New Coll–HA/BT composite materials for hard tissue engineering

Piezoelectric biomaterials for providing electrical stimulation in bone tissue engineering: Barium titanate

With the increasing clinical demand for orthopedic implants, bone tissue engineering based on a variety of bioactive materials has shown promising applications in bone repair. And various physiological cues, such as mechanical, electrical, and magnetic stimulation, can influence cell fate and participate in bone regeneration. Natural bone has a piezoelectric effect due to the non-centrosymmetric nature of collagen, which can aid in cell adhesion, proliferation and differentiation, and bone growth by converting mechanical stimuli into electrical stimuli. Piezoelectric materials have the same piezoelectric effect as human bone, and they are able to deform in response to physiological movement, thus providing electrical stimulation to cells or damaged tissue without the need for an external power source. Among them, Barium titanate (BaTiO3) is widely used in tumor therapy, tissue engineering, health detection and drug delivery because of its good biocompatibility, low cytotoxicity and good piezoelectric properties. This review describes the piezoelectric effect of natural bone and the characteristics of various types of piezoelectric materials, from the synthesis and physicochemical characteristics of BaTiO3 and its application in biomedicine. And it highlights the great potential of BaTiO3 as piezoelectric biomaterials in the field of bone tissue engineering in anticipation of providing new ideas and opportunities for researchers. The translational potential of this article: This review systematically discusses barium titanate, a bioactive material that can mimic the piezoelectric effect of natural bone tissue, which can intervene in the regenerative repair of bone by providing a sustained electrical microenvironment for bone repair scaffolds. This may help to solve the current problem of poor osteogenic properties of bioactive materials by utilizing barium titanate.

Piezoelectric Scaffolds as Smart Materials for Bone Tissue Engineering

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

Progress in the development of piezoelectric biomaterials for tissue remodeling

Piezoelectric biomaterials have demonstrated significant potential in the past few decades to heal damaged tissue and restore cellular functionalities. Herein, we discuss the role of bioelectricity in tissue remodeling and explore ways to mimic such tissue-like properties in synthetic biomaterials. In the past decade, biomedical engineers have adopted emerging functional biomaterials-based tissue engineering approaches using innovative bioelectronic stimulation protocols based on dynamic stimuli to direct cellular activation, proliferation, and differentiation on engineered biomaterial constructs. The primary focus of this review is to discuss the concepts of piezoelectric energy harvesting, piezoelectric materials, and their application in soft (skin and neural) and hard (dental and bone) tissue regeneration. While discussing the prospective applications as an engineered tissue, an important distinction has been made between piezoceramics, piezopolymers, and their composites. The superiority of piezopolymers over piezoceramics to circumvent issues such as stiffness mismatch, biocompatibility, and biodegradability are highlighted. We aim to provide a comprehensive review of the field and identify opportunities for the future to develop clinically relevant and state-of-the-art biomaterials for personalized and remote health care.

Biomimetic-inspired piezoelectric ovalbumin/BaTiO3 scaffolds synergizing with anisotropic topology for modulating Schwann cell and DRG behavior

The treatment of peripheral nerve injury is a clinical challenge that tremendously affected the patients' health and life. Anisotropic topographies and electric cues can simulate the regenerative microenvironment of nerve from physical and biological aspects, which show promising application in nerve regeneration. However, most studies just unilaterally emphasize the effect of sole topological- or electric- cue on nerve regeneration, while rarely considering the synergistic function of both cues simultaneously. In this study, a biomimetic-inspired piezoelectric topological ovalbumin/BaTiO3 scaffold that can provide non-invasive electrical stimulation in situ was constructed by combining piezoelectric BaTiO3 nanoparticles and surface microtopography. The results showed that the incorporation of piezoelectric nanoparticles could improve the mechanical properties of the scaffolds, and the piezoelectric output of the scaffolds after polarization was significantly increased. Biological evaluation revealed that the piezoelectric topological scaffolds could regulate the orientation growth of SCs, promote axon elongation of DRG, and upregulate the genes expression referring to myelination and axon growth, thus rapidly integrated chemical-mechanical signals and transmitted them for effectively promoting neuronal myelination, which was closely related to peripheral neurogenesis. The study suggests that the anisotropic surface topology combined with non-invasive electronic stimulation of the ovalbumin/BaTiO3 scaffolds possess a promising application prospect in the repair and regeneration of peripheral nerve injury.

