The environmental durability and useful life of a breast implant is of major concern to both the patient and the plastic surgery community. The influence of complex environmental factors, both chemical and physical effects, on the basic properties of breast implants are discussed in this chapter. A large variety of physical-analytical methods were used to determine what change, if any, occurred in a variety of implants prepared by several different manufactures over several generations of implant development. Implants explanted from patients after implantation periods as long as 32 years were directly compared to available control samples. Explants and controls were investigated by a broad combination of mechanical testing, chemical analysis, and scanning electron microscopy.

Breast implant strength and durability is presently an important topic in biomaterials science. Research studies are being conducted to determine the mechanisms and rates of failure in order to assess the in vivo performance of breast implants. Fatigue life is a measure of breast implant durability since fatigue failure is a potential in vivo failure mechanism. This study describes the characterization of the fracture surface morphology of breast implant shell regions that have failed due to cyclic fatigue. Saline breast implants were fatigue tested to failure using a laboratory apparatus in which flat plates cyclically compressed the implants. The implants were unimplanted control devices of both textured and smooth saline implants. The failure surfaces of the fatigued shells were examined using scanning electron microscopy (SEM). The morphological features of the failure surfaces are described for implants with short and long fatigue lifetimes. The details of both the inside and outside surfaces of the shell at the failure location are described. Two different modes of failure were observed in both the textured and smooth shells. These modes depend on the magnitude of the cyclic load and corresponding number of fatigue cycles at failure. The first mode is a tear in the shell of about 18 mm in length, and the second mode is a pinhole approximately 1 mm in diameter. Details of the surface morphology for these two types of failure modes and shell thickness data are presented herein. There was no significant change in the crosslink density of the shell as a result of fatigue.

This study analyzed the shells of single-lumen silicone gel breast implants within the general context of device durability in vivo. The investigation included the major types of gel-filled implants that were manufactured in the United States in a 30-year period. The implants analyzed were Cronin seamed (two explants and one control), Silastic 0 and Silastic I (18 explants and seven controls), and Silastic II (22 explants and 43 controls). The biodurability of the explants was investigated with measurements of the mechanical and chemical properties of the various types of silicone gel control and explanted shells, with implantation times ranging from 3 months to 32 years. The shell properties measured for the controls and explants included the stress-strain relationships, tensile strength, elongation, tear resistance, moduli, cross-link density, and amount of extractable material in the shell. In addition, the mechanical properties of shells that had been extracted with hexane were analyzed for both explants and control implants. The silicone gel explants investigated in this study included some of the oldest explants of the various major types that have been tested to date. For assessment of long-term implantation effects, the data obtained in this study were combined with all known data from other institutions on the various major types of gel implants. The study also addressed the failure mechanisms associated with silicone gel breast implants. The results of the study demonstrated that silicone gel implants have remained intact for 32 years in vivo and that degradation of the shell mechanical and chemical properties is not a primary mechanism for silicone gel breast implant failure.

The solubility and transport of toluene and carbon disulfide into amorphous and crystalline polyphenylene sulfide (PPS) was investigated. The rates of sorption, desorption, and resorption of both fluids were measured as a function of temperature. The sorption of these fluids into amorphous PPS produces a semi-crystalline material by solvent induced crystallinity (SIC). Although the rate of diffusion of carbon disulfide (CS2) into crystalline PPS, (produced either thermally or by SIC), is several orders of magnitude slower than that observed in amorphous PPS, the solubility is only slightly reduced, by approximately 10%. The PPS films exhibit highly stressed surface regions that rapidly sorb the penetrant. Thermal annealing at temperatures as high as 100degreesC (note T-S of PPS is 85degreesC) has little or no effect on the surface stress, the diffusion process or the solubility of toluene into PPS. In addition to SIC, PPS undergoes cold crystallization at 130degrees-140degreesC; however, the degree of crystallinity induced by cold crystallization is approximately 60% of that formed by cooling from the melt. (C) 2003 Wiley Periodicals, Inc.

A study was conducted to investigate the effect of in vivo aging on the physical, mechanical, and chemical properties of Silastic II gel-filled breast implants. In the study, the properties of 16 Silastic II gel-filled explants (retrieved from eight patients), with in vivo duration times ranging from 4 months to 13 years, were compared with lot-matched control (unimplanted) samples. Tensile and tear strength properties were measured for both explant and control shells by using identical testing protocols. The tensile strength properties of shells, which were extracted with hexane to remove non-cross-linked silicones, were also measured. Swelling measurements were used to determine the average molecular weight between cross-links (or entanglements). In addition, scanning electron microscopy was applied in the comparison of the morphological features of the explants and their lot-matched controls. The results of the study suggest that the silicone polymer used to fabricate the shells does not undergo appreciable degradation for up to 13 years in vivo. The study represents an investigation of the world's largest known inventory of explanted breast implants with lot-matched controls.

