Silicones : It's Pharmaceutical Applications

Table 1: Permeability of silicone in comparison with other polymers ⁽³⁾

Properties of Silicone Rubber

The backbone composition and structure of PDMS is the most flexible backbone known among all the synthetic polymers. The – Si – O – Si – bond angle is 143^o, which is much greater than the – C – C – C – bond angle in most other polymers and the oxygen atom is so small and unhindered relative to the adjacent silicon atoms that the chain is essentially freely rotating. Thus, PDMS has the lowest Tg (~ -120^oC) of any polymer. Lightly crosslinked PDMS is one of the most commonly used polymeric biomaterials, particularly when a rubbery material is required ^(4-7).

The ability to molecularly engineer” its mechanical properties, plus its inertness in biologic media, make PDMS eminently suitable as a substitute for stiffer tissues such as the ear, nose, and chin but its use as a breast implant has been controversial ^{(8, 9)}. In the early days of PDMS usage as a ball in the Star-Edwards ball-in-cage heart valve, the silicone ball absorbed lipids from the blood, swelled, and became brittle ^(10-12). This caused it to break up, and the fragments escaped the cage and flowed downstream in the arterial blood, causing vessel blockages that killed the patient. The cross-linking chemistry was changed and the silica content may also have been changed; today, the result continues to be a successful heart valve. The remarkably high oxygen and CO₂ permeability of PDMS has made it the material of choice for a blood oxygenator membrane. Oxygen and CO₂ are non-polar gases and as such they dissolve and permeate best in hydrophobic media. Other hydrophobic rubbers do not match the high permeability of PDMS; because of its highly flexible backbone chain, it is amorphous and has a low density that allows very high permeation to those two gases. Its low density is reflected in its unusually low melt viscosity. Fluorocarbons also have high permeability to these gases, and perfluoro groups have been incorporated into PDMS networks to achieve enhanced oxygen permeation.

Microporous polymers prepared from polysulfones and other polymers have replaced PDMS membranes in blood oxygenators. The coagulation of blood at the entry to the gas filled pores forms a thin protein film that acts as the barrier membrane, and it is so thin that it has an even higher permeability to oxygen and CO₂ than PDMS with perfluoro segments. Silicone Rubber is used in the more recent, long-wear contact-lens compositions to provide enhanced oxygen permeability to the underlying corneal tissues; poly (vinyl pyrrolidone) is entrapped within the Silicone Rubber to provide good wettability and lubricity for the lens on the eye surface.

The hydrophobic and amorphous low-density properties of PDMS have also made it the material of choice in the drug delivery implant called Norplant.

One application in which PDMS has not been useful is as the pumping bladder in the left ventricular assist device or the total artificial heart. It simply does not have the necessary flex life, even when cross-linked and reinforced with silica.

Toxicology & Biocompatibility

The most widely used silicones, polydimethylsiloxanes, does not show toxicity during administration via typical exposure routes. Due to their high molecular weight, they are not absorbed in the G.I. tract and are excreted without modification, nor are they absorbed through the skin. In vitro studies have not indicated mutagenic effects. Repeated oral or cutaneous dosages have not indicated effects on different species. Inhalation of aerosols of oily or fatty-type materials, including silicones, into alveolar regions of the lung may result in physical disturbances of the lining of the lung with associated effects.

Lower molecular weight siloxanes are frequently used due their volatility and generally dry skin feel. These can include linear as well as cyclic siloxanes. The lowest molecular weight linear material is hexamethyldisiloxane (HMDS), has generally shown slightly earlier incidence of testicular tumors in male rats exposed to high levels of material via inhalation; the relevance of this effect to humans is not yet known. Other linear molecules of three, four, or five siloxane units do not exhibit toxic effects though the data is limited for long-term exposure. The materials have very limited absorption via typical exposure routes. Like the higher molecular weight polymers, the low molecular weight linears are not mutagenic, irritating, or acutely toxic. Cyclic siloxanes, (SiMe₂O)_n are widely used in skin care products, in particular the four (n = 4) and five (n = 5) members cyclics. None of these materials have exhibited toxicity. Silicone elastomers are used in many classes II or III medical devices regulated by the European Medical Devices Directive such as tubing for extra-corporeal circulation used during cardiac surgery, hydrocephalic shunts or pacemakers leads.

