Silk-based nerve guidance conduits with macroscopic holes modulate the vascularization of regenerating rat sciatic nerve.

JOURNAL/nrgr/04.03/01300535-202506000-00029/figure1/v/2024-08-05T133530Z/r/image-tiff Peripheral nerve injuries induce a severe motor and sensory deficit. Since the availability of autologous nerve transplants for nerve repair is very limited, alternative treatment strategies are sought, including the use of tubular nerve guidance conduits (tNGCs). However, the use of tNGCs results in poor functional recovery and central necrosis of the regenerating tissue, which limits their application to short nerve lesion defects (typically shorter than 3 cm). Given the importance of vascularization in nerve regeneration, we hypothesized that enabling the growth of blood vessels from the surrounding tissue into the regenerating nerve within the tNGC would help eliminate necrotic processes and lead to improved regeneration. In this study, we reported the application of macroscopic holes into the tubular walls of silk-based tNGCs and compared the various features of these improved silk+ tNGCs with the tubes without holes (silk- tNGCs) and autologous nerve transplants in an 8-mm sciatic nerve defect in rats. Using a combination of micro-computed tomography and histological analyses, we were able to prove that the use of silk+ tNGCs induced the growth of blood vessels from the adjacent tissue to the intraluminal neovascular formation. A significantly higher number of blood vessels in the silk+ group was found compared with autologous nerve transplants and silk-, accompanied by improved axon regeneration at the distal coaptation point compared with the silk- tNGCs at 7 weeks postoperatively. In the 15-mm (critical size) sciatic nerve defect model, we again observed a distinct ingrowth of blood vessels through the tubular walls of silk+ tNGCs, but without improved functional recovery at 12 weeks postoperatively. Our data proves that macroporous tNGCs increase the vascular supply of regenerating nerves and facilitate improved axonal regeneration in a short-defect model but not in a critical-size defect model. This study suggests that further optimization of the macroscopic holes silk+ tNGC approach containing macroscopic holes might result in improved grafting technology suitable for future clinical use.

ESWT Diminishes Axonal Regeneration following Repair of the Rat Median Nerve with Muscle-In-Vein Conduits but Not after Autologous Nerve Grafting.

Investigations reporting positive effects of extracorporeal shockwave therapy (ESWT) on nerve regeneration are limited to the rat sciatic nerve model. The effects of ESWT on muscle-in-vein conduits (MVCs) have also not been investigated yet. This study aimed to evaluate the effects of ESWT after repair of the rat median nerve with either autografts (ANGs) or MVCs. In male Lewis rats, a 7 mm segment of the right median nerve was reconstructed either with an ANG or an MVC. For each reconstructive technique, one group of animals received one application of ESWT while the other rats served as controls. The animals were observed for 12 weeks, and nerve regeneration was assessed using computerized gait analysis, the grasping test, electrophysiological evaluations and histological quantification of axons, blood vessels and lymphatic vasculature. Here, we provide for the first time a comprehensive analysis of ESWT effects on nerve regeneration in a rat model of median nerve injury. Furthermore, this study is among the first reporting the quantification of lymphatic vessels following peripheral nerve injury and reconstruction in vivo. While we found no significant direct positive effects of ESWT on peripheral nerve regeneration, results following nerve repair with MVCs were significantly inferior to those after ANG repair.

Automated Gait Analysis to Assess Functional Recovery in Rodents with Peripheral Nerve or Spinal Cord Contusion Injury.

Peripheral and central nerve injuries are mostly studied in rodents, especially rats, given the fact that these animal models are both cost-effective and a lot of comparative data has been published in the literature. This includes a multitude of assessment methods to study functional recovery following nerve injury and repair. Besides evaluation of nerve regeneration by means of histology, electrophysiology, and other in vivo and in vitro assessment techniques, functional recovery is the most important criterion to determine the degree of neural regeneration. Automated gait analysis allows recording of a vast quantity of gait-related parameters such as Paw Print Area and Paw Swing Speed as well as measures of inter-limb coordination. Additionally, the method provides digital data of the rats' paws after neuronal damage and during nerve regeneration, adding to our understanding of how peripheral and central nervous injuries affect their locomotor behavior. Besides the predominantly used sciatic nerve injury model, other models of peripheral nerve injury such as the femoral nerve can be studied by means of this method. In addition to injuries of the peripheral nervous systems, lesions of the central nervous system, e.g., spinal cord contusion can be evaluated. Valid and reproducible data assessment is strongly dependent on meticulous adjustment of the hard- and software settings prior to data acquisition. Additionally, proper training of the experimental animals is of crucial importance. This work aims to illustrate the use of computerized automated gait analysis to assess functional recovery in different animal models of peripheral nerve injury as well as spinal cord contusion injury. It also emphasizes the method's limitations, e.g., evaluation of nerve regeneration in rats with sciatic nerve neurotmesis due to limited functional recovery. Therefore, this protocol is thought to help researchers interested in peripheral and central nervous injuries to assess functional recovery in rodent models.

