Electrospinning of fibrous polymer scaffolds using positive voltage or negative voltage: A comparative study

Electrospinning of fibrous tissue engineering scaffolds has been traditionally conducted using positive voltages. In the current study, positive voltage (PV) electrospinning and negative voltage (NV) electrospinning were investigated for forming fibrous membranes of poly(hydroxybutyrate-co- hydroxyvalerate) (PHBV). In both PV-electrospinning and NV-electrospinning, the fiber diameter generally increased with increasing needle inner diameter and PHBV concentration but decreased with increasing working distance. The use of a conductivity-enhancing surfactant, benzyl triethylammonium chloride (BTEAC), significantly reduced PHBV fiber diameters from the micron scale to the sub-micron scale. Interestingly, with increasing applied voltage, the fiber diameter increased for PV-electrospinning but decreased for NV-electrospinning. The PV-electrospun fibrous membranes from solutions without BTEAC (PVEfm) and with BTEAC (PVEfm-B) and NV-electrospun membranes from solutions without BTEAC (NVEfm) and with BTEAC (NVEfm-B) were characterized in terms of their structure, wettability, thermal properties and tensile properties. Both PVEfm and NVEfm exhibited similar water contact angles (∼104°) but the contact angle of PVEfm-B or NVEfm-B was not measurable. The elongation at break of PVEfm-B or NVEfm-B was significantly higher than that of PVEfm or NVEfm. Using NV-electrospinning or a combination of NV- and PV-electrospinning may be very useful for developing suitable scaffolds for tissue engineering applications. © 2010 IOP Publishing Ltd.postprin

An investigation into negative voltage electrospinning of PLLA and PLGA fibrous tissue engineering scaffolds

Theme of Conference: Research and Regulatory in Biomedical Engineering - Session C: Biomaterials and Tissue Engineering (I)published_or_final_versionThe International Conference and Pre-conference Workshop of Biomedical Engineering (BME2010), Hong Kong, China, 2-5 November 2010. In Proceedings of BME2010, 2010, p. C-

Electrospinning of fibrous PHBV tissue engineering scaffolds: Fiber diameter control, fiber alignment and mechanical properties

Poly(hydroxybutrate-co-hydroxyvalerate) (PHBV) fibrous membranes were fabricated through electrospinning. The effects of polymer solution properties including solution concentration and salt addition were investigated such that uniform fibers with diameters ranging from several hundred nanometers to a few micrometers were successfully produced. It was found that the fiber diameter increased with polymer solution concentration and drastically decreased with the addition of benzyl triethylammonium chloride. For each type of PHBV polymer solution, fibrous membranes with different fiber orientations such as random fibers, aligned fibers and double-layered structures consisting of aligned fibers were produced and the effect of solution properties on fiber alignment was analyzed. The mechanical properties of fibrous membranes with different fiber diameters and different fiber orientations were systematically investigated using tensile tests. The aligned fibers exhibited high tensile strength along the fiber direction. © 2008 IEEE.published_or_final_versionThe 5th International Conference on Information Technology and Application in Biomedicine (ITAB 2008), in conjunction with the 2nd International Symposium & Summer School on Biomedical and Health Engineering, Shenzhen, China, 30-31 May 2008. In Proceedings of the ITAB, 2008, p. 535-53

Electrospun fibrous tissue engineering scaffolds: topographic cues and their influence on cell behavior

Theme of Conference: Research and Regulatory in Biomedical Engineering - Session B: Best Young Engineer's Paper Competitionpublished_or_final_versionThe International Conference and Pre-conference Workshop of Biomedical Engineering (BME2010), Hong Kong, China, 2-5 November 2010. In Proceedings of BME2010, 2010, p. B-

The contribution of sidewall light extraction to efficiencies of polygonal light-emitting diodes shaped with laser micromachining

The light extraction efficiencies of InGaN/GaN blue light-emitting diodes (LEDs) of different geometries ranging from a triangle to a decagon have been simulated by ray-tracing. The conventional rectangular LED was found to be the most inefficient among the investigated polygons, and light extraction through the device sidewalls was the key factor. The results were experimentally verified by fabricating LEDs shaped into polygons by nanosecond-pulsed laser micromachining, which proved the simulated results. The mechanism of light extrac-tion in polygonal LEDs is discussed in detail. © 2010 American Institute of Physics.published_or_final_versio

