A method for obtaining AISI 316l type stainless steel biomaterial with improved mechanical properties and 100% antibacterial properties

Abstract

The invention relates to a method including box boriding process to improve some mechanical properties such as hardness, corrosion resistance and wear and to provide 100% antibacterial properties to AISI 316L quality stainless steels, which are among the most widely used and known metals in terms of biocompatibility as implant materials. The invention relates to AISI 316L type biomaterial having 100% antibacterial properties according to antibacterial tests with Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 bacteria.

Description

[0001] A Method for Obtaining AISI 316L Type Stainless Steel Biomaterial with Improved Mechanical Properties and 100% Antibacterial Properties

[0002] Technical Field

[0003] The invention relates to obtaining an AISI 316L type stainless steel biomaterial surface with antibacterial properties using powders prepared in five different boronizing powder mixing ratios, consisting of Boron Carbide (B4C), Potassium Fluoroborate (KBF4), activated carbon and Silicon Carbide (SiC) powders.

[0004] State of the Art

[0005] AISI 316L stainless steel has a wide range of uses in various industry sectors including chemical, petrochemical, paper industries and nuclear engineering due to its high corrosion resistance at high temperatures. AISI 316L stainless steel is also used as an implant material in the human body, especially in cranial skull, teeth, pacemaker, orthopedic loaded bearings, prosthetic joints and bone fixations due to its biocompatibility and high corrosion resistance. Unlike other stainless steels, AISI 316L is not ferromagnetic, allowing implanted patients to be examined using magnetic resonance. However, pitting corrosion is observed in vivo for implants made of stainless steel. Corrosion of metallic materials in implants can affect body tissue through cell reaction to electric current, pH change and metallic ion release from the implant. AISI 316L product; It is in the stainless steel group and is a material created for applications where a good cost balance, mechanical strength and corrosion resistance are required. It is also one of the widely used alloys for biomedical applications including surgical instruments, orthopedic implants, fixtures, orthodontics and pharmaceutical equipment. The widespread use of stainless steel can be attributed to its reasonable cost, ease of fabrication, biocompatibility, adequate mechanical strength and corrosion-resistant properties. However, stainless steel also has a tendency to exhibit localized corrosion, which hinders its applications, especially in the biomedical industry, and 24% of implant failures are due to this corrosion phenomenon. Localized corrosion of metallic implants leads to the release of metallic ions into the surrounding tissues, which can initiate inflammatory and adverse cellular reactions. The structural integrity of implants affects the quality of life, as implant failure can cause severe pain and repeated operations after surgery. The long- term stability and improved biocompatibility of stainless steel are still a challenge, and solutions to these problems continue to be explored. Various approaches have been adopted to overcome these problems in stainless steels, including coating application, surface modification, laser surface treatment and grain refinement.

[0006] Many types of coatings have been developed in the literature to improve the mechanical properties of AISI 316L stainless steel. Nitriding is one of the well-established industrial applications today to improve the wear and corrosion resistance of steel components. However, if austenitic stainless steels are treated at temperatures usually used for nitriding low-grade steels or tool steels (about 450 'C or higher), significant amounts of chromium nitride precipitation occur, which depletes chromium from the solid solution, preventing the formation of the protective film, resulting in a significant decrease in corrosion resistance.

[0007] Surface engineering by thermal diffusion is used to manufacture protective coatings against corrosion. Coating of metallic materials by thermo-chemical methods has recently become an area of interest in research. One of these coating types is the boronizing method. Boronizing is a chemical diffusion process in which boron is dispersed into steel at high temperatures and has properties such as high hardness (1400-3000HV), very low coefficient of friction, corrosion resistance and high temperature oxidation. Boronizing has superior properties compared to other diffusion-based surface treatments. Boronizing is carried out by the diffusion of boron into steel at high temperatures. AISI 316L type stainless steel is seen to be used as a biomaterial due to its antibacterial properties. However, as stated in these studies, 100% compatibility has not been achieved and many problems are encountered. In addition, the importance of the boron element to be used in the boronizing method is known for human health. Boron is especially used in the field of health as a sterilization agent for eye inflammations, in the production of some ointments and in the treatment of cancer in nuclear medicine.

