Riga Technical University
Recent publications
Background: Acute ischemic stroke is one of the leading causes of disability and mortality globally, with increasing incidence in Africa, as the continent is already burdened with infectious diseases. Rapid diagnosis and efficient treatment are crucial, as even a slight delay to reperfuse the brain significantly affects the recovery outcome. Neuroimaging is vital for optimal care and thrombolytic or endovascular therapy in specialised stroke care units. This review aims to discuss the burden of acute ischemic stroke in Africa and how healthcare systems have tried to reduce the incidence and improve outcomes for the disease. Methodology: Data was collected from online databases and medical journal published on PubMed, Ovid MEDLINE, ScienceDirect and Embase bibliographical data. All articles related to acute ischemic stroke in Africa were considered. Results: The medical care for acute ischemic stroke in Africa is far from optimal with little adherence to recommended protocols. There is a lack of public awareness of the disease, imaging infrastructure, personnel, stroke care units and recovery facilities, due to poor funding. Poor knowledge of stroke signs and symptoms results in delay in treatment and poor prognosis. Conclusion: We urge African leaders and private entities to invest in stroke care by building appropriate infrastructures, providing medical equipments, implementing guidelines, and sustainable follow-up systems. Telehealth is a suggested strategy to mitigate the scarcity of health personnel, and international and national efforts to increase treatment affordability should be doubled. Further extensive research on the impact of acute ischemic stroke on the African continent population is encouraged.
Out of the wide range of calcium phosphate (CaP) biomaterials, calcium phosphate bone cements (CPCs) have attracted increased attention since their discovery in the 1980s due to their valuable properties such as bioactivity, osteoconductivity, injectability, hardening ability through a low-temperature setting reaction and moldability. Thereafter numerous researches have been performed to enhance the properties of CPCs. Nonetheless, low mechanical performance of CPCs limits their clinical application in load bearing regions of bone. Also, the in vivo resorption and replacement of CPC with new bone tissue is still controversial, thus further improvements of high clinical importance are required. Bioactive glasses (BGs) are biocompatible and able to bond to bone, stimulating new bone growth while dissolving over time. In the last decades extensive research has been performed analyzing the role of BGs in combination with different CaPs. Thus, the focal point of this review paper is to summarize the available research data on how injectable CPC properties could be improved or affected by the addition of BG as a secondary powder phase. It was found that despite the variances of setting time and compressive strength results, desirable injectable properties of bone cements can be achieved by the inclusion of BGs into CPCs. The published data also revealed that the degradation rate of CPCs is significantly improved by BG addition. Moreover, the presence of BG in CPCs improves the in vitro osteogenic differentiation and cell response as well as the tissue-material interaction in vivo.
The environmental and climate crisis is gaining priority among critical human concerns; therefore, environmental knowledge and sustainable solutions play a significant role and gaining global popularity as an academic discipline. Additionally, United Nations Sustainable Development Goal no. 4 acknowledges education's role in promoting sustainable development, sustainable lifestyles, human rights, social responsibility, circular economy, and greening our economy and society. In this paper new conceptual framework that focuses on systematically analyzing environmental sustainability integration in study programs and subjects is developed. The main aim is to reflect the conceptual basis of education related to environmental sustainability topics such as sustainable development, social responsibility, circular economy, ecology, environmental protection, and greening to boost future environmental management practices in industry and services. Defining the level of integration of environmental and sustainability-related topics is divided by research field classification and study cycles (BSc, MSc, PhD). The specific added value of the developed conceptual framework is reflected by defining cross-sections and inter-and trans-disciplinary of sustainability topics integrated within specific programs and subjects. The conceptual framework was tested by assessing 1051 programs in progress in Slovenia. It was revealed that the highest share of study programs has an intermediate level of environmental sustainability with 2–3 subjects (392 study programs). These are represented mainly by integrating environmental protection, ecology, and “greening” but less with circular economy and social responsibility. Significant differences among specific study programs and study fields reflect that young intellectuals will not be equally educated and qualified for future managerial challenges. Master students gain the best insight into core sustainability and environmental topics needed for future environmental managers.
