Fabrication of Biocompatible Potassium Sodium Niobate Piezoelectric Ceramic as an Electroactive Implant

Exploring the application of piezoelectric ceramics in bone regeneration

Piezoelectric ceramics are piezoelectric materials with polycrystalline structure and have been widely used in many fields such as medical imaging and sound sensors. As knowledge about this kind of material develops, researchers find piezoelectric ceramics possess favorable piezoelectricity, biocompatibility, mechanical properties, porous structure and antibacterial effect and endeavor to apply piezoelectric ceramics to the field of bone tissue engineering. However, clinically no piezoelectric ceramics have been exercised so far. Therefore, in this paper we present a comprehensive review of the research and development of various piezoelectric ceramics including barium titanate, potassium sodium niobate and zinc oxide ceramics and aims to explore the application of piezoelectric ceramics in bone regeneration by providing a detailed overview of the current knowledge and research of piezoelectric ceramics in bone tissue regeneration.

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.

Piezoelectric materials for neuroregeneration: a review

The purpose of nerve regeneration via tissue engineering strategies is to create a microenvironment that mimics natural nerve growth for achieving functional recovery. Biomaterial scaffolds offer a promising option for the clinical treatment of large nerve gaps due to the rapid advancement of materials science and regenerative medicine. The design of biomimetic scaffolds should take into account the inherent properties of the nerve and its growth environment, such as stiffness, topography, adhesion, conductivity, and chemical functionality. Various advanced techniques have been employed to develop suitable scaffolds for nerve repair. Since neuronal cells have electrical activity, the transmission of bioelectrical signals is crucial for the functional recovery of nerves. Therefore, an ideal peripheral nerve scaffold should have electrical activity properties similar to those of natural nerves, in addition to a delicate structure. Piezoelectric materials can convert stress changes into electrical signals that can activate different intracellular signaling pathways critical for cell activity and function, which makes them potentially useful for nerve tissue regeneration. However, a comprehensive review of piezoelectric materials for neuroregeneration is still lacking. Thus, this review systematically summarizes the development of piezoelectric materials and their application in the field of nerve regeneration. First, the electrical signals and natural piezoelectricity phenomenon in various organisms are briefly introduced. Second, the most commonly used piezoelectric materials in neural tissue engineering, including biocompatible piezoelectric polymers, inorganic piezoelectric materials, and natural piezoelectric materials, are classified and discussed. Finally, the challenges and future research directions of piezoelectric materials for application in nerve regeneration are proposed.

Exploring Multifunctional Response of Ca10(PO4)6(OH)2-K0.5Na0.5NbO3 Ceramic Composite for Biomedical Applications

This study focuses on investigating the intriguing properties of Ca10(PO4)6(OH)2 (HAP)-K0.5Na0.5NbO3 (KNN) bioceramic composites, seeking to elucidate the relationship between their structural, electrical, biological, and optical behavior. The article begins with a close inspection of the O 1s spectra of the specimens obtained from X-ray photoelectron spectroscopy (XPS). The spectra reveal the peak related to lattice oxygen, O vacancy and the surface adsorbed O. The formed O vacancy strongly influences the changes in lattice parameters as observed from the X-ray diffraction (XRD) patterns. The frequency variation of the dielectric response for the composites in the radio frequency (RF) regime has electrical polarization effective for biomedical applications. Nyquist plots along with equivalent RC circuits further confirm that those electrical responses are mainly contributed from the grain boundaries. Adsorption dynamics of protein on the ceramic surface are investigated using bovine serum albumin (BSA), which established the major role of electrostatic interaction. Surface charge and O vacancies are modeled to understand the adsorption of protein and a linear correlation is reported. The role of O vacancies in modulating adsorption dynamics adds a new dimension to this study. The conformational change of BSA has also been considered by constructing the secondary structure following the protein-ceramic interaction. Excitingly, the composites are also found to be fluorescent active, a courtesy of the defects and vacancies leading to electron-hole recombination in the forbidden region. These promising properties envision an exciting future for HAP-KNN composites, especially in the domain of bioimaging and bone-tissue engineering.

