Dendritic polyglycerols (dPG), particularly dendritic polyglycerol sulfates (dPGS), have been intensively studied due to their intrinsic anti-inflammatory activity. As related to brain pathologies ...involving neuroinflammation, the current study examined if dPG and dPGS can (i) regulate neuroglial activation, and (ii) normalize the morphology and function of excitatory postsynaptic dendritic spines adversely affected by the neurotoxic 42 amino acid amyloid-β (Aβ
) peptide of Alzheimer disease (AD). The exact role of neuroglia, such as microglia and astrocytes, remains controversial especially their positive and negative impact on inflammatory processes in AD. To test dPGS effectiveness in AD models we used primary neuroglia and organotypic hippocampal slice cultures exposed to Aβ
peptide. Overall, our data indicate that dPGS is taken up by both microglia and astrocytes in a concentration- and time-dependent manner. The mechanism of action of dPGS involves binding to Aβ
, i.e., a direct interaction between dPGS and Aβ
species interfered with Aβ fibril formation and reduced the production of the neuroinflammagen lipocalin-2 (LCN2) mainly in astrocytes. Moreover, dPGS normalized the impairment of neuroglia and prevented the loss of dendritic spines at excitatory synapses in the hippocampus. In summary, dPGS has desirable therapeutic properties that may help reduce amyloid-induced neuroinflammation and neurotoxicity in AD.
Poly(3,4‐ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) based organic electrochemical transistors (OECTs) have been widely applied in bioelectronics because of their low power ...consumption, biocompatibility, and ability to convert ionic biological signals into electronic signals with high sensitivity. Here, the processing of PEDOT:PSS thin films on soft substrates is reported for stretchable OECT applications. Enhanced stretchability of PEDOT:PSS films on elastic substrates is obtained by synergistically reducing the film thickness and decreasing the baking temperature. The resultant films, together with ultrathin Au electrodes, enable the assembling of fully stretchable OECTs using conventional fabrication techniques, without prestretching the substrates. The stretchable OECTs maintain similar electrical characteristics within 30% applied strain. It is also demonstrated that brittle PEDOT:PSS films, which are not suitable for making stretchable OECTs, can be used for transparent pressure sensors.
Thin films of the conducting polymer poly(3,4‐ethylenedioxythiophene) doped with polystyrene sulfonate can be used for stretchable electrochemical transistors and pressure sensors.
A method to measure the dimensions of objects below the optical diffraction limit using diffraction analysis of out-of-focus bright-field images is presented. The method relies on the comparison of ...the diffraction patterns of an object of unknown size to those of calibration objects of known size. Correlative scanning electron microscope measurements are used to demonstrate the applicability of this method to measure 100 nm microbeads as well as objects with a geometry different from the calibration objects. This technique is important in the context of tethered particle experiments, in which bio-filaments are bound between a substrate and a microbead. This procedure is applied to obtain the diameters of axonal extensions or neurites that are mechanically created in samples of rat hippocampal neurons. The dependence of neurite geometry on mechanical pull speed is investigated, and the diameter is found to be rate independent.
This thesis details the development of a collection of methods to measure the material parameters of mechanically-created neurites. Neurites are long thin processes extending from the body of a nerve ...cell. To characterize the material response of a neurite to a deformation, information about both its tension and its geometry are required and the body of this thesis is divided accordingly. In the first part, we describe a platform to precisely control and manoeuver neurite-tethered polystyrene beads. We use a mechanical probe composed of a hollow micropipette with its tip fixed to a functionalized bead to incite the formation of a neurite in a sample of rat hippocampal neurons. In the second part, we measure neurite tension by optically tracking the deflection of the beaded tip as the neurite is extended. By calibrating the spring constant of the pipette we can convert this deflection to a force. We use this technique to investigate the dependence of the force-extension relationship on mechanical pull speeds. We develop statistically robust methods to categorize the results and describe the behaviour of neurites under tension. The third part of this work presents a method to measure dimensions of objects below the optical diffraction limit using diffraction analysis of out-of-focus images. We validate this method by applying it to calibration objects with correlative scanning electron microscope (SEM) measurements. We apply this procedure to obtain the diameters of neurites and investigate the dependence of geometry on mechanical pull speed. In the final part of the thesis, we develop a model of neurite growth in response to elastic deformation. We decompose applied stretch into an elastic component and a growth component and adopt an observationally-motivated growth law. We compute best-fit model parameters by fitting force-extension curves. We find a time constant for the growth law of 0.009~s$^{-1}$, similar to the diffusion rate of actin in a cell. These results characterize the kinematics of neurite growth and establish new limits on the growth rate of neurites
Response of mechanically-created neurites to extension Anthonisen, Madeleine; Rigby, Matthew; Sangji, M. Hussain ...
