New advances in nanocrystalline apatite colloids intended for cellular drug delivery

One-Pot Synthesis of Bioinspired Peptide-Decorated Apatite Nanoparticles for Nanomedicine

Hybrid organic-inorganic bio-inspired apatite nanoparticles (NPs) are attractive for biomedical applications and especially in nanomedicine. Unfortunately, their applications in nanomedicine are limited by their broad particle size distributions and uncontrolled drug loading due to their multistep synthesis process.  Besides, very few attempts at exposing bioactive peptides on apatite NPs are made. In this work, an original one-pot synthesis of well-defined bioactive hybrid NPs composed of a mineral core of bioinspired apatite surrounded by an organic corona of bioactive peptides is reported. Dual stabilizing-bioactive agents, phosphonated polyethylene glycol-peptide conjugates, are prepared and directly used during apatite precipitation i) to form the organic corona during apatite precipitation, driving the size and shape of resulting hybrid NPs with colloidal stabilization and ii) to expose peptide moieties (RGD or YIGSR sequences) at the NPs periphery in view of conferring additional surface properties to enhance their interaction with cells. Here, the success of this approach is demonstrated, the functionalized NPs are fully characterized by Fourier-transform infrared, Raman, X-ray diffraction, solid and liquid state NMR, transmission electron microscopy, and dynamic light scattering, and their interaction with fibroblast cells is followed, unveiling a synergistic proliferative effect.

Biomineralization of bone tissue: calcium phosphate-based inorganics in collagen fibrillar organic matrices

BACKGROUND

Bone regeneration research is currently ongoing in the scientific community. Materials approved for clinical use, and applied to patients, have been developed and produced. However, rather than directly affecting bone regeneration, these materials support bone induction, which regenerates bone. Therefore, the research community is still researching bone tissue regeneration. In the papers published so far, it is hard to find an improvement in the theory of bone regeneration. This review discusses the relationship between the existing theories on hard tissue growth and regeneration and the biomaterials developed so far for this purpose and future research directions.

MAINBODY

Highly complex nucleation and crystallization in hard tissue involves the coordinated action of ions and/or molecules that can produce different organic and inorganic composite biomaterials. In addition, the healing of bone defects is also affected by the dynamic conditions of ions and nutrients in the bone regeneration process. Inorganics in the human body, especially calcium- and/or phosphorus-based materials, play an important role in hard tissues. Inorganic crystal growth is important for treating or remodeling the bone matrix. Biomaterials used in bone tissue regeneration require expertise in various fields of the scientific community. Chemical knowledge is indispensable for interpreting the relationship between biological factors and their formation. In addition, sources of energy for the nucleation and crystallization processes of such chemical bonds and minerals that make up the bone tissue must be considered. However, the exact mechanism for this process has not yet been elucidated. Therefore, a convergence of broader scientific fields such as chemistry, materials, and biology is urgently needed to induce a distinct bone tissue regeneration mechanism.

CONCLUSION

This review provides an overview of calcium- and/or phosphorus-based inorganic properties and processes combined with organics that can be regarded as matrices of these minerals, namely collagen molecules and collagen fibrils. Furthermore, we discuss how this strategy can be applied to future bone tissue regenerative medicine in combination with other academic perspectives.

Nanohydroxyapatite-Mediated Imatinib Delivery for Specific Anticancer Applications

In the present study, a nanoapatite-mediated delivery system for imatinib has been proposed. Nanohydroxyapatite (nHAp) was obtained by co-precipitation method, and its physicochemical properties in combination with imatinib (IM) were studied by means of XRPD (X-ray Powder Diffraction), SEM-EDS (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy), FT-IR (Fourier-Transform Infrared Spectroscopy), absorption spectroscopy as well as DLS (Dynamic Light Scattering) techniques. The obtained hydroxyapatite was defined as nanosized rod-shaped particles with high crystallinity. The amorphous imatinib was obtained by conversion of its crystalline form. The beneficial effects of amorphous pharmaceutical agents have been manifested in the higher dissolution rate in body fluids improving their bioavailability. Imatinib-to-hydroxyapatite interactions on the surface were confirmed by SEM images as well as absorption and FT-IR spectroscopy. The cytotoxicity of the system was tested on NI-1, L929, and D17 cell lines. The effectiveness of imatinib was not affected by nHAp modification. The calculated IC₅₀ values for drug-modified nHAp were similar to those for the drug itself. However, higher cytotoxicity was observed at higher concentrations of imatinib, in comparison with the drug alone.

