Novel borosilicate-based bioactive glasses for coating on ti-6al-4v implants and methods thereof

Abstract

Although Ti-6Al-4V alloys are widely preferred for orthopedic implants, it is crucial to address the potential risks of genotoxicity and implant loosening caused by released metal ions and loss of osseointegration, respectively. Against this backdrop, the present invention describes novel borosilicate-based bioactive glass compositions suitable for coating applications on Ti-6Al-4V implants. The evaluated characteristics of these glasses demonstrate high thermal stability (>145°C), rapid in vitro bioactivity (24–72 h), and a linear coefficient of thermal expansion similar to that of the alloy (8.5–12.19 × 10⁻⁶). ‑6 / ℃). The advantageous combination of properties enables the formation of a well-adhered, amorphous coating on the alloy surface, ensuring osseointegration and protection against genotoxic risks. Furthermore, this invention presents a commercially viable coating technique involving cold spraying and subsequent heat treatment to produce the desired amorphous coating on the implant surface. In summary, this invention is expected to significantly improve the performance of Ti-6Al-4V-based orthopedic implants.

Description

Technical Field

[0001] This invention relates to a novel borosilicate-based bioactive glass for coating Ti-6Al-4V implants and a method thereof. Specifically, this novel glass composition possesses rapid in vitro biomineralization capability, high thermal stability, and a coefficient of thermal expansion similar to that of Ti-6Al-4V implants, making it suitable for obtaining well-adhered and crack-free coatings on such implants via simple enamel techniques. More specifically, the high thermal stability of this novel glass, even in the form of a sintered coating, helps maintain its amorphous properties, and thus the biofunctionality of the parent glass can be preserved in the applied coating. Background Technology

[0002] Currently, metallic implants (such as titanium and its alloys, stainless steel, Co-Cr, etc.) are inevitably used in load-bearing applications. Among different biocompatible metals and alloys, Ti-6Al-4V has significant advantages due to its high corrosion resistance, low density, and favorable mechanical properties associated with orthopaedic implants. However, metal ions released from implants can induce genotoxicity and carcinogenicity, while a lack of osseointegration can lead to implant loosening. To address this challenge, bioactive glass coatings on the surface of metallic implants have been found to be highly effective in improving corrosion resistance and osseointegration. Bioactive glass is well-known for its bone-bonding capabilities and its ability to stimulate new bone growth. The bone regeneration capacity of bioactive glass is mediated by apatite crystals on its surface, which enhance osteocyte proliferation. Furthermore, ions released from bioactive glass into physiological media may produce various beneficial functions, such as antibacterial properties, osteoinduction, and stimulating vascularization. While bioactive glasses are effective for such applications, achieving adhesive coatings on metallic substrates remains challenging due to imbalances in the coefficients of thermal expansion (Table 1). Furthermore, commercially available bioactive glasses exhibit a high tendency for crystallization or devitrification during processing at higher temperatures. Bioactive glass coatings deposited on metallic implants typically require consolidation via viscous flow sintering at temperatures above the glass transition temperature. Crystallization events during sintering lead to incomplete densification because the development of the crystalline phase hinders the viscous flow sintering process. Moreover, the crystalline phase dissolves at a much lower rate than the glass phase upon contact with physiological media. This slower dissolution of the crystalline phase can lead to deterioration of the osseointegration process, as it depends on the concentration of released ions in the surrounding media.

[0003] Table 1: Linear thermal expansion coefficients (α) of some commercially available bioactive glasses and Ti alloys 50-300 ) × 10 -6 / ℃) Compare

[0004] Existing technology and defects The following description contains details of some relevant prior art documents to date and their main deficiencies relevant to the field of this invention.

[0005] See European Patent EP0154513B1, which discloses a glass composition suitable for coating on a Co-Cr-Mo alloy and belonging to the SiO2-Na2O-CaO-P2O5-CaF2-B2O3-based system. This glass has a similar coefficient of thermal expansion to the substrate (difference less than 2%). However, this patent does not provide information on the properties of the sintered coating (amorphous or crystalline) or the in vitro biological properties of the glass or the coated substrate. More importantly, the coefficient of thermal expansion of the Co-Cr-Mo alloy differs significantly from that of the Ti-6Al-4V alloy, which has gained considerable importance in recent years as an orthopedic implant. The proportions of the different components in the reported glass composition also differ significantly from those of this invention.

