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Effectiveness of a bioabsorbable conduit in the repair of peripheral nerve
Abstract
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.
... One experimental model that has proven to be useful for exploring this subject is the nerve tubulization technique. This method provides a unique microenvironment to which different substances and cells can be added in order to assess their role in regeneration [5,20,21,23,31,33,60,62]. In this review, we provide an overview of the knowledge on nerve regeneration that has been gained by using the tubulization technique. ...
... Several types of biopolymers have been used as nerve conduits, with results comparable to autografts [5,11,21,24,29,30,47]. A number of variables are particularly important in order to achieve nerve regeneration, and include the method used to build the tube, the tube porosity, and the biocompatibility of the material. ...
... Of the numerous biocompatible materials available, collagen, EVA (ethylene-vinyl acetate copolymer) [1], PLLA (poly(lactic acid)) [20,21], poly(glycolic acid) (PGA) [33], Poly(Llactic acid co-glycolic acid) (PLGA) [8,30] and LA/ CPL (a copolymer of lactic acid and caprolactone) [5,17] have yielded good results in nerve regeneration. More recently, Flynn et al. [24] developed a method to create longitudinally oriented channels within poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels for neural tissue engineering applications. ...
Transection of a peripheral nerve results in a loss of function at the target organ that can rarely be recovered without surgical repair. Such an intervention usually involves nerve autografting but is complicated by problems such as the need for secondary surgery, a limited donor nerve supply and loss of sensitivity in the donor nerve area. An alternative approach involving repair by nerve tubulization has been extensively used to study substances that may improve the regenerative process. An interesting feature of the tubulization technique is the possibility of filling the tube with substances that can enhance regeneration. Such substances include collagen, laminin, hyaluronic acid, fibronectin and, more recently, glycosaminoglycans alone or with collagen. Biopolymers, purified glial cells, and neurotrophic factors have also been tested. By using the tubulization technique, it has been possible to increase the number of regenerating fibers and the gap between the stumps. In this review, we discuss some of the basic concepts of this technique, as well as recent advances in this field.
... There are many disadvantages of this method, such as an insufficient yield of transplants, morbidity at the donor site and an inappropriate diameter of donor nerves. An alternative repair method is to use a biodegradable conduit to bridge nerve gap between severed nerve ends [1,2]. The conduit prevents the fibrous tissue forming in the nerve gap and offers a guide for regenerating axons to the distal stump. ...
... When a chitosan conduit is used to bridge an amputated peripheral nerve gap, the conduit should resist the pressure from adjacent muscles and remain hollow during nerve regeneration [1,2]. The high elastic modulus and tensile strength of chitosan conduits are beneficial to withstanding the mechanical forces from adjacent muscles, keep the tubular shape and avoid tearing. ...
Three kinds of cross-linked chitosan films were prepared with hexamethylene diisocyanate (HDI), epichlorohydrin (ECH) and glutaraldehyde (GA) as cross-linking agents, respectively. The physical and mechanical properties, biodegradability and Schwann cell affinity of the cross-linked films were investigated. A significant decrease in the degradation rate in lysozyme solution and a large change in the mechanical properties were observed compared with non-cross-linked chitosan films. The protein adsorption on chitosan films was determined by means of enzyme-linked immunosorbent assay (ELISA). In comparison with the non-cross-linked films, the chitosan films cross-linked with HDI showed a significant increase (up to 40-50%) in both fibronectin and laminin adsorption, while the protein adsorption on the other two kinds of cross-linked films was similar to that on non-crosslinked films. In addition, cell culture revealed that the HDI cross-linked chitosan films enhanced the spread and proliferation of Schwann cells while the other cross-linked films delayed the cell proliferation. These results suggest that HDI cross-linking of chitosan films provides a combination of physical properties, biodegradability and Schwann cell affinity suitable for peripheral nerve regeneration.
... Giardino et al. used a similar conduit made of poly(L-lactide-6-co-caprlactone) to support peripheral nerve regeneration. 16,33 The results showed that the synthetic conduit performed superiorly compared to preserved vein segments. ...
... These later findings, attracted new research in support of finding a conduit that is not only able to support nerve regeneration through its mechanical properties, but also promotes regeneration by gradually releasing neurotrophins and growth factors. 18,23,33,44 Poly-glycolic acid nerve conduits Poly-glycolic acid conduits are the most commonly used guides, both experimentally and clinically. Early support for the PGA tube was provided by Dellon's group, who compared the regeneration achieved after 1 year in a 3-cm ulnar nerve gap in monkeys using a bioresorbable PGA acid conduit compared to an interfascicular sural nerve graft. ...
Several methods have been used for bridging nerve gaps. Much of the focus in nerve repair of peripheral nerves has focussed on creating either natural or synthetic tubular nerve guidance channels, as an alternative to nerve autografts. These conduits act to guide axons sprouting from the regenerating nerve end, provide a conduit for diffusion of neurotrophic and neurotropic factors secreted by the injured nerve stump, as well as help protect against infiltration of fibrous tissue. Among the conduits that have been studied are autogenous veins, arteries, mesothelial chambers, synthetic tubes, collagen tubes, amnion tubes, cardiac and skeletal muscle, and silicon tubes. This paper briefly reviews major studies in which bioabsorbable nerve guides were used for peripheral nerve repair, with a particular emphasis on polymeric guidance channels, in an effort to evaluate their use, their ability to support or enhance nerve regeneration and any potential problems.
... Particularly, penetration of needles and threads through epineurium evidently causes mechanical trauma and disproportionate stress followed by collagenous fibrous tissue, mismatched regenerative fibers, and neuroma formation. [12,13] Complete replacement of traditional nerve suturing has remained an unsolved challenge for surgeons over the past eighty years (1). To overcome such limitations, an unprecedented material strategy enabling i) immediate end-to-end nerve bridging even under massive tensile stress of bisected nerves, ii) little compression of the regenerated nerves so as to prevent necrosis due to chronic compression, and iii) anti-fibrosis even after long-term implantation, is urgently required. ...
The need for the development of soft materials capable of stably adhering to nerve tissues without any suturing followed by additional damages is at the fore at a time when success in postoperative recovery depends largely on the surgical experience and/or specialized microsuturing skills of the surgeon. Despite fully recognizing such prerequisite conditions, designing the materials with robust adhesion to wet nerves as well as acute/chronic anti‐inflammation remains to be resolved. Herein, a sticky and strain‐gradient artificial epineurium (SSGAE) that overcomes the most critically challenging aspect for realizing sutureless repair of severely injured nerves is presented. In this regard, the SSGAE with a skin‐inspired hierarchical structure entailing strain‐gradient layers, anisotropic Janus layers including hydrophobic top and hydrophilic bottom surfaces, and synergistic self‐healing capabilities enables immediate and stable neurorrhaphy in both rodent and nonhuman primate models, indicating that the bioinspired materials strategy significantly contributes to translational medicine for effective peripheral nerve repair.
... A nerve guidance conduit aims to suppress the invasion of inflammatory tissue by covering the nerve defect portion with a tubular structure and also provides an environment suitable for nerve reconstruction via the biological characteristics of the materials. Previously, nerve guidance conduits using various materials were fabricated, and their efficacy to facilitate peripheral nerve regeneration was shown by transplantation into laboratory animals such as rats and dogs (Archibald et al. 1991;Whitworth et al. 1995;Nicoli Aldini et al. 1996;Hadlock et al. 1998;Matsumoto et al. 2000;Nakamura et al. 2004). However, their recovery score did not replace that of autografting. ...
