RF Characterization of a Photocurable PEDOT:PSS:PEGDA Conductive Biomaterial for 3-D-Printing Implantable Antennas

In this work, we demonstrate photocurable poly-3,4-ethylene di-oxy thiophene (PEDOT):polystyrene sulfonate (PSS):poly-ethylene glycol di-acrylate (PEGDA) biomaterial as a promising candidate for 3-D-printing implantable antennas intracorporeally. Previous work has demonstrated the feasibility of a robotic probe to 3-D-print biological tissues via a minor incision. This same probe could also 3-D-print implantable antennas as long as a suitable conductive material is identified in terms of conductivity, printability, biocompatibility, and ability to cure at room/body temperature for safety purposes. We assess the frequency-dependent conductivity of this biomaterial and explore the radio frequency (RF) performance of resulting antennas operating in free space and inside tissue-emulating phantoms. Results show that PEDOT:PSS biomaterials with 21% and 30% PEGDA concentration exhibit a conductivity of
$\sim 10^{4}$
S/m up to 5 GHz, suitable for wireless implants. Comparing the two, 21% PEGDA content exhibits poorer curing abilities, while 30% PEGDA exhibits slightly lower conductivity. Measurements for 2.4 GHz free-space dipoles conducted in an anechoic chamber reveal only
$\sim $
0.8 and
$\sim $
1 dB lower gain for PEDOT:PSS:21% PEGDA and PEDOT:PSS:30% PEGDA biomaterial, respectively, as compared to their copper counterpart. For a 5 mm-deep implanted patch antenna, these two biomaterials exhibit 3.05 and 3.84 dB higher transmission loss than copper, respectively. If deemed necessary, this performance degradation can be overcome by increasing the overall antenna size since the printing process is now minimally invasive and miniaturization requirements can be relaxed.