A comprehensive review on electrical properties of hydroxyapatite based ceramic composites

Tailoring biomaterials for skin anti-aging

Skin aging is the phenomenon of degenerative changes in the structure and function of skin tissues over time and is manifested by a gradual loss of skin elasticity and firmness, an increased number of wrinkles, and hyperpigmentation. Skin anti-aging refers to a reduction in the skin aging phenomenon through medical cosmetic technologies. In recent years, new biomaterials have been continuously developed for improving the appearance of the skin through mechanical tissue filling, regulating collagen synthesis and degradation, inhibiting pigmentation, and repairing the skin barrier. This review summarizes the mechanisms associated with skin aging, describes the biomaterials that are commonly used in medical aesthetics and their possible modes of action, and discusses the application strategies of biomaterials in this area. Moreover, the synergistic effects of such biomaterials and other active ingredients, such as stem cells, exosomes, growth factors, and antioxidants, on tissue regeneration and anti-aging are evaluated. Finally, the possible challenges and development prospects of biomaterials in the field of anti-aging are discussed, and novel ideas for future innovations in this area are summarized.

Stimuli-responsive microcarriers and their application in tissue repair: A review of magnetic and electroactive microcarrier

Microcarrier applications have made great advances in tissue engineering in recent years, which can load cells, drugs, and bioactive factors. These microcarriers can be minimally injected into the defect to help reconstruct a good microenvironment for tissue repair. In order to achieve more ideal performance and face more complex tissue damage, an increasing amount of effort has been focused on microcarriers that can actively respond to external stimuli. These microcarriers have the functions of directional movement, targeted enrichment, material release control, and providing signals conducive to tissue repair. Given the high controllability and designability of magnetic and electroactive microcarriers, the research progress of these microcarriers is highlighted in this review. Their structure, function and applications, potential tissue repair mechanisms, and challenges are discussed. In summary, through the design with clinical translation ability, meaningful and comprehensive experimental characterization, and in-depth study and application of tissue repair mechanisms, stimuli-responsive microcarriers have great potential in tissue repair.

3D printed biopolymer/black phosphorus nanoscaffolds for bone implants: A review

Bone implantation is one of the recognized and effective means of treating bone defects, but osteoporosis and bone tumor-related bone abnormalities have a series of problems such as susceptibility to infection, difficulty in healing, and poor therapeutic effect, which poses a great challenge to clinical medicine. Three-dimensional things may be printed using 3D printing. Researchers can feed materials through the printer layer by layer to create the desired shape for a 3D structure. It is widely employed in the healing of bone defects, and it is an improved form of additive manufacturing technology with prospective future applications. This review's objective is to provide an overview of the findings reports pertaining to 3D printing biopolymers in recent years, provide an overview of biopolymer materials and their composites with black phosphorus for 3D printing bone implants, and the characterization methods of composite materials are also summarized. In addition, summarizes 3D printing methods based on ink printing and laser printing, pointing out their special features and advantages, and provide a combination strategy of photothermal therapy and bone regeneration materials for black phosphorus-based materials. Finally, the associations between bone implant materials and immune cells, the bio-environment, as well as the 3D printing bone implants prospects are outlined.

Enhanced electrical properties of BNKT-BMN lead-free ceramics by CaSnO3 doping and their bioactive properties

There is an increasing interest in using piezoelectric materials, including lead-free piezoceramics for medical applications. As a result, more attention has been placed on investigating the biological properties of these materials. In this research experiment, electrical, mechanical, and biological properties of lead-free 0.99Bi0.5(Na0.8K0.2)0.5TiO3-0.01Bi(Mg2/3Nb1/3)O3 or 0.99BNKT-0.01BMN doped with CaSnO3 (CSO) were investigated. The samples were synthesized by a modified solid-state reaction technique. X-ray diffraction (XRD) analysis showed that the samples presented a single perovskite phase. After adding CSO, electrical properties such as energy storage density (maximum W rec = 781 mJ cm-3) and electro-strain properties (maximum S max = 0.3%) were improved at room temperature. Mechanical properties were also enhanced for the modified samples with maximum values for Vickers hardness (H V) and elastic modulus (E m) of 6.11 GPa and 135 GPa, respectively. Biological assays for cytotoxicity, indicated that the samples had high cell viability, while the simulated body fluid (SBF) test revealed a moderate apatite forming ability. The samples were then coated with hydroxyapatite to improve their apatite-forming ability. The SBF testing for the coated samples showed that the coated samples had high apatite-forming ability. The obtained results pointed to the possibility of ceramics being used for multifunction electrical devices at room temperature and biomaterial applications.