Silicone in Pharmaceutical Formulation

Both tin catalyzed and platinum catalyzed silicones can be of use in drug delivery. In more than 358 registered products; silicones are combined with various pharmaceutical agents as useful antibiotics, antidepressants, anxiolitics, antifungal, antivirals, analgesics, antihypertensive, antiovulatory and permeable to selected vitamins. Silicones are used as actives, as Dimethicone or more often in other forms as shown in table 2.

Table 2: List of silicones used as actives and excipients in pharmaceuticals ⁽¹⁴⁾

While the purpose of the silicones as actives is well documented as antifoam in antigas or anti-acid formulations, the purpose of silicones as excipients is more difficult to determine. Some information could yet be collected indicating that silicones are used as excipients in pharmaceutical formulations for siliconisation (lubrication of syringe barrels, pistons, needles or lubrication of stoppers), as skin adhesives (drug permeable), as elastomers (drug release control membrane), as release liner coatings for transdermal patch (release coating), and, in skin topicals, as polymers, volatiles or not, or as copolymers to carry actives or to improve spreading and aesthetic qualities.

The latter is not surprising as silicones are widely used in Personal Care products, with around 60 % of today’s skin care products containing silicones where they are recognized as safe, and known to provide for a pleasant “silky touch” non-greasy and non-staining feel.

Substantial numbers of registered products contain silicones that are not described in any Compendia, e.g. methylpolysiloxane, silicone for powder treatment, silicone or fluoro silicone for polyester film coating, silicone copolyol, HMDS, Silastic®, silicone wax.

Siliconisation

Siliconisation encompasses the surface treatment with of many parenteral packaging components with silicones. It is probably one of the oldest applications for silicone in the pharmaceutical field: treating glass vials with a film of polydimethylsiloxane. This allows the reduction of the glass surface energy and stops the surface being wet out by the pharmaceutical solution, reducing wastes and allowing better dosage with complete drainage from the vial. Polydimethylsiloxanes (Dimethicone, Silicone Oil) are also used as lubricants on stoppers to ease machine ability, in syringes to ease the piston movement or on syringe needles to reduce pain when entering the skin. The surface treatment is done on clean surfaces by, at low concentrations, spraying, wiping or dipping with either a solvent solution or an emulsion of Dimethicone followed by air-drying and/or heat treatment. The film coating is helped by the low surface tension of the polydimethylsiloxanes and on glass a subsequent heat treatment improves the adhesion of the film on the surface. Quantification is not easy as the amount applied on the considered surface is very low: some technique exist e.g. using Atomic Absorption after removal with alcoholic potassium hydroxide but often users rely on a functional test, e.g. contact angle or coefficient of friction measurements to determine the efficacy or effectiveness of the coating. The silicones stability and their low reactivity allow sterilisation by steam autoclave.

Silicone solution

Silicones are fuelling innovations in topical drug excipients, due to their unique set of physicochemical properties that improve active pharmaceutical ingredient (API) delivery and ease of product application. Low surface tension, non-greasy touch, high permeability to drugs and persistence of action in various controlled release pharmaceutical devices, make silicones ideal as excipients in topical pharmaceutical products.

Silicone Surfactants

Silicone surfactants are becoming increasingly important in the pharmaceutical and cosmetic industry, because of their versatility, low cost, and technological advantages. It is used to measure the critical micellar concentration of three non-ionic silicone surfactants, one water-soluble and two lipid-soluble.

One of the advantages of new silicone surfactants is that they can be used in emulsions with a wide variety of lipophilic components. The composition of the oil phase does not interfere with stability, and the resulting mixtures provide an excellent base for the formulation of cosmetic emulsions with different characteristics. A further advantage of these products is that they can be prepared at room temperature.

