Peripheral Nerve Repair: Multimodal Comparison of the Long-Term Regenerative Potential of Adipose Tissue-Derived Cells in a Biodegradable Conduit

Exploring the neurogenic differentiation of human dental pulp stem cells

Human dental pulp stem cells (hDPSCs) have increasingly gained interest as a potential therapy for nerve regeneration in medicine and dentistry, however their neurogenic potential remains a matter of debate. This study aimed to characterize hDPSC neuronal differentiation in comparison with the human SH-SY5Y neuronal stem cell differentiation model. Both hDPSCs and SH-SY5Y could be differentiated to generate typical neuronal-like cells following sequential treatment with all-trans retinoic acid (ATRA) and brain-derived neurotrophic factor (BDNF), as evidenced by significant expression of neuronal proteins βIII-tubulin (TUBB3) and neurofilament medium (NF-M). Both cell types also expressed multiple neural gene markers including growth-associated protein 43 (GAP43), enolase 2/neuron-specific enolase (ENO2/NSE), synapsin I (SYN1), nestin (NES), and peripherin (PRPH), and exhibited measurable voltage-activated Na⁺ and K⁺ currents. In hDPSCs, upregulation of acetylcholinesterase (ACHE), choline O-acetyltransferase (CHAT), sodium channel alpha subunit 9 (SCN9A), POU class 4 homeobox 1 (POU4F1/BRN3A) along with a downregulation of motor neuron and pancreas homeobox 1 (MNX1) indicated that differentiation was more guided toward a cholinergic sensory neuronal lineage. Furthermore, the Extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor U0126 significantly impaired hDPSC neuronal differentiation and was associated with reduction of the ERK1/2 phosphorylation. In conclusion, this study demonstrates that extracellular signal-regulated kinase/Mitogen-activated protein kinase (ERK/MAPK) is necessary for sensory cholinergic neuronal differentiation of hDPSCs. hDPSC-derived cholinergic sensory neuronal-like cells represent a novel model and potential source for neuronal regeneration therapies.

Augmenting Peripheral Nerve Regeneration with Adipose-Derived Stem Cells

Peripheral nerve injuries (PNIs) are common and debilitating, cause significant health care costs for society, and rely predominately on autografts, which necessitate grafting a nerve section non-locally to repair the nerve injury. One possible approach to improving treatment is bolstering endogenous regenerative mechanisms or bioengineering new nervous tissue in the peripheral nervous system. In this review, we discuss critical-sized nerve gaps and nerve regeneration in rats, and summarize the roles of adipose-derived stem cells (ADSCs) in the treatment of PNIs. Several regenerative treatment modalities for PNI are described: ADSCs differentiating into Schwann cells (SCs), ADSCs secreting growth factors to promote peripheral nerve growth, ADSCs promoting myelination growth, and ADSCs treatments with scaffolds. ADSCs' roles in regenerative treatment and features are compared to mesenchymal stem cells, and the administration routes, cell dosages, and cell fates are discussed. ADSCs secrete neurotrophic factors and exosomes and can differentiate into Schwann cell-like cells (SCLCs) that share features with naturally occurring SCs, including the ability to promote nerve regeneration in the PNS. Future clinical applications are also discussed.

Reconstruction of the Rat Sciatic Nerve by Using Biodegradable and Non-Biodegradable Conduits

The aim of the study was to compare two types of conduits made of either non-resorbable Reperen or resorbable Tissucol for their effects on the regeneration of the rat sciatic nerve under conditions of stump diastasis.

Optimizing fibrin hydrogel toward effective neural progenitor cell delivery in spinal cord injury

Transplantation of neural progenitor cell (NPC) possessing the potential to differentiate into neurons may guard against spinal cord injury (SCI)- associated neuronal trauma. We propose that autologous-like NPC may reduce post-transplant immune response. The study used the rat SCI model to prove this concept. For isolation and expansion of rat NPC for cell-based SCI therapy, thein vitroprotocol standardized with human NPC seemed suitable. The primary aim of this study is to select a cell/neural tissue-compatible biomaterial for improving NPC survivalin vivo. The composition of the fibrin hydrogel is adjusted to obtain degradable, porous, and robust fibrin strands for supporting neural cell attachment, migration, and tissue regeneration. This study employed NPC culture to evaluate the cytocompatibility and suitability of the hydrogel, composed by adding graded concentrations of thrombin to a fixed fibrinogen concentration. The microstructure evaluation by scanning electron microscope guided the selection of a suitable composition for delivering the embedded cells. On adding more thrombin, fibrinogen clotted quickly but reduced porosity, pore size, and fiber strand thickness. The high activity of thrombin also affected NPC morphology and thein vitrocell survival. The selected hydrogel carried viable NPC and retained them at the injury site post-transplantation. The fibrin hydrogel played a protective role throughout the transfer process by providing cell attachment sites and survival signals. The fibrin and NPC together regulated the immune response at the SCI site reducing ED1^+ve/ED2^+vemacrophages in the early period of 8-16 d after injury. Migration ofβ-III tubulin^+veneural-like cells into the fibrin-injected control SCI is evident. The continuous use of a non-neurotoxic fibrin matrix could be a convenient strategy forin vitroNPC preparation, minimally invasive cell delivery, and better transplantation outcome.

