Barrier fabrics laminated with nanofiber membranes are used in protective textiles due to their ability to achieve high breathability or water vapor transmission rate (WVTR) while maintaining required barrier properties. The objective of this thesis is to investigate the factors impacting nanofiber membrane breathability. To achieve this objective, the effect of test conditions on breathability, and the relationship between fiber diameter, web porosity and breathability were explored. Nanofiber membranes were solution-spun by electrospinning from 15wt% and 20wt% PA6 solution concentrations, and by forcespinning from 20wt% and 25wt% concentrations. Three web area densities were made from each spinning method and solution combination: 5GSM, 10GSM and 15GSM. In order to investigate the impact of measurement conditions, breathability of all samples was measured by upright cup method (ASTM E96B) at two relative humidity levels (20% and 50%), and three air flow velocity levels (300fpm, 500fpm and 700fpm). The results showed that WVTR of all samples increased significantly when decreasing humidity or increasing air flow velocity. Webs with a lower density (5GSM or 10GSM) had higher changes of WVTR than those with a higher density (10GSM or 15GSM). These results indicate an interaction between the ambient conditions and the nanoweb structure, whereby conditions that are more conducive to water vapor transmission, such as 20%RH and 700fpm, are more discriminant between membranes. Both electropspun and forcespun membranes processed from the lower concentration solutions (15wt%, and 20wt%, respectively) exhibited smaller fiber diameters and smaller mean pore size. Overall, WVTR values varied with membrane thickness, and with solution concentration following a similar pattern as porosity. These effects were more accentuated for the forcespun samples, which had considerably larger pores (2811-5230nm) than the electrospun counterparts (163-298nm). Furthermore, samples forcespun by 20wt% solution were found to have clearly higher WVTR (1587-2194g/m²/24h at 700fpm) than electrospun samples (1526-1614g/m²/24h at 700fpm). This can be explained by the significant difference of pore size between electrospun and forcespun webs. It was concluded that breathability of forcespun samples, particularly those low density ones, could be effectively adjusted by solution concentration and is more sensitive to change of test conditions than that of electrospun webs. / text

The purpose of this work was to develop an automated method of measuring fiber diameters of electrospun scaffolds from scanning electron microscopy images of these scaffolds. Several automated methods were developed and evaluated by comparison to known values and data obtained via the standard manual method. Simulated images with known diameters were used as test images to evaluate the accuracy of each measurement technique. Eight scanning electron microscopy images were also used for the evaluation of the automated methods compared to the standard manual method. All diameter measurements were made in pixels. Five new automated methods coded in MATLAB were developed. The five methods varied the approach of identifying edges of fibers as well as assigning edges to single fibers and calculating the distance between edges assigned to the same fiber. One-way analysis of variance and the Tukey-Kramer tests were performed for comparison of all methods per image. The Custom Canny Slopes automated method was shown to accurately approximate the mean diameters in ten simulated images as well as microscopy image of real scaffolds (p<0.05).

The purpose of this study was to construct a flowmeter that could accurately measure the hydraulic permeability of electrospun fibrinogen scaffolds, providing insight into the transport properties of electrospun scaffolds while making the measurement of their topographical features (fiber and pore size) more accurate. Three different concentrations of fibrinogen were used (100, 120, and 150mg/ml) to create scaffolds with three different fiber diameters and pore sizes. The fiber diameters and pore sizes of the electrospun scaffolds were analyzed through scanning electron microscopy and image analysis software. The permeability of each scaffold was measured and used to calculate permeability-based fiber diameters and pore sizes, which were compared to values obtained through image analysis. Permeability measurement revealed scaffold permeability to increase linearly with fibrinogen concentration, much like average fiber diameter and pore size. Comparison between the two measurement methods proved the efficacy of the flowmeter as a way to measure scaffold features.

