Silicified collagen scaffold induces semaphorin 3A secretion by sensory nerves to improve in-situ bone regeneration

Bioactive Inorganic Materials for Innervated Multi-Tissue Regeneration

Tissue engineering aims to repair damaged tissues with physiological functions recovery. Although several therapeutic strategies are there for tissue regeneration, the functional recovery of regenerated tissues still poses significant challenges due to the lack of concerns of tissue innervation. Design rationale of multifunctional biomaterials with both tissue-induction and neural induction activities shows great potential for functional tissue regeneration. Recently, the research and application of inorganic biomaterials attracts increasing attention in innervated multi-tissue regeneration, such as central nerves, bone, and skin, because of its superior tunable chemical composition, topographical structures, and physiochemical properties. More importantly, inorganic biomaterials are easily combined with other organic materials, biological factors, and external stimuli to enhance their therapeutic effects. This review presents a comprehensive overview of recent advancements of inorganic biomaterials for innervated multi-tissue regeneration. It begins with introducing classification and properties of typical inorganic biomaterials and design rationale of inorganic-based material composites. Then, recent progresses of inorganic biomaterials in regenerating various nerves and nerve-innervated tissues with functional recovery are systematically reviewed. Finally, the existing challenges and future perspectives are proposed. This review may pave the way for the direction of inorganic biomaterials and offers a new strategy for tissue regeneration in combination of innervation.

Strategies for promoting neurovascularization in bone regeneration

Bone tissue relies on the intricate interplay between blood vessels and nerve fibers, both are essential for many physiological and pathological processes of the skeletal system. Blood vessels provide the necessary oxygen and nutrients to nerve and bone tissues, and remove metabolic waste. Concomitantly, nerve fibers precede blood vessels during growth, promote vascularization, and influence bone cells by secreting neurotransmitters to stimulate osteogenesis. Despite the critical roles of both components, current biomaterials generally focus on enhancing intraosseous blood vessel repair, while often neglecting the contribution of nerves. Understanding the distribution and main functions of blood vessels and nerve fibers in bone is crucial for developing effective biomaterials for bone tissue engineering. This review first explores the anatomy of intraosseous blood vessels and nerve fibers, highlighting their vital roles in bone embryonic development, metabolism, and repair. It covers innovative bone regeneration strategies directed at accelerating the intrabony neurovascular system over the past 10 years. The issues covered included material properties (stiffness, surface topography, pore structures, conductivity, and piezoelectricity) and acellular biological factors [neurotrophins, peptides, ribonucleic acids (RNAs), inorganic ions, and exosomes]. Major challenges encountered by neurovascularized materials during their clinical translation have also been highlighted. Furthermore, the review discusses future research directions and potential developments aimed at producing bone repair materials that more accurately mimic the natural healing processes of bone tissue. This review will serve as a valuable reference for researchers and clinicians in developing novel neurovascularized biomaterials and accelerating their translation into clinical practice. By bridging the gap between experimental research and practical application, these advancements have the potential to transform the treatment of bone defects and significantly improve the quality of life for patients with bone-related conditions.

Semaphorin 3A on Osteoporosis: An Overreview of the Literature

Semaphorin 3A (Sema3A) is a signaling protein that has attracted increasing attention in recent years for its important role in regulating bone metabolism. In this review, we searched different databases with various combinations of keywords to analyze the effects of Sema3A on osteoporosis. Sema3A promotes bone formation and inhibits bone resorption by directly affecting the osteoblast and osteoclast or indirectly targeting the nervous system. The sympathetic nervous system may be the main link between the central nervous system and bone metabolism for Sema3A. In the peripheral nervous system, Sema3A may improve bone quality via sensory nervous innervation. In addition, estrogen is found to regulate Sema3A levels to improve bone homeostasis. Lots of Sema3A agonists have been documented to exhibit anti-osteoporotic potential in preclinical investigations. Therefore, Sema3A can be considered a novel therapeutic target for preserving bone mass, highlighting an alternative strategy for the development of anti-osteoporosis drugs.

Neuroregulation during Bone Formation and Regeneration: Mechanisms and Strategies

The skeleton is highly innervated by numerous nerve fibers. These nerve fibers, in addition to transmitting information within the bone and mediating bone sensations, play a crucial role in regulating bone tissue formation and regeneration. Traditional bone tissue engineering (BTE) often fails to achieve satisfactory outcomes when dealing with large-scale bone defects, which is frequently related to the lack of effective reconstruction of the neurovascular network. In recent years, increasing research has revealed the critical role of nerves in bone metabolism. Nerve fibers regulate bone cells through neurotransmitters, neuropeptides, and peripheral glial cells. Furthermore, nerves also coordinate with the vascular and immune systems to jointly construct a microenvironment favorable for bone regeneration. As a signaling driver of bone formation, neuroregulation spans the entire process of bone physiological activities from the embryonic formation to postmaturity remodeling and repair. However, there is currently a lack of comprehensive summaries of these regulatory mechanisms. Therefore, this review sketches out the function of nerves during bone formation and regeneration. Then, we elaborate on the mechanisms of neurovascular coupling and neuromodulation of bone immunity. Finally, we discuss several novel strategies for neuro-bone tissue engineering (NBTE) based on neuroregulation of bone, focusing on the coordinated regeneration of nerve and bone tissue.

