Experimental study on the regeneration of peripheral nerve gaps through a polyglycolic acid-collagen (PGA-collagen) tube

Return of motor function after repair of a 3-cm gap in a rabbit peroneal nerve: a comparison of autograft, collagen conduit, and conduit filled with collagen-GAG matrix

BACKGROUND

The purpose of this study was to evaluate the motor nerve recovery in a rabbit model after repair of a 3-cm gap in the peroneal nerve with a conduit filled with a collagen-GAG (glycosaminoglycan) matrix and compare the results with those after reconstruction with an autograft or an empty collagen conduit.

METHODS

Forty-two male New Zealand rabbits were divided into three experimental groups. In each group, a unilateral 3-cm peroneal nerve defect was repaired with a nerve autograft, an empty collagen conduit, or a conduit filled with a collagen-GAG matrix. At six months, nerve regeneration was evaluated on the basis of the compound muscle action potentials, maximum isometric tetanic force, and wet muscle weight of the tibialis anterior muscle as well as nerve histomorphometry.

RESULTS

The autograft group had significantly better motor recovery than the conduit groups. The empty collagen conduits and conduits filled with the collagen-GAG matrix led to results that were similar to each other.

CONCLUSIONS

On the basis of this rabbit model, autologous nerve grafting remains the gold standard in the reconstruction of 3-cm segmental motor nerve defects.

CLINICAL RELEVANCE

Segmental motor nerve defects should be reconstructed with autograft nerves. The use of a collagen conduit filled with a collagen-GAG matrix for motor nerve reconstruction should be limited until additional animal studies are performed.

Electrophysiologic evaluation of inferior alveolar nerve regenerated by bifocal distraction osteogenesis in dogs

BACKGROUND

Bifocal distraction osteogenesis has been shown to be a reliable method for reconstructing missing bone segments. However, there are no reports regarding inferior alveolar nerve regeneration during bifocal distraction. In the present study, the authors evaluated the function of inferior alveolar nerve regenerated by bifocal distraction after segmental resection in the mandibles of dogs.

METHODS

Using a bifocal distraction osteogenesis method, the authors produced a 10-mm mandibular defect and distracted the transport disk at a rate of 1 mm/day. The regenerated inferior alveolar nerve was evaluated by electrophysiologic analysis that was performed on all dogs after euthanasia at 3, 6, and 12 months after the first operation.

RESULTS

At 6 and 12 months, stable evoked potential measurements were obtained from the nerves throughout the study on electrophysiologic analyses.

CONCLUSIONS

The authors' results indicate that the inferior alveolar nerve regenerated by bifocal distraction osteogenesis functioned electrophysiologically at 6 months after the first operation. Although our research is still at the stage of animal experiments, future application in humans is considered to be possible.

Advances in experimental and clinical studies of chemotaxis

The theory of chemotaxis has been widely accepted, but its mechanisms are disputed. Chemotactic growth of peripheral nerves may be tissue, topographic and end-organ specific. Recent studies indicated that peripheral nerve regeneration lacks topographic specificity, but whether it has end-organ specificity is disputed. Chemotaxis in nerve regeneration is affected by the distance between stumps, volume, and neurotrophic support, as well as the structure of distal nerve stumps. It can be applied to achieve precise repair of nerves and complete recovery of end organ function. Small gap sleeve bridging technique, which is based on this theory shows promising effects but it is still challenging to find the perfect combination of nerve conduits, cells and neurotrophic factors to put it intoits best use. In this paper, we made a comprehensive review of mechanisms, effect factors and applications of chemotaxis.

Protracted delay in taste sensation recovery after surgical lingual nerve repair: a case report

Introduction

Lingual nerve injury is sometimes caused by dental treatment. Many kinds of treatment have been reported, but many have exhibited poor recovery. Here the authors report changes in somatosensory and chemosensory impairments during a long-term observation after lingual nerve repair.

