HA Nanocrystals Research Articles

Piezocatalytically-induced controllable mineralization scaffold with bone-like microenvironment to achieve endogenous bone regeneration

Orderly hierarchical structure with balanced mechanical, chemical, and electrical properties is the basis of the natural bone microenvironment. Inspired by nature, we developed a piezocatalytically-induced controlled mineralization strategy using piezoelectric polymer poly-L-lactic acid (PLLA) fibers with ordered micro-nano structures to prepare biomimetic tissue engineering scaffolds with a bone-like microenvironment (pcm-PLLA), in which PLLA-mediated piezoelectric catalysis promoted the in-situ polymerization of dopamine and subsequently regulated the controllable growth of hydroxyapatite crystals on the fiber surface. PLLA fibers, as analogs of mineralized collagen fibers, were arranged in an oriented manner, and ultimately formed a bone-like interconnected pore structure; in addition, they also provided bone-like piezoelectric properties. The uniformly sized HA nanocrystals formed by controlled mineralization provided a bone-like mechanical strength and chemical environment. The pcm-PLLA scaffold could rapidly recruit endogenous stem cells, and promote their osteogenic differentiation by activating cell membrane calcium channels and PI3K signaling pathways through ultrasound-responsive piezoelectric signals. In addition, the scaffold also provided a suitable microenvironment to promote macrophage M2 polarization and angiogenesis, thereby enhancing bone regeneration in skull defects of rats. The proposed piezocatalytically-induced controllable mineralization strategy provides a new idea for the development of tissue engineering scaffolds that can be implemented for multimodal physical stimulation therapy.

Ultra-rapid transfer of oleic acid-coated hydroxyapatite nanocrystals into water via a sodium citrate-assisted ligand exchange strategy

Precise control of the size, morphology and surface hydrophilicity of HA nanocrystals is an important prerequisite for the realization of relevant applications, especially biologically relevant ones. Although sodium oleate-assisted hydrothermal methods have received considerable attention due to their impressive synthesis quality and extremely wide aspect ratio tunability. However, the synthesized nanocrystals are usually hydrophobic due to oleic acid encapsulation, which greatly limits their wide application in biomedical fields. In view of this, we have established a robust ligand exchange strategy with sodium citrate as the exchange ligand and a mixture of water and ethanol as the exchange environment. The ligand exchange reaction requires only 5 min of stirring at 25 °C. DLS and zeta potential results show that the ligand-exchanged HA nanocrystals are highly negatively charged in water and dispersed as individual particles in water. TG and IR results showed that the oleic acid ligands on the surface of the nanocrystals were completely replaced by citric acid ligands. TEM images showed no change in the size and morphology of the nanocrystals before and after ligand exchange. Moreover, the colloidal stability of the ligand-exchanged HA nanocrystals in water could be quickly recovered in a few seconds even after freeze-drying into powder. The success of ligand exchange is mainly attributed to the fact that sodium citrate complexes calcium ions more strongly than sodium oleate, as well as the addition of ethanol eliminates the oil-water interface providing the basis for the approach of sodium citrate molecules to HA nanocrystals. This strategy undoubtedly bridges the gap that oleic acid-coated HA nanocrystals can be quickly and efficiently transferred to water, allowing HA nanocrystals to be used in bio-related applications without any obstacles.

Functionalization of biologically inspired scaffold through selenium and gallium ion doping to promote bone regeneration

In this study, biomimetic 3D porous hybrid scaffolds were prepared from GC matrix with subsequent doping of SeHA and GaHA nanocrystals through a bioinspired wet-chemical precipitation method. The concentration of Se and Ga ions varied with Se/P and Ga/Ca molar ratio of 1 mol.%, 2.5 mol.% and 5 mol.%. The physicochemical evaluation showed that the scaffolds were hydrophilic, biodegradable and exhibited a porous network. The combined analytical results clearly show that both Se and Ga ions were successfully nucleated along the HA nanocrystals. All the scaffold groups were calcium deficient and non-hemolytic with profound anti-infection properties. Cytocompatibility results showed that both GC-SeHA and GC-GaHA scaffolds had cell recognition functions offering selective cytotoxicity to cancer cells but not towards normal cells with the ability to induce angiogenesis. To conclude, Se and Ga concentration below 2.5 mol.% can provide good morphological and crystallographic features with tunable mechanical, antibacterial and osteogenic properties.

