Mimicking the electrophysiological microenvironment of bone tissue using electroactive materials to promote its regeneration

Electroactive membranes enhance in-situ alveolar ridge preservation via spatiotemporal electrical modulation of cell motility

Post-extraction alveolar bone resorption invariably compromises implant placement and aesthetic restoration outcomes. Current non-resorbable membranes exhibit limited efficacy in alveolar ridge preservation (ARP) due to insufficient cell recruitment and osteoinductive capabilities. Herein, we introduce a multifunctional electroactive membrane (PPy-BTO/P(VDF-TrFE), PB/PT) designed to spatiotemporally regulate cell migration and osteogenesis, harmonizing with the socket healing process. Initially, the membrane's endogenous-level surface potential recruits stem cells from the socket. Subsequently, adherent cell-migration-triggered forces generate on-demand piezopotential, stimulating intracellular calcium ion fluctuations and activating the Ca2+/calcineurin/NFAT1 signaling pathway via Cav3.2 channels. This enhances cell motility and osteogenic differentiation predominantly in the coronal socket region, counteracting the natural healing trajectory. The membrane's self-powered energy supply, proportional to cell migration velocity and manifested as nanoparticle deformation, mitigates ridge shrinkage, both independently and in conjunction with bone grafts. This energy-autonomous membrane, based on the spatiotemporal modulation of cell motility, presents a novel approach for in-situ ARP treatment and the development of 4D bionic scaffolds.

Recent progress in biopolymer-based electrospun nanofibers and their potential biomedical applications: A review

Tissue engineering offers an alternative approach to developing biological substitutes that restore, maintain, or enhance tissue functionality by integrating principles from medicine, biology, and engineering. In this context, biopolymer-based electrospun nanofibers have emerged as attractive platforms due to their superior physicochemical properties, including excellent biocompatibility, non-toxicity, and desirable biodegradability, compared to synthetic polymers. Considerable efforts have been dedicated to developing suitable substitutes for various biomedical applications, with electrospinning receiving considerable attention as a versatile technique for fabricating nanofibrous platforms. While the applications of biopolymer-based electrospun nanofibers in the biomedical field have been previously reviewed, recent advancements in the electrospinning technique and its specific applications in areas such as bone regeneration, wound healing, drug delivery, and protein/peptide delivery remain underexplored from a material science perspective. This work systematically highlights the effects of biopolymers and critical parameters, including polymer molecular weight, viscosity, applied voltage, flow rate, and tip-to-collector distance, on the resulting nanofiber properties. The selection criteria for different biopolymers tailored to desired biomedical applications are also discussed. Additionally, the challenges and limitations associated with biopolymer-based electrospun nanofibers, alongside future perspectives for advancing their biomedical applications, are rationally analyzed.

Piezoelectric hydrogel with self-powered biomechanical stimulation enhances bone regeneration

Large bone defect healing remains a challenge in current clinical treatment, which suggests the need for functional bone repair materials. Piezoelectric materials can generate electrical stimulation under mechanical stress to improve the tissue healing environment, which are emerging candidates for tissue engineering. We created a self-powered piezoelectric hydrogel by simply blending the zinc oxide (ZnO) nanoparticles and regenerating silk fibroin (RSF). Our piezoelectric hydrogel showed controllable and suitable mechanical and piezoelectric properties which could generate electrical stimulation to promote bone tissue healing. Incorporating ZnO into RSF hydrogels not only enhanced their mechanical properties by 1.7 times and increased piezoelectric output by 2.8 times, but also mitigated the degradation rate. In vitro experiments showed that piezoelectric hydrogels significantly promoted osteogenesis differentiation of bone marrow mesenchymal stem cells (BMSCs) and enhanced vascular network reconstitution. In vivo experiments verified the osteogenic and angiogenic potential of ZnO/RSF piezoelectric hydrogels. ZnO/RSF piezoelectric hydrogel, a simple but universal strategy of RSF-based material to generate electric currents by body movement, provides novel insights into the applications of piezoelectric hydrogel. STATEMENT OF SIGNIFICANCE: ZnO/RSF hydrogels with stable piezoelectric properties were prepared by doping ZnO, which can generate stable and continuous electrical signals under pressure. After implantation into the bone defect site, it can promote the osteogenic differentiation of bone marrow mesenchymal stem cells and improve the vasculogenic ability of human umbilical vein endothelial cells, thus promoting the healing of bone tissue.

Precise Cell Type Electrical Stimulation Therapy Via Force-electric Hydrogel Microspheres for Cartilage Healing

Electrical stimulation enhances cellular activity, promoting tissue regeneration and repair. However, specific cells and maintaining a stable energy supply are challenges for precise cell electrical stimulation therapy. Here, force-electric conversion hydrogel microspheres (Piezo@CR MPs) is devloped to induce specific stem cell aggregation and promote chondrogenic differentiation through localized electrical stimulation. These MPs contain barium titanate (BT) nanoparticles embedded in hyaluronic acid methacrylate hydrogel MPs, with a polydopamine (pDA) coating bound to stem cell recruitment peptides (CR) via π-π conjugation and electrostatic forces. Piezo@CR MPs convert pressure (ultrasound) into electrical stimulation, directing BMSCs for colonization and chondrogenesis. In vitro, directionally migrated stem cells almost covered the Piezo@CR MP surface, generating up to 451 mV of electrical output that enhanced chondrogenic differentiation. In a rabbit osteochondral defect model, Piezo@CR MPs promoted cartilage regeneration, nearly resembling native cartilage. In a rat osteoarthritis model, they reduced cartilage degeneration and improved behavioral outcomes. Additionally, Piezo@CR MPs promoted cartilage regeneration by driving the influx of extracellular calcium and activating the p38 mitogen-activated protein kinase (MAPK) pathway. In conclusion, Piezo@CR MPs offer a new approach for precise cell type electrical stimulation therapy in treating of cartilage injuries and degeneration.

Piezoelectric stimulation enhances bone regeneration in alveolar bone defects through metabolic reprogramming of macrophages

Immunomodulation has emerged as a promising strategy for promoting bone regeneration. However, designing osteoimmunomodulatory biomaterial that can respond to mechanical stress in the unique microenvironment of alveolar bone under continuous occlusal stress remains a significant challenge. Herein, a wireless piezoelectric stimulation system, namely, piezoelectric hydrogel incorporating BaTiO3 nanoparticles (BTO NPs), is successfully developed to generate piezoelectric potentials for modulating macrophage reprogramming. The piezoelectric stimulation reprograms macrophages towards the M2 phenotype, which subsequently induces osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). RNA sequencing analysis reveals that piezoelectricity-modulated macrophage M2 polarization is closely associated with metabolic reprogramming, including increased amino acid biosynthesis and fatty acid oxidation. The composite hydrogel with excellent biocompatibility exhibits immunomodulatory and osteoinductive activities. In a rat model of alveolar bone defects, the piezoelectric hydrogel effectively promotes endogenous bone regeneration at the load-bearing sites. The piezoelectric-driven osteoimmunomodulation proposed in this study not only broadens understanding of the mechanism underlying piezoelectric biomaterials for tissue regeneration but also provides new insights into the design and development of next-generation immunomodulatory biomaterials.

