Effect of anions on the structural, morphological and dielectric properties of hydrothermally synthesized hydroxyapatite nanoparticles

Synergistic Effects of Hybrid Bio-Fillers and Modified Natural Rubber on Natural Rubber Composite Properties

This work aims to investigate the synergistic effects of hybrid bio-fillers and compatibilizers on the properties of natural rubber composites. Rice husk silica (RSi) and hydroxyapatite (HA), derived from rice husk ash and seabass fish scales, respectively, were successfully prepared and used as bio-fillers. Poly(acrylic acid-co-acrylamide)-grafted deproteinized natural rubber (gDPNR) was synthesized via emulsion graft copolymerization, achieving a grafting efficiency and grafting percentage of 15.94 and 4.23%, respectively. The gDPNR was utilized as a compatibilizer in the preparation of natural rubber composites. The addition of hybrid bio-fillers at an RSi-to-HA ratio of 25:75 exhibited superior mechanical properties compared to composites containing a single filler. The incorporation of gDPNR improved filler dispersion and interfacial adhesion between the NR matrix and the bio-fillers, further enhancing the mechanical, thermal, and dielectric properties. The composite with hybrid bio-fillers and 10 phr of gDPNR exhibited the highest tensile strength, showing a 2.10-fold and 1.06-fold improvement over neat natural rubber composite and hybrid filler composite without compatibilizer, respectively. The presence of polar functional groups in gDPNR enhanced the dielectric constant of the natural rubber composites. These composites could have potential in sustainable industrial applications, including flexible electronics and eco-friendly devices.

Development of Bioinspired Biphasic Calcium Phosphate Inks for Manufacturing Bone Scaffolds by Robocasting

Robocasting calcium phosphate compounds as a novel approach to creating customized structures with interconnected pores not only overcomes the limitations of traditional fabrication methods of calcium phosphate substitutes but also boosts the potential for bone tissue regeneration. The ink development is a key step in 3D printing. In this study, different inks consisting of magnesium- and sodium-doped carbonated hydroxyapatite, β-tricalcium phosphate, and Pluronic F-127 were prepared to design biomimetic bone scaffolds. To achieve suitable printability and subsequently, structures with high shape fidelity and appropriate mechanical properties, the selected compositions were evaluated by rheological analysis and mechanical tests. The results demonstrated that the prepared inks exhibited shear thinning behavior, and by increasing the concentration of Pluronic and biphasic calcium phosphate (BCP), more consistent gels were obtained that were able to maintain their shape after printing. The compressive strength of the scaffolds varied in the range of ∼8-60 MPa. The morphology of the sintered scaffolds in the scanning electron microscopy images also showed a dual macro- and micropore-size architecture, which can promote the adhesion of proteins and cell behavior. Our findings indicated that bioinspired BCP scaffolds can be fabricated with relatively high precision for use as cancellous bone substitutes.

Synthesis of hydroxyapatite from eggshells via wet chemical precipitation: a review

In conjunction with the global trend towards sustainable industry, this review provides a summary of the research endeavors and efforts made in the field of exploiting eggshells in the production of hydroxyapatite (HA). HA is one of the most used biomaterials and has attracted considerable attention over the years towards biomedical applications. As the traditional production of HA from calcium and phosphorus chemical precursors synthetically has bottlenecks of being expensive, complex, time consuming, and results in a low biocompatible product, natural resources have become an attractive alternative option to synthesize HA, with trace elements providing a higher performance. Eggshell, with a growing production annually, is potentially a promising natural resource for HA production. Many studies have used different wet chemical precipitation routes to produce HA with properties comparable to synthetic HA. Thus, this review provides an overview of the various routes that can be used to synthesize HA from eggshells. In this review, the synthesis of HA from eggshells via wet chemical precipitation methods is specifically discussed in term of synthesis parameters and properties of the synthesized HA. This review should aid in choosing the most suitable route for HA production with the optimum parameters for obtaining the desired properties to meet the requirements of biomedical applications such as tissue engineering.

