Techniques to improve solder joint reliability have been the recent research focus in the electronic packaging industry. In this study, Cu/SAC305/Cu solder joints were fabricated using a low-power high-frequency ultrasonic-assisted reflow soldering approach where non-ultrasonic-treated samples were served as control sample. The effect of ultrasonic vibration (USV) time (within 6s) on the solder joint properties was characterized systematically. Results showed that the solder matrix microstructure was refined at 1.5s of USV, but coarsen when the USV time reached 3s and above. The solder matrix hardness increased when the solder matrix was refined, but decreased when the solder matrix coarsened. The interfacial intermetallic compound (IMC) layer thickness was found to decrease with increasing USV time, except for the USV-treated sample with 1.5s. This is attributed to the insufficient USV time during the reflow stage and consequently accelerated the Cu dissolution at the joint interface during the post-ultrasonic reflow stage. All the USV-treated samples possessed higher shear strength than the control sample due to the USV-induced-degassing effect. The shear strength of the USV-treated sample with 6s was the lowest among the USV-treated samples due to the formation of plate-like Ag3Sn that may act as the crack initiation site.
Post-operative hypocalcemia (POH) may complicate parathyroidectomy for primary hyperparathyroidism. This study investigates the relationship between POH and pre-operative risk factors to identify a simple method to predict POH risk.
Two important criteria of an ideal biomaterial in the field of stem cells research are to regulate the cell proliferation without the loss of its pluripotency and to direct the differentiation into a specific cell lineage when desired. The present study describes the influence of TiO2 nanofibrous surface structures on the regulation of proliferation and stemness preservation of adipose-derived stem cells (ADSCs). TiO2 nanofiber arrays were produced in situ onto Ti-6Al-4V substrate via a thermal oxidation process and the successful fabrication of these nanostructures was confirmed by field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and contact angle measurement. ADSCs were seeded on two types of Ti-6Al-4V surfaces (TiO2 nanofibers and flat control), and their morphology, proliferation, and stemness expression were analyzed using FESEM, AlamarBlue assay, flow cytometry, and quantitative real-time polymerase chain reaction (qRT-PCR) after 2 weeks of incubation, respectively. The results show that ADSCs exhibit better adhesion and significantly enhanced proliferation on the TiO2 nanofibrous surfaces compared to the flat control surfaces. The greater proliferation ability of TiO2 nanofibrous surfaces was further confirmed by the results of cell cycle assay. More importantly, TiO2 nanofibrous surfaces significantly upregulate the expressions of stemness markers Sox-2, Nanog3, Rex-1, and Nestin. These results demonstrate that TiO2 nanofibrous surfaces can be used to enhance cell adhesion and proliferation while simultaneously maintaining the stemness of ADSCs, thereby representing a promising approach for their potential application in the field of bone tissue engineering as well as regenerative therapies.
A one year study was conducted to evaluate the impact of spray application of Bacillus thuringiensis israelensis (Bti), strain AM65-52 on vector populations and dengue transmission in a dengue endemic state in Malaysia. Residential sites with similar populations of Aedes aegypti (L.) and Aedes albopictus Skuse were studied. One site was treated with spray application of Bti into all outdoor target vector habitats, which consisted of natural and artificial containers. The other site was not treated. The impact of spray application was measured with an indoor and outdoor ovitrap index (OI) and epidemiologic data. Significant reductions in both Ae. aegypti and Ae. albopictus, OI were observed both indoors and outdoors, in treated sites compared to untreated sites (p < 0.05). OI reduction was achieved over time in the treated area. The OI was suppressed to below 10%. This was maintained for 4 weeks into the post-treatment phase. The outdoor OI at the untreated site remained at more than 40% for 38 weeks during the evaluation period. One dengue case occurred at the Bti treatment site at the beginning of the treatment phase, but no further cases were detected during the remainder of the treatment phase. However, there was an ongoing dengue outbreak in the untreated area with 15 serologically confirmed cases during weeks 37-54. Intensive fogging operations with pyrethroids at the untreated (Bti) site had a positive impact on Ae. albopictus, but not on Ae. aegypti.
In recent years, closed-cell porous Aluminum (Al) has drawn increasing attention, particularly in the applications requiring reduced weight and energy absorption capability such as in the automotive and aerospace industries. In the present work, porous Al with closed-cell structure was successfully fabricated by powder metallurgy technique using PMMA as a space holder. The effects of the amount of PMMA powder on the porosity, density, microstructure and compressive behaviors of the porous specimens were systematically evaluated. The results showed that closed-cell porous Al having different porosities (12%-32%) and densities (1.6478 g/cm³, 1.5125 g/cm³ and 1.305 g/cm³) could be produced by varying the amount of PMMA (20-30 wt %). Meanwhile, the compressive behavior results demonstrated that the plateau stress decreased and the energy absorption capacity increased with increasing amount of PMMA. However, the maximum energy absorption capacity was achieved in the closed-cell porous Al with the addition of 25 wt % PMMA. Therefore, fabrication of closed-cell porous Al using 25 wt % PMMA is considered as the optimal condition in the present study since the resultant closed-cell porous Al possessed good combinations of porosity, density and plateau stress, as well as energy absorption capacity.
One of the major challenges in bone grafting is the lack of sufficient bone vascularization. A rapid and stable bone vascularization at an early stage of implantation is essential for optimal functioning of the bone graft. To address this, the ability of in situ TiO2 nanofibrous surfaces fabricated via thermal oxidation method to enhance the angiogenic potential of human umbilical vein endothelial cells (HUVECs) was investigated. The cellular responses of HUVECs on TiO2 nanofibrous surfaces were studied through cell adhesion, cell proliferation, capillary-like tube formation, growth factors secretion (VEGF and BFGF), and angiogenic-endogenic-associated gene (VEGF, VEGFR2, BFGF, PGF, HGF, Ang-1, VWF, PECAM-1 and ENOS) expression analysis after 2 weeks of cell seeding. Our results show that TiO2 nanofibrous surfaces significantly enhanced adhesion, proliferation, formation of capillary-like tube networks and growth factors secretion of HUVECs, as well as leading to higher expression level of all angiogenic-endogenic-associated genes, in comparison to unmodified control surfaces. These beneficial effects suggest the potential use of such surface nanostructures to be utilized as an advantageous interface for bone grafts as they can promote angiogenesis, which improves bone vascularization.