A Complex Evaluation of the In-Vivo Biocompatibility and Degradation of an Extruded ZnMgSr Absorbable Alloy Implanted into Rabbit Bones for 360 Days.

The increasing incidence of trauma in medicine brings with it new demands on the materials used for the surgical treatment of bone fractures. Titanium, its alloys, and steel are used worldwide in the treatment of skeletal injuries. These metallic materials, although inert, are often removed after the injured bone has healed. The second-stage procedure-the removal of the plates and screws-can overwhelm patients and overload healthcare systems. The development of suitable absorbable metallic materials would help us to overcome these issues. In this experimental study, we analyzed an extruded Zn-0.8Mg-0.2Sr (wt.%) alloy on a rabbit model. From this alloy we developed screws which were implanted into the rabbit tibia. After 120, 240, and 360 days, we tested the toxicity at the site of implantation and also within the vital organs: the liver, kidneys, and brain. The results were compared with a control group, implanted with a Ti-based screw and sacrificed after 360 days. The samples were analyzed using X-ray, micro-CT, and a scanning electron microscope. Chemical analysis revealed only small concentrations of zinc, strontium, and magnesium in the liver, kidneys, and brain. Histologically, the alloy was verified to possess very good biocompatibility after 360 days, without any signs of toxicity at the site of implantation. We did not observe raised levels of Sr, Zn, or Mg in any of the vital organs when compared with the Ti group at 360 days. The material was found to slowly degrade in vivo, forming solid corrosion products on its surface.

Osteogenic capability of strontium and icariin-loaded TiO2 nanotube coatings in vitro and in osteoporotic rats.

Titanium (Ti) and Ti alloys are widely used biomaterials, but they lack osteogenic capability for rapid bone integration. To improve osseointegration of Ti implants, TiO2 nanotubes were prepared using the anodizing oxidation technique, and strontium (Sr) combined with icariin (ICA) was loaded on TiO2 nanotube coatings. Cell adhesion and proliferation of MC3T3-E1 cells, alkaline phosphatase (ALP) activity, mineralization of extracellular matrix, and bone formation around titanium implants in ovariectomized rats, were examined separately. The results showed that compared with pure Ti, TiO2 and Sr-loaded TiO2 coatings, the coatings loaded with both Sr and ICA showed better effect on cell adhesion and proliferation, higher ALP activity and more red-stained mineralized nodules. Furthermore, more bone was formed around implants loaded with both Sr and ICA in osteoporotic rats. Therefore, coating with Sr and ICA is valuable for clinical application to strengthen the osseointegration of titanium implants, especially in osteoporotic patients.

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.

Strontium accumulation by the terrestrial and aquatic plants affected by mining and municipal wastewaters (Elazig, Turkey).

The mining and municipal wastewaters in the study area are located around Elazig, Turkey. This study investigated the translocation and accumulation of Sr into 9 terrestrial-aquatic plants from the Elazig municipal wastewater, Keban Pb-Zn and Maden Cu wastewaters. Plants and their soil samples were collected from the stream/rivers on the municipal and mining areas, and Sr values in both plant parts and their soils were analyzed by ICP-MS. The mean Sr concentrations in the soil, root and shoot of the terrestrial-aquatic plants were 101, 48.2 and 80.5 ppm, respectively (on the dried weight basis). The enrichment coefficients of root (ECR) and shoots (ECS) and translocation factors of studied plants were calculated and, then, divided into several groups as a candidate, bioaccumulator and hyperaccumulator plants according to their ECR and ECSs. These groups indicated the candidate plants: Salix sp. and Tamarix tetrandra; bioaccumulator plants: Pragmites sp. and Xanthium, and hyperaccumulator plants: Typha latifolia, Bolboscholnus ascbersus and Lythnium salicaria for Sr. These results showed that both bioaccumulator and hyperaccumulator plant groups had very high ability to accumulate strontium to plant parts from their soil. Therefore, these studied plants may be helpful/useful for the rehabilitation studies of municipal and mining soils contaminated by Sr.

