|Title of Invention||
A PROCESS FOR PREPARATION OF NANOSIZED IRON OXIDE BY BIOMIMETIC ROUTE
|Abstract||The invention provides a biomimetic process for preparation of nanosized iron oxide particles used for the enhancement of magnetic resonance imaging contrast The process involves a weak complextion (via dative bond formation) of ferrous/ferric ions (acceptor atom) with the active functional groups (donor atom) of polymer. The nanosized iron oxide , is biodegradable , nontoxic and has size in the range of 4-20 nanometer.|
|Full Text||This present invention relates to a process for the preparation of nanosized iron oxide by biomimetic route. This invention particularly relates to a biomimetic process for preparation of nanosized magnetite particles used for the enhancement of magnetic resonance imaging contrast. The nanosized magnetite, a form of iron oxide, is biodegradable, nontoxic and has size in the range of 4-20 nanometer. The particles, being super-paramagnetic in nature and exhibiting a narrow size distribution, are useful generally in the fields of medical treatment and specifically for Magnetic Resonance Imaging.
Magnetic Resonance Imaging (MRI) is widely used for diagnostic imaging of the soft tissues and has been proven to be better to computed tomography for the detection of lever metastases. The screening and follow up of any kind of metastasis using contrast-enhanced MRI is an interesting tool for oncologists because ultrasound (US) is operator dependent and not always reproducible. Therefore, various contrast agents for an improved MR imaging have been developed by the pharmaceutical companies to serve the purpose.
Several metal chelates comprising of a highly magnetic cation Gd3+ e.g. Gd-DTPA (Diethylene Triamine Pentaacetic Acid) are available for ready clinical use. These agents have been applied in enhancing the image contrast either as coating material in a therapeutic device or as directed agents for a specific organ. The only commercially available iron oxide for use in MRI contrast is ferumoxide, which has a supraparamagnetic crystalline core ( nanosized magnetite) surrounded by dextran coating. Being produced by conventional chemical method these magnetite particles suffer with the limitations of the chemical synthesis route such as poor control over size and morphology. This ultimately deteriorates the supraparamagnetic behavior of the particles and makes them unsuitable for application.
In a conventional method of production of nanosized magnetite particles, as developed by David and Welch.(I. David and A. J. E. Welch, Trans. Faraday Soc. 52 (1956) 1642) wherein ferrous sulphate solution is heated to 90°C and added a solution of potassium hydroxide and potassium nitrate drop-wise over a few minutes. Heating the suspension for 60 minutes with continuous stirring followed by cooling, washing and drying leads to the formation of black precipitate of magnetite powder. It is mandatory to carry out the entire preparation under an atmosphere of nitrogen.
In another known process by Schikorr ( G. Schikorr, Z. Electrochem 35 (1929) 65) wherein the alkaline hydrolysis of ferrous sulphate solution is carried out to yield ferrous hydroxide followed by it's further oxidation at 100°C leading to the formation of magnetite powder along with evolution of hydrogen gas.
In still another known process, reaction of ferrous/ferric solution under alkaline condition at 80°C under nitrogen atmosphere leads to the formation of magnetite particles (Regazzoni A.E, Urrutia G.A., Blesa M.A. and Maroto A.J.G., Inorg. nucl. Chem., 43, (1981)1489).
In hitherto known processes the magnetite particles produced have poor crystallinity, a wide range of size distribution, random variation in morphology and magnetically induced agglomeration. The above limitations reduce the applicability of the magnetite particles in the field of medicine.
The main objective of the present invention is to provide a process for preparation of nanosized iron oxide by biomimetic route, which obviates the drawbacks as detailed above.
Another objective of the present invention is to provide a biomimetic process for preparation of nanosized magnetite particles used for the enhancement of magnetic resonance imaging contrast.
In nature, the synthesis of nano and micro sized inorganic particles is observed since the evolution of life. The process is termed as biomineralisation and it exhibits a high degree of control over the nucleation and growth of the synthesized particles, which perform different functions under different conditions and do not agglomerate. Our teeth, bones, shells etc. are the products of biomineralisation and nature carries out these in situ syntheses under the control of a biopolymeric matrix.
In the process of present invention in laboratory a method has been developed for in situ precipitation of nanosized magnetite particles in a pre-organized polymeric matrix made of a water-soluble polymer like polyvinyl alcohol at room temperature. The method produced magnetite particles in the size range of 5-10 nm having uniform morphology and orientation with supraparamagnetic behaviour.
