WO2015107537A1

WO2015107537A1 - Bioconversion of strontium added fluorophosphate glasses and method of making thereof

Info

Publication number: WO2015107537A1
Application number: PCT/IN2014/000762
Authority: WO
Inventors: Pugalanthipandian SANKARALINGAM; Rajkumar GURUSAMY
Original assignee: Pandian Bio-Medical Research Centre
Priority date: 2014-01-16
Filing date: 2014-12-09
Publication date: 2015-07-23

Abstract

The present invention discloses different composition of strontium added fluorophosphate glasses prepared using melt-quench method. The physico-chemical and bio conversion of strontium added fluorophosphate glasses were accessed using density measurements, ultrasonic measurements to determine elastic moduli, XRD pattern, FTIR spectra, XPS spectrograph, pH variations during 21 days of in vitro studies in SBF solution, SEM images and EDS spectrograph. Bioconversion was also accessed by in vivo studies of implantation of the optimized glass into animal bone for 10 weeks followed by SEM images, EDS spectra and CLSM images. The result obtained before, after in vitro and in vivo studies are discussed in terms of structure, stability, mechanical properties, bone bonding ability and bioconversion of the prepared glass samples. The sample SrFP5 is found to be more ideal and better than other samples for future clinical use.

Description

THE PATENTS ACT 1970 (39 of 1970)

The Patents Rules, 2003

COMPLETE SPECIFICATION

(See section 10 and rule 13)

Bioconversion of strontium added fluorophosphate glasses and method of making thereof

Pandian Bio-Medical Research Centre

36, Sivagangai Road

Madurai-625 001

Tamil Nadu. INDIA.

The following specification particularly describes the invention and the manner in which it is to be made DESCRIPTION

Field of invention

The present invention describes the composition of strontium oxide added fluorophosphate glasses by melt quenching technique for different bio-medical applications.

Background of invention with regard to the drawback of associated known art

A number of materials have been examined for their ability to regenerate new bone. Currently, autologous bone remains the preferred material in bone graft and regenerative procedures. This bone, taken from a secondary site within the body is often excised and reimplanted. It contains both the inorganic mineral hydroxyapatite as well as the cell characteristics of bone. Even this is not a living material, but can remodel into new and functional bone. Autografts may be combined with supplementary agents such as growth factors or synthetic bone replacement materials. The disadvantage of autologous bone usage is the creation of a secondary trauma site that has to heal. Further, its usage is limited by availability. The materials taken from cadavers (allograft) are not constrained by supply. The above material is often demineralized, leaving behind a collagenous scaffold for the growth of a new bone. Further, it fails to function as an osteoinductive but only as osteoconductive material. These materials always carry the risk of disease transmission with them.

The third generation of materials used for the regenerating new bone is bioactive glass. These materials have the unique ability to form a chemical bond with the host tissue when implanted. Thus, it allows to retain the structural integrity and to resist movement at the implantation site. The chemical bond that occurs through the formation of hydroxyapatite on the glass surface converts the glass into bone rich material. The beneficial effects of bioactive glasses on cellular growth also substantiate to their use.

Attempts were made to synthesis artificial bone graft material which is suitable for different biomedical applications. L.L. Hench in Imperial College, London succeeded in developing silica based material, named Bioglass, in the year of 1960. But, it was hard to get good compatibility with biological tissues because of their relative insoluble nature. Silica-free phosphate glasses, namely bioactive glasses, were made in the year 1996. These glasses show better bioactivity due to their chemical composition, which is compatible with that of natural bone. But still the slow rate of biological conversion and poor mechanical strength of bioactive glasses hampers its clinical application. To circumvent these pitfalls a better composition of bioactive glass with higher porosity, elastic moduli, mechanical strength, bioconversion and controlled rate of dissolution near that of natural bone is continuously searched. Object of invention

Fluorine is a time honoured molecule used in treatment of osteoporosis. It is known to increase bone formation. But its utility was limited by the toxicity on higher doses and the pain during administering the drug. But low non toxic concentration when added to phosphate based glasses yield bio-convertable glasses called fluorophosphate glasses. Its bioconversion rate and mechanical strength are further enhanced by adding certain metal oxides.

