CZ2008523A3 - Process for preparing hybrid nanoparticles from nanoparticle agglomerates of complex multicomponent metal oxides - Google Patents

Abstract

Hybrid nanoparticles of complex multicomponent metal oxides forming magnetic oxide grains. These grains are provided with a continuous layer of hydrated silicon oxide, which ensures their harmlessness in the body by their biocompatible surface. Applicable in medicine for diagnostic and therapeutic applications in magnetic resonance and magnetic fluid hyperthermia.

Description

Process for preparing hybrid nanoparticles from nanoparticle agglomerates of complex multi-component metal oxides

Technical field

The invention relates to the synthesis of biocompatible hybrid nanoparticles intended for selected medical applications, particularly magnetic fluid hyperthermia and magnetic resonance imaging. They consist of cores provided with a hydrophilic coating ensuring the biocompatibility of the material and the stability of the aqueous nanoparticle suspensions in the range of pH 3 - pH 10, in accordance with the biological environment.

BACKGROUND OF THE INVENTION

At present, hybrid magnetic nanoparticles based on magnetic cores of magnetite or maghemite are used in medicine for diagnostic and therapeutic purposes in magnetic resonance and fluid magnetic hyperthermia. Their main disadvantage is the limited possibility of modification of magnetic properties for specific applications. For magnetic fluid hyperthermia their use is hindered by, first, the difficulty in achieving the desired thermal performance and also high Curie temperature transition from ferromagnetic to paramagnetic state, namely T _c (Fe ₃ O ₄₎ = 477 ° C and a Tc (y FezOj) = 585 ° C, where the risk of overheating and the resulting necrosis of healthy tissue cannot be excluded.

They are applied to the body in the form of aqueous suspensions, for which low-molecular stabilizers such as various surfactants or hydrophilic polymers, most commonly dextran, are used for stabilization. Poor adhesion of the dextran coating to the magnetic cores reduces the stability of these aqueous suspensions and consequently leads to the formation of agglomerates. A similar problem is also encountered in the application of these materials as magnetic resonance contrast agents, in addition to dextran, the use of other polysaccharides such as arabinogalactan, or proteins such as albumin, or synthetic polymers is described. The polymer coating significantly increases the particle size, which adversely affects their penetration into cells and the rate of subsequent metabolic removal in the body. The difficulty in modifying the coating makes it difficult to specifically capture in specific cells of the target tissues or to bind drugs or ligands targeted to certain cell types.

Magnetite and maghemite nanoparticles have sufficiently high T2-relaxivity in terms of MR imaging and thus substantially increase contrast in MR image, but are practically useful only for MR imaging or detection of labeled cells. However, these nanoparticles are usually superparamagnetic and therefore do not allow MR-navigated and controllable magnetic hyperthermia.

SUMMARY OF THE INVENTION

These disadvantages are overcome by a solution based on the use of a material consisting of hybrid nanoparticles of complex multicomponent metal oxides, preferably a perovskite phase of the composition Laj. _x Sr _x MnO3, forming magnetic oxide grains. These grains are provided with a continuous layer of hydrated silica. The sol-gel citrate method is used for the synthesis of magnetic oxide grains, where the prepared grains continue to be heat treated usually at temperatures of 650 ° C to 900 ° C. Under these conditions, sintering and agglomerates of the resulting magnetic oxide grains result from the formation of bonding bridges between the grains. The formation of agglomerates makes it difficult to finish and coat with a continuous layer of hydrated silica and hence their use in medicine. Well coated grains have an isolated magnetic core, thus preventing exposure to the organism. Therefore, mechanical processing of the product is required consisting of a combination of rolling and milling to break down the synthesized agglomerates into individual grains. In the first step, the bonds between the formed grains are disturbed by rolling, in the second step, in addition to completing the separation of the individual grains, their distribution in the liquid is achieved. A significant benefit of the described and proven process is the possibility to change the composition and size of the grains and thus set precisely the magnetic properties critical for a given medical application.