Skeletal interoception and prospective application in biomaterials for bone regeneration

Accumulating research has shed light on the significance of skeletal interoception, in maintaining physiological and metabolic homeostasis related to bone health. This review provides a comprehensive analysis of how skeletal interoception influences bone homeostasis, delving into the complex interplay between the nervous system and skeletal system. One key focus of the review is the role of various factors such as prostaglandin E2 (PGE2) in skeletal health via skeletal interoception. It explores how nerves innervating the bone tissue communicate with the central nervous system to regulate bone remodeling, a process critical for maintaining bone strength and integrity. Additionally, the review highlights the advancements in biomaterials designed to utilize skeletal interoception for enhancing bone regeneration and treatment of bone disorders. These biomaterials, tailored to interact with the body's interoceptive pathways, are positioned at the forefront of innovative treatments for conditions like osteoporosis and fractures. They represent a convergence of bioengineering, neuroscience, and orthopedics, aiming to create more efficient and targeted therapies for bone-related disorders. In conclusion, the review underscores the importance of skeletal interoception in physiological regulation and its potential in developing more effective therapies for bone regeneration. It emphasizes the need for further research to fully understand the mechanisms of skeletal interoception and to harness its therapeutic potential fully.

Neuronal TRPV1-CGRP axis regulates peripheral nerve regeneration through ERK/HIF-1 signaling pathway

Severe trauma frequently leads to nerve damage. Peripheral nerves possess a degree of regenerative ability, and actively promoting their recovery can help restore the sensory and functional capacities of tissues. The neuropeptide calcitonin gene-related peptide (CGRP) is believed to regulate the repair of injured peripheral nerves, with neuronal transient receptor potential vanilloid type 1 (TRPV1) potentially serving as a crucial upstream factor. In this study, we established a mouse model of sciatic nerve (SN) crush injury and found that intrathecal injection of capsaicin (Cap) activated the neuronal TRPV1-CGRP axis, thereby promoting SN repair. Conversely, the application of capsazepine (Cpz), which inhibits the neuronal TRPV1-CGRP axis, delayed SN repair. Local restoration of CGRP expression at the injury site enhanced the repair process. In vitro experiments, we employed the rat Schwann cell (SC) line RSC96 to establish an indirect co-culture model of neurons and SCs. We observed that the proliferation, migration, expression of myelination-associated proteins, and neurotrophic secretion functions of RSC96 cells are positively correlated with the degree of activation of neuronal TRPV1. Inhibition of neuronal TRPV1, followed by the restoration of CGRP levels, improved these functions in RSC96 cells. Furthermore, activation of the neuronal TRPV1-CGRP axis resulted in an upregulation of extracellular signal-regulated kinases 1/2 (ERK1/2) phosphorylation levels and an increase in hypoxia-inducible factor 1α (HIF-1α) accumulation in RSC96 cells, thereby promoting their proliferation and migration. In summary, this study demonstrates that neuronal TRPV1-CGRP axis can regulate biological behavior of SCs and axon regeneration by activating the ERK/HIF-1 signaling pathway following peripheral nerve injury. This finding clarifies the role of CGRP in neuroregulatory networks and provides a novel reference point for the development of drugs and biomaterials for treating nerve damage.

Bioactive peptides and proteins for tissue repair: microenvironment modulation, rational delivery, and clinical potential

Bioactive peptides and proteins (BAPPs) are promising therapeutic agents for tissue repair with considerable advantages, including multifunctionality, specificity, biocompatibility, and biodegradability. However, the high complexity of tissue microenvironments and their inherent deficiencies such as short half-live and susceptibility to enzymatic degradation, adversely affect their therapeutic efficacy and clinical applications. Investigating the fundamental mechanisms by which BAPPs modulate the microenvironment and developing rational delivery strategies are essential for optimizing their administration in distinct tissue repairs and facilitating clinical translation. This review initially focuses on the mechanisms through which BAPPs influence the microenvironment for tissue repair via reactive oxygen species, blood and lymphatic vessels, immune cells, and repair cells. Then, a variety of delivery platforms, including scaffolds and hydrogels, electrospun fibers, surface coatings, assisted particles, nanotubes, two-dimensional nanomaterials, and nanoparticles engineered cells, are summarized to incorporate BAPPs for effective tissue repair, modification strategies aimed at enhancing loading efficiencies and release kinetics are also reviewed. Additionally, the delivery of BAPPs can be precisely regulated by endogenous stimuli (glucose, reactive oxygen species, enzymes, pH) or exogenous stimuli (ultrasound, heat, light, magnetic field, and electric field) to achieve on-demand release tailored for specific tissue repair needs. Furthermore, this review focuses on the clinical potential of BAPPs in facilitating tissue repair across various types, including bone, cartilage, intervertebral discs, muscle, tendons, periodontal tissues, skin, myocardium, nervous system (encompassing brain, spinal cord, and peripheral nerve), endometrium, as well as ear and ocular tissue. Finally, current challenges and prospects are discussed.

