Autologous tendons used as grafts for bridging peripheral nerve defects

4D-Printed MXene-Based Artificial Nerve Guidance Conduit for Enhanced Regeneration of Peripheral Nerve Injuries

Repairing larger defects (>5 mm) in peripheral nerve injuries (PNIs) remains a significant challenge when using traditional artificial nerve guidance conduits (NGCs). A novel approach that combines 4D printing technology with poly(L-lactide-co-trimethylene carbonate) (PLATMC) and Ti3C2Tx MXene nanosheets is proposed, thereby imparting shape memory properties to the NGCs. Upon body temperature activation, the printed sheet-like structure can quickly self-roll into a conduit-like structure, enabling optimal wrapping around nerve stumps. This design enhances nerve fixation and simplifies surgical procedures. Moreover, the integration of microchannel expertly crafted through 4D printing, along with the incorporation of MXene nanosheets, introduces electrical conductivity. This feature facilitates the guided and directional migration of nerve cells, rapidly accelerating the healing of the PNI. By leveraging these advanced technologies, the developed NGCs demonstrate remarkable potential in promoting peripheral nerve regeneration, leading to substantial improvements in muscle morphology and restored sciatic nerve function, comparable to outcomes achieved through autogenous nerve transplantation.

The role of Gel-Ppy-modified nerve conduit on the repair of sciatic nerve defect in rat model

The serious clinical challenge of peripheral nerve injury (PNI) is nerve regeneration. Nerve conduit represents a promising strategy to contribute to nerve regeneration by bridging injured nerve gaps. However, due to a unique microenvironment of nerve tissue, autologous nerves have not been substituted by nerve conduit. Nerve regeneration after nerve conduit implantation depends on many factors, such as conductivity and biocompatibility. Therefore, Gelatin (Gel) with biocompatibility and polypyrrole (Ppy) with conductivity is highly concerned. In this paper, Gel-Ppy modified nerve conduit was fabricated with great biocompatibility and conductivity to evaluate its properties of enhancing nerve regeneration in vivo and in vitro. The proliferation of Schwann cells on Gel-Ppy modified nerve conduit was remarkably increased. Consistent with in vitro results, the Gel-Ppy nerve conduit could contribute to the regeneration of Schwann cell in vivo. The axon diameters and myelin sheath thickness were also enhanced, resulting in the amelioration of muscle atrophy, nerve conduction, and motor function recovery. To explain this interesting phenomenon, western blot results indicated that the Gel-Ppy conduit facilitated nerve regeneration via upregulating the Rap1 pathway to induce neurite outgrowth. Therefore, the above results demonstrated that Gel-Ppy modified nerve conduit could provide an acceptable microenvironment for nerve regeneration and be popularized as a novel therapeutic strategy of PNI.

Biological nerve conduit model with de-epithelialized human amniotic membrane and adipose-derived mesenchymal stem cell sheet for repair of peripheral nerve defects

In this study, a biological conduit, consisting of an adipocyte-derived mesenchymal stem cell (AdMSCs) sheet and amniotic membrane (AM), was designed for the reconstruction of peripheral nerve defects. To evaluate the effect of the produced conduit on neural regeneration, a 10-mm sciatic nerve defect was created in rats, and experiments were carried out on six groups, i.e., sham control group (SC), negative control group (NC), nerve autograft group (NG), the biological conduit (AdMSCs + AM) group, the commercial PGA tube conduit (PGA) group, and the conduit only consisting of AM (AM) group. The effects of different nerve repair methods on the peripheral nerve and gastrocnemius muscle were evaluated by functional, histological, and immunohistochemical tests. When the number of myelinated axons was compared between the groups of AdMSCs + AM and PGA, it was higher in the AdMSCs + AM group (p < 0.05). The percentage of gastrocnemius collagen bundle area of AdMSCs + AM group was found to be statistically lower than the PGA group (p < 0.05). The muscle fiber diameter of AdMSCs + AM group was lower than that of the NG group, but significantly higher than that of the PGA group and the AM group (p < 0.001). Muscle weight index was significantly higher in the AdMSCs + AM group compared to the PGA group (p < 0.05). It was observed that nerve regeneration was faster in the AdMSCs + AM group, and there was an earlier improvement in pin-prick score and sciatic functional index compared to the PGA group and the AM group. In conclusion, the biological conduit prepared from the AdMSCs sheet and AM is regarded as a new biological conduit that can be used as an alternative treatment method to nerve autograft in clinical applications.

