Nerve regeneration

Capacity of Human Dental Follicle Cells to Differentiate into Neural Cells In Vitro

The dental follicle is an ectomesenchymal tissue surrounding the developing tooth germ. Human dental follicle cells (hDFCs) have the capacity to commit to differentiation into multiple cell types. Here we investigated the capacity of hDFCs to differentiate into neural cells and the efficiency of a two-step strategy involving floating neurosphere-like bodies for neural differentiation. Undifferentiated hDFCs showed a spindle-like morphology and were positive for neural markers such as nestin, β-III-tubulin, and S100β. The cellular morphology of several cells was neuronal-like including branched dendrite-like processes and neurites. Next, hDFCs were used for neurosphere formation in serum-free medium containing basic fibroblast growth factor, epidermal growth factor, and B27 supplement. The number of cells with neuronal-like morphology and that were strongly positive for neural markers increased with sphere formation. Gene expression of neural markers also increased in hDFCs with sphere formation. Next, gene expression of neural markers was examined in hDFCs during neuronal differentiation after sphere formation. Expression of Musashi-1 and Musashi-2, MAP2, GFAP, MBP, and SOX10 was upregulated in hDFCs undergoing neuronal differentiation via neurospheres, whereas expression of nestin and β-III-tubulin was downregulated. In conclusion, hDFCs may be another optimal source of neural/glial cells for cell-based therapies to treat neurological diseases.

Nerve regeneration techniques respecting the special characteristics of the inferior alveolar nerve

PURPOSE

The aim of this study was to examine the in situ regeneration of the inferior alveolar nerve (IAN) in its bony channel, using autologous tissue in combination with a recombinant human nerve growth factor (rhNGF).

MATERIALS AND METHODS

A total of 20 New Zealand rabbits were randomly divided into five groups. Following dissection of the IAN, the animals underwent reconstruction either with muscle tissue (groups 1 and 2) or with fat tissue (groups 3 and 4). In group 5 (control), the dissected nerve was resected and reconstructed by placement of the reversed autologous segment. After 2 and 4 weeks, 1 mL rhNGF was locally injected in groups 1 and 3. Nerve function was monitored by measuring the jaw-opening reflex using electromyography for a period of 24 weeks.

RESULTS

Regeneration of the nerve was achieved in all groups, but preoperative threshold values were not achieved. Comparing the experimental groups to the control, there was a significant difference in favor of the autologous nerve reconstruction. Differences between the experimental groups remained statistically not significant.

CONCLUSION

Regeneration of the IAN with autologous tissue is possible, but without achieving preoperative thresholds. Additional injection of a growth factor seems to improve the speed of regeneration for fat and muscle grafts.

Effects of cerebrolysin on rat Schwann cells in vitro

Although the peripheral nervous system (PNS) is capable of regeneration, these processes are limited. As a potential means to augment PNS regeneration, the effects of cerebrolysin (CL), a proteolytic peptide fraction, were tested in vitro on Schwann cell (SC) proliferation, stress resistance, phagocytic and cluster-forming capacity. Primary SC/fibrocyte co-cultures were prepared from dorsal root ganglia of 5-7-day-old rats. SCs were subjected to mechanical stress by media change and metabolic stress by serum glucose deprivation (SGD). Cell survival was assessed using MTT test. SC proliferation was determined by counting BrdU-labeled cells. SC clustering was studied by ImageJ analysis of S100 immunostaining. Wallerian degeneration (WD) was evaluated by measuring acetylcholine-esterase staining within sciatic nerves in vitro. It was found that CL caused no effect on MTT turnover in the tested doses. CL inhibited SC proliferation in a dose-dependent manner. Media change and additional SGD stress inhibited SC clustering. CL enhanced the reorganization of SC clusters and was able to counteract SGD-induced cluster defects. Moreover, CL accelerated WD in vitro. CL was able to enhance the functions of SCs that are relevant to nerve regeneration. Thus, our findings suggest that CL may be suitable for therapeutic usage to enhance PNS regeneration/reconstruction.

