Solubility of strontium-substituted apatite by solid titration

Biomaterial Cues for Regulation of Osteoclast Differentiation and Function in Bone Regeneration

Tissue regeneration involves dynamic dialogue between and among different cells and their surrounding matrices. Bone regeneration is specifically governed by reciprocity between osteoblasts and osteoclasts within the bone microenvironment. Osteoclast-directed resorption and osteoblast-directed formation of bone are essential to bone remodeling, and the crosstalk between these cells is vital to curating a sequence of events that culminate in the creation of bone tissue. Among bone biomaterial strategies, many have investigated the use of different material cues to direct the development and activity of osteoblasts. However, less attention has been given to exploring features that similarly target osteoclast formation and activity, with even fewer strategies demonstrating or integrating biomaterial-directed modulation of osteoblast-osteoclast coupling. This review aims to describe various biomaterial cues demonstrated to influence osteoclastogenesis and osteoclast function, emphasizing those that enhance a material construct's ability to achieve bone healing and regeneration. Additionally discussed are approaches that influence the communication between osteoclasts and osteoblasts, particularly in a manner that takes advantage of their coupling. Deepening our understanding of how biomaterial cues may dictate osteoclast differentiation, function, and influence on the microenvironment may enable the realization of bone-replacement interventions with enhanced integrative and regenerative capacities.

Regulation of osteogenesis and angiogenesis by cobalt, manganese and strontium doped apatitic materials for functional bone tissue regeneration

Strontium, cobalt, and manganese ions are present in the composition of bone and useful for bone metabolism, even when combined with calcium phosphate in the composition of biomaterials. Herein we explored the possibility to include these ions in the composition of apatitic materials prepared through the cementitious reaction between ion-substituted calcium phosphate dibasic dihydrate, CaHPO4·2H2O (DCPD) and tetracalcium phosphate, Ca4(PO4)2O (TTCP). The results of the chemical, structural, morphological and mechanical characterization indicate that cobalt and manganese exhibit a greater delaying effect than strontium (about 15 at.%) on the cementitious reaction, even though they are present in smaller amounts within the materials (about 0.8 and 4.5 at.%, respectively). Furthermore, the presence of the foreign ions in the apatitic materials leads to a slight reduction of porosity and to enhancement of compressive strength. The results of biological tests show that the presence of strontium and manganese, as well as calcium, in the apatitic materials cultured in direct contact with human mesenchymal stem cells (hMSCs) stimulates their viability and activity. In contrast, the apatitic material containing cobalt exhibits a lower metabolic activity. All the materials have a positive effect on the expression of Vascular Endothelial Growth Factor (VEGF) and Von Willebrand Factor (vWF). Moreover, the apatitic material containing strontium induces the most significant reduction in the differentiation of preosteoclasts into osteoclasts, demonstrating not only osteogenic and angiogenic properties, but also ability to regulate bone resorption.

Optimization of a tunable process for rapid production of calcium phosphate microparticles using a droplet-based microfluidic platform

Calcium phosphate (CaP) biomaterials are amongst the most widely used synthetic bone graft substitutes, owing to their chemical similarities to the mineral part of bone matrix and off-the-shelf availability. However, their ability to regenerate bone in critical-sized bone defects has remained inferior to the gold standard autologous bone. Hence, there is a need for methods that can be employed to efficiently produce CaPs with different properties, enabling the screening and consequent fine-tuning of the properties of CaPs towards effective bone regeneration. To this end, we propose the use of droplet microfluidics for rapid production of a variety of CaP microparticles. Particularly, this study aims to optimize the steps of a droplet microfluidic-based production process, including droplet generation, in-droplet CaP synthesis, purification and sintering, in order to obtain a library of CaP microparticles with fine-tuned properties. The results showed that size-controlled, monodisperse water-in-oil microdroplets containing calcium- and phosphate-rich solutions can be produced using a flow-focusing droplet-generator microfluidic chip. We optimized synthesis protocols based on in-droplet mineralization to obtain a range of CaP microparticles without and with inorganic additives. This was achieved by adjusting synthesis parameters, such as precursor concentration, pH value, and aging time, and applying heat treatment. In addition, our results indicated that the synthesis and fabrication parameters of CaPs in this method can alter the microstructure and the degradation behavior of CaPs. Overall, the results highlight the potential of the droplet microfluidic platform for engineering CaP microparticle biomaterials with fine-tuned properties.

A Comparative Study on Physicochemical Properties and In Vitro Biocompatibility of Sr-Substituted and Sr Ranelate-Loaded Hydroxyapatite Nanoparticles

Synthetic hydroxyapatite nanoparticles (nHAp) possess compositional and structural similarities to those of bone minerals and play a key role in bone regenerative medicine. Functionalization of calcium phosphate biomaterials with Sr, i.e., bone extracellular matrix trace element, has been proven to be an effective biomaterial-based strategy for promoting osteogenesis in vitro and in vivo. Functionalizing nHAp with Sr2+ ions or strontium ranelate (SrRAN) can provide favorable bone tissue regeneration by locally delivering bioactive molecules to the bone defect microenvironment. Moreover, administering an antiosteoporotic drug, SrRAN, directly into site-specific bone defects could significantly reduce the necessary drug dosage and the risk of possible side effects. Our study evaluated the impact of the Sr source (Sr2+ ions and SrRAN) used to functionalize nHAp by wet precipitation on its in vitro cellular activities. The systematic comparison of physicochemical properties, in vitro Sr2+ and Ca2+ ion release, and their effect on in vitro cellular activities of the developed Sr-functionalized nHAp was performed. The ion release tests in TRIS-HCl demonstrated a 21-day slow and continuous release of the Sr2+ and Ca2+ ions from both Sr-substituted nHAp and SrRAN-loaded HAp. Also, SrRAN and Sr2+ ion release kinetics were evaluated in DMEM to understand their correlation with in vitro cellular effects in the same time frame. Relatively low concentration (up to 2 wt %) of Sr in the nHAp led to an increase in the alkaline phosphatase activity in preosteoblasts and expression of collagen I and osteocalcin in osteoblasts, demonstrating their ability to boost bone formation.

