Clarence J. Wolf

Biodurability of retrieved silicone gel breast implants.

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.

Variability in the properties of silicone gel breast implants.

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.)

In vivo aging characteristics of silicone gel breast implants compared to lot-matched controls.

&NA; 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 noncross‐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 lotmatched 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 worlds largest known inventory of explanted breast implants with lot‐matched controls. (Plast. Reconstr. Surg. 109: 1927, 2002.)

Scanning electron microscopy characterization of surgical instrument damage to breast implants.

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. (Plast. Reconstr. Surg. 108: 52, 2001.)

Stress-enhanced transport of toluene in poly aryl ether ether ketone (PEEK)

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.

Mechanical Analysis of Explanted Saline-filled Breast Implants Exposed to Betadine Pocket Irrigation

BACKGROUND Because of concerns that exposure to povidone-iodine (Betadine) may lead to early breast implant failure, the Food and Drug Administration announced in 2000 that any contact between implants and Betadine is contraindicated. The evidence cited by the Food and Drug Administration primarily referred to Betadine added to saline implant filler solution and not to povidone-iodine used for pocket irrigation. OBJECTIVE Thirteen explanted Mentor saline solution-filled devices that had been exposed to Betadine pocket irrigation during implantation were studied for any loss of implant shell integrity. METHODS The 13 explants had been in place 1 week to 55 months, and none had intraluminal Betadine exposure. Twelve of the 13 explants were intact when removed, and one had leaked through the anterior valve. All were examined for any signs of patch-shell delamination. The mechanical properties of tensile strength, percent elongation, force-to-break, tear resistance, and patch bond strength were also measured. RESULTS No shell delamination or disruption of the sealing patch bond was found in any of the 13 explants placed in Betadine-irrigated pockets. In addition, the measured mechanical properties of the explants exceeded American Society for Testing and Materials requirements, with the exception of the textured explants (n = 2), which failed to meet the minimum elongation standards. CONCLUSIONS We found no evidence of patch or shell delamination in Mentor implants that had extraluminal contact with Betadine irrigation and were later explanted. We believe that the lower mechanical properties of the two textured implants are probably related to the texturing process rather than to Betadine pocket irritation. (Aesthetic Surg J 2002;22:438-445.).

Effect of surgical insertion on the local shell properties of SILASTIC II silicone gel breast implants.

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®II gel-filled implants. In the earlier study, the mechanical properties of 34 Dow Corning SILASTIC®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 surgeons fingers forced the implant through the incision. Our results indicate that the implant shell can be locally damaged due to the implantation process.

Effect of Implantation Surgery on the Strength Properties of Silastic® II Silicone Gel Breast Implants☆☆☆★★★

Abstract Background: The causes of silicone gel–filled breast implant rupture are uncertain, and little research has been directed toward characterizing or quantifying the multiple factors that may contribute to device failure. Breast implants are subjected to some degree of stress and deformation during the surgical procedures of insertion. Thus implantation surgery itself could be a factor in affecting the durability of breast implants. Objective: The purpose of this study was to investigate whether the surgical procedure of insertion affects the mechanical properties of the silicone elastomer shell of gel–filled implants. We wanted to determine whether the procedure of inserting a breast implant might cause a decrease in the strength properties of the shell. Methods: Thirty-four Silastic ® II gel–filled breast implants manufactured by Dow Corning were tested. All implants were from the same lot and had a volume of 300 cc. Twenty of 34 implants were tested without implantation to investigate variability within a lot and establish a baseline of control data for comparison with implanted implants. Fourteen of the 34 implants were implanted through an inframammary incision in the right breast of a cadaver. The effect of implantation surgery was investigated by comparing the mechanical properties of the anterior and posterior sides of the cadaver explants with those of the controls. Results: Statistical analysis of the data indicated that the mechanical properties of elongation and tear resistance were essentially unaffected by implantation surgery. However, the average tensile strength of the explants was reduced 4.9% to 6.2% (for shells extracted with hexane and unextracted shells, respectively) compared with the controls. Breaking energy averages for the explants were also reduced 7.8% to 5.9% (for extracted and unextracted shells, respectively) when compared with the controls and average moduli decreased by a similar magnitude. Conclusions: The surgical procedure of implanting a breast implant has a small but statistically significant effect on the average strength properties of the elastomer shell of the implant. It is unlikely that this small reduction is sufficient to be a factor in implant durability.

Analysis of Two Dow Corning Breast Implants Removed After 28 Years of Implantation

A pair of intact silicone gel breast implants that had been implanted for 28 years was analyzed after surgical removal in 1997 because of severe capsular contracture and heavily calcified capsules. The implants, manufactured by Dow Corning Corporation, were seamless, teardrop-shaped Cronin style (Silastic® 0) with Dacron® fixation patches. To determine the effects of long-term implantation, the material properties of tensile strength, elongation, tear resistance, 200% modulus, 400% modulus, and cross-link density were measured and found to be within the minimum-to-maximum range of properties for control implants of this type. This analysis indicates there was little or no large-scale material degradation of the elastomer shells after 28 years of implantation. Scanning electron microscopy examination of the shells was also performed and revealed that one implant wall had a defect caused by a scalpel cut accidentally induced at the time of explantation. The other explant had a very small area containing an unusual abrasion pattern of unknown origin. Otherwise, the surface structure of the 28-year-old explants showed no significant signs of wear, abrasion, or other indications of elastomer degradation. It may be true that breast implants are more likely to fail over time. However, our analysis of these implants indicates that these particular silicone shells showed no significant degradation after 28 years of implantation.

The effect of cyclic swelling (octamethylcyclotetrasiloxane) on the physical properties of silicone breast implant shells.

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.