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.

Biomimetic bone-periosteum scaffold for spatiotemporal regulated innervated bone regeneration and therapy of osteosarcoma

The complexity of repairing large segment defects and eradicating residual tumor cell puts the osteosarcoma clinical management challenging. Current biomaterial design often overlooks the crucial role of precisely regulating innervation in bone regeneration. Here, we develop a Germanium Selenium (GeSe) co-doped polylactic acid (PLA) nanofiber membrane-coated tricalcium phosphate bioceramic scaffold (TCP-PLA/GeSe) that mimics the bone-periosteum structure. This biomimetic scaffold offers a dual functionality, combining piezoelectric and photothermal conversion capabilities while remaining biodegradable. When subjected to ultrasound irradiation, the US-electric stimulation of TCP-PLA/GeSe enables spatiotemporal control of neurogenic differentiation. This feature supports early innervation during bone formation, promoting early neurogenic differentiation of Schwann cells (SCs) by increasing intracellular Ca2+ and subsequently activating the PI3K-Akt and Ras signaling pathways. The biomimetic scaffold also demonstrates exceptional osteogenic differentiation potential under ultrasound irradiation. In rabbit model of large segment bone defects, the TCP-PLA/GeSe demonstrates promoted osteogenesis and nerve fibre ingrowth. The combined attributes of high photothermal conversion capacity and the sustained release of anti-tumor selenium from the TCP-PLA/GeSe enable the synergistic eradication of osteosarcoma both in vitro and in vivo. This strategy provides new insights on designing advanced biomaterials of repairing large segment bone defect and osteosarcoma.

Bone-nerve crosstalk: a new state for neuralizing bone tissue engineering-A mini review

Neuro bone tissue engineering is a multidisciplinary field that combines both principles of neurobiology and bone tissue engineering to develop innovative strategies for repairing and regenerating injured bone tissues. Despite the fact that regeneration and development are considered two distinct biological processes, yet regeneration can be considered the reactivation of development in later life stages to restore missing tissues. It is noteworthy that the regeneration capabilities are distinct and vary from one organism to another (teleost fishes, hydra, humans), or even in the same organism can vary dependent on the injured tissue itself (Human central nervous system vs. peripheral nervous system). The skeletal tissue is highly innervated, peripheral nervous system plays a role in conveying the signals and connecting the central nervous system with the peripheral organs, moreover it has been shown that they play an important role in tissue regeneration. Their regeneration role is conveyed by the different cells' resident in it and in its endoneurium (fibroblasts, microphages, vasculature associated cells, and Schwann cells) these cells secrete various growth factors (NGF, BDNF, GDNF, NT-3, and bFGF) that contribute to the regenerative phenotype. The peripheral nervous system and central nervous system synchronize together in regulating bone homeostasis and regeneration through neurogenic factors and neural circuits. Receptors of important central nervous system peptides such as Serotonin, Leptin, Semaphorins, and BDNF are expressed in bone tissue playing a role in bone homeostasis, metabolism and regeneration. This review will highlight the crosstalk between peripheral nerves and bone in the developmental stages as well as in regeneration and different neuro-bone tissue engineering strategies for repairing severe bone injuries.

A comparative study of biological properties of three root canal sealers

OBJECTIVES

The aim of this study was to evaluate the effects of Hiflow with other two kinds of root canal sealers on the biological behavior of stem cells from the apical papilla (SCAP), the influence on inflammatory cytokines release and its antibacterial effects.

MATERIALS AND METHODS

Material extracts of Hiflow, iRoot SP, and AH Plus were prepared. Then, SCAP was incubated with extracts. The effects were evaluated by CCK-8, wound healing assay, ALP staining, alizarin red staining, and qRT-PCR. Meanwhile, polymorphonuclears (PMNs) and monocytes were isolated and treated with extracts for 4 h and 24 h respectively. Cell viability was analyzed by Annexin-V/PI double staining flow cytometry. The effects on the release of cytokines were observed by ELISA. The antibacterial effects of different sealers were tested against three kinds of bacteria found in chronic apical periodontitis.

RESULTS

A series of results of SCAP showed that Hiflow and iRoot SP could promote cell proliferation, migration, and osteogenesis (p < 0.05). Although Hiflow was associated with greater cell apoptosis and necrosis when incubated with PMNs and monocytes (p < 0.05), it had an approximate release of anti-inflammatory cytokines with iRoot SP, which was higher than AH plus (p < 0.05). The co-culture showed that Hiflow and iRoot SP inhibited the colony formation of F. nucleatum (p < 0.05). However, both sealers had no obvious antibacterial effect on E. faecalis and P. gingivalis (p > 0.05).

CONCLUSIONS

In summary, Hiflow and iRoot SP both had positive biological stimulus on SCAP. Meanwhile, Hiflow showed a better induction on anti-inflammatory cytokines over the others. All the properties mentioned above and its antibacterial effect of F. nucleatum promise Hiflow a bright application prospect in endodontic uses.

CLINICAL RELEVANCE

References for clinical work to use BC Sealer Hiflow as a good biological root canal sealer.

