Papers by Author: Janis Locs

Abstract: Hydrochar has already been applied directly or indirectly in various applications. It has electrochemical and catalytical properties, and can be used for sorption, ion exchange and complexing. It can also be applied as the CO₂ adsorbent, electrode material for supercapacitors and fuel cells, and as a fossil fuel. The studied hydrochar samples produced under different reaction times were chemically activated by NaOH. The obtained hydrochar samples pre-and post-activation were studied and compared depending on HTC reaction time.

Abstract: Osteoporosis is a chronic, metabolic and systemic skeletal disease characterized by low bone mineral density (BMD) and micro-architectural deterioration, resulting in increased bone fragility and fracture risk. Changes in the mineral structure occur due to aging or because of progressive pathologic processes such as osteoporosis, as well as in both aging and effects of bone diseases.

Abstract: A design of experiments based on the Taguchi method was used to evaluate the main parameters affecting the removal of textile dyes from aqueous solution. By using the adsorption capacity of textile dye as target response, several experiments were carried out using L₂₇ orthogonal array, and the higher-the-better as quality characteristics was applied. The controlling factors, including initial dye concentration, contact time and pH of solution were assessed. Analysis of variance (ANOVA) was used to determine the effects of each factor on the adsorption capacity. The optimum adsorption conditions giving higher adsorption capacity were selected as initial dye concentration of 500 mg.L^-1, contact time of 180 min and pH of solution of 2. The analysis results revealed that the most relevant factors affecting the adsorption process of textile dye are the initial dye concentration and pH of solution. After 3 cycles of thermal regeneration, the diatomite behavior did not change and more than 60 % of dye was eliminated from solution after regeneration at 600°C. From the obtained results, the Taguchi method was very successful to optimize of the adsorption parameters for maximum removal rate, and gives more credibility for industrial application.

Abstract: Variety of different bone substitutive materials are synthetized to improve bone healing potentials in pathological bone conditions. Physiologically active molecules within biomaterials, can initiate expression level of biomarkers, regulating bone remodeling. Aim of our study was to analyze bone healing process in bone defects followed by implantation with 5% strontium substituted hydroxyapatite (HAP) /tricalcium phosphate (TCP) 70/30 granules (group A) or HAP/TCP biphasic ceramic granules without strontium substitution (group B), or sham surgery affected bone (group C) in osteoporotic rabbits’ femur. Tissue samples from contralateral intact left leg were used for evaluation of systemic effects after surgery. Changes of bone volume were measured and appearance of OPG, NFkB-105, OC, COL-1, BMP-2/4, MMP-2, TIMP-2, IL-1 and IL-10-positive osteocytes in osteoporotic rabbits’ bone defect were evaluated. No statistical difference between groups of trabecular bone volume was detected. All analyzed markers showed higher appearance of positive osteocytes in groups A and B with comparison to control left leg (p<0.05). Only NFkB105-positive cells showed important difference between sham surgery affected leg and control one (p=0.034). Numerous OPG-positive cells appeared in group A, while moderate number of them was found in groups B and C (p=0.025; p=0.027). Numerous to abundant OC-positive osteocytes were detected in group A, while moderate in group C (p=0.034). Statistical difference of rest biomarkers between groups was not detected. We concluded that implantation of biomaterials in osteoporotic bone improves local bone regenerative properties. However, the notable increase of OPG-containing cells proves the increase of osteoclastogenesis suppression and gives the evidence for renew of bone functionality.

Abstract: Calcium phosphates are excellent biomaterial for hard tissue regeneration and replacement. Recently, nanohydroxylapatite (HAp) has been intensively studied as remineralization agent for tooth enamel protection and remineralization. In this research, we developed model toothpaste composition, determined viscosity and investigated weather different processed – spray-dried (spCDHAp), lyophilized (lyoCDHAp), wet precipitated (paste-like consistence, pCDHAp) – calcium deficient hydroxyapatite (CDHAp) affect bovine tooth enamel remineralization. Model toothpastes components were CDHAp, 2-hydroxyethylcelluloce, glycerol and water. Viscosity varied from 2.5 to 40 Pa∙s. Model toothpastes with 20 wt% CDHAp showed thixotropic behaviour, thereby we examined them as potential tooth remineralization pastes. After in vitro remineralization enamel surface changes were detected, the texture of demineralized surface and bundles of HAp crystals were not observed. It was suggested, that new calcium phosphate layer was formed on the enamel. In conclusion, CDHAp is very promising material for enamel regeneration, but different pretreatment of CDHAp (resulting as different morphology of agglomerates) did not give distinctive remineralization results.

