Wearable and implantable devices

Introduction

Soft micro-electro-mechanical systems (MEMS) are one area of high interest and under heavy research in micro/nano engineering and technology. Due to the configuration and properties of the materials used, soft MEMS possess several attractive properties, such as flexibility, stretchability and biocompatibility. Several polymeric materials, including poly(dimethylsiloxane) (PDMS), polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), etc., have been employed to construct soft MEMS. Besides these, natural soft materials that are environment-friendly and even biodegradable are developing rapidly. It includes for instance poly(lactic-co-glycolic acid) (PLGA) and silk fibroin.

Objectives and Methods

Our research focuses on developing new micro/nano fabrication techniques to produce soft MEMS made of innovative, natural and soft materials. Beside this, we are extending the practical applications of these soft devices, particularly in the fields of energy harvesting and drug delivery systems. As for the recent progress, we investigated silk fibroin as a novel material for MEMS energy harvester. Silk fibroin is a negative material for triboelectric generator having a top-tier position in the triboelectric series and featuring an outstanding ability of losing electrons easily. Silk fibroin film is 90% transparent to light in the visible range and is thus a promising material for wearable MEMS .Silk fibroin is also a natural protein with beneficial properties for implantable drug delivery systems such as controllable biodegradation, biocompatibility, all aqueous purification and processing options, compatibility with sterilization methods, and excellent mechanical properties. Additionally, magnesium (Mg) is investigated as a biodegradable metal to fabricate transient electronics circuits and resonators. The rapid degradation of Mg in water implies to develop fabrication processes based only on dry processing steps.

Figure 1: Materials used to fabricate soft MEMS devices. a) Silk fibroin film (with blue dye) dissolved quite quickly in water within 3 seconds. b) Mg resonator shows rapid degradation once immersed in PBS due to the propagation of cracks.

 

Applications

Wearable devices
Recently triboelectric generator (TEG) has been introduced as a promising energy conversion system to transform mechanical energy into electrical energy. To make an impact in practical applications, further improvements, in particular in the choice of the electrification materials, are needed. Here, we investigate silk fibroin as a novel TEG material. We demonstrate that by combining silk, that has a high ability to lose electrons, with PET, we obtain remarkable power densities up to 193.6 µW/cm2 with an external load impedance of 40 MΩ. Direct powering of a liquid crystal display (LED) and an electrostatic actuated cantilever are shown as concrete applications examples.

Figure 2: Electrical measurement of the silk-based triboelectric generator (TEG) by ~5 Hz body motion (i.e., finger pressing): (a) output voltage and (b) current on the matched load of 40 MΩ; (c) Two 4-bit liquid crystal displays were successfully directly driven by the silk-based triboelectric generator (TEG) without any external circuit.

 

Implantable devices
Bioresorbable implantable medical devices show a great potential for applications requiring medical care over well-defined periods of time. Once their function is fulfilled, such implants naturally degrade and resorb in the body, which eliminates adverse long-term effects or the need for a secondary surgery to extract the implanted device. The CAPSULE drug delivery system consists of a 100% biodegradable implantable capsule with multiple reservoirs filled with drug. Each reservoir is covered with a membrane and a radio-frequency resonator on top of it. Each resonator has a different resonance frequency tuned by its geometrical parameters, which makes them selectively addressable. Using an external RF magnetic field, energy is coupled only into the frequency matched resonator where an electrical current is induced by electromagnetic induction, resulting in the Joule heating of that particular device only and the breaking of the underlying membrane. Each reservoir can thus be selectively opened. This way the amount of drug which is released can be precisely controlled over time. Another fully biodegradable transient drug delivery implant is made from silk fibroin films embed with iron oxide nanoparticles. When an external alternating magnetic field is applied, magnetic nanoparticles inside silk fibroin films locally heat up which induces thermal degradation of surrounding silk fibroin. Consequently, nanopore structures are generated which facilitate the release of Rhodamine B (Rh.B) dye solution.

Figure 3: a) Concept of a biodegradable implantable drug delivery system based on the use of frequency-selective microresonators as power receivers and microheaters to release the drug on demand. b) Broken meander hot spots of the resonators after applying an RF magnetic field. c) Nanopores could be generated by applying an external magnetic field to silk/magnetic nanoparticles composite film, which facilitate the release of Rh.B through the film.

