In vitro study of the mechanical performance of hernia mesh under cyclic loading.

The use of prostheses for hernia surgery, made from synthetic polymers may lead to development of postoperative complications. The reason for this can be the mismatch of the mechanical properties of meshes and the loads acting on them. The aim of this work was to investigate the behavior of 3 different hernia meshes under in vitro simulated physiological conditions followed by cyclic loadings. Meshes, Ultrapro (poliglecaprone and polypropylene), Dynamesh (polyvinylidenefluoride) and Surgipro (polypropylene) were selected. For in vitro degradation test, samples were kept in alkaline and acid mediums at 37 °C during 42 and 90 days and analyzed in terms of their weight loss and thickness changes. This was followed by cyclic loading in three increasing load stages. The greatest weight loss and thickness reduction were suffered by Ultrapro mesh. The mesh showed pH independent characteristics. Surgipro mesh had pH independent behavior due to the degradation process, with slight weight loss and thickness reduction. The degradation mechanism of Dynamesh is highly dependent on the pH, with acid surrounding medium acting as a degradation catalyst. Mechanical hysteresis was observed in all three meshes. The larger deformations occurred in Surgipro (25%); necking phenomenon was also observed. The deformation of Dynamesh was 22%, the mesh unweaves under applied load and was unable to withstand the third period of cyclic loads. Ultrapro mesh exhibits the lowest level of deformation (10%). Despite the different compositions and architectures of the meshes, all three underwent permanent plastic deformation, which will induce decreased mesh flexibility over time.

In vitro degradation of polydimethylsiloxanes in breast implant applications.

BACKGROUND: The durability of breast implant material is associated with failure probability, increasing with time from implantation. The current study avoided the bias introduced by biological factors, to systematically investigate the degradation over time of shell materials. The same fundamental physical and chemical conditions were maintained (temperature and pH) throughout the study, to decouple biological aspects from the degradation process. METHODS: Six virgin implants of 2 brands were submitted to the in vitro degradation process, mechanical testing of shell materials, surface change analysis (via scanning electron microscopy [SEM]) and chemical composition analysis by Fourier transform infrared (FTIR) spectroscopy. RESULTS: FTIR results showed that the principal chemical bonds of the material remained intact after 12 weeks of degradation. Apparently the implants' shell structures remained unchanged. Despite this observation, there were statistically significant differences between strain at failure at different time points for the shells of both brands, translated into a stiffening of the material over time. CONCLUSIONS: Material stiffening is reported as an indicator of material degradation. This altered mechanical behavior, added to the mechanical friction from tissue-tissue and tissue-implant contact and to the external mechanical loading (physical activity), may alter the material performance in women's bodies. Ultimately these changes may affect the implants' durability. Further work is needed to understand the biological aspects of the degradation process and their impact on implant durability.

Mechanical Performance of Poly Implant Prosthesis (PIP) Breast Implants: A Comparative Study.

BACKGROUND: There is societal concern regarding potential health problems associated with breast implants. Much of this distrust climate was a reaction to the Poly Implant Prosthesis (PIP) scandal. Studying the mechanisms of implant rupture is an important step for their improvement. The mechanical behaviour of breast implant shells was studied on explanted and virgin implants. Implants from both PIP and another brand (brand X), currently in the market, were considered. METHODS: To study the mechanical behaviour of the shell, a total of 940 samples from 11 explants and 5 control implants were analysed. The experimental protocol follows the ISO standards for shell integrity and determination of tensile stress-strain properties. Pearson correlation analyses and the multi-factor ANOVA statistical tests were performed using mechanical test data. RESULTS: Both PIP control and explants had significant variations of stress (P = 0.0001) and shell thickness (P = 0.000) throughout the implant. The stress was directly related to shell thickness. Shell thickness varied significantly for PIP implants, exceeding the manufacturer's specifications. Regarding the other brand, thickness variation was within manufacturer's specifications. CONCLUSIONS: The heterogeneous nature of PIP implants was confirmed. The implant shell thickness should be considered as a relevant parameter during the manufacturing process, for quality control purposes. These results may contribute to dispel mistrust and doubt surrounding breast implants, among the medical community and patients. LEVEL OF EVIDENCE III: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Biomechanical properties of breast tissue, a state-of-the-art review.

This paper reviews the existing literature on the tests used to determine the mechanical properties of women breast tissues (fat, glandular and tumour tissue) as well as the different values of these properties. The knowledge of the mechanical properties of breast tissue is important for cancer detection, study and planning of surgical procedures such as surgical breast reconstruction using pre-surgical methods and improving the interpretation of clinical tests. Based on the data collected from the analysed studies, some important conclusions were achieved: (1) the Young's modulus of breast tissues is highly dependent on the tissue preload compression level, and (2) the results of these studies clearly indicate a wide variation in moduli not only among different types of tissue but also within each type of tissue. These differences were most evident in normal fat and fibroglandular tissues.