A comparison of peripheral nerve repair using an absorbable tubulization device and conventional suture in primates

Low-intensity pulsed ultrasound for regenerating peripheral nerves: potential for penile nerve

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.

Efficacy of Silicone Conduit in the Rat Sciatic Nerve Repair Model: Journey of a Thousand Miles

Background

A lot of options have been tried for bridging the two ends of the injured nerves. Researchers have used decellularized nerve grafts, artificial materials and even nerve growth factors to augment functional recovery. These materials are either costly or inaccessible in developing world.

Objective

The study aimed to evaluate the efficacy of the silicone conduit in a rat sciatic nerve injury model.

Materials and Methods

24 healthy Sprague-Dawley (SD) rats (250-300 grams; 8-10 weeks) were used and right sciatic nerve was exposed; transected and re-anastomosed by two different methods in 16 rats. In control group, n = 8 (Group I) the sciatic nerve was untouched; Group II (reverse nerve anastomosis, n = 8): 1-centimeter of nerve was cut and re-anastomosed by using 10-0 monofilament suture; Group III (silicone conduit, n = 8) 1-centimeter nerve segment was cut, replaced by silicone conduit and supplemented by fibrin glue]. Evaluation of nerve recovery was done functionally (pain threshold and sciatic functional index) over 3 months and histologically and electron microscopically.

Results

Functional results showed a trend of clinical improvement in Group III and II but recovery was poor and never reached up to normal. Histopathological and electron microscopic results showed an incomplete axonal regeneration in Groups II and III. Psychological analyses showed that no outwards signs of stress were present and none of the rats showed paw biting and teeth chattering.

Conclusion

The silicone conduit graft may be an economical and effective alternative to presently available interposition grafts, however for short segments only.

The Median Nerve Injury Model in Pre-clinical Research - A Critical Review on Benefits and Limitations

The successful introduction of innovative treatment strategies into clinical practise strongly depends on the availability of effective experimental models and their reliable pre-clinical assessment. Considering pre-clinical research for peripheral nerve repair and reconstruction, the far most used nerve regeneration model in the last decades is the sciatic nerve injury and repair model. More recently, the use of the median nerve injury and repair model has gained increasing attention due to some significant advantages it provides compared to sciatic nerve injury. Outstanding advantages are the availability of reliable behavioural tests for assessing posttraumatic voluntary motor recovery and a much lower impact on the animal wellbeing. In this article, the potential application of the median nerve injury and repair model in pre-clinical research is reviewed. In addition, we provide a synthetic overview of a variety of methods that can be applied in this model for nerve regeneration assessment. This article is aimed at helping researchers in adequately adopting this in vivo model for pre-clinical evaluation of peripheral nerve reconstruction as well as for interpreting the results in a translational perspective.

In Vitro and In Vivo Effects of Ginkgo biloba Extract EGb 761 on Seeded Schwann Cells within Poly(DL-lactic acid-co-glycolic acid) Conduits for Peripheral Nerve Regeneration

This study investigated the effects of Ginkgo biloba (EGb 761) extract on seeded Schwann cells within poly(DL-lactic acid-co-glycolic acid) (PLGA) conduits by in vitro and in vivo trials for peripheral nerve regeneration. The seeding efficiency of Schwann cells in serum-deprived culture medium, which simulated the environment of mechanical trauma on an injured nerve site, was improved by adding different dosages of EGb 761 (0, 1, 10, 20, 50, 100, 200 mg/mL). The analytical results showed enhanced cell attachment and survival, reduced LDH release and increased MTT values, particularly in the range 10-100 mg/mL. The PLGA nerve conduits seeded with Schwann cells (6 103 cells) and filled with gelatin containing EGb 761 (0, 10, 50, 100 mg/mL) were implanted to 10-mm right sciatic nerve defects in rats. Autograft was performed as another control. Electromyography was assessed based on the motor unit action potential (MUAP) and fibrillation potential (Fib) at 2, 4, and 6 weeks during all periods. The specimens of the experimental and control groups were harvested for histological analysis at 6 weeks after surgery. The Fib was found to gradually decay, and the MUAP was found not to be present until 4 weeks after surgery. Meanwhile, the experimental groups were all statically better than the control group (without EGb 761) and autografts were observed at 6 weeks, especially at the concentration of 10 mg/mL, where there was higher amplitude of MUAP and a significantly larger number of myelinated axons. This study concluded that a proper concentration of EGb 761 (10-50 mg/mL) promoted seeding efficiency of Schwann cells in a tissue-engineered PLGA conduit. Addition of EGb 761 in Schwann cells-seeded conduit could increase the total number of myelinated axons in nerve regeneration and improve peripheral nerve functional recovery.

