STRUCTURAL AND MECHANICAL CHARACTERIZATION OF DEFORMED POLYMER USING CONFOCAL RAMAN MICROSCOPY AND DSC

Polymers have various interesting properties, which depend largely on their inner structure. One way to influence the macroscopic behaviour is the deformation of the polymer chains, which effects the change in microstructure. For analyzing the microstructure of non-deformed and deformed polymer materials, Raman spectroscopy as well as differential scanning calorimetry (DSC) were used. In the present study we compare the results for crystallinity measurements of deformed polymers using both methods in order to characterize the differences in micro-structure due to deformation. The study is ongoing, and we present the results of the first tests

Auf der Suche nach dem optimalen Material : Möglichkeiten und Grenzen der Knochenheilung

Operative Maßnahmen zur Behandlung von knöchernen Defekten müssen bei der Versorgung von Unfallverletzten, aber auch nach der Entfernung von Knochentumoren und -zysten tagtäglich in der Unfallchirurgie durchgeführt werden. Überschreitet das Ausmaß der Defekte eine kritische Größe, kann der Körper diesen Substanzverlust nicht mehr aus eigener Kraft regenerieren, was die statischen und dynamischen Skelettfunktionen beträchtlich einschränkt. Dies ist für die betroffenen Patienten mit weitreichenden Einbußen an Lebensqualität verknüpft. Daher ist es klinisch notwendig, knöcherne Substanzverluste ab einer bestimmten Größe mit einem Material zu ersetzen, das die körpereigenen Regenerationsmechanismen unterstützt, damit letztendlich die ursprüngliche Skelettarchitektur wiederhergestellt wird. Die Überprüfung der Gewebeverträglichkeit von neu entwickelten Knochenersatzmaterialien und die Charakterisierung der Mechanismen, die für ihren Abbau im Körper verantwortlich sind, bilden einen Forschungsschwerpunkt in der Experimentellen Unfallchirurgie der Universität Gießen

Auf der Suche nach dem optimalen Material : Möglichkeiten und Grenzen der Knochenheilung

Operative Maßnahmen zur Behandlung von knöchernen Defekten müssen bei der Versorgung von Unfallverletzten, aber auch nach der Entfernung von Knochentumoren und -zysten tagtäglich in der Unfallchirurgie durchgeführt werden. Überschreitet das Ausmaß der Defekte eine kritische Größe, kann der Körper diesen Substanzverlust nicht mehr aus eigener Kraft regenerieren, was die statischen und dynamischen Skelettfunktionen beträchtlich einschränkt. Dies ist für die betroffenen Patienten mit weitreichenden Einbußen an Lebensqualität verknüpft. Daher ist es klinisch notwendig, knöcherne Substanzverluste ab einer bestimmten Größe mit einem Material zu ersetzen, das die körpereigenen Regenerationsmechanismen unterstützt, damit letztendlich die ursprüngliche Skelettarchitektur wiederhergestellt wird. Die Überprüfung der Gewebeverträglichkeit von neu entwickelten Knochenersatzmaterialien und die Charakterisierung der Mechanismen, die für ihren Abbau im Körper verantwortlich sind, bilden einen Forschungsschwerpunkt in der Experimentellen Unfallchirurgie der Universität Gießen

Podosome-Driven Defect Development in Lamellar Bone under the Conditions of Senile Osteoporosis Observed at the Nanometer Scale

The degradation mechanism of human trabecular bone harvested from the central part of the femoral head of a patient with a fragility fracture of the femoral neck under conditions of senile osteoporosis was investigated by high-resolution electron microscopy. As evidenced by light microscopy, there is a disturbance of bone metabolism leading to severe and irreparable damages to the bone structure. These defects are evoked by osteoclasts and thus podosome activity. Podosomes create typical pit marks and holes of about 300-400 nm in diameter on the bone surface. Detailed analysis of the stress field caused by the podosomes in the extracellular bone matrix was performed. The calculations yielded maximum stress in the range of few megapascals resulting in formation of microcracks around the podosomes. Disintegration of hydroxyapatite and free lying collagen fibrils were observed at the edges of the plywood structure of the bone lamella. At the ultimate state, the disintegration of the mineralized collagen fibrils to a gelatinous matrix comes along with a delamination of the apatite nanoplatelets resulting in a brittle, porous bone structure. The nanoplatelets aggregate to big hydroxyapatite plates with a size of up to 10 x 20 μm2. The enhanced plate growth can be explained by the interaction of two mechanisms in the ruffled border zone: the accumulation of delaminated hydroxyapatite nanoplatelets near clusters of podosomes and the accelerated nucleation and random growth of HAP nanoplatelets due to a nonsufficient concentration of process-directing carboxylated osteocalcin cOC. © 2021 The Authors. Published by American Chemical Society

