Magnesium- and strontium-co-substituted hydroxyapatite: the effects of doped-ions on the structure and chemico-physical properties

Tuning Mg Doping and Features of Bone-like Apatite Nanoparticles Obtained via Hydrothermal Synthesis

Nanocrystalline apatites have been intensively studied for decades, not only for their well-known mimesis of bone apatite but also for applicative purposes, whether as biomaterials for skeletal repair or more recently for a variety of nanomedical applications enabled by their peculiar surface characteristics. Particularly, ion-doped apatites are of great interest because the incorporation of foreign ions in the composition of apatite (nano)crystals alters the bulk and surface properties, modifying their ability to interact with the external environment. This is clearly seen in the physiology of bone tissue, whose mineral phase, a low crystallinity apatitic phase, can dynamically exchange ions with cells, thus driving bone metabolism. Taking bone mineral as a model, the present work describes the development of Mg-doped hydroxyapatite nanoparticles, exploiting hydrothermal synthesis to achieve extents of Mg2+ doping hardly achieved before and using citrate to develop stable apatite colloidal dispersions. Morphological and physicochemical analyses, associated with in-depth investigation of ions populating the apatitic lattice and the nonapatitic surface layer, concurred to demonstrate the cooperative presence of Mg2+ and citrate ions, affecting the dynamic ion retention/release mechanisms. Achieving high Mg2+ doping rates and understanding how Mg doping translates into surface activation of apatite-based nanoparticles is expected to foster the design of novel smart and tunable devices, to adsorb and release ionic species and cargo molecules, with potential innovations in the biomedical field or even beyond, as in catalysis or for environmental remediation.

Magnetic Hydroxyapatite Nanoparticles in Regenerative Medicine and Nanomedicine

This review focuses on the latest advancements in magnetic hydroxyapatite (mHA) nanoparticles and their potential applications in nanomedicine and regenerative medicine. mHA nanoparticles have gained significant interest over the last few years for their great potential, offering advanced multi-therapeutic strategies because of their biocompatibility, bioactivity, and unique physicochemical features, enabling on-demand activation and control. The most relevant synthetic methods to obtain magnetic apatite-based materials, either in the form of iron-doped HA nanoparticles showing intrinsic magnetic properties or composite/hybrid compounds between HA and superparamagnetic metal oxide nanoparticles, are described as highlighting structure-property correlations. Following this, this review discusses the application of various magnetic hydroxyapatite nanomaterials in bone regeneration and nanomedicine. Finally, novel perspectives are investigated with respect to the ability of mHA nanoparticles to improve nanocarriers with homogeneous structures to promote multifunctional biological applications, such as cell stimulation and instruction, antimicrobial activity, and drug release with on-demand triggering.

Hypomagnesemia may be associated with symptomatic disease in patients with primary hyperparathyroidism

AIM

Magnesium (Mg) homeostasis is closely related to calcium (Ca) metabolism. Hypercalcemia inhibits the reabsorption of Mg from the kidneys, leading to hypomagnesemia. Therefore, patients with primary hyperparathyroidism (PHPT) are predisposed to hypomagnesemia. However, there are few studies on the clinical significance of hypomagnesemia in PHPT. The aim of this study was to retrospectively evaluate the association of hypomagnesemia with the clinical outcomes of PHPT.

MATERIALS AND METHODS

A retrospective evaluation was made of the data of 538 consecutive patients (478 females, 60 males) diagnosed with PHPT in our center.

RESULTS

The mean age of the study population was 56.5 ± 11.66 years. The mean serum Mg level was 2 ± 0.26 mg/dl. Asymptomatic disease was present in 241 (44%) patients. Symptomatic patients with osteoporosis, Ca level ≥11.2 mg/dl, and estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 had lower levels of Mg (p < 0.05). Hypomagnesemia was detected in 129 of 538 patients (23.9%). The patients with hypomagnesemia had a higher rate of symptomatic disease (80% vs. 48%, p < 0.0001). The serum parathormone (PTH) level was found to be higher in patients with hypomagnesemia and the lumbar and femur T-scores and serum vitamin D levels were lower (p < 0.05). Patients with hypomagnesemia had higher rates of kidney stones (34% vs. 21%, p = 0.003) and osteoporosis (74% vs. 32%, p < 0.001). Multivariate logistic regression analysis revealed that hypomagnesemia had a significant effect on the development of symptomatic disease (OR:6.88, CI 95%: 5.20-11.27, p < 0.001).

CONCLUSIONS

The current study results demonstrate that hypomagnesemia may be associated with a higher risk of osteoporosis and kidney stones in PHPT patients. Routine evaluation of serum Mg may predict the clinical outcomes of PHPT.

Cleaner Leather Tanning and Post-Tanning Processes Using Oxidized Alginate as Biodegradable Tanning Agent and Nano-Hydroxyapatite as Potential Flame Retardant

In this study, sodium alginate (SA) was oxidized with potassium periodate to produce an alginate-based tanning agent. Using OSA as a biodegradable tanning agent and a nano-hydroxyapatite (nano-HAp) low concentration suspension to give flame retardancy to leather, eco-design concepts were applied to establish a chrome-, aldehyde-, and phenol-free tanning process. Micro-DSC, 1H unilateral nuclear magnetic resonance (NMR), attenuated total reflection mode Fourier transform infrared spectroscopy (FTIR-ATR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) were used to investigate the complex matrix collagen-OSA-nano-HAp. Micro-differential scanning calorimetry (micro-DSC) was used to assess OSA's ability to interact with collagen and stabilize the collagen-OSA matrix, while 1H unilateral (NMR) was used to investigate the aqueous environment and its limitations around collagen molecules caused by their association with OSA and nano-HAp. Industrial standard tests were used to assess the mechanical properties and fire resistance of the new leather prototype. The findings reported here indicate that both OSA and nano-HAp are suitable alternatives for cleaner tanning technologies and more sustainable leather.

Calcination and ion substitution improve physicochemical and biological properties of nanohydroxyapatite for bone tissue engineering applications

Nanohydroxyapatite (nanoHAP) is widely used in bone regeneration, but there is a need to enhance its properties to provide stimuli for cell commitment and osteoconduction. This study examines the effect of calcination at 1200 °C on the physicochemical and biological properties of nanoHAP doped with magnesium (Mg2+), strontium (Sr2+), and zinc (Zn2+). A synergistic effect of dual modification on nanoHAP biological properties was investigated. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET analysis, Fourier-transform spectroscopy, and thermal analysis methods. Furthermore, ion release tests and in vitro biological characterization, including cytocompatibility, reactive oxygen species production, osteoconductive potential and cell proliferation, were performed. The XRD results indicate that the ion substitution of nanoHAP has no effect on the apatite structure, and after calcination, β-tricalcium phosphate (β-TCP) is formed as an additional phase. SEM analysis showed that calcination induces the agglomeration of particles and changes in surface morphology. A decrease in the specific surface area and in the ion release rate was observed. Combining calcination and nanoHAP ion modification is beneficial for cell proliferation and osteoblast response and provide additional stimuli for cell commitment in bone regeneration.

