**3. Nanofibrous scaffolds applied in PNS repair**

within the first 24-hour and at all other timepoints up to 30 days post-injury. Compared with saline-treatment, SAPNS created a seamless connection across lesion site and appropriate hostscaffold interfaces which led to significantly improved repair. Further studies were conducted by Guo et al. using a rodent TBI model (Guo et al., 2009). Immediately after the infliction of severe mechanical injury to the sensory-motor cortex, 20 µL of 1% RADA16-I SAPNS was implanted at the lesion sites to bridge the injury gap. Histological, immunohistochemical and apoptosis studies were performed at 2 days, 2 weeks, and 6 weeks after injury. The SAPNStreated lesion sites had no cyst formation after injury and showed integrated host-scaffold interfaces; saline-treatment resulted in significant cyst formation. Moreover, SAPNS signifi‐ cantly reduced apoptosis in the perilesional area and effectively mitigated reactive gliosis and inflammation. Currently, a few integrative strategies of SAPNS incorporated with bioactive factors have been conducted with an aim to improve functional recovery after severe TBI.

A variety of biodegradable hydrogel have been extensively studied in the treatment of experimental SCI. IKVAV peptide amphiphile, which consists of neuroactive pentapeptide epitope from laminin, has been applied in a moderate spinal cord contusion model in which 1% aqueous solution of IKVAV-SAPNS was injected into the lesion sites 24h after injury. IKVAV-SAPNS significantly reduced the degree of oligodendroglial apoptosis perilesion and enhanced their survival rate with cleaved caspase-3 immunohistochemistry at 10 d after SCI. Additionally, astrogliosis was reduced significantly and the regeneration of motor-sensory axons were improved remarkably on BDA-labeling 11 week after treatment. Moreover, at 9wks after treatment, the mean locomotor score of IKVAV-SAPNS group was significantly better than that of the control group on BBB score measurement, and dorsal stepping was observed with IKVAV-treatment, indicating functional return in hindlimb movement (Tysseling-

One of the most important advantages of SAPNS is its ability to provide a 3-D matrice in which neural cells can survive and differentiate. Guo and coworkers incorporated neural stem cells (NSCs) and Schwann cells in SAPNS, and transplanted them into dorsal column lesion of the cervical spinal cord. At 6 wks after implantation, there was excellent integration between the implant and the host tissue. Moreover, extensive axonal regrowth was observed with immu‐ nohistochemistry staining with NF, 5-HT, and CGRP (Guo et al., 2007). Recent reports highlighted the further applications of controlled release of bioactive factors incorporated into the SAPNS *in vitro* and *in vivo*. For instance, CT04, a cell permeable RhoA inhibitor, was incorporated into RADA16-I-SAPNS and implanted in a complete transection lesion at T9 level of the spinal cord. This novel integrative SAPNS not only reconstructed the injured nerve gap, but also elicited significant axonal regeneration and motor functional recovery. Additionally it also effectively reduced the infiltration and apoptosis of activated macrophages within the injured spinal cord. The SAPNS-based delivery of RhoA inhibitor is a potentially effective therapeutic strategy by reknitting lesion gap, attenuating secondary injury and improving axonal regeneration (Fig.1). Moreover, Gelain and Zhang's group has developed functional‐ ized SAPNS that can improve the engraftment and neural differentiation of seeding neural

*2.2.2. Spinal cord injury*

190 Advances in Nanofibers

Mattiace, 2008).

