Papers by Vassilis M Papadakis
Journal of Composites Science
In this study, innovative nanocomposite materials for material extrusion (MEX) 3D printing were d... more In this study, innovative nanocomposite materials for material extrusion (MEX) 3D printing were developed using a polypropylene (PP) polymer with tungsten carbide (WC) nanopowder. The raw materials were converted into filaments using thermomechanical extrusion. The samples were then fabricated for testing according to the international standards. Extensive mechanical testing was performed on the 3D-printed specimens, including tensile, impact, flexural, and microhardness assessments. In addition, the impact of ceramic additive loading was examined. The thermal and stoichiometric characteristics of the nanocomposites were examined using thermogravimetric analysis, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and Raman spectroscopy. The 3D-printed shape, quality, and fracture process of the specimens were examined using scanning electron microscopy. The results showed that the filler significantly enhanced the mechanical characteristics of the matrix polyme...
Bookmarks Related papers MentionsView impact
Circulating cell free DNA (ccfDNA) is a liquid biopsy biomaterial attracting significant attentio... more Circulating cell free DNA (ccfDNA) is a liquid biopsy biomaterial attracting significant attention for the implementation of precision medicine diagnostics. Deeper knowledge related to its structure and biology would enable the development of such applications. In this study, we employ Raman Spectroscopy to unravel the biomolecular profile of human ccfDNA in health and disease. We established reference Raman spectra of ccfDNA samples from healthy males and females, from different conditions including cancer and diabetes, extracting information about their chemical composition. Comparative observations showed a distinct spectral pattern in ccfDNA from breast cancer patients taking neoadjuvant therapy. Raman analysis of ccfDNA from healthy, prediabetic and diabetic males uncovered some differences in their biomolecular fingerprint. We also studied ccfDNA released from human benign and cancer cell lines and compared it to their respective gDNA, confirming mirroring its cellular origin....
Bookmarks Related papers MentionsView impact
Applied Sciences
The industrial demand for functional filaments made of bio-sourced, biocompatible, biodegradable,... more The industrial demand for functional filaments made of bio-sourced, biocompatible, biodegradable, and/or recyclable polymers and composites for material extrusion (MEX) 3D printing is continuously growing. Polylactic acid (PLA), the most popular filament, combines such properties, yet its reinforcement with low-cost, inert, and/or recycled fillers remains challenging. Herein, glass in three different micro/nano-forms was the reinforcement agent in PLA. Three different experimental tiers were elaborated by producing composite filaments with glass in powder, beads, and flake forms in various loadings to optimize the concentrations. A thermomechanical process, i.e., melt filament extrusion, was exploited. The composites were evaluated for their thermal degradation stability and composition using thermogravimetric analysis and Raman. MEX 3D printing was used to produce tensile, flexural, impact, and microhardness specimens, to quantitatively evaluate their mechanical response. Field emi...
Bookmarks Related papers MentionsView impact
Nanomaterials
Acrylonitrile Butadiene Styrene (ABS) nanocomposites were developed using Material Extrusion (MEX... more Acrylonitrile Butadiene Styrene (ABS) nanocomposites were developed using Material Extrusion (MEX) Additive Manufacturing (AM) and Fused Filament Fabrication (FFF) methods. A range of mechanical tests was conducted on the produced 3D-printed structures to investigate the effect of Titanium Nitride (TiN) nanoparticles on the mechanical response of thermoplastic polymers. Detailed morphological characterization of the produced filaments and 3D-printed specimens was carried out using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). High-magnification images revealed a direct impact of the TiN concentration on the surface characteristics of the nanocomposites, indicating a strong correlation with their mechanical performance. The chemical compositions of the raw and nanocomposite materials were thoroughly investigated by conducting Raman and Energy Dispersive Spectroscopy (EDS) measurements. Most of the mechanical properties were improved with the inclusion of TiN n...