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Reconstruction of Segmental Bone Defect in Canine Tibia Model Utilizing Bi-Phasic Scaffold: Pilot Study

The reunion and restoration of large segmental bone defects pose significant clinical challenges. Conventional strategies primarily involve the combination of bone scaffolds with seeded cells and/or growth factors to regulate osteogenesis and angiogenesis. However, these therapies face inherent issues related to immunogenicity, tumorigenesis, bioactivity, and off-the-shelf transplantation. The biogenic micro-environment created by implanted bone grafts plays a crucial role in initiating the bone regeneration cascade. To address this, a highly porous bi-phasic ceramic synthetic bone graft, composed of hydroxyapatite (HA) and alumina (Al), was developed. This graft was employed to repair critical segmental defects, involving the creation of a 2 cm segmental defect in a canine tibia. The assessment of bone regeneration within the synthetic bone graft post-healing was conducted using scintigraphy, micro-CT, histology, and dynamic histomorphometry. The technique yielded pore sizes in the range of 230-430 μm as primary pores, 40-70 μm as secondary inner microchannels, and 200-400 nm as tertiary submicron surface holes. These three components are designed to mimic trabecular bone networks and to provide body fluid adsorption, diffusion, a nutritional supply, communication around the cells, and cell anchorage. The overall porosity was measured at 82.61 ± 1.28%. Both micro-CT imaging and histological analysis provided substantial evidence of robust bone formation and the successful reunion of the critical defect. Furthermore, an histology revealed the presence of vascularization within the newly formed bone area, clearly demonstrating trabecular and cortical bone formation at the 8-week mark post-implantation.

Study on Synergistic Effects of Nanohydroxyapatite/High-Viscosity Carboxymethyl Cellulose Scaffolds Stimulated by LIPUS for Bone Defect Repair of Rats

Despite the self-healing capacity of bone, the regeneration of critical-size bone defects remains a major clinical challenge. In this study, nanohydroxyapatite (nHAP)/high-viscosity carboxymethyl cellulose (hvCMC, 6500 mPa·s) scaffolds and low-intensity pulsed ultrasound (HA-LIPUS) were employed to repair bone defects. First, hvCMC was prepared from ramie fiber, and the degree of substitution (DS), purity, and content of NaCl of hvCMC samples were 0.91, 99.93, and 0.017%, respectively. Besides, toxic metal contents were below the permissible limits for pharmaceutically used materials. Our results demonstrated that the hvCMC is suitable for pharmaceutical use. Second, nHAP and hvCMC were employed to prepare scaffolds by freeze-drying. The results indicated that the scaffolds were porous, and the porosity was 35.63 ± 3.52%. Subsequently, the rats were divided into four groups (n = 8) randomly: normal control (NC), bone defect (BD), bone defect treated with nHAP/hvCMC scaffolds (HA), and bone defect treated with nHAP/hvCMC scaffolds and stimulated by LIPUS (HA-LIPUS). After drilling surgery, nHAP/hvCMC scaffolds were implanted in the defect region of HA and HA-LIPUS rats. Meanwhile, HA-LIPUS rats were treated by LIPUS (1.5 MHz, 80 mW cm-2) irradiation for 2 weeks. Compared with BD rats, the maximum load and bone mineral density of HA-LIPUS rats were increased by 20.85 and 51.97%, respectively. The gene and protein results indicated that nHAP/hvCMC scaffolds and LIPUS promoted the bone defect repair and regeneration of rats significantly by activating Wnt/β-catenin and inhibiting OPG/RANKL signaling pathways. Overall, compared with BD rats, nHAP/hvCMC scaffolds and LIPUS promoted bone defect repair significantly. Furthermore, the research results also indicated that there are synergistic effects for bone defect repair between the nHAP/hvCMC scaffolds and LIPUS.

The Effect of Doping on the Electrical and Dielectric Properties of Hydroxyapatite for Medical Applications: From Powders to Thin Films

Recently, the favorable electrical properties of biomaterials have been acknowledged as crucial for various medical applications, including both bone healing and growth processes. This review will specifically concentrate on calcium phosphate (CaP)-based bioceramics, with a notable emphasis on hydroxyapatite (HA), among the diverse range of synthetic biomaterials. HA is currently the subject of extensive research in the medical field, particularly in dentistry and orthopedics. The existing literature encompasses numerous studies exploring the physical-chemical, mechanical, and biological properties of HA-based materials produced in various forms (i.e., powders, pellets, and/or thin films) using various physical and chemical vapor deposition techniques. In comparison, there is a relative scarcity of research on the electrical and dielectric properties of HA, which have been demonstrated to be essential for understanding dipole polarization and surface charge. It is noteworthy that these electrical and dielectric properties also offer valuable insights into the structure and functioning of biological tissues and cells. In this respect, electrical impedance studies on living tissues have been performed to assess the condition of cell membranes and estimate cell shape and size. The need to fill the gap and correlate the physical-chemical, mechanical, and biological characteristics with the electrical and dielectric properties could represent a step forward in providing new avenues for the development of the next-generation of high-performance HA-doped biomaterials for future top medical applications. Therefore, this review focuses on the electrical and dielectric properties of HA-based biomaterials, covering a range from powders and pellets to thin films, with a particular emphasis on the impact of the various dopants used. Therefore, it will be revealed that each dopant possesses unique properties capable of enhancing the overall characteristics of the produced structures. Considering that the electrical and dielectric properties of HA-based biomaterials have not been extensively explored thus far, the aim of this review is to compile and thoroughly discuss the latest research findings in the field, with special attention given to biomedical applications.