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.

Type H vessels: functions in bone development and diseases

Type H vessels are specialized blood vessels found in the bone marrow that are closely associated with osteogenic activity. They are characterized by high expression of endomucin and CD31. Type H vessels form in the cancellous bone area during long bone development to provide adequate nutritional support for cells near the growth plate. They also influence the proliferation and differentiation of osteoprogenitors and osteoclasts in a paracrine manner, thereby creating a suitable microenvironment to facilitate new bone formation. Because of the close relationship between type H vessels and osteogenic activity, it has been found that type H vessels play a role in the physiological and pathological processes of bone diseases such as fracture healing, osteoporosis, osteoarthritis, osteonecrosis, and tumor bone metastasis. Moreover, experimental treatments targeting type H vessels can improve the outcomes of these diseases. Here, we reviewed the molecular mechanisms related to type H vessels and their associated osteogenic activities, which are helpful in further understanding the role of type H vessels in bone metabolism and will provide a theoretical basis and ideas for comprehending bone diseases from the vascular perspective.

Polyhedron-Like Biomaterials for Innervated and Vascularized Bone Regeneration

Neural-vascular networks are densely distributed through periosteum, cortical bone, and cancellous bone, which is of great significance for bone regeneration and remodeling. Although significant progress has been made in bone tissue engineering, ineffective bone regeneration, and delayed osteointegration still remains an issue due to the ignorance of intrabony nerves and blood vessels. Herein, inspired by space-filling polyhedra with open architectures, polyhedron-like scaffolds with spatial topologies are prepared via 3D-printing technology to mimic the meshwork structure of cancellous bone. Benefiting from its spatial topologies, polyhedron-like scaffolds greatly promoted the osteogenic differentiation of bone mesenchymal stem cells (BMSCs) via activating PI3K-Akt signals, and exhibiting satisfactory performance on angiogenesis and neurogenesis. Computational fluid dynamic (CFD) simulation elucidates that polyhedron-like scaffolds have a relatively lower area-weighted average static pressure, which is beneficial to osteogenesis. Furthermore, in vivo experiments further demonstrate that polyhedron-like scaffolds obviously promote bone formation and osteointegration, as well as inducing vascularization and ingrowth of nerves, leading to innervated and vascularized bone regeneration. Taken together, this work offers a promising approach for fabricating multifunctional scaffolds without additional exogenous seeding cells and growth factors, which holds great potential for functional tissue regeneration and further clinical translation.

Li-Mg-Si bioceramics provide a dynamic immuno-modulatory and repair-supportive microenvironment for peripheral nerve regeneration

Biomaterials can modulate the local immune and repair-supportive microenvironments to promote peripheral nerve regeneration. Inorganic bioceramics have been widely used for regulating tissue regeneration and local immune response. However, little is known on whether inorganic bioceramics can have potential for enhancing peripheral nerve regeneration and what are the mechanisms underlying their actions. Here, the inorganic lithium-magnesium-silicon (Li-Mg-Si, LMS) bioceramics containing scaffolds are fabricated and characterized. The LMS-containing scaffolds had no cytotoxicity against rat Schwann cells (SCs), but promoted their migration and differentiation towards a remyelination state by up-regulating the expression of neurotrophic factors in a β-catenin-dependent manner. Furthermore, using single cell-sequencing, we showed that LMS-containing scaffolds promoted macrophage polarization towards the pro-regenerative M2-like cells, which subsequently facilitated the migration and differentiation of SCs. Moreover, implantation with the LMS-containing nerve guidance conduits (NGCs) increased the frequency of M2-like macrophage infiltration and enhanced nerve regeneration and motor functional recovery in a rat model of sciatic nerve injury. Collectively, these findings indicated that the inorganic LMS bioceramics offered a potential strategy for enhancing peripheral nerve regeneration by modulating the immune microenvironment and promoting SCs remyelination.

Effect of Extracellular Ribonucleic Acids on Neurovascularization in Osteoarthritis

Osteoarthritis is a degenerative disease characterized by abnormal neurovascularization at the osteochondral junctions, the regulatory mechanisms of which remain poorly understood. In the present study, a murine osteoarthritic model with augmented neurovascularization at the osteochondral junction is used to examine this under-evaluated facet of degenerative joint dysfunction. Increased extracellular RNA (exRNA) content is identified in neurovascularized osteoarthritic joints. It is found that the amount of exRNA is positively correlated with the extent of neurovascularization and the expression of vascular endothelial growth factor (VEGF). In vitro binding assay and molecular docking demonstrate that synthetic RNAs bind to VEGF via electrostatic interactions. The RNA-VEGF complex promotes the migration and function of endothelial progenitor cells and trigeminal ganglion cells. The use of VEGF and VEGFR2 inhibitors significantly inhibits the amplification of the RNA-VEGF complex. Disruption of the RNA-VEGF complex by RNase and polyethyleneimine reduces its in vitro activities, as well as prevents excessive neurovascularization and osteochondral deterioration in vivo. The results of the present study suggest that exRNAs may be potential targets for regulating nerve and blood vessel ingrowth under physiological and pathological joint conditions.