Effect of Nano- and Microzinc Supplementation on the Mineral Composition of Bones of Rats with Induced Mammary Gland Cancer

BACKGROUND

The aim of this study was to determine changes in the mineral composition of the bones of rats with chemically induced mammary gland cancer and to attempt to establish whether a specific diet modification involving the inclusion of zinc ions in two forms-nano and micro-will affect the mineral composition of the bones.

METHODS

Female Sprague-Dawley rats were used for the research. The animals were randomly assigned to three experimental groups. All animals were fed a standard diet (Labofeed H), and selected groups additionally received zinc nanoparticles or microparticles in the amount of 4.6 mg/mL. To induce mammary cancer, the animals were given 7,12-dimethyl-1,2-benz[a]anthracene. The content of Ag, As, B, Ba, Cd, Cr, Cu, Mn, Ni, Pb, Rb, Se, Sr, Tl, U, and V was determined using ICP-MS, while that of Ca, Fe, K, Mg, Na, and Zn was determined using FAAS.

RESULTS

The use of a diet enriched with zinc nano- or microparticles significantly influenced the content of the elements tested. In the bones of rats fed a diet with zinc nanoparticles, changes were found in the content of Ca, Mg, Zn, Cd, U, V, and Tl, while in the case of the diet supplemented with zinc microparticles, there were differences in six elements-Ca, Mg, B, Cd, Ag, and Pb-compared to animals receiving an unsupplemented diet.

CONCLUSIONS

The content of elements in the bone tissue of rats in the experimental model indicates disturbances of mineral metabolism in the tissue at an early stage of mammary cancer.

Biostimulants derived from organic urban wastes and biomasses: An innovative approach

We used humic and fulvic acids extracted from digestate to formulate nanohybrids with potential applications in agronomy. In order to obtain a synergic co-release of plant-beneficial agents, we functionalized with humic substances two inorganic matrixes: hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HP) and silica (SiO₂) nanoparticles (NPs). The former is a potential controlled-release fertilizer of P, and the latter has a beneficial effect on soil and plants. SiO₂ NPs are obtained from rice husks by a reproducible and fast procedure, but their ability to absorb humic substances is very limited. HP NPs coated with fulvic acid are instead a very promising candidate, based on desorption and dilution studies. The different dissolutions observed for HP NPs coated with fulvic and humic acids could be related to the different interaction mechanisms, as suggested by the FT-IR study.

Current Development in Biomaterials-Hydroxyapatite and Bioglass for Applications in Biomedical Field: A Review

Inorganic biomaterials, including different types of metals and ceramics are widely used in various fields due to their biocompatibility, bioactivity, and bioresorbable capacity. In recent years, biomaterials have been used in biomedical and biological applications. Calcium phosphate (CaPs) compounds are gaining importance in the field of biomaterials used as a standalone material or in more complex structures, especially for bone substitutes and drug delivery systems. The use of multiple dopants into the structure of CaPs compounds can significantly improve their in vivo and in vitro activity. Among the general information included in the Introduction section, in the first section of this review paper, the authors provided a background on the development of hydroxyapatite, methods of synthesis, and its applications. The advantages of using different ions and co-ions for substitution into the hydroxyapatite lattice and their influence on physicochemical, antibacterial, and biological properties of hydroxyapatite are also presented in this section of the review paper. Larry Hench's 45S5 Bioglass^®, commercially named 45S5, was the first bioactive glass that revealed a chemical bond with bone, highlighting the potential of this biomaterial to be widely used in biomedicine for bone regeneration. The second section of this article is focused on the development and current products based on 45S5 Bioglass^®, covering the historical evolution, importance of the sintering method, hybrid bioglass composites, and applications. To overcome the limitations of the original biomaterials, studies were performed to combine hydroxyapatite and 45S5 Bioglass^® into new composites used for their high bioactivity and improved properties. This particular type of combined hydroxyapatite/bioglass biomaterial is discussed in the last section of this review paper.

Influence of Magnesium Content on the Physico-Chemical Properties of Hydroxyapatite Electrochemically Deposited on a Nanostructured Titanium Surface

The aim of this research was to obtain hydroxyapatite (HAp)-based coatings doped with different concentrations of Mg on a Ti nanostructured surface through electrochemical techniques and to evaluate the influence of Mg content on the properties of HAp. The undoped and doped HAp-based coatings were electrochemically deposited in galvanostatic pulsed mode on titania nanotubes with a diameter of ~72 nm, being designed to enhance the adhesion of the HAp coatings to the Ti substrate. The obtained materials were investigated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), and Fourier-Transform Infra-Red spectroscopy (FTIR). The adhesion of the coatings to the substrate was also evaluated with the help of the “tape-test” and the micro-scratch test. The morphology (SEM) of all the coatings is made of very thin and narrow ribbon-like crystals, with some alterations with respect to the Mg amount in the coatings. Thus, a concentration of 1 mM of Mg in the electrolyte leads to wider and thicker ribbon-like crystals, while a concentration of 1.5 mM in the electrolyte generated a morphology that resembles the undoped HAp. Both phase composition (XRD) and chemical bonds (FTIR) analysis proved the formation of HAp in all coatings. Moreover, according to XRD, all coatings have a strong orientation toward the (002) plane. Irrespective of the Mg content, all coatings registered an average roughness between approx. 500 and 600 nm, while the coating thickness increased after addition of Mg, from a value of 9.6 μm, for the undoped HAp, to 11.3 μm and ~13.7 μm for H/Mg1 and H/Mg2, respectively. In terms of adhesion, it was shown that the coatings a H/Mg2 had a poorer adhesion when compared to H/Mg1 and the undoped HAp (H), which registered similar adhesion, indicating that a concentration of 1.5 mM of Mg in the electrolyte reduces the adhesion of the Hap-based coatings to the nanostructured surface. The obtained results indicated that Mg concentrations up to 1 mM in the electrolyte can enhance the properties of HAp-based coatings electrochemically deposited on a nanostructured surface, while even a slightly higher concentration of 1.5 mM can negatively impact the characteristics of HAp coatings.

