Porous chitosan scaffolds with surface micropatterning and inner porosity and their effects on Schwann cells

Therapeutic Advances in Peripheral Nerve Injuries: Nerve-Guided Conduit and Beyond

Peripheral nerve injury (PNI), a challenging neurosurgery issue, often leads to partial or complete loss of neuronal functions and even neuropathic pain. Thus far, the gold standard for treating peripheral nerve deficit remains autografts. While numerous reviews have explored PNI and regeneration, this work distinctively synthesizes recent advancements in tissue engineering-particularly four-dimensional (4D) bioprinting and exosome therapies-with an emphasis on their clinical translation. By consolidating findings spanning molecular mechanisms to therapeutic applications, this review proposes an actionable framework for advancing experimental strategies toward clinically viable solutions. Our work critically evaluates emerging innovations such as dynamically adaptive 4D-printed nerve conduits and exosome-based therapies, underscoring their potential to match conventional autografts in achieving functional restoration. Impact Statement Although several previous reviews have been made on describing with great detail the degenerative and regenerative mechanisms of the peripheral nervous systems, as well as the several existing and exploratory treatment strategies, we focus more on the latest advancements of each of those topics.

Advances in biomaterial-based tissue engineering for peripheral nerve injury repair

Peripheral nerve injury is a common clinical disease. Effective post-injury nerve repair remains a challenge in neurosurgery, and clinical outcomes are often unsatisfactory, resulting in social and economic burden. Particularly, the repair of long-distance nerve defects remains a challenge. The existing nerve transplantation strategies show limitations, including donor site morbidity and immune rejection issues. The multiple studies have revealed the potential of tissue engineering strategies based on biomaterials in the repair of peripheral nerve injuries. We review the events of regeneration after peripheral nerve injury, evaluates the efficacy of existing nerve grafting strategies, and delves into the progress in the construction and application strategies of different nerve guidance conduits. A spotlight is cast on the materials, technologies, seed cells, and microenvironment within these conduits to facilitate optimal nerve regeneration. Further discussion was conducted on the approve of nerve guidance conduits and potential future research directions. This study anticipates and proposes potential avenues for future research, aiming to refine existing strategies and uncover innovative approaches in biomaterial-based nerve repair. This study endeavors to synthesize the collective insights from the fields of neuroscience, materials science, and regenerative medicine, offering a multifaceted perspective on the role of biomaterials in advancing the frontiers of peripheral nerve injury treatment.

Anisotropic microtopography surface of chitosan scaffold regulating skin precursor-derived Schwann cells towards repair phenotype promotes neural regeneration

For repairing peripheral nerve and spinal cord defects, biomaterial scaffold-based cell-therapy was emerged as an effective strategy, requiring the positive response of seed cells to biomaterial substrate and environment signals. Previous work highlighted that the imposed surface properties of scaffold could provide important guidance cues to adhered cells for polarization. However, the insufficiency of native Schwann cells and unclear cellular response mechanisms remained to be addressed. Given that, this study aimed to illuminate the micropatterned chitosan-film action on the rat skin precursor-derived Schwann cells (SKP-SCs). Chitosan-film with different ridge/groove size was fabricated and applied for the SKP-SCs induction. Results indicated that SKP-SCs cultured on 30 μm size microgroove surface showed better oriented alignment phenotype. Induced SKP-SCs presented similar genic phenotype as repair Schwann cells, increasing expression of c-Jun, neural cell adhesion molecule, and neurotrophic receptor p75. Moreover, SKP-SC-secretome was subjected to cytokine array GS67 assay, data indicated the regulation of paracrine phenotype, a panel of cytokines was verified up-regulated at secreted level and gene expression level in induced SKP-SCs. These up-regulated cytokines exhibit a series of promotive neural regeneration functions, including cell survival, cell migration, cell proliferation, angiogenesis, axon growth, and cellular organization etc. through bioinformatics analysis. Furthermore, the effectively polarized SKP-SCs-sourced secretome, promoted the proliferation and migration capacity of the primarily cultured native rat Schwann cells, and augmented neurites growth of the cultured motoneurons, as well as boosted axonal regrowth of the axotomy-injured motoneurons. Taken together, SKP-SCs obtained pro-neuroregeneration phenotype in adaptive response to the anisotropic topography surface of chitosan-film, displayed the oriented parallel growth, the transition towards repair Schwann cell genic phenotype, and the enhanced paracrine effect on neural regeneration. This study provided novel insights into the potency of anisotropic microtopography surface to Schwann-like cells phenotype regulation, that facilitating to provide promising engineered cell-scaffold in neural injury therapies.

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.

Improved Physiochemical Properties of Chitosan@PCL Nerve Conduits by Natural Molecule Crosslinking

Nerve conduits may represent a valuable alternative to autograft for the regeneration of long-gap damages. However, no NCs have currently reached market approval for the regeneration of limiting gap lesions, which still represents the very bottleneck of this technology. In recent years, a strong effort has been made to envision an engineered graft to tackle this issue. In our recent work, we presented a novel design of porous/3D-printed chitosan/poly-ε-caprolactone conduits, coupling freeze drying and additive manufacturing technologies to yield conduits with good structural properties. In this work, we studied genipin crosslinking as strategy to improve the physiochemical properties of our conduit. Genipin is a natural molecule with very low toxicity that has been used to crosslink chitosan porous matrix by binding the primary amino group of chitosan chains. Our characterization evidenced a stabilizing effect of genipin crosslinking towards the chitosan matrix, with reported modified porosity and ameliorated mechanical properties. Given the reported results, this method has the potential to improve the performance of our conduits for the regeneration of long-gap nerve injuries.

Microfluidic Systems for Neural Cell Studies

Whereas the axons of the peripheral nervous system (PNS) spontaneously regenerate after an injury, the occurring regeneration is rarely successful because axons are usually directed by inappropriate cues. Therefore, finding successful ways to guide neurite outgrowth, in vitro, is essential for neurogenesis. Microfluidic systems reflect more appropriately the in vivo environment of cells in tissues such as the normal fluid flow within the body, consistent nutrient delivery, effective waste removal, and mechanical stimulation due to fluid shear forces. At the same time, it has been well reported that topography affects neuronal outgrowth, orientation, and differentiation. In this review, we demonstrate how topography and microfluidic flow affect neuronal behavior, either separately or in synergy, and highlight the efficacy of microfluidic systems in promoting neuronal outgrowth.