Type H blood vessels in coupling angiogenesis-osteogenesis and its application in bone tissue engineering

One specific capillary subtype, termed type H vessel, has been found with unique functional characteristics in coupling angiogenesis with osteogenesis. Researchers have fabricated a variety of tissue engineering scaffolds to enhance bone healing and regeneration through the accumulation of type H vessels. However, only a limited number of reviews discussed the tissue engineering strategies for type H vessel regulation. The object of this review is to summary the current utilizes of bone tissue engineering to regulate type H vessels through various signal pathways including Notch, PDGF-BB, Slit3, HIF-1α, and VEGF signaling. Moreover, we give an insightful overview of recent research progress about the morphological, spatial and age-dependent characteristics of type H blood vessels. Their unique role in tying angiogenesis and osteogenesis together via blood flow, cellular microenvironment, immune system and nervous system are also summarized. This review article would provide an insight into the combination of tissue engineering scaffolds with type H vessels and identify future perspectives for vasculized tissue engineering research.

Neuronal TRPV1-CGRP axis regulates bone defect repair through Hippo signaling pathway

Transient receptor potential vanilloid type 1 (TRPV1) is highly expressed on sensory neurons where it serves as a polymodal receptor for detecting physical and chemical stimuli. However, the role of TRPV1 in bone metabolism remains largely unclear. This study aimed to investigate the underlying mechanism of neuronal TRPV1 in regulating bone defect repair. In vivo experiment verified that TRPV1 activation could trigger dorsal root ganglion (DRG) producing the neuropeptide calcitonin gene-related peptide (CGRP) in mice. The accelerated bone healing of femoral defect in this process was observed compared to the control group (p < 0.05). Conversely, Trpv1 knockdown led to the reduced CGRP expression in DRG and nerves innervating femur bone tissue, following impaired bone formation and osteogenic capability in the defect region (p < 0.05), which could be rescued by local CGRP treatment. In vitro, results revealed that TRPV1 function in DRG neurons contributed essentially to the regulation of osteoblast physiology through affecting the production and secretion of CGRP. The capsaicin-activated neuronal TRPV1-CGRP axis could enhance the proliferation, migration and differentiation of osteoblasts (p < 0.05). Furthermore, we found that the promoting role of neuronal TRPV1 in osteogenesis were associated with Hippo signaling pathway, reflected by the phosphorylation protein level of large tumor suppressor 1 (LATS1), MOB kinase activator 1 (MOB1) and Yes-associated protein (YAP), as well as the subcellular location of YAP. Our study clarified the effects and intrinsic mechanisms of neuronal TRPV1 on bone defect repair, which might offer us a therapeutic implication for bone disorders.

Thermodynamic 2D Silicene for Sequential and Multistage Bone Regeneration

Bone healing is a multistage process involving the recruitment of cells, revascularization, and osteogenic differentiation, all of which are modulated in the temporal sequence to maximize cascade bone regeneration. However, insufficient osteoblast cells, poor blood supply, and limited bone induction at the site of critical‐sized bone defect broadly impede bone repair. 2D SiO2‐silicene@2,2′‐,azobis(2‐[2‐imidazolin‐2‐yl] propane) (SNSs@AIPH) with inherent thermodynamic property and osteoinductive activity is therefore designed and engineered for sequentially efficient bone repair. By means of controllable NIR‐II irradiation, the integrated SNSs@AIPH stimulates the generation of appropriate intracellular reactive oxygen species, which accelerates early bone marrow mesenchymal stem cells (BMSCs) proliferation and angiogenesis remarkably. Importantly, as silicon‐based 2D nanoparticles, the engineered SNSs@AIPH with high biocompatibility features distinct bioactivity to significantly promote BMSCs osteogenesis differentiation by activating TGFβ and BMP pathways. In a rat cranial defect model, SNSs@AIPH‐NIR‐II leads to a comparable increase of BMSCs proliferation and local vascularization at an early stage, followed by significant osteogenic differentiation, synergically resulting in a highly effective bone repair. Collectively, the fascinating characteristics and exceptional bone repair efficiency of NIR‐II‐mediated SNSs@AIPH allow it to be a promising bionic‐oriented strategy for bone regeneration, broadening a new perspective in the application of cell‐instructive biomaterials in bone tissue engineering.