Biomolecule-assisted green synthesis of nanostructured calcium phosphates and their biomedical applications

Calcium phosphates (CaPs) are ubiquitous in nature and vertebrate bones and teeth, and have high biocompatibility and promising applications in various biomedical fields. Nanostructured calcium phosphates (NCaPs) are recognized as promising nanocarriers for drug/gene/protein delivery owing to their high specific surface area, pH-responsive degradability, high drug/gene/protein loading capacity and sustained release performance. In order to control the structure and surface properties of NCaPs, various biomolecules with high biocompatibility such as nucleic acids, proteins, peptides, liposomes and phosphorus-containing biomolecules are used in the synthesis of NCaPs. Moreover, biomolecules play important roles in the synthesis processes, resulting in the formation of various NCaPs with different sizes and morphologies. At room temperature, biomolecules can play the following roles: (1) acting as a biocompatible organic phase to form biomolecule/CaP hybrid nanostructured materials; (2) serving as a biotemplate for the biomimetic mineralization of NCaPs; (3) acting as a biocompatible modifier to coat the surface of NCaPs, preventing their aggregation and increasing their colloidal stability. Under heating conditions, biomolecules can (1) control the crystallization process of NCaPs by forming biomolecule/CaP nanocomposites before heating; (2) prevent the rapid and disordered growth of NCaPs by chelating with Ca2+ ions to form precursors; (3) provide the phosphorus source for the controlled synthesis of NCaPs by using phosphorus-containing biomolecules. This review focuses on the important roles of biomolecules in the synthesis of NCaPs, which are expected to guide the design and controlled synthesis of NCaPs. Moreover, we will also summarize the biomedical applications of NCaPs in nanomedicine and tissue engineering, and discuss their current research trends and future prospects.

Synthesis, characterization and in vitro anti-cancer activity of vanadium-doped nanocrystalline hydroxyapatite

Nanocrystalline V(v)-doped hydroxyapatite and its reduced analogue (V(v) and V(iv) mixture) show promising in vitro cytotoxicity against cultured human bone cancer cells.

Calcium-based biomaterials for diagnosis, treatment, and theranostics

Calcium-based biomaterials with good biosafety and bio-absorbability are promising for biomedical applications such as diagnosis, treatment, and theranostics.

Biocompatible nanostructured solid adhesives for biological soft tissues

Over the past few years, the development of novel adhesives for biological soft tissue adhesion has gained significant interest. Such adhesives should be non-toxic and biocompatible. In this study, we synthesized a novel solid adhesive using nanostructured hydroxyapatite (HAp) and evaluated its physical adhesion properties through in vitro testing with synthetic hydrogels and mouse soft tissues. The results revealed that HAp-nanoparticle dispersions and HAp-nanoparticle-assembled nanoporous plates showed efficient adhesion to hydrogels. Interestingly, the HAp plates showed different adhesive properties depending upon the shape of their nanoparticles. The HAp plate made up of 17nm-sized nanoparticles showed an adhesive strength 2.2times higher than that of the conventional fibrin glue for mouse skin tissues.

STATEMENT OF SIGNIFICANCE

The present study indicates a new application of inorganic biomaterials (bioceramics) as a soft tissue adhesive. Organic adhesives such as fibrin glues or cyanoacrylate derivatives have been commonly used clinically. However, their limited biocompatibility and/or low adhesion strength are some drawbacks that impair their clinical application. In this study, we synthesized a novel solid adhesive with biocompatible and biodegradable HAp nanoparticles without the aid of organic molecules, and showed a rapid and strong adhesion of mouse soft tissues compared to conventional fibrin glues. Given the importance of wet adhesion in biomedicine and biotechnology applications, our results will help not only in developing an efficient approach to close incised soft tissues, but also in finding novel ways to integrate soft tissues with synthetic hydrogels (such as drug reservoirs).