Amidst an ever-increasing demand for the enhancement of the lifestyle and the modulation of modern diseases, the functionalization of biomaterials is of utmost importance. One of the leading materials for the aforementioned purpose have been calcium phosphates (CaPs). They have been widely used in bone regeneration displaying favourable regenerative potential and biological properties. Many studies have placed their entire focus on facilitating the osteogenic differentiation of stem cells and bone progenitor cells, while the aspect of antibacterial properties has been surmounted. Nevertheless, increasing antibiotic resistance of bacteria requires the development of new materials and the usage of alternative approaches such as ion doping. Gallium (Ga) has been the potential star on the rise among the ions. However, the obstacle that accompanies gallium is the scarcity of research performed and the variety of amalgamations. The question that imposes itself is how a growing field of therapeutics can be further entwined with advances in material science, and how will the incorporation of gallium bring a new outlook. The present study offers a comprehensive overview of state-of-the-art gallium containing calcium phosphates (GaCaPs), their synthesis methods, antibacterial properties, and biocompatibility. Considering their vast potential as antibacterial agents, the need for a methodical perspective is highly necessary to determine if it is a direction on the brink of recognition or a fruitless endeavour. Statement of Significance : Although several studies have been published on various metal ions-containing calcium phosphates, to this date there is no systematic overview pointing out the properties and benefits of gallium containing calcium phosphates. Here we offer a critical overview, including synthesis, structure and biological properties of gallium containing calcium phosphates.
Targeted drug delivery systems using nanocarriers offer a versatile platform for breast cancer treatment; however, a robust, CD44-targeted niosomal formulation has not been developed and deeply studied (both in vitro and in vivo) yet. Here, an optimized system of epirubicin (Epi)-loaded niosomal nanoparticles (Nio) coated with hyaluronic acid (HA) has been engineered for targeting breast cancer cells. The nanoformulation was first optimized (based on size, polydispersity index, and entrapment efficiency); then, we characterized the morphology, stability, and release behavior of the nanoparticles. Epirubicin release from the HA-coated system (Epi-Nio-HA) showed a 21% (acidic buffer) and 20% (neutral buffer) reduction in comparison with the non-coated group (Epi-Nio). The cytotoxicity and apoptosis results of 4T1 and SkBr3 cells showed an approximately 2-fold increase in the Epi-Nio-HA system over Epi-Nio and free epirubicin, which confirms the superiority of the engineered nanocarriers. Moreover, real-time PCR data demonstrated the down-regulation of the MMP-2, MMP-9, cyclin D, and cyclin E genes expression while caspase-3 and caspase-9 gene expression were up-regulated. Confocal microscopy and flow cytometry studies uncovered the cellular uptake mechanism of the Epi-Nio-HA system, which was CD44-mediated. Furthermore, in vivo studies indicated Epi-Nio-HA decreased mice breast tumor volume by 28% (compared to epirubicin) without side effects on the liver and kidney. Conclusively, our results indicated that the HA-functionalized niosomes provide a promising nanoplatform for efficient and targeted delivery of epirubicin to potentially treat breast cancer.
Heavy metals (HM) toxicity is becoming a major threat to living organisms in recent years due to the increase in population and anthropogenic activities. Lead (Pb) shares about 10% of total pollution produced by heavy metals. The uptake of lead by the primary producers (plants) is found to affect their metabolic functions, growth, and photosynthetic activity. The accumulation of lead in excess can cause up to a 42% reduction in the growth of the roots. The current review addresses the global status of lead contamination in soil, potential lead sources, and the mechanism of lead uptake by the plants. This article also provides information about the lead concentration in plants in polluted and non-polluted areas. Humans are directly or indirectly dependent on plants to meet their daily requirements. So, it becomes necessary to review the problems associated with lead pollution in plants and its mode of action affecting the plant system. Factors like bioaccumulation, bioavailability, bioconcentration, transfer factor, and the role of Casparian strips as a natural physical barrier are discussed. Further, the updated literature survey about the various bioremediation strategies utilized for its elimination is also presented. The current study suggests that more attention needs to be focused on evaluating the effectiveness of bioremediation methods.