Using a three-dimensional hydroxyapatite/graphene aerogel as a high-performance anode in microbial fuel cells

Bioaffinity of anode materials is a key factor for the power output of microbial fuel cells (MFCs). Anode surfaces with excellent biocompatibility can facilitate bacterial adhesion, biofilm propagation, and extracellular electron transfer. In this study, three-dimensional (3D) hydroxyapatite/graphene aerogel (HA/GA) was synthesized using a facile three-step method: hydrothermal treatment, dialysis, and freeze-drying. The HA/GA anode presented the excellent biocompatibility of HA and high conductivity of graphene. Moreover, the unique edge-to-edge cross-linked architecture of the HA/GA offered a large surface area for bacterial adhesion. Shewanella putrefaciens can generate more flavins through the introduction of highly biocompatible HA nanocrystals on the graphene sheets, leading to a rapid extracellular electron transfer between the biofilm and anode. An MFC containing a HA/GA anode delivered a maximum power density of 2.38 W m− 2, which was 1.83 times the power density achieved using a GA anode. Furthermore, MFCs equipped with HA/GA anodes were successfully utilized to drive a series of electrical appliances. The HA/GA anode possessed excellent biocompatibility, large surface area, superior hydrophilicity, and high conductivity, which were conducive for enhancing the surface bioaffinity and accelerating the interfacial charge transfer, thereby improving the electricity generation performance of the MFCs. This study has proven that HA is beneficial for enhancing the interface bioaffinity and that it can be applicable to MFC for high-performance bioelectricity harvesting.

Conversion of lime mud waste to hydroxyapatite biomaterials

An economical method to convert a lime mud (LM) waste from the pulp and paper manufacturing process to hydroxyapatite nanoparticles (nHA) was first introduced. In this work, LM was used as a calcium precursor source to synthesize single phase nHA through the chemical precipitation method with ammonium phosphate dibasic as the phosphate precursor. Transmission electron microscopy (TEM) observation confirmed that the produced nHA had rod-like nanocrystals with an average crystal size of 30 nm. X-ray diffraction (XRD) analysis revealed the pure phase of nHA. The synthesized nHA was identified as AB-type carbonate substitution using Fourier Transform infrared spectroscopy (FTIR). The concentration of toxic elements contained in the synthesized HA was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The result showed that HA nanocrystals prepared in this work contained lower concentration of toxic heavy metals than the concentration limits suggested by ASTM.

Ultrasonic-assisted preparation of reduced graphene oxide-hydroxyapatite nanocomposite for bone remodeling

An ultrasonic-assisted preparation strategy was employed to synthesize in-situ hydroxyapatite-reduced graphene oxidenanocomposite (n-HA/rGO) as a potential biomaterial for bone regeneration under the osteoporotic condition. The results of Rietveld refinement indicated that the optimum crystallite size was 20.26 ± 0.52 nm following the ultrasonication at 400 W for 10 min. Well-dispersed plate-shaped HA nanocrystals with the mean thickness of 25 ± 2 nm were formed on the surface of rGO due to its anchoring tendency with calcium ions and hydrogen phosphate. By increasing the amount of power to 500 W, the intensity ratio of the D and G bands (ID/IG) increased due to the rise in the perturbation level in the rGO matrix and the chemical interactions between the rGO and HA.

In-Situ Synthesis and Characterization of Chitosan/Hydroxyapatite Nanocomposite Coatings to Improve the Bioactive Properties of Ti6Al4V Substrates.