The nervous system is an ensemble of organs that transmit and process external information and are responsible for the adaption to the external environment and homeostasis control of the internal environment. The nervous system of vertebrates is divided into the central nervous system (CNS) and peripheral nervous system (PNS) due to its structural features. The CNS, which includes the brain and the spinal cord, processes information from external stimuli and assembles orders suitable for these stimuli. The CNS then sends signals to control other organs/tissues. On the other hand, the PNS connects the CNS to other organs/tissues and functions as a signal pathway. Therefore, the decline and loss of various functions due to injuries of the nervous system cause an impaired quality of life (QOL) and eventually the termination of life activities. Here, we report mainly on decellularized neural tissue and its application as a substrate for the regeneration of the nervous system.
... A nerve guidance conduit aims to suppress the invasion of inflammatory tissue by covering the nerve defect portion with a tubular structure and also provides an environment suitable for nerve reconstruction via the biological characteristics of the materials. Previously, nerve guidance conduits using various materials were fabricated, and their efficacy to facilitate peripheral nerve regeneration was shown by transplantation into laboratory animals such as rats and dogs (Archibald et al. 1991;Whitworth et al. 1995;Nicoli Aldini et al. 1996;Hadlock et al. 1998;Matsumoto et al. 2000;Nakamura et al. 2004). However, their recovery score did not replace that of autografting. ...
The extracellular matrix (ECM) of mammalian organs and tissues has been applied as a substitute scaffold to simplify the restoration and reconstruction of several tissues. Such scaffolds are prepared in various arrangements including sheets, powders, and hydrogels. One of the more applicable processes is using natural scaffolds, for this purpose discarded tissues or organs are naturally derived by processes that comprised decellularization of following tissues or organs. Protection of the complex structure and 3D (three dimensional) ultrastructure of the ECM is extremely necessary but it is predictable that all protocols of decellularization end in disruption of the architecture and potential loss of surface organization and configuration. Tissue decellularization with conservation of ECM bioactivity and integrity can be improved by providing well-designed protocols regarding the agents and decellularization techniques operated during processing. An overview of the characterization of decellularized scaffolds and the role of reagnets can validate the applied methods' efficacy.
... Poly ε-caprolactone and poly L-lactide-co-ε-caprolactone have the potential to facilitate nerve regeneration (Jin et al., 2012) and are credited with restoring lost sensation in humans; while in rodents they produced a good sciatic function index, increased the numbers of myelinated axons and sensory and motor cell bodies, and allowed progressive degradation of the prosthesis (Aldini et al., 1996). The effectiveness of poly ε-caprolactone prostheses was tested in gaps of 5, 15, and 45 mm in rats. ...
Peripheral nerve injuries are relatively common and can be caused by a variety of traumatic events such as motor vehicle accidents. They can lead to long-term disability, pain, and financial burden, and contribute to poor quality of life. In this review, we systematically analyze the contemporary literature on peripheral nerve gap management using nerve prostheses in conjunction with physical therapeutic agents. The use of nerve prostheses to assist nerve regeneration across large gaps (> 30 mm) has revolutionized neural surgery. The materials used for nerve prostheses have been greatly refined, making them suitable for repairing large nerve gaps. However, research on peripheral nerve gap management using nerve prostheses reports inconsistent functional outcomes, especially when prostheses are integrated with physical therapeutic agents, and thus warrants careful investigation. This review explores the effectiveness of nerve prostheses for bridging large nerve gaps and then addresses their use in combination with physical therapeutic agents.
... Similarly to allografts, these materials can also trigger an undesirable host immune response. Because of this limitation, synthetic materials such as poly(L-lactide-co-6-caprolactone) and poly(DL-lactide-caprolactone) have also been considered as alternatives (Nicoli et al., 1996;den Dunnen et al., 1996). The chemical properties of synthetic materials allow modification of their geometric configuration, biocompatibility, porosity, degradation, and mechanical strength (Evans, 2001). ...
Repairing neurological injury, especially in the central nervous system (CNS), is one of the greatest challenges faced by modern medicine. Cellular therapies have proved promising, but are insufficient to repair major lesions. Developing a tissue engineering (TE) approach based on combining and integrating advanced functional biomaterials with cells and regulators, to mimic the natural milieu and support neuroregeneration, is critical in achieving successful repair of the nervous system. In this article, we discuss TE tools, techniques, and strategies that are used for repair and regeneration of peripheral nerves, as well as those being developed to repair damage of the CNS.
... Biodegradable nerve guides provide a successful alternative (8)(9)(10). After functioning as a temporary scaffold for nerve regeneration, they gradually degrade. ...
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.
... [36] In the recent past, several guidance techniques using artificial nerve conduits have been developed to guide nerve regeneration towards the distal stump. [37,38] The isolated environment provided by guidance channels helps confine and concentrate neurotrophic factors that are released by supporting cells while protecting the axons against collapse and invasion from immune cells. [31] The use of guidance channels eliminates functional loss at the donor site, a condition that is commonly associated with the use of autografts. ...
... Much work has been conducted to develop nerve guide tubes [6][7][8]. Use of a silicone guide tube for repair of nerve gaps less than 10 mm presents little problem [9]. However, for longer nerve defects, it is necessary to employ biodegradable artificial nerve conduits. ...
The mechanical properties of nerve guide tubes must be taken into consideration when they are being developed. We previously reported the feasibility of using 50:50 tubes in a canine 40mm peroneal nerve defect model, where 50:50 represents the proportion of poly(L-lactic) acid (PLLA) and polyglycolic acid (PGA). The aim of the current study was to show that 50:50 tubes have suitable mechanical properties for repairing long nerve defects. Four types of nerve guide tubes made with PLLA to PGA fiber ratios of 100:0 (i.e. 100% PLLA) (100:0 tube), 50:50 (50:50 tube), 10:90 (10:90 tube), and 0:100 (0:100 tube) were designed and created using a tubular braiding machine. Their mechanical properties were examined in vitro (up to 16 weeks). In compression testing, 50:50 tubes had the highest normalized force value, followed in order by the 100:0, 10:90, and 0:100 tubes up to 8 weeks after immersion. From the point of view of biomechanics and bioresorbability, out of the 4 tube types tested, 50:50 tubes appeared to have the optimal mechanical properties for longer nerve defects.
Copyright © 2015 Elsevier Masson SAS. All rights reserved.
... To circumvent these limitations, conduits that can be synthesized or constructed with properties that are easily modulated, such as increasing mechanical strength, have been explored. The properties of numerous synthetic conduit materials such as poly-L-lactic acid [29], polylactic-co-glycolic acid copolymer [29], and poly (L-lactide-co-6-caprolactone) [30] have been explored to find an optimal mix of mechanical support and rate of conduit degradation. Polymer conduits are advantageous because their range of degradation, mechanical stability, and piezoelectric properties can be modulated to benefit nerve regeneration. ...
Tissue engineering has been defined as "an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function or a whole organ". Traumatic peripheral nerve injury resulting in significant tissue loss at the zone of injury necessitates the need for a bridge or scaffold for regenerating axons from the proximal stump to reach the distal stump.
