Originally Published MPMN
Originally Published MPMN June 2004
Building Better Materials Through Nanotechnology
|By applying nanotechnology to materials development, Sandvik has developed a medical-grade stainless steel with improved tensile strength, corrosion resistance, formability, and other properties.|
The manipulation of materials at the molecular level has led to some recent advances that may benefit developers of medical devices. A metals supplier headquartered in Sweden claims to have dramatically improved the performance of stainless steel through the use of nanotechnology. On the plastics front, carbon nanotube-based additives developed by a US-based company promise to boost the properties of
Sandvik Bioline - NAFTA (Scranton, PA; www.sandvik.com/bioline) has developed a medical-grade stainless steel that combines exceptional levels of strength with ductility. "Nanometer-sized particles in a grade of stainless steel impart a range of unique properties such as tensile strength, corrosion resistance, formability, and so forth," says global technical manager Stephen Cowen. The particles are formed by means of a heat treatment process. "A novel phenomenon occurs within the material [during heat treatment], which produces nanoscale precipitates of a quasicrystalline structure," explains Cowen. "That's where the strength comes from."
To facilitate machining, Sandvik Bioline 1RK91 can be supplied in a soft unaged condition. "The mechanical properties and ductility in the unaged condition are more conducive to good machining," says Cowen. Once the part has been formed, it can be subjected to age hardening. "This gives customers the flexibility to manufacture a very complex part and then to age it to enhance the material's mechanical properties," says Cowen.
The combination of properties, surface finish, and sterilizability make this grade of stainless steel suitable for use in the fabrication of torque wrenches, bone drills, surgical needles, and other microsurgical medical and dental devices. Because of its strength, Sandvik Bioline 1RK91 may have a role to play in the development of thinner, and thus lighter, devices that will cause less tissue damage than traditional instruments.
The material is primarily produced at the company's plant in Sandviken, Sweden. "Integrated production from melting to final product form allows us to closely control all of the parameters needed to achieve these unique properties," notes Cowen.
Sandvik Bioline 1RK91 has undergone in vitro testing. It has no cytotoxic potential and meets global standards related to allergies and skin irritations.
Wire, tube, bar, strip, and rod shapes are available. For medical wire applications, Sandvik has developed a delivery system to ensure that its customers receive the product in the cleanest possible condition. The wire is wound onto white, nonreturnable spools that are protected by a plastic film and packed in a white cardboard box.
Additives Boost Polyurethane Strength, Conductivity
Increased material strength, along with thermal conductivity, is also an attribute of nanoscale additives developed by Zyvex Corp. (Richardson, TX; www.zyvex.com). The NanoSolve products, based on single-wall (SWNT) or multiwall (MWNT) nano-tubes, are designed for use as dispersion additives in polyurethanes.
Carbon nanotubes are extended buckminsterfullerene molecules, or "buckyballs," spherical molecules constructed solely from 60 carbon atoms. The molecular structure provides exceptional strength.
The additives are intended primarily for early adopters of new technology, says senior engineer Mark Banash. "These are manufacturers who need to make a rapid market-dictated increase in performance to remain competitive," he says.
MWNTs are less costly to produce than SWNTs and are suited for applications in which mechanical strength is a core concern. SWNTs tend to perform better for thermally and electrically conductive applications. They also may require lower loading than MWNTs to achieve improvements in performance. In either case, proper surface treatment is a key process step, notes Banash.
"The surface chemistry of carbon causes raw tubes to aggregate," explains Banash. A surface treatment is necessary to enable their proper dispersion and structural interaction with the matrix, he adds. Zyvex has developed a functionalization technology to ensure that this occurs.
The firm is currently developing additives for a range of polymer and metal host materials. It can also alter additives to interact in unique ways with a customer's matrix.
NanoSolve products offer manufacturers a range of formulation options that meet specific material design and price parameters, according to the company. Discussions are underway with several medical device manufacturers, adds Banash.
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