During the last decade new models for bending stiffness prediction of damaged composite laminates have been proposed in the literature advancing the earlier developed engineering approaches in accuracy and in complexity. However, experimental data for validation of complex analytical or engineering models are almost non-existent in the literature. In the present work a detailed experimental study was performed to investigate the bending stiffness reduction of composite cross-ply laminates with evolving micro-damage. Intralaminar cracks and local delaminations in the bottom surface 90-degree layer of carbon/epoxy and glass/epoxy cross-ply laminates were introduced in 4-point bending tests. Digital Image correlation (DIC) technique was used to experimentally determine the midplane curvature. The accuracy of beam theory for bending stiffness determination was assessed. The measured bending stiffness reduction with respect to transverse crack density was also compared with FEM predictions. The results show that the beam theory gives slightly underestimated curvature at low deflections, whereas at large deflections the beam theory overestimates the curvature and the moment–curvature relation becomes nonlinear. Nevertheless, the overall agreement between beam theory and DIC-based results is still very good, which leads to conclude that beam theory based data reduction schemes have sufficient accuracy for predicting bending stiffness even for highly damaged laminates.
Residual strains and shape distortions in a polymer-based composite structure may depend on the cure schedule used for manufacture. Aiming to understand the cure history effects, the influence of the curing “path” (time [Formula: see text] and temperature [Formula: see text] path during curing) on viscoelastic (VE) response of a fully cured (FC) ([Formula: see text] = 0.992) epoxy was investigated. Five different “families” of the same epoxy were manufactured in constraint-free conditions using different sets of curing parameters. Then, tensile tests were performed at different temperatures (T = 30 to 110 °C), and the time–temperature superposition principle (TTSP) and Schapery’s type of linear viscoelastic (VE) model, accounting for physical aging of specimens tested at high temperature, were used. The results show that the VE properties of the studied epoxy are independent of the curing history provided that at the end all specimens are fully cured. Also, the physical aging rate at high temperatures of all “families” is the same and it can be described by a simple aging-temperature independent equation reported in Nunes et al. ¹ It is expected that curing history of unconstrained and fully cured epoxy has an insignificant effect on final viscoelastic behavior, a knowledge which could assist in developing more time and cost-efficient cure cycles.
A simple three-step approach for the synthesis of substituted N7-arylpurines with an overall yield of the whole sequence from 40% to 71% is described. N7-Arylpurines were constructed by de novo synthesis from commercially available substituted 4-chloropyrimidine-5-amines. Different substituents at purine C2 and C6 were obtained by changing the corresponding substituents of the starting pyrimidine. Further, heteroaromatic, electron-deficient and electron-rich aromatic groups were attached to the exocyclic amino group by iodane reagents under copper catalysis. This moiety is prepared to become purine N7 position after the ring closure. Finally, purine C8 substitution was varied during the last step of the developed sequence by employing different reagents for the purine ring closing reactions or post functionalization.
The article discusses the possible ways to change and develop t-shirt patterns by applying methods of zero and less waste design - by assessing the manifestation of the reduction from the cut-off fabric in the cut and sew production system at the pre-consumer stage. The main research focus is on a classical T-shirt that generates 15% and could reach up to 25% pre-consumer waste when producing mass production, batch, or individual garments. To research T-shirt optimization possibilities, sources were gathered from existing zero and less waste patterns from practising designers. Through practical research, samples were analysed and compared to maintain the T-shirt's function, aesthetical requirements, and fit.
