Physical Stimulations for Bone and Cartilage Regeneration

Ultrasound-activated piezoelectric biomaterials for cartilage regeneration

Due to the low density of chondrocytes and limited ability to repair damaged extracellular matrix (ECM) in cartilage, many patients with congenital or acquired craniofacial trauma require filler graft materials to support facial structure, restore function, improve self-confidence, and regain socialization. Ultrasound has the capacity to stimulate piezoelectric materials, converting mechanical energy into electrical signals that can regulate the metabolism, proliferation, and differentiation of chondrocytes. This unique property has sparked growing interest in using piezoelectric biomaterials in regenerative medicine. In this review, we first explain the principle behind ultrasound-activated piezoelectric materials and how they generate piezopotential. We then review studies demonstrating how this bioelectricity promotes chondrocyte regeneration, stimulates the secretion of key extracellular components and supports cartilage regeneration by activating relevant signaling pathways. Next, we discuss the properties, synthesis, and modification strategies of various piezoelectric biomaterials. We further discuss recent progresses in the development of ultrasound-activated piezoelectric biomaterials specifically designed for cartilage regeneration. Lastly, we discuss future research challenges facing this technology, ultrasound-activated piezoelectric materials for cartilage regeneration engineering. While the technology holds great promise, certain obstacles remain, including issues related to material stability, precise control over ultrasound parameters, and the integration of these systems into clinical settings. The combination of ultrasound-activated piezoelectric technology with other emerging fields, such as Artificial Intelligence (AI) and cartilage organoid chips, may open new frontiers in regenerative medicine. We hope this review encourages further exploration of ultrasound-activated strategies for piezoelectric materials and their future applications in regenerative medicines.

Extracorporeal Magnetotransduction Therapy as a New Form of Electromagnetic Wave Therapy: From Gene Upregulation to Accelerated Matrix Mineralization in Bone Healing

BACKGROUND

Electromagnetic field therapy is gaining attention for its potential in treating bone disorders, with Extracorporeal Magnetotransduction Therapy (EMTT) emerging as an innovative approach. EMTT offers a higher oscillation frequency and magnetic field strength compared to traditional Pulsed Electromagnetic Field (PEMF) therapy, showing promise in enhancing fracture healing and non-union recovery. However, the mechanisms underlying these effects remain unclear.

RESULTS

This study demonstrates that EMTT significantly enhances osteoblast bone formation at multiple levels, from gene expression to extracellular matrix mineralization. Key osteoblastogenesis regulators, including SP7 and RUNX2, and bone-related genes such as COL1A1, ALPL, and BGLAP, were upregulated, with expression levels surpassing those of the control group by over sevenfold (p < 0.001). Enhanced collagen synthesis and mineralization were confirmed by von Kossa and Alizarin Red staining, indicating increased calcium and phosphate deposition. Additionally, calcium imaging revealed heightened calcium influx, suggesting a cellular mechanism for EMTT's osteogenic effects. Importantly, EMTT did not compromise cell viability, as confirmed by live/dead staining and WST-1 assays.

CONCLUSION

This study is the first to show that EMTT can enhance all phases of osteoblastogenesis and improve the production of critical mineralization components, offering potential clinical applications in accelerating fracture healing, treating osteonecrosis, and enhancing implant osseointegration.

Hydrogel microspheres for bone regeneration through regulation of the regenerative microenvironment

Bone defects are a prevalent category of skeletal tissue disorders in clinical practice, with a range of pathogenic factors and frequently suboptimal clinical treatment effects. In bone regeneration of bone defects, the bone regeneration microenvironment-composed of physiological, chemical, and physical components-is the core element that dynamically coordinates to promote bone regeneration. In recent years, medical biomaterials with bioactivity and functional tunability have been widely researched upon and applied in the fields of tissue replacement/regeneration, and remodelling of organ structure and function. The biomaterial treatment system based on the comprehensive regulation strategy of bone regeneration microenvironment is expected to solve the clinical problem of bone defect. Hydrogel microspheres (HMS) possess a highly specific surface area and porosity, an easily adjustable physical structure, and high encapsulation efficiency for drugs and stem cells. They can serve as highly efficient carriers for bioactive factors, gene agents, and stem cells, showing potential advantages in the comprehensive regulation of bone regeneration microenvironment to enhance bone regeneration. This review aims to clarify the components of the bone regeneration microenvironment, the application of HMS in bone regeneration, and the associated mechanisms. It also discusses various preparation materials and methods of HMS and their applications in bone tissue engineering. Furthermore, it elaborates on the relevant mechanisms by which HMS regulates the physiological, chemical, and physical microenvironment in bone regeneration to achieve bone regeneration. Finally, we discuss the future prospects of the HMS system application for comprehensive regulation of bone regeneration microenvironment, to provide novel perspectives for the research and application of HMS in the bone tissue engineering field.

HSP70-A key regulator in chondrocyte homeostasis under naturally coupled hydrostatic pressure-thermal stimuli

OBJECTIVE

During physical activities, chondrocytes experience coupled stimulation of hydrostatic pressure (HP) and a transient increase in temperature (T), with the latter varying within a physiological range from 32.5 °C to 38.7 °C. Previous short-term in vitro studies have demonstrated that the combined hydrostatic pressure-thermal (HP-T) stimuli more significantly enhance chondroinduction and chondroprotection of chondrocytes than isolated applications. Interestingly, this combined benefit is associated with a corresponding increase in HSP70 levels when HP and T are combined. The current study therefore explored the indispensable role of HSP70 in mediating the combined effects of HP-T stimuli on chondrocytes.

DESIGN

In this mid-long-term study of in vitro engineered cartilage constructs, we assessed chondrocyte responses to HP-T stimuli using customized bioreactor in standard and HSP70-inhibited cultures.

RESULTS

Surprisingly, under HSP70-inhibited conditions, the usually beneficial HP-T stimuli, especially its thermal component, exerted detrimental effects on chondrocyte homeostasis, showing a distinct and unfavorable shift in gene and protein expression patterns compared to non-HSP70-inhibited settings. Such effects were corroborated through mechanical testing and confirmed using a secondary cell source. A proteomic-based mechanistic analysis revealed a disruption in the balance between biosynthesis and fundamental cellular structural components in HSP70-inhibited conditions under HP-T stimuli.

CONCLUSIONS

Our results highlight the critical role of sufficient HSP70 induction in mediating the beneficial effects of coupled HP-T stimulation on chondrocytes. These findings help pave the way for new therapeutic approaches to enhance physiotherapy outcomes and potentially shed light on the elusive mechanisms underlying the onset of cartilage degeneration, a long-standing enigma in orthopedics.

Enhancement of hyaline cartilage and subchondral bone regeneration in a rat osteochondral defect model through focused extracorporeal shockwave therapy

Aims

To explore the efficacy of extracorporeal shockwave therapy (ESWT) in the treatment of osteochondral defect (OCD), and its effects on the levels of transforming growth factor (TGF)-β, bone morphogenetic protein (BMP)-2, -3, -4, -5, and -7 in terms of cartilage and bone regeneration.

Methods

The OCD lesion was created on the trochlear groove of left articular cartilage of femur per rat (40 rats in total). The experimental groups were Sham, OCD, and ESWT (0.25 mJ/mm2, 800 impulses, 4 Hz). The animals were euthanized at 2, 4, 8, and 12 weeks post-treatment, and histopathological analysis, micro-CT scanning, and immunohistochemical staining were performed for the specimens.

Results

In the histopathological analysis, the macro-morphological grading scale showed a significant increase, while the histological score and cartilage repair scale of ESWT exhibited a significant decrease compared to OCD at the 8- and 12-week timepoints. At the 12-week follow-up, ESWT exhibited a significant improvement in the volume of damaged bone compared to OCD. Furthermore, immunohistochemistry analysis revealed a significant decrease in type I collagen and a significant increase in type II collagen within the newly formed hyaline cartilage following ESWT, compared to OCD. Finally, SRY-box transcription factor 9 (SOX9), aggrecan, and TGF-β, BMP-2, -3, -4, -5, and -7 were significantly higher in ESWT than in OCD at 12 weeks.