Under the optimum conditions of temperature, concentration, pH and a specific volumetric ratio, the underlying polymeric matrix provides a regularly
arranged and uniformly distributed reaction as well as nucleation sites in the self assembled polymeric network formed as a result of gelation and cross-linking. The process involves a weak complextion (via dative bond formation) of ferrous/ferric ions (acceptor atom) with the active functional groups (donor atom) of the underlying polymer. An enhancement in the degree of saturation of ferrous/ferric ions locally at the complexation sites leads to the precipitation of nanosized magnetite particles under alkaline conditions at an optimum temperature. Adsorption of the polymer at the surface of the precipitate limits the dimensions of the particles in nanometer size range and the polymer matrix anisotropy induces an orientation during the particles growth. Accordingly, the present invention provides a process for preparation o nanosized iron oxide characterized in that it is prepared by biomimetic route which comprises
i) mixing polyvinyl alcohol of strength ranging between 0.1 - 0.6% and disodium tetra borate solution of strength ranging between 0.1 - 0.6% in a volumetric ratio ranging between 9:1 to 12:1 in deionised water by continuous stirring,
ii) mixing the above said reaction mixture with an iron salt solution of strength ranging between 0.01 - 0.02M in deionised in a volumetric ratio ranging from 2:1 to 5:1 under nitrogen atmosphere, at a pH in the range of 3 - 6 and stirring for about 20 minutes by a magnetic stirrer,
iii) heating the above resultant solution at a temperature in the rang o of 40 - 60°C for a period of 24 hours under nitrogen atmosphere to obtain an iron ion loaded cross linked polymer gel,
iv) soaking the above said polymer gel for a period ranging from 2 to 4 hours into sodium hydroxide solution of strength ranging between 0.002 - 0.009 M, at a temperature ranging between 40 - 50° C,
v) washing the above soaked polymer gel with de-ionized water to remove the sodium chloride salt and recovering the nanosized iron oxide particles from the soaked polymer gel by known method.
In an embodiment of the present invention the iron salt solution used is a mixture of ferric chloride and ferrous chloride in de-ionized water.
By the process of the present invention, a single phase agglomeration free magnetite particles in the size range of 5-10 nanometer and oriented in the form of linear arrays are produced.
The novelty of the present route is the in situ synthesis of the magnetite particles in preorganized polymer matrix. The polymer matrix controls the particles shape and size and regulates the precipitation process. The inventive step of the present invention is the chelation of ferric and ferrous ions by weak van der Wall bonds and hydrogen bonds present in cross-liked polymer matrix. The cross linking of the polymer provides a biopolymer like medium for mineralization which is characterized by regular arrangement of nano reactors and avoids agglomeration of the particles and induce precipitation under mild conditions of super saturation.
The following examples are given by way of illustration and should not be construed to limit the scope of the present invention.
Example - 1
60 ml 0.5% polyvinyl alcohol was mixed with 15 ml of 0.013 M iron salt solution (prepared by dissolving ferric chloride and ferrous chloride salt in the deionized water in the ratio by weight of 3:2) in the volumetric ratio of 4:lby continuous stirring using a magnetic stirrer. The pH of the solution was observed 3.The resulting solution was poured into a petri dish and subjected to gel formation in an oven at 40°C maintaining nitrogen atmosphere for 24 hours. The thin dried light yellow film (gel) was soaked for 4 hours in 0.00625M sodium hydroxide solution taken in a beaker and heated to 40°C following which color of the film changed from light yellow to black. Next, the black film was washed thoroughly by de-ionized water and again it was dried at 40°C in the same oven maintaining nitrogen atmosphere for 24 hours. Finally, the washed and dried sample was structurally characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The analysis of the results obtained confirmed the formation of single phase magnetite particles in the form of oriented and regularly arranged linear arrays having a low particle density showing agglomeration to certain extent and size in the range of 10-40 nm. Recovery of the iron oxide was close to 100%.
Example - 2
60 ml of 0.5% polyvinyl alcohol solution was mixed with 6 ml of 0.5% disodium tetra borate solution in the volume ratio of 10:1 mixed by continuous stirring using a magnetic stirrer. Next, 15 ml of 0.013 M iron salt solution (prepared by dissolving ferric chloride and ferrous chloride salts in de-ionized in the ratio 3: 2) was added in a volume ratio of 4:1 by continuous stirring using a magnetic stirrer. The pH of the solution was observed to be 5. The resulting solution was poured into a petri dish and was subjected to gel formation in an oven at 40°C maintaining nitrogen atmosphere. The dried film was soaked in 0.00625M sodium hydroxide taken in a beaker heated to 40°C, for 4 hours following which, color of the film changed from light yellow to black. Next, the film was washed thoroughly with de-ionized water and dried in an oven at 60°C for 24 hours maintaining nitrogen atmosphere. The washed and dried sample was structurally characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The analysis of the results obtained confirmed the formation of single-phase magnetite in the form of regularly oriented linear arrays widely distributed throughout the matrix network being parallel to each other. The particle size in this case was observed to be decreased to a range of 10-20 nm. More number of arrays with increased particle density and almost without any agglomeration was observed in this case. The recovery rate of iron oxide was close to 100%.