[0008] Boriding powder mixtures consist of boron source (boron or its compounds), activators, fillers or deoxidants. Activators are effective for the regular growth and formation of the boronized layer. During boronizing, fillers and deoxidants are effective in creating a reducing environment by holding the oxygen formed by the temperature and also in preventing the boronizing powder mixtures from sticking to the main material. Since the boron element is taken into the body as a mineral in nutrients, it is also very important for health. Therefore, a method has arisen to improve the mechanical properties of AISI 316L stainless steel materials used as biomaterials by boronizing and to provide 100% antibacterial properties, which eliminates the problems in question in the state of the art.

[0009] As a result, due to the negativities described above and the inadequacy of existing solutions on the subject, it has become necessary to make a development in the relevant technical field.

[0010] Brief Description of the Invention

[0011] The present invention relates to a method for obtaining an AISI 316L type stainless steel biomaterial with antibacterial properties, which meets the above-mentioned requirements, eliminates all disadvantages and brings some additional advantages.

[0012] The primary purpose of the invention is to provide 100% antibacterial properties of AISI 316L type stainless steels used as biomaterials by boronizing process.

[0013] One aim of the invention is to provide a method for improving the mechanical properties of AISI 316L stainless steel materials by boronizing process.

[0014] Another purpose of the invention is to provide 100% antibacterial properties with powder mixtures added at varying rates in the boronizing process.

[0015] Another purpose of the invention is to provide a method that will make a great contribution to the country's economy in a commercial sense and has very low cost applicability. The invention is especially aimed at paving the way for the use of usable and commercializable implants in medicine.

[0016] In order to achieve the above-mentioned purposes, the invention is a method for obtaining AISI 316L type stainless steel biomaterial with improved mechanical properties and 100% antibacterial properties, and comprises; applying box boronizing process to stainless steel with a powder mixture comprise B4C, KBF4, active carbon and SiC powders.

[0017] In order to fulfill the above-mentioned purposes, the invention is an AISI 316L type stainless steel biomaterial with improved mechanical properties that provides 100% antibacterial properties against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 bacteria. The structural and characteristic features of the invention and all its advantages will be understood more clearly thanks to the figures given below and the detailed explanation written by making references to these figures, and therefore the evaluation should be made by taking these figures and detailed explanation into consideration.

[0018] Figures to Help Understanding the Invention

[0019] Figure 1 : Schematic of Bonding (Boronizing) Box

[0020] Figure 2: Schematic of Powder Mixture

[0021] Figure 3: Images of the growth of E.coli and S. aureus bacteria in media that were in contact with the samples for 24 hours

[0022] Disclosure of References

[0023] 1 . Stainless Steel Cover

[0024] 2. Stainless Steel Boriding Box

[0025] 3. Deoxidant SiC Powder

[0026] 4. AISI 316L Sample Piece

[0027] 5. Boriding Powders (B4C, KBF4, Active Carbon)

[0028] Detailed Description of the Invention

[0029] In this detailed description, the product and method that are the subject of the invention are explained only for the purpose of better understanding the subject and in a way that does not create any limiting effect.

[0030] The invention relates to a method for obtaining AISI 316L type stainless steel biomaterial with improved mechanical properties and 100% antibacterial properties. The said method comprise box boronizing process (also called boriding) to AISI 316L type stainless steel with a powder mixture containing B4C, KBF4, active carbon and SiC powders. Figure 1 shows the schematic shape of the boronizing box.

[0031] In one application of the method according to the invention, can boriding process is applied to AISI 316L type stainless steel with a powder mixture comprise 25% B4C, 25% KBF4, 30% SiC and 20% active carbon by weight. In one application of the method according to the invention, can boriding process is applied to AISI 316L type stainless steel with a powder mixture comprising 20% B4C, 30% KBF4; 30% SiC and 20% active carbon by weight.

[0032] In one application of the method according to the invention, can boriding process is applied to AISI 316L type stainless steel with a powder mixture comprising 30% B4C, 20% KBF4; 30% SiC and 20% active carbon by weight.