Alginate templated synthesis, characterization and in vitro osteogenic evaluation of strontium-substituted hydroxyapatite

The objective of this study is to explore the potential role of alginate (Alg) in the crystallization of metal-substituted hydroxyapatite, with application in orthopaedic reconstruction. The alginate at different concentrations (0.5 and 1.0 wt%) facilitated in situ mineralization of hydroxyapatite (HA) and strontium-substituted HA (SHA, 10 and 30 mol%). The incorporation of the biopolymer and dopant induced notable changes in HA, including reduced crystal size from 31.0 to 16.4 nm and increased lattice volume from 577.3 to 598.0 Å3. The superior affinity of alginate for Sr2+ than for Ca2+ resulted in higher residual alginate in Alg/SHA (13.0 to 19.0 %) compared to Alg/HA (7.1 to 8.2 %). This residual alginate influenced composite properties: surface charge decreased from -26.5 to -45.7 mV, microhardness increased from 0.33 to 0.54 GPa, and dissolution increased from 0.17 to 0.39 %. The in vitro studies revealed that strontium substitution as well as the organization and crystallographic aspects of apatite regulated osteoblastic cell survival, proliferation, differentiation, and biomineralization. The findings suggest that an alginate concentration of 0.5 wt% is optimal for the crystallization of SHA with 10 mol% substitution, and its resulting composite possesses the ideal biomechanical properties to imitate native bone.

Alkaline earth metals for osteogenic scaffolds: From mechanisms to applications

Regeneration of bone defects is a significant challenge today. As alternative approaches to the autologous bone, scaffold materials have remarkable features in treating bone defects; however, the various properties of current scaffold materials still fall short of expectations. Due to the osteogenic capability of alkaline earth metals, their application in scaffold materials has become an effective approach to improving their properties. Furthermore, numerous studies have shown that combining alkaline earth metals leads to better osteogenic properties than applying them alone. In this review, the physicochemical and physiological characteristics of alkaline earth metals are introduced, mainly focusing on their mechanisms and applications in osteogenesis, especially magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Furthermore, this review highlights the possible cross-talk between pathways when alkaline earth metals are combined. Finally, some of the current drawbacks of scaffold materials are enumerated, such as the high corrosion rate of Mg scaffolds and defects in the mechanical properties of Ca scaffolds. Moreover, a brief perspective is also provided regarding future directions in this field. It is worth exploring that whether the levels of alkaline earth metals in newly regenerated bone differs from those in normal bone. The ideal ratio of each element in the bone tissue engineering scaffolds or the optimal concentration of each elemental ion in the created osteogenic environment still needs further exploration. The review not only summarizes the research developments in osteogenesis but also offers a direction for developing new scaffold materials.

Impact of claudin-10 deficiency on amelogenesis: Lesson from a HELIX tooth

In epithelia, claudin proteins are important components of the tight junctions as they determine the permeability and specificity to ions of the paracellular pathway. Mutations in CLDN10 cause the rare autosomal recessive HELIX syndrome (Hypohidrosis, Electrolyte imbalance, Lacrimal gland dysfunction, Ichthyosis, and Xerostomia), in which patients display severe enamel wear. Here, we assess whether this enamel wear is caused by an innate fragility directly related to claudin-10 deficiency in addition to xerostomia. A third molar collected from a female HELIX patient was analyzed by a combination of microanatomical and physicochemical approaches (i.e., electron microscopy, elemental mapping, Raman microspectroscopy, and synchrotron-based X-ray fluorescence). The enamel morphology, formation time, organization, and microstructure appeared to be within the natural variability. However, we identified accentuated strontium variations within the HELIX enamel, with alternating enrichments and depletions following the direction of the periodical striae of Retzius. These markings were also present in dentin. These data suggest that the enamel wear associated with HELIX may not be related to a disruption of enamel microstructure but rather to xerostomia. However, the occurrence of events of strontium variations within dental tissues might indicate repeated episodes of worsening of the renal dysfunction that may require further investigations.

Rapid Synthesis of Multifunctional Apatite via the Laser-Induced Hydrothermal Process

Synthetic biomaterials are used to overcome the limited quantity of human-derived biomaterials and to impart additional biofunctionality. Although numerous synthetic processes have been developed using various phases and methods, currently commonly used processes have some issues, such as a long process time and difficulties with extensive size control and high-concentration metal ion substitution to achieve additional functionality. Herein, we introduce a rapid synthesis method using a laser-induced hydrothermal process. Based on the thermal interaction between the laser pulses and titanium, which was used as a thermal reservoir, hydroxyapatite particles ranging from nanometer to micrometer scale could be synthesized in seconds. Further, this method enabled selective metal ion substitution into the apatite matrix with a controllable concentration. We calculated the maximum temperature achieved by laser irradiation at the surface of the thermal reservoir based on the validation of three simplification assumptions. Subsequent linear regression analysis showed that laser-induced hydrothermal synthesis follows an Arrhenius chemical reaction. Hydroxyapatite and Mg²⁺-, Sr²⁺-, and Zn²⁺-substituted apatite powders promoted bone cell attachment and proliferation ability due to ion release from the hydroxyapatite and the selective ion-substituted apatite powders, which had a low crystallinity and relatively high solubility. Laser-induced hydrothermal synthesis is expected to become a powerful ceramic material synthesis technology.

Immunomodulation and osseointegration activities of Na2TiO3 nanorods-arrayed coatings doped with different Sr content

To endow Ti-based orthopedic implants immunomodulatory capability and thus enhanced osseointegration, different amounts of Sr are doped in Na2TiO3 nanorods in the arrays with identical nanotopographic parameters (rod diameter, length and inter-rod spacing) by substitution of Na+ using hydrothermal treatment. The obtained arrays are denoted as STSr2, STSr4, and STSr7, where the arabic numbers indicate the incorporating amounts of Sr in Na2TiO3. The modulation effects of the Sr-doped nanorods arrays on macrophage polarization and osteogenetic functions of osteoblasts are investigated, together with the array without Sr (ST). Moreover, osseointegration of these arrays are also assayed in rat femoral condyles. Sr-doped nanorods arrays accelerate M1 (pro-inflammatory phenotype)-to-M2 (anti-inflammatory phenotype) transformation of the adhered macrophages, enhancing secretion of pro-osteogenetic cytokines and growth factors (TGF-β1 and BMP2), moreover, the Sr doped arrays directly enhance osteogenetic functions of osteoblasts. The enhancement of paracrine of M2 macrophages and osteogenetic function of osteoblasts is promoted with the increase of Sr incorporating amounts. Consequently, Sr doped arrays show significantly enhanced osseointegration in vivo compared to ST, and STSr7 exhibits the best performance. Our work sheds a new light on the design of surface chemical components and structures for orthopedic implants to enhance their osseointegration.

