By Sean Fenske, Editor-in-Chief
 
Orthopedics is a shrinking industry. Not in the size of the market, number of surgeries, or even the implants themselves. The technology used to enable implant placement, however, is being made smaller to support a preference for minimally invasive procedures. As these instruments and devices get smaller, the manufacturers need fabrication methods to enable that trend.
 
One method helping to fulfill needs for smaller components is micro metal injection molding (micro-MIM). This technique leverages the familiar injection molding processes but for metal instead of plastics. It offers an efficient and cost-effective way to manufacture parts that will require high volumes.
 
To provide additional information about this method, Raghu Vadlamudi, chief research and technology director for Donatelle, has responded to a number of questions orthopedic device makers may have about the process. He explains why it may offer a better alternative to micro machining, provides considerations for materials, and highlights applications where it could be ideal.
 
Sean Fenske: Before we get into micro-MIM, can you first provide an overview of what is involved with metal injection molding (MIM)?
 
Raghu Vadlamudi: Metal injection molding involves molding, de-binding, and sintering to manufacture metal parts economically as compared to traditional metal machining. The metal powders are blended with proprietary binders (polymers and waxes) to enable injection molding into the desired part shapes at high production rates. These molded parts are then de-bound in solvent or water to remove the binders, and then sintered at high temperatures to fuse the metal particles. Metal machining is a subtractive process whereas metal injection molding is a forming process.
 
Fenske: How does micro-MIM differ from other metal fabrication process, such as micro-machining?
 
Vadlamudi: Micro-MIM excels where micro-machining is cost prohibitive. As feature sizes get smaller, they become difficult to machine with the current equipment technology and cutting tools. Some parts have wall sections down to 150 microns. Micro-MIM needs capital investment in building the molds during the initial stages of the project, but is better in cost performance during scale-up when compared to machining.
 
Fenske: What applications in orthopedics are ideal for micro-MIM? Where is it being used?
 
Vadlamudi: With miniaturization currently a big trend in the medtech industry, micro-MIM will become the manufacturing process of choice as metal-cutting processes are limited in producing micro features and meeting tight tolerances. If a part is high volume with tight tolerances or micro features, micro-MIM may be a solution. Even though the initial investment cost may be high, micro-MIM offers better accuracy, consistency, and cost advantages for high-volume manufacturing.
 
Micro-MIM is a viable alternative for many parts currently being machined. In the orthopedic sector, screws, nails, rods, staples, and bone plates are being produced through micro-MIM, as well as surgical stapler components and endoscope components for minimally invasive surgical procedures.
 
Fenske: What material considerations and/or limitations are there when using micro-MIM?
 
Vadlamudi: The hardness of micro-MIM parts is inferior compared to machined parts due to porosity of the material. However, micro-MIM parts can meet the performance requirements of medical devices. And, depending on the application, one can employ secondary operations such as HIP, H900, and electropolishing to improve the properties to fit their needs.
 
Fenske: What are common misconceptions regarding micro-MIM and what do you say to dispel them?
 
Vadlamudi: Many are concerned about the strength and stability of a micro-MIM part. We assure them metal injection molded parts can be manufactured with porosities less than two percent. The porous structure is also not interconnected, as most believe. Metal parts molded with cobalt-chromium and titanium alloys can find their applications expanded to implantable devices.
 
Fenske: What considerations should an orthopedic device OEM take into account when selecting a micro-MIM supplier?
 
Vadlamudi: They need to be aware of critical capabilities required to produce quality parts. Through our experiences in working with medtech OEMs, Donatelle has identified four areas where micro-MIM suppliers can fail—causing delays, added costs, and often the need for a new supplier. Here’s what they should asking:
 

1. Is the supplier using scientific principles to develop manufacturing processes?
2. How vast is the supplier’s knowledge of materials?
3. Does the supplier possess the equipment and technology expertise required?
4. Does the supplier understand the product requirements?