Time course of functional recovery after 1 cm sciatic nerve resection in rats with or without surgical intervention - measured by grip strength and locomotor activity

The rat sciatic nerve (SN) is the most frequently used model in experimental research on peripheral nerve injuries. Within the broad range of evaluation methods to determine the experimental outcome, recovery of behavior represents the major criterion to assess functional regeneration. The grasping test indicates when recovery begins and its improvement with time. However, lesions of the SN have yet remained unstudied with this method. Therefore, rats received a SN resection and were divided into experimental groups: 1) control with lesion only, 2) nerve bridge, and 3) autograft. During weekly sessions, the grasping test measured the grip strength, and the locomotor behavior was assessed in the open field. Finally, the nerves were prepared for electrophysiology and histomorphometry. Autograft recovered grasping after 7 weeks with the strongest improvement afterwards. Nerve tube allowed grasping by week 12. Control animals did not recover. In the open field, no differences were observed between the groups. Recordings were possible only in the autograft group, which could be explained by higher number of regenerated fibers. This study indicates that grasping data correspond with physiological and anatomical findings. We conclude that the grasping test is a valid method to evaluate functional recovery after SN resection in rats.

Cell-instructive biomaterials in tissue engineering and regenerative medicine

The field of biomaterials aims to improve regenerative outcomes or scientific understanding for a wide range of tissue types and ailments. Biomaterials can be fabricated from natural or synthetic sources and display a plethora of mechanical, electrical, and geometrical properties dependent on their desired application. To date, most biomaterial systems designed for eventual translation to the clinic rely on soluble signaling moieties, such as growth factors, to elicit a specific cellular response. However, these soluble factors are often limited by high cost, convoluted synthesis, low stability, and difficulty in regulation, making the translation of these biomaterials systems to clinical or commercial applications a long and arduous process. In response to this, significant effort has been dedicated to researching cell-directive biomaterials which can signal for specific cell behavior in the absence of soluble factors. Cells of all tissue types have been shown to be innately in tune with their microenvironment, which is a biological phenomenon that can be exploited by researchers to design materials that direct cell behavior based on their intrinsic characteristics. This review will focus on recent developments in biomaterials that direct cell behavior using biomaterial properties such as charge, peptide presentation, and micro- or nano-geometry. These next generation biomaterials could offer significant strides in the development of clinically relevant medical devices which improve our understanding of the cellular microenvironment and enhance patient care in a variety of ailments.

Characterization of a Novel Aspect of Tissue Scarring Following Experimental Spinal Cord Injury and the Implantation of Bioengineered Type-I Collagen Scaffolds in the Adult Rat: Involvement of Perineurial-like Cells?

Numerous intervention strategies have been developed to promote functional tissue repair following experimental spinal cord injury (SCI), including the bridging of lesion-induced cystic cavities with bioengineered scaffolds. Integration between such implanted scaffolds and the lesioned host spinal cord is critical for supporting regenerative growth, but only moderate-to-low degrees of success have been reported. Light and electron microscopy were employed to better characterise the fibroadhesive scarring process taking place after implantation of a longitudinally microstructured type-I collagen scaffold into unilateral mid-cervical resection injuries of the adult rat spinal cord. At long survival times (10 weeks post-surgery), sheets of tightly packed cells (of uniform morphology) could be seen lining the inner surface of the repaired dura mater of lesion-only control animals, as well as forming a barrier along the implant–host interface of the scaffold-implanted animals. The highly uniform ultrastructural features of these scarring cells and their anatomical continuity with the local, reactive spinal nerve roots strongly suggest their identity to be perineurial-like cells. This novel aspect of the cellular composition of reactive spinal cord tissue highlights the increasingly complex nature of fibroadhesive scarring involved in traumatic injury, and particularly in response to the implantation of bioengineered collagen scaffolds.

Milestones and current achievements in development of multifunctional bioscaffolds for medical application

Tissue engineering (TE) is a rapidly growing interdisciplinary field, which aims to restore or improve lost tissue function. Despite that TE was introduced more than 20 years ago, innovative and more sophisticated trends and technologies point to new challenges and development. Current challenges involve the demand for multifunctional bioscaffolds which can stimulate tissue regrowth by biochemical curves, biomimetic patterns, active agents and proper cell types. For those purposes especially promising are carefully chosen primary cells or stem cells due to its high proliferative and differentiation potential. This review summarized a variety of recently reported advanced bioscaffolds which present new functions by combining polymers, nanomaterials, bioactive agents and cells depending on its desired application. In particular necessity of study biomaterial-cell interactions with in vitro cell culture models, and studies using animals with in vivo systems were discuss to permit the analysis of full material biocompatibility. Although these bioscaffolds have shown a significant therapeutic effect in nervous, cardiovascular and muscle, tissue engineering, there are still many remaining unsolved challenges for scaffolds improvement.

