Florian Feist

Biomechanics of far cortical locking.

The development of far cortical locking (FCL) was motivated by a conundrum: locked plating constructs provide inherently rigid stabilization, yet they should facilitate biologic fixation and secondary bone healing that relies on flexible fixation to stimulate callus formation. Recent studies have confirmed that the high stiffness of standard locked plating constructs can suppress interfragmentary motion to a level that is insufficient to reliably promote secondary fracture healing by callus formation. Furthermore, rigid locking screws cause an uneven stress distribution that may lead to stress fracture at the end screw and stress shielding under the plate. This review summarizes four key features of FCL constructs that have been shown to enhance fixation and healing of fractures: flexible fixation, load distribution, progressive stiffening, and parallel interfragmentary motion. Specifically, flexible fixation provided by FCL reduces the stiffness of a locked plating construct by 80% to 88% to actively promote callus proliferation similar to an external fixator. Load is evenly distributed between FCL screws to mitigate stress risers at the end screw. Progressive stiffening occurs by near cortex support of FCL screws and provides additional support under elevated loading. Finally, parallel interfragmentary motion by the S-shaped flexion of FCL screws promotes symmetric callus formation. In combination, these features of FCL constructs have been shown to induce more callus and to yield significantly stronger and more consistent healing compared with standard locked plating constructs. As such, FCL constructs function as true internal fixators by replicating the biomechanical behavior and biologic healing response of external fixators.

Angular Impact Mitigation system for bicycle helmets to reduce head acceleration and risk of traumatic brain injury

Angular acceleration of the head is a known cause of traumatic brain injury (TBI), but contemporary bicycle helmets lack dedicated mechanisms to mitigate angular acceleration. A novel Angular Impact Mitigation (AIM) system for bicycle helmets has been developed that employs an elastically suspended aluminum honeycomb liner to absorb linear acceleration in normal impacts as well as angular acceleration in oblique impacts. This study tested bicycle helmets with and without AIM technology to comparatively assess impact mitigation. Normal impact tests were performed to measure linear head acceleration. Oblique impact tests were performed to measure angular head acceleration and neck loading. Furthermore, acceleration histories of oblique impacts were analyzed in a computational head model to predict the resulting risk of TBI in the form of concussion and diffuse axonal injury (DAI). Compared to standard helmets, AIM helmets resulted in a 14% reduction in peak linear acceleration (p<0.001), a 34% reduction in peak angular acceleration (p<0.001), and a 22-32% reduction in neck loading (p<0.001). Computational results predicted that AIM helmets reduced the risk of concussion and DAI by 27% and 44%, respectively. In conclusion, these results demonstrated that AIM technology could effectively improve impact mitigation compared to a contemporary expanded polystyrene-based bicycle helmet, and may enhance prevention of bicycle-related TBI. Further research is required.

Integration of a crashworthy battery in a fully electric city bus

This paper focuses on a novel concept for a fully electric city bus and the crashworthy integration of a changeable battery system. The changeable battery had to be located in an accessible and safe position. By careful analysis, an acceptable battery location was found under the floor of the vehicle. Due to the absence of design drawings of the real bus, an existing finite element model of a full size van was taken as a substitute. This model has less weight than the actual bus. Therefore, the battery was downsized based on range calculations. All parts of the vehicle concerning the combustion engine were removed and the battery was implemented in the model. This vehicle model was tested virtually using different crash load cases to demonstrate the feasibility of a crashworthy integration. Additional testing was carried out to evaluate the stability of the real bus lithium-ion cells under crash conditions.

Case study of a frontal car accident involving three fatally injured children

Rear occupants are generally considered to sustain less severe injuries in frontal car impacts compared with front occupants. Contrary to this thesis, in 2009, in a serious accident involving two passenger cars took place in Austria in which three children seated in the rear were fatally injured in a frontal collision. Based on this car accident, the present study was performed to gain a better understanding of rear occupants’ injury mechanisms and potential improvements to rear-seat restraint system. The study employed a validated numerical model that shows that loads and injury criteria can be reduced by up to 70%. Also, national accident databases have been analysed. The accidentology indicates that children restrained by the vehicle rear belt are fatally injured only approximately two times more frequently than children using a child restraint system. The investigation indicates that the protection level offered to children aged 6–14 does not match the high protection level available for adults and for children up to six.