A review of the literature was used to provide information on the components necessary for the development of a tissue engineered peripheral nerve substitute. Then, a comprehensive review of the literature is presented composed of the studies devoted to this goal.
Extensive research has been directed toward the development of a tissue engineered peripheral nerve substitute to act as a bridge for regenerating axons from the proximal nerve stump seeking the distal nerve. Ideally this nerve substitute would consist of a scaffold component that mimics the extracellular matrix of the peripheral nerve and a cellular component that serves to stimulate and support regenerating peripheral nerve axons.
The field of tissue engineering should consider its challenge to not only meet the autograft "gold standard" but also to understand what drives and inhibits nerve regeneration in order to surpass the results of an autograft.
... Synthetic tubular scaffolds have similar advantages to natural scaffolds but additionally provide mechanical and structural control [86]. In the recent past, several guidance techniques using artificial nerve conduits have been developed to guide nerve regeneration towards the distal stump [87]. The isolated environment provided by guidance channels helps confinement and concentrate neurotrophic factors that are released by supporting cells while protecting the axons against collapse and invasion from immune cells [82]. ...
Biodegradable and biocompatible poly(amidoamine)-(PAA-) based hydrogels have been considered for different tissue engineering applications. First-generation AGMA1 hydrogels, amphoteric but prevailing cationic hydrogels containing carboxylic and guanidine groups as side substituents, show satisfactory results in terms of adhesion and proliferation properties towards different cell lines. Unfortunately, these hydrogels are very swellable materials, breakable on handling, and have been found inadequate for other applications. To overcome this problem, second-generation AGMA1 hydrogels have been prepared adopting a new synthetic method. These new hydrogels exhibit good biological properties in vitro with satisfactory mechanical characteristics. They are obtained in different forms and shapes and successfully tested in vivo for the regeneration of peripheral nerves. This paper reports on our recent efforts in the use of first-and second-generation PAA hydrogels as substrates for cell culturing and tubular scaffold for peripheral nerve regeneration.
... However, the main concern regarding the clinical employment of nonabsorbable synthetic material in humans is the occurrence of complications caused by local fibrosis, triggered by the implanted material ( Merle, Dellon, Campbell, & Chang, 1989). Therefore, the second generation of nerve guides has been focused on bioabsorbable tubes that have been tested both experimentally and in clinical practice (Dellon & Mackinnon, 1988; Luis et al., 2007; Mackinnon & Dellon, 1990a, 1990b Meek et al., 1999; Navarro et al., 1996; Nicoli Aldini et al., 1996; Robinson et al., 1991; Tountas et al., 1993; ValeroCabre et al., 2001; Yannas & Hill, 2004; Young, Wiberg, & Terenghi, 2002). Nerve conduits made of polyglycolic acid were shown to be effective for restoring nerve defects (Mackinnon & Dellon, 1990a) and approved by the FDA for use in humans. ...
Nerve repair is no more regarded as merely a matter of microsurgical reconstruction. To define this evolving reconstructive/regenerative approach, the term tissue engineering is being increasingly used since it reflects the search for interdisciplinary and integrated treatment strategies. However, the drawback of this new approach is its intrinsic complexity, which is the result of the variety of scientific disciplines involved. This chapter presents a synthetic overview of the state of the art in peripheral nerve tissue engineering with a look forward at the most promising innovations emerging from basic science investigation. This review is intended to set the stage for the collection of papers in the thematic issue of the International Review of Neurobiology that is focused on the various interdisciplinary approaches in peripheral nerve tissue engineering.
... A wide range of materials has been developed for use as nerve guidance channel which were divided into three groups [4][5][6][7][8][9]. The first was undegradable nerve graft that silicone tubes were one of the most common materials because of its inert and elastic properties. ...
The thermal and degradable properties of carbodiimide (EDC) or glutaraldehyde (GTA) cross-linked gelatin membranes have been investigated in order to evaluate the effects of different concentrations of two kinds of cross-linking reagent on the stability of membranes. In the thermogram recorded from a gelatin membrane cross-linked with EDC solution, the endothermic peak of 0.8% EDC cross-linking gelatin was centered at about 61°C that was higher than other samples treated with EDC solutions. Denaturation temperature (Td) of gelatin samples increased on increasing EDC concentration (0.2% to 0.8%), in agreement with the simultaneous increased of the extent of cross-linking. But increasing GTA concentration from 0.05% to 0.6%, the Td values of gelatin samples were decreased from 66.2°C to 56.3°C . In addition, two endothermic peaks were observed in 0.4% and 0.6% GTA cross-linking groups because of the GTA concentration was too high to complete cross-linking reaction. Therefore, partial of gelatin membrane was cross-linked completely but others were not. In the thermogravimetric analysis, the proportion of cracking endothermic peak of 0.6% GTA cross-linking gelatin (g15G0.6) was higher than the peak of 0.6% EDC cross-linking gelatin (g15C0.6). Therefore, g15G0.6 cracked to smaller molecules has to absorb more calorific capacity than g15C0.6. The increase in the strength of covalent binding on increasing the proportion of endothermic peak was evident. The results of degradable rate were in agreement with the lower concentration of cross-linked reagent the faster degraded rate of gelatin membrane. The MTT assay showed that 15% gelatin cross-linked by 0.8% EDC has the least cytotoxicity, and cell activity of this group was similar to control group (blank dish). As the concentration of GTA in gelatin membranes was down to 0.05% or 0.1% the cell viability was returned to approach the value of control group.
... [36] In the recent past, several guidance techniques using artificial nerve conduits have been developed to guide nerve regeneration towards the distal stump. [37,38] The isolated environment provided by guidance channels helps confine and concentrate neurotrophic factors that are released by supporting cells while protecting the axons against collapse and invasion from immune cells. [31] The use of guidance channels eliminates functional loss at the donor site, a condition that is commonly associated with the use of autografts. ...
http://doi.wiley.com/10.1002/adma.v21:32/33
Bridging peripheral nerve gaps without the use of autografts has significant clinical importance. But in order to rationally design novel scaffolds, a good understanding of the nerve regeneration process is vital. Appropriate amount of structural and chemical cues are required to stimulate the endogenous mechanisms of repair and functional recovery. Synthetic and natural materials present various opportunities to induce the growth of supporting cells as well as promote axon regeneration. An overview of tissue engineering strategies currently being explored that stimulate the different steps of the regenerative sequence is presented.
... Non-resorbable conduits remain as foreign bodies around the regenerated nerve and hence need to be removed by a second surgery. Resorbable tubes are gradually reabsorbed and hence eliminate the need for a second surgery thus showing a better perspective for clinical applications [5][6][7][8][9][10][11][12][13][14][15]. ...
For tissue engineering applications, the distribution and growth of cells on a scaffold are key requirements. The potential of biodegradable poly(l-lactide-co-glycolide) (PLGA) polymer with different microstructures, as scaffolds for nerve tissue engineering was investigated. In this study, an attempt was made to develop porous nanofibrous scaffolds by the electrospinning method. In this process, polymer fibers with diameters in the nanometer range are formed by subjecting a polymer fluid jet to a high electric field. Attempt was also made to develop microbraided and aligned microfiber scaffolds. A polymer film scaffold was made by solvent casting method. C17.2 nerve stem cells were seeded and cultured on all the four different types of scaffolds under static conditions for 3days. Scanning electron micrographs showed that the nerve stem cells adhered and differentiated on all the scaffolds and supported neurite outgrowth. Interesting observation was seen in the aligned microfiber scaffolds, where the C17.2 nerve stem cells attached and differentiated along the direction of the fibers. The size and shape of the cell-polymer constructs remained intact. The present study suggests that PLGA is a potential scaffold for nerve tissue engineering and predicts the orientation and growth of nerve stem cells on the scaffold.