Ti6Al4V alloy is still attracting great interest because of its application as an implant material for hard tissue repair. This research aims to produce and investigate in-situ chitosan/hydroxyapatite (CS/HA) nanocomposite coatings based on different amounts of HA (10, 50 and 60 wt.%) on alkali-treated Ti6Al4V substrate through the sol-gel process to enhance in vitro bioactivity. The influence of different contents of HA on the morphology, contact angle, roughness, adhesion strength, and in vitro bioactivity of the CS/HA coatings was studied. Results confirmed that, with increasing the HA content, the surface morphology of crack-free CS/HA coatings changed for nucleation modification and HA nanocrystals growth, and consequently, the surface roughness of the coatings increased. Furthermore, the bioactivity of the CS/HA nanocomposite coatings enhanced bone-like apatite layer formation on the material surface with increasing HA content. Moreover, CS/HA nanocomposite coatings were biocompatible and, in particular, CS/10 wt.% HA composition significantly promoted human mesenchymal stem cells (hMSCs) proliferation. In particular, these results demonstrate that the treatment strategy used during the bioprocess was able to improve in vitro properties enough to meet the clinical performance. Indeed, it is predicted that the dense and crack-free CS/HA nanocomposite coatings suggest good potential application as dental implants.

Homogeneously dispersed composites of hydroxyapatite nanorods and poly(lactic acid) and their mechanical properties and crystallization behavior

Aiming to disperse HA nanocrystals in a polymer matrix homogenously, uniform oil-soluble HA nanorods were synthesized via an oleic acid (OA)-assisted mixed-solvent thermal method, and then poly(lactic acid) (PLA)/HA nanorods nanocomposites were fabricated by using a solution method. The HA nanorods with an OA monolayer on the surface dispersed homogeneously in organic solvents and the dispersion in polymer solution was transparent and colloidally stable. TEM images showed that HA nanorods dispersed as single particles without aggregation in PLA matrix. The elongation at break of the composites increased from 4.24% to 8.79% by adding HA nanorods, whereas the tensile strength and Young's modulus were largely unchanged. HA nanorods accelerated evidently the PLA crystallization rate even at a low HA loading and induced a transition to an ordered crystalline morphology confirmed via non-iso/isothermal crystallization, the spherulitic morphology, calculations and wide-angle X-ray diffraction during heating and cooling cycles.

Porous PVA/SA/HA hydrogels fabricated by dual-crosslinking method for bone tissue engineering

In the present work, a new kind of porous polyvinyl alcohol/sodium alginate/hydroxyapatite (PVA/SA/HA) composite hydrogels with tunable structure and mechanical properties have been fabricated by dual-crosslinking method. The morphologies, moisture content, porosity and mechanical properties of the composite hydrogels have been investigated in detail. The PVA/SA/HA hydrogels present uniform, interpenetrating porous structure. The FTIR and XRD results indicate that PVA, SA and HA could be uniformly compounded. The mechanical properties, moisture content and porosity of the samples could be controlled by changing the mass ratio of PVA/SA/HA. The optimized compression modulus (41.74 ± 7.86 kPa), moisture content (86.99 ± 0.72%) and porosity (79.98 ± 1.61%) of the composite hydrogels could be achieved via fixing the weight ratio of PVA/SA/HA at 42:18:40. In vitro biodegradation and mineralization of the composite hydrogels show that the hydrogels could gradually be degraded in PBS solution and sheet-like HA nanocrystals are easily formed on the surface. Moreover, cell culture results indicate that the PVA/SA/HA hydrogels have no negative effects on MC3T3-E1 cell growth and proliferation. Alkaline phosphatase (ALP) activity expressions demonstrate that the nano-HA crystals incorporated composite hydrogels obviously improve the ALP activity of the cells. It confirms that the prepared PVA/SA/HA hydrogels could be a promising candidate for bone repair and bone tissue engineering.

Novel bone-mimetic nanohydroxyapatite/collagen porous scaffolds biomimetically mineralized from surface silanized mesoporous nanobioglass/collagen hybrid scaffold: Physicochemical, mechanical and in vivo evaluations.

