Measurement of Flexural Rigidity of Multi-Walled Carbon Nanotubes by Dynamic Scanning Electron Microscopy

In this work the flexural rigidity of individual large diameter multi-walled carbon nanotubes (MWCNTs) was investigated. The bending modulus were obtained by detecting the resonance frequencies of mechanically excited cantilevered carbon nanotubes using the so-called dynamic scanning electron microscopy technique, and applying the Euler–Bernoulli beam theory. For the nanotubes studied, we determined a modulus of up to 160 GPa. This agrees with values reported by other authors for MWCNTs produced by catalytic chemical vapor deposition, however, it is 6-8 times smaller than values reported for single and multi-walled carbon nanotubes produced by arc-discharge synthesis. Toxicological studies with carbon nanotubes have been showing that inhaled airborne nanofibers that reach the deep airways of the respiratory system may lead to serious, asbestos-like lung diseases. These studies suggested that their toxicity critically depends on the fiber flexural rigidity, with high rigidity causing cell lesions. To complement the correlation between observed toxicological effects and fiber rigidities, reliable and routinely applicable measurement techniques for the flexural rigidity of nanofibers are required

Microgel polymer composite fibres

In this thesis some novel ideas and advancements in the field of polymer composite fibres, specifically microgel-based polymer composite fibres have been achieved. The main task was to investigate and understand the electrospinning process of microgels and polymers and the interplay of parameter influences, in order to fabricate reproducible and continuously homogenous composite fibres. The main aim was to fabricate a composite material which combines the special properties of polymer fibres and thermo-sensitive microgels, as well as properties given by the specific choice of the fibre polymer and the microgels co-monomers. Furthermore, these fibres are supposed to enable a macroscopic access to the microgel properties, because their usual dispersion state is not applicable for many tasks, but a macroscopic fibre nonwoven consisting of microscopic fibres decorated with nanoscopic microgels will provide this opportunity, without losing the “nano” aspect. In a first step, using PVA it was already shown that the microgels retain their thermo-sensitive, smart swelling properties in the fibre structure, which gives the fibres tuneable swelling properties as well. Additional ways to crosslink these fibres chemically or physically are shown. In the next step, PCL, a polymer with more special properties (hydrophobic, degradable), was chosen to achieve fibres with these properties and to show how much these properties can be influenced by the addition of microgels. Moreover, different fibre morphologies have been fabricated, fibres with microgels located only in the core and fibres with microgels located only on the surface, which not only show differences in the tuneable swelling behaviour and the degradation process, but it also opens opportunities to more specific applications. The different morphologies were achieved by using different solvent systems: methanol/toluene and chloroform/DMF. Additionally, it should be mentioned that the simple one step electrospinning process of hydrophilic microgels and hydrophobic PCL gives access to an elegant way to completely change the hydrophobicity of the general polymer fibres. To give a possibility for a better exploitation of the newly achieved PCL fibres with microgel exclusively on the fibre surface, microgels with a special property combination have been created: microgels, crosslinked with a star-shaped acrylate-functionalised poly(epsilon-caprolactone) crosslinker, that are degradable due to the same functionality as PCL, having additionally hydrophobic domains to immobilise hydrophobic drugs. The synthesis was done via a specialised miniemulsion polymerisation and uptake as well as release of ibuprofen was shown. Fibres with these microgels on the surface could deliver drugs targeted to specific places and are completely degradable under physiological conditions. The results of a preliminary study for a project with the aim of creating PLA based stents, with a neutral degradation process for a higher tolerance in the human body. A combination of VIm modified microgels with polylactide fibres was chosen to achieve this. The fibres are successfully realised and analysed regarding their swelling properties, in the same manner as the other composite fibres presented in this work. Two small preliminary studies about different topics, which are still in an early stage, but that already show promising results are also presented in this thesis. Fibres with iron(III) oxide nanoparticles and phosphazene microsphere have also been fabricated using the same technique shown for the PCL-microgel fibres with microgel exclusively on the surface. These fibres give an insight in the process and show its limitations and possibilities. Furthermore, hollow fibre membranes with microgels as additive have been prepared using a wet spinning process, to show other options to fabricate composite materials with microgels, accessing the field of filtration and separation

