Peripheral nerve and neuromuscular allotransplantation: current status

Schwann cell-encapsulated chitosan-collagen hydrogel nerve conduit promotes peripheral nerve regeneration in rodent sciatic nerve defect models

Chitosan has various tissue regeneration effects. This study was designed to investigate the nerve regeneration effect of Schwann cell (SC)-encapsulated chitosan-collagen hydrogel nerve conduit (CCN) transplanted into a rat model of sciatic nerve defect. We prepared a CCN consisting of an outer layer of chitosan hydrogel and an inner layer of collagen hydrogel to encapsulate the intended cells. Rats with a 10-mm sciatic nerve defect were treated with SCs encapsulated in CCN (CCN+), CCN without SCs (CCN-), SC-encapsulated silicone tube (silicone+), and autologous nerve transplanting (auto). Behavioral and histological analyses indicated that motor functional recovery, axonal regrowth, and myelination of the CCN+ group were superior to those of the CCN- and silicone+ groups. Meanwhile, the CCN- and silicone+ groups showed no significant differences in the recovery of motor function and nerve histological restoration. In conclusion, SC-encapsulated CCN has a synergistic effect on peripheral nerve regeneration, especially axonal regrowth and remyelination of host SCs. In the early phase after transplantation, SC-encapsulated CCNs have a positive effect on recovery. Therefore, using SC-encapsulated CCNs may be a promising approach for massive peripheral nerve defects.

A Comparative Study of Porcine Small Intestine Submucosa and Cross-Linked Bovine Type I Collagen as a Nerve Conduit

Purpose

We compared 2 commercially available nerve conduits—the Axoguard Nerve Connector, made of porcine small intestine submucosa (SIS), and the NeuraGen Nerve Guide, made of cross-linked bovine type I collagen (Col)—using a rodent model at 4 weeks, specifically focusing on subchronic host responses to the implants.

Methods

A unilateral 5-mm sciatic nerve defect was created in 18 male Lewis rats and was repaired with SIS or Col conduits. After 4 weeks, histological evaluations of morphology, collagen content, macrophage polarization, vascularization, axonal regeneration, and myelination were conducted. To achieve a blinded examination, an independent qualified pathologist evaluated the images that were stained with hematoxylin-eosin, α-smooth muscle actin, and Masson trichrome stains.

Results

The results showed a dominant macrophage type 2 (M2) response in the SIS group and a dominant macrophage type 1 (M1) response in the Col group. The SIS group showed deeper implant vascularization and fibroblast ingrowth than the Col group. Collagen deposition was higher within the lumen of the Col group than the SIS group. All Col conduits were surrounded by a colocalized staining of Masson trichrome and α-smooth muscle actin, forming a capsule-like structure.

Conclusion

Distinctive histological features were identified for each conduit at the cellular level. The SIS conduits had a significantly higher number of host macrophages expressing M2 surface marker CD163, and the Col conduits showed a predominance of host macrophages expressing the M1 surface marker CD80. Data suggest that promoting the M2 response for tissue engineering and regenerative medicine is associated with a remodeling response. In addition, an independent analysis revealed an encapsulation-like appearance around all Col conduits, which is similar to what is seen in breast implant capsules.

Clinical relevance

The biomaterial choice for conduit material can play an important role in the host tissue response, with the potential to impact adverse events and patient outcomes.

Enhanced Nerve Regeneration by Exosomes Secreted by Adipose-Derived Stem Cells with or without FK506 Stimulation

Exosomes secreted by adipose-derived stem cells (ADSC-exo) reportedly improve nerve regeneration after peripheral nerve injury. Herein, we investigated whether pretreatment of ADSCs with FK506, an immunosuppressive drug that enhances nerve regeneration, could secret exosomes (ADSC-F-exo) that further augment nerve regeneration. Designed exosomes were topically applied to injured nerve in a mouse model of sciatic nerve crush injury to assess the nerve regeneration efficacy. Outcomes were determined by histomorphometric analysis of semi-thin nerve sections stained with toluidine blue, mouse neurogenesis PCR array, and neurotrophin expression in distal nerve segments. Isobaric tags for relative and absolute quantitation (iTRAQ) were used to profile potential exosomal proteins facilitating nerve regeneration. We observed that locally applied ADSC-exo and ADSC-F-exo significantly enhanced nerve regeneration after nerve crush injury. Pretreatment of ADSCs with FK506 failed to produce exosomes possessing more potent molecules for enhanced nerve regeneration. Proteomic analysis revealed that of 192 exosomal proteins detected in both ADSC-exo and ADSC-F-exo, histone deacetylases (HDACs), amyloid-beta A4 protein (APP), and integrin beta-1 (ITGB1) might be involved in enhancing nerve regeneration.

The role of vascularization in nerve regeneration of nerve graft

Vascularization is an important factor in nerve graft survival and function. The specific molecular regulations and patterns of angiogenesis following peripheral nerve injury are in a broad complex of pathways. This review aims to summarize current knowledge on the role of vascularization in nerve regeneration, including the key regulation molecules, and mechanisms and patterns of revascularization after nerve injury. Angiogenesis, the maturation of pre-existing vessels into new areas, is stimulated through angiogenic factors such as vascular endothelial growth factor and precedes the repair of damaged nerves. Vascular endothelial growth factor administration to nerves has demonstrated to increase revascularization after injury in basic science research. In the clinical setting, vascularized nerve grafts could be used in the reconstruction of large segmental peripheral nerve injuries. Vascularized nerve grafts are postulated to accelerate revascularization and enhance nerve regeneration by providing an optimal nutritional environment, especially in scarred beds, and decrease fibroblast infiltration. This could improve functional recovery after nerve grafting, however, conclusive evidence of the superiority of vascularized nerve grafts is lacking in human studies. A well-designed randomized controlled trial comparing vascularized nerve grafts to non-vascularized nerve grafts involving patients with similar injuries, nerve graft repair and follow-up times is necessary to demonstrate the efficacy of vascularized nerve grafts. Due to technical challenges, composite transfer of a nerve graft along with its adipose tissue has been proposed to provide a healthy tissue bed. Basic science research has shown that a vascularized fascial flap containing adipose tissue and a vascular bundle improves revascularization through excreted angiogenic factors, provided by the stem cells in the adipose tissue as well as by the blood supply and environmental support. While it was previously believed that revascularization occurred from both nerve ends, recent studies propose that revascularization occurs primarily from the proximal nerve coaptation. Fascial flaps or vascularized nerve grafts have limited applicability and future directions could lead towards off-the-shelf alternatives to autografting, such as biodegradable nerve scaffolds which include capillary-like networks to enable vascularization and avoid graft necrosis and ischemia.

