Implantable drug delivery device using frequency-controlled wireless hydrogel microvalves

Wireless Battery-free and Fully Implantable Organ Interfaces

Advances in soft materials, miniaturized electronics, sensors, stimulators, radios, and battery-free power supplies are resulting in a new generation of fully implantable organ interfaces that leverage volumetric reduction and soft mechanics by eliminating electrochemical power storage. This device class offers the ability to provide high-fidelity readouts of physiological processes, enables stimulation, and allows control over organs to realize new therapeutic and diagnostic paradigms. Driven by seamless integration with connected infrastructure, these devices enable personalized digital medicine. Key to advances are carefully designed material, electrophysical, electrochemical, and electromagnetic systems that form implantables with mechanical properties closely matched to the target organ to deliver functionality that supports high-fidelity sensors and stimulators. The elimination of electrochemical power supplies enables control over device operation, anywhere from acute, to lifetimes matching the target subject with physical dimensions that supports imperceptible operation. This review provides a comprehensive overview of the basic building blocks of battery-free organ interfaces and related topics such as implantation, delivery, sterilization, and user acceptance. State of the art examples categorized by organ system and an outlook of interconnection and advanced strategies for computation leveraging the consistent power influx to elevate functionality of this device class over current battery-powered strategies is highlighted.

Untethered Microgrippers for Precision Medicine

Microgrippers, a branch of micro/nanorobots, refer to motile miniaturized machines that are of a size in the range of several to hundreds of micrometers. Compared with tethered grippers or other microscopic diagnostic and surgical equipment, untethered microgrippers play an indispensable role in biomedical applications because of their characteristics such as miniaturized size, dexterous shape tranformation, and  controllable motion, which enables the microgrippers to enter hard-to-reach regions to execute specific medical tasks for disease diagnosis and treatment. To date, numerous medical microgrippers are developed, and their potential in cell manipulation, targeted drug delivery, biopsy, and minimally invasive surgery  are explored. To achieve controlled locomotion and efficient target-oriented actions, the materials, size, microarchitecture, and morphology of microgrippers shall be deliberately designed. In this review, the authors summarizes the latest progress in untethered micrometer-scale grippers. The working mechanisms of shape-morphing and actuation methods for effective movement are first introduced. Then, the design principle and state-of-the-art fabrication techniques of microgrippers are discussed. Finally, their applications in the precise medicine are highlighted, followed by offering future perspectives for the development of untethered medical microgrippers.

Health Care Monitoring and Treatment for Coronary Artery Diseases: Challenges and Issues

In-stent restenosis concerning the coronary artery refers to the blood clotting-caused re-narrowing of the blocked section of the artery, which is opened using a stent. The failure rate for stents is in the range of 10% to 15%, where they do not remain open, thereby leading to about 40% of the patients with stent implantations requiring repeat procedure within one year, despite increased risk factors and the administration of expensive medicines. Hence, today stent restenosis is a significant cause of deaths globally. Monitoring and treatment matter a lot when it comes to early diagnosis and treatment. A review of the present stent monitoring technology as well as the practical treatment for addressing stent restenosis was conducted. The problems and challenges associated with current stent monitoring technology were illustrated, along with its typical applications. Brief suggestions were given and the progress of stent implants was discussed. It was revealed that prime requisites are needed to achieve good quality implanted stent devices in terms of their size, reliability, etc. This review would positively prompt researchers to augment their efforts towards the expansion of healthcare systems. Lastly, the challenges and concerns associated with nurturing a healthcare system were deliberated with meaningful evaluations.

Polymer Nanocomposite Microactuators for On-Demand Chemical Release via High-Frequency Magnetic Field Excitation

On-demand delivery of substances has been demonstrated for various applications in the fields of chemistry and biomedical engineering. Single-pulse release profile has been shown previously for micro/nanoparticles in different form factors. However, to obtain a sustained release, a pulsatile release profile is needed. Here, we demonstrate such a release profile from polymer magnetic nanocomposite microspheres loaded with chemicals. By exciting the microactuators with AC magnetic fields, we could achieve up to 61% cumulative release over a five-day period. One of the main advantages of using a magnetic stimulus is that the properties of the environment (e.g., transparency, density, and depth) in which the particles are located do not affect the performance. The operating magnitude of the magnetic field used in this work is safe and does not interact with any nonmetallic materials. The proposed approach can potentially be used in microchemistry, drug delivery, lab-on-chip, and microrobots for drug delivery.