Hybrid nanoparticles of complex multicomponent metal oxides, which form a highly stable suspension in an aqueous environment at pH> 4 with a coating preventing the organism from being exposed to the magnetic core and thus harmless to the organism, are thus obtained by covering the magnetic oxide grains with a continuous layer of hydrated silica. After synthesis, the surface of these grains is activated in an acid medium and subsequently their suspension is stabilized with ammonium citrate. The deposition of the hydrated silica layer is carried out in an environment of water, ethanol and ammonia and at elevated temperature. Substituted alkoxysilanes, for example, are used to form a hydrated silica layer

J tetraalkoxysilane. By adding aminoalkylalkoxysilane, it is possible to obtain hybrid nanoparticles exhibiting on their surface aminoalkyl chains with free amino groups which can be further derivatized. Thus, other molecules or whole functional units can be bonded to the surface of hybrid nanoparticles to prepare complex nanoparticles with specific functional elements designed for special applications, such as targeting certain tissues or combined therapy mediated by bound molecules.

The hydrophilic silica coating provides sufficient biocompatibility and hence applicability for medical applications. The thickness of the hydrated silica layer can be controlled by selecting the reaction conditions (temperature, time, composition of the reaction mixture) at least in the range of 5 - 50 nm.

By suitable setting of chemical composition of magnetic cores (0,2 <x <0,5) and particle size 20 - 60 nm it is possible to achieve thermal output up to 300 W / gMn and at the same time to set transition from ferromagnetic to paramagnetic state in temperature range 40 ° C - 60 ° C, ie temperatures just above the treatment temperature. Magnetic heating self-regulation to prevent unwanted tissue overheating is thus applied.

T2-relaxivity at the 0.5 T field (ie the ability to shorten the relaxation time of the water and thereby increase the contrast in magnetic resonance imaging) achieves a value of - 600 s ^ / mNÍMn for these 20 nm - 60 nm hybrid nanoparticles higher than that of superparamagnetic iron oxides, where for the γ-Fe 2 CH 2 with aextran coating the T 2 relapsivity is 170 s -1 / mMF _e .

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The viability of the cells in the medium in the presence of hybrid nanoparticles (0.11 mM, calculated on the amount of Mn) was about 95% and the particles can therefore also be used for cell labeling.

Due to the higher relaxation of these hybrid nanoparticles, significantly lower nanoparticle concentrations in the medium are sufficient to achieve better results. By labeling cells with the standard Endor contrast agent (iron oxide contrast agent), a relaxation ratio of cell suspension of 2.1 s ^-1 (based on 10 ⁶ cells / ml) can be achieved at an iron concentration of 1.1 mM, while using The silicon-coated perovskite phase particles of La 1 _x Sr _x MnO 3 at a concentration of 0.11 mM µM in the medium (i.e. a concentration 10 times lower) achieved a relaxation rate of 2.9 s * (based on ^{10 6} cells / ml).

DETAILED DESCRIPTION OF THE INVENTION

Example 1

The nanoparticles of ferromagnetic perovskite phase with the composition Lao ^ SrojsMnCb were prepared by a two-step process, preparation of the precursor by the sol-gel counting method and subsequent heat treatment.

The starting compounds LaiCb, SrCCh and MnCCh containing cationic components determined by chemical analysis were separately dissolved in 1: 1 dilute nitric acid and mixed with citric acid and ethylene glycol in the ratio of:

(0.75 [La ³⁺ ] ⁺ 0.25 [Sr + J + LMn ² +]) / 1.5 [citric acid] / 2.25 [ethylene glycol].

The pH = 9 was adjusted by addition of NH 4 OH. Evaporation of water at 80-90 ° C and drying at 160 ° C gave a precursor whose amorphous character was determined by X-ray powder analysis. The precursor was calcined for 6 hours at 400 ° C in air and subsequently calcined in air for 3 hours at 700 ° C. A single-phase product having an average X-ray particle size of 30 nm was determined. In the next step, the synthesized material was subjected to a combined mechanical treatment by rolling and milling. For rolling, a horizontal arrangement was used with hardened steel rollers with a diameter of 54 mm and a speed of 9 rpm. With the process repeated three times, the roller gap was gradually reduced to less than 0.03 mm. For subsequent grinding of the material in an ethanol environment, a vibratory mill with a 25 ml stainless steel grinding vessel and a 20 mm diameter grinding ball was used. Grinding parameters: sample weight 0.5 g, volume of liquid (ethanol) 10 ml grinding time 60 min, grinding frequency 30 oscillations / sec.