[0033] In one application of the method according to the invention, can boriding process is applied to AISI 316L type stainless steel with a powder mixture comprising 10% B4C, 40% KBF4; 30% SiC and 20% active carbon by weight.

[0034] In one application of the method according to the invention, can boriding process is applied to AISI 316L type stainless steel with a powder mixture comprising 40% B4C, 10% KBF4; 30% SiC and 20% active carbon by weight.

[0035] The mentioned boronizing process is preferably carried out by applying heat treatment at a temperature range of 500-1000 'C for 4-12 hours, more preferably at a temperature of 1000 'C for 4 hours.

[0036] The invention is an AISI 316L type stainless steel biomaterial with improved mechanical properties that provides 100% antibacterial properties against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 bacteria.

[0037] In the method of the invention, boronizing process is applied to AISI 316L type stainless steel used as biomaterial to provide antibacterial properties. One application of the method of the invention is as follows; The powder mixture ratios prepared with 5 different parameters (the first powder mixture comprising 25% B4C, 25% KBF4, 30% SiC and 20% active carbon by weight, the second powder mixture comprising 20% B4C, 30% KBF4; 30% SiC and 20% active carbon by weight, the third powder mixture comprising 30% B4C, 20% KBF4; 30% SiC and 20% active carbon by weight, the fourth powder mixture comprising 10% B4C, 40% KBF4; 30% SiC and 20% active carbon by weight and the fifth powder mixture containing 40% B4C, 10% KBF4; 30% SiC and 20% active carbon by weight) were placed in 5 different boronizing boxes (2) separately for each powder mixture. B4C was placed at the bottom of the boronizing box as a boron source, KBF4as an activator and active carbon (5) as a reductant. AISI 316L type stainless steel piece (4) was placed in the middle of the powder mixture. Finally, SiC used as deoxidant (3) was added and the Stainless Steel cover (1) was closed. Heat treatment was applied to the boriding boxes (2) prepared at 5 different ratios at 1000°C for 4 hours. The samples, after the bonding process was completed, were taken out of the bonding boxes (2) and cleaned with alcohol in an ultrasonic cleaning device. Then antibacterial test was applied.

[0038] For antibacterial test, Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 grown in Mueller-Hinton Agar (MHA) (Merck, Germany) were used. Before starting the studies, all surfaces of the samples were sterilized with UVC in a biosafety cabinet. Studies were carried out on different days for E.coli and S. aureus bacteria in Mueller- Hinton Agar (MHA) (Merck, Germany) medium. During the comparison of bacteria with the samples, Nutrient Broth (NB) (Merck, Germany) medium diluted 1 / 250 with distilled water was used. In line with the antimicrobial activity determination procedures, bacteria were first grown in MHA medium. Some of the grown bacterial colonies were taken and suspended in NB medium. Using a spectrophotometer, a turbidity equivalent to 0.5 McFarland turbidity (OD: 0.14 at 600nm for E. coli, absorbance between 0.08-0.1 at 600nm for S. aureus) was obtained (108 CFU / mL). These bacterial suspensions were diluted with NB to prepare solutions containing 1 x 104 CFU / mL bacteria. 0.25 ml of this solution was taken and left on the samples. After that, the samples were incubated in a 37cC oven with 90% humidity for 24 hours. In order to determine the number of bacteria left on the samples, 0.02 ml of the relevant solution was taken and seeded on MHA medium. The seeded petri dishes were also incubated in a 37cC oven for 24 hours.

[0039] After incubation, samples were taken and placed in 50 mL falcon tubes containing 2.25 mL NB. The bacteria attached to the samples were separated from the metal by pipetting. 0.02 ml of liquid was taken from the solution in the tubes and inoculated on MHA medium. All inoculated petri dishes were incubated in a 37°C oven for 24 hours. After incubation, photographs of all media were taken using an imaging system (VersaDoc, BIORAD). Figure 3 shows the growth images of E. coli and S. aureus bacteria in media that were in contact with the samples for 24 hours.