Changes in the physical and mechanical properties of silica filled silicone elastomeric films were studied as a function of repeated sorption extraction cycling. The sorption of octamethylcyclotetrasiloxane (D4) on the properties of three silicone filled elastomeric films was analyzed. Two of the films, SILASTIC®I and SILASTIC®II, were shells of explanted breast implants and the third, a calendered film, prepared with similar composition to the elastomer used for the breast prosthesis were studied. The as-received (AR) SILASTIC®I and II films contained 20 and 26.5 wt% non-cross-linked material that was removed by extraction with hexane. The failure properties of the extracted films are significantly higher than those of the AR films. The amount of swelling, weight gain, volumetric change, and the stress- and strain-to-fail of the films were measured in the as-received condition, and after a series of extractions and swellings. Repeated cycling (up to 5 cycles) of extraction-swelling had essentially no effect on the failure properties of films when all the diluent was removed. The effect of diluent on the failure properties of all three films was quite large. The stress-to fail of the swollen film was reduced a factor of 6 compared to baseline extracted samples while the corresponding strain values were reduced a factor of 5. The energy to fail of the swollen compared to baseline films was reduced almost a factor of 50. However, the overall mechanical properties of the films are restored when the diluent was removed. The mechanical forces involved in the swelling process do not degrade the polymer even when cycled through five swell-extract cycles.

Several generations of silicone gel breast implants have been produced by implant manufacturers. The primary material usually viewed as the base material in the manufacture of implants is polydimethylsiloxane. Polymeric reactions are notorious for their variability and nonuniformity. The elastomer used in different types of implants can have vastly different properties. Furthermore, the material properties associated with a particular type of implant can vary considerably from one lot to the next. Considering the various designs, styles, and manufacturing techniques associated with silicone gel implants, knowledge of the original properties of the implants before implantation is important in determining the effects of aging in vivo. This study was conducted to investigate differences in key mechanical and chemical properties of silicone gel breast implant materials. The two types of implants chosen for analysis were Silastic I and Silastic II control implants. Material property data were determined for both types of controls and significant differences were found in their values. Lot‐to‐lot variability was also investigated and found to be significant. (Plast. Reconstr. Surg. 108: 647, 2001.)

The transport of octamethylcyclotetrasiloxane (D4), one of the major constituents of silicone fluids and rubbers, and low viscosity polydimethylsiloxane oil into a silica filled cross-linked silicone elastomeric rubber was measured as a function of temperature, cross-link density of the rubber, and concentration of the D4 in methanol solution. A small amount of material, approximately 3 wt%, is extracted from the rubber with hexane. The extraction process has a large effect upon D4 solubility in the rubber, increasing from approximately 160 to 180 wt% after extraction. The heats of solution for both penetrants into the rubber are essentially zero and the activation energies for diffusion are small, approximately 8 and 15 kJ mol-1 for D4 and PDMS, respectively. The diffusion process is Fickian and the diffusion coefficient of D4 into silicone/silica rubbers is essentially independent of concentration over the concentration investigated, i.e. from 1 to 100 vol% D4 in methanol. The permeability, i.e. the product of the diffusion coefficient and the solubility, decreases rapidly for D4 concentrations less than 50 vol% (0.1 mol fraction). This suggests that the permeation of D4 out of any encapsulation device, such as a silicone breast implant, is linearly dependent upon the concentration of D4 in the prosthesis. Swelling is isotropic and was measured by dimensional changes in rectangular samples and correlates well with the volume of D4 sorbed.

In this article, mechanisms of breast-implant failure caused by surgical instruments commonly used to perform implantation, breast biopsies, needle localization procedures, cyst aspirations, and explantation are described. Failure was artificially induced in breast-implant shells using various types of surgical instruments, including scalpels, suture needles, hypodermic needles, hemostats, and Adson forceps. Field-emission scanning electron microscopy (SEM) was used to document the morphology of the failure sites produced by these instruments. Micrographs were used to categorize failure according to a specific type of surgical instrument. SEM micrographs were also obtained on explants that failed in situ, and the morphology of the corresponding failure sites was examined. The study was designed to document a range of failure mechanisms associated with gel-filled, saline-filled, double-lumen (saline-gel), and soybean oil-filled implants. The results of the study also demonstrate that SEM can often be used to determine the cause of breast-implant failure.