THE EVALUATION OF THERMAL PROPERTIES AND IN VITRO TEST OF CARBODIIMIDE OR GLUTARALDEHYDE CROSS-LINKED GELATIN FOR PC 12 CELLS CULTURE

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.

Functional recovery after implantation of artificial nerve grafts in the rat- a systematic review

Purpose

The aim of this study was to compare functional data of different nerve-gap bridging materials evaluated in rat experiments by means of a systematic review.

Materials and methods

A systematic review was conducted, searching MEDLINE, HTS and CENTRAL to identify all trials evaluating functional recovery of artificial nerve conduits in the rat model.

Results

There was a trend towards a favourable outcome of conduits coated with Schwann-cells compared to the plain synthetics. Histomorphometry, electrophysiology and muscle-weight correlated poorly with functional outcome.

Conclusion

Schwann-cell coated conduits showed promising results concerning functional recovery. Further standardization in outcome reporting is encouraged.

Role of Small Intestine Submucosa (SIS) as a Nerve Conduit: Preliminary Report

The goal of peripheral nerve repair is to successfully direct the regenerating fibers into the environment of the distal terminus with minimal loss of fibers at the suture line. Successful nerve repair is dependent on sensory, motor, and autonomic axons making appropriate connection with their distal terminus. The subsequent results are dependent on parameters such as the location and extent of the injury, appropriateness of realignment of the injured nerve, and the surgical technique. Peripheral nerve repair using autograft material has several shortcomings, including donor site morbidity, inadequate return of function, and aberrant regeneration. Recent peripheral nerve research has focused on the generation of synthetic conduits for nerve guidance. Small intestine submucosa (SIS) is a biological material that might better address those outcomes and improve regeneration. Its unique properties appear to offer several advantages. The SIS graft acts as a natural conduit between the proximal and distal nerves, provides a favorable growth environment, and appears to lack antigenicity. This preliminary study to evaluate the integrity of sciatic nerve repair was conducted over a period of 90 d. Distally directed growth of the proximal nerve was demonstrated histologically. Further investigations to demonstrate the extent and integrity of this regeneration are underway.

Electrospun micro- and nanofiber tubes for functional nervous regeneration in sciatic nerve transections

Background

Although many nerve prostheses have been proposed in recent years, in the case of consistent loss of nervous tissue peripheral nerve injury is still a traumatic pathology that may impair patient's movements by interrupting his motor-sensory pathways. In the last few decades tissue engineering has opened the door to new approaches;: however most of them make use of rigid channel guides that may cause cell loss due to the lack of physiological local stresses exerted over the nervous tissue during patient's movement. Electrospinning technique makes it possible to spin microfiber and nanofiber flexible tubular scaffolds composed of a number of natural and synthetic components, showing high porosity and remarkable surface/volume ratio.

Results

In this study we used electrospun tubes made of biodegradable polymers (a blend of PLGA/PCL) to regenerate a 10-mm nerve gap in a rat sciatic nerve in vivo. Experimental groups comprise lesioned animals (control group) and lesioned animals subjected to guide conduits implantated at the severed nerve stumps, where the tubular scaffolds are filled with saline solution. Four months after surgery, sciatic nerves failed to reconnect the two stumps of transected nerves in the control animal group. In most of the treated animals the electrospun tubes induced nervous regeneration and functional reconnection of the two severed sciatic nerve tracts. Myelination and collagen IV deposition have been detected in concurrence with regenerated fibers. No significant inflammatory response has been found. Neural tracers revealed the re-establishment of functional neuronal connections and evoked potential results showed the reinnervation of the target muscles in the majority of the treated animals.

Conclusion

Corroborating previous works, this study indicates that electrospun tubes, with no additional biological coating or drug loading treatment, are promising scaffolds for functional nervous regeneration. They can be knitted in meshes and various frames depending on the cytoarchitecture of the tissue to be regenerated. The versatility of this technique gives room for further scaffold improvements, like tuning the mechanical properties of the tubular structure or providing biomimetic functionalization. Moreover, these guidance conduits can be loaded with various fillers like collagen, fibrin, or self-assembling peptide gels or loaded with neurotrophic factors and seeded with cells. Electrospun scaffolds can also be synthesized in different micro-architectures to regenerate lesions in other tissues like skin and bone.