Functional Outcomes of Nerve Allografts Seeded with Undifferentiated and Differentiated Mesenchymal Stem Cells in a Rat Sciatic Nerve Defect Model

BACKGROUND

Mesenchymal stem cells have the potential to produce neurotrophic growth factors and establish a supportive microenvironment for neural regeneration. The purpose of this study was to determine the effect of undifferentiated and differentiated mesenchymal stem cells dynamically seeded onto decellularized nerve allografts on functional outcomes when used in peripheral nerve repair.

METHODS

In 80 Lewis rats, a 10-mm sciatic nerve defect was reconstructed with (1) autograft, (2) decellularized allograft, (3) decellularized allograft seeded with undifferentiated mesenchymal stem cells, or (4) decellularized allograft seeded with mesenchymal stem cells differentiated into Schwann cell-like cells. Nerve regeneration was evaluated over time by cross-sectional tibial muscle ultrasound measurements, and at 12 and 16 weeks by isometric tetanic force measurements, compound muscle action potentials, muscle mass, histology, and immunofluorescence analyses.

RESULTS

At 12 weeks, undifferentiated mesenchymal stem cells significantly improved isometric tetanic force measurement and compound muscle action potential outcomes compared to decellularized allograft alone, whereas differentiated mesenchymal stem cells significantly improved compound muscle action potential outcomes. The autografts outperformed both stem cell groups histologically at 12 weeks. At 16 weeks, functional outcomes normalized between groups. At both time points, the effect of undifferentiated versus differentiated mesenchymal stem cells was not significantly different.

CONCLUSIONS

Undifferentiated and differentiated mesenchymal stem cells significantly improved functional outcomes of decellularized allografts at 12 weeks and were similar to autograft results in the majority of measurements. At 16 weeks, outcomes normalized as expected. Although differences between both cell types were not statistically significant, undifferentiated mesenchymal stem cells improved functional outcomes of decellularized nerve allografts to a greater extent and had practical benefits for clinical translation by limiting preparation time and costs.

Bioactive Nanofiber-Based Conduits in a Peripheral Nerve Gap Management-An Animal Model Study

The aim was to examine the efficiency of a scaffold made of poly (L-lactic acid)-co-poly(ϵ-caprolactone), collagen (COL), polyaniline (PANI), and enriched with adipose-derived stem cells (ASCs) as a nerve conduit in a rat model. P(LLA-CL)-COL-PANI scaffold was optimized and electrospun into a tubular-shaped structure. Adipose tissue from 10 Lewis rats was harvested for ASCs culture. A total of 28 inbred male Lewis rats underwent sciatic nerve transection and excision of a 10 mm nerve trunk fragment. In Group A, the nerve gap remained untouched; in Group B, an excised trunk was used as an autograft; in Group C, nerve stumps were secured with P(LLA-CL)-COL-PANI conduit; in Group D, P(LLA-CL)-COL-PANI conduit was enriched with ASCs. After 6 months of observation, rats were sacrificed. Gastrocnemius muscles and sciatic nerves were harvested for weight, histology analysis, and nerve fiber count analyses. Group A showed advanced atrophy of the muscle, and each intervention (B, C, D) prevented muscle mass decrease (p < 0.0001); however, ASCs addition decreased efficiency vs. autograft (p < 0.05). Nerve fiber count revealed a superior effect in the nerve fiber density observed in the groups with the use of conduit (D vs. B p < 0.0001, C vs. B p < 0.001). P(LLA-CL)-COL-PANI conduits with ASCs showed promising results in managing nerve gap by decreasing muscle atrophy.

