A Parylene Bellows Electrochemical Actuator

A wearable, minimally-invasive, fully electrochemically-controlled feedback minisystem for diabetes management

Diabetes is a chronic disease affecting 10% of the population globally, and can lead to serious damage in the heart, kidneys, eyes, blood vessels or nerves. Commercial artificial closed-loop feedback systems can significantly improve diabetes management and save lives. However, they are large and expensive for users. Here, we demonstrate for the first time a wearable, minimally-invasive, fully electrochemically-controlled feedback minisystem for diabetes management. Both the working principles of the sensor and pump in the feedback system are based on electrochemical reactions. The smart minisystem was constructed based on integrating the thermoplastic polyurethane hollow microneedles with an electrochemical biosensing device on its outer layer and an electrochemical micropump facing the inner layer of the microneedles. The sensing device was constructed based on sputtering thin metal films through a shadow mask and electroplating Prussian blue on the surface of the microneedles, followed by the immobilization of glucose oxidase on the working electrode. The electrochemical micropump was constructed by sputtering the interdigital electrodes, followed by sealing with a thin elastic film, which was further integrated with the inner channels of the microneedles. Both the sensor and the pump were electrically powered. Via being controlled by a printed circuit board, the biosensing device monitored the levels of interstitial glucose continuously to drive the electrochemical pump to deliver insulin intelligently, in order to control blood glucose within the normal range. The closed-loop feedback system was studied for its capability in maintaining the blood glucose levels of diabetic rats under various physiological conditions. The utility of the intelligent feedback system was successfully demonstrated on diabetic rats for controlling the blood glucose levels within the normal range. The minisystem is wearable, small, cost-effective, precise, stable and painless. It is anticipated that this approach opens a new paradigm for the development of closed-loop diabetes minisystems and may lead to a compelling future for diabetes management.

Nanoreactors in action for a durable microactuator using spontaneous combustion of gases in nanobubbles

A number of recent studies report enhancement of chemical reactions on water microdroplets or inside nanobubbles in water. This finding promises exciting applications, although the mechanism of the reaction acceleration is still not clear. Specifically, the spontaneous combustion of hydrogen and oxygen in nanobubbles opens the way to fabricate truly microscopic engines. An example is an electrochemical membrane actuator with all three dimensions in the micrometer range. The actuator is driven by short voltage pulses of alternating polarity, which generate only nanobubbles. The device operation is, however, restricted by a fast degradation of the electrodes related to a high current density. Here it is demonstrated that the actuator with ruthenium electrodes does not show signs of degradation in the long-term operation. It is the only material able to withstand the extreme conditions of the alternating polarity electrolysis. This property is due to combination of a high mechanical hardness and metallic conductivity of ruthenium oxide. The actuator combines two features considered impossible: on-water catalysis and combustion in a microscopic volume. It provides an exceptional opportunity to drive autonomous microdevices especially for medical or biological applications.

Modeling programmable drug delivery in bioelectronics with electrochemical actuation

Drug delivery systems featuring electrochemical actuation represent an emerging class of biomedical technology with programmable volume/flowrate capabilities for localized delivery. Recent work establishes applications in neuroscience experiments involving small animals in the context of pharmacological response. However, for programmable delivery, the available flowrate control and delivery time models fail to consider key variables of the drug delivery system--microfluidic resistance and membrane stiffness. Here we establish an analytical model that accounts for the missing variables and provides a scalable understanding of each variable influence in the physics of delivery process (i.e., maximum flowrate, delivery time). This analytical model accounts for the key parameters--initial environmental pressure, initial volume, microfluidic resistance, flexible membrane, current, and temperature--to control the delivery and bypasses numerical simulations allowing faster system optimization for different in vivo experiments. We show that the delivery process is controlled by three nondimensional parameters, and the volume/flowrate results from the proposed analytical model agree with the numerical results and experiments. These results have relevance to the many emerging applications of programmable delivery in clinical studies within the neuroscience and broader biomedical communities.

