Co-substituted Hydroxyapatite Research Articles

Synthesis and biomedical potential of silk fiber/methylcellulose composite containing copper and zinc co-substituted hydroxyapatite for bone tissue engineering applications

The primary feature of biomaterials is to aid in the regeneration of damaged tissues and organs. To attain a biomaterial, we fabricated a double mineral (copper and zinc) substituted hydroxyapatite/silk fiber/methylcellulose (CZ-HAP/SF/MC) nanocomposite by the E-Spin method. The as-developed CZ-HAP/SF/MC nanocomposite was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and moreover, the fabricated nanocomposites were used to investigate morphological changes, porosity, swelling test, mechanical strength, antibacterial activity and apatite growth. In addition, antimicrobial studies demonstrated that CZ-HAP/SF/MC nanocomposite exhibited excellent antimicrobial activity against S. aureus, E. coli and C. albicans and, the resultant nanocomposite revealed that the CZ-HAP/SF/MC nanocomposite will be an effective implant material for better cell growth in BTE applications.

Mechanosynthesis and microstructural characterization of F− and CO32− mono- and co-substituted hydroxyapatite

An investigation into the microstructural properties and mechanosynthesis mechanisms of three distinct calcium phosphate compounds, namely, carbonate-substituted hydroxyapatite (CHA), fluorapatite (FA), and carbonate- and fluoride-substituted hydroxyapatite (CFHA), was undertaken in this study. Significant insights into the crystalline structures of CHA, FA, and CFHA were revealed through Rietveld refinement analysis. In the CaCO3‒Ca(OH)2‒P2O5 ternary system, the transformation of the biphasic structure composed of CHA and dicalcium phosphate anhydrous (DCPA) into a single-phase A-type CHA was observed as milling duration increased. In the CaO‒Ca(OH)2‒CaF2‒P2O5 quaternary system, the formation of FA was influenced by milling time, and within 1‒5 h, a composite structure was formed. The progression from a composite structure to the formation of fully crystalline nanosized CFHA was also observed over the same milling periods in the CaCO3‒Ca(OH)2‒CaF2‒P2O5 quaternary system. The central finding highlights the substantial influence of milling time on the structural properties of the mechanosynthesized nanopowders, with marked changes in crystallite size, micro-strain, and unit cell volume being observed over different milling durations. The atomic coordinates and displacement parameters of the refined structures were also provided, revealing the presence of apatitic groups. Moreover, a detailed examination of the mechanochemical synthesis processes uncovered intricate sub-reactions that occur during ball milling. This work sets the stage for future investigations, facilitating a better grasp of their distinctive attributes and potential applications across various domains of regenerative medicine.

Iron and Magnesium Co-substituted Hydroxyapatite Nanoparticles in Orthodontic Composite: A Preliminary Assessment.

Aim The study aims to characterize Fe and Mg co-substituted hydroxyapatite nanoparticles (FeMgHAPn) and assess the antimicrobial properties of FeMgHAPn-incorporated orthodontic composite. Materials and methods FeMgHAPn was synthesized using the sol-gel method, and the prepared nanoparticle powder was characterized using Fourier Transform Infrared Spectroscopy (FTIR), energy-dispersive X-ray analysis (EDX)) and scanning electron microscopic (SEM) analysis. The FeMgHAPn was incorporated into a commercially available orthodontic composite in two concentrations (40 and 20 μL), and the structure was examined using SEM. The FeMgHAPn-incorporated composite was tested for its antimicrobial efficacy against Streptococcus mutans, Staphylococcus aureus, and Escherichia coli using the agar-well diffusion method. The zones of inhibition (ZOI) were measured in millimeters (mm). Results The characterization of the FeMgHAPn indicated the successful formation of the nanoparticle without any impurities or byproducts. The high concentration (40 μL) of FeMgHAPn-incorporated orthodontic composite showed the maximum ZOI against all three microbes, followed by the low concentration (20 μL) and the control group. Conclusion The FeMgHAPn-incorporated orthodontic composite showed promising antimicrobial activity against caries-causing S. mutans, S. aureus, and E. coli.