The synergistic effects of SrF2 nanoparticles, YSZ nanoparticles, and poly-ε-l-lysin on physicomechanical, ion release, and antibacterial-cellular behavior of the flowable dental composites.

Resin-based pit-and-fissure sealants (flowable resin composites) were formulated using bisphenol-A-glycerolatedimethacrylate (Bis-GMA)-triethylene glycol dimethacrylate-(TEGDMA)-diurethanedimethacrylate (UDMA) mixed monomers and multiple fillers, including synthetic strontium fluoride (SrF2) nanoparticles as a fluoride-releasing and antibacterial agent, yttria-stabilized zirconia (YSZ) nanoparticles as an auxiliary filler, and poly-ε-l-lysin (ε-PL) as an auxiliary antibacterial agent. Based on the physical, mechanical and initial antibacterial properties, the formulated nano-sealant containing 5 wt% SrF2, 5 wt% YSZ and 0.5 wt% ε-PL was selected as the optimal specimen and examined for ion release and cytotoxicity. The results showed an average release rate of 0.87 µg·cm-2·day-1 in the aqueous medium (pH 6.9) and 1.58 µg·cm-2·day-1 in acidic medium (pH 4.0). The maximum cytotoxicity of 20% toward human bone marrow mesenchymal stem cells (hMSCs) was observed according to the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) cytotoxicity assay and acridine orange staining test. A synergy between SrF2 nanoparticles and ε-PL exhibited a better antibacterial activity in terms of colony reduction compared to the other samples. However, the inclusion of SrF2 and ε-PL caused mechanically weakening of the sealants that was partly compensated by incorporation of YSZ nanoparticles (up to 10 wt%).

Relationship of the mobile forms of calcium and strontium in soils with their accumulation in meadow plants in the area of Kashin-Beck endemia.

This study was aimed at assessment of strontium and calcium mobility in soils and their accumulation with plants in the areas endemic for Kashin-Beck disease in Eastern Transbaikalia. The strontium and calcium mobility levels were determined using the method of sequential chemical extraction for 7 samples of meadow soils collected from the endemic region and 7 soil samples taken from conditionally control sites. To measure the Ca and Sr levels in the soil and plant samples, XRF analysis and AAS were used. The increased strontium level in the meadow soils of the endemic areas is accompanied by the element's higher mobility. The highest strontium yield was observed in the course of soil extraction using 1 M ammonium acetate, while the soils taken from the control sites gave lower amounts of the trace element. Furthermore, there is a positive correlation between the amount of the strontium extracted and its content in plants (r = + 0.86 - 0.98). At the sequential chemical extraction of calcium from the soils using the above method, the calcium yield was maximal in the ammonium acetate fraction (background sites) and in ammonium acetate and 6 M HCl fractions (endemic areas). The correlation between the amount of the calcium extracted in 1 M ammonium acetate and the macroelement levels found in plants was + 0.968. In addition, a peculiarly high accumulation of strontium in various willow species as compared to other meadow plants was revealed for the first time ever. Thus, the work introduces new data into the trace element biogeochemistry and environmental monitoring.

Vancomycin- and Strontium-Loaded Microspheres with Multifunctional Activities against Bacteria, in Angiogenesis, and in Osteogenesis for Enhancing Infected Bone Regeneration.