Interaction of Statherin-Derived Peptide with the Surface of Hydroxyapatite: Perspectives Based on Molecular Dynamics Simulations

INTRODUCTION

Statherin-derived peptide (StatpSpS) has shown promise against erosive tooth wear. To elucidate its interaction with the hydroxyapatite (HAP) surface, the mechanism related to adsorption of this peptide with HAP was investigated through nanosecond-long all-atom molecular dynamics simulations.

METHODS

StatpSpS was positioned parallel to the HAP surface in 2 orientations: 1 - neutral and negative residues facing the surface and 2 - positive residues facing the surface. A system containing StatpSpS without HAP was also simulated as control. In the case of systems with HAP, both partially restrained surface and unrestrained surface were constructed. Structural analysis, interaction pattern, and binding-free energy were calculated.

RESULTS

In the peptide system without the HAP, there were some conformational changes during the simulation. In the presence of the surface, only moderate changes were observed. Many residues exhibited short and stable distances to the surface, indicating strong interaction. Specially, the residues ASP1 and SER2 have an important role to anchor the peptide to the surface, with positively charged residues, mainly arginine, playing a major role in the further stabilization of the peptide in an extended conformation, with close contacts to the HAP surface.

CONCLUSION

The interaction between StatpSpS and HAP is strong, and the negative charged residues are important to the anchoring of the peptide in the surface, but after the initial placement the peptide rearranges itself to maximize the interactions between positive charged residues.

Synthesis of pure and doped nano-calcium phosphates using different conventional methods for biomedical applications: a review

The applications of calcium phosphates (hydroxyapatite, tetracalcium phosphate, tricalcium phosphate (alpha and beta), fluorapatite, di-calcium phosphate anhydrous, and amorphous calcium-phosphate) are increasing day by day. Calcium hydroxyapatite, commonly known as hydroxyapatite (HAp), represents a mineral form of calcium apatite. Owing to its close molecular resemblance to the mineral constituents of bones, teeth, and hard tissues, HAp is often employed in the biomedical domain. In addition, it is extensively employed in various sectors such as the remediation of water, air, and soil pollution. The key advantage of HAp lies in its potential to accommodate a wide variety of anionic and cationic substitutions. Nevertheless, HAp and tricalcium phosphate (TCP) syntheses typically involve the use of chemical precursors containing calcium and phosphorus sources and employ diverse techniques, such as solid-state, wet, and thermal methods or a combination of these processes. Researchers are increasingly favoring natural sources such as bio-waste (eggshells, oyster shells, animal bones, fish scales, etc.) as viable options for synthesizing HAp. Interestingly, the synthesis route significantly influences the morphology, size, and crystalline phase of calcium phosphates. In this review paper, we highlight both dry and wet methods, which include six commonly used synthesis methods (i.e. solid-state, mechano-chemical, wet-chemical precipitation, hydrolysis, sol-gel, and hydrothermal methods) coupled with the variation in source materials and their influence in modifying the structural morphology from a bulky state to nanoscale to explore the applications of multifunctional calcium phosphates in different formats.

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.

Regression Analysis of the Dielectric and Morphological Properties for Porous Nanohydroxyapatite/Starch Composites: A Correlative Study

This paper aims to investigate the dielectric properties, i.e., dielectric constant (ε′), dielectric loss factor (ε″), dielectric tangent loss (tan δ), electrical conductivity (σ), and penetration depth (Dp), of the porous nanohydroxyapatite/starch composites in the function of starch proportion, pore size, and porosity over a broad band frequency range of 5 MHz−12 GHz. The porous nanohydroxyapatite/starch composites were fabricated using different starch proportions ranging from 30 to 90 wt%. The results reveal that the dielectric properties and the microstructural features of the porous nanohydroxyapatite/starch composites can be enhanced by the increment in the starch proportion. Nevertheless, the composite with 80 wt% of starch proportion exhibit low dielectric properties (ε′, ε″, tan δ, and σ) and a high penetration depth because of its highly interconnected porous microstructures. The dielectric properties of the porous nanohydroxyapatite/starch composites are highly dependent on starch proportion, average pore size, and porosity. The regression models are developed to express the dielectric properties of the porous nanohydroxyapatite/starch composites (R2 > 0.96) in the function of starch proportion, pore size, and porosity from 1 to 11 GHz. This dielectric study can facilitate the assessment of bone scaffold design in bone tissue engineering applications.

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.