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The Artificial Nerve Graft: A Comparison of Blended Elastomer-Hydrogel with Polyglycolic Acid Conduits
Abstract
A study was undertaken to compare the regeneration of rat peroneal nerves across a 0.5-cm gap repaired with either a permanent, porous or a resorbable, non-porous artificial nerve graft. The resorbable, impermeable artificial nerve graft was a synthetic passive conduit made from polyglycolic acid (PGA). The permanent, porous artificial nerve graft conduit was manufactured from a hydrophilic elastomeric biopolymer (HEB), and four variations were tested. Qualitative histology on short-term animals revealed similar inflammatory reactions to HEB and PGA. Axonal regeneration was evaluated in longer-term animals after three, four, and six months by qualitative and quantitative histology. Qualitative histology on longer-term animals demonstrated both artificial nerve grafts to be anti-immunogenic. All PGA-artificial nerve graft repairs among three-, four-, and six-month rats contained myelinated axons, as did all HEB-1 repairs. However, three other HEB-graft varieties accounted for a 25 percent failed regeneration rate. Quantitative histologic comparison of repair-site cross-sections in viable PGA and HEB matched pairs demonstrated statistically equivalent myelinated axon counts but larger average myelinated fiber diameters in HEB repairs, with p = .001.
... This technique, however, has some disadvantages: harvesting of the graft causes a sensory deficit at the cutaneous distribution site of the donor nerve and the risk of neuroma formation at the donor site. To eliminate these problems, alternative techniques, such as biodurable nerve guides constructed of silicone rubber, 1,2 acrylic polymer, 3 polyethylene, 4 elastomer hydrogel, 5 and porous stainless steel, 6 have been used to bridge the nerve gap. However, non-degradable biomaterials remain in situ as a foreign body, causing a chronic foreign body response with excessive scar tissue formation, resulting in compression of the regenera-ting nerve, ultimately limiting recovery of nerve function. ...
... All procedures were carried out according to the National Guidelines for Animal Welfare. After 3,5,8,15,21, and 26 weeks of implantation, walking track analyses were carried out to evaluate sciatic nerve recovery. The number of rats for each time point of walking track analysis is shown in Table 1. ...
... I) for the test group did not differ from the control value. After 3,5,8,15, and 26 weeks of implantation, electrostimulation tests to evaluate sensory nerve recovery were carried out at three different places on the lateral side of the left (operated) foot-sole ( Fig. 1b). Electrostimulation tests were carried out after 3, 5, 8 and 15 weeks of implantation (n = 3) and after 26 weeks (n = 4). ...
The aim of this study was to evaluate functional nerve recovery after reconstruction of a 1 cm gap in the sciatic nerve of the rat, with a thin- walled biodegradable poly(DLLA-ε-CL) nerve guide. To evaluate both motor and sensory nerve recovery, walking track analysis and electrostimulation tests were carried out after implantation periods ranging from 3 to 26 weeks post- operatively. The first signs of functional nerve recovery could already be observed after 5 weeks. From the histological analysis, it could be concluded that most of the thin-walled nerve guides had collapsed. Despite collapsing, functional nerve recovery was relatively good after 26 weeks (motor nerve recovery 54% and sensory nerve recovery 100%), probably due to guidance of the regenerating nerve fibers along the outside of the poly(DLLAε-CL) nerve guide. This thin-walled nerve guide should, therefore, be used in combination with mechanical support.
... O nervo ciático foi utilizado para se criar o modelo de lesão de nervo periférico uma vez que pode ser analisado seu padrão de recuperação funcional 19 , fato este importante para se comparar a melhor técnica quando se repara defeito de tecido neural. A técnica cirúrgica utilizada para a abordagem do nervo ciático, auto-enxertia e colocação do tubo de ácido poliglicólico é a mesma utilizada por diversos autores na literatura 3,9 , assim como o padrão do tamanho do "gap" utilizado. 3 A técnica de preparo dos cortes histológicos que utiliza fixação com tetróxido de ósmio e coloração com azul de toluidina é a que melhor preserva a bainha de mielina, sendo de uso consagrado para estudo dos nervos periféricos. ...
... A técnica cirúrgica utilizada para a abordagem do nervo ciático, auto-enxertia e colocação do tubo de ácido poliglicólico é a mesma utilizada por diversos autores na literatura 3,9 , assim como o padrão do tamanho do "gap" utilizado. 3 A técnica de preparo dos cortes histológicos que utiliza fixação com tetróxido de ósmio e coloração com azul de toluidina é a que melhor preserva a bainha de mielina, sendo de uso consagrado para estudo dos nervos periféricos. 1,20 Em termos macroscópicos, a formação de neuroma foi observada apenas nos ratos submetidos a auto-enxertia. ...
INTRODUCTION: Nerve allografting is regarded as a treatment of choice in large neural tissue losses preventing repair by primary anastomosis. In these cases, a synthetic polyglycolic acid tube is an alternative for nerve grafting. On the other hand, several studies have emphasized the importance of neurotrophic factors on neural regeneration, including substances with potential to optimize neural regeneration, especially the GM1, an neurotrophic enhancer factor. OBJECTIVE: to compare, in rats, the neural regeneration degree using histological analysis, regenerated myelinized axons count, and functional analysis with the use of neurotube and GM1. METHODS: This assessment was performed by interposing allograft (group A), polyglycolic acid tube (group B) and polyglycolic acid tube associated to GM1 (group C) on 5-mm sciatic nerve defects. RESULTS: Neuroma formation was found only on group A. Groups A and C showed similar histological patterns, except for the regenerated axons on group C, which were shown to be better organized and myelinized than in group A. CONCLUSION: on functional recovery, no statistically significant difference was found for the three groups, despite of qualitative and quantitative histological differences found.
... Recently, much attention has been directed to the development of synthetic scaffolds for nerve tissue repair and regeneration [1][2][3][4][5][6][7][8][9][10]. These efforts have become increasingly important, due in part, to the shortcomings associated with autografts (limited supply, second surgical procedure [11], donor site morbidity [12], mismatch of donor nerve size with recipient site [13], occurrences of neuroma formation [13] and increased recovery time for patients) and allografts (immune rejection, increased risk of cross-contamination, possible transmission of pathogens and secondary infection [14][15][16][17]). ...
... Bioresorbable poly(lactic acid) (PLA), poly(glycolic acid) (PGA), and PLGA copolymers are attractive as matrix materials for scaffolds in tissue engineering [27,28]. These polymers have demonstrated efficacy in clinical use as resorbable sutures, meshes, and in drug delivery systems [29], and are of interest in nerve repair [3,4,6,8]. In addition to this, Pluronic F127 (F127) is a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer that can undergo sol-gel transition, depending on its concentration and ambient temperature. ...