Topographical and Chemical Inductive Cues Synergistically Enhance the Schwann Cell Differentiation of Aligned Dental Pulp Stem Cell Sheets

Peripheral nerves have an inherent capacity for regeneration, but these Schwann cell-mediated mechanisms are insufficient for severe injuries. With current clinical treatments, slow regeneration and aberrant reinnervation result in poor functional outcomes. Dental pulp stem cells (DPSCs) offer a promising source of therapeutic neurotrophic factors (NTFs), growth factors that stimulate axon regeneration. Previously, we established that DPSCs can generate scaffold-free sheets with a linearly aligned extracellular matrix (ECM). These sheets provide trophic cues via the DPSCs and directional cues through the aligned ECM to both accelerate and orient axon outgrowth, thus providing a biomaterial capable of addressing the current clinical challenges. DPSCs have a propensity for differentiating into Schwann cells (SC-DPSCs), further enhancing their endogenous NTF expression. Here, we evaluated the effect of inducing SC differentiation on the neuroregenerative bioactivity of our DPSC sheets. These sheets were formed on substrates with linear microgrooves to direct the cells to deposit an aligned ECM. Inducing differentiation using an SC differentiation medium (SCDM) increased NTF expression 2-fold compared to unaligned uDPSC sheets, and this effect was amplified in linearly oriented SC-DPSC sheets by up to 8-fold. Furthermore, these aligned SC-DPSC sheets remodeled the sheet ECM to more closely emulate a regenerative neural microenvironment, expressing 8-fold and 2 × 107-fold more collagen IV and laminin, respectively, than unaligned uDPSC sheets. These data demonstrate that the chemical cues of the SCDM and the mechanotransductive cues of the aligned cell sheet synergistically enhanced the differentiation of DPSCs into repair SC-like cells. To evaluate their functional effects on neuritogenesis, the DPSC sheets were directly cocultured with neuronally differentiated neuroblastoma SH-SY5Y cells. In this in vitro culture system, the aligned SC-DPSC sheets promoted oriented neurite-like outgrowth similar to aligned uninduced DPSC sheets and increased collateral branching, which may emulate stages associated with natural SC-mediated repair processes. Therefore, linearly aligned SC-DPSC sheets have the potential to both promote nerve regeneration and reduce aberrant reinnervation, thus providing a promising biomaterial for applications to improve the treatment of peripheral nerve injury.

Submicron-Grooved Films Modulate the Directional Alignment and Biological Function of Schwann Cells

Topographical cues on material surfaces are crucial for guiding the behavior of nerve cells and facilitating the repair of peripheral nerve defects. Previously, micron-grooved surfaces have shown great potential in controlling nerve cell alignment for studying the behavior and functions of those cells and peripheral nerve regeneration. However, the effects of smaller-sized topographical cues, such as those in the submicron- and nano-scales, on Schwann cell behavior remain poorly understood. In this study, four different submicron-grooved polystyrene films (800/400, 800/100, 400/400, and 400/100) were fabricated to study the behavior, gene expression, and membrane potential of Schwann cells. The results showed that all submicron-grooved films could guide the cell alignment and cytoskeleton in a groove depth-dependent manner. Cell proliferation and cell cycle assays revealed that there was no significant difference between the submicron groove samples and the flat control. However, the submicron grooves can direct the migration of cells and upregulate the expression of critical genes in axon regeneration and myelination (e.g., MBP and Smad6). Finally, the membrane potential of the Schwann cells was significantly altered on the grooved sample. In conclusion, this study sheds light on the role of submicron-grooved patterns in regulating the behavior and function of Schwann cells, which provides unique insights for the development of implants for peripheral nerve regeneration.

Additive Manufacturing of Polyhydroxyalkanoate-Based Blends Using Fused Deposition Modelling for the Development of Biomedical Devices

In the last few decades Additive Manufacturing has advanced and is becoming important for biomedical applications. In this study we look at a variety of biomedical devices including, bone implants, tooth implants, osteochondral tissue repair patches, general tissue repair patches, nerve guidance conduits (NGCs) and coronary artery stents to which fused deposition modelling (FDM) can be applied. We have proposed CAD designs for these devices and employed a cost-effective 3D printer to fabricate proof-of-concept prototypes. We highlight issues with current CAD design and slicing and suggest optimisations of more complex designs targeted towards biomedical applications. We demonstrate the ability to print patient specific implants from real CT scans and reconstruct missing structures by means of mirroring and mesh mixing. A blend of Polyhydroxyalkanoates (PHAs), a family of biocompatible and bioresorbable natural polymers and Poly(L-lactic acid) (PLLA), a known bioresorbable medical polymer is used. Our characterisation of the PLA/PHA filament suggest that its tensile properties might be useful to applications such as stents, NGCs, and bone scaffolds. In addition to this, the proof-of-concept work for other applications shows that FDM is very useful for a large variety of other soft tissue applications, however other more elastomeric MCL-PHAs need to be used.

Development and In Vitro Differentiation of Schwann Cells

Schwann cells are glial cells of the peripheral nervous system. They exist in several subtypes and perform a variety of functions in nerves. Their derivation and culture in vitro are interesting for applications ranging from disease modeling to tissue engineering. Since primary human Schwann cells are challenging to obtain in large quantities, in vitro differentiation from other cell types presents an alternative. Here, we first review the current knowledge on the developmental signaling mechanisms that determine neural crest and Schwann cell differentiation in vivo. Next, an overview of studies on the in vitro differentiation of Schwann cells from multipotent stem cell sources is provided. The molecules frequently used in those protocols and their involvement in the relevant signaling pathways are put into context and discussed. Focusing on hiPSC- and hESC-based studies, different protocols are described and compared, regarding cell sources, differentiation methods, characterization of cells, and protocol efficiency. A brief insight into developments regarding the culture and differentiation of Schwann cells in 3D is given. In summary, this contribution provides an overview of the current resources and methods for the differentiation of Schwann cells, it supports the comparison and refinement of protocols and aids the choice of suitable methods for specific applications.

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.

Preparation and mechanical optimization of a two-layer silk/magnesium wires braided porous artificial nerve guidance conduit

Peripheral nerve injures have long been a tricky problem in surgery and a feasible treatment is the transplantation of nerve guidance conduits (NGCs). This study presents a two-layer composite NGC with fair mechanical properties and good biocompatibility. The inner layer was made of degummed silk yarns/magnesium wires using braiding technology, and the outer layer was made from mixed solution of silk fibroin/chitosan (SF/CS) using freeze-drying treatment. Orthogonal experimental design was applied to rationally design the braided structural layer and obtain the optimal combination of technical process parameters. Meanwhile, the SF/CS porous outer layer was optimized from three concentrations of SF/CS solution. In vitro and in vivo study suggested that the textile-forming scaffold exhibited good biocompatibility and no toxicity. During 4 weeks' degradation, the skeleton of conduits retained its shape, and magnesium ions released from degraded magnesium wires contributed to sustainable release and uniform dispersion, proliferation and adhesion of Schwann cells, indicating potential approach in the development of NGCs.

Insight and Recent Advances into the Role of Topography on the Cell Differentiation and Proliferation on Biopolymeric Surfaces

It is well known that surface topography plays an important role in cell behavior, including adhesion, migration, orientation, elongation, proliferation and differentiation. Studying these cell functions is essential in order to better understand and control specific characteristics of the cells and thus to enhance their potential in various biomedical applications. This review proposes to investigate the extent to which various surface relief patterns, imprinted in biopolymer films or in polymeric films coated with biopolymers, by utilizing specific lithographic techniques, influence cell behavior and development. We aim to understand how characteristics such as shape, dimension or chemical functionality of surface relief patterns alter the orientation and elongation of cells, and thus, finally make their mark on the cell proliferation and differentiation. We infer that such an insight is a prerequisite for pushing forward the comprehension of the methodologies and technologies used in tissue engineering applications and products, including skin or bone implants and wound or fracture healing.