Cycling of potassium–carbonate co-substituted hydroxyapatite compositions for improved carbon dioxide capture at 500 °C

There is an immediate need to reduce CO2 emissions if the impacts of climate change are to be mitigated.

Chitosan/PVA reinforced boron/strontium multi-substituted hydroxyapatite-based biocomposites: Effects of synthesis pH and coating on the physicochemical, mechanical, and in vitro biological properties of scaffolds

Bioceramics are used in hard tissue applications to repair and replace damaged parts inside the human body. Hydroxyapatite (HAp) is the most widely used bioceramic due to its ability to bind to hard tissues. Furthermore, enhancing the bioactivity of HAp in hard tissue applications through co-substituted particles is of great interest. In this study, different types of HAp microparticles, including unsubstituted, boron-substituted (B-HAp), strontium-substituted (Sr-HAp), boron and strontium co-substituted HAp (B–Sr-HAp) were synthesized at pH 9 and 11 using the wet precipitation method. The impact of synthesis pH on the chemical composition and crystalline structure of the microparticles was investigated. Sintered porous three-dimensional ceramic scaffolds were prepared, polyvinyl alcohol (PVA) and chitosan (Chi) were chosen to improve the mechanical properties of the ceramic scaffolds owing to their biocompatibility and functional groups. In vitro cytotoxicity and in vitro hemocompatibility studies were conducted to evaluate the biocompatibility of the constructs. The results revealed that synthesis pH of 11 yielded the highest substitution without altering the crystalline phase. Also, the PVA/Chi coating improved the compressive strength of all scaffolds, with the most significant improvement observed in Br-HAp due to borate-diol complexation at the ceramic-polymer interface. Preliminary in vitro studies revealed that scaffolds were non-cytotoxic and hemocompatible.

Preparation and Assessment of Antimicrobial Effect of Strontium and Copper Co-substituted Hydroxyapatite Nanoparticle-Incorporated Orthodontic Composite: A Preliminary In Vitro Study.

Background and aims Enamel demineralization and white spot lesions (WSLs) during orthodontic treatment have always been a challenge to orthodontists. The advancement of nanotechnology has paved the way for the incorporation of bioactive compounds in orthodontic materials especially orthodontic composites for prevention and management of WSLs. The present study aims to prepare, characterize, and then incorporate copper and strontium doped nanohydroxyapatiteinto orthodontic composite material and test its antibacterial efficacy. Materials and methods The present in vitro study involved the preparation of the strontium and copper co-substituted hydroxyapatite (SrCuHA) nanoparticles (Nps) using the sol-gel method. The prepared Nps were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDAX), and Fourier transform infrared spectroscopy (FTIR). The Nps were incorporated into a commercially available orthodontic composite. The antimicrobial properties of the SrCuHA Nps-incorporated composite were tested using the Agar well diffusion method against Staphylococcus aureus(S. aureus), Streptococcus mutans (S. mutans), and Escherichia coli (E. coli). Results The SrCuHA Nps were successfully prepared. EDAX, FTIR, and SEM analyses revealed the successful formation of the Nps. The SrCuHA-incorporated orthodontic composite at a higher concentration of 40 μl showed the maximum zone of inhibition (ZOI) against S. mutans. The control group showed the maximum ZOI against E. coli and the SrCuHA Nps-incorporated composite at 20 μl showed the maximum inhibition against S. aureus. Conclusion In the present study, successfulpreparation of SrCuHA Nps followed by incorporation in the orthodontic adhesive was done. The prepared nanoparticle was characterized and the SrCuHA Nps-incorporated orthodontic composite demonstrated comparable ZOI against S. mutansto the control.