Strontium is generally known as network modifier for the formation of Non Bridging Oxygens (NBOs) in the glass network and hence alters the solubility of the glass after implant. The addition of strontium has an influence on the fluorophosphate glass structure and the formation of Sr-F bands instead of Ca-F bands. It may be tailored such a way that the implant dissolves in the body at a rate at which new tissue is formed. Ionic strontium in the human body enhances the physiological activity of bone formation and can also be incorporated into the mineral structure of the bone. The incorporation of SrO in fluorophosphate based glasses introduces more lattice distortions and increases its solubility. Recent studies indicates that incorporation of 5% of Sr for ca content in HAp increase its mechanical strength.

The present invention discloses the different composition of strontium oxide added fluorophosphate glasses P₂0₅— CaO— Na₂0— CaF₂— SrO (hereafter termed, respectively, as SrFPl, SrFP2, SrFP3, SrFP4 and SrFP5) are prepared by keeping the ratio of P/Ca as a constant. The addition of SrO to fluorophosphate glass system modify surface nucleation. It is known that the degradation of glass alone is not an important factor for bone-bonding ability of glass, but the composition of glass also plays an important role. The present invention discloses the improved bioactivity by adding fluoride and strontium molecules and enhanced mechanical strength, load bearing capability, elastic moduli etc. by adding strontium oxide.

Statement of invention

1. The protocol for melt quenching method to produce strontium oxide added fluorophosphate glasses.

2. The addition of strontium with fluorophosphate yield better mechanical strength.

3. Physico-chemical properties of strontium added fluorophosphate glasses are accessed. >

4. The bioconversion of strontium added fluorophosphate glass is ascertained.

5. No cytotoxicity is observed in strontium added fluorophosphate glasses up to the addition of 8 mol% of strontium content. A summary of invention

The present invention discloses the composition with different contents of P₂0₅-CaO-Na₂0-CaF₂-SrO (SrFPl, SrFP2, SrFP3, SrFP4 and SrFP5) glass systems that are prepared using normal melt-quench method by keeping the ratio of P/Ca as a constant. The physico-chemical and bioactivity of the strontium added fluorophosphate were assessed using density measurements, ultrasonic velocity measurements, x-ray diffraction (XRD) patterns, Fourier transform infrared spectra (FTIR), pH variation of the sample glasses soaked 21 days in the laboratory prepared simulated body fluid (SBF) solution, scanning electron microscope (SEM) images, energy dispersive x-ray spectra (EDS) and x-ray photo electron spectrograph (XPS). Toxic nature of the selected glass sample was assessed using cytotoxicity study in cell culture lines. Bioconversion was also accessed by in vivo studies of implantation of the glass into animal bone followed by SEM, EDS and confocal laser scanning micrograph (CLSM) images. The results obtained before and after in vitro and in vivo studies are discussed in terms of change in structure, stability, mechanical properties, bone-bonding ability and bioconversion of the prepared glass samples.

Detailed Description

SrO added fluorophosphate glass composition P2O5— CaO— Na₂0— CaF₂— SrO, methods of preparation and use thereof are disclosed. The glasses can be used for different biomedical applications such as prosthetic implants, stents, screws, plates, tubes, controlled drug delivery etc. The addition of fluorine and strontium is made at the expense of Na₂0 content in the glass composition and keeping the P/Ca ratio as constant. The glasses were prepared in the mentioned compositions include various salts in mol% with the following ranges:

S. No. Salt Ratio In mol%

1. P2O5 36-65

2. CaO 22-36

3. Na₂0 11-32

4. CaF₂ 0.01-20

5. SrO 0.1-12 To access the variation if any, the following chemicals were alternatively used its proportionate molecular weight:

S.No. Required salt Alternatively used

1. P₂0₅ Ammonium di hydrogen phosphate, Phosphorous chloride, ammonium phosphate, calcium phosphate, sodium phosphate, silver phosphate etc.

2. CaO Calcium sulphate, calcium carbonate, calcium

fluoride, calcium fluorophosphate, calcium chloride, calcium caseinate, calcium bicarbonate etc.

3. Na₂0 Sodium carbonate, sodium citrate.

4. CaF₂ Calcium di fluoride, calcium tri fluoride, calcium

fluorophosphate, sodium fluoride etc.