Bookmarks Related papers MentionsView impact
Polymers
In this work, the effect of silicon carbide (carborundum, SiC), as a boosting agent of the mechan... more In this work, the effect of silicon carbide (carborundum, SiC), as a boosting agent of the mechanical response of the polycarbonate (PC) polymer, was investigated. The work aimed to fabricate nanocomposites with an improved mechanical performance and to further expand the utilization of 3D printing in fields requiring an enhanced material response. The nanocomposites were produced by a thermomechanical process in various SiC concentrations in order to evaluate the filler loading in the mechanical enhancement. The samples were 3D printed with the material extrusion (MEX) method. Their mechanical performance was characterized, following international standards, by using dynamic mechanical analysis (DMA) and tensile, flexural, and Charpy’s impact tests. The microhardness of the samples was also measured. The morphological characteristics were examined, and Raman spectra revealed their structure. It was found that SiC can improve the mechanical performance of the PC thermoplastic. A 19....
Bookmarks Related papers MentionsView impact
Materials
Polycarbonate-based nanocomposites were developed herein through a material extrusion (MEX) addit... more Polycarbonate-based nanocomposites were developed herein through a material extrusion (MEX) additive manufacturing (AM) process. The fabrication of the final nanocomposite specimens was achieved by implementing the fused filament fabrication (FFF) 3D printing process. The impact of aluminum nitride (AlN) nanoparticles on the thermal and mechanical behavior of the polycarbonate (PC) matrix was investigated thoroughly for the fabricated nanocomposites, carrying out a range of thermomechanical tests. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) provided information about the morphological and surface characteristics of the produced specimens. Using energy dispersive spectroscopy (EDS), the elemental composition of the nanocomposite materials was validated. Raman spectroscopy revealed no chemical interactions between the two material phases. The results showed the reinforcement of most mechanical properties with the addition of the AlN nanoparticles. The nanocomp...
Bookmarks Related papers MentionsView impact
Journal of Composites Science
Aiming to develop more robust, mechanically advanced, Fused Filament Fabrication (FFF) materials,... more Aiming to develop more robust, mechanically advanced, Fused Filament Fabrication (FFF) materials, High-Density Polyethylene (HDPE) nanocomposites were developed in the current research work. Titanium Dioxide (TiO2) was selected as filler to be incorporated into the HDPE matrix in concentration steps of 0.5, 2.5, 5, and 10 wt.%. 3D printing nanocomposite filaments were extruded in ~1.75 mm diameter and used to 3D print and test tensile and flexion specimens according to international standards. Reported results indicate that the filler contributes to increasing the mechanical strength of the virgin HDPE at certain filler and filler type concentrations; with the highest values reported to be 37.8% higher in tensile strength with HDPE/TiO2 10 wt.%. Morphological and thermal characterization was performed utilizing Scanning Electron Microscopy (SEM), Raman, Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC), while the results were correlated with the available...
Bookmarks Related papers MentionsView impact
Nanomaterials
Herein, a polycarbonate (PC) polymer is melt extruded together with titanium carbide (TiC) nano p... more Herein, a polycarbonate (PC) polymer is melt extruded together with titanium carbide (TiC) nano powder for the development of advanced nanocomposite materials in material extrusion (MEX) 3D printing. Raw material for the 3D printing process was prepared in filament form with a thermomechanical extrusion process and specimens were built to be tested according to international standards. A thorough mechanical characterization testing course (tensile, flexural, impact, microhardness, and dynamic mechanical analysis-DMA) was conducted on the 3D printed specimens. The effect of the ceramic filler loading was also investigated. The nanocomposites’ thermal and stoichiometric properties were investigated with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), energy-dispersive X-ray spectroscopy (EDS), and Raman respectively. The specimens’ 3D printing morphology, quality, and fracture mechanism were investigated with atomic force microscopy (AFM) and scanning electr...
Bookmarks Related papers MentionsView impact
Fibers
In this work, we present an effective process easily adapted in industrial environments for the d... more In this work, we present an effective process easily adapted in industrial environments for the development of multifunctional nanocomposites for material extrusion (MEX) 3D printing (3DP). The literature is still very limited in this field, although the interest in such materials is constantly increasing. Nanocomposites with binary inclusions were prepared and investigated in this study. Polylactic acid (PLA) was used as the matrix material, and cuprous oxide (Cu2O) and cellulose nanofibers (CNF) were used as nanoadditives introduced in the matrix material to enhance the mechanical properties and induce antibacterial performance. Specimens were built according to international standards with a thermomechanical process. Tensile, flexural, impact, and microhardness tests were conducted. The effect on the thermal properties of the matrix material was investigated through thermogravimetric analysis, and Raman spectroscopic analysis was conducted. The morphological characteristics were ...
