Silicone: A History of Uncertainty, a Future of Possibility
Tuesday, August 02, 2005
Chemical Properties of Silicone
Silicones are a large family of inert and inorganic compounds
that possess a repetitive backbone structure of oxygen and silicon,
the second-most abundant element in the world.
The term "siloxane" is an acronym for "silicon," "oxygen," and
"methane," and when put into long chains with additional organic
radicals, these polymers are referred to as "polyorganosiloxanes."
This latter group, and more specifically dimethyl polysiloxane
(DMPS), is one of the few "medical-grade" silicones that are
typically used by dermatologists for injection. Also known as
liquid injectable silicone (LIS), this material is injected into
facial soft tissue contour deformities by a specific microdroplet
technique that causes an immunologic and fibroblastic reaction that
leads to collagen deposition and capsule formation around each
droplet several weeks after implantation. Silicone, as opposed to
other currently popular soft tissue "fillers," is advantageous
because its collagen-producing effects are permanent.
The length of the silicon-oxygen backbone determines the
viscosity of the synthetic polymer, and thus an increase in the
polymer chain will increase the viscosity of the material. In
addition, the heat stability of the substance depends on the number
of attached carbon atoms, with a greater number of silicon-methyl
bonds making the material more heat stable. It is well known that
silicone can exist in solid, liquid, and gel forms, allowing for
its widespread functionality. The viscosity of silicone is
expressed in centistokes (cS), which is a unit of measure
representing kinematic viscosity. "Medical-grade" LIS used today is
typically 350cS of pure dimethylpolysiloxane fluid, in comparison
to the viscosity of water, which is equivalent to 1cS.
The electronic structure of the bonds in the silicon-oxygen
backbone allows for an increased bond angle length and thus the
formed material can move very freely - more so than if there was a
carbon-carbon backbone.1 This property, along with DMPS
being inexpensive, easily made, inert, inorganic, and easily
stored, makes its potential use very attractive to physicians.
Furthermore, when pure, this material is resistant to bacterial
growth on its surface. Other beneficial properties of silicone
include its mechanical resiliency, biocompatibility, and lack of
Risks of Silicone
However, silicone, and LIS more specifically, are not free of
risks. Both have experienced much scrutiny in the scientific and
lay communities due to a history riddled with unethical use,
improper technique, and anecdotal reports of horrific
Moreover, a sheer lack of scientific data regarding its efficacy
and adverse-effect profile has stifled this product's potential
therapeutic uses. It is true that there can be complications from
LIS, although most of these are inherent to the procedure or
related to the technique of the physician. Allergies, granulomas,
infections, and migration can occur, yet the most common side
effects of liquid silicone injections are minor and mostly
attributable to the ineptness of the physician performing the
procedure. These include transient erythema, pain, under- or
overcorrection, and asymmetry.
Nevertheless, in order to appreciate the possible future of
silicone, one must understand its controversial past.
History of Silicone
The grandfather of silicon, Frederic Stanley Kipping, was born
in Manchester, England, in 1863. At the turn of the century, he
became Chair of Chemistry at University College of Nottingham where
he pioneered the study of silicon and coined the term "silicone" to
describe a chemical reaction between a ketone and silicon.
Although his many papers on the subject were the cardinal
experiments addressing the newly discovered substance, he could not
appreciate an application for the material at that time. But it was
soon realized during the rubber shortage of World War II that these
silicones could be used as greases, water repellents, synthetic
rubbers, and hydraulic fluids. Researchers at Corning Glass Works
and Dow Chemicals eventually joined forces to form the Dow Corning
Corporation (Midland, MI) - the major supplier of silicone products
to the U.S. government during World War II as well as the major
researcher and manufacturer of silicones throughout the remainder
of the 20th century.
Unfortunately, Kipping died in 1949, and was not able to
appreciate the profound effect that silicone would eventually have
on the future of society.
When the war came to an end, a scientist for Dow Corning - R.R.
