Preparation, properties and structure of hard carbon materials for medical applications

Glass-like carbons represent a wide family of non-graphitizing carbons, which cannot be converted into graphite, even under a high temperature treatment up to 3000 oC. They are hard carbon materials synthesized by pyrolysis of some polymeric precursors. Due to their relative ease of production and a diverse range of properties, such as high thermal resistance, extreme chemical stability, low density and great hardness compared with other carbons, gases impermeability and high electrical conductivity, these materials have been applied in industry since decades. Moreover, glassy carbons exhibit excellent biological compatibility with blood and living tissues, and therefore they have a high potential for the use in medicine. Nowadays, there is an increasing interest in interfacing glassy carbon microelectrodes with tissues for applications ranging from neural signal sensing and stimulation of brain. Furthermore, recent advances in additive manufacturing have led to the creation of ultrastrong glassy carbon microlattices which can be used as medical implants. Although glassy carbons are highly desirable for many applications and are extensively investigated, their properties such as mechanical or electronic performance as a function of the internal structure and processing are still not fully understood and cannot be predicted. The atomic structure of glass-like carbons is complex and strongly depends on the pyrolysis conditions. The most recent studies have suggested that the structure of glassy carbons consists of fullerene-related building blocks, but up to now there are no commonly adopted model of their nucleation and transformation during the carbonization process. The main aim of this work is to establish preparation-structure-properties correlations of a series of glass-like carbons produced by pyrolysis of polyfurfuryl alcohol at different temperatures and go beyond the previous state of the art. Given the complexity of their structure, that can be regarded as intermediate between crystalline and amorphous, and its sensitivity to the synthesis temperature the detailed characterization of the prepared glass-like carbons requires applications of many experimental techniques and interpretation methods. They are: wide-angle X-ray and neutron scattering, Raman spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, nanoindentaion as well as computer simulations of the atomic structure. The fundamental part of these studies was the analysis of the diffraction results in both, real and reciprocal spaces, in form of the structure factors and the pair distribution functions. Theoretical models of the atomic structure were first described in the frame of the paracrystalline structure, and then classical molecular dynamics simulations were performed for energy optimization of the atomic systems containing topological point defects. The model compatibility with the experimental data was verified by a direct comparison of the model-based calculations and the experimental diffraction data. The use of additional techniques, such as high resolution electron microscopy, Raman spectroscopy, electron energy loss spectroscopy and nanoindentation allowed obtaining detailed information about the local structure, chemical bonding between carbon atoms, and mechanical properties of the investigated materials. It has been demonstrated that the structure of the glass-like carbons at different stages of the carbonization process resembles the curvature observed in fragments of nanotubes, fullerenes or nanoonions. This curvature is responsible for hardness and mechanical strength of the glass-like carbons as well for the formation of porosity. It has been established that the constituent carbon atoms are connected mainly by the sp type bonds

Opinions on the impact of studying/working remotely on vision impairment and the use of eye hygiene principles

Introduction. The COVID-19 pandemic has forced the introduction of remote learning and working. Symptoms of digital eye fatigue are increasingly reducing the quality of life. The aim of the study was to collect opinions on the impact of studying/working remotely on vision impairment and to find out the eye hygiene methods used by the respondents. Material and methods. An original questionnaire consisting of 20 closed-ended questions was used for the study. The form was filled out by 194 people aged 18-55 years (mean: 23.15 ± 6.91 years) who were studying or working at least partially remotely. Results. Respondents working remotely were most likely to spend more than 8 hours a day in front of the computer (49.02%), those working hybrid most often marked 5-6 hours (38.04%). Less than half - 44.85% - had a subjective feeling that their eyesight had deteriorated since they started learning/working remotely, and 19.07% declared that the deterioration of their eyesight had been confirmed by an examination with a specialist. Since starting to study/work online, respondents most often complained of eye fatigue (52.58%), dry eyes (34.54%), and sore/burning eyeballs (25.78%). Among eye hygiene rules, the largest percentage declared using a matte screen (48.97%), using "night mode" on an electronic device after dark (51.55%), sleeping for 7-9 hours (45.36%), and taking a break from the screen by blinking (41.24%). Few people are familiar with and use the exercise of closing and shading their eyes (6.70%) the 20-20-20 rule (4.12%), and do not use a smartphone/computer immediately before bed (2.58%). Conclusions. Most of the respondents stated subjectively, or confirmed by a specialist, that their eyesight had deteriorated, and they associate this with learning/working remotely. The most common ocular symptom in the surveyed group was eye fatigue. There is a large deficit in the knowledge and application of eye hygiene principles that can benefit the organ of vision