Bookmarks Related papers MentionsView impact
Materials, 2022
Raman spectroscopy is a well-defined spectroscopic technique sensitive to the molecular vibration... more Raman spectroscopy is a well-defined spectroscopic technique sensitive to the molecular vibrations of materials, since it provides fingerprint-like information regarding the molecular structure of the analyzed samples. It has been extensively used for non-destructive and label-free cell characterization, particularly in the qualitative and quantitative estimation of amino acids, lipids, nucleic acids, and carbohydrates. Lymphoma cell classification is a crucial task for accurate and prompt lymphoma diagnosis, prognosis, and treatment. Currently, it is mostly based on limited information and requires costly and time-consuming approaches. In this work, we are proposing a fast characterization and differentiation methodology of lymphoma cell subtypes based on Raman spectroscopy. The study was performed in the temperature range of 15–37 °C to identify the best cell measurement conditions. The proposed methodology is fast, accurate, and requires minimal sample preparation, resulting in a...
Bookmarks Related papers MentionsView impact
Crystals, 2020
Graphene, a 2D carbon structure, due to its unique materials characteristics for energy storage a... more Graphene, a 2D carbon structure, due to its unique materials characteristics for energy storage applications has grasped the considerable attention of scientists. The highlighted properties of this material with a mechanically robust and highly conductive nature have opened new opportunities for different energy storage systems such as Li-S (lithium-sulfur), Li-ion batteries, and metal-air batteries. It is necessary to understand the intrinsic properties of graphene materials to widen its large-scale applications in energy storage systems. In this review, different routes of graphene synthesis were investigated using chemical, thermal, plasma, and other methods along with their advantages and disadvantages. Apart from this, the applications of N-doped graphene in energy storage devices were discussed.
Bookmarks Related papers MentionsView impact
Journal of Composites Science
The scope of this work was to develop novel polymer composites via melt extrusion and 3D printing... more The scope of this work was to develop novel polymer composites via melt extrusion and 3D printing, incorporating High-Density Polyethylene filled with zinc oxide particles in various wt. percentages. For each case scenario, a filament of approximately 1.75 mm in diameter was fabricated. Samples for tensile and flexural testing were fabricated with 3D printing. They were then evaluated for their mechanical response according to ASTM standards. According to the documented testing data, the filler increases the mechanical strength of pure HDPE at specific filler concentrations. The highest values reported were a 54.6% increase in the flexural strength with HDPE/ZnO 0.5 wt.% and a 53.8% increase in the tensile strength with 10 wt.% ZnO loading in the composite. Scanning Electron Microscopy (SEM), Raman, and thermal characterization techniques were used. The experimental findings were evaluated in other research areas where they were applicable.
Bookmarks Related papers MentionsView impact
Journal of Functional Biomaterials
Vat photopolymerization (VPP) is an additive manufacturing process commonly used in medical appli... more Vat photopolymerization (VPP) is an additive manufacturing process commonly used in medical applications. This work aims, for the first time in the literature, to extend and enhance the performance of a commercial medical-grade resin for the VPP process, with the development of nanocomposites, using Copper (Cu) nanoparticles as the additive at two different concentrations. The addition of the Cu nanoparticles was expected to enhance the mechanical properties of the resin and to enable biocidal properties on the nanocomposites since Cu is known for its antibacterial performance. The effect of the Cu concentration was investigated. The nanocomposites were prepared with high-shear stirring. Specimens were 3D printed following international standards for mechanical testing. Their thermal and spectroscopic response was also investigated. The morphological characteristics were examined. The antibacterial performance was evaluated with an agar well diffusion screening process. The experime...