Biomechanical microenvironment in peripheral nerve regeneration: from pathophysiological understanding to tissue engineering development

Peripheral nerve injury (PNI) caused by trauma, chronic disease and other factors may lead to partial or complete loss of sensory, motor and autonomic functions, as well as neuropathic pain. Biological activities are always accompanied by mechanical stimulation, and biomechanical microenvironmental homeostasis plays a complicated role in tissue repair and regeneration. Recent studies have focused on the effects of biomechanical microenvironment on peripheral nervous system development and function maintenance, as well as neural regrowth following PNI. For example, biomechanical factors-induced cluster gene expression changes contribute to formation of peripheral nerve structure and maintenance of physiological function. In addition, extracellular matrix and cell responses to biomechanical microenvironment alterations after PNI directly trigger a series of cascades for the well-organized peripheral nerve regeneration (PNR) process, where cell adhesion molecules, cytoskeletons and mechanically gated ion channels serve as mechanosensitive units, mechanical effector including focal adhesion kinase (FAK) and yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) as mechanotransduction elements. With the rapid development of tissue engineering techniques, a substantial number of PNR strategies such as aligned nerve guidance conduits, three-dimensional topological designs and piezoelectric scaffolds emerge expected to improve the neural biomechanical microenvironment in case of PNI. These tissue engineering nerve grafts display optimized mechanical properties and outstanding mechanomodulatory effects, but a few bottlenecks restrict their application scenes. In this review, the current understanding in biomechanical microenvironment homeostasis associated with peripheral nerve function and PNR is integrated, where we proposed the importance of balances of mechanosensitive elements, cytoskeletal structures, mechanotransduction cascades, and extracellular matrix components; a wide variety of promising tissue engineering strategies based on biomechanical modulation are introduced with some suggestions and prospects for future directions.

Nerve transfer with 3D-printed branch nerve conduits

Background

Nerve transfer is an important clinical surgical procedure for nerve repair by the coaptation of a healthy donor nerve to an injured nerve. Usually, nerve transfer is performed in an end-to-end manner, which will lead to functional loss of the donor nerve. In this study, we aimed to evaluate the efficacy of 3D-printed branch nerve conduits in nerve transfer.

Methods

Customized branch conduits were constructed using gelatine-methacryloyl by 3D printing. The nerve conduits were characterized both in vitro and in vivo. The efficacy of 3D-printed branch nerve conduits in nerve transfer was evaluated in rats through electrophysiology testing and histological evaluation.

Results

The results obtained showed that a single nerve stump could form a complex nerve network in the 3D-printed multibranch conduit. A two-branch conduit was 3D printed for transferring the tibial nerve to the peroneal nerve in rats. In this process, the two branches were connected to the distal tibial nerve and peroneal nerve. It was found that the two nerves were successfully repaired with functional recovery.

Conclusions

It is implied that the two-branch conduit could not only repair the peroneal nerve but also preserve partial function of the donor tibial nerve. This work demonstrated that 3D-printed branch nerve conduits provide a potential method for nerve transfer.

Micropatterned conductive elastomer patch based on poly(glycerol sebacate)-graphene for cardiac tissue repair

Preparing a micropatterned elastomer film with characteristics that can simulate the mechanical properties, anisotropy, and electroactivity of natural myocardial tissues is crucial in cardiac tissue engineering after myocardial infarction (MI). Therefore, in this study, we developed several elastomeric films with a surface micropattern based on poly (glycerol sebacate) (PGS) and graphene (Gr). These films have sufficient mechanical strength (0.6 ± 0.1-3.2 ± 0.08 MPa) to withstand heartbeats, and the micropatterned structure also satisfies the natural myocardium anisotropy in the transverse and vertical. Moreover, Gr makes these films conductive (up to 5.80 × 10-7 S/m), which is necessary for the conduction of electrical signals between cardiomyocytes and the cardiac tissue. Furthermore, they have good cytocompatibility and can promote cell proliferation in H9c2 rat cardiomyocyte cell lines. In vivo test results indicate that these films have good biocompatibility. Notably, a film with 1 wt% Gr content (PGS-Gr1) significantly affects the recovery of myocardial function in rats after MI. This film effectively decreased the infarct size and degree of myocardial fibrosis and reduced collagen deposition. Echocardiographic evaluation showed that after treatment with this film, the left ventricular internal dimension in systole and left ventricular internal dimension in diastole of rats exhibited a significant downward trend, whereas the fractional shortening and ejection fraction were significantly increased compared with the control group. These data indicate that this electroactive micropatterned anisotropic elastomer film can be applied in cardiac tissue engineering.

Micropatterns and peptide gradient on the inner surface of a guidance conduit synergistically promotes nerve regeneration in vivo

Both of the surface topographical features and distribution of biochemical cues can influence the cell-substrate interactions and thereby tissue regeneration in vivo. However, they have not been combined simultaneously onto a biodegradable scaffold to demonstrate the synergistic role so far. In this study, a proof-of-concept study is performed to prepare micropatterns and peptide gradient on the inner wall of a poly (D,L-lactide-co-caprolactone) (PLCL) guidance conduit and its advantages in regeneration of peripheral nerve in vivo. After linear ridges/grooves of 20/40 μm in width are created on the PLCL film, its surface is aminolyzed in a kinetically controlled manner to obtain the continuous gradient of amino groups, which are then transferred to CQAASIKVAV peptide density gradient via covalent coupling of glutaraldehyde. The Schwann cells are better aligned along with the stripes, and show a faster migration rate toward the region of higher peptide density. Implantation of the nerve guidance conduit made of the PLCL film having both the micropatterns and peptide gradient can significantly accelerate the regeneration of sciatic nerve in terms of rate, function recovery and microstructures, and reduction of fibrosis in muscle tissues. Moreover, this nerve conduit can also benefit the M2 polarization of macrophages and promote vascularization in vivo.

Co-culture of Schwann cells and endothelial cells for synergistically regulating dorsal root ganglion behavior on chitosan-based anisotropic topology for peripheral nerve regeneration

Background

Anisotropic topologies are known to regulate cell-oriented growth and induce cell differentiation, which is conducive to accelerating nerve regeneration, while co-culture of endothelial cells (ECs) and Schwann cells (SCs) can significantly promote the axon growth of dorsal root ganglion (DRG). However, the synergistic regulation of EC and SC co-culture of DRG behavior on anisotropic topologies is still rarely reported. The study aims to investigate the effect of anisotropic topology co-cultured with Schwann cells and endothelial cells on dorsal root ganglion behavior for promoting peripheral nerve regeneration.