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Polyvinylidene difluoride (PVDF) is a functional polymeric material that can be used for a wide variety of applications. There are many new future applications that were recently suggested for electrospun PVDF fibers. Electrospinning is a process capable of producing nano to micro sized PVDF fibers in a web. It is important to control the structure of the web during electrospinning because by controlling the structure of the web it is possible for the PVDF fiber web to have increased performance in comparison to other common forms of PVDF. While past scientific literature focused on applications of PVDF fibers, little was known on how to control structure of PVDF fiber webs during production. Even though defects can alter the structure and performance of the web only a few studies reported defect occurrence and how to reduce the occurrence of defects in fiber webs. This research investigated the defect free production space of electrospun PVDF and provided streamlined guidelines for manufacturers to use for electrospinning PVDF webs. Many studies looked at influencing fiber diameter and beading with one factor at a time experimentation; this work was foundational and was able to identify many important electrospinning parameters. But this methodology neglected the possibility of parameter interactions and often did not look at the effects of parameters on the occurrence of defects and the structure of those defects. Therefore a systematic understanding that included all of the important electrospinning parameters in relation to fiber and defect structure was needed to present a clear picture of the possibilities for controlling the structure of electrospun PVDF webs. This research explored ways to control the structure of PVDF fiber webs. The production space and control of web structure was explored by using a regression analysis to identify important parameters and interactions. Then the regression analysis was used to determine the effects of the important parameters that influenced the web structure. This research showed that the web structure can be controlled using solution parameters and processing parameters and monitored by system parameters. In addition, this study showed that by controlling the web structure it was possible to influence the porosity and piezoelectric properties of PVDF fiber webs. In its entirety, this research presents a systematic approach to producing PVDF fibers for tailored web performance.

The work of the Cal Poly Tissue Engineering Lab is primarily focused on the fabrication, characterization, and improvement of “Blood Vessel Mimics” (BVMs), tissue engineered constructs used to evaluate cellular response to vascular medical devices. Currently, cells are grown onto fibrous, porous tubes made using an in-house electrospinning process from PLGA, a biocompatible co-polymer. The adhesion and proliferation of cells in a BVM is reliant on the micro-scale structure of the PLGA scaffold, and as such it is of great importance for the electrospinning process to consistently produce scaffolds of similar morphologies. Additionally, it has been shown that cell proliferation increases with scaffolds of smaller fibers and pores than the current electrospinning protocol can produce. Finally, the Tissue Engineering Lab has interest in testing devices in more tortuous BVM bioreactor designs, however the use of relatively rigid PLGA scaffolds has severely limited the ability to construct more complicated vessel geometries. The overall goal of this thesis was to improve fabrication and characterization of electrospun polymer scaffolds for BVM use. The specific aims of this thesis were to: 1) Improve scaffold characterization by comparing two techniques for fiber diameter measurement and implementing a technique for pore area measurement. 2) Reduce scaffold fiber diameter and pore area by investigating humidity and solvent composition electrospinning parameters. 3) Reduce process variability by developing a more specific electrospinning protocol. 4) Improve scaffold consistency and use by understanding and reducing PLGA scaffold shrinkage. 5) Identify and evaluate more flexible polymers as potential alternatives for electrospun BVM scaffolds. In order to accomplish these aims, first, several BVM and outside literature images were taken and evaluated with current and prospective fiber diameter techniques, and with 2 prospective pore area techniques to characterize accuracy and consistency of each method. It was found that the prospective fiber diameter measurement technique was not superior to the current method. The techniques developed for pore area measurement were found to produce results that differed significantly from each other and from the published value for a given image. Next, changes to environmental and solution composition parameters were made with the hopes of reducing fiber diameter and pore area of electrospun PLGA scaffolds. Changes in relative humidity did not appear to significantly affect scaffold fiber diameter while changes to solvent composition, specifically the use of acetone, resulted in fibers significantly smaller than those regularly achieved in the BVM lab. Next, several sources of variability in the electrospinning protocol were identified and subsequently altered to improve consistency and usability. Specifically, this included redefining the precision with which PLGA mass was measured, repositioning electrical equipment to reduce the effect of stray electrostatic forces on the polymer solution jet, attempting to control the temperature and humidity inside the electrospinning enclosure, and improving the ease with which scaffolds are removed from their mandrels through alternative mandrel surface treatments. In