Bone-mimetic scaffolds are receiving much interest as such scaffolds exhibit excellent biocompatibility and very close mimic to bone structure and composition. Here, novel bone-mimetic nanohydroxyapatite (nHA)/collagen (Col) porous scaffolds (nHA/Col) were prepared from surface silanized mesoporous nanobioglass (NBG)/Col hybrid scaffold by biomimetic mineralization. Surface silanized mesoporous NBG was prepared by ultrasound-assisted sol-gel method and post treatment with 3-aminopropyltriethylsilane (APTS). The surface silanized mesoporous NBG was characterized by transmission electron microscopy (TEM), transmission electron microscopy-selected area electron diffraction (TEM-SAED) and X-ray photoelectron spectroscopy (XPS). The physicochemical/mechanical characterizations of the scaffolds included scanning electron microscopy (SEM) and TEM imaging of micro/nanostructure, energy dispersive X-ray (EDX) analysis of chemical composition, TEM-SAED and X-ray diffraction/Attenuated total Reflectance-Fourier Infrared spectroscopy (XRD/ATR-FTIR) analyses of amorphous-to-crystalline transformations, thermogravimetric/differential scanning calorimetric (TGA/DSC) analyses of thermal behaviour , porosity and dynamic mechanical analyses. The presence of NBG in collagen fibrillar network enabled progressive growth of HA nanocrystals and generation of a novel bone-mimetic hybrid structures while preserving the highly porous structure of collagen scaffold. The crystallinity, crystallite size and crystal morphology of the grown HA nanocrystals were controllable by regulation of the mineralization time. Furthermore, the osteogenic properties of the non-mineralized (NBG/Col) and mineralized (nHA/Col) hybrid porous scaffolds were examined in vivo using critical-sized calvarial bone defect model in rat. Histological and micro-computed tomography (Micro-CT) analyses after 6weeks of implantation revealed that the mineralized scaffolds possess excellent in vivo osteogenic potential compared to the non-mineralized one. Collectively, by using surface silanized mesoporous NBG hybridization with collagen fibrillar network, we successfully introduced a new approach for developing novel bone-mimetic nanohydroxyapatite/collagen hybrid scaffolds that possess significant potential for bone tissue regeneration.

Influence of hydrothermal treatment on the surface characteristics and electrochemical behavior of Ti-6Al-4V bio-functionalized through plasma electrolytic oxidation

The performance of biomaterials in general and orthopaedic biomaterials in particular is dependent on both the chemistry and topography of their surfaces. It is therefore important to tailor both of those aspects through an appropriate surface modification technique. Here, we examined the influence of hydrothermal treatment on the surface characteristics and electrochemical behavior of Ti-6Al-4V specimens whose surfaces were modified using plasma electrolytic oxidation (PEO). Even though no calcium-phosphorous related crystalline compound was identified in the XRD spectra of PEO layers, hydroxyapatite crystals were clearly detectable after the applied hydrothermal treatment. The partial water absorption of the HA crystals and their needle-like morphology resulted in a significant increase in the wettability of the surfaces. However, the application of post-PEO hydrothermal treatment also decreased the corrosion resistance of the PEO layers. The numerical results of electrochemical impedance spectroscopy demonstrated that the optimized surface properties and corrosion resistance were achieved in one of the groups, namely PEO-HT3, where the HA nanocrystals homogenously covered the entire surface of the specimens.

Antibacterial Copper-Hydroxyapatite Composite Coatings via Electrochemical Synthesis.

Antibacterial copper-hydroxyapatite (Cu-HA) composite coatings on titanium were synthesized using a novel process consisting of two consecutive electrochemical reactions. In the first stage, HA nanocrystals were grown on titanium using the cathodic electrolytic synthesis. The HA-coated titanium was then used as the cathode in a second reaction stage to electrochemically reduce Cu2+ ions in solution to metallic Cu nanoparticles. Reaction conditions were found that result in nanoscale Cu particles growing on the surface of the HA crystals. The two-stage synthesis allows facile control of copper content in the HA coatings. Antibacterial activity was measured by culturing Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) in the presence of coatings having varying copper contents. The coatings displayed copper concentration-dependent antibacterial activity against both types of bacteria, likely due to the slow release of copper ions from the coatings. The observation of antibacterial activity from a relatively low loading of copper on the bioactive HA support suggests that multifunctional implant coatings can be developed to supplement or supplant prophylactic antibiotics used in implant surgery that are responsible for creating resistant bacteria strains.