Evaluation of Functional Recovery in Rats After Median Nerve Resection and Autograft Repair Using Computerized Gait Analysis.

Computerized gait analysis is a common evaluation method in rat models of hind limb nerve injuries, but its use remains unpublished in models of segmental nerve injury of the forelimb. It was the aim of this work to investigate if computerized gait analysis is a feasible evaluation method in a rat model of segmental median nerve injury and autograft repair. Ten male Lewis rats underwent 7-mm resection of the right median nerve with immediate autograft repair. The left median nerve was resected without repair and served as an internal control. Animals were assessed for 12 weeks after surgery via CatWalk (CW) gait analysis every 2 weeks. Evaluation of motor recovery by means of the grasping test was performed weekly while electrophysiological measurements were performed at the end of the observation period. CW data were correlated with grasping strength at each post-operative time point. CW data were also correlated with electrophysiology using linear regression analysis. Principal component analysis was performed to identify clusters of outcome metrics. Recovery of motor function was observable 4 weeks after surgery, but grasping strength was significantly reduced (p < 0.01) compared to baseline values until post-operative week 6. In terms of sensory recovery, the pain-related parameter Duty Cycle showed significant (p < 0.05) recovery starting from post-operative week 8. The Print Area of the right paw was significantly (p < 0.05) increased compared to the left side starting from post-operative week 10. Various parameters of gait correlated significantly (p < 0.05) with mean and maximum grasping strength. However, only Stand Index showed a significant correlation with compound muscle action potential (CMAP) amplitude (p < 0.05). With this work, we prove that computerized gait analysis is a valid and feasible method to evaluate functional recovery after autograft repair of the rat median nerve. We were able to identify parameters such as Print Area, Duty Cycle, and Stand Index, which allow assessment of nerve regeneration. The course of these parameters following nerve resection without repair was also assessed. Additionally, external paw rotation was identified as a valid parameter to evaluate motor reinnervation. In summary, computerized gait analysis is a valuable additional tool to study nerve regeneration in rats with median nerve injury.

Iodine-Enhanced Micro-CT Imaging of Soft Tissue on the Example of Peripheral Nerve Regeneration.

Microcomputed tomography (µCT) is widely used for the study of mineralized tissues, but a similar use for soft tissues is hindered by their low X-ray attenuation. This limitation can be overcome by the recent development of different staining techniques. Staining with Lugol's solution, a mixture of one part iodine and two parts potassium iodide in water, stands out among these techniques for its low complexity and cost. Currently, Lugol staining is mostly used for anatomical examination of tissues. In the present study, we seek to optimize the quality and reproducibility of the staining for ex vivo visualization of soft tissues in the context of a peripheral nerve regeneration model in the rat. We show that the staining result not only depends on the concentration of the staining solution but also on the amount of stain in relation to the tissue volume and composition, necessitating careful adaptation of the staining protocol to the respective specimen tissue. This optimization can be simplified by a stepwise staining which we show to yield a similar result compared to staining in a single step. Lugol staining solution results in concentration-dependent tissue shrinkage which can be minimized but not eliminated. We compared the shrinkage of tendon, nerve, skeletal muscle, heart, brain, and kidney with six iterations of Lugol staining. 60 ml of 0.3% Lugol's solution per cm3 of tissue for 24 h yielded good results on the example of a peripheral nerve regeneration model, and we were able to show that the regenerating nerve inside a silk fibroin tube can be visualized in 3D using this staining technique. This information helps in deciding the region of interest for histological imaging and provides a 3D context to histological findings. Correlating both imaging modalities has the potential to improve the understanding of the regenerative process.