Neural responses to electrical stimulation on patterned silk films

Peripheral nerve injury is a critical issue for patients with trauma. Following injury, incomplete axon regeneration or misguided axon innervation into tissue will result in loss of sensory and motor functions. The objective of this study was to examine axon outgrowth and axon alignment in response to surface patterning and electrical stimulation. To accomplish our objective, metal electrodes with dimensions of 1.5 mm × 4 cm, were sputter coated onto micropatterned silk protein films, with surface grooves 3.5 μm wide × 500 nm deep. P19 neurons were seeded on the patterned electronic silk films and stimulated at 120 mV, 1 kHz, for 45 min each day for 7 days. Responses were compared with neurons on flat electronic silk films, patterned silk films without stimulation, and flat silk films without stimulation. Significant alignment was found on the patterned film groups compared with the flat film groups. Axon outgrowth was greater (p < 0.05) on electronic films on days 5 and 7 compared with the unstimulated groups. In conclusion, electrical stimulation, at 120 mV, 1 kHz, for 45 min daily, in addition to surface patterning, of 3.5 μm wide × 500 nm deep grooves, offered control of nerve axon outgrowth and alignment.

Dual regeneration of muscle and nerve by intravenous administration of human amniotic fluid-derived mesenchymal stem cells regulated by stromal cell-derived factor-1α in a sciatic nerve injury model

OBJECT

Human amniotic fluid-derived mesenchymal stem cells (AFMSCs) have been shown to promote peripheral nerve regeneration. The expression of stromal cell-derived factor-1α (SDF-1α) in the injured nerve exerts a trophic effect by recruiting progenitor cells that promote nerve regeneration. In this study, the authors investigated the feasibility of intravenous administration of AFMSCs according to SDF-1α expression time profiles to facilitate neural regeneration in a sciatic nerve crush injury model.

METHODS

Peripheral nerve injury was induced in 63 Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. The animals were randomized into 1 of 3 groups: Group I, crush injury as the control; Group II, crush injury and intravenous administration of AFMSCs (5 × 10(6) cells for 3 days) immediately after injury (early administration); and Group III, crush injury and intravenous administration of AFMSCs (5 × 10(6) cells for 3 days) 7 days after injury (late administration). Evaluation of neurobehavior, electrophysiological study, and assessment of regeneration markers were conducted every week after injury. The expression of SDF-1α and neurotrophic factors and the distribution of AFMSCs in various time profiles were also assessed.

RESULTS

Stromal cell-derived factor-1α increased the migration and wound healing of AFMSCs in vitro, and the migration ability was dose dependent. Crush injury induced the expression of SDF-1α at a peak of 10-14 days either in nerve or muscle, and this increased expression paralleled the expression of its receptor, chemokine receptor type-4 (CXCR-4). Most AFMSCs were distributed to the lung during early or late administration. Significant deposition of AFMSCs in nerve and muscle only occurred in the late administration group. Significantly enhanced neurobehavior, electrophysiological function, nerve myelination, and expression of neurotrophic factors and acetylcholine receptor were demonstrated in the late administration group.

CONCLUSIONS

Amniotic fluid-derived mesenchymal stem cells can be recruited by expression of SDF-1α in muscle and nerve after nerve crush injury. The increased deposition of AFMSCs paralleled the expression profiles of SDF-1α and its receptor CXCR-4 in either muscle or nerve. Administration of AFMSCs led to improvements in neurobehavior and expression of regeneration markers. Intravenous administration of AFMSCs may be a promising alternative treatment strategy in peripheral nerve disorder.