Effect of Systemic Adipose-derived Stem Cell Therapy on Functional Nerve Regeneration in a Rodent Model

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Regardless of etiology, peripheral nerve injuries (PNI) result in disruption/loss of neuromuscular junctions, target muscle denervation, and poor sensorimotor outcomes with associated pain and disability. Adipose-derived stem cells (ASCs) have shown promise in neuroregeneration. However, there is a paucity of objective assessments reflective of functional neuroregeneration in experimental PNI. Here, we use a multimodal, static, and dynamic approach to evaluate functional outcomes after ASC therapy in a rodent PNI model.

Current challenges and future trends in manufacturing small diameter artificial vascular grafts in bioreactors

Cardiovascular diseases are a leading cause of death. Vascular surgery is mainly used to solve this problem. However, the generation of a functional and suitable substitute for small diameter (< 6 mm) displacement is challengeable. Moreover, synthetic prostheses, made of polyethylene terephthalate and extended polytetrafluoroethylene show have shown insufficient performance. Therefore, the challenges dominating the use of autografts have prevented their efficient use. Tissue engineering is highlighted in regenerative medicine perhaps in aiming to address the issue of end-stage organ failure. While organs and complex tissues require the vascular supply to support the graft survival and render the bioartificial organ role, vascular tissue engineering has shown to be a hopeful method for cell implantation by the production of tissues in vitro. Bioreactors are a salient point in vascular tissue engineering due to the capability for reproducible and controlled variations showing a new horizon in blood vessel substitution. This review strives to display the overview of current concepts in the development of small-diameter by using bioreactors. In this work, we show a critical look at different factors for developing small-diameter and give suggestions for future studies.

Ex-Vivo Stimulation of Adipose Stem Cells by Growth Factors and Fibrin-Hydrogel Assisted Delivery Strategies for Treating Nerve Gap-Injuries

Peripheral nerve injuries often result in lifelong disabilities despite advanced surgical interventions, indicating the urgent clinical need for effective therapies. In order to improve the potency of adipose-derived stem cells (ASC) for nerve regeneration, the present study focused primarily on ex-vivo stimulation of ASC by using growth factors, i.e., nerve growth factor (NGF) or vascular endothelial growth factor (VEGF) and secondly on fibrin-hydrogel nerve conduits (FNC) assisted ASC delivery strategies, i.e., intramural vs. intraluminal loading. ASC were stimulated by NGF or VEGF for 3 days and the resulting secretome was subsequently evaluated in an in vitro axonal outgrowth assay. For the animal study, a 10 mm sciatic nerve gap-injury was created in rats and reconstructed using FNC loaded with ASC. Secretome derived from NGF-stimulated ASC promoted significant axonal outgrowth from the DRG-explants in comparison to all other conditions. Thus, NGF-stimulated ASC were further investigated in animals and found to enhance early nerve regeneration as evidenced by the increased number of β-Tubulin III+ axons. Notably, FNC assisted intramural delivery enabled the improvement of ASC’s therapeutic efficacy in comparison to the intraluminal delivery system. Thus, ex-vivo stimulation of ASC by NGF and FNC assisted intramural delivery may offer new options for developing effective therapies.

Gene expression and growth factor analysis in early nerve regeneration following segmental nerve defect reconstruction with a mesenchymal stromal cell-enhanced decellularized nerve allograft

The purpose of this study was to evaluate the molecular mechanisms underlying nerve repair by a decellularized nerve allograft seeded with adipose-derived mesenchymal stromal cells (MSCs) and compare it to the unseeded allograft and autograft nerve.

METHODS

Undifferentiated MSCs were seeded onto decellularized nerve allografts and used to reconstruct a 10 mm gap in a rat sciatic nerve model. Gene expression profiles of genes essential for nerve regeneration and immunohistochemical staining (IHC) for PGP9.5, NGF, RECA-1, and S100 were obtained 2 weeks postoperatively.

RESULTS

Semi-quantitative RT-PCR analysis showed that the angiogenic molecule VEGFA was significantly increased in seeded allografts, and transcription factor SOX2 was downregulated in seeded allografts. Seeded grafts showed a significant increase in immunohistochemical markers NGF and RECA-1, when compared with unseeded allografts.

CONCLUSIONS

MSCs contributed to the secretion of trophic factors. A beneficial effect of the MSCs on angiogenesis was found when compared with the unseeded nerve allograft, but implanted MSCs did not show evidence of differentiation into Schwann cell-like cells.

Gene expression profiles of differentiated and undifferentiated adipose derived mesenchymal stem cells dynamically seeded onto a processed nerve allograft

BACKGROUND

Differentiation of mesenchymal stem cells (MSCs) into Schwann-like cells onto processed nerve allografts may support peripheral nerve repair. The purpose of this study was to understand the biological characteristics of undifferentiated and differentiated MSCs before and after seeding onto a processed nerve allograft by comparing gene expression profiles.