Bonding methods for chip integration with Parylene devices

Flexible electronics require more compact interconnects for next-generation devices. Polymer devices can be bonded to integrated circuit chips, but combining flexible and rigid substrates poses unique technical challenges. Existing technologies either cannot achieve the density required for modern chips or employ specialized equipment and complex processes to do so. Here, we adapt several approaches to achieve fine-pitch bonding between rigid and flexible substrates including epoxy, ultrasonic wire, and anisotropic conductive film bonding and also introduce a novel technique called polymer ultrasonic on bump (PUB) bonding. Using Parylene C devices and various rigid substrates as our model testbed systems, we investigate these four methods across a range of bond pad size and pitch by measuring yield and resistance and by subjecting devices to thermomechanical reliability tests. We demonstrate that all methods are capable of bonding fine pitch interconnects (100 μm) at low temperature (<100 °C). Additionally, we focus on PUB bonding and join a packaged chip and a bare die to Parylene devices.

Techniques and Considerations in the Microfabrication of Parylene C Microelectromechanical Systems

Parylene C is a promising material for constructing flexible, biocompatible and corrosion-resistant microelectromechanical systems (MEMS) devices. Historically, Parylene C has been employed as an encapsulation material for medical implants, such as stents and pacemakers, due to its strong barrier properties and biocompatibility. In the past few decades, the adaptation of planar microfabrication processes to thin film Parylene C has encouraged its use as an insulator, structural and substrate material for MEMS and other microelectronic devices. However, Parylene C presents unique challenges during microfabrication and during use with liquids, especially for flexible, thin film electronic devices. In particular, the flexibility and low thermal budget of Parylene C require modification of the fabrication techniques inherited from silicon MEMS, and poor adhesion at Parylene-Parylene and Parylene-metal interfaces causes device failure under prolonged use in wet environments. Here, we discuss in detail the promises and challenges inherent to Parylene C and present our experience in developing thin-film Parylene MEMS devices.

Minimally invasive probes for programmed microfluidic delivery of molecules in vivo

Site-specific drug delivery carries many advantages of systemic administration, but is rarely used in the clinic. One limiting factor is the relative invasiveness of the technology to locally deliver compounds. Recent advances in materials science and electrical engineering allow for the development of ultraminiaturized microfluidic channels based on soft materials to create flexible probes capable of deep tissue targeting. A diverse set of mechanics, including micro-pumps and functional materials, used to deliver the drugs can be paired with wireless electronics for self-contained and programmable operation. These first iterations of minimally invasive fluid delivery devices foreshadow important advances needed for clinical translation.

A Self-Powered Implantable Drug-Delivery System Using Biokinetic Energy

The first triboelectric-nanogenerator (TENG)-based self-powered implantable drug-delivery system is presented. Pumping flow rates from 5.3 to 40 µL min^-1 under different rotating speeds of the TENG are realized. The implantable drug-delivery system can be powered with a TENG device rotated by human hand motion. Ex vivo trans-sclera drug delivery in porcine eyes is demonstrated by utilizing the biokinetic energies of human hands.

A Wireless Implantable Micropump for Chronic Drug Infusion Against Cancer

We present an implantable micropump with a miniature form factor and completely wireless operation that enables chronic drug administration intended for evaluation and development of cancer therapies in freely moving small research animals such as rodents. The low power electrolysis actuator avoids the need for heavy implantable batteries. The infusion system features a class E inductive powering system that provides on-demand activation of the pump as well as remote adjustment of the delivery regimen without animal handling. Micropump performance was demonstrated using a model anti-cancer application in which daily doses of 30 μL were supplied for several weeks with less than 6% variation in flow rate within a single pump and less than 8% variation across different pumps. Pumping under different back pressure, viscosity, and temperature conditions were investigated; parameters were chosen so as to mimic in vivo conditions. In benchtop tests under simulated in vivo conditions, micropumps provided consistent and reliable performance over a period of 30 days with less than 4% flow rate variation. The demonstrated prototype has potential to provide a practical solution for remote chronic administration of drugs to ambulatory small animals for research as well as drug discovery and development applications.