In Vitro Study of Degradation and Cytocompatibility of Ceramics/PLA Composite Coating on Pure Zinc for Orthopedic Application

Zinc and its alloys are considered to be next-generation materials for fabricating absorbable biomedical devices. However, cytotoxicity has been reported to be associated with rapid degradation. To address these issues, a composite coating (PLA/Li-OCP) consisting of CaHPO4 conversion coating (Ca-P) and polylactic acid (PLA) decorated with Li-octacalcium phosphate particles was constructed on pure zinc. The immersion tests showed that the presence of Ca-P coating and PLA/Li-OCP coating on pure zinc could reduce the pH value. Compared with Ca-P coating, the introduction of the PLA/Li-OCP film on the Ca-P-coated samples could enhance the corrosion resistance, and there was one order of magnitude decrease in the corrosion current density. The cytocompatibility assay suggested that the PLA/Li-OCP coating favored the cell viability and upregulated the expression of related osteogenic-genes including RUNX2, OCN, and BMP. Therefore, the presence of the PLA/Li-OCP coating on pure zinc could effectively improve the degradation rate and cytocompatibility of pure zinc.

Zn/Sr dual ions-collagen co-assembly hydroxyapatite enhances bone regeneration through procedural osteo-immunomodulation and osteogenesis

The immune microenvironment induced by biomaterials played vital roles in bone regeneration. Hydroxyapatite (HA) and its ion-substituted derivates represent a large class of core inorganic materials for bone tissue engineering. Although ion substitution was proved to be a potent way to grant HA more biological functions, few studies focused on the immunomodulatory properties of ion-doped HA. Herein, to explore the potential osteoimmunomodulatory effects of ion-doped HA, zinc and strontium co-assembled into HA through a collagen template biomimetic way (ZnSr-Col-HA) was successfully achieved. It was found that ZnSr-Col-HA could induce a favorable osteo-immune microenvironment by stimulating macrophages. Furthermore, ZnSr-Col-HA demonstrated a procedural promoting effect on osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in vitro. Specifically, the osteo-immune microenvironment acted as a dominant factor in promoting osteogenic gene expressions at the early stage through OSM signal pathway. Whereas the direct stimulating effects on BMSCs by Zn²⁺/Sr²⁺ were more effectively at the later stage with Nfatc1/Maf and Wnt signals activated. In vivo study confirmed strong promoting effects of ZnSr-Col-HA on critical-sized cranial defect repair. The current study indicated that such a combined biomaterial design philosophy of dual ion-doping and biomimetic molecular co-assembly to endow HA applicable osteoimmunomodulatory characteristics might bring up a new cutting-edge concept for bone regeneration study.

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Zn/Sr dual ions-collagen co-assembly hydroxyapatite (ZnSr-Col-HA) was achieved via a molecular template biomimetic way.

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A procedural promoting effect of ZnSr-Col-HA on osteogenic differentiation of BMSCs was firstly found.

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A novel material design philosophy was proposed for dual ions-doped biomimetic HA with osteoimmunomodulatory properties.

Porous membranes of quaternized chitosan composited with strontium-based nanobioceramic for periodontal tissue regeneration

This report demonstrates the development of a degradable quaternary ammonium derivative of chitosan (QC) composited with strontium-containing nanoapatite (SA) for bioactivity. The material was made as porous membrane by solution casting and freeze drying, for guided tissue regeneration (GTR) applications. The micromorphology, tensile strength, suture pull-out strength, degradation (in vitro, in phosphate buffered saline), and cytocompatibility (using human periodontal ligament cells) were tested to investigate the effect of derivatization and SA addition. The porosity of the membranes increased with increasing SA content and so did the tensile strength and the degradation. The suture pull-out strength, however, showed a decrease. The cell culture evaluation endorsed biocompatibility. The composite with 1.5 mg SA per 1 mL QC was found to have optimal qualities for GTR applications.

Biomimetic Strontium Substituted Calcium Phosphate Coating for Bone Regeneration

Cellulose acetate (CA)/strontium phosphate (SrP) hybrid coating has been proposed as an effective strategy to build up novel bone-like structures for bone healing since CA is soluble in most organic solvents. Strontium (Sr2+) has been reported as a potential agent to treat degenerative bone diseases due to its osteopromotive and antibacterial effects. Herein, bioactive hybrid composite SrP-based coatings (CASrP) were successfully produced for the first time. CASrP was synthesized via a modified biomimetic method (for 7—CA7dSrP, and 14 days—CA14dSrP), in which the metal ion Sr2+ was used in place of Ca2+ in the simulated body fluid. Energy-dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR) analysis confirmed the SrP incorporation chemically in the CASrP samples. Atomic absorption spectroscopy (AAS) supported EDX data, showing Sr2+ adsorption into CA, and its significant increase with the augmentation of time of treatment (ca. 92%—CA7dSrP and 96%—CA14dSrP). An increment in coating porosity and the formation of SrP crystals were evidenced by scanning electron microscopy (SEM) images. X-ray diffraction (XRD) evidenced a greater crystallinity than CA membranes and a destabilization of CA14dSrP structure compared to CA7dSrP. The composites were extremely biocompatible for fibroblast and osteoblast cells. Cell viability (%) was higher either for CA7dSrP (48 h: ca. 92% and 115%) and CA14dSrP (48 h: ca. 88% and 107%) compared to CA (48 h: ca. 70% and 51%) due to SrP formation and Sr2+ presence in its optimal dose in the culture media (4.6–9 mg·L−1). In conclusion, the findings elucidated here evidence the remarkable potential of CA7dSrP and CA14dSrP as bioactive coatings on the development of implant devices for inducing bone regeneration.