Manipulation of Heterogeneous Surface Electric Potential Promotes Osteogenesis by Strengthening RGD Peptide Binding and Cellular Mechanosensing

The heterogeneity of extracellular matrix (ECM) topology, stiffness, and architecture is a key factor modulating cellular behavior and osteogenesis. However, the effects of heterogeneous ECM electric potential at the micro- and nanoscale on osteogenesis remain to be elucidated. Here, the heterogeneous distribution of surface potential is established by incorporating ferroelectric BaTiO₃ nanofibers (BTNF) into poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) matrix based on phase-field and first-principles simulation. By optimizing the aspect ratios of BTNF fillers, the anisotropic distribution of surface potential on BTNF/P(VDF-TrFE) nanocomposite membranes can be achieved by strong spontaneous electric polarization of BTNF fillers. These results indicate that heterogeneous surface potential distribution leads to a meshwork pattern of fibronectin (FN) aggregation, which increased FN-III7-10 (FN fragment) focal flexibility and anchor points as predicted by molecular dynamics simulation. Furthermore, integrin clustering, focal adhesion formation, cell spreading, and adhesion are enhanced sequentially. Increased traction of actin fibers amplifies mechanotransduction by promoting nuclear translocation of YAP/Runx2, which enhances osteogenesis in vitro and bone regeneration in vivo. The work thus provides fundamental insights into the biological effects of surface potential heterogeneity at the micro- and nanoscale on osteogenesis, and also develops a new strategy to optimize the performance of electroactive biomaterials for tissue regenerative therapies.

Piezoelectric Biocomposites for Bone Grafting in Dentistry

In this research, Hydroxyapatite-Potassium, Sodium Niobate-Chitosan (HA-KNN-CSL) biocomposites were synthesized, both as hydrogel and ultra-porous scaffolds, to offer two commonly used alternatives to biomaterials in dental clinical practice. The biocomposites were obtained by varying the content of low deacetylated chitosan as matrix phase, mesoporous hydroxyapatite nano-powder, and potassium-sodium niobate (K_0.47Na_0.53NbO₃) sub-micron-sized powder. The resulting materials were characterized from physical, morpho-structural, and in vitro biological points of view. The porous scaffolds were obtained by freeze-drying the composite hydrogels and had a specific surface area of 18.4-24 m²/g and a strong ability to retain fluid. Chitosan degradation was studied for 7 and 28 days of immersion in simulated body fluid without enzymatic presence. All synthesized compositions proved to be biocompatible in contact with osteoblast-like MG-63 cells and showed antibacterial effects. The best antibacterial effect was shown by the 10HA-90KNN-CSL hydrogel composition against Staphylococcus aureus and the fungal strain Candida albicans, while a weaker effect was observed for the dry scaffold.

A Comprehensive Review on Barium Titanate Nanoparticles as a Persuasive Piezoelectric Material for Biomedical Applications: Prospects and Challenges

Stimulation of cells with electrical cues is an imperative approach to interact with biological systems and has been exploited in clinical practices over a wide range of pathological ailments. This bioelectric interface has been extensively explored with the help of piezoelectric materials, leading to remarkable advancement in the past two decades. Among other members of this fraternity, colloidal perovskite barium titanate (BaTiO₃ ) has gained substantial interest due to its noteworthy properties which includes high dielectric constant and excellent ferroelectric properties along with acceptable biocompatibility. Significant progression is witnessed for BaTiO₃ nanoparticles (BaTiO₃ NPs) as potent candidates for biomedical applications and in wearable bioelectronics, making them a promising personal healthcare platform. The current review highlights the nanostructured piezoelectric bio interface of BaTiO₃ NPs in applications comprising drug delivery, tissue engineering, bioimaging, bioelectronics, and wearable devices. Particular attention has been dedicated toward the fabrication routes of BaTiO₃ NPs along with different approaches for its surface modifications. This review offers a comprehensive discussion on the utility of BaTiO₃ NPs as active devices rather than passive structural unit behaving as carriers for biomolecules. The employment of BaTiO₃ NPs presents new scenarios and opportunity in the vast field of nanomedicines for biomedical applications.