McGregor - began to investigate other uses for the silicones. These
included paints, polishes, and insulation, to name a
few.3 One of the first medical applications of silicone
at this time took advantage of its ability to prevent liquid from
adhering to glass by being used to coat blood-handling glassware
and penicillin bottles.4 With more investigation into
this material, scientists and physicians alike began to appreciate
the vast potential uses. In 1950, De Nicola performed the first
documented human silicone implant where a silicone urethra was
placed into a patient whose genitals were ravaged from venereal
Subsequently, other authors began noting their own experiences
with silicone. Holter, in 1955, developed a silicone implant for
use as a shunt to drain excess fluid in children with
hydrocephalus. Around this time, Dow Corning also set a precedent
by compounding the first silicone rubber made specifically for
medical use that eventually served as an artificial bile duct.
Throughout the latter half of the 20th century and
beginning of the 21st century, silicone continued to
play a pivotal role in many fields of medicine. Its biggest impact
has come in the fields of surgery, dermatology, ophthalmology,
gynecology, and urology. (See Tables 1-4.)
Many know of Cronin and Gerow and their development, in 1961, of
a bag-like prosthesis filled with silicone for the purpose of
breast augmentation.6 However, many may not be aware
that silicone breast augmentation was first experimented 2 decades
earlier by American soldiers in Japan. Dr. M. Sharon Webb documents
correspondence with American army officers who were in Japan during
World War II, and these men stated that officers administered
"cooling fluid" that contained silicone into the breasts of Asian
sex workers who desired a more Western appearance.7 It
seems that American physicians became aware of this unsanctioned
procedure as Asian patients arrived in the United States after the
war ended. Initially, the use of silicone for breast augmentation
remained a "black market" type of procedure, carried out by
non-scientific personnel to cater to the demands of women in the
As the years progressed, more women took to the practice of
having silicone injected into their breasts, and likewise, more
side effects of the practice were noted by the medical community.
Cystic lesions, mastitis, lumpy or rock-hard breasts, and severe
pain were among the many noted adverse reactions.8 It
has been argued that much of these sequelae were attributable to
the use of non-medical grade silicone in the breasts, the
adulterants within, and excessive amounts being
injected.9 However, the unsanctioned behavior of
injecting patients with "dirty" silicone and the subsequent side
effects precipitated an epidemic of fear and distrust regarding
silicone and its use in medicine. The state of Nevada ultimately
criminalized its use in 1964.
Silicone use for soft-tissue augmentation has never received
approval from the U.S. Food and Drug Administration (FDA). When Dow
Corning finally developed its first medical-grade silicone, MDX
4-4011, in the early 1970s, it opted not to gain FDA approval
because it "could not effectively prevent misuse of the
Clinical investigations of LIS, under FDA-approved and monitored
protocol, did take place from 1978 to 1988. Patients selected to be
studied had severe facial deformities and were also refractory to
other forms of treatment. The results were promising; however,
there was one report of massive facial necrosis in a patient who
had concomitant immunologic and infectious chronic inflammatory
diseases.11 Reports such as this, combined with the
knowledge that three New York physicians and one California
physician were injecting liquid silicone for facial wrinkles and
furrows, prompted the FDA to ban LIS in 1992.