METHODS

MSCs from Lewis rats were cultured in maintenance media or differentiated into Schwann-like cells. Both treatment groups were dynamically seeded onto decellularized nerve allografts derived from Sprague-Dawley rats. Gene expression was quantified by quantitative polymerase chain reaction (qPCR) analysis of representative biomarkers, including neurotrophic (GDNF, PTN, GAP43, PMP22), angiogenic (CD31, VEGF1), extracellular matrix (ECM) (COL1A1, COL3A1, FBLN1, LAMB2) or cell cycle (CAPS3, CCBN2) genes. Gene expression values were statistically evaluated using a 2-factor ANOVA with repeated measures.

RESULTS

Baseline gene expression of undifferentiated and differentiated MSCs was significantly altered upon interaction with processed nerve allografts. Interaction between processed allografts and undifferentiated MSCs enhanced expression of neurotrophic (NGF, GDNF, PMP22), ECM (FBLN1, LAMB2) and regulatory cell cycle genes (CCNB2) during a 7-day time course. Interactions of differentiated MSCs with nerve allografts enhanced expression of neurotrophic (NGF, GDNF, GAP43), angiogenic (VEGF1), ECM (FBLN1) and regulatory cell cycle genes (CASP3, CCNB2) within one week.

CONCLUSIONS

Dynamic seeding onto processed nerve allografts modulates temporal gene expression profiles of differentiated and undifferentiated MSCs. These changes in gene expressions may support the reparative functions of MSCs in supporting nerve regeneration in different stages of axonal growth.

Differentiated human adipose-derived stromal cells exhibit the phenotypic and functional characteristics of mature Schwann cells through a modified approach

BACKGROUND AIMS

Tissue engineering technology is a promising therapeutic strategy in peripheral nerve injury. Schwann cells (SCs) are deemed to be a vital component of cell-based nerve regeneration therapies. Many methods for producing SC-like cells derived from adipose-derived stromal cells (ADSCs) have been explored, but their phenotypic and functional characteristics remain unsatisfactory.

METHODS

We investigated whether human ADSCs can be induced to differentiate into mature and stable SC-like cells with the addition of insulin, progestero``ne and glucocorticoids. The phenotypic and functional characteristics of new differentiated ADSCs (modified SC-like cells) were evaluated by real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay and immunocytochemistry in vitro. Cells loaded into collagen sponge biomaterials were implanted around transected sciatic nerves with a 10-mm gap in vivo. The axon regrowth and functional recovery of the regenerated nerves were assessed by immunohistochemistry and Walking footprint analysis.

RESULTS

After differentiation induction, the modified SC-like cells showed significantly up-regulated levels of S100B and P0 and enhanced proliferative and migratory capacities. In addition, the modified SC-like cells showed increased secretion of neurotrophic factors, and their functional characteristics were maintained for more than 3 weeks after removing the induction reagents. The modified SC-like cells exhibited significantly enhanced axon regrowth, myelination and functional recovery after sciatic nerve injury.

CONCLUSIONS

Overall, the results suggest that this modified induction method can induce human ADSCs to differentiate into cells with the molecular and functional properties of mature SCs and increase the promotion of peripheral nerve regeneration.

Adipose Stem Cells Enhance Nerve Regeneration and Muscle Function in a Peroneal Nerve Ablation Model