Recruitment by SDF-1α of CD34-positive cells involved in sciatic nerve regeneration

Object

Increased integration of CD34+ cells in injured nerve significantly promotes nerve regeneration, but this effect can be counteracted by limited migration and short survival of CD34+ cells. SDF-1α and its receptor mediate the recruitment of CD34+ cells involved in the repair mechanism of several neurological diseases. In this study, the authors investigate the potentiation of CD34+ cell recruitment triggered by SDF-1α and the involvement of CD34+ cells in peripheral nerve regeneration.

Methods

Peripheral nerve injury was induced in 147 Sprague-Dawley rats by crushing the left sciatic nerve with a vessel clamp. The animals were allocated to 3 groups: Group 1, crush injury (controls); Group 2, crush injury and local application of SDF-1α recombinant proteins; and Group 3, crush injury and local application of SDF-1α antibody. Electrophysiological studies and assessment of regeneration markers were conducted at 4 weeks after injury; neurobehavioral studies were conducted at 1, 2, 3, and 4 weeks after injury. The expression of SDF-1α, accumulation of CD34+ cells, immune cells, and angiogenesis factors in injured nerves were evaluated at 1, 3, 7, 10, 14, 21, and 28 days after injury.

Results

Application of SDF-1α increased the migration of CD34+ cells in vitro, and this effect was dose dependent. Crush injury induced the expression of SDF-1α, with a peak of 10–14 days postinjury, and this increased expression of SDF-1α paralleled the deposition of CD34+ cells, expression of VEGF, and expression of neurofilament. These effects were further enhanced by the administration of SDF-1α recombinant protein and abolished by administration of SDF-1α antibody. Furthermore, these effects were consistent with improvement in measures of neurological function such as sciatic function index, electrophysiological parameters, muscle weight, and myelination of regenerative nerve.

Conclusions

Expression of SDF-1α facilitates recruitment of CD34+ cells in peripheral nerve injury. The increased deposition of CD34+ cells paralleled significant expression of angiogenesis factors and was consistent with improvement of neurological function. Utilization of SDF-1α for enhancing the recruitment of CD34+ cells involved in peripheral nerve regeneration may be considered as an alternative treatment strategy in peripheral nerve disorders.

Enhancement of regeneration with glia cell line-derived neurotrophic factor-transduced human amniotic fluid mesenchymal stem cells after sciatic nerve crush injury

OBJECT

Human amniotic fluid-derived mesenchymal stem cells (AFMSCs) have been shown to promote peripheral nerve regeneration, and the local delivery of neurotrophic factors may additionally enhance nerve regeneration capacity. The present study evaluates whether the transplantation of glia cell line-derived neurotrophic factor (GDNF)-modified human AFMSCs may enhance regeneration of sciatic nerve after a crush injury.

METHODS

Peripheral nerve injury was produced in Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. Either GDNF-modified human AFMSCs or human AFMSCs were embedded in Matrigel and delivered to the injured nerve. Motor function and electrophysiological studies were conducted after 1 and 4 weeks. Early or later nerve regeneration markers were used to evaluate nerve regeneration. The expression of GDNF in the transplanted human AFMSCs and GDNF-modified human AFMSCs was monitored at 7-day intervals.

RESULTS

Human AFMSCs were successfully transfected with adenovirus, and a significant amount of GDNF was detected in human AFMSCs or the culture medium supernatant. Increases in the sciatic nerve function index, the compound muscle action potential ratio, conduction latency, and muscle weight were found in the groups treated with human AFMSCs or GDNF-modified human AFMSCs. Importantly, the GDNF-modified human AFMSCs induced the greatest improvement. Expression of markers of early nerve regeneration, such as increased expression of neurofilament and BrdU and reduced Schwann cell apoptosis, as well as late regeneration markers, consisting of reduced vacuole counts, increased expression of Luxol fast blue and S100 protein, paralleled the results of motor function. The expression of GDNF in GDNF-modified human AFMSCs was demonstrated up to 4 weeks; however, the expression decreased over time.