The objective of this work was to examine the main (individual), combined (interaction) and second-order (quadratic) effects
of: (i) poly(d,l-lactide-co-glycolide) (PLGA), (ii) F127, and (iii) a zinc-silicate based bioactive glass, on the cytotoxicity and ultimate tensile strength
of an experimental nerve guidance conduit (NGC). The experimental plan was carried out according to a Box–Behnken design matrix.
The effects of each compositional factor were quantified using response surface methodology (RSM) techniques. Linear and quadratic
polynomial equations were developed to examine cytotoxicity (after incubation at 3, 7 and 28days) and initial ultimate tensile
strength (UTS0). Multiple regression analyses showed that the developed models yielded a good prediction for each response examined. It
was observed that the beneficial effects of PLGA and bioactive glass on controlling cytotoxicity appeared greater than that
of F127. Furthermore, the experimental conduits (with the exception of CNGC-I and CNGC-K) generally showed superior cytocompatibility
when compared with the comparable literature for the clinically used nerve guidance conduit Neurolac®. In this investigation, optimal compositions for cell viability were obtained for the following composition: PLGA=18.89wt%/F127=0.52wt%/glass=12.71wt%.
The optimization of composition with respect to ultimate tensile strength was also established (desired UTS0 being based on the properties of the control device Neurolac® whose UTS is c.20MPa). The desired UTS0 of≤20MPa was found for the composition: PLGA=18.63wt%/F127=0.77wt%/glass=5.54wt%. A UTS0≤30MPa was recorded for the composition: PLGA=18.34wt%/F127=0.62wt%/glass=9.83wt%, such tensile strengths are comparable
to, reported values for Neurolac®. Examination of the composition–property relationships with respect to combining cell viability and UTS0 indicated preferred compositions in the range 17.97–19.90wt% PLGA, 0.16–1.13wt% F127 and between 5.54 and≤20wt% glass.
This research demonstrates the value of a design of experiments approach for the design of novel nerve guidance conduits,
and shows that the materials examined may have potential for the repair of peripheral nerve discontinuities.
... In this sense, the use of biodegradable polymers for constructing nerve guide channels is ideal because it eliminates the need of a second surgery to remove the nerve guide channels from the body to avoid chronic tissue responses or nerve compression. In particular, poly (phosphoester) [16,17], collagen [18,19], polyglycolide [20], collagen and poly-glycolide [21], poly (L-lactide-co-glycolide) (PLGA) [22,23], and poly-L-lactic acid/caprolactone [24] are among the most common biodegradable polymers used for this purpose. ...
The human nervous system lacks an inherent ability to regenerate its components upon damage or diseased conditions. During the last decade, this has motivated the development of a number of strategies for nerve regeneration. However, most of those approaches have not been used in clinical applications till today. For instance, although biomaterial-based scaffolds have been extensively used for nerve reparation, the lack of more customized structures have hampered their use in vivo. This highlight focuses mainly on how 3D bioprinting technology, using polymeric hydrogels as bio-inks, can be used for the development of new nerve guidance channels or devices for peripheral nerve cell regeneration. In this concise contribution, some of the most recent and representative examples are highlighted to discuss the challenges involved in various aspects of 3D bioprinting for nerve cell regeneration, specifically when using polymeric hydrogels.
... This technique however, has some disadvantages: loss of donor nerve function and the risk of neuroma formation at the donor site. To eliminate these problems, many alternative techniques have been developed (1)(2)(3)(4)(5)(6). One of these alternatives is a biodurable nerve guide. ...
The aim of this study was to evaluate functional nerve recovery following reconstruction of a 1 cm gap in the sciatic nerve of a rat, using a new biodegradable p (DLLA-∊-CL) nerve guide. To evaluate both motor and sensory nerve recovery, walking track analysis and electrostimulation tests were carried out after implantation periods, ranging from 3 to 15 weeks post-operatively. The first signs of functional nerve recovery were observed after 3 weeks. After 15 weeks, 70% of the motor - and 90% of the sensory nerve function was re-established. Return of nerve function was better, in comparison with results from other studies. This study demonstrated successful functional nerve recovery after the reconstruction of a 1 cm nerve gap with a biodegradable p(DLLA-∊-CL) nerve guide.
... Synthetic material-based 3-D scaffolds possessing particular features can be produced in various sizes ranging from nano to microscales using different techniques such as electrospinning , self-assembly , and phase separation among others. Several synthetic material-based scaffolds have been used for neural tissue engineering applications composed of poly(glycolic acid) (PGA) (Keeley et al. 1991 ), poly(lactic acid) (PLA) (Corey et al. 2007 ), poly( L -lactic acid) (PLLA) (Patel et al. 2007 ; Yang et al. 2005a ), or of a blend of the above such as poly( L -lactic acid)-caprolactone (PLLA-PCL) (Ghasemi-Mobarakeh et al. 2008 ; Schnell et al. 2007 ) and poly( D , L -lactide-co-glycolide) with poly(ɛcaprolactone) (PLGA/PCL) (Panseri et al. 2008 ). However, a number of potential drawbacks to the use of synthetic materials include insuffi cient similarity to the ECM and possible release of cytotoxic chemicals upon degradation, which have raised concerns and resulted in efforts to identify other biodegradable, biocompatible, and nontoxic natural materials as alternatives (Table 2.1 ). ...
A fundamental issue in biology concerns how cells establish and maintain their identity during early embryogenesis. Gaining a better understanding of these rules is key to future development of experimental therapeutics and is an important foundation of tissue engineering and regenerative medicine. With the successful isolation of embryonic stem cells and the emergence of induced pluripotent stem cell technologies, it has become achievable to recapitulate developmental processes of early development. Furthermore, the advent of cellular reprogramming and transdifferentiation technologies has made it possible to implement rational strategies to generate specific cell types in order to model neurodegenerative diseases and develop cell-based therapies for nervous system disorders. Moreover, with advances in biomaterials and in 3-D scaffold fabrication techniques, it is becoming possible to mimic the neural stem cell niche. In this chapter, we provide an overview of approaches merging stem cells, polymeric scaffolds, drug delivery systems, gene therapy, cellular engineering, and biomaterials to develop experimental strategies for neural tissue engineering. Combined, these enabling technologies are likely to be beneficial for development of therapeutic interventions for translation to the clinic. A summary of a number of current clinical trials is also presented at the end to illustrate how combination of these technologies is helping nervous system rescue and repair.
... Commonly used materials are poly(glycolic acid) (PGA), poly(lactic acid) (PLA), and their copolymers which degrade through hydrolysis (Keeley et al., 1991). Designing permeable properties into the biodegradable tubes through different processing techniques may enhance nerve regeneration (Wen and Tresco, 2006). ...