Methods

Chitosan/artemisia sphaerocephala (CS/AS) scaffolds with anisotropic topology were first prepared using micro-molding technology, and then the surface was modified with dopamine to facilitate cell adhesion and growth. The physical and chemical properties of the scaffolds were characterized through morphology, wettability, surface roughness and component variation. SCs and ECs were co-cultured with DRG cells on anisotropic topology scaffolds to evaluate the axon growth behavior.

Results

Dopamine-modified topological CS/AS scaffolds had good hydrophilicity and provided an appropriate environment for cell growth. Cellular immunofluorescence showed that in contrast to DRG growth alone, co-culture of SCs and ECs could not only promote the growth of DRG axons, but also offered a stronger guidance for orientation growth of neurons, which could effectively prevent axons from tangling and knotting, and thus may significantly inhibit neurofibroma formation. Moreover, the co-culture of SCs and ECs could promote the release of nerve growth factor and vascular endothelial growth factor, and up-regulate genes relevant to cell proliferation, myelination and skeletal development via the PI3K-Akt, MAPK and cytokine and receptor chemokine pathways.

Conclusions

The co-culture of SCs and ECs significantly improved the growth behavior of DRG on anisotropic topological scaffolds, which may provide an important basis for the development of nerve grafts in peripheral nerve regeneration.

Anisotropic scaffolds for peripheral nerve and spinal cord regeneration

The treatment of long-gap (>10 mm) peripheral nerve injury (PNI) and spinal cord injury (SCI) remains a continuous challenge due to limited native tissue regeneration capabilities. The current clinical strategy of using autografts for PNI suffers from a source shortage, while the pharmacological treatment for SCI presents dissatisfactory results. Tissue engineering, as an alternative, is a promising approach for regenerating peripheral nerves and spinal cords. Through providing a beneficial environment, a scaffold is the primary element in tissue engineering. In particular, scaffolds with anisotropic structures resembling the native extracellular matrix (ECM) can effectively guide neural outgrowth and reconnection. In this review, the anatomy of peripheral nerves and spinal cords, as well as current clinical treatments for PNI and SCI, is first summarized. An overview of the critical components in peripheral nerve and spinal cord tissue engineering and the current status of regeneration approaches are also discussed. Recent advances in the fabrication of anisotropic surface patterns, aligned fibrous substrates, and 3D hydrogel scaffolds, as well as their in vitro and in vivo effects are highlighted. Finally, we summarize potential mechanisms underlying the anisotropic architectures in orienting axonal and glial cell growth, along with their challenges and prospects.

The Influence of the Surface Topographical Cues of Biomaterials on Nerve Cells in Peripheral Nerve Regeneration: A Review

The surface topographies of artificial implants including surface roughness, surface groove size and orientation, and surface pore size and distribution have a great influence on the adhesion, migration, proliferation, and differentiation of nerve cells in the nerve regeneration process. Optimizing the surface topographies of biomaterials can be a key strategy for achieving excellent cell performance in various applications such as nerve tissue engineering. In this review, we offer a comprehensive summary of the surface topographies of nerve implants and their effects on nerve cell behavior. This review also emphasizes the latest work progress of the layered structure of the natural extracellular matrix that can be imitated by the material surface topology. Finally, the future development of surface topographies on nerve regeneration was prospectively remarked.

Bionic microenvironment-inspired synergistic effect of anisotropic micro-nanocomposite topology and biology cues on peripheral nerve regeneration

Anisotropic topographies and biological cues can simulate the regenerative microenvironment of nerve from physical and biological aspects, which show promising application in nerve regeneration. However, their synergetic influence on injured peripheral nerve is rarely reported. In the present study, we constructed a bionic microenvironment-inspired scaffold integrated with both anisotropic micro-nanocomposite topographies and IKVAV peptide. The results showed that both the topographies and peptide displayed good stability. The scaffolds could effectively induce the orientation growth of Schwann cells and up-regulate the genes and proteins relevant to myelination. Last, three signal pathways including the Wnt/β-catenin pathway, the extracellular signal-regulated kinase/mitogen-activated protein pathway, and the transforming growth factor-β pathway were put forward, revealing the main path of synergistic effects of anisotropic micro-nanocomposite topographies and biological cues on neuroregeneration. The present study may supply an important strategy for developing functional of artificial nerve implants.

3D-bioprinted gradient-structured scaffold generates anisotropic cartilage with vascularization by pore-size-dependent activation of HIF1α/FAK signaling axis

Articular cartilage injury is one of the most common diseases in orthopedics, which seriously affects patients' life quality, the development of a biomimetic scaffold that mimics the multi-layered gradient structure of native cartilage is a new cartilage repair strategy. It has been shown that scaffold topography affects cell attachment, proliferation, and differentiation; the underlying molecular mechanism of cell-scaffold interaction is still unclear. In the present study, we construct an anisotropic gradient-structured cartilage scaffold by three-dimensional (3D) bioprinting, in which bone marrow stromal cell (BMSC)-laden anisotropic hydrogels micropatterns were used for heterogeneous chondrogenic differentiation and physically gradient synthetic poly (ε-caprolactone) (PCL) to impart mechanical strength. In vitro and in vivo, we demonstrated that gradient-structured cartilage scaffold displayed better cartilage repair effect. The heterogeneous cartilage tissue maturation and blood vessel ingrowth were mediated by a pore-size-dependent mechanism and HIF1α/FAK axis activation. In summary, our results provided a theoretical basis for employing 3D bioprinting gradient-structured constructs for anisotropic cartilage regeneration and revealed HIF1α/FAK axis as a crucial regulator for cell-material interactions, so as to provide a new perspective for cartilage regeneration and repair.

Neural tissue engineering: the influence of scaffold surface topography and extracellular matrix microenvironment

Strategies using surface topography, contact guidance and biomechanical cues in the design of scaffolds as an ECM support for neural tissue engineering.

3D Free-Standing Ordered Graphene Network Geometrically Regulates Neuronal Growth and Network Formation

The control of cell-microenvironment interactions plays a pivotal role in constructing specific scaffolds for tissue engineering. Here, we fabricated a 3D free-standing ordered graphene (3D-OG) network with a precisely defined pattern. When primary cortical cells are cultured on 3D-OG scaffolds, they form well-defined 3D connections. Astrocytes have a more ramified shape similar to that seen in vivo because of the nanosized ripples and wrinkles on the surface of graphene skeleton. Neurons have axons and dendrites aligned along the graphene skeleton, allowing the formation of neuronal networks with highly controlled connections. Neuronal networks have higher electrical activity with functional signaling over a long distance along the graphene skeleton. Our study, for the first time, investigated the geometrical cues on ordered neuronal growth and network formation with the support of graphene in 3D, which therefore advanced the development of customized scaffolds for brain-machine interfaces or neuroprosthetic devices.