Peripheral nerve damage, such as that found after surgery or trauma, is a substantial clinical challenge. Much research continues in attempts to improve outcomes after peripheral nerve damage and to promote nerve repair after injury. In recent years, low-intensity pulsed ultrasound (LIPUS) has been studied as a potential method of stimulating peripheral nerve regeneration. In this review, the physiology of peripheral nerve regeneration is reviewed, and the experiments employing LIPUS to improve peripheral nerve regeneration are discussed. Application of LIPUS following nerve surgery may promote nerve regeneration and improve functional outcomes through a variety of proposed mechanisms. These include an increase of neurotrophic factors, Schwann cell (SC) activation, cellular signaling activations, and induction of mitosis. We searched PubMed for articles related to these topics in both in vitro and in vivo animal research models. We found numerous studies, suggesting that LIPUS following nerve surgery promotes nerve regeneration and improves functional outcomes. Based on these findings, LIPUS could be a novel and valuable treatment for nerve injury-induced erectile dysfunction.
Representative biodegradable-polymers are assayed to clarify the property when used as the materials for the nerve regeneration using the midbrain cell differentiation systems. As for polyglycolic acid [PGA], both the proliferation and differentiation of the midbrain cells were dose-dependently inhibited by PGA3000(Mw=3000). Poly(L-lactic acid)[PLLA]5000 (Mw=5000)showed slightly inhibitory effects on the proliferation and differentiation. In the case of the poly (L-lactic acid-co- ε -caprolactone)25 10000[P(LA-CL)25 10000] (Mw=10000), the differentiation was inhibited at 7.5,μg/ml to the levels of about 50% of the controls. But, P(LA-CA)50 18000 (Mw=18000) showed weakly inhibitory action on the differentiation of midbrain cells in comparison with P(LA-CA)2510000. The inhibitory activity of these polymers on neuronal cell differentiation were in the following order: P(LA-CA)2510000 > PGA3000> P(LA-CA)50 18000= PLLA5000. The catalyst of SnCl2 showed the strongest inhibitory action on the midbrain cell differentiation among test chemicals.
Introducion. Tissue engineering holds great promise for nerve replacement and restoration. The present study evaluated the efficacy of utilizing poly-DL-lactic-co-glycolic acid (PLGA) formed tubes through an extrusion process for peripheral nerve regeneration.
Material and Methods. Conduits were manufactured by dissolving 75:25 PLGA in methylene chloride, and salt crystals (150 and 300 µm) were added to the polymer solution. The formed suspension was allowed to evaporate, and the resulting PLGA/salt composite disks were cut, placed into a piston extrusion tool, and heated to 250 °C. After heating, the PLGA/salt composite was extruded to form a tube with an inner diameter of 1.6 mm and an outer diameter of 3.2 mm. Twenty Sprague Dawley (250 g) rats were anesthetized and had the 12-mm PLGA conduits interposed into the right sciatic nerve using 10-0 nylon sutures under microsurgical technique. Functional evaluation was performed monthly by walking track analysis. At 16 and 12 weeks, electrical conduction was performed and sections of the proximal, grafted, and distal nerve were harvested for histomorphometric analysis.
Results. All conduits remained flexible, allowing mobility of the rat extremity without breakage. No severe inflammatory reaction could be identified, and no neuromas were apparent clinically. Evaluation of the Sciatic Functional Index demonstrated improved functional recovery, noting muscle reinnervation; however, no electrical conduction could be elicited. Histomorphology demonstrated axonal migration and nerve tissue advancement through the entire conduit and into the distal nerve stump at 12 weeks. The number of axons/mm2 and nerve fiber density in the distal nerve was 5793 and 0.2231, respectively.
Conclusion. Each year, the prolonged recovery from traditionally treated nerve injuries results in millions of dollars in lost revenue and increased compensation benefits. The proposed methodology for peripheral nerve restoration described herein has the potential to lead to more cost-effective and less morbid strategies for nerve replacement.
Despite recent efforts, there is still no clinically attractive alternative to nerve or vein autografts for repair of peripheral nerve defects. Much research is being devoted to the creation of the optimum nerve guidance channel, which will most likely incorporate multiple forms of stimuli for the regenerating nerve. The synthesis of additional novel and interactive biomaterials will open many doors for tissue engineering efforts in the nervous system. Biotechnology will also play a larger role, either by incorporation of cells genetically engineered to secrete neurotrophic or survival factors, or by direct incorporation of specifically tailored recombinant peptides or proteins (for example, adhesive ligand sequences, growth factors, enzyme pockets, and catalytic or inhibitory antibody fragments). In addition, drug delivery technology will become more critical for the design of the ideal nerve guidance channel (NGC). Techniques by which a series of bioactive molecules could be released over time in sequence with stages of regeneration may ultimately enhance repair in the PNS (peripheral nervous system), and potentially even in the CNS (central nervous system). In addition, more quantitative and uniform methods of analyzing regeneration need to be realized. Quantitative molecular analyses must be conducted in parallel with more phenomenological studies, so that ultimately, mechanistic models can be developed to make a priori predictions based on the biological responses of the regenerating nerve to stimulatory and inhibitory cues.
The high outflow permeability of the nerve conduit used to emit the drained waste generated from the traumatized host nerve stump is critical in peripheral nerve regeneration. Our earlier studies have established that asymmetric conduits fulfill the basic requirements for use as nerve guide conduits. In this study, two-ply structures were prepared by particulate leaching techniques to fabricate controllable asymmetric polycaprolactone (PCL) discs. Salt crystals (0 μm, < 37 μm and 100 μm) were utilized to form asymmetric PCL-00, PCL-037 and PCL-0100 discs. These PCL discs had the same crystallinity as pure PCL, which was determined by differential scattering calorimetry (DSC). The dynamic mechanical analysis (DMA) showed that the stress decreased with the adding of salt crystals. In the in vitro trial, C6 rat glial cells and L929 stromal cells were seeded on the macro- and micro-porous sides of an asymmetric disc, respectively. The disc was maintained within a designed co-culture system that simulated the repaired nerve conduit environment. The results for the PCL-037 disc indicated statistically significant proliferation of C6 cells and the inhibition of the division of L929 cells in cell numbers and lactate dehydrogenase (LDH) release, compared with the PCL-00 and PCL-0100 discs. In this work, particulate leaching and dip-coating techniques afforded promising methods for fabrication of controllable asymmetric PCL membranes. The directional transport characteristics were established to be extremely important to the design and development of optimal nerve guide conduits.
Porosity is a key parameter in the design of tissue engineering scaffolds, as bioactivity can be controlled and tailored to the synthesis of the target tissue by finely tuning the porous structure of the scaffolding biomaterial. This chapter discusses the effect of structural parameters, such as pore volume fraction, pore size and distribution, pore shape, pore interconnectivity and pore orientation, on the performance of sponge-like scaffolds, with a special focus on those directed to nerve regeneration.
