Effects of thermal annealing in oxygen plasma for buffer layers on properties of ZnO thin films

ZnO thin films with ZnO buffer layers were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on p-type Si(100) substrates. Before the growth of the ZnO thin films, the ZnO buffer layers were deposited on the Si substrates for 20 minutes and then annealed at the different substrate temperature ranging from 600 to 800 degrees C in oxygen plasma. The structural and optical properties of the ZnO thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and room-temperature (RT) photoluminescence (PL). A narrower full width at half maximum (FWHM) of the XRD spectra for ZnO(002) and a larger grain are observed in the samples with the thermal annealed buffer layers in oxygen plasma, compared to those of the as-grown sample. The surface morphology of the samples is changed from rugged to flat surface. In the PL spectra, near-band edge emission (NBEE) at 3.2 eV (380 nm) and deep-level emission (DLE) around 1.77 to 2.75 eV (700 to 450 nm) are observed. By increasing the annealing temperatures up to 800 degrees C, the PL intensity of the NBEE peak is higher than that of the as-grown sample. These results imply that the structural and optical properties of ZnO thin films are improved by the annealing process.     

Nitric Oxide Generation and Endothelial Progenitor Cells Recruitment for Improving Hemocompatibility and Accelerating Endothelialization of Tissue Engineering Heart Valve

Tissue engineering heart valve (TEHV) offers great potential to overcome the limitations of commercial artificial valves used in clinical practice as a permanent prosthetic valve. Currently, decellularized heart valve (DHV) is the most widely used scaffold for TEHV, but showed suboptimal performance due to difficulty of endothelialization. Facilitating endothelialization of DHV is indispensable for better valve performance, and excellent hemocompatibility guarantees enough time windows for endothelialization process. Herein, a dual-functional TEHV scaffold with improving hemocompatibility and accelerating endothelialization is constructed by modifying DHV with copper ions (Cu) and growth differentiation factor 11 (GDF11). Results show the newly-constructed scaffold successfully generates endogenous nitric oxide (NO) through catalysis of Cu, and possesses improved hemocompatibility by down-regulating platelets activation and adhesion. Furthermore, GDF11 immobilization significantly accelerates scaffold endothelialization through facilitating recruitment, supporting growth, and alleviating apoptosis of endothelial progenitor cells . This TEHV scaffold shows favorable performance under in vivo hemodynamic environment with intact endothelial coverage and adaptive ECM remodeling, and without thrombus or calcification formation. This newly-constructed TEHV scaffold is expected to make up for the shortcomings of currently available prosthetic valves in clinical practice and has the potential possibility of rapid translation to the clinic as a better prosthetic valve.     

Effects of interlaminar stresses on damping of 0-degree unidirectional laminated composites

The principal aim of this paper is to formulate a general model for predicting damping in composites on the basis of the concept of strain energy-weighted dissipation. In this model, the effects of interlaminar stresses on damping have been included in addition to the effects of in-plane extension/compression and in-plane shear. Validation of the model was confirmed by performing damping measurements on 0° unidirectional composite beams with varying length and thickness. The results of theoretical predictions of damping in laminated composites were found to compare favorably with experimental data. The transverse shear (σ_xz) reveals to have a considerable effect on the damping mechanisms in 0° unidirectional polymer composites. However, the other interlaminar stresses (σ_yz, σ_z) were shown to have little influence on damping in composite beam.     

An analytical method for prediction of the damping in symmetric balanced laminated composites

To obtain the effective damping of a laminated composite beam, two different analytical methods were compared. Also, we modified the basic loss factors on the basis of experimental data. In the first method, Ni and Adams's theory was used. In the second method, new energy approach was developed to determine the damping of laminated composite beams. Five typical laminated composites with [±Θ]s, [0/±Θ]s, [0/Θ]s, [0/±Θ/90]s and [90/±Θ/0]s stacking sequences were employed for this study. The present method was favorably compared with Ni and Adams's method. In this study, we found that damping was highly influenced by fiber volume fraction, fiber orientation and stacking sequence.