Synthesis, characterization and modelling of zinc and silicate co-substituted hydroxyapatite

Evaluating various properties of nanohydroxyapatite synthesized from eggshells and dual-doped with Si4+ and Zn2+: An in vitro study

BACKGROUND

This study aimed to evaluate morphological, chemical and biocompatible properties of nanohydroxyapatite (N-HA) synthesized from eggshells and dual-doped with Si4+ and Zn2+.

METHODS

In the current study, N-HA was synthesized from chicken eggshells using the wet chemical precipitation method and doped with Si4+ and Zn2+. The physical assessment was carried out using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD) analysis. Crystal size was calculated using the Scherrer equation. Cytotoxicity was studied in vitro using the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) cytotoxicity assay. The optical density (OD) of each well was obtained and recorded at 570 nm for 24 h (t1), 48 h (t2), 72 h (t3), and 5 days (t4) using a microplate reader.

RESULTS

The results of Si-Zn-doped HA showed a high specific surface area with an irregular nano-sized spherical particle structure. The atomic percentage provided the ratio of calcium to phosphate; for non-doped HA, the atomic Ca/P ratio was 1.6, but for Si-Zn-doped HA, where Zn+2 Ca and Si + replaced 4 substituted P, the atomic ratio (Ca + Zn)/(P + Si) was 1.76. The average crystal size of Si-Zn-doped HA was 46 nm, while for non-doped HA it was 61 nm. both samples were non-toxic and statistically significantly less viable than the control group After 5 days, the mean cell viability of Si-Zn-doped HA (79.17 ± 2.18) was higher than that of non-doped HA (76.26 ± 1.71) (P = 0.091).

CONCLUSIONS

The MTT assay results showed that Si-Zn-doped HA is biocompatible. In addition, it showed characteristic physiochemical properties of a large surface area with interconnected porosity.

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 Ca_10-xZn_x(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.

Toward Smart Biomimetic Apatite-Based Bone Scaffolds with Spatially Controlled Ion Substitutions

Biomimetic apatites exhibit a high reactivity allowing ion substitutions to modulate their in vivo response. We developed a novel approach combining several bioactive ions in a spatially controlled way in view of subsequent releases to address the sequence of events occurring after implantation, including potential microorganisms' colonization. Innovative micron-sized core-shell particles were designed with an external shell enriched with an antibacterial ion and an internal core substituted with a pro-angiogenic or osteogenic ion. After developing the proof of concept, two ions were particularly considered, Ag⁺ in the outer shell and Cu²⁺ in the inner core. In vitro evaluations confirmed the cytocompatibility through Ag-/Cu-substituting and the antibacterial properties provided by Ag⁺. Then, these multifunctional "smart" particles were embedded in a polymeric matrix by freeze-casting to prepare 3D porous scaffolds for bone engineering. This approach envisions the development of a new generation of scaffolds with tailored sequential properties for optimal bone regeneration.

Understanding Zinc-Doped Hydroxyapatite Structures Using the First-Principles Calculations and Convolutional Neural Network Algorithm

Element doping is widely used to improve the performance of materials by changing their intrinsic properties. However, the lack of direct crystallographic structures for dopants has restricted the effective high-throughput...

Study of biomorphic calcium deficient hydroxyapatite fibres derived from a naturalHarakeke(Phormium tenax) leaf fibre template

The complex structure of natural bio-organic matter has inspired scientists to utilise these as templates to design 'biomorphic materials', which retain the intricate architecture of the materials while acting as a useful bioactive material. Biomorphic hydroxyapatite-based fibres were synthesised usingHarakekeleaf fibre as a template, which constitutes a powerful method for manufacturing bioactive ceramic fibres. Furthermore, in creating the hydroxyapatite-based fibres, a natural source of calcium and phosphate ions (from bovine bone) was utilised to create the digest solution in which the leaf fibres were immersed prior to their calcination to form the inorganic fibres. Chemical, thermogravimetric and microscopic characterisation confirmed that the final product was able to successfully replicate the shape of the fibres and furthermore be transformed into calcium deficient, bone-like hydroxyapatite.

Sol–Gel and Electrospinning Synthesis of Silica–Hydroxyapatite–Silver Nanofibers for SEIRAS and SERS

Surface-enhanced Raman spectroscopy (SERS) and Surface-enhanced infrared absorption spectroscopy (SEIRAS) are both novel techniques favored by the excitation of surface plasmons onto metal nanostructures. The light emitted from the metal surface couples with the vibrational transitions of molecules in proximity, enhancing its spectral response and leading to more sensitive and effective spectroscopic analysis. The absence of inexpensive and reproducible substrates is among the major impediments to the accurate implementation and optimal performance of the technique. The development of a low-cost active substrate based on silica–hydroxyapatite through sol–gel synthesis and electrospinning is addressed in the present study. Fibers of 512 ± 199 nm diameter were produced after sintering at 1150 °C on the electrospun mats. The fibers are fixed to an indium tin oxide (ITO) glass base for electrodeposition with 10 and 20 mM AgNO3 at 1.5 and 3.3 V at different time periods. Electrodeposition produced silver nanorods and nanocubes on the fibers. The SERS and SEIRAS activity of each one of the nine supports was tested using pyridine 1 nM, comparing it with the spectrum of pyridine 1 mM. An enhancement factor of 2.01 × 106 for the band at 3335 cm−1 was obtained during a SEIRAS essay for the support doped for 2 min at 3.3 V with 10 mM silver nitrate solution. The highest SERS enhancement factor was 3.46 × 108, for the band at 1567 cm−1 in the substrate doped for 5 min at 1.5 V with silver nitrate solution at 10 mM. After testing both samples with 10−4 M violet crystal solution, no SERS enhancement factor was found, but higher band resolution in the spectra was observed.