Laser-induced topographies enable the spatial patterning of co-cultured peripheral nervous system cells

The peripheral nervous system comprises glia and neurons that receive the necessary cues for their adhesion and proliferation from their extracellular milieu. In this study, a spatial platform of pseudoperiodic morphologies including patterns of nano- and micro- structures on Si were developed via direct ultrafast-laser structuring and were used as substrates for the patterning of co-cultured neuronal cells. The response of murine Schwann (SW10) and Neuro2a (N2a) cells were investigated both in monocultures and in a glia and neuronal co-culture system. Our results denoted that different types of neural tissue cells respond differently to the underlying topography, but furthermore, the presence of the glial cells alters the adhesion behavior of the neuronal cells in their co-culture. Therefore, we envisage that direct laser structuring that enables spatial patterning of the cells of the nervous system in a controllable manner according to the research needs, could in the future be a useful tool for understanding neural network interfaces and their electrical activity, synaptic processes and myelin formation.

Biodegradable Polymers as the Pivotal Player in the Design of Tissue Engineering Scaffolds

Biodegradable polymers play a pivotal role in in situ tissue engineering. Utilizing various technologies, researchers have been able to fabricate 3D tissue engineering scaffolds using biodegradable polymers. They serve as temporary templates, providing physical and biochemical signals to the cells and determining the successful outcome of tissue remodeling. Furthermore, a biodegradable scaffold also presents the fourth dimension for tissue engineering, namely time. The properties of the biodegradable polymer change over time, presenting continuously changing features during the degradation process. These changes become more complicated when different materials are combined together to fabricate a composite or heterogeneous scaffold. This review undertakes a systematic analysis of the basic characteristics of biodegradable polymers and describe recent advances in making composite biodegradable scaffolds for in situ tissue engineering and regenerative medicine. The interaction between implanted biodegradable biomaterials and the in vivo environment are also discussed, including the properties and functional changes of the degradable scaffold, the local effect of degradation on the contiguous tissue and their evaluation using both in vitro and in vivo models.

Tripolyphosphate-Crosslinked Chitosan/Gelatin Biocomposite Ink for 3D Printing of Uniaxial Scaffolds

Chitosan is a natural polymer widely investigated and used due to its antibacterial activity, mucoadhesive, analgesic, and hemostatic properties. Its biocompatibility makes chitosan a favorable candidate for different applications in tissue engineering (TE), such as skin, bone, and cartilage tissue regeneration. Despite promising results obtained with chitosan 3D scaffolds, significant challenges persist in fabricating hydrogel structures with ordered architectures and biological properties to mimic native tissues. In this work, chitosan has been investigated aiming at designing and fabricating uniaxial scaffolds which can be proposed for the regeneration of anisotropic tissues (i.e., skin, skeletal muscle, myocardium) by 3D printing technology. Chitosan was blended with gelatin to form a polyelectrolyte complex in two different ratios, to improve printability and shape retention. After the optimization of the printing process parameters, different crosslinking conditions were investigated, and the 3D printed samples were characterized. Tripolyphosphate (TPP) was used as crosslinker for chitosan-based scaffolds. For the optimization of the printing temperature, the sol-gel temperature of the chitosan-gelatin blend was determined by rheological measurements and extrusion temperature was set to 20°C (i.e., below sol-gel temperature). The shape fidelity and surface morphology of the 3D printed scaffolds after crosslinking was dependent on crosslinking conditions. Interestingly, mechanical properties of the scaffolds were also significantly affected by the crosslinking conditions, nonetheless the stability of the scaffolds was strongly determined by the content of gelatin in the blend. Lastly, in vitro cytocompatibility test was performed to evaluate the interactions between L929 cells and the 3D printed samples. 2% w/v chitosan and 4% w/v gelatin hydrogel scaffolds crosslinked with 10% TPP, 30 min at 4°C following 30 min at 37°C have shown cytocompatible and stable characteristics, compared to all other tested conditions, showing suitable properties for the regeneration of anisotropic tissues.

Fibre guiding scaffolds for periodontal tissue engineering

The periodontium is a highly hierarchically organized organ composed of gingiva, alveolar bone, periodontal ligament and cementum. Periodontitis leads to the destruction of hard and soft tissues ultimately leading to a loss of the teeth supporting apparatus. Current treatments are capable of limiting the disease progression; however, true regeneration, characterized by perpendicularly oriented periodontal ligament fibre attachment to cementum on the root surface remains challenging. Tissue engineering approaches have been developed to enhance regeneration via micro-engineered topographical features, purposely designed to guide the insertion of the regenerated ligament to the root surface. This review reports on the recent advancements in scaffold manufacturing methodologies for generating fibre guiding properties and provides a critical insight in the current limitations of these techniques for the formation of functional periodontal attachment.

Surface-Anchored Graphene Oxide Nanosheets on Cell-Scale Micropatterned Poly(d,l-lactide-co-caprolactone) Conduits Promote Peripheral Nerve Regeneration

Regeneration and functional recovery of peripheral nerves remain formidable due to the inefficient physical and chemical cues in the available nerve guidance conduits (NGCs). Introducing micropatterns and bioactive substances into the inner wall of NGCs can effectively regulate the behavior of Schwann cells, the elongation of axons, and the phenotype of macrophages, thereby aiding the regeneration of injured nerve. In this study, linear micropatterns with ridges and grooves of 3/3, 5/5, 10/10, and 30/30 μm were created on poly(d,l-lactide-co-caprolactone) (PLCL) films following with surface aminolysis and electrostatic adsorption of graphene oxide (GO) nanosheets. The GO-modified micropatterns could significantly accelerate the collective migration of Schwann cells (SCs) and migration of SCs from their spheroids in vitro. Moreover, the SCs migrated directionally along the stripes with a fastest rate on the 3/3-GO film that had the largest cell adhesion force. The neurites of N2a cells were oriented along the micropatterns, and the macrophages tended to differentiate into the M2 type on the 3/3-GO film judged by the higher expression of Arg 1 and IL-10. The systematic histological and functional assessments of the regenerated nerves at 4 and 8 weeks post-surgery in vivo confirmed that the 3/3-GO NGCs had better performance to promote the nerve regeneration, and the CMAP, NCV, wet weight of gastrocnemius muscle, positive S100β and NF200 area percentages, and average myelinated axon diameter were more close to those of the autograft group at 8 weeks. This type of NGCs thus has a great potential for nerve regeneration.

