Unravelling Doped Biphasic Calcium Phosphate: Synthesis to Application

Physico-Chemical and Biological Features of Fluorine-Substituted Hydroxyapatite Suspensions

Infections related to orthopedic/stomatology surgery are widely recognized as a significant health concern. Therefore, the development of new materials with superior biological properties and good stability could represent a valuable alternative to the classical treatments. In this paper, the fluorine-substituted hydroxyapatite (FHAp) suspension, with the chemical formula Ca10(PO4)6(OH)2-2xF2x (where x = 0.05), was prepared using a modified coprecipitation technique. Stability studies were conducted by zeta potential and ultrasound measurements for the first time. The X-ray diffraction (XRD) patterns of FHAp powders displayed a hexagonal structure akin to that of pure hydroxyapatite (HAp). The XPS general spectrum revealed peaks corresponding to the constituent elements of fluorine-substituted hydroxyapatite such as calcium, phosphorus, oxygen, and fluorine. The purity of the obtained FHAp samples was confirmed by energy-dispersive X-ray spectroscopy (EDS) studies. The FHAp morphology was evaluated by scanning electron microscopy (SEM) measurements. Fourier-transform infrared spectroscopy (FTIR) studies were performed in order to study the vibrational properties of the FHAp samples. The FHAp suspensions were tested for antibacterial activity against reference strains such as Staphylococcus aureus 25923 ATCC, Escherichia coli ATCC 25922, and Candida albicans ATCC 10231. Additionally, the biocompatibility of the FHAp suspensions was assessed using human fetal osteoblastic cells (hFOB 1.19 cell line). The results of our biological tests suggest that FHAp suspensions are promising candidates for the future development of new biocompatible and antimicrobial agents for use in the biomedical field.

Combination of a Synthetic Bioceramic Associated with a Polydioxanone-Based Membrane as an Alternative to Autogenous Bone Grafting

The purpose of this study was to evaluate the repair process in rat calvaria filled with synthetic biphasic bioceramics (Plenum® Osshp-70:30, HA:βTCP) or autogenous bone, covered with a polydioxanone membrane (PDO). A total of 48 rats were divided into two groups (n = 24): particulate autogenous bone + Plenum® Guide (AUTOPT+PG) or Plenum® Osshp + Plenum® Guide (PO+PG). A defect was created in the calvaria, filled with the grafts, and covered with a PDO membrane, and euthanasia took place at 7, 30, and 60 days. Micro-CT showed no statistical difference between the groups, but there was an increase in bone volume (56.26%), the number of trabeculae (2.76 mm), and intersection surface (26.76 mm2) and a decrease in total porosity (43.79%) in the PO+PG group, as well as higher values for the daily mineral apposition rate (7.16 µm/day). Histometric analysis presented material replacement and increased bone formation at 30 days compared to 7 days in both groups. Immunostaining showed a similar pattern between the groups, with an increase in proteins related to bone remodeling and formation. In conclusion, Plenum® Osshp + Plenum® Guide showed similar and sometimes superior results when compared to autogenous bone, making it a competent option as a bone substitute.

Improved electrochemical detection of levofloxacin in diverse aquatic samples using 3D flower-like Co@CaPO4 nanospheres

The misuse of antibiotics has become a concerning environmental issue, posing a significant threat to public health. Levofloxacin (LFX), a fluoroquinolone antibiotic, is particularly worrisome due to its detrimental impact on human health and the ecosystem. Therefore, the selective and accurate identification of LFX is of utmost importance. In this study, we have developed an electrochemical sensor based on cobalt-doped calcium phosphate (Co@CaHPO) for the sensitive and selective detection of LFX in various water samples. Under optimized conditions, the Co@CaHPO-modified glassy carbon electrode (GCE) exhibited exceptional electrochemical activity, low charge transfer resistance, and a fast electron transfer rate, outperforming the unmodified GCE. The proposed Co@CaHPO-modified GCE demonstrated remarkable electrochemical characteristics, including a wide linear range (0.3-460 μM) and a lower detection limit (0.151 μM) with high sensitivity (0.676 μAμM-1 cm2). This detection approach may enable the direct detection of LFX in the pharmaceutical environment. Furthermore, the resulting sensor exhibited good selectivity, excellent cyclic and storage stability, reproducibility, and repeatability. The practical application of this LFX sensor can be extended to various water samples, yielding reliable and satisfactory results.