Donors for nerve transplantation in craniofacial soft tissue injuries

Neural tissue is an important soft tissue; for instance, craniofacial nerves govern several aspects of human behavior, including the expression of speech, emotion transmission, sensation, and motor function. Therefore, nerve repair to promote functional recovery after craniofacial soft tissue injuries is indispensable. However, the repair and regeneration of craniofacial nerves are challenging due to their intricate anatomical and physiological characteristics. Currently, nerve transplantation is an irreplaceable treatment for segmental nerve defects. With the development of emerging technologies, transplantation donors have become more diverse. The present article reviews the traditional and emerging alternative materials aimed at advancing cutting-edge research on craniofacial nerve repair and facilitating the transition from the laboratory to the clinic. It also provides a reference for donor selection for nerve repair after clinical craniofacial soft tissue injuries. We found that autografts are still widely accepted as the first options for segmental nerve defects. However, allogeneic composite functional units have a strong advantage for nerve transplantation for nerve defects accompanied by several tissue damages or loss. As an alternative to autografts, decellularized tissue has attracted increasing attention because of its low immunogenicity. Nerve conduits have been developed from traditional autologous tissue to composite conduits based on various synthetic materials, with developments in tissue engineering technology. Nerve conduits have great potential to replace traditional donors because their structures are more consistent with the physiological microenvironment and show self-regulation performance with improvements in 3D technology. New materials, such as hydrogels and nanomaterials, have attracted increasing attention in the biomedical field. Their biocompatibility and stimuli-responsiveness have been gradually explored by researchers in the regeneration and regulation of neural networks.

Functional polymeric nerve guidance conduits and drug delivery strategies for peripheral nerve repair and regeneration

Peripheral nerve injuries can be extremely debilitating, resulting in sensory and motor loss-of-function. Endogenous repair is limited to non-severe injuries in which transection of nerves necessitates surgical intervention. Traditional treatment approaches include the use of biological grafts and alternative engineering approaches have made progress. The current article serves as a comprehensive, in-depth perspective on peripheral nerve regeneration, particularly nerve guidance conduits and drug delivery strategies. A detailed background of peripheral nerve injury and repair pathology, and an in-depth look into augmented nerve regeneration, nerve guidance conduits, and drug delivery strategies provide a state-of-the-art perspective on the field.

Reconstruction of a 10-mm-long median nerve gap in an ischemic environment using autologous conduits with different patterns of blood supply: A comparative study in the rat

The aim of this study was to evaluate in the Wistar rat the efficacy of various autologous nerve conduits with various forms of blood supply in reconstructing a 10-mm-long gap in the median nerve (MN) under conditions of local ischemia. A 10-mm-long median nerve defect was created in the right arm. A loose silicone tube was placed around the nerve gap zone, in order to simulate a local ischemic environment. Rats were divided in the following experimental groups (each with 20 rats): the nerve Graft (NG) group, in which the excised MN segment was reattached; the conventional nerve flap (CNF) and the arterialized neurovenous flap (ANVF) groups in which the gap was bridged with homonymous median nerve flaps; the prefabricated nerve flap (PNF) group in which the gap was reconstructed with a fabricated flap created by leaving an arteriovenous fistula in contact with the sciatic nerve for 5 weeks; and the two control groups, Sham and Excision groups. In the latter group, the proximal stump of the MN nerve was ligated and no repair was performed. The rats were followed for 100 days. During this time, they did physiotherapy. Functional, electroneuromyographic and histological studies were performed. The CNF and ANVF groups presented better results than the NG group in the following assessments: grasping test, nociception, motor stimulation threshold, muscle weight, and histomorphometric evaluation. Radial deviation of the operated forepaw was more common in rats that presented worse results in the other outcome variables. Overall, CNFs and ANVFs produced a faster and more complete recovery than NGs in the reconstruction of a 10-mm-long median nerve gap in an ischemic environment in the Wistar rat. Although, results obtained with CNFs were in most cases were better than ANVFs, these differences were not statistically significant for most of the outcome variables.

