Pokročilé polymerní materiály a kompozit
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- ItemGraphene quantum dots-From spectroscopic performance to 3D printing applications and interaction studies with normal and cancer cells(Elsevier, 2024-05-27) Krok-Janiszewska, Dominika; Wielgus, Weronika; Środa, Patrycja; Tyszka-Czochara, Małgorzata; Lepcio, Petr; Kasprzyk, Wiktor; Ortyl, JoannaIn this study, different types of graphene quantum dots (GQDs) are investigated to understand their spectroscopic properties. Morphological and size analyses were performed. The mechanism of action of radical photopolymerization was evaluated. The obtained materials proved to be useful for developing efficient photoinitiating systems for 3D printing applications. In addition, the cytotoxicity of the GQDs was studied, and their effects on living cells were investigated. We demonstrated that GQDs can not only act as efficient photoinitiators but also as constituents of hydrogels that express very low toxicity and may interact with cells. The latter makes it possible to study them in the future as useful modern biosensors.
- ItemAnatase and rutile nanoparticles in photopolymer 3D-printed nanocomposites: Band gap-controlled electron interactions in free-radical and cationic photocuring(Elsevier, 2024-07-01) Korčušková, Martina; Svatík, Juraj; Tomal, Wiktoria; Šikyňová, Aneta; Vishakha, Vishakha; Petko, Filip; Galek, Mariusz; Stalmach, Paweł; Ortyl, Joanna; Lepcio, PetrThe preparation of functional photopolymer nanocomposites is affected by both the physical and chemical interactions of nanoparticles (NPs) and polymer resin. Some NPs, such as semiconducting metal oxides, may contribute by their photocatalytic behavior and electron transfer, influencing the kinetics of the photopolymerization reaction. This study has investigated the complex effect of titanium dioxide (TiO 2 ) NPs in anatase and rutile form on the conversion, kinetics, and printability of free -radical and cationic photopolymerization resin. Two different polymorphs of TiO 2 NPs ensured identical chemical properties, but different physical effects related to their varying band gap energies and electron transfer efficiency. These parameters were found to be crucial for influencing the photopolymerization kinetics. While rutile showed a more pronounced enhancement of the free -radical photopolymerization ' s conversion and kinetics, cationic photopolymerization was favourably affected only by anatase NPs due to the photosensitization effect. These findings are critical in understanding and designing functional nanocomposite materials processed by vat photopolymerization 3D printing that could find use in optical, medical, or environmental applications.
- ItemBiaxial porosity gradient and cell size adjustment improve energy absorption in rigid and flexible 3D-printed reentrant honeycomb auxetic structures(Elsevier, 2024-06-01) Štaffová, Martina; Ondreáš, František; Žídek, Jan; Jančář, Josef; Lepcio, PetrThis paper compares different uniaxial and biaxial graded designs of auxetic reentrant honeycomb structures to enhance their mechanical properties, especially the specific energy absorption under compressive load. The lattice structures were 3D printed using the vat photopolymerization masked-stereolithography technique from two different materials - tough (OR) and flexible (FR). The results were evaluated from a material and structural point of view, investigating the effect of porosity, cell number, size, graded design, and fracture mode. The universally best energy-absorbing performance was found in a biaxially graded structure with a center-wise location of the highest local porosity. Depending on the used resin, its energy absorption capacity was up to 2-3 times enhanced compared to a reference uniform-porosity auxetic design. The presented data constitutes a fundamental understanding of auxetic structures and identifies practical approaches for tuning the auxetic structures' performance regarding their mechanical response. Finally, this study demonstrates the potential of shape versatility offered by 3D printing and other additive manufacturing techniques.
- ItemThe Effect of PLGA-PEG-PLGA Modification on the Sol-gel Transition and Degradation Properties(Budapest University of Technology and Economics Faculty of Mechanical Engineering Department of Polymer Engineering, 2016-02-26) Oborná, Jana; Mravcová, Ludmila; Michlovská, Lenka; Vojtová, Lucy; Vávrová, MiladaThis paper deals with the influence of an incubation medium pH on the hydrolytic degradation of a novel thermosensitive biodegradable triblock copolymer based on hydrophilic poly(ethylene glycol) and hydrophobic copolymer poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA), consequently modified at alpha,omega-ends with itaconic acid (ITA) resulting in alpha,omega-itaconyl(PLGA-PEG-PLGA). Itaconic acid, gained from renewable resources, delivers a reactive double bond and carboxylic functional group to the end of PLGA-PEG-PLGA copolymer: this is important for a reaction with biologically active substances. The suitability of the sample degradation was assessed depending on whether the copolymer formed a gel at 37 °C. Two reversible physical sol-gel-sol transitions from a sol (liquid phase) to a gel (solid phase) and back to a sol (suspension) were verified using the tube inverting method. The hydrolytical degradation was evaluated at a physiological temperature (37 °C) in the presence of phosphate solutions, at a pH either 4.2 or 7.4 by monitoring the decrease of the number average molecular weight of copolymers by GPC. Moreover, the degradation kinetics was confirmed by the HPLC/DAD method, where the increasing amount of final degradation products (lactic and glycolic acids) was detected. The study demonstrated that the carboxylic groups modified copolymer is more susceptible to hydrolytical degradation than the unmodified copolymer within first days of degradation at 7.4.
- ItemPLA toughening via bamboo-inspired 3D printed structural design(Elsevier, 2021-12-01) Svatík, Juraj; Lepcio, Petr; Ondreáš, František; Zárybnická, Klára; Zbončák, Marek; Menčík, Přemysl; Jančář, JosefBioinspired structures can attain mechanical properties unseen in conventional artificial materials. Specifically, the introduction of a cellular structure with a precisely designed distribution of cells, cell sizes, and cell walls is expected to enhance the mechanical response. Polylactic acid (PLA) is a biodegradable polymer produced from renewable resources with very interesting properties and good three-dimensional (3D) printing processability. However, its embrittlement during ageing at room temperature after a very short period of time (a few hours) significantly reduces its usability for advanced applications. Intense effort has been invested in improving its toughness via composition modification. However, this approach can worsen some other properties, make processing more difficult, and increase the carbon footprint. Therefore, fused deposition modelling (FDM) 3D printing was used to manufacture porous bamboo-inspired structures of unmodified PLA. The toughening of PLA solely by the pore gradient, which controlled the energy dissipation mechanism, was introduced for the first time. Improvement of the ductility and work at break was observed especially for notched specimens. Prevention of catastrophic failure could enable the use of gradient porous materials in structural components. The fundamental relationships and practical hints resulting from the work provide a foundation for the future design of toughened 3D printed structures.