Biodegradable passive resonant circuits for wireless implant applications

“Diagnosis is not the end, but the beginning of practice”, said the Nobel Laureate in medicine Martin H. Fischer. A main objective for engineers working in the biomedical field is to provide tools to medical doctors which help them in making accurate diagnose. In particular, getting access to in vivo physiological parameters in real-time is of great interest. The concept presented in this thesis is the development of wireless biomedical implants which are partially or even fully biodegradable. The benefit would be to avoid a second surgery to remove the implant after its period of use, a significant improvement for the patient’s comfort and safety. In particular, one field of application was identified, which is the use of wireless biodegradable sensors in intensive care nursing of patients that just had a heavy surgery or an accident, to avoid infections. This work focuses on the development of the passive resonant circuit used for wireless data transmission. It is demonstrated that passive resonant circuits more specifically RF (radio frequency)-driven RLC (resistor inductor capacitor) resonators can be made of biodegradable materials. The fabrication of biodegradable RLC resonators is a first step towards the ultimate goal of making a fully biodegradable wireless implant for in vivo operation. This is the first time that such biodegradable passive resonant circuits are demonstrated. Two biodegradable polymers, poly(L-lactide) (PLLA) and poly(e-caprolactone) (PCL), are selected for support and packaging applications. Their chemical, mechanical and viscoelastic properties upon degradation are investigated. It is concluded that PCL is more appropriate if a long-term mechanical stability is required, while PLLA offers a better protection against external fluids over time. Moreover, the biodegradable conducting polymer composites poly(L-lactide)polypyrrole (PLLA-PPy) and poly(e-caprolactone)-polypyrrole (PCL-PPy) are developed for passive resonant circuit applications, and characterized. The objective is to synthesize composites with high conductivity and good processability. The influence of PPy content on the conductivity is studied, and a percolation threshold of ∼6 Wt% PPy is found for both composites. The polymerization process is improved by investigating the polymerization conditions (temperature and atmosphere) and by varying the reactants (oxidant, surfactant, additive). Conductivities of∼2.7 S/cm and∼7.8 S/cm are achieved for PLLA-PPy and PCLPPy with 40 Wt% PPy, respectively. The best polymerization conditions are found