Pleiotropic effects of nitric oxide sustained-release system for peripheral nerve repair.

The regenerative microenvironment after peripheral nerve injury is imbalanced and difficult to rebalance, which is mainly affected by inflammation, oxidative stress, and inadequate blood supply. The difficulty in remodeling the nerve regeneration microenvironment is the main reason for slow nerve regeneration. Traditional drug treatments have certain limitations, such as difficulty in penetrating the blood-nerve barrier and lack of pleiotropic effects. Therefore, there is an urgent need to build multifunctional nerve grafts that can effectively regulate the regenerative microenvironment and promote nerve regeneration. Nitric oxide (NO), a highly effective gas transmitter with diatomic radicals, is an important regulator of axonal growth and migration, synaptic plasticity, proliferation of neural precursor cells, and neuronal survival. Moreover, NO provides potential anti-inflammation, anti-oxidation, and blood vessel promotion applications. However, excess NO may cause cell death and neuroinflammatory cell damage. The prerequisite for NO treatment of peripheral nerve injury is that it is gradually released over time. In this study, we constructed an injectable NO slow-release system with two main components, including macromolecular NO donor nanoparticles (mPEG-P(MSNO-EG) nanoparticles, NO-NPs) and a carrier for the nanoparticles, mPEG-PA-PP injectable temperature-sensitive hydrogel. Due to the multiple physiological regulation of NO and better physiological barrier penetration, the conduit effectively regulates the inflammatory response and oxidative stress of damaged peripheral nerves, promotes nerve vascularization, and nerve regeneration and docking, accelerating the nerve regeneration process. STATEMENT OF SIGNIFICANCE: The slow regeneration speed of peripheral nerves is mainly due to the destruction of the regeneration microenvironment. Neural conduits with drug delivery capabilities have the potential to improve the microenvironment of nerve regeneration. However, traditional drugs are hindered by the blood nerve barrier and cannot effectively target the injured area. NO, an endogenous gas signaling molecule, can freely cross the blood nerve barrier and act on target cells. However, excessive NO can lead to cell apoptosis. In this study, a NO sustained-release system was constructed to regulate the microenvironment of nerve regeneration through various pathways and promote nerve regeneration.

An injectable hydrogel dressing for controlled release of hydrogen sulfide pleiotropically mediates the wound microenvironment.

The healing of scalded wounds faces many challenges such as chronic inflammation, oxidative stress, wound infection, and difficulties in vascular and nerve regeneration. Treating a single problem cannot effectively coordinate the complex regenerative microenvironment of scalded wounds, limiting the healing and functional recovery of the skin. Therefore, there is a need to develop a multi-effect treatment plan that can adaptively address the issues at each stage of wound healing. In this study, we propose a scheme for on-demand release of hydrogen sulfide (H2S) based on the concentration of reactive oxygen species (ROS) in the wound microenvironment. This is achieved by encapsulating peroxythiocarbamate (PTCM) in the ROS-responsive polymer poly(ethylene glycol)-poly(L-methionine) (PMet) to form nanoparticles, which are loaded into a thermosensitive injectable hydrogel, F127-poly(L-aspartic acid-N-hydroxysuccinimide) (F127-P(Asp-NHS)), to create a scald dressing. The H2S released by the hydrogel dressing on demand regulates the wound microenvironment by alleviating infection, reducing oxidative stress, and remodeling inflammation, thereby accelerating the healing of full-thickness scalded wounds. This hydrogel dressing for the adaptive release of H2S has great potential in addressing complex scalded wounds associated with infection and chronic inflammation.

An Adaptable Drug Delivery System Facilitates Peripheral Nerve Repair by Remodeling the Microenvironment.

The multifaceted process of nerve regeneration following damage remains a significant clinical issue, due to the lack of a favorable regenerative microenvironment and insufficient endogenous biochemical signaling. However, the current nerve grafts have limitations in functionality, as they require a greater capacity to effectively regulate the intricate microenvironment associated with nerve regeneration. In this regard, we proposed the construction of a functional artificial scaffold based on a "two-pronged" approach. The whole system was developed by encapsulating Tazarotene within nanomicelles formed through self-assembly of reactive oxygen species (ROS)-responsive amphiphilic triblock copolymer, all of which were further loaded into a thermosensitive injectable hydrogel. Notably, the hydrogel exhibits obvious temperature sensitivity at a concentration of 6 wt %, and the nanoparticles possess concentration-dependent H2O2-response capability with a controlled release profile in 48 h. The combined strategy promoted the repair of injured peripheral nerves, attributed to the dual role of the materials, which mainly involved providing structural support, modulating the immune microenvironment, and enhancing angiogenesis. Overall, this study opens up intriguing prospects in tissue engineering.