Thermodynamic 2D Silicene for Sequential and Multistage Bone Regeneration

Bone healing is a multistage process involving the recruitment of cells, revascularization, and osteogenic differentiation, all of which are modulated in the temporal sequence to maximize cascade bone regeneration. However, insufficient osteoblast cells, poor blood supply, and limited bone induction at the site of critical-sized bone defect broadly impede bone repair. 2D SiO2 -silicene@2,2'-,azobis(2-[2-imidazolin-2-yl] propane) (SNSs@AIPH) with inherent thermodynamic property and osteoinductive activity is therefore designed and engineered for sequentially efficient bone repair. By means of controllable NIR-II irradiation, the integrated SNSs@AIPH stimulates the generation of appropriate intracellular reactive oxygen species, which accelerates early bone marrow mesenchymal stem cells (BMSCs) proliferation and angiogenesis remarkably. Importantly, as silicon-based 2D nanoparticles, the engineered SNSs@AIPH with high biocompatibility features distinct bioactivity to significantly promote BMSCs osteogenesis differentiation by activating TGFβ and BMP pathways. In a rat cranial defect model, SNSs@AIPH-NIR-II leads to a comparable increase of BMSCs proliferation and local vascularization at an early stage, followed by significant osteogenic differentiation, synergically resulting in a highly effective bone repair. Collectively, the fascinating characteristics and exceptional bone repair efficiency of NIR-II-mediated SNSs@AIPH allow it to be a promising bionic-oriented strategy for bone regeneration, broadening a new perspective in the application of cell-instructive biomaterials in bone tissue engineering.

Collagen-Based Biomaterials for Tissue Engineering

Collagen is commonly used as a regenerative biomaterial due to its excellent biocompatibility and wide distribution in tissues. Different kinds of hybridization or cross-links are favored to offer improvements to satisfy various needs of biomedical applications. Previous reviews have been made to introduce the sources and structures of collagen. In addition, biological and mechanical properties of collagen-based biomaterials, their modification and application forms, and their interactions with host tissues are pinpointed. However, there is still no review about collagen-based biomaterials for tissue engineering. Therefore, we aim to summarize and discuss the progress of collagen-based materials for tissue regeneration applications in this review. We focus on the utilization of collagen-based biomaterials for bones, cartilages, skin, dental, neuron, cornea, and urological applications and hope these experiences and outcomes can provide inspiration and practical techniques for the future development of collagen-based biomaterials in related application fields. Moreover, future improving directions and challenges for collagen-based biomaterials are proposed as well.

3D printing of biomaterials for vascularized and innervated tissue regeneration

Neurovascular networks play significant roles in the metabolism and regeneration of many tissues and organs in the human body. Blood vessels can transport sufficient oxygen, nutrients, and biological factors, while nerve fibers transmit excitation signals to targeted cells. However, traditional scaffolds cannot satisfy the requirement of stimulating angiogenesis and innervation in a timely manner due to the complexity of host neurovascular networks. Three-dimensional (3D) printing, as a versatile and favorable technique, provides an effective approach to fabricating biological scaffolds with biomimetic architectures and multimaterial compositions, which are capable of regulating multiple cell behaviors. This review paper presents a summary of the current progress in 3D-printed biomaterials for vascularized and innervated tissue regeneration by presenting skin, bone, and skeletal muscle tissues as an example. In addition, we highlight the crucial roles of blood vessels and nerve fibers in the process of tissue regeneration and discuss the future perspectives for engineering novel biomaterials. It is expected that 3D-printed biomaterials with angiogenesis and innervation properties can not only recapitulate the physiological microenvironment of damaged tissues but also rapidly integrate with host neurovascular networks, resulting in accelerated functional tissue regeneration.

Advances in materials-based therapeutic strategies against osteoporosis

Osteoporosis is caused by the disruption in homeostasis between bone formation and bone resorption. Conventional management of osteoporosis involves systematic drug administration and hormonal therapy. These treatment strategies have limited curative efficacy and multiple adverse effects. Biomaterials-based therapeutic strategies have recently emerged as promising alternatives for the treatment of osteoporosis. The present review summarizes the current status of biomaterials designed for managing osteoporosis. The advantages of biomaterials-based strategies over conventional systematic drug treatment are presented. Different anti-osteoporotic delivery systems are concisely addressed. These materials include injectable hydrogels and nanoparticles, as well as anti-osteoporotic bone tissue engineering materials. Fabrication techniques such as 3D printing, electrostatic spinning and artificial intelligence are appraised in the context of how the use of these adjunctive techniques may improve treatment efficacy. The limitations of existing biomaterials are critically analyzed, together with deliberation of the future directions in biomaterials-based therapies. The latter include discussion on the use of combination strategies to enhance therapeutic efficacy in the osteoporosis niche.

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.

A biomimetic piezoelectric scaffold with sustained Mg2+ release promotes neurogenic and angiogenic differentiation for enhanced bone regeneration

Natural bone is a composite tissue made of organic and inorganic components, showing piezoelectricity. Whitlockite (WH), which is a natural magnesium-containing calcium phosphate, has attracted great attention in bone formation recently due to its unique piezoelectric property after sintering treatment and sustained release of magnesium ion (Mg²⁺). Herein, a composite scaffold (denoted as PWH scaffold) composed of piezoelectric WH (PWH) and poly(ε-caprolactone) (PCL) was 3D printed to meet the physiological demands for the regeneration of neuro-vascularized bone tissue, namely, providing endogenous electric field at the defect site. The sustained release of Mg²⁺ from the PWH scaffold, displaying multiple biological activities, and thus exhibits a strong synergistic effect with the piezoelectricity on inhibiting osteoclast activation, promoting the neurogenic, angiogenic, and osteogenic differentiation of bone marrow mesenchymal stromal cells (BMSCs) in vitro. In a rat calvarial defect model, this PWH scaffold is remarkably conducive to efficient neo-bone formation with rich neurogenic and angiogenic expressions. Overall, this study presents the first example of biomimetic piezoelectric scaffold with sustained Mg²⁺ release for promoting the regeneration of neuro-vascularized bone tissue in vivo, which offers new insights for regenerative medicine.