Example - 3
60 ml of 0.5% polyvinyl alcohol solution was mixed with 6 ml 0.5% disodium tetra borate solution with continuous stirring using magnetic stirrer at room temperature. The pH of the solution was observed to be 5. To this, 15 ml of iron salt solution (prepared by dissolving ferric chloride and ferrous chloride salt in deionized water in the ratio 3:2) was added, again with continuous stirring and the resulting solution was poured into a petri dish and kept in an oven for gel formation at 40°C under nitrogen atmosphere for 24 hours. Next, the dried light yellow gel was soaked for 4 hours in 0.00625M sodium hydroxide solution taken in a beaker and heated to 40°C, following which color of the gel changes from light yellow to black. It was washed 4 to 5 times with de- ionized water and dried at 40°C in an oven under nitrogen atmosphere. The washed and dried film was structurally characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy.
The analysis of data indicated the presence of single-phase magnetite in the form of linearly oriented arrays, arranged regularly, parallel to each other widely distributed throughout the matrix with high particle density in the matrix nucleation sites. The particle size in this case ranged from 5-10 nm, had a high aspect ratio and were with no agglomeration. The recovery rate of iron oxide was close to 100%. The main advantages of the present inventions are:
1. The invention provides a room temperature process for the preparation of
nanosized magnetite particles suitable for application in magnetic resonance
image contrast enhancement.
2. The invention leads to agglomeration free magnetite particles with uniform shape
3. The size distribution of the particles is very narrow.
4. The produced particles being super-paramagnetic in nature can be used in other
applications also involving ferro fluids.
1. A PROCESS FOR PREPARATION OF NANOSIZED IRON OXIDE CHARACTERIZED IN THAT IT IS PREPARED BY BIOMIMETIC ROUTE WHICH COMPRISES
I) MIXING POLYVINYL ALCOHOL OF STRENGTH RANGING BETWEEN 0.1 - 0.6% AND DISODIUM TETRA BORATE
SOLUTION OF STRENGTH RANGING BETWEEN 0.1 - 0.6% IN A VOLUMETRIC RATIO RANGING BETWEEN 9:1 TO
12:1 IN DEIONISED WATER BY CONTINUOUS STIRRING, II) MIXING THE ABOVE SAID REACTION MIXTURE WITH AN IRON SALT SOLUTION OF STRENGTH RANGING BETWEEN
0.01 - 0.02M IN DEIONISED IN A VOLUMETRIC RATIO RANGING FROM 2:1 TO 5:1 UNDER NITROGEN
ATMOSPHERE, AT A PH IN THE RANGE OF 3 - 6 AND STIRRING FOR ABOUT 20 MINUTES BY A MAGNETIC
STIRRER, III) HEATING THE ABOVE RESULTANT SOLUTION AT A TEMPERATURE IN THE RANGE OF 40 - 60° C FOR A PERIOD
OF A24 HOURS UNDER NITROGEN ATMOSPHERE TO OBTAIN AN IRON ION LOADED CROSS LINKED POLYMER
GEL, IV) SOAKING THE ABOVE SAID POLYMER GEL FOR A PERIOD RANGING FROM 2 TO 4 HOURS INTO SODIUM
HYDROXIDE SOLUTION OF STRENGTH RANGING BETWEEN 0.002 - 0.009 M, AT A TEMPERATURE RANGING
BETWEEN 40 - 50" C, V) WASHING THE ABOVE SOAKED POLYMER GEL WITH DE-IONIZED WATER TO REMOVE THE SODIUM CHLORIDE
SALT AND RECOVERING THE NANOSIZED IRON OXIDE PARTICLES FROM THE SOAKED POLYMER GEL.
2. A PROCESS AS CLAIMED IN CLAIM 1 WHEREIN THE IRON SALT SOLUTION USED IS A SOLUTION OF FERRIC CHLORIDE
AND FERROUS CHLORIDE IN DE-IONIZED WATER.
3. A PROCESS FOR PREPARATION OF NANOSIZED IRON OXIDE BY BIOMIMETIC ROUTE SUBSTANTIALLY AS HEREIN
DESCRIBED WITH REFERENCE TO THE EXAMPLES.
|Indian Patent Application Number||909/DEL/2001|
|PG Journal Number||13/2009|
|Date of Filing||03-Sep-2001|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH,|
|Applicant Address||RAFI MARG NEW DELHI-110001, INDIA.|
|PCT International Classification Number||NA|
|PCT International Application Number||N/A|
|PCT International Filing date|