Microgel polymer composite fibres

In this thesis some novel ideas and advancements in the field of polymer composite fibres, specifically microgel-based polymer composite fibres have been achieved. The main task was to investigate and understand the electrospinning process of microgels and polymers and the interplay of parameter influences, in order to fabricate reproducible and continuously homogenous composite fibres. The main aim was to fabricate a composite material which combines the special properties of polymer fibres and thermo-sensitive microgels, as well as properties given by the specific choice of the fibre polymer and the microgels co-monomers. Furthermore, these fibres are supposed to enable a macroscopic access to the microgel properties, because their usual dispersion state is not applicable for many tasks, but a macroscopic fibre nonwoven consisting of microscopic fibres decorated with nanoscopic microgels will provide this opportunity, without losing the “nano” aspect. In a first step, using PVA it was already shown that the microgels retain their thermo-sensitive, smart swelling properties in the fibre structure, which gives the fibres tuneable swelling properties as well. Additional ways to crosslink these fibres chemically or physically are shown. In the next step, PCL, a polymer with more special properties (hydrophobic, degradable), was chosen to achieve fibres with these properties and to show how much these properties can be influenced by the addition of microgels. Moreover, different fibre morphologies have been fabricated, fibres with microgels located only in the core and fibres with microgels located only on the surface, which not only show differences in the tuneable swelling behaviour and the degradation process, but it also opens opportunities to more specific applications. The different morphologies were achieved by using different solvent systems: methanol/toluene and chloroform/DMF. Additionally, it should be mentioned that the simple one step electrospinning process of hydrophilic microgels and hydrophobic PCL gives access to an elegant way to completely change the hydrophobicity of the general polymer fibres. To give a possibility for a better exploitation of the newly achieved PCL fibres with microgel exclusively on the fibre surface, microgels with a special property combination have been created: microgels, crosslinked with a star-shaped acrylate-functionalised poly(epsilon-caprolactone) crosslinker, that are degradable due to the same functionality as PCL, having additionally hydrophobic domains to immobilise hydrophobic drugs. The synthesis was done via a specialised miniemulsion polymerisation and uptake as well as release of ibuprofen was shown. Fibres with these microgels on the surface could deliver drugs targeted to specific places and are completely degradable under physiological conditions. The results of a preliminary study for a project with the aim of creating PLA based stents, with a neutral degradation process for a higher tolerance in the human body. A combination of VIm modified microgels with polylactide fibres was chosen to achieve this. The fibres are successfully realised and analysed regarding their swelling properties, in the same manner as the other composite fibres presented in this work. Two small preliminary studies about different topics, which are still in an early stage, but that already show promising results are also presented in this thesis. Fibres with iron(III) oxide nanoparticles and phosphazene microsphere have also been fabricated using the same technique shown for the PCL-microgel fibres with microgel exclusively on the surface. These fibres give an insight in the process and show its limitations and possibilities. Furthermore, hollow fibre membranes with microgels as additive have been prepared using a wet spinning process, to show other options to fabricate composite materials with microgels, accessing the field of filtration and separation

Investigation of the Tendency of Carbon Fibers to Disintegrate into Respirable Fiber-Shaped Fragments

Recent reports of the release of large numbers of respirable and critically long fiber-shaped fragments from mesophase pitch-based carbon fiber polymer composites during machining and tensile testing have raised inhalation toxicological concerns. As carbon fibers and their fragments are to be considered as inherently biodurable, the fiber pathogenicity paradigm motivated the development of a laboratory test method to assess the propensity of different types of carbon fibers to form such fragments. It uses spallation testing of carbon fibers by impact grinding in an oscillating ball mill. The resulting fragments were dispersed on track-etched membrane filters and morphologically analyzed by scanning electron microscopy. The method was applied to nine different carbon fiber types synthesized from polyacrylonitrile, mesophase or isotropic pitch, covering a broad range of material properties. Significant differences in the morphology of formed fragments were observed between the materials studied. These were statistically analyzed to relate disintegration characteristics to material properties and to rank the carbon fiber types according to their propensity to form respirable fiber fragments. This tendency was found to be lower for polyacrylonitrile-based and isotropic pitch-based carbon fibers than for mesophase pitch-based carbon fibers, but still significant. Although there are currently only few reports in the literature of increased respirable fiber dust concentrations during the machining of polyacrylonitrile-based carbon fiber composites, we conclude that such materials have the potential to form critical fiber morphologies of WHO dimensions. For safe-and-sustainable carbon fiber-reinforced composites, a better understanding of the material properties that control the carbon fiber fragmentation is imperative

LifeTime and improving European healthcare through cell-based interceptive medicine

AUTEURS : LifeTime Community Working GroupsInternational audienceHere we describe the LifeTime Initiative, which aims to track, understand and target human cells during the onset and progression of complex diseases, and to analyse their response to therapy at single-cell resolution. This mission will be implemented through the development, integration and application of single-cell multi-omics and imaging, artificial intelligence and patient-derived experimental disease models during the progression from health to disease. The analysis of large molecular and clinical datasets will identify molecular mechanisms, create predictive computational models of disease progression, and reveal new drug targets and therapies. The timely detection and interception of disease embedded in an ethical and patient-centred vision will be achieved through interactions across academia, hospitals, patient associations, health data management systems and industry. The application of this strategy to key medical challenges in cancer, neurological and neuropsychiatric disorders, and infectious, chronic inflammatory and cardiovascular diseases at the single-cell level will usher in cell-based interceptive medicine in Europe over the next decade

LifeTime and improving European healthcare through cell-based interceptive medicine

LifeTime aims to track, understand and target human cells during the onset and progression of complex diseases and their response to therapy at single-cell resolution. This mission will be implemented through the development and integration of single-cell multi-omics and imaging, artificial intelligence and patient-derived experimental disease models during progression from health to disease. Analysis of such large molecular and clinical datasets will discover molecular mechanisms, create predictive computational models of disease progression, and reveal new drug targets and therapies. Timely detection and interception of disease embedded in an ethical and patient-centered vision will be achieved through interactions across academia, hospitals, patient-associations, health data management systems and industry. Applying this strategy to key medical challenges in cancer, neurological, infectious, chronic inflammatory and cardiovascular diseases at the single-cell level will usher in cell-based interceptive medicine in Europe over the next decade.We would like to acknowledge all participants that have attended and contributed to LifeTime meetings and workshops through many exciting presentations and discussions. We thank Johannes Richers for artwork. LifeTime has received funding from the European Unionʼs Horizon 2020 research and innovation framework programme under Grant agreement 820431