CONCLUSIONS

The GDNF-modified human AFMSCs appeared to promote nerve regeneration. The consecutive expression of GDNF was demonstrated in GDNF-modified human AFMSCs up to 4 weeks. These findings support a nerve regeneration scenario involving cell transplantation with additional neurotrophic factor secretion.

Escalated regeneration in sciatic nerve crush injury by the combined therapy of human amniotic fluid mesenchymal stem cells and fermented soybean extracts, Natto

Attenuation of inflammatory cell deposits and associated cytokines prevented the apoptosis of transplanted stem cells in a sciatic nerve crush injury model. Suppression of inflammatory cytokines by fermented soybean extracts (Natto) was also beneficial to nerve regeneration. In this study, the effect of Natto on transplanted human amniotic fluid mesenchymal stem cells (AFS) was evaluated. Peripheral nerve injury was induced in SD rats by crushing a sciatic nerve using a vessel clamp. Animals were categorized into four groups: Group I: no treatment; Group II: fed with Natto (16 mg/day for 7 consecutive days); Group III: AFS embedded in fibrin glue; Group IV: Combination of group II and III therapy. Transplanted AFS and Schwann cell apoptosis, inflammatory cell deposits and associated cytokines, motor function, and nerve regeneration were evaluated 7 or 28 days after injury. The deterioration of neurological function was attenuated by AFS, Natto, or the combined therapy. The combined therapy caused the most significantly beneficial effects. Administration of Natto suppressed the inflammatory responses and correlated with decreased AFS and Schwann cell apoptosis. The decreased AFS apoptosis was in line with neurological improvement such as expression of early regeneration marker of neurofilament and late markers of S-100 and decreased vacuole formation. Administration of either AFS, or Natto, or combined therapy augmented the nerve regeneration. In conclusion, administration of Natto may rescue the AFS and Schwann cells from apoptosis by suppressing the macrophage deposits, associated inflammatory cytokines, and fibrin deposits.

Human amniotic fluid mesenchymal stem cells in combination with hyperbaric oxygen augment peripheral nerve regeneration

PURPOSE

Attenuation of pro-inflammatory cytokines and associated inflammatory cell deposits rescues human amniotic fluid mesenchymal stem cells (AFS) from apoptosis. Hyperbaric oxygen (HBO) suppressed stimulus-induced pro-inflammatory cytokine production in blood-derived monocyte-macrophages. Herein, we evaluate the beneficial effect of hyperbaric oxygen on transplanted AFS in a sciatic nerve injury model.

METHODS

Peripheral nerve injury was produced in Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. The AFS were embedded in fibrin glue and delivered to the injured site. Hyperbaric oxygen (100% oxygen, 2 ATA, 60 min/day) was administered 12 h after operation for seven consecutive days. Transplanted cell apoptosis, oxidative stress, inflammatory cell deposits and associated chemokines, pro-inflammatory cytokines, motor function, and nerve regeneration were evaluated 7 and 28 days after injury.

RESULTS

Crush injury induced an inflammatory response, disrupted nerve integrity, and impaired nerve function in the sciatic nerve. However, crush injury-provoked inflammatory cytokines, deposits of inflammatory cytokines, and associated macrophage migration chemokines were attenuated in groups receiving hyperbaric oxygen but not in the AFS-only group. No significant increase in oxidative stress was observed after administration of HBO. In transplanted AFS, marked apoptosis was detected and this event was reduced by HBO treatment. Increased nerve myelination and improved motor function were observed in AFS-transplant, HBO-administrated, and AFS/HBO-combined treatment groups. Significantly, the AFS/HBO combined treatment showed the most beneficial effect.

CONCLUSION

AFS in combination with HBO augment peripheral nerve regeneration, which may involve the suppression of apoptotic death in implanted AFS and the attenuation of an inflammatory response detrimental to peripheral nerve regeneration.