Nerve guidance channels fabricated from different biomaterials with different physical and chemical properties have been designed to enhance regeneration of severed peripheral nerves. The goal is to produce a readily available implant to replace missing nerve cable when the two ends cannot be sutured together, thus eliminating the need to harvest a nerve segment from the patient. Currently, there are several clinically approved implants made mostly from singular material components that in general show recovery equivalent to nerve grafts for short gaps. The challenge remains in bridging longer gaps. This may someday be overcome by combining different tube properties along with engineering the constituents placed within the tube.
... Ele guia o crescimento axonal e une as extremidades do coto distal e proximal, reduzindo a tensão na linha de sutura, fator esse que inibiria a regeneração neural (1) . Com a utilização da auto-enxertia, alguns fatores devem ser considerados: 1) sempre produz morbidade da área doadora; 2) extensas perdas de tecido neural demandam grande quantidade de tecido autólogo, às vezes insuficiente; 3) a utilização de materiais sintéticos reduz o tempo de cirurgia (2,3) . Estudos sobre grandes perdas de tecido neural e a necessidade de pontes conectando as extremidades proximais e distais foram realizados durante a segunda metade do século dezenove (4) . ...
... Ces premiers conduits nerveux étaient construits en os, silicone, veine, artère (Cataltepe et al., 1993), amnion (Ozcan et al., 1993, polyglactine 910 (Molander et al., 1982) et collagène (Mackinnon et Dellon, 1990b). De nombreux matériels d'origine biologique ou synthétiques imperméables ou semiperméables, résorbables ou non résorbables (polyéthylène, polyvinyle,…) ont été utilisés par la suite (Dahlin et al., 1988 ;Danielsen et al., 1988aDanielsen et al., , 1988bDanielsen et al., , 1988cDanielsen et al., , 1988dGibson et al., 1989 ;Merle et al., 1989aMerle et al., , 1989bKeeley et al., 1991 ;Den Dunnen et al., 1993 ;Nicoli-Aldini et al., 1993 ;den Dunnen et al., 1995den Dunnen et al., , 1996aden Dunnen et al., , 1996bDoolabh et al., 1996 ;Meek et al., 1996 ;den Dunnen et al., 1997 ;Meek et al., 1997 ;Meek et al., 1999aMeek et al., , 1999bMeek et al., , 1999cLundborg, 2000c). Ils évitent de prélever un nerf autologue et d'entraîner un neurome et une perte de fonction au niveau du site donneur. ...
Introduction
Nerve injury compromises sensory and motor functions. Techniques of peripheral nerve repair are based on our knowledge regarding regeneration. Microsurgical techniques introduced in the late 1950s and widely developed for the past 20 years have improved repairs. However, functional recovery following a peripheral mixed nerve injury is still incomplete.
State of art
Good motor and sensory function after nerve injury depends on the reinnervation of the motor end plates and sensory receptors. Nerve regeneration does not begin if the cell body has not survived the initial injury or if it is unable to initiate regeneration. The regenerated axons must reach and reinnervate the appropriate target end-organs in a timely fashion. Recovery of motor function requires a critical number of motor axons reinnervating the muscle fibers. Sensory recovery is possible if the delay in reinnervation is short. Many additional factors influence the success of nerve repair or reconstruction. The timing of the repair, the level of injury, the extent of the zone of injury, the technical skill of the surgeon, and the method of repair and reconstruction contribute to the functional outcome after nerve injury.
Conclusion
This review presents the recent advances in understanding of neural regeneration and their application to the management of primary repairs and nerve gaps.
... Ele guia o crescimento axonal e une as extremidades do coto distal e proximal, reduzindo a tensão na linha de sutura, fator esse que inibiria a regeneração neural (1) . Com a utilização da auto-enxertia, alguns fatores devem ser considerados: 1) sempre produz morbidade da área doadora; 2) extensas perdas de tecido neural demandam grande quantidade de tecido autólogo, às vezes insuficiente; 3) a utilização de materiais sintéticos reduz o tempo de cirurgia (2,3) . Estudos sobre grandes perdas de tecido neural e a necessidade de pontes conectando as extremidades proximais e distais foram realizados durante a segunda metade do século dezenove (4) . ...
Extensive losses of neural tissue preclude the repair performed by means of primary anastomosis. In those cases, nerve autograft is considered as the treatment of choice. The synthetic tube constituted by polyglycoic acid is an option for nerve graft. The FK506 is an immunosuppressive agent, which increases the neural regeneration rates in vivo and in vitro. The purpose of this study was to compare, in rats, the degree of neural regeneration, by using histological analysis, a count of the number of regenerated myelinated axons, and a functional analysis, obtained by interposing the autogenous graft (group A), polyglycoic acid tube (group B) and a combination of polyglycoic acid tube with FK506 (group C) in 5-cm defects of the sciatic nerve. Neuroma formation was observed only in group A. Groups B and C presented similar histological patterns. The quantitative analysis of the number of regenerated myelinated axons has determined that: 1) group B presented, in average, a lower number when compared to the other groups; 2) there was no significant difference between control group A and group C. For functional recovery, there was no statistically significant change between the three groups, despite the qualitative and quantitative histological differences seen.
... Synthetic guides are usually made with polymeric materials, and may be nonresorbable (9,10) or resorbable (11,12). Non resorbable conduits remain foreign bodies around the regenerated nerve, hence impairing function recovery. ...
Two different types of conduits, one biological, obtained with homologous glutaraldehyde preserved vein segments and the other synthetic bioabsorbable, made with Poly [L-lactide-co-6-caprolactone], were evaluated as guides for nerve repair in alternative to autologous grafts in an experimental animal model. Under general anesthetic, the ischiatic nerve of a number Wistar rats was transected to create a 1 cm gap, which was then repaired by means of the conduits or autologous grafts. Controls were performed at 1, 3 and 6 months; nerve regeneration was effective with both conduits, but the count of myelinated axons showed a significant difference between the synthetic and biological tubes (p < 0.001). The Poly [L-lactide-co-6-caprolactone] guide was still intact 30 days after implant; progressive signs of degradation were present at 90 and 180 days. These results show that the synthetic conduits are better than those obtained with preserved vein segments and might be considered in alternative to autologous grafts in peripheral nerve reconstruction.
The current approach to regulating mechanical properties of elastomeric materials is predominately based on the exploratory mixing of different polymers, solvents, and fillers—which is both inflexible in application and imprecise in property control. Here we overview a new materials design approach that harnesses well-defined molecular codes of independently controlled architectural parameters to program grand variation of mechanical “phenotypes”. This design-by-architecture approach generates a set of universal correlations between the molecular architecture and the physical behavior of elastomers. In turn, this will lead to novel solvent-free materials that closely mimic the mechanical behavior of biological tissues, ranging from soft fat tissue to firm skin, and fundamentally change high-impact technologies such as soft robotics, wearable electronics, and biomedical devices.