Scaffoldless tissue-engineered nerve conduit promotes peripheral nerve regeneration and functional recovery after tibial nerve injury in rats

Damage to peripheral nerve tissue may cause loss of function in both the nerve and the targeted muscles it innervates. This study compared the repair capability of engineered nerve conduit (ENC), engineered fibroblast conduit (EFC), and autograft in a 10-mm tibial nerve gap. ENCs were fabricated utilizing primary fibroblasts and the nerve cells of rats on embryonic day 15 (E15). EFCs were fabricated utilizing primary fibroblasts only. Following a 12-week recovery, nerve repair was assessed by measuring contractile properties in the medial gastrocnemius muscle, distal motor nerve conduction velocity in the lateral gastrocnemius, and histology of muscle and nerve. The autografts, ENCs and EFCs reestablished 96%, 87% and 84% of native distal motor nerve conduction velocity in the lateral gastrocnemius, 100%, 44% and 44% of native specific force of medical gastrocnemius, and 63%, 61% and 67% of native medial gastrocnemius mass, respectively. Histology of the repaired nerve revealed large axons in the autograft, larger but fewer axons in the ENC repair, and many smaller axons in the EFC repair. Muscle histology revealed similar muscle fiber cross-sectional areas among autograft, ENC and EFC repairs. In conclusion, both ENCs and EFCs promoted nerve regeneration in a 10-mm tibial nerve gap repair, suggesting that the E15 rat nerve cells may not be necessary for nerve regeneration, and EFC alone can suffice for peripheral nerve injury repair.

Peripheral Nerve Regeneration: Current Status and New Strategies Using Polymeric Materials

Experiments concerning peripheral nerve regeneration have been reported since the end of the 19^th century. The need to implement an effective surgical procedure in terms of functional recovery has resulted in the appearance of several approaches to solve this problem. Nerve autograft was the first approach studied and is still considered the gold standard. Since autografts require donor harvesting, other strategies involving the use of natural materials have also been studied. Nevertheless, the results were not very encouraging and attention has moved towards the use of nerve conduits made from polymers, whose properties can be easily tailored and which allow the nerve conduit to be easily processed into a variety of shapes and forms. Some of these materials are already approved by the US Food and Drug Administration (FDA), as is presented here. Furthermore, polymers with conductive properties have very recently been subject to intensive study in this field, since it is believed that such properties have a positive influence in the regeneration of the new axons. This manuscript intends to give a global view of the mechanisms involved in peripheral nerve regeneration and the main strategies used to recover motor and sensorial function of injured nerves.

Recent Strategies in Tissue Engineering for Guided Peripheral Nerve Regeneration

The repair of large crushed or sectioned segments of peripheral nerves remains a challenge in regenerative medicine due to the complexity of the biological environment and the lack of proper biomaterials and architecture to foster reconstruction. Traditionally such reconstruction is only achieved by using fresh human tissue as a surrogate for the absence of the nerve. However, recent focus in the field has been on new polymer structures and specific biofunctionalization to achieve the goal of peripheral nerve regeneration by developing artificial nerve prostheses. This review presents various tested approaches as well their effectiveness for nerve regrowth and functional recovery.

Nerve allografts and conduits in peripheral nerve repair

Since the last update on nerve conduits and allograft in 2000, investigations have established the efficacy of these alternatives to autograft in the repair of small sensory neural gaps. However, limited insights into the biology of the regenerating nerve continue to preclude intelligent conduit design. Ongoing discoveries in neuroscience and biomaterial engineering hold promise for the eventual development of allograft and conduits with potential of surpassing nerve autografts in clinical efficacy. In this review, we summarize the history, recent advances, and emerging developments in nerve conduits and allograft.

