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Micromachines
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Smart Implants
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Smart Implants

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "E：Engineering and Technology".

Deadline for manuscript submissions: closed (30 December 2021) | Viewed by 25947

Special Issue Editors

Prof. Dr. Maaike Op de Beeck

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Guest Editor
Department of Electronics and information systems, Faculty of Engineering and Architecture, Ghent University, 9000 Gent, Belgium and IMEC/CMST, 9052 Gent, Belgium
Interests: smart implants; hermetic implant encapsulation; flexible implants; miniaturization of implants
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Sung-Min Park​​

E-Mail Website
Guest Editor
Department of Creative IT Engineering, Electricl Engineering, Pohang University of Science and Technology, 77 Cheongam-Ro Namgu, Pohang 37673, Republic of Korea
Interests: biomedical instrumentation; implantable medical devices; wearable sensors; electrical stimulators; flexible actuators

Special Issue Information

Dear colleagues,

Smart implants are medical implantable devices which have one or more sensors, some intelligence (typically electronics) to judge the sensory input and decide on a response, and finally a part realizing a smart response (i.e., stimulation electrode, drug release, etc.). Most smart implants are also equipped with telemetry: Communication between the implant and the outside world is important. Examples are pacemakers, cochlear implants, neural probes, etc. Although pacemakers and cochlear implants have already been on the medical market for a long time, these implants are still improving regarding their functionality, while their size is typically decreasing. Additionally, many novel smart implant applications are receiving attention at present: tiny neural probes, smart drug delivery systems, flexible retinal implants, etc. Several trends are obvious: Smart implants should have a wide functionality; they should be small, preferably allowing for minimally invasive implantation; they should be biomimetic (round shapes, flexible device, etc.) to reduce the foreign body reaction upon implantation; etc. power consumption should be minimal to avoid tissue heating and short battery life; devices should be hermetic and biostable for the total duration of the implant, etc. Lots of challenges still remain, resulting in interesting scientific activities with promising contributions to enable the fabrication of miniature, biomimetic, hermetically encapsulated smart implants with superior functionality. With this Special Issue, we want to give room to research papers, short communications, and review articles that focus on investigating hardware solutions to solve remaining issues regarding the fabrication of future smart implants, such as novel miniaturized implantable sensors, novel hardware parts for telecommunication between the implant and the outside world, new approaches to realize miniaturized hermetic implant encapsulations, polymer-based flexible smart implants, approaches to improve biostability or biomimetics of an implant, efficient but small implant powering systems, etc.

Prof. Dr. Maaike Op de Beeck
Prof. Dr. Sung-Min Park
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Smart implants
  • Implant miniaturization
  • Hermetic implant encapsulation
  • Flexible smart implants
  • Smart implant components

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Published Papers (7 papers)

