Nerve lengthening and subsequent end-to-end repair yield more favourable outcomes compared with autograft repair of rat sciatic nerve defects

The Role of Nerve Tension on Nerve Repair Success

Peripheral nerve injuries that are not acutely repaired may lead to a nerve gap because of the surrounding zone of injury and elastic recoil of nerve tissue after laceration. This can result in tension across the repair site during primary neurorrhaphy. Decades of basic science literature using in vivo models consistently demonstrate a relationship between increasing strain at a neurorrhaphy site and compromised microvascular blood flow. Clinical and laboratory data suggest tension-free repairs are associated with optimal outcomes; in the setting of a short segmental nerve gap, data suggest primary repair may continue to yield good functional results. In the case of high strain, nerve grafting or other methods should be considered given poor results of primary repairs performed under high tension because of local ischemia and fibrosis on a cellular level.

Improved Neurotization in High Peripheral Nerve Injury: Side to Side H-shaped Nerve Graft at the Most Distal Part of an Injured Extremity in a Rabbit Model

Background

We aimed to investigate the effects of nerve repair by setting a side-to-side (H-shaped) nerve graft on the most distal part of the damaged nerve to the adjacent intact nerve to accelerate its regeneration in the end organ.

Methods

This pure experimental study was done on the lower extremities of two groups of rabbits in Animal Laboratory Department, 15 Khordad Hospital Tehran, Iran. In both groups, the sciatic nerve at the proximal part of the extremity below the superficial femoral branch was first cut and then repaired. In the investigation group, side-to-side H-shaped nerve grafts were applied between the sciatic and superficial femoral nerves (i.e., two branches) at the most distal to the cut site of the sciatic nerve below the superficial femoral branch at the lower extremity. The sciatic nerve was conventionally repaired in the control group.

Results

None of the rabbits' feet in the control group respond to pain stimulation (were without senses) and had ulcers. They had numb legs and went lame. All had muscular atrophy and lacked nerve growth (regeneration) according to pathology. In the investigation group, 86.7% of the rabbits responded to pain stimulation and only 13.3% of them had ulcers. In addition, in pathology report, 13.3% had suffered muscular atrophy and lacked nerve regeneration. Therefore, nerve regeneration was successful in 86.7% of rabbits who underwent H-shaped nerve grafts.

Conclusion

Side-to-side H-shaped nerve graft at the most distal part of an injured nerve may cause successful recovery of high (proximal) nerve injury.

Inversely engineered biomimetic flexible network scaffolds for soft tissue regeneration

Graft-host mechanical mismatch has been a longstanding issue in clinical applications of synthetic scaffolds for soft tissue regeneration. Although numerous efforts have been devoted to resolve this grand challenge, the regenerative performance of existing synthetic scaffolds remains limited by slow tissue growth (comparing to autograft) and mechanical failures. We demonstrate a class of rationally designed flexible network scaffolds that can precisely replicate nonlinear mechanical responses of soft tissues and enhance tissue regeneration via reduced graft-host mechanical mismatch. Such flexible network scaffold includes a tubular network frame containing inversely engineered curved microstructures to produce desired mechanical properties, with an electrospun ultrathin film wrapped around the network to offer a proper microenvironment for cell growth. Using rat models with sciatic nerve defects or Achilles tendon injuries, our network scaffolds show regenerative performances evidently superior to that of clinically approved electrospun conduit scaffolds and achieve similar outcomes to autologous nerve transplantation in prevention of target organ atrophy and recovery of static sciatic index.

Influences of Repair Site Tension and Conduit Splinting on Peripheral Nerve Reconstruction

BACKGROUND

We investigated the use of a conduit splinting technique to mitigate tension at the coaptation site of a rodent nerve defect model to determine the optimal reconstruction method for segmental nerve defects.

METHODS

A rat sciatic nerve segmental defect model was created by excising 5mm of the sciatic nerve unilaterally. Four groups of 10 rats were each reconstructed using 1 of 4 techniques: primary repair, repair with conduit splinting, reverse isograft with conduit splinting, and reverse isograft without splinting. Functional outcomes were assessed at 6 weeks by measurement of Sciatic Functional Index (SFI), and sciatic nerves were harvested at the nonsurvival surgery. Histomorphologic measurements were reported as a value normalized to the average measurements of the control side. The primary outcomes were assessment of nerve continuity and the proportion of nerve fibers in the regenerating nerve compared with the uninjured side.

RESULTS

The number of repair site rupture rates was lower when a conduit splint was used-less than half of the primary repairs under tension remained intact at 6 weeks. No difference was seen in axon number, size, and density between primary repairs and those augmented by conduit splints, but worse functional outcomes and more debris were present compared with the intact primary repairs.