The Surgical Management of Nerve Gaps: Present and Future

Peripheral nerve injuries can result in significant morbidity, including motor and/or sensory loss, which can affect significantly the life of the patient. Nowadays, the gold standard for the treatment of nerve section is end-to-end neurorrhaphy. Unfortunately, in some cases, there is segmental loss of the nerve trunk. Nerve mobilization allows primary repair of the sectioned nerve by end-to-end neurorrhaphy if the gap is less than 1 cm. When the nerve gap exceeds 1 cm, autologous nerve grafting is the gold standard of treatment. To overcome the limited availability and the donor site morbidity, other techniques have been used: vascularized nerve grafts, cellular and acellular allografts, nerve conduits, nerve transfers, and end-to-side neurorrhaphy. The purpose of this review is to present an overview of the literature on the applications of these techniques in peripheral nerve repair. Furthermore, preoperative evaluation, timing of repair, and future perspectives are also discussed.

Vascularized Brachial Plexus Allotransplantation-An Experimental Study in Brown Norway and Lewis Rats

BACKGROUND

Brachial plexus injuries are devastating. Current reconstructive treatments achieve limited partial functionality. Vascularized brachial plexus allotransplantation could offer the best nerve graft fulfilling the like-with-like principle. In this experimental study, we assessed the feasibility of rat brachial plexus allotransplantation and analyzed its functional outcomes.

METHODS

A free vascularized brachial plexus with a chimeric compound skin paddle flap based on the subclavian vessels was transplanted from a Brown Norway rat to a Lewis rat. This study has 2 parts. Protocol I aimed to develop the vascularized brachial plexus allotransplantation (VBP-allo) model. Four groups are compared: no reconstruction, VBP-allo with and without cyclosporine A immunosuppression, VBP autotransplantation (VBP-auto). Protocol II compared the recovery of the biceps muscle and forearm flexors when using all 5, 2 (C5 + C6) or 1 (isolated C6) spinal nerve as the donor nerves. The assessment was performed on week 16 and included muscle weight, functionality (grooming tests, muscle strength), electrophysiology and histomorphology of the targeted muscles.

RESULTS

Protocol I showed, the VBP-allo with cyclosporine A immunosuppression was electrophysiologically and functionally comparable to VBP-auto and significantly superior to negative controls and absent immunosuppression. In protocol II, all groups had a comparable functional recovery in the biceps muscle. Only with 5 donor nerves did the forearm show good results compared with only 1 or 2 donor nerves.

CONCLUSIONS

This study demonstrated a useful vascularized complete brachial plexus allotransplantation rodent model with successful forelimb function restoration under immunosuppression. Only the allotransplantation including all 5 roots as donor nerves achieved a forearm recovery.

Identification of Circulating miRNAs in a Mouse Model of Nerve Allograft Transplantation under FK506 Immunosuppression by Illumina Small RNA Deep Sequencing

Background. This study aimed to establish the expression profile of circulating microRNAs (miRNAs) during nerve allotransplantation in the presence and absence of FK506 immunosuppression. Methods. A 1 cm BALB/c donor sciatic nerve graft was transplanted into the sciatic nerve gaps created in recipient C57BL/6 mice with or without daily FK506 immunosuppression [1 mg/(kg·d)]. At 3, 7, and 14 d after nerve allotransplantation, serum samples were collected for miRNA expression analysis by Illumina small RNA deep sequencing. Results. Sequence analysis showed that the dominant size of circulating small RNAs after nerve allotransplantation was 22 nucleotides, followed by 23-nucleotide sequences. Nine upregulated circulating miRNAs (let-7e-5p, miR-101a-3p, miR-151-5p, miR-181a-5p, miR-204-5p, miR-340-5p, miR-381-3p, miR-411-5p, miR-9-5p, and miR-219-2-3p) were identified at 3 d, but none was identified at 7 or 14 d. Among them, miR-9-5p had the highest fold-change of >50-fold, followed by miR-340-5p with 38.8-fold. The presence of these nine miRNAs was not significant at 7 and 14 d after nerve allotransplantation with or without immunosuppression, showing that these miRNAs are not ideal biomarkers for monitoring rejection of deep-buried nerve allografts, a response usually observed later. Conclusions. We identified nine upregulated circulating miRNAs, which may have a biological function, particularly during the early stages after nerve allotransplantation under FK506 immunosuppression.

Carbon nanomaterials for nerve tissue stimulation and regeneration

Nanotechnology offers new perspectives in the field of innovative medicine, especially for reparation and regeneration of irreversibly damaged or diseased nerve tissues due to lack of effective self-repair mechanisms in the peripheral and central nervous systems (PNS and CNS, respectively) of the human body. Carbon nanomaterials, due to their unique physical, chemical and biological properties, are currently considered as promising candidates for applications in regenerative medicine. This chapter discusses the potential applications of various carbon nanomaterials including carbon nanotubes, nanofibers and graphene for regeneration and stimulation of nerve tissue, as well as in drug delivery systems for nerve disease therapy.

Laminin Functionalized Biomimetic Nanofibers For Nerve Tissue Engineering

Large-gap peripheral nerve injuries present a significant challenge for nerve regeneration due to lack of suitable grafts, insufficient cell penetration, and repair. Biomimetic nanofibrous scaffolds, functionalized on the surface with extracellular matrix proteins, can lead to novel therapies for repair and regeneration of damaged peripheral nerves. Here, nanofibrous scaffolds electrospun from blends of poly(caprolactone) (PCL) and chitosan were fabricated. Taking advantage of the amine groups on the chitosan, the surface of the scaffolds were functionalized with laminin by carbodiimide based crosslinking. Crosslinking allowed laminin to be attached to the surfaces of the PCL-chitosan nanofibers at relatively high concentrations that were not possible using conventional adsorption methods. The nanofibrous meshes were tested for wettability, mechanical properties and cell attachment and proliferation. Blending of chitosan with PCL provided more favorable surfaces for attachment of Schwann cells due to the reduction of the contact angle in comparison to neat PCL. Proliferation rates of Schwann cells grown on PCL-chitosan scaffolds with crosslinked laminin were significantly higher than the rates for PCL-chitosan nanofibrous matrices with adsorbed laminin. PCL-chitosan scaffolds with modified surfaces via crosslinking of laminin could potentially serves as versatile substrates with excellent mechanical and surface properties for in vivo cell delivery for nerve tissue engineering applications.