3D-Printed Piezoelectric Scaffolds with Shape Memory Polymer for Bone Regeneration

The application of piezoelectric nanoparticles with shape memory polymer (SMP) to 3D-printed piezoelectric scaffolds for bone defect repair is an attractive research direction. However, there is a significant difference in dielectric constants between the piezoelectric phase and polymer phase, limiting the piezoelectric property. Therefore, novel piezoelectric acrylate epoxidized soybean oil (AESO) scaffolds doped with piezoelectric Ag-TMSPM-pBT (ATP) nanoparticles (AESO-ATP scaffolds) are prepared via digital light procession 3D-printing. The Ag-TMSPM-pBT nanoparticles improve the piezoelectric properties of the AESO scaffolds by TMSPM covalent functionalization and conductive Ag nanoparticles. The AESO scaffolds doped with 10 wt% Ag-TMSPM-pBT nanoparticles (AESO-10ATP scaffolds) exhibit promising piezoelectrical properties, with a piezoelectric coefficient (d33) of 0.9 pC N-1 and an output current of 146.4 nA, which are close to the piezoelectric constants of bone tissue. In addition, these scaffolds exhibit good shape memory function and can quickly recover their original shape under near-infrared (NIR) light irradiation. The results of osteogenesis capability evaluation indicate that the AESO-10ATP scaffolds can promote osteogenic differentiation of BMSCs in vitro and bone defect repair in vivo, indicating the 3D-printed AESO-10ATP piezoelectric scaffolds may have great application potential for bone regeneration.

3D printing of piezoelectric and bioactive barium titanate-bioactive glass scaffolds for bone tissue engineering

Bone healing is a complex process orchestrated by various factors, such as mechanical, chemical and electrical cues. Creating synthetic biomaterials that combine several of these factors leading to tailored and controlled tissue regeneration, is the goal of scientists worldwide. Among those factors is piezoelectricity which creates a physiological electrical microenvironment that plays an important role in stimulating bone cells and fostering bone regeneration. However, only a limited number of studies have addressed the potential of combining piezoelectric biomaterials with state-of-the-art fabrication methods to fabricate tailored scaffolds for bone tissue engineering. Here, we present an approach that takes advantage of modern additive manufacturing techniques to create macroporous biomaterial scaffolds based on a piezoelectric and bioactive ceramic-crystallised glass composite. Using binder jetting, scaffolds made of barium titanate and 45S5 bioactive glass are fabricated and extensively characterised with respect to their physical and functional properties. The 3D-printed ceramic-crystallised glass composite scaffolds show both suitable mechanical strength and bioactive behaviour, as represented by the accumulation of bone-like calcium phosphate on the surface. Piezoelectric scaffolds that mimic or even surpass bone with piezoelectric constants ranging from 1 to 21 pC/N are achieved, depending on the composition of the composite. Using MC3T3-E1 osteoblast precursor cells, the scaffolds show high cytocompatibility coupled with cell attachment and proliferation, rendering the barium titanate/45S5 ceramic-crystallised glass composites promising candidates for bone tissue engineering.

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.

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

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

Wirelessly Powered Electrical-Stimulation Based on Biodegradable 3D Piezoelectric Scaffolds Promotes the Spinal Cord Injury Repair

An electroactive scaffold integrated with noninvasive in vivo electrical-stimulation (ES) capability shows great promise in the repair and regeneration of damaged tissues. Developing high-performance piezoelectric biomaterials which can simultaneously serve as both a biodegradable tissue scaffold and controllable electrical stimulator remains a great challenge. Herein, we constructed a biodegradable high-performance 3D piezoelectric scaffold with ultrasound (US)-driven wireless ES capability, and demonstrated its successful application for the repair of spinal cord injuries in a rat model. The 3D multichannel piezoelectric scaffold was prepared by electrospinning of poly(lactic acid) (PLA) nanofibers incorporated with biodegradable high-performance piezoelectric potassium sodium niobate (K_0.5Na_0.5NbO₃, KNN) nanowires. With programmed US irradiation as a remote mechanical stimulus, the on-demand in vivo ES with an adjustable timeline, duration, and strength can be delivered by the 3D piezoelectric scaffold. Under proper US excitation, the 3D tissue scaffolds made of the piezoelectric composite nanofibers can accelerate the recovery of motor functions and enhance the repair of spinal cord injury. The immunohistofluorescence investigation indicated that the 3D piezoelectric scaffolds combined with the US-driven in vivo ES promoted neural stem cell differentiation and endogenous angiogenesis in the lesion. This work highlights the potential application of a biodegradable high-performance piezoelectric scaffold providing US-driven on-demand electrical cues for regenerative medicine.

