The specific example shown, polydimethylsiloxane PDMS , is the most common polysiloxane [4]. PDMS is an oily, sticky liquid with a viscosity that increases as the average chain length molecular weight is increased. This is the siloxane used to form both the silicone rubber and the silicone gel used in breast implants. Other organic groups can be attached instead of methyl to produce other siloxanes with other properties.
Source: Wikimedia Commons. PDMS is the basis for the both breast implant silicone gel and the silicone rubber sac or shell which contains the gel. The molecular weight of PDMS or any polymer is an average, and thus some PDMS molecules will be far shorter than the average — or even cyclic rather than linear. This is important to the behaviour of PDMS in breast implant gels as discussed later.
Silicones can be liquids, gels, elastomers rubbers and even hard plastics. Production of silicones starts with sand fig. The siloxane backbone, due to its large bond angles and bond lengths fig. As a result all silicones are rubbery to varying extents.
Liquid PDMS also has especially peculiar mechanical properties. It runs and flows if poured slowly, and spreads under the influence of gravity. However, if deformed rapidly, the flexible polymer chains easily become entangled. As a result viscous forms of PDMS can be molded by hand into a ball — which will bounce if thrown against a hard surface. The inorganic siloxane backbone also causes silicones and silicone-based materials to have other special properties.
Although the -Si-O- linkage is flexible, it is extremely chemically stable, as is the bond between Si and O in quartz mineral silica, SiO 2.
Thus silicones can be viewed as liquid or solid polymeric materials which have some properties of ceramics. These include:. For medical use, a consequence of thermal stability and resistance to chemical attack is that many silicone-based materials e.
Silicone breast implant shells are filled with either saline solution fig. The general consensus is that post-surgical mechanical behaviour of implants filled with silicone gel is more like natural breast tissue [5]. Gels are defined as substantially cross-linked material systems, usually comprised of polymers liquid or solid.
Cross linking means that many of the starting units of the gel e. As a result, true gels exhibit no flow as long as their structure is intact [6]. Also, if a true gel is deformed by a non-damaging load, and the load is released, the gel specimen will in time return to its original dimensions.
Flow chart of the process — starting with sand — for making siloxane-based materials, including silicone rubber and silicone gel used in breast implants. Three-dimensional representation of polydimethylsiloxane molecular structure. When a polymer is described as cross-linked, it means a given batch of material has been exposed to a cross-linking method [7].
It does not mean that every molecule is cross linked or that cross-linking is uniform. This is a crucial factor in the behaviour of PDMS breast implant gels. The degree of cross linking is usually controllable, and increased cross-linking results in materials — including gels — which are stronger and stiffer. Breast implants containing PDMS gels have been produced since the s, and over the years gels with different amounts of cross-linking — and thus different properties — have been used [5].
PDMS gels with lower amounts of cross-linking may not strictly be gels but instead just rather viscous liquids. Also, their small size means that they can disperse through body tissues with relative ease.
Increasing cross-linking of PDMS decreases the amount of these molecules that are free. In general, the latest generation of PDMS breast implant gels are more highly cross-linked, thus minimising the amount of free low molecular weight molecules available to pass into the surrounding tissues through the silicone rubber shell [5]. However, even with the latest generation implants, low molecular weight PDMS molecules have been found in the breast tissues of implanted persons — even when the silicone rubber shell is intact [9].
In addition to low molecular weight PDMS, silicone gels can contain trace amounts of platinum — present because platinum is used as a catalyst to promote PDMS cross linking [1]. Platinum in amounts significantly greater than controls has also been found in the breast tissues of women with silicone rubber shells which are intact [9].
It is certainly conservative and appropriate to minimise the dispersion of foreign materials into the body from implants of any kind — except drug delivery devices.
Also specific concerns have been voiced that low molecular weight PDMS — especially cyclic molecules — might mimic estrogens or CNS-active drugs [8]. In addition platinum can evoke toxic responses [10]. For example, cisplatin cis -PtCl 2 NH 3 2 , used in tumor chemotherapy, damages numerous types of non-tumorous cells. Silicon sic rubber is a misnomer for silicone rubber , and the misuse appears in the media and even journal publications.
The misuse should be avoided as there are industrial silicon rubbers elastomers filled with silicon particles [11]. The terms rubber and elastomer are generally interchangeable. Silicone rubber breast implant shell, to be filled with saline during surgery. In-situ filling allows for custom volume adjustment. If later e. The exceptional flexibility and extensibility of certain formulations of PDMS silicone rubber compared to organic rubbers contribute along with silicone gel to the overall ability of these implants to mechanically mimic breast tissue [5, 13].