Enhanced Photocatalysis of Electrically Polarized Titania Nanosheets

Titania (TiO2) nanosheets are crystals with controlled, highly ordered structures that improve the functionality of conventional TiO2 nanoparticles. Various surface modification methods have been studied to enhance the effectiveness of these materials as photocatalysts. Surface modifications using electrical polarization have attracted considerable attention in recent years because they can improve the function of titania without changing its composition. However, the combination of facet engineering and electrical polarization has not been shown to improve the functionality of TiO2 nanosheets. In the present study, the dye-degradation performance of polarized TiO2 nanosheets was evaluated. TiO2 nanosheets with a F/Ti ratio of 0.3 were synthesized via a hydrothermal method. The crystal morphology and structure were evaluated using transmission electron microscopy and X-ray diffraction. Then, electrical polarization was performed under a DC electric field of 300 V at 300 °C. The polarized material was evaluated using thermally stimulated current measurements. A dye-degradation assay was performed using a methylene blue solution under ultraviolet irradiation. The polarized TiO2 nanosheets exhibited a dense surface charge and accelerated decolorization. These results indicate that electrical polarization can be used to enhance the photocatalytic activity of TiO2.

Nanoceramic-based coatings for corrosion protection: a review on synthesis, mechanisms, and applications

Corrosion is a pervasive issue with significant economic and safety implications across various industries. Nanoceramic-based coatings have emerged as a promising solution for corrosion protection due to their unique properties and mechanisms. This review aims to comprehensively examine the synthesis, mechanisms, and applications of nanoceramic-based coatings for corrosion protection. The review begins by highlighting the importance of corrosion protection and its impact on different industries. It introduces nanoceramic-based coatings as a potential solution to address this challenge. The objective is to provide a thorough understanding of the synthesis methods, mechanisms, and applications of these coatings. The fundamental principles of corrosion and different corrosion mechanisms are discussed, along with the limitations of traditional corrosion protection methods. The review emphasizes how nanoceramic-based coatings can overcome these limitations and provide superior corrosion resistance. Various synthesis methods, including sol-gel, electrodeposition, and physical vapor deposition, are described in detail, along with the factors influencing the synthesis process. Recent advancements and innovations in nanoceramic coating synthesis techniques are also highlighted. This looks at how coatings made with tiny ceramic particles protect against corrosion. It examines the importance of small-scale details like particle size, shape, and what the particles are made of. The formation of passive layers, self-healing mechanisms, and barrier properties of nanoceramic coatings are explained. The diverse applications of nanoceramic coatings for corrosion protection in industries such as automotive, aerospace, and marine are comprehensively discussed. Case studies and examples demonstrating the significant corrosion resistance and improved performance achieved with nanoceramic coatings are presented.

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.

Piezoelectric signals of HAp and collagen with different glucose concentrations: A method for diabetes detection

Piezoelectric signals were obtained from samples based on hydroxyapatite (HAp) and collagen (C) containing different glucose (G) concentrations. HAp was obtained by coprecipitation using Ca2+ and HPO42- as precursor ions in solution. C and G were added at the beginning of the coprecipitation method during the HAp growth. The presence of glucose in HAp and collagen samples drastically reduces the voltage amplitudes and considerably increases the relaxation times of the piezoelectric signals. HAp and collagen are the main constituents of bone, muscle, etc., then, it is possible to use piezoelectric technology for local and early detection of high glucose concentrations: small pressures applied by electrodes or by actuators placed in appropriate places on the body to establish a background concentration and, from this, to determine regions of the body with high local glucose concentrations: weak signals and large relaxation times are associated with a diminishing in the sensitivity, and are indicative of the presence of regions of abnormally high glucose concentrations.

Expedient secondary functions of flexible piezoelectrics for biomedical energy harvesting

Flexible piezoelectrics realise the conversion between mechanical movements and electrical power by conformally attaching onto curvilinear surfaces, which are promising for energy harvesting of biomedical devices due to their sustainable body movements and/or deformations. Developing secondary functions of flexible piezoelectric energy harvesters is becoming increasingly significant in recent years via aiming at issues that cannot be addressed or mitigated by merely increasing piezoelectric efficiencies. These issues include loose interfacial contact and pucker generation by stretching, power shortage or instability induced by inadequate mechanical energy, and premature function degeneration or failure caused by fatigue fracture after cyclic deformations. Herein, the expedient secondary functions of flexible piezoelectrics to mitigate above issues are reviewed, including stretchability, hybrid energy harvesting, and self-healing. Efforts have been devoted to understanding the state-of-the-art strategies and their mechanisms of achieving secondary functions based on piezoelectric fundamentals. The link between structural characteristic and function performance is unravelled by providing insights into carefully selected progresses. The remaining challenges of developing secondary functions are proposed in the end with corresponding outlooks. The current work hopes to help and inspire future research in this promising field focusing on developing the secondary functions of flexible piezoelectric energy harvesters.

