Polyacrylamide Hydrogel Composite E-skin Fully Mimicking Human Skin.

Transparent e-skin that can fully mimic human skin with J-shaped mechanical-behavior and tactile sensing attributes have not yet been reported. In this work, the skin-like hydrogel composite with J-shaped mechanical behavior and highly transparent, tactile, soft but strong, flexible, and stretchable attributes is developed as structural strain sensing element for e-skin. Piezo-resistive polyacrylamide (PAAm) hydrogel is used as supporting matrix to endow high transparency, softness, flexibility, stretch-ability and strain sensing capability desired for e-skin. Ultrahigh molecular weight polyethylene (UHMWPE) fiber with a wavy configuration is designed as reinforcement filler to provide the tunable strain-limiting effect. As a result, the as-prepared UHMWPE fiber/PAAm composite e-skin presents unique "J-shape" stress-strain behavior akin to human skin. And the PAAm composite can switch from supersoft to highly stiff in the designed strain range up to 100% with a prominent tensile strength of 48.3 MPa, which enables it to have the high stretch-ability and excellent load-bearing ability, simultaneously. Moreover, finite element model is developed to clarify the stress distribution and damage evolution for the UHMWPE fiber/PAAm composite during the tensile process. The PAAm composite exhibits not only an excellent strain sensing performance with a long-term reliability up to 5000 loading-unloading cycles but also an extraordinary softness and mechanical strength with a low initial modulus of 6.7 kPa, which is matchable with soft human epidermis. Finally, the e-skin is used for demonstrations in monitoring various human activities and protecting structural integrity in designed strain ranges. The strategy for reinforcing piezo-resistive hydrogel with wavy-shaped UHMWPE fibers proposed here is promising for the development of transparent, flexible, soft but strong e-skin with a tunable strain-limiting effect akin to human skin.

Bioinspired Color-Changeable Organogel Tactile Sensor with Excellent Overall Performance.

Inspired by chameleons' structural color regulation capability, a simple, but effective, swelling method is proposed for the first time to prepare an ionic polyacrylamide (PAAm) organogel for simultaneous tactile sensing and interactive color changing. The PAAm organogel obtained by swelling the PAAm scaffold in the dimethyl sulfoxide solution of organic electrochromic material (OECM) shows an extremely large stretchability with an elongation of 1600%, a supersoftness with a compressive modulus of 7.2 kPa, an excellent transmittance up to 90%, and a very fast response time of 0.5 s combined with the characteristic of interactive color changing. The PAAm organogel also suggests a universal design ability to tailor coloration spectra for tactile sensors via simply changing the type and content of OECM. The tactile sensor based on a PAAm organogel is capable of serving as a wearable device for precisely tracing human body motion performance and directly visualizing the stress distribution via interactive color changing capability. It is demonstrated that the swelling method proposed here is a simple and practical strategy to prepare ionic organogels with both piezo-resistive and electrochromic effects.

Hepatocellular adenoma: comparison between real-time contrast-enhanced ultrasound and dynamic computed tomography.

PURPOSE: To investigate and compare the contrast-enhanced ultrasound (CEUS) features of histologically proven HCA with those of contrast-enhanced computed tomography (CECT). METHODS: Eighteen patients with proven hepatic adenoma by pathology were retrospectively selected from the CEUS database. Fourteen of them had undergone liver CECT exams. The basic features on unenhanced imaging and the enhancement level and specific features on contrast-enhanced imaging were retrospectively analyzed, and the differences between CEUS and CECT were compared. RESULTS: All the HCAs showed hyper-enhancement in the arterial phase. During the portal and late phases, 12 HCAs (12/18, 66.7 %) on CEUS and 11 (11/14, 78.6 %) on CT showed washout. On CEUS, 10 (10/18, 55.5 %) showed centripetal filling in the arterial phase and persistent peripheral rim enhancement. Five of them (61.1 %, 11/18) showed delayed central washout in the portal or late phase. However, on CECT, 2 (14.3 %, 2/14) and 4 (28.6 %, 4/14) HCAs showed persistent enhancement of the peripheral rim and central non-enhancing hemorrhage areas, respectively. CONCLUSIONS: Compared with dynamic CT, CEUS was superior at characterizing specific dynamic features. Considering that it is radiation-free, readily availability and easy to use, CEUS is suggested as the first line imaging tool to diagnose HCA.