu

Micromachines 2019, 10(9), 603; https://doi.org/10.3390/mi10090603 - 12 Sep 2019

Viewed by 1679

Implantable microdevices, providing accurate measurement of target analytes in animals and humans, have always been important in biological science, medical diagnostics, clinical therapy, and personal healthcare [...] Full article

(This article belongs to the Special Issue Implantable Microdevices)

Research

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15 pages, 5498 KiB

Open AccessArticle

Constructing a Dual-Function Surface by Microcasting and Nanospraying for Efficient Drag Reduction and Potential Antifouling Capabilities

by Liguo Qin, Mahshid Hafezi, Hao Yang, Guangneng Dong and Yali Zhang

Micromachines 2019, 10(7), 490; https://doi.org/10.3390/mi10070490 - 23 Jul 2019

Cited by 34 | Viewed by 3897

Abstract

To improve the drag-reducing and antifouling performance of marine equipment, it is indispensable to learn from structures and materials that are found in nature. This is due to their excellent properties, such as intelligence, microminiaturization, hierarchical assembly, and adaptability. Considerable interest has arisen [...] Read more.

To improve the drag-reducing and antifouling performance of marine equipment, it is indispensable to learn from structures and materials that are found in nature. This is due to their excellent properties, such as intelligence, microminiaturization, hierarchical assembly, and adaptability. Considerable interest has arisen in fabricating surfaces with various types of biomimetic structures, which exhibit promising and synergistic performances similar to living organisms. In this study, a dual bio-inspired shark-skin and lotus-structure (BSLS) surface was developed for fabrication on commercial polyurethane (PU) polymer. Firstly, the shark-skin pattern was transferred on the PU by microcasting. Secondly, hierarchical micro- and nanostructures were introduced by spraying mesoporous silica nanospheres (MSNs). The dual biomimetic substrates were characterized by scanning electron microscopy, water contact angle characterization, antifouling, self-cleaning, and water flow impacting experiments. The results revealed that the BSLS surface exhibited dual biomimetic features. The micro- and nano-lotus-like structures were localized on a replicated shark dermal denticle. A contact angle of 147° was observed on the dual-treated surface and the contact angle hysteresis was decreased by 20% compared with that of the nontreated surface. Fluid drag was determined with shear stress measurements and a drag reduction of 36.7% was found for the biomimetic surface. With continuous impacting of high-speed water for up to 10 h, the biomimetic surface stayed superhydrophobic. Material properties such as inhibition of protein adsorption, mechanical robustness, and self-cleaning performances were evaluated, and the data indicated these behaviors were significantly improved. The mechanisms of drag reduction and self-cleaning are discussed. Our results indicate that this method is a potential strategy for efficient drag reduction and antifouling capabilities. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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9 pages, 2740 KiB

Open AccessArticle

Fabrication and Characterization of Micro-Nano Electrodes for Implantable BCI

by Ye Xi, Bowen Ji, Zhejun Guo, Wen Li and Jingquan Liu

Micromachines 2019, 10(4), 242; https://doi.org/10.3390/mi10040242 - 11 Apr 2019

Cited by 3 | Viewed by 3475

Abstract

Signal recording and stimulation with high spatial and temporal resolution are of increasing interest with the development of implantable brain-computer interfaces (BCIs). However, implantable BCI technology still faces challenges in the biocompatibility and long-term stability of devices after implantation. Due to the cone [...] Read more.

Signal recording and stimulation with high spatial and temporal resolution are of increasing interest with the development of implantable brain-computer interfaces (BCIs). However, implantable BCI technology still faces challenges in the biocompatibility and long-term stability of devices after implantation. Due to the cone structure, needle electrodes have advantages in the biocompatibility and stability as nerve recording electrodes. This paper develops the fabrication of Ag needle micro/nano electrodes with a laser-assisted pulling method and modifies the electrode surface by electrochemical oxidation. A significant impedance reduction of the modified Ag/AgCl electrodes compared to the Ag electrodes is demonstrated by the electrochemical impedance spectrum (EIS). Furthermore, the stability of modified Ag/AgCl electrodes is confirmed by cyclic voltammogram (CV) scanning. These findings suggest that these micro/nano electrodes have a great application prospect in neural interfaces. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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9 pages, 8019 KiB

Open AccessArticle

Single-Sided Near-Field Wireless Power Transfer by A Three-Dimensional Coil Array

by Amirhossein Hajiaghajani and Seungyoung Ahn

Micromachines 2019, 10(3), 200; https://doi.org/10.3390/mi10030200 - 21 Mar 2019

Cited by 13 | Viewed by 3920

Abstract

Wirelessly powered medical microrobots are often driven or localized by magnetic resonance imaging coils, whose signal-to-noise ratio is easily affected by the power transmitter coils that supply the microrobot. A controlled single-sided wireless power transmitter can enhance the imaging quality and suppress the [...] Read more.