Physiological silicon incorporation into bone mineral requires orthosilicic acid metabolism to SiO44

Under physiological conditions, the predominant form of bioavailable silicon (Si) is orthosilicic acid (OSA). In this study, given Si's recognized positive effect on bone growth and integrity, we examined the chemical form and position of this natural Si source in the inorganic bone mineral hydroxyapatite (HA). X-ray diffraction (XRD) of rat tibia bone mineral showed that the mineral phase was similar to that of phase-pure HA. However, theoretical XRD patterns revealed that at the levels found in bone, the 'Si effect' would be virtually undetectable. Thus we used first principles density functional theory calculations to explore the energetic and geometric consequences of substituting OSA into a large HA model. Formation energy analysis revealed that OSA is not favourable as a neutral interstitial substitution but can be incorporated as a silicate ion substituting for a phosphate ion, suggesting that incorporation will only occur under specific conditions at the bone-remodelling interface and that dietary forms of Si will be metabolized to simpler chemical forms, specifically [Formula: see text]. Furthermore, we show that this substitution, at the low silicate concentrations found in the biological environment, is likely to be a driver of calcium phosphate crystallization from an amorphous to a fully mineralized state.

Nanocrystalline Zn2+ and SO42- binary doped fluorohydroxyapatite: A novel biomaterial with enhanced osteoconductive and osteoinconductive properties

In this study, we have successfully doped hydroxyapatite (HA) with zinc (Zn²⁺), sulphate (SO₄^2-) and fluoride (F^-) ions to develop a new composition of bioceramic, Ca_10-x Zn_x(PO₄)_6-y(SO₄)_y(OH)_2-z-yF_z(SO₄)_y, (x = 0, 0.2, 0.6, 1.0, y = 0, 0.5 and z = 0,1.0 mol), using wet precipitation method. The obtained materials were analysed using XRD, FTIR, FESEM, and XPS techniques to investigate the phase purity, particle morphology and elemental composition, respectively. A model anticancer drug (Doxorubicin, DOX) was loaded onto the surface of the Zn/SO₄-FHA materials. About 100% loading of DOX with a controlled release profile was obtained. Degradation of materials in Simulated body fluid (SBF) was greatly improved with the incorporation of Zn²⁺/SO₄^2- ions in comparison to HA/FHA, which makes it highly bioactive materials. In vitro cell viability and adhesion of Human fetal osteoblast (hFOB) cell were investigated. Cell viability has demonstrated that the hFOB cells proliferated at a high rate on Zn/SO₄-FHA materials, confirming the in vitro biocompatibility of the materials. Alkaline phosphatase (ALP) activity and intracellular calcium deposition of hFOB cells seeded on 1ZnSO₄-FHA disc surface was statistically higher than observed on pure HA and FHA discs, indicating that hFOB cells differentiated into mature osteoblasts on 1Zn/SO₄-FHA disc surfaces. Taken together, our results suggest that HA substituted by (Zn²⁺, 0.2 mol), (SO₄^2-, 0.5 mol) and (F^-, 1 mol) (1Zn/SO₄-FHA) material was a promising material for hard tissue scaffolds.

Zinc Incorporated Nano Hydroxyapatite: A Novel Bone Graft Used for Regeneration of Intrabony Defects

BACKGROUND

To enhance the bioactivity of hydroxyapatite (HA), various ions have been incorporated into its porous structure such as zinc. Zinc has shown to have a stimulatory effect on osteoblastic cells. This study attempts to evaluate the efficacy of an indigenously prepared zinc incorporated nanohydroxyapatite (ZINH) bone graft in the treatment of intrabony defects.

MATERIALS AND METHODS

A split-mouth study, which consists of 11 systemically healthy subjects with 45 sites, were randomly treated with ZINH or with nanoHA alone. Plaque index, gingival index, gingival bleeding index, pocket depth (PD) and clinical attachment level (CAL) were assessed at baseline, 3, 6, 9, and 12 months. Bone probing depth (BPD) and radiographic parameters were assessed at baseline, 6, and 12 months. Statistical analysis used was student's t-test and one-way analysis of variance.