Journal of the mechanical behavior of biomedical materials,
October 2019, 2019-10-00, 20191001, Letnik:
98
Journal Article
Recenzirano
We use micromanipulation techniques and real-time particle tracking to develop an approach to study specific attributes of neuron mechanics. We use a mechanical probe composed of a hollow ...micropipette with its tip fixed to a functionalized bead to induce the formation of a neurite in a sample of rat hippocampal neurons. We then move the sample relative to the pipette tip, elongating the neurite while simultaneously measuring its tension by optically tracking the deflection of the beaded tip. By calibrating the spring constant of the pipette, we can convert this deflection to a force. We use this technique to obtain uniaxial strain measurements of induced neurites and investigate the dependence of the force-extension relationship on mechanical pull speed. We show that in the range of pull speeds studied (0.05–1.8 μm/s), the variation in the work to extend a neurite 10 μm is consistent across pull speeds. We do not observe statistically significant rate-dependent effects in the force-extension profiles; instead we find the same quadratic behaviour (with parameters drawn from the same distributions) at each pull speed.
This thesis examines the role of string loops in large-scale structure formation and ultimately puts constraints on cosmic strings as was done in 1. Cosmic strings are expected to form loops. These ...can act as seeds for accretion of dark matter, leading to the formation of ultracompact minihalos (UCMHs). We perform a detailed study of the accretion of dark matter onto cosmic string loops and compute the resulting mass distribution of UCMHs. We then apply observational limits on the present-day abundance of UCMHs to derive corresponding limits on the cosmic string tension Gµ. The bounds are strongly dependent upon the assumed distribution of loop velocities and their impacts on UCMH formation. Under the assumption that a loop can move up to a thousand times its own radius and still form a UCMH, we and a limit of Gµ ≤ 1 x 10-7. We show, in opposition to previous results, that strong limits on the cosmic string tension are not obtainable from UCMHs when more stringent (and realistic) requirements are placed on loop velocities.
Brain and spinal cord injury may lead to permanent disability and death because it is still not possible to regenerate neurons over long distances and accurately reconnect them with an appropriate ...target. Here a procedure is described to rapidly initiate, elongate, and precisely connect new functional neuronal circuits over long distances. The extension rates achieved reach over 1.2 mm/h, 30-60 times faster than the in vivo rates of the fastest growing axons from the peripheral nervous system (0.02 to 0.04 mm/h)
and 10 times faster than previously reported for the same neuronal type at an earlier stage of development
. First, isolated populations of rat hippocampal neurons are grown for 2-3 weeks in microfluidic devices to precisely position the cells, enabling easy micromanipulation and experimental reproducibility. Next, beads coated with poly-D-lysine (PDL) are placed on neurites to form adhesive contacts and pipette micromanipulation is used to move the resulting bead-neurite complex. As the bead is moved, it pulls out a new neurite that can be extended over hundreds of micrometers and functionally connected to a target cell in less than 1 h. This process enables experimental reproducibility and ease of manipulation while bypassing slower chemical strategies to induce neurite growth. Preliminary measurements presented here demonstrate a neuronal growth rate far exceeding physiological ones. Combining these innovations allows for the precise establishment of neuronal networks in culture with an unprecedented degree of control. It is a novel method that opens the door to a plethora of information and insights into signal transmission and communication within the neuronal network as well as being a playground in which to explore the limits of neuronal growth. The potential applications and experiments are widespread with direct implications for therapies that aim to reconnect neuronal circuits after trauma or in neurodegenerative diseases.
PDF