Case presentation

A 30-year-old Japanese woman claimed dysesthesia and difficulty eating. Quantitative sensory test results indicated complete loss of sensation in the right side of her tongue. She underwent a repair surgery involving complete resection of her lingual nerve using a polyglycolic acid tube containing collagen 9 months after the injury. A year after the operation, her mechanical touch threshold recovered, but no other sensations recovered. Long-term observation of her somatosensory and chemosensory function after the nerve repair suggested that recovery of taste sensation was greatly delayed compared with that of somatosensory function.

Conclusion

This case shows characteristic changes in somatosensory and chemosensory recoveries during 7 postoperative years and suggests that taste and thermal sensations require a very long time to recover after repair surgery.

Neuregulin 1 role in Schwann cell regulation and potential applications to promote peripheral nerve regeneration

Neuregulin 1 (NRG1) is a multifunctional and versatile protein: its numerous isoforms can signal in a paracrine, autocrine, or juxtacrine manner, playing a fundamental role during the development of the peripheral nervous system and during the process of nerve repair, suggesting that the treatment with NRG1 could improve functional outcome following injury. Accordingly, the use of NRG1 in vivo has already yielded encouraging results. The aim of this review is to focus on the role played by the different NRG1 isoforms during peripheral nerve regeneration and remyelination and to identify good candidates to be used for the development of tissue engineered medical devices delivering NRG1, with the objective of promoting better nerve repair.

Mesenchymal stem cells in a polycaprolactone conduit promote sciatic nerve regeneration and sensory neuron survival after nerve injury

Despite the fact that the peripheral nervous system is able to regenerate after traumatic injury, the functional outcomes following damage are limited and poor. Bone marrow mesenchymal stem cells (MSCs) are multipotent cells that have been used in studies of peripheral nerve regeneration and have yielded promising results. The aim of this study was to evaluate sciatic nerve regeneration and neuronal survival in mice after nerve transection followed by MSC treatment into a polycaprolactone (PCL) nerve guide. The left sciatic nerve of C57BL/6 mice was transected and the nerve stumps were placed into a biodegradable PCL tube leaving a 3-mm gap between them; the tube was filled with MSCs obtained from GFP+ animals (MSC-treated group) or with a culture medium (Dulbecco's modified Eagle's medium group). Motor function was analyzed according to the sciatic functional index (SFI). After 6 weeks, animals were euthanized, and the regenerated sciatic nerve, the dorsal root ganglion (DRG), the spinal cord, and the gastrocnemius muscle were collected and processed for light and electron microscopy. A quantitative analysis of regenerated nerves showed a significant increase in the number of myelinated fibers in the group that received, within the nerve guide, stem cells. The number of neurons in the DRG was significantly higher in the MSC-treated group, while there was no difference in the number of motor neurons in the spinal cord. We also found higher values of trophic factors expression in MSC-treated groups, especially a nerve growth factor. The SFI revealed a significant improvement in the MSC-treated group. The gastrocnemius muscle showed an increase in weight and in the levels of creatine phosphokinase enzyme, suggesting an improvement of reinnervation and activity in animals that received MSCs. Immunohistochemistry documented that some GFP+ -transplanted cells assumed a Schwann-cell-like phenotype, as evidenced by their expression of the S-100 protein, a Schwann cell marker. Our findings suggest that using a PCL tube filled with MSCs is a good strategy to improve nerve regeneration after a nerve transection in mice.

Influence of cross-linking degree of a biodegradable genipin-cross-linked gelatin guide on peripheral nerve regeneration

We evaluated peripheral nerve regeneration using biodegradable genipin-cross-linked gelatin nerve conduits (GGCs) with three different cross-linking degrees, 24, 36 and 51%. Biocompatibility and biodegradability of the GGC and its efficiency as a guidance channel were examined based on the repair process of a 10-mm gap in the rat sciatic nerve. From this pilot study we concluded that GGCs with a mean cross-linking degree of 36% can ensure nerve regeneration with a more mature structure, as demonstrated by better developed epineural and perineural organisation and axonal development, as well as better-recovered electrophysiology with a relatively positive sciatic functional index and a shorter latency of the muscle action potential curve. Regenerated nerves in the GGCs with mean cross-linking degrees of 24 and 51% were less favourable, due to irritation caused by degradation material and compression by the remaining tube walls, respectively.