Biomaterials that have capacities to simultaneously induce bone regeneration and kill bacteria are in demand because bone defects face risks of severe infection in clinical therapy. To meet the demand, multifunctional biodegradable microspheres are fabricated, which contain vancomycin to provide antibacterial activity and strontium-doped apatite to provide osteocompatibility. Moreover, the strontium component shows activity in promoting angiogenesis, which further favors osteogenesis. For producing the microspheres, vancomycin is loaded into mesoporous silica and embedded in polylactide-based microspheres via the double emulsion technique and the strontium-doped apatite is deposited onto the microspheres via biomineralization in strontium-containing simulated body fluid. Sustained release behaviors of both vancomycin and Sr2+ ions are achieved. The microspheres exhibit strong antibacterial effect against Staphylococcus aureus, while demonstrating excellent cell/tissue compatibility. Studies of differentiation confirm that the introduction of strontium element strengthens the angiogenic and osteogenic expressions of mesenchymal stromal cells. Subcutaneous injection of the microspheres into rabbit's back confirms their effectiveness in inducing neovascularization and ectopic osteogenesis. Finally, an infected rabbit femoral condyle defect model is created with S. aureus infection and the multifunctional microspheres are injected, which display significant antibacterial activity in vivo and achieve efficient new bone formation in comparison with biomineralized microspheres without vancomycin loading. The vancomycin- and strontium-loaded microspheres, being biomineralized, injectable, and biodegradable, are attractive because of their flexibility in integrating multiple functions into one design, whose potentials in treating infected bone defects are highly expected.

Strontium released bi-lineage scaffolds with immunomodulatory properties induce a pro-regenerative environment for osteochondral regeneration.

The different lineage-specific biological properties of articular cartilage and subchondral bone present a great challenge in the construction of bi-lineage scaffolds for simultaneous osteochondral regeneration. To overcome this challenge, strontium incorporated calcium silicate (Sr-CS) ceramic was prepared for bi-lineage formation of scaffolds in this study. The positive result of Sr-CS in the regeneration of osteochondral defects was first proven by its improved effect on the osteogenesis and chondrogenesis induction of mesenchymal stem cells (MSCs). After that, scaffold-mediated macrophage polarization between classically activated inflammatory macrophages (termed M1Ф) and alternatively activated inflammatory macrophages (termed M2Ф) was assayed to investigate whether the incorporation of Sr into calcium silicate could alter host-to-scaffold immune response. Furthermore, the interactions between Sr-CS pretreated macrophages and MSCs differentiation were performed to prove the enhancement effect of suppressed inflammatory response on osteogenesis and chondrogenesis. In vivo transplantation showed that the Sr-CS scaffolds distinctly improved the regeneration of cartilage and subchondral bone, as compared to the calcium silicate scaffolds. On the one hand, the mechanism attributes to enhancement of strontium on the osteogenic and chondrogenic differentiation of MSCs. On the other hand, the reason can partially be attributed to suppressed synovial inflammatory response, which has improved effects on enhancement of osteogenesis and chondrogenesis. These findings suggest that monophasic Sr-CS scaffolds with a bi-lineage conducive property and an inflammatory response regulatory property represents a viable strategy for simultaneous regeneration of osteochondral defects.

Investigation of strontium transport and strontium quantification in cortical rat bone by time-of-flight secondary ion mass spectrometry.

Next-generation bone implants will be functionalized with drugs for stimulating bone growth. Modelling of drug release by such functionalized biomaterials and drug dispersion into bone can be used as predicting tool for biomaterials testing in future. Therefore, the determination of experimental parameters to describe and simulate drug release in bone is essential. Here, we focus on Sr2+ transport and quantification in cortical rat bone. Sr2+ dose-dependently stimulates bone-building osteoblasts and inhibits bone-resorbing osteoclasts. It should be preferentially applied in the case of bone fracture in the context of osteoporotic bone status. Transport properties of cortical rat bone were investigated by dipping experiments of bone sections in aqueous Sr2+ solution followed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling. Data evaluation was carried out by fitting a suitable mathematical diffusion equation to the experimental data. An average diffusion coefficient of D = (1.68 ± 0.57) · 10-13 cm2 s-1 for healthy cortical bone was obtained. This value differed only slightly from the value of D = (4.30 ± 1.43) · 10-13 cm2 s-1 for osteoporotic cortical bone. Transmission electron microscopy investigations revealed a comparable nano- and ultrastructure for both types of bone status. Additionally, Sr2+-enriched mineralized collagen standards were prepared for ToF-SIMS quantification of Sr2+ content. The obtained calibration curve was used for Sr2+ quantification in cortical and trabecular bone in real bone sections. The results allow important insights regarding the Sr2+ transport properties in healthy and osteoporotic bone and can ultimately be used to perform a simulation of drug release and mobility in bone.