Injectable Bone Cement Reinforced with Gold Nanodots Decorated rGO-Hydroxyapatite Nanocomposites, Augment Bone Regeneration

Interest in the development of new generation injectable bone cements having appropriate mechanical properties, biodegradability, and bioactivity has been rekindled with the advent of nanoscience. Injectable bone cements made with calcium sulfate (CS) are of significant interest, owing to its compatibility and optimal self-setting property. Its rapid resorption rate, lack of bioactivity, and poor mechanical strength serve as a deterrent for its wide application. Herein, a significantly improved CS-based injectable bone cement (modified calcium sulfate termed as CS_mod ), reinforced with various concentrations (0-15%) of a conductive nanocomposite containing gold nanodots and nanohydroxyapatite decorated reduced graphene oxide (rGO) sheets (AuHp@rGO), and functionalized with vancomycin, is presented. The piezo-responsive cement exhibits favorable injectability and setting times, along with improved mechanical properties. The antimicrobial, osteoinductive, and osteoconductive properties of the CS_mod cement are confirmed using appropriate in vitro studies. There is an upregulation of the paracrine signaling mediated crosstalk between mesenchymal stem cells and human umbilical vein endothelial cells seeded on these cements. The ability of CS_mod to induce endothelial cell recruitment and augment bone regeneration is evidenced in relevant rat models. The results imply that the multipronged activity exhibited by the novel-CS_mod cement would be beneficial for bone repair.

Bioactivity Enhancement of Plasma-Sprayed Hydroxyapatite Coatings through Non-Contact Corona Electrical Charging

Atmospheric plasma spray (APS) remains the only certified industrial process to produce hydroxyapatite (Hap) coatings on orthopaedic and dental implants intended for commercialization. Despite the established clinical success of Hap-coated implants, such as hip and knee arthroplasties, a concern is being raised regarding the failure and revision rates in younger patients, which are increasing rapidly worldwide. The lifetime risk of replacement for patients in the 50-60 age interval is about 35%, which is significantly higher than 5% for patients aged 70 or older. Improved implants targeted at younger patients are a necessity that experts have been alerted to. One approach is to enhance their bioactivity. For this purpose, the method with the most outstanding biological results is the electrical polarization of Hap, which remarkably accelerates implant osteointegration. There is, however, the technical challenge of charging the coatings. Although this is straightforward on bulk samples with planar faces, it is not easy on coatings, and there are several problems regarding the application of electrodes. To the best of our knowledge, this study demonstrates, for the first time, the electrical charging of APS Hap coatings using a non-contact, electrode-free method: corona charging. Bioactivity enhancement is observed, establishing the promising potential of corona charging in orthopedics and dental implantology. It is found that the coatings can store charge at the surface and bulk levels up to high surface potentials (>1000 V). The biological in vitro results show higher Ca²⁺ and P⁵⁺ intakes in charged coatings compared to non-charged coatings. Moreover, a higher osteoblastic cellular proliferation is promoted in the charged coatings, indicating the promising potential of corona-charged coatings when applied in orthopedics and dental implantology.

Thickness effect of an alumina-zirconia-mullite composite coating on the properties of zirconia

It is predicted that the thickness of a coating has major effects on a substrate in terms of mechanical and thermal properties. In this study, an Al₂O₃-ZrO₂-SiO₂ slurry was prepared as a coating material, which formed an alumina-zirconia-mullite composite coating after sintering. The alumina-zirconia-mullite composite coating was coated on a zirconia substrate to generate compressive stress in the coating due to the mismatch of the coefficient of thermal expansion (CTE). A series of coated samples with different coating thicknesses from ∼10 μm to ∼200 μm were prepared to investigate the effects of coating thickness. The residual compressive stress, thermal conductivity, CTE, and Young's modulus of the coating material were determined by relative methods, and the flexural strength of the coated and uncoated samples was measured by 3-point bending. The strength of the coated samples was 1362.98 ± 30.29 MPa, which is a 54.07% enhancement compared to the uncoated samples. The thermal conductivity of the coated samples was also increased compared to that of the uncoated samples. For a given thickness of the substrate of 2 mm, there was an optimum thickness of the coating of 90 μm, which showed the greatest strength compared to the other samples. Coatings that were too thin or too thick did not show the best reinforcement. Moreover, the porosity of the coated samples was also determined and discussed in this study. Comparison samples without SiO₂ were also manufactured, and their flexural strength and thermal conductivity were found to not be as good as the samples with SiO₂.

Complex Impedance and Modulus Analysis on Porous and Non-Porous Scaffold Composites Due to Effect of Hydroxyapatite/Starch Proportion

This study aims to investigate the electric responses (complex modulus and complex impedance analysis) of hydroxyapatite/starch bone scaffold as a function of hydroxyapatite/starch proportion and the microstructural features. Hence, the non-porous and porous hydroxyapatite/starch composites were fabricated with various hydroxyapatite/starch proportions (70/30, 60/40, 50/50, 40/60, 30/70, 20/80, and 10/90 wt/wt%). Microstructural analysis of the porous hydroxyapatite/starch composites was carried out by using scanning electron microscopy. It shows that the formation of hierarchical porous microstructures with high porosity is more significant at a high starch proportion. The complex modulus and complex impedance analysis were conducted to investigate the electrical conduction mechanism of the hydroxyapatite/starch composites via dielectric spectroscopy within a frequency range from 5 MHz to 12 GHz. The electrical responses of the hydroxyapatite/starch composites are highly dependent on the frequency, material proportion, and microstructures. High starch proportion and highly porous hierarchical microstructures enhance the electrical responses of the hydroxyapatite/starch composite. The material proportion and microstructure features of the hydroxyapatite/starch composites can be indirectly reflected by the simulated electrical parameters of the equivalent electrical circuit models.