Acceleration Techniques for Recombination of Gases in Electrolysis Microactuators with Nafion®-Coated Electrocatalyst

Recombination of electrolysis gases (oxidation of hydrogen and reduction of oxygen) is an important factor in operation efficiency of devices employing electrolysis such as actuators and also unitized regenerative fuel cells. Several methods of improving recombination speed and repeatability were developed for application to electrolysis microactuators with Nafion®-coated catalytic electrodes. Decreasing the electrolysis chamber volume increased the speed, consistency, and repeatability of the gas recombination rate. To further improve recombination performance, methods to increase the catalyst surface area, hydrophobicity, and availability were developed and evaluated. Of these, including in the electrolyte pyrolyzed-Nafion®-coated Pt segments contained in the actuator chamber accelerated recombination by increasing the catalyst surface area and decreasing the gas transport diffusion path. This approach also reduced variability in recombination encountered under varying actuator orientation (resulting in differing catalyst/gas bubble proximity) and increased the rate of recombination by 2.3 times across all actuator orientations. Repeatability of complete recombination for different generated gas volumes was studied through cycling.

Materials for microfabricated implantable devices: a review

The application of microfabrication to the development of biomedical implants has produced a new generation of miniaturized technology for assisting treatment and research. Microfabricated implantable devices (μID) are an increasingly important tool, and the development of new μIDs is a rapidly growing field that requires new microtechnologies able to safely and accurately function in vivo. Here, we present a review of μID research that examines the critical role of material choice in design and fabrication. Materials commonly used for μID production are identified and presented along with their relevant physical properties and a survey of the state-of-the-art in μID development. The consequence of material choice as it pertains to microfabrication and biocompatibility is discussed in detail with a particular focus on the divide between hard, rigid materials and soft, pliable polymers.

An in-vivo evaluation of a MEMS drug delivery device using Kunming mice model

The use of MEMS implantable drug delivery pump device enables one to program the desired drug delivery profile in the device for individualized medicine treatment to patients. In this study, a MEMS drug delivery device is prepared and employed for in vivo applications. 12 devices are implanted subcutaneously into Kunming mice for evaluating their long term biocompatibility and drug-delivery efficiency in vivo. All the mice survived after device implantation surgery procedures. Histological analysis result reveals a normal wound healing progression within the tissues-to-device contact areas. Serum analysis shows that all measured factors are within normal ranges and do not indicate any adverse responses associated with the implanted device. Phenylephrine formulation is chosen and delivered to the abdominal cavity of the mice by using either the implanted MEMS device (experimental group) or the syringe injection method (control group). Both groups show that they are able to precisely control and manipulate the increment rate of blood pressure in the small animals. Our result strongly suggests that the developed refillable implantable MEMS devices will serve as a viable option for future individualized medicine applications such as glaucoma, HIV-dementia and diabetes therapy.

A cyclically actuated electrolytic drug delivery device

This work, focusing on an implantable drug delivery system, presents the first prototype electrolytic pump that combines a catalytic reformer and a cyclically actuated mode. These features improve the release performance and extend the lifetime of the device. Using our platinum (Pt)-coated carbon fiber mesh that acts as a catalytic reforming element, the cyclical mode is improved because the faster recombination rate allows for a shorter cycling time for drug delivery. Another feature of our device is that it uses a solid-drug-in-reservoir (SDR) approach, which allows small amounts of a solid drug to be dissolved in human fluid, forming a reproducible drug solution for long-term therapies. We have conducted proof-of-principle drug delivery studies using such an electrolytic pump and solvent blue 38 as the drug substitute. These tests demonstrate power-controlled and pulsatile release profiles of the chemical substance, as well as the feasibility of this device. A drug delivery rate of 11.44 ± 0.56 μg min(-1) was achieved by using an input power of 4 mW for multiple pulses, which indicates the stability of our system.

