Task Force on Corrosion of Medical Implants and Devices

Mission and objectives

Mission

Interactions of implanted materials and devices with the human body are still largely unknown and their detrimental effect on the material stability and body responses are sometimes clearly underestimated, evident from a raising number of failure reports. Nevertheless, the medical field relies more and more on the use of medical materials for various therapies ranging from implants for fracture fixation or cardiovascular intervention, including those with drug-delivery capabilities, to more and more advanced medical devices including those for monitoring and sensing. Consequently, reliable testing protocols are required that reflect the dynamic, aggressive local chemical environment that cells and tissues create (e.g. large pH variation in wound and inflammation conditions). Additionally, these testing protocols need to provide the required level of details, i.e. at relevant sensitivity and magnification at which material dissolution may occur. 

In fact, considering the current understanding of the material-biology interface interactions, it is evident that macroscopic aspects of implant/medical device failure, such as fractured implants or material particle release, are already documented. There is however, a clear lack of understanding of the processes occurring that underlie the formation of micro- and nanoscale corrosion products and ionic leaching, as well as their consequences.

OBJECTIVES

As depicted in the figure, the new Task Force (TF) activities aim at a better understanding of these "invisible" processes for a better biocorrosion prediction and ultimately prevention of implant & medical device failure. The TF thus addresses patient safety as the prime stakeholder. The work of the TF on "corrosion of medical implants and devices" focusses on the following fundamental and practical topics:

• improving in vitro protocols for corrosion susceptibility assessment of permanent and biodegradable implants/devices
• identifying mechanisms underlying the formation of nanoscale and ionic products and deriving structure-stability/reactivity correlations. This understanding will support development of corrosion prevention strategies
• developing new analytical methodologies to advance the detection limit (trace element, lateral resolution) for more detailed investigation of degradation mechanisms.

The TF will foster collaboration and exchange between various academic fields from material science, electrochemistry to biology, with their fundamental knowledge and experimental capabilities. We will increase awareness for chemical surface reactivity and enhance visibility of the topic to attract biomaterials expert and clinicians to foster the discussion through their input on clinical challenges and patient needs. The TF actions aim at supporting a responsible medical technology development behaviour.

Figure: Task Force focus towards extending the current understanding of biocorrosion mechanism (design: courtesy of Martina Cihova)

What is urgently needed, especially from a patient health perspective, is better tracking (detection) and tracing (distribution in human body) of released particles and ions. The prime focus of the TF is on metallic implants/devices but not restricted to, acknowledging that polymer degradation can also cause problems. For either material class, processes occurring at the nanoscale seem to be overlooked according to 'what cannot be seen does not exist' and will consequently not be assessed for their toxicity or other adverse biological reactions.

In the corrosion mechanisms description, the TF will work on experimental protocols integrating chemical stability criteria in implant/device validation processes, considering also worst-case scenarios. For instance, it should be considered that most implanted objects will experience some degree of micromotion and corrosion-fatigue, making simple immersion tests insufficient for validation. The TF aims at defining improved testing protocols that also include mechanical loading situations.