In this chapter, we aim at providing an up-to-date review on nerve tissue engineering, focusing on both the peripheral and the central nervous systems (PNS and CNS, respectively). After introducing the pathophysiology of nerves and the social impact of nerve injuries, we overview the therapeutic approaches oriented toward inducing nerve regeneration, involving cellular, molecular, and scaffold-based strategies. A section is dedicated specifically to the PNS, with a critical focus on the actual therapeutic potential of experimental devices for the development of tissue-engineered medical products. A case study regarding the implementation of micropatterned collagen-based conduits in a clinical trial on PNS regeneration is also presented. Another section is dedicated to the ongoing research investigating the regenerative mechanisms of the CNS. In this context, spinal cord injury is assumed as a model lesion, for which complex tissue-engineered devices are being developed, at least in animal studies. With such a structure, this chapter is intended to provide a comprehensive, though not exhaustive, overview of nerve tissue engineering, which might be useful to students, researchers, clinicians, and biomedical entrepreneurs.
Biomaterials poly L-lactic acid (PLLA) and poly caprolactone (PCL) are the most studied in the area of bioresorbable materials. Among the main features that contribute to cell interaction, we have the specific surface chemistry, electrical, hydrophobicity and topography. Also, is observed the degradation time, porosity, biocompatibility with biological tissue, as well as the preparation of the most varied shapes and sizes. The practice of cell culture, aims to study the adhesion, migration, differentiation and cell proliferation using a given material or substance. However, few studies were performed using these biomaterials and the application of neuro2A cells. It is known that this cell type is derived from the embryonic neural crest cells, which originate in sympathetic neurons and have the characteristic of immortality, therefore, are excellent models in vitro assays. Accordingly, the present study evaluates the adhesion and proliferation of this cell line on the biopolymers poly caprolactone (PCL) and poly L-lactic acid (PLLA).
Soluble royal jelly protein is a candidate factor responsible for mammiferous cell proliferation. Major royal jelly protein 1 (MRJP1), which consists of oligomeric and monomeric forms, is an abundant proliferative protein in royal jelly. We previously reported that MRJP1 oligomer has biochemical heat resistance. Therefore, in the present study, we investigated the effects of several heat treatments (56, 65 and 96°C) on the proliferative activity of MRJP1 oligomer. Heat resistance studies showed that the oligomer molecular forms were slightly maintained until 56℃, but the molecular forms were converted to macromolecular heat-aggregated MRJP1 oligomer at 65℃ and 96℃. But, the growth activity of MRJP1 oligomer treated with 96°C was slightly attenuated when compared to unheated MRJP1 oligomer. On the other hand, the cell proliferation activity was preserved until 96℃ by the cell culture analysis of Jurkat cells. In contrast, those of IEC-6 cells were not preserved even at 56°C. The present observations suggest that the bioactive heat-resistance properties were different by the origin of the cells. The cell proliferation analysis showed that MRJP1 oligomer, but not MRJP2 and MRJP3, significantly increased cell numbers, suggesting that MRJP1 oligomer is the predominant proliferation factor for mammiferous cells.
We previously developed a biodegradable composite with potentially good biocompatibility composed by tricalcium phosphate and gluataraldehyde cross-linking gelatin (GTG) with good mechanical property feasible for surgical manipulation. The purpose of this study was to evaluate the feasibility of immobilizing nerve growth factor (NGF) onto the composite (GTG) with carbodiimide (GEN composite). Cultured Schwann cells were seeded onto the GTG and GEN composites. For comparison, GTG membrane soaked in NGF solution without carbodiimide (GN composite) as cross-linking agent was also used to culture Schwann cells. Cell morphology was observed by a scanning electron microscope. Cell survival, cytotoxicity and cellular metabolism on the NGF-grafted GTG membrane were assessed quantitatively in terms of cell protein content, leakage of cytosolic lactate dehydrogenase (LDH) activity and by the well-established MTT assay, respectively. The result of LDH study did not show significant difference among GTG, NGF-modified GTG and control group. This indicated that GTG composite, whether cross-linking with NGF or not, has little cytotoxic effect. Comparing the protein content and MTT assay among GEN, GN composite and control group, the data confirmed more attachment of Schwann cells on GEN composite. Although GTG cross-linking with NGF did not promote Schwann cell proliferation, the techniques we used in this study provided a method to fabricate a novel biomaterial incorporation of Schwann cells and covalently immobilized NGF.
Silicone rubber multiple-lumen (ML) nerve cuffs were used for side-by-side comparisons of the effectiveness of two varieties of nerve growth stimulants (collagen gel and a gel mixture of collagen, fibronectin, and laminin) for regenerating cables across a 15 mm gap in 10 adult Sprague-Dawley rats. The filling pattern of the six tubes of the multiple-lumen portion of the cuff alternated with the collagen gel and the gel mixture of collagen, fibronectin, and laminin. After an 8 week implantation period, 53% (32 of 60) of the 0.5 mm diameter lumens displayed successful cable regeneration for both material fillings. The ML cuff experiments demonstrate the ability to bridge a 15 mm gap in the sciatic nerve of the rat by 8 weeks for relatively small diameter conduits in ML cuffs loaded with two varieties of growth stimulants. A more advanced organization including a smaller acellular region fraction and a higher vascularity is seen in the cables from the mixture-filled lumens compared to those in the cables from the collagen-filled lumens.
The use of autologous sural nerve grafts is still the current gold standard for the repair of peripheral nerve injuries with wide substance losses, but with a poor rate of functional recovery after repair of mixed and motor nerves, a limited donor nerve supply, and morbidity of donor site. At present, tubulization through the muscle vein combined graft, is a viable alternative to the nerve autografts and certainly is a matter of tissue engineering still open to continuous development, although this technique is currently limited to a critical gap of 3 cm with less favorable results for motor function recovery. In this report, we present a completely new tubulization method, the amnion muscle combined graft (AMCG) technique, that consists in the combination of the human amniotic membrane hollow conduit with autologous skeletal muscle fragments for repairing the substance loss of peripheral nerves and recover both sensory and motor functions. In a series of five patients with loss of substance of the median nerve ranging 3–5 cm at the wrist, excellent results graded as S4 in two cases, S3+ in two cases, and S3 in one case; M4 in four cases and M3 in one case were achieved. No iatrogenic damage due to withdrawal of a healthy nerve from donor site was observed. This technique allows to repair extensive loss of substance up to 5 cm with a good sensory and motor recovery. The AMCG thus may be considered a reasonable alternative to traditional nerve autograft in selected clinical conditions. © 2014 Wiley Periodicals, Inc. Microsurgery, 2014.
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.
After injury to the peripheral nervous system, axons from regenerating nerve cells must reach their innervation target to restore function. Polymeric substrates are currently being evaluated as nerve guides to enhance recovery after peripheral nerve injury. Degradable organic polymer substrates are highly suitable materials as matrices for tissue engineering because they can be specifically designed to serve as scaffolds then be absorbed by the body leaving only native tissue. Protein patterns on polymeric nerve guides may help maximize functional repair after injury because chemical cues can direct cellular components to their intended targets. Using microcontact printing techniques, protein stripes were patterned onto several different degradable polymeric substrates including poly(caprolactone), poly(caprolactam) and poly(3-hydroxybutyrate). The fluorescently tagged protein micro-patterns were visualized by confocal scanning laser fluorescence microscopy. The micropatterned polymer substrates were evaluated for their ability to direct attachment and alignment of Schwann cells (a cellular component of the peripheral nervous system).