A study was conducted to examine the physical, mechanical and chemical properties of composite (silicone/silica) breast implants as a function of implantation time. In the study the properties of SILASTC®II gel-filled explants with in vivo duration times ranging from 4 months to 10 years were compared to lot-matched control (unimplanted) samples. Tensile strength properties were measured for both explant and control shells using identical testing protocols. The tensile strength properties of shells which were extracted with hexane to remove non-cross linked silicones were also measured. In addition, swelling measurements were used to determine the average molecular weight between cross-links (and/or entanglements). The tensile strength properties obtained from the present study were correlated with implantation time. The results of the study suggest that the silicone elastomer shells do not undergo appreciable degradation during in vivo aging.

The reasons for the failure of silicone gel breast implants are unclear. One potential failure mechanism is the weakening of the implant shell during its insertion into the breast. Such local weakening could eventually lead to implant failure. We recently reported on the effect of implant surgery on the overall mechanical properties of SILASTIC(R)II gel-filled implants. In the earlier study, the mechanical properties of 34 Dow Coming SILASTIC(R)II gel-filled breast implants from the same manufacturing lot were measured. Twenty of the thirty four implants were not implanted but were evaluated to establish a baseline of control data. The other fourteen lot-matched implants were inserted into a subglandular pocket through an inframammary incision in a cadaver breast and then removed. The experimental augmentation scenario was designed to represent actual breast implantation as closely as possible. The mechanical properties of the anterior and posterior sides of the control implants (not implanted) and explants (implanted in a cadaver) were measured and compared to determine whether differences existed between the explant and control groups. We found that the implantation surgery process did slightly reduce the average tensile strength. Although not as statistically significant, other mechanical properties such as breaking energy and moduli were less for the explants than the controls. The reduction was a relatively small percentage in the context of overall shell properties. Elongation and tear resistance were unaffected. Our findings suggested that the surgical act of implanting a breast implant has a small but detectable weakening effect on the average tensile strength, breaking energy and moduli of the elastomeric shell of the device. The present study is an extension of the previous investigation. Here we have analyzed the explant shell region where the surgeon's fingers forced the implant through the incision. Our results indicate that the implant shell can be locally damaged due to the implantation process.

The sorption of water in poly(ether ether ketone) (PEEK) from aqueous solutions containing a small (5 x 10(-5) mol fraction) of three different surfactants was investigated as a function of external tensile stress. One of the surfactants, a polyoxyethylene alcohol, exhibited a strong stress effect, producing an increase in water solubility of nearly an order of magnitude for stress levels > 40 MPa in amorphous PEEK. The solubility and diffusion coefficient for the sorption of water into PEEK were also investigated. The critical stress (strain) for water sorption, the rate of wetting, and surface deformation morphology were determined. In these aqueous solutions, the primary factor affecting stress-enhanced sorption is a reduction in surface energy and associated surface mobility. (C) 1997 John Wiley & Sons, Inc.

The slow degradation or deterioration of a material due to the long-term effects of the environment are usually referred to as aging. Aging is an extremely complex process which may represent a myriad of physical and/or chemical processes. In polymeric materials the physical processes accompanying aging range from loss of additives, such as plasticizers or anti-oxidants to swelling by liquids. Chemical aging includes diverse phenomenon such as cross-linking, depolymerization, or reaction with environmental species, such as oxygen, to produce new or different compounds. The aging of silicones is of great interest, particularly with respect to changes which may occur in body implants during long-term implantation.

The transport of fluids in the semicrystalline polymer, poly(aryl ether ether ketone) (PEEK), was investigated. Both solubility and rate of penetration of toluene into PEEK are markedly increased by the application of an external stress. The induction period (i.e., the time for the sorption to begin) is a function of applied stress as well as temperature and crystallinity. At 22°C in 29% crystalline PEEK the induction period was reduced from more than 2000 h to approximately 10 h whereas the solubility of toluene was increased from 9 to 44 wt % upon the application of an external tensile stress of 30 MPa. A critical stress (i.e., a stress value below which the stress-enhanced effects are not observed) was determined. The critical stress is a strong function of crystallinity and temperature. © 1996 John Wiley & Sons, Inc.