Regeneration and functional recovery of intrapelvic nerves removed during extensive surgery by a new artificial nerve conduit: a breakthrough to radical operation for locally advanced and recurrent rectal cancers

PURPOSE

In the current strategy against locally advanced and recurrent rectal cancers possibly involving intrapelvic nerves, there has been a serious dilemma between extensive surgery and limited surgery. The former can attain high tumor curability by sacrificing the nerve functions while the latter prioritizes the patient quality of life by preserving the nerve functions but with a compromised curability. Here we present a new surgical strategy for locally advanced and recurrent rectal cancers, which realize both high tumor curability and good quality of life.

METHODS

A new artificial nerve conduit (polyglycolic acid collagen tube) developed by in site tissue engineering technology was applied to recovery the disturbed functions after removing the nerves from 11 patients undergoing extensive surgery for intrapelvic advanced or recurrent colorectal cancers. The reconstructed nerves included eight autonomic nerves which are essential for the genitourinary function and three somatic nerves which control the sensation and mobility of the legs.

RESULTS

Out of ten cases followed up more than 2 years and evaluated fully, eight including two report cases showed a functional recovery of the disturbed autonomic and somatic nerves clinically. The nerve function started to recover from 3 to 6 months after the operation and continued to improve with times. No specific complications associated with the nerve repair have been noted.

CONCLUSIONS

The new strategy utilizing the nerve conduit can be a breakthrough in radical operations for locally advanced and recurrent rectal cancers to resolve the problems between tumor curability and the patient quality of life.

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.

Thyroid hormone enhances transected axonal regeneration and muscle reinnervation following rat sciatic nerve injury

Improvement of nerve regeneration and functional recovery following nerve injury is a challenging problem in clinical research. We have already shown that following rat sciatic nerve transection, the local administration of triiodothyronine (T3) significantly increased the number and the myelination of regenerated axons. Functional recovery is a sum of the number of regenerated axons and reinnervation of denervated peripheral targets. In the present study, we investigated whether the increased number of regenerated axons by T3-treatment is linked to improved reinnervation of hind limb muscles. After transection of rat sciatic nerves, silicone or biodegradable nerve guides were implanted and filled with either T3 or phosphate buffer solution (PBS). Neuromuscular junctions (NMJs) were analyzed on gastrocnemius and plantar muscle sections stained with rhodamine alpha-bungarotoxin and neurofilament antibody. Four weeks after surgery, most end-plates (EPs) of operated limbs were still denervated and no effect of T3 on muscle reinnervation was detected at this stage of nerve repair. In contrast, after 14 weeks of nerve regeneration, T3 clearly enhanced the reinnervation of gastrocnemius and plantar EPs, demonstrated by significantly higher recovery of size and shape complexity of reinnervated EPs and also by increased acetylcholine receptor (AChRs) density on post synaptic membranes compared to PBS-treated EPs. The stimulating effect of T3 on EP reinnervation is confirmed by a higher index of compound muscle action potentials recorded in gastrocnemius muscles. In conclusion, our results provide for the first time strong evidence that T3 enhances the restoration of NMJ structure and improves synaptic transmission.

Transplantation of bone-marrow-derived cells into a nerve guide resulted in transdifferentiation into Schwann cells and effective regeneration of transected mouse sciatic nerve

Peripheral nerves possess the capacity of self-regeneration after traumatic injury. Nevertheless, the functional outcome after peripheral-nerve regeneration is often poor, especially if the nerve injuries occur far from their targets. Aiming to optimize axon regeneration, we grafted bone-marrow-derived cells (BMDCs) into a collagen-tube nerve guide after transection of the mouse sciatic nerve. The control group received only the culture medium. Motor function was tested at 2, 4, and 6 weeks after surgery, using the sciatic functional index (SFI), and showed that functional recovery was significantly improved in animals that received the cell grafts. After 6 weeks, the mice were anesthetized, perfused transcardially, and the sciatic nerves were dissected and processed for transmission electron microscopy and light microscopy. The proximal and distal segments of the nerves were compared, to address the question of improvement in growth rate; the results revealed a maintenance and increase of nerve regeneration for both myelinated and non-myelinated fibers in distal segments of the experimental group. Also, quantitative analysis of the distal region of the regenerating nerves showed that the numbers of myelinated fibers, Schwann cells (SCs) and g-ratio were significantly increased in the experimental group compared to the control group. The transdifferentiation of BMDCs into Schwann cells was confirmed by double labeling with S100/and Hoechst staining. Our data suggest that BMDCs transplanted into a nerve guide can differentiate into SCs, and improve the growth rate of nerve fibers and motor function in a transected sciatic-nerve model.