Physicochemical, mechanical, dielectric, and biological properties of sintered hydroxyapatite/barium titanate nanocomposites for bone regeneration

Bone implants fabricated using nanocomposites containing hydroxyapatite (HA) and barium titanate (BT) show osteoconductive, osteoinductive, osteointegration, and piezoelectricity properties for bone regeneration applications. In our present study, HA and BT nanopowders were synthesized using high-energy ball-milling-assisted solid-state reaction with precursors of calcium carbonate and ammonium dihydrogen phosphate, and barium carbonate and titanium oxide powder mixtures, respectively. Hexagonal HA and tetragonal BT phases were formed after calcination at 700 and 1000 °C, respectively. Subsequently, hydroxyapatite/barium titanate (HA/BT) nanocomposites with different weight percentages of HA and BT were prepared by ball-milling, then compacted and sintered at two different temperatures to endow these bioceramics with better mechanical, dielectric, and biological properties for bone regeneration. Microstructure, crystal phases, and molecular structure characterizations of these sintered HA/BT nanocomposite compacts (SHBNCs) were performed using field-emission scanning electron microscopy, x-ray diffraction, and Fourier-transform infrared spectroscopy, respectively. Bulk density was evaluated using the Archimedes method. HA/BT nanocomposites with increased BT content showed enhanced dielectric properties, and the dielectric constant (ϵr) value for 5HA/95BT was ∼182 at 100 Hz. Mechanical properties such as Vicker's hardness, fracture toughness, yield strength, and diametral tensile strength were also investigated. The hemolysis assay of SHBNCs exhibited hemocompatibility. The effect of these SHBNCs as implants on thein vitrocytocompatibility and cell viability of MG-63 osteoblast-like cells was assessed by MTT assay and live/dead staining, respectively. 15HA/85BT showed increased metabolic activity with a higher number of live cells than BT after the culture period. Overall, the SHBNCs can be used as orthopedic implants for bone regeneration applications.

Effects of barium titanate on the dielectric constant, radiopacity, and biological properties of tricalcium silicate-based bioceramics

This study evaluated the effect of barium titanate (BT) on the dielectricity, radiopacity, and biological properties of tricalcium silicate (C3S). C3S/BT samples were prepared with varying proportions of BT (0, 20, 40, and 60 wt%; referred to as BT00, BT20, BT40, and BT60, respectively). Dielectric constant and radiopacity were measured. Cytocompatibility was evaluated on human dental pulp cells. After surgical procedures on rat mandible, immunohistochemistry and Masson's trichrome staining were performed. The dielectric constant increased with higher proportions of BT (p<0.05). BT40 and BT60 satisfied the clinical guideline of radiopacity. There were no significant differences among groups in the cytocompatibility tests (p>0.05). New bone was observed well, along with the expressions of the dentin matrix protein 1 (DMP1), osteocalcin (OC), and osteonectin (ON) in BT40 and BT60. Conclusively, the contents of 40-60 wt% of BT in C3S provided proper radiopacity, favorable cytocompatibility, and beneficial effect on bone regeneration.

Smart piezoelectric biomaterials for tissue engineering and regenerative medicine: a review

Due to the presence of electric fields and piezoelectricity in various living tissues, piezoelectric materials have been incorporated into biomedical applications especially for tissue regeneration. The piezoelectric scaffolds can perfectly mimic the environment of natural tissues. The ability of scaffolds which have been made from piezoelectric materials in promoting cell proliferation and regeneration of damaged tissues has encouraged researchers in biomedical areas to work on various piezoelectric materials for fabricating tissue engineering scaffolds. In this review article, the way that cells of different tissues like cardio, bone, cartilage, bladder, nerve, skin, tendon, and ligament respond to electric fields and the mechanism of tissue regeneration with the help of piezoelectric effect will be discussed. Furthermore, all of the piezoelectric materials are not suitable for biomedical applications even if they have high piezoelectricity since other properties such as biocompatibility are vital. Seen in this light, the proper piezoelectric materials which are approved for biomedical applications are mentioned. Totally, the present review introduces the recent materials and technologies that have been used for tissue engineering besides the role of electric fields in living tissues.

Development and Characterization of 3D Printed Multifunctional Bioscaffolds Based on PLA/PCL/HAp/BaTiO3 Composites

Bone substitute materials are placed in bone defects and play an important role in bone regeneration and fracture healing. The main objective of the present research is fabrication through the technique of 3D printing and the characterization of innovative composite bone scaffolds composed of polylactic acid (PLA), poly (ε-caprolactone) (PCL) while hydroxyapatite (HAp), and/or barium titanate (BaTiO3—BT) used as fillers. Composite filaments were prepared using a single screw melt extruder, and finally, 3D composite scaffolds were fabricated using the fused deposition modeling (FDM) technique. Scanning electron microscopy (SEM) images showed a satisfactory distribution of the fillers into the filaments and the printed objects. Furthermore, differential scanning calorimetry (DSC) measurements revealed that PLA/PCL filaments exhibit lower glass transition and melting point temperatures than the pure PLA filaments. Finally, piezoelectric and dielectric measurements of the 3D objects showed that composite PLA/PCL scaffolds containing HAp and BT exhibited piezoelectric coefficient (d33) values close to the human bone and high dielectric permittivity values.

