Substance P-embedded multilayer on titanium substrates promotes local osseointegration via MSC recruitment

Emerging roles of nerve-bone axis in modulating skeletal system

Over the past decades, emerging evidence in the literature has demonstrated that the innervation of bone is a crucial modulator for skeletal physiology and pathophysiology. The nerve-bone axis sparked extensive preclinical and clinical investigations aimed at elucidating the contribution of nerve-bone crosstalks to skeleton metabolism, homeostasis, and injury repair through the perspective of skeletal neurobiology. To date, peripheral nerves have been widely reported to mediate bone growth and development and fracture healing via the secretion of neurotransmitters, neuropeptides, axon guidance factors, and neurotrophins. Relevant studies have further identified several critical neural pathways that stimulate profound alterations in bone cell biology, revealing a complex interplay between the skeleton and nerve systems. In addition, inspired by nerve-bone crosstalk, novel drug delivery systems and bioactive materials have been developed to emulate and facilitate the process of natural bone repair through neuromodulation, eventually boosting osteogenesis for ideal skeletal tissue regeneration. Overall, this work aims to review the novel research findings that contribute to deepening the current understanding of the nerve-bone axis, bringing forth some schemas that can be translated into the clinical scenario to highlight the critical roles of neuromodulation in the skeletal system.

Coaxial Electrospun Polycaprolactone/Gelatin Nanofiber Membrane Loaded with Salidroside and Cryptotanshinone Synergistically Promotes Vascularization and Osteogenesis

Background

Salidroside (SAL) is the most effective component of Rhodiola rosea, a traditional Chinese medicine. Cryptotanshinone (CT) is the main fat-soluble extract of Salvia miltiorrhiza, exhibiting considerable potential for application in osteogenesis. Herein, a polycaprolactone/gelatin nanofiber membrane loaded with CT and SAL (PSGC membrane) was successfully fabricated via coaxial electrospinning and characterized.

Methods and Results

This membrane capable of sustained and controlled drug release was employed in this study. Co-culturing the membrane with bone marrow mesenchymal stem cells and human umbilical vein endothelial cells revealed excellent biocompatibility and demonstrated osteogenic and angiogenic capabilities. Furthermore, drug release from the PSGC membrane activated the Wnt/β-catenin signaling pathway and promoted osteogenic differentiation and vascularization. Evaluation of the membrane's vascularization and osteogenic capacities involved transplantation onto a rat's subcutaneous area and assessing rat cranium defects for bone regeneration, respectively. Microcomputed tomography, histological tests, immunohistochemistry, and immunofluorescence staining confirmed the membrane's outstanding angiogenic capacity two weeks post-operation, with a higher incidence of osteogenesis observed in rat cranial defects eight weeks post-surgery.

Conclusion

Overall, the SAL- and CT-loaded coaxial electrospun nanofiber membrane synergistically enhances bone repair and regeneration.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

The ratio of alpha-calcitonin gene-related peptide to substance P is associated with the transition of bone metabolic states during aging and healing

Alpha-calcitonin gene-related peptide (αCGRP) and substance P (SP) are functionally correlated sensory neuropeptides deeply involved in bone homeostasis. However, they are usually studied individually rather than as an organic whole. To figure out whether they are interdependent, we firstly recorded the real-time αCGRP and SP levels in aging bone and healing fracture, which revealed a moderate to high level of αCGRP coupled with a low αCGRP/SP ratio in an anabolic state, and a high level of αCGRP coupled with a high αCGRP/SP ratio in a catabolic state, suggesting the importance of αCGRP/SP ratio in driving aging and healing scenarios. During facture healing, increase in αCGRP/SP ratio by adding αCGRP led to better callus formation and faster callus remodeling, while simultaneous addition of αCGRP and SP resulted in hypertrophic callus and delayed remodeling. The characteristics in inflammation and osteoclast activation further confirmed the importance of high αCGRP/SP ratio during catabolic bone remodeling. In vitro assays using different mixtures of αCGRP-SP proved that the osteogenic potential of the mixtures depended mostly on αCGRP, while their effects on osteoclasts and neutrophils relied on both peptides. These results demonstrated that αCGRP and SP were spatiotemporally interdependent. The αCGRP/SP ratio may be more important than the dose of a single neuropeptide in managing age-related and trauma-related bone diseases.

