Functionalized hydrogels in neural injury repairing

Biocompatible EDOT-Pyrrole Conjugated Conductive Polymer Coating for Augmenting Cell Attachment, Activity, and Differentiation

Developing scaffolds supporting functional cell attachment and tissue growth is critical in basic cell research, tissue engineering, and regenerative medicine approaches. Though poly(ethylene glycol) (PEG) and its derivatives are attractive for hydrogels and scaffold fabrication, they often require bioactive modifications due to their bioinert nature. In this work, biomimetic synthesized conductive polypyrrole-poly(3,4-ethylenedioxythiophene) copolymer doped with poly(styrenesulfonate) (PPy-PEDOT:PSS) was used as a biocompatible coating for poly(ethylene glycol) diacrylate (PEGDA) hydrogel to support neuronal and muscle cells' attachment, activity, and differentiation. The synthesized copolymer was characterized by Raman spectroscopy and dynamic light scattering. Its electrochemical properties were studied using galvanostatic charge-discharge (GCD) and voltammetry. PPy-PEDOT:PSS-coated hydrogels were characterized by Raman spectroscopy and atomic force microscopy, and protein adsorption was assessed using a quartz crystal microbalance with dissipation monitoring. Attachment and differentiation of the ND7/23 neuron hybrid cell line and C2C12 myoblasts were evaluated by cell cytoskeleton staining and quantification of morphological parameters. Viability was assessed by live/dead staining using flow cytometry. Cortex neural activity was studied by calcium ion influx that could be detected through the dynamic fluorescence changes of Fluo-4. The PPy-PEDOT:PSS coating supported cell attachment and differentiation and was nontoxic to cells. Primary neurons attached and remained responsive to electrical stimulation. Altogether, the biocompatible copolymer PPy-PEDOT:PSS is a simple yet effective alternative for hydrogel coating and presents great potential as an interface for nervous and other electrically excitable tissues.

Hydrogels for Peripheral Nerve Repair: Emerging Materials and Therapeutic Applications

Peripheral nerve injuries pose a significant clinical challenge due to the complex biological processes involved in nerve repair and their limited regenerative capacity. Despite advances in surgical techniques, conventional treatments, such as nerve autografts, are faced with limitations like donor site morbidity and inconsistent functional outcomes. As such, there is a growing interest in new, novel, and innovative strategies to enhance nerve regeneration. Tissue engineering/regenerative medicine and its use of biomaterials is an emerging example of an innovative strategy. Within the realm of tissue engineering, functionalized hydrogels have gained considerable attention due to their ability to mimic the extracellular matrix, support cell growth and differentiation, and even deliver bioactive molecules that can promote nerve repair. These hydrogels can be engineered to incorporate growth factors, bioactive peptides, and stem cells, creating a conducive microenvironment for cellular growth and axonal regeneration. Recent advancements in materials as well as cell biology have led to the development of sophisticated hydrogel systems, that not only provide structural support, but also actively modulate inflammation, promote cell recruitment, and stimulate neurogenesis. This review explores the potential of functionalized hydrogels for peripheral nerve repair, highlighting their composition, biofunctionalization, and mechanisms of action. A comprehensive analysis of preclinical studies provides insights into the efficacy of these hydrogels in promoting axonal growth, neuronal survival, nerve regeneration, and, ultimately, functional recovery. Thus, this review aims to illuminate the promise of functionalized hydrogels as a transformative tool in the field of peripheral nerve regeneration, bridging the gap between biological complexity and clinical feasibility.

Optimizing Electroconductive PPy-PCL Scaffolds for Enhanced Tissue Engineering Performance

The integration of electrically conductive materials is a promising approach in tissue regeneration research. The study presented focuses on the creation of electroconductive scaffolds made from polypyrrole-polycaprolactone (PPy-PCL) using optimal processing parameters. Utilizing Box-Behnken response surface methodology for in situ chemical polymerization of PPy, the scaffolds exhibited a maximum conductivity of 2.542 mS/cm. Morphological examination via scanning electron microscopy (SEM) indicated uniform dispersion of PPy particles within PCL fibers. Fourier transform infrared spectroscopy (FTIR) and energy dispersive x-ray (EDX) analysis validated the composition of the scaffolds, while mechanical testing revealed that the optimized scaffolds exhibit superior tensile strength and Young's modulus compared to scaffolds comprised only of PCL. The hydrophilicity of the scaffolds was improved considerably, transitioning from initially hydrophobic to fully hydrophilic for the optimum scaffold, making it suitable for tissue engineering applications. Cell viability assays, including MTT with L929 fibroblasts and Alamar Blue with bone marrow mesenchymal stem cells (bmMSCs), reflected no cytotoxicity. They showed an increase in metabolic activity, suggesting the capability of the scaffolds to support cellular functions. In conclusion, the in situ synthesis of PPy in the PCL matrix by optimizing the fabrication parameters resulted in conductive scaffolds with promising structural and functional properties for tissue engineering.

In Vitro Models for Peripheral Nerve Regeneration

Peripheral nerve injury (PNI) resulting in lesions is highly prevalent clinically, but current therapeutic approaches fail to provide satisfactory outcomes in many patients. While peripheral nerves have intrinsic regenerative capacity, the regenerative capabilities of peripheral nerves are often insufficient to restore full functionality. This highlights an unmet need for developing more effective strategies to repair damaged peripheral nerves and improve regenerative success. Consequently, researchers are actively exploring a variety of therapeutic strategies, encompassing the local delivery of trophic factors or bioactive molecules, the design of advanced biomaterials that interact with regenerating axons, and augmentation with nerve guidance conduits or complex prostheses. However, clinical translation of these technologies remains limited, emphasizing the need for continued research on peripheral nerve regeneration modalities that can enhance functional restoration. Experimental models that accurately recapitulate key aspects of peripheral nerve injury and repair biology can accelerate therapeutic development by enabling systematic testing of new techniques. Advancing regenerative therapies for PNI requires bridging the gap between basic science discoveries and clinical application. This review discusses different in vitro models of peripheral nerve injury and repair, including their advantages, limitations, and potential applications.