Piezoelectric Scaffolds as Smart Materials for Bone Tissue Engineering

Bone repair and regeneration require physiological cues, including mechanical, electrical, and biochemical activity. Many biomaterials have been investigated as bioactive scaffolds with excellent electrical properties. Amongst biomaterials, piezoelectric materials (PMs) are gaining attention in biomedicine, power harvesting, biomedical devices, and structural health monitoring. PMs have unique properties, such as the ability to affect physiological movements and deliver electrical stimuli to damaged bone or cells without an external power source. The crucial bone property is its piezoelectricity. Bones can generate electrical charges and potential in response to mechanical stimuli, as they influence bone growth and regeneration. Piezoelectric materials respond to human microenvironment stimuli and are an important factor in bone regeneration and repair. This manuscript is an overview of the fundamentals of the materials generating the piezoelectric effect and their influence on bone repair and regeneration. This paper focuses on the state of the art of piezoelectric materials, such as polymers, ceramics, and composites, and their application in bone tissue engineering. We present important information from the point of view of bone tissue engineering. We highlight promising upcoming approaches and new generations of piezoelectric materials.

Development of novel hybrid nanomaterials with potential application in bone/dental tissue engineering: design, fabrication and characterization enriched-SAPO-34/CS/PANI scaffold

Fe-Ca-SAPO-34/CS/PANI, a novel hybrid bio-composite scaffold with potential application in dental tissue engineering, was prepared by freeze drying technique. The scaffold was characterized using FT-IR and SEM methods. The effects of PANI on the physicochemical properties of the Fe-Ca-SAPO-34/CS scaffold were investigated, including changes in swelling ratio, mechanical behavior, density, porosity, biodegradation, and biomineralization. Compared to the Fe-Ca-SAPO-34/CS scaffold, adding PANI decreased the pore size, porosity, swelling ratio, and biodegradation, while increasing the mechanical strength and biomineralization. Cell viability, cytotoxicity, and adhesion of human dental pulp stem cells (hDPSCs) on the scaffolds were investigated by MTT assay and SEM. The Fe-Ca-SAPO-34/CS/PANI scaffold promoted hDPSC proliferation and osteogenic differentiation compared to the Fe-Ca-SAPO-34/CS scaffold. Alizarin red staining, alkaline phosphatase activity, and qRT-PCR results revealed that Fe-Ca-SAPO-34/CS/PANI triggered osteoblast/odontoblast differentiation in hDPSCs through the up-regulation of osteogenic marker genes BGLAP, RUNX2, and SPARC. The significance of this study lies in developing a novel scaffold that synergistically combines the beneficial properties of Fe-Ca-SAPO-34, chitosan, and PANI to create an optimized microenvironment for dental tissue regeneration. These findings highlight the potential of the Fe-Ca-SAPO-34/CS/PANI scaffold as a promising biomaterial for dental tissue engineering applications, paving the way for future research and clinical translation in regenerative dentistry.

Bioelectret Materials and Their Bioelectric Effects for Tissue Repair: A Review

Biophysical and clinical medical studies have confirmed that biological tissue lesions and trauma are related to the damage of an intrinsic electret (i.e., endogenous electric field), such as wound healing, embryonic development, the occurrence of various diseases, immune regulation, tissue regeneration, and cancer metastasis. As exogenous electrical signals, such as conductivity, piezoelectricity, ferroelectricity, and pyroelectricity, bioelectroactives can regulate the endogenous electric field, thus controlling the function of cells and promoting the repair and regeneration of tissues. Materials, once polarized, can harness their inherent polarized static electric fields to generate an electric field through direct stimulation or indirect interactions facilitated by physical signals, such as friction, ultrasound, or mechanical stimulation. The interaction with the biological microenvironment allows for the regulation and compensation of polarized electric signals in damaged tissue microenvironments, leading to tissue regeneration and repair. The technique shows great promise for applications in the field of tissue regeneration. In this paper, the generation and change of the endogenous electric field and the regulation of exogenous electroactive substances are expounded, and the latest research progress of the electret and its biological effects in the field of tissue repair include bone repair, nerve repair, drug penetration promotion, wound healing, etc. Finally, the opportunities and challenges of electret materials in tissue repair were summarized. Exploring the research and development of new polarized materials and the mechanism of regulating endogenous electric field changes may provide new insights and innovative methods for tissue repair and disease treatment in biological applications.

Dynamic regulation of stem cell adhesion and differentiation on degradable piezoelectric poly (L-lactic acid) (PLLA) nanofibers

Degradable piezoelectric materials possess significant potential for application in the realm of bone tissue regeneration. However, the correlation between cell regulation mechanisms and the dynamic variation caused by material degradation has not been explained, hindering the optimization of material design and its in vivo application. Herein, piezoelectric poly (L-lactic acid) (PLLA) nanofibers with different molecular weights (MW) were fabricated, and the effects of their piezoelectric properties, structural morphology, and material products during degradation on the adhesion and osteogenic differentiation of mesenchymal stem cells (MSCs) were investigated. Our results demonstrated that cell adhesion-mediated piezoelectric stimulation could significantly enhance cell spreading, cell orientation, and upregulate the expression of calmodulin, which further triggers downstream signaling cascade to regulate osteogenic differentiation markers of type I collagen and runt-related transcription factor 2. Additionally, during the degradation of the nanofibers, the piezoelectric properties of PLLA weakened, the fibrous structure gradually diminished, and pH levels in the vicinity decreased, which resulting in reduced osteogenic differentiation capability of MSCs. However, nanofibers with higher MW (280 kDa) have the ability to maintain the fibrous morphology and piezoelectricity for a longer time, which can regulate the osteogenic differentiation of stem cells for more than 4 weeks. These findings have provide a new insight to correlate cell behavior with MW and the biodegradability of piezopolymers, which revealed an active method for cell regulation through material optimization for bone tissue engineering in near future.

Advances in electroactive biomaterials: Through the lens of electrical stimulation promoting bone regeneration strategy

The regenerative capacity of bone is indispensable for growth, given that accidental injury is almost inevitable. Bone regenerative capacity is relevant for the aging population globally and for the repair of large bone defects after osteotomy (e.g., following removal of malignant bone tumours). Among the many therapeutic modalities proposed to bone regeneration, electrical stimulation has attracted significant attention owing to its economic convenience and exceptional curative effects, and various electroactive biomaterials have emerged. This review summarizes the current knowledge and progress regarding electrical stimulation strategies for improving bone repair. Such strategies range from traditional methods of delivering electrical stimulation via electroconductive materials using external power sources to self-powered biomaterials, such as piezoelectric materials and nanogenerators. Electrical stimulation and osteogenesis are related via bone piezoelectricity. This review examines cell behaviour and the potential mechanisms of electrostimulation via electroactive biomaterials in bone healing, aiming to provide new insights regarding the mechanisms of bone regeneration using electroactive biomaterials.

