S. Himmelstein – 09 May 2018
Traditionally manufactured implants have their limitations, as they can only be produced in a certain number of shapes and sizes, posing problems in terms of patient fit. Joint replacement devices can be agents of stress shielding — the process whereby metal implants remove stress from the patient’s bone, which responds by reducing in density and becoming weaker. Cardiac implants require routine removals to replace batteries.
What’s a medical device designer to do? Make the implants smarter. The smart implant is medicine’s latest innovation, a tiny chip implanted in surgery which is able to measure patients’ pH and hormone levels, blood glucose concentration, bacteria, electrical activity and temperature, providing doctors with real-time biofeedback. Patients equipped with smart implants have a lower risk of serious infection post-op, suffer from less discomfort and pain, and could also be less likely to need revision surgeries in the future. 
The advent of additive manufacturing offers a route to the design of patient-specific implants (PSIs). The manufacturing method also imposes fewer geometric constraints than subtractive manufacturing. PSIs designed and manufactured according to a patient’s computed tomography scan encourages the implant to integrate with the patient’s bone, reducing the risk of loosening. The use of 3D printing enables surgeons to control additional material properties and design implants that mimic a patient’s bone stiffness, density and trabecular structure, which can reduce stress shielding and improve physical function.
The European Union’s PRosPERoS (PRinting PERsonalized orthopedic implantS) research project is developing smart, 3D-printed implants for the repair of large bone defects. Personalized and biodegradable implants are being engineered based on magnesium and zinc alloys. By accurately scanning the vertebrae with advanced imaging techniques, PSI implants can be designed and printed.
Built-in sensors represent another opportunity for smartening up implants. Advanced sensor technology is fostering development of implants that can detect an infection and subsequently secrete the appropriate dose of antibiotic. Sensors can measure the strain exerted on the implant, which indicates the extent the fracture has healed.