Nanoscale Strontium-Substituted Hydroxyapatite Pastes and Gels for Bone Tissue Regeneration

Injectable nanoscale hydroxyapatite (nHA) systems are highly promising biomaterials to address clinical needs in bone tissue regeneration, due to their excellent biocompatibility, bioinspired nature, and ability to be delivered in a minimally invasive manner. Bulk strontium-substituted hydroxyapatite (SrHA) is reported to encourage bone tissue growth by stimulating bone deposition and reducing bone resorption, but there are no detailed reports describing the preparation of a systematic substitution up to 100% at the nanoscale. The aim of this work was therefore to fabricate systematic series (0–100 atomic% Sr) of SrHA pastes and gels using two different rapid-mixing methodological approaches, wet precipitation and sol-gel. The full range of nanoscale SrHA materials were successfully prepared using both methods, with a measured substitution very close to the calculated amounts. As anticipated, the SrHA samples showed increased radiopacity, a beneficial property to aid in vivo or clinical monitoring of the material in situ over time. For indirect methods, the greatest cell viabilities were observed for the 100% substituted SrHA paste and gel, while direct viability results were most likely influenced by material disaggregation in the tissue culture media. It was concluded that nanoscale SrHAs were superior biomaterials for applications in bone surgery, due to increased radiopacity and improved biocompatibility.

Bioactive Sr2+/Fe3+co-substituted hydroxyapatite in cryogenically 3D printed porous scaffolds for bone tissue engineering

Developing multi-doped bioceramics that possess biological multifunctionality is becoming increasingly attractive and promising for bone tissue engineering. In this view innovative Sr²⁺/Fe³⁺co-substituted nano-hydroxyapatite with gradient doping concentrations fixed at 10 mol% has been deliberately designed previously. Herein, to evaluate their therapeutic potentials for bone healing, novel gradient SrFeHA/PCL scaffolds are fabricated by extrusion cryogenic 3D printing technology with subsequent lyophilization. The obtained scaffolds exhibit desired 3D interconnected porous structure and rough microsurface, along with appreciable release of bioactive Sr²⁺/Fe³⁺from SrFeHA components. These favorable physicochemical properties render printed scaffolds realizing effective biological applications bothin vitroandin vivo, particularly the moderate co-substituted Sr7.5Fe2.5HA and Sr5Fe5HA groups exhibit remarkably enhanced bioactivity that not only promotes the functions of MC3T3 osteoblasts and HUVECs directly, but also energetically manipulates favorable macrophages activation to concurrently facilitate osteogenesis/angiogenesis. Moreover,in vivosubcutaneous implantation and cranial defects repair outcomes further confirm their superior capacity to dictate immune reaction, implants vascularization andin situbone regeneration, mainly dependent on the synergetic effects of released Sr²⁺/Fe³⁺. Accordingly, for the first time, present study highlights the great potential of Sr7.5Fe2.5HA and Sr5Fe5HA for ameliorating bone regeneration process by coupling of immunomodulation with enhanced angio- and osteogenesis and hence may provide a new promising alternative for future bone tissue engineering.

Three-Dimensional Printing of Hydroxyapatite Composites for Biomedical Application

Hydroxyapatite (HA) and HA-based nanocomposites have been recognized as ideal biomaterials in hard tissue engineering because of their compositional similarity to bioapatite. However, the traditional HA-based nanocomposites fabrication techniques still limit the utilization of HA in bone, cartilage, dental, applications, and other fields. In recent years, three-dimensional (3D) printing has been shown to provide a fast, precise, controllable, and scalable fabrication approach for the synthesis of HA-based scaffolds. This review therefore explores available 3D printing technologies for the preparation of porous HA-based nanocomposites. In the present review, different 3D printed HA-based scaffolds composited with natural polymers and/or synthetic polymers are discussed. Furthermore, the desired properties of HA-based composites via 3D printing such as porosity, mechanical properties, biodegradability, and antibacterial properties are extensively explored. Lastly, the applications and the next generation of HA-based nanocomposites for tissue engineering are discussed.

Synthesis and properties of Sr2+ doping α-tricalcium phosphate at low temperature

Strontium has been widely used in bone repair materials due to its roles in promoting osteoclast apoptosis and enhancing osteoblast proliferation. In this work, synthesis and the effects of Sr²⁺ doping α-tricalcium phosphate at low-temperature was studied. The setting time and the mechanical properties of α-tricalcium phosphate were controlled by varying the content of Sr²⁺. The synthesized compounds were evaluated by XRD, SEM, XPS, setting time, compressive strength, SBF immersion, and colorimetric CCK-8 assay. The results showed that Sr²⁺ can improve the compressive strength and cell activity of calcium phosphate bone cement.

Long-term in vitro degradation and in vivo evaluation of resorbable bioceramics

An essential criterion for the selection of resorbable bioceramics is their ability to degrade inside human body within a reasonable time frame. Furthermore, if the bioceramic can release beneficial ions, such as strontium, as it degrades, recovery time might be shortened. The present study demonstrates that strontium-containing calcium sulfate (Sr,Ca)SO₄ can fulfill these criteria. A long-term in vitro degradation analysis for 12 weeks using sintered (Sr,Ca)SO₄ discs in phosphate buffered solution (PBS) was conducted. The sintered (Sr,Ca)SO₄ disc was then implanted into defects in the distal femur of rats. The degradation rate of (Sr,Ca)SO₄ discs showed a strong dependence on the Sr content. Similar results were observed between the long-term in vitro degradation analysis and the in vivo evaluation. The sintered (3.8%Sr,Ca)SO₄ disc lost more than 80% of its initial weight after soaking in PBS with shaking at 37 °C for 12 weeks. After 12 weeks in vivo, the remaining volume of the (3.8%Sr,Ca)SO₄ disc within the bone defect was ~25%. Over the same time period, new bone was formed at a relative volume of 40%. This study demonstrates the potential of (Sr,Ca)SO₄ bioceramic, and the benefits of using a long-term degradation test during the evaluation of resorbable bioceramics.

Rational design of nonstoichiometric bioceramic scaffolds via digital light processing: tuning chemical composition and pore geometry evaluation

Bioactive ceramics are promising candidates as 3D porous substrates for bone repair in bone regenerative medicine. However, they are often inefficient in clinical applications due to mismatching mechanical properties and compromised biological performances. Herein, the additional Sr dopant is hypothesized to readily adjust the mechanical and biodegradable properties of the dilute Mg-doped wollastonite bioceramic scaffolds with different pore geometries (cylindrical-, cubic-, gyroid-) by ceramic stereolithography. The results indicate that the compressive strength of Mg/Sr co-doped bioceramic scaffolds could be tuned simultaneously by the Sr dopant and pore geometry. The cylindrical-pore scaffolds exhibit strength decay with increasing Sr content, whereas the gyroid-pore scaffolds show increasing strength and Young's modulus as the Sr concentration is increased from 0 to 5%. The ion release could also be adjusted by pore geometry in Tris buffer, and the high Sr content may trigger a faster scaffold bio-dissolution. These results demonstrate that the mechanical strengths of the bioceramic scaffolds can be controlled from the point at which their porous structures are designed. Moreover, scaffold bio-dissolution can be tuned by pore geometry and doping foreign ions. It is reasonable to consider the nonstoichiometric bioceramic scaffolds are promising for bone regeneration, especially when dealing with pathological bone defects.

