Vibrant reflective sensors with percolation film Fabry-Pérot nanocavities.

Dynamically reconfigurable structural colors are promising materials for new smart optical systems. However, improved reflected color quality (e.g., saturation, optical contrast, angular invariance) and larger tuning range/sensitivity are needed. Here, we demonstrate a vibrant, actively tunable system which meets these needs via coupling broadband plasmonic resonators to a responsive polymer film. Our structure consists of near-percolation gold nanoislands deposited on a poly[methyl methacrylate] (PMMA) spacer above a gold mirror, forming a Fabry-Pérot nanocavity. Broadband absorption in this system creates vivid reflected colors, while the polymer spacer enables continuous tuning over a wide color space. By exploiting swelling effects in PMMA, we show fast, reversible color switching in response to organic vapors. Our sensitive optical structure amplifies small vapor-induced changes in the spacer thickness, enabling naked-eye detection of changes as small as 10 nm. Additionally, optical absorption >99% yields modulation contrasts up to 80:1, opening the door to ultra-sensitive on-chip signal measurements, complementing the visual colorimetric readout. This structure has immediate implications for colorimetric bio/chemical sensing and may also find application to reflective displays and flexible/adaptive optical coatings.

Flexible Electrostatic Transducer Array with Displacement Control for Haptic Sensing and Actuation.

We developed flexible electrostatic transducers with both a single element and a 2×2 array format to actuate at a precise displacement across a range of loads with a control circuitry and algorithm. The transducer, composed of a moving buckled film with an integrated electrode and a rigid electrode, can be used to simultaneously generate and sense displacements. A circuit and computer program were designed to demonstrate displacement control and quantify the sensing precision of the transducer. Specifically, we applied a range of voltage and load conditions to the transducer and array and measured the displacement while under loading through capacitive sensing. The change in capacitance was linear with respect to the area of the electrode in contact and matched theoretical predictions when described as a function of the displacement. The transducer was loaded with weights in the range of 5-27 mN and capacitance-driving voltage graphs were obtained. An 8Hz driving frequency was used to move the transducer, while a 10.8kHz signal was used to sense the capacitance. These were used to build a predictive model to correct for sensed load to maintain a average displacement. It was found that a transducer of dimensions 10mm × 40mm was able to maintain displacement under loads of 5-27mN, while a matrix composed of 10mm × 20mm transducers was able to maintain displacement under loads of 2.5-11mN. In general, the detection thresholds of human skin can range between 5-20mN of force and 2-20um of displacement for frequencies between 1Hz and 250Hz, so these values are in line with what is needed to build a functional haptic wearable device. The present work provides a method to quantitatively measure and control a new type of flexible transducer for a variety of haptic applications.

Flexible Piezoelectric Nanogenerators Using Metal-doped ZnO-PVDF Films.

Piezoelectric nanomaterial-polymer composites represent a unique paradigm for making flexible energy harvesting and sensing devices with enhanced devices' performance. In this work, we studied various metal doped ZnO nanostructures, fabricated and characterized ZnO nanoparticle-PVDF composite thin film, and demonstrated both enhanced energy generation and motion sensing capabilities. Specifically, a series of flexible piezoelectric nanogenerators (PENGs) were designed based on these piezoelectric composite thin films. The voltage output from cobalt (Co), sodium (Na), silver (Ag), and lithium (Li) doped ZnO-PVDF composite as well as pure ZnO-PVDF samples were individually studied and compared. Under the same experimental conditions, the Li-ZnO based device produces the largest peak-to-peak voltage (3.43 Vpp) which is about 9 times of that of the pure ZnO based device, where Co-ZnO, Na-ZnO and Ag-ZnO are 1.2, 4.9 and 5.4 times, respectively. In addition, the effect of doping ratio of Li-ZnO is studied, and we found that 5% is the best doping ratio in terms of output voltage. Finally, we demonstrated that the energy harvested by the device from finger tapping at ~2 Hz can charge a capacitor with a large output power density of 0.45 W/cm3 and light up an ultraviolet (UV) light-emitting diode (LED). We also showed the device as a flexible wearable motion sensor, where different hand gestures were detected by the device with distinctive output voltage amplitudes and patterns.

Helical Structures Mimicking Chiral Seedpod Opening and Tendril Coiling.

Helical structures are ubiquitous in natural and engineered systems across multiple length scales. Examples include DNA molecules, plants' tendrils, sea snails' shells, and spiral nanoribbons. Although this symmetry-breaking shape has shown excellent performance in elastic springs or propulsion generation in a low-Reynolds-number environment, a general principle to produce a helical structure with programmable geometry regardless of length scales is still in demand. In recent years, inspired by the chiral opening of Bauhinia variegata's seedpod and the coiling of plant's tendril, researchers have made significant breakthroughs in synthesizing state-of-the-art 3D helical structures through creating intrinsic curvatures in 2D rod-like or ribbon-like precursors. The intrinsic curvature results from the differential response to a variety of external stimuli of functional materials, such as hydrogels, liquid crystal elastomers, and shape memory polymers. In this review, we give a brief overview of the shape transformation mechanisms of these two plant's structures and then review recent progress in the fabrication of biomimetic helical structures that are categorized by the stimuli-responsive materials involved. By providing this survey on important recent advances along with our perspectives, we hope to solicit new inspirations and insights on the development and fabrication of helical structures, as well as the future development of interdisciplinary research at the interface of physics, engineering, and biology.