Conclusion

ESWT promoted the effect of TGF-β/BMPs, thereby modulating the production of extracellular matrix proteins and transcription factor involved in the regeneration of articular cartilage and subchondral bone in an OCD rat model.

An Encapsulation-Free and Hierarchical Porous Triboelectric Scaffold with Dynamic Hydrophilicity for Efficient Cartilage Regeneration

Tissue engineering and electrotherapy are two promising methods to promote tissue repair. However, their integration remains an underexplored area, because their requirements on devices are usually distinct. Triboelectric nanogenerators (TENGs) have shown great potential to develop self-powered devices. However, due to their susceptibility to moisture, TENGs have to be encapsulated in vivo. Therefore, existing TENGs cannot be employed as tissue engineering scaffolds, which require direct interaction with surrounding cells. Here, the concept of triboelectric scaffolds (TESs) is proposed. Poly(glycerol sebacate), a biodegradable and relatively hydrophobic elastomer, is selected as the matrix of TESs. Each hydrophobic micropore in multi-hierarchical porous TESs efficiently serves as a moisture-resistant working unit of TENGs. Integration of tons of micropores ensures the electrotherapy ability of TESs in vivo without encapsulation. Originally hydrophobic TESs are degraded by surface erosion and transformed into hydrophilic surfaces, facilitating their role as tissue engineering scaffolds. Notably, TESs seeded with chondrocytes obtain dense and large matured cartilages after subcutaneous implantation in nude mice. Importantly, rabbits with osteochondral defects receiving TES implantation show favorable hyaline cartilage regeneration and complete cartilage healing. This work provides a promising electronic biomedical device and will inspire a series of new in vivo applications.

Double crosslinked hyaluronic acid and collagen as a potential bioink for cartilage tissue engineering

The avascular nature of hyaline cartilage results in limited spontaneous self-repair and regenerative capabilities when damaged. Recent advances in three-dimensional bioprinting have enabled the precise dispensing of cell-laden biomaterials, commonly referred to as 'bioinks', which are emerging as promising solutions for tissue regeneration. An effective bioink for cartilage tissue engineering needs to create a micro-environment that promotes cell differentiation and supports neocartilage tissue formation. In this study, we introduced an innovative bioink composed of photocurable acrylated type I collagen (COLMA), thiol-modified hyaluronic acid (THA), and poly(ethylene glycol) diacrylate (PEGDA) for 3D bioprinting cartilage grafts using human nasal chondrocytes. Both collagen and hyaluronic acid, being key components of the extracellular matrix (ECM) in the human body, provide essential biological cues for tissue regeneration. We evaluated three formulations - COLMA, COLMA+THA, and COLMA+THA+PEGDA - for their printability, cell viability, structural integrity, and capabilities in forming cartilage-like ECM. The addition of THA and PEGDA significantly enhanced these properties, showcasing the potential of this bioink in advancing applications in cartilage repair and reconstructive surgery.

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.

Application of magnetism in tissue regeneration: recent progress and future prospects

Tissue regeneration is a hot topic in the field of biomedical research in this century. Material composition, surface topology, light, ultrasonic, electric field and magnetic fields (MFs) all have important effects on the regeneration process. Among them, MFs can provide nearly non-invasive signal transmission within biological tissues, and magnetic materials can convert MFs into a series of signals related to biological processes, such as mechanical force, magnetic heat, drug release, etc. By adjusting the MFs and magnetic materials, desired cellular or molecular-level responses can be achieved to promote better tissue regeneration. This review summarizes the definition, classification and latest progress of MFs and magnetic materials in tissue engineering. It also explores the differences and potential applications of MFs in different tissue cells, aiming to connect the applications of magnetism in various subfields of tissue engineering and provide new insights for the use of magnetism in tissue regeneration.

Magnetic field application in bone tissue regeneration: issue current status and prospects for method development

Relevance. Magnets have long been used to treat various diseases, especially in inflammatory processes. According to existing historical data, magnetotherapy was already used in ancient times by the Chinese, Egyptians and Greeks. Different magnetic field strengths affect cells in different ways, with medium-strength magnetic fields being the most widely used. The review presents a brief history and current state of the issue of using a magnetic field in bone tissue regeneration. Modern knowledge about the mechanisms of physiological and reparative regeneration, restoration of bone tissue is clarified, and modern areas of bone tissue engineering are considered, taking into account the characteristics of microcirculation and the effect of a magnetic field on the physiology of bone tissue and reparative regeneration. One of the key findings of the review is that the magnetic field improves bone tissue repair by influencing the metabolic behavior of cells. Studies show that magnetotherapy promotes the activation of cellular processes, accelerates the formation of new bone tissue and improves its quality. It is also noted that the magnetic field has a positive effect on microcirculation, improving the blood supply to tissues and facilitating a better supply of nutrients to the site of injury. This contributes to faster wound healing and early rehabilitation of patients. Conclusion. Magnetotherapy is one of the effective physical and rehabilitation methods of treatment that will become increasingly important in modern medicine. However, further research is needed to better understand the mechanisms of action of a magnetic field on bone tissue and to determine the optimal parameters for its application.

Osteo-inductive effect of piezoelectric stimulation from the poly(l-lactic acid) scaffolds

Piezoelectric biomaterials can generate piezoelectrical charges in response to mechanical activation. These generated charges can directly stimulate bone regeneration by triggering signaling pathway that is important for regulating osteogenesis of cells seeded on the materials. On the other hand, mechanical forces applied to the biomaterials play an important role in bone regeneration through the process called mechanotransduction. While mechanical force and electrical charges are both important contributing factors to bone tissue regeneration, they operate through different underlying mechanisms. The utilizations of piezoelectric biomaterials have been explored to serve as self-charged scaffolds which can promote stem cell differentiation and the formation of functional bone tissues. However, it is still not clear how mechanical activation and electrical charge act together on such a scaffold and which factors play more important role in the piezoelectric stimulation to induce osteogenesis. In our study, we found Poly(l-lactic acid) (PLLA)-based piezoelectric scaffolds with higher piezoelectric charges had a more pronounced osteoinductive effect than those with lower charges. This provided a new mechanistic insight that the observed osteoinductive effect of the piezoelectric PLLA scaffolds is likely due to the piezoelectric stimulation they provide, rather than mechanical stimulation alone. Our findings provide a crucial guide for the optimization of piezoelectric material design and usage.

Callus formation and bone remodeling in a tibial nonunion after minimal invasive percutaneous screw fixation followed by extracorporeal shockwave therapy 17-months after initial trauma - A case report

INTRODUCTION

The treatment of tibial nonunion is challenging and treatment may be conservative or surgical. Conservative strategies include functional braces and weight bearing, or focused extracorporeal shockwave therapy (fESWT).

CASE DESCRIPTION

A 45-year-old male patient sustained spiral tibial shaft fractures and was treated surgically within 24 hours after the initial accident with intramedullary nails. The tibial fracture was later classified as nonunion after 11 months. Radiologic evaluation 17 months after the initial trauma demonstrated clinical nonunion, and subsequently the patient was offered a conservative approach with fESWT to facilitate an increase in callus formation. The handpiece was fitted with a stand-off II (long), penetration depth of 15 mm. Three cycles were administered in month 17, 19 and 20 after baseline. Each cycle consisted of three treatments sessions spaced with 6-8 days apart, and consisted of 3000 to 4000 impulses each given at 0.25-0.84 mJ/mm2. The number of impulses and the power at the focus point varied according to the pain response.

OUTCOMES

The patient achieved union 23 months after fracture. A clinical important improvement was observed with both Lower Extremity Functional Scale (LEFS) (18-point difference) and Patient Specific Functional Scale (PSFS) (average: 4.7 points,) The "worst pain last 24 hours" was reduced by 5 points. These values express minimal clinically important difference (MCID) values in these functional patient-reported outcome measures.

CONCLUSION

This treatment strategy may be viable in a broader setting, including private practice physiotherapy thereby treating the patient in close proximity to the patient's everyday life.

