Effect of accelerated aging on the viscoelastic properties of a medical grade silicone

Abstract

The viscoelastic properties of cylinders (diameter 5 mm, height 2.2 ± 0.2 mm) of Nagor silicone elastomer of medium hardness, were investigated before and after the specimens had undergone accelerated aging in saline solution at 70°C for 38, 76 and 114 days (to simulate aging at 37°C, for 1, 2 and 3 years, respectively). All sets of specimens were immersed in physiological saline solution at 37°C during testing and the properties were measured using dynamic mechanical analysis (DMA). A sinusoidal cyclic compression of 40 N ± 5 N was applied over a frequency range, f, of 0.02-25 Hz. Values of the storage, E', and loss, E″, moduli were found to depend on f; the dependence of E' or E″ on the logarithm (base 10) of f was represented by a second-order polynomial. After accelerated aging, the E' and E″ values did not increase significantly (p<0.05). Furthermore, scanning electron microscopy (SEM) showed that accelerated aging did not affect the surface morphology of silicone. Attenuated total reflectance Fourier transform infra-red spectroscopy (ATR-FTIR) showed that accelerated aging had a negligible effect on the surface chemical structures of the material. Differential scanning calorimetry (DSC) showed no changes to the bulk properties of silicone, following accelerated aging.

Influence of Aging, Sterilization, and Composition on the Degradation of Polyurethane Foams

“…Accelerated aging is a commonly used technique to determine the appropriate shelf life of a material. Often, physical changes in the material are measured throughout aging, such as colorimetric changes [21][22][23][24], changes in mechanical strength or integrity [25][26][27][28][29][30][31][32], or thermomechanical changes in the glass transition or melting temperatures [27,33]. Additionally, chemical changes can be measured using FTIR and/or mass spectroscopy.…”

Two-year performance study of porous, thermoset, shape memory polyurethanes intended for vascular medical devices

“…By contrast, medical grade silicone elastomeric cylinders did not display altered mechanical properties over the course of four months of accelerated age testing for the equivalent of three years. [9] However, in many of these cases the temperature used for accelerated aging was found to be more important than the duration of the test, at least out to approximately 12–36 months. [6] While factors such as strain, solvent, temperature, and environmental conditions can be tailored, a key focus of medical devices is long-term storage, which can be limited to thermal aging in a controlled environment [9–11].…”

Arterial pulse attenuation prediction using the decaying rate of a pressure wave in a viscoelastic material model

“…Several materials with medical applications, like polydimethylsiloxane (PDMS), popularly called silicone or polytetrafluoroethylene (PTFE), popularly called Teflon, show viscoelastic behavior (Calvo Aguilar 2013 ; Mahomed et al. 2015 ). These materials are inert and non-degradable, but their mechanical properties are very different to those of healthy arteries.…”

“…PTFE and especially PDMS (Mahomed et al. 2015 ) are significantly stiffer than arteries (Clough et al. 2015 ; Bijnens et al.…”

“…Several materials with medical applications, like polydimethylsiloxane (PDMS, silicone) or polytetrafluoroethylene (PTFE), show viscoelastic behavior (Calvo Aguilar 2013 ; Mahomed et al. 2015 ). These materials, widely used in many medical devices, vary the vessel stiffness and affect the propagation of blood pulses.…”