[0006] See Chinese Patent CN114558177B, which describes the preparation of a multilayer porous structure on a metal surface for better anchoring of the coating and the fabrication of a bioactive glass coating on the surface of an implant. Furthermore, this coating is applied in a textured manner by laser spraying, followed by a chemical treatment to partially convert the glass coating into hydroxyapatite. This glass contains 10-25% SiO2, 10-20% CaO, 1-3% P2O5, 3-8% Na2O, 6-10% K2O, 5-10% MgO, 5-8% SrO, and 30-50% B2O3. This process is very complex, and because the glass is partially converted into HCA, the benefits of ionic dissolution products for the tissue healing process cannot be fully realized. The composition and related properties of the glass described in that patent are significantly different from those of this invention.

[0007] RO130068 describes a method for producing dental implants coated with alkali-free bioactive glass using radio frequency magnetron sputtering. This bioactive glass composition belongs to the SiO2-CaO-MgO-P2O5-ZnO-SrO system and maintains a coefficient of thermal expansion close to that of titanium and its alloys. However, this patent document does not disclose detailed information regarding the composition range, coefficient of thermal expansion values, and thermal stability. Furthermore, this composition differs significantly from that of the present invention, containing additional components such as MgO, ZnO, and SrO.

[0008] WO2009081120A1 relates to a bioactive glass coating for Ti-6Al-4V alloys and chromium-cobalt alloys, wherein the coefficient of thermal expansion of the glass coating matches that of the alloy. The bioactive glass comprises SiO2, Na2O, CaO, MgO, K2O, ZnO, B2O3, and P2O5. The coefficient of thermal expansion of the claimed composition is in the range of 8.8 × 10⁻⁶.-6 K -1 and 12×10 -6 K -1 The composition exhibits a processing temperature window of at least 90°C when measured using glass powder with an average particle size of less than 100 μm. The composition contains MgO and ZnO, which should result in a delayed bioactivity unlike that of the present invention. Furthermore, this patent application does not provide information on whether the coating remains amorphous or partially crystalline after sintering. The present invention comprises a glass system free of MgO or ZnO and demonstrates fairly rapid in vitro bioactivity in simulated body fluids.

[0009] See Chinese Patent CN102258432B, which reports a mixture of a bioactive glass exhibiting pH buffering activity, solid acidic particles, glycerol, polyethylene glycol, and resin. This reported glass mixture can prevent pH elevation in the surrounding physiological medium, thereby helping to eliminate irritation to the patient. However, the composition of this glass differs significantly from that of the present invention, and its thermal stability, coefficient of thermal expansion, and in vitro bioactivity have not been reported. Furthermore, the reported glass is not designed for coating applications on metallic implants.

[0010] See Chinese Patent CN105582571B, which discloses the preparation of a bio-ink comprising a mixture of 45S5 bioglass powder and calcium silicate in a PVA-based gel solution for use in 3D printing to fabricate mechanically strong porous structures. The 45S5 bioglass powder contains SiO2, Na2O, CaO, P2O5, and B2O3, and is prepared via a sol-gel method, followed by sintering at a temperature range of 950-1000°C. However, the glass composition, preparation technique, and applications of this invention are entirely different from those of this invention.

[0011] See World Patent WO2004031086A1, which describes bioactive glass and glass-ceramic bone substitutes in granular form. Granular materials can be used to fill bone defects of any irregular shape, thus offering advantages over block implants. However, the large surface area to volume ratio of granular bone substitutes necessitates materials with lower reactivity than commercially available 45S5 for rapid healing. The disclosed glass composition has moderate reactivity (lower than 45S5 compositions), thus allowing for effective use in granular form, mitigating the effects of a large surface area to volume ratio. This glass composition is very different from that of the present invention, and its coefficient of thermal expansion or thermal stability is not disclosed at all in this specification.

[0012] Canadian Patent CA2210070C discloses glass compositions with a wide working range, controlled durability, and chemical bonding ability with both hard and soft tissues. The disclosed glass compositions contain additional oxides, such as K₂O and MgO, which are not used in the glass compositions related to this invention. Furthermore, this patent document does not address the coefficient of thermal expansion and suitability of the glass compositions for coating on metal alloys. This invention focuses primarily on the thermal expansion behavior, devitrification resistance, and in vitro bioactivity of the glass compositions, making them suitable for coating applications on Ti-6Al-4V implants.

