Hierarchically aligned gradient collagen micropatterns for rapidly screening Schwann cells behavior

Laser-Assisted Micropatterned 3D Printed Scaffolds with Customizable Surface Topography and Porosity for Modulation of Cell Function

The dynamic interaction between cells and their substrate is a cornerstone of biomaterial-based tissue regeneration focused on unraveling the complex factors that govern this crucial relationship. A key challenge is translating physical cues from 2D to 3D due to limitations in current biofabrication techniques. In response, this study introduces an innovative approach that combines additive and subtractive manufacturing for precise surface patterning of 3D printed scaffolds. Using poly(𝜀-caprolactone) as the scaffold material, polymeric fibers are 3D printed and subsequently laser-engraved with femtosecond laser to precisely create controlled microtopographies, including microgrooves (10 and 80 µm in width) and micropits (25 µm in diameter). Testing shows that the process does not compromise the mechanical properties of the fibers, which is critical for structural applications in tissue engineering. Human mesenchymal stem cells are used to investigate the effects of these topographical features on cell behavior. The 10 µm wide microgrooves notably enhance cell attachment, with cells aligning in elongated forms along the grooves, while micropits and unpatterned surfaces promote polygonal cell shapes. This combined approach demonstrates that precisely engineered microtopographies on 3D printed scaffolds can better mimic the natural extracellular matrix, improving cellular responses and offering a promising strategy for advancing tissue regeneration.

Fabrication and characterization of metformin-loaded PLGA/Collagen nanofibers for modulation of macrophage polarization for tissue engineering and regenerative medicine

In tissue engineering (TE) and regenerative medicine, the accessibility of engineered scaffolds that modulate inflammatory states is extremely necessary. The aim of the current work was to assess the efficacy of metformin (MET) incorporated in PLGA/Collagen nanofibers (Met-PLGA/Col NFs) to modulate RAW264.7 macrophage phenotype from pro-inflammatory status (M1) to anti-inflammatory status (M2). Given this, MET-PLGA/Col NFs were fabricated using an electrospinning technique. Structural characterization such as morphology, chemical and mechanical properties, and drug discharge pattern were assessed. MTT assay test exposed that MET-PLGA/Col NFs remarkably had increased cell survival in comparison with pure PLGA/Collagen NFs and control (p < 0.05) 72 h after incubation. Based on the qPCR assay, a reduction in the expression of iNOS-2 and SOCS3 was found in the cells seeded on MET-PLGA/Col NFs, demonstrating the substantial modulation of the M1 phenotype to the M2 phenotype. Moreover, it was determined a main decrease in the pro-inflammatory cytokines and mediator's expression but the growth factors amount related to anti-inflammatory M2 were meaningfully upregulated. Finally, MET-PLGA/Col NFs possibly will ensure a beneficial potential for effective variation of the macrophage response from an inflammatory phase (M1) to a pro-regenerative (M2) phase.

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.

Polydopamine-Decorated PLCL Conduit to Induce Synergetic Effect of Electrical Stimulation and Topological Morphology for Peripheral Nerve Regeneration

Due to the limited self-repairing capacity after peripheral nerve injuries (PNI), artificial nerve conduits are widely applied to facilitate neural regeneration. Exogenous electrical stimulation (ES) that is carried out by the conductive conduit regulates the biological behavior of Schwann cells (SCs). Meanwhile, a longitudinal surface structure counts to guide axonal growth to accelerate the end-to-end connection. Currently, there are no conduits equipped with both electrical conduction and axon-guiding surface structure. Herein, a biodegradable, conductive poly(l-lactide-co-caprolactone)/graphene (PLCL/GN) composite conduit is designed. The conduit with 20.96 ± 1.26 MPa tensile strength has a micropatterned surface of 20 µm groove fabricated by microimprint technology and self-assembled polydopamine (PDA). In vitro evaluation shows that the conduits with ES effectively stimulate the directional cell migration, adhesion, and elongation, and enhance neuronal expression of SCs. The rat sciatic nerve crush model demonstrates that the conductive micropatterned conduit with ES promotes the growth of myelin sheath, faster nerve regeneration, and 20-fold functional recovery in vivo. These discoveries prove that the PLCL(G)/PDA/GN composite conduit is a promising tool for PNI treatment by providing the functional integration of physical guidance, biomimetic biological regulation, and bioelectrical stimulation, which inspires a novel therapeutic approach for nerve regeneration in the future.