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Research

Jump to: Review

13 pages, 1575 KiB  
Article
Cold Laser Micro-Machining of PDMS as an Encapsulation Layer for Soft Implantable Neural Interface
by Minjie Wang, Yuan Zhang, Jianxiong Bin, Lan Niu, Jing Zhang, Lusheng Liu, Aiping Wang, Jin Tao, Jingqiu Liang, Lihua Zhang and Xiaoyang Kang
Micromachines 2022, 13(9), 1484; https://doi.org/10.3390/mi13091484 - 7 Sep 2022
Cited by 3 | Viewed by 2543
Abstract
PDMS (polydimethylsiloxane) is an important soft biocompatible material, which has various applications such as an implantable neural interface, a microfluidic chip, a wearable brain–computer interface, etc. However, the selective removal of the PDMS encapsulation layer is still a big challenge due to its [...] Read more.
PDMS (polydimethylsiloxane) is an important soft biocompatible material, which has various applications such as an implantable neural interface, a microfluidic chip, a wearable brain–computer interface, etc. However, the selective removal of the PDMS encapsulation layer is still a big challenge due to its chemical inertness and soft mechanical properties. Here, we use an excimer laser as a cold micro-machining tool for the precise removal of the PDMS encapsulation layer which can expose the electrode sites in an implantable neural interface. This study investigated and optimized the effect of excimer laser cutting parameters on the electrochemical impedance of a neural electrode by using orthogonal experiment design. Electrochemical impedance at the representative frequencies is discussed, which helps to construct the equivalent circuit model. Furthermore, the parameters of the equivalent circuit model are fitted, which reveals details about the electrochemical property of neural electrode using PDMS as an encapsulation layer. Our experimental findings suggest the promising application of excimer lasers in the micro-machining of implantable neural interface. Full article
(This article belongs to the Special Issue Smart Implants)
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14 pages, 5177 KiB  
Article
A Broad Dual-Band Implantable Antenna for RF Energy Harvesting and Data Transmitting
by Yi Fan, Xiongying Liu and Chao Xu
Micromachines 2022, 13(4), 563; https://doi.org/10.3390/mi13040563 - 31 Mar 2022
Cited by 12 | Viewed by 2934
Abstract
An implantable antenna, operating at the dual Industrial, Scientific, and Medical (ISM) bands of 902–928 MHz and 2.4–2.48 GHz, is presented for RF energy harvesting and data transmission. By introducing multiple radiating branches and etching a C-shaped slot, multiple resonant frequencies were generated [...] Read more.
An implantable antenna, operating at the dual Industrial, Scientific, and Medical (ISM) bands of 902–928 MHz and 2.4–2.48 GHz, is presented for RF energy harvesting and data transmission. By introducing multiple radiating branches and etching a C-shaped slot, multiple resonant frequencies were generated to produce the wide dual bands. The proposed antenna has compact dimensions of 7.9 × 7.7 × 1.27 mm3. The simulated impedance bandwidths of the antenna are 0.67–1.05 GHz (44.2%) and 2.11–2.96 GHz (33.5%), and the peak gains are −28.9 dBi and −29.5 dBi, respectively. The lower band can be applied in RF energy harvesting, while the upper band is designed for data transmission with external medical equipment. Furthermore, to convert RF power into DC power, in RF energy harvesting, a voltage-doubled rectifier was positioned under the ground plane of the proposed antenna. The rectifier circuit can achieve a maximum conversion efficiency of 52% at an input power of 5 dBm. Furthermore, the integrated scheme of the implantable rectenna was fabricated and the numerical performance of the wireless power transfer was verified with the measurement results. Full article
(This article belongs to the Special Issue Smart Implants)
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12 pages, 8675 KiB  
Article
A Circularly Polarized Implantable Rectenna for Microwave Wireless Power Transfer
by Chao Xu, Yi Fan and Xiongying Liu
Micromachines 2022, 13(1), 121; https://doi.org/10.3390/mi13010121 - 12 Jan 2022
Cited by 10 | Viewed by 2331
Abstract
A circularly polarized implantable antenna integrated with a voltage-doubled rectifier (abbr., rectenna) is investigated for microwave wireless power transfer in the industrial, scientific, and medical (ISM) band of 2.4–2.48 GHz. The proposed antenna is miniaturized with the dimensions of 7.5 mm × 7.5 [...] Read more.
A circularly polarized implantable antenna integrated with a voltage-doubled rectifier (abbr., rectenna) is investigated for microwave wireless power transfer in the industrial, scientific, and medical (ISM) band of 2.4–2.48 GHz. The proposed antenna is miniaturized with the dimensions of 7.5 mm × 7.5 mm × 1.27 mm by etching four C-shaped open slots on the patch. A rectangular slot truncated diagonally is cut to improve the circular polarization performance of the antenna. The simulated impedance bandwidth in a three-layer phantom is 30.4% (1.9–2.58 GHz) with |S11| below −10 dB, and the 3-dB axial-ratio bandwidth is 16.9% (2.17–2.57 GHz). Furthermore, a voltage-doubled rectifier circuit that converts RF power to DC power is designed on the back of the antenna. The simulated RF-to-DC conversion efficiency can be up to 45% at the input power of 0 dBm. The proposed rectenna was fabricated and measured in fresh pork to verify the simulated results and evaluate the performance of wireless power transfer. Full article
(This article belongs to the Special Issue Smart Implants)
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14 pages, 3728 KiB  
Article
Hydrogel Surface-Modified Polyurethane Copolymer Film with Water Permeation Resistance and Biocompatibility for Implantable Biomedical Devices
by Hey In Jeong, Dae Hyeok An, Jun Woo Lim, Taehoon Oh, Hojin Lee, Sung-Min Park, Jae Hyun Jeong and Jae Woo Chung
Micromachines 2021, 12(4), 447; https://doi.org/10.3390/mi12040447 - 16 Apr 2021
Cited by 4 | Viewed by 3329
Abstract
To use implantable biomedical devices such as electrocardiograms and neurostimulators in the human body, it is necessary to package them with biocompatible materials that protect the internal electronic circuits from the body’s internal electrolytes and moisture without causing foreign body reactions. Herein, we [...] Read more.
To use implantable biomedical devices such as electrocardiograms and neurostimulators in the human body, it is necessary to package them with biocompatible materials that protect the internal electronic circuits from the body’s internal electrolytes and moisture without causing foreign body reactions. Herein, we describe a hydrogel surface-modified polyurethane copolymer film with concurrent water permeation resistance and biocompatibility properties for application to an implantable biomedical device. To achieve this, hydrophobic polyurethane copolymers comprising hydrogenated poly(ethylene-co-butylene) (HPEB) and aliphatic poly(carbonate) (PC) were synthesized and their hydrophobicity degree and mechanical properties were adjusted by controlling the copolymer composition ratio. When 10 wt% PC was introduced, the polyurethane copolymer exhibited hydrophobicity and water permeation resistance similar to those of HPEB; however, with improved mechanical properties. Subsequently, a hydrophilic poly(vinyl pyrrolidone) (PVP) hydrogel layer was formed on the surface of the polyurethane copolymer film by Fenton reaction using an initiator and crosslinking agent and the effect of the initiator and crosslinking agent immobilization time, PVP concentration and crosslinking agent concentration on the hydrogel properties were investigated. Finally, MTT assay showed that the hydrogel surface-modified polyurethane copolymer film displays excellent biocompatibility. Full article
(This article belongs to the Special Issue Smart Implants)
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Review

