Med-Tech Innovation 3D printing


Figure 1: SEM image of the surface of a regular ALM porous structure


Figure 2: SEM image of the cross section of a deep EBM porous structure with semi-closed porosity


unfused particles and chemical residues have all been documented on finished ALM medical implants. In addition, normal best practice in manufacturing involves the use of gloves and proper part handling such as the use of containers and packaging materials to help prevent damage to parts. Contact with these materials may also result in residue and debris being transferred to the part itself, which may interact with the surface of the metal. This includes mechanical and chemical interactions with debris and contamination. Rough surfaces and substructures pick up debris from the air, from handling materials such as baskets and plastic bags and may also absorb fluids and humidity from air. Removal of these residues, liquids and debris is a challenge. Many of these complex ALM structures involve a combination of interconnected and closed cell porosity. Exposure to cutting fluids, cleaning fluids, solvents, blast media, grinding media, passivation solutions and many other chemical agents during processing presents several possible means of contamination. These potential contaminants tend to become entrapped in unique ways in these complex porous structures and need to be completely removed prior to packaging as finished goods. Open porous structures pose less of a challenge with


is a combination of open, closed and interconnected pores that presents unique challenges.


Figure 3: SEM images of an ALM part surface before (left) and after (upper and lower right) chemical processing was performed. Organic residue is visible on the processed part, likely a result of contamination within the cleaning process


The processing challenges Manufacturers in the medical device industry implementing the use of ALM technology must address certain concerns related to the cleanliness of their products, not only in their final state, but also throughout the manufacturing process. ALM structures often act as sponges, picking up anything they come into contact with, which often results in debris being trapped on the surface and in the outermost layers of the porous layer. There is also a high risk that ALM parts will entrap processing fluids, which can include acids, caustics and other solutions used during the cleaning and processing of the component. The types of residual contaminant seen on finished goods have been classified. Trapped debris, loose and


regard to entrapment. Open cells stay open during all stages of processing, and closed cells remain closed during all stages of processing. Fluids enter through open porosity or interconnected porosity and have the ability to exit the part through the same path. However, semi- closed porosity may be closed at ambient temperatures and open when heated due to thermal expansion. Many chemical processing and cleaning operations involve the use of heated immersion tanks, which provide the perfect conditions for entrapment of fluid within the porous structure. Strict process parameters and cleaning processes tailored to the treatment of ALM product should be considered. There is the also the risk that in-house processing operations will contaminate parts, including applied cleaning procedures. Liquid exposures can be problematic. Drag out between processing tanks can add contamination to solutions that is then transferred to parts. The frequency of solution replacement has a great effect on the final cleanliness of the product, and the cost of this process parameter can be great. Rinsing methods can aid in the cleanliness of ALM parts, but may also be a contributing factor depending on rinse method, water quality and level of contamination remaining from prior processes. Figure 3 shows a comparison of scanning electron microscope (SEM) backscatter electron images of an ALM part analysed before (left) and after (right) cleaning was performed. The cleaning procedure actually resulted in a contaminated part due to chemical residues left behind on the part surface. Effective removal of these solutions and residues is a


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