Polymers are being extensively investigated to help facilitate nerve regeneration. Entubulization methods involving polymers where a conduit is used to connect the nerve endings has great potential as a repair method for peripheral nerve regeneration. The conduit allows for neurotropic and neurotrophic communication between the nerve stumps and provides physical guidance for the regenerating axons similar to the grafts. The closely fitting tubes facilitate axonal regeneration by inducing rapid development of a highly organized capsule that isolates the repair site and guides and aligns endoneurial components. Entubulization minimizes unregulated axonal growth at the site of injury by providing a distinct environment, and allows for trophic factors emitted from the distal stump to reach the proximal segment, which enhances physiological conditions for nerve regeneration. The spatial cues also induce a change in tissue architecture, with the cabling of cells within the microconduit. The conduits can also be environmentally enhanced with chemical stimulants like laminin and nerve growth factor (NGF), biological cues such as from Schwann cells and astrocytes, the satellite cells of the peripheral and central nervous systems, and lastly, physical guidance cues.
To compare a processed nerve allograft, laminin derived peptide incorporated nerve conduit, and autograft in terms of electrodiagnostic testing and nerve histomorphometry for peripheral nerve regeneration in a rabbit sciatic nerve defect model.
In the United States more than 200 000 people per year are treated for severe peripheral nerve injuries that require surgical intervention. Functional recovery of motor and sensory capability is limited after autografting, the most common surgical intervention for severe peripheral nerve injuries. The process of peripheral nerve regeneration has been studied extensively in a variety of animal models using a tubular conduit. This model has been used to generate a large base of data from a wide variety of experimental devices; however, this data has not been analyzed comparatively due to a lack of standardization of experimental conditions, assays, and reported measures of the quality of regeneration. As a result, progress in understanding conditions for optimal nerve regeneration has been stunted and the optimal characteristics for such an implant have not been identified. So while tubulation repair of a transected peripheral nerve presents an attractive alternative to autograft, it has not yet shown the ability to satisfactorily restore lost function. In this article, we provide an overview of mammalian wound healing following severe injury, the physiology of the peripheral nervous system, the standardized wound models used to study peripheral nerve regeneration, and the critical axon elongation criteria and how it can be used to directly compare results from dissimilar studies. We complete this review article with a description of the critical features of tubular implants used to induce peripheral nerve regeneration that can be optimized in order to improve the quality of regeneration.
This study uses a critical realist perspective to investigate relations between social constructions and the dynamics of nature. The material metabolism of the modern city is based on the redeployment of the processes of nature. This redeployment provides energy for anabolic processes in which complex social and physical hybrids (heating, lighting, transportation, communication, water-supply systems and climate-controlled micro-environments) are built from simpler structures. Massive energy flows of nature can, however, confront the city, unleashing catabolic reactions in which complex social and physical hybrids are broken down to simpler ones. This case-study of the 1998 ice storm in north-eastern North America documents the learning that occurs as a result of nature's overwhelming energy flows destroying the essential infrastructures of modern urban life. This extreme weather event knocked out for an unusually long period the electrical transmission system that provides the energy for a metropolitan area situated in a dark, frigid environment, and thereby produced the most costly disaster in Canada's history.
Electrospinning has emerged as one of the most elegant and versatile processes to fabricate fibers of micron and submicron diameters from a wide range of polymers. Biodegradable polymeric electrospun nanofiber matrices are attracting significant attention for various biomedical applications including tissue engineering. Biodegradable polyphosphazenes constitute a unique class of polymers with an inorganic backbone of nitrogen and phosphorous atoms with suitable organic side groups. The objective of the present study was to develop nanofibers from a biodegradable and biocompatible polyphosphazene, specifically poly[bis(ethyl alanato)phosphazene] (PNEA) by electrospinning. The effect of a range of process parameters such as the nature of solvents, concentration of the solution, applied electric potential, needle to target distance and flow rate of the polymer solution on the morphology, and diameter of the electrospun fibers were investigated. PNEA fibers spun using 9% (w/v) of polymer concentration, an electrical potential of 15 kV, a working distance of 30 cm, and a flow rate of 2 mL/hr resulted in bead/defect free nanofibers having fiber diameter of 331 ± 108 nm. These biodegradable and biocompatible polyphosphazene nanofiber matrices could find a number of biomedical applications including tissue engineering and drug delivery.
Nanotechnology is an area receiving increasing attention as progress is made towards tailoring the morphology of polymeric biomaterial for a variety of applications. In the present study an attempt was made to electrospin poly(L-lactide-co-glycolide) biodegradable polymer nanofibres. In this process, polymer fibres with diameters down to the nanometre range are formed by subjecting a fluid jet to a high electric field. The nanofibres were collected on to a rotating Teflon mandrel and fabricated to tubes or conduits, to function as nerve guidance channels. The feasibility of in vivo nerve regeneration was investigated through several of these conduits. The biological performance of the conduits were examined in the rat sciatic nerve model with a 10 mm gap length. After implantation of the nanofibre nerve guidance conduit to the right sciatic nerve of the rat, there was no inflammatory response. One month after implantation five out of eleven rats showed successful nerve regeneration. None of the implanted tubes showed tube breakage. The nanofibre nerve guidance conduits were flexible, permeable and showed no swelling. Thus, these new poly(L-lactide-co-glycolide) nanofibre conduits can be effective aids for nerve regeneration and repair. Improvements could be done by impregnating nerve growth factors or Schwann cells and may lead to clinical applications.
Future surgical strategies to restore neurological function in the damaged human spinal cord may involve replacement of nerve tissue with cultured Schwann cells using biodegradable guiding implants. We have studied the in vitro and in vivo degradability of various aliphatic polyesters as well as their effects on rat Schwann cells in vitro and on spinal cord tissue in vivo. In vitro, cylinders made of poly(D,L-lactic-co-glycolic acid) 50:50 (PLA25GA50) started to degrade at 7 days, compared with 28 days for cylinders made of poly(D,L-lactic acid) (PLA50). This faster degradation of PLA25GA50 was reflected by a much higher absorption of water. In vivo, after implantation of PLA25GA50 or PLA50 cylinders between the stumps of a completely transected adult rat spinal cord, the decrease in molecular weight of both polymers was similar to that found in vitro. In vitro degradation of poly(L-lactic acid) (PLA100) mixed with increasing amounts of PLA100 oligomers also was determined. The degradation rate of PLA100 mixed with 30% oligomers was found to be similar to that of PLA50. In vitro, PLA25GA50 and the breakdown products had no adverse effect on the morphology, survival, and proliferation of cultured rat Schwann cells. In vivo, PLA25GA50 cylinders were integrated into the spinal tissue 2 weeks after implantation, unlike PLA50 cylinders. At all time points after surgery, the glial and inflammatory response near the lesion site was largely similar in both experimental and control animals. At time points later than 1 week, neurofilament-positive fibers were found within PLA25GA50 cylinders or the remains thereof. Growth-associated protein 43, which is indicative of regenerating axons, was observed in fibers in the vicinity of the injury site and in the remains of PLA25GA50 cylinders. The results suggest that poly(alpha-hydroxyacids) are likely candidates for application in spinal cord regeneration paradigms involving Schwann cells.
