[dipl] Kemian tekniikan korkeakoulu / CHEM

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  • Overproduction of L-tyrosine in Yeast
    (2025-02-24) Salminen, Pinja
     School of Chemical Engineering | Master's thesis
    L-tyrosine is an industrially relevant compound and a precursor for many oth-ers. Several strategies to create L-tyrosine overproducing Saccharomyces cere-visiae strains have been reported. This project aimed at reviewing strategies pre-viously found successful and implementing selected modifications in S. cerevisiae CEN.PK113-7D through targeted genome-editing. Using CRISPR-Cas9 technology, mutant versions of the ARO3 and ARO4 were introduced to release the feedback inhibition of the shikimic acid pathway. Additionally, TKL1 was overexpressed to favor the pathway through transketolase in the pentose phosphate pathway for increasing the precursors availability for aromatic amino acid synthesis. The feed-back inhibition relieved point-mutation variants of ARO3 and ARO4 were inte-grated into the genome. TKL1 was overexpressed by changing the native promoter to a strong TDH3 promoter. The engineered strains were analyzed for amino acid accumulation.; L-tyrosine and L-phenylalanine accumulated notably in S. cere-visiae CEN.PK113-7D strain harboring the feedback inhibition relieved mutants of ARO3 and ARO4 while in wild type and TKL1 overexpression strains L-tyrosine and L-phenylalanine were below detection level. The developed strains could be used as pre- optimized platform strains for expressing heterologous pathways having L-tyrosine as a precursor. Such heterologous pathways could allow for sustainable biotechnological production of e.g., hydroquinone whose synthesis is currently oil-based.
  • From biotemplate to wearable sensor: Creating a piezoresistive sensor textile for healthcare applications
    (2025-02-21) Mäkelä, Viivi
     School of Chemical Engineering | Master's thesis
    The field of wearable strain sensors has been a target of extensive research in recent years due to their unique features and diverse application range. However, the conventional strain sensors currently used in healthcare lack many of the measurement criteria required to accurately assess the human body due to its complex structure and dynamic nature. The new generation of flexible and textile-based sensors addresses these shortcomings of the conventional sensors and provide improved platforms for healthcare applications. In this thesis work a highly sensitive piezoresistive yarn which can be incorporated into a wearable sensor textile is developed. The developed sensor combines three different elements from previous research into one novel sensor material that has not been studied before. The substrate used for the sensor is starch-nylon yarn, which is incorporated into a twisted/coiled spring structure and coated with Potato virus A (PVA) and silver nanoparticle (AgNP) template. The development process of creating an optimally performing sensor consisted of first optimizing the coating conditions of the starch-nylon yarn and then testing the properties of different spring structures made from the yarn. By combining the optimized coating protocol with the most suitable spring structure, the highly performing piezoresistive sensor was created. This was followed by validating the sensing performance of the created sensor focusing on similar movement ranges that can be seen in the human body. Subsequently, the textile integration of the sensor was demonstrated by fabricating a sensor textile sample. This thesis work shows that a functional piezoresistive sensor can be created by combining the PVA and AgNP coating with the starch-nylon spring structure. Furthermore, the created sensor shows promising preliminary results for the key performance metrics highlighting its potential to be used as wearable sensor. The sensor exhibits high sensitivity, good detection range, relatively short response and recov-ery times and promising results for durability. This thesis also shows that the sensor can be integrated into a textile, showing its potential to be further explored for wearable healthcare applications. This thesis serves a good starting point for further development of the introduced piezoresistive sensor and provides a new platform that can be utilized in future research.
  • Fabrication and investigation of thermoelectric device based on p-type and n-type CoSbS components
    (2024-12-31) Liu, Hanru
     School of Chemical Engineering | Master's thesis
    Thermoelectric materials have garnered significant interest in recent years due to their promising applications in energy conversion and waste heat recovery. This study systematically investigates the thermoelectric properties of CoSbS-based materials, with a focus on the effects of doping elements (Ge, Ni, Se, Te). By precisely controlling the doping concentration and substitution sites, the impact of these elements on optimizing the Seebeck coefficient and reducing thermal conductivity is thoroughly examined. The results reveal that Co0.9Ni0.1Sb0.9Ge0.1S demonstrates outstanding thermoelectric performance. Furthermore, Se and Te doping effectively reduce lattice thermal conductivity; however, their contributions to improving overall thermoelectric performance remain limited. This study highlights the critical role of optimizing doping sites and concentrations in enhancing the thermoelectric properties of CoSbS-based materials, providing valuable in-sights for the future design and development of high-performance thermoelectric materials. In addition, the methods of assembling thermoelectric devices and corresponding application prospects are also discussed.