Ion release from hydroxyapatite and substituted hydroxyapatites in different immersion liquids: in vitro experiments and theoretical modelling study

Multi-substituted hydroxyapatites (ms-HAPs) are currently gaining more consideration owing to their multifunctional properties and biomimetic structure, owning thus an enhanced biological potential in orthopaedic and dental applications. In this study, nano-hydroxyapatite (HAP) substituted with multiple cations (Sr2+, Mg2+ and Zn2+) for Ca2+ and anion ( Si O 4 4 - ) for P O 4 3 - and OH-, specifically HAPc-5%Sr and HAPc-10%Sr (where HAPc is HAP-1.5%Mg-0.2%Zn-0.2%Si), both lyophilized non-calcined and lyophilized calcined, were evaluated for their in vitro ions release. These nanomaterials were characterized by scanning electron microscopy, field emission-scanning electron microscopy and energy-dispersive X-ray, as well as by atomic force microscope images and by surface specific areas and porosity. Further, the release of cations and of phosphate anions were assessed from nano-HAP and ms-HAPs, both in water and in simulated body fluid, in static and simulated dynamic conditions, using inductively coupled plasma optical emission spectrometry. The release profiles were analysed and the influence of experimental conditions was determined for each of the six nanomaterials and for various periods of time. The pH of the samples soaked in the immersion liquids was also measured. The ion release mechanism was theoretically investigated using the Korsmeyer-Peppas model. The results indicated a mechanism principally based on diffusion and dissolution, with possible contribution of ion exchange. The surface of ms-HAP nanoparticles is more susceptible to dissolution into immersion liquids owing to the lattice strain provoked by simultaneous multi-substitution in HAP structure. According to the findings, it is rational to suggest that both materials HAPc-5%Sr and HAPc-10%Sr are bioactive and can be potential candidates in bone tissue regeneration.

Spectroscopic and microscopic examination of teeth exposed to green tea at different temperatures

Tea is a popular beverage consumed at different temperatures. The effect of tea on teeth at different temperatures has not been studied previously. The present study used an in vitro green tea immersed tooth model at different tea temperatures (hot and cold) compared to an in vivo tea administration model allowing rats to drink tea over the course of a week. The elements present in tea leaves were identified by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and compared to the elements in teeth (enamel surface) using Laser-Induced Breakdown Spectroscopy (LIBS). Here, LIBS demonstrated in vivo and in vitro green tea treatments resulted in a significant increase in the mineral elements found in enamel. For the in vitro assessment, elements in enamel varied based on cold-tea and hot-tea treatment; however, hot water reduced the elements in enamel. Atomic force microscopy found the in vivo tea group had a higher roughness average (RA) compared with the in vivo water group. Cold tea and hot tea in vitro groups demonstrated lower RA than in vitro water controls. Scanning electron microscopy found hot water induced cracks more than 1.3μm in enamel while cold tea and hot tea promoted the adhering of extrinsic matter to teeth. Overall, teeth treated to high temperature lost the mineral phase leading to demineralization. Our results indicate that green tea protects enamel, but its protective action in dental structures is enhanced at cold temperature.

An in vivo Comparison Study Between Strontium Nanoparticles and rhBMP2

The osteoinductive property of strontium was repeatedly proven in the last decades. Compelling in vitro data demonstrated that strontium hydroxyapatite nanoparticles exert a dual action, by promoting osteoblasts-driven matrix secretion and inhibiting osteoclasts-driven matrix resorption. Recombinant human bone morphogenetic protein 2 (rhBMP2) is a powerful osteoinductive biologic, used for the treatment of vertebral fractures and critically-sized bone defects. Although effective, the use of rhBMP2 has limitations due its recombinant morphogen nature. In this study, we examined the comparison between two osteoinductive agents: rhBMP2 and the innovative strontium-substituted hydroxyapatite nanoparticles. To test their effectiveness, we independently loaded Gelfoam sponges with the two osteoinductive agents and used the sponges as agent-carriers. Gelfoam are FDA-approved biodegradable medical devices used as delivery system for musculoskeletal defects. Their porous structure and spongy morphology make them attractive in orthopedic field. The abiotic characterization of the loaded sponges, involving ion release pattern and structure investigation, was followed by in vivo implantation onto the periosteum of healthy mice and comparison of the effects induced by each implant was performed. Abiotic analysis demonstrated that strontium was continuously released from the sponges over 28 days with a pattern similar to rhBMP2. Histological observations and gene expression analysis showed stronger endochondral ossification elicited by strontium compared to rhBMP2. Osteoclast activity was more inhibited by strontium than by rhBMP2. These results demonstrated the use of sponges loaded with strontium nanoparticles as potential bone grafts might provide better outcomes for complex fractures. Strontium nanoparticles are a novel and effective non-biologic treatment for bone injuries and can be used as novel powerful therapeutics for bone regeneration.