The application of collagen in the repair of peripheral nerve defect

Collagen is a natural polymer expressed in the extracellular matrix of the peripheral nervous system. It has become increasingly crucial in peripheral nerve reconstruction as it was involved in regulating Schwann cell behaviors, maintaining peripheral nerve functions during peripheral nerve development, and being strongly upregulated after nerve injury to promote peripheral nerve regeneration. Moreover, its biological properties, such as low immunogenicity, excellent biocompatibility, and biodegradability make it a suitable biomaterial for peripheral nerve repair. Collagen provides a suitable microenvironment to support Schwann cells’ growth, proliferation, and migration, thereby improving the regeneration and functional recovery of peripheral nerves. This review aims to summarize the characteristics of collagen as a biomaterial, analyze its role in peripheral nerve regeneration, and provide a detailed overview of the recent advances concerning the optimization of collagen nerve conduits in terms of physical properties and structure, as well as the application of the combination with the bioactive component in peripheral nerve regeneration.

Development of a polyacrylamide/chitosan composite hydrogel conduit containing synergistic cues of elasticity and topographies for promoting peripheral nerve regeneration

Substrate elasticity and topographical guidance are crucial factors for regulating tissue regeneration, but the synergistic effects of both cues on peripheral nerve regeneration are still unclear. In this paper, polyacrylamide/chitosan (PAM/CS) composite hydrogels with synergistic characteristics of elasticity and morphology were prepared using in situ free-radical polymerization and micro-molding. The physicochemical properties of hydrogels were characterized, and the effect on peripheral nerve regeneration was systematically evaluated via in vitro and in vivo experiments, respectively. The in vitro experiments showed that on a PAM/CS composite hydrogel with an elastic modulus of 5.822 kPa/8.41 kPa and a surface groove width of 30 μm, the dorsal root ganglion (DRG) neurite had a strong growth ability and better-oriented status. The samples were taken from each group at 2 and 12 weeks after bridging rabbit sciatic nerve defects with a PAM/CS composite hydrogel conduit. General observation of the rabbit body and transplanted nerve, nerve electro-physiological examination, muscle wet weight recovery rate detection and comparison, observation of sciatic nerve frozen section immunofluorescence staining and myelinated nerve fiber recovery rate comparison were used to evaluate the effect of nerve transplantation. The elastic modulus of 8.41 kPa and groove width of 30 μm were similar to those of the autograft group. At the same time, the signaling pathways, including the focal adhesion markers vinculin, p-FAK, and Rho A protein, referring to axon adhesion and extension, were initially revealed. In summary, our developed hydrogel implants containing synergistic cues of elasticity and topographies may provide a new and effective strategy for the treatment of peripheral nerve injury in the future.

Regulatory Effects of Gradient Microtopographies on Synapse Formation and Neurite Growth in Hippocampal Neurons

Among approaches aiming toward functional nervous system restoration, those implementing microfabrication techniques allow the manufacture of platforms with distinct geometry where neurons can develop and be guided to form patterned connections in vitro. The interplay between neuronal development and the microenvironment, shaped by the physical limitations, remains largely unknown. Therefore, it is crucial to have an efficient way to quantify neuronal morphological changes induced by physical or contact guidance of the microenvironment. In this study, we first devise and assess a method to prepare anisotropic, gradient poly(dimethylsiloxane) micro-ridge/groove arrays featuring variable local pattern width. We then demonstrate the ability of this single substrate to simultaneously profile the morphologcial and synaptic connectivity changes of primary cultured hippocampal neurons reacting to variable physical conditons, throughout neurodevelopment, in vitro. The gradient microtopography enhanced adhesion within microgrooves, increasing soma density with decreasing pattern width. Decreasing pattern width also reduced dendritic arborization and increased preferential axon growth. Finally, decreasing pattern geometry inhibited presynaptic puncta architecture. Collectively, a method to examine structural development and connectivity in response to physical stimuli is established, and potentially provides insight into microfabricated geometries which promote neural regeneration and repair.