The translational potential of this article

This review examines the roles of electroactive biomaterials in rehabilitating the electrical microenvironment to facilitate bone regeneration, addressing current progress in electrical biomaterials and the mechanisms whereby electrical cues mediate bone regeneration. Interactions between osteogenesis-related cells and electroactive biomaterials are summarized, leading to proposals regarding the use of electrical stimulation-based therapies to accelerate bone healing.

Electroactive Biomaterials Regulate the Electrophysiological Microenvironment to Promote Bone and Cartilage Tissue Regeneration

The incidence of large bone and articular cartilage defects caused by traumatic injury is increasing worldwide; the tissue regeneration process for these injuries is lengthy due to limited self‐healing ability. Endogenous bioelectrical phenomenon has been well recognized to play an important role in bone and cartilage homeostasis and regeneration. Studies have reported that electrical stimulation (ES) can effectively regulate various biological processes and holds promise as an external intervention to enhance the synthesis of the extracellular matrix, thereby accelerating the process of bone and cartilage regeneration. Hence, electroactive biomaterials have been considered a biomimetic approach to ensure functional recovery by integrating various physiological signals, including electrical, biochemical, and mechanical signals. This review will discuss the role of endogenous bioelectricity in bone and cartilage tissue, as well as the effects of ES on cellular behaviors. Then, recent advances in electroactive materials and their applications in bone and cartilage tissue regeneration are systematically overviewed, with a focus on their advantages and disadvantages as tissue repair materials and performances in the modulation of cell fate. Finally, the significance of mimicking the electrophysiological microenvironment of target tissue is emphasized and future development challenges of electroactive biomaterials for bone and cartilage repair strategies are proposed.

Recent Advancements in Bone Tissue Engineering: Integrating Smart Scaffold Technologies and Bio-Responsive Systems for Enhanced Regeneration

In exploring the challenges of bone repair and regeneration, this review evaluates the potential of bone tissue engineering (BTE) as a viable alternative to traditional methods, such as autografts and allografts. Key developments in biomaterials and scaffold fabrication techniques, such as additive manufacturing and cell and bioactive molecule-laden scaffolds, are discussed, along with the integration of bio-responsive scaffolds, which can respond to physical and chemical stimuli. These advancements collectively aim to mimic the natural microenvironment of bone, thereby enhancing osteogenesis and facilitating the formation of new tissue. Through a comprehensive combination of in vitro and in vivo studies, we scrutinize the biocompatibility, osteoinductivity, and osteoconductivity of these engineered scaffolds, as well as their interactions with critical cellular players in bone healing processes. Findings from scaffold fabrication techniques and bio-responsive scaffolds indicate that incorporating nanostructured materials and bioactive compounds is particularly effective in promoting the recruitment and differentiation of osteoprogenitor cells. The therapeutic potential of these advanced biomaterials in clinical settings is widely recognized and the paper advocates continued research into multi-responsive scaffold systems.

Trends in bioactivity: inducing and detecting mineralization of regenerative polymeric scaffolds

Due to limitations of biological and alloplastic grafts, regenerative engineering has emerged as a promising alternative to treat bone defects. Bioactive polymeric scaffolds are an integral part of such an approach. Bioactivity importantly induces hydroxyapatite mineralization that promotes osteoinductivity and osseointegration with surrounding bone tissue. Strategies to confer bioactivity to polymeric scaffolds utilize bioceramic fillers, coatings and surface treatments, and additives. These approaches can also favorably impact mechanical and degradation properties. A variety of fabrication methods are utilized to prepare scaffolds with requisite morphological features. The bioactivity of scaffolds may be evaluated with a broad set of techniques, including in vitro (acellular and cellular) and in vivo methods. Herein, we highlight contemporary and emerging approaches to prepare and assess scaffold bioactivity, as well as existing challenges.

Porous Titanium Scaffolds with Mechanoelectrical Conversion and Photothermal Function: A Win-Win Strategy for Bone Reconstruction of Tumor-Resected Defects

Bone metastases severely threaten the lives of patients. Although surgical treatment combined with adjuvant chemotherapy significantly improves the survival rate of patients, tumor recurrence, or metastasis after surgical resection and bone defects caused by surgical treatment remain major challenges for clinicians. Given the abovementioned clinical requirements, barium titanate-containing iron-coated porous titanium alloy scaffolds have been proposed to promote bone defect repair and inhibit tumor recurrence. Fortunately, in vitro and in vivo experimental research confirms that barium titanate containing iron-coated porous titanium alloy scaffolds promote osteogenesis and bone reconstruction in defect repair via mechanoelectric conversion and inhibit tumor recurrence via photothermal effects. Furthermore, the underlying and intricate mechanisms of bone defect repair and tumor recurrence prevention of barium titanate-containing iron-coated porous titanium alloy scaffolds are explored. A win-win strategy for mechanoelectrical conversion and photothermal functionalization provides promising insights into bone reconstruction of tumor-resected defects.

Biomimetic Therapeutics for Bone Regeneration: A Perspective on Antiaging Strategies

Advances in modern medicine and the significant reduction in infant mortality have steadily increased the population's lifespan. As more and more people in the world grow older, incidence of chronic, noncommunicable disease is anticipated to drastically increase. Recent studies have shown that improving the health of the aging population is anticipated to provide the most cost-effective and impactful improvement in quality of life during aging-driven disease. In bone, aging is tightly linked to increased risk of fracture, and markedly decreased regenerative potential, deeming it critical to develop therapeutics to improve aging-driven bone regeneration. Biomimetics offer a cost-effective method in regenerative therapeutics for bone, where there are numerous innovations improving outcomes in young models, but adapting biomimetics to aged models is still a challenge. Chronic inflammation, accumulation of reactive oxygen species, and cellular senescence are among three of the more unique challenges facing aging-induced defect repair. This review dissects many of the innovative biomimetic approaches research groups have taken to tackle these challenges, and discusses the further uncertainties that need to be addressed to push the field further. Through these research innovations, it can be noted that biomimetic therapeutics hold great potential for the future of aging-complicated defect repair.

Biomaterials regulates BMSCs differentiation via mechanical microenvironment

Bone mesenchymal stem cells (BMSCs) are crucial for bone tissue regeneration, the mechanical microenvironment of hard tissues, including bone and teeth, significantly affects the osteogenic differentiation of BMSCs. Biomaterials may mimic the microenvironment of the extracellular matrix and provide mechanical signals to regulate BMSCs differentiation via inducing the secretion of various intracellular factors. Biomaterials direct the differentiation of BMSCs via mechanical signals, including tension, compression, shear, hydrostatic pressure, stiffness, elasticity, and viscoelasticity, which can be transmitted to cells through mechanical signalling pathways. Besides, biomaterials with piezoelectric effects regulate BMSCs differentiation via indirect mechanical signals, such as, electronic signals, which are transformed from mechanical stimuli by piezoelectric biomaterials. Mechanical stimulation facilitates achieving vectored stem cell fate regulation, while understanding the underlying mechanisms remains challenging. Herein, this review summarizes the intracellular factors, including translation factors, epigenetic modifications, and miRNA level, as well as the extracellular factor, including direct and indirect mechanical signals, which regulate the osteogenic differentiation of BMSCs. Besides, this review will also give a comprehensive summary about how mechanical stimuli regulate cellular behaviours, as well as how biomaterials promote the osteogenic differentiation of BMSCs via mechanical microenvironments. The cellular behaviours and activated signal pathways will give more implications for the design of biomaterials with superior properties for bone tissue engineering. Moreover, it will also provide inspiration for the construction of bone organoids which is a useful tool for mimicking in vivo bone tissue microenvironments.