Formation of stable strontium-rich amorphous calcium phosphate: Possible effects on bone mineral

Bone, tooth enamel, and dentin accumulate Sr²⁺, a natural trace element in the human body. Sr²⁺ comes from dietary and environmental sources and is thought to play a key role in osteoporosis treatments. However, the underlying impacts of Sr²⁺on bone mineralization remain unclear and the use of synthetic apatites (which are structurally different from bone mineral) and non-physiological conditions have led to contradictory results. Here, we report on the formation of a new Sr²⁺-rich and stable amorphous calcium phosphate phase, Sr(ACP). Relying on a bioinspired pathway, a series of Sr²⁺ substituted hydroxyapatite (HA) that combines the major bone mineral features is depicted as model to investigate how this phase forms and Sr²⁺ affects bone. In addition, by means of a comprehensive investigation the biomineralization pathway of Sr²⁺ bearing HA is described showing that not more than 10 at% of Sr²⁺, i.e. a physiological limit incorporated in bone, can be incorporated into HA without phase segregation. A combination of ³¹P and ¹H solid state NMR, energy electron loss spectromicroscopy, transmission electron microscopy, electron diffraction, and Raman spectroscopy shows that Sr²⁺ introduces disorder in the HA culminating with the unexpected Sr(ACP), which co-exists with the HA under physiological conditions. These results suggest that heterogeneous Sr²⁺ distribution in bone is associated with regions of low structural organization. Going further, such observations give clues from the physicochemical standpoint to understand the defects in bone formation induced by high Sr²⁺ doses. STATEMENT OF SIGNIFICANCE: Understanding the role played by Sr²⁺ has a relevant impact in physiological biomineralization and provides insights for its use as osteoporosis treatments. Previous studies inspired by the bone remodelling pathway led to the formation of biomimetic HA in terms of composition, structures and properties in water. Herein, by investigating different atomic percentage of Sr²⁺ related to Ca²⁺ in the synthesis, we demonstrate that 10% of Sr²⁺ is the critical loads into the biomimetic HA phase; similarly to bone. Unexpectedly, using higher amount leads to the formation of a stable Sr²⁺-rich amorphous calcium phosphate phase that may high-dose related pathologies. Our results provide further understanding of the different ways Sr²⁺ impacts bone.

Effect of strontium doping on the biocompatibility of calcium phosphate-coated titanium substrates

BACKGROUND:

Titanium biomedical devices coated with strontium-doped calcium phosphate ceramics can support desirable bone regeneration through anabolic and anti-catabolic effects of strontium and the compositions close to that of natural mineral tissue.

METHODS:

Strontium was doped into the calcium phosphate coating using the cyclic pre-calcification method on the anodized titanium plate. The effects of the different concentration of strontium in treatment solution and cycle numbers of the pre-calcification treatment on the biocompatibility were investigated in terms of the changes in morphology and chemical composition of coating, ion release pattern and cytocompatibility in vitro.

RESULTS:

At a high substitution ratio of strontium in the calcium phosphate coating, the size of precipitated particles was decreased and the solubility of the coating was increased. ASH55 group, which was coated by pre-calcification treatment of 20 cycles in coating solution with Sr:Ca molar ratio of 5:5, exhibited superior cellular attachment at 1 day and proliferation after 7 days of culturing in comparison with the non-doped surface and other doped surfaces.

CONCLUSION:

Sufficient strontium doping concentrations in calcium phosphate coating can enhance cell adhesion and proliferation on the titanium biomedical devices for bone regeneration.

Strontium-substituted hydroxyapatite stimulates osteogenesis on poly(propylene fumarate) nanocomposite scaffolds

Incorporation of hydroxyapatite (HA) into polymer networks is a promising strategy to enhance the mechanical properties and osteoinductivity of the composite scaffolds for bone tissue engineering. In this study, we designed a group of nanocomposite scaffolds based on cross-linkable poly(propylene fumarate) (PPF) and 30 wt % strontium-hydroxyapatite (Sr-HA) nanoparticles. Four different Sr contents [Sr:(Sr + Ca), molar ratio] in the Sr-HA particles were studied: 0% (HA), 5% (Sr5-HA), 10% (Sr10-HA), and 20% (Sr20-HA). Two-dimensional (2D) disks were prepared using a thermal crosslinking method. The structure and surface morphology of different Sr-HA and PPF/Sr-HA composites were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). To detect cellular responses in vitro, MC3T3-E1 cells were seeded and cultured on the different PPF/Sr-HA composite disks. Cell morphology after 24 h and 5 days were imaged using Live/Dead live cell staining and SEM, respectively. Cell proliferation was quantified using an MTS assay at 1, 4, and 7 days. Osteogenic differentiation of the cells was examined by alkaline phosphatase (ALP) staining at 10 days and quantified using ALP activity and osteocalcin assays at 7, 14, and 21 days. The sizes of the HA, Sr5-HA, Sr10-HA, and Sr20-HA particles were mainly between 10 × 20 nm and 10 × 250 nm, and these nanoparticles were dispersed or clustered in the composite scaffolds. in vitro cell studies showed that the PPF/Sr10-HA scaffold was significantly better than the other three groups (PPF/HA, PPF/Sr5-HA, and PPF/Sr20-HA) in supporting MC3T3-E1 cell adhesion, proliferation, and differentiation. PPF/Sr10-HA may, therefore, serve as a promising scaffold material for bone tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 631-642, 2019.

Degradation and biocompatibility of a series of strontium substituted hydroxyapatite coatings on magnesium alloys

Sr-HA coatings could simply improve the degradation and osteoblast response of Mg in a Sr-dose dependent manner.

Strontium ions promote in vitro human bone marrow stromal cell proliferation and differentiation in calcium-lacking media

In order to investigate the influence of calcium and strontium ion concentration on human bone marrow stromal cells and their differentiation to osteoblasts, different cell culture media have been used. Even though this study does not contain a bone substitute material, the reason for this study was the decrease of cation concentration by many biomaterials, due to induced apatite precipitation. As a consequence, the reduced calcium ion concentration is known to affect osteoblastic development. Therefore, the main focus was put on the question, whether an increased strontium concentration (in the range of mM) might be suitable to compensate the lack of calcium ions. The effect of solely strontium ions-with only calcium in the media resulting from fetal calf serum-was investigated. Commercially available calcium-free medium (modified α-MEM) was tested in comparison with media with varied calcium ion concentrations (0.9, 1.8, and 3.6 mM), or strontium ion concentration (0.4, 0.9, 1.8, and 3.6 mM). In case of calcium, higher concentrations cause increased proliferation, while differentiation was shifted to earlier points of time. Differentiation was increased by solely strontium ions only at 0.4-0.9 mM, while proliferation was highest for 0.9-1.8 mM. From these results, it can be concluded that strontium is able to compensate a lack of calcium to a certain degree. Thus, in contrast to calcium ion release, a strontium ion release from bone substitute materials might be applicable for stimulation of bone regeneration without influencing the media saturation.