Rolling disturbs the stability of the agglomerates and breaks the bonding bridges between the grains resulting from the incipient sintering process during the previous heat treatment. The individual particles are then dispersed in the liquid medium by vibration grinding.

The efficiency of the process used is evident from observation of the particle microstructure by transmission electron microscopy. The significant, approximately three-fold reduction in the hydrodynamic particle size, while maintaining the average grain size before and after the mechanical treatment, determined by X-ray, confirms the distinct suppression of the agglomerate formation tendency.

Next, nanoparticles (130 mg) were exposed to 1 M nitric acid (20 mL) for 15 min in an ice bath under ultrasound, after centrifugation of nitric acid, cooled 0.1 M citric acid (20 mL) was added to the nanoparticles and the mixture placed in an ice bath was ultrasonically homogenized for 15 min. After centrifugation of the citric acid solution, its excess amount in the nanoparticle sediment was removed during one wash cycle by dispersing and centrifuging (20 ml of water). The particles were redispersed in water (10 mL) and by adding a small amount of aqueous ammonia solution (5 drops) the residual citric acid bound to the surface of the nanoparticles was converted to ammonium citrate, which stabilizes the nanoparticles in an aqueous suspension. A powerful ultrasonic probe was introduced into the suspension and the nanoparticles were scattered for 30 min. Thereafter, the suspension was added dropwise under ultrasonic and mechanical stirring to a round flask containing ethanol (96% azeotropic) -water-ammonia (25% aqueous solution) in a ratio of 15: 4: 1 (400 mL) thermostated to 40 ° C. Subsequently, the mixture was stirred only by mechanical stirring. An amount of tetraethoxysilane corresponding to the desired coating thickness (2670 μΐ at 25 nm) was added to the suspension in one portion and the mixture was left in a thermostatic bath for 24 hours.

After encapsulation of the nanoparticles into the hydrated silica layer, their desired fraction was isolated from the reaction mixture. Isolation included collecting the supernatant after centrifugation at an angle rotor at 3000 rpm for 15 min and then separating the nanoparticles from the supernatant by centrifugation at 8000 rpm for 40 min. The nanoparticles thus separated were subsequently purified by two washing cycles in ethanol and four cycles in water (60 ml of washing liquid each). After the last cycle, the nanoparticle sediment was made up to 20 ml with water, and the nanoparticles were redispersed by ultrasound. To remove residual traces of ethanol, the suspension was placed in a vacuum oven, tempered to 35 ° C at a pressure of ~ 1 Pa for 1 hour. Measurement of the hydrodynamic size of the coated particles showed a narrow distribution described at 80% by scattering values of 134 + 18 nm. Transmission electron microscopy confirmed the presence of a coating layer with a thickness of approximately 25 nm, whose chemical nature was proved by IR spectroscopy. Measurement of the zeta-potential in the pH 11 area has demonstrated the stability of the coated nanoparticle suspensions in the aqueous environment in the pH range required for medical use.