Fic Proteins of Campylobacter fetus subsp. venerealis Form a Network of Functional Toxin–Antitoxin Systems

Enzymes containing the FIC (filamentation induced by cyclic AMP) domain catalyze post-translational modifications of target proteins. In bacteria the activity of some Fic proteins resembles classical toxin–antitoxin (TA) systems. An excess of toxin over neutralizing antitoxin can enable bacteria to survive some stress conditions by slowing metabolic processes and promoting dormancy. The cell can return to normal growth when sufficient antitoxin is present to block toxin activity. Fic genes of the human and animal pathogen Campylobacter fetus are significantly associated with just one subspecies, which is specifically adapted to the urogenital tract. Here, we demonstrate that the fic genes of virulent isolate C. fetus subsp. venerealis 84-112 form multiple TA systems. Expression of the toxins in Escherichia coli caused filamentation and growth inhibition phenotypes reversible by concomitant antitoxin expression. Key active site residues involved in adenylylation by Fic proteins are conserved in Fic1, Fic3 and Fic4, but degenerated in Fic2. We show that both Fic3 and the non-canonical Fic2 disrupt assembly and function of E. coli ribosomes when expressed independently of a trans-acting antitoxin. Toxicity of the Fic proteins is controlled by different mechanisms. The first involves intramolecular regulation by an inhibitory helix typical for Fic proteins. The second is an unusual neutralization by heterologous Fic–Fic protein interactions. Moreover, a small interacting antitoxin called Fic inhibitory protein 3, which appears unrelated to known Fic antitoxins, has the novel capacity to bind and neutralize Fic toxins encoded in cis and at distant sites. These findings reveal a remarkable system of functional crosstalk occurring between Fic proteins expressed from chromosomal and extrachromosomal modules. Conservation of fic genes in other bacteria that either inhabit or establish pathology in the urogenital tract of humans and animals underscores the significance of these factors for niche-specific adaptation and virulence.

Measuring Poisson’s ratio: mechanical characterization of spruce wood by means of non-contact optical gauging techniques

In contemporary wood science, computer-aided engineering (CAE) systems are commonly used for designing and engineering of high-value products. In diverse CAE systems, high-fidelity models with a full material description, including elastic constants such as Poisson’s ratios, are needed. Only few studies have dealt so far with the investigation of the Poisson’s ratio of spruce wood (Picea abies (L.) Karst.) or wood in general. Therefore, in the present study all six main Poisson’s ratios of spruce wood were determined in uniaxial tensile experiments by employing optical gauging techniques like electronic speckle pattern interferometry and a combination of laser and video extensometry. Consistent results for the Poisson’s ratios were found by applying these different optical gauging techniques. However, values found in the literature are sometimes considerably different from values established in this study. For that reason, the optical gauging techniques were evaluated with a conventional mechanical extensometer, which proved that there were no significant differences between the established measurements. Finally, in this study the feasibility of different non-contact optical gauging techniques was evaluated and compared through the comparison of the Poisson’s ratios, which showed that non-contact optical gauging techniques are suitable for establishing the Poisson’s ratio of (spruce) wood.

Safety Measures for Avoiding or Mitigating the Occupant Exposure in Collisions with Large Animals

Road accidents involving large animals are responsible for a considerable number of fatalities; these are e.g. elk in Northern Europe or camels in Middle East, Horn of Africa and Maghreb. In order to address this topic, investigations concerning active and passive road safety have been launched at the King Saud University and at Graz University of Technology. Data of real accidents or accident statistics are not available in the required quality to gather typical accident scenarios. Therefore generic accidents types were derived and critical load cases were determined by means of multi body and finite element simulations. It was found that the vehicle acceleration due to the impact is not a safety issue, but the finite element simulations showed that massive local intrusions into the passenger compartment are the main cause for severe occupant injuries. Therefore, concepts for the prevention of critical intrusions were examined. In a first step the space required for the occupant movement due to the rather mediocre acceleration levels in car-to-large animal accidents was determined by multi-body simulation. In a second step different approaches preventing intrusions into the occupant-movement-space were analyzed by finite element simulation. In addition, the possible effects and requirements of active systems have been studied to demonstrate the potential of combined measures.