Schwann cell interactions with polymer films are affected by groove geometry and film hydrophilicity

Analogies and Differences Between Dental Stem Cells: Focus on Secretome in Combination with Scaffolds in Neurological Disorders

Mesenchymal stem cells (MSCs) are well known for their beneficial effects, differentiation capacity and regenerative potential. Dental-derived MSCs (DSCs) are more easily accessible and have a non-invasive isolation method rather than MSCs isolated from other sources (umbilical cord, bone marrow, and adipose tissue). In addition, DSCs appear to have a relevant neuro-regenerative potential due to their neural crest origin. However, it is now known that the beneficial effects of MSCs depend, at least in part, on their secretome, referring to all the bioactive molecules (neurotrophic factors) released in the conditioned medium (CM) or in the extracellular vesicles (EVs) in particular exosomes (Exos). In this review, we described the similarities and differences between various DSCs. Our focus was on the secretome of DSCs and their applications in cell therapy for neurological disorders. For neuro-regenerative purposes, the secretome of different DSCs has been tested. Among these, the secretome of dental pulp stem cells and stem cells from human exfoliated deciduous teeth have been the most widely studied. Both CM and Exos obtained from DSCs have been shown to promote neurite outgrowth and neuroprotective effects as well as their combination with scaffold materials (to improve their functional integration in the tissue). For these reasons, the secretome obtained from DSCs in combination with scaffold materials may represent a promising tissue engineering approach for neuroprotective and neuro-regenerative treatments.

The role of mechanobiology on the Schwann cell response: A tissue engineering perspective

Schwann cells (SCs), the glial cells of the peripheral nervous system (PNS), do not only form myelin sheaths thereby insulating the electrical signal propagated by the axons, but also play an essential role in the regeneration of injured axons. SCs are inextricably connected with their extracellular environment and the mechanical stimuli that are received determine their response during development, myelination and injuries. To this end, the mechanobiological response of SCs is being actively researched, as it can determine the suitability of fabricated scaffolds for tissue engineering and regenerative medicine applications. There is growing evidence that SCs are sensitive to changes in the mechanical properties of the surrounding environment (such as the type of material, its elasticity and stiffness), different topographical features provided by the environment, as well as shear stress. In this review, we explore how different mechanical stimuli affect SC behaviour and highlight the importance of exploring many different avenues when designing scaffolds for the repair of PNS injuries.

Chitosan Tubes Prefilled with Aligned Fibrin Nanofiber Hydrogel Enhance Facial Nerve Regeneration in Rabbits

Facial nerves are fragile and easily injured, for example, by traffic accidents or operations. Facial nerve injury drastically reduces the quality of life in affected patients, and its treatment presents clinical challenges. A promising therapeutic strategy includes nerve conduits with appropriate fillers capable of guiding nerve regeneration. In this study, a three-dimensional hierarchically aligned fibrin nanofiber hydrogel (AFG) assembled via electrospinning and molecular self-assembly was first used to mimic the architecture of the native fibrin cable, which is similar to the nerve extracellular matrix (ECM). AFG as a substrate in chitosan tubes (CST) was used to bridge a 7 mm-long gap in a rabbit buccal branch facial nerve defect model. The results showed that AFG and CST showed good compatibility to support the adhesion, activity, and proliferation of Schwann cells (SCs). Further morphological, histological, and functional analyses demonstrated that the regenerative outcome of AFG-prefilled CST was close to that of autologous nerve grafts and superior to that of CST alone or CSTs prefilled with random fibrin nanofiber hydrogel (RFG), which indicated that AFG-prefilled CST markedly improved axonal regeneration with enhanced remyelination and functional recovery, thus showing great potential for clinical application for facial nerve regeneration treatments.

Protocol for a phase I trial of a novel synthetic polymer nerve conduit 'Polynerve' in participants with sensory digital nerve injury (UMANC)

Background: Peripheral nerve injuries are common, with approximately 9,000 cases in the UK annually. Young working individuals are predominantly affected, leading to significant health and social implications. Functional recovery is often poor with impaired hand sensation, reduced motor function and pain and cold intolerance. Where a nerve gap exists, nerve grafting remains the gold-standard treatment but creates a second surgical site, sensory deficit at the donor site, possible neuroma formation and has limited availability. Current commercially available synthetic and resorbable nerve conduit alternatives are reported to be rigid and inflexible. This study will set out to examine the first-in-man use of a new nerve conduit device ‘Polynerve’ to repair small nerve gaps in digital sensory nerves of the hand. Polynerve is a degradable co-polymer of poly-ε-caprolactone and poly-l-lactic acid, which is shaped as a cylinder that has greater tensile strength, flexibility and less acidic degradation compared with current commercially available synthetic nerve conduits. In addition, it has a novel micro-grooved internal lumen that aids Schwann cell ingress and alignment to improve nerve regeneration.

Methods: In total, 17 eligible participants will be recruited to undergo repair of a transected sensory nerve of the hand using the Polynerve device. All participants that receive the nerve conduit device will be followed for a period of 12 months post-surgery. The primary endpoint is safety of the device and the secondary endpoint is degree of sensory nerve regeneration through the conduit assessed using standard sensory testing (2-PD, WEST monofilament testing and locognosia).