Tolerance and effects of FK506 (tacrolimus) on nerve regeneration: a pilot study

In adults, the outcome of nerve suture and nerve autograft remains generally unsatisfactory. FK506 (tacrolimus), an immunosuppressant drug used in transplantation, has been reported in animal studies to enhance nerve regeneration. In hand transplantation patients, nerve regeneration was unexpectedly good and rapid, and this observation has been attributed to FK506. The present Phase II experiment investigated the tolerance to FK506 after nerve suture or autograft, and the potential effects of the drug on axonal regeneration. Following strict criteria, five patients were included in this study. Within 7 days of nerve repair (median, ulnar and sciatic transections), patients received FK506 (aiming for blood concentrations between 5 and 8 ng/ml) for a total duration of 60 days. The patients were carefully followed with clinical and biological monitoring in order to detect side-effects. A clinical and electrophysiological assessment of the effect of FK506 on nerve regeneration was conducted. No undesirable side-effect was observed during or after FK506 treatment, but one non-compliant patient discontinued treatment. There was no evident improvement of sensory, motor or functional recovery at the end of the follow-up period (average duration 39.8 months), as compared to the expected clinical result without treatment. Although statistically non-significant, FK506 seemed to accelerate the progression of the Hoffmann-Tinel sign, but without impact on the final result.

TISSUE ENGINEERING FOR NERVE REPAIR

Nerve regeneration is a complex biological phenomenon. Once the nervous system is impaired, its recovery is difficult and malfunctions in other parts of the body may occur because mature neurons don't undergo cell division. To increase the prospects of axonal regeneration and functional recovery, researches have focused on designing “nerve guidance channels” or “nerve conduits”. For developing tissue engineered nerve conduits, four components come to mind, including a scaffold for axonal proliferation, supporting cells such as Schwann cells, growth factors, and extracelluar matrix. This article reviews the nervous system physiology, the factors that are critical for nerve repair, and the advanced technologies that are explored to fabricate nerve conduits. Furthermore, we also introduce a new method we developed to create longitudinally oriented channels within biodegradable polymers, Chitosan and PLGA, using a combined lyophilizing and wire-heating process. This innovative method using Ni-Cr wires as mandrels to create nerve guidance channels. The process is easy, straightforward, highly reproducible, and could easily be tailored to other polymer and solvent systems. These scaffolds could be useful for guided regeneration after transection injury in either the peripheral nerve or spinal cord.

Optimizing chimerism level through bone marrow transplantation and irradiation to induce long-term tolerance to composite tissue allotransplantation

BACKGROUND

Mixed chimerism with long-term composite tissue allotransplant (CTA) acceptance can be achieved through allogeneic bone marrow transplantation (BMT). The present study investigated the optimal chimerism level by giving different irradiation dosages to recipients to induce tolerance to CTA.

METHODS

Chimera were prepared using Brown-Norway and Lewis rats with strong major histocompatibility complex incompatibility. The Lewis rats received 5 mg antilymphocyte globulin (day -1 and 10) and 16 mg/kg cyclosporine (day 0-10) and were separated into groups 1, 2, 3, 4, and 5 according to the day -1 irradiation dosage: 0, 200, 400, 600, and 950 cGy, respectively. The Lewis rats were then reconstituted with 100 × 10(6) T-cell-depleted Brown-Norway bone marrow cells (day 0) and received vascularized Brown-Norway-CTA on day 28. Chimerism was assessed monthly by flow cytometry starting on day 28 after BMT. Graft-versus-host disease (GVHD) was assessed clinically and histologically.

RESULTS

Chimerism, 4 weeks after BMT, averaged 0.2%, 9.2%, 30.7%, 58%, and 99.3% in groups 1 to 5, respectively. GVHD occurred as follows: groups 1 and 2, none; group 3, 1 case of GVHD; group 4, 7 cases of GVHD (of which 3 died); and group 5, 10 cases of GVHD (of which 6 died). The percentage of long-term CTA acceptance was 0%, 0%, 90%, 70%, and 40% in groups 1 to 5, respectively. The percentage of regulatory T cells was significantly lower in high-chimerism (≥ 20%, n = 15) than in low-chimerism (<20%, n = 5) rats that accepted CTA long-term .

CONCLUSIONS

The chimerism level correlated positively with GVHD occurrence and long-term CTA acceptance but correlated negatively with regulatory T-cell levels. Optimal chimerism for CTA acceptance through pre-CTA BMT and irradiation occurs at 20-50% at day 28 after BMT in the rat model.

Allotransplanted neurons used to repair peripheral nerve injury do not elicit overt immunogenicity

A major problem hindering the development of autograft alternatives for repairing peripheral nerve injuries is immunogenicity. We have previously shown successful regeneration in transected rat sciatic nerves using conduits filled with allogeneic dorsal root ganglion (DRG) cells without any immunosuppression. In this study, we re-examined the immunogenicity of our DRG neuron implanted conduits as a potential strategy to overcome transplant rejection. A biodegradable NeuraGen® tube was infused with pure DRG neurons or Schwann cells cultured from a rat strain differing from the host rats and used to repair 8 mm gaps in the sciatic nerve. We observed enhanced regeneration with allogeneic cells compared to empty conduits 16 weeks post-surgery, but morphological analyses suggest recovery comparable to the healthy nerves was not achieved. The degree of regeneration was indistinguishable between DRG and Schwann cell allografts although immunogenicity assessments revealed substantially increased presence of Interferon gamma (IFN-γ) in Schwann cell allografts compared to the DRG allografts by two weeks post-surgery. Macrophage infiltration of the regenerated nerve graft in the DRG group 16 weeks post-surgery was below the level of the empty conduit (0.56 fold change from NG; p<0.05) while the Schwann cell group revealed significantly higher counts (1.29 fold change from NG; p<0.001). Major histocompatibility complex I (MHC I) molecules were present in significantly increased levels in the DRG and Schwann cell allograft groups compared to the hollow NG conduit and the Sham healthy nerve. Our results confirmed previous studies that have reported Schwann cells as being immunogenic, likely due to MHC I expression. Nerve gap injuries are difficult to repair; our data suggest that DRG neurons are superior medium to implant inside conduit tubes due to reduced immunogenicity and represent a potential treatment strategy that could be preferable to the current gold standard of autologous nerve transplant.

