Key considerations during testing include the following: type of device, duration of contact with the human body, and nature of contact with the human body ( Table 2). During device development, the stringent testing of physical and chemical properties is regulated by the United States Food and Drug Administration (FDA) to ensure the mitigation of these risks prior to clinical implementation. Examples of biocompatible medical-grade coating materials include titanium, parylene, and gold. Considerations when selecting a coating include adhesion of the coating to the magnet, avoidance of magnet oxidation during the coating process, and the coating’s durability, biocompatibility, and cost. These limitations are mitigated by hermetically sealing the Nd-Fe-B magnetic core in a durable biocompatible coating. Additionally, Nd is a brittle material that can break easily. Nd and Fe are known to oxidize rapidly in air, leading not only to the corrosion and weakening of the magnet but also to the formation of reactive oxygen species (ROS) that have been shown to be cytotoxic to human cells. Īnother potential limitation is the relatively poor durability and potential toxicity of Nd-Fe-B magnets to human tissues. One limitation of Nd-Fe-B magnets for industrial use is their relatively low Curie temperature, or the temperature at which a material loses its dipole alignment and subsequently its magnetism however, the Curie temperature for Nd-Fe-B at 310 ☌ is well above environmental temperatures in medical use. This corresponds to a magnetic field of approximately 10,000 Gauss, which is 100 times stronger than a household refrigerator magnet at 100 Gauss. Currently, rare-earth elements, such as N52-grade neodymium-iron-boron (Nd-Fe-B), are commonly used for industrial magnetic devices as they have the highest recorded maximum energy product (474 kJ/m 3). This is known as the energy product (Gauss Oersted or Joules/m 3) which is graded on the N grading system-increasing strength correlating with a higher grade. The strength of a material is based on the elements that comprise it and is determined by the product of a material’s strength as well as the force required to demagnetize it (i.e., coercivity). The utility of a magnetic material in surgical device development is dependent on its strength, durability, and mitigation of potential toxicity in the human body. Biomedical Considerations for Magnetic Surgical Devices Paired magnets to form compression anastomosis between proximal common bile duct and stomach or duodenumĢ. Intraluminal paired magnets to form compression anastomosis bypassing intestinal fistula Intraurethral miniaturized magnets for stricturoplasty Internal–external paired magnetic ring system for colostomy closure Intravascular paired ring magnets for side-to-side anastomosis between two blood vessels Intermittent application of electromagnetic field to metal bougies that lengthen atretic esophageal pouches Historical in-human application of magnets in surgery.
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