Michaël Papaloïzos

Nerve conduits and growth factor delivery in peripheral nerve repair.

Abstractu2003 Peripheral nerves possess the capacity of self‐regeneration after traumatic injury. Transected peripheral nerves can be bridged by direct surgical coaptation of the two nerve stumps or by interposing autografts or biological (veins) or synthetic nerve conduits (NC). NC are tubular structures that guide the regenerating axons to the distal nerve stump. Early synthetic NC have primarily been made of silicone because of the relative flexibility and biocompatibility of this material and because medical‐grade silicone tubes were readily available in various dimensions. Nowadays, NC are preferably made of biodegradable materials such as collagen, aliphatic polyesters, or polyurethanes. Although NC assist in guiding regenerating nerves, satisfactory functional restoration of severed nerves may further require exogenous growth factors. Therefore, authors have proposed NC with integrated delivery systems for growth factors or growth factor–producing cells. This article reviews the most important designs of NC with integrated delivery systems for localized release of growth factors. The various systems discussed comprise NC with growth factors being released from various types of matrices, from transplanted cells (Schwann cells or mesenchymal stem cells), or through genetic modification of cells naturally present at the site of injured tissue. Acellular delivery systems for growth factors include the NC wall itself, biodegradable microspheres seeded onto the internal surface of the NC wall, or matrices that are filled into the lumen of the NC and immobilize the growth factors through physical‐chemical interactions or specific ligand‐receptor interactions. A very promising and elegant system appears to be longitudinally aligned fibers inserted in the lumen of a NC that deliver the growth factors and provide additional guidance for Schwann cells and axons. This review also attempts to appreciate the most promising approaches and emphasize the importance of growth factor delivery kinetics.

Trophically and topographically functionalized silk fibroin nerve conduits for guided peripheral nerve regeneration

Artificial nerve conduits (NC) can be used as an alternative to autologous nerve grafts to enhance the repair of small nerve gaps. Current NC lack adequate molecular and structural functionalities. Thus, we developed silk fibroin NC (SF NC) that were loaded with glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) and topographically functionalized with aligned and non-aligned SF nanofibers. The SF NC were produced from fully functionalized SF membranes on which initial experiments were performed. DRG (dorsal root ganglions) sensory neurons and spinal cord (SpC) motor neurons, both from chicken embryos, exhibited an augmented length and rate of axonal outgrowth parallel to the aligned nanofibers. In addition, glial cells from DRG proliferated and migrated in close association and even slightly ahead of the outgrowing axons. On the contrary, axonal and glial growth was slower and randomly oriented on non-aligned nanofibers. The DRG and SpC explants were also inserted into the lumen of the finished SF NC. The unidirectional orientation of axo-glial outgrowth from the explants evidenced the preservation of the trophic and topographical functionalities in the SF NC. Bioactive GDNF and NGF were released in vitro from SF NC over 4 weeks. Thus, the developed functionalized SF NC hold promise to enhance functional recovery of injured peripheral nerves.

Synergistic effect of GDNF and NGF on axonal branching and elongation in vitro

There is a clinical need to enhance functional recovery of injured peripheral nerves. Local administration of neurotrophic factors (NTFs) after surgical repair has been proposed for this purpose. Little is known, however, on the optimal local dose and dosing frequency of NTFs in a peripheral nerve defect. For increasing our knowledge on biologically relevant local NTFs concentrations and for making available an in vitro assay for assessing the bioactivity of NTFs in connection with implantable localized delivery systems, we developed in this study a bioassay for NTFs, which is based on dorsal root ganglion (DRG) explants from E9 (9 days old) chicken embryos. Axonal elongation and extent of axonal branching was analyzed microscopically after addition of glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF), each alone and in combination. GDNF significantly promoted axonal elongation, but only little axonal branching, whereas NGF induced extensive axonal branching with modest axonal elongation. The combination of GDNF and NGF exerted a synergistic effect on the axonal elongation, axonal branching and growth kinetics. GDNF and NGF also enhanced the expression of their respective functional receptors Ret and TrkA on the DRG neurons. This information should be relevant for the development of implants containing NTFs and on drug therapy of damaged peripheral nerves.

