![]() It contains the blood vessels in the epineurium, which provide the nerve fibers with trophic support. A connective tissue can be divided into three layers: epineurium, perineurium, and endoneurium. The nerve bundles include the nerve fibers and connective tissue, which constitute the nerves as mentioned above. The first two types of nerve fibers with myelin sheath are Schwann cells (SCs) wrapped in several layers, while the third nerve fibers are generally non-myelinated. The periphery nerve system consists of all the nerves from the three main categories: the spine nerve, cranial nerve, visceral nerve, and their associated ganglia ( 8). Here, we aimed to review the pathophysiology and repairing strategies for PNI, focusing on the latest advances in nerve tissue engineering. ![]() To find a more suitable clinical treatment, the researchers need to pay attention to the regeneration effect of axons and focus on the transformation of basic research to clinical. In recent years, the research on neural tissue engineering has become more in-depth, and various NGCs have emerged one after another. The ideal NGCs should have excellent mechanical strength, good biocompatibility, biodegradability, and permeability ( 7). Even in some injury models, the clinical effect is similar to that of autologous nerve transplantation. Implantation of the NGCs in the injured site can simulate the neural structure after Wallerian degeneration and avoid immune reactions. They contain the essential cells and neurotrophic factors that support axon regeneration. The catheters are active scaffolds that can effectively guide axon regeneration. ![]() The core of nerve tissue engineering is to build a three-dimensional complex composed of cells and biomaterials and make the nerve guiding catheters (NGCs). With the rapid development of cell biology and materials science, a new discipline, tissue engineering, is established to construct a different method of peripheral nerve repair. However, this damages the healthy nerves, and the number of donors is limited ( 6). When the damage gap is more significant (more than 5 mm), it is not possibly repaired by the meticulous microscopic surgery, and nerve autograft is regarded as the gold standard ( 3, 5). An end-to-end nerve suture requires that the nerve stumps are aligned to achieve the best repair effect, and only the short nerve gap (<5 mm) can be used ( 5). The nerve suture and nerve grafts are extensively used for surgical nerve repair in the experiment and the clinic. In the previous studies, substantial functional recovery of mild and moderate nerve injury can be achieved by surgical operation (such as, nerve suture and nerve transplantation) or non-surgical operation (such as, magnetic field, electric field, He-Ne Laser, and traditional Chinese Medicine) ( 3). The recovery of the distal injury is better than that of the proximal injury, because axon growth only needs a short distance to reach the distal stump. ![]() ![]() In general, the stretch or crush injury results are better than those of transection. However, the repair is often slow and incomplete because axon extension depends on the synthesis and transportation of the intracellular substances, and the regeneration speed is similar to that of axon transportation, about 1–3 mm/day ( 4). The peripheral nervous system can self-regenerate and repair itself after injury. People often underestimate the incidence of PNI, which seriously affects the quality of life of the patients ( 1– 3). In the United States, the economic loss caused by nerve injury exceeds $150 billion annually, and the treatment cost exceeds billions of dollars every year. ( 1) It has attracted social attention because of its enormous social and economic pressure. A peripheral nerve injury (PNI) is a medical problem mainly caused by external trauma after stretching, tearing, or extrusion of peripheral nerves. ![]()
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