4. SrO Strontium, strontium chloride, strontium iodide, strontium fluoride, strontium sulphate etc.

The influence of strontium on added phosphate glass system is studied in terms of pH variations during in vitro studies, FTIR spectra, XRD pattern, X-ray photoelectron spectrograph (XPS) etc. The structural role of strontium in loose packing of glass network is noticed. The hydroxyapatite (HAp) forming ability of prepared glasses is carried through in vitro studies in simulated body fluid (SBF). The scanning electron microscopy (SEM) images before and after in vitro studies show the formation of HAp in all glass surfaces, while a higher rate of formation of HAp is evidenced on strontium added fluorophosphate glasses rather than strontium free glass. FTIR spectra and XRD patterns that are observed support its higher bioactivity. Further, the cell viability test showed no cytotoxicity on MIT assays and hence these glasses are suitable for synthetic bone graft material for human use. The in vivo studies were done on rabbit by implanting the optimised sample SrFP5 into the femoral condyle. SEM EDS and CLSM studies on the un-decalcified sectioning of the implant after 10 weeks confirm the bioconversion of glass into bone. Materials and method

SrO added fiuorophosphate glasses were prepared by melting the homogeneous mixture of phosphate, calcium, sodium, strontium and fluoride salts followed by sudden quenching of the melt. The derivatives of phosphate, calcium, sodium, strontium and fluoride salts were weighed accurately and ground using mortar and pestle/ planetary ball mill. The mixture was fed into alumina crucible and then preheated at a temperature ranging from 140 °C to 190 °C for 1 h in a closed furnace and cooled to room temperature at a rate of 1 °C per minute. The preheated mixture was ground using mortar and pestle/ planetary ball mill. The mixture was taken in a platinum crucible and melted at the temperature ranging from 1050 °C to 1400 °C for 1 h. The temperature in the furnace was kept constant throughout the process. The melt was poured in a preheated graphite/ steel mould and cooled to room temperature. In this method, the entire synthesis protocol is successfully done without the usage of any toxic chemicals.

The method for preparing strontium added fiuorophosphate glasses compare the following steps:

a) The calculated quantities of the chemicals were weighed accurately using an electronic balance. b) The weighed chemicals were ground using mortar and pestle/ planetary ball mill for 1 h to obtain a homogeneous mixture. c) The mixture was preheated at a temperature ranging from 140 °C to 190 °C for 1 h in a closed furnace and cooled to room temperature at a rate of 1 °C per minute. d) The preheated mixture was ground using mortar and pestle/ planetary ball mill to obtain a homogeneous powder. e) The obtained homogeneous powder was taken in a platinum crucible (10% Rhodium doped) and melted at the temperature ranging from 1050 °C to 1400 °C for 1 h in electric furnace. f) The melt was suddenly quenched in a preheated steel/ graphite mould of temperature 300 °C - 600 °C and then cooled to room temperature. g) The obtained solid glass sample is annealed at 300 °C - 500 °C for 1 h and cooled at the rate of 0.5 °C - 2 °C per minute. h) The prepared glass sample was cut into required shape and size using a diamond cutter for different characterisation studies. Example 1:

21.3221 g of P₂0₅, 4.78991 g of CaO, 2.783 g of Na₂0 and 1.4973 g of CaF₂pure chemicals were taken in agate mortar/ planetary ball mill . Ethanol was added with the mixture and ground for 1 h to obtain a homogeneous mixture. The mixture was dried at 100 °C -200 °C for 1 h and ground using agate mortar/ planetary ball mill to obtain a fine powder. The powdered mixture was melted in platinum doped with 10% Rhodium crucible and heated at the temperature of 1050 °C - 1400 °C for 1-4 h and then quenched in a preheated stainless steel/ graphite mould at a temperature of 300 °C - 600 °C and then cooled. The prepared glass sample was annealed at 300 °C- 500 °C for 1 h then cooled at the rate of 0.5 °C - 2 °C per minute to release the stress in the glass sample. The prepared glass sample was cut into required size and shape using diamond cutter. The code for the present sample is called as SrFPl.

Example 2:

20.9791 g of P₂0₅, 4.7128 g of CaO, 1.9758 g of Na₂0, 1.1312 g of CaF₂ and 1.2011 g of SrO and pure chemicals were taken in agate mortar/ planetary ball mill. Ethanol was added with the mixture and ground for 1 h to obtain a homogeneous mixture. The mixture was dried at 100 °C - 200 °C for 1 h and ground using agate mortar/ planetary ball mill to obtain a fine powder. The powdered mixture was melted in platinum doped with 10% Rhodium crucible and heated at the temperature of 1050 °C - 1400 °C for 1-4 h and then quenched in a preheated stainless steel/ graphite mould at a temperature of 300 °C - 600 °C and then cooled. The prepared glass sample was annealed at 300 °C- 500 °C for 1 h and then cooled at the rate of 0.5 °C - 2 °C per minute to release the stress in the glass sample. The prepared glass sample was cut into required size and shape using diamond cutter. The code for the present sample is called as SrFP2.