Unraveling cartilage degeneration through synergistic effects of hydrostatic pressure and biomimetic temperature increase

Cartilage degeneration, typically viewed as an irreversible, vicious cycle, sees a significant reduction in two essential biophysical cues: the well-established hydrostatic pressure (HP) and the recently discovered transient temperature increase. Our study aimed to evaluate the combined influence of these cues on maintaining cartilage homeostasis. To achieve this, we developed a customized bioreactor, designed to mimic the specific hydrostatic pressure and transient thermal increase experienced during human knee physiological activities. This system enabled us to investigate the response of human 3D-cultured chondrocytes and human cartilage explants to either isolated or combined hydrostatic pressure and thermal stimuli. Our study found that chondroinduction (SOX9, aggrecan, and sulfated glycosaminoglycan) and chondroprotection (HSP70) reached maximum expression levels when hydrostatic pressure and transient thermal increase acted in tandem, underscoring the critical role of these combined cues in preserving cartilage homeostasis. These findings led us to propose a refined model of the vicious cycle of cartilage degeneration.

Titanium Biohybrid Middle Ear Prostheses: A Preliminary In Vitro Study

Ossiculoplasty is a surgical operation performed to restore auditory transmission through the reconstruction of the ossicular chain using prosthetics. Tissue bioengineering has assumed a pivotal role in implementing alternatives to conventional ossicular middle ear replacement prostheses, to overcome extrusion while preserving acoustic properties. This in vitro study aims to explore, for the first time in current literature, the feasibility of a biohybrid middle ear prosthesis, composed of titanium surrounded by a bone extracellular matrix as bio-coating. We have hereby studied the adhesion and proliferation of human adipose-derived mesenchymal stem cells (hASC) on titanium scaffolds in vitro. Moreover, we identified the osteogenic differentiation of hASC using an immunofluorescence assay to analyze osteoblasts' gene expression profiles (Alp, Runx2, Col1a1, Osx, and Bglap), and we counted the presence of collagen as a marker of hASC's ability to secrete an extracellular matrix. We utilized scanning electron microscopy to evaluate the presence of an extracellular matrix on the scaffolds. Our preliminary data demonstrated the titanium's ability to support human adipose-derived mesenchymal stem cell colonization, proliferation, and osteoblastic differentiation, in order to obtain a biohybrid device. Our experience seems encouraging; thus, we advocate for further in vivo research to corroborate our results regarding bone transplantation.

Induced regeneration of articular cartilage - identification of a dormant regeneration program for a non-regenerative tissue

A mouse organoid culture model was developed to regenerate articular cartilage by sequential treatment with BMP2 and BMP9 (or GDF2) that parallels induced joint regeneration at digit amputation wounds in vivo. BMP9-induced chondrogenesis was used to identify clonal cell lines for articular chondrocyte and hypertrophic chondrocyte progenitor cells from digit fibroblasts. A protocol that includes cell aggregation enhanced by BMP2 followed by BMP9-induced chondrogenesis resulted in the differentiation of organized layers of articular chondrocytes, similar to the organization of middle and deep zones of articular cartilage in situ, and retained a differentiated phenotype following transplantation. In addition, the differentiation of a non-chondrogenic connective tissue layer containing articular chondrocyte progenitor cells demonstrated that progenitor cell sequestration is coupled with articular cartilage differentiation at a clonal level. The studies identify a dormant endogenous regenerative program for a non-regenerative tissue in which fibroblast-derived progenitor cells can be induced to initiate morphogenetic and differentiative programs that include progenitor cell sequestration. The identification of dormant regenerative programs in non-regenerative tissues such as articular cartilage represents a novel strategy that integrates regeneration biology with regenerative medicine.

Bioadhesive and Injectable Hydrogels and Their Correlation with Mesenchymal Stem Cells Differentiation for Cartilage Repair: A Mini-Review

Injectable bioadhesive hydrogels, known for their capacity to carry substances and adaptability in processing, offer great potential across various biomedical applications. They are especially promising in minimally invasive stem cell-based therapies for treating cartilage damage. This approach harnesses readily available mesenchymal stem cells (MSCs) to differentiate into chondrocytes for cartilage regeneration. In this review, we investigate the relationship between bioadhesion and MSC differentiation. We summarize the fundamental principles of bioadhesion and discuss recent trends in bioadhesive hydrogels. Furthermore, we highlight their specific applications in conjunction with stem cells, particularly in the context of cartilage repair. The review also encompasses a discussion on testing methods for bioadhesive hydrogels and direct techniques for differentiating MSCs into hyaline cartilage chondrocytes. These approaches are explored within both clinical and laboratory settings, including the use of genetic tools. While this review offers valuable insights into the interconnected aspects of these topics, it underscores the need for further research to fully grasp the complexities of their relationship.

A Review on Electroactive Polymer-Metal Composites: Development and Applications for Tissue Regeneration

Electroactive polymer-metal composites (EAPMCs) have gained significant attention in tissue engineering owing to their exceptional mechanical and electrical properties. EAPMCs develop by combining an electroactive polymer matrix and a conductive metal. The design considerations include choosing an appropriate metal that provides mechanical strength and electrical conductivity and selecting an electroactive polymer that displays biocompatibility and electrical responsiveness. Interface engineering and surface modification techniques are also crucial for enhancing the adhesion and biocompatibility of composites. The potential of EAPMC-based tissue engineering revolves around its ability to promote cellular responses, such as cell adhesion, proliferation, and differentiation, through electrical stimulation. The electrical properties of these composites can be used to mimic natural electrical signals within tissues and organs, thereby aiding tissue regeneration. Furthermore, the mechanical characteristics of the metallic components provide structural reinforcement and can be modified to align with the distinct demands of various tissues. EAPMCs have extraordinary potential as regenerative biomaterials owing to their ability to promote beneficial effects in numerous electrically responsive cells. This study emphasizes the characteristics and applications of EAPMCs in tissue engineering.

Injectable and biodegradable piezoelectric hydrogel for osteoarthritis treatment

Osteoarthritis affects millions of people worldwide but current treatments using analgesics or anti-inflammatory drugs only alleviate symptoms of this disease. Here, we present an injectable, biodegradable piezoelectric hydrogel, made of short electrospun poly-L-lactic acid nanofibers embedded inside a collagen matrix, which can be injected into the joints and self-produce localized electrical cues under ultrasound activation to drive cartilage healing. In vitro, data shows that the piezoelectric hydrogel with ultrasound can enhance cell migration and induce stem cells to secrete TGF-β1, which promotes chondrogenesis. In vivo, the rabbits with osteochondral critical-size defects receiving the ultrasound-activated piezoelectric hydrogel show increased subchondral bone formation, improved hyaline-cartilage structure, and good mechanical properties, close to healthy native cartilage. This piezoelectric hydrogel is not only useful for cartilage healing but also potentially applicable to other tissue regeneration, offering a significant impact on the field of regenerative tissue engineering.

Biodegradable piezoelectric skin-wound scaffold

Electrical stimulation (ES) induces wound healing and skin regeneration. Combining ES with the tissue-engineering approach, which relies on biomaterials to construct a replacement tissue graft, could offer a self-stimulated scaffold to heal skin-wounds without using potentially toxic growth factors and exogenous cells. Unfortunately, current ES technologies are either ineffective (external stimulations) or unsafe (implanted electrical devices using toxic batteries). Hence, we propose a novel wound-healing strategy that integrates ES with tissue engineering techniques by utilizing a biodegradable self-charged piezoelectric PLLA (Poly (l-lactic acid)) nanofiber matrix. This unique, safe, and stable piezoelectric scaffold can be activated by an external ultrasound (US) to produce well-controlled surface-charges with different polarities, thus serving multiple functions to suppress bacterial growth (negative surface charge) and promote skin regeneration (positive surface charge) at the same time. We demonstrate that the scaffold activated by low intensity/low frequency US can facilitate the proliferation of fibroblast/epithelial cells, enhance expression of genes (collagen I, III, and fibronectin) typical for the wound healing process, and suppress the growth of S. aureus and P. aeruginosa bacteria in vitro simultaneously. This approach induces rapid skin regeneration in a critical-sized skin wound mouse model in vivo. The piezoelectric PLLA skin scaffold thus assumes the role of a multi-tasking, biodegradable, battery-free electrical stimulator which is important for skin-wound healing and bacterial infection prevention simultaneuosly.