One injection for one-week controlled release: In vitro and in vivo assessment of ultrasound-triggered drug release from injectable thermoresponsive biocompatible hydrogels

Episodic release of bioactive compounds is often necessary for appropriate biological effects under specific physiological conditions. Here, we aimed to develop an injectable, biocompatible, and thermosensitive hydrogel system for ultrasound (US)-triggered drug release. An mPEG-PLGA-BOX block copolymer hydrogel was synthesized. The viscosity of 15 wt% hydrogel is 0.03 Pa*s at 25 °C (liquid form) and 34.37 Pa*s at 37 °C (gel form). Baseline and US-responsive in vitro release profile of a small molecule (doxorubicin) and that of a large molecule (FITC-dextran), from the hydrogel, was tested. A constant baseline release was observed in vitro for 7 d. When triggered by US (1 MHz, continuous, 0.4 W/cm²), the release rate increased by approximately 70 times. Without US, the release rate returned to baseline. Baseline and US-responsive in vivo release profile of doxorubicin was tested by subcutaneous injection in the back of mice and rats. Following injection into the subcutaneous layer, in vivo results also suggested that the hydrogels remained in situ and provided a steady release for at least 7 d; in the presence of the US-trigger, in vivo release from the hydrogel increased by approximately 10 times. Therefore, the mPEG-PLGA-BOX block copolymer hydrogel may serve as an injectable, biocompatible, and thermosensitive hydrogel system that is applicable for US-triggered drug release.

Electrothermally Driven Hydrogel-on-Flex-Circuit Actuator for Smart Steerable Catheters

This paper reports an active catheter-tip device functionalized by integrating a temperature-responsive smart polymer onto a microfabricated flexible heater strip, targeting at enabling the controlled steering of catheters through complex vascular networks. A bimorph-like strip structure is enabled by photo-polymerizing a layer of poly(N-isopropylacrylamide) hydrogel (PNIPAM), on top of a 20 × 3.5 mm² flexible polyimide film that embeds a micropatterned heater fabricated using a low-cost flex-circuit manufacturing process. The heater activation stimulates the PNIPAM layer to shrink and bend the tip structure. The bending angle is shown to be adjustable with the amount of power fed to the device, proving the device’s feasibility to provide the integrated catheter with a controlled steering ability for a wide range of navigation angles. The powered device exhibits uniform heat distribution across the entire PNIPAM layer, with a temperature variation of <2 °C. The operation of fabricated prototypes assembled on commercial catheter tubes demonstrates their bending angles of up to 200°, significantly larger than those reported with other smart-material-based steerable catheters. The temporal responses and bending forces of their actuations are also characterized to reveal consistent and reproducible behaviors. This proof-of-concept study verifies the promising features of the prototyped approach to the targeted application area.

Untethered microgripper-the dexterous hand at microscale

Untethered microgrippers that can navigate in hard-to-reach and unpredictable environments are significantly important for biomedical applications such as targeted drug delivery, micromanipulation, minimally invasive surgery and in vivo biopsy. Compared with the traditional tethered microgrippers, the wireless microgrippers, due to the exceptional characteristics such as miniaturized size, untethered actuation, dexterous and autonomous motion, are projected to be promising microtools in various future applications. In this review, we categorize the untethered microgrippers into five major classes, i.e. microgrippers responsive to thermal, microgrippers actuated by magnetic fields, microgrippers responsive to chemicals, light-driven microgrippers and hybrid actuated microgrippers. Firstly, the actuation mechanisms of these microgrippers are introduced. The challenges faced by these microgrippers are also covered in this part. With that, the fabrication methods of these microgrippers are summarized. Subsequently, the applications of microgrippers are presented. Additionally, we conduct a comparison among different actuation mechanisms to explore the advantages and potential challenges of various types of microgrippers. In the end of this review, conclusions and outlook of the development and potential applications of the microgrippers are discussed.

A zero power harmonic transponder sensor for ubiquitous wireless μL liquid-volume monitoring

Autonomous liquid-volume monitoring is crucial in ubiquitous healthcare. However, conventional approach is based on either human visual observation or expensive detectors, which are costly for future pervasive monitoring. Here we introduce a novel approach based on passive harmonic transponder antenna sensor and frequency hopping spread spectrum (FHSS) pattern analysis, to provide a very low cost wireless μL-resolution liquid-volume monitoring without battery or digital circuits. In our conceptual demonstration, the harmonic transponder comprises of a passive nonlinear frequency multiplier connected to a metamaterial-inspired 3-D antenna designed to be highly sensitive to the liquid-volume within a confined region. The transponder first receives some FHSS signal from an interrogator, then converts such signal to its harmonic band and re-radiates through the antenna sensor. The harmonic signal is picked up by a sniffer receiver and decoded through pattern analysis of the high dimensional FHSS signal strength data. A robust, zero power, absolute accuracy wireless liquid-volume monitoring is realized in the presence of strong direct coupling, background scatters, distance variance as well as near-field human-body interference. The concepts of passive harmonic transponder sensor, metamaterial-inspired antenna sensor, and FHSS pattern analysis based sensor decoding may help establishing cost-effective, energy-efficient and intelligent wireless pervasive healthcare monitoring platforms.