Enhanced compressive strengths and induced cell growth of 1-3-type BaTiO3/PMMA bio-piezoelectric composites

Barium titanate (BaTiO₃) has been used as a bone implant material because of its piezoelectric properties and the ability to promote cell growth when combined with hydroxyapatite. However, the brittleness of BaTiO₃ inhibits its use as a bone replacement material at load-bearing sites, and the reduction of BaTiO₃ content in the composite reduces its piezoelectric effect on bone growth. In this study, we explored a preparation method, which included directional freeze casting and self-solidification of bone cement, to obtain 1-3-type BaTiO₃/PMMA bio-piezoelectric composites with a lamellar structure. The lamellar BaTiO₃ layer through the composite from the bottom to the top significantly improved the piezoelectric properties of the composite. In addition, the dendritic ceramic bridges on the BaTiO₃ pore walls can improve the compressive strength and elastic modulus of BaTiO₃/PMMA bio-piezoelectric composites with a lamellar structure. More importantly, it was found that polarized lamellar BaTiO₃ could induce osteoblasts to grow in the direction of the BaTiO₃ layers. When the width of the BaTiO₃ layer was in the range of 8-21 μm, osteoblasts along the BaTiO₃ layer showed well growth, which can be of great value for the production of biomimetic bone units.

Piezoelectric and Magnetoelectric Scaffolds for Tissue Regeneration and Biomedicine: A Review

Electric fields are ubiquitous throughout the body, playing important role in a multitude of biological processes including osteo-regeneration, cell signaling, nerve regeneration, cardiac function, and DNA replication. An increased understanding of the role of electric fields in the body has led to the development of devices for biomedical applications that incorporate electromagnetic fields as an intrinsically novel functionality (e.g., bioactuators, biosensors, cardiac/neural electrodes, and tissues scaffolds). However, in the majority of the aforementioned devices, an implanted power supply is necessary for operation, and therefore requires highly invasive procedures. Thus, the ability to apply electric fields in a minimally invasive manner to remote areas of the body remains a critical and unmet need. Here, we report on the potential of magnetoelectric (ME)-based composites to overcome this challenge. ME materials are capable of producing localized electric fields in response to an applied magnetic field, which the body is permeable to. Yet, the use of ME materials for biomedical applications is just beginning to be explored. Here, we present on the potential of ME materials to be utilized in biomedical applications. This will be presented alongside current state-of-the-art for in vitro and in vivo electrical stimulation of cells and tissues. We will discuss key findings in the field, while also identifying challenges, such as the synthesis and characterization of biocompatible ME materials, challenges in experimental design, and opportunities for future research that would lead to the increased development of ME biomaterials and their applications.

Time-lapsed imaging of nanocomposite scaffolds reveals increased bone formation in dynamic compression bioreactors

Progress in bone scaffold development relies on cost-intensive and hardly scalable animal studies. In contrast to in vivo, in vitro studies are often conducted in the absence of dynamic compression. Here, we present an in vitro dynamic compression bioreactor approach to monitor bone formation in scaffolds under cyclic loading. A biopolymer was processed into mechanically competent bone scaffolds that incorporate a high-volume content of ultrasonically treated hydroxyapatite or a mixture with barium titanate nanoparticles. After seeding with human bone marrow stromal cells, time-lapsed imaging of scaffolds in bioreactors revealed increased bone formation in hydroxyapatite scaffolds under cyclic loading. This stimulatory effect was even more pronounced in scaffolds containing a mixture of barium titanate and hydroxyapatite and corroborated by immunohistological staining. Therefore, by combining mechanical loading and time-lapsed imaging, this in vitro bioreactor strategy may potentially accelerate development of engineered bone scaffolds and reduce the use of animals for experimentation.

Schädli et al. present a bioreactor system that combines mechanical loading with longitudinal microCT imaging to assess bone mineralization in a poly(lactic-co-glycolic acid) (PLGA) scaffold reinforced with nanoparticles. This approach allows rapid and rigorous evaluation of engineered bone scaffolds performance in vitro and might reduce the use of animals for experimentation.