In peripheral nerve reconstruction, various procedures are used. One of the procedures that received the most interest in the past decade is the tubulization technique for small nerve gaps. A disadvantage in the use of non-biodegradable tubes is that the material often has to be removed owing to its mechanical properties. Some investigators, in exploring the use of collagen tubes, being a natural biodegradable material, found either allogenicity or xenogenicity and immune responses that may inhibit nerve regeneration. Processed porcine collagen (PPC) is a new inert and biodegradable material that has a favorable effect on wound healing, as demonstrated by experiments on other tissues. The aim of our study was to compare the healing of nerve sutures with PPC tubes with conventional end-to-end sutures. In our experiments, we reconstructed the saphenous nerves of 27 rabbits. In series 1 (n = 12) and 2 (n = 12), PPC tubes were slid over an end-to-end nerve suture without or with a 10-mm nerve gap, respectively. In series 3 (n = 12), conventional suturing was performed in the collateral saphenous nerves of the animals of series 1. Epineurial suturing was performed. Three other non-operated saphenous nerves served as controls. The healing was studied after 3, 6, and 12 months in sections stained by monoclonal antibodies and by conventional histologic staining. Morphometric analysis of the regenerating axons was done by using confocal scanning laser microscopy (CLSM). Data analysis was carried out using a software program especially developed for this purpose. All results were evaluated statistically. Our results showed that during the healing period in the distal nerve stump, the number of axons of the PPC procedure with a 10-mm gap was significantly higher than that in the procedure without a gap. At 12 months, the mean number of axons of all procedures was significantly lower than in the non-operated nerve, and the mean axon diameter in all distal stumps did not differ significantly from that of the non-operated nerve. In the distal nerve stump, the ratio of total axon area to total fascicle area in the PPC procedure with a gap was significantly higher than that in the conventional suturing procedure. After 12 months, there was no significant difference between the percentages of axon outgrowth of the PPC procedure without a gap, the conventional suturing procedure, and the non-operated nerve (100%). The percentage of axon outgrowth in PPC with a gap was significantly higher than in the other procedures. © 2001 Wiley-Liss, Inc. Microsurgery 21:84–95 2001
The omentum has several properties that are advantageous for neuronal sprouting and direction. We have therefore analyzed functional recovery following transection of rat sciatic nerve using omental graft to bridge the nerve defect. In group 1, a 25–30-mm nerve defect was produced and bridged with omental graft, whereas in group 2, an end-to-end repair was performed. The sciatic function index (SFI) was assessed at 2-week intervals until 8 weeks after surgery. Functional recovery was faster in group 1 than in group 2. After 8 weeks, SFI was improved significantly from −100% to −45% (± −4%) in group 1 (P < 0.001) compared to −72% ± −2% in group 2 (n = 10). Histologically, the omental graft contained more newly developed nerve fibers and less scar tissue than the end-to-end repair. Thus, omental graft appears to improve directional growth of regenerating axon sprouts and may be a means of treating peripheral nerve injury. © 2002 Wiley Periodicals, Inc. Muscle Nerve 26: 527–532, 2002
The purpose of this study was to determine whether 0.8–1 mA, 2 Hz of percutaneous electrical stimulation could affect the regeneration of a 10-mm gap of rat sciatic nerve created between the proximal and distal nerve stumps, which were sutured into silicone rubber tubes. Six weeks after implantation, though the group receiving the electrical stimulation had a lower success percentage of regeneration (57%) compared with the controls receiving no stimulation (70%), quantitative histology of the successfully regenerated nerves revealed that the mean values of the axon density, blood vessel number, blood vessel area, and percentage of blood vessel area in total nerve area in the group with the electrical stimulation were all significantly larger than those in the controls (p < 0.05). These results showed that the electrical stimulation could elicit rehabilitating effects on the regenerated nerves. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 57: 541–549, 2001
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
A 10 mm gap of rat sciatic nerve was created between the proximal and distal nerve stumps, which were sutured into silicone rubber tubes filled with an extracellular gel containing collagen, laminin and fibronectin. Empty silicone rubber tubes were used as controls. Six weeks after implantation, all extracellular elements were completely degraded and absorbed, and 90% of the animals from the extracellular gel group exhibited regeneration across the nerve gaps, whereas only 60% in the control group. Both qualitative and quantitative histology of the regenerated nerves revealed a more mature ultrastructural organization with 28% larger cross-sectional area and 28% higher number of myelinated axons in the extracellular gel group than the controls. These results showed that the gel mixture of collagen, laminin and fibronectin could offer a suitable growth medium for the regeneration of axons.
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.
The restricted capacity of the nervous system to regenerate calls for novel therapeutic concepts. We have tested biocompatible polylactide fibers as potential nerve guides that could bridge proximal nerve stumps and synaptic target regions after nerve lesion. Polylactides have the great advantage that they degrade and resorb after completion of regeneration. Material surface properties were optimized three-fold by oxygen plasma treatment, polyanion coating and the seeding of Schwann cells from rat sciatic nerve. Immunocytochemistry and scanning electron microscopy revealed that in vitro axonal outgrowth of dorsal root ganglia on two specifically synthesized lactide polymers can be greatly improved by these surface treatments. The approach aims to develop an ‘intelligent neuroprosthesis’ that in vivo facilitates directed axonal regrowth in the first place and disappears thereafter.
A synthetic biodegradable nerve guide was constructed of two polymeric layers: an inner microporous layer prepared from a copolymer of L-lactide and epsilon-caprolactone (pore size range 0.5-1 micron) and an outer microporous layer prepared from a polyurethane/poly(L-lactide) mixture (pore size range 30-70 microns). This nerve guide was used to bridge a 7 mm gap in the right sciatic nerve of rats. It enabled the sciatic nerve to regenerate across the gap, forming a new, well-defined nerve that effectively re-established the contact between the proximial and distal nerve end, as effective as an autograft.
Sciatic nerve regeneration through implanted silicone tubes was compared to allogenic nerve grafting in 30 adult female Sprague-Dawley rats. Regeneration was assessed at 10, 24, and 90 days post-transection. Axonal regrowth through the implanted neural prostheses was evaluated with electromyography and histologic examination.
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 study compared standard methods of nerve repair, epineurial or perineurial sutures with a technique termed fascicular tubulization using a biodegradable polyglycolic acid tube in a nonhuman primate model. Electrophysiologic analysis demonstrated that the percentage of proximal axons that conducted across the repair site did not significantly differ among the three techniques while epineurial suture repairs were associated with significantly longer conduction delays across the repair site compared with the other two techniques. Even though fascicular tubulization using the current polyglycolic acid tube resulted in regeneration equal to the currently perceived best suture repair technique, associated technical problems with the current tube design indicate that this fascicular tubulization technique cannot, at present, be considered as an alternative to present clinically used nerve suture techniques.