β-tricalcium phosphate synthesized in organic medium for controlled release drug delivery application in bio-scaffolds

β-tricalcium phosphate (β-TCP) was synthesized in an organic medium (acetone) to obtain a single-phase product while calcium carbonate (CaCO3) and ortho-phosphoric acid (H3PO4) were the sources of Ca, and P, respectively. The synthesized β-TCP was characterized by employing a number of sophisticated techniques vis. XRD, FTIR, FESEM, VSM and UV-Vis-NIR spectrometry. On the other hand, cytotoxicity, hemolysis, and antimicrobial activity for Gram-negative as well as Gram-positive (E. coli and S. aureus) bacteria were explored using this synthesized sample in powder format. However, to assess the drug loading and releasing profile, these powdered samples were first compressed into disks followed by sintering at 900 °C. Prior to loading the drug, porosity, density, and water absorbance characteristics of the scaffolds were examined in deionized water. Both loading and releasing profiles of the antibiotic (ciprofloxacin) were looked over at various selected time intervals which were continued up to 28 days. The observed results revealed that 2.87% of ciprofloxacin was loaded while 37% of this loaded drug was released within the selected time frame as set in this study. The scaffold was also immersed in SBF solution maintaining identical interim periods for the bioactivity evaluation. Furthermore, all three types of samples (e.g. drug-loaded, drug-released, and SBF-soaked) were characterized by FESEM and EDX while antimicrobial activity (against E. coli, S. typhi, and S. aureus) and efficacy to prevent hemolysis were also investigated. The drug-loaded scaffold presented a larger inhibition zone than the standard for all three types of microbes. Although powdered β-TCP was inactive in killing the Gram-negative bacteria, surprisingly the drug-released scaffold showed an inhibition zone.

In vitro hemocompatibility studies on small-caliber stents for cardiovascular applications

The doping of biologically meaningful ions into biphasic calcium phosphate (BCP) bioceramics, which exhibit biocompatibility with human body parts, has led to their effective use in biomedical applications in recent years. Doping with metal ions while changing the characteristics of the dopant ions, an arrangement of various ions in the Ca/P crystal structure. In our work, small-diameter vascular stents based on BCP and biologically appropriate ion substitute-BCP bioceramic materials were developed for cardiovascular applications. The small-diameter vascular stents were created using an extrusion process. FTIR, XRD, and FESEM were used to identify the functional groups, crystallinity, and morphology of the synthesized bioceramic materials. In addition, investigation of the blood compatibility of the 3D porous vascular stents was carried out via hemolysis. The outcomes indicate that the prepared grafts are appropriate for clinical requirements.

In silico study on probing atomistic insights into structural stability and tensile properties of Fe-doped hydroxyapatite single crystals

Hydroxyapatite (HA, Ca10PO4(OH)2) is a widely explored material in the experimental domain of biomaterials science, because of its resemblance with natural bone minerals. Specifically, in the bioceramic community, HA doped with multivalent cations (e.g., Mg2+, Fe2+, Sr2+, etc.) has been extensively investigated in the last few decades. Experimental research largely established the critical role of dopant content on mechanical and biocompatibility properties. The plethora of experimental measurements of mechanical response on doped HA is based on compression or indentation testing of polycrystalline materials. Such measurements, and more importantly the computational predictions of mechanical properties of single crystalline (doped) HA are scarce. On that premise, the present study aims to build atomistic models of Fe2+-doped HA with varying Fe content (10, 20, 30, and 40 mol%) and to explore their uniaxial tensile response, by means of molecular dynamics (MD) simulation. In the equilibrated unit cell structures, Ca(1) sites were found to be energetically favourable for Fe2+ substitution. The local distribution of Fe2+ ions significantly affects the atomic partial charge distribution and chemical symmetry surrounding the functional groups, and such signatures are found in the MD analyzed IR spectra. The significant decrease in the intensity of the IR bands found in the Fe-doped HA together with band splitting, because of the symmetry changes in the crystal structure. Another important objective of this work is to computationally predict the mechanical response of doped HA in their single crystal format. An interesting observation is that the elastic anisotropy of undoped HA was not compromised with Fe-doping. Tensile strength (TS) is systematically reduced in doped HA with Fe2+ dopant content and a decrease in TS with temperature can be attributed to the increased thermal agitation of atoms at elevated temperatures. The physics of the tensile response was rationalized in terms of the strain dependent changes in covalent/ionic bond framework (Ca-P distance, P-O bond strain, O-P-O angular strain, O-H bond distance). Further, the dynamic changes in covalent bond network were energetically analyzed by calculating the changes in O-H and P-O bond vibrational energy. Summarizing, the current work establishes our foundational understanding of the atomistic phenomena involved in the structural stability and tensile response of Fe-doped HA single crystals.