addition to overall process variability, the issue of scaffold shrinkage during BVM use was investigated and two possible treatments, exposure to either ethanol or elevated temperatures, were proposed based on previous electrospinning literature results. Each was tested for their effectiveness in mitigating shrinkage through exposure to BVM setup-mimicking conditions. It was found that both treatments reduced scaffold shrinkage compared to control samples when exposed to BVM setup-mimicking conditions. Finally, 3 flexible polymers were selected and electrospun to compare against typical PLGA results and to conduct a kink radius test as a metric for measuring flexibility as it pertains to the proposed BVM lab application. It was concluded that two types of thermoplastic polyurethane (tPU) were not acceptable electrospinning materials for use in the BVM lab. Additionally, while polycaprolactone (PCL) could be successfully electrospun it could not undergo the amount bending required for more tortuous BVM bioreactor designs without kinking. Overall, the work in this thesis provided insight into multiple scaffold characterization techniques, reduced overall electrospinning variability in the fabrication and use of PLGA scaffolds, and defined processing parameters that have been shown to yield scaffolds with smaller morphological features than all prior Tissue Engineering Lab work. By creating better, more effective scaffolds, researchers in the Tissue Engineering Lab can more accurately mimic the structure and properties of native blood vessels; this, in turn, will result in BVM cell responses that more closely resemble that of native tissue. Creating consistent and appropriate BVMs will then lead to impactful contributions to the existing body of tissue engineering research and to better preclinical device testing.

This work is focused on extruded fiber diameter measurement problem. For this purpose a procedure has been proposed. This procedure makes use of numerical methods for image processing, which are described in theoretical part of work. The proposed procedure has been processed into single-purpose software and in the final part is assessed its repeatability and reproducibility.

In previous studies it was determined that the fiber diameter distribution in a peripheral nerve could be estimated by a simulation technique known as group delay. These results could be further improved using a combinatorial optimization algorithm called simulated annealing. This paper explores the structure and behavior of simulated annealing for the application of optimizing the group delay estimated fiber diameter distribution. Specifically, a set of parameters known as the cooling schedule is investigated to determine its effectiveness in the optimization process. Simulated annealing is a technique for finding the global minimum (or maximum) of a cost function which may have many local minima. The set of parameters which comprise the cooling schedule dictate the rate at which simulated annealing reaches its final solution. Converging too quickly can result in sub-optimal solutions while taking too long to determine a solution can result in an unnecessarily large computational effort that would be impractical in a real-world setting. The goal of this study is to minimize the computational effort of simulated annealing without sacrificing its effectiveness at minimizing the cost function. The cost function for this application is an error value computed as the difference in the maximum compound evoked potentials between an empirically-determined template distribution of fiber diameters and an optimized set of fiber diameters. The resulting information will be useful when developing the group delay estimation and subsequent simulated annealing optimization in an experimental laboratory setting.

Peripheral neuropathy refers to diseases of or injuries to the peripheral nerves in the human body. The damage can interfere with the vital connection between the central nervous system and other parts of the body, and can significantly reduce the quality of life of those affected. In the US, approximately between 15 and 20 million people over the age of 40 have some forms of peripheral neuropathy. The diagnosis of peripheral neuropathy often requires an invasive operation such as a biopsy because different forms of peripheral neuropathy can affect different types of nerve fibers. There are non-invasive methods available to diagnose peripheral neuropathy such as the nerve conduction velocity test (NCV). Although the NCV is useful to test the viability of an entire nerve trunk, it does not provide adequate information about the individual functioning nerve fibers in the nerve trunk to differentiate between the different forms of peripheral neuropathy. A novel technique was proposed to estimate the individual nerve fiber diameters using group delay and simulated annealing optimization. However, this technique assumed that the fiber depth is always constant at 1 mm and the fiber activation due to a stimulus is depth independent. This study aims to incorporate the effect of fiber depth into the fiber diameter estimation technique and to make the simulation more realistic, as well as to move a step closer to making this technique a viable diagnostic tool. From the simulation data, this study found that changing the assumption of the fiber depth significantly impacts the accuracy of the fiber diameter estimation. The results suggest that the accuracy of the fiber diameter estimation is dependent on whether the type of activation function is depth dependent or not, and whether the template fiber diameter distribution contains mostly large fibers or both small and large fibers, but not dependent on whether the fiber depth is constant or variable.

