Development and characterization of silicone-based tissue phantoms for pulse oximeter performance testing

Pulse oximeter measurements are commonly relied upon for managing patient care and thus often require human testing before they can be legally marketed. Recent clinical studies have also identified disparities in their measurement of blood oxygen saturation by race or skin pigmentation.

The development of a reliable bench-top performance test method based on tissue-simulating phantoms has the potential to facilitate pre-market assessment and the development of more accurate and equitable devices. To generate phantoms capable of mimicking physical mechanisms and providing realistic results, customized tissue-mimicking materials (TMMs) are needed.

We focused on the development of channelized finger phantoms based on flexible silicone elastomers and their implementation in a pulsatile pressurized fluid network. Candidate TMMs were formulated to achieve a range of biologically relevant mechanical and optical properties by modifying components and curing protocols.

Our final optimized TMM had a Shore OO hardness of 32 and an elastic modulus of 130 kPa. TMM samples with sub-millimeter diameter channels exhibited compliance-increase in channel diameter with internal fluid pressure, as measured by optical coherence tomography-that was linearly dependent on internal pressure. Phantoms implemented in the pressurized network with an absorber-doped fluid and measured by a photoplethysmographic (PPG) sensor displayed tunable modulation levels ranging from 0.6% to 18.1% at 940 nm. Finally, we demonstrated that the system could be used to generate measurements in several clinical pulse oximeters and variations in PPG waveform could be produced by varying the simulated epidermal melanin content.

Overall, we provide significant insights into potential best practices for creating silicone-based tissue phantom tools for pulse oximetry performance testing.