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.

Current Development in Biomaterials-Hydroxyapatite and Bioglass for Applications in Biomedical Field: A Review

Inorganic biomaterials, including different types of metals and ceramics are widely used in various fields due to their biocompatibility, bioactivity, and bioresorbable capacity. In recent years, biomaterials have been used in biomedical and biological applications. Calcium phosphate (CaPs) compounds are gaining importance in the field of biomaterials used as a standalone material or in more complex structures, especially for bone substitutes and drug delivery systems. The use of multiple dopants into the structure of CaPs compounds can significantly improve their in vivo and in vitro activity. Among the general information included in the Introduction section, in the first section of this review paper, the authors provided a background on the development of hydroxyapatite, methods of synthesis, and its applications. The advantages of using different ions and co-ions for substitution into the hydroxyapatite lattice and their influence on physicochemical, antibacterial, and biological properties of hydroxyapatite are also presented in this section of the review paper. Larry Hench's 45S5 Bioglass®, commercially named 45S5, was the first bioactive glass that revealed a chemical bond with bone, highlighting the potential of this biomaterial to be widely used in biomedicine for bone regeneration. The second section of this article is focused on the development and current products based on 45S5 Bioglass®, covering the historical evolution, importance of the sintering method, hybrid bioglass composites, and applications. To overcome the limitations of the original biomaterials, studies were performed to combine hydroxyapatite and 45S5 Bioglass® into new composites used for their high bioactivity and improved properties. This particular type of combined hydroxyapatite/bioglass biomaterial is discussed in the last section of this review paper.

3D Bioprinted Hydroxyapatite or Graphene Oxide Containing Nanocellulose-Based Scaffolds for Bone Regeneration

Bone tissue is usually damaged after big traumas, tumors, and increasing aging-related diseases such as osteoporosis and osteoarthritis. Current treatments are based on implanting grafts, which are shown to have several inconveniences. In this regard, tissue engineering through the 3D bioprinting technique has arisen to manufacture structures that would be a feasible therapeutic option for bone regenerative medicine. In this study, nanocellulose-alginate (NC-Alg)-based bioink is improved by adding two different inorganic components such as hydroxyapatite (HAP) and graphene oxide (GO). First, ink rheological properties and biocompatibility are evaluated as well as the influence of the sterilization process on them. Then, scaffolds are characterized. Finally, biological studies of embedded murine D1 mesenchymal stem cells engineered to secrete erythropoietin are performed. Results show that the addition of both HAP and GO prevents NC-Alg ink from viscosity lost in the sterilization process. However, GO is reduced due to short cycle autoclave sterilization, making it incompatible with this ink. In addition, HAP and GO have different influences on scaffold architecture and surface as well as in swelling capacity. Scaffolds mechanics, as well as cell viability and functionality, are promoted by both elements addition. Additionally, GO demonstrates an enhanced bone differentiation capacity.

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.

Calcium Orthophosphate (CaPO4)-Based Bioceramics: Preparation, Properties, and Applications

Various types of materials have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A short time later, such synthetic biomaterials were called bioceramics. Bioceramics can be prepared from diverse inorganic substances, but this review is limited to calcium orthophosphate (CaPO4)-based formulations only, due to its chemical similarity to mammalian bones and teeth. During the past 50 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the CaPO4-based implants would remain biologically stable once incorporated into the skeletal structure or whether they would be resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed, and such formulations became an integrated part of the tissue engineering approach. Now, CaPO4-based scaffolds are designed to induce bone formation and vascularization. These scaffolds are usually porous and harbor various biomolecules and/or cells. Therefore, current biomedical applications of CaPO4-based bioceramics include artificial bone grafts, bone augmentations, maxillofacial reconstruction, spinal fusion, and periodontal disease repairs, as well as bone fillers after tumor surgery. Prospective future applications comprise drug delivery and tissue engineering purposes because CaPO4 appear to be promising carriers of growth factors, bioactive peptides, and various types of cells.

DLP Fabrication of Zirconia Scaffolds Coated with HA/β-TCP Layer: Role of Scaffold Architecture on Mechanical and Biological Properties

In order to merge high-mechanical properties and suitable bioactivity in a single scaffold, zirconia porous structures are here coated with a hydroxyapatite layer. The digital light processing (DLP) technique is used to fabricate two types of scaffolds: simple lattice structures, with different sizes between struts (750, 900 and 1050 µm), and more complex trabecular ones, these latter designed to better mimic the bone structure. Mechanical tests performed on samples sintered at 1400 °C provided a linear trend with a decrease in the compressive strength by increasing the porosity amount, achieving compressive strengths ranging between 128–177 MPa for lattice scaffolds and 34 MPa for trabecular ones. Scaffolds were successfully coated by dipping the sintered samples in a hydroxyapatite (HA) alcoholic suspension, after optimizing the HA solid loading at 20 wt%. After calcination at 1300 °C, the coating layer, composed of a mixture of HA and β-TCP (β-TriCalcium Phospate) adhered well to the zirconia substrate. The coated samples showed a proper bioactivity, well pronounced after 14 days of immersion into simulated body fluid (SBF), with a more homogeneous apatite layer formation into the trabecular samples compared to the lattice ones.

