Stainless Steel Tubing for Medical Devices
Servicing the medical market has been a key part of Vita’s business -- in our early years, we supplied needles for the Allied forces in World War II! It’s still at the core of what we do best.
Medical Grade Tubing
Medical grade metal tubing can broadly be described as a series of tubing alloys fabricated in a manner that makes them functional and reliable for use in medical device products. While plastic, glass and composite solutions have their place as material options for some applications; medical grade stainless steel tubing is considered to be the dependable material of choice for a variety of products. Starting with its humble beginnings in fluid transfer tools in early research laboratories to medical needles for testing, treatments and vaccination drives, medical grade stainless steel tubing has been used in countless life saving and life supporting products. This article specifically discusses medical grade stainless steel tubing and high level options to consider when specifying its use.
Materials for medical grade tubing
Time tested for decades and relied upon for countless medical devices in the world, alloys 304 and 316 are considered “medical grade stainless steel tubing”. Known for their biocompatibility, these grades of medical grade tubing are used in both disposable and reusable applications. 304 and 316 stainless steel alloys have a long history of biocompatibility in FDA approved products. Compared to 304, both 316 and 316 L have improved corrosion resistance and are often selected when product contact with substances, tissue or duration of contact calls for a higher performance product that has improved resistance to corrosion. 316 LVM---316 stainless steel that is vacuum arc remelted to improve the purity of the alloy and eliminate undesired impurities---is usually the material of choice for implanted products. 17-7 is another stainless steel alloy used for applications calling for high strength, frequently orthopedic products because of its precipitation hardening characteristics.Considering the environment that the tubing will be used in is critical. Hostile settings prone to generating corrosion need to be carefully considered when selecting the optimal alloy or there is risk of product damage or failure.
Mechanical performance, tempers and construction
Most medical grade applications call for hard temper (also known as #3 temper) tube which has ultimate tensile strengths typically exceeding 140 KPSI. Hard tempers yield a stiff, rigid tube which delivers strength needed to resist bending---for example, in a needle application. Hard tempers are also easier to grind and machine because the material tends to chip away from the work surface and not fold over in a gummy manner expected from an annealed (or soft) temper tube. Some specific medical applications require annealed tempers, however as a general rule, medical grade tubing is sold as hard temper tubing. 17-7 alloy hard tempered tube can approach 200 KPSI for certain OD/ID combinations after including a final heat treatment to increase temper achieved from cold working alone. 304 and 316 are reliably used from cryogenic temperatures to approximately 800 degrees Fahrenheit, above which chromium carbide precipitation may occur and lead to intergranular corrosion if environmental conditions support it. Alternative high temperature alloys may be appropriate if frequent sustained or cycled high temperature exposures are expected. Construction can be welded and drawn tube or seamless tube. Seamless products at typical outside diameters required for medical applications are generally more expensive, however either option will suffice as both seamless and welded and drawn products are offered in the same alloys and temper options. More details on the differences between the seamless and welded and drawn processes can be found here. Both welded and drawn products are plug (mandrel) drawn to ensure proper sizing, tempering and ID finishes typical of medical grade products.
Surface finishes and treatments
Normally bright drawn tube is acceptable for most medical applications. It has a shiny, silver-like appearance. However, some applications require a smoother, slicker finish to limit compounds or biological products from sticking to the tube surface. Additional treatments can be applied to the OD (outside diameter) or ID (inside diameter) to make these surfaces smoother and less prone to retention of these substances. For example, products transferring blood may require a fine ID finish so that delicate blood vessels are not torn while transiting the inside of the tube. Surface treatment options for tubing include centerless ground OD, polished OD, triple plug drawn for improved ID finish, or polished ID. These functions improve the surface conditions on the OD or ID. Some medical grade tubing products require surface roughening for either echogenic (ultrasound) applications or for generating surface with sufficient purchase / friction to avoid pulling out when molded to a plastic component of the device. Vita can provide medical grade tubing with the additional treatments described above when specified.
Driving costs for the various options described above are several primary factors:
- Alloy selection. Listed from least expensive to most expensive, generally: 304, 316, 17-7, 316 LVM
- Tolerancing. Certain applications demand precise tolerances to meet functional product requirements. Where relief can be given from exacting tolerances, cost savings can usually be achieved.
- Extremely thin or heavy walls. Walls .003” or less and greater than .035” generally cost more.
- Finish. Surface finishes other than typical bright drawn can increase cost. Surface roughening treatments (grit blast or sand blast) can also add cost.
A considerable portion of our production for the medical market consists of stainless steel tubular fabricated products and needle assemblies. We supply cannula/needle components for countless medical applications, including but not limited to:
- Fabricated orthopedic instrument components for cutting and drilling
- Custom manufactured tubular and needle products for fluid or gas transfer
- Fabricated tubular components for ophthalmologic, neurology or cardiac applications
- Sharp cutter tubes, including lancet points or tapered razor edge parts for cutting and coring/biopsy applications
- Components for instruments used in suturing devices
- Solid wire trocars
- Radiopaque marker bands
- Liposuction and embalming applications
- Many other unique applications not listed here
Because we’ve manufactured a wide range of medical device products since 1932, chances are that we’ve built something similar to a design you’re considering in your application.
All of the fabrication options described here can be utilized on medical grade tubing, subject to certain size limitations. These include but are not limited to:
- Cutting and deburring to length.
- Cold forming including bending, flaring, corseting and dimpling.
- Forming end closures or grinding sharp needle tips/ points.
- Forming holes or slots.
- Assembling tubes to other components via welding, soldering, or mechanical means.
Vita Needle is ISO 9001 and 13485 certified and FDA registered. Our quality group utilizes a range of instruments and sampling/control methods to ensure product quality, ranging from 1” Mitutoyo micrometers to various NIST calibrated custom gauges to Keyence IM vision systems capable of accurate readings to millionths of an inch. We also work closely with customers to ensure special quality requirements, such as aesthetics or special details, unique to each customer.
Why Vita Needle?
Vita Needle has the materials on hand, manufacturing capabilities and know how to produce high quality products for medical applications. Our decades of experience---starting in 1932---gives us a supreme advantage over peers who have comparatively less experience to draw from when developing stable yet creative processes to build complex parts. Quality isn’t an option in the medical device business---it’s a prerequisite.
How can Vita Needle help?
We welcome the opportunity to help on your next project, whether prototype or production. Often the best way we can help is if you send us details---such as an engineering drawing, or specifications of some kind---as well as specifics on your intended application. Then we can get to work figuring out the best way to manufacture your product. Your desired quantities are also helpful so we can optimize processes based on volumes and provide a cost effective quotation. If you’re just starting out and would like some direction on the options we can provide, please call us and ask to speak to one of our technical customer service representatives. Our experienced team will be glad to assist.