In the European Union, only 1% of the building stock is renovated every year. According to the EU strategy, around 75% of the existing building stock needs to be renovated by 2050. Energy efficiency programs mainly support residential and public building stocks; this article considers military dormitories as a type of unclassified building. It is very important to improve energy efficiency to reduce energy consumption and improve the microclimate in these buildings, since the staff is there 24/7. This paper analyzes the energy consumption and measures the indoor air quality in 13 nonrenovated military dormitories. The personnel in unclassified buildings have limited options for remote work in the case of COVID-19 outbreak. Thus, the retrofitting and maintenance of such buildings must be planned carefully. There is a significant lack of IAQ measurements in unclassified buildings. This study presents a wide analysis of energy consumption, indoor air parameters, and occupant satisfaction. On the basis of real data, four retrofitting scenarios were evaluated in IDA ICE dynamic simulation software. The simulation results showed that, in the case of a deep renovation scenario, the theoretical energy savings could be 77.6–79.3% of the used energy. This paper discusses the solar energy potential of onsite energy production for increasing the efficiency and energy supply resilience of unclassified buildings. The results of this study can be applied to other countries with climate conditions similar to Latvia.
The aim of this study was to investigate the change in clindamycin phosphate antibacterial properties against Gram-positive bacteria using the platelet-rich fibrin as a carrier matrix, and evaluate the changes in the antibiotic within the matrix. The antibacterial properties of CLP and its combination with PRF were tested in a microdilution test against reference cultures and clinical isolates of Staphylococcus aureus (S. aureus) or Staphylococcus epidermidis (S. epidermidis). Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) analysis was done to evaluate the changes in the PRF_CLP matrix. Release kinetics of CLP was defined with ultra-performance liquid chromatography (UPLC). According to FTIR data, the use of PRF as a carrier for CLP ensured the structural changes in the CLP toward a more active form of clindamycin. A significant decrease in minimal bactericidal concentration values (from 1000 µg/mL to 62 µg/mL) against reference cultures and clinical isolates of S. aureus and S. epidermidis was observed for the CLP and PRF samples if compared to pure CLP solution. In vitro cell viability tests showed that PRF and PRF with CLP have higher cell viability than 70% after 24 h and 48 h time points. This article indicates that CLP in combination with PRF showed higher antibacterial activity against S. aureus and S. epidermidis compared to pure CLP solution. This modified PRF could be used as a novel method to increase drug delivery and efficacy, and to reduce the risk of postoperative infection.
An alternative method for the biodiesel or fatty acid alkyl ester (FAAE) synthesis has been proposed—rapeseed oil interesterification with methyl formate. Reaction with methyl formate proceeds at a relatively low temperature (28 °C) instead of 55–65 °C necessary for triglyceride reactions with methanol and other monoesters. Similarly to transesterification with methanol, the product of the reaction with methyl formate consists of two layers. The main product the fatty acid methyl ester (FAME) is located in the top layer, but the process by-product formins forms the bottom layer. In this work, solutions of potassium alkoxides (methoxide, ethoxide, isopropoxide, tert-butoxide) in appropriate alcohols as homogeneous catalysts were used, adhering to the catalyst to oil molar ratio (COMR) 0.1 and methyl formate to oil molar ratio (MFOMR) 18. The FAAE content in the biodiesel layer in presence of all catalysts was 77–81 wt.%, which is lower than the level required by the EN14214 but significantly higher than the FAME content in reactions with methyl acetate under the same conditions. Fuel properties such as flash point, carbon residue, density, viscosity, and cold flow properties were investigated. For samples with MFOMR equal to or higher than 36 FAAE exceed 93% and the main characteristics of samples correspond to the EN14214 limits even without product purification.
Microplastics are one of the major contaminants of aquatic nature where they can interact with organic and inorganic pollutants, including trace metals, and adsorb them. At the same time, after the microplastics have entered the aquatic environments, they are quickly covered with a biofilm - microorganisms which are able to produce extracellular polymeric substances (EPS) that can facilitate sorption of trace metals from surrounding water. The microbial community of biofilm contains bacteria which synthesizes EPS with antimicrobial activity making them more competitive than other microbial inhabitants. The trace metal trapping by bacterial EPS can inhibit the development of certain microorganisms, therefore, a single microparticle participates in complex interactions of the diverse elements surrounding it. The presented review aims to consider the variety of interactions associated with the adsorption of trace metal ions on the surface of microplastics covered with biofilm, the fate of such microplastics and the ever-increasing risk to the environment caused by the combination of these large-scale pollutants - microplastics and trace metals. Since aquatic pollution problems affect the entire planet, strict regulation of the production, use, and disposal of plastic materials is needed to mitigate the effects of this emerging pollutant and its complexes could have on the environment and human health.