Multifunctional Pacemaker Lead for Cardiac Energy Harvesting and Pressure Sensing.

Biomedical self-sustainable energy generation represents a new frontier of power solution for implantable biomedical devices (IMDs), such as cardiac pacemakers. However, almost all reported cardiac energy harvesting designs have not yet reached the stage of clinical translation. A major bottleneck has been the need of additional surgeries for the placements of these devices. Here, integrated piezoelectric-based energy harvesting and sensing designs are reported, which can be seamlessly incorporated into existing IMDs for ease of clinical translation. In vitro experiments validate the energy harvesting process by simulating the bending and twisting motion during heart cycle. Clinical translation is demonstrated in four porcine hearts in vivo under various conditions. Energy harvesting strategy utilizes pacemaker leads as a means of reducing the reliance on batteries and demonstrates the charging ability for extending the lifetime of a pacemaker battery by 20%, which provides a promising self-sustainable energy solution for IMDs. The additional self-powered blood pressure sensing is discussed, and the reported results demonstrate the potential in alerting arrhythmias by monitoring the right ventricular pressure variations. This combined cardiac energy harvesting and blood pressure sensing strategy provides a multifunctional, transformative while practical power and diagnosis solution for cardiac pacemakers and next generation of IMDs.

Flexible Energy Harvester on a Pacemaker Lead Using Multibeam Piezoelectric Composite Thin Films.

Implantable medical devices, such as cardiac pacemakers and defibrillators, rely on batteries for operation. However, conventional batteries only last for a few years, and additional surgeries are needed for replacement. Harvesting energy directly from the human body enables a new paradigm of self-sustainable power sources for implantable medical devices without being constrained by the battery's limited lifetime. Here, we report the design of a multibeam cardiac energy harvester using polydimethylsiloxane (PDMS)-infilled microporous P(VDF-TrFE) composite films. We first added ZnO nanoparticles and multiwall carbon nanotubes into microporous P(VDF-TrFE) films to increase the energy output. The mixing ratios of 30% ZnO and 0.1% MWCNTs yielded 3.22 ± 0.24 V output, which resulted in a voltage output 46 times higher than that of pure P(VDF-TrFE) films. Next, we discovered that the voltage generated by the composite film with PDMS is approximately 105% higher than that of the one without PDMS. For the application in cardiac pacemakers, we developed a facile fabrication method by building a cylindrical multibeam device that resides on the pacemaker lead to harvest energy from the complex motion of the lead driven by the heartbeat. Since the energy harvesting component is integrated into the pacemaker, it significantly reduces the risks and expenses associated with pacemaker-related surgeries. This work paves the way toward the new generation of energy harvesters that will benefit patients with a variety of implantable biomedical devices.

Vibration-Energy-Harvesting System: Transduction Mechanisms, Frequency Tuning Techniques, and Biomechanical Applications.

Vibration-based energy-harvesting technology, as an alternative power source, represents one of the most promising solutions to the problem of battery capacity limitations in wearable and implantable electronics, in particular implantable biomedical devices. Four primary energy transduction mechanisms are reviewed, namely piezoelectric, electromagnetic, electrostatic, and triboelectric mechanisms for vibration-based energy harvesters. Through generic modeling and analyses, it is shown that various approaches can be used to tune the operation bandwidth to collect appreciable power. Recent progress in biomechanical energy harvesters is also shown by utilizing various types of motion from bodies and organs of humans and animals. To conclude, perspectives on next-generation energy-harvesting systems are given, whereby the ultimate intelligent, autonomous, and tunable energy harvesters will provide a new energy platform for electronics and wearable and implantable medical devices.

Design of Nanoparticle-Based Carriers for Targeted Drug Delivery.

Nanoparticles have shown promise as both drug delivery vehicles and direct antitumor systems, but they must be properly designed in order to maximize efficacy. Computational modeling is often used both to design new nanoparticles and to better understand existing ones. Modeled processes include the release of drugs at the tumor site and the physical interaction between the nanoparticle and cancer cells. In this article, we provide an overview of three different targeted drug delivery methods (passive targeting, active targeting and physical targeting), compare methods of action, advantages, limitations, and the current stage of research. For the most commonly used nanoparticle carriers, fabrication methods are also reviewed. This is followed by a review of computational simulations and models on nanoparticle-based drug delivery.