Combination of G-CSF administration and human amniotic fluid mesenchymal stem cell transplantation promotes peripheral nerve regeneration

Amniotic fluid mesenchymal stem cells (AFS) harbor the potential to improve peripheral nerve injury by inherited neurotrophic factor secretion, but present the drawback of the short-term survival after transplantation. Granulocyte-colony stimulating factor (G-CSF) has a diversity of functions, including anti-inflammatory and anti-apoptotic effects. This study was conducted to evaluate whether G-CSF could augment the neuroprotective effect of transplanted AFS against peripheral nerve injury. The potential involvement of anti-inflammation/anti-apoptosis effect was also investigated. Peripheral nerve injury was produced in Sprauge-Dawley rats by crushing left sciatic nerve using a vessel clamp. The AFS were embedded in fibrin glue and delivered to the injured site. G-CSF (50 microg/kg) was administrated by intra-peritoneal injection for 7 consecutive days. Cell apoptosis, inflammatory cytokines, motor function, and nerve regeneration were evaluated 7 or 28 days after injury. Crush injury induced inflammatory response, disrupted nerve integrity, and impaired nerve function in sciatic nerve. Crush injury-provoked inflammation was attenuated in groups receiving G-CSF but not in AFS only group. In transplanted AFS, marked apoptosis was detected and this event was reduced by G-CSF treatment. Increased nerve myelination and improved motor function were observed in AFS transplanted, G-CSF administrated, and AFS/G-CSF combined treatment groups. Significantly, the combined treatment showed the most beneficial effect. In conclusion, the concomitant treatment of AFS with G-CSF augments peripheral nerve regeneration which may involve the suppression of apoptotic death in implanted AFS and the attenuation of inflammatory response.

Evaluation and management of peripheral nerve injury

Common etiologies of acute traumatic peripheral nerve injury (TPNI) include penetrating injury, crush, stretch, and ischemia. Management of TPNI requires familiarity with the relevant anatomy, pathology, pathophysiology, and the surgical principles, approaches and concerns. Surgical repair of TPNI is done at varying time intervals after the injury, and there are a number of considerations in deciding whether and when to operate. In neurapraxia, the compound muscle and nerve action potentials on stimulating distal to the lesion are maintained indefinitely; stimulation above the lesion reveals partial or complete conduction block. The picture in axonotmesis and neurotmesis depends on the time since injury. The optimal timing for an electrodiagnostic study depends upon the clinical question being asked. Although conventional teaching usually holds that an electrodiagnostic study should not be done until about 3 weeks after the injury, in fact a great deal of important information can be obtained by studies done in the first week. Proximal nerve injuries are problematic because the long distance makes it difficult to reinnervate distal muscles before irreversible changes occur. Decision making regarding exploration must occur more quickly, and exploration using intraoperative nerve action potential recording to guide the choice of surgical procedure is often useful.

Enhanced regeneration in injured sciatic nerve by human amniotic mesenchymal stem cell

OBJECTIVE

Amniotic fluid mesenchymal stem cells (MSCs) have the potential to differentiate into neuronal stem cells in vitro. We evaluated using amniotic fluid MSCs to support or enhance the ability of the injured sciatic nerve to cross a nerve gap.

MATERIALS AND METHODS

We created a 5 mm nerve defect in Sprague Dawley rats. One group received therapy with MSCs embedded into woven oxidised regenerated cellulose gauze (Surgical; Ethicon, Somerville, NJ) and fibrin glue, while a control group received woven Surgicel and fibrin glue only. Evaluation methods included behavioural, electrophysiological and immunohistochemical studies.

RESULTS

In gait analysis, the angle of the ankles in the treatment and control group were 46.4 degrees (standard deviation [SD]=15 degrees) and 36 degrees (SD=8.2 degrees), respectively, which was statistically significant (p=0.045). Five of 10 treated rats (50%) demonstrated partial foot movement, while none of the control group had any movement. The percentage amplitude of muscle compound action potential in the experimental group was 43% (SD=12.5%) compared to 29% (SD=8.8%) in the control group (p=0.038). The conduction latencies in the control and experimental groups was 2.5 ms (SD=0.45) and 1.7 ms (SD=0.47), respectively (p=0.005). Histological examination demonstrated that 70% of the treatment group achieved a maximum axon diameter percentage across the nerve gap of greater than 50%, compared with 0% in the control group. There were no differences in direction of fibre growth and fibrotic reaction between the two groups.