  • Novel use of blood products: Using existing omics data from extracellular vesicles from differently activated platelets to fine-tune modelling of functionality
    (2024-12-20) Österberg, Anna
     School of Chemical Engineering | Master's thesis
    Platelets are crucial for hemostasis and, upon activation, release extracellular vesicles (PEVs). PEVs are a heterogeneous population, whose contents vary depending on the platelet-activating stimulus. This study re-analyzed existing omics data of PEVs from differently activated platelets, focusing on their immunomodulatory roles. We validated our findings in vitro using primary cells. Dimensionality reduction techniques, including principal component analysis (PCA) and multi-omics factor analysis (MOFA), were applied. For validation, we established a human macrophage in vitro model and isolated PEVs from differently activated platelets with ultracentrifugation. Our re-analysis revealed that TNF-a secretion in THP-1 cells in vitro differed from previous in vivo results, particularly for PEVs derived from thrombin and collagen coactivated platelets (TC PEVs). Additionally, PEVs derived from platelets activated with rhodocytin through the CLEC-2 receptor (CLEC-2 PEVs) exhibited distinct protein and cytokine profiles. Due to unavailability of the rhodocytin reagent, we could not analyze CLEC-2 PEVs further and therefore, our experiments focused on TC PEVs, using PEVs from unstimulated platelets (US PEVs) as controls. We compared TNF-a secretion in M1 (pro-inflammatory) versus M2 (anti-inflammatory) polarized primary macrophages. Results indicated significantly higher TNF-a secretion in M1 cells compared to M2 cells, highlighting the biological differences between the two cell types. No significant variation between PEV-treated and untreated cells was found. However, we observed donor-dependent variation, so further studies with more biological replicates are needed to validate these findings.
  • Artifical intelligence based prediction of protein complexes formed via transient interactions
    (2024-12-28) Hammarberg, Linnéa
     School of Chemical Engineering | Master's thesis
    Transient protein-protein interactions (tPPIs) are interactions between multiple proteins which swiftly switch between an associated and a dissociated state. Such interactions play a crucial role in many dynamical processes in the cell, such as in the regulatory and signaling pathways. Because of their adaptable nature, tPPIs are attractive targets for the development of novel biomaterials. tPPIs have previously been overlooked, due to their low cellular concentrations as well as being hard to capture both experimentally and with computational methods. As a result, there exists a knowledge gap of the structures and functions of tPPIs. This thesis provides a comprehensive analysis of predicting tPPIs with the front-runner of the AI-driven structure predicting algorithms, AlphaFold (AF). Prior to this work, no publications have addressed AI-driven structure predictions of tPPIs. The AF generated tPPI-models are compared against experimental data when available, and against the output of the protein docking algorithm ClusPro. The AF performance is further validated through molecular dynamics simulations. AF showed to be much less confident about predicting tPPIs than stable protein complexes in general. High sampling should therefore be employed to acquire a wider range of models. The AF generated models did not significantly differ from those predicted by ClusPro, and were also fairly close to the experimentally determined interaction site. Interaction site families were readily identifiable from the sample by isolating and comparing the residues predicted to be in contact. Simulating models from each family with MD, showed that AF is able to predict a range of stable interaction sites. The interaction site features varied among the studied proteins, but the most commonly predicted interaction sites included beta-strand residues and disordered loops for all studied proteins. The detailing of the benefits and limitations of predicting tPPIs with AF presented in this work might aid in the engineering of new tPPI-based biomaterials.