Controlling the resolution and duration of pulsatile release from injectable magnetic ‘plum-pudding’ nanocomposite hydrogels

Injectable hydrogel nanocomposites with entrapped SPIONs, thermosensitive microgels, and model drugs generate heat when an alternating magnetic field is applied, causing the microgels to deswell and create pore space to promote enhanced drug release.

Stick-slip water penetration into capillaries coated with swelling hydrogel

We have observed intriguing stick-slip behavior during capillary pressure driven filling of borosilicate microtubes coated with hydrogel on their inner wall. Swelling of hydrogel upon exposure to a translating waterfront is accompanied by "stick-and-slip" motion. This results in the macroscopic filling velocity for water penetration into glass capillaries coated with poly(N-isopropylacrylamide) (PNIPAM) being constant throughout the filling process, and reduced by three orders of magnitude when compared to filling of uncoated capillaries. A simple scaling analysis is used to introduce a possible explanation by considering the mechanisms responsible for pinning and unpinning of the contact line. The explanation assumes that the time scale for water diffusion into a hydrogel film and the resulting swelling/change of the local meniscus contact angle define the duration of each "stick" event. The "slip" length scale is in turn established by the elastocapillary deformation of dry hydrogel at the pinning point of the contact line. The sequential dynamics of these processes then determine the rate of water filling into a swelling capillary. Collectively, these experimental and theoretical results provide a new conceptual framework for liquid motion confined by soft, dynamically evolving polymer interfaces, in which the system creates an energy barrier to further motion through elasto-capillary deformation, and then lowers the barrier through diffusive softening. This insight has implications for optimal design of microfluidic and lab-on-a-chip devices based on stimuli-responsive smart polymers.

Wireless implantable chip with integrated nitinol-based pump for radio-controlled local drug delivery

We demonstrate an active, implantable drug delivery device embedded with a microfluidic pump that is driven by a radio-controlled actuator for temporal drug delivery. The polyimide-packaged 10 × 10 × 2 mm(3) chip contains a micromachined pump chamber and check valves of Parylene C to force the release of the drug from a 76 μL reservoir by wirelessly activating the actuator using external radio-frequency (RF) electromagnetic fields. The rectangular-shaped spiral-coil actuator based on nitinol, a biocompatible shape-memory alloy, is developed to perform cantilever-like actuation for pumping operation. The nitinol-coil actuator itself forms a passive 185 MHz resonant circuit that serves as a self-heat source activated via RF power transfer to enable frequency-selective actuation and pumping. Experimental wireless operation of fabricated prototypes shows successful release of test agents from the devices placed in liquid and excited by radiating tuned RF fields with an output power of 1.1 W. These tests reveal a single release volume of 219 nL, suggesting a device's capacity of ~350 individual ejections of drug from its reservoir. The thermal behavior of the activated device is also reported in detail. This proof-of-concept prototype validates the effectiveness of wireless RF pumping for fully controlled, long-lasting drug delivery, a key step towards enabling patient-tailored, targeted local drug delivery through highly miniaturized implants.

Active drug release systems: current status, applications and perspectives

Active drug release systems offer an important privilege to manage the dosage, time and sometimes site of drug release after the implantation procedure has been performed. Once developed, they could cover such applications as hormone therapy, implantation surgery, and delivery of immunization boosters. A number of existing approaches towards such systems include arrays of microreservoirs equipped with stimuli-responsive actuators or valves. The very first developed system has reached the stage of in-human trials recently. A breakthrough could happen if microreservoirs themselves are made of responsive material susceptible towards remote triggers. A promising candidate is a material made of Layer-by-Layer assembled films which currently are widely exploited only as passive implantable drug release systems.