Preparation of co-electrospinning membrane loaded with simvastatin and substance P to accelerate bone regeneration by promoting cell homing, angiogenesis and osteogenesis

Bone regeneration is a complex process that requires the coordination of various biological events. Developing a tissue regeneration membrane that can regulate this cascade of events is challenging. In this study, we aimed to fabricate a membrane that can enrich the damaged area with mesenchymal stem cells, improve angiogenesis, and continuously induce osteogenesis. Our approach involved creating a hierarchical polycaprolactone/gelatin (PCL/GEL) co-electrospinning membrane that incorporated substance P (SP)-loaded GEL fibers and simvastatin (SIM)-loaded PCL fibers. The membrane could initiate a burst release of SP and a slow/sustained release of SIM for over a month. In vitro experiments, including those related to angiogenesis and osteogenesis (e.g., migration, endothelial network formation, alkaline phosphatase activity, mineralization, and gene expression), clearly demonstrated the membrane's superior ability to improve cell homing, revascularization, and osteogenic differentiation. Furthermore, a series of in vivo studies, including immunofluorescence of CD29⁺/CD90⁺ double-positive cells and immunohistochemical staining for CD34 and vWF, confirmed the co-electrospinning membrane's ability to enhance MSC migration and revascularization response after five days of implantation. After one month, the Micro-CT and histological (Masson and H&E) results showed accelerated bone regeneration. Our findings suggest that a co-electrospinning membrane with time-tunable drug delivery could advance the development of tissue engineering therapeutic strategies and potentially improve patient outcomes.

Nerves within bone and their application in tissue engineering of bone regeneration

Nerves within bone play an irreplaceable role in promoting bone regeneration. Crosstalk between the nerve system and bone has arisen to the attention of researchers in the field of basic medicine, clinical medicine, and biomaterials science. Successful bone regeneration relies on the appropriate participation of neural system components including nerve fibers, signaling molecules, and neural-related cells. Furthermore, more about the mechanisms through which nerves took part in bone regeneration and how these mechanisms could be integrated into tissue engineering scaffolds were under exploration. In the present review, we aimed to systematically elaborate on the structural and functional interrelationship between the nerve system and bone. In particular, peripheral nerves interact with the bone through innervated axons, multiple neurotrophins, and bone resident cells. Also, we aimed to summarize research that took advantage of the neuro-osteogenic network to design tissue engineering scaffolds for bone repair.

Hallmarks of peripheral nerve function in bone regeneration

Skeletal tissue is highly innervated. Although different types of nerves have been recently identified in the bone, the crosstalk between bone and nerves remains unclear. In this review, we outline the role of the peripheral nervous system (PNS) in bone regeneration following injury. We first introduce the conserved role of nerves in tissue regeneration in species ranging from amphibians to mammals. We then present the distribution of the PNS in the skeletal system under physiological conditions, fractures, or regeneration. Furthermore, we summarize the ways in which the PNS communicates with bone-lineage cells, the vasculature, and immune cells in the bone microenvironment. Based on this comprehensive and timely review, we conclude that the PNS regulates bone regeneration through neuropeptides or neurotransmitters and cells in the peripheral nerves. An in-depth understanding of the roles of peripheral nerves in bone regeneration will inform the development of new strategies based on bone-nerve crosstalk in promoting bone repair and regeneration.

Constructions of ROS-responsive titanium-hydroxyapatite implant for mesenchymal stem cell recruitment in peri-implant space and bone formation in osteoporosis microenvironment

To solve the issue of unsatisfactory recruitment of mesenchymal stem cells (MSCs) around implant in osteoporotic fractures, we fabricated a ROS-responsive system on titanium surface through hydroxyapatite coating and biomolecule grafting. The porous hydroxyapatite and phosphorylated osteogenic growth peptides (p-OGP) were introduced onto titanium surface to synergistically improve osteogenic differentiation of MSCs. After the p-OGP-promoted expression of osteogenic related proteins, the calcium and phosphate ions were released through the degradation of hydroxyapatite and integrated into bone tissues to boost the mineralization of bone matrix. The ROS-triggered release of DNA aptamer (Apt) 19S in the osteoporotic microenvironment guides MSC migration to implant site due to its high affinity with alkaline phosphatase on the membrane of MSCs. Once MSCs reached the implant interface, their osteogenic differentiation potential was enhanced by p-OGP and hydroxyapatite to promote bone regeneration. The study here provided a simple and novel strategy to prepare functional titanium implants for osteoporotic bone fracture repair.

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ROS-responsive system was constructed on Titanium surface.

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Aptamer 19S boosted the migration of MSC to the injury site.

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Hydroxyapatite and OGP synergistically promoted the biomineralized of MSC.

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Osseointegration was improved in osteoporotic fracture site.

[Mo3S13]2− as bidirectional cluster catalysts for high-performance Li–S batteries

[Mo3S13]2− bidirectional cluster catalysts combined with mesoporous carbon hollow spheres (MCHS) as a sulfur host material can improve the performance of Li–S batteries.