A new group of w/o emulsifiers based on the linkage of polymethoxysiloxane chains with alkyl side chains and polyol groups has been constituted.⁽⁴³⁾ These emulsifiers, known as organosilicone polymers, have the capability of producing w/o emulsions with a high water content. Although the polymethylsiloxane chains possess both hydrophilic and lipophilic properties, the alkyl side chains supply the necessary lipophilic and polyol groups to provide the hydrophilic characteristics of the emulsifier.

Silicone Dressings

Soft silicones are a particular family of solid silicones that are soft and tacky. These properties enable them to adhere to dry surfaces. A soft silicone dressing is coated with soft silicone as an adhesive or wound contact layer and may be removed without trauma to the wound or surrounding skin. Silicone dressings have been used clinically as an alternative to paraffin gauze for the fixation of pediatric skin grafts where it was found that changing the outer absorbent dressing was painless as was the removal of the silicone dressing itself so that no analgesia or anesthesia was required.⁽¹⁵⁾

Generally, silicone dressings have a porous, semitransparent wound contact layer consisting of a flexible, polyamide net that is coated with silicone. The dressing is non-absorbent but the pores within its matrix allow the passage of exudate from the wound to the secondary dressing. Its use is limited to minor skin grafts because the dressing requires a margin of healthy skin for application of at least 2 cm surrounding the wound.

Silicone dressings have also been used to manage wounds generated by radiotherapy, fingertip injuries, severe mycosis fungicides, and epidermolysis bullosa.

The silicone material needs to be kept in intimate contact with the surface of the wound to function effectively which means that wounds in convex areas present few problems whereas those on concave, jointed, or contoured areas need adequate padding to be applied to exclude voids beneath the dressing where exudate could accumulate. As silicone is an inert material, it has been shown that, where clinically indicated, topical steroids or antimicrobial agents can be applied either over or under the silicone material without diminishing their efficacy.

There have been reports indicating that use of silicone dressings leads to improvements in the appearance (scar size, erythema, elasticity) and symptoms (pruritis, burning pain) after application to hypertrophic scars and keloids.⁽¹⁶⁾ Silicone dressings are thought to effect this by promoting hydration of the scar and applying pressure, thereby flattening scar tissue, increasing wound elasticity, and reducing discoloration.

Silicones in Ophthalmic Drug Delivery

Ophthalmic practice has long employed silicone polymers in surgeries utilizing scleral buckles and sponges, retinal tamponade and foldable intraocular lenses. Silicone elastomers and rubbers are hydrophobic in nature and therefore support long term payout characteristics for many drugs. Silicone polymer disks of 4–5mm diameter termed minidiscs have been studied for the release of gentamicin when placed in the conjunctival cul-de-sac.⁽¹⁷⁾ Slow release of the drug is observed over a period of 10–14 days with tear concentrations in the range of 2.5 ppm during this period.

Nanoparticles of silicone in the 150–200 mm size range can be made and when containing timolol effectively prolonged release of the drug.⁽¹⁸⁾ Sealed silicone tubes 1.46mm ID by 15mm length and filled with 2.5–20 mg/ml solutions of timolol slow release the drug over 8 h in vitro⁽¹⁹⁾ or in vivo.⁽²⁰⁾ Recently, development of a solid noodle-like silicone controlled drug delivery rod for the deep cul-de-sac (fornix) known as the Ocufit SR® has been reported.^{( 22)} These rods have been shown to slow release oxytetracycline or diclofenac over several weeks and have shown good wear compliance in humans.^{(23, 24)} Liquid silicone can also be used as a surface coat in developing delivery devices. This approach has been reported for polydimethylsiloxane coated solid drug implants that are used to enhance sustained delivery in the eye. ^{(25, 26)}

Silicone as Antifoam in Pharmaceutical Formulation

Dimethicones and Simethicones are declared as actives and used as antifoams in numerous anti-flatulent or anti-acid formulations, even if their efficacy has been questioned in some indications. Overall, this is the largest single application for silicones in registered products (64 registered products or 16 % of the ones retrieved in the above databases): among them Maalox®, Mylanta® and Gel de Polysilane-Midy®.