The effect of hyperbranched poly(acrylic acid)s on the morphology and size of precipitated nanoscale (fluor)hydroxyapatite

Hydroxyapatite and fluorhydroxyapatite (F)HA nanoparticles were synthesised in the presence of branched poly(acrylic acid)s and compared to those synthesised in the presence of linear PAA.

Preparation of CaP/pDNA nanoparticles by reverse micro-emulsion method: Optimization of formulation variables using experimental design

In this study, the CaP/pDNA nanoparticles were prepared using Triton X-100/Butanol/Cyclohexane/Water reverse microemulsion system. Optimization of preparation conditions was based on evaluation of particle size by Box–Behnken design method. The particle sizes of the optimized CaP/pDNA nanoparticles were found to be 60.23 ± 4.72 nm, polydispersity index was 0.252 and pDNA encapsulate efficiency was more than 90%. The optimized CaP/pDNA nanoparticles have pH sensitivity and biocompatibility. Further, optimized CaP/pDNA nanoparticles showed higher transfection efficiency.

Nanomedicine: Interaction of biomimetic apatite colloidal nanoparticles with human blood components

This contribution investigates the interaction of two types of biomimetic-apatite colloidal nanoparticles (negatively-charged 47nm, and positively-charged 190nm NPs) with blood components, namely red blood cells (RBC) and plasma proteins, with the view to inspect their hemocompatibility. The NPs, preliminarily characterized by XRD, FTIR and DLS, showed low hemolysis ratio (typically lower than 5%) illustrating the high compatibility of such NPs with respect to RBC, even at high concentration (up to 10mg/ml). The presence of glucose as water-soluble matrix for freeze-dried and re-dispersed colloids led to slightly increased hemolysis as compared to glucose-free formulations. NPs/plasma protein interaction was then followed, via non-specific protein fluorescence quenching assays, by contact with whole human blood plasma. The amount of plasma proteins in interaction with the NPs was evaluated experimentally, and the data were fitted with the Hill plot and Stern-Volmer models. In all cases, binding constants of the order of 10(1)-10(2) were found. These values, significantly lower than those reported for other types of nanoparticles or molecular interactions, illustrate the fairly inert character of these colloidal NPs with respect to plasma proteins, which is desirable for circulating injectable suspensions. Results were discussed in relation with particle surface charge and mean particle hydrodynamic diameter (HD). On the basis of these hemocompatibility data, this study significantly complements previous results relative to the development and nontoxicity of biomimetic-apatite-based colloids stabilized by non-drug biocompatible organic molecules, intended for use in nanomedicine.

Biocompatible and colloidally stabilized mPEG-PE/calcium phosphate hybrid nanoparticles loaded with siRNAs targeting tumors

Calcium phosphate nanoparticles are safe and effective delivery vehicles for small interfering RNA (siRNA), as a result of their excellent biocompatibility. In this work, mPEG-PE (polyethylene glycol-L-α-phosphatidylethanolamine) was synthesized and used to prepare nanoparticles composed of mPEG-PE and calcium phosphate for siRNA delivery. Calcium phosphate and mPEG-PE formed the stable hybrid nanoparticles through self-assembly resulting from electrostatic interaction in water. The average size of the hybrid nanoparticles was approximately 53.2 nm with a negative charge of approximately -16.7 mV, which was confirmed by dynamic light scattering (DLS) measurements. The nanoparticles exhibited excellent stability in serum and could protect siRNA from ribonuclease (RNase) degradation. The cellular internalization of siRNA-loaded nanoparticles was evaluated in SMMC-7721 cells using a laser scanning confocal microscope (CLSM) and flow cytometry. The hybrid nanoparticles could efficiently deliver siRNA to cells compared with free siRNA. Moreover, the in vivo distribution of Cy5-siRNA-loaded hybrid nanoparticles was observed after being injected into tumor-bearing nude mice. The nanoparticles concentrated in the tumor regions through an enhanced permeability and retention (EPR) effect based on the fluorescence intensities of tissue distribution. A safety evaluation of the nanoparticles was performed both in vitro and in vivo demonstrating that the hybrid nanoparticle delivery system had almost no toxicity. These results indicated that the mPEG-PE/CaP hybrid nanoparticles could be a stable, safe and promising siRNA nanocarrier for anticancer therapy.

