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A closed‐loop system that can mini‐invasively track blood glucose and intelligently treat diabetes is in great demand for modern medicine, yet it remains challenging to realize. Microneedles technologies have recently emerged as powerful tools for transdermal applications with inherent painlessness and biosafety. In this work, for the first time to the authors' knowledge, a fully integrated wearable closed‐loop system (IWCS) based on mini‐invasive microneedle platform is developed for in situ diabetic sensing and treatment. The IWCS consists of three connected modules: 1) a mesoporous microneedle‐reverse iontophoretic glucose sensor; 2) a flexible printed circuit board as integrated and control; and 3) a microneedle‐iontophoretic insulin delivery component. As the key component, mesoporous microneedles enable the painless penetration of stratum corneum, implementing subcutaneous substance exchange. The coupling with iontophoresis significantly enhances glucose extraction and insulin delivery and enables electrical control. This IWCS is demonstrated to accurately monitor glucose fluctuations, and responsively deliver insulin to regulate hyperglycemia in diabetic rat model. The painless microneedles and wearable design endows this IWCS as a highly promising platform to improve the therapies of diabetic patients.

This work proposes and validates a novel idea of using plasmonic nanoparticles (PNP) to improve the solar thermal conversion efficiency. Gold nanoparticle (GNP) is synthesized from an improved citrate-reduction method, and used as an example to illustrate the photothermal conversion characteristics of PNPs under a solar simulator. The experimental results show that GNP has the best photo-thermal conversion capability comparing to other reported materials. At the lowest particle concentration examined (i.e., 0.15 ppm), GNP increases the photo-thermal conversion efficiency of the base fluid by 20% and reaches a specific absorption rate (SAR) of ~10 kW/g. The photo-thermal conversion efficiency increases with increasing particle concentrations, but the SAR shows a reverse trend, which is unexpected as all GNPs should be still in the independent scattering regime.

Patterning and alignment of conductive nanowires are essential for good electrical isolation and high conductivity in various applications. Herein a facile bottom-up, additive technique is developed to pattern and align silver nanowires (AgNWs) by manipulating wetting of dispersions in microchannels. By forming hydrophobic/hydrophilic micropatterns down to 8 μm with fluoropolymer (Cytop) and SiO2, the aqueous AgNW dispersions with the optimized surface tension and viscosity self-assemble into microdroplets and then dry to form anisotropic AgNW networks. The alignment degree characterized by the full width at half-maximum (FWHM) can be well-controlled from 39.8° to 84.1° by changing the width of microchannels. A mechanism is proposed and validated by statistical analysis on AgNW alignment, and a static model is proposed to guide the patterning of general NWs. The alignment reduced well the electrical resistivity of AgNW networks by a factor of 5 because of the formation of efficient percolation path for carrier conduction.

Recently gold nanoparticles (GNPs) have been proposed in non-invasive thermal therapies for cancer treatment coupled with radiofrequency (RF) waves. In this work, the dissipation of RF energy by GNPs is systematically investigated both experimentally and theoretically under an EM frequency of 13.56 MHz. To elucidate the impurity effect, purified GNP dispersions are obtained through an ultrasonic-aided method. The result reveals a small bulk temperature increase, i.e., less than one centigrade for impurified samples, and even smaller for purified samples, which contrasts significantly to some earlier publications. The measured dielectric properties of GNP dispersions show a negligible change in the effective conductivities for purified samples, which indicates that the dielectric loss alone does not predict substantial temperature increase of GNPs. Further discussion shows that none of the established theories supports the idea that GNPs can dissipate RF energy significantly.

A variety of nanomaterial‐based biosensors have been developed to sensitively detect biomolecules in vitro, yet limited success has been achieved in real‐time sensing in vivo. The application of microneedles (MN) may offer a solution for painless and minimally‐invasive transdermal biosensing. However, integration of nanostructural materials on microneedle surface as transdermal electrodes remains challenging in applications. Here, a transdermal H2O2 electrochemical biosensor based on MNs integrated with nanohybrid consisting of reduced graphene oxide and Pt nanoparticles (Pt/rGO) is developed. The Pt/rGO significantly improves the detection sensitivity of the MN electrode, while the MNs are utilized as a painless transdermal tool to access the in vivo environment. The Pt/rGO nanostructures are protected by a water‐soluble polymer layer to avoid mechanical destruction during the MN skin insertion process. The polymer layer can readily be dissolved by the interstitial fluid and exposes the Pt/rGO on MNs for biosensing in vivo. The applications of the Pt/rGO‐integrated MNs for in situ and real‐time sensing of H2O2 in vivo are demonstrated both on pigskin and living mice. This work offers a unique real‐time transdermal biosensing system, which is a promising tool for sensing in vivo with high sensitivity but in a minimally‐invasive manner.

Nanomaterials with low-dimensional morphology have been explored for enhancing the performance of strain sensors, but it remains difficult to achieve high stretchability and sensitivity simultaneously. In this work, a composite structure strain sensor based on nanomaterials and conductive liquid is designed, demonstrated, and engineered. The nanowire-microfluidic hybrid (NMH) strain sensor responds to multiscale strains from 4% to over 400%, with a high sensitivity and durability under small strain. Metal nanowires and carbon nanotubes are used to fabricate the NMH strain sensors, which simultaneously exhibit record-high average gauge factors and stretchability, far better than the conventional nanowire devices. Quantitative modeling of the electrical characteristics reveals that the effective conductivity percolation through the hybrid structures is the key to achieving high gauge factors for multiscale sensing. The sensors can operate at low voltages and are capable of responding to various mechanical deformations. When fixed on human skin, the sensors can monitor large-scale deformations (skeleton motion) and small-scale deformations (facial expressions and pulses). The sensors are also employed in multichannel, interactive electronic system for wireless control of robotics. Such demonstrations indicate the potential of the sensors as wearable detectors for human motion or as bionic ligaments in soft robotics.

Techniques used to understand the dynamic expression of intracellular proteins are critical in both fundamental biological research and biomedical engineering. Various methods for analyzing proteins have been developed, but these methods require the extraction of intracellular proteins from the cells resulting in cell lysis and subsequent protein purifications from the lysate, which limits the potential of repetitive extraction from the same set of viable cells to track dynamic intracellular protein expression. Therefore, it is crucial to develop novel methods that enable nondestructive and repeated extraction of intracellular proteins. This work reports a hollow nanoneedle-electroporation system for the repeated extraction of intracellular proteins from living cells. Hollow nanoneedles with ∼450 nm diameter were fabricated by a material deposition and etching process, followed by integration with a microfluidic device. Long-lasting electrical pulses were coupled with the nanoneedles to permeate the cell membrane, allowing intracellular contents to diffuse into the microfluidic channels located below the cells via hollow nanoneedles. Using lactate dehydrogenase B (LDHB) as the model intracellular protein, the nanoneedle-electroporation system effectively and repeatedly extracted LDHB from the same set of cells at different time points, followed by quantitative analysis of LDHB via standard enzyme-linked immunosorbent assay. Our work demonstrated an efficient method to nondestructively probe intracellular protein levels and monitor the dynamic protein expression, with great potential to help understanding cell behaviors and functions.