  • Optimization of cell culture models for calpain-2 studies for prostate cancer
    (2024-12-19) Hansson, Cecilia
     School of Chemical Engineering | Master's thesis
    Prostate cancer affects millions of men annually and is the second most leading cause of cancer related death for men. Many patients eventually develop castration-resistant prostate cancer (CRPC), a highly aggressive form that is resistant to standard treat-ments. The protease calpain-2 has shown to contribute to cancer progression. Many studies fail due to a poorly designed in vitro model that does not replicate the tumour microenvironment enough. To achieve reliable study outcomes, the in vitro culturing environment must closely mimic the complex conditions of human tumours. In this Master’s thesis a suitable culturing environment for studies of calpain-2 was investigated. Two widely used prostate cancer cell lines, PC3 and LNCaP, were cultured on two different extracellular matrix mimics (Matrigel and collagen) and compare to cells grown directly on plastic wells. Experiments were performed under hypoxic (0.2% oxygen) and normoxic (21% oxygen) conditions. The objective was to explore how these culture conditions and oxygen levels affect cell behaviour, including phenotype and protein expression. The results underscore the importance of using in vitro mod-els that closely replicate human cancer conditions to gain the meaningful insights. Such approach is essential for advancing future research on calpain-2 and its role in prostate cancer.
  • Cleaning Verification in Pharmaceutical production — Direct measurement of Swab samples with FTIR
    (2024-12-30) Jäntti, Hermanni
     School of Chemical Engineering | Master's thesis
    Cleaning verification in pharmaceutical manufacturing is a crucial step in preventing cross-contamination and its potential adverse effects on patient safety. Cleaning methods go through a documented cleaning validation procedure to ensure they can achieve acceptable level of residue. Traditional cleaning validation methods such as swab sampling combined with time-consuming and environmentally unsustainable analyses like HPLC are widely used. Visual cleanliness is also used to verify cleaning results but due to its challenges and tightening regulation it may become insufficient in the future. The pharmaceutical industry urgently needs a rapid, sensitive and portable method for in situ cleaning verification. Handheld FTIR spectrometer presents a potential method for cleaning verification directly from production surface. Swab sampling remains essential for complex or irregular surfaces where direct FTIR measurement is impractical. This thesis explores the background of cleaning verification regulation and the role of swab sampling. It also explores the principles of FTIR spectroscopy and highlights its current applications in rapid spectroscopy analysis. The experimental work focuses on studying the suitability of various swab materials for measurement with a handheld FTIR spectrometer. Six swab types and five chemically different active pharmaceutical ingredients (APIs) were tested by dipping the swab in API solution and measuring directly with FTIR. The study assessed how the swab materials influenced the spectral background. Cotton swabs were proven as the most suitable for detecting API related absorption bands due to their minimal interference. Cotton swab was used to sample Ibuprofen residues from a stainless-steel surface. Ibuprofen related peaks were successfully detected at concentration as low as 0.4 𝜇𝑔/𝑐𝑚2. While further research and method development are necessary, the results of this thesis demonstrate the significant potential of cotton swabs in FTIR-based cleaning verification.
  • Chemical recycling of polyurethanes
    (2024-12-21) Voitsekhovski, Ariana
     School of Chemical Engineering | Master's thesis
    Polyurethanes (PUs) compose one of the most produced polymers worldwide, an-nually resulting in significant waste, of which above half is still landfilled. Unfortu-nately, polyurethane foams (PUFs) and polyurethane-based elastane face major challenges in recycling due to their versatile and complex structures. Thus, this work studies chemical recycling of non-segmented, methylene diphenyl diisocyanate (MDI) -based PUF and segmented polyol-containing elastane. Both materials were recycled via chemical recycling methods, concentrating on aminolysis and glycolysis routes. The first part of the research concentrates on glycolysis and aminolysis recycling of MDI-PUF using ethylene glycol (EG) or hexamethylenediamine (HMDA) as chemical agents and sodium hydroxide and zinc acetate (ZnAc) as catalysts. At 180˚C, PUF was completely degraded in 2 hours during glycolysis and in 40 minutes during aminolysis. However, decomposed PU resulted in significant challenges regarding the purification. Hence, according to nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) results, purified end-products mainly composed of aromatic amines, MDI-residues, excess glycol, and carbamates. Thus, due to the major purification challenges, glycolysis was also studied on segmented, polyether polyol-based elastane, implementing higher temperature of 200 ˚C and longer reaction time. Polyol content of elastane was successfully recycled and recovered. Additionally, other end-products of elastane glycolysis were characterized as aromatic amines, excess glycols, and carbamates.