Sericin nano-gel agglomerates mimicking the pericellular matrix induce the condensation of mesenchymal stem cells and trigger cartilage micro-tissue formation without exogenous stimulation of growth factors in vitro

Mesenchymal stem cells (MSCs) are excellent seed cells for cartilage tissue engineering and regenerative medicine. Though the condensation of MSCs is the first step of their differentiation into chondrocytes in skeletal development, the process is a challenge in cartilage repairing by MSCs. The pericellular matrix (PCM), a distinct region surrounding the chondrocytes, acts as an extracellular linker among cells and forms the microenvironment of chondrocytes. Inspired by this, sericin nano-gel soft-agglomerates were prepared and used as linkers to induce MSCs to assemble into micro-spheres and differentiate into cartilage-like micro-tissues without exogenous stimulation of growth factors. These sericin nano-gel soft-agglomerates are composed of sericin nano-gels prepared by the chelation of metal ions and sericin protein. The MSCs cultured on 2D culture plates self-assembled into cell-microspheres centered by sericin nano-gel agglomerates. The self-assembly progress of MSCs is superior to the traditional centrifugation to achieve MSC condensation due to its facility, friendliness to MSCs and avoidance of the side-effects of growth factors. The analysis of transcriptomic results suggested that sericin nano-gel agglomerates offered a soft mechanical stimulation to MSCs similar to that of the PCM to chondrocytes and triggered some signaling pathways as associated with MSC chondrogenesis. The strategy of utilizing biomaterials to mimic the PCM as a linker and as a mechanical micro-environment and to induce cell aggregation and trigger the differentiation of MSCs can be employed to drive 3D cellular organization and micro-tissue fabrication in vitro. These cartilage micro-masses reported in this study can be potential candidates for cartilage repairing, cellular building blocks for 3D bio-printing and a model for cartilage development and drug screening.

Effects of Photobiomodulation Using Low-Level Laser Therapy on Alveolar Bone Repair

Alveolar bone repair is a complex and extremely important process, so that functions such as the mastication, occlusion and osseointegration of implants can be properly reestablished. Therefore, in order to optimize this process, many procedures have been used, such as grafting with biomaterials and the application of platelet-rich fibrin (PRF). Another method that has been studied is the use of photobiomodulation (PBM) with the use of low-level laser therapy (LLLT), which, through the absorption of photons by the tissue, triggers photochemical mechanisms in the cells so that they start to act in the search for homeostasis of the affected region. Therefore, the objective of this review was to analyze the use of LLLT as a possible auxiliary tool in the alveolar bone repair process. A search was carried out in scientific databases (PubMed/MEDLINE, Web of Science, Scopus and Cochrane) regarding the following descriptors: “low-level laser therapy AND alveolar bone repair” and “photobiomodulation AND alveolar bone repair”. Eighteen studies were selected for detailed analysis, after excluding duplicates and articles that did not meet predetermined inclusion or non-inclusion criteria. According to the studies, it has been seen that LLLT promotes the acceleration of alveolar repair due to the stimulation of ATP production, activation of transcription and growth factors, attenuation of the inflammatory process and induction of angiogenesis. These factors depend on the laser application protocol, and the Gallium Aluminum Arsenide—GaAlAs laser, with a wavelength of 830 nm, was the most used and, when applications of different energy densities were compared, the highest dosages showed themselves to be more efficient. Thus, it was possible to conclude that PBM with LLLT has beneficial effects on the alveolar bone repair process due to its ability to reduce pain, the inflammatory process, induce vascular sprouting and, consequently, accelerate the formation of a new bone matrix, favoring the maintenance or increase in height and/or thickness of the alveolar bone ridge.

Stimulus-Responsive Drug Delivery Nanoplatforms for Osteoarthritis Therapy

Osteoarthritis (OA) is one of the most prevalent age-related degenerative diseases. With an increasingly aging global population, greater numbers of OA patients are providing clear economic and societal burdens. Surgical and pharmacological treatments are the most common and conventional therapeutic strategies for OA, but often fall considerably short of desired or optimal outcomes. With the development of stimulus-responsive nanoplatforms has come the potential for improved therapeutic strategies for OA. Enhanced control, longer retention time, higher loading rates, and increased sensitivity are among the potential benefits. This review summarizes the advanced application of stimulus-responsive drug delivery nanoplatforms for OA, categorized by either those that depend on endogenous stimulus (reactive oxygen species, pH, enzyme, and temperature), or those that depend on exogenous stimulus (near-infrared ray, ultrasound, magnetic fields). The opportunities, restrictions, and limitations related to these various drug delivery systems, or their combinations, are discussed in areas such as multi-functionality, image guidance, and multi-stimulus response. The remaining constraints and potential solutions that are represented by the clinical application of stimulus-responsive drug delivery nanoplatforms are finally summarized.

Low-intensity pulsed ultrasound promotes mesenchymal stem cell transplantation-based articular cartilage regeneration via inhibiting the TNF signaling pathway

BACKGROUND

Mesenchymal stem cell (MSC) transplantation therapy is highly investigated for the regenerative repair of cartilage defects. Low-intensity pulsed ultrasound (LIPUS) has the potential to promote chondrogenic differentiation of MSCs. However, its underlying mechanism remains unclear. Here, we investigated the promoting effects and mechanisms underlying LIPUS stimulation on the chondrogenic differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs) and further evaluated its regenerative application value in articular cartilage defects in rats.

METHODS

LIPUS was applied to stimulate cultured hUC-MSCs and C28/I2 cells in vitro. Immunofluorescence staining, qPCR analysis, and transcriptome sequencing were used to detect mature cartilage-related markers of gene and protein expression for a comprehensive evaluation of differentiation. Injured articular cartilage rat models were established for further hUC-MSC transplantation and LIPUS stimulation in vivo. Histopathology and H&E staining were used to evaluate the repair effects of the injured articular cartilage with LIPUS stimulation.

RESULTS

The results showed that LIPUS stimulation with specific parameters effectively promoted the expression of mature cartilage-related genes and proteins, inhibited TNF-α gene expression in hUC-MSCs, and exhibited anti-inflammation in C28/I2 cells. In addition, the articular cartilage defects of rats were significantly repaired after hUC-MSC transplantation and LIPUS stimulation.

CONCLUSIONS

Taken together, LIPUS stimulation could realize articular cartilage regeneration based on hUC-MSC transplantation due to the inhibition of the TNF signaling pathway, which is of clinical value for the relief of osteoarthritis.

Electrical Stimulation in Cartilage Tissue Engineering

Electrical stimulation (ES) has been frequently used in different biomedical applications both in vitro and in vivo. Numerous studies have demonstrated positive effects of ES on cellular functions, including metabolism, proliferation, and differentiation. The application of ES to cartilage tissue for increasing extracellular matrix formation is of interest, as cartilage is not able to restore its lesions owing to its avascular nature and lack of cells. Various ES approaches have been used to stimulate chondrogenic differentiation in chondrocytes and stem cells; however, there is a huge gap in systematizing ES protocols used for chondrogenic differentiation of cells. This review focuses on the application of ES for chondrocyte and mesenchymal stem cell chondrogenesis for cartilage tissue regeneration. The effects of different types of ES on cellular functions and chondrogenic differentiation are reviewed, systematically providing ES protocols and their advantageous effects. Moreover, cartilage 3D modeling using cells in scaffolds/hydrogels under ES are observed, and recommendations on reporting about the use of ES in different studies are provided to ensure adequate consolidation of knowledge in the area of ES. This review brings novel insights into the further application of ES in in vitro studies, which are promising for further cartilage repair techniques.

Inflammation Responses to Bone Scaffolds under Mechanical Stimuli in Bone Regeneration

Physical stimuli play an important role in one tissue engineering. Mechanical stimuli, such as ultrasound with cyclic loading, are widely used to promote bone osteogenesis; however, the inflammatory response under physical stimuli has not been well studied. In this paper, the signaling pathways related to inflammatory responses in bone tissue engineering are evaluated, and the application of physical stimulation to promote osteogenesis and its related mechanisms are reviewed in detail; in particular, how physical stimulation alleviates inflammatory responses during transplantation when employing a bone scaffolding strategy is discussed. It is concluded that physical stimulation (e.g., ultrasound and cyclic stress) helps to promote osteogenesis while reducing the inflammatory response. In addition, apart from 2D cell culture, more consideration should be given to the mechanical stimuli applied to 3D scaffolds and the effects of different force moduli while evaluating inflammatory responses. This will facilitate the application of physiotherapy in bone tissue engineering.