Composites of Eu(3+)-doped calcium apatite nanoparticles and silica particles: comparative study of two preparation methods

We synthesized composites of Eu(3+)-doped calcium apatite (CaAp:Eu(3+)) nanoparticles and silica particles via two methods: (i) in situ synthesis of CaAp:Eu(3+) in the presence of silica particles and (ii) electrostatic adsorption of CaAp:Eu(3+) nanoparticles on silica particle surfaces. In both methods, submicrometer spherical silica particles were covered with CaAp:Eu(3+) nanoparticles without forming any impurity phases, as confirmed by X-ray diffractometry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. In method i, part of the silica surface acted as a nucleation site for apatite crystals and silica particles were inhomogeneously covered with CaAp:Eu(3+) nanoparticles. In method ii, positively charged CaAp:Eu(3+) nanoparticles were homogeneously adsorbed on the negatively charged silica surface through electrostatic interactions. The bonds between the silica surface and CaAp:Eu(3+) nanoparticles are strong enough not to break under ultrasonic irradiation, irrespective of the synthetic method used. The composite particles showed red photoluminescence corresponding to 4f → 4f transitions of Eu(3+) under near-UV irradiation. Although the absorption coefficient of the forbidden 4f → 4f transitions of Eu(3+) was small, the red emission was detectable with a commercial fluorescence microscope because the CaAp:Eu(3+) nanoparticles accumulated on the silica particle surfaces.

Advances in synthesis of calcium phosphate crystals with controlled size and shape

Calcium phosphate (CaP) materials have a wide range of applications, including biomaterials, adsorbents, chemical engineering materials, catalysts and catalyst supports and mechanical reinforcements. The size and shape of CaP crystals and aggregates play critical roles in their applications. The main inorganic building blocks of human bones and teeth are nanocrystalline CaPs; recently, much progress has been made in the application of CaP nanocrystals and their composites for clinical repair of damaged bone and tooth. For example, CaPs with special micro- and nanostructures can better imitate the biomimetic features of human bone and tooth, and this offers significantly enhanced biological performances. Therefore, the design of CaP nano-/microcrystals, and the shape and hierarchical structures of CaPs, have great potential to revolutionize the field of hard tissue engineering, starting from bone/tooth repair and augmentation to controlled drug delivery devices. Previously, a number of reviews have reported the synthesis and properties of CaP materials, especially for hydroxyapatite (HAp). However, most of them mainly focused on the characterizations and physicochemical and biological properties of HAp particles. There are few reviews about the control of particle size and size distribution of CaPs, and in particular the control of nano-/microstructures on bulk CaP ceramic surfaces, which is a big challenge technically and may have great potential in tissue engineering applications. This review summarizes the current state of the art for the synthesis of CaP crystals with controlled sizes from the nano- to the macroscale, and the diverse shapes including the zero-dimensional shapes of particles and spheres, the one-dimensional shapes of rods, fibers, wires and whiskers, the two-dimensional shapes of sheets, disks, plates, belts, ribbons and flakes and the three-dimensional (3-D) shapes of porous, hollow, and biomimetic structures similar to biological bone and tooth. In addition, this review will also summarize studies on the controlled formation of nano-/microstructures on the surface of bulk ceramics, and the preparation of macroscopical bone grafts with 3-D architecture nano-/microstructured surfaces. Moreover, the possible directions of future research and development in this field, such as the detailed mechanisms behind the size and shape control in various strategies, the importance of theoretical simulation, self-assembly, biomineralization and sacrificial precursor strategies in the fabrication of biomimetic bone-like and enamel-like CaP materials are proposed.