Silicones in these products help to suppress the formation of foam in the stomach without modifying the gastric pH. Silicones are often compounded with other anti-acid actives such as Al or Mg hydroxides, Mg or Ca carbonates.

Simethicones and Dimethicones also appear in many other anti-acid or antiflatulant formulations yet where the silicones are only declared as excipients and not as actives. Also declared as excipients, silicones appear in many liquid formulations like syrups as well as in effervescent tablets formulations, most likely either to control foaming during processing and filling operations or during use. As actives, silicones are also used in diagnostic formulations to eliminate foam in the stomach during endoscopy or, in conjunction with barium sulphate, during X-Ray examination.

Silicone based skin care product

The invention is concerned with silicone-based skin care products which are applied to the skin as aerosols and form a clear gel on the skin. The skin care products comprise 20-70% w/w of a silicone based water-in-oil microemulsion and 30-80% w/w of a volatile diluent. Preferably the microemulsion has a viscosity of between 1000 and 10,000 mPas. Skin care composition in the form of a substantially oil-free aqueous gel comprising water-soluble humectant, hydrophilic gelling agent, specific silicone component and specific cationic surfactant component. The compositions provide improved oil control along with improved skin feel and residue characteristics together with excellent moisturizing, emolliency, rub-in and absorption characteristics.

Silicone as Excipients in Topical Medical Formulation

After their use as antifoams (see above), the next largest application for silicones is in topical formulations. In the above databases, 36 products (10 % of the retrieved registered products) could be identified where silicones are used as excipients in topicals. The largest indication is for skin diseases, mainly as creams followed by gels and lotions for the treatment of acne, fungal diseases or psoriasis. Other topical applications include contact with fragile mucosa in the treatment of haemorrhoids, anal dermatoses or itch relief as well as for the delivery of antibiotics in gynaecological capsules or cream. Dimethicones and Simethicones account for most of the occurrences yet some other specific silicones used as excipients could be retrieved in registered products using the above databases:

• Cyclomethicone, registered in Diprolene® (Schering Plough) or as decamethylpentacyclosiloxane in the formulation Dexeryl Crème® (Pierre Fabre Santé); the exact purpose is not known, as for many excipients, but cyclomethicones are widely used in personal care because of their volatility, “aesthetic” and safety profile;
• Hexamethyldisiloxane: recent work shows that the hexamethyldisiloxane, can be used as a volatile excipient in spray pump systems for topical applications, e.g. in combination with fungicides and was registered in Pevaryl® (Janssen-Cilag). The low surface tension of this disiloxane improves the coverage of the skin and possibly increases the bio-availability of the active drug. The advantage of this disiloxane, despite its flammability, is its very low heat of vaporisation, which, despite its rather high boiling point, allows the film to dry quickly;
• Stearyloxytrimethylsilane, a wax with pleasant silky feel although occlusive, registered in Retinova® (Roc - Johnson and Johnson);
• Dimethicone copolyol used in conjunction with Cyclomethicones in Retin-A Micro® (Ortho Dermatological - Johnson and Johnson), yet the exact structure of this silicone glycol copolymer cannot be determined from the databases used.

Biocompatibility and aesthetic quality of silicones makes it suitable for personal care products but it also it helps to improve the bioavailability of drugs as shown below:

Table 4: Comparison of the penetration rates of different actives through hairless rat skin in Franz diffusion cells from silicone gum (2 % by weight) in silicone volatile formulations versus commercial products (without silicone).

While silicone elastomers are solids, it is possible to prepare paste like products if the polymer cross linking is carried out in the presence of a large amount of a noncreative fluid, e.g. a volatile silicone. These products can be applied to the skin in large quantities while maintaining an exceptional feel. They are widely used in Personal Care products and it has recently been shown that they can be used as carrier for the release of actives.