[0013] See BRPI1014607B1, which discloses a glass composition that can be used for the prevention and treatment of bone infections. As disclosed in that patent, the glass composition of the invention has been successfully used to treat chronic osteomyelitis in multiple patients. However, the thermal expansion behavior, devitrification resistance, or in vitro bioactivity of the glass of the invention is not mentioned in that patent document.

[0014] JP2008518650A relates to the development of glass compositions for treating lesions associated with impaired or insufficient angiogenesis and for preventing avascular fibrosis. This glass composition belongs to the SiO2-Na2O-CaO-K2O-MgO-B2O3-P2O5 system and is used in unsintered form or as fibers. This patent lacks any information regarding thermal expansion behavior and thermal stability, and the glass composition is completely different from that of the present invention.

[0015] Peddi et al. (Peddi L, Brow RK, Brown RF. Bioactive borate glass coatings for titanium alloys. Journal of Materials Science: Materials in Medicine. Sep 2008; 19: 3145-52.) reported a bioactive borate glass composition for coating applications on Ti-6Al-4V implants. The glass, containing Na₂O, CaO, B₂O₃, SiO₂, Al₂O₃, and P₂O₅, has a coefficient of thermal expansion close to that of titanium alloys. Coatings using this glass composition were achieved via enamel technology, resulting in good adhesion strength. However, the thermal stability or amorphous properties of the coating remained unresolved, and in vitro bioactivity results highlighted delayed bioactivity (2 weeks). The reported glass composition also differs significantly from that of this invention.

[0016] Khalil et al. (Khalil EM, Youness RA, Amer MS, Taha MA. Mechanical properties, in vitro and in vivo bioactivity assessment of Na2O-CaO-P2O5-B2O3-SiO2glass-ceramics. Ceramics International. May 2018 1;44(7):7867-76) reported the synthesis and property evaluation of bioactive glass-ceramics containing Na2O, CaO, B2O3, SiO2, and P2O5. The properties examined highlighted the degradation of both in vitro bioactivity and in vivo bone adhesion caused by the crystallization process involved in the preparation of the glass-ceramics. However, the favorable mechanical properties suggest the potential of such glass-ceramic materials for dental restorative applications. Although reported parent glass compositions contain similar components to those of this invention, the proportions of the different components vary significantly. For example, reported glasses contain 25-45 mol% P2O5 and 15 mol% SiO2, while the glass from this invention contains 1-2 mol% P2O5 and 30-32 mol% SiO2. Furthermore, this report primarily focuses on the derived glass-ceramics and does not mention important properties of the parent glass relevant to coating applications on metal implants (linear coefficient of thermal expansion, processing window, or thermal stability).

[0017] In summary, bioactive glasses from existing technologies have significantly different compositions compared to this invention. The use of additional reactants such as MgO, ZnO, CaF2, K2O, and SrO is noted in most prior art documents. The use of MgO, ZnO, CaF2, and SrO is known to delay their in vitro biomineralization ability. Furthermore, the in vitro bioactivity and thermal stability factors of glasses from existing technologies are not discussed in most cases. More importantly, the properties of the coating (amorphous or crystalline) are not reported in any of the prior art documents. Therefore, developing a bioactive glass composition with excellent devitrification resistance, rapid in vitro bioactivity, and a coefficient of thermal expansion comparable to Ti-6Al-4V alloys is of technical importance for commercial success.

[0018] Purpose of the invention One object of the present invention is to provide a bioactive glass composition having a coefficient of thermal expansion similar to that of Ti-6Al-4V implants, thereby eliminating or minimizing the problems described in the background and prior art sections.

[0019] Another object of the present invention is to provide a bioactive glass composition exhibiting fairly rapid in vitro bioactivity and sufficiently high thermal stability, which retains amorphous properties even when present in the form of a sintered coating.

[0020] Another object of the present invention is to provide a bioactive glass composition for coating on Ti-6Al-4V implants, which has a suitable balance between in vitro bioactivity, thermal stability or resistance to devitrification.