Purpose:
To compare recovery in a rat model of sciatic nerve injury using a novel polyglycolic acid (PGA) conduit, which contains collagen fibers within the tube, as compared with both a hollow collagen conduit and nerve autograft. We hypothesize that a conduit with a scaffold will provide improved nerve regeneration over hollow conduits and demonstrate no significant differences when compared with autograft.
Methods:
A total of 72 Sprague-Dawley rats were randomized into 3 experimental groups, in which a unilateral 10-mm sciatic defect was repaired using either nerve autograft, a hollow collagen conduit, or a PGA collagen-filled conduit. Outcomes were measured at 12 and 16 weeks after surgery, and included bilateral tibialis anterior muscle weight, voltage and force maximal contractility, assessment of ankle contracture, and nerve histology.
Results:
In all groups, outcomes improved between 12 and 16 weeks. On average, the autograft group outperformed both conduit groups, and the hollow conduit demonstrated improved outcomes when compared with the PGA collagen-filled conduit. Differences in contractile force, however, were significant only at 12 weeks (autograft > hollow collagen conduit > PGA collagen-filled conduit). At 16 weeks, contractile force demonstrated no significant difference but corroborated the same absolute results (autograft > hollow collagen conduit > PGA collagen-filled conduit).
Conclusions:
Nerve repair using autograft provided superior motor nerve recovery over the 2 conduits for a 10-mm nerve gap in a murine acute transection injury model. The hollow collagen conduit demonstrated superior results when compared with the PGA collagen-filled conduit.
Clinical relevance:
The use of a hollow collagen conduit provides superior motor nerve recovery as compared with a PGA collagen-filled conduit.
A fibrin sealant sleeve treated with 2.5% glutaraldehyde to delay in vivo resorption was investigated as a conduit for nerve repair. In six Sprague- Dawley rats the ischiatic nerve was transected to obtain a 1 cm gap, which was bridged by grafting the conduit between the proximal and distal ends. The surgical procedure was performed under general anesthesia using a micro surgical technique. Controls at 3 and 6 months demonstrated a recovery of electrical properties of the nerve and morphological evidence of axonal regeneration through the lumen of the conduit. The wall of the conduit was easily recognizable in every case. These results confirm that the conduit is effective as a nerve prosthesis. Our preliminary results, confirming that sealant properties are lost, show that the degradation of Tissucol is modified by glutaraldehyde treatment.
Introduction: Nerve allografting is regarded as a treatment of choice in large neural tissue losses preventing repair by primary anastomosis. In these cases, a synthetic polyglycolic acid tube is an alternative for nerve grafting. On the other hand, several studies have emphasized the importance of neurotrophic factors on neural regeneration, including substances with potential to optimize neural regeneration, especially the GM1, an neurotrophic enhancer factor. Objective: to compare, in rats, the neural regeneration degree using histological analysis, regenerated myelinized axons count, and functional analysis with the use of neurotube and GM1. Methods: This assessment was performed by interposing allograft (group A), polyglycolic acid tube (group B) and polyglycolic acid tube associated to GM1 (group C) on 5-mm sciatic nerve defects. Results: Neuroma formation was found only on group A. Groups A and C showed similar histological patterns, except for the regenerated axons on group C, which were shown to be better organized and myelinized than in group A. Conclusion: on functional recovery, no statistically significant difference was found for the three groups, despite of qualitative and quantitative histological differences found.
To compare sciatic nerve regeneration in rats using three different techniques of repair.
Fifteen isogonics rats were divided into three groups according to the method used to repair a 5-mm long defect created in the sciatic nerve: autogenous graft (Group A), polyglycolic acid tube (PGAt) (Group B), and of the association of PGAt with the graft (Group C). Histological analysis, regenerated myelinated axon number count and functional analysis were used to compare after six weeks.
There was no difference in fiber diameter and degree of myelinization presented by Groups A, B and C. Group B presented the lowest number of regenerated axons. The groups did not display any significant functional difference after walking track analysis (p<0.05).
No differences between the three groups in terms of functional recovery, although there were histological differences among them.
We evaluated facial nerve regeneration using a collagen tube as a nerve conduit in five cats. In three 5 mm of the facial nerve were resected, a collagen tube was implanted, and a 5 mm segment of the opposite facial nerve was resected, reversed 180°, and sutured back as an autologous nerve graft. In one a collagen tube was implanted on one side, and in the remaining one a 5 mm nerve segment was reversed. Histological, electrophysiological, and horseradish peroxidase labelling examinations were carried out 4-24 weeks postoperatively. Histological study showed that the nerve was well vascularised and regenerated. Electrophysiological examination confirmed the recovery of evoked electromyograms through to the regenerated axons. Horseradish peroxidase examination also confirmed restoration of the whole facial nerve. The collagen tube is an efficient nerve conduit.
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.
Tubes of poly[bis(ethylalanato)phosphazene], obtained by evaporating the polymer around a 1.3 mm diameter capillary, were evaluated as guides for nerve regeneration in an experimental animal model. In six Wistar rats, under general anesthesia and with microsurgical technique, the ischiatic nerve was bilaterally isolated. On the right side, a segment was removed to create a defect of 10 mm, that was repaired with the conduit; on the left side the defect was repaired with harvested nerve segment from the right side. Controls at 30, 90, 180 days showed slow and gradual absorption of the conduit without signs of local or general toxicity. Nerve fiber regeneration in the conduits was not significantly different from that obtained with autologous grafts. Polyphosphazene conduits may be considered effective as a guide for nerve regeneration mainly in the perspective of using the polymer matrix as a carrier for neurite-promoting factors.
Polylactide-co-glycolide (PLGA) and PLGA/Bioglass® foams of tubular shape were assessed for their use as soft-tissue engineering scaffolds. The Bioglass® content was 1wt%. Porous membranes were fabricated via a thermally induced phase separation process, from which tubes of 3 mm diameter, 20 mm length and a nominal wall thickness of 1.5 mm were produced. Scanning electron microscopy revealed that the structure of the tubular foams consisted of radially oriented and highly interconnected pores with a large size distribution (50-300 μm). Foams with Bioglass® inclusions showed similarly well-defined tubular and interconnected pore morphology. Cell culture studies using mouse fibroblast (L929) cells were conducted to assess the biocompatibility of the scaffolds in vitro. Preconditioned medium, produced by incubating the foams with 5% w/v cell culture medium for 24 hours at 37°C, was shown to have a significant (p<0.0001; unpaired t-test) inhibitory effect on fibroblast proliferation compared with control medium. This may be beneficial as reduced fibroblast infiltration/proliferation response to a bioactive material might prevent fibroblast overgrowth, enabling other cell types, (e.g. endothelial cells) to migrate into the scaffold. The PLGA and PLGA/Bioglass® tubular foams developed here are candidate materials for soft-tissue engineering scaffolds, holding promise for the regeneration of tissues requiring a tubular shape scaffold.