CONCLUSION

Amniotic fluid MSC can augment growth of injured nerve across a nerve gap. This effect may be due to neurotrophic or induction effects of the MSC interacting with Schwann cells. Further study is required to determine the underlying mechanism of this effect.

Efficacy of low level laser therapy on neurosensory recovery after injury to the inferior alveolar nerve

BACKGROUND

The most severe complication after the removal of mandibular third molars is injury to the inferior alveolar nerve or the lingual nerve. These complications are rather uncommon (0.4% to 8.4%) and most of them are transient. However, some of them persist for longer than 6 months, which can leave various degrees of long-term permanent disability. While several methods such as pharmacologic therapy, microneurosurgery, autogenous and alloplastic grafting can be used for the treatment of long-standing sensory aberrations in the inferior alveolar nerve, there are few reports regarding low level laser treatment. This paper reports the effects of low level laser therapy in 4 patients with longstanding sensory nerve impairment following mandibular third molar surgery.

METHODS

Four female patients had complaints of paresthesia and dysesthesia of the lip, chin and gingiva, and buccal regions. Each patient had undergone mandibular third molar surgery at least 1 year before. All patients were treated with low level laser therapy. Clinical neurosensory tests (the brush stroke directional discrimination test, 2-point discrimination test, and a subjective assessment of neurosensory function using a visual analog scale) were used before and after treatment, and the responses were plotted over time.

RESULTS

When the neurosensory assessment scores after treatment with LLL therapy were compared with the baseline values prior to treatment, there was a significant acceleration in the time course, as well as in the magnitude, of neurosensory return. The VAS analysis revealed progressive improvement over time.

CONCLUSION

Low level laser therapy seemed to be conducive to the reduction of long-standing sensory nerve impairment following third molar surgery. Further studies are worthwhile regarding the clinical application of this treatment modality.

Micropatterning proteins and cells on polylactic acid and poly(lactide-co-glycolide)

Techniques for micropatterning proteins and cells on biomaterials are important in tissue engineering applications. Here, we present a method for patterning proteins and cells on poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA) substrates that are routinely used as scaffolds in engineering tissues. Poly(oligoethyleneglycol methacrylate) (poly-OEGMA) or poly(oligoethyleneglycol methacrylate-co-methacrylic acid) (poly(OEGMA-co-MA)) was microcontact printed onto substrates to create cell resistant areas. Proteins adsorbed onto the unprinted regions whereas the polymer printed regions effectively repel non-specific protein adsorption. NIH 3T3 fibroblasts remain confined within the patterns on the PLGA and PLA films for up to 2 weeks and aligned their actin cytoskeleton along the line patterns. In comparison to unpatterned cells, fibroblasts confined within line-shaped patterns show fewer actin filaments. This method for controlling the spatial morphology and distribution of cells on synthetic biomaterials could have significant applications in tissue engineering.

Baiting the cross-face nerve graft with temporary hypoglossal hookup

BACKGROUND

Cross-face nerve grafting yields inconsistent neural regeneration, and methods that promote more robust axonal traversing of the graft would expand the indications for this procedure.

OBJECTIVE

To test the hypothesis that hooking a cross-face nerve graft distally to a source of denervated muscle, rather than leaving it in the subcutaneous space, would positively affect neural ingrowth across the graft, based on elaboration of neurotrophins from the musculature.