Bookmarks Related papers MentionsView impact
Lecture notes in mechanical engineering, Oct 12, 2022
Bookmarks Related papers MentionsView impact
Microplastics
Food packaging has been demonstrated as a crucial issue for the migration of microplastics (MPs) ... more Food packaging has been demonstrated as a crucial issue for the migration of microplastics (MPs) into foodstuffs, concerning human health risk factors. Polymeric materials called plastics are continuously utilized in food packaging. Polyethylene (PE) is commonly used as a food packaging material, because it offers easy handling during transportation and optimal storage conditions for food preservation. In this work, three types of cured meat products of different fat compositions and meat processing methods—bacon, mortadella, and salami—were studied using spectroscopic methods (Raman and FT–IR/ATR) to determine the migration of low-density polyethylene (LDPE) from plastic packaging to the surface of the meat samples. The experimental duration of this study was set to be 28 days owing to the selected meat samples’ degradation, which started to become visible to the human eye after 10 days of storage in vacuum LDPE packaging, under refrigerated conditions at 4 °C. Spectroscopic measur...
Bookmarks Related papers MentionsView impact
Microplastics
In ancient Greece, people said that “honey is the Food of the Gods”, and they were right. They be... more In ancient Greece, people said that “honey is the Food of the Gods”, and they were right. They believed that honey fell from the sky, with the morning dew, on the flowers and leaves, and from this point, the bees collected it. Honey is one of the most nutritious food products, which can be found in most homes. A lot of honey products are stored in different types of packaging materials, including plastics. Plastic packaging has been studied for the migration of plasticizers, chemical compounds, and MPs and NPs in foodstuffs. Most of them have been achieved through food simulations, while some studies managed to detect and isolate MPs/NPs. Recent studies presented evidence for the presence of MPs/NPs in honey products but not directly connected to food packaging or to the different types of honey and their properties (viscosity, pH value, and moisture content) or their storing conditions (temperature, humidity, light, and time). Spectroscopic and analytical techniques like Raman, FTI...
Bookmarks Related papers MentionsView impact
Polymers
This study introduced binary nanoparticle (NP) inclusions into a biomedical-grade photosensitive ... more This study introduced binary nanoparticle (NP) inclusions into a biomedical-grade photosensitive resin (Biomed Clear-BC). Multi-functional, three-dimensional (3D) printed objects were manufactured via the vat photopolymerization additive manufacturing (AM) technique. Cellulose nanofibers (CNFs) as one dimensional (1D) nanomaterial have been utilized for the mechanical reinforcement of the resin, while three different spherical NPs, namely copper NPs (nCu), copper oxide NPs (nCuO), and a commercial antimicrobial powder (nAP), endowed the antimicrobial character. The nanoparticle loading was kept constant at 1.0 wt.% to elucidate any synergistic effects as a function of the filler loading. Raman, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) revealed the chemical/spectroscopic and thermal properties of the different manufactured samples. Scanning electron microscopy and Atomic Force Microscopy (AFM) revealed the morphology of the samples. Mechanical pro...
Bookmarks Related papers MentionsView impact
ABSTRACT This paper discusses a novel application of optical coherence tomography (OCT) by using ... more ABSTRACT This paper discusses a novel application of optical coherence tomography (OCT) by using it as a way to study and characterize coatings on wood for a variety of applications and research fields. The coatings studied in this work are transparent layers applied to protect the wood from external influences. OCT can be used to assess the quality or damages of such a coating, to monitor its penetration into the wood structure and to measure its thickness. This study will apply OCT as a non-destructive technique that can both be used to test the quality of applied coatings as well to lay a basis to study coatings on wood in the field of cultural heritage. Measurements of deteriorated coated wood and reference coated wood show that both time-domain and Fourier-domain OCT are successful in imaging the coated layer. In order to deal with noise and to fully utilize information provided by the obtained data, post-processing plays an important role. Results from the two OCT techniques and their comparison will be presented and discussed.