Hydroxyapatite Nanocrystal Deposited Titanium Dioxide Nanotubes Loaded with Antibiotics for Combining Biocompatibility and Antibacterial Properties

ABSTRACTHydroxyapatite (HA)/nanotubular titanium dioxide (TiO2) composite coatings loaded with antibiotics were developed to combine biocompatibility and antibacterial property. TiO2 nanotubes were first fabricated on Ti plates using anodization techniques. Then HA nanocrystals were synthesized on the TiO2 nanotubes by electrochemical deposition, followed by loading of a model drug compound, streptomycin. The streptomycin release profile of the composite coating was investigated. Bacterial tests demonstrate that the streptomycin-loaded composite coatings were highly effective in inhibiting bacterial growth. Simulated body fluid (SBF) experiments indicated that the composite coatings possessed good osseointegration capability.

Multiscale characterization of the mineral phase at skeletal sites of breast cancer metastasis

Skeletal metastases, the leading cause of death in advanced breast cancer patients, depend on tumor cell interactions with the mineralized bone extracellular matrix. Bone mineral is largely composed of hydroxyapatite (HA) nanocrystals with physicochemical properties that vary significantly by anatomical location, age, and pathology. However, it remains unclear whether bone regions typically targeted by metastatic breast cancer feature distinct HA materials properties. Here we combined high-resolution X-ray scattering analysis with large-area Raman imaging, backscattered electron microscopy, histopathology, and microcomputed tomography to characterize HA in mouse models of advanced breast cancer in relevant skeletal locations. The proximal tibial metaphysis served as a common metastatic site in our studies; we identified that in disease-free bones this skeletal region contained smaller and less-oriented HA nanocrystals relative to ones that constitute the diaphysis. We further observed that osteolytic bone metastasis led to a decrease in HA nanocrystal size and perfection in remnant metaphyseal trabecular bone. Interestingly, in a model of localized breast cancer, metaphyseal HA nanocrystals were also smaller and less perfect than in corresponding bone in disease-free controls. Collectively, these results suggest that skeletal sites prone to tumor cell dissemination contain less-mature HA (i.e., smaller, less-perfect, and less-oriented crystals) and that primary tumors can further increase HA immaturity even before secondary tumor formation, mimicking alterations present during tibial metastasis. Engineered tumor models recapitulating these spatiotemporal dynamics will permit assessing the functional relevance of the detected changes to the progression and treatment of breast cancer bone metastasis.

Microscale electrohydrodynamic printing of biomimetic PCL/nHA composite scaffolds for bone tissue engineering

Electrohydrodynamic printing provides an innovative strategy to fabricate high-resolution tissue-engineering scaffolds with fiber orientation and scale similar to native extracellular matrix. However, few studies have been conducted to incorporate functional nanobiomaterials into microscale fibrous structures. In this study, we presented to fabricate microscale poly (ε-caprolactone) (PCL) and hydroxyapatite nanoparticles (nHA) composite scaffolds with the average fiber diameter of 8.85±1.12µm based on electrohydrodynamic 3D printing to better mimic collagen fibers and HA nanocrystals in natural bones. The composite scaffolds exhibited good biocompatibility and facilitated cell alignment and proliferation in vitro. This strategy might be useful to regulate cellular microenvironment in multiscale and multimaterial levels for improved tissue regeneration.