Influence of the chain microstructure on the properties of metallocene-based thermoplastic elastic polyolefines

Polymeric materials are unmatched in the diversity of their properties, such as flexibility, stiffness or mechanical strength. One still open point is to tailor these material properties by controlling the molecular architecture. Olefin-based polymers have attracted considerable interest because the development of metallocene catalysts with defined molecular structures and geometries enables the synthesis of polymers with controlled composition and stereoregularity. Certain catalysts are capable of producing low crystalline olefines showing thermoplastic-elastic properties. Since the mechanical properties of elastomers depend on the amount and distribution of crosslinks, one important point in the development of semicrystalline thermoplastic elastomeric polymers is to direct the distribution of crystallizable segments und to study the resulting morphology with respect to the macroscopic properties. In this work the morphology of propene based polymers polymerized by homogeneous transition metal catalysis in a single polymerization step but at various polymerization conditions was explored. Two types of polymers were investigated: Polyketones, which consist of two chemically different phases, propene/ethene/CO, and propene homopolymers. The origin and the nature of the crystalline network are described. The influence of the polymer morphology in the macroscopic properties is explored on different length scales combining various analytical techniques, such as DSC, WAXS and scanning force microscopy. The results obtained clearly show that changing the polymerization conditions can open new possibilities to modify the chain microstructure without any change on the chemical side. The length and the distribution of crystallizable blocks can be varied in such a way that new materials with tailored mechanical properties become available. The incorporation of CO functionalities in the polymer backbone leads to materials with distinct differences in the chemical properties

An Evaluation of Local Thermal Analysis of Polymers on the Sub-Micrometer Scale Using Heated Scanning Probe Microscopy Cantilevers

A basic understanding of thermal properties of polymers is of fundamental importance for the development of advanced polymers. However, up to now, mainly bulk properties have been investigated. To characterize local softening processes in polymers, a local thermal analysis (LTA) technique is applied as an add-on to a scanning probe microscope. The development of a new generation of heatable cantilever probes enables thermal analysis in the sub-μm range. This method is based on an appropriate temperature calibration, which provides a reliable correlation of the applied voltage heating the tip and the actual temperature at the tip–sample interface. As the presented technique is more susceptible to environmental changes than comparable macroscopic methods, different parameters that might influence its performance are evaluated like a strong dependence on sample temperature. It is shown that the measured softening temperature on a polystyrene (PS) sample decreases from 102.2 to 66.4 °C as the temperature of the substrate is increased by 50 °C. The interaction between heat from the cantilever and the substrate is the reason for local sample softening, which opens new perspectives to understand the temperature calibration process using the melting standard method. A stepwise guideline for a suitable temperature calibration is provided

Podosome-Driven Defect Development in Lamellar Bone under the Conditions of Senile Osteoporosis Observed at the Nanometer Scale

The degradation mechanism of human trabecular bone harvested from the central part of the femoral head of a patient with a fragility fracture of the femoral neck under conditions of senile osteoporosis was investigated by high-resolution electron microscopy. As evidenced by light microscopy, there is a disturbance of bone metabolism leading to severe and irreparable damages to the bone structure. These defects are evoked by osteoclasts and thus podosome activity. Podosomes create typical pit marks and holes of about 300-400 nm in diameter on the bone surface. Detailed analysis of the stress field caused by the podosomes in the extracellular bone matrix was performed. The calculations yielded maximum stress in the range of few megapascals resulting in formation of microcracks around the podosomes. Disintegration of hydroxyapatite and free lying collagen fibrils were observed at the edges of the plywood structure of the bone lamella. At the ultimate state, the disintegration of the mineralized collagen fibrils to a gelatinous matrix comes along with a delamination of the apatite nanoplatelets resulting in a brittle, porous bone structure. The nanoplatelets aggregate to big hydroxyapatite plates with a size of up to 10 x 20 μm2. The enhanced plate growth can be explained by the interaction of two mechanisms in the ruffled border zone: the accumulation of delaminated hydroxyapatite nanoplatelets near clusters of podosomes and the accelerated nucleation and random growth of HAP nanoplatelets due to a nonsufficient concentration of process-directing carboxylated osteocalcin cOC.publishe