Biomimetic ion substituted and Co-substituted hydroxyapatite nanoparticle synthesis using Serratia Marcescens

Biomimicry is becoming deep-rooted as part of bioceramics owing to its numerous functional advantages. Naturally occurring hydroxyapatite (HA) apart from primary nano structures are also characterised by various ionic substitutions. The ease of accommodating such key elements into the HA lattice is known to enhance bone healing properties of bioceramics. In this work, hydroxyapatite synthesized via biomimetic approach was substituted with individual as well as multiple cations for potential applications in bone repair. Ion substitutions of Sr, Mg and Zn was carried out on HA for the first time by using Serratia grown in a defined biomineralization medium. The individual ions of varying concentration substituted in Serratia HA (SHA) (Sr SHA, Mg SHA and Zn SHA) were analysed for crystallinity, functional groups, morphology and crystal size. All three showed decreased crystallinity, phase purity, large agglomerated aggregates and needle-shaped morphologies. Fourier transform infrared spectroscopy (FTIR) spectra indicated increased carbonate content of 5.8% resembling that of natural bone. Additionally, the reduced O–H intensities clearly portrayed disruption of HA lattice and subsequent ion-substitution. The novelty of this study lies primarily in investigating the co-substitution of a combination of 1% Sr, Zn and Mg in SHA and establishing the associated change in bone parameters. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images clearly illustrated uniform nano-sized agglomerates of average dimensions of 20–50 nm length and 8–15 nm width for Sr SHA; 10–40 nm length and 8–10 nm width for both Zn SHA and Mg SHA and 40–70 nm length and 4–10 nm width in the case of 1% Sr, Zn, Mg SHA. In both individual as well as co-substitutions, significant peak shifts were not observed possibly due to the lower concentrations. However, cell volumes increased in both cases due to presence of Sr2+ validating its dominant integration into the SHA lattice. Rich trace ion deposition was presented by energy dispersive X-ray spectroscopy (EDS) and quantified using inductively coupled plasma optical emission spectrometer (ICP-OES). In vitro cytotoxicity studies in three cell lines viz. NIH/3T3 fibroblast cells, MG-63 osteosarcoma cells and RAW 264.7 macrophages showed more than 90% cell viability proving the biocompatible nature of 1% Sr, Zn and Mg in SHA. Microbial biomineralization by Serratia produced nanocrystals of HA that mimicked “bone-like apatite” as evidenced by pure phase, carbonated groups, reduced crystallinity, nano agglomerates, variations in cell parameters, rich ion deposition and non-toxic nature. Therefore ion-substituted and co-substituted biomineralized nano SHA appears to be a suitable candidate for applications in biomedicine addressing bone injuries and aiding regeneration as a result of its characteristics close to that of the human bone.

Hydroxyapatite Double Substituted with Zinc and Silicate Ions: Possibility of Mechanochemical Synthesis and In Vitro Properties

In this study, the mechanochemical synthesis of substituted hydroxyapatite (HA) containing zinc and silicon ions having a chemical formula of Ca10-xZnx(PO4)6-x(SiO4)x(OH)2-x, where x = 0.2, 0.6, 1.0, 1.5, and 2.0, was carried out. The synthesized materials were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and inductively coupled plasma spectroscopy. We found that HA co-substituted with zinc and silicate formed up to x = 1.0. At higher concentrations of the substituents, the formation of large amounts of an amorphous phase was observed. The cytotoxicity and biocompatibility of the co-substituted HA was studied in vitro on Hek293 and MG-63 cell lines. The HA co-substituted with zinc and silicate demonstrated high biocompatibility; the lowest cytotoxicity was observed at x = 0.2. For this composition, good proliferation of MG-63 osteoblast-like cells and an increased solubility compared with that of HA were detected. These properties allow us to recommend the synthesized material for medical applications, namely, for the restoration of bone tissue and manufacture of biodegradable implants.

Retraction: Investigation of anticorrosive, antibacterial and in vitro biological properties of a sulphonated poly(etheretherketone)/strontium, cerium co-substituted hydroxyapatite composite coating developed on surface treated surgical grade stainless steel for orthopedic applications.

[This retracts the article DOI: 10.1039/C4RA12207K.].