Nerve regeneration along bioengineered scaffolds

Tissue engineering has recently seen great advancements in many medical fields, including peripheral nerve reconstruction. In the rat median nerve model, we investigated nerve repair by means of bioengineered tissue scaffolds (muscle-vein-combined tubes) focusing on changes in the neuregulin-1/ErbB-receptor system which represents one of the main regulatory systems of axo-glial interaction in peripheral nerves. Repaired nerves were withdrawn at 5, 15, and 30 days postoperative and processed for morphological and retro-transcriptase polymerase chain reaction (RT-PCR) analysis. Results revealed an early and progressive increase in the expression of NRG1alpha isoform only, while the appearance of the beta isoform of NRG1, which is normally present in peripheral nerves, was delayed. In regards to ErbB2 and ErbB3 receptors, their expression increased progressively inside the muscle-vein-combined scaffolds, though with different kinetics. Taken together, these results suggest that variations in neuregulin-1/ErbB system activation play a key role in peripheral nerve regeneration along bioengineered muscle-vein-combined scaffolds. Since similar variations are also detectable in denervated skeletal muscles, it can be hypothesized that the existence of a NRG1's autocrine/paracrine trophic loop shared by both glial and muscle fibers could be responsible for the effectiveness of muscle-vein-combined conduits for repairing nerve defects.

Effects of unidirectional permeability in asymmetric poly(DL-lactic acid-co-glycolic acid) conduits on peripheral nerve regeneration: Anin vitro andin vivo study

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, the inflow characteristics of optimal nerve conduits were further examined using in vivo and in vitro trials. Various asymmetric poly(DL-lactic acid-co-glycolic acid) (PLGA) conduits were controlled by modifying precipitation baths using 0, 20, and 95% isopropyl alcohol, with high-porosity (permeability), medium-porosity (high outflow and low inflow), and low-porosity (permeability), respectively. In the in vitro trial, the Schwann cells and fibroblasts were seeded on either side of the asymmetric PLGA films in a newly designed coculture system that simulated the repaired nerve conduit environment. The results of the directional permeable films indicated the statistically significant proliferation of Schwann cells and the inhibition of the division of fibroblasts in lactate dehydrogenase release and inhibition of 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide (MTT) reduction, compared with the other films. In the in vivo trial, the PLGA conduits seeded with Schwann cells were implanted into 10 mm right sciatic nerve defects in rats. After 6 weeks, implanted conduits were harvested. Histological examination verified that directional permeable conduits had markedly more A-type and B-type myelin fibers in the midconduit and distal nerve. In this work, the directional transport characteristics were established as an extremely important factor to the design and development of optimal nerve guide conduits in peripheral nerve regeneration.

The effect of high outflow permeability in asymmetric poly(dl-lactic acid-co-glycolic acid) conduits for peripheral nerve regeneration

This study attempted to accelerate the peripheral nerve regeneration, using the high outflow rate of asymmetric poly(dl-lactic acid-co-glycolic acid) (PLGA) nerve conduits. Asymmetric PLGA nerve conduits of monomer ratio 85/15 were prepared by immersion-precipitation method to serve as possible materials. In this study, mandrels were immersed into a 20% (wt/wt) of PLGA/1,4-dioxane solution and precipitated in a non-solvent bath followed by freeze-drying. Different concentrations of isopropyl alcohol (95%, 40% and 20%) were used as precipitation baths where non-asymmetric (95%) and asymmetric (40% and 20%) conduits could easily form. The asymmetric nerve conduits that consisted of macrovoids on the outer layer, and interconnected micropores in the inner sublayer, possessed characters of larger outflow rate than inflow rate. The asymmetric conduits were implanted to 10mm right sciatic nerve defects in rats. Autografts, silicone and non-asymmetric PLGA conduits were performed as the control and the contrast groups. Implanted graft specimens of all groups were harvested for histological analysis at 4 and 6 weeks following surgery. The asymmetric PLGA conduits maintained a stable supporting structure and inhibited exogenous cells invasion during entire regeneration process. Asymmetric PLGA conduits were found to have statistically greater number of regenerated axons at the midconduit and distal nerve site of implanted grafts, as compared to the silicone and non-asymmetric groups at 4 and 6 weeks. Of interest was that the results of 4 weeks in asymmetric groups were better than the non-asymmetric groups at 6 weeks in number of axons. According to the results of permeability, the asymmetric structure in the conduit wall seemed to enhance the removal of the blockage of the waste drain from the inner inflamed wound in the early stage, which may have improved the efficacy of the peripheral nerve regeneration. The asymmetric structure could be adequately employed in the future as optimal nerve conduits in peripheral nerve regeneration.