Silicone rubbers were first formulated ca. The purpose was to create flexible electrical insulating materials with high resistance to degradation at elevated temperatures or in hostile chemical environments. Thus it was the flexibility of the -Si-O-Si- linkage combined with its ceramic-like properties that made silicone elastomers attractive compared to most organic-based rubber insulators.
PDMS silicone rubbers are thus an old technology. Even their clinical use in breast implants dates back to the s [2].
Since the technology is an old one, there are few recent journal papers devoted to mechanical and physical properties of PDMS silicone rubbers — except when proposed for some new use: for example in when PDMS rubbers was considered for use in creating micro-machined chemical sensors [14]. Besides providing a highly stable, flexible insulating material for use in chemical sensors, PDMS silicone rubbers were advantageous because of another property — high gas permeability.
This also makes them attractive for contact lens and blood oxyenator applications. This filler increases strength, tear-resistance and the amount the rubber can be stretched under tension before failure. After adding the particles, a PDMS silicone rubber is then formed by chemically cross-linking the formulation to various extents and in various ways.
Thus PDMS silicone rubbers can have a wide range of structures and properties. Finally, while it is possible to buy finished PDMS silicone rubber stock e. The cross-linked, finished PDMS rubber in breast implants is created from liquid components during formation of the shell. Breast implants are either saline-filled or silicone gel-filled. Both types of implants have a silicone outer shell.
For patients with silicone gel-filled breast implants, it is recommended that they obtain an MRI screening for silent rupture three years after implantation and every two years afterward. A silent rupture is the leakage of silicone from the implant into the tissue that forms around the implant. A ruptured silicone breast implant can cause breast pain or changes in the shape of the breast.
The risks for silicone and saline breast implants are similar. To correct some of these complications, additional surgery may be required. The FDA notes that breast implants are not meant to last a lifetime, and the longer you have them, the more likely it is that you will need surgery to remove or replace them. The FDA issued a safety update in and said silicone gel breast implants are reasonably safe when used as labeled.
Systematic reviews of the safety of silicone breast implants show that there are few randomized controlled trials RCT that are of good quality to assess. This is despite the huge numbers of women who get silicone breast implants either for breast reconstruction or for breast augmentation. One review published in the Annals of Internal Medicine concluded, "The evidence remains inconclusive about any association between silicone gel implants and long-term health outcomes. Better evidence is needed from existing large studies, which can be reanalyzed to clarify the strength of associations between silicone gel implants and health outcomes.
The Cochrane Database of Systematic Reviews review of whether there was a difference in outcomes between saline-filled and silicone-filled breast implants for breast reconstruction likewise found they didn't have enough evidence to draw conclusions or for surgeons to properly advise women about which was best, "Despite the central role of breast reconstruction in women with breast cancer, the best implants to use in reconstructive surgery have been studied rarely in the context of RCTs.
Furthermore, the quality of these studies and the overall evidence they provide is largely unsatisfactory. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. The procedure is carried out at a doctor's rooms. The length of time will depend on what corrections are being made.
Silicone implants are considered to be permanent. However, as the body ages and thinning of the skin occurs, the implant may start to show through and you may be able to feel it. In addition, there is always the possibility of infection even years after implantation. Because silicone implants do not integrate with the skin tissue and they are encapsulated within scar tissue, their removal is relatively easy compared with other implant types.
Silicone implants are usually well tolerated. Correcting any of these complications might require additional surgery, either to remove or replace the implants. In addition, with certain breast implants there is a low risk of developing a type of cancer known as breast implant-associated anaplastic large cell lymphoma BIA-ALCL. Implants with textured silicone and polyurethane outer shells seem to have the highest risk.
Although this type of cancer occurs in the breast tissue, it isn't breast cancer. It might require treatment with surgery, radiation and chemotherapy. If an implant ruptures, the approach might vary depending on whether the implant is saline or silicone.
If a saline breast implant ruptures, the implant will deflate — causing the affected breast to change in size and shape. Your body will absorb the leaking saline solution without health risks, but you'll probably need surgery to remove the silicone shell.
If you want, a new implant can likely be inserted at the same time. If a silicone breast implant ruptures, you might not notice right away — or ever — because any free silicone tends to remain trapped in the fibrous tissue capsule that forms around the implant. This is known as a silent rupture. Leaking silicone gel isn't thought to cause health problems, such as breast cancer, reproductive problems or rheumatoid arthritis.
Still, a ruptured silicone breast implant might eventually cause breast pain, breast thickening, or changes in the contour or shape of the breast. If this happens, your doctor will likely recommend surgical removal of the implant. If you want a new implant, it can usually be inserted at the same time.
Both saline and silicone breast implants are considered safe for breast augmentation and breast reconstruction. Research on the safety and effectiveness of both types of implants is ongoing. If you're thinking about breast augmentation or reconstruction, it's important to understand what it means to have breast implants. In addition to changing your appearance, keep in mind:.
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