A Comparative Study of the Sintering Behavior of Pure and Manganese-Substituted Hydroxyapatite

Functional role of inorganic trace elements in dentin apatite-Part II: Copper, manganese, silicon, and lithium

Trace elements are recognized as being essential in dentin and bone apatite. The effects of zinc, strontium, magnesium, and iron were discussed in part I. In part II, we evaluated the functional role of copper, manganese, silicon, and lithium on dentin apatite, with critical effects on morphology, crystallinity, and solubility. An electronic search was performed on the role of these trace elements in dentin apatite from January 2000 to January 2022. The recent aspects of the relationship between four different trace elements and their critical role in the structure and mechanics of dentin were assessed. These findings show that elements play a vital role in the human body, especially in the crystalline structure of dentin apatite. Copper presents immense benefits in dental restorative biomaterials because of its importance in enhancing odontogenesis. The biological role of manganese in dentin apatite is still largely unknown, but it has gained attention for many of its broad physiological functions such as modulating osteoblast proliferation, differentiation, and metabolism in bones. The functional role of silicon in dentin apatite is similarly lacking, but findings reveal its importance in mineralization and collagen formation, making it useful for the field of restorative dentistry. Likewise, lithium was found to have important roles in dentin mineralization as well as in the formation of dentin bridges and tissues. Therefore, there is growing importance in studying the aforementioned elements in the context of dentin apatite.

Dual response of osteoblast activity and antibacterial properties of polarized strontium substituted hydroxyapatite-Barium strontium titanate composites with controlled strontium substitution

To mimic the electrical properties of natural bone, controlled strontium substitution of both hydroxyapatite and ferroelectric barium titanate were achieved by mixing in the ratio 30:70 by weight. The composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy to investigate the phase composition and microstructure of the composites. Unpolarized and polarized strontium hydroxyapatite (SrHA)-barium strontium titanate (BST) composites with controlled degree of Sr substitution were examined, including 5SrHA-5BST (5% Sr substitution in both components) and 10SrHA-10BST composites. The 10SrHA-10BST composite showed a higher osteoblast activity, as observed from the cell viability studies performed using CCK-8 assay. The polarized composites showed promise against Staphylococcus aureus bacteria by minimizing the adhesion and growth of bacteria, as compared with their unpolarized counterparts. The polarized 10SrHA-10BST was found to be superior than all other composites. As a result, the approach of polarization of SrHA-BST composites has been found to be an effective bone substitute material in controlled enhancement of osteoblast growth with simultaneous reduction of bacterial infection.

Intrafibrillar Mineralized Collagen-Hydroxyapatite-Based Scaffolds for Bone Regeneration

As one of the major challenges in the field of tissue engineering, large skeletal defects have attracted wide attention from researchers. Collagen (Col) and hydroxyapatite (HA), the most abundant protein and the main component in natural bone, respectively, are usually used as a biomimetic composite material in tissue engineering due to their excellent biocompatibility and biodegradability. In this study, novel intrafibrillar mineralized Col-HA-based scaffolds, constructed in either cellular or lamellar microstructures, were established through a biomimetic method to enhance the new bone-regenerating capability of tissue engineering scaffolds. Moreover, iron (Fe) and manganese (Mn), two of the essential trace elements in the body, were successfully incorporated into the lamellar scaffold to further improve the osteoinductivity of these biomaterials. It was found that the lamellar scaffolds demonstrated better osteogenic abilities compared to both in-house and commercial Col-HA-based cellular scaffolds in vitro and in vivo. Meanwhile, Fe/Mn incorporation further amplified the osteogenic promotion of the lamellar scaffolds. More importantly, a synergistic effect was observed in the Fe and Mn dual-element-incorporated lamellar scaffolds for both in vitro osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and in vivo bone regeneration loaded with fresh bone marrow cells. This study provides a simple but practical strategy for the creation of functional scaffolds for bone regeneration.

