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Many diverse applications utilizehydrogels as carriers, sensors,and actuators, and these applications rely on the refined controlof physical properties of the hydrogel, such as elastic modulus anddegree of swelling. Often, hydrogel properties are interdependent;for example, when elastic modulus is increased, degree of swellingis decreased. Controlling these inverse dependencies remains a majorbarrier for broader hydrogel applications. We hypothesized that polymercross-linkers with varied chain flexibility would allow us to tunethe inverse dependency between the elastic modulus and the degreeof swelling of the hydrogels. We examined this hypothesis by usingalginate and poly(acrylic acid) (PAA) modified with a controlled numberof methacrylic groups as model inflexible and flexible cross-linkers,respectively. Interestingly, the polyacrylamide hydrogel cross-linkedby the inflexible alginate methacrylates exhibited less dependencybetween the degree of swelling and the elastic modulus than the hydrogelcross-linked by flexible PAA methacrylates. This critical role ofthe cross-linker’s inflexibility was related to the differenceof the degree of hydrophobic association between polymer cross-linkers,as confirmed with pyrene probes added in pregel solutions. Furthermore,hydrogels cross-linked with alginate methacrylates could tune theprojection area of adhered cells by solely altering elastic moduli.In contrast, gels cross-linked with PAA methacrylates failed to modulatethe cellular adhesion morphology due to a lower, and smaller, elasticmodulus range to be controlled. Overall, the results of this studywill significantly advance the controllability of hydrogel propertiesand greatly enhance the performance of hydrogels in various biologicalapplications. [ABSTRACT FROM AUTHOR]

The stereolithography apparatus (SLA) is a computer-assisted, three-dimensional (3D) printing system that is gaining attention in the medical field for the fabrication of patient-specific prosthetics and implants. An attractive class of implantable biomaterials for the SLA is photopolymerisable hydrogels because of their resemblance to soft tissues and intrinsic support of living cells. However, most laser-based SLA machines lack the minimum feature size required to imitate cell growth and alignment patterns in complex tissue architecture. In this study, we demonstrate a simple method for aligning cells on 3D hydrogels by combining the micro-contact printing (µCP) technique with the stereolithographic process. Fibronectin modified with acrylate groups was printed on glass coverslips with unpatterned, 10, 50, and 100 µm wide line patterns, which were then transferred to hydrogels through chemical linkages during photopolymerisation. Fibroblasts cultured on protein-printed 3D hydrogels aligned in the direction of the patterns, as confirmed by fast Fourier transform and cell morphometrics. [ABSTRACT FROM AUTHOR]

A high-performance normally off GaN-based MOSFET was fabricated. The buffer layer of the MOSFET was grown by varying the growth temperature to control the size of nucleation sites which results in an extremely high buffer resistance (> \10^12\ \Omega/\sq). The fabricated small-area MOSFET exhibited excellent normally off device characteristics, such as a threshold voltage of 2 V, maximum drain current of 253 mA/mm, on–off current ratio of \5.5 \times \10^7, destructive breakdown voltage of 830 V, and leakage current of 0.7 \mu\A/mm at a VDS of 600 V. The corresponding values of the large-area MOSFET with a multifinger pattern were 0.6 V, 6 A, \1.3 \times \10^7, 670 V, and 50 \mu\A (0.28 \mu \A/mm). [ABSTRACT FROM AUTHOR]

AlGaN/GaN Schottky barrier diodes (SBDs) with and without the in situ silicon carbon nitride (SiCN) cap layer were investigated. The fabricated SBD with the SiCN cap layer exhibited improved electrical characteristics, such as the forward turn-on voltage of about 0.7 V, the forward current of 4.1 A at 1.5 V, and the reverse breakdown voltage of 630 V, as compared with the corresponding values of 0.8 V, 3.8 A, and 580 V for the reference SBD without the SiCN cap layer. This improvement in the device performance of the SiCN-SBD is because the in situ SiCN cap layer not only lowers the barrier height but also effectively passivates the surface of the device with better surface morphology. [ABSTRACT FROM AUTHOR]

Ni-AlGaN/GaN Schottky barrier diodes (SBDs) with lateral geometry were fabricated on sapphire substrates. At 300 K, devices with 500-μm-diameter Schottky contacts exhibited breakdown voltage (VB) of 765 V, forward current (IF) of 0.065 A at 1.5 V, and specific on-resistance (Ron) of 81.3 mΩ cm2, producing a figure-of-merit (VB2/Ron) of ∼7.2 MW cm-2. Measured in multifinger patterns, the same parameters were 420 V, 3.2 A, 4.6 mΩ cm2, and 38.4 MW cm-2, respectively, at 300 K. With the increase in measurement temperature from 300 to 450 K, SBDs with dimensions of 3000×3000 μm2 showed larger effective barrier heights (0.8 eV at 300 K and 1.27 eV at 475 K) and a slightly negative temperature coefficient (-0.48 V K-1) for reverse breakdown voltage, while there was a little change in reverse leakage current. These results show the strong influence of barrier height inhomogeneity on the temperature dependence of apparent barrier heights obtained through current-voltage measurements. [ABSTRACT FROM AUTHOR]