We present the first cell-attachable and visible-light-crosslinkable bioinks based on gelatin methacryloyl (GelMA) with eosin Y (EY) photoinitiation for stereolithography three-dimensional (3D) bioprinting. To develop a visible-light-crosslinkable hydrogel, we systematically studied five combinations of GelMA and EY photoinitiator with various concentrations. Their mechanical properties, microstructures, and cell viability and confluency after encapsulation were investigated rigorously to elucidate the effects of the EY and GelMA macromer concentrations on the characteristics of the hydrogel. Experimental results show that the compressive Young's modulus and pore size are positively affected by the concentration of EY, whereas the mass swelling ratio and cell viability are negatively affected. Increasing the concentration of GelMA helps in improving the compressive Young's modulus and cell attachment. We further employed the developed visible-light-based stereolithography bioprinting system to print the patterned cell-laden hydrogels to demonstrate the bioprinting applications of the developed hydrogel. We observed good cell proliferation and the formation of a 3D cellular network inside the printed pattern at day 5, which proves the great feasibility of using EY-GelMA as the bioinks for biofabrication and tissue engineering.

We developed an ultrafast photocrosslinking method using a low-cost blue laser diode. Cell-laden hydrogels can be crosslinked within 10 seconds with over 90% cell viability. A microtube was fabricated using the system for bioprinting applications.

A new composite fading model is introduced. This shadowed Beaulieu-Xie model is developed to characterize wireless communication in an environment with an arbitrary number of line-of-sight and non-line-of-sight signals, in contrast to the existing Rayleigh, Ricean, generalized Ricean (i.e., κ − µ), and Nakagami-m models. The proposed model benefits from four parameters that characterize a wide range of fading conditions, unlike existing composite models such as the shadowed Ricean model, the two-wave with diffuse power model, and the fluctuating two-ray model. The proposed shadowed Beaulieu-Xie model is used here to characterize experimental data obtained from fading measurements in 28 GHz outdoor millimeter-wave channels, and it is found to describe the communication environment accurately. We conclude that the proposed composite fading model is particularly useful for characterizing emerging (millimeter-wave and terahertz) wireless communication systems.

A direct laser bioprinting (DLBP) system is introduced in this work. The DLBP system applies visible-laser-induced photo-crosslinking at a wavelength of 405 nm using the photoinitiator VA-086. It is shown that such a system can fabricate vertical structures with fine features (less than 50 µm) and high cell viability (greater than 95%). Experimental characterizations and theoretical simulations are presented, and good agreement is seen between the experiments and theory. The DLBP system is applied to the fabrication of (1) cell-laden hydrogel microgrids, (2) hydrogel microwells, as well as a test of (3) cell encapsulation, and (4) cell seeding. The DLBP system is found to be a promising tool for bioprinting.

In this work, a detailed investigation is carried out on copper oxide, in the form of cupric oxide (CuO) nanocrystals. Particular attention is paid to the bandstructure and ultrafast charge-carrier dynamics. Transient absorption spectroscopy is carried out with an above-bandgap pump beam and below-bandgap probe beam to glean insight on the relaxation and recombination dynamics of the CuO nanocrystals at various pump fluences. Three time constants are apparent. The first time constant varies with pump fluence from 330 fs to 630 fs, and it is attributed to momentum relaxation via carrier-carrier scattering in the valence band as well as exciton-exciton annihilation. The second time constant is constant at 2 ps, and it is attributed to energy relaxation via carrier-phonon scattering within the valence band. The third time constant is constant at 50 ps, and it is attributed to trapping and recombination, due to the high density of trap states within the CuO nanocrystals. Such findings lay the foundation for future studies and applications of the emerging CuO material system.