Severe peripheral nerve injuries have devastating consequences on the quality of life in affected patients, and they represent a significant unmet medical need. Destruction of nerve fibers results in denervation of targeted muscles, which, subsequently, undergo progressive atrophy and loss of function. Timely restoration of neural innervation to muscle fibers is crucial to the preservation of muscle homeostasis and function. The goal of this study was to evaluate the impact of addition of adipose stem cells (ASCs) to polycaprolactone (PCL) nerve conduit guides on peripheral nerve repair and functional muscle recovery in the setting of a critical size nerve defect. To this end, peripheral nerve injury was created by surgically ablating 6 mm of the common peroneal nerve in a rat model. A PCL nerve guide, filled with ASCs and/or poloxamer hydrogel, was sutured to the nerve ends. Negative and positive controls included nerve ablation only (no repair), and reversed polarity autograft nerve implant, respectively. Tibialis anterior (TA) muscle function was assessed at 4, 8, and 12 weeks postinjury, and nerve and muscle tissue was retrieved at the 12-week terminal time point. Inclusion of ASCs in the PCL nerve guide elicited statistically significant time-dependent increases in functional recovery (contraction) after denervation; ∼25% higher than observed in acellular (poloxamer-filled) implants and indistinguishable from autograft implants, respectively, at 12 weeks postinjury (p < 0.05, n = 7-8 in each group). Analysis of single muscle fiber cross-sectional area (CSA) revealed that ASC-based treatment of nerve injury provided a better recapitulation of the overall distribution of muscle fiber CSAs observed in the contralateral TA muscle of uninjured limbs. In addition, the presence of ASCs was associated with improved features of re-innervation distal to the defect, with respect to neurofilament and S100 (Schwann cell marker) expression. In conclusion, these initial studies indicate significant benefits of inclusion of ASCs to the rate and magnitude of both peripheral nerve regeneration and functional recovery of muscle contraction, to levels equivalent to autograft implantation. These findings have important implications to improved nerve repair, and they provide input for future work directed to restoration of nerve and muscle function after polytraumatic injury. Impact Statement This works explores the application of adipose stem cells (ASCs) for peripheral nerve regeneration in a rat model. Herein, we demonstrate that the addition of ASCs in poloxamer-filled PCL nerve guide conduits impacts nerve regeneration and recovery of muscle function, to levels equivalent to autograft implantation, which is considered to be the current gold standard treatment. This study builds on the importance of a timely restoration of innervation to muscle fibers for preservation of muscle homeostasis, and it will provide input for future work aiming at restoring nerve and muscle function after polytraumatic injury.

Regeneration of nerve crush injury using adipose-derived stem cells: A multimodal comparison

Introduction: To restore full function following nerve crush injuries is critical but challenging. In an attempt to develop a viable therapy, we evaluated the effect of rat adipose‐derived stem cells (rASC) in 2 different settings of a sciatic crush injury model. Methods: In the first group, after 14 days of nerve crush injury, rASCs were injected distal to the lesion under ultrasound guidance. In the other group, alleviation of compression through clip removal (CR) was combined with epineural injection of rASCs. Gait analyses, MRI, gastrocnemius muscle weight ratio (MWR), and histomorphometry were performed for outcome analysis. Results: CR combined with rASC injection resulted in less muscle atrophy, as evidenced by MWR. These findings are further supported by better functional and anatomical outcomes. Discussion: Animals treated with CR and epineural stem cell injection showed enhanced anatomical and functional recovery. Muscle Nerve58: 566–572, 2018

Targeted stimulation of MSCs in peripheral nerve repair

Mesenchymal stem cells (MSCs) have considerable translational potential in a wide variety of clinical disciplines and are the cellular foundation of individualized treatments of auto-immune, cardiac, neurologic and musculoskeletal diseases and disorders. While the cellular mechanisms by which MSCs exert their biological effects remain to be ascertained, it has been hypothesized that MSCs are supportive of local tissue repair through secretion of essential growth factors. Therapeutic applications of MSCs in peripheral nerve repair have recently been reported. This review focuses on how MSCs can promote nerve regeneration by conversion into Schwann-like cells, and discusses differentiation methods including delivery and dosing of naive or differentiated MSCs, as well as in vitro and in vivo outcomes. While MSC-based therapies for nerve repair are still in early stages of development, current progress in the field provides encouragement that MSCs may have utility in the treatment of patients with peripheral nerve injury.

Novel approaches using mesenchymal stem cells for curing peripheral nerve injuries

Peripheral nerve injury (PNI) is a common life-changing disability of peripheral nervous system with significant socioeconomic consequences. Conventional therapeutic approaches for PNI have several drawbacks such as need to autologous nerve scarifying, surplus surgery, and difficult accessibility to donor nerve; therefore, other therapeutic strategies such as mesenchymal stem cells (MSCs) therapy are getting more interesting. MSCs have been proved to be safe and efficient in numerous degenerative diseases of central and peripheral nervous systems. In this paper, we review novel biotechnological advancements in treating PNI using MSCs.