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31 pages, 6020 KiB  
Review
New Era of Electroceuticals: Clinically Driven Smart Implantable Electronic Devices Moving towards Precision Therapy
by RaviPrakash Magisetty and Sung-Min Park
Micromachines 2022, 13(2), 161; https://doi.org/10.3390/mi13020161 - 22 Jan 2022
Cited by 15 | Viewed by 5814
Abstract
In the name of electroceuticals, bioelectronic devices have transformed and become essential for dealing with all physiological responses. This significant advancement is attributable to its interdisciplinary nature from engineering and sciences and also the progress in micro and nanotechnologies. Undoubtedly, in the future, [...] Read more.
In the name of electroceuticals, bioelectronic devices have transformed and become essential for dealing with all physiological responses. This significant advancement is attributable to its interdisciplinary nature from engineering and sciences and also the progress in micro and nanotechnologies. Undoubtedly, in the future, bioelectronics would lead in such a way that diagnosing and treating patients’ diseases is more efficient. In this context, we have reviewed the current advancement of implantable medical electronics (electroceuticals) with their immense potential advantages. Specifically, the article discusses pacemakers, neural stimulation, artificial retinae, and vagus nerve stimulation, their micro/nanoscale features, and material aspects as value addition. Over the past years, most researchers have only focused on the electroceuticals metamorphically transforming from a concept to a device stage to positively impact the therapeutic outcomes. Herein, the article discusses the smart implants’ development challenges and opportunities, electromagnetic field effects, and their potential consequences, which will be useful for developing a reliable and qualified smart electroceutical implant for targeted clinical use. Finally, this review article highlights the importance of wirelessly supplying the necessary power and wirelessly triggering functional electronic circuits with ultra-low power consumption and multi-functional advantages such as monitoring and treating the disease in real-time. Full article
(This article belongs to the Special Issue Smart Implants)
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23 pages, 4666 KiB  
Review
A Review of the Commercially Available ECG Detection and Transmission Systems—The Fuzzy Logic Approach in the Prevention of Sudden Cardiac Arrest
by Michał Lewandowski
Micromachines 2021, 12(12), 1489; https://doi.org/10.3390/mi12121489 - 30 Nov 2021
Cited by 2 | Viewed by 2618
Abstract
Sudden cardiac death (SCD) constitutes a major clinical and public health problem, whose death burden is comparable to the current worldwide pandemic. This comprehensive review encompasses the following topics: available rescue systems, wearable electrocardiograms (ECG), detection and transmission technology, and a newly developed [...] Read more.
Sudden cardiac death (SCD) constitutes a major clinical and public health problem, whose death burden is comparable to the current worldwide pandemic. This comprehensive review encompasses the following topics: available rescue systems, wearable electrocardiograms (ECG), detection and transmission technology, and a newly developed fuzzy logic algorithm (FA) for heart rhythm classification which is state-of-the art in the field of SCD prevention. Project “PROTECTOR”, the Polish Rapid Transtelephonic ECG to Obtain Resuscitation for development of a rapid rescue system for patients at risk of sudden cardiac arrest (SCA), is presented. If a lethal arrhythmia is detected on the basis of FA, the system produces an alarm signal audible for bystanders and transmits the alarm message along with location to the emergency medical center. Phone guided resuscitation can be started immediately because an automated external defibrillator (AED) localization map is available. An automatic, very fast diagnosis is a unique feature of the PROTECTOR prototype. The rapid detection of SCA is based on a processor characterized by 100% sensitivity and 97.8% specificity (as measured in the pilot studies). An integrated circuit which implements FA has already been designed and a diagnosis is made within few seconds, which is extremely important in ischemic brain damage prophylaxis. This circuit could be implemented in smart implants (Sis). Full article
(This article belongs to the Special Issue Smart Implants)
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Graphical abstract