Controlled Sr(ii) ion release from in situ crosslinking electroactive hydrogels with potential for the treatment of infections

The development of electrochemical stimuli-responsive drug delivery systems is of both academic and industrial interest due to the ease with which it is possible to trigger payload release, providing drug delivery in a controllable manner. Herein, the preparation of in situ forming hydrogels including electroactive polypyrrole nanoparticles (PPy-NPs) where Sr2+ ions are electrochemically loaded for electrically triggered release of Sr2+ ions is reported. The hydrogels were characterized by a variety of techniques including Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), X-ray diffraction (XRD), cyclic voltammetry (CV), etc. The cytocompatibility towards human mesenchymal stem cells (MSCs) and fibroblasts were also studied. The Sr2+ ion loaded PEC-ALD/CS/PPy-NPs hydrogel showed no significant cytotoxicity towards human mesenchymal stem cells (MSCs) and fibroblasts. Sr2+ ions were electrochemically loaded and released from the electroactive hydrogels, and the application of an electrical stimulus enhanced the release of Sr2+ ions from gels by ca. 2-4 fold relative to the passive release control experiment. The antibacterial activity of Sr2+ ions against E. coli and S. aureus was demonstrated in vitro. Although these prototypical examples of Sr2+ loaded electroactive gels don't release sufficient Sr2+ ions to show antibacterial activity against E. coli and S. aureus, we believe future iterations with optimised physical properties of the gels will be capable of doing so.

Adhesion of Escherichia coli and Lactobacillus fermentum to Films and Electrospun Fibrous Scaffolds from Composites of Poly(3-hydroxybutyrate) with Magnetic Nanoparticles in a Low-Frequency Magnetic Field

The ability of materials to adhere bacteria on their surface is one of the most important aspects of their development and application in bioengineering. In this work, the effect of the properties of films and electrospun scaffolds made of composite materials based on biosynthetic poly(3-hydroxybutyrate) (PHB) with the addition of magnetite nanoparticles (MNP) and their complex with graphene oxide (MNP/GO) on the adhesion of E. coli and L. fermentum under the influence of a low-frequency magnetic field and without it was investigated. The physicochemical properties (crystallinity; surface hydrophilicity) of the materials were investigated by X-ray structural analysis, differential scanning calorimetry and "drop deposition" methods, and their surface topography was studied by scanning electron and atomic force microscopy. Crystal violet staining made it possible to reveal differences in the surface charge value and to study the adhesion of bacteria to it. It was shown that the differences in physicochemical properties of materials and the manifestation of magnetoactive properties of materials have a multidirectional effect on the adhesion of model microorganisms. Compared to pure PHB, the adhesion of E. coli to PHB-MNP/GO, and for L. fermentum to both composite materials, was higher. In the magnetic field, the adhesion of E. coli increased markedly compared to PHB-MNP/GO, whereas the effect on the adhesion of L. fermentum was reversed and was only evident in samples with PHB-MNP. Thus, the resultant factors enhancing and impairing the substrate binding of Gram-negative E. coli and Gram-positive L. fermentum turned out to be multidirectional, as they probably have different sensitivity to them. The results obtained will allow for the development of materials with externally controlled adhesion of bacteria to them for biotechnology and medicine.

Recent advances of responsive scaffolds in bone tissue engineering

The investigation of bone defect repair has been a significant focus in clinical research. The gradual progress and utilization of different scaffolds for bone repair have been facilitated by advancements in material science and tissue engineering. In recent times, the attainment of precise regulation and targeted drug release has emerged as a crucial concern in bone tissue engineering. As a result, we present a comprehensive review of recent developments in responsive scaffolds pertaining to the field of bone defect repair. The objective of this review is to provide a comprehensive summary and forecast of prospects, thereby contributing novel insights to the field of bone defect repair.

Integrated Piezoelectric/Conductive Composite Cryogel Creates Electroactive Microenvironment for Enhanced Bone Regeneration

Natural bone tissue possesses inherent electrophysiological characteristics, displaying conductivity and piezoelectricity simultaneously; hence, the reconstruction of local electrical microenvironment at defect site provides an effective strategy to enhance osteogenesis. Herein, a composite cryogel-type scaffold (referred to as Gel-PD-CMBT) is developed for bone regeneration, utilizing gelatin (Gel) in combination with a conductive poly(ethylene dioxythiophene)/polystyrene sulfonate matrix and Ca/Mn co-doped barium titanate (CMBT) nanofibers as the piezoelectric filler. The incorporation of these components results in the formation of an integrated piezoelectric/conductive network within the scaffold, facilitating charge migration and yielding a conductivity of 0.59 S cm-1 . This conductive scaffold creates a promising electroactive microenvironment, which is capable of up-regulating biological responses. Furthermore, the interconnected porous structure of the Gel-PD-CMBT scaffold not only provides mechanical stability but also offered ample space for cellular and tissue ingrowth. This Gel-PD-CMBT scaffold demonstrates a greater capacity to promote cellular osteogenic differentiation in vitro and neo-bone formation in vivo. In summary, the Gel-PD-CMBT scaffold, with its integrated piezoelectricity and conductivity, effectively restores the local electroactive microenvironment, offering an ideal platform for the regeneration of electrophysiological bone tissue.

Hydroxyapatite-filled osteoinductive and piezoelectric nanofibers for bone tissue engineering

Osteoporotic-related fractures are among the leading causes of chronic disease morbidity in Europe and in the US. While a significant percentage of fractures can be repaired naturally, in delayed-union and non-union fractures surgical intervention is necessary for proper bone regeneration. Given the current lack of optimized clinical techniques to adequately address this issue, bone tissue engineering (BTE) strategies focusing on the development of scaffolds for temporarily replacing damaged bone and supporting its regeneration process have been gaining interest. The piezoelectric properties of bone, which have an important role in tissue homeostasis and regeneration, have been frequently neglected in the design of BTE scaffolds. Therefore, in this study, we developed novel hydroxyapatite (HAp)-filled osteoinductive and piezoelectric poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TrFE) nanofibers via electrospinning capable of replicating the tissue's fibrous extracellular matrix (ECM) composition and native piezoelectric properties. The developed PVDF-TrFE/HAp nanofibers had biomimetic collagen fibril-like diameters, as well as enhanced piezoelectric and surface properties, which translated into a better capacity to assist the mineralization process and cell proliferation. The biological cues provided by the HAp nanoparticles enhanced the osteogenic differentiation of seeded human mesenchymal stem/stromal cells (MSCs) as observed by the increased ALP activity, cell-secreted calcium deposition and osteogenic gene expression levels observed for the HAp-containing fibers. Overall, our findings describe the potential of combining PVDF-TrFE and HAp for developing electroactive and osteoinductive nanofibers capable of supporting bone tissue regeneration.