Smart Biomaterials for Articular Cartilage Repair and Regeneration

Articular cartilage defects bring about disability and worldwide socioeconomic loss, therefore, articular cartilage repair and regeneration is recognized as a global issue. However, due to its avascular and nearly acellular characteristic, cartilage tissue regeneration ability is limited to some extent. Despite the availability of various treatment methods, including palliative drugs and surgical regenerative therapy, articular cartilage repair and regeneration still face major challenges due to the lack of appropriate methods and materials. Smart biomaterials can regulate cell behavior and provide excellent tissue repair and regeneration microenvironment, thus inducing articular cartilage repair and regeneration. This process is adjusted by controlling drug/bioactive factors release via responding to exogenous/endogenous stimuli, tailoring materials’ structure and function similar to native cartilage or providing physiochemical and physical signaling factors. Herein, smart biomaterials, recently applied in articular cartilage repair and regeneration, are elaborated from two aspects: smart drug release system and smart scaffolds. Furthermore, articular cartilage and its defects and advanced manufacturing techniques of smart biomaterials are discussed in brief. Finally, perspectives for smart biomaterials used in articular cartilage repair and regeneration are presented and the clinical translation of smart biomaterials is emphasized.

Electric/Magnetic Intervention for Bone Regeneration: A Systematic Review and Network Meta-Analysis

Electric/magnetic material or field is a promising strategy for bone regeneration. The aim of this systematic review and network meta-analysis was to analyze the evidence regarding the efficacy of electric and magnetic intervention for bone regeneration and provide directions for further research. A comprehensive search was performed to identify the rats/rabbits/mice research that involved the electric/magnetic treatment with quantitative radiographic assessment of bone formation. Network meta-analyses were also conducted to assess different interventions and outcomes for osteogenesis. In total, there were 51 articles included in the systematic review and 19 articles in the network meta-analyses. The majority used microcomputerized tomography bone volume/tissue volume (BV/TV) to evaluate outcomes in rats. Results showed that placing electric/magnetic materials in situ had more prominent effects than the electric/magnetic field on bone regeneration. For all species, electrical materials with zeta potential of -53 mV proved to be the most effective in increasing BV (mean difference [MD]: 4.20 mm³, 95% confidence interval [CI]: [1.72-6.68]) and bone mineral density (MD: 312 mg/cm³, 95% CI: [172.43-451.57]). Magnetic materials with external magnetic fields topped in BV/TV (MD: 43%, 95% CI: [36.04-49.96]). It also led in trabecular number (MD: 2.00 mm^-1, 95% CI: [1.45-2.55]), trabecular thickness (MD: 61.00 μm, 95% CI: [44.31- 77.69]), and trabecular separation (MD: -0.40 mm, 95% CI: [-0.56 to -0.24]) on the condition of lacking electric materials. Biomaterials implantation is the most effective method for stimulating osteogenesis in rats, especially in electrical materials with negative charge. The combination of diverse interventions shows promising effects but needs further research, so does the underlying mechanism. Impact Statement Bone defect, especially for the large defect from aging, trauma, or pathology, which cannot be completely healed, remains a clinical challenge. Mimicking physical microenvironment has emerged as a new strategy for tissue regeneration. Electric and magnetic material and field used as the physical stimulation for bone regeneration have attracted interest due to their potential and facile application in clinic. This article reviewed related animal studies and carried out a network meta-analysis to thoroughly understand how electric and magnetic interventions impacted on tissues and created an osteogenic microenvironment.

Combined application of BMP-2 and naturally occurring bioactive factor mixtures for the optimized therapy of segmental bone defects

Critical bone defects are the result of traumatic, infection- or tumor-induced segmental bone loss and represent a therapeutic problem that has not been solved by current reconstructive or regenerative strategies yet. Scaffolds functionalized with naturally occurring bioactive factor mixtures show a promising chemotactic and angiogenic potential in vitro and therefore might stimulate bone regeneration in vivo. To assess this prospect, the study targets at heparin-modified mineralized collagen scaffolds functionalized with naturally occurring bioactive factor mixtures and/or rhBMP-2. These scaffolds were implanted into a 2-mm segmental femoral defect in mice and analyzed in respect to newly formed bone volume (BV) and bone mineral density (BMD) by micro-computed tomography scans after an observation period of 6 weeks. To rate the degree of defect healing, the number of vessels, and the activity of osteoclasts and osteoblasts were analyzed histologically. The sole application of bioactive factor mixtures is inferior to the use of the recombinant growth factor rhBMP-2 regarding BV and degree of defect healing. A higher rhBMP-2 concentration or the combination with bioactive factor mixtures does not lead to a further enhancement in defect healing. Possibly, a synergistic effect can be achieved by further concentration or a prolonged release of bioactive factor mixtures. STATEMENT OF SIGNIFICANCE: The successful therapy of extended bone defects is still a major challenge in clinical routine. In this study we investigated the bone regenerative potential of naturally occuring bioactive factor mixtures derived from platelet concentrates, adipose tissue and cell secretomes as a cheap and promising alternative to recombinant growth factors in a murine segmental bone defect model. The mixtures alone were not able to induce complete bridging of the bone defect, but in combination with bone morphogenetic protein 2 bone healing seemed to be more physiological. The results show that naturally occuring bioactive factor mixtures are a promising add-on in a clinical setting.

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.

Mechanically conditioned cell sheets cultured on thermo-responsive surfaces promote bone regeneration

Cell sheet-based scaffold-free technology holds promise for tissue engineering applications and has been extensively explored during the past decades. However, efficient harvest and handling of cell sheets remain challenging, including insufficient extracellular matrix content and poor mechanical strength. Mechanical loading has been widely used to enhance extracellular matrix production in a variety of cell types. However, currently, there are no effective ways to apply mechanical loading to cell sheets. In this study, we prepared thermo-responsive elastomer substrates by grafting poly(N-isopropyl acrylamide) (PNIPAAm) to poly(dimethylsiloxane) (PDMS) surfaces. The effect of PNIPAAm grafting yields on cell behaviours was investigated to optimize surfaces suitable for cell sheet culturing and harvesting. Subsequently, MC3T3-E1 cells were cultured on the PDMS-g-PNIPAAm substrates under mechanical stimulation by cyclically stretching the substrates. Upon maturation, the cell sheets were harvested by lowering the temperature. We found that the extracellular matrix content and thickness of cell sheet were markedly elevated upon appropriate mechanical conditioning. Reverse transcription quantitative polymerase chain reaction and Western blot analyses further confirmed that the expression of osteogenic-specific genes and major matrix components were up-regulated. After implantation into the critical-sized calvarial defects of mice, the mechanically conditioned cell sheets significantly promoted new bone formation. Findings from this study reveal that thermo-responsive elastomer, together with mechanical conditioning, can potentially be applied to prepare high-quality cell sheets for bone tissue engineering.

Recent Advances in "Functional Engineering of Articular Cartilage Zones by Polymeric Biomaterials Mediated with Physical, Mechanical, and Biological/Chemical Cues"

Articular cartilage (AC) plays an unquestionable role in joint movements but unfortunately the healing capacity is restricted due to its avascular and acellular nature. While cartilage tissue engineering has been lifesaving, it is very challenging to remodel the complex cartilage composition and architecture with gradient physio-mechanical properties vital to proper tissue functions. To address these issues, a better understanding of the intrinsic AC properties and how cells respond to stimuli from the external microenvironment must be better understood. This is essential in order to take one step closer to producing functional cartilaginous constructs for clinical use. Recently, biopolymers have aroused much attention due to their versatility, processability, and flexibility because the properties can be tailored to match the requirements of AC. This review highlights polymeric scaffolds developed in the past decade for reconstruction of zonal AC layers including the superficial zone, middle zone, and deep zone by means of exogenous stimuli such as physical, mechanical, and biological/chemical signals. The mimicked properties are reviewed in terms of the biochemical composition and organization, cell fate (morphology, orientation, and differentiation), as well as mechanical properties and finally, the challenges and potential ways to tackle them are discussed.

