Where bones fracture, surgeons often have to join the fragments with
implants. Magnesium orthopedic screws, which over time dissolve in the
body, spare patients another operation after healing is completed and
reduce the risk of infection. What happens inside the body during this
process, though, is still largely unknown. To develop optimized alloys
and orthopedic screws with functionalized surfaces, Empa researchers are
now investigating magnesium corrosion.
When surgeons want to fix bone fragments after a fracture, the critical question is what type of implants to use: screws and plates made of titanium or steel, which are mechanically and chemically very stable in the body, but have to be removed later on by another surgical procedure? Or implants made of organic materials that dissolve over time but can have certain other drawbacks, such as lack of mechanical strength or unfavorable degradation products? Empa researchers are currently working on solving this dilemma: tiny magnesium implants and screws. These are mechanically robust at first but dissolve later on in the body in a controlled way that does not cause tissue damage.
Such magnesium implants are particularly interesting for medical orthopedic applications in children whose bones are growing rapidly. The biodegradable screws do not impair the child's bone growth and save the small patients a second surgery. In addition, the risks of infection can be minimized and costs can be cut. "Magnesium is more commonly regarded as a white powder that is often taken as a dietary supplement," says Arie Bruinink from Empa's Laboratory for "Joining Technologies and Corrosion." Implants made of magnesium alloys are not only biocompatible, however; they also have mechanical properties during the first delicate healing phase that are bonelike and, therefore, even more suitable than those of titanium.
The blessing of a resorbable screw can also be its curse. After all, the dissolution is associated with complex corrosion processes that alter the surface structure and yield a number of products—that might or might not be hazardous. Depending on the type of magnesium alloy, hydrogen gas can develop during degradation due to insufficient corrosion resistance—to an extent that even a gas cushion is being formed under the patient's skin. Although it is in the surgeon's intention that magnesium screws are degraded by corrosion, during which magnesium oxidizes and hydrogen is produced, the formation of gas cushions should be avoided. If all of a sudden more hydrogen gas is formed than the body can remove, the healing process of the fragile bone can be disturbed.
When surgeons want to fix bone fragments after a fracture, the critical question is what type of implants to use: screws and plates made of titanium or steel, which are mechanically and chemically very stable in the body, but have to be removed later on by another surgical procedure? Or implants made of organic materials that dissolve over time but can have certain other drawbacks, such as lack of mechanical strength or unfavorable degradation products? Empa researchers are currently working on solving this dilemma: tiny magnesium implants and screws. These are mechanically robust at first but dissolve later on in the body in a controlled way that does not cause tissue damage.
Such magnesium implants are particularly interesting for medical orthopedic applications in children whose bones are growing rapidly. The biodegradable screws do not impair the child's bone growth and save the small patients a second surgery. In addition, the risks of infection can be minimized and costs can be cut. "Magnesium is more commonly regarded as a white powder that is often taken as a dietary supplement," says Arie Bruinink from Empa's Laboratory for "Joining Technologies and Corrosion." Implants made of magnesium alloys are not only biocompatible, however; they also have mechanical properties during the first delicate healing phase that are bonelike and, therefore, even more suitable than those of titanium.
The blessing of a resorbable screw can also be its curse. After all, the dissolution is associated with complex corrosion processes that alter the surface structure and yield a number of products—that might or might not be hazardous. Depending on the type of magnesium alloy, hydrogen gas can develop during degradation due to insufficient corrosion resistance—to an extent that even a gas cushion is being formed under the patient's skin. Although it is in the surgeon's intention that magnesium screws are degraded by corrosion, during which magnesium oxidizes and hydrogen is produced, the formation of gas cushions should be avoided. If all of a sudden more hydrogen gas is formed than the body can remove, the healing process of the fragile bone can be disturbed.
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