30 pages, 2866 KiB  
Review
Technological Challenges in the Development of Optogenetic Closed-Loop Therapy Approaches in Epilepsy and Related Network Disorders of the Brain
by Bram Vandekerckhove, Jeroen Missinne, Kristl Vonck, Pieter Bauwens, Rik Verplancke, Paul Boon, Robrecht Raedt and Jan Vanfleteren
Micromachines 2021, 12(1), 38; https://doi.org/10.3390/mi12010038 - 31 Dec 2020
Cited by 9 | Viewed by 4564
Abstract
Epilepsy is a chronic, neurological disorder affecting millions of people every year. The current available pharmacological and surgical treatments are lacking in overall efficacy and cause side-effects like cognitive impairment, depression, tremor, abnormal liver and kidney function. In recent years, the application of [...] Read more.
Epilepsy is a chronic, neurological disorder affecting millions of people every year. The current available pharmacological and surgical treatments are lacking in overall efficacy and cause side-effects like cognitive impairment, depression, tremor, abnormal liver and kidney function. In recent years, the application of optogenetic implants have shown promise to target aberrant neuronal circuits in epilepsy with the advantage of both high spatial and temporal resolution and high cell-specificity, a feature that could tackle both the efficacy and side-effect problems in epilepsy treatment. Optrodes consist of electrodes to record local field potentials and an optical component to modulate neurons via activation of opsin expressed by these neurons. The goal of optogenetics in epilepsy is to interrupt seizure activity in its earliest state, providing a so-called closed-loop therapeutic intervention. The chronic implantation in vivo poses specific demands for the engineering of therapeutic optrodes. Enzymatic degradation and glial encapsulation of implants may compromise long-term recording and sufficient illumination of the opsin-expressing neural tissue. Engineering efforts for optimal optrode design have to be directed towards limitation of the foreign body reaction by reducing the implant’s elastic modulus and overall size, while still providing stable long-term recording and large-area illumination, and guaranteeing successful intracerebral implantation. This paper presents an overview of the challenges and recent advances in the field of electrode design, neural-tissue illumination, and neural-probe implantation, with the goal of identifying a suitable candidate to be incorporated in a therapeutic approach for long-term treatment of epilepsy patients. Full article
(This article belongs to the Special Issue Smart Implants)
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