This article aims to provide an overview of all clinical studies reporting sensory outcome as measured by two-point discrimination after digital nerve repair in the hand using resorbable Food and Drug Administration (FDA)- and CE-approved nerve conduits. The minimum follow-up for inclusion in this review was 11 months. In total, 235 nerve reconstructions could be classified. A total of 169 (72%) nerve reconstructions with a synthetic polyester-based nerve conduit were included; the other 66 nerves were reconstructed with collagen-based nerve conduits. To obtain the most reliable and comparable data, outcomes of each study were reclassified in the classification system as was used in the first two prospective randomised multicentre studies on the use of resorbable nerve conduits for repair of digital nerve gaps in the hand. Of the 235 nerve reconstructions, 171 (73%) nerve reconstructions showed good to excellent functional outcome. As many as 64 (27%) of the nerve reconstructions had a poor outcome. Based on the available data in this article at this moment, we conclude that digital nerve gaps up to 4 cm can be bridged by resorbable nerve conduits with a sensory outcome that can be qualified as good to excellent in almost 75% of cases after 11 months. Differences between FDA- and CE-approved nerve conduits could not be detected, apart from the rates of protrusion that were not observed using collagen-based nerve conduits.
The aim of this study was to evaluate the functional effects of bridging a gap in the sciatic nerve of the rat with either a biodegradable copolymer of DL-lactide and ϵ-caprolactone [p(DLLA-ϵ-CL)] nerve guide or an autologous nerve graft. Electromyograms (EMGs) of the gastrocnemius (GC) and tibialis anterior (TA) muscles were recorded 3.5 and 5 months after bridging the nerve gaps. Furthermore, the rats' gait was recorded on video and the quality of the gait was analyzed. EMG patterns of the contralateral nonoperated side were essentially normal. The EMG patterns on the operated side were irregular in all animals, but the quality of gait was better in the nerve guide group. We conclude that the surgical technique (nerve guide or nerve graft) does not influence the occurrence of abnormal EMG patterns, but gait improves to a greater extent when the nerve gap is bridged by a nerve guide. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 753–759, 2001
The aim of this study is to evaluate the functional and cell biological applicability of a two-ply nerve guide constructed of a PLLA/PCL (i.e. poly-l-lactide and poly--caprolactone) copolymer. To do so, we performed a cytotoxicity test, a subcutaneous biodegradation test and an in situ implantation study in the sciatic nerve of the rat. The nerve guide copolymer was found to be non-toxic, according to ISO/EN standards, and it showed a mild foreign body reaction and complete fibrous encapsulation after implantation. Onset of biodegradation of the inner layer was seen after one month of implantation. After 18 months of implantation complete fragmentation was observed, as well as a secondary inflammatory response characterized by foreign body giant cell activity and phagocytosis of polymer debris. Recovery of both motor and sensory nerve function was observed in all nerve guides.
Facial nerve paralysis due to resection of tumors or as a consequence of trauma is a frequently observed complication. Thus, in the present study, we evaluated a collagen nerve guide in facial nerve regeneration across a 5-mm nerve gap. This biological tube was manufactured from 3% collagen, coated over a Teflon tube used only as a template and submitted to thermal dehydration at 105C for 24h. The collagen tube was implanted at the dorsal ramous of the facial nerve of five adult cats over a gap of 5mm. The facial nerve of the contralateral side was kept intact and used as control. Electrophysiological study was performed from 3 weeks after surgery, and histological and horseradish peroxidase labeling examination was carried out 8 weeks after implantation. Electrophysiological study confirmed the recovery of electrical activity of the collagenimplanted regenerated nerve. Light-microscopic examination of collagen tube-implanted specimens revealed a well vascularized regenerated nerve, which under an electron microscope showed many myelinated axons surrounded by Schwann cells and unmyelinated axons. Horseradish peroxidase staining demonstrated labeling of facial motoneurons in the brainstem and facial nerve terminals in the neuromuscular junction, also confirming restoration of the whole facial nerve tract from the reinnervated muscles, passing through the regenerated site to the brainstem. The collagen tube was very efficient as a nerve guide over a 5mm facial nerve gap and shows great promise as a nerve conduit.
Regenerative medicine is an interdisciplinary field of medical science that brings together the principles of tissue engineering
and the life sciences to develop biologic “components” for the maintenance, regeneration, and replacement of tissue and organs.
The principal components of regenerative medicine are cells, scaffolds, and specific physical, chemical, and biochemical signals
that replicate the natural microenvironments within the body.
KeywordsRegenerative medicine-Tissue engineering-Stem cells-Biomaterials
Immersion precipitation was employed as a method for the fabrication of polymeric conduits from P(BHET-EOP/TC), a poly(phosphoester) with an ethylene terephthalate backbone, to be applied as guidance channels for nerve regeneration. Coatings of various porosities could be obtained by immersing mandrels coated with a solution of the polymer in chloroform into non-solvent immersion baths, followed by freeze or vacuum-drying. The porosity of the coatings decreased with an increase in polymer molecular weight, drying time before precipitation and concentration of polymer solution. The effects of these parameters can be rationalized by employing ternary phase diagrams, where porosity is directly related to the degree of phase separation available to the system before gelation occurs. To afford improved porosity control, a new system was developed which employed the contrasting phase-separation behavior of P(BHET-EOP/TC)/chloroform solution in methanol and water. As water is essentially a non-solvent for the polymer, the demixing boundary of the P(BHET-EOP/TC)–CHCl3–H2O system is located close to the polymer-solvent edge of the phase diagram, while that of the P(BHET-EOP/TC)–CHCl3–MeOH system is located further away. A mixture of methanol and water allows the demixing boundary to be shifted to intermediate coordinates. By immersing P(BHET-EOP/TC) coatings in immersion baths containing different ratios of water and methanol, then gradually titrating the bath with methanol to a concentration of 70% (v/v) methanol, surface porosities ranging from 2 to 58% could be achieved.
Solid conducting biodegradable composite membranes have shown to enhance nerve regeneration. However, few efforts have been directed toward porous conducting biodegradable composite membranes for the same purpose. In this study, we have fabricated some porous conducting poly(dl-lactide) composite membranes which can be used for the biodegradable nerve conduits. The porous poly(dl-lactide) membranes were first prepared through a phase separation method, and then they were incorporated with polypyrrole to produce porous conducting composite membranes by polymerizing pyrrole monomer in gas phase using FeCl3 as oxidant. The preparation conditions were optimized to obtain membranes with controlled pore size and porosity. The direct current conductivity of composite membrane was investigated using standard four-point technique. The effects of polymerization time and the concentration of oxidant on the conductivity of the composite membrane were examined. Under optimized polymerization conditions, some composite membranes showed a conductivity close to 10−3 S cm−1 with a lower polypyrrole loading between 2 and 3 wt.%. A consecutive degradation in Ringer's solution at 37 °C indicated that the conductivity of composite membrane did not exhibit significant changes until 9 weeks although a noticeable weight loss of the composite membrane could be seen since the end of the second week.