Mesoscopically ordered bone mimetic nanocomposites

Event Abstract Back to Event Mesoscopically ordered bone mimetic nanocomposites Martin Andersson1, Wenxiao He1 and Anand K. Rajasekharan1 1 Chalmers University of Technology, Chemistry and Chemical Engineering, Sweden Introduction: Bone provides protection and support for the movements of our body through its excellent load-bearing properties. Though the macrostructure differs depending on bone type, the nanostructure of natural bone universally comprises collagen fibrils possessing periodic gaps, within which elongated bone apatite nanoparticles are aligned and embedded. To synthetically reproduce the complexity of bone has been proven challenging, and the fact that simple mixing of proteins, such as collagen 1, with precipitated apatite crystals does not form materials having mechanical properties even close to that of bone, clearly demonstrates that the hierarchical arrangement of the structure is of outmost importance. Figure 1(A) Formation and nanostructure of bone and our biomimetic composite. (B) SAXS scattering confirms presence of order and anisotropy in composite. (C) TEM image shows alignment of HA nanocrystals with the material. Methods: Herein we demonstrate a novel, synthetic approach, highly inspired by the architecture of natural bone, to design mechanically stable nanocomposites incorporating aligned apatite nanocrystals. To mimic the nanostructure of natural bone, we first combine molecular self-assembly and intermolecular crosslinking to create resilient polymeric matrices with long-range periodicity; then we employ compartmentalized mineral growth via a transient amorphous phase for the biomimetic formation of bone-like apatite, see Fig. 1. Results and Discussion: Small angle X-ray scattering (SAXS) data of the nanocomposite confirmed the presence of meso-ordered (hexagonal) structure with long-range anisotropy of the nanocomposite similar to bone (Figure 1B)[1]. Moreover electron microscopy images of grounded composites show alignment of the HA nanoparticles due to the orientation from the PLC matrix (Figure 1C)[1]. The nanoscale confinements within the polymeric matrices controled the phase purity of calcium phosphates. When CaP is precipitated in confinements of sizes 11-27 nm, multiple phases including acidic polymorphs coexisted. Contrastingly, confinements smaller than 10 nm produced phase pure ACPs, which on aging converted to nanocrystalline apatite[2]. A general hypothesis is proposed that in absence of chemical control, confinements might need to be smaller than naturally occurring ones to control the mineral phase purity in both synthetic and biological systems. The results also provide an insight into designing biomaterials with an ordered structure and high mineral content while maintaining chemical homogeneity. Mechanically, the composite showed compressive strength of 3-4 MPa, which is comparable to cancellous bone, an important result for further developing the implant. Current work focuses on developing the composite with a 3-D hierarchical structure and a porous network for functioning as a scaffold. Conclusion: Molecular self-assembly of synthetic polymers can be used to form mesoscopically ordered polymer-apatite nanocomposites having similar apatite chemistry and a highly ordered nanostructure inspired from bone. We acknowledge the Swedish Research Council, Nano-Sphere Centre/Formas and the Wallenberg Foundation through their Wallenberg Academy Fellow Program for financial support. We also thank MAX-lab (Lund, Sweden) for the allocation of beam time and assistance with SAXS measurements

Preparation and characterization of gelatin/hydroxyapatite nanocomposite for bone tissue engineering

Homogeneous gelatin/hydroxyapatite (GEL/HA) nano-composites were synthesized by a novel in situ precipitation method, and its corresponding characterizations, including composition, morphology, pore structure, thermal stability, mechanical strength, and biocompatibility, were carried out. High-magnified scanning electron microscope (SEM) images indicated that nano-HA with particle size ranging from 20 to 50 nm were uniformly distributed in GEL matrix and tightly integrated with organic phase. Wide angle X-ray diffraction (XRD) analysis and transmission electron microscope (TEM) images showed that, during the process of mineralization, there existed preferred oriented growth of HA crystals along (002) and (211) crystal planes. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) indicated that, the thermal stability of GEL molecules enhanced by hybridizing with HA nanocrystals. Interconnected porous GEL/HA nanocomposites with pore size ranging between 50 and 350 μm were prepared by a freeze-drying method. This pore size was adequate for bone tissue engineering (BTE) applications. In addition, in vitro MG63 osteoblast-like cell culture illuminated that GEL/HA nanocomposites had excellent cytocompatibility and could promote proliferation of cells. These results suggested that GEL/HA nanocomposite might be an ideal bone substitute. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Quantitative analyses of the effect of silk fibroin/nano-hydroxyapatite composites on osteogenic differentiation of MG-63 human osteosarcoma cells