Strontium-Substituted Hydroxyapatite-Gelatin Biomimetic Scaffolds Modulate Bone Cell Response

Strontium has a beneficial role on bone remodeling and is proposed for the treatment of pathologies associated to excessive bone resorption, such as osteoporosis. Herein, the possibility to utilize a biomimetic scaffold as strontium delivery system is explored. Porous 3D gelatin scaffolds containing about 30% of strontium substituted hydroxyapatite (SrHA) or pure hydroxyapatite (HA) are prepared by freeze-drying. The scaffolds display a very high open porosity, with an interconnectivity of 100%. Reinforcement with further amount of gelatin provokes a modest decrease of the average pore size, without reducing interconnectivity. Moreover, reinforced scaffolds display reduced water uptake ability and increased values of mechanical parameters when compared to as-prepared scaffolds. Strontium displays a sustained release in phosphate buffered saline: the quantities released after 14 d from as-prepared and reinforced scaffolds are just 14 and 18% of the initial content, respectively. Coculture of osteoblasts and osteoclasts shows that SrHA-containing scaffolds promote osteoblast viability and activity when compared to HA-containing scaffolds. On the other hand, osteoclastogenesis and osteoclast differentiation are significantly inhibited on SrHA-containing scaffolds, suggesting that these systems could be usefully applied for local delivery of strontium in loci characterized by excessive bone resorption.

Strontium-releasing fluorapatite glass-ceramics: Crystallization behavior, microstructure, and solubility

The purpose of this work was to investigate the effect of strontium partial replacement for calcium on the crystallization behavior, microstructure and solubility of fluorapatite glass-ceramics. Four glass compositions were prepared with increasing amounts of strontium partially replacing calcium. The crystallization behavior was analyzed by differential scanning calorimetry and X-ray diffraction (XRD). The microstructure was investigated by scanning electron microscopy. The chemical solubility was quantified according to ISO standard 10993-14. The amount of strontium released in solution after incubation in TRIS-HCl or citric acid buffer was measured by atomic absorption spectroscopy. XRD analyses revealed that partially substituted strontium-fluorapatite and strontium-åkermanite crystallized after strontium additions. The lattice cell volume of both phases increased linearly with the amount of strontium in the composition. Strontium additions led to a reduction in crystal size and an increase in crystal number density. The chemical solubility and amount of strontium released in solution increased linearly with the amount of strontium present in the composition in both TRIS-HCl and citric acid buffers. Total amounts of strontium released reached a maximum of 547 ± 80 ppm in TRIS-HCl and 1252 ± 290 ppm in citric acid buffer for the glass composition with the highest amount of strontium. For all strontium-containing compositions, the amount released in TRIS-HCl continued to increase between 70 and 120 h, indicating sustained release rather than burst release. © 2017 Wiley Periodicals, Inc. J Biomater Res Part B: 106B: 1421-1430, 2018.

Functionalized biomimetic calcium phosphates for bone tissue repair

The design and development of novel materials for biomineralized tissues is an extremely attractive field of research where calcium phosphates (CaPs)-based materials for biomedical applications play a leading role. The biological performance of these compounds can be enhanced through functionalization with biologically active ions and molecules. This review reports on some important recent achievements in creating functionalized biomimetic CaP materials for applications in the musculoskeletal field. Particular attention is focused on the modifications of these inorganic compounds with bioactive ions, growth factors and drugs, as well as on recent trends in some important CaP applications as biomaterials - namely, as bone cements, coatings of metallic implants and scaffolds for regenerative medicine.

Strontium release from Sr2+-loaded bone cements and dispersion in healthy and osteoporotic rat bone

Drug functionalization of biomaterials is a modern and popular approach in biomaterials research. Amongst others this concept is used for the functionalization of bone implants to locally stimulate the bone healing process. For example strontium ions (Sr²⁺) are administered in osteoporosis therapy to stimulate bone growth and have recently been integrated into bone cements. Based on results of different analytical experiments we developed a two-phase model for the transport of therapeutically active Sr²⁺-ions in bone in combination with Korsmeyer-Peppas kinetics for the Sr²⁺ release from bone cement. Data of cement dissolution experiments into water in combination with inductively coupled plasma mass spectrometry (ICP-MS) analysis account for dissolution kinetics following Noyes-Whitney rule. For dissolution in α-MEM cell culture media the process is kinetically hindered and can be described by Korsmeyer-Peppas kinetics. Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to determine the Sr²⁺ diffusion coefficient in healthy and osteoporotic trabecular rat bone. Therefore, bone sections were dipped in aqueous Sr²⁺-solution by one side and the Sr²⁺-profile was measured by classical SIMS depth profiling. The Sr²⁺ mobility can be described by a simple diffusion model and we obtained diffusion coefficients of (2.28±2.97)⋅10^-12cm²/s for healthy and of (1.55±0.93)⋅10^-10cm²/s for osteoporotic bone. This finding can be explained by a different bone nanostructure, which was observed by focused ion beam scanning electron microscopy (FIB-SEM) and transmission electron microscopy (TEM). Finally, the time and spatially resolved drug transport was calculated by finite element method for the femur of healthy and osteoporotic rats. The obtained results were compared to mass images that were obtained from sections of in vivo experiments by ToF-SIMS. The simulated data fits quite well to experimental results. The successfully applied model for the description of drug dispersion can help to reduce the number of animal experiments in the future.

Competing Roles of Substrate Composition, Microstructure, and Sustained Strontium Release in Directing Osteogenic Differentiation of hMSCs

Strontium releasing bioactive ceramics constitute an important class of biomaterials for osteoporosis treatment. In the present study, we evaluated the synthesis, phase assemblage, and magnetic properties of strontium hexaferrite, SrFe₁₂O₁₉, (SrFe) nanoparticles. On the biocompatibility front, the size- and dose-dependent cytotoxicity of SrFe against human mesenchymal stem cells (hMSCs) were investigated. After establishing their non-toxic nature, we used the strontium hexaferrite nanoparticles (SrFeNPs) in varying amount (x = 0, 10, and 20 wt %) to consolidate bioactive composites with hydroxyapatite (HA) by multi-stage spark plasma sintering (SPS). Rietveld refinement of these spark plasma sintered composites revealed a near complete decomposition of SrFe₁₂O₁₉ to magnetite (Fe₃O₄) along with a marked increase in the unit cell volume of HA, commensurate with strontium-doped HA. The cytocompatibility of SrHA-Fe composites with hMSCs was assessed using qualitative and quantitative morphological analysis along with phenotypic and genotypic expression for stem cell differentiation. A marked decrease in the stemness of hMSCs, indicated by reduced vimentin expression and acquisition of osteogenic phenotype, evinced by alkaline phosphatase (ALP) and collagen deposition was recorded on SrHA-Fe composites in osteoinductive culture. A significant upregulation of osteogenic marker genes (Runx2, ALP and OPN) was detected in case of the SrHA-Fe composites, whereas OCN and Col IA expression were similarly high for baseline HA. However, matrix mineralization was elevated on SrHA-Fe composites in commensurate with the release of Sr²⁺ and Fe²⁺. Summarizing, the current work is the first report of strontium hexaferrite as a non-toxic nanobiomaterial. Also, SrHA-based iron oxide composites can potentially better facilitate bone formation, when compared to pristine HA.

