BackgroundCellulose and its derivatives such as carboxymethyl cellulose (CMC) have been employed as a biomaterial for their diverse applications such as tissue engineering, drug delivery and other medical materials. Porosity of the scaffolds has advantages in their applications to tissue engineering such as more cell adhesion and migration leading to better tissue regeneration. After synthesis of CMC-poly(ethylene oxide) (PEO) hydrogel by mixing the solutions of both CMC-acrylate and PEO-hexa-thiols, fabrication and evaluation of a CMC-PEO gel and its film in porous form have been made for its possible applications to tissue regeneration. Physicochemical and biological properties of both CMC-PEO hydrogel and porous films have been evaluated by using physicochemical assays by SEM, FTIR and swelling behaviors as well as in vitro assays of MTT, Neutral red, BrdU, gel covering and tissue ingrowth into the pores of the CMC-PEO gel films. Degradation of CMC-PEO hydrogel was also evaluated by treating with esterase over time.ResultsChemical grafting of acrylate to CMC was verified by analyses of both FTIR and NMR. CMC-PEO hydrogel was obtained by mixing two precursor polymer solutions of CMC-acrylate and PEO-hexa-thiols and by transforming into a porous CMC-PEO gel film by gas forming of ammonium bicarbonate particles. The fabricated hydrogel has swollen in buffer to more than 6 times and degraded by esterase. The results of in vitro assays of live and dead, MTT, BrdU, Neutral red and gel covering on the cells showed excellent cell compatibility of CMC-PEO hydrogel and porous gel films. Furthermore the porous films showed excellent in vitro adhesion and migration of cells into their pore channels as observed by H&E and MT stains.ConclusionsBoth CMC-PEO hydrogel and porous gel films showed excellent biocompatibility and were expected to be a good candidate scaffold for tissue engineering.
A facile and novel technique for the fabrication of pressure sensors is reported based on the hybridization of one-dimensional nanomaterials and two-dimensional graphene film. In particular, piezoelectric pressure sensors are fabricated by using vertically aligned and position- and dimension-controlled ZnO nanotube arrays grown on graphene layers. Graphene layers act not only as substrates for catalyst-free growth of high-quality ZnO nanotubes but also as flexible conduction channels connecting ZnO nanotubes and metal electrodes. Freestanding and flexible sensors have been efficiently obtained via mechanical lift-off of hybrid ZnO nanotube/graphene film structures and by exploiting the weak van der Waals forces existing between the graphene film and the original substrates. A prototype of such devices shows a high pressure sensitivity (−4.4 kPa−1), which would enable the detection of weak flows of inert gas. The relatively low wall thickness and large length of the ZnO nanotubes suggest a relatively high sensitivity to external pressures. The obtained nanotube sensors are attached to the philtrum and wrist of a volunteer and used to monitor his breath and heart rate. Overall, the prototype hybrid sensing device has great potential as wearable technology, especially in the sector of advanced healthcare devices.
We report the fabrication of individually addressable, high-density, vertical zinc oxide (ZnO) nanotube pressure sensor arrays. High-sensitivity and flexible piezoelectric sensors were fabricated using dimension- and position-controlled, vertical, and free-standing ZnO nanotubes on a graphene substrate. Significant pressure/force responses were achieved from small devices composed of only single, 3 × 3, 5 × 5, and 250 × 250 ZnO nanotube arrays on graphene. An individually addressable pixel matrix was fabricated by arranging the top and bottom electrodes of the sensors in a crossbar configuration. We investigated the uniformity and robustness of pressure/force spatial mapping by considering the pixel size, the number of ZnO nanotubes in each pixel, and the lateral dimensions of individual ZnO nanotubes. A spatial resolution as high as 1058 dpi was achieved for a Schottky diode-based force/pressure sensor composed of ZnO nanotubes on a flexible substrate. Additionally, we confirmed the excellent flexibility and electrical robustness of the free-standing sensor arrays for high-resolution tactile imaging. We believe that this work opens important opportunities for 1D piezoelectric pressure/force sensor arrays with enormous applications in human-electronics interfaces, smart skin, and micro- and nanoelectromechanical systems.
Thermal oxidation resistance is an important property in printed electronics for sustaining electrical conductivity for long time and/or under harsh environments such as high temperature. This study reports the fabrication of copper nanoparticles (CuNPs)-based conductive tracks using large pulsed electron beam (LPEB) by irradiation on CuNPs to be sintered. With an acceleration voltage of 11 kV, the LPEB irradiation induced deep-sintering of CuNPs so that the sintered CuNPs exhibited bulk-like electrical conductivity. Consequently, the sintered Cu tracks maintained high electrical conductivity at 220 °C without using any thermal oxidation protection additive, such as silver, carbon nanotube, and graphene. In contrast, the films irradiated with an acceleration voltage of 8 kV and irradiated by intense pulsed light (IPL) showed fast oxidation characteristics and a corresponding reduction of electrical conductivities under high temperatures owing to a thin sintered layer. The performance of highly thermal oxidation-resistant Cu films sintered by LPEB irradiations was demonstrated through the device performance of a Joule heater.
The biological properties of self cross-linked chondroitin sulfate (CS)-poly(ethylene oxide) (PEO) hydrogel including degradation, in vitro bone cell behaviors, and cellular compatibility were evaluated after the induction of its gel formation through use of different experimental conditions such as precursor composition, reaction temperatures, and precursor solution concentrations. The compositions of the CS-acrylate and PEO-thiol precursors had ratios of 25:75, 50:50, and 75:25. Hydrogel formations were induced with a mechanism of self cross-linking at the solution temperatures of 7, 23, 37, and 50 o C through use of different precursor solutions (2%, 3%, 5%, and 10%). Higher reaction temperatures and precursor concentrations induced quicker formation of the CS-PEO gel. While the 10% precursor solution became a hydrogel within 2 min at 50 o C, the 2% solution took approximately 462 min at 7 o C. While the CS-PEO gel with higher PEO content (25:75) swelled to 330%, the hydrogel with lower PEO content (75:25) swelled to 147% at 23 o C, indicating that higher PEO content induced higher gel swelling. The CS-PEO hydrogel (50:50) gradually degraded in vitro through addition of 0.5 unit of chondroitinase ABC every 2 days, which led to approximately 7% degradation over 24 days. A CCK-8 assay performed on the hydrogel surface showed initially higher cell adhesion on the higher concentration CS gel (75:25), even though the adhered cells seemed to detach from their surfaces over time. Live and dead assays demonstrated that both cells on the surface of and inside the hydrogel were viable for 7 days. The results of in vitro bromodeoxyuridine, 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide, and neutral red assays and evaluation of the gel covering on the cells cultured on the culture flask demonstrated excellent hydrogel cell compatibility (25:75, 50:50, and 75:25) compared to that of latex, the negative control.
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