Extrusion-Printing of Multi-Channeled Two-Component Hydrogel Constructs from Gelatinous Peptides and Anhydride-Containing Oligomers

The performance of artificial nerve guidance conduits (NGC) in peripheral nerve regeneration can be improved by providing structures with multiple small channels instead of a single wide lumen. 3D-printing is a strategy to access such multi-channeled structures in a defined and reproducible way. This study explores extrusion-based 3D-printing of two-component hydrogels from a single cartridge printhead into multi-channeled structures under aseptic conditions. The gels are based on a platform of synthetic, anhydride-containing oligomers for cross-linking of gelatinous peptides. Stable constructs with continuous small channels and a variety of footprints and sizes were successfully generated from formulations containing either an organic or inorganic gelation base. The adjustability of the system was investigated by varying the cross-linking oligomer and substituting the gelation bases controlling the cross-linking kinetics. Formulations with organic N-methyl-piperidin-3-ol and inorganic K₂HPO₄ yielded hydrogels with comparable properties after manual processing and extrusion-based 3D-printing. The slower reaction kinetics of formulations with K₂HPO₄ can be beneficial for extending the time frame for printing. The two-component hydrogels displayed both slow hydrolytic and activity-dependent enzymatic degradability. Together with satisfying in vitro cell proliferation data, these results indicate the suitability of our cross-linked hydrogels as multi-channeled NGC for enhanced peripheral nerve regeneration.

Adjustable conduits for guided peripheral nerve regeneration prepared from bi-zonal unidirectional and multidirectional laminar scaffold of type I collagen

Shortness of donor nerves has led to the development of nerve conduits that connect sectioned peripheral nerve stumps and help to prevent the formation of neuromas. Often, the standard diameters of these devices cannot be adapted at the time of surgery to the diameter of the nerve injured. In this work, scaffolds were developed to form filled nerve conduits with an inner matrix with unidirectional channels covered by a multidirectional pore zone. Collagen type I dispersions (5 mg/g and 8 mg/g) were sequentially frozen using different methods to obtain six laminar scaffolds (P1 to P5) formed by a unidirectional (U) pore/channel zone adjacent to a multidirectional (M) pore zone. The physicochemical and microstructural properties of the scaffolds were determined and compared, as well as their biodegradability, residual glutaraldehyde and cytocompatibility. Also, the Young's modulus of the conduits made by rolling up the bizonal scaffolds from the unidirectional to the multidirectional zone was determined. Based on these comparisons, the proliferation and differentiation of hASC were assessed only in the P3 scaffolds. The cells adhered, aligned in the same direction as the unidirectional porous fibers, proliferated, and differentiated into Schwann-like cells. Adjustable conduits made with the P3 scaffold were implanted in rats 10 mm sciatic nerve lesions to compare their performance with that of autologous sciatic nerve grafted lesions. The in vivo results demonstrated that the tested conduit can be adapted to the diameter of the nerve stumps to guide their growth and promote their regeneration.

Modification of tubular chitosan-based peripheral nerve implants: applications for simple or more complex approaches

Surgical treatment of peripheral nerve injuries is still a major challenge in human clinic. Up to now, none of the well-developed microsurgical treatment options is able to guarantee a complete restoration of nerve function. This restriction is also effective for novel clinically approved artificial nerve guides. In this review, we compare surgical repair techniques primarily for digital nerve injuries reported with relatively high prevalence to be valuable attempts in clinical digital nerve repair and point out their advantages and shortcomings. We furthermore discuss the use of artificial nerve grafts with a focus on chitosan-based nerve guides, for which our own studies contributed to their approval for clinical use. In the second part of this review, very recent future perspectives for the enhancement of tubular (commonly hollow) nerve guides are discussed in terms of their clinical translatability and ability to form three-dimensional constructs that biomimick the natural nerve structure. This includes materials that have already shown their beneficial potential in in vivo studies like fibrous intraluminal guidance structures, hydrogels, growth factors, and approaches of cell transplantation. Additionally, we highlight upcoming future perspectives comprising co-application of stem cell secretome. From our overview, we conclude that already simple attempts are highly effective to increase the regeneration supporting properties of nerve guides in experimental studies. But for bringing nerve repair with bioartificial nerve grafts to the next level, e.g. repair of defects > 3 cm in human patients, more complex intraluminal guidance structures such as innovatively manufactured hydrogels and likely supplementation of stem cells or their secretome for therapeutic purposes may represent promising future perspectives.

