Mechanical properties of silicon breast implants

Breast augmentation with silicone implants is one of the most common aesthetic procedures. Rupture of the implant is the main reason for repeated surgery and for the removal of the implant. The aim of the study is to investigate the changes in toughness and deformability of the shell of breast implants leading to their rupture depending on the conditions of mechanical loading. The methods of continuum mechanics utilized to model the behavior of elastomers are used. Cyclic stretching and cyclic stretching with increasing amplitude were performed on implant shells from different manufactures, and mechanical tests on Eurosilicone, Mentor and Motiva implant shells. The initial sections of the stress-strain curves up to 200 % are shown for the Mentor (8 year function), Eurosilicone (8 year function) and Motiva (2 year function) shells. The obtained experimental results are compared with the data for the unused (control) implant shell. The cyclic stretching test data show that, after the first elongation to a given strain, the implant shell softens and the next stress-strain curve is much lower than the first. At a strain greater than the previous strain, the stress-strain curve returns to the initial curve of the unstretched specimen. In the presence of microdamage, the shells of breast implants soften (Mul-lins effect), and the curves fall below the curve of the control test. It is shown that the implants lose some of their strength over time due to microdamage accumulation at systematic cyclic strain in the range of 100–130 %. At large deformations, the implant strength decreases significantly, and rupture of the implant can occur much earlier than its shelf life.