Structure of Carbon Materials Explored by Local Transmission Electron Microscopy and Global Powder Diffraction Probes

Transmission electron microscopy and neutron or X-ray diffraction are powerful techniques available today for characterization of the structure of various carbon materials at nano and atomic levels. They provide complementary information but each one has advantages and limitations. Powder X-ray or neutron diffraction measurements provide structural information representative for the whole volume of a material under probe but features of singular nano-objects cannot be identified. Transmission electron microscopy, in turn, is able to probe single nanoscale objects. In this review, it is demonstrated how transmission electron microscopy and powder X-ray and neutron diffraction methods complement each other by providing consistent structural models for different types of carbons such as carbon blacks, glass-like carbons, graphene, nanotubes, nanodiamonds, and nanoonions

Characteristics of multiwalled carbon nanotubes-rhenium nanocomposites with varied rhenium mass fractions

The purpose of the article is to discuss the process of oxidation of carbon nanotubes subsequently subjected to the process of decoration with rhenium nanoparticles. The influence of functionalization in an oxidizing medium is presented and the results of investigations using Raman spectroscopy and infrared spectroscopy are discussed. Multiwalled carbon nanotubes rhenium-type nanocomposites with the weight percentage of 10%, 20% and 30% of rhenium are also presented in the article. The structural components of such nanocomposites are carbon nanotubes decorated with rhenium nanoparticles. Microscopic examinations under transmission electron microscope and scanning transmission electron microscope using the bright and dark field confirm that nanocomposites containing about 20% of rhenium have the most homogenous structure

Charakterystyki tribologiczne materiałów węglowych poddanych wygrzewaniu przeznaczonych na płatki zastawek serca

Materiały węglowe typu węgiel szklisty lub kompozyt C/C nie zawsze spełniają wymagania im stawiane w zastosowaniach technicznych i biomechanicznych. Najistotniejszym problemem procesu wytwarzania, który udało się autorom pokonać było wyeliminowanie pęknięć wewnętrznych w gotowych próbkach powodujących ich podzielenie. Uzyskany jednolity materiał badawczy ze względu na niezwykle newralgiczne miejsce wszczepienia musi spełniać liczne wymagania: wykazywać wysoką wytrzymałość mechaniczną i chemiczną, biotolerancję oraz wysoką odporność na zużycie tribologiczne. W pracy przedstawiono wyniki badań tribologicznych, stereometrycznych i mikromechanicznych materiałów węglowych, które zostały wygrzane w piecu grafitowym, w temperaturach odpowiednio: 1500°C, 2000°C i 2500°C. W celu przeprowadzenia analiz charakterystyk tribologicznych opracowano metodykę badań na stanowisku kula-tarcza (tester T-01), która powinna odzwierciedlić warunki obciążeniowe panujące w rzeczywistym węźle. Przeprowadzone badania tribologiczne węgla szklistego potwierdziły przypuszczenia, iż temperatura wytwarzania tego materiału ma duży wpływ na jego własności tribologiczne, a wyższa temperatura wygrzewania nie zawsze oznacza poprawę właściwości materiału

Physical Stability and Viscoelastic Properties of Co-Amorphous Ezetimibe/Simvastatin System

