This study aimed to improve the dissolution rate and oral bioavailability of valsartan (VAL), a poorly soluble drug using solid dispersions (SDs). The SDs were prepared by a freeze-drying technique with polyethylene glycol 6000 (PEG6000) and hydroxypropylmethylcellulose (HPMC 100KV) as hydrophilic polymers, sodium hydroxide (NaOH) as an alkalizer, and poloxamer 188 as a surfactant without using any organic solvents. In vitro dissolution rate and physicochemical properties of the SDs were characterized using the USP paddle method, differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and Fourier transform-infrared (FT-IR) spectroscopy, respectively. In addition, the oral bioavailability of SDs in rats was evaluated by using VAL (pure drug) as a reference. The dissolution rates of the SDs were significantly improved at pH 1.2 and pH 6.8 compared to those of the pure drug. The results from DSC, XRD showed that VAL was molecularly dispersed in the SDs as an amorphous form. The FT-IR results suggested that intermolecular hydrogen bonding had formed between VAL and its carriers. The SDs exhibited significantly higher values of AUC 0-24 h and C max in comparison with the pure drug. In conclusion, hydrophilic polymer-based SDs prepared by a freeze-drying technique can be a promising method to enhance dissolution rate and oral bioavailability of VAL.

Here, we numerically prove that the severe polarization-induced electric field in the active region for [0001]-oriented InGaN-based green light-emitting diodes (LEDs) is reduced when heavily Si-doped GaN quantum barriers are adopted. However, the electron injection is accordingly sacrificed for the insufficient confinement capability of the p-type electron blocking layer (p-EBL). Hence, p-EBL structures with/without gradient AlN alloys are discussed to reduce the electron leakage, and the importance of the positive sheet polarization charges at the interface between the last quantum barrier (LQB) and the p-EBL on affecting the blocking barrier height for electrons is especially highlighted. Moreover, we also suggest utilizing specially designed p-AlGaN/p-GaN structure instead of p-GaN structure to serve as the p-type hole supplier, which is able to increase the kinetic energy of holes, thus assisting holes to overcome the energy band barrier height in p-EBL and increasing the hole concentration within the quantum wells.