Low-intensity-ultrasound-accelerated nerve regeneration using cell-seeded poly(D,L-lactic acid-co-glycolic acid) conduits: an in vivo and in vitro study

This study investigated the effects of low intensity ultrasound on seeded Schwann cells within poly(DL-lactic acid-co-glycolic acid) (PLGA) conduits by in vitro and in vivo trials for peripheral nerve regeneration. The possible differences in the ultrasonic effects when using biodegradable and non-biodegradable materials as the conduits were also studied, using silicone rubber tubes as comparisons. In the in vitro study, seeded Schwann cells were cultured in serum deprivation culture medium that simulated the environment of mechanical trauma on injury nerve site. After 12, 24, and 48 h, only the PLGA conduit groups exposed to 0.05 W/cm(2), 3 min/treatment of ultrasound exhibited decreased LDH release and increased MTT values compared to the sham groups. Based on the results of the in vitro experiment in LDH and MTT testing, the silicone conduits with seeded Schwann cells group was ignored in the in vivo study. The PLGA nerve conduits seeded with Schwann cells (9 x 10(3) cells) were implanted to 15-mm right sciatic nerve defects in rats. Each conduit received 12 ultrasonic treatment sessions over 2 weeks after 1 day of rest. Ultrasound was applied as follows: frequency, 1MHz; intensity, 0.3 W/cm(2) (SATP); treatment, 5 min/day. Implanted graft specimens were harvested for histological analysis at 8 weeks following surgery. PLGA groups (with and without Schwann cells) treated with pulsed ultrasonic stimulation were found to have significantly greater number and area of regenerated axons at the mid-conduit of implanted grafts, as compared to the sham groups. Ultrasonic stimulation on silicone groups was found to induce a mass of fibrous tissues that covered the nerve conduits and retarded axon regeneration.

Anin vivo study of tricalcium phosphate and glutaraldehyde crosslinking gelatin conduits in peripheral nerve repair

In order to modulate the mechanical properties of gelatin, we previously developed a biodegradable composite composed by tricalcium phosphate and glutaraldehyde crosslinking gelatin (GTG) feasible for surgical manipulation. In this study, we evaluated the in vivo applications of GTG conduit for peripheral nerve repair. The effect of sciatic nerve reconstruction was compared between resorbable permeable GTG conduits and durable impermeable silicone tubes. Traditional methods of assessing nerve recovery following peripheral nerve repair including histomorphometric and electrophysiologic features were conducted in our study. In addition, autotomy score and sciatic function index (SFI) in walking tract analysis were used as additional parameters for assessing the return of nerve function. Twenty-four weeks after sciatic nerve repair, the GTG conduits were harvested. Microscopically, regeneration of nerves was observed in the cross-section at the mid portion of all implanted GTG conduits. The cross-sectional area of regenerated nerve of the GTG group was significant larger than that of the silicone group. In the compound muscle action potentials (CMAP), the mean recovery index of CMAP amplitude was 0.24 +/- 0.02 for the silicone group, 0.41 +/- 0.07 for the GTG group. The mean SFI increased with time in the GTG group during the evaluation period until 24 weeks. Walking tract analysis showed a higher SFI score in the GTG group at both 12 and 24 weeks. The difference reached a significant level at 24 weeks. Thus, the histomorphometric, electrophysiologic, and functional assessments demonstrate that GTG can be a candidate for peripheral nerve repair.