Nerve allograft transplantation for functional restoration of the upper extremity: case series

BACKGROUND

Major trauma to the spinal cord or upper extremity often results in severe sensory and motor disturbances from injuries to the brachial plexus and its insertion into the spinal cord. Functional restoration with nerve grafting neurotization and tendon transfers is the mainstay of treatment. Results may be incomplete due to a limited supply of autologous material for nerve grafts. The factors deemed most integral for success are early surgical intervention, reconstruction of all levels of injury, and maximization of the number of axonal conduits per nerve repair.

OBJECTIVE

To report the second series of nerve allograft transplantation using cadaveric nerve graft and our experience with living-related nerve transplants.

PARTICIPANTS

Eight patients, seven men and one woman, average age 23 years (range 18-34), with multi-level brachial plexus injuries were selected for transplantation using either cadaveric allografts or living-related donors.

METHODS

Grafts were harvested and preserved in the University of Wisconsin Cold Storage Solution at 5 degrees C for up to 7 days. The immunosuppressive protocol was initiated at the time of surgery and was discontinued at approximately 1 year, or when signs of regeneration were evident. Parameters for assessment included mechanism of injury, interval between injury and treatment, level(s) of deficit, post-operative return of function, pain relief, need for revision surgery, complications, and improvement in quality of life.

RESULTS

Surgery was performed using living-related donor grafts in six patients, and cadaveric grafts in two patients. Immunosuppression was tolerated for the duration of treatment in all but one patient in whom early termination occurred due to non-compliance. There were no cases of graft rejection as of most recent followup. Seven patients showed signs of regeneration, demonstrated by return of sensory and motor function and/or a migrating Tinel's sign. One patient was non-compliant with the post-operative regimen and experienced minimal return of function despite a reduction in pain.

CONCLUSIONS

Despite the small number of subjects, it appears that nerve allograft transplantation may be performed safely, permitting non-prioritized repair of long-segment peripheral nerve defects and maximizing the number of axonal conduits per nerve repair. For patients with long, multi-level brachial plexus injuries or combined upper and lower extremity nerve deficits, the use of nerve allograft allows a more complete repair that may translate into greater functional restoration than autografting alone.

Harvey Cushing's innovative attempt at xenotransplanting a rabbit spinal cord in a patient after resection of a peripheral nerve tumor in 1902

OBJECTIVE

A review of Harvey Cushing's surgical cases at Johns Hopkins Hospital revealed new information about his early work using nerve xenografts to repair peripheral nerve injuries.

METHODS

The Johns Hopkins Hospital surgical records from 1896 to 1912 were reviewed. A single case in which Cushing used a xenograft to repair a peripheral nerve defect was selected for further study.

RESULTS

In August 1902, a 23-year-old woman presented with tingling and numbness in her left foot and focal tenderness in the popliteal region. Cushing performed an exploratory operation, revealing an encapsulated tumor originating from the internal popliteal nerve. After resecting the segment of involved nerve, Cushing harvested the spinal cord from a rabbit and used it to span the 18-cm defect. At a 5-month postoperative follow-up, according to Cushing's clinical notes, the patient had partially regained some sensation in her leg and foot. Seven months later, the patient presented with a local tumor recurrence, and her leg was amputated. An examination of the amputated specimen demonstrated that the xenograft was still intact without gross evidence of xenograft rejection.

CONCLUSION

Despite its questionable functional success, we report a previously unpublished operative case by Harvey Cushing in which a rabbit spinal cord was transplanted into a human to bridge a sciatic nerve gap. This sheds light on the potential for animal tissue as a source for the treatment of neurological disease in humans.

Peripheral nerve injuries of the pediatric hand: issues in diagnosis and management

Peripheral nerve injuries resulting in significant neural disruption frequently present complex management challenges. Typically the product of fracture, dislocation, or crush injuries, pediatric peripheral nerve injuries may be difficult to accurately characterize. Thorough clinical examination coupled with electromyogram and neurophysiologic studies are extremely useful. When possible, primary repair should be attempted. If, however, defect size precludes primary reanastomosis, use of a nerve graft may be advantageous. Alternatively, nerve conduits, such as veins, pseudosheaths, and bioabsorbable tubes, are also effective facilitators of nerve regeneration. Although nerve injuries of the pediatric hand often present complex challenges, a thorough knowledge of diagnostic methods and advances in surgical interventions offers better outcomes.

Carbon nanofibers and carbon nanotubes in regenerative medicine

Carbon nanotubes and carbon nanofibers have long been investigated for applications in composite structural materials, semiconductor devices, and sensors. With the recent well-documented ability to chemically modify nanofibrous carbon materials to improve their solubility and biocompatibility properties: a whole new class of bioactive carbon nanostructures has been created for biological applications. This review focuses on the latest applications of carbon nanofibers and carbon nanotubes in regenerative medicine.

[Organ transplantation, composite tissue allotransplantation, and plastic surgery]

Transplantations play an increasing role for plastic reconstructive surgeons. The increasing number of solid organ transplantations and the improved long-term survival rates lead to increased numbers of these patients also undergoing plastic and reconstructive procedures. Free flap transfer in solid organ transplant patients is feasible with no higher risk to both transplant function and postoperative complications than for nontransplant patients, even during immune suppression. Composite tissue allotransplantation (CTA) is an evolving field in plastic reconstructive surgery with hands, arms, partial faces, abdominal walls, and knee joints being transferred in clinical settings. However only an interdisciplinary approach using all available resources in highly selected patients after exhausting all other plastic reconstructive procedures is able to achieve reasonable results. The potential complications of long-term immune suppression and patient compliance have to be balanced with the expected and achieved functional result of CTA, whose procedures must be discussed as a potential tissue or organ transplantation, given the legal and logistic implications. The interdisciplinary cooperation of transplant surgeons, microsurgeons, psychologists, and ergo- and physiotherapists is mandatory to achieve successful CTA results.

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.

Chapter 18: Enhancement of nerve regeneration and recovery by immunosuppressive agents

Clinically, little can be done to induce restoration of good to excellent neurological function following nervous system trauma, and time is required before an effective technique is developed and applied clinically. However, there are novel techniques that have not been tested experimentally or clinically that may induce significantly faster, reliable, and extensive neurological recovery following nervous system trauma than is presently possible, even for techniques currently being tested on animal models. To repair peripheral nerves following trauma in which a length of the nerve pathway is destroyed, many clinicians consider autologous sensory nerve grafts to be the "gold standard" for inducing neurological recovery. However, this technique has severe limitations, such as being effective only across gaps less than 2 cm, for repairs performed less than 2 months posttrauma, and in young patients. As a consequence, many patients suffer permanent neurological deficits or recover only limited neurological function, and they frequently develop irreversible neuropathic pain. This review examines the clinical role that immunosuppressants might play, in the presence or absence of autologous, allografts, or xenografts, in increasing the rate, success, and extent of neurological recovery following nervous system trauma.