Example 2

The nanoparticles of the ferromagnetic perovskite phase of Lao2 SrojsMnCh composition and average grain size of 30 nm were prepared according to the procedure described in Example 1. Their weight (200 mg) was exposed to 1 M nitric acid (20 ml) for 15 min in an ice bath with dispersion ultrasound. Removal of nitric acid residues was performed in three washes with water (25 ml each). Then the nanoparticles were dispersed in water (50 ml) by ultrasonic probe for 1 hour. After cooling in an ice bath, their suspension was added dropwise to a pre-prepared solution of polyvinylpyrrolidone (PVP) (350 ml) with an average molecular weight M _r = 24,000 g / mol. . This was placed in an ultrasonic bath for 1 hour before the addition of the nanoparticles, in which the polymer developed highly. The volume of the prepared suspension (400 ml) was chosen so that the concentration of perovskite phase was 0.5 g / ml and the total amount of PVP in suspension (3.67 g) corresponded to 15 polymer molecules per nm of ² nanoparticle surface with a diameter of 30 nm. The suspension was homogenized for 24 hours in an ultrasonic bath thermostated at 25 ° C. During ultrasound exposure, PVP adsorption equilibrium was established on the nanoparticle surface, resulting in a stable aqueous suspension. The stabilized nanoparticles were separated by centrifugation and then the excess PVP was removed by washing with ethanol (20 mL) in one wash cycle. The solid residue was transferred to a 500 mL round flask, supplemented with ethanol (400 mL). The suspension was dispersed for 5 min in a 25 ° C thermostated bath under ultrasonic and mechanical agitation. Subsequently, the mixture was stirred only by mechanical stirring. Tetraethoxysilane was added to the flask in one portion, which would correspond to the formation of a continuous layer of hydrated silica with a thickness of 4 nm (236 μΐ). Subsequently, four times less 3-aminopropyltriethoxysilane (59 μΐ) was added and after brief mixing 64 ml of ammonia (25% aqueous solution) was added to catalyze the basic hydrolysis of the alkoxysilanes. The mixture was left in a thermostated bath for 24 hours.

Upon completion of the encapsulation, all nanoparticles were separated by centrifugation, the solid residue being washed with ethanol in three wash cycles (60 ml each). Subsequently, the desired size fraction of coated nanoparticles was isolated. The product was first dispersed by sonication in ethanol (200 mL). After centrifugation in an angle rotor at 3000 rpm for 15 min, the supernatant was separated and finally the nanoparticles were separated by centrifugation at 8000 rpm for 40 min. The corresponding sediment was redispersed in ethanol (50 ml) by ultrasonic homogenization. Transmission electron microscopy confirmed the presence of a coating layer less than 10 nm thick, with the presence of Si-O-Si and Si-OH binding motifs confirmed by IR spectroscopy. The spectrophotometric determination of p-nitrobenzaldehyde was used to determine the concentration of surface-available amino groups (0.23 pmol (NH ₂ R, surface) / mg (Mn)), by which the nanoparticles were covalently derivatized to form imine bonds which were hydrolyzed again.

Industrial applicability

Hybrid nanoparticles of complex multicomponent metal oxides are useful in medicine, for example for diagnostic imaging as a magnetic resonance contrast agent, for magnetic fluid hyperthermia therapy. Another possibility is a combination therapy mediated by molecules bound to amino groups on the surface of complex siliceous layers.

Claims (5)

PATENT CLAIMS Process for the preparation of hybrid nanoparticles of nanoparticles of complex multicomponent metal oxides characterized in that these agglomerates are broken up into individual grains, their surface is activated in an acid medium, these grains are dispersed in water to form a suspension stabilized by ammonium citrate, dispersed in ethanol, water and ammonia environments, a substituted alkoxysilane is added to form a hydrated silica layer by adding 10 to 50 μΐ of substituted alkoxysilane to each 1 m ² of grain surface and every 1 nm of hydrated silica layer thickness. Process for the preparation of hybrid nanoparticles of nanoparticle nanoparticles of complex multicomponent metal oxides according to claim 1, characterized in that tetraethoxysilane is used as the substituted alkoxysilane. A process for the preparation of hybrid nanoparticles of nanoparticle nanoparticles of complex multicomponent metal oxides according to claim 1, characterized in that aminoalkyltriethoxysilane is used as the substituted alkoxysilane. 4. A process for the preparation of hybrid nanoparticles of nanoparticle nanoparticles of complex multicomponent metal oxides according to claim 1, wherein the substituted alkoxysilane is aminoalkyltriethoxysilane together with tetraalkoxysilane. 5. A method for preparing hybrid nanoparticles _t zaglomerátů nanoparticles multicomponent complex metallic oxides according to claim Ivyznačující sowing the acidic environment of nitric acid.