Ultrasound-Assisted Extraction of Micro- and Macroelements in Fruit Peel Powder Mineral Supplement for Osteoporosis Patients and Their Determination by Flame Atomic Absorption Spectrometry

Osteoporosis is a worldwide disease depicted by the reduced bone mass, an adequate supply of minerals is needed to support bone remodeling, and their deficiency causes bone-related diseases, osteoporosis in particular, and has osteoprotective effects. The aim of this recent research was to quantify the micro- (Mn, Fe, Cu, and Zn) and macroelements (Mg, K, and Ca) in the peel powder of some common fruits (pomegranate, orange, lemon, mango, and grapefruit) by flame atomic absorption spectrometer (FAAS). The extraction of micro- and macroelements in peel powder was done by using dilute acids in an ultrasonic bath. Apple leaves were used as standard reference material (SRM, NIST 1515) to optimize the ultrasound-assisted extraction (UAE) method at varied operating parameters. Maximum response was obtained for extracting of minerals in 500 mg SRM at 60°C temperature, setting a vortexing time of 5 min while using 5.0 mL extracting agent HNO3 (0.5 M)-H2O2 (10%) at 90% sonication amplitude of ultrasound bath for 6 min. While analyzing the SRM, the percentage recovery was obtained in a range between 96.8 and 102.7% to assure the accuracy whereas repeatability (n = 10) study in terms of % RSD yielding ≤2.29 supports well the precision of the proposed method, and limits of quantitation (μg/g) were 0.034, 0.061, 0.065, 0.057, 0.017, 0.175, and 0.053 for Mn, Fe, Cu, Zn, Mg, K, and Ca, respectively. The proposed UAE method was reliable, efficient, and advantageous over the conventionally employed acid digestion method with regard to less consumption of reagents and short analysis time for the determination of micro- and macroelements in fruit peel powder.

Biocompatible magnesium-doped biphasic calcium phosphate for bone regeneration

Autologous bone grafting remains the gold standard for almost all bone void-filling orthopedic surgery. However, autologous bone grafting has several limitations, thus scientists are trying to identify an ideal synthetic material as an alternative bone graft substitute. Magnesium-doped biphasic calcium phosphate (Mg-BCP) has recently been in the spotlight and is considered to be a potential bone substitute. The Mg-BCP is a mixture of two bioceramics, that is, hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP), doped with Mg2+ , and can be synthesized through chemical wet-precipitation, sol-gel, single diffusion gel, and solid state reactions. Regardless of the synthesis routes, it is found that the Mg2+ preferentially accommodates in β-TCP lattice instead of the HA lattice. The addition of Mg2+ to BCP leads to desirable physicochemical properties and is found to enhance the apatite-forming ability as compared to pristine BCP. In vitro results suggest that the Mg-BCP is bioactive and not toxic to cells. Implantation of Mg-BCP in in vivo models further affirmed its biocompatibility and efficacy as a bone substitute. However, like the other bioceramics, the optimum physicochemical properties of the Mg-BCP scaffold have yet to be determined. Further investigations are required regarding Mg-BCP applications in bone tissue engineering.

PCL-Coated Multi-Substituted Calcium Phosphate Bone Scaffolds with Enhanced Properties

Ionic substitutions within the hydroxyapatite lattice are a widely used approach to mimic the chemical composition of the bone mineral. In this work, Sr-substituted and Mg- and Sr-co-substituted calcium phosphate (CaP) scaffolds, with various levels of strontium and magnesium substitution, were prepared using the hydrothermal method at 200 °C. Calcium carbonate skeletons of cuttlefish bone, ammonium dihydrogenphosphate (NH₄H₂PO₄), strontium nitrate (Sr(NO₃)₂), and magnesium perchlorate (Mg(ClO₄)₂) were used as reagents. Materials were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Whole powder pattern decomposition refinements of XRD data indicated that increased magnesium content in the Mg- and Sr-co-substituted scaffolds was related to an increased proportion of the whitlockite (WH) phase in the biphasic hydroxyapatite (HAp)/WH scaffolds. In addition, refinements indicate that Sr²⁺ ions have replaced Ca²⁺ sites in the WH phase. Furthermore, PCL-coated Mg-substituted and Sr- and Mg-co-substituted scaffolds, with the HAp:WH wt. ratio of 90:10 were prepared by vacuum impregnation. Results of compression tests showed a positive impact of the WH phase and PCL coating on the mechanical properties of scaffolds. Human mesenchymal stem cells (hMSCs) were cultured on composite scaffolds in an osteogenic medium for 21 days. Immunohistochemical staining showed that Mg-Sr-CaP/PCL scaffold exhibited higher expression of collagen type I than the Mg-CaP/PCL scaffold, indicating the positive effect of Sr²⁺ ions on the differentiation of hMSCs, in concordance with histology results. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis confirmed an early stage of osteogenic differentiation.

La3+ and F- dual-doped multifunctional hydroxyapatite nanoparticles: Synthesis and characterization

Hydroxyapatite (HA) co-doped with La³⁺ and F^- ions were synthesized by the precipitation method and sintered at 1,100°C for 1 hr. Samples were characterized by the standard experimental methods including the density, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) to investigate their microstructure, phase formation, and bonding characteristics in detail. Moreover, the materials produced were identified using the microhardness tests. It was observed that in the most of materials, the hydroxyapatite was found to be the main phase with a minor amount of β-tricalcium phosphate (β-TCP). Furthermore, the presence of fluoride and small amount of β-TCP was verified with all the characteristic FTIR bands of hydroxyapatite for the majority of samples studied. The result in SEM evaluation is that the produced HA powders have less deformed, uniformly distributed, and regularly shaped particles. Here, the material density has changed towards a less dense state with the increasing rate of La doping, but statistically significant difference was not obtained (p, .1942 > .05) with increase of the F doping. A significant difference was obtained the microhardness values between La³⁺ and F^- ions co-doped HA materials and pure HA (p [.0053] < .05). Accordingly, this study confirmed that since the La³⁺ and F^- ions can potentially increase the efficacy of HA. According to the spectral, mechanical, and microstructure analysis result, this material can be as a good candidate product for use as an occluding material for dental application.

The Physico-Chemical Properties and Exploratory Real-Time Cell Analysis of Hydroxyapatite Nanopowders Substituted with Ce, Mg, Sr, and Zn (0.5-5 at.%)

Cation-substituted hydroxyapatite (HA), standalone or as a composite (blended with polymers or metals), is currently regarded as a noteworthy candidate material for bone repair/regeneration either in the form of powders, porous scaffolds or coatings for endo-osseous dental and orthopaedic implants. As a response to the numerous contradictions reported in literature, this work presents, in one study, the physico-chemical properties and the cytocompatibility response of single cation-doped (Ce, Mg, Sr or Zn) HA nanopowders in a wide concentration range (0.5–5 at.%). The modification of composition, morphology, and structure was multiparametrically monitored via energy dispersive X-ray, X-ray photoelectron, Fourier-transform infrared and micro-Raman spectroscopy methods, as well as by transmission electron microscopy and X-ray diffraction. From a compositional point of view, Ce and Sr were well-incorporated in HA, while slight and pronounced deviations were observed for Mg and Zn, respectively. The change of the lattice parameters, crystallite size, and substituting cation occupation factors either in the Ca(I) or Ca(II) sites were further determined. Sr produced the most important HA structural changes. The in vitro biological performance was evaluated by the (i) determination of leached therapeutic cations (by inductively coupled plasma mass spectrometry) and (ii) assessment of cell behaviour by both conventional assays (e.g., proliferation—3-(4,5-dimethyl thiazol-2-yl) 5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay; cytotoxicity—lactate dehydrogenase release assay) and, for the first time, real-time cell analysis (RTCA). Three cell lines were employed: fibroblast, osteoblast, and endothelial. When monophasic, the substituted HA supported the cells’ viability and proliferation without signs of toxicity. The RTCA results indicate the excellent adherence of cells. The study strived to offer a perspective on the behaviour of Ce-, Mg-, Sr-, or Zn-substituted HAs and to deliver a well-encompassing viewpoint on their effects. This can be highly important for the future development of such bioceramics, paving the road toward the identification of candidates with highly promising therapeutic effects.