Nerve regeneration along collagen filament and the presence of distal nerve stump

This article describes the regeneration of severed peripheral nerve axons along collagen filaments in the absence of the distal nerve stump. 22-mm long nerve guides made of collagen filaments were sutured to the proximal ends of severed rat sciatic nerves. The distal ends of the guides were sutured to the distal stumps of the nerves in a group and not sutured in the other. Nerve autografts and collagen tubes were used as controls. At 8 weeks postoperatively, the mean number and the mean diameter of myelinated axons were 5491 +/- 617 (mean +/- SD) and 2.3 +/- 1.3 microns at the distal ends of the collagen filaments nerve guides those the distal ends were sutured to the distal stumps of the nerves, while in the nerve autografts these were 4837 +/- 604 and 3.3 +/- 1.4 microns. These were 1992 +/- 770 and 2.7 +/- 1.2 microns at the distal ends of the collagen-filaments guides those the distal ends were not sutured to the distal stumps of the nerves, while in the nerve autografts these were 3041 +/- 847 and 2.3 +/- 1.1 microns. No axon was found at the distal ends of the collagen tubes. The results suggested that the contact guidance and the chemotaxis guided regenerating axons along the collagen filaments.

A novel internal fixator device for peripheral nerve regeneration

Recovery from peripheral nerve damage, especially for a transected nerve, is rarely complete, resulting in impaired motor function, sensory loss, and chronic pain with inappropriate autonomic responses that seriously impair quality of life. In consequence, strategies for enhancing peripheral nerve repair are of high clinical importance. Tension is a key determinant of neuronal growth and function. In vitro and in vivo experiments have shown that moderate levels of imposed tension (strain) can encourage axonal outgrowth; however, few strategies of peripheral nerve repair emphasize the mechanical environment of the injured nerve. Toward the development of more effective nerve regeneration strategies, we demonstrate the design, fabrication, and implementation of a novel, modular nerve-lengthening device, which allows the imposition of moderate tensile loads in parallel with existing scaffold-based tissue engineering strategies for nerve repair. This concept would enable nerve regeneration in two superposed regimes of nerve extension--traditional extension through axonal outgrowth into a scaffold and extension in intact regions of the proximal nerve, such as that occurring during growth or limb-lengthening. Self-sizing silicone nerve cuffs were fabricated to grip nerve stumps without slippage, and nerves were deformed by actuating a telescoping internal fixator. Poly(lactic co-glycolic) acid (PLGA) constructs mounted on the telescoping rods were apposed to the nerve stumps to guide axonal outgrowth. Neuronal cells were exposed to PLGA using direct contact and extract methods, and they exhibited no signs of cytotoxic effects in terms of cell morphology and viability. We confirmed the feasibility of implanting and actuating our device within a sciatic nerve gap and observed axonal outgrowth following device implantation. The successful fabrication and implementation of our device provides a novel method for examining mechanical influences on nerve regeneration.

Regeneration and repair of peripheral nerves with different biomaterials: review

Peripheral nerve injury may cause gaps between the nerve stumps. Axonal proliferation in nerve conduits is limited to 10-15 mm. Most of the supportive research has been done on rat or mouse models which are different from humans. Herein we review autografts and biomaterials which are commonly used for nerve gap repair and their respective outcomes. Nerve autografting has been the first choice for repairing peripheral nerve gaps. However, it has been demonstrated experimentally that tissue engineered tubes can also permit lead to effective nerve repair over gaps longer than 4 cm repair that was previously thought to be restorable by means of nerve graft only. All of the discoveries in the nerve armamentarium are making their way into the clinic, where they are, showing great potential for improving both the extent and rate of functional recovery compared with alternative nerve guides.