Complications of plate fixation in metacarpal fractures

BACKGROUNDnThe objective of this study is to assess the complications after open reduction and plate fixation of extra-articular metacarpal fractures.nnnMETHODSnWe retrospectively reviewed the clinical and radiologic records of 129 consecutive patients with 157 metacarpal fractures treated by open reduction and internal fixation with plates between 1993 and 1999. Intra-articular fractures and fractures of the thumb metacarpal were excluded. Eighty-one patients (64 men and 17 women) with 104 fractures were available for review, at an average follow-up of 13.6 months (range, 6-27 months).nnnRESULTSnTwenty-eight patients (35%) and 33 fractures (32%) had one or more complications, including difficulty with fracture healing (12 patients [15%]), stiffness (eight patients [10%]), plate loosening or breakage (seven patients [8%]), complex regional pain syndrome (two patients), and one patient who developed a deep infection.nnnCONCLUSIONnDespite technical advances in implant material, design, and instrumentation, plate fixation of metacarpal fractures remains fraught with complications and unsatisfactory results.

Collagen nerve conduits releasing the neurotrophic factors GDNF and NGF

Artificial nerve conduits (NC) can clinically be instrumental for facilitating the surgery of damaged peripheral nerves. To improve axonal regeneration of injured peripheral nerves, we have developed collagen nerve conduits (NC) releasing glial cell line-derived neurotrophic factor (GDNF) alone or in combination with nerve growth factor (NGF), which exert synergistic action on axonal growth. Degradation of the NC and their mechanical and drug release properties were controlled by two means: (i) cross-linking the collagen tubes by physical means, through a dehydro-thermal treatment (DHT), before loading with the neurotrophic factors (NTFs) GDNF or GDNF/NGF; and (ii) coating the drug-loaded collagen tubes with layers of poly(lactide-co-glycolide) (PLGA). Non-cross-linked collagen NC (C-NC) released high amounts of NTFs during the initial 2-3 days of incubation, whereas the DHT-treated collagen NC (C(dht)-NC) did not show a prominent burst effect. The release kinetics was similar for GDNF alone and GDNF co-delivered with NGF. Within 30 days, the C-NC released 78% and 83% of the total doses of GDNF and NGF, respectively, whereas the C(dht)-NC released only 68% of GDNF and 56% of NGF. The bioactivity of the NTFs released up to 30 days was confirmed by an in vitro bioassay using chicken embryonic dorsal root ganglion (DRG) explants. The C(dht)-NC also possessed adequate mechanical resistance against radial compression, the pull-out of a suture thread, and loss of patency upon bending. Modulus and pull-out strength increased in the order of C-NC, C(dht)-NC approximately Neuragen, and Neurolac, with the latter two products being commercially available collagen and polyester NC, respectively. In vitro degradation time upon incubation with collagenase increased in the same order for the collagen-based NC. In conclusion, co-delivery of synergistically acting GDNF and NGF from structurally improved NC may be a promising tool for the successful repair of peripheral nerve defects.

Variations in glial cell line-derived neurotrophic factor release from biodegradable nerve conduits modify the rate of functional motor recovery after rat primary nerve repairs

Accelerating axonal regeneration to shorten the delay of reinnervation and improve functional recovery after a peripheral nerve lesion is a clinical demand and an experimental challenge. We developed a resorbable nerve conduit (NC) for controlled release of glial cell line‐derived neurotrophic factor (GDNF) with the aim of assessing motor functional recovery according to the release kinetics of this factor in a short gap model. Different types of resorbable NCs were manufactured from a collagen tube and multiple coating layers of poly(lactide‐coglycolide), varying in poly(lactide‐coglycolide) type and coating thickness to afford three distinct release kinetics of the neurotrophic factor. GDNF release was quantified inu2003vitro. End‐to‐end suture and GDNF‐free NC served as controls. Thirty‐five Wistar rats underwent surgery. Motor recovery was followed from 1 to 12u2003weeks after surgery by video gait analysis. Morphometrical data were obtained at mid‐tube level and distal to the NC. NCs were completely resorbed within 3u2003months with minimal inflammation. GDNF induced a threefold overgrowth of fibers at mid‐tube level. However, the number of fibers was similar in the distal segment of all groups. The speed of recovery was inversely proportional to the number of fibers at the NC level but the level of recovery was similar for all groups at 3u2003months. The resorbable conduits proved their ability to modulate axonal regrowth through controlled release of GDNF. In relation to the dose delivered, GDNF strikingly multiplied the number of myelinated fibers within the NC but this increase was not positively correlated with the return of motor function in this model.