Fabrication of gelatin-based and Zn2+-incorporated composite hydrogel for accelerated infected wound healing

Gelatin-based hydrogels have a broad range of biomedical fields due to their biocompatibility, convenience for chemical modifications, and degradability. However, gelatin-based hydrogels present poor antibacterial ability that hinders their applications in treating infected wound healing. Herein, a series of multifunctional hydrogels (Gel@Zn) were fabricated through free-radical polymerization interaction based on gelatin methacrylate (GelMA) and dopamine methacrylate (DMA), and then immersed them into zinc nitrate solutions based on the metal coordination and ionic bonding interaction. These designed hydrogels wound dressings show strong antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by increasing intracellular reactive oxygen species (ROS) level and changing bacterial membrane permeability. Meanwhile, the hydrogels exhibit good cytocompatibility, enhance the adhesion, proliferation, and migration of NIH-3T3 cells. Furthermore, Gel@Zn-0.08 (0.08 ​M Zn2+ immersed with Gel sample) presents a good balance between antibacterial effect, cell viability, and hemolytic property. Compared with 3 ​M commercial dressings, Gel@Zn-0.04, and Gel@Zn-0.16, the Gel@Zn-0.08 could significantly improve the healing process of S. aureus-infected full-thickness wounds via restrained the inflammatory responses, enhanced epidermis and granulation tissue information, and stimulated angiogenesis. Our study indicates that the Zn-incorporated hydrogels are promising bioactive materials as wound dressings for infected full-thickness wound healing and skin regeneration.

Programmed core-shell electrospun nanofibers to sequentially regulate osteogenesis-osteoclastogenesis balance for promoting immediate implant osseointegration

The biology of immediate post-extraction implant osseointegration is mediated by a coordinated cascade of osteoblast-osteoclast interactions. The aim of this study was to develop a dual-delivery system that allowed sequential release of substance P (SP) to promote bone regeneration and alendronate (ALN) to reduce bone resorption, which will improve the implant osseointegration. We used coaxial electrospinning to fabricate the core-shell poly lactic-co-glycolic acid (PLGA)/gelatin nanofibers, which consists of SP in the shell and ALN in the core. This programmed delivery system was shown to release SP and ALN sequentially to match the spatio-temporal specificity of bone healing. The migration assay demonstrated that the SP-ALN dual-delivery system increased bone marrow mesenchymal stem cells (BMSCs) transmigration. Besides, the expression of osteogenic/osteoclastic markers, Alizarin Red staining, tartrate-resistant acid phosphatase (TRAP) staining, F-actin staining and bone resorption experiment showed that the dual-delivery system can render a microenvironment favorable for osteogenic differentiation and adverse to osteoclastogenesis. Using a rat immediate implant model, we validated the promoted osteogenic property and osseointegration around the implants of SP-ALN dual-delivery system by micro-computed tomography (micro-CT) and histological analysis. These findings suggest that the dual-delivery system with time-controlled release of SP and ALN by core-shell nanofibers provides a promising strategy to facilitate immediate implant osseointegration through favorable osteogenesis. STATEMENT OF SIGNIFICANCE: Immediate implant placement is potentially challenged by the difficulties in achieving primary implant stability and early osteogenesis. Initial period of osteointegration is regulated by osteoblastic/osteoclastic cells resulting in a coordinated healing process. To have an efficient bone regeneration, the coaxial electrospinning was used to fabricate a programmed dual-delivery system. The SP released rapidly and favored for BMSCs migration and osteogenic differentiation, while the sustained release of ALN can reduce the bone resorption. The rat immediate implant model indicated that the SP-ALN dual-delivery system could present the promoted peri‑implant osteogenic property and osseointegration through modulating the osteogenesis-osteoclastogenesis balance. This work highlights the sequential dual delivery of SP and ALN has a promising potential of achieving enhanced osseointegration for immediate implant placement.

Recent advances in chitosan-based layer-by-layer biomaterials and their biomedical applications

In recent years, chitosan-based biomaterials have been continually and extensively researched by using layer-by-layer (LBL) assembly, due to their potentials in biomedicine. Various chitosan-based LBL materials have been newly developed and applied in different areas along with the development of technologies. This work reviews the recent advances of chitosan-based biomaterials produced by LBL assembly. Driving forces of LBL, for example electrostatic interactions, hydrogen bond as well as Schiff base linkage have been discussed. Various forms of chitosan-based LBL materials such as films/coatings, capsules and fibers have been reviewed. The applications of these biomaterials in the field of antimicrobial applications, drug delivery, wound dressings and tissue engineering have been comprehensively reviewed.