Enhancing Bioactivity of Hydroxyapatite Scaffolds Using Fibrous Type I Collagen

In the field of bone tissue regeneration, the development of osteoconductive and osteoinductive scaffolds is an open challenge. The purpose of this work was the design and characterization of composite structures made of hydroxyapatite scaffold impregnated with a collagen slurry in order to mimic the bone tissue structure. The effect of magnesium and silicon ions enhancing both mechanical and biological properties of partially substituted hydroxyapatite were evaluated and compared with that of pure hydroxyapatite. The use of an innovative freeze-drying approach was developed, in which composite scaffolds were immersed in cold water, frozen and then lyophilized, thereby creating an open-pore structure, an essential feature for tissue regeneration. The mechanical stability of bone scaffolds is very important in the first weeks of slow bone regeneration process. Therefore, the biodegradation behavior of 3D scaffolds was evaluated by incubating them for different periods of time in Tris-HCl buffer. The microstructure observation, the weight loss measurements and mechanical stability up to 28 days of incubation (particularly for HA-Mg_Coll scaffolds), revealed moderate weight loss and mechanical performances reduction due to collagen dissolution. At the same time, the presence of collagen helps to protect the ceramic structure until it degrades. These results, combined with MTT tests, confirm that HA-Mg_Coll scaffolds may be the suitable candidate for bone remodeling.

The associations between serum trace elements and bone mineral density in children under 3 years of age

We examined the associations of age and serum magnesium, iron, lead, copper, and zinc levels with bone mineral density (BMD) in 2412 children under 3 years of age in order to find a tool to monitor BMD in children without the use of expensive imaging techniques. One-way ANOVA and chi-square tests were used to determine the associations of age and serum trace elements with BMD. Multivariable logistic regression analysis was used to test the correlation of five serum trace elements with BMD after adjustments for potential confounding factors in children under 3 years of age. Significant associations between age and four serum trace elements and BMD were found. Compared to the group with the lowest serum levels detected, the adjusted odds ratio (OR) for the incidence of normal bone mineral density in the third magnesium concentration tertile, the third iron concentration tertile, the fifth copper concentration quintile, the third zinc concentration quintile, and the fifth zinc concentration quintile were 1.30 (95% confidence interval (CI) 1.02–1.67), 1.43 (95% CI 1.11–1.84), 1.42 (95% CI 1.04–1.94), 1.46 (95% CI 1.05–2.04), and 1.48 (95% CI 1.06–2.06), respectively. However, there was no significant correlation between serum lead level and BMD in this study. Age and serum magnesium, iron, copper, and zinc levels are positively associated with BMD in children under 3 years old.

The local concentration of Ca2+ correlates with BMP7 expression and osseointegration in patients with total hip arthroplasty

BACKGROUND

A successful osseointegration of total hip arthroplasty (THA) relies on the interplay of implant surface and bone marrow microenvironment. This study was undertaken to investigate the impact of perioperative biochemical molecules (Ca²⁺, Mg²⁺, Zn²⁺, VD, PTH) on the bone marrow osteogenetic factors (BMP2, BMP7, Stro-1⁺ cells) in the metaphyseal region of the femoral head, and further on the bone mineral density (BMD) of Gruen R3.

METHODS

Bone marrow aspirates were obtained from the discarded metaphysis region of the femoral head in 51 patients with THA. Flow cytometry was used to measure the Stro-1⁺ expressing cells. ELISA was used to measure the concentrations of bone morphologic proteins (BMP2 and BMP7) and the content of TRACP5b in serum. TRAP staining was used to detect the osteoclast activity in the hip joint. The perioperative concentrations of the biochemical molecules above were measured by radioimmunoassay. The BMD of Gruen zone R3 was examined at 6 months after THA, using dual-energy X-ray absorptiometry (DEXA).

RESULTS

Our data demonstrated that the concentration of Ca²⁺ was positively correlated with BMP7 expression, and with the postoperative BMD of Gruen zone R3. However, the concentration of Mg²⁺ had little impact on the R3 BMD, although it was negatively correlated with the expression of BMP7. Osteoclast activity in hip joint tissue of patients with femoral neck fractures was increased. Compared with the patients before THA, the levels of TRACP5b in serum of patients after THA were decreased. The data also suggested that the other biochemical molecules, such as Zn²⁺, VD, and PTH, were not significantly correlated with any bone marrow osteogenetic factors (BMP2, BMP7, Stro-1⁺ cells). The postoperative R3 BMD of patients of different gender and age had no significant difference.

CONCLUSIONS

These results indicate the local concentration of Ca²⁺ may be an indicator for the prognosis of THA patients.

Obtaining and Characterizing Thin Layers of Magnesium Doped Hydroxyapatite by Dip Coating Procedure

A simple dip coating procedure was used to prepare the magnesium doped hydroxyapatite coatings. An adapted co-precipitation method was used in order to obtain a Ca25−xMgx(PO4)6(OH)2, 25MgHAp (xMg = 0.25) suspension for preparing the coatings. The stabilities of 25MgHAp suspensions were evaluated using ultrasound measurements, zeta potential (ZP), and dynamic light scattering (DLS). Using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) information at nanometric resolution regarding the shape and distribution of the 25MgHAp particles in suspension was obtained. The surfaces of obtained layers were evaluated using SEM and atomic force microscopy (AFM) analysis. The antimicrobial evaluation of 25MgHAp suspensions and coatings on various bacterial strains and fungus were realized. The present study presents important results regarding the physico-chemical and antimicrobial studies of the magnesium doped hydroxyapatite suspensions, as well as the coatings. The studies have shown that magnesium doped hydroxyapatite suspensions prepared with xMg = 0.25 presented a good stability and relevant antimicrobial properties. The coatings made using 25MgHAp suspension were homogeneous and showed remarkable antimicrobial properties. Also, it was observed that the layer realized has antimicrobial properties very close to those of the suspension. Both samples of the 25MgHAp suspensions and coatings have very good biocompatible properties.