Construction of tissue engineered nerve grafts and their application in peripheral nerve regeneration

Surgical repair of severe peripheral nerve injuries represents not only a pressing medical need, but also a great clinical challenge. Autologous nerve grafting remains a golden standard for bridging an extended gap in transected nerves. The formidable limitations related to this approach, however, have evoked the development of tissue engineered nerve grafts as a promising alternative to autologous nerve grafts. A tissue engineered nerve graft is typically constructed through a combination of a neural scaffold and a variety of cellular and molecular components. The initial and basic structure of the neural scaffold that serves to provide mechanical guidance and optimal environment for nerve regeneration was a single hollow nerve guidance conduit. Later there have been several improvements to the basic structure, especially introduction of physical fillers into the lumen of a hollow nerve guidance conduit. Up to now, a diverse array of biomaterials, either of natural or of synthetic origin, together with well-defined fabrication techniques, has been employed to prepare neural scaffolds with different structures and properties. Meanwhile different types of support cells and/or growth factors have been incorporated into the neural scaffold, producing unique biochemical effects on nerve regeneration and function restoration. This review attempts to summarize different nerve grafts used for peripheral nerve repair, to highlight various basic components of tissue engineered nerve grafts in terms of their structures, features, and nerve regeneration-promoting actions, and finally to discuss current clinical applications and future perspectives of tissue engineered nerve grafts.

Repairing injured peripheral nerves: Bridging the gap

Peripheral nerve injuries that induce gaps larger than 1-2 cm require bridging strategies for repair. Autologous nerve grafts are still the gold standard for such interventions, although alternative treatments, as well as treatments to improve the therapeutic efficacy of autologous nerve grafting are generating increasing interest. Investigations are still mostly experimental, although some clinical studies have been undertaken. In this review, we aim to describe the developments in bridging technology which aim to replace the autograft. A multi-disciplinary approach is of utmost importance to develop and optimise treatments of the most challenging peripheral nerve injuries.

Peripheral Nerve Gap Repair Facilitated By a Dynamic Tension Device

End-to-end neurorrhaphy remains the gold standard for transected nerve repair. However, the current dogma is that to be successful, nerve repairs must be tension free. Therefore, nerve gaps are most commonly repaired with grafts. While there is evidence that nerves can regenerate successfully after initial approximation under a tensile force, the amount of tension that deters regeneration of human nerves remains unclear. The present paper describes a case in which a favourable functional outcome was obtained following repair of a median nerve gap that was reduced by a dynamic tension device. The case provides some evidence that modest separations between stumps can be overcome by dynamic tension, enabling primary end-to-end repair of nerve gaps.

Acutely-dissociated Schwann cells used in tendon autografts for bridging nerve defects in rats: A new principle for tissue engineering in nerve reconstruction

A new method of acute dissociation of Schwann cells was used to study the effect of addition of such cells to a tendon autograft--a recently-described graft material--on peripheral nerve regeneration in rats. Autologous Schwann cells were obtained from enzymatic dissociation of predegenerated nerves. The tendon autografts were supplied with Schwann cells through brief in vitro coincubation. Schwann cell-free tendon autografts were used as controls. Axonal outgrowth was measured immunohistochemically after four, seven, and 10 days. At seven days, outgrowth was significantly longer in the pretreated autografts. The use of acutely-dissociated Schwann cells is a new approach to tissue engineering in nerve reconstruction, and may abolish the need for time-consuming culture of Schwann cells.

Functional recovery after peripheral nerve injury and implantation of a collagen guide