Nerve repair by means of tubulization: literature review and personal clinical experience comparing biological and synthetic conduits for sensory nerve repair

Nerve repair is usually accomplished by direct suture when the two stumps can be approximated without tension. In the presence of a nerve defect, the placement of an autologous nerve graft is the current gold standard for nerve restoration. However, over the last 20 years, an increasing number of research articles reported on the use of non-nervous tubes (tubulization) for repairing nerve defects. The clinical employment of tubes (both biological and synthetic) as an alternative to autogenous nerve grafts is mainly justified by the limited availability of donor tissue for nerve autografts and the related morbidity. In addition, tubulization was proposed as an alternative to direct nerve sutures in order to create optimal conditions for nerve regeneration over the short empty space intentionally left between two nerve stumps. This paper outlines recent important advances in this field. Different tubulization techniques proposed so far are described, focusing in particular on studies that reported on the employment of tubes with patients. Our personal clinical experience on tubulization repair of sensory nerve lesions (digital nerves), using both biological and synthetic tubes, is presented, and the clinical results are compared. In our case series, both types of tubes led to good clinical results. Finally, we speculate about the prospects in the clinical application of tubulization for peripheral nerve repair.

Peripheral nerve regeneration by microbraided poly(L-lactide-co-glycolide) biodegradable polymer fibers

Tiny tubes with fiber architecture were developed by a novel method of fabrication upon introducing some modification to the microbraiding technique, to function as nerve guide conduit and the feasibility of in vivo nerve regeneration was investigated through several of these conduits. Poly(L-lactide-co-glycolide) (10:90) polymer fibers being biocompatible and biodegradable were used for the fabrication of the conduits. The microbraided nerve guide conduits (MNGCs) were characterized using scanning electron microscopy to study the surface morphology and fiber arrangement. Degradation tests were performed and the micrographs of the conduit showed that the degradation of the conduit is by fiber breakage indicating bulk hydrolysis of the polymer. Biological performances of the conduits were examined in the rat sciatic nerve model with a 12-mm gap. After implantation of the MNGC to the right sciatic nerve of the rat, there was no inflammatory response. One week after implantation, a thin tissue capsule was formed on the outer surface of the conduit, indicating good biological response of the conduit. Fibrin matrix cable formation was seen inside the MNGC after 1 week implantation. One month after implantation, 9 of 10 rats showed successful nerve regeneration. None of the implanted tubes showed tube breakage. The MNGCs were flexible, permeable, and showed no swelling apart from its other advantages. Thus, these new poly(L-lactide-co-glycolide) microbraided conduits can be effective aids for nerve regeneration and repair and may lead to clinical applications.

The effects of low-intensity ultrasound on peripheral nerve regeneration in poly(DL-lactic acid-co-glycolic acid) conduits seeded with Schwann cells

This study attempted to improve the efficacy of peripheral nerve regeneration, using the stimulus of low-intensity ultrasound (US) on poly(DL-lactic acid-co-glycolic acid) (PLGA) nerve guidance conduits seeded with Schwann cells. The possible differences between the ultrasonic effects of biodegradable and nonbiodegradable materials used as conduits were also investigated, by comparison with a group of silicone conduits. The PLGA conduits were seeded with or without Schwann cells (6 x 10(3) cells). All conduits were implanted 10 mm into right sciatic nerve defects in rats and underwent 12 ultrasonic treatment sessions over 2 weeks. Ultrasound was applied at a frequency of 1 MHz and an intensity of 0.2 W/cm2 spatial average temporal peak (SATP) for 5 min/day. Histologic analysis was used to evaluate the recovery of the nerve after 6 weeks. Ultrasonically stimulated animals, especially those whose PLGA conduits, seeded with Schwann cells, exhibited considerably more myelinated axons with a larger mean area at the midconduit of the implanted grafts than those in any other group. Ultrasonic stimulation of a silicone conduit induced the generation of mass fibrous tissues that covered the nerve conduits and retarded axon regeneration. These results showed that ultrasonic stimulation may directly stimulate the seeded Schwann cells within the PLGA conduits to regenerate nerves. Nevertheless, the applying of US may not allow incorporation with the silicone rubber as a material from which to form nerve guidance conduits.

Factors that influence peripheral nerve regeneration: an electrophysiological study of the monkey median nerve