CONCLUSIONS

Nerve conduit splinting reduced rupture rates, particularly for nerve repairs associated with a segmental defect. No significant difference was seen in the number of axons among techniques. Primary nerve repair under tension that did not rupture demonstrated superior SFI.

Multimodular Bio-Inspired Organized Structures Guiding Long-Distance Axonal Regeneration

Axonal bundles or axonal tracts have an aligned and unidirectional architecture present in many neural structures with different lengths. When peripheral nerve injury (PNI), spinal cord injury (SCI), traumatic brain injury (TBI), or neurodegenerative disease occur, the intricate architecture undergoes alterations leading to growth inhibition and loss of guidance through large distance. In order to overcome the limitations of long-distance axonal regeneration, here we combine a poly-L-lactide acid (PLA) fiber bundle in the common lumen of a sequence of hyaluronic acid (HA) conduits or modules and pre-cultured Schwann cells (SC) as cells supportive of axon extension. This multimodular preseeded conduit is then used to induce axon growth from a dorsal root ganglion (DRG) explant placed at one of its ends and left for 21 days to follow axon outgrowth. The multimodular conduit proved effective in promoting directed axon growth, and the results may thus be of interest for the regeneration of long tissue defects in the nervous system. Furthermore, the hybrid structure grown within the HA modules consisting in the PLA fibers and the SC can be extracted from the conduit and cultured independently. This “neural cord” proved to be viable outside its scaffold and opens the door to the generation of ex vivo living nerve in vitro for transplantation.

Use of ultrasound and targeted physiotherapy to manage nerve sutures placed under joint flexion: a case series

Background

Joint flexion to diminish the gap and avoid nerve grafts fell into disuse for decades, but recently attention for using this technique was regained. We report a case series of nerve suture under joint flexion, ultrasound monitoring, and physiotherapy. Our main objective was to determine how effective this multimodality treatment is.

Methods

A retrospective review of 8 patients treated with direct repair with joint flexion was done. Depending on the affected nerve, either the knee or the elbow was flexed intraoperatively to determine if direct suturing was possible. After surgery, the limb was held immobilized. Through serial ultrasounds and a physiotherapy program, the limb was fully extended. If a nerve repair rupture was observed, the patient was re-operated and grafts were used.

Results

Of the eight nerve sutures analyzed, four sustained a nerve rupture revealed by US at an early stage, while four did not show any sign of dehiscence. In the patients in whom the nerve suture was preserved, an early and very good response was observed. Ultrasound was 100% accurate at identifying nerve suture preservation. Early detection of nerve failure permitted early re-do surgery using grafts without flexion, ultimately determining good final results.

Conclusions

We observed a high rate of dehiscence in our group of patients treated with direct repair and joint flexion. We believe this was due to an incorrect use of the immobilization device, excessive movement, or a broken device. In opposition to this, we observed that applying direct nerve sutures and joint flexion offers unusually good and fast results. If this technique is employed, it is mandatory to closely monitor suture status with US, together with physiotherapy providing progressive, US-guided extension of the flexed joint. If nerve rupture occurs, the close monitoring dictated by this protocol should ensure the timely application of a successful graft repair.

Novel immortalization approach defers senescence of cultured canine adipose-derived mesenchymal stromal cells

In the last decades, the scientific community spared no effort to elucidate the therapeutic potential of mesenchymal stromal cells (MSCs). Unfortunately, in vitro cellular senescence occurring along with a loss of proliferative capacity is a major drawback in view of future therapeutic applications of these cells in the field of regenerative medicine. Even though insight into the mechanisms of replicative senescence in human medicine has evolved dramatically, knowledge about replicative senescence of canine MSCs is still scarce. Thus, we developed a high-content analysis workflow to simultaneously investigate three important characteristics of senescence in canine adipose-derived MSCs (cAD-MSCs): morphological changes, activation of the cell cycle arrest machinery, and increased activity of the senescence-associated β-galactosidase. We took advantage of this tool to demonstrate that passaging of cAD-MSCs results in the appearance of a senescence phenotype and proliferation arrest. This was partially prevented upon immortalization of these cells using a newly designed PiggyBac™ Transposon System, which allows for the expression of the human polycomb ring finger proto-oncogene BMI1 and the human telomerase reverse transcriptase under the same promotor. Our results indicate that cAD-MSCs immortalized with this new vector maintain their proliferation capacity and differentiation potential for a longer time than untreated cAD-MSCs. This study not only offers a workflow to investigate replicative senescence in eukaryotic cells with a high-content analysis approach but also paves the way for a rapid and effective generation of immortalized MSC lines. This promotes a better understanding of these cells in view of future applications in regenerative medicine.

