Effects of root dehydration on biomechanical properties of woody roots of <i>Ulex europaeus</i>

Aims: Effects of root water status on root tensile strength and Young’s modulus were studied in relation to root reinforcement of slopes. Methods: Biomechanical properties of woody roots, Ulex europaeus, were tested during progressive dehydration and after thirty-day moisture equilibration in soil with contrasting water contents. Root diameter, water content and water loss were recorded and root water potential versus water content relation was investigated. Tensile stresses induced by root contraction upon dehydration were measured. Results: Root tensile strength and Young’s modulus increased abruptly when root water content dropped below 0.5 g g −1. The strength increase was due to root radial and axial contraction induced by root water potential drop. Diameter decrease and strength gain were the largest for thin roots because of the relatively larger evaporative surface per volume of thin roots. Largely negative water potentials in dry soil induced root drying, affecting root biomechanical properties. Conclusion: Root water status is a factor that can cause (inappropriately) high strength values and the large variability reported in literature for thin roots. Therefore, all root diameter classes should have consistent moisture for fair comparison. Testing fully hydrated roots should be the routine protocol, given that slope instability occurs after heavy rainfall. </p

Centrifuge modelling of the effects of root geometry on transpiration-induced suction and stability of vegetated slopes

Shallow landslides (i.e., 1 - 2 m depth) on both man-made and natural slopes are of major concern worldwide that has led to huge amount of socio-economical losses. The use of vegetation has been considered as an environmentally friendly means of stabilising slopes. Existing studies have focused on the use of plant roots with different geometries to mechanically stabilise soil slopes, but there are little data available on the contribution of transpiration-induced suction to slope stability. This study was designed to quantify both the hydrological and mechanical effects of root geometry on the stability of shallow slopes. Centrifuge tests were conducted to measure soil suction in slope models supported by newly-developed artificial roots. These artificial roots exhibit three different representative geometries (i.e., tap, heart and plate) and could simulate the effects of transpiration. The measured suction was then back-analysed through a series of finite element seepage-stability analyses to determine the factor of safety (FOS). It is revealed that after a rainfall event with a return period of 1000 years, the slope supported by heart-shaped roots retained the highest suction of 3 kPa within the root depth and thus this type of root provided the greatest stabilisation effects. The FOS of the slope supported by the heart-shaped roots, through both mechanical reinforcement and transpiration-induced suction, is 16% and 28% higher than that supported by the tap- and plate-shaped roots, respectively

Small-scale modelling of plant root systems using 3D printing, with applications to investigate the role of vegetation on earthquake-induced landslides

Vegetation has been previously proposed as a method for protecting artificial and natural slopes against shallow landslides (e.g. as may be triggered by an earthquake); however, previous research has concentrated on individual root soil interaction during shear deformation rather than the global slope behaviour due to the extreme expense and difficulty involved in conducting full-scale field tests. Geotechnical centrifuge modelling offers an opportunity to investigate in detail the engineering performance of vegetated slopes, but its application has been restricted due to the lack of availability of suitable root analogues that can repeatably replicate appropriate mechanical properties (stiffness and strength) and realistic 3-D geometry. This study employed 3-D printing to develop a representative and repeatable 1:10 scale model of a tree root cluster representing roots up to 1.5 m deep at prototype scale) that can be used within a geotechnical centrifuge to investigate the response of a vegetated slope subject to earthquake ground motion. The printed Acrylonitrile Butadiene Styrene (ABS) plastic root model was identified to be highly representative of the geometry and mechanical behaviour (stiffness and strength) of real woody root systems. A programme of large direct shear tests was also performed to evaluate the additional strength provided by the root analogues within soil that is slipping and investigate the influence of various characteristics (including root area ratio, soil confining effective stress and root morphology) on this reinforcing effect. Our results show that root reinforcement is not only a function of root mechanical properties, but also depends on factors including surrounding effective confining stress (resulting in depth dependency even for the same RAR), depth of the slip plane and root morphology. When subject to shear loading in soil, the tap root appeared to structurally transfer load within the root system, including to smaller and deeper roots which subsequently broke or were pulled out. Finally, the root analogues were added to model slopes subjected toearthquake ground motion in the centrifuge, where it was revealed that vegetation can substantially reduce earthquake-induced slope deformation in the soil conditions tested (76% reduction on crest permanent settlement during slippage). Both the realistic 3-D geometry and highly simplified root morphologies, as characterised mechanically by the shear tests, were tested in the centrifuge which, despite exhibiting very different levels of additional strength in the shear tests, resulted in very similar responses of the slopes. This suggests that once a certain minimum level of reinforcement has been reached which will alter the deformation mechanism within the slope, further increases of root contribution (e.g. due to differences in root morphology) do not have a large further effect on improving slope stability.<br/

In vivo recordings of brain activity using organic transistors.