The Role of PEMFs on Bone Healing: An In Vitro Study

Bone responses to pulsed electromagnetic fields (PEMFs) have been extensively studied by using devices that expose bone cells to PEMFs to stimulate extracellular matrix (ECM) synthesis for bone and cartilage repair. The aim of this work was to highlight in which bone healing phase PEMFs exert their action. Specifically, we evaluated the effects of PEMFs both on human adipose mesenchymal stem cells (hASCs) and on primary human osteoblasts (hOBs) by testing gene and protein expression of early bone markers (on hASCs) and the synthesis of late bone-specific proteins (on hOBs) as markers of bone remodeling. Our results indicate that PEMFs seem to exert their action on bone formation, acting on osteogenic precursors (hASCs) and inducing the commitment towards the differentiation pathways, unlike mature and terminally differentiated cells (hOBs), which are known to resist homeostasis perturbation more and seem to be much less responsive than mesenchymal stem cells. Understanding the role of PEMFs on bone regenerative processes provides important details for their clinical application.

Piezoelectric effect stimulates the rearrangement of chondrogenic cells and alters ciliary orientation via atypical PKCζ

Therapeutic ultrasound was administered to patients suffering from bone fracture with FDA approval. Bone and cartilage are piezoelectric materials. To investigate the effects of piezoelectricity on the cells of chondrogenic lineage, we applied ultrasound stimulation on an AT-cut quartz coverslip to generate electric field fluctuations. The bone-marrow-derived mesenchymal stem cells (BMMSC) and primary chondrocytes were cultured on either glass or quartz coverslips for ultrasound stimulation. The cells were immunofluorescent-labeled for the assessment of cell arrangement and ciliary orientation. Ultrasound and piezoelectricity both stimulate cell migration and disrupt ciliary orientation induced by directional migration. In particular, piezoelectric effects on cell rearrangement can be abolished by the inhibitor specifically targeting atypical Protein kinase C zeta (PKCζ). Our findings shed light on the possibility of cellular modulation by using piezoelectric manipulation.

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Separating the effect of piezoelectric stimulation from ultrasound stimulation.

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Cell migration accelerates upon ultrasound and piezoelectric stimulation.

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Piezoelectric stimulation influences cell polarity of chondrogenic lineage.

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Piezoelectric stimulation induces cell rearrangement via PKCζ.

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Novel strategy for modulating cell growth, cell differentiation or tissue engineering via piezoelectric stimulation.

Concepts and clinical aspects of active implants for the treatment of bone fractures

Nonunion is a complication of long bone fractures that leads to disability, morbidity and high costs. Early detection is difficult and treatment through external stimulation and revision surgery is often a lengthy process. Therefore, alternative diagnostic and therapeutic options are currently being explored, including the use of external and internal sensors. Apart from monitoring fracture stiffness and displacement directly at the fracture site, it would be desirable if an implant could also vary its stiffness and apply an intervention to promote healing, if needed. This could be achieved either by a predetermined protocol, by remote control, or even by processing data and triggering the intervention itself (self-regulated 'intelligent' or 'smart' implant). So-called active or smart materials like shape memory alloys (SMA) have opened up opportunities to build active implants. For example, implants could stimulate fracture healing by active shortening and lengthening via SMA actuator wires; by emitting pulses, waves, or electromagnetic fields. However, it remains undefined which modes of application, forces, frequencies, force directions, time durations and periods, or other stimuli such implants should ideally deliver for the best result. The present paper reviews the literature on active implants and interventions for nonunion, discusses possible mechanisms of active implants and points out where further research and development are needed to build an active implant that applies the most ideal intervention. STATEMENT OF SIGNIFICANCE: Early detection of delays during fracture healing and timely intervention are difficult due to limitations of the current diagnostic strategies. New diagnostic options are under evaluation, including the use of external and internal sensors. In addition, it would be desirable if an implant could actively facilitate healing ('Intelligent' or 'smart' implant). Implants could stimulate fracture healing via active shortening and lengthening; by emitting pulses, waves, or electromagnetic fields. No such implants exist to date, but new composite materials and alloys have opened up opportunities to build such active implants, and several groups across the globe are currently working on their development. The present paper is the first review on this topic to date.

Research progress in seed cells for cartilage tissue engineering

Cartilage defects trouble millions of patients worldwide and their repair via conventional treatment is difficult. Excitingly, tissue engineering technology provides a promising strategy for efficient cartilage regeneration with structural regeneration and functional reconstruction. Seed cells, as biological prerequisites for cartilage regeneration, determine the quality of regenerated cartilage. The proliferation, differentiation and chondrogenesis of seed cells are greatly affected by their type, origin and generation. Thus, a systematic description of the characteristics of seed cells is necessary. This article reviews in detail the cellular characteristics, research progress, clinical translation challenges and future research directions of seed cells while providing guidelines for selecting appropriate seed cells for cartilage regeneration.

Effect of Photobiomodulation Therapy on Peri-Implant Bone Healing in Extra-Short Implants in a Rabbit Model: A Pilot Study

Objective: To evaluate the effects of photobiomodulation therapy (PBMT) at distinct energy levels on peri-implant bone healing in extra-short implants in a experimental rabbit model. Background: The effect of PBMT on peri-implant bone healing in short implants remains unclear. This explored the effect of PBMT on extra-short implants in terms of bone-implant contact (BIC) length and rate, and implant stability quotient (ISQ). Methods: Fifteen white New Zealand rabbits were randomly divided into five groups. In all groups, extra-short implants (3.5 × 4 mm; Nucleoss T6, İzmir/Turkey) were placed in both tibias of the rabbits. PBMT was performed in four groups (group 1, 5 J/cm2; group 2, 10 J/cm2; group 3, 20 J/cm2; and group 4, 25 J/cm2); no PBMT was performed in the control group. On the 30th day, the rabbits were sacrificed and peri-implant tissue samples were obtained to determine the BIC length and BIC rate. Implant stability levels were measured by resonance frequency analysis using the Osstell penguin device and were determined as ISQ values on the 1st and 30th days of the study. Results: PBMT significantly increased the BIC length and BIC rate in groups 3 and 4 (p < 0.001). For the ISQ values, there were significant differences between the 1st and 30th day (p < 0.001). On the 30th day, the ISQ values were significantly higher in groups 3 and 4 compared with the remaining groups (p < 0.001). Conclusions: In this study, PBMT improved peri-implant bone healing through increase in BIC length, BIC rate, and ISQ parameter values in extra-short implants.

Exercise-induced piezoelectric stimulation for cartilage regeneration in rabbits

More than 32.5 million American adults suffer from osteoarthritis, and current treatments including pain medicines and anti-inflammatory drugs only alleviate symptoms but do not cure the disease. Here, we have demonstrated that a biodegradable piezoelectric poly(L-lactic acid) (PLLA) nanofiber scaffold under applied force or joint load could act as a battery-less electrical stimulator to promote chondrogenesis and cartilage regeneration. The PLLA scaffold under applied force or joint load generated a controllable piezoelectric charge, which promoted extracellular protein adsorption, facilitated cell migration or recruitment, induced endogenous TGF-β via calcium signaling pathway, and improved chondrogenesis and cartilage regeneration both in vitro and in vivo. Rabbits with critical-sized osteochondral defects receiving the piezoelectric scaffold and exercise treatment experienced hyaline-cartilage regeneration and completely healed cartilage with abundant chondrocytes and type II collagen after 1 to 2 months of exercise (2 to 3 months after surgery including 1 month of recovery before exercise), whereas rabbits treated with nonpiezoelectric scaffold and exercise treatment had unfilled defect and limited healing. The approach of combining biodegradable piezoelectric tissue scaffolds with controlled mechanical activation (via physical exercise) may therefore be useful for the treatment of osteoarthritis and is potentially applicable to regenerating other injured tissues.