In vivo Evaluation of Nanostructured Fibrin-Agarose Hydrogels With Mesenchymal Stem Cells for Peripheral Nerve Repair

The regenerative capability of peripheral nerves is very limited, and several strategies have been proposed to increase nerve regeneration. In the present work, we have analyzed the in vivo usefulness of a novel nanostructured fibrin-agarose bio-artificial nerve substitute (Nano) used alone or in combination with NeuraGen^® collagen type I conduits (Coll-Nano) in laboratory rats with a 10-mm sciatic nerve defect. Control animals were subjected to the gold-standard autograft technique (Auto). Results first demonstrated that the percentage of self-amputations was lower in Nano and Coll-Nano groups as compared to the Auto group. Neurotrophic ulcers were more abundant in the Auto group (60%, with 66.6% of them being >2-mm) than Nano and Coll-Nano groups (0%) at 4 weeks, although Nano showed more ulcers after 12 weeks. Foot length was significantly altered in Auto animals due to neurogenic retraction, but not in Nano and Coll-Nano groups after 12 weeks. At the functional level, all animals showed a partial sensory recovery as determined by the pinch test, especially in Nano and Auto groups, but did not reach the levels of native animals. Toe-spread test revealed a partial motor function recovery only in Nano animals at 4 weeks and Auto and Nano at 12 weeks. Electromyography showed clear denervation signs in all experimental groups, with few differences between Auto and Nano animals. After 12 weeks, an important denervation decrease and an increase of the reinnervation process was found in Auto and Nano groups, with no differences between these groups. Histological analyses demonstrated an active peripheral nerve regeneration process with newly formed peripheral nerve fascicles showing S-100, GAP-43 and myelin in all experimental groups. The peripheral nerve regeneration process was more abundant in Auto group, followed by Nano group, and both were better than Coll-Nano group. Muscle histology confirmed the electromyography results and showed some atrophy and fibrosis signs and an important weight and volume loss in all groups, especially in the Coll-Nano group (56.8% weight and 60.4% volume loss). All these results suggest that the novel Nano substitutes used in in vivo were able to contribute to bridge a 10-mm peripheral nerve defect in rats.

A basic fibroblast growth factor slow-release system combined to a biodegradable nerve conduit improves endothelial cell and Schwann cell proliferation: A preliminary study in a rat model

BACKGROUND

A basic fibroblast growth factor (bFGF) slow-release system was combined to a biodegradable nerve conduit with the hypothesis this slow-release system would increase the capacity to promote nerve vascularization and Schwann cell proliferation in a rat model.

MATERIALS AND METHODS

Slow-release of bFGF was determined using Enzyme-Linked ImmunoSorbent Assay (ELISA). A total of 60 rats were used to create a 10 mm gap in the sciatic nerve. A polyglycolic acid-based nerve conduit was used to bridge the gap, either without or with a bFGF slow-release incorporated around the conduit (n = 30 in each group). At 2 (n = 6), 4 (n = 6), 8 (n = 6), and 20 (n = 12) weeks after surgery, samples were resected and subjected to histological, immunohistochemical, and transmission electron microscopic evaluation for nerve regeneration.

RESULTS

Continuous release of bFGF was found during the observation period of 2 weeks. After in vivo implantation of the nerve conduit, greater endothelial cell migration and vascularization resulted at 2 weeks (proximal: 20.0 ± 2.0 vs. 12.7 ± 2.1, P = .01, middle: 17.3 ± 3.5 vs. 8.7 ± 3.2, P = .03). Schwann cells showed a trend toward greater proliferation and axonal growth had significant elongation (4.9 ± 1.1 mm vs. 2.8 ± 1.5 mm, P = .04) at 4 weeks after implantation. The number of myelinated nerve fibers, indicating nerve maturation, were increased 20 weeks after implantation (proximal: 83.3 ± 7.5 vs. 53.3 ± 5.5, P = .06, distal: 71.0 ± 12.5 vs. 44.0 ± 11.1, P = .04).

CONCLUSIONS

These findings suggest that the bFGF slow-release system improves nerve vascularization and Schwann cell proliferation through the biodegradable nerve conduit.

Epineural adipose-derived stem cell injection in a sciatic rodent model

BACKGROUND

The aim was to evaluate the regenerative effect of epineural injection of rat ASCs (rASCs) in three different settings of acute and chronic compression in a rat sciatic nerve model.

METHODS

Acute compression (60 s) with a vessel clamp over a distance of 1 mm (group 1) or 10 mm (group 2), as well as chronic compression with a permanent remaining, nonabsorbable polymeric clip over a distance of 1 mm (group 3) was performed. Depending on the group, either 5 × 106 rASCs or the same volume (25 μl) of culture medium (CM) was injected with a 30G needle in the epineurium at the time of compression. Outcome measures were functional gait evaluations, imaging analysis, histomorphometric analyses, and muscle weight.