Injectable Hydrogel System Incorporating Black Phosphorus Nanosheets and Tazarotene Drug for Enhanced Vascular and Nerve Regeneration in Spinal Cord Injury Repair.

Spinal cord injury (SCI) often leads to cell death, vascular disruption, axonal signal interruption, and permanent functional damage. Currently, there are no clearly effective therapeutic options available for SCI. Considering the inhospitable SCI milieu typified by ischemia, hypoxia, and restricted neural regeneration, a novel injectable hydrogel system containing conductive black phosphorus (BP) nanosheets within a lipoic acid-modified chitosan hydrogel matrix (LAMC) is explored. The incorporation of tannic acid (TA)-modified BP nanosheets (BP@TA) into the LAMC hydrogel matrix significantly improved its conductivity. Further, by embedding a bicyclodextrin-conjugated tazarotene drug, the hydrogel showcased amplified angiogenic potential in vitro. In a rat model of complete SCI, implantation of LAMC/BP@TA hydrogel markedly improved the recovery of motor function. Immunofluorescence evaluations confirmed that the composite hydrogel facilitated endogenous angiogenesis and neurogenesis at the injury site. Collectively, this work elucidates an innovative drug-incorporated hydrogel system enriched with BP, underscoring its potential to foster vascular and neural regeneration.

An injectable and adaptable hydrogen sulfide delivery system for modulating neuroregenerative microenvironment.

Peripheral nerve regeneration is a complex physiological process. Single-function nerve scaffolds often struggle to quickly adapt to the imbalanced regenerative microenvironment, leading to slow nerve regeneration and limited functional recovery. In this study, we demonstrate a "pleiotropic gas transmitter" strategy based on endogenous reactive oxygen species (ROS), which trigger the on-demand H2S release at the defect area for transected peripheral nerve injury (PNI) repair through concurrent neuroregeneration and neuroprotection processing. This H2S delivery system consists of an H2S donor (peroxyTCM) encapsulated in a ROS-responsive polymer (mPEG-PMet) and loaded into a temperature-sensitive poly (amino acid) hydrogel (mPEG-PA-PP). This multi-effect combination strategy greatly promotes the regeneration of PNI, attributed to the physiological effects of H2S. These effects include the inhibition of inflammation and oxidative stress, protection of nerve cells, promotion of angiogenesis, and the restoration of normal mitochondrial function. The adaptive release of pleiotropic messengers to modulate the tissue regeneration microenvironment offers promising peripheral nerve repair and tissue engineering opportunities.

Dopamine-modified chitosan hydrogel for spinal cord injury.

Spinal cord injury (SCI) decreases people's both physical and psychological levels. The rehabilitation of SCI is still a clinical challenging process owing to the inflammatory environment for cell survival. Herein, we designed a dopamine-modified chitosan hydrogel to improve poor microenvironment of spinal cord injury. Dopamine modified chitosan hydrogel was fabricated by crosslinking with citric acid (CS-CA-DA), which address the insufficient mechanical properties. In vitro analysis showed that dopamine modification improved the cell survival and cell adhesion. Moreover, implantation of CS-CA-DA hydrogel alone into rat injured spinal cord helped improving cell survivals, modulating immunity, promoting macrophage polarization to the M2 phenotype and promoting axonal regeneration in vivo in brutal areas of SCI. This strategy of modified chitosan with dopamine undergoing a high mechanical properties, excellent cell compatibility and antioxidant performance, providing a new insight into repairing spinal cord injury.

Enhanced sciatic nerve regeneration by relieving iron-overloading and organelle stress with the nanofibrous P(MMD-co-LA)/DFO conduits.

Wallerian degeneration after peripheral nerve injury (PNI), that is, the autonomous degeneration of distal axons, leads to an imbalance of iron homeostasis and easily induces oxidative stress caused by iron overload. Inspired by the process of nerve degeneration and regeneration, the design of a functional electrospinning scaffold with iron chelating ability exhibited the importance of reconstructing a suitable microenvironment. Here, an electrospinning scaffold based on deferoxamine and poly(3(S)-methyl-morpholine-2,5-dione-co-lactone) (PDPLA/DFO) was constructed. This work aims to explore the promotion of nerve regeneration by the physiological regulation of the scaffold. In vitro, PDPLA/DFO films mitigated the reduction of glutathione and the inactivation of Glutathione peroxidase 4 caused by iron overload. In addition, they decreased reactive oxygen species, relieve the stress of the endoplasmic reticulum and mitochondria, and reduce cell apoptosis. In vivo, PDPLA/DFO conduits constructed the anti-inflammatory microenvironment and promoted cell survival by alleviating iron overload and organelle stress. In conclusion, PDPLA/DFO guidance conduits targeted the distal iron overload and promoted nerve regeneration. It provides novel ideas for designing nerve conduits targeting the distal microenvironment.

