In vitro study of poly(ethylene terephthalate) implants for long-term durability

Abstract

In vitro investigation was carried out using two loading conditions (applied and pre-loading) and three aqueous chemicals to study the in vivo formation of longitudinal and circumferential cracks in poly(ethylene terephthalate) or PET implants. Scanning electron microscopy determined that in vivo formation of longitudinal cracks can be detected by treating the PET with aqueous NaOH in relaxed and loading conditions; both longitudinal and circumferential cracks can be detected by treating the PET with aqueous NaOH under applied and pre-loading conditions above the yield load. The detected longitudinal and circumferential cracks were similar to those found in PET implants in vivo. Treatments using acid and ammonium hydroxide did not produce any longitudinal or circumferential cracks either in relaxed (zero load) or applied loading conditions. The calculated lifetime was approximately 50 years under zero applied loading conditions and pH of 10–11. The major contributing factor for the premature rupture of medical-grade PET implants resulting in numerous human deaths was physiological load.

Degradation of Polyesters in Medical Applications

“…Weight loss (%) and Mechanical properties: Table 9. Effect of residual stress (pre-loaded samples) in alkaline environment on PET weight loss (%), breaking load loss (%), and surface characteristics [82].…”

“…Table 11. Weight loss (%), breaking load loss (%), and surface characteristics of the NH4OH treated samples in relaxed and applied loading condition [82] a :concentration of NH4OH:2%; b : concentration of NH4OH:5%; treatment time:120 days. c :breaking load value in cN.…”

“…Since it is evident that the surface defects can be detected by treating PET with NaOH in relaxed and applied loading conditions, further investigations were carried out to find out whether residual stressing condition, which can be exist in the implant while in the human body, could be responsible for the formation of cracks. The residual stressing condition is created in the polyester by 'pre-loading' the PET samples [82] and then treating with alkaline solution in relaxed condition. This pre-loading condition creates residual stress in the samples.…”

“…Micrograph of pre-stressed sample (pre-stressed for 48 hours) treated with 10% NaOH in relaxed condition, 40°C for 96 hours[82].…”