Industriella processer genererar utsläpp i form av bland annat luftföroreningar via processluften som i sin tur försämrar arbetsmiljön för industrins anställda. Enligt arbetsmiljölagen är arbetsgivaren skyldig att skydda de anställdas hälsa via en god arbetsmiljö och måste därmed rena processluften. Luftföroreningar består av aerosoler och definieras som en samling solida- eller vätskepartiklar svävandes i en gas. I rapporten behandlades aerosoler i form av oljepartiklar som genereras från källor som till exempel industriella processer som gjutning, slipning och värmebehandling. En sådan process kan släppa ut sex fat olja i luften per år och utan partikelavskiljning ökar processernas olje- och energiförbrukning markant. Avskiljning av aerosola oljepartiklar samlar upp oljan så den kan återanvändas samt minskar exponering som kan ge cancer och Hodgkins disease. Aerosol olja bör därför avskiljas ur processluften på grund av hälsoaspekter. Oljepartiklar avskiljs ur processluften via porösa material. Materialet ansluts till processen med skräddarsydda kanalsystem där processluften ventileras bort med undertryck via en fläktmotor. Oljepartiklar avskiljs i det porösa materialet och därmed ökar materialets mättnadsgrad, det vill säga att ackumulerad olja minskar materialets porositet. Materialets dräneringskapacitet ser till att mättnadsgraden begränsas och att oljan kan återanvändas. Ett effektivt material har lågt tryckfall och hög avskiljningsgrad. Dessa varierar med materialets struktur som fiberdiameter, fibermattans tjocklek samt antal veckningar av materialet. Ett material veckas för att öka materialarean och dess avskiljningsgrad men tryckfallet ökas också, därför är balans mellan tryckfall och avskiljningsgrad viktigt vid konstruktion av materialet. Ett icke veckat material benämns som platt material i rapporten. Utvärdering av tryckfall och avskiljningsgrad i ett veckat material är kostsamt både ekonomiskt och tidsmässigt medan platta material är effektivt ur båda aspekterna och därför är ett bättre alternativ med avseende på utvärdering. Syftet med examensarbetet var att öka kunskapen kring avskiljning av aerosola oljepartiklar i porösa material. Målet var att modellera veckade material utifrån experimentella tester av platta- och veckade material. I rapporten testades porösa material med olika fiberdiametrar experimentellt som både platta- och veckade material. Experimentella tester innebar att materialen testades praktiskt för tryckfall och avskiljningsgrader. Avskiljningsgrader mättes vid tre intervall av partikeldiametrar enligt 0,25–0,60 μm, 0,931–1,075 μm och 1,911–2,207 μm. Platta material testades vid fyra lufthastigheter för att illustrera ökningen av lufthastighet inom veckat material på grund av en ökande mättnadsgrad. Modellering innebar att en beräkningsmodell för veckat material byggdes och gavs indata utifrån experimentella tester av platta- och veckade material. Regressionsanalyser utfördes på mätresultaten från platta material och gav matematiska funktioner som användes i modellering av veckade material. Antal veckningar och mättnadsgrader modellerades utifrån experimentella resultat från veckade material. Mät- och modelleringsresultat varierade med materialets struktur. Det gav att tryckfall, avskiljnings- och mättnadsgrader ökade med minskande fiberdiameter och ökande mattjocklek för både platt- och veckat material. Modellering av tryckfall i veckat material avvek från praktiken med -30 % och -6 % för fiberdiameter 8 μm respektive 6 μm. Modellering av avskiljningsgrader i veckat material hade störst avvikelse på +30 % för partikeldiameter 0,25–0,60 μm i material med fiberdiameter 6 μm. Modelleringsresultat av veckat material varierade över materialets struktur och avvek därmed olika mycket från praktiken. Avvikelser i modellerat tryckfall och avskiljningsgrader i veckade material var på grund av luftens dynamiska tryck. Trycket på oljepartiklarna påverkade dräneringskapacitet och oljefördelning inom materialet. Oljefördelningen är därmed heterogen i praktiken vilket påverkar tryckfall och avskiljning i både praktik och modellering. Detta skapade osäkerheter och gjorde modelleringen mindre tillförlitlig. Därför kunde tryckfall och avskiljning inte modelleras i veckat material endast utifrån platta material. Förbättrad modellering kräver vidare studier angående oljefördelning inom materialet samt inverkan av luftflödets dynamiska tryck på dräneringskapacitet för att förbättra modellering av veckade material. / Industrial processes generate emissions in the form of, among other things, air pollution via the process air, which in turn degrades the working environment for industrial