Abstract: The present study focuses on the preparation and use of biosorbents produced from eggshells. Hen eggshells are produced as a by-product in large quantities by food manufacturers. The costs associated with eggshell disposal (mainly on landfill sites) are significant and expected to continue increasing as landfill taxes increase.The environmental significance of phosphorus arises from its role as a major nutrient for both plants and microorganisms. The adsorption efficiency of phosphate ions from the obtained biosorbents - raw eggshell powders - is studied at room temperature in static conditions. The effect of phosphate concentration and sorbent mass on the efficiency of the process is evaluated, as well as sorption kinetics are investigated. The structure, phase composition, porosity, specific surface area and morphology of obtained biosorbents is determined. The utilization of eggshells as an abundant, cheap and biodegradable material for the removal of phosphates is studied and discussed.

Abstract: Osteoporosis is a disease characterized with reduced density and quality of bone. Novel treatment strategies have been developed with the aim to inhibit excessive bone resorption and to increase bone formation. Strontium ranelate (SrRan), a novel orally active agent consisting of two atoms of stable strontium and the organic moiety ranelic acid, has proven drug ability to increase not only the bone mass but also mechanical properties. Despite the advantages it has been shown that systemic administration of SrRan can cause such side effects as diarrhea, hypersensitivity and myocardial infarction. Microencapsulation of SrRan could overcome the possible side effects from the systemic drug use as well as to increase its efficiency by local delivery of drug right to the affected bone site. Thus in the current research an attempt was made to prepare and characterize poly (lactic acid)/srontium ranelate microcapsules and to evaluate the drug interaction with the polymer during the microparticle formation.

Abstract: The addition of certain co-solvents to the hydrothermal synthesis starting solution can greatly alter morphology and enhance different morphology dependent properties of the synthesized material. While ethanol is the most common co-solvent used for the synthesis of various SnO₂ nano/microstructures by hydro/solvothermal process, it is not clear how the use of some other alcoholic co-solvents (for example, methanol or isopropanol) affect morphology and properties of SnO₂, especially if synthesis is done under similar conditions as in the case of ethanol co-solvent. In the present study, we investigated how the use of various alcoholic co-solvents (methanol, ethanol, 2-propanol, ethylene glycol and glycerol) affects crystal structure, morphology and specific surface area of the hydrothermally synthesized SnO₂. Additionally, sensitivity towards 100 ppm ethanol of the synthesized materials was tested. The formation of nanoparticles, rod-cluster structures and spherical SnO₂ structures were observed depending on the alcoholic co-solvent used. The highest sensitivity (~22 at 250 °C) showed the material that was synthesized in the presence of ethanol co-solvent.

Abstract: Amorphous and low crystalline calcium phosphates are prospective candidates for bone implant manufacturing. Amorphous calcium phosphate (ACP) preparation technologies could be improved in terms of specific surface area (SSA) of obtained products. Current study is dedicated to the effect of synthesis temperature and Ca and P molar ratios (Ca/P) on SSA of ACP. Higher SSA can improve bioactivity of biomaterials. ACP was characterized by XRD, FT-IR, SEM and BET N₂ adsorption techniques. Spherical nanoparticles (<45 nm in size) were obtained independently of initial Ca/P ratio and synthesis temperature. For the first time comparison of SSA was shown for ACP obtained at different temperatures (0 °C and 20 °C) and Ca/P molar ratios (1.5, 1.67 and 2.2).

Abstract: To target areas of the skeletal system which are clinically significant sites is a new strategy as the"local treatment of osteoporosis". Synthetic bioceramics implanted into critical sized bone defect of rats with experimental osteoporosis demonstrateds better effect to bone tissue repair in osteoporosis and/or osteoporosis status. Stem cell transplantation may improve bone mineral density in animal models of osteoporosis. An adequate blood supply of mesenchymal cells (MSCs and osteoprogenitors) is important for efficient bone regeneration. The concentration and quality of MSCs may vary significantly, depending on the individual (especially in older people), the cell obtaining sites and techniques used. Combination of BCP and stem cells are not studied on old experimental animals with double induced osteoporosis.