Chapter 8: Current techniques and concepts in peripheral nerve repair

Despite the progress in understanding the pathophysiology of peripheral nervous system injury and regeneration, as well as advancements in microsurgical techniques, peripheral nerve injuries are still a major challenge for reconstructive surgeons. Thorough knowledge of anatomy, pathophysiology, and surgical reconstruction is a prerequisite of proper peripheral nerve injury management. This chapter reviews the currently available surgical treatment options for different types of nerve injuries in clinical conditions. In overview of direct nerve repair, various end-to-end coaptation techniques and the role of end-to-side repair for proximal nerve injuries is described. When primary repair cannot be performed without undue tension, nerve grafting or tubulization techniques are required. Current gold standard for bridging nerve gaps is nerve autografting. However, disadvantages of this approach, such as donor site morbidity and limited length of available graft material encouraged the search for alternative means of nerve gap reconstruction. Nerve allografting was introduced for repair of extensive nerve injuries. Tubulization techniques with natural or artificial conduits are applicable as an alternative for bridging short nerve defects without the morbidities associated with harvesting of autologous nerve grafts. Achieving better outcomes depends both on the advancements in microsurgical techniques and introduction of molecular biology discoveries into clinical practice. The field of peripheral nerve research is dynamically developing and concentrates on more sophisticated approaches tested at the basic science level. Future directions in peripheral nerve reconstruction including, tolerance induction and minimal immunosuppression for nerve allografting, cell based supportive therapies and bioengineering of nerve conduits are also reviewed in this chapter.

A modified model of hindlimb osteomyocutaneous flap for the study of tolerance to composite tissue allografts

Composite tissue allotransplantation (CTA) is the new frontier in transplantation. More than 25 hand allograft transplants have been performed worldwide, and the feasibility has been well established. The classical experimental model of CTA involves rat orthotopic hindlimb transplantation, a time-consuming procedure associated with high mortality and morbidity. We describe a rat heterotopic osteomyocutaneous flap that serves as a nonfunctional CTA, allowing the study of tolerance induction to a highly antigenic vascularized allograft of bone, muscle, and skin while minimizing the morbidity and mortality of full hind limb transplantation. In the present studies, we explored whether establishing chimerism by nonmyeloablative conditioning would induce tolerance to CTA. When compared with the classic hind limb transplantation model, these results demonstrate that our heterotopic hind limb flap is less morbid and as an effective experimental model for the study of CTA tolerance.

Composite tissue allotransplantation: a review of relevant immunological issues for plastic surgeons

BACKGROUND

Composite tissue allotransplantation of hand, facial and other tissues is now a clinical reality. The terminology, treatment principles, drug combinations, dosage schedules and mechanisms of the immunosuppression medications on which contemporary transplant surgery is based are unfamiliar to plastic surgeons and most healthcare providers outside the field of transplantation medicine. With this in mind, the purpose of this manuscript is to provide plastic surgeons with a comprehensive and understandable review of key immunological principles relevant to composite tissue allotransplantation.

METHODS

We present an overview of the immunological basis of composite tissue allotransplantation aimed at the plastic surgery readership, based on our own experience plus manuscripts sourced from MEDLINE, EMBASE, text books, ancient manuscripts and illustrations.

RESULTS

In this manuscript we provide the reader with a brief history of composite tissue allotransplantation (CTA), a concise description of the immunological terminology, treatment approaches, risks associated with immunosuppressive therapy, risk acceptance, and current research avenues relating to contemporary CTA.

CONCLUSION

Today, as transplant and reconstructive surgeons join forces to move hand and facial tissue allotransplantation into the clinical arena, it is important that plastic surgeons have an understanding of the major immunological principles upon which this new treatment is based.

[Experimental and clinical experience of composite tissues allotransplantation in reconstructive surgery]

Composite tissue allotransplantation (CTA) is a new concept in reconstructive surgery to improve major physical defects with no current solution. Although not a life-saving procedure, tissue replacement by CTA offers great potential for improving quality of life but relies on lifelong immunotherapy. This new practice has become achievable with the refinement of microsurgical techniques, with experience gained from limb and scalp replantations, with the development of organ transplantation and the release of new immunosuppressive drugs. Experimental and clinical research made it possible. The first human cases of CTA proved the reality and the feasibility of the concept. While the early functional results of these allografts are encouraging, they will need to be assessed in the long-term, and development of less toxic - more efficient immonu-suppressive drugs will be a permanent requisite to the broadening of CTA. Although long-term outcome and potential adverse effects of chronic immunosuppression remain uncertain, as for organ transplantation, CTA is already a potential solution for some highly selected patients carrying physical disabilities such as large facial defects and bilateral hand amputation.

Immunomodulation by costimulation blockade inhibits rejection of nerve allografts

The aim of this study was to investigate if costimulation blockade could be used to modulate the immune response, to prevent rejection, and to stimulate regeneration into nerve allografts. Nerve allografts from Balb/C mice, and isogenic nerve grafts (isografts) from C57/BL6 mice, were used to bridge a 7-mm gap of the sciatic nerve in C57/BL6 mice. Allograft recipients were treated with either a triple treatment with anti-lymphocyte function antigen-1 (anti-LFA), anti-CD40 ligand (anti-CD40L), and cytotoxic T-lymphocyte antigen 4 immunoglobulin (anti-CTLA4Ig) or isotype antibodies (placebo) at postoperative days 0, 2, 4, and 6 (intraperitoneal). After 5 or 9 days, the nerve grafts, together with the proximal and the distal nerve segments, were evaluated by histology and immunocytochemistry for inflammatory cells [CD4-positive (CD4+) and CD8-positive (CD8+) staining cells] and axonal outgrowth (neurofilaments). The immune response was inhibited by costimulation blockade with less extensive inflammation and a lower number of CD4+ staining cells in triple-treated allografts at 9 days. The regeneration rate was significantly faster in isografts (0.75 mm/day) compared with allografts with placebo treatment (0.39 mm/day), but not when compared with triple-treated allografts (0.49 mm/day). At 9 days, the axons were significantly longer in nerve isografts than in nerve allografts, irrespective of treatment. Hence, costimulation blockade neither increased the regeneration rate nor the outgrowth length in triple-treated allografts. We conclude that costimulation blockade inhibits the immune response in nerve allografts without deterring early axonal outgrowth.

