China
Africa
Explore chapters and articles related to this topic
Propagation of the Action Potential
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The solution, in the form of myelinated axons, is ingeniously simple and highly effective. The axon is surrounded by a myelin sheath consisting of up to 200 layers or so of passive cell membrane interrupted at regular intervals in what are referred to as the nodes of Ranvier (Figure 4.7). The region between adjacent nodes is the internode, whose length is roughly 100–150 times the axon diameter and ranges in length between about 200 µm and 2.5 mm, depending on axon diameter. The sheath is wrapped around the axon during embryonic development by specialized satellite cells of the nervous system – the glial cells (Section 1.2.3). In the central nervous system, the glial cells that form the myelin sheath are referred to as oligodendrocytes, with each oligodendrocyte forming one internode of myelin for up to about 50 adjacent axons. In the peripheral nervous system, a glial cell referred to as a Schwann cell forms one internode of only a single axon.
Regeneration: Nanomaterials for Tissue Regeneration
Published in Harry F. Tibbals, Medical Nanotechnology and Nanomedicine, 2017
There is a critical difference between regeneration in peripheral nerves and those of the central nervous system. In the peripheral nervous system, axons are myelinated by Schwann cells, which wrap around axons to form a myelin sheath. Myelination insulates the axons and provides a mechanism for speeding and strengthening the propagation of action potentials by which the nerves communicate with each other, and with sensory and motor cells. The Schwann cells promote axon repair by at least two mechanisms. After injury, the myelin sheath formed by Schwann cells can be retained and form a channel to guide the regrowth of a renewed axon. Schwann cells can also regress to an earlier developmental state as glial cells, which promote the regeneration of the axon. Schwann cells are absent from the central nervous system—the spinal cord and the brain. Therefore, research and clinical progress has tended to start with repair of peripheral nerves and progress to the spinal cord and brain.
The neurotrophic factor rationale for using brief electrical stimulation to promote peripheral nerve regeneration in animal models and human patients
Published in Ze Zhang, Mahmoud Rouabhia, Simon E. Moulton, Conductive Polymers, 2018
The glial Schwann cells of the peripheral nervous system provide support for the regeneration of lost axons (Fenrich and Gordon 2004). Peripheral nerve injuries that disrupt the continuity of the axons result in the degeneration of the axons distal to the injury and the activation of regenerative programs in the injured neurons (Gordon and Sulaiman 2013; Gordon, 2015). Nerve injuries are sustained in association with trauma, including brachial plexus injuries in babies, and gunshot and knife injuries in children and adults (Midha 2011; Sulaiman et al. 2011; Sulaiman and Gordon 2013).
Recent advances in micro-sized oxygen carriers inspired by red blood cells
Published in Science and Technology of Advanced Materials, 2023
Qiming Zhang, Natsuko F. Inagaki, Taichi Ito
Peripheral nerve injury is another indication for HOBT because oxygen promotes nerve regeneration and reduces inflammatory cells. For instance, Schwann cells are involved in peripheral nerve regeneration, including myelin formation, the secretion of neurotrophins, and the production of extracellular matrix molecules. In 2013, Ma et al. revealed that perfluorotributylamine (PFTBA) with a thrombin-enriched fibrin hydrogel increased the viability of Schwann cells and the expression of regeneration-related genes under hypoxia in both 2D and 3D cultures [152]. In rats with 12-mm-sciatic nerve defects, transplantation of Schwann cells with the PFTBA hydrogel showed better sciatic nerve regeneration in comparison to a control without the hydrogel [153]. However, the time for releasing oxygen from the PFTBA hydrogel was limited to 48 hours. Later, Teng et al. modified the PFTBA hydrogel using a coaxial electrospinning technique to prolong the oxygen supply [69]. PFTBA core-shell fibers containing PFTBA in the core and PCL-chitosan in the shell were able to extend the oxygen supply to up to 144 hours. The Schwann cells in the PFTBA core-shell fibers increased the survival and expression of regeneration-related genes under hypoxic conditions in vitro. Furthermore, improved axonal regeneration and remyelination by the PFTBA core-shell fibers were observed in a 17-mm rat sciatic nerve defect model.
Influence of ionic crosslinkers (Ca2+/Ba2+/Zn2+) on the mechanical and biological properties of 3D Bioplotted Hydrogel Scaffolds
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Md. Sarker, Mohammad Izadifar, David Schreyer, Xiongbiao Chen
Implanted nerve guidance conduits (NGC) featuring micro/nano-scale physical cues across a damaged peripheral nerve have promoted axon regeneration in a number of studies [37,38]. Biofabricated and aligned micro-strands could be used in NGCs to obtain directional outgrowth of axons. In particular, Schwann cells embedded in hydrogel strands facilitate the regeneration process by producing growth factors and guiding the axon growth cone to the distal end of damaged nerves [39,40]. However, complex interactions among various metal ions, mannuronic acid, guluronic acid, and incorporated cells might significantly affect the survival and biological performance of Schwann cells in possible applications for peripheral nerve regeneration. To address this issue, Schwann cells were used in this study in the biofabrication of alginate scaffolds.
PCL and PCL-based materials in biomedical applications
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Elbay Malikmammadov, Tugba Endogan Tanir, Aysel Kiziltay, Vasif Hasirci, Nesrin Hasirci
Recently, electrospinning process has been the choice of manufacturing of 2D or 3D scaffolds with nanoscale fibers mimicking ECM filaments for soft tissue engineering [148]. Scaffolds with fibrous structures are considered to be suitable for nerve tissue regeneration due to their structural similarity of the organization of neurons. Many natural polymers required chemical crosslinking e.g. with glutaraldehyde and carbodiimide, to improve structural stability. However, these crosslinking agents have toxic effects which make their use challenging in biomedical applications. Cooper et al. [159] developed electrospun chitosan-PCL scaffolds without using any chemical crosslinking. The aim was to use them in nerve regeneration and they compared the organization of Schwann cells on aligned fibers, randomly oriented fibers, and cast films. Neural cells exhibited good attachment and proliferation on all substrate morphologies, but bipolar morphology and unidirectional extension which is specific to neural cells were observed on aligned chitosan-PCL fibers. In another study, chitosan was used to reinforce electrospun PCL nanofibers [160]. Chitosan was either used to blend with PCL and was electrospun in a single step or was air sprayed on electrospun PCL nanofibers. Mesenchymal stem cells (MSCs) demonstrated better biological responses on chitosan-PCL composites than on pure PCL scaffold.