SBF assays, direct and indirect cell culture tests to evaluate the biological performance of bioglasses and bioglass-based composites: Three paradigmatic cases.

A novel bioglass composition (BGMS10), containing strontium and magnesium and characterized by an ultra-high crystallization temperature, is here employed for the first time to produce different composites with the addition of specific amounts of hydroxyapatite. After an investigation of the samples' bioactivity in vitro in a simulated body fluid solution (SBF) - according to a widely used protocol -, the biocompatibility of the new materials was tested with respect to murine fibroblasts both by direct and indirect tests, in order to evaluate possible cytotoxic effects of the materials' eluates. Although none of the samples were cytotoxic and their bioactivity in SBF increased with the increasing amount of the glass in the composite, thus showing the best performance in the case of pure BGMS10 glass, the findings of the biological investigation did not confirm those arising from the SBF assay. Surprisingly, while the composites with the lowest glass amount showed an enhanced biocompatibility in direct tests, on the contrary their biological responsiveness is typically lower in the indirect ones, based on filtered materials' extracts. This fact could be ascribed to the high release of particulate from the composites, which are more porous than the glassy samples: in fact, such pronounced dissolution may affect both the cell viability and the absorbance readings used in the colorimetric assays. The pure BGMS10 glass showed the best biological response only in the cell proliferation test (which is an indirect contact test), being able to stimulate cell proliferation in particular after 24 h. For these reasons, when considering bioactive glasses and bioglass-based composites, the results of direct cell culture assays should be integrated with those obtained by indirect ones, while the findings regarding the in vitro bioactivity in SBF should be interpreted with great care.

Strontium-releasing fluorapatite glass-ceramic scaffolds: Structural characterization and in vivo performance.

There is increasing interest in biodegradable ceramic scaffolds for bone tissue engineering capable of in situ delivery of ionic species favoring bone formation. Strontium has been shown to be osteogenic, but strontium-containing drugs such as strontium ranelate, used in Europe for the treatment of osteoporosis, are now restricted due to clinical evidence of systemic effects. By doping fluorapatite-based glasses with strontium, we developed ceramic scaffolds with fully interconnected macroporosity and cell size similar to that of cancellous bone, that are also capable of releasing strontium. The crystallization behavior, investigated by XRD and SEM, revealed the formation of akermanite and fluorapatite at the surface of strontium-free glass-ceramic scaffolds, and strontium-substituted fluorapatite at the surface of the strontium-doped scaffolds. At 8 weeks after implantation in a rat calvarial critical size defect, scaffolds doped with the highest amount of strontium led to the highest mineral apposition rate. A significantly higher amount of newly-formed bone was found with the strontium-free glass-ceramic scaffold, and possibly linked to the presence of akermanite at the scaffold surface. We demonstrate by energy dispersive XRF analyses of skull sections that strontium was present in newly formed bone with the strontium-doped scaffolds, while a significant amount of fluorine was incorporated in newly formed bone, regardless of composition or crystallization state. STATEMENT OF SIGNIFICANCE: The present work demonstrates the in vivo action of strontium-containing glass-ceramic scaffolds. These bone graft substitutes are targeted at non load-bearing bone defects. Results show that strontium is successfully incorporated in newly formed bone. This is associated with a significantly higher Mineral Apposition Rate. The benefits of in situ release of strontium are demonstrated. The broader scientific impact of this works builds on the concept of resorbable ceramic scaffolds as reservoirs of ionic species capable of enhancing bone regeneration.

A comparative in vivo study of strontium-functionalized and SLActive™ implant surfaces in early bone healing.