METHODS

Twenty-four rats underwent cross-face nerve grafting in which the right facial nerve buccal branch was transected and coapted to the graft. The graft was placed across the neck and into the left side of the face. The distal end of the graft was placed either in the left subcutaneous space, coapted to the marginal mandibular branch of the left facial nerve, or coapted to the distal stump of the transected left hypoglossal nerve. Eight control animals underwent right buccal branch transection and placement of a cross-face nerve graft without any proximal and distal hookup. After 12 weeks, all experimental groups underwent hookup of the distal nerve graft to the left facial nerve buccal branch. Vibrissal function was assessed during the ensuing 12 weeks, and then the graft was harvested for histomorphometric analysis.

RESULTS

After 12 weeks, there was a significant difference in axon counts between the group coapted distally to the tongue (hypoglossal hookup) and that coapted to the facial musculature (marginal hookup). Twelve weeks later, after distal cross-face nerve graft hookup, this difference was not statistically significant, although the hypoglossally baited group demonstrated statistically significantly greater fiber maturity. Recovery of vibrissal movement did not differ among treatment groups.

CONCLUSION

Baiting the cross-face nerve graft via temporary hookup to the distal hypoglossal nerve and tongue musculature appears to improve nerve ingrowth through a nerve graft across the face, although a corresponding improvement in facial muscle function was not observed.

Biomimetic materials for tissue engineering

The development of biomaterials for tissue engineering applications has recently focused on the design of biomimetic materials that are capable of eliciting specific cellular responses and directing new tissue formation mediated by biomolecular recognition, which can be manipulated by altering design parameters of the material. Biomolecular recognition of materials by cells has been achieved by surface and bulk modification of biomaterials via chemical or physical methods with bioactive molecules such as a native long chain of extracellular matrix (ECM) proteins as well as short peptide sequences derived from intact ECM proteins that can incur specific interactions with cell receptors. The biomimetic materials potentially mimic many roles of ECM in tissues. For example, biomimetic scaffolds can provide biological cues for cell-matrix interactions to promote tissue growth, and the incorporation of peptide sequences into materials can also make the material degradable by specific protease enzymes. This review discusses the surface and bulk modification of biomaterials with cell recognition molecules to design biomimetic materials for tissue engineering. The criteria to design biomimetic materials such as the concentration and spatial distribution of modified bioactive molecules are addressed. Recent advances for the development of biomimetic materials in bone, nerve, and cardiovascular tissue engineering are also summarized.

Low-level laser effect on neural regeneration in Gore-Tex tubes

PURPOSE

The purpose of this investigation was to determine the effects of low-level laser (LLL) irradiation on neural regeneration in surgically created defects in the rabbit inferior alveolar nerve.

STUDY DESIGN

Five adult female New Zealand White rabbits underwent bilateral exposure of the inferior alveolar nerve. A 6-mm segment of nerve was resected, and the nerve gap was repaired via entubulation by using a Gore-Tex conduit. The experimental side received 10 postoperative LLL treatments with a 70-mW gallium-aluminum-arsenide diode at 4 sites per treatment. At 15 weeks after surgery, the nerve segments were harvested bilaterally and prepared for light microscopy. Basic fuchsin and toluidine blue were used to highlight myelinated axons. The segments were examined histomorphometrically by using computer analysis to determine mean axonal diameter, total fascicular surface area, and axonal density along the repair sites.

RESULTS

Gross examination of all nerves showed intact neural bundles with variable degrees of osseous remodeling. Light microscopic evaluation revealed organized regenerated neural tissue in both groups with more intrafascicular perineural tissue in the control group. Histomorphometric evaluation revealed increased axonal density in the laser treated group as compared with the control.

CONCLUSIONS

LLL irradiation may be a useful noninvasive adjunct to promote neuronal wound healing in surgically created defects repaired with expanded polytetrafluoroethylene entubulation.

