The work quality of metal component manufacturers who supply the medical device industry has recently improved significantly. The product quality of these alloys has never been better since the implementation of statistical process control, ISO 9000 certifications, and other initiatives.
Manufacturers of medical equipment and implanted devices have access to a wide variety of metals today. Manufacturers have a variety of options when determining which grade or alloy is best for a given application, as a result of their understanding of the differences between these materials and the options that each one provides. High strength and formability may be combined with surfaces that are sterile-friendly, bright, and clean.
Given the extreme difficulty of many modern surgical procedures and the ongoing concerns regarding patient comfort and safety, device manufacturers want assurances that the components and materials they purchase are the best available for the task at hand. As a result of the advent of minimally invasive and noninvasive procedures, which allow surgeons to operate without making direct eye contact with the operative field, more emphasis than ever before is being placed on technology that operates flawlessly the first time, every time.
Metal components purchased from stamping houses and fabricators, as well as the raw materials from which they are manufactured, are subject to heightened scrutiny due to consumers’ ongoing search for less expensive and more efficient alternatives. Metals are still required for many vital medical applications, despite the fact that plastics continue to make significant strides in the medical industry, including the replacement of metals in certain equipment. To assist the medical equipment industry in achieving its goals of higher quality levels and enhanced device performance, designers now have access to an expanding variety of metal materials and shapes.
How does metal selection play a role?
Metals are selected for parts that require exceptional strength and rigidity, particularly in small cross sections. In addition, they are ideal for components that must be formed or machined into complex shapes, such as blades, points, and probes; for mechanical components that must work with other metal components, such as gears, triggers, slides, and levers; for components that must be sterilized in high-temperature conditions; and for any other parts requiring mechanical or physical properties superior to those of polymer-based materials.
When a metal component is required to construct a medical device, 300-series stainless steel is the most popular option. These alloys have excellent mechanical and physical properties, and a variety of surface finishes, including reflective and matte, and are relatively straightforward to cold form or fabricate into specialized components. Additionally, they are essentially non-corrosive.
Stainless steel alloys are composed of 17 to 25% chromium and 8 to 25% nickel. By producing a strong, vicious, and invisible chromium oxide coating on the surface of the alloy, chromium aids in the corrosion resistance of stainless steel. If this film sustains mechanical or chemical damage, it is capable of self-repair. Occasionally, additions of up to 7 percent molybdenum are used to increase corrosion resistance.
The stainless steel grades 301, 304, 304L, and 305 are the most frequently used for medical products. The alloy composition of these variants differs slightly, and the choice of grade depends on factors such as formability, corrosion requirements, or the thickness and temper availability desired. Surface strength and condition are two additional crucial design elements.
Stainless steel alloys can be cold-treated to achieve high tensile and yield strengths while maintaining their ductility and toughness. Depending on the composition and amount of cold work, their yield strengths at a room temperature range between 30 and 200 ksi. The terms “austenitic” and “martensitic” are used to describe the metallurgical structure of stainless steel grades. This occurs when metals are rapidly cooled after being heated above their critical temperature. Temperature and heat treatment duration determine the alloy composition, time and temperature of heat treatment, and final structure. Austenitic stainless steels are stronger and more formable than martensitic grades.
Austenitic Stainless Steel
The majority of components for medical devices are made from austenitic stainless steel, which contains between 16 and 20 percent chromium and 6 to 14 percent nickel. On the surface of the alloy, chromium creates a durable, undetectable, and adhering chromium oxide coating that provides the necessary corrosion resistance. If this film sustains mechanical or chemical damage, it is capable of self-repair. To further enhance corrosion resistance, certain grades contain up to 7% molybdenum additives.
Surgical stapler frames, springs, anvils, cartridge slides, and jaws are a virtual showcase of 300-series stainless steel components used in contemporary medicine. Different grades of stainless steel wire are used to create the staples. Catheters, diagnostic equipment, and other items are made from stainless steel of the 300 series. Due to its high creep strength at elevated temperatures, stainless grade 316 is occasionally specified for braces. When welding is anticipated, grades 304L and 316L of the corresponding low-carbon alloys are recommended.