Example 3:

20.2733 g of P₂0₅, 4.5052 g of CaO, 3.1351 g of Na₂0, 1.1615 g of CaF₂, and 0.9250 g of SrO pure chemicals were taken in agate mortar/ planetary ball mill. Ethanol was added with the mixture and ground for 1 h to obtain the homogeneous mixture. The mixture was dried at 100 °C - 200 °C for 1 h and ground using agate mortar/ planetary ball mill to obtain a fine powder. The powdered mixture was melted in platinum doped with 10% Rhodium crucible and heated at the temperature of 1050 °C - 1400 °C for 1 - 4 h and then quenched in a preheated stainless steel/ graphite mould at a temperature of 300 °C - 600 °C then cooled. The prepared glass sample was annealed at 300 °C- 500 °C for 1 h and then cooled at the rate of 0.5 °C - 2 °C per minute to release the stress in the glass sample. The prepared glass sample was cut into required size and shape using diamond cutter. The code for the present sample is called as SrFP3. Example 4:

20.0251 g of P₂0₅, 4.4500 g of CaO, 2.5503 g of Na₂0, 1.1473 g of CaF₂, and 1.8273 g of SrO and pure chemicals were taken in agate mortar/ planetary ball mill. Ethanol was added with the mixture and ground for 1 h to obtain the homogeneous mixture. The mixture was dried at 100 °C - 200 °C for 1 h and ground using agate mortar/ planetary ball mill to obtain the fine powder. The powdered mixture was melted in platinum doped with 10% Rhodium crucible and heated at the temperature 1050 °C - 1400 °C for 1 - 4 h then quenched in a preheated stainless steel/ graphite mould of temperature 300 °C - 600 °C then cooled. The prepared glass sample was annealed at 300 °C - 500 °C for 1 h then cooled at the rate of 0.5 °C - 2 °C per minute to release the stress in the glass sample. The prepared glass sample was cut into required size and shape using diamond cutter. The code for the present sample is called as SrFP4.

Example 5:

19.2831 g of P₂0₅, 4.2322 g of CaO, 3.7421 g of Na₂0, 1.1781 g of CaF₂, 1.5641 g of SrO and pure chemicals were taken in agate mortar/ planetary ball mill. Ethanol was added with the mixture and ground for 1 h to obtain a homogeneous mixture. The mixture was dried at 100 °C - 200 °C for 1 h and ground powder using agate mortar/ planetary ball mill to obtain a fine powder. The powdered mixture was melted in platinum doped with 10% Rhodium crucible and heated at the temperature ranging from 1050 °C to 1400 °C for 1- 4 h and then quenched in a preheated stainless steel/ graphite mould at a temperature ranging from 300 °C to 600 °C and then cooled. The prepared glass sample was annealed at 300 °C - 500 °C for 1 h then cooled at the rate of 0.5 °C - 2 °C per minute to release the stress in the glass sample. The prepared glass sample was cut into required size and shape using diamond cutter. The code for the present sample is called as SrFP5.

Physico-chemical and in vitro studies

1. Density Measurements

The density of the prepared glass samples was measured using Archimedes' principle with water as a buoyant and the relation, P ~ ^~——^x P_b , where W_a is weight in air,

W_a - W_b

W_b is the weight in water, and p_b is the density of water. A digital balance (model

BSA224S-CW; Sartorius, Goettingen, Germany) with an accuracy of ±0.0001 g was used for weight measurements. The measurements were repeated five times to find an average and an accurate value. The overall accuracy in density measurement is ±0.5 kgm^"3. The percentage error in the measurement of density is ±0.05.

