*4.10. Nervous Tissue*

The nervous system is a complex system of specialized cells that connect the parts of the body and coordinate it using signals. The main cells that transmit said signals are neurons, while they require a network of nonneural supportive cells, i.e., glia cells. In this context, the nervous tissue's ECM is indeed created by glia cells, which protect, isolate, and feed neurons, thereby allowing synapsis. The main structural components of the ECM are collagen (types II and IV) and laminin. Fibronectin guides axon growth, and acetylcholinesterase helps to regulate neural signals [170].

Damage of the nervous system can be caused by multiple conditions, diseases, and injuries, while symptoms related to tissue damage can be multiple, from mild to severe, including the loss of motor functions [171]. The regeneration of damaged nerve connections is a long-time pursued aim and it has been widely assayed using di fferent approaches. There is consensus in defining the properties of the ideal graft for nerve regeneration, which should be of a flexible, thin, neuro-inductive, conductive, and biocompatible structure, capable of promoting axon proliferation and of guiding its growth toward the reconnection of damaged nervous edges [172,173]. To do this, the structure should be able to be molded by Schwann cells, which are specific glia cells related to the guidance of neural regeneration processes. In this context, the usefulness of dECM-derived nerve sca ffolds as implantable grafts has been assessed in in vitro and in vivo animal trials, with some promising results [174]. Some studies have shown the capacity of the dECM to promote axon growth and the regeneration of peripheral nerve connections in rats [69,172,175]. The regeneration process requires weeks, and the subjects are in need of rehabilitation in order to begin proper recovery.

For decellularization of nervous tissue, the most commonly used approach is washing with detergents. Note that in the peripheral nerves, the main DNA source is that of Schwann cells, which protect the axons that carry signals. The detergent that shows the best results in this tissue is usually Triton X-200 [28]. A low concentration and prolonged Triton X-200 treatment has been proven successful in eliminating both the axon and Schwann cells, as well as myelin waste. The elimination causes slight damage to the ECM proteins, but it retains good condition of the structure. This treatment is commonly used in combination with an osmotic cell burst, which breaks the cells, facilitating cell waste removal by Triton X-200. Other detergents, such as SDS or Triton-100, are used without osmotic shock [33,171]. Other than these, nucleases have been used in combination with detergents and osmotic methods to ensure that the DNA is properly removed.