  • Environmental impact and energy payback time of recycling solar photovoltaic panels: A comparative life cycle analysis
    (2024-12-26) Tochenaia, Anastasiia
     School of Chemical Engineering | Master's thesis
    Photovoltaic (PV) technology helps to decrease the dependency on fossil fuels and ful-filling the worlds energy needs effectively. Due to the continuous rise in the production of solar panels, the volume of PV waste has grown significantly and is projected to reach millions of tons by 2050. Another issue of PV panels is the energy-intensive PV manufacturing process that emits pollution. Research has demonstrated that PV waste can be recycled, decreasing the environmental problems caused by the disposal of waste. One solution to reduce the overall emissions of the PV manufacturing process could be the manufacture of new solar PV panels from materials recovered from PV waste, in other words secondary production. Therefore, this thesis focuses on assessing the impacts on the environment and energy payback time (EPBT) associated with the secondary production of solar photovoltaic panels, concentrating on two types of PV panels, monocrystalline silicon (mono c Si) and cadmium telluride (CdTe) PV panels. The scope of the study included three stages of secondary production: recycling PV waste, pre-manufacturing and remanufacturing of new PV panels, as well as trans-portation between these stages. The total energy usage and total air emissions were also considered. The evaluation of environmental effects was conducted using Life Cycle Assessment (LCA) and openLCA software. It was observed that monocrystalline silicon PV panels have a higher impact than cadmium telluride PV panels. In addition, the energy consumption of the secondary production of the solar panels was also in-vestigated. Transportation was determined to be the most energy-intensive stage for both types of PV panels due to the long distances required for material transportation. With the knowledge of consumed energy and energy generated by PV panels, energy payback time (EPBT) was calculated. These EPBT results indicated that CdTe PV panels required less time to recover the imbodied energy investment, 2.6 years, com-pared to 3.8 years, for mono c-Si PV panels. However, the raw materials used in CdTe PV panels are rarer compared to raw materials in mono c-Si PV panels. Overall, this study emphasizes the importance of reducing energy use during mate-rials transportation. Additionally, it is suggested that future research related to the investigation of the ecological effects related to secondary production of upcoming solar technologies is necessary to secure more sustainable designs of future PV panels.
  • Life cycle assessment of lithium conversion
    (2024-12-20) Terho, Tara
     School of Chemical Engineering | Master's thesis
    The demand for lithium hydroxide is increasing due to modern electric vehicle (EV) batteries containing high-nickel cathode materials prepared by using lithium hydroxide. Nevertheless, the most prevalent product in the lithium value chain is lithium carbonate. Consequently, there is a need for technologies that can further process lithium carbonate into lithium hydroxide to meet the increasing demand. One proposed solution involves the use of a lithium conversion plant for converting lithium carbonate to lithium hydroxide. In this study, a lithium conversion plant was simulated, and a Life Cycle Assessment (LCA) was conducted for the plant. In this work, a conventional process of converting lithium carbonate to lithium hydroxide with calcium hydroxide was studied. The effects of conversion rate and impurity reaction rates in the conversion reactor were examined. Additionally, three different feed materials were implemented: battery grade lithium carbonate from battery recycling and brine, and technical grade lithium carbonate. In the process design, it is recommended to aim for a high conversion rate, as it leads to better product yield, improved product purity, and lower impurities in the crystallizer recycle. Impurity reaction rates had minimal effect on the process due to the low impurity contents of the selected feed materials. Furthermore, the process simulation demonstrated that conventional conversion can be utilized in this way to produce lithium hydroxide from various sources of lithium carbonate. In the LCA, the simulated process scenarios were compared in different environmental impact categories. Additionally, a contribution analysis was conducted, and the conversion process was compared with primary production of lithium hydroxide. The results indicated that feed selection is the primary contributor to the differences in environmental impacts between scenarios. Additionally, increasing the conversion rate was seen to marginally increase the environmental impact. However, simultaneously process efficiency increases. Of the feed options explored in this study, the best option is lithium carbonate from brine and lowest performing option is technical grade lithium carbonate. Furthermore, it was determined that the most environmentally straining factors of the process were feed consumption and electricity use. The comparison with primary production demonstrated that in most impact categories lithium conversion is more favorable. The main limitation of the conversion process was found to be extensive water consumption.