Piezoelectric Nanomaterials Activated by Ultrasound in Disease Treatment

Electric stimulation has been used in changing the morphology, status, membrane permeability, and life cycle of cells to treat certain diseases such as trauma, degenerative disease, tumor, and infection. To minimize the side effects of invasive electric stimulation, recent studies attempt to apply ultrasound to control the piezoelectric effect of nano piezoelectric material. This method not only generates an electric field but also utilizes the benefits of ultrasound such as non-invasive and mechanical effects. In this review, important elements in the system, piezoelectricity nanomaterial and ultrasound, are first analyzed. Then, we summarize recent studies categorized into five kinds, nervous system diseases treatment, musculoskeletal tissues treatment, cancer treatment, anti-bacteria therapy, and others, to prove two main mechanics under activated piezoelectricity: one is biological change on a cellular level, the other is a piezo-chemical reaction. However, there are still technical problems to be solved and regulation processes to be completed before widespread use. The core problems include how to accurately measure piezoelectricity properties, how to concisely control electricity release through complex energy transfer processes, and a deeper understanding of related bioeffects. If these problems are conquered in the future, piezoelectric nanomaterials activated by ultrasound will provide a new pathway and realize application in disease treatment.

The bioelectrical properties of bone tissue

Understanding the bioelectrical properties of bone tissue is key to developing new treatment strategies for bone diseases and injuries, as well as improving the design and fabrication of scaffold implants for bone tissue engineering. The bioelectrical properties of bone tissue can be attributed to the interaction of its various cell lineages (osteocyte, osteoblast and osteoclast) with the surrounding extracellular matrix, in the presence of various biomechanical stimuli arising from routine physical activities; and is best described as a combination and overlap of dielectric, piezoelectric, pyroelectric and ferroelectric properties, together with streaming potential and electro-osmosis. There is close interdependence and interaction of the various electroactive and electrosensitive components of bone tissue, including cell membrane potential, voltage-gated ion channels, intracellular signaling pathways, and cell surface receptors, together with various matrix components such as collagen, hydroxyapatite, proteoglycans and glycosaminoglycans. It is the remarkably complex web of interactive cross-talk between the organic and non-organic components of bone that define its electrophysiological properties, which in turn exerts a profound influence on its metabolism, homeostasis and regeneration in health and disease. This has spurred increasing interest in application of electroactive scaffolds in bone tissue engineering, to recapitulate the natural electrophysiological microenvironment of healthy bone tissue to facilitate bone defect repair.

Effects of Electrical Stimulation on Articular Cartilage Regeneration with a Focus on Piezoelectric Biomaterials for Articular Cartilage Tissue Repair and Engineering

There is increasing evidence that chondrocytes within articular cartilage are affected by endogenous force-related electrical potentials. Furthermore, electrical stimulation (ES) promotes the proliferation of chondrocytes and the synthesis of extracellular matrix (ECM) molecules, which accelerate the healing of cartilage defects. These findings suggest the potential application of ES in cartilage repair. In this review, we summarize the pathogenesis of articular cartilage injuries and the current clinical strategies for the treatment of articular cartilage injuries. We then focus on the application of ES in the repair of articular cartilage in vivo. The ES-induced chondrogenic differentiation of mesenchymal stem cells (MSCs) and its potential regulatory mechanism are discussed in detail. In addition, we discuss the potential of applying piezoelectric materials in the process of constructing engineering articular cartilage, highlighting the important advances in the unique field of tissue engineering.

Piezocatalytic Medicine: An Emerging Frontier using Piezoelectric Materials for Biomedical Applications

Emerging piezocatalysts have demonstrated their remarkable application potential in diverse medical fields. In addition to their ultrahigh catalytic activities, their inherent and unique charge-carrier-releasing properties can be used to initiate various redox catalytic reactions, displaying bright prospects for future medical applications. Triggered by mechanical energy, piezocatalytic materials can release electrons/holes, catalyze redox reactions of substrates, or intervene in biological processes to promote the production of effector molecules for medical purposes, such as decontamination, sterilization, and therapy. Such a medical application of piezocatalysis is termed as piezocatalytic medicine (PCM) herein. To pioneer novel medical technologies, especially therapeutic modalities, this review provides an overview of the state-of-the-art research progress in piezocatalytic medicine. First, the principle of piezocatalysis and the preparation methodologies of piezoelectric materials are introduced. Then, a comprehensive summary of the medical applications of piezocatalytic materials in tumor treatment, antisepsis, organic degradation, tissue repair and regeneration, and biosensing is provided. Finally, the main challenges and future perspectives in piezocatalytic medicine are discussed and proposed, expecting to fuel the development of this emerging scientific discipline.

Electroactive Biomaterials for Facilitating Bone Defect Repair under Pathological Conditions

Bone degeneration associated with various diseases is increasing due to rapid aging, sedentary lifestyles, and unhealthy diets. Living bone tissue has bioelectric properties critical to bone remodeling, and bone degeneration under various pathological conditions results in significant changes to these bioelectric properties. There is growing interest in utilizing biomimetic electroactive biomaterials that recapitulate the natural electrophysiological microenvironment of healthy bone tissue to promote bone repair. This review first summarizes the etiology of degenerative bone conditions associated with various diseases such as type II diabetes, osteoporosis, periodontitis, osteoarthritis, rheumatoid arthritis, osteomyelitis, and metastatic osteolysis. Next, the diverse array of natural and synthetic electroactive biomaterials with therapeutic potential are discussed. Putative mechanistic pathways by which electroactive biomaterials can mitigate bone degeneration are critically examined, including the enhancement of osteogenesis and angiogenesis, suppression of inflammation and osteoclastogenesis, as well as their anti-bacterial effects. Finally, the limited research on utilization of electroactive biomaterials in the treatment of bone degeneration associated with the aforementioned diseases are examined. Previous studies have mostly focused on using electroactive biomaterials to treat bone traumatic injuries. It is hoped that this review will encourage more research efforts on the use of electroactive biomaterials for treating degenerative bone conditions.

Surface charge and dynamic mechanoelectrical stimuli improves adhesion, proliferation and differentiation of neuron-like cells

Neuronal diseases and trauma are among the current major health-care problems. Patients frequently develop an irreversible state of neuronal disfunction that lacks treatment, strongly reducing life quality and expectancy. Novel strategies are thus necessary and tissue engineering research is struggling to provide alternatives to current treatments, making use of biomaterials capable to provide cell supports and active stimuli to develop permissive environments for neural regeneration. As neuronal cells are naturally found in electrical microenvironments, the electrically active materials can pave the way for new and effective neuroregenerative therapies. In this work the influence of piezoelectric poly(vinylidene fluoride) with different surface charges and dynamic mechanoelectrical stimuli on neuron-like cells adhesion, proliferation and differentiation was addressed. It is successfully demonstrated that both surface charge and electrically active dynamic microenvironments can be suitable to improve neuron-like cells adhesion, proliferation, and differentiation. These findings provide new knowledge to develop effective approaches for preclinical applications.