PURPOSE: Studies have shown that strontium-doped medical applications benefit bone metabolism leading to improved bone healing and osseointegration. Based on this knowledge, the aim of the study was to evaluate the performance of an implant surface, functionalized by a physical vapor deposition (PVD) coating (Ti-Sr-O), designed to yield predictable release of strontium. The Ti-Sr-O functionalized surface is compared to a routinely used, commercially available surface (SLActive™) with respect to bone-to-implant contact (BIC%) and new bone formation (BF%) in two defined regions of interest (ROI-I and ROI-II, respectively). MATERIALS AND METHODS: Ti-Sr-O functionalized, SLActive, and Grade 4 titanium implants were inserted in the femoral condyle of adult male New Zealand White rabbits. The PVD magnetron-sputtered Ti-Sr-O surface coating was characterized using scanning electron microscopy (SEM) for morphology and coating thickness. Strontium release and mechanical stability of the coating, under simulated insertion conditions, were evaluated. Furthermore, histomorphometrical BIC and BF were carried out 2 weeks after insertion. RESULTS: Histomorphometry revealed increased bone formation of Ti-Sr-O with significant differences compared to SLActive and Grade 4 titanium in both regions of interest, ROI-I and ROI-II, at 0-250 µm and 250-500 µm distance from the implant surfaces. Analogous results of bone-to-implant contact were observed for the two modified surfaces. CONCLUSION: The results show that a nanopatterned Ti-Sr-O functionalized titanium surface, with sustained release of strontium, increases peri-implant bone volume and could potentially contribute to enhancement of bone anchorage of osseointegrated implants.

Effect of strontium surface-functionalized implants on early and late osseointegration: A histological, spectrometric and tomographic evaluation.

Numerous in vivo, in vitro and clinical studies report on beneficial effects of strontium with respect to increased bone growth. Based on this knowledge the aim of this study was to evaluate early and late osseointegration stages of functionalized titanium implants showing sustained release of strontium (Sr) and further investigate its potential systemic effect. Strontium functionalized (Ti-Sr-O) and Grade 4 (Control) titanium implants were inserted in the femoral condyle of New Zealand White rabbits. The Ti-Sr-O coating was characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectrometry (EDX) for structure, coating thickness and chemical composition. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) was used to evaluate released strontium in vitro while Atomic Absorption Spectrometry (AAS) was utilized to monitor serum levels of strontium and calcium. Additionally, histological and tomographic analysis of bone-to-implant contact (BIC%) and bone formation (BF%) was performed, following implantation periods of two or twelve weeks, respectively. Median values for BIC% for Ti-Sr-O revealed significant differences within the two- and twelve-week observation periods, while exceeding BF% was discovered especially after twelve weeks when performing the histological evaluation. The results from the micro-computed tomography (µ-CT) showed no significant differences, when comparing the experimental groups. AAS measurements did not indicate a systemic effect by the local strontium release. Within the limitations of the study, it was shown that a Ti-Sr-O coating with sustained release characteristics of strontium, accelerates bone apposition and represents a potential potent surface modification for endosseous medical implant devices. STATEMENT OF SIGNIFICANCE: This study presents first data with respect to early and late in vivo response on a strontium functionalized titanium surface comprising a nanotopography manufactured by a magnetron sputtering process. We investigated different osseointegration stages of screw-shaped implants with dental implant geometries in a rabbit femur model observing beneficial effects of the functionalized surface on bone-to-implant contact and bone formation caused by tailored release of the bone anabolic strontium. Histomorphometrical data revealed that a functionalized titanium surface with controlled liberation of strontium accelerates osseointegration while spectrometry measurements did not indicate a potential systemic effect of this osteoinductive agent and could thus have impact on modifications of medical implant devices.

The degradation and transport mechanism of a Mg-Nd-Zn-Zr stent in rabbit common carotid artery: A 20-month study.