Aligned chitosan nanofiber hydrogel grafted with peptides mimicking bioactive brain-derived neurotrophic factor and vascular endothelial growth factor repair long-distance sciatic nerve defects in rats

Autologous nerve transplantation, which is the gold standard for clinical treatment of peripheral nerve injury, still has many limitations. In this study, aligned chitosan fiber hydrogel (ACG) grafted with a bioactive peptide mixture consisting of RGI (Ac-RGIDKRHWNSQGG) and KLT (Ac-KLTWQELYQLKYKGIGG), designated as ACG-RGI/KLT, was used as nerve conduit filler to repair sciatic nerve defects in rats. Methods: Chitosan nanofiber hydrogel was prepared by a combination of electrospinning and mechanical stretching methods, and was then grafted with RGI and KLT, which are peptides mimicking brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), respectively. The physicochemical properties of ACG-RGI/KLT were fully characterized. In vitro, the distribution, proliferation, and secretory activity of Schwann cells were analyzed. Next, the in vivo repair potential for 15-mm rat sciatic nerve defects was examined. The recovery of regenerated nerve, muscle, and motor function was evaluated by neuromuscular histology, electrophysiology, and catwalk gait analysis. Results: We first constructed directionally aligned chitosan nanofiber hydrogel grafted with RGI/KLT peptide mixture (ACG-RGI/KLT). ACG-RGI/KLT oriented the Schwann cells, and promoted the proliferation and secretion of neurotrophic factors by Schwann cells. At an early injury stage, ACG-RGI/KLT not only enhanced nerve regeneration, but also promoted vascular penetration. At 12 weeks, ACG-RGI/KLT facilitated nerve regeneration and functional recovery in rats. Conclusions: Aligned chitosan nanofiber hydrogel grafted with RGI/KLT peptide provides an effective means of repairing sciatic nerve defects and shows great potential for clinical application.

The progress of biomaterials in peripheral nerve repair and regeneration

Repair and regeneration of the injured peripheral nerve (PN) is a challenging issue in clinics. Although the regeneration outcome of large PN defects is currently unsatisfactory, recently, the study of PN repair has considerably progressed. In particular, biomaterials for repairing PNs, such as nerve guidance conduits and nerve repair membranes, have been well developed. Herein, we summarize the anatomy of the PN, the pathophysiological features of the nerve injury, and the repair process post injury. Then, we highlight the progress in the development of natural and synthetic biomaterials and summarize the applications, advantages, and disadvantages of these materials. These materials can be used as nerve repair membranes and nerve conduits in the field of PN repair. Finally, we discuss the challenges encountered and development strategies for PN repair in the future.

Bone marrow-derived neural crest precursors improve nerve defect repair partially through secreted trophic factors

BACKGROUND

Emerging evidence suggests that neural crest-derived cells (NCCs) present important functions in peripheral nerve regeneration to correct the insufficiency of autogenous Schwann cells. Postmigratory NCCs have been successfully isolated from adult rat bone marrow in our previous work. In this study, we aim to provide neural crest-derived Schwann cell precursors (SCPs) for repair of nerve defects in adult rats, and partially reveal the mechanisms involved in neuroregeneration of cell therapy.

METHODS

A clonal cell line of neural crest precursors of rat bone marrow origin (rBM-NCPs) with SCP identity was expanded in adherent monolayer culture to ensure the stable cell viability of NCPs and potentiate the repair of nerve defects after rBM-NCPs implantation based on tissue engineering nerve grafts (TENG). Here the behavioral, morphological, and electrophysiological detection was performed to evaluate the therapy efficacy. We further investigated the treatment with NCP-conditioned medium (NCP-CM) to sensory neurons after exposure to oxygen-glucose-deprivation (OGD) and partially compared the expression of trophic factor genes in rBM-NCPs with that in mesenchymal stem cells of bone marrow origin (rBM-MSCs).

RESULTS

It was showed that the constructed TENG with rBM-NCPs loaded into silk fibroin fiber scaffolds/chitosan conduits repaired 10-mm long sciatic nerve defects more efficiently than conduits alone. The axonal regrowth, remyelination promoted the reinnervation of the denervated hind limb muscle and skin and thereby alleviated muscle atrophy and facilitated the rehabilitation of motor and sensory function. Moreover, it was demonstrated that treatment with NCP-CM could restore the cultured primary sensory neurons after OGD through trophic factors including epidermal growth factor (EGF), platelet-derived growth factor alpha (PDGFα), ciliary neurotrophic factor (CNTF), and vascular endothelial growth factor alpha (VEGFα).

CONCLUSIONS

In summary, our findings indicated that monolayer-cultured rBM-NCPs cell-based therapy might effectively repair peripheral nerve defects partially through secreted trophic factors, which represented the secretome of rBM-NCPs differing from that of rBM-MSCs.

Construction of Biofunctionalized Anisotropic Hydrogel Micropatterns and Their Effect on Schwann Cell Behavior in Peripheral Nerve Regeneration

Hydrogels have promising application in tissue regeneration due to their excellent physicochemical and biocompatible properties, whereas anisotropic micropatterns are been proven to directionally induce cell alignment and accelerate cell migration. However, an effect of biofunctionalized anisotropic hydrogel micropatterns on nerve regeneration has rarely been reported. In this study, the anisotropic polyacrylamide (PAM) hydrogel micropatterns with aligned ridge/groove structures were first prepared via in situ free radical polymerization and micromolding, and then biofunctionalized using YIGSR peptide for better promoting cell growth. The morphology, swelling ratio, wettability, mechanical properties, and stability of the prepared hydrogel were characterized. The successful immobilization of YIGSR peptide on the PAM hydrogel was monitored using FTIR, immunofluorescence staining, and ELISA. The effects on adhesion, directional growth, and biological function of Schwann cells were evaluated. The results displayed that the anisotropic PAM hydrogel micropatterns with inner porous structure possessed good stability, swelling, and mechanical properties. The YIGSR peptide could be well immobilized on hydrogel micropatterns with a percentage of 62.6%. The biofunctionalized anisotropic hydrogel micropatterns could effectively regulate the orientation growth of Schwann cells, and obviously up-regulate BDNF (40%) and β-actin (50%) expression compared with single hydrogel micropatterns, without negatively affecting the normal secretion of neurotropic factors by Schwann cells. To the best of our knowledge, this is the first time to study the construction and effect of biofunctionalized anisotropic hydrogel micropatterns on nerve regeneration, which may provide an experimental and theoretical basis for the design and development of artificial implants for nerve regeneration application.

Aligned conductive core-shell biomimetic scaffolds based on nanofiber yarns/hydrogel for enhanced 3D neurite outgrowth alignment and elongation