Although surgery techniques improved over the years, the clinical results of peripheral nerve repair remain unsatisfactory. In the present study, we compare the results of a collagen nerve guide conduit to the standard clinical procedure of nerve autografting to promote repair of transected peripheral nerves. We assessed behavioral and functional sensori-motor recovery in a rat model of peroneal nerve transection. A 1cm segment of the peroneal nerve innervating the Tibialis anterior muscle was removed and immediately replaced by a new biodegradable nerve guide fabricated from highly purified type I+III collagens derived from porcine skin. Four groups of animals were included: control animals (C, n=12), transected animals grafted with either an autologous nerve graft (Gold Standard; GS, n=12) or a collagen tube filled with an acellular skeletal muscle matrix (Tube-Muscle; TM, n=12) or an empty collagen tube (Collagen-Tube; CT, n=12). We observed that 1) the locomotor recovery pattern, analyzed with kinetic parameters and peroneal functional index, was superior in the GS and CT groups; 2) a muscle contraction was obtained in all groups after stimulation of the proximal nerve but the mechanical muscle properties (twitch and tetanus threshold) parameters indicated a fast to slow fiber transition in all operated groups; 3) the muscular atrophy was greater in animals from TM group; 4) the metabosensitive afferent responses to electrically induced fatigue and to two chemical agents (KCl and lactic acid) was altered in GS, CT and TM groups; 5) the empty collagen tube supported motor axonal regeneration. Altogether, these data indicate that motor axonal regeneration and locomotor recovery can be obtained with the insertion of the collagen tube RevolNerv. Future studies may include engineered conduits that mimic as closely as possible the internal organization of uninjured nerve.

Tissue engineering for the hand surgeon: a clinical perspective

Hand surgeons may be faced with tissue shortages for reconstruction after trauma, tumor resection, or congenital deficiency. Tissue engineering is a developing scientific field that combines the principles of life sciences and engineering in developing biologic substitutes that will restore, maintain, or improve tissue function. This article reviews the general principles of tissue engineering as applied to musculoskeletal tissues including nerve, bone, tendon, skin, vessels, and cartilage and focuses on the application of tissue engineering that is relevant to clinical hand surgery.

Neural Tissue Engineering: A Self-Organizing Collagen Guidance Conduit

We report a novel implantable device that will deliver a tethered aligned collagen guidance conduit containing Schwann cells into a peripheral nerve injury site. Cells (Schwann cells and fibroblasts) incorporated into tethered rectangular collagen gels contracted and resulted in uniaxial alignment. This tissue-engineered construct was tested in three-dimensional culture and demonstrated the ability to guide neurite extension from dissociated dorsal root ganglia. A silicone tube was adapted to provide tethering sites for an implantable construct such that uniaxial cell-generated tension resulted in the formation of a bridge of aligned collagen fibrils, with a resident Schwann cell population. The potential of this device for surgical nerve regeneration was assessed in a 5-mm defect in a rat sciatic nerve model. Neural regeneration through this device was significantly greater than in controls, demonstrating that this system has potential both as a simple robust clinical implant and as a three-dimensional engineered tissue model.

Bridging a 30-mm nerve defect using collagen filaments

This article describes a 30-mm regeneration of severed peripheral nerve axons along collagen filaments. Two thousand or 4000 31-mm-long collagen filaments were grafted to bridge a 30-mm defect of the rat sciatic nerve. A collagen tube was grafted as a control. The mean number and mean fiber diameter of regenerated myelinated axons were 330 +/- 227 and 2.7 +/- 0.9 microm in the distal end of the 2000 collagen-filaments nerve guide, and 564 +/- 275 and 2.5 +/- 1.1 microm in the distal end of the 4000 collagen-filaments nerve guide at 12 weeks postoperatively, whereas in the distal end of the collagen tube, no regenerated axon was found. These results suggest that the collagen filaments guide axons of the rat's sciatic nerve to regenerate for 30 mm and act as a scaffold for axonal regeneration. Thirty-millimeter nerve regeneration of a 1-mm-diameter rat sciatic nerve by an artificial nerve guarantees a clinical application of the implant which should be very important for patients and surgeons.

