Browsing by Department "University of Eastern Finland"

Filter results by typing the first few letters
Now showing 1 - 8 of 8
  • Cellulose fiber and nanofibril characteristics in a continuous sono-assisted process for production of TEMPO-oxidized nanofibrillated cellulose
    (2022-11) Levanič, Jaka; Svedström, Kirsi; Liljeström, Ville; Šernek, Milan; Osojnik Črnivec, Ilja Gasan; Poklar Ulrih, Nataša; Haapala, Antti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A hardwood dissolving pulp and bleached softwood Kraft pulp were subjected to continuous ultrasonic cavitation assisted TEMPO-mediated oxidation. The effects of such processing on the yield of carboxylic groups, morphological changes of the fibers as well as the effects on the final nanocellulose dispersion were studied. Ultrasonic cavitation in the TEMPO-mediated oxidation phase enhanced the yield of carboxylic groups on both pulps while having a negligible effect on materials losses due to fiber fines formation. The effect of ultrasonic cavitation was purely mechanical and acted as an additional high-shear mixer in the pre-treatment phase. As a result, the morphological changes on the fibers were enhanced, with additional swelling and fiber straightening being observed. Furthermore, the ultrasonic cavitation also influenced the properties of the nanocellulose dispersion obtained from subsequent microfluidization. The sonicated samples exhibited higher optical clarity, higher elasticity in gels while also having somewhat lower viscosities. On nanoscale, ultrasonic cavitation helped the subsequent microfluidization in releasing better individualized nanofibrils as they had smaller diameters than in non-sonicated samples. Sonication also had no effect on the crystallinity properties of the nanocellulose, the observed slight reduction was a result of intense microfluidization that was used to produce the nanocellulose dispersion. Ultrasonic cavitation in the TEMPO-oxidized pre-treatment phase was shown to be a method that can increase the throughput in lab-scale by mechanical activation of pulps and enabling shorter processing times for TEMPO-mediated oxidation. Graphical abstract: [Figure not available: see fulltext.].
  • The effect of paired associative stimulation with a high-intensity cortical component and a high-frequency peripheral component on heart rate and heart rate variability in healthy subjects
    (2023-07-26) Haakana, P.; Holopainen, K.; Nätkynmäki, A.; Kirveskari, E.; Tarvainen, M. P.; Shulga, A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Objective: A novel protocol for paired associative stimulation (PAS), called high PAS, consists of high-intensity transcranial magnetic stimulation (TMS) and high-frequency peripheral nerve stimulation (PNS). High PAS was developed for spinal cord injury rehabilitation and targets plastic changes in stimulated pathways in the corticospinal tract, which improves motor function. As therapy interventions can last many weeks, it is important to fully understand the effects of high PAS, including its effect on the cardiovascular system. Heart rate variability (HRV) has been used to measure changes in both sympathetic and parasympathetic systems. Methods: We used short-term HRV measurements to evaluate the effects of one 20-min session of high PAS on 17 healthy individuals. HRV was recorded for 5 min before (PRE), during (STIM), immediately after (POST), 30 min after (POST30), and 60 min after (POST60) the stimulation. Five participants repeated the HRV setup with sham stimulation. Results: A significant decrease in low-frequency (LF) power (n.u.) (p = 0.002), low-frequency to high-frequency (HF) ratio (p = 0.017), in Poincaré plot [the standard deviation of RR intervals perpendicular to (SD1) and along (SD2) the line of identity SD2/SD1 ratio p < 0.001], and an increase in HF power (n.u.) (p = 0.002) were observed between PRE and STIM conditions; these changes were fully reversible immediately after stimulation. PRE to POST by 3% (p = 0.015) and continued to decline until POST60 by 5% (p = 0.011). LF power (ms2) (p = 0.017) and SD2 (p = 0.015) decreased from PRE to STIM and increased from PRE to POST (p = 0.025 and p = 0.017, respectively). The results from sham PAS exhibited a trend similar to active high-PAS stimulation. Conclusions: High PAS does not have sustained effects during 60-min follow-up on cardiovascular functions, as measured by HRV. None of the short-term results indicates activation of the sympathetic nervous system in healthy individuals. Observed changes in HRV indicate higher parasympathetic activity during stimulation, which is reversible, and is plausibly explained by the fact that the participants spend 20 min without moving, talking, or using phones while being stimulated.