Novel use of X-ray micro computed tomography to image rat sciatic nerve and integration into scaffold

This paper describes how specimens of nervous tissue can be prepared for successful imaging in X-ray Micro Computed Tomography (microCT), and how this method can be used to study the integration of nervous tissue into a polymeric scaffold. The sample preparation involves staining the biological tissue with osmium tetroxide to increase its X-ray attenuation, and a technique for maintaining the specimen in a moist environment during the experiment to prevent drying and shrinkage. Using this method it was possible to observe individual nerve fascicles and their relationship to the 3-D tissue structure. A scaffold supporting a regenerated sciatic nerve was similarly stained to distinguish the nervous tissue from the scaffold, and to observe how the nerve grew through a 2.5 mm long, 100 microm x 100 microm cross-section channel polyimide array. Furthermore, blood vessels could be identified in these images, and it was possible to monitor how a large proximal blood vessel split through the channel scaffold and proceeded down individual channels. This paper explains how microCT is a useful tool both for studying the location and extent of growth into a polymeric scaffold, and for determining whether the regenerated tissue has blood supply.

History of microsurgery

In the mid-1500s, the techniques of vascular ligature and vascular suture were developed sporadically by several pioneers in this field. However, vascular surgery became realistic experimentally as a result of the work by Carrel and Guthrie in the early 1900s, in which they performed replantations and transplantations of several composite tissues and organs, including amputated limbs, kidneys, and others using experimental animals. In contrast, the development of heparin by Howell and Holt in 1918 accelerated the rate of these types of operations being performed with increasing success in humans. Since the first use of a monocular microscope for ear surgery by Nylen in 1921 and a binocular microscope by Holmgren in 1923, in addition to the timely developments of the Zeiss operating microscope, microsurgical instruments, and suture materials, microsurgery was born in several surgical disciplines in the ensuing 50-year period. The application of microvascular surgery and microneurosurgery in the fields of hand, plastic, and reconstructive surgery resulted in revolutionary advances in clinical replantation and transplantation of composite tissues and more allotransplantations.

Polymers for Fabricating Nerve Conduits

Peripheral nerve regeneration is a complicated and long-term medical challenge that requires suitable guides for bridging nerve injury gaps and restoring nerve functions. Many natural and synthetic polymers have been used to fabricate nerve conduits as well as luminal fillers for achieving desired nerve regenerative functions. It is important to understand the intrinsic properties of these polymers and techniques that have been used for fabricating nerve conduits. Previously extensive reviews have been focused on the biological functions and in vivo performance of polymeric nerve conduits. In this paper, we emphasize on the structures, thermal and mechanical properties of these naturally derived synthetic polymers, and their fabrication methods. These aspects are critical for the performance of fabricated nerve conduits. By learning from the existing candidates, we can advance the strategies for designing novel polymeric systems with better properties for nerve regeneration.

In situ tissue engineering of canine skull with guided bone regeneration

CONCLUSION

Calcium alginate (CA) membrane prevents excessive fibrous tissue intrusion and/or dislocation of a bone scaffold. However, CA membrane did not always accelerate cranial bone regeneration.

OBJECTIVE

We previously reported skull regeneration using a bone substitute material (BSM), which consisted of collagen-coated beta-tricalcium phosphate and autologous bone fragments, and bone marrow-derived stromal cells (BSCs). However, excessive fibrous tissue intrusion or dislocation of the BSM occasionally interrupted bone regeneration. To avoid such problems, we examined CA membrane, which is useful for guided bone regeneration (GBR), to investigate whether this material maintains the bone regenerative space.