Aligned topographical cue has been demonstrated as a critical role in neuronal guidance, and it is highly beneficial to develop a scaffold with aligned structure for peripheral nerve tissue regeneration. Although considerable efforts have been devoted to guiding neurite alignment and extension, it remains a remarkable challenge for developing a biomimetic scaffold for enhancing 3D aligned neuronal outgrowth. Herein, we present a core-shell scaffold based on aligned conductive nanofiber yarns (NFYs) within the hydrogel to mimic the 3D hierarchically aligned structure of the native nerve tissue. The aligned NFYs assembled by a bundle of aligned nanofibers composed of polycaprolactone (PCL), silk fibroin (SF), and carbon nanotubes (CNTs) are prepared by a developed dry-wet electrospinning method, which has the ability to induce neurite alignment and elongation when PC12 cells and dorsal root ganglia (DRG) cells are cultured on their 3D peripheral surface. Particularly, such an aligned nanofibrous structure also induces aligned neurite extension and cell migration from DRG explants along the direction of nanofibers. 3D core-shell scaffolds are fabricated by encapsulating NFYs within the hydrogel shell after photocrosslinking, and these 3D aligned scaffolds are able to control cellular alignment and elongation of nerve cells in this 3D environment. Our results suggest that such 3D hierarchically aligned core-shell scaffold consists of NFYs that mimic the aligned nerve fiber structure to induce neurite alignment and extension and a hydrogel shell that mimics the epineurium layer to protect nerve cell organization within a 3D environment, which is largely promising for the design of biomimetic scaffolds in nerve tissue engineering. STATEMENT OF SIGNIFICANCE: Designing scaffolds with 3D aligned structure has been paid more attention for peripheral nerve tissue regeneration, because the aligned topographical cue is able to induce neurites alignment and extension. However, developing scaffolds mimicking the hierarchically aligned structure of native nerve tissue for directing 3D aligned neuronal outgrowth without external stimulation remains challenging. This work presented a simple and efficient strategy to prepare a 3D biomimetic core-shell scaffold based on electrospun aligned conductive nanofiber yarns within photocurable hydrogel shell to mimic the hierarchically aligned structure of native nerve tissue. These 3D aligned composite scaffolds performed the ability to direct 3D cellular alignment and elongation of nerve cells along with the nanofiber yarn direction, and the hydrogel shell mimicking the epineurium layer was able to protect nerve cells organization within the 3D environment, which indicated their great potential in peripheral nerve tissue engineering applications.

Biomimetic porous Mg with tunable mechanical properties and biodegradation rates for bone regeneration

The medical applications of porous Mg scaffolds are limited owing to its rapid corrosion, which dramatically decreases the mechanical strength of the scaffold. Mimicking the bone structure and composition can improve the mechanical and biological properties of porous Mg scaffolds. The Mg structure can also be coated with HA by an aqueous precipitation coating method to enhance both the corrosion resistance and the biocompatibility. However, due to the brittleness of HA coating layer, cracks tend to form in the HA coating layer, which may influence the corrosion and biological functionality of the scaffold. Consequently, in this study, hybrid poly(ether imide) (PEI)-SiO₂ layers were applied to the HA-coated biomimetic porous Mg to impart the structure with the high corrosion resistance associated with PEI and excellent bioactivity with SiO₂. The porosity of the Mg was controlled by adjusting the concentration of the sodium chloride (NaCl) particles used in the fabrication via the space-holder method. The mechanical measurements showed that the compressive strength and stiffness of the biomimetic porous Mg increased as the portion of the dense region increased. In addition, following results show that HA/(PEI-SiO₂) hybrid-coated biomimetic Mg is a promising biodegradable scaffold for orthopedic applications. In-vitro testing revealed that the proposed hybrid coating reduced the degradation rate and facilitated osteoblast spreading compared to HA- and HA/PEI-coating scaffolds. Moreover, in-vivo testing with a rabbit femoropatellar groove model showed improved tissue formation, reduced corrosion and degradation, and improved bone formation on the scaffold. STATEMENT OF SIGNIFICANCE: Porous Mg is a promising biodegradable scaffold for orthopedic applications. However, there are limitations in applying porous Mg for an orthopedic biomaterial due to its poor mechanical properties and susceptibility to rapid corrosion. Here, we strategically designed the structure and coating layer of porous Mg to overcome these limitations. First, porous Mg was fabricated by mimicking the bone structure which has a combined structure of dense and porous regions, thus resulting in an enhancement of mechanical properties. Furthermore, the biomimetic porous Mg was coated with HA/(PEI-SiO₂) hybrid layer to improve both corrosion resistance and biocompatibility. As the final outcome, with tunable mechanical and biodegradable properties, HA/(PEI-SiO₂)-coated biomimetic porous Mg could be a promising candidate material for load-bearing orthopedic applications.

Hierarchically aligned gradient collagen micropatterns for rapidly screening Schwann cells behavior

To penetrate the effect of protein gradient micropattern on peripheral nerve regeneration, the hierarchically aligned gradient collagen micropattern was prepared by micromoulding method and the influence on Schwann cells growth behavior was studied. The morphology, wettability, stability and component variation of the micropatterns were firstly characterized. Then, Schwann cells were cultured and the related mechanism was penetrated. The results showed that the gradient collagen micropattern could be well fabricated. The surface wettability varied with the change of collagen concentration, and the prepared gradient micropattern showed a good stability after PBS immersion for 15 days. The results of Schwann cells culture and morphological index analysis displayed that the prepared gradient collagen micropatten could well regulate the orientation growth of Schwann cells, while a much better cell alignment growth was obtained on the gradient micropattern with higher collagen concentration and wider pattern size. PCR and WB showed that the micropattern structure could effectively up-regulate the key specific genes for axon regeneration and myelination process. Overall, the study provides a systematic and facile method for understanding the effect of various sized micropatterns on cell behavior, which may have a great significance for the development of artificial implants for tissue engineering and regenerative medicine.

Silk-Graphene Hybrid Hydrogels with Multiple Cues to Induce Nerve Cell Behavior

Cell behavior is dependent in part on chemical and physical cues from the extracellular matrix. Although the influence of various cues on cell behavior has been studied, challenges remain to incorporate multiple cues to matrix systems to optimize and control cell outcomes. Here, aligned silk fibroin (SF)-graphene hydrogels with preferable stiffness were developed through arranging SF nanofibers and SF-modified graphene sheets under an electric field. Different signals, such as bioactive graphene, nanofibrous structure, aligned topography, and mechanical stiffness, were tailored into the hydrogel system, providing niches for nerve cell responses. The desired adhesion, proliferation, differentiation, extensio,n and growth factor secretion of multiple nerve-related cells was achieved on these hydrogels, suggesting strong synergistic action through the combination of different cues. Based on the fabrication strategy, our present study provides a useful materials engineering platform for revealing cooperative influences of different signals on nerve cell behavior, to help in the understanding of cell-biomaterial interactions, with potential toward studies related to nerve regeneration.

Morphology, Migration, and Transcriptome Analysis of Schwann Cell Culture on Butterfly Wings with Different Surface Architectures

It has been shown that material surface topography greatly affects cell attachment, growth, proliferation, and differentiation. However, the underlying molecular mechanisms for cell-material interactions are still not understood well. Here, two kinds of butterfly wings with different surface architectures were employed for addressing such an issue. Papilio ulysses telegonus (P.u.t.) butterfly wing surface is composed of micro/nanoconcaves, whereas Morpho menelaus (M.m.) butterfly wings are decorated with grooves. RSC96 cells grown on M.m. wings showed a regular sorting pattern along with the grooves. On the contrary, the cells seeded on P.u.t. wings exhibited random arrangement. Transcriptome sequencing and bioinformatics analysis revealed that huntingtin (Htt)-regulated lysosome activity is a potential key factor for determining cell growth behavior on M.m. butterfly wings. Gene silence further confirmed this notion. In vivo experiments showed that the silicone tubes fabricated with M.m. wings markedly facilitate rat sciatic nerve regeneration after injury. Lysosome activity and Htt expression were greatly increased in the M.m. wing-fabricated graft-bridged nerves. Collectively, our data provide a theoretical basis for employing butterfly wings to construct biomimetic nerve grafts and establish Htt lysosome as a crucial regulator for cell-material interactions.