Effect of encapsulation of curcumin in polymeric nanoparticles: how efficient to control ESIPT process?

This paper demonstrates the photophysics of curcumin inside polymeric nanoparticles (NPs), which are being recently used as targeted drug delivery vehicles. For this purpose, we have prepared three polymeric NPs by ultrasonication method from three well-defined water-insoluble random copolymers. These copolymers having various degrees of hydrophobicity were synthesized via reversible addition-fragmentation transfer (RAFT) method using styrene and three different functional monomers, namely, 2-hydroxyethyl acrylate, 4-formylphenyl acrylate, and 4-vinylbenzyl chloride. The photophysics of the curcumin molecules inside the polymeric NPs have been monitored by applying tools like steady state and time-resolved fluorescence spectroscopy. An increase in fluorescence intensity along with an increase in the lifetime values indicated a perturbation of the excited state intramolecular proton transfer (ESIPT) process of curcumin inside the polymeric NPs.

Novel contributions on luminescent apatite-based colloids intended for medical imaging

The setup of colloidal hybrid nanosystems based on biomimetic calcium phosphate apatites doped with europium ions has recently raised great interest in the pharmacological community, especially due to their bio-inspired character. This is especially relevant in relation with medical imaging for cancer diagnosis. Questions however remain in relation to a number of applicability aspects, some of which have been examined in this contribution. In a first part of this work, we explored further the luminescence properties of such colloidal nanoparticles. We pointed out, upon excitation of europium, the existence of some non-radiative de-excitation via the vibration of O-H oscillators located at the vicinity of the Eu3+ luminescent centers. The replacement of Eu3+ by Tb3+ ions, less prone to non-radiative de-excitation, was then tested in a preliminary way and can be seen as a promising alternative. In a second part of this work, we inspected the possibility to store these colloids in a dry state while retaining a re-suspension ability preserving the nanometer size of the initial nanoparticles, and we propose a functional protocol involving the addition of glucose prior to freeze-drying. We finally showed for the first time, based on titrations of intracellular Ca2+ and Eu3+ ions, that folic acid-functionalized biomimetic apatite nanoparticles were able to target cancer cells that overexpress folate receptors on their membrane, which we point out here in the case of T-47-D breast carcinoma cells, as opposed to ZR-75-1 cells that do not express folate receptors. This contribution thus opens new exciting perspectives in the field of targeted cancer diagnosis, thus confirming the promise of biomimetic apatites-based colloidal formulations.

Ultrasound-assisted synthesis of mesoporous zirconia-hydroxyapatite nanocomposites and their dual surface affinity for Cr3+/Cr2O7(2-) ions

Zirconia-hydroxyapatite nanocomposites were prepared by sol-gel deposition of zirconium oxide from a zirconium alkoxide in the presence of apatite colloidal suspension under ultrasonication. The material porosity evolves from mainly microporous zirconia to mesoporous hydroxyapatite, with decreasing surface area and increasing pore volume. XRD studies indicate that the apatite phase is well-preserved within the composite materials. The homogeneous dispersion of apatite colloids within the zirconia network was supported by TEM observations and nitrogen sorption measurements. (31)P solid-state NMR studies suggest that partial dissolution of apatite may have occurred during the preparation, leading to the adsorption of phosphate species on zirconia particles. This is confirmed by XRD studies of nanocomposites after thermal treatment that demonstrate the preferred formation of tetragonal over monoclinic ZrO(2) in the presence of hydroxyapatite. In order to investigate the surface properties of these novel materials, the adsorption of Pb(2+), Cr(3+), and Cr(2)O(7)(2-) was evaluated. Metal cations were preferentially adsorbed on apatite-rich composites, whereas Cr(2)O(7)(2-) shows a good affinity for the zirconia-rich phases. Zirconia-apatite materials showed the most promising performance in terms of recyclability. These nanocomposites that combine microporosity, mesoporosity and dual sorption properties for these species appear as interesting materials for metal ion remediation and may also find applications as biomaterials.