Mechanochemical synthesis of strontium- and magnesium-substituted and cosubstituted hydroxyapatite powders for a variety of biomedical applications

Hydroxyapatite (HA) is a biocompatible material widely used in various biomedical applications. Stoichiometric HA has low bioactivity and does not possess antibacterial properties. One way to modify HA properties is to substitute some ions in stoichiometric HA, i.e., to dope HA, for attaining desired properties, e.g., improved bioactivity or an antibacterial effect. This work shows that a soft mechanochemical method of HA synthesis allows to obtain bioactive HA containing strontium ions, magnesium ions, or both. Substituted HAs with substitution degree x(Mg) = 0.5 mol or x(Sr) = 1.5 mol were synthesized, as was cosubstituted HAs contained both magnesium and strontium ions with x(Mg) = 0.5 mol or x(Sr) = 1.5 mol. The resulting materials were investigated by simultaneous thermal analysis, scanning electron microscopy, granulometry, powder X-ray diffraction, Fourier transform infrared, Raman spectroscopy, and X-ray photoelectron spectroscopy. Thermal stability of the obtained materials was studied too. The partial calcium substitution with strontium and/or magnesium changed both HA crystal lattice parameters and positions of absorption bands of phosphate groups in Fourier transform infrared and Raman spectra. X-ray photoelectron spectra of the synthesized materials contain peaks of all elements with binding energies corresponding to substituted HA. The strontium substitution, unlike the magnesium substitution, did not reduce HA thermal stability. The crystal lattice of Sr-substituted HA is stable up to 1300 °C, just as stoichiometric HA. Magnesium cations left HA at 800 °C, forming Mg-substituted β-Ca3(PO4)2. At the cosubstitution, thermal stability of HA became slightly lower. Partial decomposition of the material began already at 700 °C. Accordingly, during manufacturing of medical devices from the proposed materials, their low thermal stability should be taken into account. To preserve the structure of Mg-Sr-cosubstituted HA, heat treatment conditions should not exceed 700 °C.

Physicochemical studies of iron/vanadate doped hydroxyapatite/polycaprolactone nanofibers scaffolds

Altering nanofibrous structures to be used for wound healing applications is crucially needed to improve quality of life. Co-substituted hydroxyapatite (HAP) with different iron (Fe)/vanadate (VO43−) ions contributions are involved in polycaprolactone (PCL), where the electrospinning method is used to fabricate PCL polymer. XRD explains both powder and nanofibrous scaffold structural features. The surface morphology for powdered Fe/V-HAP@PCL shows changes in grains size from 1.59–6.26 µm to 2.0–3.76 for the minimum and maximum Fe composition. The roughness average increased by increasing Fe substitution from 37.0 to 56.5 nm, while (Rq) rises from 49.8 to 73.7 nm. The surface morphology of nanofibers shows a diameter range from around 0.97–3.19 µm to 0.44–1.91 µm. Further, the roughness parameter of Ra rose from 34.96 to 59.49 nm. TEM micrographs revealed the diameters of nanofibrous scaffolds are around 200–360 nm. Mechanical parameters vary upon increasing dopant ions in HAP; tensile strength rises from 1.61 ± 0.8 to 4.93 ± 0.8 MPa. Moreover, the contact angle decreased by increasing Fe ion, in which values declined from 101.2 ± 2.5 to 85 ± 4.3°. Enhancing cell viability from 90.3 ± 3.1% to 97.5 ± 2.8% for the minimum and maximum Fe ions composition., The porosity of the nanofibrous surface improved, which illustrated increasing cell growth upon increasing dopant ion. Hence, modulating the nanofibrous scaffold by controlling the composition of doped metal ions could be advantageous for biomedical applications.