#### **3.1. Development of nanofiber biomaterials used for PNS regeneration**

A variety of biodegradable materials have been processed into nanofibrous scaffold using eletrospining technique for PNI repair (Xie et al., 2010). In an early study, a bilayer chitosan conduit with inner layer of nano/microfibrous structure modified with oligopeptide was generated to repair a 15mm sciatic nerve gap in rats (Wang et al., 2008). This novel integrative chitosan conduit effectively promoted the axonal regeneration that was comparable to that of autologous nerve grafting? on histological assessment. Recently, a blend of biodegradable polymers PLGA/PCL was used to produce electrospun tubes to bridge a 10mm long sciatic nerve lesion gap in rat. Four months after surgery, most of the electrospin conduit-treated animals showed neural regeneration and functional restora‐ tion on immunohistochemial studies and electrophysiological assessment (Panseri et al., 2008). More interestingly, a novel bi-layer nanofibrous nerve conduit made of poly (Llactide-co-caprolactone) and poly(propylene glycol) has been fabricated with electrospin‐ ning technique for PNI repair. The electrospin nerve conduit was designed as the luminal layer composed of longitudinally aligned nanofibers to promote axon regeneration, while the outer layer was equipped with random- organized nanofibers for mechanical support. After being implanted to bridge a 10mm gap of sciatic nerve, the nanofibrous nerve conduit significantly improved the regeneration of injured peripheral axons and motor functional recovery at 2 and 12 month post-surgery (Zhu et al., 2011). More recently, the effects of fibre diameter of electrospun conduits on peripheral nerve regeneration was analyzed with a 15mm sciatic nerve injury model. These fibrous conduits consisted of aligned electro‐ spun poly (ε-caprolactone) (PCL) nanofibers (251±32 nm) and microfibers (981±83 nm). The nanofiber-treated group showed significantly greater total number of myelinated fibers and thicker myelin sheaths when compared with groups that received Microfiber and Film conduits at 3 month post-treatment. The number of regenerated dorsal root ganglion neurons in animals that received nanofiber conduits was increased significantly by retrograde labeling with fluorogold. On electrophysiological testing including compound muscle action potential and distal motor latency, the nanofibre-group showed greater improvement than the microfiber group (Jiang et al., 2012). These positive observations provide useful insights for the applications of electrospun nanofibrous nerve conduits with designed nanostructure in the development of peripheral nerve guide conduits.

DAPI area (blue) indicated the gross structure of the injured spinal cord. (B) is the high power magnification corresponding to the boxed area of (A) demonstrated the NF-positive axons in the center of lesion area. Quantification analysis of the NF-positive axons in the center of the lesion area indicated that axonal regeneration was significantly improved by the SAPNS+CT04

Use of Self-Assembly Nanofibre Biomaterials for Neural Repair After Injury

http://dx.doi.org/10.5772/57098

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With NF/MBP-double immunofluoresent labeling, in sharp contrast to that of Empty Nerve Conduit (ENC) group (A-C), significant remyelination of regenerated axons was detected throughout the entire Nanofiber Nerve Conduit (NNC) 16 weeks after treatment (D-F). Representative transverse sections of proximal, middle and distal parts of Nerve Conduit (NC) were demonstrated at panel (A, D), (B, E), and (C, F) in ENC and NNC group, respectively. (G) is the higher magnification of boxed area of (E) with arrows indicating the representative remyelinated fibers. Furthermore, with electron microscopy, typical remyelinated fibers (arrowheads) could be found in both NC groups, while the diameter of the fiber and the thickness of the myelin are greater in NNC (H) compared with ENC (I). (J,K) showed the quantification analysis of the myelinated fiber caliber and the G-ratio ( an index of myelin thickness) separately. Both comparisons using student's t test indicated significantly statistical

implants compared to the only SAPNS group (Student t test, \*p<0.05).

**Figure 1.** Axonal regeneration in the SAPNS-treated groups.

differences (\*p<0.05;\*\*p<0.01).

#### **3.2. Reconstruction of injured PNS with SAPNS**

SAPNS has a well-defined sequence of L-amino acids that self-assemble under physiologi‐ cal conditions to form a fibrous scaffold within the nanoscale (∼10 nm in diameter). In the recent decades, SAPNS has been shown to facilitate the survival and growth of various neural cells within a 3D matrice, and effectively improved the axonal regeneration and tissue repair in context of CNS injuries. It also has significant potential for PNI repair. For example, a novel SAPNS-based nerve conduit was generated by RAD-I SAPNS ensheath‐ ed with a segment of aortic wall. With a sciatic nerve transection model of rat, the SAPNSnerve conduit was used to bridge a 10mm nerve gap. Neural histomorphology, retrogradelabeling and locomotor functional assessments demonstrated significant therapeutic effects of SAPNS-based nanofiber conduit implant on axonal regeneration, remyelination and target reinnervation (Fig.2,). Additionally, SAPNS acts as a designer peptide backbone and provides the opportunity to integrate various growth factor, or functional motifs for cell adhesion, differentiation and homing, and to define and direct biological commitment of seeding cells; furthermore, functional SAPNS will provide better support for viability, migration and differentiation of engrafted stem cells in vivo and lead to better perform‐ ance of neural repair in vivo.