Mg-based stent is a promising candidate of the next generation fully degradable vascular stents. The latest progress includes the CE approval of the Magmaris ® WE43 based drug eluting stent. However, so far, the long term (more than 1 year implantation) in vivo degradation and the physiological effects caused by the degradation products were still unclear. In this study, a 20 month observation was carried out after the bare Mg-Nd-Zn-Zr (abbr. JDBM) stent prototype was implanted into the common carotid artery of New Zealand white rabbit in order to evaluate its safety, efficacy and especially degradation behavior. The degradation of the main second phase Mg12Nd was also studied. Results showed that the bare JDBM stent had good safety and efficacy with a complete re-endothelialization within 28 days. The JDBM stent struts were mostly replaced in situ by degradation products in 4 month. The important finding was that the volume and Ca concentration of the degradation products decreased in the long term, eliminating the clinicians' concern of possible vessel calcification. In addition, the alloying elements Mg and Zn in the stent could be safely metabolized as continuous enrichment in any of the main organs were not detected although Nd and Zr showed an abrupt increase in spleen and liver after 1 month implantation. Collectively, the long term in vivo results showed the rapid re-endothelialization of JDBM stent and the long term safety of the degradation products, indicating its great potential as the backbone of the fully degradable vascular stent. STATEMENT OF SIGNIFICANCE: Mg-based stent is a promising candidate of the next generation fully degradable stents, especially after the recent market launch of one of its kind (Magmaris). However the fundamental question about the long term degradation and metabolic mechanism of Mg-based stent and its degradation products remain unanswered. We implanted our patented Mg-Nd-Zn-Zr bare stent into the common carotid artery of rabbits and conducted a 20 months observation. We found that the Ca containing degradation products could be further degraded in vivo. All the alloying elements showed no continuous enrichment in the main organs of rabbits. These findings eliminate the clinicians' concern of possible vessel calcification and element enrichment after the implantation of Mg alloy based stents to some extent.

Synergistic interface behavior of strontium adsorption using mixed microorganisms.

The proper handling of low-level radioactive waste is crucial to promote the sustainable development of nuclear power. Research into the mechanism for interactions between bacterium and radionuclides is the starting point for achieving successful remediation of radionuclides with microorganisms. Using Sr(II) as a simulation radionuclide and the mixed microorganisms of Saccharomyces cerevisiae and Bacillus subtilis as the biological adsorbent, this study investigates behavior at the interface between Sr(II) and the microorganisms as well as the mechanisms governing that behavior. The results show that the optimal ratio of mixed microorganisms is S. cerevisiae 2.0 g L-1 to B. subtilis 0.05 g L-1, and the optimal pH is about 6.3. Sr(II) biosorption onto the mixed microorganisms is spontaneous and endothermic in nature. The kinetics and the equilibrium isotherm data of the biosorption process can be described with pseudo-second-order equation and the Langmuir isotherm equation, respectively. The key interaction between the biological adsorbent and Sr(II) involves shared electronic pairs arising from chemical reactions via bond complexation or electronic exchange, and spectral and energy spectrum analysis show that functional groups (e.g., hydroxyl, carboxyl, amino, amide) at the interface between the radionuclide and the mixed microorganisms are the main active sites of the interface reactions.

Intracellular co-delivery of Sr ion and phenamil drug through mesoporous bioglass nanocarriers synergizes BMP signaling and tissue mineralization.

