One of the blends that is usable for 3D printing while not being toxic to cell cultures is the lactic acid (PLA)/polyhydroxybutyrate (PHB)/thermoplastic starch (TPS) blend. The addition of plasticizers can change the rate of biodegradation and the biological behavior of the material. In order to evaluate the potential of the PLA/PHB/TPS material in combination with additives (plasticizers: acetyl tributyl citrate (ATBC) and oligomeric lactic acid (OLA)), for use in the field of biomedical tissue engineering, we performed a comprehensive in vitro characterization of selected mixture materials. Three types of materials were tested: I: PLA/PHB/TPS + 25% OLA, II: PLA/PHB/TPS + 30% ATBC, and III: PLA/PHB/TPS + 30% OLA. The assessment of the biocompatibility of the materials included cytotoxicity tests, such as monitoring the viability, proliferation and morphology of cells and their deposition on the surface of the materials. The cell line 7F2 osteoblasts (Mus musculus) was used in the experiments. Based on the test results, the significant influence of plasticizers on the material was confirmed, with their specific proportions in the mixtures. PLA/PHB/TPS + 25% OLA was evaluated as the optimal material for biocompatibility with 7F2 osteoblasts. The tested biomaterials have the potential for further investigation with a possible change in the proportion of plasticizers, which can have a fundamental impact on their biological properties.

Aeromonas spp. is a major pathogen in aquaculture with a great negative economic impact. Essential oils (EOs) are compounds of the secondary metabolism of plants known for their antibacterial and antibiofilm activities. In this study, in vitro antibacterial activity of eight EOs: tea tree (extracted from Melaleuca alternifolia), eucalyptus (extracted from Eucalyptus globulus LABILL.), knee timber (extracted from Pini mungo L.), peppermint (extracted from Mentha piperita L.), oregano (extracted from Origanum vulgare L.), rosemary (extracted from Rosmarinus officinalis L.), thyme (extracted from Thymus vulgaris L.) and pine EO (extracted from Pinus silvestris L.), obtained from Calendula a.s., was evaluated. Their antibacterial activity was demonstrated against Aeromonas spp. isolates. Oregano and thyme EOs showed the strongest activity against all tested isolates at low concentrations, followed by tea tree and peppermint EOs. The MIC value ranged from 0.06 µL/mL to 1.0 µL/mL. The tested EOs showed a significant antibiofilm activity against biofilm-forming isolates with MBIC₅₀ ranging from 0.015 µL/mL to 0.25 µL/mL. All tested isolates were obtained from rainbow trout free of clinical signs of infection. Twelve isolates of Aeromonas salmonicida subsp. masoucida, four Aeromonas hydrophila, and four isolates of Aeromonas veronii were identified. The results of the in vitro study showed a significant effect of EOs against Aeromonas spp., which confirmed their potential for use in aquaculture as a prevention against bacterial diseases and a way of reducing the use of antibiotics.

The present study deals with the effects of laser surface treatment on microstructure evolution and wear resistance of AISI H11 hot work tool steel in quenched and tempered condition. The most upper laser-affected zone is characterized by re-melted microstructure consisting of dendrite cells with fresh non-tempered martensite, retained austenite and inter-dendritic carbidic network. The subsolidus microstructure just beneath the re-melted zone represents the most laser surface hardened zone consisting of fresh non-tempered martensite with fine and coarse carbides as a result of overheating the original QT substrate microstructure. The highest microhardness values in the range from 775 to 857 HV were measured for the LSH microstructure and the most softened microstructure exhibited the minimum hardness of 530 HV. The laser treated samples showed the improvement of their surface wear resistance by 35%.

This study describes the water vapour effect on the oxidation resistance of 9Cr creep resistant steels. Boiler P91 and MarBN steels were oxidized for 3000 h in a simulated humid atmosphere with ~10% water vapour. The oxidation kinetics had a stable course for 1000 h and was evaluated by the weight gain curves for both experimental steels and both oxidation temperatures. The oxidation rate was higher at 650 °C versus 600 °C, as reflected by the oxidation rate coefficient. A significant increase occurred after 1000 h of oxidation, which was related to the local breakdown oxide scale and oxide nodules were formed on steel. This oxidation behavior was influenced by the fact that a compact spinel structure of iron oxides and alloying elements were not formed on the steel. Analysis after 3000 h of exposure showed hematite Fe₂O₃ formed on the outer layer, magnetite Fe₃O₄ on the middle layer, and the bottom layer consisted of iron-chromium-spinel (Fe,Cr)₂O₃.

The aim of this study was to analyse the biocompatibility of a material based on lactic acid (PLA)/polyhydroxybutyrate(PHB)/thermoplastic starch (TPS) in combination with additives (plasticizers: acetyltributyl citrate (ATBC) and oligomeric lactic acid ( OLA)). Three types of materials were tested: I: PLA/PHB/TPS + 25% OLA, II: PLA/PHB/TPS + 30% ATBC, III: PLA/PHB/TPS + 30% OLA. The 3D printing itself was preceded by the creation of filaments from granulate and the design of samples. A filament production machine – Composer 450 (3devo; The Netherlands) was used to produce the filaments. Experimental samples were produced by FDM technology on a 3D printer DeltiQ2 (Trilab, Czech Republic). The evaluation of the biocompatibility of the materials included cytotoxicity tests such as the monitoring of viability, proliferation, morphology of cells, and their settlement on the surface of the materials. The cell line 7F2 osteoblasts (Mus musculus) was used in the experiments. Based on the tests, results confirmed the significant influence of plasticizers and their proportions in the mixtures. PLA/PHB/ATBC + 25% OLA was evaluated as the optimal material for biocompatibility with 7F2 osteoblasts. The tested biomaterials have the potential for further investigation, with a possible change in the proportion of the plasticizer, which has a fundamental impact on their biological properties.

The applicability of flowdrill technology to join steel and aluminum alloys is studied. When used to flowdrill two overlapped thin-walled materials, a joint is formed as a secondary effect. The quality of the resulting bushings forming the interference fit joint was investigated by metallography. The joints were formed using a combination of uncoated deep drawn steel, galvanized high-strength low alloy steel and aluminum alloy, in different positions in the joint. Subsequently, tensile shear testing of single joints was performed. The load-carrying capacity of the joints was also tested in combination with adhesive bonding. The combination of both technologies yields an increase in the dissipated energy of the joint at failure. The bonded connection provides a high maximum force at failure, the mechanical connection through bushings leads to an increase in the displacement value at failure, thereby increasing the area under the loading curve. The DC-Al joint showed the highest load-carrying capacity, up to 9 kN, as well as dissipative energy, up to 10.3 J. The joints were fractured by shearing of the inner bushing under tensile stress. The failure surfaces exhibited a typical ductile character with dimpled morphology. It was found that from the point of view of the load-carrying capacity of the joint, it is advisable to place a material with a higher melting temperature in the upper position in the joint. The combination of flowdrill technology with adhesive bonding results in a sealed joint with high load-bearing capacity, reduction in the risk of crevice and galvanic corrosion.