Preparation and characterization of polysaccharide-based conductive hydrogels for nerve repair

Peripheral nerve injury is a serious medical condition, but the limited availability of autologous grafts often delays timely treatment for many patients. The implantation of functional hydrogels with good biocompatibility provides an effective solution to this challenge. In this study, a novel chitosan derivative, choline functionalized catechol carboxymethyl chitosan (CF-Catechol-CMCS), was synthesized by modifying carboxymethyl chitosan (CMCS) with choline functionalized (CF) molecule and catechol. CF-Catechol-CMCS, sodium alginate (SA), and pyrrole monomer (Py) were then combined, crosslinked with Fe3+ and Ca2+, and polymerized in situ to form polypyrrole (PPy), resulting in the CF-Catechol-CMCS/SA/PPy hydrogel. This hydrogel exhibits excellent thermal stability, with a maximum thermal degradation temperature of 580 °C. By adjusting the ratio of PPy to CF-Catechol-CMCS/SA in the hydrogel, its degradation properties, swelling behavior, mechanical properties, and electrical conductivity can be fine-tuned. Specifically, when the mass ratio of PPy to CF-Catechol-CMCS/SA is 8:10, the hydrogel achieves optimal conductivity within a safe range (1.82 × 10-3 S·cm-1). By controlling the mass ratio of CF-Catechol-CMCS to SA in the hydrogel, the acetylcholine concentration can be regulated. When the CF-Catechol-CMCS:SA ratio is 2:1, the measured Sciatic Function Index (SFI) value is -34.54, indicating that the CF-Catechol-CMCS/SA/PPy hydrogel has excellent nerve repair potential.

Advances in conductive hydrogels for neural recording and stimulation

The brain-computer interface (BCI) allows the human or animal brain to directly interact with the external environment through the neural interfaces, thus playing the role of monitoring, protecting, improving/restoring, enhancing, and replacing. Recording electrophysiological information such as brain neural signals is of great importance in health monitoring and disease diagnosis. According to the electrode position, it can be divided into non-implantable, semi-implantable, and implantable. Among them, implantable neural electrodes can obtain the highest-quality electrophysiological information, so they have the most promising application. However, due to the chemo-mechanical mismatch between devices and tissues, the adverse foreign body response and performance loss over time seriously restrict the development and application of implantable neural electrodes. Given the challenges, conductive hydrogel-based neural electrodes have recently attracted much attention, owing to many advantages such as good mechanical match with the native tissues, negligible foreign body response, and minimal signal attenuation. This review mainly focuses on the current development of conductive hydrogels as a biocompatible framework for neural tissue and conductivity-supporting substrates for the transmission of electrical signals of neural tissue to speed up electrical regeneration and their applications in neural sensing and recording as well as stimulation.

Injectable Hydrogels for Nervous Tissue Repair-A Brief Review

The repair of nervous tissue is a critical research field in tissue engineering because of the degenerative process in the injured nervous system. In this review, we summarize the progress of injectable hydrogels using in vitro and in vivo studies for the regeneration and repair of nervous tissue. Traditional treatments have not been favorable for patients, as they are invasive and inefficient; therefore, injectable hydrogels are promising for the treatment of damaged tissue. This review will contribute to a better understanding of injectable hydrogels as potential scaffolds and drug delivery system for neural tissue engineering applications.

Hydrogel-encapsulated extracellular vesicles for the regeneration of spinal cord injury

Spinal cord injury (SCI) is a critical neurological condition that may impair motor, sensory, and autonomous functions. At the cellular level, inflammation, impairment of axonal regeneration, and neuronal death are responsible for SCI-related complications. Regarding the high mortality and morbidity rates associated with SCI, there is a need for effective treatment. Despite advances in SCI repair, an optimal treatment for complete recovery after SCI has not been found so far. Therefore, an effective strategy is needed to promote neuronal regeneration and repair after SCI. In recent years, regenerative treatments have become a potential option for achieving improved functional recovery after SCI by promoting the growth of new neurons, protecting surviving neurons, and preventing additional damage to the spinal cord. Transplantation of cells and cells-derived extracellular vesicles (EVs) can be effective for SCI recovery. However, there are some limitations and challenges related to cell-based strategies. Ethical concerns and limited efficacy due to the low survival rate, immune rejection, and tumor formation are limitations of cell-based therapies. Using EVs is a helpful strategy to overcome these limitations. It should be considered that short half-life, poor accumulation, rapid clearance, and difficulty in targeting specific tissues are limitations of EVs-based therapies. Hydrogel-encapsulated exosomes have overcome these limitations by enhancing the efficacy of exosomes through maintaining their bioactivity, protecting EVs from rapid clearance, and facilitating the sustained release of EVs at the target site. These hydrogel-encapsulated EVs can promote neuroregeneration through improving functional recovery, reducing inflammation, and enhancing neuronal regeneration after SCI. This review aims to provide an overview of the current research status, challenges, and future clinical opportunities of hydrogel-encapsulated EVs in the treatment of SCI.