[0040] As a result, in the invention, for E.coli and S. aureus colony counts (log10CFU / ml) that were brought into contact with the samples for 24 hours, there were 5.28 colonies at 0 (zero) hour for all samples, while after 24 hours, there was 7.27 colonies for E.coli in 316L, while it was obtained as 0.00 in boronized 316L samples. For S. aureus, there were 6.17 colonies at 0 (zero) hour for all samples, while after 24 hours, there was 7.58 colonies in 316L, while it was obtained as 0.00 in boronized 316L samples. Bacteria decreased by 100% in boronized samples. In this way, a biomaterial surface with antibacterial properties of AISI 316L type stainless steel was obtained. In the invention, surface treatment technologies are used to improve some mechanical properties such as hardness, corrosion resistance and wear of AISI 316L quality stainless steels, which are among the most widely used and known metals in terms of biocompatibility as implant materials. Since 100% antibacterial properties are targeted in the invention, boronizing process was applied. Box boronizing method was used for boronizing process. Instead of commercial boron powder mixture, powder mixtures prepared with 30% SiC and 20% active carbon in fixed ratios and B4C and KBF4added at different ratios (1 -Mixture: 25% B4C, 25% KBF4; 2-Mixture: 20% B4C, 30% KBF4; 3- Mixture: 30% B4C, 20% KBF4; 4-Mixture: 10% B4C, 40% KBF4and 5-Mixture: 40% B4C, 10% KBF4) were used (2). Antibacterial test was applied to the obtained samples with Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 bacteria. As a result, it was seen that the study, which was tested with 5 different powder mixture process parameters used for the first time, had 100% antibacterial properties. In this way, AISI 316L type biomaterial with antibacterial properties was produced.

[0041] In the preliminary studies carried out with the invention; 5 AISI 316L type stainless steel samples with a diameter of 20 mm and a height of 15 mm were cut. Powder mixtures prepared in 5 different ratios were used for the boronizing process. A boronizing box was used for each ratio. Thus, boronizing process was carried out in 5 different boronizing boxes in 5 different samples at the specified ratios. The tests applied for antibacterial properties were carried out with 3 repetitions. In particular, the effects of boron source and activator at different ratios were examined. In the preliminary studies carried out, boronizing process was tried at temperatures of 500, 800 and 1000 0C and periods of 4, 8 and 12 hours. It was observed that the parameter in which the boronizing layer thickness formed on the surface of the material, the mechanical properties of the material and the antibacterial properties were best in this temperature and time range was obtained at 1000 'C and 4 hours. Therefore, the temperature and time were applied as constant for each powder mixture.

Claims

CLAIMS1. A method for obtaining AISI 316L type stainless steel biomaterial with improved mechanical properties and 100% antibacterial properties, characterized by comprising; applying box boronizing process to stainless steel with a powder mixture comprise B4C, KBF4, active carbon and SiC powders.

2. The method according to claim 1 , characterized in that; the powder mixture comprising 25% B4C, 25% KBF4, 30% SiC and 20% active carbon by weight is applied to AISI 316L type stainless steel by box boronizing process.

3. The method according to claim 1 , characterized in that; the powder mixture comprising 20% B4C, 30% KBF4; 30% SiC and 20% active carbon by weight is applied to AISI 316L type stainless steel by box boronizing process.

4. The method according to claim 1 , characterized in that; the powder mixture comprising 30% B4C, 20% KBF4; 30% SiC and 20% active carbon by weight is applied to AISI 316L type stainless steel by box boronizing process.

5. The method according to claim 1 , characterized in that; the powder mixture comprising 10% B4C, 40% KBF4; 30% SiC and 20% active carbon by weight is applied to AISI 316L type stainless steel by box boronizing process.

6. The method according to claim 1 , characterized in that; the powder mixture comprising 40% B4C, 10% KBF4; 30% SiC and 20% active carbon by weight is applied to AISI 316L type stainless steel by box boronizing process.

7. The method according to claim 1 , characterized in that; the said boronizing process is carried out by applying heat treatment at 1000 °C for 4 hours.

8. AISI 316L type stainless steel biomaterial with improved mechanical properties providing 100% antibacterial properties against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 bacteria.

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