Wirelessly powered medical microrobots are often driven or localized by magnetic resonance imaging coils, whose signal-to-noise ratio is easily affected by the power transmitter coils that supply the microrobot. A controlled single-sided wireless power transmitter can enhance the imaging quality and suppress the radiation leakage. This paper presents a new form of electromagnet which automatically cancels the magnetic field to the back lobes by replacing the traditional circular coils with a three-dimensional (3D) coil scheme inspired by a generalized form of Halbach arrays. It is shown that, along with the miniaturization of the transmitter system, it allows for improved magnetic field intensity in the target side. Measurement of the produced magnetic patterns verifies that the power transfer to the back lobe is 15-fold smaller compared to the corresponding distance on the main lobe side, whilst maintaining a powering efficiency similar to that of conventional planar coils. To show the application of the proposed array, a wireless charging pad with an effective powering area of 144 cm² is fabricated on 3D-assembled printed circuit boards. This 3D structure obviates the need for traditional magnetic shield materials that place limitations on the working frequency and suffer from non-linearity and hysteresis effects. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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11 pages, 8786 KiB

Open AccessArticle

A Miniaturized Circularly-Polarized Antenna for In-Body Wireless Communications

by Yi Fan, Xiongying Liu, Jiming Li and Tianhai Chang

Micromachines 2019, 10(1), 70; https://doi.org/10.3390/mi10010070 - 19 Jan 2019

Cited by 15 | Viewed by 4701

Abstract

A novel miniaturized single-fed circularly-polarized (CP) microstrip patch antenna operating in the Industrial, Scientific, Medical (ISM) band of 2.40–2.48 GHz, is comprehensively proposed for implantable wireless communications. By employing reactive loading in the arrow-shaped slotted patch to form slow wave effect and embedding [...] Read more.

A novel miniaturized single-fed circularly-polarized (CP) microstrip patch antenna operating in the Industrial, Scientific, Medical (ISM) band of 2.40–2.48 GHz, is comprehensively proposed for implantable wireless communications. By employing reactive loading in the arrow-shaped slotted patch to form slow wave effect and embedding V-shaped slots into patch to lengthen the current path, the proposed implantable antenna is minimized with the overall dimensions of 9.2 mm × 9.2 mm × 1.27 mm. The radiation patterns of the proposed antenna illustrate the performance of left-handed circular polarization. The simulated results show that an impedance bandwidth of 7.2% (2.39–2.57 GHz) and an axial ratio bandwidth of 3.7% (2.39–2.48 GHz) at the ISM band are achieved, respectively. Ex vivo measured results are in good agreement with the corresponding simulated ones. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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7 pages, 2831 KiB

Open AccessArticle

A Compact Broadband Antenna with Dual-Resonance for Implantable Devices

by Rongqiang Li, Bo Li, Guohong Du, Xiaofeng Sun and Haoran Sun

Micromachines 2019, 10(1), 59; https://doi.org/10.3390/mi10010059 - 16 Jan 2019

Cited by 28 | Viewed by 3815

Abstract

A compact broadband implantable patch antenna is designed for the field of biotelemetry and experimentally demonstrated using the Medical Device Radiocommunications Service (MedRadio) band (401–406 MHz). The proposed antenna can obtain a broad impedance bandwidth by exciting dual-resonant frequencies, and has a compact [...] Read more.

A compact broadband implantable patch antenna is designed for the field of biotelemetry and experimentally demonstrated using the Medical Device Radiocommunications Service (MedRadio) band (401–406 MHz). The proposed antenna can obtain a broad impedance bandwidth by exciting dual-resonant frequencies, and has a compact structure using bent metal radiating strips and a short strategy. The total volume of the proposed antenna, including substrate and superstrate, is about 479 mm³ (23 × 16.4 × 1.27 mm³). The measured bandwidth is 52 MHz (382–434 MHz) at a return loss of −10 dB. The resonance, radiation and specific absorption rate (SAR) performance of the antenna are examined and characterized. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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16 pages, 34746 KiB

Open AccessArticle

Numerical Study and Optimization of a Novel Piezoelectric Transducer for a Round-Window Stimulating Type Middle-Ear Implant

by Houguang Liu, Hehe Wang, Zhushi Rao, Jianhua Yang and Shanguo Yang

Micromachines 2019, 10(1), 40; https://doi.org/10.3390/mi10010040 - 09 Jan 2019

Cited by 9 | Viewed by 6379

Abstract

Round window (RW) stimulation is a new application of middle ear implants for treating hearing loss, especially for those with middle ear disease. However, most reports on it are based on the use of the floating mass transducer (FMT), which was not originally [...] Read more.