Isoquercitrin promotes peripheral nerve regeneration through inhibiting oxidative stress following sciatic crush injury in mice

Background

Oxidative stress has been recognized to play a crucial role in the pathogenesis of peripheral nerve injury. Isoquercitrin (quercetin-3-glucoside) is a flavonoid that exhibited many biological activities, including anti-oxidative effect. However, it is unclear whether isoquercitrin has protective effects on peripheral nerve injury.

Methods

Mice treated by isoquercitrin were used as a case group, and mice injected with saline was the control group. Sciatic behavioral function was assessed using SFI and CMAPs were measured by electrophysiology. Schwann cells proliferation and migration were tested using EdU staining and Transwell migration chambers respectively. The expression of oxidative stress related factors were detected by qRT-PCR and Western blotting.

Results

In present study, our results demonstrated that isoquercitrin (20 mg/kg/day) treatment achieved significantly higher SFI and higher amplitude of CMAP, promoted the nerve regeneration and remyelination, increased the production of GAP43, NF200, MAG and PMP22, alleviated target muscle atrophy and autophagy, and suppressed the expression of ATG7, PINK1 and Beclin1 in soleus muscles after sciatic nerve crush. In vitro studies found that isoquercitrin promoted the axonal regeneration of DRGs neurons, the proliferation and migration of Schwann cells, and the expression of proliferating cell nuclear antigen (PCNA) in Schwann cells. The administration of isoquercitrin at 40 and 320 µM showed a dose dependent, and high doses of isoquercitrin (160 and 320 µM) showed better performance in promoting axonal regeneration of DRGs neurons, and the proliferation and migration of Schwann cells than low dose of isoquercitrin (40 µM). Furthermore, isoquercitrin significantly inhibited oxidative stress through reducing the production of Nox4 and Duox1, and promoting the expression of Nrf2 and SOD2 in soleus muscles after sciatic nerve crush.

Conclusions

Isoquercitrin may promote motor functional recovery and nerve regeneration following peripheral nerve injury though inhibition of oxidative stress, which highlighted the therapeutic values of isoquercitrin as a neuroprotective drug for peripheral nerve repair applications.

Tissue Models for Neurogenesis and Repair in 3D

Development and maturation of vascular and neuronal tissues occurs simultaneously in utero, and are regulated by significant crosstalk. We report on the development of a 3D tissue system to model neurogenesis and recapitulate developmental signaling conditions. Human umbilical vein endothelial cells (HUVECs) were seeded inside channels within collagen gels to represent nascent vascular networks. Axons extending from chicken dorsal root ganglia (DRGs) grew significantly longer and preferentially towards the HUVEC seeded channels with respect to unloaded channels. To replicate these findings without the vascular component, channels were loaded with brain-derived neurotrophic factor (BDNF), the principle signaling molecule in HUVEC-stimulated axonal growth, and axons likewise were significantly longer and grew preferentially towards the BDNF-loaded channels with respect to controls. This 3D tissue system was then used as an in vitro replicate for peripheral nerve injury, with neural repair observed within 2 weeks. These results demonstrate that our 3D tissue system can model neural network formation, repair after laceration injuries, and can be utilized to further study how these networks form and interact with other tissues, such as skin or skeletal muscle.

SIL1 deficiency causes degenerative changes of peripheral nerves and neuromuscular junctions in fish, mice and human

BACKGROUND

Marinesco-Sjögren Syndrome (MSS) is a rare neuromuscular condition caused by recessive mutations in the SIL1 gene resulting in the absence of functional SIL1 protein, a co-chaperone for the major ER chaperone, BiP. As BiP is decisive for proper protein processing, loss of SIL1 results in the accumulation of misshaped proteins. This accumulation likely damages and destroys cells in vulnerable tissues, leading to congenital cataracts, cerebellar ataxia, vacuolar myopathy and other MSS phenotypes. Whether the peripheral nervous system (PNS) is affected in MSS has not been conclusively shown.

METHODS

To study PNS vulnerability in MSS, intramuscular nerves fibres from MSS patients and from SIL1-deficient mice (woozy) as well as sciatic nerves and neuromuscular junctions (NMJ) from these mice have been investigated via transmission electron microscopic and immunofluorescence studies accompanied by transcript studies and unbiased proteomic profiling. In addition, PNS and NMJ integrity were analyzed via immunofluorescence studies in an MSS-zebrafish model which has been generated for that purpose.