Nerve Decellularized Matrix Composite Scaffold With High Antibacterial Activity for Nerve Regeneration

Nerve decellularized matrix (NDM) has received much attention due to its natural composition and structural advantages that had proven to be an excellent candidate for peripheral nerve regeneration. However, NDM with simultaneous biocompatibility, promoting nerve regeneration, as well as resistant to infection was rarely reporter. In this study, a porous NDM-CS scaffold with high antimicrobial activity and high biocompatibility was prepared by combining the advantages of both NDM and chitosan (CS) in a one-step method. The NDM-CS scaffold possessed high porosity and hydrophilicity, exhibited excellent biocompatibility which was suitable for cell growth and nutrient exchange. Meanwhile, NDM-CS scaffold had a significant antibacterial effect on both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), which could avoid wound infection during the repair process. In addition, the NDM-CS scaffold could support the growth and viability of Schwann cells effectively. Among them, the E2C1 group had the strongest ability to enhance proliferation, polarization and migration of Schwann cells among the three groups. The positive effect on Schwann cells indicated their ability in the process of nerve injury repair. Therefore, this NDM-CS scaffold may have potential prospects for application in neural tissue engineering.

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.

Reduced graphene oxide-coated electrospun fibre: effect of orientation, coverage and electrical stimulation on Schwann cells behavior

Electrical signals are present in the extracellular spaces between neural cells. To mimic the electrophysiological environment for peripheral nerve regeneration, this study was intended to investigate how conductive graphene-based fibrous scaffolds with aligned topography regulate Schwann cell behavior in vitro via electrical stimulation (ES). To this end, randomly- and uniaxially-aligned polycaprolactone fibrous scaffolds were fabricated by electrospinning, followed by coating with reduced graphene oxide (rGO) via vacuum filteration. SEM revealed that rGO was successfully coated on the fibers without changing their alignment, and also brought about an improvement in mechanical properties and hydrophilicity. The electrical conductivity of the rGO-coated fibrous scaffold was up to 0.105 S m^-1. When Schwann cells were seeded on the scaffolds and stimulated by 10 mV in vitro, it was found that either the alignment of the fibers or ES led to a higher level of proliferation and nerve growth factor (NGF) expression of Schwann cells. Further, ES at the aligned fibrous topography enhanced the expression of NGF, the proliferation of Schwann cells, and enhanced the cell migration rate by more than 60% compared to either ES or the oriented fibers alone. The application of exogenous electric cues mediated by templated biomaterials provides profound insights for nerve regeneration.

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.

Effect of oblique polymer pillars on spreading and elongation of rat mesenchymal stem cells

Stiffness and anisotropy of culture substrates are important factors influencing the cell behavior and their responses to external stimuli. Herein, we report a fabrication method of oblique polymer pillars which allow modulating both stiffness and anisotropy of the substrate for spreading and elongation studies of Rat Mesenchymal Stem Cells (RMSCs). Poly (Lactic-co-Glycolic Acid) (PLGA) has been chosen to produce micro-pillars of different heights and different pitches using a combined method of soft-lithography and hot embossing. The stiffness of such pillar substrates varies over a large range so that RMSCs show effectively different spreading behaviors which are also sensitive to the inclining angle of the pillars. Our results showed that with the increase of the pillar height the area of cell spreading decreases but the cell elongation aspect ratio increases. Moreover, cells preferentially elongate along the direction perpendicular to that of the pillars' inclining, which is in agreement with the calculated anisotropy of the pillar substrate stiffness.