One of the biggest challenges in peripheral nerve tissue engineering is to create an artificial nerve graft that could mimic the extracellular matrix (ECM) and assist in nerve regeneration. Bio-composite nanofibrous scaffolds made from synthetic and natural polymeric blends provide suitable substrate for tissue engineering and it can be used as nerve guides eliminating the need of autologous nerve grafts. Nanotopography or orientation of the fibers within the scaffolds greatly influences the nerve cell morphology and outgrowth, and the alignment of the fibers ensures better contact guidance of the cells. In this study, poly (L-lactic acid)-co-poly(ε-caprolactone) or P(LLA-CL), collagen I and collagen III are utilized for the fabrication of nanofibers of different compositions and orientations (random and aligned) by electrospinning. The morphology, mechanical, physical, and chemical properties of the electrospun scaffolds along with their biocompatibility using C17.2 nerve stem cells are studied to identify the suitable material compositions and topography of the electrospun scaffolds required for peripheral nerve regeneration. Aligned P(LLA-CL)/collagen I/collagen III nanofibrous scaffolds with average diameter of 253 ± 102 nm were fabricated and characterized with a tensile strength of 11.59 ± 1.68 MPa. Cell proliferation studies showed 22% increase in cell proliferation on aligned P(LLA-CL)/collagen I/collagen III scaffolds compared with aligned pure P(LLA-CL) scaffolds. Results of our in vitro cell proliferation, cell-scaffold interaction, and neurofilament protein expression studies demonstrated that the electrospun aligned P(LLA-CL)/collagen I/collagen III nanofibrous scaffolds mimic more closely towards the ECM of nerve and have great potential as a substrate for accelerated regeneration of the nerve.
The use of nerve guidance conduits to repair peripheral nerve discontinuities has attracted much attention from the biomaterials community, with many resorbable and non-resorbable materials in clinical use. However, a material with ideal biocompatibility, sufficient mechanical properties (to match that of the regenerating nerve) coupled with a suitable degradation rate, has yet to be realized. Recently, potential solutions (composite nerve guidance conduits) which support the emerging philosophy of allowing synthetic materials to establish key interactions with cells in ways that encourage self-repair (i.e. ionic mediators of repair such as those observed in hard tissue regeneration) have been proposed in the literature; such composites comprise specially designed bioactive phosphate-free glasses embedded in degradable polymeric matrices. Whilst much research has focussed on the optimization of such composites, there is no published literature on the performance of these experimental compositions under simulated physiological conditions. To address this key limitation, this paper explores the time-dependent variations in wet-state mechanical properties (tensile modulus and ultimate tensile strength) for NGC composites containing various compositions of PLGA (at 12.5, and 20 wt%), F127 (at 0, 2.5 and 5 wt%) and various loadings of Si-Na-Ca-Zn-Ce glass (at 0 and 20 wt%). It was observed that Young's modulus and ultimate tensile strength of these composites were in the range 5-203 MPa and 1-7 MPa respectively, indicating comparable mechanical performance to clinical materials. Furthermore, an analysis of the cytocompatibility of experimental compositions showed comparable (in some instances superior), compatibility when compared with the commercial product Neurolac(®). Based on current synthetic devices and the demands of the indication, the CNGCs examined in this work offer appropriate mechanical properties and compatibility to warrant enhanced development.
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.
Unlabelled:
Effective nerve regeneration and functional recovery subsequent to peripheral nerve injury is still a clinical challenge. Autologous nerve graft transplantation is a feasible treatment in several clinical cases, but it is limited by donor site morbidity and insufficient donor tissue, impairing complete functional recovery. Tissue engineering has introduced innovative approaches to promote and guide peripheral nerve regeneration by using biomimetic conduits creating favorable microenvironments for nervous ingrowth, but despite the development of a plethora of nerve prostheses, few approaches have as yet entered the clinic. Promising strategies using nanotechnology have recently been proposed, such as the use of scaffolds with functionalized cell-binding domains, the use of guidance channels with cell-scale internally oriented fibers, and the possibility of sustained release of neurotrophic factors. This review addresses the fabrication, advantages, drawbacks, and results achieved by the most recent nanotechnology approaches in view of future solutions for peripheral nerve repair.
From the clinical editor:
Peripheral nerve repair strategies are very limited despite numerous advances on the field of neurosciences and regenerative medicine. This review discusses nanotechnology based strategies including scaffolds with functionalized cell binding domains, the use of guidance channels, and the potential use of sustained release neurotropic factors.
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.
In this study, the physicochemical properties of microporous poly (epsilon-caprolactone) (PCL) films and a composite material made of PCL and polylactic acid (PLA) blend were tested. Fabricated by solvent casting using dichloromethane, these ultra-thin films (60 +/- 5 microm in thickness) have a novel double-sided surface topography, i.e. a porous surface with pores 1-10 microm in diameter and a relatively smooth surface with nano-scaled texture. Porous surfaces were found to be associated with increased protein adsorption and the treatment of these polyester scaffolds with NaOH rendered them more hydrophilic. Differential Scanning Calorimetry (DSC) showed that the incorporation of PLA reduced the crystallinity of the original homopolymer. Chemical changes were investigated by means of Fourier Transform Infrared Spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Average surface roughness (Ra), hydrophilicity/hydrophobicity and mechanical properties of these materials were also assessed for the suitability of these materials as nerve conduits.
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.
In the present study the authors consider the influence of the porosity of synthetic nerve grafts on peripheral nerve regeneration.
Microporous (1-13 microm) and nonporous nerve grafts made of a copolymer of trimethylene carbonate and epsilon-caprolactone were tested in an animal model. Twelve weeks after surgery, nerve and muscle morphological and electrophysiological results of regenerated nerves that had grown through the synthetic nerve grafts were compared with autografted and untreated (control) sciatic nerves. Based on the observed changes in the number and diameter of the nerve fibers, the predicted values of the electrophysiological parameters were calculated.
The values of the morphometric parameters of the peroneal nerves and the gastrocnemius and anterior tibial muscles were similar if not equal in the rats receiving synthetic nerve grafts. The refractory periods, however, were shorter in porous compared with nonporous grafted nerves, and thus were closer to control values.
