Godard C.W. de Ruiter

Designing ideal conduits for peripheral nerve repair

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

Controlling dispersion of axonal regeneration using a multichannel collagen nerve conduit

Single channel conduits are used clinically in nerve repair as an alternative to the autologous nerve graft. Axons regenerating across single channel tubes, however, may disperse resulting in inappropriate target reinnervation. This dispersion may be limited by multichannel nerve conduits as they resemble the structure of nerve multiple basal lamina tubes. In this study, we investigated the influence of channel number on the axonal regeneration using a series of 1-, 2-, 4-, and 7-channel collagen conduits and commercial (NeuraGen) single channel conduits. Nerve conduits were implanted in rats with a 1 cm gap of sciatic nerve. After four months, quantitative results of regeneration were evaluated with nerve morphometry and the accuracy of regeneration was assessed using retrograde tracing: two tracers being applied simultaneously to tibial and peroneal nerves to determine the percentage of motor neurons with double projections. Recovery of function was investigated with compound muscle action potential recordings and ankle motion analysis. We showed that the fabricated 1-channel and 4-channel conduits are superior to other types of conduits in axonal regeneration. Simultaneous tracing showed a significantly lower percentage of motor neurons with double projections after 2- and 4-channel compared with 1-channel conduit repair. This study shows the potential influence of multichannel guidance on limiting dispersion without decreasing quantitative results of regeneration.

Misdirection of regenerating motor axons after nerve injury and repair in the rat sciatic nerve model

Misdirection of regenerating axons is one of the factors that can explain the poor results often found after nerve injury and repair. In this study, we quantified the degree of misdirection and the effect on recovery of function after different types of nerve injury and repair in the rat sciatic nerve model; crush injury, direct coaptation, and autograft repair. Sequential tracing with retrograde labeling of the peroneal nerve before and 8 weeks after nerve injury and repair was performed to quantify the accuracy of motor axon regeneration. Digital video analysis of ankle motion was used to investigate the recovery of function. In addition, serial compound action potential recordings and nerve and muscle morphometry were performed. In our study, accuracy of motor axon regeneration was found to be limited; only 71% (+/-4.9%) of the peroneal motoneurons were correctly directed 2 months after sciatic crush injury, 42% (+/-4.2%) after direct coaptation, and 25% (+/-6.6%) after autograft repair. Recovery of ankle motion was incomplete after all types of nerve injury and repair and demonstrated a disturbed balance of ankle plantar and dorsiflexion. The number of motoneurons from which axons had regenerated was not significantly different from normal. The number of myelinated axons was significantly increased distal to the site of injury. Misdirection of regenerating motor axons is a major factor in the poor recovery of nerves that innervate different muscles. The results of this study can be used as basis for developing new nerve repair techniques that may improve the accuracy of regeneration.

Accuracy of motor axon regeneration across autograft, single-lumen, and multichannel poly(lactic-co-glycolic acid) nerve tubes.

OBJECTIVE The accuracy of motor axon regeneration becomes an important issue in the development of a nerve tube for motor nerve repair. Dispersion of regeneration across the nerve tube may lead to misdirection and polyinnervation. In this study, we present a series of methods to investigate the accuracy of regeneration, which we used to compare regeneration across autografts and single-lumen poly(lactic-co-glycolic acid) (PLGA) nerve tubes. We also present the concept of the multichannel nerve tube that may limit dispersion by separately guiding groups of regenerating axons. METHODS The simultaneous tracing of the tibial and peroneal nerves with fast blue and diamidino yellow was performed 8 weeks after the repair of a 1-cm nerve gap in the rat sciatic nerve to determine the percentage of double-projecting motoneurons. Sequential tracing of the peroneal nerve with diamidino yellow 1 week before repair and fast blue 8 weeks after repair was performed to determine the percentage of correctly directed peroneal motoneurons. RESULTS In the cases in which there was successful regeneration across single-lumen nerve tubes, more motoneurons had double projections to both the tibial and peroneal nerve branches after single-lumen nerve tube repair (21.4%) than after autograft repair (5.9%). After multichannel nerve tube repair, this percentage was slightly reduced (16.9%), although not significantly. The direction of regeneration was nonspecific after all types of repair. CONCLUSION Retrograde tracing techniques provide new insights into the process of regeneration across nerve tubes. The methods and data presented in this study can be used as a basis for the development of a nerve tube for motor nerve repair.

Two-dimensional digital video ankle motion analysis for assessment of function in the rat sciatic nerve model

Abstract  Ankle motion analysis may provide a better method to assess function in the rat sciatic nerve model than the standard method, the sciatic functional index (SFI), but it is not widely used in experiments on nerve regeneration possibly because of complicated analysis. In this study, we investigated the practical use of a two‐dimensional (2D) digital video motion analysis system. Reproducibility was investigated in normal rats. Recovery of ankle motion was analyzed after sciatic, tibial, and peroneal nerve crush injury. Results were compared with scores for the SFI. Results were not significantly different from animal‐to‐animal and day‐to‐day. Interobserver variability also was small. In the analysis of recovery after separate nerve crush injuries, subtle differences in ankle plantar flexion and dorsiflexion could be detected. The method was also more sensitive than the SFI: whereas scores for the SFI had returned to normal 4 weeks after sciatic nerve crush injury, the ankle angle at mid‐stance was still significantly different from that in sham‐operated animals 6 weeks after the injury. 2D digital video ankle motion analysis is a practical and sensitive method to assess function in the rat sciatic nerve model.