Browsing by Subject "stability"

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  • Mikkonen, Kirsi S. (2020)
    Wood biomass is an abundant renewable source of materials, but due to the accelerating depletion of natural resources, it is important to explore new ways to use it in a more sustainable manner. Modern technologies enable the recovery and valorization of the main components of wood—namely, cellulose, lignin, and hemicelluloses—contributing to sustainability. However, the method of isolation and resulting structure and purity of lignocellulosic materials determine their functionality and applicability. This review discusses the properties of all three main wood-based compounds that can stabilize emulsions, a class of industrial dispersions that are widely used in life science applications and chemicals. Due to the multi-billion-dollar annual market for hydrocolloids, the food, pharmaceutical, cosmetic, coating, and paint industries are actively seeking new sustainable emulsion stabilizers that fulfill the demanding requirements regarding safety and functionality. Wood-derived stabilizers facilitate various mechanisms involved in emulsion stabilization: (1) development of amphiphilic structures that decrease interfacial tension, (2) stabilization of interfaces by particles according to the Pickering theory, and (3) increase in the viscosity of emulsions’ continuous phase. This review presents pathways for treating cellulose, lignin, and hemicelluloses to achieve efficient stabilization and provides suggestions for their broad use in emulsions.
  • Ståhlberg, Jenny; Tuominen, Heta; Pulkka, Antti-Tuomas; Niemivirta, Markku (2021)
    In this study, we examined what kind of perfectionistic profiles (i.e., different patterns of perfectionistic strivings and concerns) can be identified among general upper‐secondary school students, how stable those profiles are over the school year, and how they are connected with students' motivation (i.e., achievement goal orientations). Four distinct profiles were identified. Students with high strivings and low concerns had their focus mainly on mastery, while students with an opposite profile emphasized performance‐avoidance and work‐avoidance orientations. Students with high strivings and concerns favored both performance‐ and mastery‐related goals, whereas students characterized by low strivings and low concerns did not display a dominant tendency toward any orientation. Perfectionistic profiles were relatively stable over time, with the majority of students reporting similar tendencies across the measurements, and with no extreme changes observed. Some indications of more students displaying less adaptive perfectionistic tendencies by the end of the school year were nevertheless found. Our findings demonstrate not only stability in perfectionistic tendencies, but also their motivational relevance in the academic context where students' goals and performance concerns play an important role.
  • Savolainen, Roosa (Helsingfors universitet, 2018)
    Liposomes are nano-sized vesicles in which the aqueous phase is surrounded by lipid-derived bilayer. They are excellent drug vehicles for example in ocular drug delivery because they can, among other things, increase the bioavailability and stability of the drug molecules and reduce their toxicity. Liposomes are known to be safe to use, because they degrade within a certain period of time and they are biocompatible with the cells and tissues of the body. Owing to its structure, the surface of liposomes can also be easily modified and functionalized. Light-activated ICG liposomes allow drug release in a controlled manner at a given time and specific site. Their function is based on a small molecule called indocyanine green (ICG) which, after being exposed to laser light, absorbs light energy and thereby locally elevates the temperature of the lipid bilayer. As a result, the drug inside is released into the surroundings. The blood circulation time of liposomes has often been prolonged by coating the liposomes with polyethylene glycol (PEG). Although PEG is generally regarded as a safe and biocompatible polymer, it has been found to increase immunological reactions and PEG-specific antibodies upon repeated dosing. Conversely, hyaluronic acid (HA), is an endogenous polysaccharide, which is present in abundance for instance in vitreous. Thus, it could serve as a stealth coating material which extends the otherwise short half-life of liposomes. One of the main objectives of this thesis was to find out whether HA could be used to coat liposomes instead of PEG. In order to prepare HA-coated liposomes, one of the lipid bilayer phospholipids, DSPE, had to be first conjugated with HA. For the conjugation, potential synthesis protocols were sought from the literature. Ultimately two different reductive amination-based protocols were tested. Consequently, the protocol in which the conjugation was achieved via the aldehyde group of HA, proved to be working. Thereafter, HA-coated liposomes were prepared by thin film hydration from the newly synthesised conjugate as well as DPPC, DSPC and 18:0 Lyso PC. Calcein was encapsulated in the liposomes. HA-covered liposomes were then compared with uncoated and PEGylated liposomes by examining their phase transition temperatures, ICG absorbances, sizes, polydispersities, and both light and heat-induced drug releases. The aforementioned tests were also conducted when the effects of the HA and ICG doubling were examined and the possibility to manufacture HA liposomes with small size was assessed. HA-liposomes showed similar results as PEG-coated liposomes. In addition, successful extrusion of HA-liposomes through a 30 nm membrane was also demonstrated in the results. Doubling of HA did not significantly affect the results. In contrast, increasing the molar amount of ICG by double caused spontaneous calcein leakage even before any heat or light exposure. Based on these findings, HA could work as a coating material instead of PEG, yet further studies are required for ensuring this conclusion. The other key objective was to evaluate the stability of four different formulations, named as AL, AL18, AL16 and AL14, in storage and biological conditions. Based on the differences in the formulation phospholipid composition, the assumption was that AL would be the most stable of the group and that the stability would decrease so that AL18 and AL16 would be the next most stable and eventually AL14 would be the least stable formulation. As in the previous study, the liposomes were prepared by thin film hydration with calcein being encapsulated inside the liposomes. In the storage stability test, liposomes were stored in HEPES buffer at either 4 °C or at room temperature for one month. In the test conducted in physiological conditions, the liposomes were added either to porcine vitreous or fetal bovine serum (FBS) and the samples were incubated at 37 ºC for five days. Regardless of the experiment, phase transition temperatures as well as light and heat-induced drug releases were initially measured. As the test progressed, calcein release, ICG absorbance, size, and polydispersity were measured at each time point. The initial measurements confirmed the hypothesis about the stability differences of tested formulations. In the storage stability test, all formulations, except AL14, appeared to be stable throughout the study and no apparent differences between the formulations or temperatures were observed. On the other hand, the stability of liposomes stored in biological matrices varied so that the liposomes were more stable in vitreous than in FBS and the stability decreased in both media as expected.