Cortical reorganization after digit-to-hand replantation

Functional recovery after digit-to-hand replantation depends on the interaction of various factors. In addition to peripheral mechanisms, cortical and subcortical reorganization of digit representation may play a substantial role in the recovery process. However, cortical processes during the first months after replantation are not well understood. In this 25-year-old man who had traumatically lost digits II to V (DII-V) on his right hand, the authors used magnetoencephalographic source imaging to document the recovery of somatosensory cortical responses after tactile stimulation at four sites on the replanted digits. Successful replantation of DIV and DV was accomplished at the original position of DIII and DIV with mixed innervation. Cortical evoked fields could be recorded starting from the 10th week after digit-to-hand replantation. Initially, signals from all sites showed decreased amplitudes and prolonged latencies. In the subsequent six recordings obtained between the 12th and 55th week postreplantation, a continuous increase in amplitude but only a slight recovery of latencies were observed. Components of the recorded somatosensory evoked fields were localized in the primary somatosensory cortex (SI). The localizations of the replanted DIV showed a gradual lateral-inferior shift in the somatosensory cortex over time, indicating cortical reorganization caused by altered peripheral input. The authors infer from this shift that the original cortical area of the missing finger (DII) was taken over by the replanted finger. From these data the authors conclude that magnetic source imaging might be a reliable noninvasive method to evaluate surgical nerve repair and that cortical reorganization of SI is involved in the regeneration process following peripheral nerve injury.

Peripheral nerve injuries associated with anaesthesia

Peripheral nerve injuries can occur at any time during the peri-operative period. The long-term disability that results may have serious consequences for a patient. The incidence of peri-operative nerve injuries can be reduced by anaesthetists being aware of their causes and pathophysiology. This review article aims to explain the incidence, pathophysiology and medicolegal implications of peri-operative nerve injury and provides suggestions as to how they may best be avoided.

Schwann cells, neurotrophic factors, and peripheral nerve regeneration

The peripheral nervous system retains a considerable capacity for regeneration. However, functional recovery rarely returns to the preinjury level no matter how accurate the nerve repair is, and the more proximal the injury the worse the recovery. Among a variety of approaches being used to enhance peripheral nerve regeneration are the manipulation of Schwann cells and the use of neurotrophic factors. Such factors include, first, nerve growth factor (NGF) and the other recently identified members of the neurotrophin family, namely, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5); second, the neurokines ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF); and third, the transforming growth factors (TGFs)-beta and their distant relative, glial cell line-derived neurotrophic factor (GDNF). In this review article we focus on the roles in peripheral nerve regeneration of Schwann cells and of the neurotrophin family, CNTF and GDNF, and the relationship between these. Finally, we discuss what remains to be understood about the possible clinical use of neurotrophic factors.

Spatially controlled cell engineering on biodegradable polymer surfaces

Controlling receptor-mediated interactions between cells and template surfaces is a central principle in many tissue engineering procedures (1-3). Biomaterial surfaces engineered to present cell adhesion ligands undergo integrin-mediated molecular interactions with cells (1, 4, 5), stimulating cell spreading, and differentiation (6-8). This provides a mechanism for mimicking natural cell-to-matrix interactions. Further sophistication in the control of cell interactions can be achieved by fabricating surfaces on which the spatial distribution of ligands is restricted to micron-scale pattern features (9-14). Patterning technology promises to facilitate spatially controlled tissue engineering with applications in the regeneration of highly organized tissues. These new applications require the formation of ligand patterns on biocompatible and biodegradable templates, which control tissue regeneration processes, before removal by metabolism. We have developed a method of generating micron-scale patterns of any biotinylated ligand on the surface of a biodegradable block copolymer, polylactide-poly(ethylene glycol). The technique achieves control of biomolecule deposition with nanometer precision. Spatial control over cell development has been observed when using these templates to culture bovine aortic endothelial cells and PC12 nerve cells. Furthermore, neurite extension on the biodegradable polymer surface is directed by pattern features composed of peptides containing the IKVAV sequence (15, 16), suggesting that directional control over nerve regeneration on biodegradable biomaterials can be achieved.