Round window (RW) stimulation is a new application of middle ear implants for treating hearing loss, especially for those with middle ear disease. However, most reports on it are based on the use of the floating mass transducer (FMT), which was not originally designed for round window stimulation. The mismatch of the FMT’s diameter and the round window membrane’s diameter and the uncontrollable preload of the transducer, leads to a high variability in its clinical outcomes. Accordingly, a new piezoelectric transducer for the round-window-stimulating-type middle ear implant is proposed in this paper. The transducer consists of a piezoelectric stack, a flextensional amplifier, a coupling rod, a salver, a plate, a titanium housing and a supporting spring. Based on a constructed coupling finite element model of the human ear and the transducer, the influences of the transducer design parameters on its performance were analyzed. The optimal structure of the supporting spring, which determines the transducer’s resonance frequency, was ascertained. The results demonstrate that our designed transducer generates better output than the FMT, especially at low frequency. Besides this, the power consumption of the transducer was significantly decreased compared with a recently reported RW-stimulating piezoelectric transducer. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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15 pages, 16582 KiB

Open AccessArticle

Development of ECG Monitoring System and Implantable Device with Wireless Charging

by Jae-Ho Lee and Dong-Wook Seo

Micromachines 2019, 10(1), 38; https://doi.org/10.3390/mi10010038 - 08 Jan 2019

Cited by 17 | Viewed by 7012

Abstract

We developed an implantable electrocardiogram (ECG) monitoring system and demonstrated its performance through an in vivo test. In the system, the implantable device senses not only the ECG signal of the animal but also the voltage level of the secondary cell and temperature [...] Read more.

We developed an implantable electrocardiogram (ECG) monitoring system and demonstrated its performance through an in vivo test. In the system, the implantable device senses not only the ECG signal of the animal but also the voltage level of the secondary cell and temperature inside the implantable device, and users can check the transmitted information through a PC program or a mobile application. The adoption of wireless charging technology eliminates the use of a lead wire and repetitive surgery to replace the implantable device. The proposed wireless charging technology demonstrated experimentally a wireless power transfer efficiency of approximately 30%. To minimize the size of the implantable device, the antenna and coil were integrated into a size of 34 mm × 14 mm. Communication between the implantable device and the basestation can reach up to 2.4 m when the implantable device is inserted into a porcine skin sample. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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15 pages, 7203 KiB

Open AccessArticle

Tongue Pressure Sensing Array Integrated with a System-on-Chip Embedded in a Mandibular Advancement Splint

by Yun-Ting Chen, Kun-Ying Yeh, Szu-Han Chen, Chuang-Yin Wang, Chao-Chi Yeh, Ming-Xin Xu, Shey-Shi Lu, Yunn-Jy Chen and Yao-Joe Yang

Micromachines 2018, 9(7), 352; https://doi.org/10.3390/mi9070352 - 14 Jul 2018

Cited by 5 | Viewed by 7875

Abstract

Obstructive sleep apnea (OSA), which is caused by obstructions of the upper airway, is a syndrome with rising prevalence. Mandibular advancement splints (MAS) are oral appliances for potential treatment of OSA. This work proposes a highly-sensitive pressure sensing array integrated with a system-on-chip [...] Read more.

Obstructive sleep apnea (OSA), which is caused by obstructions of the upper airway, is a syndrome with rising prevalence. Mandibular advancement splints (MAS) are oral appliances for potential treatment of OSA. This work proposes a highly-sensitive pressure sensing array integrated with a system-on-chip (SoC) embedded in a MAS. The device aims to measure tongue pressure distribution in order to determine the efficacy of the MAS for treating OSA. The flexible sensing array consists of an interdigital electrode pair array assembled with conductive polymer films and an SoC capable of retrieving/storing data during sleep, and transmitting data for analysis after sleep monitoring. The surfaces of the conductive polymer films were patterned with microdomed structures, which effectively increased the sensitivity and reduced the pressure sensing response time. The measured results also show that the crosstalk effect between the sensing elements of the array was negligible. The sensitivity of the sensing array changed minimally after the device was submerged in water for up to 100 h. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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Review

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22 pages, 7551 KiB

Open AccessReview

Micro/Nano Technologies for High-Density Retinal Implant

by Qi Zeng, Saisai Zhao, Hangao Yang, Yi Zhang and Tianzhun Wu

Micromachines 2019, 10(6), 419; https://doi.org/10.3390/mi10060419 - 22 Jun 2019

Cited by 23 | Viewed by 9162

Abstract

During the past decades, there have been leaps in the development of micro/nano retinal implant technologies, which is one of the emerging applications in neural interfaces to restore vision. However, higher feedthroughs within a limited space are needed for more complex electronic systems [...] Read more.

During the past decades, there have been leaps in the development of micro/nano retinal implant technologies, which is one of the emerging applications in neural interfaces to restore vision. However, higher feedthroughs within a limited space are needed for more complex electronic systems and precise neural modulations. Active implantable medical electronics are required to have good electrical and mechanical properties, such as being small, light, and biocompatible, and with low power consumption and minimal immunological reactions during long-term implantation. For this purpose, high-density implantable packaging and flexible microelectrode arrays (fMEAs) as well as high-performance coating materials for retinal stimulation are crucial to achieve high resolution. In this review, we mainly focus on the considerations of the high-feedthrough encapsulation of implantable biomedical components to prolong working life, and fMEAs for different implant sites to deliver electrical stimulation to targeted retinal neuron cells. In addition, the functional electrode materials to achieve superior stimulation efficiency are also reviewed. The existing challenge and future research directions of micro/nano technologies for retinal implant are briefly discussed at the end of the review. Full article

(This article belongs to the Special Issue Implantable Microdevices)

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