Permanently polarized hydroxyapatite, an outstanding catalytic material for carbon and nitrogen fixation

Hydroxyapatite (HAp) is a well-known ceramic material widely used in the biomedical field. This review summarizes the very recent developments on permanently polarized HAp (pp-HAp), a HAp variety with tuned electrical properties that confer remarkable catalytic activity. pp-HAp is obtained by applying a thermal stimulation polarization process (TSP), which consists on a DC electric voltage of 500 V at 1000 °C, to previously sintered HAp. The TSP not only increases the crystallinity, reducing the defects in the crystal lattice, but also creates charges that accumulate at the crystalline boundaries and at the surface of microscopic grains, boosting the electrical conductivity. Finally, the successful utilization of pp-HAp in the catalytic fixation of carbon and nitrogen from CO₂ and N₂ gases, respectively, is reported and the formation of different products of chemical interest (e.g. amino acids, ethanol and ammonium) as a function of the reaction conditions (i.e. feeding gases and presence/absence of UV illumination) and catalyst plasticity is discussed. pp-HAp exhibits important advantages with respect to other consolidated catalysts, which drastically increases the final energetic net balance of the reactions.

Novel Trends into the Development of Natural Hydroxyapatite-Based Polymeric Composites for Bone Tissue Engineering

In recent years, the number of people needing bone replacements for the treatment of defects caused by chronic diseases or accidents has continuously increased. To solve these problems, tissue engineering has gained significant attention in the biomedical field, by focusing on the development of suitable materials that improve osseointegration and biologic activity. In this direction, the development of an ideal material that provides good osseointegration, increased antimicrobial activity and preserves good mechanical properties has been the main challenge. Currently, bone tissue engineering focuses on the development of materials with tailorable properties, by combining polymers and ceramics to meet the necessary complex requirements. This study presents the main polymers applied in tissue engineering, considering their advantages and drawbacks. Considering the potential disadvantages of polymers, improving the applicability of the material and the combination with a ceramic material is the optimum pathway to increase the mechanical stability and mineralization process. Thus, ceramic materials obtained from natural sources (e.g., hydroxyapatite) are preferred to improve bioactivity, due to their similarity to the native hydroxyapatite found in the composition of human bone.

Microstructural, electrical and biological activity in [Formula: see text] ceramic composites designed for tissue engineering applications

The article investigates electrically active ceramic composite of [Formula: see text] (HAP) and [Formula: see text] (BST) for biomedical applications. The study is a systematic blend of the materials science aspect of composites with a special focus on the dielectric and biological properties and their relationships. The article emphasized primarily extracting the dielectric constant ([Formula: see text] of the specimens (that lay in the range of 3-65) and related them to microstructural properties like the grain size and at.% of BST. A broad outlook on the importance of [Formula: see text] in determining the suitability of bioceramics for clinical applications is presented. Bioactivity analysis of the specimens led to probing the surface charges (that were negative), and it was found crucial to the growth of dense apatite layers. Furthermore, the cytocompatibility of the specimens displayed cell viability above 100% for Day 1, which increased substantially for Day 3. To reveal other biological properties of the composites, protein adsorption studies using bovine serum albumin (BSA) and fetal bovine serum (FBS) was carried out. Electrostatic interactions govern the adsorption, and the mathematical dependence on surface charges is linear. The protein adsorption is also linearly correlated with the [Formula: see text], intrinsic to the biomaterials. We delve deeper into protein-biomaterials interactions by considering the evolution of the secondary structure of BSA adsorbed into the specimens. Based on the investigations, 20 at.% HAP-80 at.% BST (20H-80B) was established as a suitable composite comprising the desired features of HAP and BST. Such explorations of electrical and biological properties are interesting for modulating the behavior of bioceramic composites. The results project the suitability of 20H-80B for designing electrically active smart scaffolds for the proposed biomedical applications and are expected to incite further clinical trials.

Synthesis and Characterization of Yttrium-Doped Hydroxyapatite Nanoparticles and Their Potential Antimicrobial Activity

This study reports a detailed analysis of the yttrium doping effects into hydroxyapatite (HAp) nano-structures at different amounts (e.g., 0, 1, 2.5, 5, 7.5, 10, and 15%) on the structural, spectroscopic, dielectric, and antimicrobial properties. For this purpose, seven HAp samples having the Y-contents mentioned above were prepared using the microwave-assisted sol-gel precipitation technique. The structure of synthesized samples was fully described via X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transforms infrared (FTIR). Raman spectroscopy and dielectric measurements were used to characterize the spectroscopic properties. Furthermore, the samples’ antimicrobial features have been assisted through the agar disk diffusion technique. This study showed that the crystallinity decreased with the adding of Y-ions inside the HAp matrix. The Y-contents have influenced the crystallite size, lattice parameters, dislocation density, lattice strain, and unit cell volume. The surface morphology is composed of the agglomerated smaller particles. Remarkable changes in the dielectric properties were observed with the adding of Y-ions. The alternating current conductivity obeys the Jonscher’s relation. Y-doped hydroxyapatite nanoparticles have a considerable inhibitory effect against bacteria and fungi (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans). The Y-doped hydroxyapatite nanoparticles are a promising material for bone cement engineering with a potential bio-activity