Bookmarks Related papers MentionsView impact
Materials, 2021
For multiple years, food packaging migration has been a major concern in food and health sciences... more For multiple years, food packaging migration has been a major concern in food and health sciences. Plastics, such as polyethylene, are continuously utilized in food packaging for preservation and easy handling purposes during transportation and storage. In this work, three types of cheese, Edam, Kefalotyri and Parmesan, of different hardness were studied under two complementary vibrational spectroscopy methods, ATR-FTIR and Raman spectroscopy, to determine the migration of low-density polyethylene from plastic packaging to the surface of cheese samples. The experimental duration of this study was set to 28 days due to the degradation time of the selected cheese samples, which is clearly visible after 1 month in refrigerated conditions at 4 °C. Raman and ATR-FTIR measurements were performed at a 4–3–4–3 day pattern to obtain comparative results. Initially, consistency/repeatability measurement tests were performed on Day0 for each sample of all cheese specimens to understand if there...
Bookmarks Related papers MentionsView impact
Agriculture, 2022
Long storage periods have been associated with decreased vase life. In this study, the processes ... more Long storage periods have been associated with decreased vase life. In this study, the processes underlying the vase life response to prolonged storage were investigated, along with the potential of light reflectance profiles to estimate storage duration. Three cut chrysanthemum cultivars were exposed to four cold (5 °C) storage periods (0, 7, 14, and 21 d). Stomata were present on the leaves (either side) and stem, but not on petals. As compared to the leaves, stomata on the stem were non-functional, smaller, and less dense. Floral transpiration was a small portion of the whole-cut flower transpiration, with the major contributor being the leaves or stem depending on the cut flower hydration. Storage duration linearly decreased vase life, with the rate of decrease being cultivar specific. Storage duration (0–21 d) did not affect leaf stomatal functioning, non-leaf tissue transpiration, or the relative contribution of each organ to the whole-cut flower transpiration. Cut flower hydr...
Bookmarks Related papers MentionsView impact
Uploads
Papers by Vassilis M Papadakis
From the result it can be concluded that feeding condition is strongly related with fish’s motivation to escape. The highest escape rate that was observed belongs to feeding condition (1%) and can be attributed to fish activity of the tank due to intensified prey searching (Sogard et al., 1996). Τhe frequency of escapes was increased at the latter phases of the experiment, which comes in agreement with related studies indicating that intensified prey search is proportional to the hunger level of fish in other species. Furthermore prolonged starvation is required to cause major behavioral changes that can lead to an increased motivation to escape. Nevertheless, we should keep under consideration that the study was carried out under small-scale experimental conditions. The variations in the escape behavior due to food supply arise the question of which is the appropriate feeding schedule that provides quite good welfare of farmed species.
From the result it can be concluded that feeding condition is strongly related with fish’s motivation to escape. The highest escape rate that was observed belongs to feeding condition (1%) and can be attributed to fish activity of the tank due to intensified prey searching (Sogard et al., 1996). Τhe frequency of escapes was increased at the latter phases of the experiment, which comes in agreement with related studies indicating that intensified prey search is proportional to the hunger level of fish in other species
Furthermore prolonged starvation is required to cause major behavioral changes that can lead to an increased motivation to escape. Nevertheless, we should keep under consideration that the study was carried out under small-scale experimental conditions. The variations in the escape behavior due to food supply arise the question of which is the appropriate feeding schedule that provides quite good welfare of farmed species.
From the result it can be concluded that feeding condition is strongly related with fish’s motivation to escape. The highest escape rate that was observed belongs to feeding condition (1%) and can be attributed to fish activity of the tank due to intensified prey searching (Sogard et al., 1996). Τhe frequency of escapes was increased at the latter phases of the experiment, which comes in agreement with related studies indicating that intensified prey search is proportional to the hunger level of fish in other species
Furthermore prolonged starvation is required to cause major behavioral changes that can lead to an increased motivation to escape. Nevertheless, we should keep under consideration that the study was carried out under small-scale experimental conditions. The variations in the escape behavior due to food supply arise the question of which is the appropriate feeding schedule that provides quite good welfare of farmed species.
The system is designed to accept nine colour digital CCD cameras (HD Webcam C310, Logitech) enabling the monitoring of nine experimental tanks. The cameras are connected to three desktop computers to achieve an almost loss-less acquisition of video at 10 frames per second per camera. The cameras have been modified to focus eight cm away from the water surface, resulting to a spatial resolution of less than 100um per pixel. Acquisition was performed with custom made software, written in LabView (National Instruments), able to record up to 24 hours per day. In order to reduce the size of the saved video files, DivX compression was used.