Mechanical, Biological, and Antibacterial Characteristics of Plasma-Sprayed (Sr,Zn) Substituted Hydroxyapatite Coating

Implant-related infections are a major concern in total joint prostheses, occurring up to 3% in operations. In this work, 5% Zn²⁺ was added in HA to offset bacterial activity and 5% Sr²⁺ was also incorporated as a binary dopant to reduce the cytotoxic effect of Zn²⁺. The nanosized HA powder was synthesized by the hydrothermal method and then heat-treated at 600 °C for 4 h. The heat-treated powder was plasma-sprayed on a titanium alloy Ti-6Al-4V substrate. The addition of the dopant did not significantly influence the physical and mechanical properties of the coating. However, the cytocompatibility, antimicrobial, and contact-angle properties statistically enhanced. Moreover, the (Sr,Zn)-HA coating was post-heat treated at 500 and 600 °C for 3 h. X-ray diffraction confirmed that after heat treatment phase purity and crystallinity increased and residual stress decreased. Mechanical stability was evaluated by adhesive bond strength, and the results showed that after heat-treatment bonding strength increased from 26.81 ± 2.93 to 29.84 ± 3.62 and 34.66 ± 2.57 MPa, at 500 and 600 °C, respectively. Similar to the mechanical property, antibacterial activities and biological functions are also significantly improved. More interestingly, it was also observed that the Zn²⁺ ions released from the coating depend on Ca²⁺, P, and Sr²⁺ ions while Ca²⁺, P, and Sr²⁺ ions relied on heat treatment temperatures. However, (Sr,Zn)-HA coating at 600 °C demonstrates cytotoxic effects on MC3T3-E1 cells, characterized by poor cellular morphology on the coating surface and ultimately, cell death. The doping of Sr²⁺ with Zn²⁺, therefore, can offset the cytotoxic effects and enhanced biological performance. All of the outcomes of this study signify that (Sr,Zn)-HA coating heat-treated at 500 °C showed not only excellent mechanical and biological performance but also enhanced the antibacterial properties.

Advanced Mg, Zn, Sr, Si Multi-Substituted Hydroxyapatites for Bone Regeneration

Purpose

Compositional tailoring is gaining more attention in the development of advanced biomimetic nanomaterials. In this study, we aimed to prepare advanced multi-substituted hydroxyapatites (ms-HAPs), which show similarity with the inorganic phase of bones and might have therapeutic potential for bone regeneration.

Materials

Novel nano hydroxyapatites substituted simultaneously with divalent cations: Mg²⁺ (1.5%), Zn²⁺ (0.2%), Sr²⁺ (5% and 10%), and Si (0.2%) as orthosilicate (SiO₄^4-) were designed and successfully synthesized for the first time.

Methods

The ms-HAPs were obtained via a wet-chemistry precipitation route without the use of surfactants, which is a safe and ecologically friendly method. The composition of synthesized materials was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The materials were characterized by X-ray powder diffraction (XRD), FT-IR and FT-Raman spectroscopy, BET measurements and by imaging techniques using high-resolution TEM (HR-TEM), FE-SEM coupled with EDX, and atomic force microscopy (AFM). The ion release was measured in water and in simulated body fluid (SBF).

Results

Characterization methods confirmed the presence of the unique phase of pure stoichiometric HAP structure and high compositional purity of all synthesized nanomaterials. The doping elements influenced the crystallite size, the crystallinity, lattice parameters, morphology, particle size and shape, specific surface area, and porosity. Results showed a decrease in both nanoparticle size and crystallinity degree, coupled with an increase in specific surface area of these advanced ms-HAP materials, in comparison with pure stoichiometric HAP. The release of biologically important ions was confirmed in different liquid media, both in static and simulated dynamic conditions.

Conclusion

The incorporation of the four substituting elements into the HAP structure is demonstrated. Synthesized nanostructured ms-HAP materials might inherit the in vivo effects of substituting functional elements and properties of hydroxyapatite for bone healing and regeneration. Results revealed a rational tailoring approach for the design of a next generation of bioactive ms-HAPs as promising candidates for bone regeneration.

Hierarchically designed bone scaffolds: From internal cues to external stimuli

Bone tissue engineering utilizes three critical elements - cells, scaffolds, and bioactive factors - to recapitulate the bone tissue microenvironment, inducing the formation of new bone. Recent advances in materials development have enabled the production of scaffolds that more effectively mimic the hierarchical features of bone matrix, ranging from molecular composition to nano/micro-scale biochemical and physical features. This review summarizes recent advances within the field in utilizing these features of native bone to guide the hierarchical design of materials and scaffolds. Biomimetic strategies discussed in this review cover several levels of hierarchical design, including the development of element-doped compositions of bioceramics, the usage of molecular templates for in vitro biomineralization at the nanoscale, the fabrication of biomimetic scaffold architecture at the micro- and nanoscale, and the application of external physical stimuli at the macroscale to regulate bone growth. Developments at each level are discussed with an emphasis on their in vitro and in vivo outcomes in promoting osteogenic tissue development. Ultimately, these hierarchically designed scaffolds can complement or even replace the usage of cells and biological elements, which present clinical and regulatory barriers to translation. As the field progresses ever closer to clinical translation, the creation of viable therapies will thus benefit from further development of hierarchically designed materials and scaffolds.

Synthesis, Characterization, and Antimicrobial Activity of Magnesium-Doped Hydroxyapatite Suspensions

Obtaining nanoscale materials has allowed for the miniaturization of components, which has led to the possibility of achieving more efficient devices with faster functions and much lower costs. While hydroxyapatite [HAp, Ca10(PO4)6(OH)2] is considered the most widely used material for medical applications in orthopedics, dentistry, and general surgery, the magnesium (Mg) is viewed as a promising biodegradable and biocompatible implant material. Furthermore, Mg is regarded as a strong candidate for developing medical implants due to its biocompatibility and antimicrobial properties against gram-positive and gram-negative bacteria. For this study, magnesium-doped hydroxyapatite (Ca10-xMgx (PO4)6 (OH)2, xMg = 0.1), 10MgHAp, suspensions were successfully obtained by an adapted and simple chemical co-precipitation method. The information regarding the stability of the nanosized 10MgHAp particles suspension obtained by ζ-potential analysis were confirmed for the first time by a non-destructive ultrasound-based technique. Structural and morphological studies of synthesized 10MgHAp were conducted by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy in attenuated total reflectance (ATR) mode and scanning electron microscopy (SEM). The XRD analysis of the 10MgHAp samples confirmed that a single crystalline phase associated to HAp with an average grain size about 93.3 nm was obtained. The FTIR-ATR spectra revealed that the 10MgHAp sample presented broader IR bands with less visible peaks when compared to a well-crystallized pure HAp. The SEM results evidenced uniform MgHAp nanoparticles with spherical shape. The antimicrobial activity of the 10MgHAp suspension against gram-positive strains (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212), gram-negative strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853), as well as a fungal strain (Candida albicans ATCC 90029) were evaluated.