  • High kappa pulp properties and dewatering characteristics
    (2024-12-29) Winqvist, Jonathan
     School of Chemical Engineering | Master's thesis
    High kappa pulp is produced using a variation of the sulphate process, producing higher yield pulps for packaging-grade papers in a growing market. Washing is a central unit operation in pulping and has a significant effect on the mill’s total economic profitability. As yield increases, pulp and fibre properties change, investigations are necessary to optimize the capacity and efficiency of the washing step for high kappa application. In this thesis, the displacement speed behaviour and pulp mat formation of sack paper grade pulp was investigated. The behaviour change was compared to the changing pulp and fibre properties of a range of laboratory cooked unrefined pulps from kappa 31 to 62. Additionally, three different mill pulps within this range were analysed and compared. Displacement speed trails were conducted using the PertiTest device, which measures pulp bed height and displacement speed. These trials included samples with both the original fibre fractions and with the fines fraction removed. Fibre properties were analysed with optical analysers, while network strength was measured using a shear rheometer. In the range of laboratory cooked pulps, the displacement speed increased significantly from kappa 31 to 62. Key fibre properties that showed linear correlation with displacement speed included fibre width, coarseness, cross sectional area, kink, and curl. The increase in kappa number showed a linear relationship with the initial dis-placement speed behaviour across the range, which is linked to the increased fibre network strength. Additionally, the composition of fines has significant impact on the displacement results, and accumulation of fines within the same fibre line will lower the displacement speed of the pulp. Further investigation into particle migration is recommended, as fines removal had greater effect on higher kappa pulps and a clear change in the pulp bed formation was observed. As the results suggest, understanding the characteristics of pulp bed formation and displacement speed behaviour is essential for developing washers for unique applications and specific pulp properties.
  • Application of circularity indicators to bio-based products — Testing the new ISO 59020 framework on product level in a case study
    (2024-12-21) Toivanen, Iines
     School of Chemical Engineering | Master's thesis
    The transition to a circular economy and the adoption of bio-based products are recognized as critical strategies for addressing the existential threats posed by global warming, biodiversity loss, and unsustainable resource consumption. Circularity indicators can be utilized to assess and monitor circularity performance at different levels. This thesis examines the practicality of circularity indicators for bio-based products, focusing on products in the developmental stage. The primary objective is to analyse the suitability of the ISO 59020:2024 framework in this regard through a case study. This study offers valuable insights for the development of circularity indicators, bridging the bio-based industry with circular economy principles, while acknowledging the limitations of the CE paradigm. The circularity assessment process, following the ISO 59020 guidelines, was applied to two wood-based products at a pre-commercial technology readiness level. The study combines quantitative measurement of circularity indicators with qualitative analysis of practical challenges and opportunities. The results demonstrate that while it was possible to conduct the ISO 59020 circularity assessment for one of the two products, the circularity indicators do not fully reflect the product system flows. The system boundaries were narrowed to the production phase due to limitations in data availability and the novelty of the products. Gathering suitable circularity data, especially for energy and water flows, was found challenging, but previous LCA models aided the process. The ISO 59020 indicators address many attributes relevant to bio-based systems, such as the renewability of inflows, and aim to incorporate sustainability considerations. However, specific verification methods are not defined due to the framework's general nature. The results suggest that the ISO 59020 framework can be useful in the design and development stages of products to highlight key circularity aspects, even if extensive circularity measurement is difficult in the pre-commercial phase. Further research is needed on the framework applicability to different bio-based products and the establishment of product category-specific criteria.
