Background: During periodontitis and orthodontic tooth movement, periodontal vasculature is severely impaired, leading to a hypoxic microenvironment of periodontal cells. However, the impact of hypoxia on periodontal cells is poorly defined. The present study investigates responses of cocultured endothelial cells (ECs) and periodontal ligament stem cells (PDLSCs) to hypoxia.Methods: Osteogenic differentiation, molecular characterization, and various behaviors of PDLSCs and human umbilical venous ECs under hypoxia were assessed by quantitative real‐time reverse‐transcription polymerase chain reaction, Western blot, and enzyme‐linked immunosorbent assay. Moreover, the effect of ECs on PDLSC osteogenic differentiation was tested using NS398 (cyclooxygenase 2 blocker), SU5416 (vascular endothelial growth factor [VEGF] receptor inhibitor), AH6809, L‐798106, and L‐161982 (EP1/2/3/4 antagonists).Results: First, hypoxia promoted osteogenic differentiation in PDLSCs and enhanced EC migration, whereas PD98059 (extracellular signal‐regulated protein kinase [ERK] inhibitor) blocked, and cocultured ECs further enhanced, hypoxia‐induced osteogenic differentiation. Second, NS398 impaired EC migration and prostaglandin E₂ (PGE₂)/VEGF release, whereas cocultured PDLSCs and exogenous PGE₂ partially reversed it. Third, NS398 (pretreated ECs) decreased PGE₂/VEGF concentrations. NS398‐treated ECs and AH6809/SU5416‐treated PDLSCs impaired cocultured EC–induced enhancement of PDLSC osteogenic differentiation.Conclusions: Hypoxia enhances ERK‐mediated osteogenic differentiation in PDLSCs. Coculture with EC further augments PDLSC osteogenic differentiation via cyclooxygenase‐2/PGE₂/VEGF signaling.

In this study, the photonic crystal structure is employed to increase both the light extraction efficiency and the modulation bandwidth of flip-chip GaN-based light-emitting diodes (LEDs). The finite difference time domain method is utilized to investigate the influence of structure of photonic crystals on the Purcell factor and light extraction efficiency of flip-chip GaN-based LEDs. Simulation results show that the modulation bandwidth is estimated to be 202 MHz at current densities of 1000 A/cm². The experimental result of modulation bandwidth is in accord with the simulation. The optical f-3dB of the device achieves 212 MHz at current densities of 1000 A/cm² and up to 285 MHz at current densities of 2000 A/cm². This design of photonic crystal flip-chip LED has the potential for applications in high-frequency visible light communication.

We systemically investigated the effect of chip structures on the optical characteristics of micro-size LEDs. The total internal reflection (TIR) can be improved by selecting a suitable chip structure, thereby increasing the light efficiency. The saturation light output power (LOP) of the micro-size LED using pentagon-type structure is 44.78 mW, an increase of 6.08% compared with that of micro-size LED using circular-type structure. Simulation and experimental results indicate that chip structure of pentagon-type can effectively enhance the light extraction from the top or side of the micro-size LED.

We proposed and fabricated an indium tin oxide (ITO)/Ag/Ga ₂ O ₃ multilayer as transparent conductive electrode (TCE) for AlGaN-based ultraviolet light-emitting diode (UV LED). The effects of thickness dependence of Ga ₂ O ₃ layer on the optical and electrical properties of the ITO/Ag/Ga ₂ O ₃ multilayer are investigated. The ITO/Ag/Ga ₂ O ₃ (12nm/17.5nm/37.5nm) multilayer exhibits a small sheet resistance of 2.82 Q/sq and a good ohmic contact characteristic with a specific contact resistance of 2.61 × 10 ^-3 Ω·cm ² . The multilayer film has a good transmittance of 86.7% at 365 nm. Compared to reference UV LED with traditional ITO as TCE, the UV LED with ITO/Ag/Ga ₂ O ₃ multilayer as TCE shows an increase of 19.8% in light output power and a 0.34 V reduction in forward voltage at 120 mA.

We demonstrate that the concave-convex circular composite structure sidewall prepared by inductively coupled plasma (ICP) etching is an effective approach to increase the light efficiency without deteriorating the electrical characteristics for micro light-emitting diodes (LEDs). The saturated light output power of the device using the concave-convex circular composite structure sidewalls with a radius of 2 μm is 39.75 mW, an improvement of 7.2% compared with that of the device using flat sidewalls. The enhanced light output characteristics are primarily attributed to the increased photon emitting due by decreasing the total internal reflection without losing the active region area.