Cryogenically 3D printed biomimetic scaffolds containing decellularized small intestinal submucosa and Sr2+/Fe3+ co-substituted hydroxyapatite for bone tissue engineering

• Novel SIS/SrFeHA biomimetic scaffolds are developed by extrusion cryogenic 3D printing. • The cryogenic printing endows scaffolds with improved porous and bioactive features. • SIS/SrFeHA coordinates favorable immunomodulation with enhanced angio-/osteogenesis and biomineralization. • A new finding of angiogenic mechanism of SIS/SrFeHA is clarified to be Amot + /YAP − /Hippo signaling pathway. • Combination of SIS and SrFeHA provides a new potential for bone tissue engineering. Currently, advanced bone biomaterials are preferred able to mimic the architecture/composition of natural bone and possess sufficient biological multifunctionality to chronologically dictate bone regeneration events. Such biomaterials are increasingly being researched and quite promising in bone tissue engineering. In this view, novel biomimetic scaffolds composed of decellularized small intestinal submucosa matrix (SIS-ECM) and Sr 2+ /Fe 3+ co-substituted hydroxyapatite (SrFeHA) were constructed via extrusion cryogenic 3D printing method. The produced SIS/SrFeHA scaffolds revealed desirable 3D interconnected macro/micro-porous structures, rough microsurfaces and improved mechanical strength, along with appreciable synergic releasing of bioactive ECM components and Sr 2+ /Fe 3+ . These favorable physico-chemical properties rendered composite SIS/SrFeHA inducing a highly biomimetic bony environment which manipulated desired immunoregulation coupled with enhanced angiogenesis, osteogenesis, and biomineralization. Consistently, in vivo cranial defects and subcutaneous implantation outcomes yet affirmed the superior ability of SIS/SrFeHA to well dictate early immune reaction, neovascularization, and in vivo bone regeneration, suggesting the potent combined actions of SIS and SrFeHA to accelerate bone healing. Moreover, as examined by RNA sequencing assay, a new finding of up-regulated Amot + /YAP − /Hippo signaling pathway responsible for the enhanced angiogenesis in SIS/SrFeHA scaffolds was further clarified. Consequently, for the first time, present research highlights the considerable potential of SIS/SrFeHA scaffolds for inducing bone healing and simultaneously afford a new finding for better understanding underlying mechanism of bioactive SrFeHA components, thus may generating a new promising alternative for future bone tissue engineering.

Structural, thermal and in-vitro analysis of sol-gel derived zinc and fluorine co-substituted nanodimensional hydroxyapatite for biomedical applications

Hydroxyapatite (HA) is widely used as a bone and dental substitute material due to its biocompatible and bioactive nature. Improvements in HA can be achieved by substituting various ions that are present in the bone. The present study of co-substitution of Zinc and Fluorine in HA was intended to investigate the influence of substituent ions on the structural, thermal, and bioactive behavior of HA. The co-substituted hydroxyapatite nanopowder was synthesized by water-based sol-gel method. Characterization studies from XRD, FTIR and TEM confirmed the substitution of Zn and F ions in HA and the formation of nanorods. The thermal stability of as-synthesized nanopowder was assessed by calcining it at three different temperatures i.e. 800 °C, 1000 °C and 1200 °C. The bioactivity of as-synthesized and calcined nanopowders was assessed by measuring the change in pH of simulated body fluid (SBF) and FTIR spectra after immersion in SBF for 30 days. The results revealed the bioactive behavior of as-synthesized and calcined nanopowders.

Synthesis and characterization of zinc and fluorine co-substituted hydroxyapatite for bone and dental applications