Variable Range Hopping in SrTiO3-Ca10(PO4)6(OH)2 Bio-Ceramic Composites

We investigate the electrical properties in ceramics, focusing primarily on the conductivity mechanisms crucial to bio-electrets' service life. A biocompatible ceramic composite of varying concentrations of SrTiO₃ (ST) and Ca₁₀(PO₄)₆(OH)₂ (HAP) is developed. By X-ray diffraction, we establish the microstructural and phase evolution of the bio-composites. The crystallite sizes are found to increase with the increasing concentration of ST in the composites. The composites' micrograph reveals the presence of pores, and the grain sizes calculated from it are found to follow a trend similar to the crystallite size. The conduction mechanisms in the composites are studied to explore the composites' electrical properties from the perspective of biological applications. The conductivity is very low (≃10^-8 S/cm), and the porous structure of the composites revealed from the micrographs is one of the factors for such low conductivity. From a plethora of conduction mechanisms, Motts' variable range hopping (VRH) conduction is projected as the most appropriate mechanism that appropriately describes the conduction process in the composites. Motts' VRH is also related to the polarization mechanism associated with the development of electrets. Our study points toward the practical potential of applying the designed bio-composites in generating bio-electrets or understanding the electrical properties that are at the forefront of research in designing electro-active smart scaffolds for bone tissue engineering applications.

Functionalized Porous Hydroxyapatite Scaffolds for Tissue Engineering Applications: A Focused Review

Biomaterials have been widely used in tissue engineering applications at an increasing rate in recent years. The increased clinical demand for safe scaffolds, as well as the diversity and availability of biomaterials, has sparked rapid interest in fabricating diverse scaffolds to make significant progress in tissue engineering. Hydroxyapatite (HAP) has drawn substantial attention in recent years owing to its excellent physical, chemical, and biological properties and facile adaptable surface functionalization with other innumerable essential materials. This focused review spotlights a brief introduction on HAP, scope, a historical outline, basic structural features/properties, various synthetic strategies, and their scientific applications concentrating on functionalized HAP in the diverse area of tissue engineering fields such as bone, skin, periodontal, bone tissue fixation, cartilage, blood vessel, liver, tendon/ligament, and corneal are emphasized. Besides clinical translation aspects, the future challenges and prospects of HAP based biomaterials involved in tissue engineering are also discussed. Furthermore, it is expected that researchers may find this review expedient in gaining an overall understanding of the latest advancement of HAP based biomaterials.

Electrical therapies act on the Ca2+ /CaM signaling pathway to enhance bone regeneration with bioactive glass [S53P4] and allogeneic grafts

This study aimed to investigate the application of low-intensity electrostimulation (ES) and electromagnetic stimulation (EM) associated with bioactive glass (BG) or allogeneic grafts (BB) in bone regeneration. A cell viability test on osteoblasts (UMR-106) was performed in the presence of BB and BG grafts associated with ES (10 μA/5 min) and EM (500 Hz/2 min). Critical defects (25 mm² ) in calvaria were generated in male Wistar rats, and bone regeneration was evaluated on the 30th, 60th, and 120th days after surgery. Cell proliferation increased with the application of ES in both grafts and after EM with BG. Bone remodeling was more effective using the allogeneic graft in both therapies, with increased angiogenesis, osteoblast proliferation, and OPN expression in the BB + EM group. A higher number of osteoblasts and osteoclasts, and an increase in bone sialoprotein, Runx-2, and Opn gene expression were found in the BB + ES group. The BG graft associated with EM therapy had an increased proliferation of osteoblasts and increased expression of Runx-2 and Opn. Groups that had BG and ES therapy had increased numbers of osteoblasts, osteoclasts, and increased OPN expression. The expression of voltage-gated calcium channels increased in groups with ES, while calmodulin expression increased in therapies without grafting. ES and EM therapies favored the repair of bone defects upon grafting by improving angiogenesis, osteogenic gene expression, and tissue reorganization. Despite activating different pathways, both therapies increased the intracellular concentrations of calmodulin, leading to cell proliferation and bone regeneration.

Impedance Spectroscopy and ac Conductivity in Ba0.5Sr0.5TiO3-Ca10(PO4)6(OH)2 Ceramic Composites: An Electrical Approach to Unveil Biocomposites

We report bioceramic composites of varying concentrations of Ba_0.5Sr_0.5TiO₃ (BST) and Ca₁₀(PO₄)₆(OH)₂ (HAP) for the analysis of electrical properties. The motivation is to predict the suitability of the composites for bio-electrets or the practical possibility in designing electro-active scaffolds. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) are used to analyze the microstructural evolution of the composites. A systematic variation in the grain and crystallite sizes is noticed from the FESEM and XRD, along with the presence of Sr₅(PO₄)₃(OH) (SAP). The temperature and frequency variations of the dielectric properties of the composites are studied. Modeling of the dielectric properties with the microstructural properties and at. % of the monolith BST is presented. Cole-Cole formalism is adopted to model the electrical behavior of the synthesized composites. Furthermore, the ac conductivity analysis reveals that Mott's variable range hopping (VRH) conduction is the most appropriate formalism that successfully describes the conduction process. The established Mott's VRH is also related to the polarization mechanisms active in the specimens. Our study projects a correlation between the electrical and biological properties by predicting the protein adsorption behavior from the perspective of impedance spectroscopy.