MATERIALS AND METHODS

Bone defects (2x2 cm) were created in the skulls of 12 adult beagle dogs using the same clinical procedure. Four experimental models were tested with or without BSM plus BSCs or CA membrane. In group I, the original free bone flap was replaced at the defect. In group II, after replacing the bone flap, the defect was covered with CA membrane. In group III, BSM plus BSCs were used as a gap filler. In group IV, BSM plus BSCs and CA membrane were applied. Histological examinations were performed 3 and 6 months after the operation.

RESULTS

In groups I and II, bone regeneration was not observed but fibrous tissue intrusion was prevented in group II. Bone neogenesis was more observed in group III than in group IV at 3 months (p<0.05). At 6 months, the regenerated areas were larger than those observed at 3 months, but the differences between groups III and IV were not statistically significant.

Development of a new tissue-engineered sheet for reconstruction of the stomach

We have developed tissue-engineered digestive tracts composed of collagen scaffold and an inner silicon sheet and successfully used it to repair defects in parts of the esophagus, stomach, and small intestine. However, some improvements were demanded for clinical usage because the silicon sheet presented technical difficulties for suturing and endoscopic removal. New tissue-engineered sheet (New-sheet) was composed of a single-piece and reinforced collagen scaffold with biodegradable copolymer. One beagle dog was used to evaluate whether New-sheet could withstand suturing in comparison with native digestive tracts using a tensile tester. Seven beagle dogs had a 5-cm circular defect created in the stomach. New-sheet soaked with autologous peripheral blood or bone marrow aspirate was sutured to the gastric wall. Endoscopic, histological, and immunohistochemical assessment was performed to evaluate regeneration of the stomach up to 16 weeks. Tensile strength testing showed that the mucosal side of New-sheet had strength almost equivalent to the mucosa of the esophagus (P = 0.61). Endoscopically, regeneration of the mucosa started from the circumference after 4 weeks, but a small linear ulcer was still evident at 16 weeks. The regenerated stomach shrank by 60-80% of its original size and histologically showed villous mucosa and underlying dense connective tissue. Immunohistochemically, the regenerated area expressed alpha-smooth-muscle actin but was negative for basic calponin, irrespective of the source of soaked blood. New-sheet shows sufficient strength for suturing, no dehiscence, and better biocompatibility for clinical use, although further examination will be necessary to create a functional digestive tract.

Biocompatibility of Different Nerve Tubes

Bridging nerve gaps with suitable grafts is a major clinical problem. The autologous nerve graft is considered to be the gold standard, providing the best functional results; however, donor site morbidity is still a major disadvantage. Various attempts have been made to overcome the problems of autologous nerve grafts with artificial nerve tubes, which are “ready-to-use” in almost every situation. A wide range of materials have been used in animal models but only few have been applied to date clinically, where biocompatibility is an inevitable prerequisite. This review gives an idea about artificial nerve tubes with special focus on their biocompatibility in animals and humans.

Aligned and random nanofibrous substrate for the in vitro culture of Schwann cells for neural tissue engineering

The current challenge in peripheral nerve tissue engineering is to produce an implantable scaffold capable of bridging long nerve gaps that will produce results similar to autograft without requiring the harvest of autologous donor tissue. Aligned and random polycaprolactone/gelatin (PCL/gelatin) nanofibrous scaffolds were fabricated for the in vitro culture of Schwann cells that assist in directing the growth of regenerating axons in nerve tissue engineering. The average fiber diameter attained by electrospinning of polymer blend (PCL/gelatin) ranged from 232+/-194 to 160+/-86nm with high porosity (90%). Blending PCL with gelatin resulted in increased hydrophilicity of nanofibrous scaffolds and yielded better mechanical properties, approaching those of PCL nanofibers. The biocompatibility of fabricated nanofibers was assessed for culturing and proliferation of Schwann cells by MTS assay. The results of the MTS assay and scanning electron microscopy confirmed that aligned and random PCL/gelatin nanofibrous scaffolds are suitable substrates for Schwann cell growth as compared to PCL nanofibrous scaffolds for neural tissue engineering.

