In vivo evaluation of polyurethanes based on novel macrodiols and MDI

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Biomedical Engineering

Background:

• Polyurethane elastomers are widely used in biomedical applications.
• Environmental stress cracking (ESC) is a major failure mode for implanted polyurethanes.
• Developing polyurethanes with enhanced ESC resistance is critical for device longevity.

Purpose of the Study:

• To synthesize and evaluate novel polyurethane elastomers for improved resistance to environmental stress cracking.
• To compare the ESC performance of novel polyurethanes against established commercial materials under simulated physiological conditions.

Main Methods:

• Synthesis of novel polyurethane elastomers using methylenediphenyl diisocyanate, 1,4-butanediol, and varying macrodiols (poly(hexamethylene oxide), poly(octamethylene oxide), poly(decamethylene oxide)).
• Subcutaneous implantation in sheep for 3 and 6 months, with specimens subjected to 250% strain (3 months) or no strain (6 months).
• Scanning Electron Microscopy (SEM) examination of explanted specimens to assess stress cracking and material degradation.

Main Results:

• Novel polyurethane elastomers exhibited significant resistance to environmental stress cracking.
• Commercial polyurethanes (Pellethane 2363-80A, Biomer, Tecoflex EG-80A) showed substantial stress cracking under identical conditions.
• Stress cracking was observed in Pellethane 2363-55D after 6 months of unstrained implantation.
• Changes in molecular weight and tensile properties did not reliably predict susceptibility to ESC.

Conclusions:

• The novel polyurethane elastomers offer a promising alternative to current materials due to their superior resistance to environmental stress cracking.
• These findings have implications for the design and selection of long-term implantable medical devices.
• Further research should explore the long-term performance and biocompatibility of these novel materials in vivo.