Inducing differentiation and maturation of resident multipotent stem cells (MSCs) is an important strategy to regenerate hard tissues in mal-calcification conditions. Here we explore a co-delivery approach of therapeutic molecules comprised of ion and drug through a mesoporous bioglass nanoparticle (MBN) for this purpose. Recently, MBN has offered unique potential as a nanocarrier for hard tissues, in terms of high mesoporosity, bone bioactivity (and possibly degradability), tunable delivery of biomolecules, and ionic modification. Herein Sr ion is structurally doped to MBN while drug Phenamil is externally loaded as a small molecule activator of BMP signaling, for the stimulation of osteo/odontogenesis and mineralization of human MSCs derived from dental pulp. The Sr-doped MBN (85Si:10Ca:5Sr) sol-gel processed presents a high mesoporosity with a pore size of ∼6nm. In particular, Sr ion is released slowly at a daily rate of ∼3ppm per mg nanoparticles for up to 7days, a level therapeutically effective for cellular stimulation. The Sr-MBN is internalized to most MSCs via an ATP dependent macropinocytosis within hours, increasing the intracellular levels of Sr, Ca and Si ions. Phenamil is loaded maximally ∼30% into Sr-MBN and then released slowly for up to 7days. The co-delivered molecules (Sr ion and Phenamil drug) have profound effects on the differentiation and maturation of cells, i.e., significantly enhancing expression of osteo/odontogenic genes, alkaline phosphatase activity, and mineralization of cells. Of note, the stimulation is a result of a synergism of Sr and Phenamil, through a Trb3-dependent BMP signaling pathway. This biological synergism is further evidenced in vivo in a mal-calcification condition involving an extracted tooth implantation in dorsal subcutaneous tissues of rats. Six weeks post operation evidences the osseous-dentinal hard tissue formation, which is significantly stimulated by the Sr/Phenamil delivery, based on histomorphometric and micro-computed tomographic analyses. The bioactive nanoparticles releasing both Sr ion and Phenamil drug are considered to be a promising therapeutic nanocarrier platform for hard tissue regeneration. Furthermore, this novel ion/drug co-delivery concept through nanoparticles can be extensively used for other tissues that require different therapeutic treatment. STATEMENT OF SIGNIFICANCE: This study reports a novel design concept in inorganic nanoparticle delivery system for hard tissues - the co-delivery of therapeutic molecules comprised of ion (Sr) and drug (Phenamil) through a unique nanoparticle of mesoporous bioactive glass (MBN). The physico-chemical and biological properties of MBN enabled an effective loading of both therapeutic molecules and a subsequently sustained/controlled release. The co-delivered Sr and Phenamil demonstrated significant stimulation of adult stem cell differentiation in vitro and osseous/dentinal regeneration in vivo, through BMP signaling pathways. We consider the current combination of Sr ion with Phenamil is suited for the osteo/odontogenesis of stem cells for hard tissue regeneration, and further, this ion/drug co-delivery concept can extend the applications to other areas that require specific cellular and tissue functions.

Host responses to a strontium releasing high boron glass using a rabbit bilateral femoral defect model.

Borate glasses have shown promising potential as bioactive materials. With recent research demonstrating that glass properties may be modulated by appropriate compositional design. This may provide for indication specific material characteristics and controlled release of therapeutic inorganic ions (i.e., strontium); controlling such release is critical in order to harness the therapeutic potential. Within this sub-chronic pilot study, a rabbit long-bone model was utilized to explore the safety and efficacy of a high borate glass (LB102: 70B2 O3 -20SrO-6Na2 O-4La2 O3 ) particulate (90 - 710 µm) for bone regeneration. Six bilateral full-thickness defects (Ø = 3.5 mm; L = 8 mm) were created in three white New Zealand rabbits. Longitudinal non-decalcified sections of each defect site were produced and stained with Goldner's Trichrome. Histopathological examination revealed that LB102 demonstrated osteoconductive and osseointegrative properties with greater new bone being formed within and surrounding LB102 particles, when compared to the sham control. The inflammatory cell infiltration was observed to be slightly higher in the control when compared to LB102 defect sites, while no significant difference in fibrosis and neovascularization was determined, indicating that healing was occurring in a normal fashion. These data further suggest the possible utility of high borate glasses with appropriate compositional design for medical applications, such as bone augmentation. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1818-1827, 2017.

Strontium-doped organic-inorganic hybrids towards three-dimensional scaffolds for osteogenic cells.