Strontium-doped calcium silicate bioceramic with enhanced in vitro osteogenic properties

Gehlenite (GLN, Ca₂SiAl₂O₇) is a bioceramic that has been recently shown to possess excellent mechanical strength and in vitro osteogenic properties for bone regeneration. Substitutional incorporation of strontium in place of calcium is an effective way to further enhance biological properties of calcium-based bioceramics and glasses. However, such strategy has the potential to affect other important physicochemical parameters such as strength and degradation due to differences in the ionic radius of strontium and calcium. This study is the first to investigate the effect of a range of concentrations of strontium substitution of calcium at 1, 2, 5, 10 mol% (S1-GLN, S2-GLN, S5-GLN and S10-GLN) on the physicochemical and biological properties of GLN. We showed that up to 2 mol% strontium ion substitution retains the monophasic GLN structure when sintered at 1450 °C, whereas higher concentrations resulted in presence of calcium silicate impurities. Increased strontium incorporation resulted in changes in grain morphology and reduced densification when the ceramics were sintered at 1450 °C. Porous GLN, S1-GLN and S2-GLN scaffolds (∼80% porosity) showed compressive strengths of 2.05 ± 0.46 MPa, 1.76 ± 0.79 MPa and 1.57 ± 0.52 MPa respectively. S1-GLN and S2-GLN immersed in simulated body fluid showed increased strontium ion release but reduced calcium and silicon ion release compared to GLN without affecting overall weight loss and pH over a 21 d period. The bioactivity of the S2-GLN ceramics was significantly improved as reflected in the significant upregulation of HOB proliferation and differentiation compared to GLN. Overall, these results suggest that increased incorporation of strontium presents a trade-off between bioactivity and mechanical strength for GLN bioceramics. This is an important consideration in the development of strontium-doped bioceramics.

Dentin remineralizing ability and enhanced antibacterial activity of strontium and hydroxyl ion co-releasing radiopaque hydroxyapatite cement

Dental caries is an infection of the mineralized tooth structures that advances when acid secreted by bacterial action on dietary carbohydrates diffuses and dissolves the tooth mineral leading to demineralization. During treatment, clinicians often remove only the superficial infected tooth structures and retain a part of affected carious dentin to prevent excessive dentin loss and pulp exposure. Calcium hydroxide is used to treat the affected dentin because it is alkaline, induces pulp-dentin remineralization and decreases bacterial infection. Presence of strontium ions has also been reported to exhibit anticariogenic activity, and promote enamel and dentin remineralization. The objective of the present study was to develop novel hydroxyapatite cement from tetracalcium phosphate which gradually releases hydroxyl and strontium ions to exhibit antibacterial activity. Its potential to remineralize the dentin sections collected from extracted human molar tooth was studied in detail. The pH of all the experimental cements exhibited a gradual increase to ~10.5 in 10 days with 10% strontium substituted tetracalcium phosphate cement (10SC) showing the highest pH value which was sustained for 6 weeks. 10SC showed better antibacterial property against S. aureus and E. coli at the end of 1 week compared to other cements studied. It also exhibited the highest radiopacity equivalent to 4.8 mm of Al standard. 10SC treated dentin section showed better remineralization ability and highest elastic modulus. We can conclude that the hydroxyl and strontium ions releasing tetracalcium phosphate cement exhibits good antibacterial property, radiopacity and has the potential to encourage dentin remineralization.

Sr-substituted bone cements direct mesenchymal stem cells, osteoblasts and osteoclasts fate

Strontium-substituted apatitic bone cements enriched with sodium alginate were developed as a potential modulator of bone cells fate. The biological impact of the bone cement were investigated in vitro through the study of the effect of the nanostructured apatitic composition and the doping of strontium on mesenchymal stem cells, pre-osteoblasts and osteoclasts behaviours. Up to 14 days of culture the bone cells viability, proliferation, morphology and gene expression profiles were evaluated. The results showed that different concentrations of strontium were able to evoke a cell-specific response, in fact an inductive effect on mesenchymal stem cells differentiation and pre-osteoblasts proliferation and an inhibitory effect on osteoclasts activity were observed. Moreover, the apatitic structure of the cements provided a biomimetic environment suitable for bone cells growth. Therefore, the combination of biological features of this bone cement makes it as promising biomaterials for tissue regeneration.

Controlling the strontium-doping in calcium phosphate microcapsules through yeast-regulated biomimetic mineralization

Yeast cells have controllable biosorption on metallic ions during metabolism. However, few studies were dedicated to using yeast-regulated biomimetic mineralization process to control the strontium-doped positions in calcium phosphate microcapsules. In this study, the yeast cells were allowed to pre-adsorb strontium ions metabolically and then served as sacrificing template for the precipitation and calcination of mineral shell. The pre-adsorption enabled the microorganism to enrich of strontium ions into the inner part of the microcapsules, which ensured a slow-release profile of the trace element from the microcapsule. The co-culture with human marrow stromal cells showed that gene expressions of alkaline phosphatase and Collagen-I were promoted. The promotion of osteogenic differentiation was further confirmed in the 3D culture of cell-material complexes. The strategy using living microorganism as 'smart doping apparatus' to control incorporation of trace element into calcium phosphate paved a pathway to new functional materials for hard tissue regeneration.

Growth of strontium hydrogen phosphate/gelatin composites: a biomimetic approach

Our study has focused on the crystal growth of strontium phosphatesviagel growth method due to the bioactivity and biocompatibility of these materials with bone tissue.