Low-temperature synthesis of nanoparticle-assembled, transparent, and low-crystallized hydroxyapatite blocks

The conditions for preparing transparent blocks assembled with low-crystallized hydroxyapatite (HAp) nanoparticles were examined. An aqueous dispersion of 32-nm-sized HAp nanoparticles was prepared by a wet chemical process at room temperature (18-22 °C), and then the nanoparticle-assembled block was prepared by casting the dispersion at 60 °C. We also proposed a novel casting method on flowable substrates to fabricate crack-free nanoparticle-assembled blocks, because large and thick blocks were not obtained by a conventional casting method on solid substrates due to crack formation. The nanoparticle-assembled transparent HAp had nanosized pores among the particles. Cell adhesion and proliferation on the block could be directly observed with an optical microscope.

Purification of biomimetic apatite-based hybrid colloids intended for biomedical applications: A dialysis study

The field of nanobiotechnology has lately attracted much attention both from therapeutic and diagnosis viewpoints. Of particular relevance is the development of colloidal formulations of biocompatible nanoparticles capable of interacting with selected cells or tissues. In this context, the purification of such nanoparticle suspensions appears as a critical step as residues of unreacted species may jeopardize biological and medical outcomes, and sample purity is thus increasingly taken into account by regulatory committees. In the present work, we have investigated from a physico-chemical point of view the purification by dialysis of recently developed hybrid colloids based on biomimetic nanocrystalline apatites intended for interacting with cells. Both Eu-doped (2mol.% relative to Ca) and Eu-free suspensions were studied. The follow-up of the dialysis process was carried out by way of FTIR, TEM, XRD, pH and conductivity measurements. Mathematical modelling of conductivity data was reported. The effects of a change in temperature (25 and 45°C), dialysis medium, and starting colloid composition were evaluated and discussed. We show that the dialysis method is a well-adapted and cheap technique to purify such mineral-organic hybrid suspensions in view of biomedical applications, and we point out some of the characterization techniques that may prove helpful for following the evolution of the purification process with time.

Quick synthesis of lipid-polymer hybrid nanoparticles with low polydispersity using a single-step sonication method

Lipid-polymer hybrid nanoparticle, consisting of a hydrophobic polymeric core and a lipid monolayer shell, represents a new and promising drug delivery platform that has shown controllable particle size and surface functionality, high drug loading yield, sustained drug release profile, and excellent in vitro and in vivo stability. These lipid monolayer-coated polymeric nanoparticles are typically fabricated through a modified nanoprecipitation method, which involves sample heating, vortexing, and solvent evaporation. Herein we report a new and fast method to synthesize lipid-polymer hybrid nanoparticles with controllable and nearly uniform particle size. Using a bath sonication approach, we demonstrate that the whole hybrid nanoparticle synthesis process can be completed in about 5 min compared with a few hours for previous synthesis approaches. The size and polydispersity of the resulting nanoparticles can be readily controlled by tuning the relative concentrations of individual building components. Colloidal stability tests of the synthesized hybrid nanoparticles in PBS buffer and serum show no signs of aggregation over a period of 5 days. The present method improves the production rate of the hybrid nanoparticles by near 20-fold while not compromising the physicochemical properties of the particles. This work may facilitate the bench-to-bedside translation of lipid-polymer hybrid nanoparticles as a robust drug nanocarrier by allowing for fabricating a large amount of these nanoparticles at high production rate.

Pathological calcification and replicating calcifying-nanoparticles: general approach and correlation

Calcification, a phenomenon often regarded by pathologists little more than evidence of cell death, is becoming recognized to be important in the dynamics of a variety of diseases from which millions of beings suffer in all ages. In calcification, all that is needed for crystal formation to start is nidi (nuclei) and an environment of available dissolved components at or near saturation concentrations, along with the absence of inhibitors for crystal formation. Calcifying nanoparticles (CNP) are the first calcium phosphate mineral containing particles isolated from human blood and were detected in numerous pathologic calcification related diseases. Controversy and critical role of CNP as nidi and triggering factor in human pathologic calcification are discussed.