Biomimetic organic-inorganic hybrid bioscaffolds are developed to complement or replace damaged fragments in bone tissue surgery. The aim of this work was to develop a simple and fast method to prepare composite material for bone engineering, avoiding time consuming and complex methodologies. The resulting materials (also called in this work as hybrid composites or hybrid scaffolds) have a three-dimensional macroporous polymer-like network derived from triethoxyvinylsilane (TEVS) and 2-hydroxyethylmethacrylate (HEMA) monomers, with incorporated calcium, strontium, and phosphate ions. The materials were fully characterized using FT-IR, biomineralization studies, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, scratch tests, Young's modulus and compressive strength tests, and gas physisorption. We report a comprehensive study on the in vitro effect of novel strontium doped materials on human bone cells. In vitro investigations were conducted using a normal human osteoblast cell line that mimics the cellular events of the in vivo intramembranous bone formation process. The materials do not have a negative impact on the survival of the normal human osteoblasts; moreover, materials doped with strontium show that not only are cells able to survive, but they also attach to and grow on a bioscaffolds surface. For this reason, they may be used in future in vivo experiments.

Bone regenerating effect of surface-functionalized titanium implants with sustained-release characteristics of strontium in ovariectomized rats.

Since strontium (Sr) is known for its anabolic and anticatabolic effect on bone, research has been focused on its potential impact on osseointegration. The objective of this study was to investigate the performance of nanotopographic implants with a Sr-functionalized titanium (Ti) coating (Ti-Sr-O) with respect to osseointegration in osteoporotic bone. The trial was designed to examine the effect of sustained-release characteristics of Sr in poor-quality bone. Three Ti-Sr-O groups, which differed from each other in coating thickness, Sr contents, and Sr release, were examined. These were prepared by a magnetron sputtering process and compared to uncoated grade 4 Ti. Composition, morphology, and mechanical stability of the coatings were analyzed, and Sr release data were gained from in vitro washout experiments. In vivo investigation was carried out in an osteoporotic rat model and analyzed histologically, 6 weeks and 12 weeks after implantation. Median values of bone-to-implant contact and new bone formation after 6 weeks were found to be 84.7% and 54.9% (best performing Sr group) as compared to 65.2% and 23.8% (grade 4 Ti reference), respectively. The 12-week observation period revealed 84.3% and 56.5% (best performing Sr group) and 81.3% and 39.4% (grade 4 Ti reference), respectively, for the same measurements. The increase in new bone formation was found to correlate with the amount of Sr released in vitro. The results indicate that sputtered nanostructured Ti-Sr-O coatings showed sustained release of Sr and accelerate osseointegration even in poor-quality bone, and thus, may have impact on practical applications for medical implants.

A biocompatible hybrid material with simultaneous calcium and strontium release capability for bone tissue repair.

The increasing interest in the effect of strontium in bone tissue repair has promoted the development of bioactive materials with strontium release capability. According to literature, hybrid materials based on the system PDMS-SiO2 have been considered a plausible alternative as they present a mechanical behavior similar to the one of the human bone. The main purpose of this study was to obtain a biocompatible hybrid material with simultaneous calcium and strontium release capability. A hybrid material, in the system PDMS-SiO2-CaO-SrO, was prepared with the incorporation of 0.05 mol of titanium per mol of SiO2. Calcium and strontium were added using the respective acetates as sources, following a sol-gel technique previously developed by the present authors. The obtained samples were characterized by FT-IR, solid-state NMR, and SAXS, and surface roughness was analyzed by 3D optical profilometry. In vitro studies were performed by immersion of the samples in Kokubo's SBF for different periods of time, in order to determine the bioactive potential of these hybrids. Surfaces of the immersed samples were observed by SEM, EDS and PIXE, showing the formation of calcium phosphate precipitates. Supernatants were analyzed by ICP, revealing the capability of the material to simultaneously fix phosphorus ions and to release calcium and strontium, in a concentration range within the values reported as suitable for the induction of the bone tissue repair. The material demonstrated to be cytocompatible when tested with MG63 osteoblastic cells, exhibiting an inductive effect on cell proliferation and alkaline phosphatase activity.