Environmental stress cracking performance of polyether and PDMS-based polyurethanes in an in vitro oxidation model

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Medical Device Engineering

Background:

• Environmental stress cracking (ESC) is a critical failure mode for polyurethane-based medical devices, particularly cardiac leads.
• Optim™ (OPT), a polydimethylsiloxane-based polyurethane, is used clinically in cardiac leads, but its resistance to ESC requires evaluation.
• Existing polyether urethanes like Pellethane® (P80A and P55D) are susceptible to ESC, necessitating the development of more robust materials.

Purpose of the Study:

• To evaluate the in vitro environmental stress cracking (ESC) resistance of Optim™ (OPT) insulation.
• To compare the ESC performance of OPT against two industry-standard polyether urethanes (Pellethane® 80A and 55D).
• To identify optimal aging conditions for replicating ESC in vitro using a Zhao-type oxidation model.

Main Methods:

• Cardiac lead segments insulated with OPT, P80A, and P55D were subjected to a Zhao-type oxidation model.
• Samples were pretreated in human plasma and aged in oxidative solutions (NaCl, H2O2, CoCl2) under specific conditions.
• Visual inspection, Scanning Electron Microscopy (SEM), Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR), and molecular weight analysis were used to assess ESC and material degradation.

Main Results:

• Significant surface cracking consistent with ESC was observed on all P80A and P55D samples, with many exhibiting breaches.
• Seven of twenty OPT samples showed shallow surface cracking, indicating better ESC resistance than P80A and P55D.
• Molecular weight decreased significantly for P80A (86%) and P55D (56%), but less so for OPT (31%), confirming material degradation.

Conclusions:

• Optim™ (OPT) insulation demonstrates superior performance against environmental stress cracking (ESC) in vitro compared to Pellethane® 80A and 55D.
• The developed Zhao-type oxidation model, particularly with NaCl, H2O2, CoCl2, and glass wool, effectively replicates ESC.
• OPT's improved ESC resistance suggests its potential for enhanced durability in clinical applications like cardiac leads.