Oriented nanofibrous P(MMD-co-LA)/Deferoxamine nerve scaffold facilitates peripheral nerve regeneration by regulating macrophage phenotype and revascularization.

Delayed injured nerve regeneration remains a clinical problem, partly ascribing to the lack of regulation of regenerative microenvironment, topographical cues, and blood nourishment. Functional electrospun conduits have been established as an efficacious strategy to facilitate nerve regeneration by providing structural guidance, regulating the regenerative immune microenvironment, and improving vascular regeneration. However, the synthetic polymers conventionally used to fabricate electrospinning scaffolds, such as poly(L-lactic acid), poly(glycolic acid), and poly(lactic-co-glycolic acid), can cause aseptic inflammation due to acidic degradation products. Therefore, a poly[3(S)-methyl-morpholine-2,5-dione-co-lactic] [P(MMD-co-LA)] containing alanine units with good mechanical properties and reduced acid degradation products, was obtained by melt ring-opening polymerization (ROP). Here, we aimed to explore the effect of oriented nanofiber/Deferoxamine (DFO, a hydrophilic angiogenic drug) scaffold in the rapid construction of a favorable regenerative microenvironment, including cell bridge, polarized vascular system, and immune microenvironment. In vitro studies have shown that the scaffold can sustainably release DFO, which accelerates the migration and tube formation of human umbilical vein endothelial cells (HUVECs), as well as the expression of genes related to angiogenesis. The physical clues provided by the arranged nanofibers can regulate the polarization of macrophages and reduce the expression of inflammatory factors. Furthermore, the in vivo results demonstrated a higher M2 polarization level of the oriented nanofibrous scaffold treatment group with reducedinflammation reaction in the injured nerve. Moreover, the in-situ release of DFO up-regulated the expression of HIF1-α and SDF-1α genes, as well as the expression of HIF1-α's target gene VEGF, further promoting revascularization and enhancing nerve regeneration at the defect site. The obtained results provide essential insights on accelerating the creation of the nerve regeneration microenvironment by combining the physiological processes of nerve regeneration with topographical cues and chemical signal induction.

Improved functional recovery of rat transected spinal cord by peptide-grafted PNIPAM based hydrogel.

Facilitating angiogenesis, reducing the formation of glial scar tissue, and the occurrence of a strong inflammatory response are of great importance for the repair of central nerve damage. In our previous study, a temperature-sensitive hydrogel grafted with bioactive isoleucine-lysine-valine-alanine-valine (IKVAV) peptide was prepared and it showed regular three-dimensional porous structure, rapid (de)swelling performance and good biological activity. Therefore, in this study, we used this hydrogel scaffold to treat for SCI to study the effect of it to facilitate angiogenesis, inhibit the differentiation and adhesion of keratinocytes, and further reduce the formation of glial scar tissue. The results reveal that the peptide hydrogel scaffold achieved excellent performance and can also promote the expression of angiogenic factors and reduce the secretion of pro-inflammatory factors to a certain extent. Particularly, it can also inhibit the formation of glial scar tissue and repair damaged tissue. The proposed strategy for developing this hydrogel scaffold provides a new insight into designing biomaterials for a broad range of applications in the tissue engineering of the central nervous system (CNS).

Enhanced proliferation and differentiation of neural stem cells by peptide-containing temperature-sensitive hydrogel scaffold.

Hydrogel has attracted great attention in the past few years as a widely used material for repairing central nerve damage. However, conventional hydrogel bio-scaffold, such as chitosan, gelatin, and sodium alginate, lack sufficient biological activity and have limited nerve repair capabilities. Therefore, to explore biologically active and intelligent hydrogel materials is particularly important and necessary for central nerve repair. Herein, we developed a temperature-sensitive hydrogel grafted with a bioactive peptide IKVAV (Ile-Lys-Val-Ala-Val, IKVAV). The hydrogel was prepared by copolymerization of N-propan-2-ylprop-2-enamide (NIPAM) and AC-PEG-IKVAV copolymers via reversible addition-fracture chain transfer (RAFT) polymerization, using polyethylene glycol (PEGDA) and N, N'-Methylenebisacrylamide (BISAM) as cross-linking agents. The prepared hydrogel scaffold demonstrates a series of excellent properties such as rapid (de)swelling performance, good biocompatibility, regular three-dimensional porous structure, and in particular good biological activity, which can guide cell fate and mediate neuron's differentiation. Therefore, the developed peptide hydrogel scaffold provides a new strategy for designing biomaterials that are widely used in tissue engineering for central nervous system injury.