The Osteogenic Role of Barium Titanate/Polylactic Acid Piezoelectric Composite Membranes as Guiding Membranes for Bone Tissue Regeneration

Purpose

Biopiezoelectric materials have good biocompatibility and excellent piezoelectric properties, and they can generate local currents in vivo to restore the physiological electrical microenvironment of the defect and promote bone regeneration. Previous studies of guided bone regeneration membranes have rarely addressed the point of restoring it, so this study prepared a Barium titanate/Polylactic acid (BT/PLA) piezoelectric composite membrane and investigated its bone-formation, with a view to providing an experimental basis for clinical studies of guided bone tissue regeneration membranes.

Methods

BT/PLA composite membranes with different BT ratio were prepared by solution casting method, and piezoelectric properties were performed after corona polarization treatment. The optimal BT ratio was selected and then subjected to in vitro cytological experiments and in vivo osteogenic studies in rats. The effects on adhesion, proliferation and osteogenic differentiation of the pre-osteoblastic cell line (MC3T3-E1) were investigated. The effect of composite membranes on bone repair of cranial defects in rats was investigated after 4 and 12 weeks.

Results

The highest piezoelectric coefficient d33 were obtained when the BT content was 20%, reaching (7.03 ± 0.26) pC/N. The value could still be maintained at (4.47±0.17) pC/N after 12 weeks, meeting the piezoelectric constant range of bone. In vitro, the MC3T3-E1 cells showed better adhesion and proliferative activity in the group of polarized 20%BT. The highest alkaline phosphatase (ALP) content was observed in cells of this group. In vivo, it promoted rapid bone regeneration. At 4 weeks postoperatively, new bone formation was evident at the edges of the defect, with extensive marrow cavity formation; after 12 weeks, the defect was essentially completely closed, with density approximating normal bone tissue and significant mineralization.

Conclusion

The BT/PLA piezoelectric composite membrane has good osteogenic properties and provides a new idea for guiding the research of membrane materials for bone tissue regeneration.

The hEag1 K+ Channel Inhibitor Astemizole Stimulates Ca2+ Deposition in SaOS-2 and MG-63 Osteosarcoma Cultures

The hEag1 (Kv10.1) K⁺ channel is normally found in the brain, but it is ectopically expressed in tumor cells, including osteosarcoma. Based on the pivotal role of ion channels in osteogenesis, we tested whether pharmacological modulation of hEag1 may affect osteogenic differentiation of osteosarcoma cell lines. Using molecular biology (RT-PCR), electrophysiology (patch-clamp) and pharmacology (astemizole sensitivity, IC₅₀ = 0.135 μM) we demonstrated that SaOS-2 osteosarcoma cells also express hEag1 channels. SaOS-2 cells also express to KCa1.1 K⁺ channels as shown by mRNA expression and paxilline sensitivity of the current. The inhibition of hEag1 (2 μM astemizole) or KCa1.1 (1 mM TEA) alone did not induce Ca²⁺ deposition in SaOS-2 cultures, however, these inhibitors, at identical concentrations, increased Ca²⁺ deposition evoked by the classical or pathological (inorganic phosphate, Pi) induction pathway without causing cytotoxicity, as reported by three completer assays (LDH release, MTT assay and SRB protein assay). We observed a similar effect of astemizole on Ca²⁺ deposition in MG-63 osteosarcoma cultures as well. We propose that the increase in the osteogenic stimuli-induced mineral matrix formation of osteosarcoma cell lines by inhibiting hEag1 may be a useful tool to drive terminal differentiation of osteosarcoma.

Bioceramic Scaffold Materials in Joint Movement Rehabilitation of Patients with Osteoarthritis

Arthritis occurs when the bones and joints have focal or degenerative diseases. This can lead to impaired performance and quality of life of the patient. Surgical treatment is used when the bones and joints are worn out or tumors, but often due to incomplete surgery, repeated attacks will occur. Bioceramic scaffold materials can assist in repairing cartilage tissue defects and, at the same time, contribute to arthritis rehabilitation. Therefore, this article will take this as the starting point of the research and use the new porous nanoceramic scaffold material to study its effect on joint repair in patients with osteoarthritis. The research results confirmed that the porous nanoceramic scaffold material has good biocompatibility in the treatment.

Alkali Niobate Powder Synthesis Using an Emerging Microwave-Assisted Hydrothermal Method

For more than five decades, alkali niobate-based materials (K_xNa_1-xNbO₃) have been one of the most promising lead-free piezoelectric materials researched to be used in electronics, photocatalysis, energy storage/conversion and medical applications, due to their important health and environmentally friendly nature. In this paper, our strategy was to synthetize the nearest reproductible composition to K_xNa_1-xNbO₃ (KNN) with x = 0.5, placed at the limit of the morphotropic phase boundary (MPB) with the presence of both polymorphic phases, orthorhombic and tetragonal. The wet synthesis route was chosen to make the mix crystal powders, starting with the suspension preparation of Nb₂O₅ powder and KOH and NaOH alkaline solutions. Hydrothermal microwave-assisted maturation (HTMW), following the parameter variation T = 200-250 °C, p = 47-60 bar and dwelling time of 30-90 min, was performed. All powders therefore synthesized were entirely K_xN_1-xNbO₃ solid solutions with x = 0.06-0.69, and the compositional, elemental, structural and morphological characterization highlighted polycrystalline particle assemblage with cubic and prismatic morphology, with sizes between 0.28 nm and 2.95 μm and polymorphic O-T phase coexistence, and a d₃₃ piezoelectric constant under 1 pC/N of the compacted unsintered and unpoled discs were found.

Comparative review of piezoelectric biomaterials approach for bone tissue engineering

Bone as a minerals' reservoir and rigid tissue of the body generating red and white blood cells supports various organs. Although the self-regeneration property of bone, it cannot regenerate spontaneously in severe damages and still remains as a challenging issue. Tissue engineering offers several techniques for regenerating damaged bones, where various biomaterials are examined to fabricate scaffolds for bone repair. Piezoelectric characteristic plays a crucial role in repairing and regenerating damaged bone by mimicking the bone niche behavior. Piezoelectric biomaterials show significant potential for bone tissue engineering. Herein we try to have a comparative review on piezoelectric and non-piezoelectric biomaterials used in bone tissue engineering, classified them, and discussed their effects on implanted cells and manufacturing techniques. Especially, Polyvinylidene fluoride (PVDF) and its composites are the most practically used piezoelectric biomaterials for bone regeneration. PVDF and its composites have been summarized and discussed to repair damaged bone tissues.