Ionic substituted hydroxyapatites are widely used in bone tissue engineering applications. The present research is aimed at the synthesis of zinc and fluorine co-substituted hydroxyapatite (ZnFHA10, Ca9.0Zn1.0(PO4)6(OH)F) using a sol–gel method. This research investigates the effect of zinc and fluorine co-substitution on the structure of synthesized hydroxyapatite. The as-synthesized nanopowder was heat-treated in the temperature range 800 °C–1200 °C. The physicochemical properties were investigated using X-ray fluorescence spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy and transmission electron microscopy. The thermal stability of nanopowder was assessed by the thermogravimetric analysis. Bioactive behavior was evaluated by studying the variation in pH of simulated body fluid on immersion of nanopowders. Peaks of zinc and fluorine in the XRF spectra confirmed the substitution of ions. TEM images of as-synthesized and calcined nanopowders showed rod-like and spherical morphology. X-ray diffraction pattern of as-synthesized nanopowder showed the formation of nanoparticles of low crystallinity. On calcination, the crystallinity and crystallite size increased and the biphasic mixture of hydroxyapatite and tricalcium phosphate was formed. Spectra obtained from Fourier-transform infrared spectroscopy showed the presence of OH…F…OH group, depicting the presence of fluorine in hydroxyapatite. FTIR spectra of nanopowders obtained after immersion in simulated body fluid and change in pH values on immersion of nanopowders in simulated body fluid confirmed the bioactive behavior of nanopowders. The study revealed that the substitution of ions in hydroxyapatite could significantly increase the bioactivity and bioresorbability of hydroxyapatite, thus finding a wide range of clinical applications in orthopedics and dentistry.

New Sintered Porous Scaffolds of Mg,Sr Co-Substituted Hydroxyapatite Support Growth and Differentiation of Primary Human Osteoblasts In Vitro

Strontium (Sr) and Magnesium (Mg) are bioactive ions that have been proven to exert a beneficial effect on bone; therefore, their incorporation into bone substitutes has long been viewed as a possible approach to improve tissue integration. However, the thermal instability of Mg-substituted hydroxyapatites has hitherto limited development. We previously described the creation of thermally consolidated porous constructs of Mg,Sr co-substituted apatites with adequate mechanical properties for their clinical use. The present paper describes the biocompatibility of Mg,Sr co-substituted granules using an alveolar-bone-derived primary model of human osteoblasts. Cells were cultured in the presence of different amounts of hydroxyapatite (HA), Sr-substituted HA, or MgSrHA porous macrogranules (with a size of 400–600 microns, obtained by grinding and sieving the sintered scaffolds) for three and seven days, and their viability was measured by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Protein content was measured using the Lowry assay at the same time points. Cell viability was not impaired by any of the tested compounds. Indirect and direct biocompatibility of these macrogranules was assessed by culturing cells in a previously conditioned medium with HA, SrHA, or MgSrHA, or in the presence of material granules. Osteoblasts formed larger and more numerous nodules around SrHA or MgSrHA granules. Furthermore, cell differentiation was evaluated by alkaline phosphatase staining of primary cells cultured in the presence of HA, SrHA, or MgSrHA granules, confirming the increased osteoconductivity of the doped materials.

Silver, silicon co-substituted hydroxyapatite modulates bacteria-cell competition for enhanced osteogenic function

Combating bacteria while promoting tissue regeneration is an aim of highest priority for employing biomaterials in orthopedics that often embroiled with pre-operative contamination. Through simulating a surgical site infection environment and an infected implant site, we showcase the ability of a functionally modified hydroxyapatite, Ag,Si-HA that permits preferential adhesion of human bone marrow derived mesenchymal stem cells (BMSCs) over co-cultured bacterial pathogen, Pseudomonas aeruginosa, by displaying immediate suppression and killing of the bacteria present with minimum cytotoxicity for 28 d. And, at the same time, Ag,Si-HA stimulates BMSCs towards osteogenic differentiation despite being within the contaminated milieu. These findings provide well-defined requirements for incorporating antibacterial properties to biomaterials in managing pre-operative contamination. In addition, it highlights the dual positive attributes of Ag,Si-HA as an effective antibacterial biomaterial and at the same time, promotes bone tissue regeneration.

New Prospects in Nano Phased Co-substituted Hydroxyapatite Enrolled in Polymeric Nanofiber Mats for Bone Tissue Engineering Applications.