RESULTS

The rats in group 2 had a better function than those with group 1 at one and especially at 2 weeks. After 4 weeks however, almost all rats were close to a normal function. There was a similar Muscle Weight Ratio (MWR) after 2 weeks in all groups, whereas after 4 weeks, the MWR in group 3 was lower compared with group 1 and 2. Histomorphometric analysis showed a better myelination in group 1 & 2 compared to group 3 after 4 weeks. ASCs have a beneficial effect on myelin thickness (G-Ratio).

CONCLUSIONS

We successfully evaluated the regenerative effect of epineural injection of rASCs in three different settings of acute and chronic compression. However, there were no significant differences in outcomes between the ASC-treated groups and control groups.

The role of undifferentiated adipose-derived stem cells in peripheral nerve repair

Peripheral nerve injuries impose significant health and economic consequences, yet no surgical repair can deliver a complete recovery of sensory or motor function. Traditional methods of repair are less than ideal: direct coaptation can only be performed when tension-free repair is possible, and transplantation of nerve autograft can cause donor-site morbidity and neuroma formation. Cell-based therapy delivered via nerve conduits has thus been explored as an alternative method of nerve repair in recent years. Stem cells are promising sources of the regenerative core material in a nerve conduit because stem cells are multipotent in function, abundant in supply, and more accessible than the myelinating Schwann cells. Among different types of stem cells, undifferentiated adipose-derived stem cell (uASC), which can be processed from adipose tissue in less than two hours, is a promising yet underexplored cell type. Studies of uASC have emerged in the past decade and have shown that autologous uASCs are non-immunogenic, easy to access, abundant in supply, and efficacious at promoting nerve regeneration. Two theories have been proposed as the primary regenerative mechanisms of uASC: in situ trans-differentiation towards Schwann cells, and secretion of trophic and anti-inflammatory factors. Future studies need to fully elucidate the mechanisms, side effects, and efficacy of uASC-based nerve regeneration so that uASCs can be utilized in clinical settings.

Tissue engineering; strategies, tissues, and biomaterials

Current tissue regenerative strategies rely mainly on tissue repair by transplantation of the synthetic/natural implants. However, limitations of the existing strategies have increased the demand for tissue engineering approaches. Appropriate cell source, effective cell modification, and proper supportive matrices are three bases of tissue engineering. Selection of appropriate methods for cell stimulation, scaffold synthesis, and tissue transplantation play a definitive role in successful tissue engineering. Although the variety of the players are available, but proper combination and functional synergism determine the practical efficacy. Hence, in this review, a comprehensive view of tissue engineering and its different aspects are investigated.

Split-sciatic nerve surgery: A new microsurgical model in experimental nerve repair

INTRODUCTION

Sciatic experimental surgery in rat often leads to hindlimb autophagy, with considerable ethical and research issues. In this work, the distal part of the sciatic nerve was split following the natural bifurcation between tibial and peroneal branches, before applying regenerative stem cells in a fibrin conduit on the peroneal segment. The new microsurgical model was tested in terms of animal morbidity and consistency of research outcomes, particularly comparing to the standard total sciatic axotomy procedure.

MATERIALS AND METHODS

After dissection of sciatic the nerve, the tibial and peroneal fibres were split upwards and a total axotomy was performed in the peroneal side. The 1 cm nerve gap between the proximal sciatic nerve and peroneal nerve was crossed using fibrin conduits. The tibial nerve was not included. Experimental groups involved either empty or fibrin conduit seeded with Schwann cell-like differentiated adipose derived stem cells (dASC) (Fib + dASC). Autografts and sham rats were used as controls (total n = 20). At 12 weeks post-implantation, an extensive histomorphometric analysis was performed. Functional aspects of regeneration were analysed by walking track analysis.

RESULTS

No major autophagy occurred using the split-sciatic technique. A detailed histomorphometric analysis showed consistent results with previous literature using fibrin conduits in a full sciatic axotomy experimental setting. Walking track analysis reflected the histological regeneration pattern, displaying superior regeneration in both autograft and dASC groups.

CONCLUSION

Split-Sciatic nerve surgery reduced animal morbidity, while being representative of the whole nerve as regeneration outcomes were consistent with previous data obtained on the whole sciatic nerve. The decreased autophagy rate allowed for a more efficient functional evaluation.

Validity and reliability of the CatWalk system as a static and dynamic gait analysis tool for the assessment of functional nerve recovery in small animal models

INTRODUCTION

A range of behavioral testing paradigms have been developed for the research of central and peripheral nerve injuries with the help of small animal models. Following any nerve repair strategy, improved functional outcome may be the most important evidence of axon regeneration. A novel automated gait analysis system, the CatWalk^™, can measure dynamic as well as static gait patterns of small animals. Of most interest in detecting functional recovery are in particular dynamic gait parameters, coordination measures, and the intensity of the animals paw prints. This article is designed to lead to a more efficient choice of CatWalk parameters in future studies concerning the functional evaluation of nerve regeneration and simultaneously add to better interstudy comparability.