Effect of Chemical Treatments on the Properties of High-Density Luffa Mattress Filling Materials

Luffa is a lightweight porous material with excellent biocompatibility and abundant resources. In this paper, three kinds of softening treatment methods, alkali-hydrogen peroxide (Method 1), alkali-acetic acid (Method 2), and alkali-urea (Method 3), were used to soften high-density (HD) cylindrical luffa (CL) mattress-filling materials (MFM). Microscopic observation, mechanical performance testing and other analyses were performed to evaluate the effects of the three kinds of softening methods on the wettability, compression resilience and support performance of CL MFM. The results showed that: (1) After the treatment by Method 1, Method 2 and Method 3, the peak stress of CL decreased by 73%, 10% and 27%, respectively. In addition, after three kinds of softening treatments, the uniformity of CL increased. (2) When the CL MFM of high density rank treated by Method 1 was compressed by 40%, the firmness values of the surface, core and bottom reduced by 53.49% 40.72%, and 46.17%, respectively, compared to that of untreated CL. In addition, for the CL MFM of high density rank treated by Method 3 and then compressed to 60%, the firmness of the surface layer, core layer and bottom layer reduced by 41.2%, 33.7%, and 36.9%, respectively. (3) The contact angle of luffa treated by Method 3 was the smallest, next came Method 1 and Method 2, and untreated was the largest. (4) After the treatment by Method 3, the fiber bundle of luffa was intact, and the compression resilience of the CL was obviously increased. Therefore, this method can effectively reduce the firmness of MFM and also improve the uniformity and wettability of CL.

Study on MgxSr3-x(PO4)2 bioceramics as potential bone grafts

Magnesium (Mg) and strontium (Sr), which are essential nutrient elements in the natural bone, positively affect the osteogenic activity even in wide ranges of ion concentrations. However, it remains unknown whether magnesium-strontium phosphates [Mg_xSr_3-x(PO₄)₂] are potential bone grafts for accelerating bone regeneration. Herein, a serial of Mg_xSr_3-x(PO₄)₂, including Mg₃(PO₄)₂, Mg₂Sr(PO₄)₂, Mg_1.5Sr_1.5(PO₄)₂, MgSr₂(PO₄)₂ and Sr₃(PO₄)₂, were synthesized using a solid-state reaction approach. The physicochemical properties and cell behaviors of Mg_xSr_3-x(PO₄)₂ bioceramics were characterized and compared with the common bone graft β-tricalcium phosphate (β-TCP). The results indicated that various Mg_xSr_3-x(PO₄)₂ bioceramics differed in compressive strength and in vitro degradation rate. All the Mg_xSr_3-x(PO₄)₂ bioceramics had excellent biocompatibility. In contrast to β-TCP, the Mg_xSr_3-x(PO₄)₂ enhanced alkaline phosphatase activity of mouse bone mesenchymal stem cells (mBMSCs), and inhibited osteoclastogenesis-related gene expression of RAW264.7 cells, but did not enhance osteogenesis-related gene expression of mBMSCs which were treated with osteogenesis induction supplements. However, Mg₃(PO₄)₂ stimulated osteogenesis-related gene expression of mBMSCs without the treatment of osteogenesis induction supplements. This work contributes to the design of bone graft and may open a new avenue for the bone regeneration field.

Magnesium-based bioceramics in orthopedic applications

Magnesium ions are directly involved in numerous biological mechanisms; for example, they play an important part in the regulation of ion channels, DNA stabilization, enzyme activation and stimulation of cell growth and proliferation. This alkaline earth metal has gained great popularity in orthopedic applications in recent years. Magnesium-based bioceramics include a large group of magnesium containing compounds such as oxides, phosphates and silicates, that are involved in orthopedic applications like bone cements, bone scaffolds or implant coatings. This article aims to give a comprehensive review on different magnesium-based bioceramics, e.g. magnesium phosphates (MgO-P₂O₅), calcium magnesium phosphates (CaO-MgO-P₂O₅), and magnesium glasses (SiO₂-MgO) with a strong focus on the chemistry and properties of magnesium phosphate containing cements as the main application form. In addition, the processing of magnesium phosphate minerals into macroporous scaffolds for tissue engineering applications by either using traditional porogens or by additive manufacturing approaches are reflected. Finally, the biological in vitro and in vivo properties of magnesium phosphates for bone regeneration are summarized, which show promising results regarding the application as bone replacement material, but still lack in terms of testing in large animal models, load-bearing application sites and clinical data.

STATEMENT OF SIGNIFICANCE

Though bone substitutes from calcium phosphates have been investigated for a long time, a new trend is visible in the biomaterials sector: magnesium based bioceramics from magnesium phosphates and silicates due to the special biological significance of magnesium ions in enzymatic activation, cell growth and proliferation, etc. In contrast to pure magnesium implants, such formulations do not release hydrogen during degradation. As with calcium based bioceramics, magnesium based bioceramics are used for the development of diverse applications such as cements, macroporous scaffolds and coatings. From this perspective, we present a systematic overview on diverse kinds of magnesium based bioceramics, their processing regimes for different clinical purposes and their behavior both in vitro and in vivo.

Strontium-modification of porous scaffolds from mineralized collagen for potential use in bone defect therapy

The present study describes the development and characterization of strontium(II)-modified biomimetic scaffolds based on mineralized collagen type I as potential biomaterial for the local treatment of defects in systemically impaired (e.g. osteoporotic) bone. In contrast to already described collagen/hydroxyapatite nanocomposites calcium was substituted with strontium to the extent of 25, 50, 75 and 100mol% by substituting the CaCl₂-stock solution (0.1M) with SrCl₂ (0.1M) during the scaffold synthesis. Simultaneous fibrillation and mineralization of collagen led to the formation of collagen-mineral nanocomposites with mineral phases shifting from nanocrystalline hydroxyapatite (Sr0) over poorly crystalline Sr-rich phases towards a mixed mineral phase (Sr100), consisting of an amorphous strontium phosphate (identified as Collin's salt, Sr₆H₃(PO₄)₅∗2 H₂O, CS) and highly crystalline strontium hydroxyapatite (Sr₅(PO₄)₃OH, SrHA). The formed mineral phases were characterized by transmission electron microscopy (TEM) and RAMAN spectroscopy. All collagen/mineral nanocomposites with graded strontium content were processed to scaffolds exhibiting an interconnected porosity suitable for homogenous cell seeding in vitro. Strontium ions (Sr²⁺) were released in a sustained manner from the modified scaffolds, with a clear correlation between the released Sr²⁺ concentration and the degree of Sr-substitution. The accumulated specific Sr²⁺ release over the course of 28days reached 141.2μg (~27μgmg^-1) from Sr50 and 266.1μg (~35μgmg^-1) from Sr100, respectively. Under cell culture conditions this led to maximum Sr²⁺ concentrations of 0.41mM (Sr50) and 0.73mM (Sr100) measured on day 1, which declined to 0.08mM and 0.16mM, respectively, at day 28. Since Sr²⁺ concentrations in this range are known to have an osteo-anabolic effect, these scaffolds are promising biomaterials for the clinical treatment of defects in systemically impaired bone.