Effect of controlled co-delivery of synergistic neurotrophic factors on early nerve regeneration in rats

Present interventions to repair severed peripheral nerves provide slow and poor early axonal regeneration, which may cause unsatisfactory functional reinnervation. To improve early axonal regeneration in a 10 mm rat sciatic nerve gap model, we developed collagen nerve conduits loaded with the synergistically acting glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF). For controlling the concomitant GDNF and NGF release, the collagen tubes were cross-linked by a dehydro-thermal treatment (110 degrees C; 20 mbar; 5 days) prior to impregnating the tubes with GDNF and NGF and by coating drug-loaded tubes with layers of poly(lactide-co-glycolide). The conduits made of cross-linked collagen released low initial amounts of GDNF and NGF (2% of both during first 3 days) and enhanced significantly the early (2 weeks) nerve regeneration in terms of axonal outgrowth and Schwann cell migration in a 10 mm rat sciatic nerve gap model, as compared to the conduits made of non-cross-linked collagen releasing higher initial amounts of GDNF and NGF (12-16% within 3 days), or those releasing GDNF alone. The enhancement of early axonal regeneration using controlled co-delivery of multiple synergistic neurotrophic factors is an important requisite for eventually establishing functional connections with the target organ.

Controlled nerve growth factor release from multi-ply alginate/chitosan-based nerve conduits

The delivery kinetics of growth factors has been suggested to play an important role in the regeneration of peripheral nerves following axotomy. In this context, we designed a nerve conduit (NC) with adjustable release kinetics of nerve growth factor (NGF). A multi-ply system was designed where NC consisting of a polyelectrolyte alginate/chitosan complex was coated with layers of poly(lactide-co-glycolide) (PLGA) to control the release of embedded NGF. Prior to assessing the in vitro NGF release from NC, various release test media, with and without stabilizers for NGF, were evaluated to ensure adequate quantification of NGF by ELISA. Citrate (pH 5.0) and acetate (pH 5.5) buffered saline solutions containing 0.05% Tween 20 yielded the most reliable results for ELISA active NGF. The in vitro release experiments revealed that the best results in terms of reproducibility and release control were achieved when the NGF was embedded between two PLGA layers and the ends of the NC tightly sealed by the PLGA coatings. The release kinetics could be efficiently adjusted by accommodating NGF at different radial locations within the NC. A sustained release of bioactive NGF in the low nanogram per day range was obtained for at least 15days. In conclusion, the developed multi-ply NGF loaded NC is considered a suitable candidate for future implantation studies to gain insight into the relationship between local growth factor availability and nerve regeneration.

Development of neuropathic pain in the rat spared nerve injury model is not prevented by a Peripheral nerve block

Background The mechanisms responsible for initiation of persistent neuropathic pain after peripheral nerve injury are unclear. One hypothesis is that injury discharge and early ectopic discharges in injured nerves produce activity-dependent irreversible changes in the central nervous system. The aim of this study was to determine whether blockade of peripheral discharge by blocking nerve conduction before and 1 week after nerve injury could prevent the development and persistence of neuropathic pain–like behavior in the spared nerve injury model. Methods Bupivacaine-loaded biodegradable microspheres embedded in fibrin glue were placed in a silicone tube around the sciatic nerve to produce a conduction block. After sensory–motor testing of block efficacy, a spared nerve injury procedure was performed. Development of neuropathic pain behavior was assessed for 4 weeks by withdrawal responses to stimulation (i.e., von Frey filaments, acetone, pinprick, radiant heat) in bupivacaine microspheres–treated animals (n = 12) and in controls (n = 11). Results Bupivacaine microspheres treatment produced conduction blockade with a complete lack of sensory responsiveness in the sural territory for 6 to 10 days. Once the block wore off, the degree of hypersensitivity to stimuli was similar in both groups. Conclusions Peripheral long-term nerve blockade has no detectable effect on the development of allodynia or hyperalgesia in the spared nerve injury model. It is unlikely that injury discharge at the time of nerve damage or the early onset of ectopic discharges arising from the injury site contributes significantly to the persistence of stimulus-evoked neuropathic pain in this model.

Minimally Invasive Fixation versus Conservative Treatment of Undisplaced Scaphoid Fractures: A Cost-Effectiveness Study

This study compares the direct and indirect costs of conservative and minimally invasive treatment for undisplaced scaphoid fractures. Costs data concerning groups of non-operated and operated patients were analysed. Direct costs were higher in operated patients. Although highly variable, indirect costs were significantly smaller in operated patients and the total costs were higher in nonoperated patients. In conclusion, operative treatment of scaphoid fractures is initially more expensive than conservative treatment but markedly decreases the work compensation costs.