A shorter refractory period enables the axon to follow the firing frequency of the neuron more effectively and allows a more adequate target organ stimulation. Therefore, porous are preferred over nonporous nerve grafts.
Nerve regeneration using artificial biodegradable conduits is of increasing interest. The aim of this study is to evaluate the regeneration and maturation of a nerve after long-term implantation (2 years) of a biodegradable poly-L-lactide/poly-epsilon-caprolactone (PLLA/PCL) copolymeric nerve guide in the sciatic nerve of the rat. After harvesting, we evaluated both the regenerated nerves and the controls, using light microscopy, transmission electron microscopy, and morphometric techniques. Remnants of biomaterial were still present after 2 years of implantation, but the foreign body reaction was very mild at this stage, due to the rounded shapes of the polymer debris. Morphometric analysis showed significant differences between the regenerated nerve and the normal sciatic nerve: the number of myelinated fibers is higher, and the mean fiber diameter of the myelinated fibers in the regenerated nerve is smaller. In conclusion, the results demonstrate that the new PLLA/PCL nerve guide can provide optimal conditions for regeneration and maturation of damaged nerves.
A new conduit made with a bioabsorbable copolymer, poly (L-lactide-co-6-caprolactone), was evaluated in an animal model as a guide for nerve regeneration. The conduit had an inner diameter of 1.3 mm and a wall thickness of 175 microns. Segments of length 1.2 cm were interposed between the proximal and distal stumps of transected ischiatic nerves in Wistar rats, bridging a nerve gap of 1 cm. All of the procedure was performed under general anaesthesia using microsurgical techniques. Controls were performed at 1, 3 and 6 months and it was demonstrated that the conduit was still undamaged after 30 d. Progressive signs of degradation appeared at 90 and 180 d. Nerve regeneration in the lumen was effective as confirmed by histological and electron microscopical investigations. These preliminary results emphasize the interesting properties of the conduit with regard to the achievement of a neural prosthesis.
Absorbable implants are being increasingly used in various fields of medicine. Important materials for these applications include the polyesters polylactide and polyglycolide. Following implantation of any absorbable device there occurs a proliferation of fibrous tissue, which along with material from the degrading implant forms a composite membranous structure-a neomembrane. Neomembranes can be exploited in guiding tissue regeneration. Success in this respect has been achieved in treatment of bone defects, nerve defects, and periodontal ligaments. Future research may ultimately permit taking advantage of neomembranes in the reconstruction of more complex organs such as the liver. Gaining an understanding of implant characteristics and implant-tissue interaction is essential for further progress in this area.
The aim of this study was to compare the speed of functional nerve recovery after reconstruction with a biodegradable p(DLLA-ε-CL) nerve guide, as filled with either modified denatured muscle tissue (MDMT) or phosphate- buffered saline (PBS). To evaluate both motor and sensory nerve recovery, walking-track analysis and electrostimulation tests were carded out after implantation periods, ranging from 3-15 weeks. Functional nerve recovery after reconstruction of a 15-mm nerve gap, with a biodegradable p(DLLA-ε- CL) nerve guide filled with modified denatured muscle tissue, was slightly faster, compared with nerve reconstruction of a 10-mm gap with a biodegradable p(DLLA-ε-CL) nerve guide filled with PBS. We conclude that our experiments have demonstrated that the use of MDMT increases the speed of recovery after reconstruction of a nerve gap with a p(DLLA-ε-CL) biodegradable nerve guide. Furthermore, the use of MDMT might open perspectives for repair of longer nerve gaps.
This article describes recent, significant scientific advances leading to the development of the bioartificial nerve graft. Schwann cells, which play an active role in the repair and function of peripheral nerves, are used to seed a synthetic, often resorbable conduit, which is then used to bridge and repair nerve gaps caused by injury or disease. By enhancing the rate and extent of regeneration, the bioartificial nerve graft holds great promise for improving recovery in the peripheral (and central) nervous system.
We have fabricated porous, biodegradable tubular conduits for guided tissue regeneration using a combined solvent casting and extrusion technique. The biodegradable polymers used in this study were poly(DL-lactic-co-glycolic acid) (PLGA) and poly(L-lactic acid) (PLLA). A polymer/salt composite was first prepared by a solvent casting process. After drying, the composite was extruded to form a tubular construct. The salt particles in the construct were then leached out leaving a conduit with an open-pore structure. PLGA was studied as a model polymer to analyze the effects of salt weight fraction, salt particle size, and processing temperature on porosity and pore size of the extruded conduits. The porosity and pore size were found to increase with increasing salt weight fraction. Increasing the salt particle size increased the pore diameter but did not affect the porosity. High extrusion temperatures decreased the pore diameter without altering the porosity. Greater decrease in molecular weight was observed for conduits manufactured at higher temperatures. The mechanical properties of both PLGA and PLLA conduits were tested after degradation in vitro for up to 8 weeks. The modulus and failure strength of PLLA conduits were approximately 10 times higher than those of PLGA conduits. Failure strain was similar for both conduits. After degradation for 8 weeks, the molecular weights of the PLGA and PLLA conduits decreased to 38% and 43% of the initial values, respectively. However, both conduits maintained their shape and did not collapse. The PLGA also remained amorphous throughout the time course, while the crystallinity of PLLA increased from 5.2% to 11.5%. The potential of seeding the conduits with cells for transplantation or with biodegradable polymer microparticles for drug delivery was also tested with dyed microspheres. These porous tubular structures hold great promise for the regeneration of tissues which require tubular scaffolds such as peripheral nerve, long bone, intestine, or blood vessel.
Epidemiological data indicate that in females cigarette smoking exerts antiestrogenic effects that manifest clinically in an increased incidence of osteoporosis, earlier menopause, increased spot bleeding, and decreased risk of endometrial cancer for female smokers. The molecular mechanism of this effect is unclear; however, decreased serum estrogen levels in female smokers have been correlated with increased concentrations of the metabolite 2-hydroxyestrogen in females who smoke. Induction of estrogen metabolizing enzymes, CYP1A1 and 1A2, is one mechanism by which increased 2-hydroxyestrogen concentrations may occur. It has also been suggested that the estrogen receptor (ER) may contribute to this anti-estrogenic effect by binding to antagonist(s) in cigarette smoke.
Gel retardation analysis was employed to determine if diluted mainstream cigarette smoke condensates (DMCSCs) could activate the aryl hydrocarbon receptor (AhR). AhR-regulated ethoxyresorufin-O-deethylase (EROD) activity and dioxin response element (DRE)-mediated luciferase induction were assessed in Hepa1c1c7 mouse hepatoma cells. A competitive ligand binding assay was utilized to determine if DMCSCs could bind to the ER. ER-dependent luciferase activity was assessed in MCF-7 cells.
