Magnetic nanoparticles for magnetically guided therapies against neural diseases

© 2014 Materials Research Society MRS BULLETIN • VOLUME 39 • NOVEMBER 2014 • www.mrs.org/bulletin Introduction A nerve in the peripheral nervous system is a cord-like structure that contains many axons. It includes neurons and nonneuronal Schwann cells that coat the axons in myelin. Myelin is an electrically insulating material and forms a sheath around the axon, which is fundamental for the proper conduction and transmission of electrochemical impulses, by insulating the axons from electrically charged atoms and molecules. Complete nerve injury (neurotmesis) results in the death of both distal axons and Schwann cells (i.e., those cells responsible to supply the myelin for peripheral neurons) with consequent functional loss in innervated organs. In contrast to the central nervous system, the peripheral nervous system has relevant regenerative capability, although complete functional recovery is rarely reached. There are a large number of different cell types involved in the healing and regeneration of an injured nerve; for example, in a peripheral nerve lesion, the axon distal from the injury site degenerates, and Schwann cells and later macrophages clean the neural tubes of cell debris and myelin, so-called Wallerian degeneration. 1 Myelin is a layer of membranous structure around axons responsible for the fast and effi cient propagation of electrical impulses through the neural system. When an injury occurs, a gap between the nerve’s damaged ends is produced, and surgical intervention is necessary. Nowadays, there are two main strategies for those injuries with a long gap. In the fi rst strategy, synthetic or biological conduits are sutured to each stump in order to target the distal end, avoiding scar tissue infi ltration. A second approach to long gaps uses autologous nerve grafts (autografts) to provide a natural guidance channel populated with functioning Schwann cells, but this is challenging due to donor site collateral effects and patient condition. 2 , 3 Because the axon regrows quite slowly (about 2–5 mm per day), it is extremely important to accelerate Magnetic nanoparticles for magnetically guided therapies against neural diseases