[0021] Another object of the present invention is to provide an easy and economical method for coating the above-mentioned glass onto a Ti-6Al-4V substrate.

[0022] Novelty and non-obvious creativity This invention discloses a series of novel bioactive glass compositions exhibiting a unique combination of related properties such as coefficient of thermal expansion, thermal stability, and bioactivity, which are relevant to coating and maintaining amorphous properties on Ti-6Al-4V-based medical implants. These bioactive glass compositions comprise 30-32 mol% SiO2, 21-23 mol% B2O3, 1-2 mol% P2O5, 0-23 mol% Na2O, and 22-45 mol% CaO. Glasses within this composition range exhibit a unique combination of properties, making them more suitable and advantageous for coating applications on Ti-6Al-4V implants compared to compositions reported in the prior art. The investigated properties that highlight these glasses are as follows: In 8.5-12.19 × 10 6 The linear thermal expansion coefficient (α) in the range of / ℃ 50-300 It is compatible with Ti-6Al-4V alloy, overcoming the problem of mismatch in thermal expansion coefficients.

[0023] A thermal stability factor (ΔT) greater than 145°C ensures good processability at high temperatures and prevents crystallization.

[0024] In vitro bioactivity during 24-72 hours of immersion in simulated body fluids when tested according to the TC-04 protocol.

[0025] This unique combination of properties ensures a well-adhered, crack-free, and amorphous coating on Ti-6Al-4V implants, with the ability to integrate with host tissue. A commercially feasible and simple process for coating the glass composition onto a metallic substrate is also described. The coating is applied via cold spraying followed by sintering. This coating technique is commercially feasible and very simple to employ, producing an amorphous coating layer on the implant. The process parameters involved in slurry preparation (slurry formulation, solid load, powder particle size, grinding parameters) and coating process (spraying parameters and sintering procedure) are crucial, as the desired coating can only be obtained by strictly adhering to optimized process parameters. Attached Figure Description

[0026] The accompanying drawings are attached to this specification. Figures 1 to 4 The invention is described herein. In the accompanying drawings, similar reference numerals / letters denote corresponding parts in each figure.

[0027] Figure 1 The images show the DSC thermograms of the glasses from Examples 1 to 5.

[0028] Figure 2 The expansion curves of the glass from Examples 1 to 5 are shown.

[0029] Figure 3 The image shows the XRD pattern of the glass from Examples 1 to 5 after 3 days of in vitro bioactivity studies.

[0030] Figure 4 The XRD patterns show the sintered coatings of commercial 45S5 glass and glass from Example 5.

[0031] Figure 5 Optical images showing sintered coatings on Ti-6Al-4V substrates using 45S5 glass (Example 6) (a) and glass from Example 5 (b).

[0032] This document includes accompanying drawings to provide a better understanding of the invention, to illustrate embodiments of the invention, and the drawings, together with the description, serve to explain the importance of the invention. Summary of the Invention

[0033] Therefore, the present invention provides a novel borosilicate-based bioactive glass and method for coating Ti-6Al-4V implants, comprising 30-32 mol% SiO2, 21-23 mol% B2O3, 1-2 mol% P2O5, 0-23 mol% Na2O and 22-45 mol% CaO as the chemical composition of the glass.

[0034] In one embodiment of the invention, the glass of the invention (the compositions shown in Table 2) has a thickness of 8.5-12.19 × 10⁻⁶. 6 The linear thermal expansion coefficient (α) in the range of / ℃ 50-300 Because the linear thermal expansion coefficient of commercially available bioactive glass (45S5, S53P4) is between 15 and 13.5 × 10⁻⁶. 6 The temperature varies within a range of / ℃ (which is a significant mismatch with the substrate), causing peeling issues when these glasses are coated on Ti-6Al-4V-based medical implants. The novel glass composition has a coefficient of thermal expansion similar to the substrate, thus allowing for well-adhered coatings.

[0035] In another embodiment of the invention, the glass exhibits a thermal stability factor (ΔT) greater than 145°C. It is noteworthy that the thermal stability factors of currently developed commercially available bioactive glasses vary in the range of 50-100°C, leading to incomplete densification and degraded biofunctionality due to premature crystallization during the sintering process. The higher thermal stability factor of the novel glass compositions indicates that these glasses can retain completely amorphous properties while being sintered.