employees. According to the Work Environment Act, the employer is obliged to protect the health of the employees via a good work environment and must therefore clean the process air. Air pollutants consist of aerosols and are defined as a collection of solid or liquid particles floating in a gas. The report dealt with aerosols in the form of oil particles generated from sources such as industrial processes such as molding, grinding and heat treatment. Such a process can release six barrels of oil into the air per year and without particle separation, the processes' oil and energy consumption increases markedly. Separation of aerosol oil particles collects the oil so that it can be reused and reduces exposure that can cause cancer and Hodgkin's disease. Aerosol oil should therefore be separated from the process air due to health aspects. Oil particles are separated from the process air via porous materials. The material is connected to the process with tailor-made duct systems where the process air is ventilated away with negative pressure via a fan motor. Oil particles are separated in the porous material and thus the degree of saturation of the material increases, that is accumulated oil reduces the porosity of the material. The drainage capacity of the material ensures that the degree of saturation is limited and that the oil can be reused. An efficient material has a low pressure drop and a high separation rate. These vary with the structure of the material such as fiber diameter, the thickness of the fiber carpet and the number of folds of the material. A material is folded to increase the material area and its separation rate, but the pressure drop is also increased, therefore a balance between pressure drop and separation rate is important when designing the material. A non-pleated material is referred to as flat material in the report. Evaluation of pressure drop and separation rate in a pleated material is costly both financially and in terms of time, while flat materials are effective from both aspects and are therefore a better alternative regarding evaluation. The purpose of the thesis was to increase knowledge about the separation of aerosol oil particles in porous materials. The goal was to model pleated materials based on experimental tests of flat and pleated materials. In the report, porous materials with different fiber diameters were tested experimentally as both flat and pleated materials. Experimental tests meant that the materials were tested practically for pressure drops and separation rate. Separation rate was measured at three ranges of particle diameters according to 0.25–0.60 μm, 0.931–1.075 μm and 1.911–2.207 μm. Flat materials were tested at four air velocities to illustrate the increase in air velocity within pleated material due to an increasing degree of saturation. Modeling meant that a calculation model for pleated material was built and input data was given based on experimental tests of plate and pleated materials. Regression analyzes were performed on the measurement results from flat materials and gave mathematical functions that were used in modeling of pleated materials. The number of folds and degrees of saturation were modeled based on experimental results from pleated materials. Measurement and modeling results varied with the structure of the material. As a result, pressure drops, separation rate and degree of saturation increased with decreasing fiber diameter and increasing carpet thickness for both flat and pleated materials. Modeling of pressure drop in pleated material deviated from praxis by -30% and -6% for fiber diameters of 8 μm and 6μm, respectively. Modeling of separation rates in pleated material had the largest deviation of + 30% for particle diameter 0.25–0.60 μm in material with fiber diameter 6 μm. Modeling results of pleated material varied across the structure of the material and thus deviated differently from praxis. Deviations in modeled pressure drop and separation rates in pleated materials were due to the dynamic pressure of the air. The pressure on the oil particles affected drainage capacity and oil distribution within the material. The oil distribution is thus heterogeneous in praxis, which affects pressure drop and separation rate in both praxis and modeling. This created uncertainties and made modeling less reliable. Therefore, pressure drop and separation rate could not be modeled in pleated material based solely on flat materials. Improved modeling further requires studies regarding oil distribution within the material as well as the impact of the dynamic pressure of the air flow on drainage capacity to improve modeling of pleated materials.