The most common forms of tissue impairment are fracturebones and significant bone disorders caused by multiple traumas or normal aging. Surgical care sometimes necessitates the placement of a temporary or permanent prosthesis, which continues to be a challenge for orthopedic surgeons, including those with large bone defects. Electrospun scaffolds made from natural and synthetic nanofiber-based polymers are studied as natural extracellular matrix (ECM)-like scaffolds for tissue engineering. Besides, nanostructured materials have properties and functions depending on the scale of natural materials such as hydroxyapatite (HAP),rangingfrom1 to 100nm, which activity was proficient upon enrolled in nanofiber mats. The use of nanofibers in combination with nano-HAP has increased the scaffold's ability to replicate the construction of natural bone tissue that is the aim of the present text. In bone engineering, nanofiber substrates facilitate cell adhesion, proliferation, and differentiation, while HAP induces cells to secrete ECM for bone mineralization and development. This review aims to draw the reader's attention to the critical issues with synthetic and natural polymers containing HAP in bone tissue engineering; co-substituted hydroxyapatite has also been mentioned.

Multifunctional strontium-sulphate co-substituted hydroxyapatite nanopowders

The development of materials having customized properties to suit any therapeutic environment has been a dream for a long. Hydroxyapatite (HAP) as a biomaterial offers excellent ionic substitution flexibility, propagating numerous materials with desirable behavior. The present work reports the co-substitution of strontium and sulphate into HAP structure by microwave synthesis to obtain the nanopowders blended with useful properties for combined antibacterial and drug delivery applications. The XRD, FTIR, HRTEM, EDX, TGA, and BET techniques were employed to investigate the structure of strontium-sulphate (SrS-HAP) co-substituted nanopowders. The nanopowders were tested against Escherichia-coli and Staphylococcus aureus bacterial strains. In addition, nanopowders were soaked in SBF to test their in-vitro bioactivity. Finally, products were also tested to deliver Ibuprofen drug under different pH environments. The dual ionic substitution conferred the nanopowders with appropriate properties suitable for multifunctional therapeutic applications, including tissue regeneration, antibacterial, and drug delivery applications.

Ionic substituted hydroxyapatite for bone regeneration applications: A review

Biological apatites are characterised by various ionic substitutions within the HAp lattice that are crucial for bone metabolism. The introduction of key role elements within synthetic calcium phosphates (CaP), mainly hydroxyapatite (HAp), can increase osteogenesis and enhance bone regeneration process. The lattice structure of HAp enables cationic and anionic substitutions leading to the enhanced biological performance of synthetic bone graft materials. This review summarises recent and relevant studies on cationic and anionic substitutions in the HAp lattice that are commonly found in the human body. Furthermore, co-substituted HAp obtained from synthetic and biological precursors, along with their influence on the bone regeneration process, has been discussed. Finally, future perspectives for the use of substituted HAp have been presented.

Synthesis, Characterization, Antibacterial Properties, and In Vitro Studies of Selenium and Strontium Co-Substituted Hydroxyapatite.

In this study, as a measure to enhance the antimicrobial activity of biomaterials, the selenium ions have been substituted into hydroxyapatite (HA) at different concentration levels. To balance the potential cytotoxic effects of selenite ions (SeO32−) in HA, strontium (Sr2+) was co-substituted at the same concentration. Selenium and strontium-substituted hydroxyapatites (Se-Sr-HA) at equal molar ratios of x Se/(Se + P) and x Sr/(Sr + Ca) at (x = 0, 0.01, 0.03, 0.05, 0.1, and 0.2) were synthesized via the wet precipitation route and sintered at 900 °C. The effect of the two-ion concentration on morphology, surface charge, composition, antibacterial ability, and cell viability were studied. X-ray diffraction verified the phase purity and confirmed the substitution of selenium and strontium ions. Acellular in vitro bioactivity tests revealed that Se-Sr-HA was highly bioactive compared to pure HA. Se-Sr-HA samples showed excellent antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus carnosus) bacterial strains. In vitro cell–material interaction, using human osteosarcoma cells MG-63 studied by WST-8 assay, showed that Se-HA has a cytotoxic effect; however, the co-substitution of strontium in Se-HA offsets the negative impact of selenium and enhanced the biological properties of HA. Hence, the prepared samples are a suitable choice for antibacterial coatings and bone filler applications.