Rat sciatic nerve regeneration through three synthetic neural prostheses was compared with regeneration through nerve allografts. The synthetic prostheses were either nonpermeable nonabsorbable (Silastic), permeable absorbable (polyglactin mesh), or permeable nonabsorbable (polypropylene mesh). Animals were evaluated at 10, 24, and 90 days. Functional analysis of nerve regeneration was performed by noninvasive methods: electromyography and walking tracks. Nerve tissue was examined with routine histologic and immunofluorescent techniques. A compressive neuropathy developed with the use of the Silastic implant. A neutrophilic inflammatory infiltrate was consistently associated with implantation of the polyglactin mesh. A strong connective tissue response was noted around the polypropylene mesh. Early recovery of nerve function was seen with the Silastic implants, however, overall nerve function was best in the nerve allograft and polypropylene mesh groups. Polyglactin implantation increases the local inflammatory response and should not be used for nerve anastomoses. If Silastic entubulation is used, it should be removed between 24 and 90 days.
Microneurosurgical techniques to reconstruct nerve gaps with nerve grafts frequently fail to achieve excellent functional results and create donor-site morbidity. In the present study, 15 patients had gaps of 0.5 to 3.0 cm (mean 1.7 cm) in digital nerves reconstructed by one surgeon with a bioabsorbable polyglycolic acid (PGA) tube. A final evaluation of sensibility was done by a second surgeon at a mean postoperative interval of 22.4 months (range 11 to 32 months). These were all secondary reconstructions. The evaluation included a digital nerve block with local anesthetic for the intact (not reconstructed) digital nerve. Excellent functional sensation (moving two-point discrimination less than or equal to 3 mm and/or static two-point discrimination less than or equal to 6 mm) was present in 33 percent and good functional sensation (moving two-point discrimination of 4 to 7 mm and/or static two-point discrimination of 7 to 15 mm) in 53 percent of the digital nerve reconstructions. One patient with poor sensory recovery and one with no recovery were judged as functional failures (14 percent). Absence of pain at the site of reconstruction was judged by the patient to be excellent in 40 percent, good in 33 percent, and poor in 27 percent. We conclude that reconstruction of nerve gaps of up to 3.0 cm with a bioabsorbable PGA tube gives clinical results at least comparable to the classic nerve graft technique while avoiding donor-site morbidity.
The purpose of this study was to determine the efficacy of autogenous vein grafts as nerve grafts (AVNC) for bridging of small peripheral sensory nerve gaps as compared with direct repair and with conventional nerve grafting techniques (ANG). Patients with painful neuroma or segmental nerve injury of 3 cm were chosen as the test group. Those amenable to direct repair were classified as controls. Between 1982 to 1988, a total of 22 patients were enrolled in this study. A total of 34 nerves were repaired, 15 with a venous nerve conduit, 4 with a sural nerve graft, and 15 with direct repair. Significant symptom relief and satisfactory sensory function return were uniformly observed. The two-point discrimination measurements indicated superiority of direct repair and probably of conventional nerve grafting. However, the universally favorable patient acceptance and the return of measurable two-point discrimination indicates the effectiveness of autogenous vein grafts as nerve conduits when selectively applied to bridge a small nerve gap (less than or equal to 3 cm) on nonessential peripheral sensory nerves.
A large gap in peripheral nerve will not allow effective regeneration unless a grafting conduit is used to bridge the defect. Conventionally, nerve tissue has been used as such a conduit in nerve reconstruction; however, results from techniques using these grafts are often unsatisfactory. A number of recent investigations have indicated that nerve fibers will regenerate through a non-neural tube. The purpose of this review is: 1) to provide an overview of the various tubulation techniques previously reported for peripheral nerve gap repair; 2) to investigate new possibilities for enhancing the regenerative capacity of nerves following these tubulation techniques by drawing from technical innovations in microsurgery and recent progress in immunology and neurobiology. The interposed graft thus may perform a more positive role, not merely as a pathway for deregenerating axons, but as a source for neuronotrophic factors and neurite-promoting factors, which would nurture and guide the neurons and axons. Such modifications in graft materials may lead to clinical applications of tubulation of nerve defects that would result in an improvement in clinical results.
Three cases are reported to illustrate the potential danger of silicon-polymer intubulation of nerve for either nerve repair or following neurolysis. Since silicon-polymer intubulation of nerve is now a proven model for producing chronic nerve compression, its use clinically may be contraindicated where neural regeneration is the desired goal.
Sciatic nerve regeneration through implanted silicone tubes was compared to allogenic nerve grafting in 30 adult female Sprague-Dawley rats. Regeneration was assessed at 10, 24, and 90 days post-transection. Axonal regrowth through the implanted neural prostheses was evaluated with electromyography and histologic examination.
Polyglactin 910, a resorbable synthetic material, was used as a mesh-tube to bridge defects (7 to 9 mm in length) in a sectioned rabbit tibial nerve. After absorption of the mesh a new nerve sheath was formed which enclosed numerous minute fascicles of regenerating axons. The polyglactin tube influenced the direction taken by the regenerating axons and guided them into the distal segment. The tube also reduced the formation of neuromas and the growth of scar tissue from surrounding structures.
This study was performed to determine whether vein grafts might serve as a conduit for nerve regeneration. A 1 cm segment of sciatic nerve was removed bilaterally in 12 Sprague-Dawley rats. On one side the gap was not repaired, and on the other side a segment of femoral vein was used to bridge the nerve gap. Nerve conduction studies and necropsies were performed at intervals. Reconstitution of nerve trunk continuity and healing of plantar ulcers occurred only in the vein-grafted side. Histologic examination revealed orderly growth of nerve fibers within the lumen of the vein grafts as early as 1 month after repair. Most regenerating nerve fibers passed through the proximal junction in an orderly pattern and reached the distal stumps within 2 months after repair. Results of nerve conduction study at 4 months after operation demonstrated restoration of conduction through the vein-grafted sciatic nerves with muscle reinnervation. Nearly normal muscle fibers in the gastrocnemius on the repaired side were confirmed at necropsy. This study demonstrated that autogenous vein grafts can serve as a conduit for nerve regeneration in rodents.
The interest in developing a prosthesis that may be effective in nerve repair as an alternative to autologous grafts, promotes experimental investigations in order to improve the so called tubulization techniques. A review of the literature of the last 10 years is performed to draw an outline of the state of the research, pointing out three main topics: the animal model, the type of the conduit and the length of the repaired gap. The rat, the rabbit and non human primates are the species with which experimental models are most often fashioned for this purpose. Among the great number of investigated conduits, interesting perspectives are arrived at mainly by those obtained with biologic or degradable materials; until now, experimental nerve defects of 3 cm or less are better repaired with artificial guides while unsatisfactory results were reported for the repair of longer gaps. The introduction in the micro-environment of the conduit of neurotrophic substances represents a challenge for the future development of these investigations aimed at improving healing and obtaining nerve regeneration through extensive defects.
A copolymer of L-lactide and 6-caprolactone (50:50, w/w) was synthesized and characterized. The thermal behaviour of this material did not show any crystallinity for several months; only after more than 1 yr of aging at room temperature and, particularly, in the in vitro degradation tests did it partially crystallize. The values of tensile strength, percent elongation at break and elastic modulus were, respectively, 25 MPa, 490% and 3 MPa. Transparent, elastic nerve guides having inner diameter of 1.3 mm and wall thickness of 175 microns were prepared.
La tubulizzazione nella ricostruzione del sistema nervoso periferico: stato attuale della sperimentazione
- Nicoli Aldini
PTFE versus biological prosthesis to bridge a nerve gap: experimental evaluation
- Nicoli Aldini
Tubulization with preserved vein allografts for nerve repair
- Nicoli Aldini