Calcium Phosphate Functionalization and Applications in Dentistry

The oral and maxillofacial hard tissues support the maxillofacial shape and serve as the foundation for functional activities. Defects in these tissues not only impair patients’ ability to perform their normal physiological functions but also have a significant negative impact on their psychological well-being. Moreover, these tissues have a limited capacity for self-healing, necessitating the use of artificial materials to repair defects. Calcium phosphate is a fine-grained inorganic biomineral found in vertebrate teeth and bones that has a comparable composition to human hard tissues. Calcium phosphate materials are biocompatible, bioactive, and osteogenic for hard tissue repair, despite drawbacks such as poor mechanical qualities, limiting their clinical efficacy and application. With the advancement of materials science and technology, numerous techniques have been developed to enhance the characteristics of calcium phosphate, and one of them is functionalization. Calcium phosphate can be functionally modified by changing its size, morphology, or composition through various preparation processes to achieve multifunctionality and improve physical and chemical properties, biocompatibility, and osteogenic potential. The purpose of this review is to provide new ideas for the treatment of oralmaxillofacial hard tissue defects and deficiencies by summarizing the functionalization strategies of calcium phosphate materials and their applications in dentistry.

Plasma sprayed fluoride and zinc doped hydroxyapatite coated titanium for load-bearing implants

Titanium (Ti) alloys show excellent fatigue and corrosion resistance, high strength to weight ratio, and no toxicity; however, poor osseointegration ability of Ti may lead to implant loosening in vivo. Plasma spraying of hydroxyapatite [HA, Ca10 (PO4)6 (OH)2] coating on Ti surfaces is commercially used to enhance osseointegration and the long-term stability of these implants. The biological properties of HA can be improved with the addition of both cationic and anionic dopants, such as zinc ions (Zn2+) and fluoride (F-). However, the hygroscopic nature of fluoride restricts its utilization in the radiofrequency (RF) plasma spray process. In addition, the amount of doping needs to be optimized to ensure cytocompatibility. We have fabricated zinc and fluoride doped HA-coated Ti6Al4V (Ti64) to mitigate these challenges using compositional and parametric optimizations. The RF induction plasma spraying method is utilized to prepare the coatings. Multiple parametric optimizations with amplitude and frequency during the processing result in coating thicknesses between 80 and 145 μm. No adverse effects on the adhesion properties of the coating are noticed because of doping. The antibacterial efficacy of each composition is tested against S. aureus for 24, 48, and 72 h, and showed that the addition of zinc oxide and calcium fluoride to HA leads to nearly 70 % higher antibacterial efficacy than pure HA-coated samples. The addition of osteogenic Zn2+and F- leads to 1.5 times higher osteoblast viability for the doped samples than pure HA-coated samples after 7-days of cell culture. Zn2+ and F- doped HA-coated Ti64 with simultaneous improvements in anti-bacterial efficacy and in vitro biocompatibility can find application in load-bearing implants, particularly in revision surgeries and immune-compromised patients.