The system performed successfully for a period of 2 months, providing images of sea bream larvae activity in tanks. The system was able to recognize larvae right after post hatching. The size of each larvae individual could be easily measured from the extracted frames. Further analysis was performed using a tailor made software in our lab to assist monitoring of video files and extraction of various behavioral traits. Analysis focused on foraging behavior of sea bream larvae and information extracted included the number of attacks occurred in a period of time as well the different types of attack. Additionally, information upon angle and speed variation of larvae movement was calculated.
The application of this advanced computer vision system resulted to a detailed analysis of sea bream larvae foraging behaviour. Thus, it can be applied to monitor fish larvae behaviour in captivity, allowing the better understanding of the rearing process in aquaculture industry.
The study was carrying out into nine groups (15individuals/tank). Each tank was previously split into two compartments. The food supplied to fish individual was tested using, as stimuli, the food provided to fish. Experiment lasted 21 days. The observation of fish activity in tanks was achieved by a digital computer vision system.
Dominance presence among fish population was analyzed on specific experimental days, while it was observed throughout the whole period. The number of dominant fish per group was differentiated within the day and also throughout the total experimental period.
The maximum percentage of dominant fish/group was 40% (6 individuals). Food supply to fish individuals influenced the dominance presence throughout the days. Unfed fish groups had a gradually decrease on dominance presence during the study. At the feeding time, the number of dominant individuals was the minimum. The number of dominant fish impressively increased after feeding time. Lastly, dominant fish were mainly distributed close to the feeding area.
Dominance is a social hierarchy; being studied several times but not from the behavioral perspective. Results indicate that behavioral aspects of dominance could provide knowledge on social interactions of farmed species.
Our present research focuses on the development of efficient computer vision and video processing systems in laboratory conditions testing species-specific characteristics of fish behaviour. Such studies include: mapping of fish movement in confined environment and detection of body posture in several developmental stages of fish. In addition, time parameter is significantly considered in our studies, since it reveals each one of the discrete steps of fish behaviour. Expansion to Infrared light may also contribute to detailed analysis under different light regimes. Therefore, real time observation of fish population could provide new implications towards monitor and handling procedures in aquaculture.
After a series of successful experiments in laboratory scale conditions, our challenges and perspectives are to extrapolate this technology to open farming facilities and apply these technologies in commercial scale aquaculture. New implementations and cost effective systems might contribute to solutions against problems encountered in farm industry, such as fish diseases, welfare aspects and eventually production and growth.
to escape from sea cage installations. Fish escapes are caused mainly by operational and technical failures that eventually create
tears. Escapees may interact with wild stocks through interbreeding, transfer of pathogens and competition for food. The aim of this study was to examine to what extent the presence of a visible obstacle close to a tear in the net influences sea bass propensity to escape. Fish were initially confined into small sea cages, with a tear on one side. The escape behaviour was tested under experimental conditions. It is clearly demonstrated that sea bass were able to locate a tear in the net pen, immediately after its
appearance. Crossings occurred in all cages, in singles or in a series of up to seven individuals. The presence of an obstacle close to the net tear altered the escape behaviour of D. labrax, resulting in a delay that eventually reduced the escape rate. To conclude, it is highly recommended that sea bass cages should be kept internally the culture array. Furthermore, the placement of artificial obstacles close to the sea cages could be an efficient practice that mitigates the escape risk after severe environmental conditions.
individuals per tank) and three net conditions (a net pen with a tear, a net pen with a cut twine and a flawless net pen) were tested. Sea bream individuals initiate escapes shortly after a tear was created on the net. Altering the number of fish confined in tanks resulted into an exponential increase of the escape rate. Variations on fish interactions towards the net penwere also found and were associated with both rearing density and the condition of the net. Particularly, sea bream increased net inspection and biting in relation with the rearing density. Additionally, sea bream
was further attracted by damages on the net pen, while individuals were capable of extending existing damages. Results presented were statistically significant and could act as recommendations
to improve the rearing process protocols.""