A maximum excess volume ΔV/V ≈ 1.9 × 10−3 in ultrafine-grained Fe prepared by high-pressure torsion is determined by measurements of the irreversible length change upon annealing employing a high-resolution differential dilatometer. Since dislocations and equilibrium-type grain boundaries cannot fully account for the observed released excess volume, the present study yields evidence for a high concentration of free volume-type defects inherent to nanophase materials, which is considered to be the main source of their particular properties, such as strongly enhanced diffusivities.

Optical microcavities and microlasers were recently introduced as probes inside living cells and tissues. Their main advantages are spectrally narrow emission lines and high sensitivity to the environment. Despite numerous novel methods for optical imaging in strongly scattering biological tissues, imaging at single-cell resolution beyond the ballistic light transport regime remains very challenging. Here, we show that optical microcavity probes embedded inside cells enable three-dimensional localization and tracking of individual cells over extended time periods, as well as sensing of their environment, at depths well beyond the light transport length. This is achieved by utilizing unique spectral features of the whispering-gallery modes, which are unaffected by tissue scattering, absorption, and autofluorescence. In addition, microcavities can be functionalized for simultaneous sensing of various parameters, such as temperature or pH value, which extends their versatility beyond the capabilities of standard fluorescent labels.

In the expanding field of physiological pH skin sensors, thin temporary tattoo‐based devices have gained attention because of ultra‐conformal adhesion while providing excellent water vapor transmission. Here, a pH sensor tattoo made of temporary tattoo paper, screen‐printed poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate electrodes, and pH‐responsive hydrogel deposited via initiated chemical vapor deposition, is proposed. The tattoo sensor is easily transferred on skin, maintaining full functionality, and shows excellent conformability to topographical features of epidermis. The investigation of the morphology of all layers within the sensor verifies full control of the desired width of electrodes, thickness of hydrogel, and deposition shielded areas. The hydrogel layer exhibits a reversible pH‐responsive swelling of 24.7 ± 0.3% to 38 ± 1%, with respect to the dry state, at pH 4 to pH 6, respectively. Impedance spectroscopy identifies the phase shift at 10 and 1000 Hz as an excellent pH‐related property of the sensor, which can be only ascribed to the presence of the hydrogel. The sensors ability to be operated with non‐sophisticated read‐out hardware and software is also demonstrated.

Glucose-responsive materials are of great importance in the field of monitoring the physiological glucose level or smart insulin management. This study presents the first vacuum-based deposition of a glucose-responsive hydrogel thin film. The successful vacuum-based synthesis of a glucose-responsive hydrogel may open the door to a vast variety of new applications, where, for example, the hydrogel thin film is applied on new possible substrates. In addition, vacuum-deposited films are free of leachables (e.g., plasticizers and residual solvents). Therefore, they are, in principle, safe for in-body applications. A hydrogel made of but-3-enylboronic acid units, a boronic acid compound, was synthesized via initiated chemical vapor deposition. The thin film was characterized in terms of chemical composition, surface morphology, and swelling response toward pH and sucrose, a glucose-fructose compound. The film was stable in aqueous solutions, consisting of polymerized boronic acid and the initiator unit, and had an undulating texture appearance (rms 2.1 nm). The hydrogel was in its shrunken state at pH 4-7 and swelled by increasing the pH to 9. The pK_a was 8.2 ± 0.2. The response to glucose was observed at pH 10 and resulted in thickness shrinking.