Medical springs are an important component in the manufacturing of devices and equipment used throughout the medical industry. The three main types of springs used in medical devices—compression, torsion, and extension—and each serve a valuable purpose in varying types of equipment, large and small.
Springs are devices that store mechanical energy. Though they are relatively simple in design, they are ubiquitous components in all kinds of devices and machines in a wide range of products from medical devices and equipment to consumer goods and heavy industrial equipment. Nearly anything at all that involves a mechanism more than likely has a spring component.
It is no surprise then that springs are an indispensable part in some of the most common and advanced medical equipment used today. They are used in such noninvasive applications as diagnostic and monitoring devices, syringes and pill dispensers. They are also used as components in such surgical and nonsurgical devices as pacemakers and catheters. Some applications require micro-dimensions manufactured for components of 0.1 to 0.8 millimeters, and even down to 0.03 millimeter in wire size for arterial widening.
This makes precision in the design and manufacturing of springs for medical devices essential. Components must be reliable and durable. The proper functioning of medical devices can literally mean the difference between life and death. Selecting the correct materials for springs used in medical devices is also vital. The part not only has to be strong enough, but hygienic enough for the medical device. Stainless steel alloys are commonly used in medical devices, particularly grade 316. Stainless Steel 316 is a very clean material type and is also 90% non-magnetic, and can be found in such spring-loaded medical applications as auto-injector syringes or inhalers. The 316 grade stainless is also a choice material for biomedical implants, along with a titanium-aluminum alloy called Ti6Al4V. Where micro-spring technology is necessary, such alloys as platinum-iridium and platinum-tungsten are commonly used in the manufacturing for their strength but for the cleanliness required varying medical devices used in implants.
Other important spring materials for medical devices are the alloys Elgiloy and Hastelloy. Elgiloy, dubbed the ‘super-alloy’, is an exotic mix of the metals molybdenum, cobalt, chromium, nickel, and iron. It is non-magnetic and has a unique combination of very high fatigue strength with excellent biocompatible characteristics. The alloy Hastelloy C-22 is a nickel-based, high-temperature alloy with a unique combination of properties suitable for material used in springs for medical applications. Each alloy is used in an assortment of medical devices and applications such as stents, pacemakers, surgical clips, and orthopedic cables to name a few.
Choosing the right spring for the component in the medical device is also essential for the part to function as designed. Spring classification is determined by how a load is applied. The load of a compression spring is designed to perform when force is compressed. Think of springs used for such compressive loads as in shock absorbers, spring mattresses, and retractable pens. In medical devices, compression springs are necessary where squeezing actions occur, for a switch or a surgical stapler.
Torsion springs are those springs that are designed to function with torque, i.e., a twisting action or rotational movement. Think clothespins or garage doors. Such medical equipment as x-ray machines and MRI devices are good examples that use torsion springs.
Extension springs, also called tension springs, are those springs that pull two components back to together. Designed to operate with a tensile load, the pulling action provides return force to components that have been extended. Some medical devices that use extension springs include surgical lights, stretchers, and numerous handheld devices.
The medical industry relies heavily on springs for a wide range of applications in many products and devices. Material, design, and performance requirements must meet the stringent regulatory requirements of the FDA. Springs are but one component in a long list of surgical instruments, equipment, and medical devices such as monitors and indicators, booms, lifts, and fluid control devices, booms, wheelchairs, medical testing and monitoring equipment, anesthetic infusion devices, sterilization valves, and shunt valves to name a few applications. For manufacturers, choosing the right spring to use in a medical device will ultimately relate to its application.