 


Journal papers

  

Biodegradable Frequency‐Selective Magnesium Radio‐Frequency Microresonators for Transient Biomedical Implants

M. Rüegg; R. Blum; G. Boero; J. Brugger 

Advanced Functional Materials. 2019-08-07. Vol. 29, num. 39, p. 1903051. DOI : 10.1002/adfm.201903051.

All-in-one self-powered flexible microsystems based on triboelectric nanogenerators

X-S. Zhang; M. Han; B. Kim; J-F. Bao; J. Brugger et al. 

Nano Energy. 2018. Vol. 47, p. 410-426. DOI : 10.1016/j.nanoen.2018.02.046.

All-fiber hybrid piezoelectric-enhanced triboelectric nanogenerator for wearable gesture monitoring

Y. Guo; X. Zhang; Y. Wang; W. Gong; Q. Zhang et al. 

Nano Energy. 2018-02-26. Vol. 48, p. 152-160. DOI : 10.1016/j.nanoen.2018.03.033.

Penciling a triboelectric nanogenerator on paper for autonomous power MEMS applications

X. Zhang; M. Su; J. Brugger; B. Kim 

Nano Energy. 2017. Vol. 33, p. 393-401. DOI : 10.1016/j.nanoen.2017.01.053.

A silk-fibroin-based transparent triboelectric generator suitable for autonomous sensor network

X. Zhang; J. Brugger; B. Kim 

Nano Energy. 2016. Vol. 20, p. 37-47. DOI : 10.1016/j.nanoen.2015.11.036.

Conference papers

  

Fabrication and Characterization of Biodegradable, Thermal-Responsive Silk Composite Membrane

Y. Wang; X. Zhang; J. Brugger 

2018-01-01. 13th Annual IEEE International Conference on Nano/Micro Engineered and Molecular Systems (IEEE-NEMS), Singapore, SINGAPORE, Apr 22-26, 2018. p. 479-482.

Wearable Triboelectric Generator based on a hybrid mix of carbon nanotube and polymer layers

M. Su; J. Brugger; B. Kim 

2018-07-18. IEEE Power MEMS, Daytona Beach, December 4-7, 2018.

Fabrication and Characterization of Biodegradable, Thermal-Responsive Silk Composite Membrane

Y. Wang; X. Zhang; J. Brugger 

2018. The International Conference on Nano/Micro Engineered and Molecular Systems (NEMS) , Singapore, 22-26, April 2018 .

A transparent silk-fibroin-based triboelectric microgenerator for airflow energy harvesting

X. Zhang; Y. Guo; Y. Wang; H. Zhang; J. Brugger 

2017. IEEE 12th International Conference on Nano/Micro Engineered and Molecular Systems (NEMS), Los Angeles, CA, USA, April 9-12, 2017. p. 65-68. DOI : 10.1109/NEMS.2017.8016975.

Penciling A Triboelectric Power Source On Paper

X. Zhang; J. Brugger; B. Kim 

2016. 29th IEEE International Conference on Micro Electro Mechanical Systems (MEMS), Shanghai, PEOPLES R CHINA, JAN 24-28, 2016. p. 1169-1172.

FUTURE POWER POWERING FUTURE: HIGH-PERFORMANCE TRIBOELECTRIC NANOGENERATOR FOR WEARABLE ELECTRONICS

X. Zhang; B. Kim; J. Brugger 

2015. 2015 JSME-IIP/ASME-ISPS Joint Conference on Micromechatronics for Information and Precision Equipment (MIPE 2015), Kobe, Japan, June 14-17, 2015.

Posters

  

Novel Wearable Triboelectric Generator based on a Hybrid Mix of Carbon Nanotube and Natural Polymer

M. Su; J. Brugger; K. Beomjoon 

MEMS, Seoul, Korea,

Bioresorbable Frequency-Selective Magnesium Microresonators Fabricated by Ion Beam Etching

M. Rüegg; R. Blum 

Microtechnologies in Medicine and Biology, Monterey, USA, 26-28 March 2018.

Thermal-responsive biodegradable composite membrane for drug delivery application

Y. Wang 

11th NAMIS international Autumn school “Micro & nano systems engineering: from fundamentals to industrial applications”, Freiburg, Germany, October 2-6, 2017.