RESULTS

Electron microscopy revealed morphological changes indicative of impaired autophagy and mitochondrial maintenance in distal axons and in Schwann cells. Moreover, changes of the morphology of NMJs as well as of transcripts encoding proteins important for NMJ function were detected in woozy mice. These findings were in line with a grossly abnormal structure of NMJs in SIL1-deficient zebrafish embryos. Proteome profiling of sciatic nerve specimens from woozy mice revealed altered levels of proteins implicated in neuronal maintenance suggesting the activation of compensatory mechanisms.

CONCLUSION

Taken together, our combined data expand the spectrum of tissues affected by SIL1-loss and suggest that impaired neuromuscular transmission might be part of MSS pathophysiology.

The role of precisely matching fascicles in the quick recovery of nerve function in long peripheral nerve defects

Peripheral nerve injury therapy in the clinic remains less than satisfactory. The gold standard of treatment for long peripheral nerve defects is autologous nerve grafts; however, numerous clinical complications are associated with this treatment. As tissue engineering has developed, tissue-engineered nerve grafts (TENGs) have shown potential applications as alternatives to autologous nerve grafts. To verify the important role of the biomimetic pathway of fascicle design in TENGs, we designed an animal model to study the role of the precise matching of fascicles in the effectiveness of nerve function recovery. 24 Sprague-Dawley rats were divided randomly into three groups (eight/group) that corresponded to 100% fascicle matching (100%FM), 50%FM and 0%FM. We selected Sprague–Dawley rat long-gap (15 mm) sciatic nerve defects. In the 6 weeks after surgery, we found that the 100%FM group showed the most effective functional recovery among the three groups. The 100%FM group showed better functional recovery on the basis of the sciatic functional index than the 50%FM and 0%FM groups. According to histological evaluation, the 100%FM group showed more regenerating nerve fibres. Moreover, in terms of the prevention of muscle atrophy, the 100%FM group showed excellent physiological outcomes. The 100%FM as tissue-engineered scaffolds can enhance nerve regeneration and effective functional recovery after the repair of large nerve defects. The results of this study provide a theoretical basis for future TENG designs including biomimetic fascicle pathways for repairing long nerve defects.

Biomimetic Architectures for Peripheral Nerve Repair: A Review of Biofabrication Strategies

Biofabrication techniques have endeavored to improve the regeneration of the peripheral nervous system (PNS), but nothing has surpassed the performance of current clinical practices. However, these current approaches have intrinsic limitations that compromise patient care. The "gold standard" autograft provides the best outcomes but requires suitable donor material, while implantable hollow nerve guide conduits (NGCs) can only repair small nerve defects. This review places emphasis on approaches that create structural cues within a hollow NGC lumen in order to match or exceed the regenerative performance of the autograft. An overview of the PNS and nerve regeneration is provided. This is followed by an assessment of reported devices, divided into three major categories: isotropic hydrogel fillers, acting as unstructured interluminal support for regenerating nerves; fibrous interluminal fillers, presenting neurites with topographical guidance within the lumen; and patterned interluminal scaffolds, providing 3D support for nerve growth via structures that mimic native PNS tissue. Also presented is a critical framework to evaluate the impact of reported outcomes. While a universal and versatile nerve repair strategy remains elusive, outlined here is a roadmap of past, present, and emerging fabrication techniques to inform and motivate new developments in the field of peripheral nerve regeneration.

Clinical and biometrical 12-month follow-up in patients after reconstruction of the sural nerve biopsy defect by the collagen-based nerve guide Neuromaix

Many new strategies for the reconstruction of peripheral nerve injuries have been explored for their effectiveness in supporting nerve regeneration. However only a few of these materials were actually clinically evaluated and approved for human use. This open, mono-center, non-randomized clinical study summarizes the 12-month follow-up of patients receiving reconstruction of the sural nerve biopsy defect by the collagen-based nerve guide Neuromaix. Neuromaix was implanted as a micro-structured, two-component scaffold bridging 20–40 mm nerve defects after sural nerve biopsy in twenty patients (eighteen evaluated, two lost in follow-up). Safety of the material was evaluated by clinical examination of wound healing. Performance was assessed by sensory testing of modalities, pain assessment, and palpation for the Hoffmann–Tinel’s sign as well as demarcating the asensitive area at each follow-up visit. Every patient demonstrated uneventful wound healing during the complete 12-month time course of the study. Two patients reported complete return of sensation, whereas eleven out of eighteen patients reported a positive Hoffmann–Tinel’s sign at the lower leg with simultaneous reduction of the asensitive area by 12 months. Our data show that Neuromaix can be implanted safely in humans to bridge sural nerve gaps. No procedure-related, adverse events, or severe adverse events were reported. These first clinical data on Neuromaix provide promising perspectives for the bridging of larger nerve gaps in combined nerves, which should be investigated more through extensive, multi-center clinical trials in the near future.