Despite the bone ability of self-regeneration, large bone defects require surgical intervention. Likewise, when it comes to osteoporotic bone fractures, new approaches should be considered a supportive mechanism for the surgery. In recent years, more and more attention has been attracted to advanced drug delivery systems for local osteoporosis treatment, combining appropriate biomaterials with antiosteoporotic drugs, allowing simultaneously to regenerate the bone and locally treat the osteoporosis. Within the current research, hyaluronic acid/strontium ranelate (HA/SrRan), HA/calcium phosphate nanoparticles (HA/CaP NPs), and HA/CaP NPs/SrRan hydrogels were prepared. The effect of CaP and SrRan presence in the composites on the swelling behavior, gel fraction, molecular structure, microstructure, and SrRan and Sr2+ release, as well as in vitro cell viability was evaluated. Obtained results revealed that the route of CaP nanoparticle incorporation into the HA matrix had a significant effect on the hydrogel gel fraction, rheological properties, swelling behavior, and microstructure. Nevertheless, it had a negligible effect on the release kinetics of SrRan and Sr2+. The highest cell (3T3) viability (>80%) was observed for HA hydrogels, with and without SrRan. Moreover, the positive effect of SrRan on 3T3 cells was also demonstrated, showing a significant increase (up to 50%) in cell viability if the used concentrations of SrRan were in the range of 0.05–0.2 μg/ml.
Acrylic resins have various applications, which range from coatings to 3D printing, among others. Following green chemistry and environmental preservation trends, the demand for bio-based acrylic resins is growing. Vegetable oil-based resins have arisen to meet the present challenge. However, the performance and tuning of sustainable resin properties still need improvement. Hence, we undertook this study to research tuneable and durable vegetable oil-based UV-curing composite resins. This work reports on vegetable oil-based resin loaded with lignocellulosic components of cellulose nanocrystals (CNC), cellulose nanofibres (CNF), hemicellulose (HC), and lignin (LN). The effects of lignocellulosic components on thermal stability, thermomechanical properties, transparency, surface morphology, and wettability were evaluated in detail. In addition, the interaction of lignocellulosic components with the polymer matrix and interface was thoroughly investigated. The intense interaction between lignocellulosic components and the polymer matrix helps to form a strong interface and creates a polymer composite with enhanced thermomechanical properties. The composite surface morphology and wettability can be tuned depending on the lignocellulosic component, i.e., with the addition of HC, CNC, and CNF. Hydrophilic affinity is improved and water wetting angles as low as 8° can be achieved, but with LN a value of 96° was observed, a slight increase in hydrophobicity compared to the vegetable oil (VO) matrix value of 90°. Adding HC and CNC reduced transparency at 500 nm by 14 and 16%, while adding LN and CNF by 18 and 25%, respectively. Fourier-transform infrared spectroscopy revealed strong interfacial interactions through the hydrogen bonding between CNC, CNF, HC, and the VO polymer. This work will shed light on the lignocellulosic components' future role in UV-curing resin applications. It also broadens lignocellulosic particles' application as reinforcing additives for UV-light sensitive polymeric resins.
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2,692 members
Talis Juhna
  • Institute of Heat, Gas, and Water Technology & Head of Water Research and Environmetal Biotehnology Laboratory
Sabīne Upnere
  • Faculty of Mechanical Engineering, Transport and Aeronautics
Dmitry Pikulin
  • Faculty of Electronics and Telecommunications (FET)
Gundars Mezinskis
  • Institute of Materials and Surface Enginering
Maris Knite
  • Institute of Technical Physics, Faculty of Materials Science and Applied Chemistry
Riga, Latvia