A remotely operated drug delivery system with an electrolytic pump and a thermo-responsive valve

Implantable drug delivery devices are becoming attractive due to their abilities of targeted and controlled dose release. Currently, two important issues are functional lifetime and non-controlled drug diffusion. In this work, we present a drug delivery device combining an electrolytic pump and a thermo-responsive valve, which are both remotely controlled by an electromagnetic field (40.5 mT and 450 kHz). Our proposed device exhibits a novel operation mechanism for long-term therapeutic treatments using a solid drug in reservoir approach. Our device also prevents undesired drug liquid diffusions. When the electromagnetic field is on, the electrolysis-induced bubble drives the drug liquid towards the Poly (N-Isopropylacrylamide) (PNIPAM) valve that consists of PNIPAM and iron micro-particles. The heat generated by the iron micro-particles causes the PNIPAM to shrink, resulting in an open valve. When the electromagnetic field is turned off, the PNIPAM starts to swell. In the meantime, the bubbles are catalytically recombined into water, reducing the pressure inside the pumping chamber, which leads to the refilling of the fresh liquid from outside the device. A catalytic reformer is included, allowing more liquid refilling during the limited valve's closing time. The amount of body liquid that refills the drug reservoir can further dissolve the solid drug, forming a reproducible drug solution for the next dose. By repeatedly turning on and off the electromagnetic field, the drug dose can be cyclically released, and the exit port of the device is effectively controlled.

New type of microengine using internal combustion of hydrogen and oxygen

Microsystems become part of everyday life but their application is restricted by lack of strong and fast motors (actuators) converting energy into motion. For example, widespread internal combustion engines cannot be scaled down because combustion reactions are quenched in a small space. Here we present an actuator with the dimensions 100 × 100 × 5 μm³ that is using internal combustion of hydrogen and oxygen as part of its working cycle. Water electrolysis driven by short voltage pulses creates an extra pressure of 0.5–4 bar for a time of 100–400 μs in a chamber closed by a flexible membrane. When the pulses are switched off this pressure is released even faster allowing production of mechanical work in short cycles. We provide arguments that this unexpectedly fast pressure decrease is due to spontaneous combustion of the gases in the chamber. This actuator is the first step to truly microscopic combustion engines.

BioMEMS in drug delivery

The drive to design micro-scale medical devices which can be reliably and uniformly mass produced has prompted many researchers to adapt processing technologies from the semiconductor industry. By operating at a much smaller length scale, the resulting biologically-oriented microelectromechanical systems (BioMEMS) provide many opportunities for improved drug delivery: Low-dose vaccinations and painless transdermal drug delivery are possible through precisely engineered microneedles which pierce the skin's barrier layer without reaching the nerves. Low-power, low-volume BioMEMS pumps and reservoirs can be implanted where conventional pumping systems cannot. Drug formulations with geometrically complex, extremely uniform micro- and nano-particles are formed through micromolding or with microfluidic devices. This review describes these BioMEMS technologies and discusses their current state of implementation. As these technologies continue to develop and capitalize on their simpler integration with other MEMS-based systems such as computer controls and telemetry, BioMEMS' impact on the field of drug delivery will continue to increase.

An electrochemically actuated MEMS device for individualized drug delivery: an in vitro study

Individualized disease treatment is a promising branch for future medicine. In this work, we introduce an implantable microelectromechanical system (MEMS) based drug delivery device for programmable drug delivery. An in vitro study on cancer cell treatment has been conducted to demonstrate a proof-of-concept that the engineered device is suitable for individualized disease treatment. This is the first study to demonstrate that MEMS drug delivery devices can influence the outcome of cancer drug treatment through the use of individualized disease treatment regimes, where the strategy for drug dosages is tailored according to different individuals. The presented device is electrochemically actuated through a diaphragm membrane and made of polydimethylsiloxane (PDMS) for biocompatibility using simple and cost-effective microfabrication techniques. Individualized disease treatment was investigated using the in vitro programmed delivery of a chemotherapy drug, doxorubicin, to pancreatic cancer cell cultures. Cultured cell colonies of two pancreatic cancer cell lines (Panc-1 and MiaPaCa-2) were treated with three programmed schedules and monitored for 7 days. The result shows that the colony growth has been successfully inhibited for both cell lines among all the three treatment schedules. Also, the different observations between the two cell lines under different schedules reveal that MiaPaCa-2 cells are more sensitive to the drug applied. These results demonstrate that further development on the device will provide a promising novel platform for individualized disease treatment in future medicine as well as for automatic in vitro assays in drug development industry.