Electrical Stimulation for Immune Modulation in Cancer Treatments

Immunotherapy is becoming a very common treatment for cancer, using approaches like checkpoint inhibition, T cell transfer therapy, monoclonal antibodies and cancer vaccination. However, these approaches involve high doses of immune therapeutics with problematic side effects. A promising approach to reducing the dose of immunotherapeutic agents given to a cancer patient is to combine it with electrical stimulation, which can act in two ways; it can either modulate the immune system to produce the immune cytokines and agents in the patient's body or it can increase the cellular uptake of these immune agents via electroporation. Electrical stimulation in form of direct current has been shown to reduce tumor sizes in immune-competent mice while having no effect on tumor sizes in immune-deficient mice. Several studies have used nano-pulsed electrical stimulations to activate the immune system and drive it against tumor cells. This approach has been utilized for different types of cancers, like fibrosarcoma, hepatocellular carcinoma, human papillomavirus etc. Another common approach is to combine electrochemotherapy with immune modulation, either by inducing immunogenic cell death or injecting immunostimulants that increase the effectiveness of the treatments. Several therapies utilize electroporation to deliver immunostimulants (like genes encoded with cytokine producing sequences, cancer specific antigens or fragments of anti-tumor toxins) more effectively. Lastly, electrical stimulation of the vagus nerve can trigger production and activation of anti-tumor immune cells and immune reactions. Hence, the use of electrical stimulation to modulate the immune system in different ways can be a promising approach to treat cancer.

Current Development in Interdigital Transducer (IDT) Surface Acoustic Wave Devices for Live Cell In Vitro Studies: A Review

Acoustics have a wide range of uses, from noise-cancelling to ultrasonic imaging. There has been a surge in interest in developing acoustic-based approaches for biological and biomedical applications in the last decade. This review focused on the application of surface acoustic waves (SAW) based on interdigital transducers (IDT) for live-cell investigations, such as cell manipulation, cell separation, cell seeding, cell migration, cell characteristics, and cell behaviours. The approach is also known as acoustofluidic, because the SAW device is coupled with a microfluidic system that contains live cells. This article provides an overview of several forms of IDT of SAW devices on recently used cells. Conclusively, a brief viewpoint and overview of the future application of SAW techniques in live-cell investigations were presented.

Methods of Modification of Mesenchymal Stem Cells and Conditions of Their Culturing for Hyaline Cartilage Tissue Engineering

The use of mesenchymal stromal cells (MSCs) for tissue engineering of hyaline cartilage is a topical area of regenerative medicine that has already entered clinical practice. The key stage of this procedure is to create conditions for chondrogenic differentiation of MSCs, increase the synthesis of hyaline cartilage extracellular matrix proteins by these cells and activate their proliferation. The first such works consisted in the indirect modification of cells, namely, in changing the conditions in which they are located, including microfracturing of the subchondral bone and the use of 3D biodegradable scaffolds. The most effective methods for modifying the cell culture of MSCs are protein and physical, which have already been partially introduced into clinical practice. Genetic methods for modifying MSCs, despite their effectiveness, have significant limitations. Techniques have not yet been developed that allow studying the effectiveness of their application even in limited groups of patients. The use of MSC modification methods allows precise regulation of cell culture proliferation, and in combination with the use of a 3D biodegradable scaffold, it allows obtaining a hyaline-like regenerate in the damaged area. This review is devoted to the consideration and comparison of various methods used to modify the cell culture of MSCs for their use in regenerative medicine of cartilage tissue.

Electroactive Biomaterials and Systems for Cell Fate Determination and Tissue Regeneration: Design and Applications

During natural tissue regeneration, tissue microenvironment and stem cell niche including cell-cell interaction, soluble factors, and extracellular matrix (ECM) provide a train of biochemical and biophysical cues for modulation of cell behaviors and tissue functions. Design of functional biomaterials to mimic the tissue/cell microenvironment have great potentials for tissue regeneration applications. Recently, electroactive biomaterials have drawn increasing attentions not only as scaffolds for cell adhesion and structural support, but also as modulators to regulate cell/tissue behaviors and function, especially for electrically excitable cells and tissues. More importantly, electrostimulation can further modulate a myriad of biological processes, from cell cycle, migration, proliferation and differentiation to neural conduction, muscle contraction, embryogenesis, and tissue regeneration. In this review, endogenous bioelectricity and piezoelectricity are introduced. Then, design rationale of electroactive biomaterials is discussed for imitating dynamic cell microenvironment, as well as their mediated electrostimulation and the applying pathways. Recent advances in electroactive biomaterials are systematically overviewed for modulation of stem cell fate and tissue regeneration, mainly including nerve regeneration, bone tissue engineering, and cardiac tissue engineering. Finally, the significance for simulating the native tissue microenvironment is emphasized and the open challenges and future perspectives of electroactive biomaterials are concluded.

Association between patellar tendon moment arm and running performance in endurance runners

A shorter joint moment arm (MA) may help maintain the necessary muscle force when muscle contractions are repeated. This beneficial effect may contribute to reducing the energy cost during running. In this study, we examined the correlation between patellar tendon MA and running performance in endurance runners. The patellar tendon MA and quadriceps femoris muscle volume (MV) in 42 male endurance runners and 14 body size-matched male untrained participants were measured using a 1.5-T magnetic resonance system. The patellar tendon MA was significantly shorter in endurance runners than in untrained participants (p = 0.034, d = 0.65). In endurance runners, shorter patellar tendon MA correlated significantly with better personal best 5000-m race rime (r = 0.322, p = 0.034). A trend toward such a significant correlation was obtained between quadriceps femoris MV and personal best 5000-m race time (r = 0.303, p = 0.051). Although the correlation between patellar tendon MA and personal best 5000-m race time did not remain significant after adjusting for the quadriceps femoris MV (partial r = 0.247, p = 0.120), a stepwise multiple regression analysis (conducted with body height, body mass, patellar tendon MA, and quadriceps femoris MV) selected the patellar tendon MA (β = 0.322) as only a predictive variable for the personal best 5000-m race time (adjusted R2  = 0.081, p = 0.038). These findings suggest that the shorter patellar tendon MA, partially accorded with the smaller quadriceps femoris size, may be a favorable morphological variable for better running performance in endurance runners.

Pulsed Electromagnetic Fields in Bone Healing: Molecular Pathways and Clinical Applications

In this article, we provide an extensive review of the recent literature of the signaling pathways modulated by Pulsed Electromagnetic Fields (PEMFs) and PEMFs clinical application. A review of the literature was performed on two medical electronic databases (PubMed and Embase) from 3 to 5 March 2021. Three authors performed the evaluation of the studies and the data extraction. All studies for this review were selected following these inclusion criteria: studies written in English, studies available in full text and studies published in peer-reviewed journal. Molecular biology, identifying cell membrane receptors and pathways involved in bone healing, and studying PEMFs target of action are giving a solid basis for clinical applications of PEMFs. However, further biology studies and clinical trials with clear and standardized parameters (intensity, frequency, dose, duration, type of coil) are required to clarify the precise dose-response relationship and to understand the real applications in clinical practice of PEMFs.

Three-dimensional-printed individualized porous implants: A new "implant-bone" interface fusion concept for large bone defect treatment

Bone defect repairs are based on bone graft fusion or replacement. Current large bone defect treatments are inadequate and lack of reliable technology. Therefore, we aimed to investigate a simple technique using three-dimensional (3D)-printed individualized porous implants without any bone grafts, osteoinductive agents, or surface biofunctionalization to treat large bone defects, and systematically study its long-term therapeutic effects and osseointegration characteristics. Twenty-six patients with large bone defects caused by tumor, infection, or trauma received treatment with individualized porous implants; among them, three typical cases underwent a detailed study. Additionally, a large segmental femur defect sheep model was used to study the osseointegration characteristics. Immediate and long-term biomechanical stability was achieved, and the animal study revealed that the bone grew into the pores with gradual remodeling, resulting in a long-term mechanically stable implant-bone complex. Advantages of 3D-printed microporous implants for the repair of bone defects included 1) that the stabilization devices were immediately designed and constructed to achieve early postoperative mobility, and 2) that osseointegration between the host bone and implants was achieved without bone grafting. Our osseointegration method, in which the “implant-bone” interface fusion concept was used instead of “bone-bone” fusion, subverts the traditional idea of osseointegration.

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A new “implant-bone” interface fusion concept for large bone defect treatment was realized using 3D-printed porous implants.

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Osseointegration was achieved without bone grafting.

