A Study of the Effects of Solution and Process Parameters on the Electrospinning Process and Nanofibre Morphology

Nanofibres have been the subject of recent intensive research due to their unique properties, especially their large surface-area-to-volume ratio, which is about one thousand times higher than that of a human hair. They also have several other remarkable characteristics, such as flexibility in surface functionality, superior mechanical properties such as stiffness and tensile strength, their capacity to be formed into a variety of shapes, and the fact that they can be produced from a wide range of organic and inorganic polymers. These outstanding properties make polymer nanofibres the optimal candidates for providing significant improvement in current technology and for opening the door to novel applications in many research areas. Electrospinning is a straightforward and inexpensive process that produces continuous nanofibres from submicron diameters down to nanometre diameters. Many researchers have successfully electrospun a variety of polymer solutions into nanofibres. However, electrospinning any polymer solution directly is not straightforward or simple because of the number of parameters that influence the electrospinning process. The characteristics of the electrospun jet and the morphology of the resultant fibres are highly dependent on the properties of the polymer solution. In addition, what are favourable processing conditions for one polymer solution may not be suitable for another solution. A literature review revealed that there is no clear understanding of the behaviour of the electrospun jet and the way in which fibre morphology varies with variations in influential parameters. In addition, reported results contain significant inconsistencies and very little research has examined the effects of electrical parameters such as the electric field, the polarity of the electrode, and the conductivity and permittivity of the solution. Furthermore, no research has been conducted with respect to optimizing the electrospinning process. In this thesis, a comprehensive study was carried out by giving a special attention to the effects of electric field that have not been thoroughly investigated in the past. The electric field between the needle tip and the collector plate was altered by varying the applied voltage, distance between the needle tip and the collector plate, the inner diameter of the needle, and polarity of the voltage. Based on the experimental work, it was found that the behavior of Taylor cone, the length of the straight jet portion, and whipping jet region is highly influenced by the distribution of the electric field between the needle tip and the collector plate. Based on the stability of the Taylor cone, it was concluded that the stable operating region of the electrospun jet is a very narrow region and it is between 0.9 – 1.1kV/mm for the range of experiments that were carried out in this study. The length of the straight jet portion of the electrospun jet shows a linear relationship to the applied electric field at the tip of the fluid droplet and the whipping jet region is influenced by both the electric field at the tip of the fluid droplet and the distance between the needle and the collector plate. A confirmation were made that there must be enough distance between the needle tip and the collector plate (>200mm) to operate over the complete range of voltages without affecting drying of nanofibres. It was also concluded that the morphology and diameter of the collected nanofibres depend significantly on both the length of the straight jet portion and size of the whipping region. The effects of polarity of the applied voltage on the electrospinning process and nanofibre morphology were investigated using the positive, negative, and AC voltages. However, it was found that the electrospinning can not be achieved with the application of 60Hz AC voltage. It was observed that the behavior of Taylor cone, the straight jet portion, and the whipping jet region depend on the polarity of the applied voltage. During the study, it was accomplished that the reason for this different behavior is the disparity of ionization in the polymer solution with the application of positive and negative high voltages. In this thesis, the effects of multi-needle arrangements on the electrospinning process and fibre morphology were also explained. Finite element method (FEM) simulation results revealed that the local electric field strength around each needle tip weakens significantly in the case of multi-needle schemes due to the mutual influence of other needles in the arrangement compared to the single-needle system. The spacing between the needles was varied, and the effects of the needle spacing were examined. The experimental and simulation results were concealed the correlation between the degree of field distortion and the variation in the measured vertical angle of the straight jet portion for different needle spacing. It was concluded that the local field deterioration at the needle tips in multi-needle schemes degrades the electrospinning process significantly and produces considerable variation in the fibre morphology even though the influence of needle spacing on the average jet current and the fibre diameter are not very significant. In this work, the effects of conductivity and ionic carriers on the process of electrospinning and hence on the morphology of nanofibres were studied using polyethylene oxide (PEO) and polyacrylic acid (PAA) aqueous solutions. Different salts including lithium chloride (LiCl), sodium chloride (NaCl), sodium fluoride (NaF), sodium bicarbonate (NaHCO3), potassium chloride (KCl), and cesium chloride (CsCl) were added in different concentrations to the polymer solutions for introducing different ionic carriers into the solution. The results showed that the average fiber diameter decreases with increase in the conductivity of the solution. In addition, it was discovered that the formation of Taylor cone highly depends on the conductivity in the polymer solution. Formation of multi-jets at the fluid droplet when the conductivity of the polymer solution is increased during the electrospinning was also observed. These behaviors were completely explained using the distribution of the surface charge around the electrospun jet and the variation in the tangential electric field along the surface of the fluid droplet. The stretching of the polymer jet can be related to the amount of ionic carries and the size and mobility of positive and negative ions. The increasing amount of ionic carriers and smaller size positive ions enhance the stretching of the electrospun jet. In contrast, the lesser diameter negative ions decrease the stretching of the electrospun jet. The morphology of electrospun nanofibres can also be varied by altering the type of ionic carriers. A charge modifier, which is a container that is used to hold a solvent surrounding the needle tip during the electrospinning, was introduced to facilitate the electrospinning of insulating and high conductivity polymer solutions. The co-axial flow of the filled solvent on the outer surface of the polymer solution helps to induce enough surface charges during electrospinning and it also keeps the electric field tangential to the fluid surface during the process. Therefore, the introduction of charge modifier greatly enhanced the electrospinning behavior of highly insulating and conductive polymer solutions and liquids. The developed charge modifier method was verified by using sodium alginate which is a biopolymer that cannot electrospin alone due to its high electrical conductivity and silicone rubber which is an insulating liquid polymer at room temperature. One of the most commonly used theoretical model of the electrospinning process was modified to incorporate the non-uniform characteristics of the electric field at the tip of the needle. The non-uniform electric field between the needle tip (spinneret) and the collector plate was calculated based on the charge simulation technique (CST). It gives a better representation of the true electrospinning environment compared to the uniform field calculation in the existing model. In addition, a localized approximation was used to calculate the bending electric force acting on the electrospinning jet segments. It was also introduced a constant velocity to initiate the electrospinning jet during simulation. The incorporated modifications gave better results that closely match with the real electrospinning jet. The modified electrospinning model was used to understand the effects of parameters on the electrospinning process and fibre morphology