2. Ultrasonic Measurements

Ultrasonic velocities (U_L, longitudinal and U_s, shear) and attenuations (Ut, longitudinal and U_s, shear) measurements were carried out using pulse echo method and cross-correlation technique. The measurement system consists of an ultrasonic process control system (model FUII050; Fallon Ultrasonics Inc. Ltd., ON, Canada), a 100-MHz digital storage oscilloscope (model 54600B; Hewlett Packard, Palo Alto, CA), and a computer. The measurements were carried out by generating longitudinal and shear waves using X- and Y- cut transducers operated at a fundamental frequency of 5 MHz;

3. X-ray Photoelectron Spectroscopy

Elemental analysis of the prepared glass sample was done using X-ray photo electron spectroscopy (model AXIS Ultra DLD; Kratos, Kyoto, Japan) with Al K source operating at 210 W. The glass sample was ground using planetary ball mill (model PM 100; Retsch, Haan, Germany) and the powdered glass sample was used for XPS analysis. A survey spectrum (0-1200 eV) was recorded and high-resolution spectra for Cls and Nls band were obtained. X-ray as the excitation radiation was used for the XPS measurements. The spectra were collected in a fixed retarding ratio mode with bandpass energy of about 10 eV.

4. Fourier Transform Infrared Analysis

Infrared absorption of powdered glass samples after in vitro studies were analyzed from FTIR spectra. The FTIR absorption spectra were recorded at room temperature using an FTIR from 4000 to 400 cm^"1, (model 8700; Shimatzu, Tokyo, Japan) spectrometer. A 2.0 mg sample was mixed with 200 mg KBr in an agate mortar and then pressed under a pressure of 100 kg/cm^"1. It gave a pellet of 13 mm diameter. For each sample, FTIR spectrum was normalized with blank KBr pellet. 5. X- ay Diffraction Analysis

To confirm the amorphous nature of prepared glasses and the presence of HAp layer on the surface of glass samples, XRD studies were carried out on each glass sample. An X-ray diffractometer (model PW 1700; Philips, Eindhoven, The Netherlands) was used with CuKa as a radiation source to obtain the XRD pattern in the range of a scanning angle between 20° and 80°. The glass samples were removed from SBF solution after 21 days in vitro studies and then washed gently with double distilled water. The washed glass samples were dried at room temperature. The dried glass was subjected to obtain the XRD pattern as discussed above.

6. pH Measurements

The prepared glass samples were soaked for 21 days in laboratory prepared SBF solution and kept in C0₂ incubator at the temperature of 37 °C in 6% C0₂. The variation in pH values of simulated body fluid (SBF) solutions was measured on all the 21 days using a pH meter (model 3-star; Thermo Orion, Beverly, MA) for all glasses under identical conditions. The pH electrode was calibrated using the standard buffer solution with a pH value of 4.01, 7.00, and 10.01 before taking the measurements. The percentage error in the measurement of pH is ±0.005.

7. Scanning Electron Microscopy

The surface morphology of the prepared glass sample was analysed using SEM studies. The glass samples were gently washed with double-distilled water and dried at room temperature. A thin layer of a gold film was coated on the surface of glass sample using sputtering technique. The SEM (model Ultra 55; Zeiss, Oberkochen, Germany) was used to obtain a surface image of all glass samples before and after in vitro studies to analyse their surface morphology.

8. Energy Dispersive X-ray spectroscopy

Energy dispersive X-ray spectrograph (EDS) was taken for all the prepared glass samples before and after in vitro studies using EDS (model X-max 50 mm²; Oxford, Abingdon, England) for obtaining semi quantitative elemental information of the surface of samples. The percentage of error associated with the elemental composition analysis is ±0.1.

9. Cell culture and cytotoxicity assay

Nontoxic nature of the selected glass sample was assessed using cytotoxicity study in cell culture lines. Human gastric adenocarcinoma (AGS) cell line (ATCC-1739) was obtained from the National Centre for Cell Science, Pune, India. The cells were grown and maintained in Dulbecco's modified Eagle's medium (DMEM)/nutrient mixture F-12 HAM (1 : 1) with 2 mM L^'1 glutamine supplemented with 10% fetal bovine serum, 45 IU ml ¹ penicillin and 45 IU ml ¹ streptomycin. Growth ingredients were also added and incubated in a humidified atmosphere at 37 °C in 5% C0₂. After a number of passaging, the pure confluent AGS cell lines were obtained and cells at a density of 10³ were used to evaluate the cytotoxicity at a concentration of 100 mg ml^"1 for the selected bioactive glass samples. The morphology of AGS cell lines was observed regularly under binocular inverted microscope. After 48 h of incubation, MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay was performed to evaluate the viability of the bioactive glass treated AGS cells. The percentage of cell viability from triplicates of the bioactive glass treated and non-treated cells was calculated using optical density (OD 590 nm) as follows:

OD of the glass particles treated cells

Cell viability % = x lOO

OD of the cells

In vivo animal studies

Animal studies were done after getting the approval from animal ethical committee (Approval number IAEC-LDC/8/14/1 dated 14^th February 2014). Young rabbits of weight about 1.600 Kg were purchased from King Institute, Chennai as per CPCSEA guidelines. Under ketamine anaesthesia, one centimetre incision was made over the medical epicondyle of femur under image control. Under microscopic magnification, Periosteum was opened and a 2 mm drill hole was made. The selected sample of fluorophosphate glass rod of diameter 2 mm was pegged into the hole. After saline wash, wound was closed using single layer 3-0 ethilon sutures and then 250 mg of ceftriaxone was given intra-muscularly.

Rabbit was allowed to move freely immediately after recovery from anaesthesia. Fluorescent calcein (Sigma Aldrich, Japan) (10 mgkg^"1) was administrated intramuscularly on the day of surgery and then every week until 2 days before euthanising to label newly formed bone continuously. After 10 weeks, the animals were euthanised using a lethal dose of ketamine and the lower end of femur harvested and preserved in 10% formalin and used for SEM, EDS, CLSM studies. Un-decalcified sectioning was done on the harvested femur perpendicular to the implant rod using microtome (Model SP1600; Leica, Nussloch, Germany) to get slices of 1 mm thickness.

10. Histomorphological studies

The un-decalcified section of the implant was dried at room temperature using desiccator. A thin layer of a gold film was coated on the surface of glass sample using sputtering technique. SEM and EDS studies were done on the dried slice to find the formation of HAp at the glass-bone interface.

11. Histophysiological analysis

Calcein fluorescence was used to examine the newly formed bone using a confocal laser scanning microscope (model: LSM 510 META; Zeiss, Gottingen, Germany). The excitation wavelength was set at 488nm (Ar laser). Calcein fluorescence was detected through a BP 515 -565 nm bandpass filter. Details obtained from the Figures:

Fig. 1 illustrates the protocol used for the synthesis of strontium added fluorophosphate glass samples with different contents of strontium.

The density variation of the prepared fluorophosphate glass samples as a function of added SrO content is shown in Fig. 2. A gradual increase in the density of fluorophosphate glasses from 2628.3 kgm ³ to 2725.1 kgm^"3 due to the addition of SrO is noted. The increase in density value is due to the tight packing of glass network when the addition of SrO content. The observed behaviour explains the alteration of glass network by strontium atom. Fig. 3a and 3b shows the variation of elastic moduli of all the prepared glass samples as a function of SrO content. Shear modulus and young's modulus show the same trend with the density variations during the addition of SrO content. A negligible change is noted in young's modulus values except for 4 mol% of SrO content. An anomalous decrease in longitudinal modulus and bulk modulus values are noted with the addition of 4 mol% of SrO content.

Fig. 4 shows the elemental composition of the glass sample SrFP5 using XPS. The observed intensity at the binding energies at 31.8 eV, 135.5 eV, 193.1 eV, 349.8 eV, 437.6 eV, 533.1 eV, 1021.9 eV, 1072.5 eV, shows respectively the presence of CaF₂, SrO, P₄Oio, CaO, Ca, O, SrO, NaP0₃ the glass sample SrFP5. SEM image of the prepared glass sample SrFP5 is showed in Fig. 5. The smooth surface of the glass sample SrFP5 obtained from SEM image exhibits the amorphous nature of the sample. Fig.6 shows EDS spectrograph of the glass sample SrFP5. A close agreement is noted between experimental and nominal composition of the glass sample SrFP5. Fig. 5 and Fig. 6 confirm the presence of strontium oxide and fluorine atoms in the glass network.

21 days of in vitro studies were made on all the prepared glass samples. The observed pH variations during 21 days in vitro studies help to assess the bioactivity of the prepared glasses. The pH variations of all the prepared glasses during in vitro studies are given in Fig. 7. The initial release of phosphate ions lead to form phosphoric acid resulting in sudden decrease in pH value of all the glass samples. At the end of second day of immersion, sodium ions are released and hence the increase in pH value. At the end of 21 days in vitro studies, the sample SrFP5 shows higher pH value than all the other samples.