A MEMS electrochemical bellows actuator for fluid metering applications

We present a high efficiency wireless MEMS electrochemical bellows actuator capable of rapid and repeatable delivery of boluses for fluid metering and drug delivery applications. Nafion®-coated Pt electrodes were combined with Parylene bellows filled with DI water to form the electrolysis-based actuator. The performance of actuators with several bellows configurations was compared for a range of applied currents (1-10 mA). Up to 75 boluses were delivered with an average pumping flow rate of 114.40 ± 1.63 μL/min. Recombination of gases into water, an important factor in repeatable and reliable actuation, was studied for uncoated and Nafion®-coated actuators. Real-time pressure measurements were conducted and the effects of temperature, physiological back pressure, and drug viscosity on delivery performance were investigated. Lastly, we present wireless powering of the actuator using a class D inductive powering system that allowed for repeatable delivery with less than 2 % variation in flow rate values.

Micro- and nano-fabricated implantable drug-delivery systems

Implantable drug-delivery systems provide new means for achieving therapeutic drug concentrations over entire treatment durations in order to optimize drug action. This article focuses on new drug administration modalities achieved using implantable drug-delivery systems that are enabled by micro- and nano-fabrication technologies, and microfluidics. Recent advances in drug administration technologies are discussed and remaining challenges are highlighted.

Polymeric microdevices for transdermal and subcutaneous drug delivery

Low cost manufacturing of polymeric microdevices for transdermal and subcutaneous drug delivery is slated to have a major impact on next generation devices for administration of biopharmaceuticals and other emerging new formulations. These devices range in complexity from simple microneedle arrays to more complicated systems incorporating micropumps, micro-reservoirs, on-board sensors, and electronic intelligence. In this paper, we review devices currently in the market and those in the earlier stages of research and development. We also present two examples of the research in our laboratory towards using phase change liquids in polymeric structures to create disposable micropumps and the development of an elastomeric reservoir for MEMS-based transdermal drug delivery systems.

MEMS-enabled implantable drug infusion pumps for laboratory animal research, preclinical, and clinical applications

Innovation in implantable drug delivery devices is needed for novel pharmaceutical compounds such as certain biologics, gene therapy, and other small molecules that are not suitable for administration by oral, topical, or intravenous routes. This invasive dosing scheme seeks to directly bypass physiological barriers presented by the human body, release the appropriate drug amount at the site of treatment, and maintain the drug bioavailability for the required duration of administration to achieve drug efficacy. Advances in microtechnologies have led to novel MEMS-enabled implantable drug infusion pumps with unique performance and feature sets. In vivo demonstration of micropumps for laboratory animal research and preclinical studies include acute rapid radiolabeling, short-term delivery of nanomedicine for cancer treatment, and chronic ocular drug dosing. Investigation of MEMS actuators, valves, and other microstructures for on-demand dosing control may enable next generation implantable pumps with high performance within a miniaturized form factor for clinical applications.

An implantable MEMS micropump system for drug delivery in small animals

We present the first implantable drug delivery system for controlled timing and location of dosing in small animals. Current implantable drug delivery devices do not provide control over these factors nor are they feasible for implantation in research animals as small as mice. Our system utilizes an integrated electrolysis micropump, is refillable, has an inert drug reservoir for broad drug compatibility, and is capable of adjustment to the delivery regimen while implanted. Electrochemical impedance spectroscopy (EIS) was used for characterization of electrodes on glass substrate and a flexible Parylene substrate. Benchtop testing of the electrolysis actuator resulted in flow rates from 1 μL/min to 34 μL/min on glass substrate and up to 6.8 μL/min on Parylene substrate. The fully integrated system generated a flow rate of 4.72 ± 0.35 μL/min under applied constant current of 1.0 mA while maintaining a power consumption of only ~3 mW. Finally, we demonstrated in vivo application of the system for anti-cancer drug delivery in mice.