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.

Influence of P(VDF-TrFE) Membranes with Different Surface Potentials on the Activity and Angiogenic Function of Human Umbilical Vein Endothelial Cells

During bone tissue regeneration, neovascularization is critical, and the formation of a blood supply network is crucial for bone growth stimulation and remodeling. Previous studies suggest that bioelectric signals facilitate the process of angiogenesis. Owing to their biomimetic electroactivity, piezoelectric membranes have garnered substantial interest in the field of guided bone regeneration. Nevertheless, the knowledge of their influence due to varying surface potentials on the progression of angiogenesis remains ambiguous. Therefore, we proposed the preparation of an electroactive material, P(VDF-TrFE), and investigated its effects on the activity and angiogenic functions of human umbilical vein endothelial cells (HUVECs). The HUVECs were directly cultured on P(VDF-TrFE) membranes with different surface potentials. Subsequently, cell viability, proliferation, migration, tube formation, and expressions of related factors were assessed through appropriate assays. Our results revealed that the negative surface potential groups exerted differential effects on the modulation of angiogenesis in vitro. The P(VDF-TrFE) membranes with negative surface potential exhibited the greatest effect on cellular behaviors, including proliferation, migration, tube formation, and promotion of angiogenesis by releasing key factors such as VEGF-A and CD31. Overall, these results indicated that the surface potential of piezoelectric P(VDF-TrFE) membranes could exert differential effects on angiogenesis in vitro. We present a novel approach for designing bioactive materials for guided bone regeneration.

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.

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.

Processing Optimization and Toxicological Evaluation of "Lead-Free" Piezoceramics: A KNN-Based Case Study

Due to the ever-increasing limitations of the use of lead-based materials, the manufacturing of lead-free piezoceramics with competitive piezoelectric properties and established nontoxicity is considered a priority for the scientific and industrial community. In this work, a lead-free system based on sodium potassium niobate (KNN), opportunely modified with MgNb₂O₆ (MN), was prepared through a combination of a mechanochemical activation method and air sintering, and its toxicity was evaluated. The effect of the mechanical processing on the microstructure refinement of the processed powders was established by X-ray diffraction and the average crystallite size content of the Nb₂O₅ species was evaluated. The experimental evidence was rationalized using a phenomenological model which permitted us to obtain the amount of powder processed at each collision and to optimize the activation step of the pre-calcined reagents. This influenced the final density and piezoresponse of the as-sintered pellets, which showed optimal properties compared with other KNN systems. Their toxicological potential was evaluated through exposure experiments to the pulverized KNN-based pellets, employing two widely used human and environmental cellular models. The in vitro assays proved, under the selected conditions, the absence of cytotoxicity of KNN-bases systems here studied.

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.

Improved antibacterial and cellular response of electrets and piezobioceramics

The bacterial contamination in implants has been recognized as one of the key issues in orthopedics. In this article, a new technique of electrical polarization of various non-piezoelectric and piezoelectric biocompatible ceramics has been explored to develop antibacterial implants. Optimally processed hydroxyapatite (HA), BaTiO₃ (BT), CaTiO₃ (CT), Na_0.5K_0.5NbO₃ (NKN) and their composites have been used as model biomaterials to verify the concept. The phase evolution analyses and microstructural characterizations were performed for sintered samples. The samples were polarized at polarizing voltage and temperature of 20 kV and 500°C, respectively, for 30 min. The hydrophilicity of polarized surfaces was examined using deionized water and culture media. The polarization induced in-vitro antibacterial study was performed for both, gram positive and gram negative bacteria. The viability of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria reduces significantly on the polarized surfaces. In addition, the influence of polarization on antibacterial response has been explored via various mechanisms such as development of reactive oxygen species (ROS), catalase activity and lipoperoxidation. Furthermore, the cellular response of polarized surfaces was also examined using SaOS2 and MG-63 cells. The viability of SaOS2 and MG-63 cells was observed to increase significantly on negatively polarized surfaces. Overall, the surface treatment enhances the antibacterial response of HA, NKN, BT, CT and their composites surfaces with positive influence on cellular response.