Poly lactic acid--caprolactone copolymer tube with a denatured skeletal muscle segment inside as a guide for peripheral nerve regeneration: a morphological and electrophysiological evaluation of the regenerated nerves

A biodegradable copolymer of poly L-lactic acid and epsilon-caprolactone (PLAC) was manufactured into a tube, in which a denatured skeletal muscle segment was placed longitudinally. This model tube was implanted as a guide to promote nerve regeneration across a 5 cm gap in the rabbit sciatic nerve. Five months after implantation, good nerve regeneration was found throughout the graft and in the distal host nerve. The population (29.6/16 x 10(2) microm(2)) of regenerated nerves in the graft was higher than that of the contralateral normal sciatic nerve (18.0/16 x 10(2) microm(2)). Regenerated nerve fibers extended to the distal host nerve. The number of myelinated fibers was 13.7/16 x 10(2) microm(2) at a level 1.5 cm from the distal suture. The diameters (below 2 microm) of most regenerated myelinated (nerves in the graft and in the distal host nerve were much smaller than those (6-8 microm) of normal nerves. Electrophysiological evaluation showed that the hindlimb muscle (gastrocnemius) was innervated by motor nerves in all animals 5 months after implantation. These results indicate that the PLAC tube with a denatured muscle segment inside provided good conditions for nerve fiber regrowth. The PLAC tube is thought to protect the denatured muscle segment from rapid dissociation in the host tissue.

Neural tissue engineering: strategies for repair and regeneration

Nerve regeneration is a complex biological phenomenon. In the peripheral nervous system, nerves can regenerate on their own if injuries are small. Larger injuries must be surgically treated, typically with nerve grafts harvested from elsewhere in the body. Spinal cord injury is more complicated, as there are factors in the body that inhibit repair. Unfortunately, a solution to completely repair spinal cord injury has not been found. Thus, bioengineering strategies for the peripheral nervous system are focused on alternatives to the nerve graft, whereas efforts for spinal cord injury are focused on creating a permissive environment for regeneration. Fortunately, recent advances in neuroscience, cell culture, genetic techniques, and biomaterials provide optimism for new treatments for nerve injuries. This article reviews the nervous system physiology, the factors that are critical for nerve repair, and the current approaches that are being explored to aid peripheral nerve regeneration and spinal cord repair.

Restoration of function after spinal cord transection using a collagen bridge

The restoration of function of transected adult mammalian spinal cord without living tissue has not been reported previously. We report the first success of functional restoration of transected spinal cord without living tissue. We grafted collagen filaments parallel or transverse to the axis of the spinal cord to bridge 5-mm defects of 47 adult rat spinal cords. Twenty-five rats were used as a control. Of the 72 rats, 42 rats survived the experimental period. At 4 weeks postoperatively, regenerated axons crossed the proximal and distal spinal cord-implant interfaces in all 5 rats of the parallel-grafted group. At 12 weeks postoperatively, the rats in the parallel-grafted group (8 rats) could walk, run, and climb with hind-forelimb coordination. The somatosensory-evoked potentials were seen. Results suggest that the collagen filaments support the axonal regeneration of the transected spinal cord and the restoration of function when grafted parallel to the axis of the spinal cord. The functional restoration appeared to be permanent, raising the possibility of therapeutic application in humans.

Bridging a spinal cord defect using collagen filament

STUDY DESIGN

A rat model of spinal cord defect was designed to evaluate the effect of collagen filament implant on nerve regeneration in the spinal cord defect.

OBJECTIVES

To bridge a spinal cord defect and restore the function in adult mammals.

SUMMARY OF BACKGROUND DATA

Resection of the spinal cord in mammals is always followed by motor paralysis and loss of voluntary function below the lesion. Partial success in bridging the ends of the spinal cord after complete resection was reported. However, restoration of function has not been reported in adult mammalian.

MATERIALS AND METHODS

Four thousand collagen filaments 5-mm-long were grafted to bridge a 5-mm defect of rat spinal cord. Controls had their spinal cord defect left ungrafted after resection. At 1-week intervals, animals were evaluated functionally. After 4 and 12 weeks, animals were evaluated histologically. After 12 weeks, animals were evaluated electrophysiologically.

RESULTS

The severed spinal cord axons regenerated along the collagen filament implant crossing the proximal and distal spinal cord implant interfaces at 4 weeks after surgery. The rats with collagen filament grafts could walk, run, and climb with hind forelimb coordination at 12 weeks after surgery. Sensory-evoked potential waveform was found in the rats with collagen filament at 12 weeks after surgery.