Research and Events Leading to Facial Transplantation

Facial transplantation has long captured the interest and imagination of scientists, the media, and the lay public. Facial transplantation could provide an excellent alternative to current treatments for facial disfigurement caused by burns, trauma, cancer extirpation, or congenital birth defects. This article discusses the major technical, immunologic, psychosocial and ethical hurdles that have been overcome to bring facial transplantation from an idea to a clinical reality by providing the reader with a chronologic overview of the research and events that have led this exciting new treatment into the clinical arena.

Composite tissue allotransplantation of the hand and face: a new frontier in transplant and reconstructive surgery

Each year an estimated 7-million people in the USA need composite tissue reconstruction because of surgical excision of tumors, accidents and congenital malformations. Limb amputees alone comprise over 1.2 million of these. This figure is more than double the number of solid organs needed for transplantation. Composite tissue allotransplantation in the form of hand and facial tissue transplantation are now a clinical reality. The discovery, in the late 1990s, that the same immunotherapy used routinely in kidney transplantation was also effective in preventing skin rejection made this possible. While these new treatments seem like major advancements most of the surgical, immunological and ethical methods used are not new at all and have been around and routinely used in clinical practice for some time. In this review of composite tissue allotransplantation, we: (i) outline the limitations of conventional reconstructive methods for treating severe facial disfigurement, (ii) review the history of composite tissue allotransplantation, (iii) discuss the chronological scientific advances that have made it possible, (iv) focus on the two unique clinical scenarios of hand and face transplantation, and (v) reflect on the critical issues that must be addressed as we move this new frontier toward becoming a treatment in mainstream medicine.

Angiosome territories of the nerves of the upper limbs

BACKGROUND

The use of free vascularized nerve grafts requires intimate knowledge of the blood supply of peripheral nerves. The authors aimed to demonstrate radiographically the topography of the upper limb nerves with their blood supply, and to examine them as an application of the angiosome concept. An angiosome is a three-dimensional block of composite tissue supplied by a single source artery.

METHODS

This anatomical study involved the meticulous dissection of four fresh upper limb specimens injected intraarterially with a gelatin-lead oxide mixture. The nerves were tagged circumferentially with copper wire and radiographs were taken of the nerves with their arterial blood supply. The median, ulnar, radial, musculocutaneous, and axillary nerves were examined.

RESULTS

The authors showed that the nerves of the upper limb were supplied segmentally by source vessels, which reinforced the angiosome concept. The suitability of each nerve for harvest in free vascularized nerve transfer was assessed according to its pattern of blood supply.

CONCLUSIONS

The authors' work has a wide range of clinical applications and provides an anatomical basis for neurovascular and neurocutaneous flaps and free vascularized nerve grafting.

Neuroregenerative Effects of Preinjury FK-506 Administration

BACKGROUND

FK-506 is used in organ transplantation because it promotes neurite outgrowth in vitro and enhances neuroregeneration in peripheral nerve injury transection models. Immunosuppressive mechanisms of FK-506 are well defined, with demonstration of decreased neuroregenerative effects with delayed administration. The purpose of this study was to describe the effects of preinjury administration of FK-506 in rats with tibial nerve transection injury.

METHODS

Eight inbred male Lewis rats per group in three separate groups underwent tibial nerve transection with primary repair. Group I received placebo, group II received FK-506 treatment at 1 day before surgery, and group III received FK-506 preloading 3 days before surgery.

RESULTS

Histologic and histomorphometric results demonstrated the preload FK-506 group had superior results compared with the immediate FK-506 group. Both FK-506 groups were superior to the placebo group. The preload FK-506 demonstrated superior regeneration in mean total nerve fiber counts (p < 0.05), greater percentage neural tissue (p < 0.05), greater mean nerve fiber density (p < 0.05), and lower percentage of debris (p > 0.05). Mean nerve fiber widths were similar in the preload and immediate FK-506 groups but superior to the placebo group.

CONCLUSION

These data suggest that enhancement of FK-506's neuroregenerative effect is enhanced when administered before nerve injury such as when performing elective surgery.

Biomaterials and Strategies for Nerve Regeneration

Nerve regeneration is a complex biological phenomenon. Once the nervous system is impaired, its recovery is difficult and malfunctions in other parts of the body may occur because mature neurons do not undergo cell division. To increase the prospects of axonal regeneration and functional recovery, researches have focused on designing "nerve guidance channels" or "nerve conduits." When developing ideal tissue-engineered nerve conduits, several components come to mind. They include a biodegradable and porous channel wall, the ability to deliver bioactive growth factors, incorporation of support cells, an internal oriented matrix to support cell migration, intraluminal channels to mimic the structure of nerve fascicles, and electrical activities. This article reviews the factors that are critical for nerve repair, and the advanced technologies that are explored to fabricate nerve conduits. To more accurately mimic natural repair in the body, recent studies have focused on the use of various advanced approaches to create ideal nerve conduits that combine multiple stimuli in an effort to better mimic the complex signals normally found in the body.

Short-Term Anti-CD40 Ligand Costimulatory Blockade Induces Tolerance to Peripheral Nerve Allografts, Resulting in Improved Skeletal Muscle Function

BACKGROUND

Reconstruction of long or multiple peripheral nerve defects with peripheral nerve autografts may not be possible due to insufficient quantities of donor nerve. There are promising preliminary data that nerve allografting has the potential to improve functional outcome and quality of life after devastating nerve injuries or large tumor resections. The authors previously demonstrated that blockade of the CD40/CD40 ligand costimulatory pathway, via anti-CD40 ligand monoclonal antibody (MR1) therapy, induces tolerance to peripheral nerve allografts in mice. In this study, the authors sought to correlate the immunomodulatory effects of MR1 treatment with functional muscle recovery after peripheral nerve allografting in the murine model.

METHODS

In the mouse hindlimb model, peroneal nerve isografts (C57BL/6 into C57BL/6) and allografts (BALB/c into C57BL/6) were utilized to reconstruct 0.8-cm peroneal nerve gaps. MR1 versus vehicle was administered on days 0, 1, and 2. At 60 days after transplantation, splenocyte production of interferon-gamma and interleukins 2, 4, and 5 were quantified using ELISPOT analysis, and in vitro maximum tetanic isometric force of the extensor digitorum longus muscle was measured.