Neuro-bone tissue engineering: Multiple potential translational strategies between nerve and bone

Numerous tissue regeneration paradigms show evident neurological dependence, including mammalian fingertip, skin, and bone regeneration. The mature skeleton is innervated by an abundant nervous system that infiltrates the developing axial and appendicular bones and maintains the stability of the systemic skeletal system by controlling blood flow, regulating bone metabolism, secreting neurotransmitters, and regulating stem cell behavior. In recent years, neurotization in tissue-engineered bone has been considered as a promising strategy to effectively overcome the challenge of vascularization and innervation regeneration in the central zone of "critical-sized bone defects" that conventional tissue-engineered scaffolds are unable to handle, however, further validation is needed in relevant clinical applications. Therefore, this study reviews the mechanisms by which the nervous system regulates bone metabolism and regeneration through a variety of neurogenic or non-neurogenic factors, as well as the recent progress and design strategies of neuralized tissue-engineered bone, to provide new ideas for further studies on subsequent neural bone tissue engineering. STATEMENT OF SIGNIFICANCE: The interaction of nerve and bone tissue during skeletal development and repair has attracted widespread attention, with emerging evidences highlighting the regulation of bone metabolism and regeneration by the nervous system, but the underlying mechanisms have not been elucidated. Thus, further applications of neuro-bone tissue engineering still needs careful consideration. In this review, we summarize the numerous neurogenic and non-neurogenic factors which are involved in bone repair and regeneration, and further explore the current status of their application and biomaterial design in neuro-bone tissue engineering, and finally discuss the challenge and prospective for neuro-bone tissue engineering to facilitate its further development.

Nervous System-Driven Osseointegration

Implants are essential therapeutic tools for treating bone fractures and joint replacements. Despite the in-depth study of osseointegration for more than fifty years, poor osseointegration caused by aseptic loosening remains one of the leading causes of late implant failures. Osseointegration is a highly sophisticated and spatiotemporal process in vivo involving the immune response, angiogenesis, and osteogenesis. It has been unraveled that the nervous system plays a pivotal role in skeletal health via manipulating neurotrophins, neuropeptides, and nerve cells. Herein, the research related to nervous system-driven osseointegration was systematically analyzed and reviewed, aiming to demonstrate the prominent role of neuromodulation in osseointegration. Additionally, it is indicated that the implant design considering the role of neuromodulation might be a promising way to prevent aseptic loosening.

The osteo-angiogenic signaling crosstalk for bone regeneration: harmony out of complexity

In recent years it has been increasingly appreciated that blood vessels are not simply suppliers of nutrients and oxygen, but actually play an exquisite regulatory role in bone development and repair. A specialized kind of endothelium, named type H because of its high expression of CD31 and Endomucin, constitutes anatomically defined vessels in proximity of the epiphyseal growth plate. Type H endothelium regulates the proliferation and differentiation of both osteoblasts and osteoclasts through the secretion of angiocrine signals and is a hub for the bidirectional molecular crosstalk between the different cell populations of the osteogenic microenvironment. Type H vessels are a key target for current translational approaches aiming at coupling angiogenesis and osteogenesis for bone repair. Open questions remain about their presence and features in notstereotyped tissues, like engineered osteogenic grafts, and the opportunities for their clinical stimulation by pharmacological treatments.

Multifunctional silicon calcium phosphate composite scaffolds promote stem cell recruitment and bone regeneration

A scaffold is one of the most significant implants for treating bone injury, while the precise control of stem cell proliferation and differentiation within a scaffold is still challenging. In this work, a composite scaffold was designed to be capable of recruiting endogenous stem cells, stimulating osteogenic differentiation and achieving significant bone repair function. The designed SiCP + SF@PFS silica-calcium phosphate composite scaffold was obtained by mixing the peptide PFS containing silk fibroin solution with the SiCP scaffold, and treating with horseradish peroxidase and H₂O₂. The results showed that the composite scaffold was able to release the PFS peptide continuously to induce the migration of mesenchymal stem cells. Meanwhile, cell proliferation and osteogenic differentiation were also improved after being seeded on the scaffold. In the cranial defect rat model, the composite scaffold was able to recruit CD29⁺ and CD90⁺ cells one week after implantation around the injury sites. The results of Micro-CT, H&E staining, Masson's staining and immunohistochemical staining indicated that the composite scaffold was able to promote new bone formation significantly.

Interaction of Neurovascular Signals in the Degraded Condylar Cartilage

Introduction: Degradation of the condylar cartilage during temporomandibular joint osteoarthritis (TMJ-OA) results in the infiltration of nerves, blood vessels and inflammatory cells from the subchondral bone into the cartilage. The interaction among innervation, angiogenesis and inflammation in the condylar cartilage of TMJ-OA remains largely unknown.