In gel retardation assays, DMCSCs induced a protein-DNA complex when incubated with a radiolabeled wild-type DRE oligonucleotide. The complex was effectively competed by excess unlabeled DRE but not by excess unlabeled mutant DRE. In Hepa1c1c7 mouse hepatoma cells transiently transfected with a DRE-regulated luciferase reporter gene, pGudluc1.1, treatment with DMCSCs resulted in a 23- and 25-fold increase in luciferase activity (P<0.01) and an 8.5- and 10.5-fold (P<0.01) induction in EROD activity, respectively. DMCSCs completely displaced bound tritiated E2 from the ER in a dose-dependent manner and induced ER-regulated luciferase activity significantly 6-fold (P<0.01), representing 86% of the maximal induction observed with E2.
DMCSCs can bind to and transcriptionally activate the AhR and ER nuclear receptors and cause induction of DRE- and ER-regulated genes. Further study is required to identify the specific compound(s) responsible for these activities.
The aim of this study was to (1) evaluate the effect of several preparation techniques of denatured muscle tissue to obtain an open three-dimensional structure, and (2) test if this scaffold is suitable for peripheral nerve regeneration. Four samples (A-D) of muscle tissue specimens were evaluated using light microscopy, immunohistochemistry and cryo-scanning electron microscopy. Sample C showed the most open extracellular matrix, whilst collagen type IV and laminin (in the basal lamina) could still be observed using immunohistochemistry. An in vivo pilot study showed that the first signs of functional nerve recovery and axon regeneration could be observed after 3 weeks of implantation. We conclude that sample C has the most open structure and leads to good nerve regeneration and functional nerve recovery.
We evaluated facial nerve regeneration using a collagen tube as a nerve conduit in five cats. In three 5 mm of the facial nerve were resected, a collagen tube was implanted, and a 5 mm segment of the opposite facial nerve was resected, reversed 180 degrees, and sutured back as an autologous nerve graft. In one a collagen tube was implanted on one side, and in the remaining one a 5 mm nerve segment was reversed. Histological, electrophysiological, and horseradish peroxidase labelling examinations were carried out 4-24 weeks postoperatively. Histological study showed that the nerve was well vascularised and regenerated. Electrophysiological examination confirmed the recovery of evoked electromyograms through to the regenerated axons. Horseradish peroxidase examination also confirmed restoration of the whole facial nerve. The collagen tube is an efficient nerve conduit.
Guided tissue regeneration is a procedure to improve tissue repair, which creates an optimal environment for the intrinsic growth ability of tissues.
A prerequisite for guided tissue regeneration is the availability of materials with suitable physicochemical and biocompatibility properties for the preparation of the devices. We investigated bone and peripheral nerve guided tissue regeneration, making two conduits from poly[L-lactide-co-6-caprolactone] (PLLC--peripheral nerve) and with poly [DL-lactide] (PDLLA--bone) with different features. After the polymer synthesis and chemical characterization, the conduits were evaluated in vivo in rat sciatic nerve gaps and in rabbit radius defects.
The results demonstrated good biocompatibility of both polymeric conduits. A good axonal regeneration and the restoration of the nerve trunk continuity, similar to that observed with autologous grafts has been obtained with PLLC conduits, that slowly degrade in about 6 months. PDLLA conduits protected the bone defect against the invasion of surrounding soft tissues; an effective bone growth bridging the defect was observed in their lumen.
These results confirm the versatility of polylactides as biomaterials and will encourage further investigations on hard and soft tissues.
We compared regeneration and functional reinnervation after sciatic nerve resection and tubulization repair with bioresorbable guides of poly(L-lactide-co-epsilon-caprolactone) (PLC) and permanent guides of polysulfone (POS) with different degrees of permeability, leaving a 6 mm gap in different groups of mice. Functional reinnervation was assessed to determine recovery of motor, sensory and sweating functions in the hindpaw during four months postoperation. Highly permeable PLC guides allowed for faster and higher levels of reinnervation for the four functions tested than impermeable or low-permeable PLC guides, while semipermeable 30 and 100 kDa POS tubes yielded very low levels of reinnervation. The regeneration success rate was higher with PLC than with POS tubes. Morphometrical analysis of cross-sectional nerves under light microscopy showed the highest number of regenerated myelinated fibers at mid tube and distal nerve in high-permeable PLC guides. Impermeable PLC guides allowed slightly worse levels of regeneration, while low-permeable PLC guides promoted neuroma and limited distal regeneration. The lowest number of regenerated fibers were found in POS tubes. In summary, highly permeable bioresorbable PLC guides offer a suitable alternative for repairing long gaps in injured nerves, approaching the success of autologous nerve grafts.
Studies on nerve conduits for peripheral nerve regeneration have concentrated on the manipulation of various conduit materials to avoid sacrificing native nerve in the clinical situation. With the proliferation of available nerve growth-stimulating factors, the focus is shifting experimentally toward molecular biologic manipulation, with the addition of these materials as substrates within the conduit. The clinical use of conduits has concentrated on the use of autogenous tissue, with a few examples of polyglactin (PGA) mesh and silicone. Ultimately, as yet, conduit material does not seem to have a profound effect on outcome. Substrate manipulation has not yet had clinical application.
An important problem that remains, both experimentally and clinically, is overriding the size of the maximal gap that can be bridged successfully, as well as obtaining good functional sensory and motor recovery, compared with the use of nerve grafts. Advances in molecular biology may reveal further details about the nerve growth phenomenon, the precise sequencing of the substrate materials that are effective in promoting nerve growth, and when they should be applied. Advances in chemical engineering may provide additional biologically stable materials that have the ability to integrate growthenhancing agents or factors into the lumen of the conduit.
Facial nerve paralysis due to a surgical procedure or trauma is a frequently observed complication. The authors evaluated facial nerve repair achieved by the interposition of a collagen nerve guide.
Ten cats were divided into three groups. Group 1 consisted of six animals in which a 5-mm facial nerve segment on one side was resected and replaced by a collagen tube that was sutured to bridge both nerve stumps. On the opposite side a 5-mm segment of facial nerve was resected, reversed 180 degrees, and sutured to the stumps as an autograft nerve. Group 2 consisted of two cats in which the collagen nerve guide was interposed on one side and the nerve on the other side was left intact. Group 3 consisted of two cats in which a reversed autograft nerve was placed on one side and the nerve on the other side was left intact. Histological, electrophysiological, and horseradish peroxidase labeling examinations were performed starting 3 weeks after surgery. Light and electron microscopic examinations of collagen tube-implanted specimens revealed a well-vascularized regenerated nerve. The electrophysiological study confirmed the recovery of electrical activity in regenerated axons. Horseradish peroxidase labeling also confirmed restoration of the whole facial nerve tract.
The collagen nerve guide shows great promise as a nerve conduit.
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