  • Seaweed-based dispersion barrier for paperboard
    (2024-12-07) Wallius, Jenna
     School of Chemical Engineering | Master's thesis
    The extensive use of plastics is overwhelming the global ecosystems and posing a threat on animal and human health. To mitigate the harmful impact of plastics, Eu ropean Union issued the Single-Use Plastics (SUP) Directive in 2019. The SUP Directive calls for innovative solutions to ultimately replace the conventional petroleum-based plastics with biobased alternatives. However, the replacements should be chemically unmodified natural polymers, or otherwise it is defined as plastic in the Directive. Food products are often packed in paperboard that has been coated with a protective barrier layer, conventionally made out of plastics. While the paperboard brings rigidity to the packaging, the barrier layer offers resistance against other factors, such as grease, water and water vapor, oxygen and microorganisms. This study has taken on the challenge set in the SUP Directive by finding alternatives for the plastic barrier coating in paperboard packaging. The barrier coating was applied on the paperboard substrate as a water-based barrier dispersion. Seaweed-based sodium alginate was selected as the binder polymer in the dispersions. As fillers, talc, kaolin and calcium carbonate were used to for mulate multiple dispersion recipes. Sodium alginate is known to improve its water resistance when reacted with calcium ions. This approach was utilised in this study by incorporating the calcium ions as calcium chloride spray. Most of the barrier coatings showed excellence grease resistance. Calcium chloride treatment improved the coatings' water resistance. The sodium alginate coating also showed potential for being an oxygen barrier. Additionally, the coat ings were subjected to sensory analysis for off-flavour and odour in order to assess their suitability in food packaging. Based on the analysis, the coatings are suitable for food packaging applications.
  • Tuulivoimalan materiaalien käyttö elinkaaren lopussa
    (2024-12-19) Jormakka, Taru
     School of Chemical Engineering | Master's thesis
    As the need for clean energy is rising, wind turbines have been considered as key to reducing emissions in energy production. The number of wind turbines and wind farms in Finland has increased significantly in recent years. Thus, more attention is being given to the material flows caused by their decommissioning or demolition with regards to the circular economy. In this thesis, different ways to handle wind turbine materials in their end-of-life were researched. In addition, any limits that different materials or structures pose to the lifetime of a single turbine were addressed. The materials and structure of wind turbine components were researched through a literary review. Additionally, a case study was conducted to determine the end-of-life options for a wind turbine in Finland and if we have the capacity to recycle the decommissioned material flows. The case study estimated the amount of materials to be decommissioned through the material volumes of a single reference wind turbine and statistics of the built wind turbines in Finland. The results of the case study showed that the recycling material flows caused by wind turbine decommissioning can be managed in Finland. The estimate showed that Finland will face a surge in wind turbine material recycling in the 2050s, and these amounts could be more difficult to recycle with the current capacity in Finland.
  • Effects of pretreated oat hulls on the growth and gut microbiota profiles of black soldier fly larvae
    (2024-12-31) Vähätaini, Saku
     School of Chemical Engineering | Master's thesis
    Food industry currently produces large amounts of fibrous side-streams that are poorly utilized. This contributes to the inefficient use of raw materials in food industry, leading to increased greenhouse gas emissions and land-use. Oat hulls are a good example of a poorly utilized fibrous side-stream, as they are currently mainly burnt for energy. Black soldier fly larvae can be used to convert the fibrous side-streams of food industry back into valuable raw materials. This maintains the proteins, lipids, fats, and nutrients in the circulation, adapting the concept of circular economy. The larvae’s efficient conversion of wide variety of organic material is mainly attributed to the dynamic gut microbiota and enzymes produced by it. However, black soldier fly larvae do not utilize the fibrous side-streams efficiently unless they are pretreated. Therefore, the aim of this thesis was to improve the utilization of oat hulls by black soldier fly larvae through pretreatment by microbial fermentation. Additionally, the aim was to assess the effect of the feeding with fermented oat hulls to the gut microbiota of the larvae. Trichoderma reesei and Bacillus subtilis were used in the biological pretreatment along with frass produced by the larvae as a by-product. T. reesei and B. subtilis were expected to produce enzymes capable of degrading some of the fibers in the oat hulls, improving the feed availability for the larvae. Frass was hypothesised to improve larvae growth by providing nutritional supplement and stabilizing the microbiota of the feeding substrate. T. reesei was found to have the most notable effect on larvae growth and the composition of gut microbiota. This pretreatment method yielded significant improvements in larvae dry weight and bioconversion efficiency. Conversely, significant decrease was observed in survival rate of the larvae and diversity of the gut microbiota. The results highlight a potential trade-of between larvae growth and survivability. Bioconversion efficiency is a critical parameter considering the financial viability of black soldier fly larvae production. In this study, the positive effects outperformed the negative effects, suggesting potential for T. reesei to be used in the pretreatment of oat hulls in this context.