CONCLUSIONS

The collagen filaments support the axonal regeneration of the transected spinal cord and the restoration of function.

30 mm regeneration of rat sciatic nerve along collagen filaments

This paper describes 30 mm regeneration of peripheral nerve axons along collagen filaments; 31-mm-long collagen filaments or collagen tube were grafted to bridge a 30-mm defect of rat sciatic nerve. The mean number and the diameter of regenerated myelinated axons were 330+/-227 and 2.7+/-0.9 microm at the distal end of the collagen-filaments 12 weeks postoperatively; while at the distal end of the tube no axon was found.

Bridging a peripheral nerve defect using collagen filaments

We describe bridging a peripheral nerve defect using collagen filaments instead of a tube. Cords of collagen filaments were grafted to bridge 20-mm defects of rat sciatic nerves. Nerve autografts were grafted as the control. The mean number and the mean fiber diameter of regenerated myelinated axons were approximately 4,800 and 3.3 microm, respectively, in the distal end of the nerve autograft and approximately 5,500 and 2.3 microm, respectively, in the distal end of the collagen-filaments nerve guide 8 weeks after surgery. The mean number and the mean fiber diameter of regenerated myelinated axons were approximately 6,900 and 3.1 microm, respectively, in the distal end of the nerve autograft and approximately 6,300 and 3.3 microm, respectively, in the distal end of the collagen-filaments nerve guide 25 weeks after surgery. Histologic studies suggested that the collagen filaments guided regenerating axons effectively. This new procedure offers a possible solution for the need to sacrifice a healthy nerve and for the shortage of graft material available for the repair of severed nerves.

A 25-year perspective of peripheral nerve surgery: evolving neuroscientific concepts and clinical significance

In spite of an enormous amount of new experimental laboratory data based on evolving neuroscientific concepts during the last 25 years peripheral nerve injuries still belong to the most challenging and difficult surgical reconstructive problems. Our understanding of biological mechanisms regulating posttraumatic nerve regeneration has increased substantially with respect to the role of neurotrophic and neurite-outgrowth promoting substances, but new molecular biological knowledge has so far gained very limited clinical applications. Techniques for clinical approximation of severed nerve ends have reached an optimal technical refinement and new concepts are needed to further increase the results from nerve repair. For bridging gaps in nerve continuity little has changed during the last 25 years. However, evolving principles for immunosuppression may open new perspectives regarding the use of nerve allografts, and various types of tissue engineering combined by bioartificial conduits may also be important. Posttraumatic functional reorganizations occurring in brain cortex are key phenomena explaining much of the inferior functional outcome following nerve repair, and increased knowledge regarding factors involved in brain plasticity may help to further improve the results. Implantation of microchips in the nervous system may provide a new interface between biology and technology and developing gene technology may introduce new possibilities in the manipulation of nerve degeneration and regeneration.

Spatiotemporal progress of nerve regeneration in a tendon autograft used for bridging a peripheral nerve defect

We have previously shown that a tendon autograft from the rat tail can support regeneration across a gap in the continuity of the rat sciatic nerve. In this study, we characterized the spatiotemporal progress of regeneration in such a graft bridging a 10-mm defect in the sciatic nerve of the rat. Regeneration was assessed 7, 10, 14, or 18 days postoperatively, by immunocytochemistry for axons, Schwann cells, and macrophages and histochemistry for blood vessels. Axonal regrowth into the grafts showed an initial delay period of 6.8 days, whereafter axons grew at a rate of 1.0 mm/day. Schwann cells grew into the grafts from both the proximal and distal nerve segments, proximally just ahead of the axonal front. Macrophages were initially preferentially located at the periphery of the grafts, but gradually increased inside the grafts. Blood vessels entered the grafts from both the proximal and distal aspects of the severed nerve. The onset of vascularization appeared to coincide with axonal regeneration into the grafts.