  • Palttala, Iida (Helsingfors universitet, 2010)
    Automated dose dispensing is an increasing field in which medicines are packaged mechanically into small one-dose pouches in portions of two weeks. Suitability of tablets for automated dose dispensing has not been researched systematically earlier. The study was made in collaboration with the dose dispensing unit of Espoonlahti pharmacy. The aim of the study was to define optimal characteristics for an automatically dispensed tablet from a viewpoint of the dose dispensing process to reduce breakings and transitions. Breaking means that tablet crumbles, splits up or breaks up otherwise during mechanical dose dispensing process. Transition means that tablet is dispensed in a wrong dose pouch. Percentually breakings and transitions occur very little, but quantitatively plenty and increasingly when automated dose dispensing is becoming more common. Breakings and transitions cause plenty extra work because of correcting pouches, so their amount should be aimed to reduce. In addition, the aim is to find out matters to enquire from the manufacturers of medicines that would help concluding whether a product is suitable for automated dose dispensing based on written information. Results of the study indicate that to reduce breakings and transitions, an optimal tablet product for dose dispensing is rather small or middle sized, coated, strong and without a breakline and the optimal relative humidity of air in the product room of dose dispensing unit would be around 30 - 40 %. Matters to enquire from the manufacturers of medicines besides size, coating, breaking strength and breakline are stability of the product outside of its original package and light, heat and moisture sensitiveness of the product. Besides breakings and transitions, also stability of a moisture sensitive acetylsalicylic acid product (Disperin 100 mg) was investigated in 25 °C/60 % RH because air humidity in the product room is not adjustable. Duration of the test was four weeks. It is enough since it is the maximum time that tablets are outside their original packages during drug dispensing process before use. Tablets were kept in opened original container (bottle), in closed original container, in cassette of dispensing machine and in two different dose pouches (new material and the one in use). According to the results, cassettes are protecting tablets from moisture as poorly as an opened bottle. Instead, new pouch material protects tablets better than the material in use. Results of Raman spectroscopy measurements indicate no change in acetylsalicylic acid to salicylic acid during four weeks test. Moisture affects to tablets by decreasing breaking strength, which may cause more breakings. Air humidity should be adjusted in product rooms or tablets should be unpacked into cassettes as near operating the machine as possible to prevent breakings. Especially when air humidity is high. Among others, a heat sensitive drug product was researched because of the seaming unit of dose dispensing machine which is radiating heat of about 75 °C to pouches if machine is pulled over in the middle of work. Study was performed with variable temperature XRPD. Results of the study of heat sensitiveness indicate that 75 °C for 60 minutes doesn't induce changes in carbamazepine tablet (Neurotol 200 mg). However, results of the study reveal that researched product did not contain the most heat sensitive form of carbamazepine, so other heat sensitive drug products should be examined to get more information about effects of heat.
  • Yan, Zhi-Yong; Cheng, De-Jie; Liu, Ling-Zhi; Geng, Chao; Tian, Yan-Ping; Li, Xiang-Dong; Valkonen, Jari P. T. (2021)
    Coat proteins (CPs) play critical roles in potyvirus cell-to-cell movement. However, the underlying mechanism controlling them remains unclear. Here, we show that substitutions of alanine, glutamic acid, or lysine for the conserved residue tryptophan at position 122 (W-122) in tobacco vein banding mosaic virus (TVBMV) CP abolished virus cell-to-cell movement in Nicotiana benthamiana plants. In agroinfiltrated N. benthamiana leaf patches, both the CP and RNA accumulation levels of three W-122 mutant viruses were significantly reduced compared with those of wild-type TVBMV, and CP accumulated to a low level similar to that of a replication-deficient mutant. The results of polyprotein transient expression experiments indicated that CP instability was responsible for the significantly low CP accumulation levels of the three W-122 mutant viruses. The substitution of W-122 did not affect CP plasmodesmata localization or virus particle formation; however, the substitution significantly reduced the number of virus particles. The wild-type TVBMV CP could complement the reduced replication and abolished cell-to-cell movement of the mutant viruses. When the codon for W-122 was mutated to that for a different aromatic residue, phenylalanine or tyrosine, the resultant mutant viruses moved systemically and accumulated up to 80% of the wild-type TVBMV level. Similar results were obtained for the corresponding amino acids of W-122 in the watermelon mosaic virus and potato virus Y CPs. Therefore, we conclude that the aromatic ring in W-122 in the core domain of the potyviral CP is critical for cell-to-cell movement through the effects on CP stability and viral replication.