Trace elements have beneficial, as well as detrimental effects on bone homeostasis

The protective role of nutrition factors such as calcium, vitamin D and vitamin K for the integrity of the skeleton is well understood. In addition, integrity of the skeleton is positively influenced by certain trace elements (e.g. zinc, copper, manganese, magnesium, iron, selenium, boron and fluoride) and negatively by others (lead, cadmium, cobalt). Deficiency or excess of these elements influence bone mass and bone quality in adulthood as well as in childhood and adolescence. However, some protective elements may become toxic under certain conditions, depending on dosage (serum concentration), duration of treatment and interactions among individual elements. We review the beneficial and toxic effects of key elements on bone homeostasis.

Facile microwave-assisted synthesis of Te-doped hydroxyapatite nanorods and nanosheets and their characterizations for bone cement applications

In this work, the authors have fabricated the nanorods and nanosheets of pure and Te-doped HAp with different Te concentrations (0.04, 0.08, 0.16, 0.24wt%) by microwave-assisted technique at low temperature. The crystallite size, degree of crystallinity and lattice parameters are calculated. FE-SEM study confirms that the fabricated nanostructures are nanorods of diameter about 10nm in undoped and at low concentration of Te doping. However, at and higher concentration, it becomes nanosheets of about 5nm thickness. X-ray diffraction, FT-IR and FT-Raman studies shows that the prepared products are of HAp and Te has been successfully incorporated. From EDX the Ca/P molar ratio of the pure HAp is about 1.740, while this ratio for 0.04, 0.08, 0.16, 0.24 wt% Te doped is about 1.53, 1.678, 1.724, 1.792, respectively. Crystallite size was found to be increased with Te doping from 15nm to 62nm. The value of dielectric constant is found to be enhanced at higher concentrations of Te. The values of linear absorption coefficient were also determined and show that the prepared material with Te doping is more absorbable than pure and will be highly applicable in radiation detection applications. Furthermore, the antimicrobial potential of pure and Te doped HAp was examined against some Gram- negative and positive bacteria and fungi by agar disk diffusion method. The results demonstrated that the antimicrobial activity of Te doped HAp is stronger than that of pure HAp where it exhibited the highest activity against Bacillus subtilis>Candida albicans>Shigella dysenteriae.

Synthesis, characterization and biological evaluation of strontium/magnesium-co-substituted hydroxyapatite

The present study aims to investigate the contribution of two biologically important cations, Mg2+ and Sr2+, when co-substituted into the structure of hydroxyapatite (Ca10(PO4)6(OH)2, HA). The substituted samples were synthesized by a hydrothermal method that involved the addition of Mg2+ and Sr2+ containing precursors to partially replace Ca2+ in the apatite structure. Four co-substituted HA samples with different concentrations of Mg2+ and Sr2+ ((Mg + Sr)/(Mg + Sr + Ca) = 30%) were investigated, and they were compared with pure HA. Experimental results showed that only a limited amount of Mg (Mg/(Mg + Ca + Sr) < 14%) could successfully substitute for Ca in HA. In addition, Mg substitution resulted in reduced crystallinity, thermal stability and lattice parameters of HA. In contrast, Sr could fully substitute for Ca. Furthermore, the addition of Sr increased the lattice parameters of HA. Here, we obtained the cation leach liquor by immersing the prepared samples in a culture medium for cell experiments. The in vitro study showed that 10Mg20Sr promoted better MG63 cell attachment, proliferation and differentiation than HA. Thus, the presence of an appropriate proportion of Mg and Sr could play a significant role in the increased biocompatibility of HA.

Ion-doping as a strategy to modulate hydroxyapatite nanoparticle internalization

Although it is widely acknowledged that ionic substitutions on bulk hydroxyapatite substrates have a strong impact on their biological performance, little is known of their effect on nanoparticles (NPs) especially when used for gene transfection or drug delivery. The fact that NPs would be internalized poses many questions but also opens up many new possibilities. The objective of the present work is to synthesize and assess the effect of a series of hydroxyapatite-like (HA) NPs doped with various ions on cell behavior, i.e. carbonate, magnesium and co-addition. We synthesized NPs under similar conditions to allow comparison of results and different aspects in addition to assessing the effect of the doping ion(s) were investigated: (1) the effect of performing the cell culture study on citrate-dispersed NPs and on agglomerated NPs, (2) the effect of adding/excluding 10% of foetal bovine serum (FBS) in the cell culture media and (3) the type of cell, i.e. MG-63 versus rat mesenchymal stem cells (rMSCs). The results clearly demonstrated that Mg-doping had a major effect on MG-63 cells with high cytotoxicity but not to rMSCs. This was a very important finding because it proved that doping could be a tool to modify NP internalization. The results also suggest that NP surface charge had a large impact on MG-63 cells and prevents their internalization if it is too negative-this effect was less critical for rMSCs.

Magnesium from bioresorbable implants: Distribution and impact on the nano- and mineral structure of bone

Biocompatibility is a key issue in the development of new implant materials. In this context, a novel class of biodegrading Mg implants exhibits promising properties with regard to inflammatory response and mechanical properties. The interaction between Mg degradation products and the nanoscale structure and mineralization of bone, however, is not yet sufficiently understood. Investigations by synchrotron microbeam x-ray fluorescence (μXRF), small angle x-ray scattering (μSAXS) and x-ray diffraction (μXRD) have shown the impact of degradation speed on the sites of Mg accumulation in the bone, which are around blood vessels, lacunae and the bone marrow. Only at the highest degradation rates was Mg found at the implant-bone interface. The Mg inclusion into the bone matrix appeared to be non-permanent as the Mg-level decreased after completed implant degradation. μSAXS and μXRD showed that Mg influences the hydroxyl apatite (HAP) crystallite structure, because markedly shorter and thinner HAP crystallites were found in zones of high Mg concentration. These zones also exhibited a contraction of the HAP lattice and lower crystalline order.

Dual mode antibacterial activity of ion substituted calcium phosphate nanocarriers for bone infections

Nanotechnology has tremendous potential for the management of infectious diseases caused by multi-drug resistant bacteria, through the development of newer antibacterial materials and efficient modes of antibiotic delivery. Calcium phosphate (CaP) bioceramics are commonly used as bone substitutes due to their similarity to bone mineral and are widely researched upon for the treatment of bone infections associated with bone loss. CaPs can be used as local antibiotic delivery agents for bone infections and can be substituted with antibacterial ions in their crystal structure to have a wide spectrum, sustained antibacterial activity even against drug resistant bacteria. In the present work, a dual mode antibiotic delivery system with antibacterial ion substituted calcium deficient hydroxyapatite (CDHA) nanoparticles has been developed. Antibacterial ions such as zinc, silver, and strontium have been incorporated into CDHA at concentrations of 6, 0.25–0.75, and 2.5–7.5 at. %, respectively. The samples were found to be phase pure, acicular nanoparticles of length 40–50 nm and width 5–6 nm approximately. The loading and release profile of doxycycline, a commonly used antibiotic, was studied from the nanocarriers. The drug release was studied for 5 days and the release profile was influenced by the ion concentrations. The release of antibacterial ions was studied over a period of 21 days. The ion substituted CDHA samples were tested for antibacterial efficacy on Staphylococcus aureus and Escherichia coli by MIC/MBC studies and time-kill assay. AgCDHA and ZnCDHA showed high antibacterial activity against both bacteria, while SrCDHA was weakly active against S. aureus. Present study shows that the antibiotic release can provide the initial high antibacterial activity, and the sustained ion release can provide a long-term antibacterial activity. Such dual mode antibiotic and antibacterial ion release offers an efficient and potent way to treat an incumbent drug resistant infection.