On the road to smart biomaterials for bone research: definitions, concepts, advances, and outlook

The demand for biomaterials that promote the repair, replacement, or restoration of hard and soft tissues continues to grow as the population ages. Traditionally, smart biomaterials have been thought as those that respond to stimuli. However, the continuous evolution of the field warrants a fresh look at the concept of smartness of biomaterials. This review presents a redefinition of the term "Smart Biomaterial" and discusses recent advances in and applications of smart biomaterials for hard tissue restoration and regeneration. To clarify the use of the term "smart biomaterials", we propose four degrees of smartness according to the level of interaction of the biomaterials with the bio-environment and the biological/cellular responses they elicit, defining these materials as inert, active, responsive, and autonomous. Then, we present an up-to-date survey of applications of smart biomaterials for hard tissues, based on the materials' responses (external and internal stimuli) and their use as immune-modulatory biomaterials. Finally, we discuss the limitations and obstacles to the translation from basic research (bench) to clinical utilization that is required for the development of clinically relevant applications of these technologies.

Beta-Titanium Alloy Covered by Ferroelectric Coating–Physicochemical Properties and Human Osteoblast-Like Cell Response

Beta-titanium alloys are promising materials for bone implants due to their advantageous mechanical properties. For enhancing the interaction of bone cells with this perspective material, we developed a ferroelectric barium titanate (BaTiO3) coating on a Ti39Nb alloy by hydrothermal synthesis. This coating was analyzed by scanning electron and Raman microscopy, X-ray diffraction, piezoresponse force microscopy, X-ray photoelectron spectroscopy, nanoindentation, and roughness measurement. Leaching experiments in a saline solution revealed that Ba is released from the coating. A progressive decrease of Ba concentration in the material was also found after 1, 3, and 7 days of cultivation of human osteoblast-like Saos-2 cells. On day 1, the Saos-2 cells adhered on the BaTiO3 film in higher initial numbers than on the bare alloy, but they were less spread, and their initial proliferation rate was slower. These cells also contained a lower amount of beta1-integrins and vinculin, i.e., molecules involved in cell adhesion, and produced a lower amount of collagen I. This cell behavior was attributed to a higher surface roughness of BaTiO3 film rather than to its potential cytotoxicity, because the cell viability on this film was very high, reaching almost 99%. The amount of alkaline phosphatase, an enzyme involved in bone matrix mineralization, was similar in cells on the BaTiO3-coated and uncoated alloy, and on day 7, the cells on BaTiO3 film attained a higher final cell population density. These results indicate that after some improvements, particularly in its roughness and stability, the hydrothermal ferroelectric BaTiO3 film could be promising coating for improved osseointegration of bone implants.

Sizing up (K1−xNax)NbO3 films: a review of synthesis routes, properties & applications

This review discusses (K,Na)NbO₃ thin films, with a focus on synthesis, chemically modifying properties, plus piezoelectric and biomedical KNN devices.

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

The process of bone tissue repair and regeneration is complex and requires a variety of physiological signals, including biochemical, electrical and mechanical signals, which collaborate to ensure functional recovery. The inherent piezoelectric properties of bone tissues can convert mechanical stimulation into electrical effects, which play significant roles in bone maturation, remodeling and reconstruction. Electroactive materials, including conductive materials, piezoelectric materials and electret materials, can simulate the physiological and electrical microenvironment of bone tissue, thereby promoting bone regeneration and reconstruction. In this paper, the structures and performances of different types of electroactive materials and their applications in the field of bone repair and regeneration are reviewed, particularly by providing the results from in vivo evaluations using various animal models. Their advantages and disadvantages as bone repair materials are discussed, and the methods for tuning their performances are also described, with the aim of providing an up-to-date account of the proposed topics.

Wireless Electrochemotherapy by Selenium-Doped Piezoelectric Biomaterials to Enhance Cancer Cell Apoptosis

Cancer residues around the surgical site remain a significant cause of treatment failure with cancer recurrence. To prevent cancer recurrence and simultaneously repair surgery-caused defects, it is urgent to develop implantable biomaterials with anticancer ability and good biological activity. In this work, a functionalized implant is successfully fabricated by doping the effective anticancer element selenium (Se) into the potassium-sodium niobate piezoceramic, which realizes the wireless combination of electrotherapy and chemotherapy. Herein, we demonstrate that the Se-doped piezoelectric implant can cause mitochondrial damage by increasing intracellular reactive oxygen species levels and then trigger the caspase-3 pathway to significantly promote apoptosis of osteosarcoma cells in vitro. Meanwhile, its good biocompatibility has been verified. These results are of great importance for future deployment of wireless electro- and chemostimulation to modulate biological process around the defective tissue.