Silk fibroin (SF)/nano-hydroxyapatite (n-HA) composites are potential biomaterials for bone defect repair. Up to now, the biological evaluation studies of SF/n-HA composites have primarily concentrated on their biocompatibility at cell level such as cell viability and proliferation and tissue level such as material absorption and new bone formation. In this work, SF/n-HA composites were fabricated using a simplified coprecipitation methods and were deposited onto Ti alloy substrates. Then the cell adhesion ability of SF/n-HA composites was observed by SEM and cell proliferation ability of SF/n-HA composites was determined by MTT assay. The ALP activity, BGP contents, and Col I contents of MG-63 human osteosarcoma cells on SF/n-HA composites were quantitatively analyzed. HA nanocrystals were used as controls. These experiments showed that SF/n-HA composites had better cell adhesion and osteogenic differentiation abilities than n-HA materials. This work provides quantitative data to analyze the effect of SF/n-HA composites on cell osteogenic differentiation.

Combined effect of strontium and zoledronate on hydroxyapatite structure and bone cell responses

The influence of the simultaneous presence of the two inhibitors of bone degradation, strontium and zoledronate, on the direct synthesis of hydroxyapatite was explored in the range of Sr concentration up to 50 atom% at two different bisphosphonate concentrations (ZOL7 and ZOL14). The results of structural analysis indicated that HA can be obtained as a single crystalline phase up to a Sr concentration in solution of 20 and 10 atom% within the ZOL7 and ZOL14 series respectively. Both Sr substitution and ZOL incorporation affect the length of the coherently scattering crystalline domains and the dimensions of HA nanocrystals. At greater Sr content, XRD full profile fitting data indicate that zoledronate provokes the segregation of Sr in two crystalline apatitic phases, at different strontium content. Co-cultures of osteoblast-like MG63 cells and human osteoclast show that ZOL displays a greater inhibitory influence than Sr on osteoclast proliferation and activity. On the other hand, the results obtained on osteoblast surnatant and on gene expression indicate that Sr exerts a greater promotion on osteoblast proliferation and differentiation. The co-presence of Sr and ZOL has a combined effect on the differentiation markers, so that HA containing about 4 wt% ZOL and 4 Sr atom%, and even more HA containing about 4 wt% ZOL and 8 Sr atom%, result the best compromise for osteoblast promotion and osteoclast inhibition.

Preparation of core–shell poly(l-lactic) acid-nanocrystalline apatite hollow microspheres for bone repairing applications

In this paper, hybrid inorganic-organic core-shell hollow microspheres, made of poly(L-lactic acid) (PLLA) and biomimetic nano apatites (HA), were prepared from biodegradable and biocompatible substances, suitable for bone tissue applications. Preparation is started from Pickering emulsification, i.e., solid particle-stabilized emulsions in the absence of any molecular surfactant, where solid particles adsorbed to an oil-water interface. Stable oil-in-water emulsions were produced using biomimetic 20 nm sized HA nanocrystals as particulate emulsifier and a dichloromethane (CH(2)Cl(2)) solution of PLLA as oil phase. Hybrid hollow PLLA microspheres at three different HA nanocrystals surface coverage, ranging from 10 to 50 μm, were produced. The resulting materials were completely characterized with spectroscopic, calorimetric and microscopic techniques and the cytocompatibility was established by indirect contact tests with both fibroblasts and osteoblasts and direct contact with these latter. They displayed a high level of cytocompatibility and thus represent promising materials for drug delivery systems, cell carriers and scaffolds for regeneration of bone useful in the treatment of orthopaedic, maxillofacial and dental fields.