Method: In the present study, microarray-based transcriptome analysis was used to detect, and quantitative real-time polymerase chain reaction was used to validate transcriptome changes in the condylar cartilage from a well-established rat TMJ-OA model. Gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG) pathway and protein-protein interaction (PPI) analyses were conducted.

Result: There were 1817 differentially expressed genes (DEGs, fold change ≥2, p < 0.05) between TMJ-OA and control cartilages, with 553 up-regulated and 1,264 down-regulated genes. Among those genes, representative DEGs with known/suspected roles in innervation, angiogenesis and inflammation were further validated by enriched GO terms and KEGG pathways. The DEGs related to innervation were predominately enriched in the GO terms of neurogenesis, generation of neurons, and KEGG pathways of cholinergic synapse and neurotrophin signaling. Genes related to angiogenesis were enriched in GO terms of vasculature and blood vessel development, and KEGG pathways of hypoxia-inducible factor 1 (HIF-1) pathway and calcium signaling pathway. For inflammation, the DEGs were enriched in the GO terms of immune system process and immune response, and KEGG pathways of Toll-like receptor and transforming growth factor β (TGFβ) signaling. Analysis with PPI indicated that the aforementioned DEGs were highly-interacted. Several hub genes such as v-akt murine thymoma viral oncogene homolog 1 (Akt1), glycogen synthase kinase 3β (Gsk3b), fibroblast growth factor 2 (Fgf2) and nerve growth factor receptor (Ngfr) were validated.

Conclusion: The present study demonstrated, for the first time, that intimate interactions exist among innervation, angiogenesis and inflammation in the condylar cartilage of TMJ-OA.

Smart, Biomimetic Periosteum Created from the Cerium(III, IV) Oxide-Mineralized Eggshell Membrane

The periosteum orchestrates the microenvironment of bone regeneration, including facilitating local neuro-vascularization and regulating immune responses. To mimic the role of natural periosteum for bone repair enhancement, we adopted the principle of biomimetic mineralization to delicately inlay amorphous cerium oxide within eggshell membranes (ESMs) for the first time. Cerium from cerium oxide possesses unique ability to switch its oxidation state from cerium III to cerium IV and vice versa, which provides itself promising potential for biomedical applications. ESMs are mineralized with cerium(III, IV) oxide and examined for their biocompatibility. Apart from serving as physical barriers, periosteum-like cerium(III, IV) oxide-mineralized ESMs are biocompatible and can actively regulate immune responses and facilitate local neuro-vascularization along with early-stage bone regeneration in a murine cranial defect model. During the healing process, cerium-inlayed biomimetic periosteum can boost early osteoclastic differentiation of macrophage lineage cells, which may be the dominant mediator of the local repair microenvironment. The present work provides novel insights into expanding the definition and function of a biomimetic periosteum to boost early-stage bone repair and optimize long-term repair with robust neuro-vascularization. This new treatment strategy which employs multifunctional bone-and-periosteum-mimicking systems creates a highly concerted microenvironment to expedite bone regeneration.

Application Value of the Workshop Practice Teaching Method Based on Target-Oriented Study Modules on the Internet in Orthopedic Rehabilitation

Objective

To explore the application value of the workshop practice teaching method based on target-oriented study modules on the internet in orthopedic rehabilitation.

Methods

Thirty interns (2019-2020) in the rehabilitation department of our hospital were selected as the control group, another thirty interns (2021) in the rehabilitation department of our hospital were selected as the experimental group, and their materials were retrospectively reviewed. Both groups were given the three-month practice teaching. Besides, the conventional practice teaching method was applied to the control group, and the workshop practice teaching method based on target-oriented study modules on the internet was applied to the experimental group. After the practice teaching, the united examination paper and assessment table of the rehabilitation operation process were used to evaluate the interns' scores of theoretical knowledge about orthopedic rehabilitation, scores of practical skills, and comprehensive scores of clinical practice in the two groups. The evaluation team consisting of 5 guiding experts in the scientific research office assessed the teaching quality of the two methods.

Results

Compared with the control group, the experimental group had a notably higher score of theoretical knowledge about orthopedic rehabilitation, higher score of practical skills, and higher comprehensive score of clinical practice (92.47 ± 4.81 vs. 86.43 ± 5.12, 91.30 ± 5.68 vs. 81.53 ± 7.21, and 91.88 ± 2.45 vs. 83.98 ± 4.42, P < 0.001). According to the evaluation team, the teaching quality of the experimental group was observably higher than that in the control group (P < 0.05), and there was no remarkable difference in the scores of teachers' performance between the two groups (P > 0.05).

Conclusion

The workshop practice teaching method based on target-oriented study modules on the internet, as a high-quality “Internet+” practice teaching mode, can improve the orthopedic interns' scores of theoretical knowledge and practical operation ability and enhance their comprehensive qualities of orthopedic rehabilitation in all respects.

Multi-functional SiO32--releasing hydrogel with bioinspired mechanical properties and biodegradability for vascularized skeletal muscle regeneration

Vascularized skeletal muscle regeneration remains a great medical need but significant challenge. Biomaterial strategies that can facilitate the regeneration of muscle fibers and blood vessels are unavailable. Herein, we report...