Biological behavior of magnesium-substituted hydroxyapatite during bone repair

The aim of this study was to analyze the biological behavior and osteogenic potential of magnesium (Mg) substituted hydroxyapatite (HA) microspheres, implanted in a critical bone defect, considering that this ion is of great clinical interest, since it is closely associated with homeostasis and bone mineralization. For the purpose of this study, 30 rats were used to compose three experimental groups: GI - bone defect filled with HA microspheres; GII - bone defect filled with HA microspheres replaced with Mg; GIII - empty bone defect; evaluated at biological points of 15 and 45 days. The histological results, at 15 days, showed, in all the groups, a discrete chronic inflammatory infiltrate; biomaterials intact and surrounded by connective tissue; and bone neoformation restricted to the borders. At 45 days, in the GI and GII groups, an inflammatory response of discrete granulomatous chronic type was observed, and in the GIII there was a scarce presence of mononuclear inflammatory cells; in GI and GII, the microspheres were seen to be either intact or fragmented, surrounded by fibrous connective tissue rich in blood vessels; and discrete bone neoformation near the edges and surrounding some microspheres. In GIII, the mineralization was limited to the borders and the remaining area was filled by fibrous connective tissue. It was concluded that the biomaterials were biocompatible and osteoconductive, and the percentage of Mg used as replacement ion in the HA did not favor a greater bone neoformation in relation to the HA without the metal.

Hydroxyapatite, a multifunctional material for air, water and soil pollution control: A review

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂), a calcium phosphate biomaterial, is a very promising candidate for the treatment of air, water and soil pollution. Indeed, hydroxyapatite (Hap) can be extremely useful in the field of environmental management, due in one part to its particular structure and attractive properties, such as its great adsorption capacities, its acid-base adjustability, its ion-exchange capability and its good thermal stability. Moreover, Hap is able to constitute a valuable resource recovery route. The first part of this review will be dedicated towards presenting Hap's structure and defining properties that result in its viability as an environmental remediation material. The second will focus on its use as adsorbent for wastewater and soil treatment, while indicating the mechanisms involved in this remediation process. Finally, the last part will impart all findings on Hap's applications in the field of catalysis, whether it be as catalyst, as photocatalyst, or as active phase support. Hence, all of the above will have served in showcasing the benefits gained by employing hydroxyapatite in air, water and soil clean-up.

Magnetic properties and cytocompatibility of transition-metal-incorporated hydroxyapatite

A detailed magnetization study, along with an assessment of the cellular proliferation, has been carried out on transition-metal-doped hydroxyapatite (HA), Ca_10-xM_x(PO₄)₆(OH)₂, where M = Mn, Co, and Fe. In particular, a series of MnHA powder samples with an x value of 0.04 ≤ x ≤ 1.21, one CoHA (x = 0.48) and one FeHA sample (x = 1.06) were synthesized using a wet chemical method along with an ion-exchange procedure. Characterization by transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) indicated that the substitution of M elements does not change the morphology and crystalline structure of pure HA that showing a single phased HA nano-rod. In every case, the magnetization isotherms for 10 K ≤ T ≤ 300 K were linear through the origin characteristic of a paramagnetic response with no indication of superparamagnetic behavior, hysteresis, or magnetic ordering. The magnetic behavior for all samples could be fit to the Curie-Weiss law yielding values for the M ion magnetic moments. The Mn²⁺ magnetic moments were close to the spin-only value of S = 5/2 or 5.92 μ_B, while the Co²⁺ moment (4.41 μ_B) was larger than the spin-only value for S = 3/2, indicating an orbital contribution due to incomplete quenching. The magnetic behavior for the FeHA sample showed a possible spin-state transition. In addition, no statistically significant differences were observed when cells were treated with the same dose of HA or MnHA up to 50 μg/mL, suggesting that the substituted Mn introduces no cytotoxicity to the HA powders.