Diagnostic salivary biomarkers in oral cancer and oral potentially malignant disorders and their relationships to risk factors ? : A systematic review

Acknowledgements NP was financially supported by University of Aberdeen (Elphinstone scholarship) and University grants commission of Sri Lanka. Authors would like to thank the library staff at Medical library and Sri Duncan Rice library for their support in the literature search and recovery of research articles.Peer reviewedPublisher PD

Fabrication of PEOT/PBT nanofibers by atmospheric pressure plasma jet treatment of electrospinning solutions for tissue engineering

This study focuses on the enhanced electrospinning of 300-Polyethylene oxide-polyethylene oxide terephthalate/polybutylene terephthalate (PEOT/PBT). An atmospheric pressure plasma jet for liquid treatment is applied to a solution with 9 w/v% PEOT/PBT dissolved in either chloroform (CHCl3), CHCl3 + N,N-dimethylformamide (DMF), CHCl3 + methanol (MeOH), or CHCl3 + hexafluoroisopropanol (HFIP). For all conditions, the plasma-treated samples present better-quality fibers: less or no-beads and uniform fiber diameter distribution. Except for CHCl3 + DMF, no significant changes to the material bulk are detected, as shown with size exclusion chromatography (SEC). X-ray photoelectron spectroscopy (XPS) spectra performed on nanofibers record an increase in C-C bonds for the CHCl3 + DMF combination upon plasma modification, while a shift and slight increase in oxygen-containing bonds is found for the CHCl3 + HFIP and CHCl3 + MeOH mixtures. MTT assay shows no-cytotoxic effects for CHCl3 + DMF, while a better cellular adhesion is found on nanofibers from CHCl3 + MeOH and CHCl3 + HFIP. Among the examined additives, MeOH is preferable as it produces beadless electrospun nanofibers with an average diameter of 290 +/- 100 nm without causing significant changes to the final nanofiber surface properties

Health and safety management practices of road construction projects in Sri Lanka