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An animal study revealed that the bone grew into the pores with gradual remodeling.

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Immediate and long-term biomechanical stability was achieved by this method.

Review of physical stimulation techniques for assisting distraction osteogenesis in maxillofacial reconstruction applications

Distraction Osteogenesis (DO) is an emerging limb lengthening method for the reconstruction of the hard tissue and the surrounding soft tissue, in different human body zones. DO plays an important role in treating bone defects in Maxillofacial Reconstruction Applications (MRA) due to reduced side effects and better formed bone tissue compared to conventional reconstruction methods i.e. autologous bone graft, and alloplast implantation. Recently, varying techniques have been evaluated to enhance the characteristics of the newly formed tissues and process parameters. Promising results have been shown in assisting DO treatments while benefiting bone formation mechanisms by using physical stimulation techniques, including photonic, electromagnetic, electrical, and mechanical stimulation technique. Using assisted DO techniques has provided superior results in the outcome of the DO procedure compared to a standard DO procedure. However, DO methods, as well as assisting technologies applied during the DO procedure, are still emerging. Studies and experiments on developed solutions related to this field have been limited to animal and clinical trials. In this review paper, recent advances in physical stimulation techniques and their effects on the outcome of the DO treatment in MRA are surveyed. By studying the effects of using assisting techniques during the DO treatment, enabling an ideal assisted DO technique in MRA can be possible. Although mentioned techniques have shown constructive effects during the DO procedure, there is still a need for more research and investigation to be done to fully understand the effects of assisting techniques and advanced technologies for use in an ultimate DO procedure in MRA.

Matrix Vesicles: Role in Bone Mineralization and Potential Use as Therapeutics

Bone is a complex organ maintained by three main cell types: osteoblasts, osteoclasts, and osteocytes. During bone formation, osteoblasts deposit a mineralized organic matrix. Evidence shows that bone cells release extracellular vesicles (EVs): nano-sized bilayer vesicles, which are involved in intercellular communication by delivering their cargoes through protein–ligand interactions or fusion to the plasma membrane of the recipient cell. Osteoblasts shed a subset of EVs known as matrix vesicles (MtVs), which contain phosphatases, calcium, and inorganic phosphate. These vesicles are believed to have a major role in matrix mineralization, and they feature bone-targeting and osteo-inductive properties. Understanding their contribution in bone formation and mineralization could help to target bone pathologies or bone regeneration using novel approaches such as stimulating MtV secretion in vivo, or the administration of in vitro or biomimetically produced MtVs. This review attempts to discuss the role of MtVs in biomineralization and their potential application for bone pathologies and bone regeneration.

Tissue Engineering Strategies to Increase Osteochondral Regeneration of Stem Cells; a Close Look at Different Modalities

The homeostasis of osteochondral tissue is tightly controlled by articular cartilage chondrocytes and underlying subchondral bone osteoblasts via different internal and external clues. As a correlate, the osteochondral region is frequently exposed to physical forces and mechanical pressure. On this basis, distinct sets of substrates and physicochemical properties of the surrounding matrix affect the regeneration capacity of chondrocytes and osteoblasts. Stem cells are touted as an alternative cell source for the alleviation of osteochondral diseases. These cells appropriately respond to the physicochemical properties of different biomaterials. This review aimed to address some of the essential factors which participate in the chondrogenic and osteogenic capacity of stem cells. Elements consisted of biomechanical forces, electrical fields, and biochemical and physical properties of the extracellular matrix are the major determinant of stem cell differentiation capacity. It is suggested that an additional certain mechanism related to signal-transduction pathways could also mediate the chondro-osteogenic differentiation of stem cells. The discovery of these clues can enable us to modulate the regeneration capacity of stem cells in osteochondral injuries and lead to the improvement of more operative approaches using tissue engineering modalities.

Fluid shear stress and endothelial cells synergistically promote osteogenesis of mesenchymal stem cells via integrin β1-FAK-ERK1/2 pathway

Prevascularization and mechanical stimulation have been reported as effective methods for the construction of functional bone tissue. However, their combined effects on osteogenic differentiation and its mechanism remain to be explored. Here, the effects of fluid shear stress (FSS) on osteogenic differentiation of rat bone-marrow-derived mesenchymal stem cells (BMSCs) when cocultured with human umbilical vein endothelial cells (HUVECs) were investigated, and underlying signaling mechanisms were further explored. FSS stimulation for 1-4 h/day increased alkaline phosphatase (ALP) activity and calcium deposition in coculture systems and promoted the proliferation of cocultured cells. FSS stimulation for 2 h/day was selected as the optimized protocol according to osteogenesis in the coculture. In this situation, the mRNA levels of ALP, runt-related transcriptional factor 2 (Runx2) and osteocalcin (OCN), and protein levels of OCN and osteopontin (OPN) in BMSCs were upregulated. Furthermore, FSS and coculture with HUVECs synergistically increased integrin β1 expression in BMSCs and further activated focal adhesion kinases (FAKs) and downstream extracellular signal-related kinase (ERK), leading to the enhancement of Runx2 expression. Blocking the phosphorylation of FAK abrogated FSS-induced ERK phosphorylation and inhibited osteogenesis of cocultured BMSCs. These results revealed that FSS and coculture with HUVECs synergistically promotes the osteogenesis of BMSCs, which was mediated by the integrin β1-FAK-ERK signaling pathway.

Establishment of a New Device for Electrical Stimulation of Non-Degenerative Cartilage Cells In Vitro

In cell-based therapies for cartilage lesions, the main problem is still the formation of fibrous cartilage, caused by underlying de-differentiation processes ex vivo. Biophysical stimulation is a promising approach to optimize cell-based procedures and to adapt them more closely to physiological conditions. The occurrence of mechano-electrical transduction phenomena within cartilage tissue is physiological and based on streaming and diffusion potentials. The application of exogenous electric fields can be used to mimic endogenous fields and, thus, support the differentiation of chondrocytes in vitro. For this purpose, we have developed a new device for electrical stimulation of chondrocytes, which operates on the basis of capacitive coupling of alternating electric fields. The reusable and sterilizable stimulation device allows the simultaneous use of 12 cavities with independently applicable fields using only one main supply. The first parameter settings for the stimulation of human non-degenerative chondrocytes, seeded on collagen type I elastin-based scaffolds, were derived from numerical electric field simulations. Our first results suggest that applied alternating electric fields induce chondrogenic re-differentiation at the gene and especially at the protein level of human de-differentiated chondrocytes in a frequency-dependent manner. In future studies, further parameter optimizations will be performed to improve the differentiation capacity of human cartilage cells.

Computational study on electromechanics of electroactive hydrogels for cartilage-tissue repair

BACKGROUND AND OBJECTIVE

The self-repair capability of articular cartilage is limited because of non-vascularization and low turnover of its extracellular matrix. Regenerating hyaline cartilage remains a significant clinical challenge as most non-surgical and surgical treatments provide only mid-term relief. Eventually, further pain and mobility loss occur for many patients in the long run due to further joint deterioration. Repair of articular cartilage tissue using electroactive scaffolds and biophysical stimuli like electrical and osmotic stimulation may have the potential to heal cartilage defects occurring due to trauma, osteoarthritis, or sport-related injuries. Therefore, the focus of the current study is to present a computational model of electroactive hydrogels for the cartilage-tissue repair as a first step towards an optimized experimental design.

METHODS

The multiphysics transport model that mainly includes the Poisson-Nernst-Planck equations and the mechanical equation is used to find the electrical stimulation response of the polyelectrolyte hydrogels. Based upon this, a numerical model on electromechanics of electroactive hydrogels seeded with chondrocytes is presented employing the open-source software FEniCS, which is a Python library for finite-element analysis.

RESULTS

We analyzed the ionic concentrations and electric potential in a hydrogel sample and the cell culture medium, the osmotic pressure created due to ionic concentration variations and the resulting hydrogel displacement. The proposed mathematical model was validated with examples from literature.

CONCLUSIONS

The presented model for the electrical and osmotic stimulation of a hydrogel sample can serve as a useful tool for the development and analysis of a cartilaginous scaffold employing electrical stimulation. By analyzing various parameters, we pave the way for future research on a finer scale using open-source software.