  • The effect of citrate utilizing lactic acid bacteria on propionic acid production and growth of propionibacteria used in cheese making
    (2024-12-30) Ståhlberg, Katri
     School of Chemical Engineering | Master's thesis
    Propionic acid fermentation is essential for formation of flavour and structure in Swiss-type cheeses. Excess or insufficient propionic acid production may lead to structural or aromatic defects. Other microbial cultures, especially some facultatively heterofermentative lactobacilli (FHL), are known to inhibit the propionic acid fermentation and growth of propionic acid bacteria (PAB). This study focused on citrate fermentation of lactic acid bacteria (LAB) and the potential interactions between the metabolites and propionic acid fermentation. The citrate consumption and produced metabolites of 8 LAB cultures were studied in modified M17 growth broth. After LAB cultivation, the supernatants were filter sterilized and Propionibacterium freudenreichii cultures were inoculated to the media. The growth and propionic acid production of PAB were measured to study the interactions between citrate utilizing LAB and two PAB cultures with differing aspartase activity. Three out of five citrate positive LAB cultures were consuming citrate and producing acetate, formate, acetoin, diacetyl and ethanol. None of these compounds was found specifically responsible for the inhibition. Inhibition of propionic acid fermentation was found culture specific for both LAB and PAB. Aspartase activity did not likely have a role in inhibition of propionic acid fermentation. Incubation in the LAB supernatants increased the aspartate consumption of PAB culture with weak aspartase activity. Propionic acid fermentation of P. freudenreichii with stronger aspartase activity was inhibited by Lactococcus lactis ssp. lactis biovar. diacetylactis and Leuconostoc mesenteroides. P. freudenreichii with weaker aspartase activity was weakly inhibited by L. lactis ssp. lactis biovar. diacetylactis but the propionic acid fermentation was slightly stimulated by L. mesenteroides. Cheese slurry was tested as a complex medium mimicking ripening cheese. The matrix was found non-functional without heavy optimization, especially improved control over lactic acid fermentation.
  • Performance of a palladium-titanium dioxide core-shell electrocatalyst towards hydrogen energy conversion in alkaline media
    (2024-11-20) Schiwek, Cedric
     School of Chemical Engineering | Master's thesis
    The hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) remain the limiting reactions in alkaline media for hydrogen energy conversion, thus attracting great attention from researchers working towards hydrogen as a clean energysource. This work presents a way to produce size-controlled palladium nanoparticles on commonly used carbon support Vulcan XC-72R (PdTiO2x/VC, with x = number of TiO2 deposition cycles) by wet impregnation, followed by a subsequent atomic layer deposition of porous and amorphous TiO2. Electrochemical measurements of PdTiO2x/VC show a significant improvement in catalytic activity compared to pure Pd/VC, with a current density increase from 1.42 mA/cm2 to 1.95 mA/cm2 at 0.1 V in 0.1 M KOH towards the HOR. Measurements towards HER in simulated a seawater solution indicate a significant a lower overpotential needed to achieve 10 mA/cm2, 275 mV for Pd/VC compared to 140 mV for PdTiO2 12/VC. Furthermore, a maximum of 0.07 Wcm−2 was achieved by the fuel cell based on the PdTiO2x/VC catalysts, which is 13% higher than the fuel cell based on Pd/VC. Experiments with the electrolyzer showed an initial improvement of catalytic activity; however, a precise measurement could not be carried out due to unstable conditions. As performance-enhancing mechanisms, the hydrogen binding energy theory is considered.