Nanostructured platforms for the sustained and local delivery of antibiotics in the treatment of osteomyelitis

This article provides a critical view of the current state of the development of nanoparticulate and other solid-state carriers for the local delivery of antibiotics in the treatment of osteomyelitis. Mentioned are the downsides of traditional means for treating bone infection, which involve systemic administration of antibiotics and surgical debridement, along with the rather imperfect local delivery options currently available in the clinic. Envisaged are more sophisticated carriers for the local and sustained delivery of antimicrobials, including bioresorbable polymeric, collagenous, liquid crystalline, and bioglass- and nanotube-based carriers, as well as those composed of calcium phosphate, the mineral component of bone and teeth. A special emphasis is placed on composite multifunctional antibiotic carriers of a nanoparticulate nature and on their ability to induce osteogenesis of hard tissues demineralized due to disease. An ideal carrier of this type would prevent the long-term, repetitive, and systemic administration of antibiotics and either minimize or completely eliminate the need for surgical debridement of necrotic tissue. Potential problems faced by even hypothetically "perfect" antibiotic delivery vehicles are mentioned too, including (i) intracellular bacterial colonies involved in recurrent, chronic osteomyelitis; (ii) the need for mechanical and release properties to be adjusted to the area of surgical placement; (iii) different environments in which in vitro and in vivo testings are carried out; (iv) unpredictable synergies between drug delivery system components; and (v) experimental sensitivity issues entailing the increasing subtlety of the design of nanoplatforms for the controlled delivery of therapeutics.

Evaluation of Sr- and/or Mg-Containing Hydroxyapatite Behavior in Simulated Body Fluid

The main goal of this study was to evaluate the behavior of Sr- and/or Mg-containing hydroxyapatite (HAp) bioceramics in simulated body fluid (SBF). Sr-and/or Mg-containing HAp powders were synthesized by modified wet chemical precipitation method. Sr-and/or Mg-containing HAp bioceramics were prepared by uniaxial pressing of the precipitated powders and subsequent sintering at 1100 °C for 1 h. The synthesis products were characterized in terms of chemical, phase and molecular composition. Influence of the substitutions on thermal stability, morphology and microstructure of the HAp products were evaluated. Results suggest that incorporation of Sr (up to 1.45 wt.%) in HAp structure induced an increasing of particle sizes, but incorporation of Mg (up to 1.05 wt.%) led to a reduction of particle sizes of the HAp powders. The ability to simultaneously release bioactive ions and the apatite-formation ability of the Sr-and/or Mg-containing HAp bioceramics were evaluated through immersing the samples in SBF for different time periods. Ca ions release and apatite-formation ability on the surfaces of the Sr-and/or Mg-containing HAp bioceramics in SBF depends on Sr and/or Mg concentration in the samples.

Substituted hydroxyapatites with antibacterial properties

Reconstructive surgery is presently struggling with the problem of infections located within implantation biomaterials. Of course, the best antibacterial protection is antibiotic therapy. However, oral antibiotic therapy is sometimes ineffective, while administering an antibiotic at the location of infection is often associated with an unfavourable ratio of dosage efficiency and toxic effect. Thus, the present study aims to find a new factor which may improve antibacterial activity while also presenting low toxicity to the human cells. Such factors are usually implemented along with the implant itself and may be an integral part of it. Many recent studies have focused on inorganic factors, such as metal nanoparticles, salts, and metal oxides. The advantages of inorganic factors include the ease with which they can be combined with ceramic and polymeric biomaterials. The following review focuses on hydroxyapatites substituted with ions with antibacterial properties. It considers materials that have already been applied in regenerative medicine (e.g., hydroxyapatites with silver ions) and those that are only at the preliminary stage of research and which could potentially be used in implantology or dentistry. We present methods for the synthesis of modified apatites and the antibacterial mechanisms of various ions as well as their antibacterial efficiency.

Trace elements and bone health

The importance of nutrition factors such as calcium, vitamin D and vitamin K for the integrity of the skeleton is well known. Moreover, bone health is positively influenced by certain elements (e.g., zinc, copper, fluorine, manganese, magnesium, iron and boron). Deficiency of these elements slows down the increase of bone mass in childhood and/or in adolescence and accelerates bone loss after menopause or in old age. Deterioration of bone quality increases the risk of fractures. Monitoring of homeostasis of the trace elements together with the measurement of bone density and biochemical markers of bone metabolism should be used to identify and treat patients at risk of non-traumatic fractures. Factors determining the effectivity of supplementation include dose, duration of treatment, serum concentrations, as well as interactions among individual elements. Here, we review the effect of the most important trace elements on the skeleton and evaluate their clinical importance.

Biomimetic magnesium-carbonate-apatite nanocrystals endowed with strontium ions as anti-osteoporotic trigger

The present work investigates the preparation of biomimetic nanocrystalline apatites co-substituted with Mg, CO3 and Sr to be used as starting materials for the development of nanostructured bio-devices for regeneration of osteoporotic bone. Biological-like amounts of Mg and CO3 ions were inserted in the apatite structure to mimic the composition of bone apatite, whereas the addition of increasing quantities of Sr ions, from 0 up to 12 wt.%, as anti-osteoporotic agent, was evaluated. The chemical-physical features, the morphology, the degradation rates, the ion release kinetics as well as the in vitro bioactivity of the as-prepared apatites were fully evaluated. The results indicated that the incorporation of 12 wt.% of Sr can be viewed as a threshold for the structural stability of Mg-CO3-apatite. Indeed, incorporation of lower quantity of Sr did not induce considerable variations in the chemical structure of Mg-CO3-apatite, while when the Sr doping extent reached 12 wt.%, a dramatically destabilizing effect was detected on the crystal structure thus yielding alteration of the symmetry and distortion of the PO4. As a consequence, this apatite exhibited the fastest degradation kinetic and the highest amount of Sr ions released when tested in physiological conditions. In this respect, the surface crystallization of new calcium phosphate phase when immersed in physiological-like solution occurred by different mechanisms and extents due to the different structural chemistry of the variously doped apatites. Nevertheless, all the apatites synthesized in this work exhibited in vitro bioactivity demonstrating their potential use to develop biomedical devices with anti-osteoporotic functionality.