The sorption/desorption of carbon disulfide into/from PEEK as a function of crystallinity and temperature was investigated. The sorption curves of carbon disulfide into PEEK show only two major regions: (a) an increase of penetrant weight with time, and (b) a limiting equilibrium value (solubility). This is in contrast to the sorption of toluene into PEEK which shows three regions. The solubility of carbon disulfide decreases with increasing crystallinity, but temperature has little effect on the solubility in the temperature range of 25-40 degrees C. An acceleration in penetration rate at the later stage of diffusion is observed for PEEK films whose crystallinity is greater than 13.4%, suggesting Supercase II diffusion. Carbon disulfide can be desorbed completely from PEEK in contrast to other fluids, such as toluene or methylene chloride, which are difficult to desorb. The normalized weight loss of carbon disulfide during desorption is an exponential function of square-root time. Solvent-induced crystallization was observed. Crystallinity was estimated from both the measured density and microhardness of the desorbed polymer and polymer which had undergone a sorption/desorption/resorption/desorption cycle. (C) 1996 John Wiley & Sons, Inc.

The absorption and swelling of poly(aryl-ether-ether-ketone) (PEEK) in toluene as a function of resin morphology and temperature in the range 35-95-degrees-C was investigated. In all cases the weight gain curves exhibit three characteristics: (1) an induction period, which is a strong function of both temperature and initial crystallinity, (2) a main absorption region, which is linear with square-root time, and (3) a final equilibrium value, namely, solubility. The solubility of amorphous PEEK decreases with temperature and the heat of solution is -0.93 kcal/mol. The induction period varies with the fourth power of the crystallinity and decreases with temperature with an apparent activation energy of 50 kcal/mol. The strength of the interaction between the crystalline regions is markedly reduced at temperatures greater than 80-degrees-C. Swelling accompanying the absorption of the toluene is highly anisotropic with most of the dimensional changes occurring in the thickness direction. The deswelling process, however, is essentially isotropic. The concentration of toluene in solution has a strong effect on the transport process; the equilibrium solubility of toluene in amorphous PEEK immersed in a toluene/iso-octane mixture is a linear function of toluene concentration; but the pseudo-diffusion coefficient for the absorption of toluene varies approximately with the fourth power of its concentration.

The amount and structure of the crystals formed by the solvent-induced crystallization (SIC) following a sorption-desorption cycle of five fluids (benzene, toluene, chloroform, methylene chloride, and carbon disulfide) in amorphous PEEK was determined by wide-angle x-ray scattering (WAXS). The SIC crystal structure was compared with that produced by thermal methods, both those formed at low temperature by heating the amorphous material 10-20-degrees-C above T(g) or by cooling from the melt. Although smaller in size, the SIC crystals are tighter and more organized than those produced thermally. The WAXS data indicates that all five fluids produce approximately 35% crystallinity in PEEK. Gravimetric data suggest that a low-density region, consisting of either microvoids or highly disordered amorphous region, surrounds the crystals.

A multidisciplinary spectroscopic evaluation of a commerical wire insulation based on a cross-linked copolymer of ethylene and tetrafluoroethylene (X-ETFE) was conducted to determine the chemical changes taking place during thermal aging. These studies provided insight into the roles of the various additives, such as triallylisocyanurate (TAIC) and antimony oxide, in the formulated X-ETFE insulation. During irradiation processing, a large fraction of the TAIC is converted to a cross-linked isocyanurate moiety; the unconverted TAIC is released during aging. Thermal aging of the X-ETFE wire insulations was performed in air at 200-degrees-C for up to 5 months and resulted in oxidation of the base ETFE, loss of unreacted TAIC, and a small amount of dehydrofluorination. The antimony oxide serves the multiple roles of flame retardant and scavenger for the pyrolytically generated hydrogen fluoride.

The absorption and subsequent desorption of benzene, toluene, carbon disulfide, and chloroform in amorphous and 27% crystalline poly(aryl-ether-ether-ketone) (PEEK) were determined. At 35-degrees-C, the equilibrium weight gain (solubility) of benzene, toluene, chloroform, and CS2 are 23.5, 19.8, 51.2, and 21.2 wt %, respectively. The initial weight gain is linear with root-time and pseudodiffusion constants for absorption into amorphous PEEK ranging from 0.35 to 9.85 X 10(-12) m2/s were calculated. The desorption processes are two-step and are controlled by the T(g) of the penetrant-resin mixture. The rate of diffusion into the crystalline material is extremely slow; crystalline PEEK reaches saturation (12.5 wt %) after immersion in CS2 (35-degrees-C) for several hundred hours but, even after 1300 h immersion, the other fluids do not reach saturation.