RFID Tag Helix Antenna Sensors for Wireless Drug Dosage Monitoring

Miniaturized helix antennas are integrated with drug reservoirs to function as RFID wireless tag sensors for real-time drug dosage monitoring. The general design procedure of this type of biomedical antenna sensors is proposed based on electromagnetic theory and finite element simulation. A cost effective fabrication process is utilized to encapsulate the antenna sensor within a biocompatible package layer using PDMS material, and at the same time form a drug storage or drug delivery unit inside the sensor. The in vitro experiment on two prototypes of antenna sensor-drug reservoir assembly have shown the ability to monitor the drug dosage by tracking antenna resonant frequency shift from 2.4–2.5-GHz ISM band with realized sensitivity of 1.27 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\mu~{\rm l}/{\rm MHz}$\end{document} for transdermal drug delivery monitoring and 2.76-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\mu~{\rm l}/{\rm MHz}$\end{document} sensitivity for implanted drug delivery monitoring.

Reagents in microfluidics: an 'in' and 'out' challenge

Microfluidic devices are excellent at downscaling chemical and biochemical reactions and thereby can make reactions faster, better and more efficient. It is therefore understandable that we are seeing these devices being developed and used for many applications and research areas. However, microfluidic devices are more complex than test tubes or microtitre plates and the integration of reagents into them is a real challenge. This review looks at state-of-the-art methods and strategies for integrating various classes of reagents inside microfluidics and similarly surveys how reagents can be released inside microfluidics. The number of methods used for integrating and releasing reagents is surprisingly large and involves reagents in dry and liquid forms, directly-integrated reagents or reagents linked to carriers, as well as active, passive and hybrid release methods. We also made a brief excursion into the field of drug release and delivery. With this review, we hope to provide a large number of examples of integrating and releasing reagents that can be used by developers and users of microfluidics for their specific needs.

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.

Responsive hydrogels--structurally and dimensionally optimized smart frameworks for applications in catalysis, micro-system technology and material science

Although the technological and scientific importance of functional polymers has been well established over the last few decades, the most recent focus that has attracted much attention has been on stimuli-responsive polymers. This group of materials is of particular interest due to its ability to respond to internal and/or external chemico-physical stimuli, which is often manifested as large macroscopic responses. Aside from scientific challenges of designing stimuli-responsive polymers, the main technological interest lies in their numerous applications ranging from catalysis through microsystem technology and chemomechanical actuators to sensors that have been extensively explored. Since the phase transition phenomenon of hydrogels is theoretically well understood advanced materials based on the predictions can be prepared. Since the volume phase transition of hydrogels is a diffusion-limited process the size of the synthesized hydrogels is an important factor. Consistent downscaling of the gel size will result in fast smart gels with sufficient response times. In order to apply smart gels in microsystems and sensors, new preparation techniques for hydrogels have to be developed. For the up-coming nanotechnology, nano-sized gels as actuating materials would be of great interest.

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.

Intelligent drug-delivery devices based on micro- and nano-technologies

This review focuses on the current drug-delivery modalities in R&D, as well as commercially available. Intelligent drug-delivery systems are described as novel technological innovations and clinical approaches to improve conventional treatments. These systems differ in methodology of therapeutic administration, intricacy, materials and patient compliance to address numerous clinical conditions that require various pharmacological therapies. These systems have been primarily described as active and passive microelectrical mechanical system devices, injectors and nanoparticle-based therapies, optimized to tailor specific pharmacokinetic profiles. The most critical considerations for the design of these intelligent delivery systems include the controlled release, target specificity, on-demand dosage adjustment, mass transfer and stability of the pharmacological agents. Drug-delivery systems continue to be developed and enhanced to provide better and more sophisticated treatments, promising an improvement in quality of life and extension of life expectancy.

A magnetically controlled MEMS device for drug delivery: design, fabrication, and testing

We report the development of a magnetically controlled drug delivery device for on-demand drug release to treat chronic diseases. The devices consist of drug-loaded micro-reservoirs (6 mm in diameter and ∼550 μm in depth), sealed by magnetic PDMS (polydimethylsiloxane) membranes (Ø 6 mm × 40 μm) with laser-drilled apertures and actuated by an external magnetic field. We present a detailed analysis of the magnetic actuation forces and provide an estimate of the resulting membrane deflections. The reservoirs are fabricated by PDMS molding and loaded with drugs using solvent evaporation methods. Post-processing procedures using bovine serum albumin (BSA) adsorption on magnetic PDMS surfaces are carried out to modify the surface wettability and to allow water filling and dissolution of the drugs in the reservoirs. Detailed surface modification processes are described and characterized. The device demonstrates on-demand delivery of methylene blue (MB) as a model drug. Intermittent magnetic actuations of the device in a ∼200 mT magnetic field show 10-fold increase in MB release compared to background release when the device is not actuated.