  • The effects of S. aureus infections on Treg functionality in the bleeding disorder (hemophilia A)
    (2024-12-27) Sergeeva, Anastasia
     School of Chemical Engineering | Master's thesis
    Regulatory T cells (Tregs) are essential for maintaining immune tolerance and regulating immune responses, which makes them crucial in bleeding disorders such as hemophilia A. This thesis investigated the impact of Staphylococcus aureus infection on Treg function and phenotype, with a focus on determining whether direct bacterial interaction or some other alternative mechanisms drive the observed effects. This research builds upon previous findings by the Becker-Gotot group, that demonstrated the significance of PD-L1+ Tregs in mediating FVIII-specific tolerance during immune tolerance induction (ITI) therapy. Previous in vivo studies showed a marked decrease in FoxP3 expression and the suppressive capacity of infected Tregs, which raised the need to investigate this phenomenon more deeply in in vitro in order to assess potential underlying mechanisms. To investigate these mechanisms, Tregs derived from murine splenocytes were subjected to either S. aureus infection or treatment with TLR2 ligands (Pam3CSK4 and Pam2CSK4), which simulate bacterial infection components. Functional and phenotypical changes were assessed through flow cytometry and statistical analysis. The findings confirmed that this in vitro model was sufficient to examine Treg modulation. Infected nTregs exhibited reduced FoxP3 expression, diminished suppressive capacity, and a shift towards a pro-inflammatory phenotype based on cytokine profiling. Furthermore, a direct bacterial contact was not strictly necessary for these changes, highlighting the potential involvement of soluble factors secreted by S. aureus in these processes. The effect of S. aureus infection on Treg-mediated immune regulation observed in this work was significant and demonstrated also the pivotal role of cytokine-mediated pathways in this process, underscoring the need for further investigations to understand this phenomenon more thoroughly in order to improve therapy options for patients suffering from infections like S. aureus.
  • Modification of natural fibers for biobased packaging
    (2024-11-20) Sattar, Hamza
     School of Chemical Engineering | Master's thesis
    This thesis investigates the modification of natural fibers to enhance their suitability for biobased packaging. The primary goal is to improve the dimensional stability and strength of paper made from natural wood fibers by refining the fibers under different mechanical and chemical conditions. The study uses kraft pulp from both hardwood and softwood sources (Eucalyptus, Birch, Pine), subjecting them to refining processes under neutral and alkaline conditions. Key methods include measuring Schopper Riegler (SR) number, tensile strength, water retention value, and hygroexpansion. The results demonstrate that fiber refinement improves bonding and mechanical properties, leading to more stable and durable paper. Birch fibers showed the highest increase in SR numbers, while Pine fibers, although more resilient, exhibited the least refinement response. Elevated pH conditions further enhanced fiber bonding and water retention across all species. These findings provide insights into optimizing fiber treatments for sustainable packaging materials.
  • Cobalt-free protective coatings for solid oxide stack components
    (2024-12-20) Silva Souza, Luiza
     School of Chemical Engineering | Master's thesis
    Ferritic stainless-steel (FSS) components used in solid oxide fuel cells (SOFCs) stack are rich in chromium content. During stack operating conditions, chromia scales (CrO3), otherwise beneficial for FSS protection, are formed on the component surface. This continuous growth of chromia scale becomes problematic when in contact to water vapour, forming volatile chromium species like CrO3(g) and CrO2(OH)2(g). These volatile species, released from the protective chromia layer, can migrate, and deteriorate the performance of the cathode. To address this issue, a protective conducting coating needs to be applied onto the ferritic interconnector (ICs). Most successful researched protective coatings are composed of conductive metal oxides containing cobalt, more specifically spinel-type (A,B)3O4, due to their high electrical conductivity and chemical/structural stability. While cobalt-based spinel coatings e.g., (Co,Mn)3O4 have been effective protecting SOFCs ICs from oxidation and corrosion, there is a demand for research alternative materials as a protective spinel coating (e.g., Mn-Fe, Mn-Cu), that can offer similar or improved performance without the use of cobalt. Previous work has indicated that highly doped spinels by various cations known as high entropy oxides (HEO) can contribute to better coating performance. This study investigates several cobalt-free coatings compositions, primarily focusing on manganese-based spinel systems doped with different elements such as Cu, Fe, Ni, Ce and Y. These coatings were deposited using thermal spray process onto ferritic stainless-steel substrate and evaluated for their microstructural integrity and ability to hinder the growth chromia scale layer and high temperature corrosion under single atmospheric oxidations (SAO) at 650℃ and double atmospheric oxidation (DAO) at 600℃ over 1000h. Although few coating experienced spallation and phase separation after extended testing, most maintained protective properties, withstanding the harsh operating conditions im-posed by thermal cycling and high-temperature exposure. The area specific resistance (ASR) results showed that most coatings demonstrated stable and low area specific resistance over time averaging results bellow 5 mΩ∙cm2.