Histologic and electrophysiological study of nerve regeneration using a polyglycolic acid-collagen nerve conduit filled with collagen sponge in canine model

OBJECTIVES

To determine the rate of achieving electrophysiologically proved functional recovery by autonomic nerve regeneration, with the aid of an artificial nerve conduit.

METHODS

A polyglycolic acid (PGA) collagen nerve conduit filled with collagen sponge was interposed in a 10-mm-long gap of the right hypogastric nerve (HGN) in 16 dogs. Histologic evaluation of nerve regeneration and electrophysiological analysis at 2 weeks and 2, 3, 4, 5, 6, 7, and 8 months (n = 2, each) after surgery was performed, measuring the responses for the spermatic ducts (SD), bladder neck (BN), and prostate contraction, by stimulating the right lumbar splanchnic nerves (LSNs) from L2 to L4, after transection of the left HGN to eliminate substitutive pathways.

RESULTS

Two months after implantation, the regenerated neurofilaments were successfully extended through the graft from the proximal-to-distal direction. In 2 control dogs, electrostimulation of the right LSNs induced elevation of the intraluminal pressure of the SD, elevation of the BN pressure, and prostate contraction. No responses were observed in all dogs up to 6 months of follow-up after implantation. In 1 dog with a 7-month follow-up, electrostimulation elicited elevation of BN pressure alone. In both dogs with an 8-month follow-up, electrostimulation induced similar responses to control in all SD, BN, and prostate; however, after excision of the area of the interposed right HGN, no response was observed.

CONCLUSIONS

These results proved that regeneration of a 10-mm gap of the HGN, using a novel PGA-collagen nerve conduit could be achieved within 8 months.

Designing ideal conduits for peripheral nerve repair

Nerve tubes, guides, or conduits are a promising alternative for autologous nerve graft repair. The first biodegradable empty single lumen or hollow nerve tubes are currently available for clinical use and are being used mostly in the repair of small-diameter nerves with nerve defects of < 3 cm. These nerve tubes are made of different biomaterials using various fabrication techniques. As a result these tubes also differ in physical properties. In addition, several modifications to the common hollow nerve tube (for example, the addition of Schwann cells, growth factors, and internal frameworks) are being investigated that may increase the gap that can be bridged. This combination of chemical, physical, and biological factors has made the design of a nerve conduit into a complex process that demands close collaboration of bioengineers, neuroscientists, and peripheral nerve surgeons. In this article the authors discuss the different steps that are involved in the process of the design of an ideal nerve conduit for peripheral nerve repair.

[Retrospective monocentric comparative evaluation by sifting of vein grafts versus nerve grafts in palmar digital nerves defects. Report of 32 cases]

AIM

Palmar digital nerves defects can be treated by conventional nerve grafts or by means of a conduit, such as a vein. We compared a vein graft technique to a nerve graft technique in a retrospective monocentric study.

MATERIAL AND METHOD

A surgeon who was not involved in the treatment reviewed blind 15 nerve grafts and 17 vein grafts. The evaluation concerned sensitivity, pain, donor site morbidity, social integration and autoassessment of the benefits by the patient. Data were compacted by a sifting method eliminating bad results. The classical functional scores (British Medical Research Council, Möberg, Chanson, Alnot, Dumontier) were also used.

RESULTS

The evaluation was carried out at least 11 months after treatment. Defect was never greater than 30 mm. After sifting, vein grafts appeared less efficient than nerve grafts (41% good results against 73%), except in emergencies (86% good results).

CONCLUSION

For defect loss of no more than 30 mm in emergencies, the authors propose to use vein grafting. In other situations, the surgeon must take into account the patient's profile and the hemi-pulp concerned, dominant or non-dominant, before opting for a nerve or a vein graft.

Nerve tubes for peripheral nerve repair

The concept of the nerve tube has been a major topic of research in the field of peripheral nerve regeneration for more than 25 years. The first nerve tubes are currently available for clinical use. This article gives an overview of the experimental and clinical data on nerve tubes for peripheral nerve repair and critically analyzes the data on which the step from laboratory to clinical use is based. In addition, it briefly discusses the different modifications to the common single lumen nerve tubes that may improve the results of generation.