  • Overexpression of VEGF-B alters cardiac lipid metabolism and predisposes to heart failure
    (2022) Tirronen, Annakaisa; Huusko, Jenni; Lehtonen, Marko; Hämäläinen, Wilhelmiina; Hokkanen, Krista; Auriola, Seppo; Ylä-Herttuala, Seppo
     Meeting Abstract
  • Recovery of nitrogen and phosphorus from human urine using membrane and precipitation process
    (2019-10-01) Pradhan, Surendra K.; Mikola, Anna; Heinonen-Tanski, Helvi; Vahala, Riku
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The nitrogen (N) and phosphorus (P) contents in human urine have been recovered using struvite precipitation and N-stripping techniques. Struvite precipitation technique recovers mainly phosphorus whereas N-stripping technique only recovers nitrogen. In this study, we developed an NPharvest technique which recovered both nitrogen and phosphorus separately in the same process, enabling their use independently. The technique used Ca(OH)2 to increase the pH of urine converting ammonium into NH3 gas and simultaneously precipitating P with Ca. The NH3 gas is passed through a gas permeable hydrophobic membrane (GPHM) and reacts with H2SO4 forming ammonium sulfate. Our result showed that more than 98% (w/w) of N and P can be harvested from urine in 8 h at 30 °C. The harvested ammonium sulfate contained 19% (w/w) N, and the sediment contained 1–2% (w/w) P. The extraction of N and P from 1 m3 of urine could give a profit of 1.5 €.
  • SERS Activity of Photoreduced Silver Chloride Crystals
    (2020) Dutta, Arpan; Matikainen, Antti; Andoh, Sampson; Nuutinen, Tarmo
     Conference article in proceedings
    Metal nanoparticles are widely acclaimed as plasmonic substrates for surface -enhanced Raman spectroscopy (SERS) due to their unique particle plasmon resonances at visible and near infrared regions. Silver nanoparticles are typically employed in SERS when the targeted Raman signature zone of analytes lies at ultra-violet and/or blue to green spectral regimes. Even though silver has strong plasmonic properties, silver-based substrates are often affected by the atmospheric oxidation and show degradation in their SERS performance. One way to overcome this limitation is to use silver chloride crystals as oxidation resistant intermediate and photoreduce them to 'fresh' silver just before SERS analysis. In this work, we study the SERS activity of the photoreduced silver chloride crystals. We perform Raman analysis of three Raman active analytes, adenine, rhodamine 6G and riboflavin at both visible (514 nm) and near-infrared (785 nm) excitations. Our experimental outcomes show that such photoreduced silver chloride crystals can be exploited as SERS active substrates for both visible and near-infrared applications. Our numerical simulations reveal that these photoreduced silver chloride crystals are strong scatterers at multiple wavelengths and hence, could be very useful for plasmon-enhanced spectroscopic applications where multiple wavelengths are involved.
  • Simultaneous investigation of the liquid transport and swelling performance during tablet disintegration
    (2020-06-30) Al-Sharabi, Mohammed; Markl, Daniel; Mudley, Theona; Bawuah, Prince; Karttunen, Anssi Pekka; Ridgway, Cathy; Gane, Patrick; Ketolainen, Jarkko; Peiponen, Kai Erik; Rades, Thomas; Zeitler, J. Axel
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Fast disintegrating tablets have commonly been used for fast oral drug delivery to patients with swallowing difficulties. The different characteristics of the pore structure of such formulations influence the liquid transport through the tablet and hence affect the disintegration time and the release of the drug in the body. In this work, terahertz time-domain spectroscopy and terahertz pulsed imaging were used as promising analytical techniques to quantitatively analyse the impact of the structural properties on the liquid uptake and swelling rates upon contact with the dissolution medium. Both the impact of porosity and formulation were investigated for theophylline and paracetamol based tablets. The drug substances were either formulated with functionalised calcium carbonate (FCC) with porosities of 45% and 60% or with microcrystalline cellulose (MCC) with porosities of 10% and 25%. The terahertz results reveal that the rate of liquid uptake is clearly influenced by the porosity of the tablets with a faster liquid transport observed for tablets with higher porosity, indicating that the samples exhibit structural similarity in respect to pore connectivity and pore size distribution characteristics in respect to permeability. The swelling of the FCC based tablets is fully controlled by the amount of disintegrant, whereas the liquid uptake is driven by the FCC material and the interparticle pores created during compaction. The MCC based formulations are more complex as the MCC significantly contributes to the overall tablet swelling. An increase in swelling with increasing porosity is observed in these tablets, which indicates that such formulations are performance-limited by their ability to take up liquid. Investigating the effect of the microstructure characteristics on the liquid transport and swelling kinetics is of great importance for reaching the next level of understanding of the drug delivery, and, depending on the surface nature of the pore carrier function, in turn controlling the performance of the drug mainly in respect to dissolution in the body.