Synthesis and Characterization of Calcium Phosphate Materials Derived from Eggshells from Different Poultry with and without the Eggshell Membrane

Calcium phosphate materials such as hydroxyapatite (HA) or tricalcium phosphate (β-TCP) are highly attractive due to their multitude of applications in bone replacement as well as their environmental and ecological credentials. In this research, quail, hen, duck, and pigeon eggshells were used as a calcium source to obtain calcium phosphate materials via the environmentally friendly wet synthesis. Using the eggshells with the organic membrane, the biphasic calcium phosphate materials composed mainly of HA were obtained. The second mineral phase was β-TCP in the case of using quail, hen, and pigeon eggshells and octacalcium phosphate (OCP) in the case of duck eggshells. The HA content in the obtained materials depended on the amount of membrane in the eggshells and decreased in the order of pigeon, duck, hen, and quail eggshells. The eggshell membrane removal from the eggshells caused the reduced content of HA and the presence of the more soluble β-TCP or OCP phase in the obtained materials. The calcium ions release profile in the PBS buffer indicates the potential biomedical application of these materials.

A Review on Biphasic Calcium Phosphate Materials Derived from Fish Discards

This review summarizes the results reported on the production of biphasic calcium phosphate (BCP) materials derived from fish wastes (i.e., heads, bones, skins, and viscera), known as fish discards, and offers an in-depth discussion on their promising potential for various applications in many fields, especially the biomedical one. Thus, considerable scientific and technological efforts were recently focused on the capability of these sustainable materials to be transformed into economically attractive and highly valuable by-products. As a consequence of using these wastes, plenty of beneficial social effects, with both economic and environmental impact, will arise. In the biomedical field, there is a strong and continuous interest for the development of innovative solutions for healthcare improvement using alternative materials of biogenic origin. Thus, the orthopedic field has witnessed a significant development due to an increased demand for a large variety of implants, grafts, and/or scaffolds. This is mainly due to the increase of life expectancy and higher frequency of bone-associated injuries and diseases. As a consequence, the domain of bone-tissue engineering has expanded to be able to address a plethora of bone-related traumas and to deliver a viable and efficient substitute to allografts or autografts by combining bioactive materials and cells for bone-tissue ingrowth. Among biomaterials, calcium phosphate (CaP)-based bio-ceramics are widely used in medicine, in particular in orthopedics and dentistry, due to their excellent bioactive, osteoconductive, and osteointegrative characteristics. Recently, BCP materials (synthetic or natural), a class of CaP, which consist of a mixture of two phases, hydroxyapatite (HA) and beta tricalcium phosphate (β-TCP), in different concentrations, gained increased attention due to their superior overall performances as compared to single-phase formulations. Moreover, the exploitation of BCP materials from by-products of fish industry was reported to be a safe, cheap, and simple procedure. In the dedicated literature, there are many reviews on synthetic HA, β-TCP, or BCP materials, but to the best of our knowledge, this is the first collection of results on the effects of processing conditions on the morphological, compositional, structural, mechanical, and biological properties of the fish discard-derived BCPs along with the tailoring of their features for various applications.

Biphasic calcium phosphate microspheres in biomedical applications

Biphasic calcium phosphate (BCP) microspheres benefit from, on the one hand, a desired shape offering improved flowability and injectability to fill complex-shaped bone defects and on the other hand, a promising combination of bioresorbability, bioactivity, biocompatibility, osteogenesis and angiogenesis. The biofunctional characteristics of BCP microspheres are mainly controlled by varying the constitute phase ratio, porosity and surface roughness, which are all determined by the used production route and its parameters. In this paper, the manufacturing methods, properties and applications of BCP microspheres are reviewed and concluded in terms of future work directions to develop their uses in biomedicine, particularly in bone tissue regenerative and delivery applications.