Peroneal Nerve Regeneration Using a Unique Bilayer Polyurethane-collagen Guide Conduit

Unique double layer polyurethane (PU)-collagen nerve guide conduits with desirable biocompatibility and mechanical properties were fabricated using a newly developed double-nozzle low-temperature deposition manufacturing (DLDM) technique. The inner collagen layer of the conduit had oriented nano-size filaments with micro-pores (pore size 20—100μm) that permitted nutrient infiltration, while the outer PU layer had micro-pores (pore size 15—20 μm) preventing fibrous tissue invasion. In vivo animal tests (n = 6) on bridging a 10 mm long peroneal nerve defect was conducted using rats. Single layer pure PU conduit (n = 6) was used as the positive control and the same size defect with no implantation (n = 2) as the negative control. Through walk track analysis as well as electrophysiological and histological evaluations of the regenerated nerves, the double layer PU-collagen conduit demonstrated better nerve repair than the controls. This new PU-collagen has the potential for significant clinical applications in peripheral nerve repair.

Artificial nerve tubes and their application for repair of peripheral nerve injury: an update of current concepts

Over the last 20 years, an increasing number of research articles have reported on the use of artificial nerve tubes to repair nerve defects. The development of an artificial nerve tube as an alternative to autogenous nerve grafting is currently a focus of interest for peripheral nerve repair. The clinical employment of tubes as an alternative to autogenous nerve grafts is mainly justified by the limited availability of donor tissue for nerve autografts and the related morbidity. Numerous studies indicate that short-distance defects in humans can be successfully treated by implantation of artificial nerve guides. This review provides a brief overview of various preclinical and clinical trials conducted to evaluate the utility of artificial nerve tubes for the regeneration of peripheral nerves. This review is also intended to help update hand surgeons on the rapid advances in tubulization techniques, and to provide them with indications of the various directions toward which future research can proceed. Future studies need to provide us with as much comparative information as possible on the effectiveness of different tubulization techniques, in order to guide the surgeon in choosing the best indications for their optimal clinical employment. Future progress in implant development can be expected from interdisciplinary approaches involving both materials and life sciences, leading to advances in neuro-tissue engineering that will be needed to effectively treat larger nerve defects.

Replacement of the left main bronchus with a tissue-engineered prosthesis in a canine model

BACKGROUND

Stenosis of the left main bronchus caused by inflammatory diseases and neoplasms is a serious clinical problem because it can cause obstructive pneumonia and may require pneumonectomy. As an alternative to various treatments currently available, including balloon dilatation, stenting, and bronchoplasty, we propose the use of a prosthesis developed based on the concept of in situ tissue engineering for replacement of the left main bronchus.

METHODS

The main frame of the tissue-engineered prosthesis is a polypropylene mesh tube, 12 to 15 mm in inner diameter and 30 mm in length, with reinforcing rings. Collagen extracted from porcine skin is conjugated to this frame. A consecutive series of 8 beagle dogs underwent replacement of the left main bronchus with this tissue-engineered prosthesis.

RESULTS

All dogs survived the postoperative period with no morbidity except 1, which required intravenous administration of antibiotic for a week for pneumonia and recovered. Three dogs were euthanized for examination at 3 and 4 months after bronchus replacement, and the other five were monitored for more than 1 year. In two dogs, histologic examination revealed that the luminal surface was completely covered with ciliated columnar epithelium or nonciliated squamous epithelium. Exposure of the polypropylene mesh to various degrees was observed in 6 dogs, but the prosthesis remained stable and no adverse effects such as infection, sputum retention, or dehiscence were observed.

CONCLUSIONS

These long-term results suggest that our tissue-engineered prosthesis is applicable for replacement of the left main bronchus.