Discussion: The ‘UMANC’ trial is a single-centre UK-based, prospective, unblinded, phase I clinical trial of a novel nerve conduit device. We aim to demonstrate the safety of Polynerve as a synthetic, biodegradable nerve conduit and improve the treatment options available to patients with significant nerve injuries.

Registration: Clinicaltrials.gov: NCT02970864; EudraCT: 2016-001667-37.

Engineering a platform for nerve regeneration with direct application to nerve repair technology

The development of effective treatment options for repair of peripheral nerves is complicated by lack of knowledge concerning the interactions between cells and implants. A promising device, the multichannel scaffold, incorporates microporous channels, aligning glia and directing axonal growth across a nerve gap. To enhance clinical outcomes of nerve repair, a platform, representative of current implant technology, was engineered which 1) recapitulated key device features (porosity and linearity) and 2) demonstrated remyelination of adult neurons. The in vitro platform began with the study of Schwann cells on porous polycaprolactone (PCL) and poly(lactide co-glycolide) (PLGA) substrates. Surface roughness determined glial cell attachment, and an additional layer of topography, 40 μm linear features, aligned Schwann cells and axons. In addition, direct co-culture of sensory neurons with Schwann cells significantly increased neurite outgrowth, compared to neurons cultured alone (naive or pre-conditioned). In contrast to the control substrate (glass), on porous PCL substrates, Schwann cells differentiated into a mature myelinating phenotype, expressing Oct-6, MPZ and MBP. The direct applicability of this platform to nerve implants, including its response to physiological cues, allows for optimization of cell-material interactions, close observation of the regeneration process, and the study of therapeutics, necessary to advance peripheral nerve repair technology.

Hierarchical thermoplastic rippled nanostructures regulate Schwann cell adhesion, morphology and spatial organization

Periodic ripples are a variety of anisotropic nanostructures that can be realized by ion beam irradiation on a wide range of solid surfaces. Only a few authors have investigated these surfaces for tuning the response of biological systems, probably because it is challenging to directly produce them in materials that well sustain long-term cellular cultures. Here, hierarchical rippled nanotopographies with a lateral periodicity of ∼300 nm are produced from a gold-irradiated germanium mold in polyethylene terephthalate (PET), a biocompatible polymer approved by the US Food and Drug Administration for clinical applications, by a novel three-step embossing process. The effects of nano-ripples on Schwann Cells (SCs) are studied in view of their possible use for nerve-repair applications. The data demonstrate that nano-ripples can enhance short-term SC adhesion and proliferation (3-24 h after seeding), drive their actin cytoskeleton spatial organization and sustain long-term cell growth. Notably, SCs are oriented perpendicularly with respect to the nanopattern lines. These results provide information about the possible use of hierarchical nano-rippled elements for nerve-regeneration protocols.

Prompt peripheral nerve regeneration induced by a hierarchically aligned fibrin nanofiber hydrogel

Fibrin plays a crucial role in peripheral nerve regeneration, which could occur spontaneously in the format of longitudinally oriented fibrin cables during the initial stage of nerve regeneration. This fibrin cable can direct migration and proliferation of Schwann cells and axonal regrowth, which is very important to nerve regeneration. In the present study, we prepared a three-dimensional hierarchically aligned fibrin nanofiber hydrogel (AFG) through electrospinning and molecular self-assembly to resemble the architecture and biological function of the native fibrin cable. The AFG displayed a hierarchically aligned topography as well as low elasticity (∼1.5kPa) that were similar to nerve extracellular matrix (ECM) and the native fibrin cable. Rapid, directional cell adhesion and migration of Schwann cells (SCs) and dorsal root ganglions were observed in vitro. The AFG was then used as a potential intraluminal substrate in a bioengineered chitosan tube to bridge a 10-mm-long sciatic nerve gap in rats. We found that the AFG served as a beneficial microenvironment to support SCs cable formation and axonal regrowth within 2weeks. Further histological and morphological analyses as well as electrophysiological and functional examinations were performed after AFG implantation for up to 12weeks. The results from morphological analysis and electrophysiological examination indicated that regenerative outcomes achieved by our developed graft were close to those by an autologous nerve graft, but superior to those by hollow chitosan tubes (hCST) and random fibrin nanofiber hydrogel (RFG). Our results demonstrate that the AFG creates an instructive microenvironment by mimicking the native fibrin cable as well as the oriented and soft features of nerve ECM to accelerate axonal regrowth, thus showing great promising potential for applications in neural regeneration.

STATEMENT OF SIGNIFICANCE

In peripheral nervous system defect repair, a wide variety of strategies have been proposed for preparing functionalized nerve guidance conduits (NGC) with more complex configurations to obtain optimal repair effects. Longitudinally oriented fibrin cables were reported to form spontaneously during the initial stages of peripheral nerve regeneration in an empty NGC, which can direct the migration and proliferation of Schwann cells and promote axonal regrowth. Therefore, based on the biomimetic idea, we prepared a three-dimensional hierarchically aligned fibrin nanofiber hydrogel (AFG) through electrospinning and molecular self-assembly, resembling the architecture and biological function of the native fibrin cable and serving as an intraluminal filling to accelerate axon regeneration. We found that the AFG was a beneficial microenvironment to support SCs cable formation and accelerate axonal regrowth with improved motor functional recovery.