RESULTS

At 60 days after transplantation, immunomodulation persisted in MR1-treated, allografted animals, as evidenced by significantly muted interferon-gamma, interleukin 4, and interleukin 2 splenocyte production. Functional extensor digitorum longus muscle recovery after nerve allografting and MR1 administration was improved due to the tolerance induced by MR1 compared with untreated allograft recipients.

CONCLUSIONS

Three-day inductive therapy with MR1 produces 60-day immunologic tolerance to peripheral nerve allografts, as evidenced by dramatic decreases in interferon-gamma, interleukin 4, and interleukin 2 production, and results in increased muscle force recovery. This work emphasizes the potential promise of CD40-CD40 ligand costimulatory blockade in reducing or eliminating peripheral nerve allograft rejection.

Immunomodulation with anti-αβ T-cell receptor monoclonal antibodies in combination with cyclosporine a improves regeneration in nerve allografts

OBJECTIVES

To investigate the use of nerve allografts in animals treated with a short-term combined protocol of anti-alpha/beta T-cell receptor monoclonal antibodies and Cyclosporine A (CsA) to induce tolerance and allow for nerve regeneration.

STUDY DESIGN

An established rat sciatic nerve model was used. A total of 76 rats were used in this experiment (Lew RT1L n=44, Lewis-Brown-Norway (LBN RT1L+N, n=22), Brown-Norway (BN RT1N, n=10). Sciatic nerve (1.5 cm) deficits were created in the Lewis rats and the animals were randomized to seven treatment groups to allow for repair with isograft controls (LEW-LEW) and with both semiallogeneic (LBN-LEW) and full major histocompatability (MHC) mismatched (BN-Lew) allografts.

METHODS

Nerve regeneration was evaluated at 6 and 12 weeks by somatosensory evoked potentials (SSEP) and standardized pin-prick and toe-spread tests. Nerve samples were harvested at 12 weeks and stained with toluidine blue to assess the total number of myelinated axons, axon area, and myelin sheath thickness. Muscle denervation atrophy was evaluated by gastrocnemius weights. Immunocompetence was investigated through skin grafting and fluorescent activated cell sorting (FACS) analysis.

RESULTS

Improved functional, electrophysiologic, and histomorphometric outcomes were observed in animals treated with anti-alpha/betaTCR mAbs and CsA after nerve allograft transplantation when compared to animals receiving no treatment and CsA alone.

CONCLUSIONS

The immunomodulating protocol of combination anti-alpha/beta TCR mAbs and CsA for a 5 week period altered the rejection process, affording nerve regeneration. It may provide for an expanded source of nerve tissue to alleviate the morbidity of harvesting peripheral nerves from multiple sites for those afflicted with extensive peripheral nerve injuries.

Immunosuppressants: neuroprotection and promoting neurological recovery following peripheral nerve and spinal cord lesions

No clinical techniques induce restoration of neurological losses following spinal cord trauma. Peripheral nerve damage also leads to permanent neurological deficits, but neurological recovery can be relatively good, especially if the ends of a transected nerve are anastomosed soon after the injury. The time until recovery generally depends on the distance the axons must regenerate to their targets. Neurological recovery following the destruction of a length of a peripheral nerve requires a graft to bridge the gap that is permissive to, and promotes, axon regeneration. But neurological recovery is slow and limited, especially for gaps longer than 1.5 cm, even using autologous peripheral nerve grafts. Without a reliable means of bridging long nerve gaps, such injuries commonly result in amputations. Promoting extensive neurological recovery requires techniques that simultaneously provide protection to injured neurons and increase the numbers of neurons that extend axons, while inducing more rapid and extensive axon regeneration across long nerve gaps. Although conduits filled with various materials enhance axon regeneration across short nerve gaps, pure sensory nerve graft remains the gold standard for use across long nerve gaps, even though they lead to only limited neurological recovery. Consistent results demonstrate that several immunosuppressive agents enhance the number of axons and the rate at which they regenerate. This review examines the roles played by immunosuppressants, especially FK506, with primary focus on its role as a neuroprotectant and neurotrophic agent, and its potential clinical use to promote improved neurological recovery following peripheral nerve and spinal cord injuries.

Perspectives on Hand Transplantation

The early experience of hand transplantation has yielded a mixture of successes and failures. No life-threatening adverse effects have been encountered from immunosuppression, yet additional medications were required in some cases with unknown long-term efficacy or side effects. Limited functional returns have been observed, but any effect of chronic rejection is too early to determine. Although the experience has confirmed the benefits of hand transplantation to patients and their families, the future of hand transplantation on a wide scale is dependent on further research to alter its risk-benefit balance.

Premier cas mondial d'autoréimplantation de membre associé à un traitement immunosuppresseur (FK 506-Tacrolimus®) : rapport préliminaire à 18 mois

This is the case of the replantation of the upper limb of a sixty year old woman. The nature of the traumatism is an avulsion of the upper limb, at the junction of the middle third and the lower third of the humerus, which has a very bad prognosis. The originality of this report is the administration of Tacrolimus (immunosuppressive molecule) in an autotransplant. Tracolimus stimulates the nerve growing back, as already demonstrated in the animal and the fetus. In this preliminary report, the use of Tacrolimus over one year showed exceptional results. Indeed, the autors noticed clinical signs of intrinsic reinervation of the hand in the territory of the ulnar and median nerve. This has been confirmed with the use of electromyography. This is, as far as we know, the first observation of such results with adults and when the level of amputation is located so high. The authors think that the use of Tacrolimus should be tested in numerous cases of nerve lesions with bad prognosis such as high ulnar nerve lesions, serious plexus suffering or even in spinal cord trauma.

Functional MRI activation of somatosensory and motor cortices in a hand-grafted patient with early clinical sensorimotor recovery

The aim of this study was to investigate somatosensory and motor cortical activity with functional MRI (fMRI) in a hand-grafted patient with early clinical recovery. The patient had motor fMRI examinations before transplantation, and motor and passive tactile stimulations after surgery. His normal hand and a normal group were studied for comparison. A patient with complete brachial plexus palsy was studied to assess the lack of a fMRI signal in somatosensory areas in the case of total axonal disconnection. Stimulating the grafted hand revealed significant activation in the contralateral somatosensory cortical areas in all fMRI examinations. The activation was seen as early as 10 days after surgery; this effect cannot be explained by the known physiological mechanisms of nerve regeneration. Although an imagination effect cannot be excluded, the objective clinical recovery of sensory function led us to formulate the hypothesis that a connection to the somatosensory cortex was rapidly established. Additional cases and fundamental studies are needed to assess this hypothesis, but several observations were compatible with this explanation. Before surgery, imaginary motion of the amputated hand produced less intense responses than executed movements of the intact hand, whereas the normal activation pattern for right-handed subjects was found after surgery, in agreement with the good clinical motor recovery.