FTIR spectrograph of all the prepared glass samples after in vitro studies is shown in the Fig. 8. The FTIR absorption assignment band at 530 cm^"1, 720 cm^"1, 887 cm^"1, 1116 cm^"1, 1275 cm^"1, 1560 cm^"1, 3430 cm^"1 are respectively of vibration bands of HAp, P— O— P (symmetric mode), C— O, Ca_{2 2}0₇, P0₂ (asymmetric mode), bending mode of OH-, and water associated in HAp. The presence of HAp confirms the bone bonding ability of from all the glass samples. XRD patterns of all the glass after in vitro studies are shown in Fig. 9. In the obtained XRD shoulder peak at 31.92° and a weak ones at 44.6°, 66.6°, 72.7° in the sample SrFP5 shows respectively the rich concentration of HAp and Weak concentration of FAp.

Fig. 10 shows the SEM image of the glass sample SrFP5 after in vitro studies. The SEM image confirms the rich deposit of Ca-P layer on SrFP5 glass surface. The size of the deposited particles is in the order of 20-100 nm. Fig. 11 shows the elemental composition of the deposited precipitate using EDS. The Ca/P ratio of the deposit is about 1.6 indicating the deposit is HAp. But the presence of fluorine molecules in the surface precipitate confirms the existence of fluoroapatite. The EDS spectrograph clearly indicates the presence of hydroxyapatite and fluoroapatite on the surface of the glass sample SrFP5.

Fig. 12 shows the optical microscope image of cell viability test for the sample SrFP5. The image clearly shows there is no cytotoxicity observed in the glass sample SrFP5. Fig. 13a shows the SEM image at 100X magnification of un-decalcified section of the femoral condyle of the rabbit after 10 weeks of glass implanting. There is a definitive distinct layer of transformation all around the glass in contact with the bone. Fig. 13b shows the SEM image at 1000X magnification where the distinctive interface between bone and glass is well seen. Fig. 14 shows the molecular disposition at the interface that it is transforming to HAp and this proves the bond the glass has made with the bone.

Fig. 15 shows the magnified view of the bone and the newly formed interface. When illuminated by Ar laser, there is brilliant fluorescence over the ring of the bone and interface. On super imposition of both it is clearly made out active apatite formation has extended to a depth of 281 pm in the glass form the periphery confirming the bioconversion of strontium added fluorophosphate glass.

Claims

We claim:

1. A fluorophosphate glass having the composition of (36-65)phosphorus pentoxide — (22-36)calcium oxide — (ll-32)sodium oxide — (0.01— 20)calcium fluoride— (0.01-12)strontium oxide, said percentages being molar percentages.

2. The composition for prosthetic device or fluorophosphate glass or coating as claimed in claim 1, wherein phosphorus pentoxide is substituted by any of the following :

Ammonium di hydrogen phosphate, Phosphorus chloride, ammonium phosphate, calcium phosphate, sodium phosphate, and silver phosphate.

3. The composition for prosthetic device or fluorophosphate glass or coating as claimed in claim 1, wherein calcium oxide is substituted by any of the following :

Calcium sulphate, calcium carbonate, calcium fluoride, calcium fluorophosphate, calcium chloride, calcium caseinate, and calcium bicarbonate.

4. The composition for prosthetic device or fluorophosphate glass or coating as claimed in claim 1, wherein sodium oxide is substituted by any of the following :

Sodium carbonate, and sodium citrate.

5. The composition for prosthetic device or fluorophosphate glass or coating as claimed in claim 1, wherein calcium fluoride is substituted by any of the following :

Calcium di fluoride, calcium tri fluoride, calcium fluorophosphate, and sodium fluoride.

6. The composition for prosthetic device or fluorophosphate glass or coating as claimed in claim 1, wherein strontium oxide is substituted by any of the following:

Strontium, strontium chloride, strontium iodide, strontium fluoride, strontium oxide, strontium sulphate.

7. The composition of claim 1, wherein the bioactive glass has a composition by either molar percentage or weight percentage:

Compound Mol% Wt.%

2Os 35-65 60-70

CaO 22-36 12-20

Na₂0 11-32 6-20

SrO 0.01-12 0.1-12

CaF₂ 0.01-20 0.1-10

Any prosthetic device or implant or bone substitute containing the composition of claim 1, wherein said device is made essentially of said fluorophosphate glass or coated with said fluoro hosphate glass.

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