[0036] In another embodiment of the invention, the in vitro bioactivity of the glass is comparable to that of the commercial S53P4 composition, demonstrating the formation of a surface apatite layer during 24-72 hours of immersion in simulated body fluids when tested according to the TC04 protocol.

[0037] In another embodiment of the invention, the glass can be processed into a slurry containing 30-45% by volume of glass powder in distilled water, ethanol or isopropanol, with a particle size of 10-45 μm.

[0038] In another embodiment of the invention, a glass slurry is deposited on a metal substrate using a spray gun via a simple and commercially viable cold spraying technique, followed by sintering at a temperature (50-70)°C higher than the glass transition temperature for 1-2 hours.

[0039] In another embodiment of the invention, it was observed that the final coating was completely amorphous and crack-free. Detailed Implementation

[0040] According to the present invention, a bioactive glass composition has been developed with various advantages related to coating applications on Ti-6Al-4V implants. The glass composition comprises 30-32 mol% SiO2, 21-23 mol% B2O3, 1-2 mol% P2O5, 0-23 mol% Na2O, and 22-45 mol% CaO.

[0041] The bioactive glass compositions reported herein have a similar coefficient of linear thermal expansion to Ti-6Al-4V implants, resulting in well-adhered and crack-free coatings when applied to metal substrates. Coatings applied with conventional bioactive glasses typically contain microcracks that arise during the cooling process after sintering. These microcracks are caused by the different shrinkage behaviors of the coating and the substrate, resulting from the mismatch in their coefficients of linear thermal expansion. Any dislodged particles from such coatings can lead to inflammation and other complications. The glass from this invention is well-suited to mitigate these problems. Furthermore, well-adhered coatings offer greater protection against corrosion of metal implants compared to coatings with cracking and peeling issues. Therefore, the novel glass, existing as a coating on metal implants, can limit the release of metal ions into physiological media and thus minimize the risk of complex medical conditions such as genotoxicity or carcinogenicity. The borosilicate glass reported herein also offers advantages over silicate compositions for coating applications on Ti alloys. This advantage stems from the possible formation of a Ti-boride layer at the glass-metal interface, which acts as a barrier to interdiffusion and thus prevents weakening of the bond between the two materials. Another aspect of this invention is the excellent resistance to crystallization or devitrification of these glasses during high-temperature processing. The high thermal stability factor (>145°C) indicates that these glasses can be sintered without any hindrance from crystallization. Conventional glasses are prone to crystallization, and the crystallization process often interferes with the sintering process. Crystallization during sintering has several negative effects on processing and properties, such as requiring much higher temperatures for proper densification and the loss or degradation of many biological functions. Ti-6Al-4V alloys undergo a phase transition (α↔β) at such high temperatures required for proper densification of those easily crystallizing glasses, thus the alloy can be damaged. On the other hand, when the glass partially or completely transforms into the crystalline phase, the dissolution rate of the glass in the physiological medium slows down. Since all biological functions are primarily governed by ions released from the glass into the physiological medium, they may undergo degradation. Furthermore, due to the selective distribution of elements into the crystalline phase, the residual glass composition does not remain identical to the parent glass. The glass of the present invention exhibits high resistance to devitrification, thus minimizing the possibility of such functional alterations. In addition, the bioactive glass coating using the composition of the present invention enables rapid osseointegration, which can prevent implant loosening. In vitro bioactivity studies can serve as an indicator of in vivo osseointegration capacity. Generally, faster in vitro apatite formation or bioactivity is a marker of faster in vivo bone adhesion. The glass of the present invention shows apatite layer formation within 1-3 days of immersion in simulated body fluids. Commercially available glasses such as 45S5 and S53P4 require 1 day and 3 days, respectively, to exhibit the same results.However, these glasses undergo partial crystallization during sintering, which can lead to delayed bioactivity when used as coatings. The glass reported in this paper retains its apatite-forming ability even when present as a sintered coating. A glass coating on a metal substrate can be obtained by a simple cold spraying technique followed by sintering. This commercially viable method is simple to employ, and the sintering conditions can be well maintained below the phase transition temperature of the Ti-6Al-4V alloy.