The purpose of this paper is to examine the physical stability as well as viscoelastic properties of the binary amorphous ezetimibe–simvastatin system. According to our knowledge, this is the first time that such an amorphous composition is prepared and investigated. The tendency toward re-crystallization of the amorphous ezetimibe–simvastatin system, at both standard storage and elevated temperature conditions, have been studied by means of X-ray diffraction (XRD). Our investigations have revealed that simvastatin remarkably improves the physical stability of ezetimibe, despite the fact that it works as a plasticizer. Pure amorphous ezetimibe, when stored at room temperature, begins to re-crystallize after 14 days after amorphization. On the other hand, the ezetimibe-simvastatin binary mixture (at the same storage conditions) is physically stable for at least 1 year. However, the devitrification of the binary amorphous composition was observed at elevated temperature conditions (T = 373 K). Therefore, we used a third compound to hinder the re-crystallization. Finally, both the physical stability as well as viscoelastic properties of the ternary systems containing different concentrations of the latter component have been thoroughly investigated

Tribological characteristics of materials used for carbon disc heart valve

Carbon materials (glassy carbon or C/C composite) are used for the production of mechanical heart valves. Due to the extremely sensitive place of their implantation, they must meet numerous requirements: mechanical strength, chemical resistance, biotolerance, and a high resistance to tribological wear. The paper presents tribological and micromechanical research results of carbon materials at various stages of their production. In order to perform the analysis of tribological characteristics, the measurement methodology for the ball-on-disk tester (T-01) has been developed. This may allow a comparison of the results obtained with those received on the nanotribometers

Supramolecular Structure of Phenyl Derivatives of Butanol Isomers

Wide-angle X-ray scattering patterns were recorded for a series of aliphatic butanol isomers (n-, iso-, sec-, tert-butanol) and their phenyl derivatives (4-phenyl-1-butanol, 2-methyl-3- phenyl-1-propanol, 4-phenyl-2-butanol, and 2-methyl-1-phenyl-2- propanol, respectively) to determine their atomic-scale structure with particular emphasis on the formation of supramolecular clusters. In addition, molecular dynamics simulations were carried out and yielded good agreement with experimental data. The combination of experimental and theoretical results allowed clarification of the origin of the pre-peak appearing at low scattering angles for the aliphatic butanols and its absence for their phenyl counterparts. It was demonstrated that the location of the hydroxyl group in the molecule of alkyl butanol, its geometry, and rigidity determine the morphology of the supramolecular clusters, while the addition of the aromatic moiety causes more disordered organization of molecules. The phenyl group significantly decreases the number of hydrogen bonds and size of the supramolecular clusters formed via the O−H···O scheme. The lower association ability of phenyl alcohols via H-bonds is additionally attenuated by the appearance of competing π−π configurations evidenced by the structural models

Interplay between the static ordering and dynamical heterogeneities determining the dynamics of rotation and ordinary liquid phases in 1,6-anhydro-β-D-glucose

In this letter, we reported thorough the structural and molecular dynamics studies on 1,6-Anhydro-β-D-glucose, the second compound reported so far that is capable to form rotator and supercooled liquid phases. In contrast to the data presented for ethanol, temperature dependences of structural dynamics in both phases are very comparable. On the other hand, X ray measurements revealed unusually long range ordering/correlations between molecules in the ODIC (d â ‰ 95 Å) and supercooled phases (d â ‰ 30-40 Å) of this carbohydrate. Our consideration clearly demonstrated that the interplay between length scales of static range ordering and dynamical heterogeneities as well as internal molecular arrangement seem to be the key to understanding the molecular dynamics of different materials characterized by varying degree of disorder in the vicinity of the glass transition temperature

Secondary relaxation in ultrastable etoricoxib : evidence of correlation with structural relaxation

Secondary relaxations are fundamental for their impact in the properties of glasses and for their inseparable connection to the structural relaxation. Understanding their density dependence and aging behavior is key to fully address the nature of glasses. Ultrastable glasses establish a new benchmark to study the characteristics of secondary relaxations, since their enthalpy and density levels are unattainable by other routes. Here, we use dielectric spectroscopy at ambient and elevated pressures to study the characteristics of the secondary relaxation in ultrastable etoricoxib, reporting a 71% decrease in dielectric strength and one decade increase in relaxation time compared to the ordinary glass. Interestingly, we find an unprecedented connection between secondary and structural relaxations in ultrastable etoricoxib in exactly the same manner as in the ordinary glass, manifested through different properties, such as aging and devitrification. These results further support and extend the general validity of the connection between the secondary and structural relaxation