Materials in the human body

Photo: A stirrup-shaped ossicle next to a 10 cent coin

The conclusion: a metal allergy – the artificial hip joint has to be removed. To prevent such events from happening, researchers study a long time to prepare before a foreign object can be implanted into the human body. Doctor Philipp Imgrund of the Fraunhofer IFAM in Bremen, Germany, knows however that reactions to the foreign object, for instance because it contains nickel, cannot always be prevented despite prior research: ”Generally, biocompatibility is met for these materials. Yet needless to say allergies to nickel or intolerance to titanium could occur, since metal is not a material that is found in the body per se.“ Admittedly, he personally does not know of a case where the use of a material resulted in severe side effects: “We know this more from drugs that have been tested in animal experiments and then proved to be intolerable for the human being. Currently the case is that all new materials that are meant to hit the market are also accordingly being tested beforehand in field tests, in the laboratory, in subsequent animal experiments and also in a clinical trial. Given all of this I think that compatibility is well assured. “

Long-term results – everything takes its time

To really be able to tell whether a material proves to be optimally biocompatible, scientists usually have to wait a long time, because oftentimes the true qualities of a material don’t show until they have long since been in practical use. On the flipside this means that currently used materials – for example biodegradable materials and implants – cannot be one-hundred percent rated yet. What’s more is that although people might be similar to each other, they are not the same. In the same way two people might respond differently well to a drug, some patients might have problems with a material and others don‘t.

Of course this also needs to be juxtapositioned with the benefit people get from these “laboratory replacement parts”. By now there is a large spectrum of implants that replace even the smallest of body parts – like for instance the stirrup-shaped auditory ossicle (ear bone). To do this, manufacturing processes are necessary that work quickly and precisely. Imgrund himself at the moment researches in the area of metal powder injection molding processes with which even the tiniest structures can be manufactured in large quantities. “Metal power injection molding is a process that basically modifies the plastic injection molding as the known process by way of inserting metal powder into polymers. The polymer is the carrier to mold the materials and to give implants their shape. Basically, metallic powder is being used and mixed into a binder matrix. This binder material is the carrier for the metal powder that can pour into the mold. During the subsequent steps, the binder is being extracted and you get the finished metal piece via a heat treatment. This works for all of the popular metals such as titanium, stainless steel or cobalt-chrome. “ Even though the process itself has already been used for more than ten years, it keeps offering new variation possibilities, for example in creating functional surfaces to which for instance bone cells adhere to or which have an antimicrobial and anti-adhesive effect. In this area further research is being expedited that is explicitly dedicated to the design of surfaces.

Simone Ernst

(Translated by Elena O'Meara)