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  1. Free, publicly-accessible full text available August 19, 2025
  2. Abstract

    Current joint angle monitoring techniques—essential for evaluating biomechanical functions and rehabilitation outcomes—face significant challenges. These may include dependency on specific environmental lighting and clear line‐of‐sight, complex setup and calibration, or sensing modalities that may interfere with natural motion. Additionally, the durability of these methods is often compromised by mechanical failures due to repetitive motion. Here, textile (or skin‐borne) strongly coupled magnetic resonators that can be distributed cross‐body to form advanced joint monitoring networks is demonstrated. Flexible magneto‐inductive loops can be positioned adjacent to joints, continuously monitoring limb coordination without being directly subjected to large joint strains. Such a technique minimizes both impediments to joint motion and material fatigue. Networks are lastly utilized to monitor and identify limb activity during diverse user stretches and exercises.

     
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  4. Abstract

    Passive and wireless Radio‐Frequency (RF) sensors are a unique, enabling modality for emerging applications in environmental sensing. These sensors exhibit several key features that may unlock new functionalities in complex environments: sensors are composed of zero electronic components, are wirelessly interrogated even in opaque media, and structures are often inherently biocompatible. Such capabilities make it unique in the realm of sensing architectures. Here, the broadside‐coupled, split‐ring resonator is studied as a compact and versatile model structure for RF sensing (of potentially mechanical and biochemical environments). A new analytical model is derived to assess resonator behavior—these yield a rapid, first‐order approximation of the resonator resonant frequency or sensitivity. Finally, experimental investigations into how sensors may be optimally designed, sized, and interrogated to enhance sensitivity or spectral intensity are performed. These studies encompass a wide variety of potential dimensional and dielectric modifications that may be relevant to emerging sensors. Last, hydrogel polymeric sensors are synthesized and studied to assess how practical sensors may deviate in response from expectations. Such investigations lay the groundwork for how such sensing architectures may be adapted to fit application needs.

     
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  5. Abstract

    The rapid advancements in wearable technologies are allowing for personal and tailored monitoring systems for core bodily metrics. Modern smartwatches accurately and frequently stream physical signals such as heart rate and respiratory rate. However, smartwatches have yet to track a multitude of physiological parameters, including sweat rate. This work presents a new wearable device that tracks sweat rate, the body's most important thermoregulatory function. The device is tape‐free and utilizes an off‐the‐shelf humidity sensor, with the potential to be integrated with existing smartwatch bands. It features a 3D‐printed chamber with a humidity sensor and microheater, and it interfaces the skin with a malleable and concave sweat collector. Through various experiments and trials, the authors seek to understand the relationship between sweat‐induced humidity within the chamber and the amount of sweat secreted when worn. Compared to existing sweat rate sensing devices, this hygrometer‐based device can be worn for extensive periods of time without overfilling. The device's reusability and compactness make it a good candidate for use alongside modern, microfluidic‐based sweat rate devices.

     
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  6. Abstract

    Nutrition measurement has broad applications in science, ranging from dietary assessment, to food monitoring, personalized health, and more. Despite its importance, there are currently no tools that offer continuous cotracking of nutrients direct from food. In this study, the multiscale engineering of silk biopolymer‐interlayer sensors is reported for comonitoring of nutrients. By manipulating various nano‐ to mesostructural properties of such biosensors, sensors are obtained with programmable sensitivity and selectivity to salts, sugars, and oils/fats. Notably, this approach requires no specialized nanomaterials or delicate biomolecules. Programmable biosensors are further formatted for wireless readout and characteristics of these passive, wireless nutrient monitors are studied in vitro. As a proof of concept, the discrimination and comonitoring of salt, sugar, and fat content direct from real, complex foods such as milk, meat, soup, and tea drinks are demonstrated. It is anticipated that such sensors can be utilized in emerging dietary tools for applications across food tracking and human health. In addition, such strategies are expected in structural engineering of sensors to be adaptable to existing or emerging selective or partially selective sensors.

     
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  7. Abstract

    Manipulation of magnetic materials (including remote‐controlled motions or structural deformations) plays a major role in modern micro‐ to macro‐scale systems. Magnetic operations create highly predicable outcomes in the behavior of systems, however these have difficulty performing subordinate and/or higher‐order operations. This lack of selectivity remains a critical drawback of magnetic manipulation schemes. Here, a strategy of engineering highly selective magnetic responses is studied and implemented. This is achieved by combining magnetic barcodes (“keys” encoded with layers of magnetic anisotropy) with programmable magnetic platforms (locking select codes in place with matching spatiotemporal magnetic fields). Presently, barcodes are realized by encoding hydrogel with sequences of magnetic microchains with binary spatial orientations. A number of unique capabilities of this approach are studied, including the untethered, selective anchoring of magnetic barcodes to programmable sites, as well as the selective latching of barcodes against background magnetic tags during flow. This approach may be used as a building block in micro‐ to macro‐scale magnetic interfaces.

     
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