  • Spatial extent of cortical motor hotspot in navigated transcranial magnetic stimulation
    (2020-12-01) Reijonen, Jusa; Pitkänen, Minna; Kallioniemi, Elisa; Mohammadi, Ali; Ilmoniemi, Risto J.; Julkunen, Petro
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Background: Motor mapping with navigated transcranial magnetic stimulation (nTMS) requires defining a “hotspot”, a stimulation site consistently producing the highest-amplitude motor-evoked potentials (MEPs). The exact location of the hotspot is difficult to determine, and the spatial extent of high-amplitude MEPs usually remains undefined due to MEP variability and the spread of the TMS-induced electric field (E-field). Therefore, here we aim to define the hotspot as a sub-region of a motor map. New method: We analyzed MEP amplitude distributions in motor mappings of 30 healthy subjects in two orthogonal directions on the motor cortex. Based on the widths of these distributions, the hotspot extent was estimated as an elliptic area. In addition, E-field distributions induced by motor map edge stimulations were simulated for ten subjects, and the E-field attenuation was analyzed to obtain another estimate for hotspot extent. Results: The median MEP-based hotspot area was 13 mm2 (95% confidence interval (CI) = [10, 18] mm2). The mean E-field-based hotspot area was 26 mm2 (95% CI = [13, 38] mm2). Comparison with existing methods: In contrast to the conventional hotspot, the new definition considers its spatial extent, indicating the most easily excited area where subsequent nTMS stimuli should be targeted for maximal response. The E-field-based hotspot provides an estimate for the extent of cortical structures where the E-field is close to its maximum. Conclusions: The nTMS hotspot should be considered as an area rather than a single qualitatively defined spot due to MEP variability and E-field spread.
  • Surface-enhanced Raman spectroscopy of organic molecules and living cells with gold-plated black silicon
    (2020-11-11) Golubewa, Lena; Karpicz, Renata; Matulaitiene, Ieva; Selskis, Algirdas; Rutkauskas, Danielis; Pushkarchuk, Aliaksandr; Khlopina, Tatsiana; Michels, Dominik; Lyakhov, Dmitry; Kulahava, Tatsiana; Shah, Ali; Svirko, Yuri; Kuzhir, Polina
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Black silicon (bSi) refers to an etched silicon surface comprising arrays of microcones that effectively suppress reflection from UV to near-infrared (NIR) while simultaneously enhancing the scattering and absorption of light. This makes bSi covered with a nmthin layer of plasmonic metal, i.e., gold, an attractive substrate material for sensing of bio-macromolecules and living cells using surface-enhanced Raman spectroscopy (SERS). The performed Raman measurements accompanied with finite element numerical simulation and density functional theory analysis revealed that at the 785 nm excitation wavelength, the SERS enhancement factor of the bSi/Au substrate is as high as 108 due to a combination of electromagnetic and chemical mechanisms. This finding makes the SERS-active bSi/Au substrate suitable for detecting trace amounts of organic molecules. We demonstrate the outstanding performance of this substrate by highly sensitive and specific detection of a small organic molecule of 4-mercaptobenzoic acid and living C6 rat glioma cell nucleic acids/proteins/lipids. Specifically, the bSi/Au SERS-active substrate offers a unique opportunity to investigate the living cells' malignant transformation using characteristic protein disulfide Raman bands as a marker. Our findings evidence that bSi/Au provides a pathway to the highly sensitive and selective, scalable, and low-cost substrate for lab-on-a-chip SERS biosensors that can be integrated into silicon-based photonics devices.