Health and Safety Management Practices of Road Construction Projects in Sri Lanka Road construction workers are exposed to hazards. This study attempts to identify, health and safety practices prevailing in road construction projects, issues and propose measures to mitigate.The study was confined to seven contract packages implemented under Northern Road Connectivity Project (Additional Financing) funded by Asian Development Bank (ADB). Five of them were located in the North Central Province while the other two were in Northern Province. Data was gathered through questionnaires, interviews and observations. Questionnaire comprised six major criteria, namely, training and supervision, safe work procedures, communication, reporting safety, management commitment and injury and return to work. Study revealed that workers are exposed to hazards of frequent and heavy lifting, noise and vibration, hazardous substances such as oil, gas, hydraulic fluid, welding fumes, heavy vehicle operation, working in blasting faces, clearing operations, slips, trips and falls, struck by, being struck by falling objects, hand-arm-whole body vibration, dust, sources of noise, electrical hazards etc. In asphalting areas workers are exposed to high temperatures and Polycyclic Aromatic Hydro Carbons (PAHC) which are carcinogenic. Working in excavated areas is prone to collapse of slopes. Workers are also prone to ergonomic issues caused due to manual handling and awkward postures. Main causes of accidents have been identified as fall from height, fall of objects, struck on stationary objects, struck by moving objects, struck on moving objects, caught in between, exposure to heat, exposure to electricity and exposure to harmful substances. Information gathered from 250 respondents revealed a high positive response in overall health and safety management practices. Five of the six criteria concerned showed a high positive response of greater than 78 percent. Communication recorded the lowest. Contract package wise comparison shows that P3 and P4 had a low positive response in the criteria concerned other than management commitment. Interviews conducted with Project Managers revealed a high commitment. Safety Committees were nonexistent in six of the seven packages except (P2). Observations revealed safety lapses such as working without PPE, working under unsafe conditions, non barricading hazardous zones, lack of warning sign boards and deploying non competent flagmen etc. It is recommended to conduct awareness programmes through Labour Department Officials prior to commencement of construction work, qualified Safety Officers should be employed, sites should be thoroughly inspected to eradicate hazards, work zones should be safe for workers, consultant’s field staff should check adequacy of precautionary measures, importance of PPE should be emphasized, hazard areas should be properly barricaded, trained flagman should be deployed, records of toolbox meetings should be maintained, near misses should be recorded, Safety Policy should be accessible to all workers, officials from the Labour Department should visit the sites to check compliance

Towards Implementing Board Gender Diversity in Sri Lanka

Corporate governance is an increasingly topical theme. The voluminous literature on corporate governance is specifically affirmed by International Financial Institutions (IFIs) in reasoning out that good corporate governance practices can develop the economy by attracting investors and securing foreign direct investment. Accordingly, these IFIs have included corporate governance reform as a condition for funding to developing countries. Sri Lanka is an illustrative example of a developing country forced by IFIs to improve its corporate governance practices as a step towards advancing economic growth. The Sri Lankan legislators have been incorporating corporate governance rules of the United Kingdom (UK) to reform corporate governance practices within the country. Among these, board gender diversity is acknowledged as a legal strategy that is capable of providing economic and equality benefits. The economic benefits are based on the contribution women directors can make towards advancing board effectiveness. The equality benefits underpinning this strategy depict the manner in which gender equality could be promoted by board gender diversity rules. While the UK corporate governance rules have incorporated this strategy, the Sri Lankan legislators have not considered this approach. This study builds on this gap and explores through a socio-legal lens the feasibility of implementing board gender diversity rules in Sri Lanka. It demonstrates that board gender diversity rules could be a valuable tool for corporate governance development and to promote gender equality in society.</p

Oral Health Status and the Impact of Socio-behavioral Factors in Institutionalized Children -Sri Lanka

Abstract There is an under-researched area in scientific literature, regarding the oral health status and dental epidemiological investigations of the socially marginalized groups such as institutionalized children. The aim of this survey was to determine &quot;the oral health status and impact of socio-behavioral factors of children under probationary care in Sri Lanka. A cross sectional population based study was conducted at 36 homes of institutionalized children in Central Province, Sri Lanka. All the children (1104) were screened and those who were above 6 years old has included to the study. An interview administered questionnaire was filled out for each child. Comprehensive oral examination was conducted by three calibrated examiners. The prevalence of dental caries in deciduous teeth was 26.86% while 56.79% in permanent teeth. The mean dmft was 0.75±1.61 while the mean DMFT was 1.19±1.43. Gingival bleeding presented in 44.67% of study subjects. Despite reporting higher usage of tooth brush and tooth paste, high percentage of bleeding gums were found in these children and this could be attributable to improper tooth brushing techniques and lack of individual supervision

Influence of artificial intelligence on warehouse performance: The case study of the Colombo area, Sri Lanka

This study is focused on the influence that artificial intelligence can bring on warehouse performance. A sample of 329 workers from selected warehouses was used for this study, and a self-administered questionnaire was used to collect data. An index was constructed using the Principal Component Analysis (PCA) method to measure the influence on warehouse performance. Mann Whitney U test and Kruskal-Wallis H test were used to determine the effect of demographic factors on warehouse performance. The association among the variables was identified by employing correlation analysis. A regression analysis was performed to determine the relationship between the identified factors and warehouse performance. When the study tests for the association among the variables, it depicts a positive correlation. Finally, based on the analysis, it illustrates the influence of machine learning, robotics, the Internet of things (IoT), and fuzzy logic on warehouse performance. The warehouse performance was mentioned in three categories: time, inventory, and cost