Use of Skeletal Muscle Tissue in Peripheral Nerve Repair: Review of the Literature

The management of peripheral nerve injury continues to be a major clinical challenge. The most widely used technique for bridging defects in peripheral nerves is the use of autologous nerve grafts. This technique, however, necessitates a donor nerve and corresponding deficit. Many alternative techniques have thus been developed. The use of skeletal muscle tissue as graft material for nerve repair is one example. The rationale regarding the use of the skeletal muscle tissue technique is the availability of a longitudinally oriented basal lamina and extracellular matrix components that direct and enhance regenerating nerve fibers. These factors provide superiority over other bridging methods as vein grafts or (non)degradable nerve conduits. The main disadvantages of this technique are the risk that nerve fibers can grow out of the muscle tissue during nerve regeneration, and that a donor site is necessary to harvest the muscle tissue. Despite publications on nerve conduits as an alternative for peripheral nerve repair, autologous nerve grafting is still the standard care for treatment of a nerve gap in the clinical situation; however, the use of the skeletal muscle tissue technique can be added to the surgeon's arsenal of peripheral nerve repair tools, especially for bridging short nerve defects or when traditional nerve autografts cannot be employed. This technique has been investigated both experimentally and clinically and, in this article, an overview of the literature on skeletal muscle grafts for bridging peripheral nerve defects is presented.

FK506 enhances regeneration of axons across long peripheral nerve gaps repaired with collagen guides seeded with allogeneic Schwann cells

We assessed the effects of FK506 administration on regeneration after a 6-mm gap repair with a collagen guide seeded with allogeneic Schwann cells (SCs) in the mouse sciatic nerve. SCs were isolated from predegenerated adult sciatic nerves and expanded in culture using a defined medium, before being seeded in the collagen guide embedded in Matrigel. Functional reinnervation was evaluated by noninvasive methods to determine recovery of motor, sensory, and autonomic functions in the hindpaw over 4 months postoperation. Histological analysis of the regenerated nerves was performed at the end of the study. Using simple collagen guides for tubulization repair, treatment with an immunosuppressant dose of FK506 (5 mg/kg/day) resulted in significant improvement of the onset and the degree of reinnervation. While the introduction of allogeneic SCs did not improve regeneration versus a collagen guide filled only with Matrigel, treatment with FK506 allowed for successful regeneration in all the mice and for significant improvement in the levels of functional recovery. Compared with the untreated group, there was greater survival of transplanted pre-labeled SCs in the FK506-treated animals. Morphologically, the best nerve regeneration (in terms of nerve caliber and numbers of myelinated axons) was obtained with SC-seeded guides from FK506-treated animals. Thus, FK506 should be considered as adjunct therapy for various types of tubulization repair.

Pre-degenerated nerve shows enhanced regeneration after incremental elongation in rats

Following nerve degeneration, we investigated effects of linear elongation on subsequent nerve regeneration in a total of 92 Wistar rats (weight 380-430 g). The nerve was ligated at the midthigh and then elongated incrementally by a total of 15 mm by leg lengthening at a rate of 3 or 5 mm/day. Seven days after initiation of nerve elongation, the external fixator was removed and normal leg length was restored with internal fixation. Then a 10 mm nerve segment at the ligature site was excised, and the nerve was repaired with sutures (group D). At 2, 4, 6, and 8 weeks after nerve suturing, we examined transverse semi-thin nerve sections compared with group I (severed and repaired after leg lengthening without a nerve ligature) and control group (severed and repaired without leg lengthening). After lengthening at 3 mm/day, nerve regeneration in group D was enhanced at 4 weeks. After lengthening at 5 mm/day, nerve regeneration in group D also was enhanced at 6 and 8 weeks. Pre-degenerated nerve showed better regeneration after suturing than intact nerve. Elongation holds promise as an alternative to nerve grafting in treatment of nerve injury.

Immune rejection of a facial nerve xenograft does not prevent regeneration and the return of function: an experimental study

Nerve grafts may be used to repair damaged peripheral nerves and also to facilitate spinal cord regeneration after experimental trauma. Little is known, however, about the possible use of xenografts and the role of immune rejection in the outcome of repair. In rats, excision of a short (7-8 mm) segment of facial nerve at its exit point from the skull base results in a permanent deficit in eye closure in the blink reflex. This deficit can be repaired by transplantation of a segment of either syngeneic rat facial nerve or xenogeneic Balb-C mouse sciatic nerve either with or without cyclosporine immunosuppression. With longer (15-20 mm) transplants, however, restoration of eye closure becomes dependent on cyclosporine administration. Thus, in a situation where nerve repair does not occur without a graft, a host immune attack has an attritional effect which is not sufficient to prevent repair over short distances, but becomes obvious when the regenerating fibres have to cross longer segments of transplanted tissue.

Bio-compatibility of type I/III collagen matrix for peripheral nerve reconstruction

Nerve gaps are usually bridged by autografts. With improving technical methods biocompatible conduits may become an alternative graft to reconstruct nerves. Non-neural conduits fail to support regeneration over larger gaps due to lacking viable Schwann cells. Thus, tissue engineering of nerves is focusing on implantation of viable Schwann cells into suitable scaffolds. In this study, we tested collagen type I/III tubes as a potential nerve guiding matrix. Revascularization, foreign body reaction, biodegradation and Schwann cell settlement were evaluated by immunocytochemistry, light, fluorescence and scanning electron microscopy, after different implantation times. The conduits were completely revascularized between day 5 and 7 post-operatively and well integrated into the host tissue. Host response was characterized by a moderate invasion of ED1/ED2-positive macrophages. Biodegradation of the tubes was slowly enough to maintain a stable support structure for extended regeneration processes. Implanted Schwann cells adhered, survived and proliferated on the inner surface of the conduits and were able to form nerve guiding columns of Büngner. From this results, we conclude that collagen-type I/III can serve as template to design "living" nerve conduits, which may be able to ensure nerve regeneration through extended nerve gaps.