Study of Electron-Nuclear Interactions in Doped Calcium Phosphates by Various Pulsed EPR Spectroscopy Techniques

Substituted calcium phosphates (CaPs) are vital materials for the treatment of bone diseases and repairing and replacement of defects in human hard tissues. In this paper, we present some applications of the rarely used pulsed electron paramagnetic resonance (EPR) and hyperfine interaction spectroscopy approaches [namely, electron spin-echo envelope modulation (ESEEM) and electron-electron double-resonance detected nuclear magnetic resonance (EDNMR)] to investigate synthetic CaPs (hydroxyapatite, tricalcium, and octacalcium phosphate) doped with various cations (Li+, Na+, Mn2+, Cu2+, Fe3+, and Ba2+). These resonance techniques provide reliable tools to obtain unique information about the presence and localization of impurity centers and values of hyperfine and quadrupole tensors. We show that revealed in CaPs by EPR techniques, radiation-induced stable nitrogen-containing species and carbonate radicals can serve as sensitive paramagnetic probes to follow CaPs' structural changes caused by cation doping. The most pulsed EPR, ESEEM, and EDNMR spectra can be detected at room temperature, reducing the costs of the measurements and facilitating the usage of pulsed EPR techniques for CaP characterization.

Direct 3D Printing of Seashell Precursor toward Engineering a Multiphasic Calcium Phosphate Bone Graft

Multiphasic calcium phosphate (Ca-P) has widely been explored for bone graft replacement. This study represents a simple method of developing osteoinductive scaffolds by direct printing of seashell resources. The process demonstrates a coagulation-assisted extrusion-based three-dimensional (3D) printing process for rapid fabrication of multiphasic calcium phosphate-incorporated 3D scaffolds. These scaffolds demonstrated an interconnected open porous architecture with improved compressive strength and higher surface area. Multiphasic calcium phosphate (Ca-P) and hydroxyapatite present in the multi-scalar naturally resourced scaffold displayed differential protein adsorption, thus facilitating cell adhesion, migration, and differentiation, resulting in enhanced deposition of the extracellular matrix. The microstructural and physicochemical attributes of the scaffolds also lead to enhanced stem cell differentiation as witnessed from gene and protein expression analysis. Furthermore, the histological study of subcutaneous implantation evidently portrays promising biocompatibility without foreign body reaction. Neo-tissue in-growth was manifested with abundant blood vessels, thus indicative of excellent vascularization. Notably, cartilaginous and proteoglycan-rich tissue deposition indicated ectopic bone formation via an endochondral ossification pathway. The hierarchical interconnected porous architectural tribology accompanied with multiphasic calcium phosphate composition manifests its successful implication in enhancing stem cell differentiation and promoting excellent tissue in-growth, thus making it a plausible alternative in bone tissue engineering applications.

Inflammation and biomaterials: role of the immune response in bone regeneration by inorganic scaffolds

The regulatory role of the immune system in maintaining bone homeostasis and restoring its functionality, when disturbed due to trauma or injury, has become evident in recent years. The polarization of macrophages, one of the main constituents of the immune system, into the pro-inflammatory or anti-inflammatory phenotype has great repercussions for cellular crosstalk and the subsequent processes needed for proper bone regeneration such as angiogenesis and osteogenesis. In certain scenarios, the damaged osseous tissue requires the placement of synthetic bone grafts to facilitate the healing process. Inorganic biomaterials such as bioceramics or bioactive glasses are the most widely used due to their resemblance to the mineral phase of bone and superior osteogenic properties. The immune response of the host to the inorganic biomaterial, which is of an exogenous nature, might determine its fate, leading either to active bone regeneration or its failure. Therefore, various strategies have been employed, like the modification of structural/chemical features or the incorporation of bioactive molecules, to tune the interplay with the immune cells. Understanding how these particular modifications impact the polarization of macrophages and further osteogenic and osteoclastogenic events is of great interest in view of designing a new generation of osteoimmunomodulatory materials that support the regeneration of osseous tissue during all stages of bone healing.