[0042] Table 2: Composition of Novel Borosilicate Bioactive Glass

[0043] The glass composition of this invention is synthesized using a pure platinum crucible and conventional melt-quenching technique. A well-mixed batch of analytical grade raw materials, such as SiO2 (99.8%, Sipur Al Bremthelar Quartz-itwerk), Na2CO3 (99.5%, Sigma Aldrich), CaCO3 (99.5%, Sigma Aldrich), CaHPO4·2H2O (98%, Sigma Aldrich), and H3BO3 (99.5%, Fluka), is melted in a raising hearth furnace (Kanthal) at 1150–1450 °C. The homogeneity of the glass melt is ensured by intermittent stirring with a fused quartz rod during the 1.5–2.5 hour melting time. The glass melt is then cast into stainless steel molds, and the castings are immediately transferred to a muffle furnace for annealing. Annealing is carried out for 2–3 hours, followed by gradual cooling to room temperature to obtain stress-free glass blocks. Finally, these annealed glass blocks are broken up and further ground in a planetary ball mill to obtain fine glass powder (<45 microns).

[0044] The thermal stability of the glass was measured using differential scanning calorimetry (DSC) (STA 449F3, Netzsch GmbH, Selb, Germany). The temperature was measured at 10 °C for [time missing]. -1 DSC thermograms of glass powder with a particle size of less than 45 µm were recorded at the heating rate. Glass transition temperature (Tg) g ) and crystallization initiation temperature (T) x The temperature window between ΔT and T is used to measure thermal stability (ΔT = T). x -T g A higher ΔT value indicates greater resistance to devitrification. The thermal stability of the glass compositions described in this invention is listed in Table 3.

[0045] The linear thermal expansion coefficient (α) of glass was measured using a pusher-type dilatometer (Netsch, DIL402PC). 50-300 A cylindrical sample with a diameter of 6 mm and a length of 25 mm was heated at a rate of 5 °C / min, and the ratio of the change in length to the original length (thermal strain) was recorded as a function of temperature. The linear coefficient of thermal expansion of the glass sample was obtained by measuring the slope of the thermal expansion versus temperature curve, and the values ​​obtained for different glasses in the temperature range of 50–300 °C are reported in Table 3.

[0046] Table 3: Properties of Borosilicate Bioactive Glass

[0047] In vitro bioactivity refers to the time required for a crystalline apatite layer to form on the surface of a material when it is immersed in an aqueous medium such as a simulated body fluid or a Tris buffer. Generally, faster in vitro bioactivity is a marker of faster bone adhesion in vivo. The in vitro bioactivity of glass was investigated according to the TC04 protocol. TC04 represents Technical Subcommittee 04 of the International Commission on Glass (ICG), concerning glasses used in medicine and biotechnology. Members of the TC04 Subcommittee conducted cyclical studies in several different laboratories to develop this reliable and simple protocol for comparing the bioactivity of different glasses. This protocol is frequently used by researchers of bioactive glasses to compare the bioactivity of different samples. In short, 150 mg of glass powder with a particle size of less than 45 µm is immersed in 100 ml of simulated body fluid and then held in an incubator (37°C) for orbital oscillation at 120 rpm. After different time points (e.g., 24 hours, 72 hours, etc.), the glass powder is filtered from the solution and examined by X-ray diffraction and Fourier transform infrared spectroscopy to check for the formation of the apatite layer. The in vitro bioactivity of the different glass samples described in this invention is listed in Table 3.

[0048] For the coating, initial substrate preparation is performed. First, the Ti-6Al-4V substrate is sandblasted with alumina powder to provide a rough surface, which allows for better anchoring of the coating. The sandblasted substrate is then ultrasonically cleaned with ethanol. Glass powder must be used in slurry form to apply the coating to the prepared substrate via cold spraying. The slurry is prepared by mixing fine glass powder (30-45 vol%) with a particle size of 10-45 µm with a solution of distilled water and polyvinyl alcohol (0.5-1.5 wt% of the glass powder). A stable dispersion is obtained by grinding the mixture in a planetary ball mill at 200-300 rpm for 1-3 hours. The slurry is then sprayed onto the prepared substrate using a spray gun. The coating thickness on the substrate can be controlled by varying the number of sprays. After the spraying process, the coated sample is dried in an oven at 110°C. Finally, depending on their composition, the dried sample is dried at 550-720°C (compared to T). g The sample was sintered in a muffle furnace at a temperature of 50-70°C for 1-2 hours. The sintered sample was then cooled to room temperature at a cooling rate of 2-4°C / min.