Expression and regulation of Sef, a novel signaling inhibitor of receptor tyrosine kinases-mediated signaling in the nervous system

Fibroblast growth factors (FGFs) signal via four distinct high affinity cell surface tyrosine kinase receptors, termed FGFR1-FGFR4 (FGFR-FGF-receptor). Recently, a new modulator of the FGF signaling pathway, the transmembrane protein 'similar expression to FGF genes' (Sef), has been identified in zebrafish and subsequently in mammals. Sef from mouse and human inhibits FGF mitogenic activity. In the present study, we analyzed the expression of Sef in distinct rat brain areas, in the spinal cord and in peripheral nerves and spinal ganglia using semi-quantitative RT-PCR. Furthermore, we studied the cellular expression pattern of Sef in intact spinal ganglia and sciatic nerves and, in addition, after crush lesion, using in situ hybridization and immunohistochemistry. Sef transcripts were expressed in all brain areas evaluated and in the spinal cord. A neuronal expression was found in both intact and injured spinal ganglia. Intact sciatic nerves, however, showed little or no Sef expression. Seven days after injury, high Sef expression was concentrated to the crush site, and Schwann cells seemed to be the source of Sef. The labeling pattern of up-regulated Sef was complementary to the patterns of FGF-2 and FGFR1-3, which were localized proximal and distal to the crush site. These results suggest an involvement of Sef during the nerve regeneration process, possibly by fine-tuning the effects of FGF signaling.

Fabrication of a PLGA-collagen peripheral nerve scaffold and investigation of its sustained release property in vitro

This study deals with the fabrication of a peripheral nerve scaffold prepared with poly (lactic acid-co-glycolic acid) [PLGA] and acellularized pigskin collagen micro particles and the investigation of its sustained release property in vitro. We took bovine serum albumin [BSA] as model drug to investigate the sustained-release property of the scaffold in vitro. The results showed the scaffold could release BSA steadily with a rate of 6.6 ng/d (r=0.994) or so. In a 1-month test period, the accumulative release ratio of BSA from the scaffold was up to 43%, and the shape of the scaffold was still originally well kept. In addition, the scaffold outcome non-immunogenicity, good cell adhesion and biodegradability. The results indicated a scaffold constructed by this technique would be a potential implanting support with prolonged sustained release function, such as for the use of nerve scaffold.

Regeneration of peripheral motor nerve gaps with a polyglycolic acid-collagen tube: technical case report

OBJECTIVE

After previous success in regenerating canine peripheral nerves over 80 mm gaps using a bioabsorbable nerve guide tube, we have extended this method to the treatment of patients experiencing various types of nerve injury. This report describes the treatment of two cases of motor nerve disorder.

METHODS

The bioabsorbable nerve tube was a cylindrically woven polyglycolic acid (PGA) tube filled with collagen. A peripheral motor nerve defect (the frontalis branch of the facial nerve) was reconstructed using this PGA-collagen tube in two patients who experienced posttraumatic unilateral eyebrow ptosis for 3 months.

RESULTS

Five months after surgery, both patients regained their ability to voluntarily lift their eyebrows symmetrically. Electrophysiological examination at 5 months revealed recovery of compound muscle action potential and disappearance of distal latency on the affected side.

CONCLUSION

This is the first clinical report of motor nerve recovery achieved using the PGA-collagen nerve guide tube. The results suggest that use of a PGA-collagen tube is a promising option for the repair of motor nerve defects.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(ε-caprolactone) blends for tissue engineering applications in the form of hollow fibers

In this work, hollow fibers to be used as guides for tissue engineering applications were produced by dry-jet-wet spinning of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(epsilon-caprolactone) (PHBHV/PCL) solutions in chloroform with various weight ratios between the components (PHBHV/PCL 100/0; 80/20; 60/40; 50/50; 40/60; 20/80; 0/100 w/w). Fibers obtained from PHBHV/PCL blends had a low degree of surface and bulk porosity, depending on composition. Physicochemical characterization involving scanning electron microscopy and differential scanning calorimetry (DSC) showed that PHBHV/PCL blends are compatible. Interactions between blend components were studied by Fourier transform infrared total reflectance spectroscopy, DSC analysis, and polarized optical microscopy analysis. Homogeneity of blend composition was assessed by IR-chemical imaging analysis. PHBHV/PCL samples were found to be weakly hydrophilic and their biocompatibility was proved by in vitro tests using mouse fibroblasts. Mechanical properties of PHBHV/PCL blends were investigated by stress-strain tests, showing an increasing ductility of blend samples with increasing PCL amount. Hollow fibers supported fibroblasts attachment and proliferation depending on composition and porosity degree.