The 400 series of stainless steels, which are commonly used for surgical instruments, are less resistant to corrosion than the 300 series but can be heat treated to achieve higher levels of strength and hardness. Unlike the two most common grades, 410 and 420, these materials contain no nickel and a negligible amount of chromium. 410 is the general-purpose grade, whereas 420 is harder and contains more carbon.
Surgical instruments are also fabricated from martensitic stainless steel of type 410. Even though it has a lower corrosion resistance than the grades in the 300 series, it can still be heat-treated to improve its strength and hardness. Type 410 contains no nickel and between 11.5% and 13.5% chromium.
Precipitation-hardening stainless steel, such as 17-7 PH or 17-4 PH, may be used by the designer when a component requires increased strength and stiffness, such as in equipment housing.
Trace amounts of copper, aluminum, phosphorous, or titanium are the only difference between these metallurgical hybrids and stainless type 301.
A component is given an age-hardening treatment following its final moulding, which causes the phase transformation caused by the additional components.
Creating intermetallic compounds. Consequently, they are frequently increasing the part’s hardness and strength by up to 40 percent.
Pure titanium, the most expensive and inert of the commonly used metals, is used to create ultra-high dependability components or those that remain inside a patient following surgery. Metal implants include artificial joints, pacemaker casings, and various others. Titanium alloys are also used in the medical industry, primarily for components when stainless steel cannot meet the necessary standards for strength, hardness, corrosion resistance, or other factors.
Titanium is an excellent biomaterial because it has the same tensile strength as steel but weighs only one-third as much. Due to its extraordinary ability to form a protective oxide film that adheres tightly to the surface when exposed to air or other oxidizing agents, it possesses exceptional corrosion resistance. This passive layer regenerates after metal surface damage and is resistant to all types of corrosion.
One of the most demanding applications in the medical industry, in terms of fabrication and use of available alloys, is also one of the most unusual. Since the popular hip-joint replacement is intended to last a lifetime, it requires materials with high strength, excellent wear resistance, and superior corrosion resistance. Different manufacturers’ designs vary slightly, but a typical hip implant consists of a cobalt-chromium stem that fits into the femur and a titanium-alloy cup that fits into the hip socket. The cup’s cobalt-chromium head is attached.
Manufacturers of titanium hip stem joints favor Ti-6AL-4V titanium alloys, particularly the low oxygen ELI grade, for implantable bar and plate applications. When a product is forged, the most common starting material is a bar with a diameter of up to seven inches.
Why are certain products preferred?
Stainless steels, hardenable alloys, and titanium alloys can be fabricated in a number of forms required by the medical industry, including foil, strip, sheet, wire, rod, bar, and plate. Because components of medical devices are typically small and intricate, automatic stamping presses are typically used to create the shapes. The best starting materials for this type of processing are strips and wire, which are the most commonly used materials. These mill forms are available in numerous sizes. Flat wire is available in thicknesses of 0.010 in. to 0.100 in. and widths of 0.150 in. to 0.750 in. Strip, for example, is available in thicknesses ranging from ultrathin foil to 0.125 in.
Which metal is suitable for the medical device?
Despite the fact that stainless steel, titanium, and nickel-based alloys are considerably more sophisticated than conventional materials, they offer a vastly expanded range of applications. Heating, cooling, and quenching can alter the mechanical properties of these “metallurgical animals.” They can be modified further during processing, if necessary. For example, rolling out metals with narrower gauges can harden them, whereas annealing can restore their precise temper for economical shaping.
Once designers are comfortable with the complexity of the materials, these unique metals offer a number of exceptional advantages in a variety of medical products, including unmatched corrosion resistance, high mechanical capabilities, a vast array of surface treatments, and excellent production versatility.
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Benefits of Stainless Steel 310 Sheets: Austenitic stainless steel in Grade 310 is easy to weld and bend, and it has great properties at high temperatures. Type 310 stainless steel tubing is often used in situations with high temperatures. Because they have a lot of chromium and nickel, 310-grade steel pipes are very resistant to corrosion and rust, and they are also very strong, even at temperatures as high as 2100°F.
All About Mild Steel: Mild steel is a type of carbon steel that has very little carbon in it. It is also called “low carbon steel.” Depending on the source, the amount of carbon in mild steel ranges from 0.05% to 0.25% by weight. On the other hand, higher carbon steels usually have a carbon content of between 0.30% and 2.0%. If more than that amount of carbon is added, the steel becomes cast iron.