Laser micro-machining of three-dimensional microstructures in optical materials

We demostrate an advanced precision cutting tool using a 349 nm nanosecond pulsed UV laser micromachining setup. After expansion and collimation, the laser beam is directed vertically and focused with a high performance triplet lens. With an Al mirror inserted in the path of the convergent beam, the beam can be focused on a horizontal machining plane at any desired tilting angles. Microstructures of a wide range of geometries on hard materials can be formed using this custom machining method. Conventional linear and rotary machining on sapphire materials have been demonstrated.published_or_final_versionThe 2009 Spring Meeting of the Materials Research Society (MRS), San Francisco, CA., 13-17 April 2009. In Materials Research Society Symposium Proceedings, 2009, v. 1179, p. 99-10

Laser micro-machining of three-dimensional microstructures in optical materials

We demostrate an advanced precision cutting tool using a 349 nm nanosecond pulsed UV laser micromachining setup. After expansion and collimation, the laser beam is directed vertically and focused with a high performance triplet lens. With an Al mirror inserted in the path of the convergent beam, the beam can be focused on a horizontal machining plane at any desired tilting angles. Microstructures of a wide range of geometries on hard materials can be formed using this custom machining method. Conventional linear and rotary machining on sapphire materials have been demonstrated.published_or_final_versionThe 2009 Spring Meeting of the Materials Research Society (MRS), San Francisco, CA., 13-17 April 2009. In Materials Research Society Symposium Proceedings, 2009, v. 1179, p. 99-10

Laser micromachining of optical microstructures with inclined sidewall profile

Laser micromachining has been proved to be a useful tool for the formation of microstructures in semiconductor and optical materials. It is also widely adopted for dicing of light-emitting diode chips. The authors propose a modified laser micromachining setup which enables three-dimensional structures to be formed. A mirror is inserted in the optical path between the focusing optics and the machining plane so that the beam strikes the sample at an oblique angle. By translating and/or rotating the sample as micromachining is carried out, various three-dimensional structures such as a pyramid or a conic section can be obtained. Trenches as small as 10 μm on sapphire have been realized with nanosecond ultraviolet laser pulses. Laser-induced damage, due to resolidification of the ablation melt, accumulates with increasing scans of the beam; it can be removed by chemical and mechanical treatment. © 2009 American Vacuum Society.published_or_final_versio

Arts, mental distress, mental health functioning & life satisfaction: fixed-effects analyses of a nationally-representative panel study

Background: Arts engagement within communities is ubiquitous across cultures globally and previous research has suggested its benefits for mental health and wellbeing. However, it remains unclear whether these benefits are driven by arts engagement itself or by important confounders such as socio-economic status (SES), childhood arts engagement, previous mental health, personality, or self-selection bias. The aim of this study is to use fixed effects models that account for unidentified time-constant confounding measures to examine the longitudinal association between arts (frequency of both arts participation and cultural attendance), mental distress, mental health functioning and life satisfaction. / Methods: Data from 23,660 individuals (with a mean age of 47 years) included in the UK Understanding Society wave 2 (2010–2012) and wave 5 (2013–2015) were analyzed. Aside from controlling for all time-constant variables using fixed-effects models, we additionally adjusted for time-varying demographic factors (e.g. age and marital status), health behaviors and social support variables. / Results: After controlling for all time-constant variables and identified time-varying confounders, frequent arts participation and cultural attendance were associated with lower levels of mental distress and higher levels of life satisfaction, with arts participation additionally associated with better mental health functioning. Health-related and social time-varying factors were shown partly but not wholly to explain the observed associations. / Conclusion: Arts engagement amongst the population as a whole may help enhance positive mental health and life satisfaction, and protect against mental distress. These results are independent of a wide range of time-constant confounding factors

Hierarchical task network approach for time and budget constrained construction project planning

© 2019 The Author(s). Completing a construction project on time and within budget is of great importance in the construction industry. To achieve this goal, a construction plan satisfying the time and cost constraints is crucial. While a rich amount of literature on the time-cost trade-off scheduling and time/cost optimization scheduling has been presented, developing a construction plan for the time and cost-constrained construction project has not been fully explored. This study presented a hierarchical task network (HTN) based construction planning model to fill this gap. First of all, a knowledge formalism catering to the HTN planning was provided to accommodate the construction planning knowledge. Then, the planning process was explained in detail, including temporal reasoning used to sequence the construction activities, and backtracking evasion mechanism used to avoid the trouble of backtracking due to inappropriate selection of execution modes for construction activities. Finally, two sets of comparisons based on a fictional construction project were performed, the results of which demonstrate that the time and budget constraints have an impact on the sec-tion of execution modes for construction methods, and the proposed planning model can develop construction plan that satisfies the specified deadline and budget limitations effectively regardless of the existing of backtracking