Bioimpedance Spectroscopy: Basics and Applications

In this review, we aim to introduce the reader to the technique of electrical impedance spectroscopy (EIS) with a focus on its biological, biomaterials, and medical applications. We explain the theoretical and experimental aspects of the EIS with the details essential for biological studies, i.e., interaction of metal electrodes with biological matter and liquids, strategies of measurement rate increasing, noise reduction in bio-EIS experiments, etc. We also give various examples of successful bio-EIS practical implementations in science and technology, from whole-body health monitoring and sensors for vision prosthetic care to single living cell examination platforms, virus disease research, biomolecules detection, and implementation of novel biomaterials. The present review can be used as a bio-EIS tutorial for students as well as a handbook for scientists and engineers because of the extensive references covering the contemporary research papers in the field.

Black phosphorus-based 2D materials for bone therapy

Since their discovery, Black Phosphorus (BP)-based nanomaterials have received extensive attentions in the fields of electromechanics, optics and biomedicine, due to their remarkable properties and excellent biocompatibility. The most essential feature of BP is that it is composed of a single phosphorus element, which has a high degree of homology with the inorganic components of natural bone, therefore it has a full advantage in the treatment of bone defects. This review will first introduce the source, physicochemical properties, and degradation products of BP, then introduce the remodeling process of bone, and comprehensively summarize the progress of BP-based materials for bone therapy in the form of hydrogels, polymer membranes, microspheres, and three-dimensional (3D) printed scaffolds. Finally, we discuss the challenges and prospects of BP-based implant materials in bone immune regulation and outlook the future clinical application.

Impact of Dopants on the Electrical and Optical Properties of Hydroxyapatite

This chapter deals with the effect of alternating electrical current on hydroxyapatite [HAp, Ca10(PO4)6(OH)2] and doped HAp along with their optical response and the processes involved. The dielectric constant, permittivity and ac conductivity were analyzed to have an insight into the surface charge polarization phenomenon. Further, the magnitude and the polarity of the surface charges, microstructure, and phases also play significant role in the cell proliferation and growth on the implants. Besides, the mechanism behind the electrical properties and the healing of bone fracture are discussed. The influence of various dopants on the optical properties of HAp viz., absorbance, transmission, band gaps and defects energy levels are analyzed along with the photoluminescence and excitation independent emission. In the future outlook, the analysis of effect of doping is summarized and its impact on the next generation biomaterials are elucidated.

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.

Effect of Printing Parameters on Dimensional Error and Surface Roughness Obtained in Direct Ink Writing (DIW) Processes

Prostheses made from ceramic materials have the advantages of producing little debris and having good durability, compared with those made from metal and plastic. For example, hip prostheses require a porous external area that allows their fixation by means of osseointegration and a solid internal area that will be in contact with the femoral head. The manufacturing of complex ceramic shapes, by means of machining processes, for example, is complicated and can lead to breakage of the parts because of their fragility. The direct ink writing (DIW) process allows the printing of ceramic pastes into complex shapes that achieve their final strength after a heat treatment operation. This paper studies both the dimensional error and surface finish of porous zirconia prismatic parts prior to sintering. The variables considered are infill, layer height, printing speed, extrusion multiplier and bed temperature. The responses are the dimensional error of the lateral walls of the samples and an areal roughness parameter, the arithmetical mean height, Sa. Mathematical models are found for each response, and multiobjective optimization is carried out by means of the desirability function. The dimensional error depends mainly on the interaction between layer height and infill, while the roughness on the interaction between infill and printing speed. Thus, infill is an important factor for both responses. In the future, the behavior of compact printed parts will be addressed.

Hierarchically Porous Hydroxyapatite Hybrid Scaffold Incorporated with Reduced Graphene Oxide for Rapid Bone Ingrowth and Repair

Hydroxyapatite (HA), the traditional bone tissue replacement material was widely used in the clinical treatment of bone defects because of its excellent biocompatibility. However, the processing difficulty and poor osteoinductive ability greatly limit the application of HA. Although many strategies have been reported to improve the machinability and osteointegration ability, the performance including mechanical strength, porosity, cell adhesion, etc. of material still can not meet the requirements. In this work, a soft template method was developed and a porous scaffold with hierarchical pore structure, nano surface morphology, suitable porosity and pore size, and good biomechanical strength was successfully prepared. The hierarchical pore structure is beneficial for cell adhesion, fluid transfer, and cell ingrowth. Moreover, the loaded reduced graphene oxide (rGO) can improve the adhesion and promote the proliferation and spontaneous osteogenic differentiation bone marrow mesenchymal stem cells. The scaffold is then crushed, degraded and wrapped by the newly formed bone and the newly formed bone gradually replaces the scaffold. The degradation rate of the scaffold well matches the rate of the new bone formation. The hierarchical porous HA/rGO composite scaffolds can greatly accelerate the bone ingrowth in the scaffold and bone repair in critical bone defects, thus providing a clinical potential candidate for large segment bone tissue engineering.