Current Trends in Fabrication of Biomaterials for Bone and Cartilage Regeneration: Materials Modifications and Biophysical Stimulations

The aim of engineering of biomaterials is to fabricate implantable biocompatible scaffold that would accelerate regeneration of the tissue and ideally protect the wound against biodevice-related infections, which may cause prolonged inflammation and biomaterial failure. To obtain antimicrobial and highly biocompatible scaffolds promoting cell adhesion and growth, materials scientists are still searching for novel modifications of biomaterials. This review presents current trends in the field of engineering of biomaterials concerning application of various modifications and biophysical stimulation of scaffolds to obtain implants allowing for fast regeneration process of bone and cartilage as well as providing long-lasting antimicrobial protection at the site of injury. The article describes metal ion and plasma modifications of biomaterials as well as post-surgery external stimulations of implants with ultrasound and magnetic field, providing accelerated regeneration process. Finally, the review summarizes recent findings concerning the use of piezoelectric biomaterials in regenerative medicine.

Functionalized-ferroelectric-coating-driven enhanced biomineralization and protein-conformation on metallic implants

In the context of bone regeneration, it is important to have platforms that with appropriate stimuli can support the attachment and direct the growth, proliferation and differentiation of cells.

A built-in electric field with nanoscale distinction for cell behavior regulation

To mimic the electrical properties of collagen fibrils on a bone surface, a built-in nanoscale electric field is formed on the surface of a polypyrrole (PPy) coating-decorated potassium-sodium niobate (KNN) piezoceramic. With the fabrication strategy, the piezoelectricity of KNN after polarization results in the formation of an electric field on the surface, which could be regulated by adjusting the polarization process. Then, conductive PPy nanoarrays (CPNAs) are obtained on the surfaces of the KNN piezoceramics. The conductive PPy transports the electric field to the coating surface, and the nanoarray morphology results in variations in the surface potential, leading to a built-in nanoscale electric field. Biological characterization indicates that CPNAs exhibit acceptable biocompatibility. Moreover, the nanoscale electric field regulates cell behavior, and the relatively high surface potential promotes cell proliferation, cell attachment and osteogenic differentiation.

Laser-synthesized nanocrystalline, ferroelectric, bioactive BaTiO3/Pt/FS for bone implants

The goal of our study is to design BaTiO₃ ferroelectric layers that will cover metal implants and provide improved osseointegration. We synthesized ferroelectric BaTiO₃ layers on Pt/fused silica substrates, and we studied their physical and bio-properties. BaTiO₃ and Pt layers were prepared using KrF excimer laser ablation at substrate temperature T_s in the range from 200°C to 750°C in vacuum or under oxygen pressure of 10 Pa, 15 Pa, and 20 Pa. The BaTiO₃/Pt and Pt layers adhered well to the substrates. BaTiO₃ films of crystallite size 60-140 nm were fabricated. Ferroelectric loops were measured and ferroelectricity was also confirmed using Raman scattering measurements. Results of atomic force microscopy topology and the X-ray diffraction structure of the BaTiO₃/Pt/fused silica multilayers are presented. The adhesion, viability, growth, and osteogenic differentiation of human osteoblast-like Saos-2 cells were also studied. On days 1, 3, and 7 after seeding, the lowest cell numbers were found on non-ferroelectric BaTiO₃, while the values on ferroelectric BaTiO₃, on non-annealed and annealed Pt interlayers, and on the control tissue culture polystyrene dishes and microscopic glass slides were similar, and were usually significantly higher than on non-ferroelectric BaTiO₃. A similar trend was observed for the intensity of the fluorescence of alkaline phosphatase, a medium-term marker of osteogenic differentiation, and of osteocalcin, a late marker of osteogenic differentiation. At the same time, the cell viability, tested on day 1 after seeding, was very high on all tested samples, reaching 93-99%. Ferroelectric BaTiO₃ films deposited on metallic bone implants through a Pt interlayer can therefore markedly improve the osseointegration of these implants in comparison with non-ferroelectric BaTiO₃ films.