Fabrication of alignment polycaprolactone scaffolds by combining use of electrospinning and micromolding for regulating Schwann cells behavior

In the present study, a new approach for fabricating micropatterned polycaprolactone (PCL) scaffolds with ridge/groove structure on the surface was developed by combining use of electrospinning and micromolding method. A series of physicochemical properties, including morphology, wettability, component, crystal pattern and mechanical properties, of prepared PCL scaffolds were characterization, respectively. Stability of the micropatterned PCL scaffolds was measured using phosphate buffer solution immersion for a certain period. Then, the regulating effects of the micropatterned PCL scaffolds on attachment, orientation and normal biological function of Schwann cells were evaluated. And the protein adsorption behavior in various PCL scaffolds was also detected. The results showed that the micropatterned PCL scaffolds demonstrated a porous micro/nano complex structure with enhanced hydrophobicity and mechanical properties as a function of electrospun flow-rate of PCL solution. The micropatterned PCL scaffolds possessed good stability and could effectively regulate the attachment and orientation of Schwann cells at the early stage after cell culture. Importantly, the electrospun flow-rate of PCL solution was found to play an important role in scaffold properties, cell behavior and protein adsorption. The micropatterned scaffolds with a flow-rate of PCL solution at 0.12 mL h^-1 demonstrated the better regulation on Schwann cells attachment and alignment without negatively affect the normal biological function of the cells. To the best of our knowledge, this is the first report of combining use of electrospinning and micromolding method for preparing artificial nerve implants. The study is anticipated to have potential application in peripheral nerve and other tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3123-3134, 2018.

Micropatterned biodegradable polyesters clicked with CQAASIKVAV promote cell alignment, directional migration, and neurite outgrowth

The interplay of microstructures and biological cues is critical to regulate the behaviors of Schwann cells (SCs) in terms of cellular spatial arrangement and directional migration as well as neurite orientation for bridging the proximal and distal stumps of the injured peripheral nervous system. In this study, stripe micropatterns having ridges/grooves of width 20/20 and 20/40 μm were fabricated on the surface of maleimide-functionalized biodegradable poly(ester carbonate) (P(LLA-MTMC)) films by the polydimethylsiloxane mold-pressing method, respectively. The laminin-derived CQAASIKVAV peptides end-capped with an SH group were then grafted by the thiol-ene click reaction under mild conditions to obtain micropatterned and peptide-grafted films. SCs cultured on these films, especially on the 20/40-μm film, displayed faster and aligned adhesion as well as a larger number of elongated cells with a higher length-to-width (L/W) ratio along the stripe direction than those on the flat-pep film. The migration rate of SCs was significantly enhanced in parallel to the stripe direction with a large net displacement. The micropatterned and peptide-grafted films, especially the 20/40-μm film, could promote SC proliferation and nerve growth factor (NGF) secretion in a manner similar to that of the peptide-grafted planar film. Moreover, the neurites of rat pheochromocytoma 12 (PC12) cells sprouted along the ridges with a longer average length on the micropatterned and peptide-grafted films. The synergistic effect of physical patterns and biological cues was evaluated by considering the results of cell adhesion force; immunofluorescence staining of vinculin; fluorescence staining of F-actin and the nucleus; as well as gene expression of neural cadherin (NCAD), neurocan (NCAN), and myelin protein zero (P0).

STATEMENT OF SIGNIFICANCE

The interplay of microstructures and biological cues is critical to regulate the behaviors of Schwann cells (SCs) and nerve cells, and thereby the regeneration of peripheral nerve system. In this study, the combined micropatterning and CQAASIKVAV grafting endowed the modified P(LLA-MTMC) films with both contact guidance and bioactive chemical cues to enhance cell proliferation, directional alignment and migration, longer net displacement and larger NGF secretion, and stronger neurite outgrowth of SCs and PC12 cells. Hence, the integration of physical micropatterns and bioactive molecules is an effective way to obtain featured biomaterials for the regeneration of nerves and other types of tissues.

Biomimetic neural scaffolds: a crucial step towards optimal peripheral nerve regeneration

Peripheral nerve injury is a common disease that affects more than 20 million people in the United States alone and remains a major burden to society. The current gold standard treatment for critical-sized nerve defects is autologous nerve graft transplantation; however, this method is limited in many ways and does not always lead to satisfactory outcomes. The limitations of autografts have prompted investigations into artificial neural scaffolds as replacements, and some neural scaffold devices have progressed to widespread clinical use; scaffold technology overall has yet to be shown to be consistently on a par with or superior to autografts. Recent advances in biomimetic scaffold technologies have opened up many new and exciting opportunities, and novel improvements in material, fabrication technique, scaffold architecture, and lumen surface modifications that better reflect biological anatomy and physiology have independently been shown to benefit overall nerve regeneration. Furthermore, biomimetic features of neural scaffolds have also been shown to work synergistically with other nerve regeneration therapy strategies such as growth factor supplementation, stem cell transplantation, and cell surface glycoengineering. This review summarizes the current state of neural scaffolds, highlights major advances in biomimetic technologies, and discusses future opportunities in the field of peripheral nerve regeneration.

Controlled release of FK506 from micropatterned PLGA films: potential for application in peripheral nerve repair

After decades of research, peripheral nerve injury and repair still frequently results in paralysis, chronic pain and neuropathies leading to severe disability in patients. Current clinically available nerve conduits only provide crude guidance of regenerating axons across nerve gap without additional functionality. FK506 (Tacrolimus), an FDA approved immunosuppressant, has been shown to enhance peripheral nerve regeneration but carries harsh side-effects when delivered systemically. The objective of this study was to develop and evaluate a bioresorbable drug delivery system capable of local extended delivery of FK506 that also provides topological guidance cues to guide axon growth via microgrooves. Photolithography was used to create micropatterned poly(lactide-co-glycolic acid) (PLGA) films embedded with FK506. Non-patterned, 10/10 μm (ridge/groove width), and 30/30 μm patterned films loaded with 0, 1, and 3 μg/cm² FK506 were manufactured and characterized. In vitro FK506 rate of release testing indicated that the films are capable of an extended (at least 56 days), controlled, and scalable release of FK506. Neurite extension bioactivity assay indicated that FK506 released from the films (concentration of samples tested ranged between 8.46–19.7 ng/mL) maintained its neural bioactivity and promoted neurite extension similar to control FK506 dosages (10 ng/mL FK506). The multi-functional FK506 embedded, micropatterned poly(lactide-co-glycolic acid) films developed in this study have potential to be used in the construction of peripheral nerve repair devices.

Micropatterned poly(d,l-lactide-co-caprolactone) films entrapped with gelatin for promoting the alignment and directional migration of Schwann cells

Gelatin entrapped and micropatterned poly(d,l-lactide-co-caprolactone) (PLCL) film promotes the alignment and directional migration of Schwann cells.