[0049] Example The following examples are provided to illustrate how the invention operates in practice and should not be construed as limiting the scope of the invention in any way.

[0050] Example 1 The glass contains 31.43 mol% SiO2, 22.45 mol% B2O3, 22.21 mol% CaO, 22.21 mol% Na2O, and 1.7 mol% P2O5. For glass preparation, appropriate amounts of each raw material are mixed and placed in a platinum crucible inside a lifting-bottom furnace. Glass melting is carried out at 1150 °C, and the ingot is annealed at 485 °C. The linear thermal expansion coefficient (α) of the glass is estimated. 50-300 The value is 12.19 × 10 -6 / ℃. At 10℃ min -1 At a heating rate of 180 °C, the thermal stability of glass powder with a particle size of less than 45 µm was measured. In vitro bioactivity results highlight the formation of an apatite layer after immersion in simulated body fluids for one day (24 hours).

[0051] Example 2 The glass contains 31.43 mol% SiO2, 22.45 mol% B2O3, 27.76 mol% CaO, 16.66 mol% Na2O, and 1.7 mol% P2O5. For glass preparation, appropriate amounts of each raw material are mixed and placed in a platinum crucible inside a lifting-bottom furnace. Glass melting is carried out at 1200 °C, and the ingot is annealed at 515 °C. The linear thermal expansion coefficient (α) of the glass is estimated. 50-300 The value is 10.96 × 10 -6 / ℃. At 10℃ min -1 At the heating rate, the thermal stability of glass powder with a particle size of less than 45 µm was measured at 149 °C. In vitro bioactivity results highlight the formation of an apatite layer after immersion in simulated body fluids for 3 days (72 hours).

[0052] Example 3 The glass contains 31.43 mol% SiO2, 22.45 mol% B2O3, 33.31 mol% CaO, 11.11 mol% Na2O, and 1.7 mol% P2O5. For glass preparation, appropriate amounts of each raw material are mixed and placed in a platinum crucible inside a lifting-bottom furnace. Glass melting is carried out at 1250 °C, and the ingot is annealed at 545 °C. The linear thermal expansion coefficient (α) of the glass is estimated. 50-300 The value is 10.07 × 10 -6 / ℃. At 10℃ min -1 At the heating rate, the thermal stability of the glass powder with a particle size of less than 45 µm was measured at 169 °C. In vitro bioactivity results highlight the formation of an apatite layer after immersion in simulated body fluids for 3 days (72 hours).

[0053] Example 4 The glass contains 31.43 mol% SiO2, 22.45 mol% B2O3, 38.87 mol% CaO, 5.55 mol% Na2O, and 1.7 mol% P2O5. For glass preparation, appropriate amounts of each raw material are mixed and placed in a platinum crucible inside a lifting-bottom furnace. Glass melting is carried out at 1300 °C, and the ingot is annealed at 575 °C. The linear thermal expansion coefficient (α) of the glass is estimated. 50-300 The value is 9.44 × 10 -6 / ℃. At 10℃ min -1 At the heating rate, the thermal stability of glass powder with a particle size of less than 45 µm was measured at 167 °C. In vitro bioactivity results highlight the formation of an apatite layer after immersion in simulated body fluids for 3 days (72 hours).

[0054] Example 5 The glass contains 31.43 mol% SiO2, 22.45 mol% B2O3, 44.42 mol% CaO, and 1.7 mol% P2O5. For glass preparation, appropriate amounts of each raw material are mixed and placed in a platinum crucible inside a lifting-bottom furnace. Glass melting is carried out at 1350 °C, and the ingot is annealed at 605 °C. The linear thermal expansion coefficient (α) of the glass is estimated. 50-300 The value is 8.5 × 10 -6 / ℃. At 10℃ min -1 At a heating rate of 187°C, the thermal stability of glass powder with a particle size of less than 45 µm was measured. In vitro bioactivity results highlighted the formation of an apatite layer after immersion in simulated body fluid for 3 days (72 hours). Furthermore, glass from Example 5 was applied as a coating onto a Ti-6Al-4V substrate. The coating method has been previously described. In short, an aqueous slurry containing 30-45 vol% glass powder with a particle size of 10-45 µm and a small amount (1 wt% of the glass powder) of polyvinyl alcohol as a binder was prepared. The prepared slurry was then applied to a sandblasted Ti-6Al-4V substrate using a spray gun. Finally, the applied coating was sintered at 710°C for 1 hour and then slowly cooled to room temperature to obtain a solidified coating. Both visual and microscopic examination confirmed that the coating was free of cracks. Figure 5 X-ray diffraction techniques revealed that the sintered coating obtained from the glass composition in Example 5 was completely amorphous in nature. Figure 4 The mechanical properties of the coating were investigated using nanoindentation technology. The coating containing the glass from Example 5 had a hardness of 99.5 GPa and a modulus of 1.83 GPa.