Electrospun Fibre Webs Templated Synthesis of Mineral Scaffolds Based on Calcium Phosphates and Barium Titanate

The current work focuses on the development of mineral scaffolds with complex composition and controlled morphology by using a polymeric template in the form of nonwoven fibre webs fabricated through electrospinning. By a cross-linking process, gelatine fibres stable in aqueous solutions were achieved, these being further subjected to a loading step with two types of mineral phases: calcium phosphates deposited by chemical reaction and barium titanate nanoparticles as decoration on the previously achieved structures. Thus, hybrid materials were obtained and subsequently processed in terms of freeze-drying and heat treating with the purpose of burning the template and consolidating the mineral part as potential bone implants with improved biological response by external stimulation. The results confirmed the tunable morphology, as well as the considerable applicability of both as-prepared and final samples for the development of medical devices, which encourages the continuation of research in the direction of assessing the synergistic contribution of barium titanate domains polarisation/magnetisation by external applied fields.

Composite scaffolds based on calcium phosphates and barium titanate obtained through bacterial cellulose templated synthesis

Taking into account the potential of barium titanate to deliver electrical stimulation to the physiological microenvironment and offer beneficial conditions for the cellular metabolism, this mineral phase was selected for the development of new composites. In this context, calcium phosphates and barium titanate were deposited on bacterial cellulose membranes under ultrasonic irradiation, the resulting system being subjected to a thermal treatment in optimized conditions in order to remove the polymeric template and achieve 3D porous architectures. The complex characterization performed on the intermediate and final samples demonstrated the suitability of such materials for hard tissue engineering applications.

Development of Vitroceramic Coatings and Analysis of Their Suitability for Biomedical Applications

Within the field of tissue engineering, thin films have been studied to improve implant fixation of metallic or ceramic materials in bone, connective tissue, oral mucosa or skin. In this context, to enhance their suitability as implantable devices, titanium-based substrates received a superficial vitroceramic coating by means of laser ablation. Further, this study describes the details of fabrication and corresponding tests in order to demonstrate the bioactivity and biocompatibility of the newly engineered surfaces. Thus, the metallic supports were covered with a complex material composed of SiO2, P2O5, CaO, MgO, ZnO and CaF2, in the form of thin layers via a physical deposition techniques, namely pulsed laser deposition. The resulting products were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, selected area electron diffraction, and electron energy loss spectroscopy. It was found that a higher substrate temperature and a lower working pressure lead to the highest quality film. Finally, the samples biocompatibility was assessed and they were found to be bioactive after simulated body fluid soaking and biocompatible through the MTT cell viability test.

Piezoelectric materials as stimulatory biomedical materials and scaffolds for bone repair

The process of bone repair and regeneration requires multiple physiological cues including biochemical, electrical and mechanical - that act together to ensure functional recovery. Myriad materials have been explored as bioactive scaffolds to deliver these cues locally to the damage site, amongst these piezoelectric materials have demonstrated significant potential for tissue engineering and regeneration, especially for bone repair. Piezoelectric materials have been widely explored for power generation and harvesting, structural health monitoring, and use in biomedical devices. They have the ability to deform with physiological movements and consequently deliver electrical stimulation to cells or damaged tissue without the need of an external power source. Bone itself is piezoelectric and the charges/potentials it generates in response to mechanical activity are capable of enhancing bone growth. Piezoelectric materials are capable of stimulating the physiological electrical microenvironment, and can play a vital role to stimulate regeneration and repair. This review gives an overview of the association of piezoelectric effect with bone repair, and focuses on state-of-the-art piezoelectric materials (polymers, ceramics and their composites), the fabrication routes to produce piezoelectric scaffolds, and their application in bone repair. Important characteristics of these materials from the perspective of bone tissue engineering are highlighted. Promising upcoming strategies and new piezoelectric materials for this application are presented.

STATEMENT OF SIGNIFICANCE

Electrical stimulation/electrical microenvironment are known effect the process of bone regeneration by altering the cellular response and are crucial in maintaining tissue functionality. Piezoelectric materials, owing to their capability of generating charges/potentials in response to mechanical deformations, have displayed great potential for fabricating smart stimulatory scaffolds for bone tissue engineering. The growing interest of the scientific community and compelling results of the published research articles has been the motivation of this review article. This article summarizes the significant progress in the field with a focus on the fabrication aspects of piezoelectric materials. The review of both material and cellular aspects on this topic ensures that this paper appeals to both material scientists and tissue engineers.