Controlled release of ciliary neurotrophic factor from bioactive nerve grafts promotes nerve regeneration in rats with facial nerve injuries

It is critical to repair severed facial nerves, as lack of treatment may cause long-term motor and sensory impairments. Ciliary neurotrophic factor (CNTF) plays an important role in terms of enhancing nerve axon regrowth and maturation during peripheral nerve regeneration after injury. However, simple application of CNTF to the transected nerve site does not afford functional recovery, because it is rapidly flushed away by bodily fluids. The aim of the present study was the construction of a new, bioactive composite nerve graft facilitating persistent CNTF delivery to aid the reconstruction of facial nerve defects. The in vitro study showed that the bioactive nerve graft generated sustainable CNTF release for more than 25 days. The bioactive nerve graft was then transplanted into the injury sites of rat facial nerves. At 6 and 12 weeks post-transplantation, functional and histological analyses showed that the bioactive nerve graft featuring immobilized CNTF significantly enhanced nerve regeneration in terms of both axonal outgrowth and Schwann cell proliferation in the rat facial nerve gap model, compared to a collagen tube with adsorbed CNTF that initially released high levels of CNTF. The bioactive nerve graft may serve as novel, controlled bioactive release therapy for facial nerve regeneration.

Self-healing polyurethane-elastomer with mechanical tunability for multiple biomedical applications in vivo

The unique properties of self-healing materials hold great potential in the field of biomedical engineering. Although previous studies have focused on the design and synthesis of self-healing materials, their application in in vivo settings remains limited. Here, we design a series of biodegradable and biocompatible self-healing elastomers (SHEs) with tunable mechanical properties, and apply them to various disease models in vivo, in order to test their reparative potential in multiple tissues and at physiological conditions. We validate the effectiveness of SHEs as promising therapies for aortic aneurysm, nerve coaptation and bone immobilization in three animal models. The data presented here support the translation potential of SHEs in diverse settings, and pave the way for the development of self-healing materials in clinical contexts.

A guide to reducing adverse outcomes in rabbit models of sciatic nerve injury

Background

Peripheral nerve damage can have debilitating consequences. Rabbit sciatic nerve transection models allow the effective evaluation of surgical repair strategies for large nerve gaps. Despite advantages in size, ease of handling, and functional utility, rabbits can suffer from a number of side effects that affect animal welfare and the quality of scientific inquiry. Such side-effects, which include pressure ulcers and traumatic damage to the foot, are primarily a consequence of insensitivity of the distal hindlimb following sciatic nerve injury. In this study, we present a number of methodologies for identifying, treating, and preventing unintended adverse effects in rabbit sciatic nerve injury models.

Results

First, we categorize pressure ulcers according to their severity and describe the deployment of a padded bandaging technique to enable ulcer healing. We also introduce a proactive bandaging approach to reduce the likelihood of pressure ulcer formation. Second, we define phenotypes that distinguish between foot injuries resulting from self-mutilation (autotomy) from those caused by incidental traumatic injury secondary to sensori-motor damage. Finally, we detail an effective strategy to reduce the usage of Elizabethan collars; through a gradual weaning protocol, their usefulness in preventing autotomy is retained, while their propensity to impede rabbit grooming and cause abrasion-injury to the neck region is minimized.

Conclusions

We suggest that application of these methods offer a practical and systematic approach to avoid adverse side effects associated with rabbit sciatic nerve damage, enabling improved animal welfare and scientific outcomes in a powerful nerve injury model.

Nerve guidance conduit promoted peripheral nerve regeneration in rats

Nerve growth factor (NGF) is important for peripheral nerve regeneration. However, its short half-life and rapid diffusion in body fluids limit its clinical efficacy. Collagen has favorable biocompatibility and biodegradability, and weak immunogenicity. Because it possesses an NGF binding domain, we cross-linked heparin to collagen tubes to construct nerve guidance conduits for delivering NGF. The conduits were implanted to bridge a facial nerve defect in rats. Histological and functional analyses were performed to assess the effect of the nerve guidance conduit on facial nerve regeneration. Heparin enhanced the binding of NGF to collagen while retaining its bioactivity. Also, the nerve guidance conduit significantly promoted axonal growth and Schwan cell proliferation at 12 weeks after surgery. The nerve regeneration and functional recovery outcomes using the nerve guidance conduit were similar to those of autologous nerve grafting. Therefore, the nerve guidance conduit may promote safer nerve regeneration.