METHODS

The aims of the present paper are threefold: (1) to describe the functional method of CatWalk gait analysis, (2) to characterize different parameters acquired by CatWalk gait analysis, and to find the most frequently used parameters as well as (3) to compare their reliability and validity throughout the different studies.

RESULTS

In the reviewed articles, the most frequently used parameters were Swing Duration (30), Print Size (27), Stride Length (26), and Max Contact Area (24). Swing Duration was not only frequently used but was also the most reliable and valid parameter. Therefore, we hypothesize that Swing Duration constitutes an important parameter to be chosen for future studies, as it has the highest level of reliability and validity.

CONCLUSION

In conclusion, CatWalk can be used as a complementary approach to other behavioral testing paradigms to assess clinically relevant behavioral benefits, with the main advantage that this system demonstrates both static and dynamic gait parameters at the same time. Due to limited reliability and validity of certain parameters, we recommend that only the most frequently assessed parameters should be used in the future.

Stem Cell Transplantation for Peripheral Nerve Regeneration: Current Options and Opportunities

Peripheral nerve regeneration is a complicated process highlighted by Wallerian degeneration, axonal sprouting, and remyelination. Schwann cells play an integral role in multiple facets of nerve regeneration but obtaining Schwann cells for cell-based therapy is limited by the invasive nature of harvesting and donor site morbidity. Stem cell transplantation for peripheral nerve regeneration offers an alternative cell-based therapy with several regenerative benefits. Stem cells have the potential to differentiate into Schwann-like cells that recruit macrophages for removal of cellular debris. They also can secrete neurotrophic factors to promote axonal growth, and remyelination. Currently, various types of stem cell sources are being investigated for their application to peripheral nerve regeneration. This review highlights studies involving the stem cell types, the mechanisms of their action, methods of delivery to the injury site, and relevant pre-clinical or clinical data. The purpose of this article is to review the current point of view on the application of stem cell based strategy for peripheral nerve regeneration.

Collagen Type I Conduits for the Regeneration of Nerve Defects

To date, reliable data to support the general use of biodegradable materials for bridging nerve defects are still scarce. We present the outcome of nerve regeneration following type I collagen conduit nerve repair in patients with large-diameter nerve gaps. Ten patients underwent nerve repair using a type I collagen nerve conduit. Patients were re-examined at a minimal follow-up of 14.0 months and a mean follow-up of 19.9 months. Regeneration of nerve tissue within the conduits was assessed by nerve conduction velocity (NCV), a static two-point discrimination (S2PD) test, and as disability of arm shoulder and hand (DASH) outcome measure scoring. Quality of life measures including patients’ perceived satisfaction and residual pain were evaluated using a visual analog scale (VAS). No implant-related complications were observed. Seven out of 10 patients reported being free of pain, and the mean VAS was 1.1. The mean DASH score was 17.0. The S2PD was below 6 mm in 40%, between 6 and 10 mm in another 40% and above 10 mm in 20% of the patients. Eight out of 10 patients were satisfied with the procedure and would undergo surgery again. Early treatment correlated with lower DASH score levels. The use of type I collagen in large-diameter gaps in young patients and early treatment presented superior functional outcomes.

Analysis of migration rate and chemotaxis of human adipose-derived mesenchymal stem cells in response to LPS and LTA in vitro

Mesenchymal stem cells (MSC) are able to stimulate the regeneration of injured tissue. Since bacterial infections are common complications in wound healing, bacterial pathogens and their components come into direct contact with MSC. The interaction with bacterial structures influences the proliferation, differentiation and migratory activity of the MSC, which might be of relevance during regeneration. Studies on MSC migration in response to bacterial components have shown different results depending on the cell type. Here, we analyzed the migration rate and chemotaxis of human adipose-derived MSC (adMSC) in response to the basic cell-wall components lipopolysaccharide (LPS) of Gram-negative bacteria and lipoteichoic acid (LTA) of Gram-positive bacteria in vitro. To this end, we used transwell and scratch assays, as well as a specific chemotaxis assay combined with live-cell imaging. We found no significant influence of LPS or LTA on the migration rate of adMSC in transwell or scratch assays. Furthermore, in the µ-slide chemotaxis assay, the stimulation with LPS did not exert any chemotactic effect on adMSC.