Electreted Sandwich Membranes with Persistent Electrical Stimulation for Enhanced Bone Regeneration

Physiologically relevant electrical microenvironments play an indispensable role in manipulating bone metabolism. Although implanted biomaterials that simulate the electrical properties of natural tissues using conductive or piezoelectric materials have been introduced in the field of bone regeneration, the application of electret materials to provide stable and persistent electrical stimulation has rarely been studied in biomaterial design. In this study, a silicon dioxide electret-incorporated poly(dimethylsiloxane) (SiO₂/PDMS) composite electroactive membrane was designed and fabricated to explore its bone regeneration efficacy. SiO₂ electrets were homogeneously dispersed in the PDMS matrix, and sandwich-like composite membranes were fabricated using a facile layer-by-layer blade-coating method. Following the encapsulation, electret polarization was conducted to obtain the electreted composite membranes. The surface potential of the composite membrane could be adjusted to a bone-promotive biopotential by tuning the electret concentration, and the prepared membranes exhibited favorable electrical stability during an observation period of up to 42 days. In vitro biological experiments indicated that the electreted SiO₂/PDMS membrane promoted cellular activity and osteogenic differentiation of mesenchymal stem cells. In vivo, the electreted composite membrane remarkably facilitated bone regeneration through persistent endogenous electrical stimulation. These findings suggest that the electreted sandwich-like membranes, which maintain a stable and physiological electrical microenvironment, are promising candidates for enhancing bone regeneration.

Criteria, Challenges, and Opportunities for Acellularized Allogeneic/Xenogeneic Bone Grafts in Bone Repairing

As bone grafts become more commonly needed by patients and as donors become scarcer, acellularized bone grafts (ABGs) are becoming more popular for restorative purposes. While autogeneic grafts are reliable as a gold standard, allogeneic and xenogeneic ABGs have been shown to be of particular interest due to the limited availability of autogeneic resources and reduced patient well-being in long-term surgeries. Because of the complete similarity of their structures with native bone, excellent mechanical properties, high biocompatibility, and similarities of biological behaviors (osteoinductive and osteoconductive) with local bones, successful outcomes of allogeneic and xenogeneic ABGs in both in vitro and in vivo research have raised hopes of repairing patients' bone injuries in clinical applications. However, clinical trials have been delayed due to a lack of standardized protocols pertaining to acellularization, cell seeding, maintenance, and diversity of ABG evaluation criteria. This study sought to uncover these factors by exploring the bone structures, ossification properties of ABGs, sources, benefits, and challenges of acellularization approaches (physical, chemical, and enzymatic), cell loading, and type of cells used and effects of each of the above items on the regenerative technologies. To gain a perspective on the repair and commercialization of products before implementing new research activities, this study describes the differences between ABGs created by various techniques and methods applied to them. With a comprehensive understanding of ABG behavior, future research focused on treating bone defects could provide a better way to combine the treatment approaches needed to treat bone defects.

Electrical stimulation: Effective cue to direct osteogenic differentiation of mesenchymal stem cells?

Mesenchymal stem cells (MSCs) play a major role in bone tissue engineering (BTE) thanks to their capacity for osteogenic differentiation and being easily available. In vivo, MSCs are exposed to an electroactive microenvironment in the bone niche, which has piezoelectric properties. The correlation between the electrically active milieu and bone's ability to adapt to mechanical stress and self-regenerate has led to using electrical stimulation (ES) as physical cue to direct MSCs differentiation towards the osteogenic lineage in BTE. This review summarizes the different techniques to electrically stimulate MSCs to induce their osteoblastogenesis in vitro, including general electrical stimulation and substrate mediated stimulation by means of conductive or piezoelectric cell culture supports. Several aspects are covered, including stimulation parameters, treatment times and cell culture media to summarize the best conditions for inducing MSCs osteogenic commitment by electrical stimulation, from a critical point of view. Electrical stimulation activates different signaling pathways, including bone morphogenetic protein (BMP) Smad-dependent or independent, regulated by mitogen activated protein kinases (MAPK), extracellular signal-regulated kinases (ERK) and p38. The roles of voltage gate calcium channels (VGCC) and integrins are also highlighted according to their application technique and parameters, mainly converging in the expression of RUNX2, the master regulator of the osteogenic differentiation pathway. Despite the evident lack of homogeneity in the approaches used, the ever-increasing scientific evidence confirms ES potential as an osteoinductive cue, mimicking aspects of the in vivo microenvironment and moving one step forward to the translation of this approach into clinic.

Micropatterned Polypyrrole/Hydroxyapatite Composite Coatings Promoting Osteoinductive Activity by Electrical Stimulation

Conductive polypyrrole (PPy) has excellent biocompatibility and structural stability. It is an ideal electroactive biomaterial that can apply exogenous electrical stimulation to promote osteoblast differentiation. However, PPy is a kind of bio-inert material, which does not have osteoinductive capacity. Therefore, we have introduced a kind of bioactive material, hydroxyapatite (HA), to construct PPy/HA composite to enhance bioactivity and osteoinduction. In addition, micron-topological morphology of scattered grid pattern has been designed and introduced to the PPy/HA coatings, which can further enhance the regulation ability of the coatings to the adhesion, proliferation and differentiation of MC3T3-E1 cells. In vitro simulated body fluids (SBFs) immersion test results have demonstrated that the fabricated micropatterned PPy/HA composite coatings perform bioactivity well and can promote the mineral deposition of HA on the surface. Moreover, it can also benefit the proliferation and osteognetic differentiation of MC3T3-E1 cells, when accompanied by external electrical stimulation (ES). In this study, we have successfully constructed electroactive and bioactive coatings, the method of which can potentially be applied to the surface functional modification of traditional bone repair metals.

Overview of Physical and Pharmacological Therapy in Enhancing Bone Regeneration Formation During Distraction Osteogenesis

Distraction osteogenesis (DO) is a kind of bone regeneration technology. The principle is to incise the cortical bone and apply continuous and stable distraction force to the fractured end of the cortical bone, thereby promoting the proliferation of osteoblastic cells in the tension microenvironment and stimulating new bone formation. However, the long consolidation course of DO presumably lead to several complications such as infection, fracture, scar formation, delayed union and malunion. Therefore, it is of clinical significance to reduce the long treatment duration. The current treatment strategy to promote osteogenesis in DO includes gene, growth factor, stem-cell, physical and pharmacological therapies. Among these methods, pharmacological and physical therapies are considered as safe, economical, convenience and effective. Recently, several physical and pharmacological therapies have been demonstrated with a decent ability to enhance bone regeneration during DO. In this review, we have comprehensively summarized the latest evidence for physical (Photonic, Waves, Gas, Mechanical, Electrical and Electromagnetic stimulation) and pharmacological (Bisphosphonates, Hormone, Metal compounds, Biologics, Chinese medicine, etc) therapies in DO. These evidences will bring novel and significant information for the bone healing during DO in the future.

Modification of polyether ether ketone for the repairing of bone defects

Bone damage as a consequence of disease or trauma is a common global occurrence. For bone damage treatment - bone implant materials are necessary across three classifications of surgical intervention (i.e. fixation, repair, and replacement). Many types of bone implant materials have been developed to meet the requirements of bone repair. Among them, polyether ether ketone (PEEK) has been considered as one of the next generation of bone implant materials, owing to its advantages related to good biocompatibility, chemical stability, X-ray permeability, elastic modulus comparable to natural bone, as well as the ease of processing and modification. However, as PEEK is a naturally bioinert material, some modification is needed to improve its integration with adjacent bones after implantation. Therefore, it has become a very hot topic of biomaterials research and various strategies for the modification of PEEK including blending, 3D printing, coating, chemical modification and the introduction of bioactive and/or antibacterial substances have been proposed. In this systematic review, the recent advances in modification of PEEK and its application prospect as bone implants are summarized, and the remaining challenges are also discussed.