The Microdroplet Technique and the Future of Silicone
It must be noted that the injections of massive amounts of
"dirty," adulterated silicone from over 40 years ago were much
different than the currently available pure forms of liquid
silicone. Furthermore, there are now guidelines for suggested sites
of injection, and when performed by responsible physicians this
allows for much safer use of the product. For example, lips and
breasts should not be injected with silicone.12
Areas that respond well to LIS include the nasolabial and
glabellar furrows as well as perioral lines.12
HIV-associated facial lipoatrophy has been another realm of success
for LIS where microdroplets are injected into the cheeks and
temples to restore the faces of patients damaged by the sequelae of
this infectious disease.13 Serial punctures injecting
small droplets of LIS into these depressed skin areas over the
course of multiple visits can lead to dramatic results. Not only
does the use of purified silicone in such small needles decrease
the pain associated with injection, but this microdroplet protocol
also prevents drifting or shifting of the injected liquid and
Drs. Benedetto and Lewis have described a specific protocol that
allows for easy and precise injection of LIS while minimizing the
common unwanted adverse effects.14 They have found that
the Becton Dickinson (Franklin Lakes, NJ) 3/10cc insulin U-100
syringe with a swaged 28-gauge 0.5-inch long Micro-Fine IV needle
is better than any other standard syringe for injecting controlled
microdroplets of LIS intradermally. Not only does the syringe allow
for better control, the swaged needle helps reduce inaccurate
dosing because there is no dead space between the hub and barrel.
Also, the shorter needle length reduces resistance to the flow of
the viscous fluid.
There are many variations of actual technique; however, most
dermatologists abide by a protocol similar to the following:
- After thoroughly cleansing and marking the areas to be injected
and positioning the lights to properly illuminate the facial
anatomy, needle punctures should be 2-4mm apart.
- No more than 0.01cc should be injected at each needle
- Finger pressure should also be applied immediately after
injection to reduce patient bruising.
- Topical anesthetic 45 minutes prior to injection can also be
added to this microdroplet technique for patient comfort.
- Visits for follow-up injections should be spaced at
approximately one-month intervals.
Medical-grade silicone used properly by the microdroplet
technique for filling defects such as facial furrows and wrinkles
is considered a very effective cosmetic procedure. Drs.
Duffy,9 Orentreich,15 and
Aronsohn16 adamantly state that they treated well over
100,000 patients safely and effectively with silicone over the
course of multiple decades. Dr. David Duffy defends the merits of
silicone and contends that "almost no good news regarding the
benefits of its use ever appears in the lay or scientific
Seeing that the potentially therapeutic uses of silicone could
be marred by its unsightly past, the American Society of
Dermatologic Surgery defended the product by saying, "there was a
wealth of clinical experience in dermatology with the use of liquid
injectable silicone by the microdroplet technique, which showed its
efficacy and safety in many individuals over many
In 1994, the FDA approved silicone oil for certain complicated
cases of retinal detachment to prevent blindness. There are
currently two FDA-approved LIS available for this indication -
Adatosil 5000 (Escalon Medical Corp, Chicago, IL) and Silikon 1000
(Alcon Laboratories, Fort Worth, TX). This approval has allowed
dermatologists to use silicone in an off-label manner -
specifically for soft-tissue augmentation.
Hexsel et al.12 address the aformentioned
history and controversial issues regarding silicone and contend
that LIS is a highly useful filler substance for a number of
indications. Unfortunately, because the literature is riddled with
anecdotal reports of horrific adverse effects of silicone, many
physicians remain hesitant to use the product in their practices.
However, it must be understood that in almost all of these reports
there is a lack of uniformity with respect to the exact nature and
quality of material injected, and thus, the true number of adverse
cases treated with LIS cannot be known.18
In an attempt to rid silicone of its historical stigma and
understand its actual side-effect profile, there are two current
trials to obtain FDA-approval for silicone as a soft-tissue
augmenting product. Maybe only after success in these trials will
much of the medical and lay community see the unadulterated side of
Table 1. Surgical Uses of
|Eustachian tube insufficiency21
Table 2. Dermatologic Uses of
|Soft tissue augmentation33
|Painful digit and sole scars35
|Bilamellar artificial skin38
|Diabetic foot ulcers39
|Skin surface impressions40
|Prevention of post-graft cobblestoning41
|Prevention of onchyocryptosis42
Table 3. Ophthalmic Uses of
|Reconstruction of conjuctival fornices43
|Lacrimal system obstructions47
|Corneal refractive surgery50
Table 4. Genitourinary Uses of
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