RESULTS

At 12 months, PD and BPD reduction was more in test (4.37 ± 0.989 mm and 3.36 ± 0.446 mm) than control (2.81 ± 0.084 mm and 2.15 ± 0.159 mm). Gain in CAL for test (3.08 ± 0.148 mm) was higher than control (2.33 ± 0.278 mm). Furthermore amount and percentage of bone fill was higher in test (1.92 ± 0.702 mm, 54.7 ± 20.286, respectively) than control (1.38 ± 0.650 mm, 40.2 ± 20.972, respectively). Statistically significant improvements in all parameters were seen in the test sites at 12 months.

CONCLUSION

ZINH bone graft can be considered as a prospective bone regenerative material.

A comparative study of the dissolubility of pure and silicon substituted hydroxyapatite from density functional theory calculations

Introduction of silicon into hydroxyapatite (HA) is one of the effective ways to modulate the bioactivity of HA-based biomaterials. The bulk and surface structures of silicate-substituted HA (Si-HA) were characterized by using density functional theory calculations. The energetically favorable structures were identified from a number of candidate structures. Particular attention was paid to the surface structures of Si-HA, whose bioactivity is closely relevant to their surface atoms. Compared to the surface of pure HA, the Si-HA surface has similar surface energy but different charge distribution. Under the implicit solvent model, the exposed calcium/oxygen atoms become more positive/negative in net charge, resulting in a considerable change in the surface electrostatic potential at van der Waals distances. However, changes in the dissolution of surface calcium ions are not remarkable, as depicted by their activation energy leaving from the surface. Our calculations reveal that the surface structures and properties of HA were changed to some extent by silicate substitution, which provides some hints for understanding the experimentally observed changes in bioactivity and biodegradability of Si-HA that still remain controversial in many aspects.

Exploratory Testing of Diatom Silica to Map the Role of Material Attributes on Cell Fate

Porous silica is an attractive biomaterial in many applications, including drug-delivery systems, bone-graft fillers and medical devices. The issue with porous silica biomaterials is the rate at which they resorb and the significant role played by interfacial chemistry on the host response in vivo. This paper explores the potential of diatom-biosilica as a model tool to assist in the task of mapping and quantifying the role of surface topography and chemical cues on cell fate. Diatoms are unicellular microalgae whose cell walls are composed of, amorphous nanopatterned biosilica that cannot be replicated synthetically. Their unique nanotopography has the potential to improve understanding of interface reactions between materials and cells. This study used Cyclotella meneghiniana as a test subject to assess cytotoxicity and pro-inflammatory reactions to diatom-biosilica. The results suggest that diatom-biosilica is non-cytotoxic to J774.2 macrophage cells, and supports cell proliferation and growth. The addition of amine and thiol linkers have shown a significant effect on cytotoxicity, growth and cytokine response, thus warranting further investigation into the interfacial effects of small chemical modifications to substrate surfaces. The overall findings suggest diatom-biosilica offers a unique platform for in-depth investigation of the role played by nanotopography and chemistry in biomedical applications.

A multi-material coating containing chemically-modified apatites for combined enhanced bioactivity and reduced infection via a drop-on-demand micro-dispensing technique

Prevention of infection and enhanced osseointegration are closely related, and required for a successful orthopaedic implant, which necessitate implant designs to consider both criteria in tandem. A multi-material coating containing 1:1 ratio of silicon-substituted hydroxyapatite and silver-substituted hydroxyapatite as the top functional layer, and hydroxyapatite as the base layer, was produced via the drop-on-demand micro-dispensing technique, as a strategic approach in the fight against infection along with the promotion of bone tissue regeneration. The homogeneous distribution of silicon-substituted hydroxyapatite and silver-substituted hydroxyapatite micro-droplets at alternate position in silicon-substituted hydroxyapatite-silver-substituted hydroxyapatite/hydroxyapatite coating delayed the exponential growth of Staphylococcus aureus for up to 24 h, and gave rise to up-regulated expression of alkaline phosphatase activity, type I collagen and osteocalcin as compared to hydroxyapatite and silver-substituted hydroxyapatite coatings. Despite containing reduced amounts of silicon-substituted hydroxyapatite and silver-substituted hydroxyapatite micro-droplets over the coated area than silicon-substituted hydroxyapatite and silver-substituted hydroxyapatite coatings, silicon-substituted hydroxyapatite-silver-substituted hydroxyapatite/hydroxyapatite coating exhibited effective antibacterial property with enhanced bioactivity. By exhibiting good controllability of distributing silicon-substituted hydroxyapatite, silver-substituted hydroxyapatite and hydroxyapatite micro-droplets, it was demonstrated that drop-on-demand micro-dispensing technique was capable in harnessing the advantages of silver-substituted hydroxyapatite, silicon-substituted hydroxyapatite and hydroxyapatite to produce a multi-material coating along with enhanced bioactivity and reduced infection.

Design and evaluation of multifunctional antibacterial ion-doped β-dicalcium silicate cements favorable for root canal sealing

Cu or Zn-doping dicalcium silicate-based cements exhibit multifunctional physiochemical and biological performances and meet some challenging criteria in root canal treatment.