Electric Field-Mediated Fibronectin-Hydroxyapatite Interaction: A Molecular Insight

In experimental research-driven biomaterials science, the influence of different material properties (elastic stiffness, surface energy, etc.) and, to a relatively lesser extent, biophysical stimulation (electric/magnetic) on cell-material interactions has been extensively investigated. Despite the central importance of protein adsorption on cell-material interactions, the quantitative analysis to probe into the role of physicochemical factors in protein adsorption remains largely unexplored in biomaterials science. In recent studies, the critical role of electric field stimulation toward the modulation of cell functionality in implantable biomaterials has been experimentally demonstrated. Given this background, we investigated the influence of external electric field stimulation (upto 1.00 V/nm) on fibronectin (FN) adsorption on a hydroxyapatite (HA) (001) surface at 300 K using the all-atom molecular dynamics (MD) simulation method. FN adsorption was found to be governed by attractive electrostatic interactions, which changed with the electric field strength. Nonmonotonous changes in the structural integrity of FN were recorded with the change in the field strength and direction. This can be attributed to the spatial rearrangement of the positions of local charges and the global structural changes of proteins. The dipole moment vectors of FN, water, and HA quantitatively exhibited a similar pattern of orienting themselves parallel to the field direction, with field strength-dependent increase in their magnitudes. No significant change has been recorded for the radial distribution function of water surrounding FN. Field-dependent variation in the salt bridge nets and the number of hydrogen bonds between FN and HA were also examined. One of the important results in the context of cell-material interaction is that the RGD (Arg-Gly-Asp) sequence of FN was exposed to the solvent side when the field was applied along an outward direction perpendicular to the HA (001) surface. In summary, the present study provides molecular insights into the influence of electric field stimulation on phenomenological interactions involved in FN adsorption on the HA surface.

Molecular docking and molecular dynamics simulation studies on the adsorption/desorption behavior of bone morphogenetic protein-7 on the β-tricalcium phosphate surface

The adsorption/desorption behavior, and conformational and orientational changes of proteins on the surface of biomaterials are significant parameters for understanding how biomaterials perform their biological functions. In this study, for the first time, the interactions between BMP-7 and β-TCP (001) surface models with different ion-rich terminations (Ca-rich and P-rich) were investigated by molecular dynamics simulation (MD) and steered molecular dynamics simulation (SMD). The results indicated that BMP-7 preferentially interacts with both Ca-rich and P-rich β-TCP (001) surfaces at its wrist epitope residues with certain conformational changes, which led to more exposure of BMP-7 knuckle epitope residues to the environment and facilitation for binding to the type II receptor. Compared to the P-rich surface, it is speculated that the Ca-rich surface was more conducive to BMP-7 signal transduction since the upright orientation of the protein adsorption would lead to smaller hindrance for receptor binding. This study provided more atomistic and molecular information for better understanding the process of Ca-P surfaces affecting BMP-7 biological properties and further interpreted the osteoinductive mechanism from the perspective of growth factor adsorption. Moreover, the docking screening method adopted in this study is of guiding significance to the design and development of bioactive materials.

Effect of Foreign Ion Substitution and Micropore Tuning in Robocasting Single-Phase Bioceramic Scaffolds on the Physicochemical Property and Vascularization

The inorganic powder slurry extrusion printing technique known as robocasting is an interesting method to fabricate complex porous architectures whereby feedstocks containing organic binders and powders are printed and the resulting scaffolds are subjected to sintering. A major limiting factor of this technique is the simultaneous tailoring of vascularization efficacy and osteogenic activity, usually done by adding the secondary phase in the organic slurry before the writing step. Mechanical mixing of biphasic powders is required to avoid compromising the biological performance and physical defects caused by significantly different physicochemical properties. This study addresses this issue by developing a selective ion doping and microstructure tuning for the production of bioceramic scaffolds with a binozzle robocasting process. Different metal ions (Sr²⁺, Mg²⁺) were doped into wollastonite (CaSiO₃; CSi) powders considering the mechanical stability and bioactive enhancement of the bioceramic scaffolds. Subsequently, the Mg-doped CSi slurries were used as shell-nozzle feedstocks added with 5, 10, and 15 μm diameter polystyrene microbeads that allowed shell-layer micropore production in pore struts during sintering. Finally, the most promising pore-strut microstructures and mechanical evolution of scaffolds were evaluated, and especially the enhanced fibrovascularization potential was confirmed in dorsal muscle embedding model in rabbits. This study may open an avenue to designing multiproperty-tuned macro- and microporous bioceramics for bone regenerative medicine, especially in challenging bone defect conditions.