Abrasion and fatigue resistance of PDMS containing multiblock polyurethanes after accelerated water exposure at elevated temperature

Abstract

Segmented polyurethane multiblock polymers containing polydimethylsiloxane and polyether soft segments form tough and easily processed thermoplastic elastomers (PDMS-urethanes). Two commercially available examples, PurSil 35 (denoted as P35) and Elast-Eon E2A (denoted as E2A), were evaluated for abrasion and fatigue resistance after immersion in 85 °C buffered water for up to 80 weeks. We previously reported that water exposure in these experiments resulted in a molar mass reduction, where the kinetics of the hydrolysis reaction is supported by a straight forward Arrhenius analysis over a range of accelerated temperatures (37-85 °C). We also showed that the ultimate tensile properties of P35 and E2A were significantly compromised when the molar mass was reduced. Here, we show that the reduction in molar mass also correlated with a reduction in both the abrasion and fatigue resistance. The instantaneous wear rate of both P35 and E2A, when exposed to the reciprocating motion of an ethylene tetrafluoroethylene (ETFE) jacketed cable, increased with the inverse of the number averaged molar mass (1/Mn). Both materials showed a change in the wear surface when the number-averaged molar mass was reduced to ≈ 16 kg/mole, where a smooth wear surface transitioned to a 'spalling-like' pattern, leaving the wear surface with ≈ 0.3 mm cracks that propagated beyond the contact surface. The fatigue crack growth rate for P35 and E2A also increased in proportion to 1/Mn, after the molar mass was reduced below a critical value of ≈30 kg/mole. Interestingly, this critical molar mass coincided with that at which the single cycle stress-strain response changed from strain hardening to strain softening. The changes in both abrasion and fatigue resistance, key predictors for long term reliability of cardiac leads, after exposure of this class of PDMS-urethanes to water suggests that these materials are susceptible to mechanical compromise in vivo.

Hydrolytically stable polyurethanes

“…The molecular weight of PUs is an important predictor of mechanical properties and performance. According to Chaffin et al, above a critical molecular weight ( M c ) of ∼30,000 g mol −1 the properties of PUs are independent of molecular weight, while below this M c PUs exhibit poor abrasion and fatigue resistance, and accelerated rate of crack growth. Thus, the fact that the M n of the PIB‐based PU was comfortably above M c = 30,000 g mol −1 , and that it remained unchanged for 10 weeks under accelerated hydrolytic test conditions, likely indicates that this material may be suitable for long‐term implantation in vivo .…”

User-reported abrasion-related lead failure is more common with durata compared to other implantable cardiac defibrillator leads

“…This is intended to maintain the strength and structural integrity of the polyurethane, while avoiding the progressive stiffness and cracking that can occur with metal ion oxidation. Optim, however, does demonstrate time and temperature dependent and hydrolytic damage 16,17 . This causes a progressive reduction in molar mass due to shorting of polymer chain length in vivo.…”

Outstanding cavitation erosion resistance of hydrophobic polydimethylsiloxane‐based polyurethane coatings

“…It has high strength, high elongation, fatigue resistance, and good adhesion. However, few studies have applied PU elastomers in the field of cavitation protective coatings, especially hydrophobic PU coatings . Because PU is apt to absorb water and has poor water resistance, it results in a decrease in coating adhesion and seriously restricts the anticavitation performance of the elastomer.…”

“…However, few studies have applied PU elastomers in the field of cavitation protective coatings, especially hydrophobic PU coatings. [19][20][21][22] Because PU is apt to absorb water and has poor water resistance, it results in a decrease in coating adhesion and seriously restricts the anticavitation performance of the elastomer. At present, there are two methods to solve the PU water resistance: one is to increase the waterproof performance of the coating by adjusting the crosslink density of the PU, the other is to enhance water repellency by introducing fluorine or silicon-containing segments.…”