[0055] Example 6 In addition, a commercially available 45S5 bioactive glass (its composition is mentioned in Table 4) was synthesized (Brauer DS. Bioactive glasses—structure and properties. Angewandte Chemie International Edition. 2015 Mar 27;54(14):4160-81), and was coated on the same metallic substrate (Ti-6Al-4V) with similar coating techniques and parameters as used in Example 5 (as given in Table 4) to understand the efficacy of the present invention relative to the commercially available 45S5 bioactive glass composition. However, the 45S5 glass coating was found to be riddled with visible cracks, while the present invention demonstrated the formation of a well-adhered and crack-free coating. Figure 5 The 45S5 coating exhibits crystalline properties and its crystal phase is combeite or sodium calcium silicate. Figure 4 ), and it is noted that the sintered coating obtained from the glass composition of Example 5 is completely amorphous in nature ( Figure 4 ).

[0056] Table 4: Properties of the glass from Example 6 and process parameters for coating on Ti-6Al-4V substrate.

[0057] Advantages of the present invention The main advantages of this invention are as follows: The described composition can be used as a well-adhered coating on Ti-6Al-4V implants, which does not exhibit any type of peeling problem due to thermal expansion mismatch.

[0058] The developed compositions described in this invention can be used for coating applications on Ti-6Al-4V implants. Metal implants coated with the novel glass exhibit proper osseointegration, which in turn avoids the problem of implant loosening in the long term.

[0059] When this novel glass composition is used as a coating on metal implants, it also helps reduce the release of metal ions into physiological media, and thus reduces the risk of carcinogenicity and genotoxicity.

[0060] This novel composition also exhibits high thermal stability values, indicating that it retains its amorphous properties even after sintering. This amorphous coating helps preserve the biological functions derived from the dissolution behavior of the parent glass.

[0061] The developed glass exhibited rapid in vitro bioactivity, suggesting that a well-adhered coating would also have rapid osseointegration capabilities.

[0062] The glass compositions described in this invention have been achieved using a smaller amount of reactants, since reactants such as MgO, K2O, and CaF2 described in prior art glass compositions have not been incorporated.

[0063] Coatings on metal substrates can be achieved through an economical and commercially viable cold spraying technique followed by sintering.

Claims

1. A bioactive glass composition for coating on Ti-6Al-4V implants, comprising: a. SiO2 30-32 mol%, b. B2O3 21-23 mol%, c. P2O5 1-2 mol% d. Na₂O 0-23 mol%, and e. CaO 22-45 mol%.

2. The glass composition according to claim 1, wherein the linear coefficient of thermal expansion (α) 50-300 (8.5-12.19 ×10) 6 It varies within the range of / ℃.

3. The glass composition according to claim 1, wherein the particle size of the glass powder is in the range of 10 to 45 μm.

4. The glass composition according to claim 1, which exhibits thermal stability in the range of 149 to 187°C.

5. The composition according to claim 1, wherein, when tested according to the TC04 method, in vitro bioactivity or biomineralization can be observed within 24-72 hours of immersion in simulated body fluid.

6. A method of coating the composition according to claim 1, comprising the following steps: a. Prepare a slurry containing 30-45% by volume of glass powder with a particle size of 10 to 45 μm in distilled water, ethanol, or isopropanol. b. Apply glass slurry to the sandblasted Ti-6Al-4V substrate using a spray gun, and c. Sintering of the sprayed coating, wherein the sintering temperature is in the range of 550 to 720°C.

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