Regeneration in the peripheral nervous system is often incomplete though it is uncertain which factors, such as the type and extent of the injury or the method or timing of repair, determine the degree of functional recovery. Serial electrophysiological techniques were used to follow recovery from median nerve lesions (n = 46) in nonhuman primates over 3 to 4 years, a time span comparable with such lesions in humans. Nerve gap distances of 5, 20, or 50mm were repaired with nerve grafts or collagen-based nerve guide tubes, and three electrophysiological outcome measures were followed: (1) compound muscle action potentials in the abductor pollicis brevis muscle, (2) the number and size of motor units in reinnervated muscle, and (3) compound sensory action potentials from digital nerve. A statistical model was used to assess the influence of three variables (repair type, nerve gap distance, and time to earliest muscle reinnervation) on the final recovery of the outcome measures. Nerve gap distance and the repair type, individually and concertedly, strongly influenced the time to earliest muscle reinnervation, and only time to reinnervation was significant when all three variables were included as outcome predictors. Thus, nerve gap distance and repair type exert their influence through time to muscle reinnervation. These findings emphasize that factors that control early axonal outgrowth influence the final level of recovery attained years later. They also highlight that a time window exists within which axons must grow through the distal nerve stump in order for recovery after nerve lesions to be optimal. Future work should focus on interventions that may accelerate the growth of axons from the lesion site into the distal nerve stump.

Processed porcine collagen tubulization versus conventional suturing in peripheral nerve reconstruction: An experimental study in rabbits

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.

Collagen-GAG substrate enhances the quality of nerve regeneration through collagen tubes up to level of autograft

Peripheral nerve regeneration was studied across a tubulated 10-mm gap in the rat sciatic nerve using histomorphometry and electrophysiological measurements of A-fiber, B-fiber, and C-fiber peaks of the evoked action potentials. Tubes fabricated from large-pore collagen (max. pore diameter, 22 nm), small-pore collagen (max. pore diameter, 4 nm), and silicone were implanted either saline-filled or filled with a highly porous, collagen-glycosaminoglycan (CG) matrix. The CG matrix was deliberately synthesized, based on a previous optimization study, to degrade with a half-life of about 6 weeks and to have a very high specific surface through a combination of high pore volume fraction (0.95) and relatively small average pore diameter (35 microm). Nerves regenerated through tubes fabricated from large-pore collagen and filled with the CG matrix had significantly more large-diameter axons, more total axons, and significantly higher A-fiber conduction velocities than any other tubulated group; and, although lower than normal, their histomorphometric and electrophysiological properties were statistically indistinguishable from those of the autograft control. Although the total number of myelinated axons in nerves regenerated by tubulation had reached a plateau by 30 weeks, the number of axons with diameter larger than 6 microm, which have been uniquely associated with the A-fiber peak of the action potential, continued to increase at substantial rates through the completion of the study (60 weeks). The kinetic data strongly suggest that a nerve trunk maturation process, not previously reported in studies of the tubulated 10-mm gap in the rat sciatic nerve, and consisting in increase of axonal tissue area with decrease in total tissue area, continues beyond 60 weeks after injury, resulting in a nerve trunk which increasingly approaches the structure of the normal control.

Orientation of cell adhesion and growth on patterned heterogeneous polystyrene surface

Studies of neurite outgrowth or cell migration, two important processes in neuronal networks formation, are facilitated by cell culture models capable of orientating cellular growth and of designing a well-defined cellular pattern. Heterogeneous polystyrene surfaces composed of oxygen plasma-treated stripes (PSox) with a low hydrophobicity separated by non-treated areas (PS) have these properties. In this study, to guide cell growth, we developed a cell culture model using these supports and we identified the molecular factors involved in cellular orientation. When the heterogeneous supports were not coated, proteins from a serum culture medium were required for cells to line up on PSox. On the other hand, cell orientation on coated surfaces was clearly influenced by competitive adsorption of adhesive proteins such as fibronectin or collagen and anti-adhesive molecules as pluronic F68 or albumin. Attachment factors were adsorbed on PSox stripes while adsorption of anti-adhesive molecules on the most hydrophobic PS areas prevented cell adhesion or growth. Thus, we describe the preparation of a cell culture substrate that succeeded in orientating cell growth and that led to a line of cells on adhesive PSox stripes ranging from 2 to 100 microns width.

Pore morphology effects on the fibrovascular tissue growth in porous polymer substrates

The feasibility of developing biodegradable polymer scaffolds to engineer tissues was investigated by studying the effects of pore size on the dynamics of fibrovascular tissue ingrowth. Tissue advanced into amorphous poly(L-lactic acid) porous substrates faster as the pore diameter increased. Porous cylindrical devices of 13.5 mm diameter, 5 mm thickness, and approximately 500 microns pore size were filled completely by tissue 5 days postimplantation. Although prevascularized devices possessed minimal void volume for cell seeding to regenerate metabolic organs, they hold promise in the regeneration of tubular tissues by relying on the epithelization of prevascularized grafts.