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WIREs Nanomed Nanobiotechnol
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Axon repair: surgical application at a subcellular scale

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Abstract Injury to the nervous system is a common occurrence after trauma. Severe cases of injury exact a tremendous personal cost and place a significant healthcare burden on society. Unlike some tissues in the body that exhibit self healing, nerve cells that are injured, particularly those in the brain and spinal cord, are incapable of regenerating circuits by themselves to restore neurological function. In recent years, researchers have begun to explore whether micro/nanoscale tools and materials can be used to address this major challenge in neuromedicine. Efforts in this area have proceeded along two lines. One is the development of new nanoscale tissue scaffold materials to act as conduits and stimulate axon regeneration. The other is the use of novel cellular‐scale surgical micro/nanodevices designed to perform surgical microsplicing and the functional repair of severed axons. We discuss results generated by these two approaches and hurdles confronting both strategies. WIREs Nanomed Nanobiotechnol 2010 2 151–161 This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery

Nanoknife for microscale axon cutting. (a) Schematic planar view of microsuspension and cutting shell microassembled into a nanoknife. Black arrow, serpentine flexures acting as compliant microsuspension. White arrow, 1‐µm thick silicon nitride cutting shell. Footprint of entire structure is 1 mm2. (b) Scanning electron microscope (SEM) view of pyramidal shaped cutting shell with apex serving as cutting edge (scale = 20 µm). (c) SEM showing cutting edge with an ∼20 nm radius of curvature (scale = 100 nm). (d) Image of assembled nanokife (scale = 200 µm). (e) Nanoknife mounted at an angle to a rod and held by a micromanipulator (not in view). For axon cutting in vitro, the nanoknife is positioned and angled, so that its planar footprint is parallel to the cell culture dish. The cutting stroke is executed as a downward movement delivered via the micromanipulator (scale = 500 µm). (f) Examples of cuts made by a nanoknife in an unmyelinated axon (arrow) and a myelinated axon (arrowhead) (scale = 25 µm).

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Axon microelectrofusion demonstrated by the passage of soluble cytoplasmic green fluorescent protein (GFP) from one axon fusion partner into another. (a) Brightfield image showing hippocampal axons in culture. Single arrow points to location where microelectrofusion was induced. (b) Prefusion image of the same field as in ‘a’ showing axons containing soluble cytoplasmic fluorescent GFP. (c) After microelectrofusion, GFP passed from the axon at the bottom left into an axon fusion partner that did not originally have GFP, indicating successful fusion of the two axonal compartments.

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Axon movement induced by dielectrophoresis (DEP). (a–d) A myelinated axon from the sciatic nerve of an adult mouse was positioned in between microfabricated electrodes (white arrows). Upon application of DEP, the axon was bent toward the electrode on the right, moving at a velocity of ∼5µ m/s.

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Single axon surgery in an anesthetized mouse. (a–f) Images showing the isolation of a short segment from a single axon using a nanoknife (black profile in ‘b’ and ‘c’). The arrows in ‘d’ and ‘e’ show the location of the first cut. The arrow in ‘f’ points to the isolated axon segment (scale a–f = 200 µm).

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Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease
Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement
Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery

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