Aspartic Acid-Assisted Synthesis of Multifunctional Strontium-Substituted Hydroxyapatite Microspheres

Strontium-substituted hydroxyapatite (SrHAP) microspheres with three-dimensional (3D) structures were successfully prepared via hydrothermal method using self-assembled poly­(aspartic acid) (PASP) as a template. By controlling various parameters, including hydrothermal reaction time, amount of l-aspartic acid (l-Asp), and ratio of Sr ions, we were able to investigate the influences of the additive l-Asp on morphology and properties of final products as well as the role of self-assembled PASP template on the formation of HAP microspheres. The change in the amount of Sr substitution significantly affected the particle size, morphology, and concurrent surface area. This difference caused variation in the drug-release properties. In addition, substitution of Sr ions into Ca ion sites affected luminescence of HAP powders. Particularly, multifunctional SrHAP with molar ratios (Sr/[Ca+Sr]) of 0.25 possessed the strongest luminescence as well as superior drug-loading and sustained-releasing properties. These properties were associated with large surface area and large pore size of the SrHAP. This study suggests that the optical and structural properties of the HAP particles can be carefully tuned by controlling the amount of Sr ions doped into HAP particles during synthesis. This work provides new opportunities to synthesize HAP particles suitable for diverse applications including bone regeneration and drug delivery

Improvement in Electrical Characteristics of Eco-friendly Indium Zinc Oxide Thin-Film Transistors by Photocatalytic Reaction

Eco-friendly solution-processed oxide thin-film transistors (TFTs) were fabricated through photocatalytic reaction of titanium dioxide (PRT). The titanium dioxide (TiO₂) surface reacts with H₂O under ultraviolet (UV) light irradiation and generates hydroxyl radicals (OH•). These hydroxyl radicals accelerate the decomposition of large organic compounds such as 2-methoxyethanol (2ME; one of the representative solvents for solution-processed metal oxides), creating smaller organic molecular structures compared with 2ME. The decomposed small organic materials have low molar masses and low boiling points, which help improving electrical properties via diminishing defect sites in oxide channel layers and fabricating low-temperature solution-processed oxide TFTs. As a result, the field-effect mobility improved from 4.29 to 10.24 cm²/V·s for IGZO TFTs and from 2.78 to 7.82 cm²/V·s for IZO TFTs, and the <i>V</i>_th shift caused by positive bias stress and negative bias illumination stress over 1000 s under 5700 lux decreased from 6.2 to 2.9 V and from 15.3 to 2.8 V, respectively. In theory, TiO₂ has a permanent photocatalytic reaction; as such, hydroxyl radicals are generated continuously under UV irradiation, improving the electrical characteristics of solution-processed IZO TFTs even after four iterations of TiO₂ recycling in this study. Thus, the PRT method provides an eco-friendly approach for high-performance solution-processed oxide TFTs