Piezoelectric Electrospun Fibrous Scaffolds for Bone, Articular Cartilage and Osteochondral Tissue Engineering

Osteochondral tissue (OCT) related diseases, particularly osteoarthritis, number among the most prevalent in the adult population worldwide. However, no satisfactory clinical treatments have been developed to date to resolve this unmet medical issue. Osteochondral tissue engineering (OCTE) strategies involving the fabrication of OCT-mimicking scaffold structures capable of replacing damaged tissue and promoting its regeneration are currently under development. While the piezoelectric properties of the OCT have been extensively reported in different studies, they keep being neglected in the design of novel OCT scaffolds, which focus primarily on the tissue's structural and mechanical properties. Given the promising potential of piezoelectric electrospun scaffolds capable of both recapitulating the piezoelectric nature of the tissue's fibrous ECM and of providing a platform for electrical and mechanical stimulation to promote the regeneration of damaged OCT, the present review aims to examine the current state of the art of these electroactive smart scaffolds in OCTE strategies. A summary of the piezoelectric properties of the different regions of the OCT and an overview of the main piezoelectric biomaterials applied in OCTE applications are presented. Some recent examples of piezoelectric electrospun scaffolds developed for potentially replacing damaged OCT as well as for the bone or articular cartilage segments of this interfacial tissue are summarized. Finally, the current challenges and future perspectives concerning the use of piezoelectric electrospun scaffolds in OCT regeneration are discussed.

Conductive Polymeric-Based Electroactive Scaffolds for Tissue Engineering Applications: Current Progress and Challenges from Biomaterials and Manufacturing Perspectives

The practice of combining external stimulation therapy alongside stimuli-responsive bio-scaffolds has shown massive potential for tissue engineering applications. One promising example is the combination of electrical stimulation (ES) and electroactive scaffolds because ES could enhance cell adhesion and proliferation as well as modulating cellular specialization. Even though electroactive scaffolds have the potential to revolutionize the field of tissue engineering due to their ability to distribute ES directly to the target tissues, the development of effective electroactive scaffolds with specific properties remains a major issue in their practical uses. Conductive polymers (CPs) offer ease of modification that allows for tailoring the scaffold's various properties, making them an attractive option for conductive component in electroactive scaffolds. This review provides an up-to-date narrative of the progress of CPs-based electroactive scaffolds and the challenge of their use in various tissue engineering applications from biomaterials perspectives. The general issues with CP-based scaffolds relevant to its application as electroactive scaffolds were discussed, followed by a more specific discussion in their applications for specific tissues, including bone, nerve, skin, skeletal muscle and cardiac muscle scaffolds. Furthermore, this review also highlighted the importance of the manufacturing process relative to the scaffold's performance, with particular emphasis on additive manufacturing, and various strategies to overcome the CPs' limitations in the development of electroactive scaffolds.

Enhancement of osteoporotic bone regeneration by strontium-substituted 45S5 bioglass via time-dependent modulation of autophagy and the Akt/mTOR signaling pathway

Osteoporosis (OP) is a major systemic bone disease leading to an imbalance in bone homeostasis which remains a challenge in the current treatment of bone defects. Our previous studies on strontium (Sr) doping apparently stimulated osteogenesis of bioceramics, which suggested a promising strategy for the treatment of bone defects. However, the potential effects and the underlying mechanisms of Sr-doping on osteoporotic bone defects still remain unclear. Autophagy is a conventional self-degradation process of cells involved in bone homeostasis and regeneration under physiological and pathological conditions. Therefore, it is essential to design appropriate biomaterials and investigate the associated osteogenic mechanisms via autophagy. Based on this hypothesis, Sr-doped 45S5 bioglass (Sr/45S5) was fabricated, and ovariectomy bone marrow-derived mesenchymal stem cells (OVX-BMSCs) were applied as the in vitro cell culture model. First, the optimal Sr-doping concentration of 10 mol% was screened by cell proliferation, ALP staining, alizarin red S staining and the real-time PCR assay. Then, the results of western blot (WB) analysis showed that Sr-induced osteogenic differentiation of OVX-BMSCs was associated with time-dependent modulation of autophagy and related to the AKT/mTOR signaling pathway. Meanwhile, the autophagy in Sr-induced osteogenic differentiation of OVX-BMSCs was detected by WB, immunofluorescence staining and transmission electron microscopy. Furthermore, the effect of osteogenic differentiation of OVX-BMSCs has been significantly inhibited by the administration of autophagy inhibitors and the AKT/mTOR pathway inhibitors, respectively, in the early and late periods of osteogenic differentiation. Finally, the results of the model of femoral condyle defects in OVX-rats indicated that Sr10/45S5 granules remarkably enhanced bone regeneration which provided the evidences in vivo. Our research indicates that Sr-doping provides a promising strategy to promote osteogenic differentiation of OVX-BMSCs and bone regeneration in osteoporotic bone defects via early improvement of autophagy and late activation of the Akt/mTOR signaling pathway.

Cutting Edge Endogenous Promoting and Exogenous Driven Strategies for Bone Regeneration

Bone damage leading to bone loss can arise from a wide range of causes, including those intrinsic to individuals such as infections or diseases with metabolic (diabetes), genetic (osteogenesis imperfecta), and/or age-related (osteoporosis) etiology, or extrinsic ones coming from external insults such as trauma or surgery. Although bone tissue has an intrinsic capacity of self-repair, large bone defects often require anabolic treatments targeting bone formation process and/or bone grafts, aiming to restore bone loss. The current bone surrogates used for clinical purposes are autologous, allogeneic, or xenogeneic bone grafts, which although effective imply a number of limitations: the need to remove bone from another location in the case of autologous transplants and the possibility of an immune rejection when using allogeneic or xenogeneic grafts. To overcome these limitations, cutting edge therapies for skeletal regeneration of bone defects are currently under extensive research with promising results; such as those boosting endogenous bone regeneration, by the stimulation of host cells, or the ones driven exogenously with scaffolds, biomolecules, and mesenchymal stem cells as key players of bone healing process.

In-Vitro Cytotoxicity Study: Cell Viability and Cell Morphology of Carbon Nanofibrous Scaffold/Hydroxyapatite Nanocomposites

Electrospun carbon nanofibers (CNFs), which were modified with hydroxyapatite, were fabricated to be used as a substrate for bone cell proliferation. The CNFs were derived from electrospun polyacrylonitrile (PAN) nanofibers after two steps of heat treatment: stabilization and carbonization. Carbon nanofibrous (CNF)/hydroxyapatite (HA) nanocomposites were prepared by two different methods; one of them being modification during electrospinning (CNF-8HA) and the second method being hydrothermal modification after carbonization (CNF-8HA; hydrothermally) to be used as a platform for bone tissue engineering. The biological investigations were performed using in-vitro cell counting, WST cell viability and cell morphology after three and seven days. L929 mouse fibroblasts were found to be more viable on the hydrothermally-modified CNF scaffolds than on the unmodified CNF scaffolds. The biological characterizations of the synthesized CNF/HA nanofibrous composites indicated higher capability of bone regeneration.