In vivo electrophysiological recordings of neuronal circuits are necessary for diagnostic purposes and for brain-machine interfaces. Organic electronic devices constitute a promising candidate because of their mechanical flexibility and biocompatibility. Here we demonstrate the engineering of an organic electrochemical transistor embedded in an ultrathin organic film designed to record electrophysiological signals on the surface of the brain. The device, tested in vivo on epileptiform discharges, displayed superior signal-to-noise ratio due to local amplification compared with surface electrodes. The organic transistor was able to record on the surface low-amplitude brain activities, which were poorly resolved with surface electrodes. This study introduces a new class of biocompatible, highly flexible devices for recording brain activity with superior signal-to-noise ratio that hold great promise for medical applications

Electrophoretic drug delivery for seizure control.

The persistence of intractable neurological disorders necessitates novel therapeutic solutions. We demonstrate the utility of direct in situ electrophoretic drug delivery to treat neurological disorders. We present a neural probe incorporating a microfluidic ion pump (μFIP) for on-demand drug delivery and electrodes for recording local neural activity. The μFIP works by electrophoretically pumping ions across an ion exchange membrane and thereby delivers only the drug of interest and not the solvent. This "dry" delivery enables precise drug release into the brain region with negligible local pressure increase. The therapeutic potential of the μFIP probe is tested in a rodent model of epilepsy. The μFIP probe can detect pathological activity and then intervene to stop seizures by delivering inhibitory neurotransmitters directly to the seizure source. We anticipate that further tailored engineering of the μFIP platform will enable additional applications in neural interfacing and the treatment of neurological disorders

Two-Dimensional Electrophoresis of Tau Mutants Reveals Specific Phosphorylation Pattern Likely Linked to Early Tau Conformational Changes

The role of Tau phosphorylation in neurofibrillary degeneration linked to Alzheimer's disease remains to be established. While transgenic mice based on FTDP-17 Tau mutations recapitulate hallmarks of neurofibrillary degeneration, cell models could be helpful for exploratory studies on molecular mechanisms underlying Tau pathology. Here, “human neuronal cell lines” overexpressing Wild Type or mutated Tau were established. Two-dimensional electrophoresis highlights that mutated Tau displayed a specific phosphorylation pattern, which occurs in parallel to the formation of Tau clusters as visualized by electron microscopy. In fact, this pattern is also displayed before Tau pathology onset in a well established mouse model relevant to Tau aggregation in Alzheimer's disease. This study suggests first that pathological Tau mutations may change the distribution of phosphate groups. Secondly, it is possible that this molecular event could be one of the first Tau modifications in the neurofibrillary degenerative process, as this phenomenon appears prior to Tau pathology in an in vivo model and is linked to early steps of Tau nucleation in Tau mutants cell lines. Such cell lines consist in suitable and evolving models to investigate additional factors involved in molecular pathways leading to whole Tau aggregation

Impact of Transplantation Timing on Renal Graft Survival Outcomes and Perioperative Complications

Nighttime organ transplantation aims to decrease cold ischemia duration, yet conflicting data exists on its impact on graft function and perioperative complications. This multicenter TRANSPLANT’AFUF study including 2,854 patients, transplanted between 1 January 2011, and 31 December 2022, investigated nighttime kidney transplantation’s impact (8:00 p.m.–8:00 a.m.) versus daytime (8:00 a.m.–8:00 p.m.) on surgical complications and graft survival. Overall, 2043 patients (71.6%) underwent daytime graft, while 811 (28.4%) underwent nighttime graft. No impact was observed of timing of graft surgery on graft survival with a median survival of 98 months and 132 months for daytime and nightime grafting, respectively (p = 0.1749). Moreover, no impact was observed on early surgical complications (Clavien I-II = 20.95% for DG and 20.10% for NG; Clavien III-IV-V = 15.42% for DG and 12.94% for NG; p = 0.0889) and late complications (&gt;30 days) (Clavien I-II = 6.80% for DG and 5.67% for NG; Clavien III-IV-V = 12.78% for DG and 12.82% for NG; p = 0.2444). Noteworthy, we found a significant increase in Maastricht 3 donors’ rates in nighttime transplantation (5.53% DG vs. 21.45% NG; p &lt; 0.0001). In conclusion, nighttime kidney transplantation did not impact early/late surgical complications nor graft survival