Silicone as Excipients in Release Device Controlled

The controlled release of active drugs with polydimethylsiloxane goes back to the 60’s. Today different registered products using silicone elastomers or silicone PSA’s are commercialized:

• Implants like the Norplant® (Leiras), a sub-cutaneous contraceptive implant releasing levonorgestrel for contraception over a 5 years period;
• Inserts in the form of vaginal ring like the Estring® (Pharmacia and Upjohn) releasing 17- ß estradiol and used for the treatment of menopause symptoms, or the Mirena® (Schering), an IUD releasing levonorgestrel for contraception; Femring - a low-dose estradiol-acetate releasing ring, manufactured from silicone elastomer, for the relief of hot flashes and vaginal atrophy associated with menopause , NuvaRing - a low-dose contraceptive vaginal ring, manufactured from poly(ethylene-co-vinyl acetate), and releasing etonogestrel (a progesterone) ethinyl estradiol (an estrogen).

Basically, vaginal rings (Also known as intravaginal rings or V-Rings) are ‘doughnut-shaped’ polymeric drug delivery devices designed to provide controlled release of drugs to the vagina over extended periods of time, manufactured from silicone elastomer.

Vaginal rings are made of biocompatible silicone elastomers that consist of a drug-free core ring and a drug-containing coat. Vaginal rings are inserted and positioned around the cervix. Those designed for contraception, are kept intra-vaginally for 21 days and removed for 7 days to allow menstrual flow.

The concept of intravaginal dual administration of progestin and estrogen in combination was recently extended to the development of a combined contraceptive vaginal ring. This new design (Fig. 1) is constructed from two drug reservoir compartments; the major compartment consists of a 3-keto-desogestrel loaded core, and the other, minor compartment consists of a core loaded with a combination of 3-keto-desogestrel and ethinylestradiol, a synthetic estrogen. These drug reservoir compartments are separated by two steroid-impermeable glass closures, as the partitions, and release the steroids at a fixed ratio through a rate limiting silicone membrane. ⁽²⁷⁾

Figure 1: Structural components of contraceptive vaginal ring

Work evaluating a cylindrical, drug-free polyurethane vaginal sponge coated by a laminate of fluorogestone containing silicone matrix and a drug-free silicone coating membrane was conducted. ^{(28 - 30)}

The system itself was modified and the release rates studied in vitro and in vivo. It was found that the drug-containing silicone layer needed to be in contact with the vaginal wall. A silicone coating did not result in adequate release rate. Also, as the surface area of the drug-containing silicone increased, the drug delivery rate increased. This effort has resulted in two new pessary designs (Fig. 2). Both types make use of the polyurethane sponge in the vaginal pessary as the mechanical support for vaginal insertion and retention, but the drug reservoir is relocated from the porous sponge matrix to a sheet-type rate-controlled silicone device that covers the circumferential surface of the sponge. The type I rate-controlled silicone device consists of a homogeneous dispersion of drug in a silicone polymer matrix. The type II drug-dispersing polymer matrix is sandwiched between two sheets of silicone polymer membrane to form a three layered laminate.

Figure 2: Progestin releasing vaginal pessaries

• Transdermal patches, like Nitriderm (Novartis), releasing nitroglycerine for the treatment of angina pectoris, Durogesic® (Janssen-Cilag), releasing Fentanyl for the treatment of chronic pain or Vivelle-Dot® (Novartis) releasing Estradiol for the treatment of menopause symptoms (HRT).

Progestasert^® IUD

 

In this controlled-release intrauterine device, the drug reservoir exists as a dispersion of progesterone crystals in silicone (medical grade) fluid encapsulated in the vertical limb of a T-shaped device walled by a nonporous membrane of ethylene–vinyl acetate copolymer (Fig. 3). It is engineered to release continuously a daily dose of 65 mg progesterone inside the uterine cavity to achieve contraception for one year. ⁽³¹⁾ The same technology has been utilized in the development of the Mirena^® system, a plastic T-shaped frame with a steroid reservoir containing 52 mg levonorgestrel, which is designed to release a daily dose of levonorgestrel at ~20 mg/day for achieving effective contraception for five years. ^{(32 - 34)}

Figure 3: Progestasert^® IUD, controlled release intra-uterine device

Norplant^® subdermal implant

The controlled-release subdermal implant is fabricated from a non-porous silicone (medical-grade) tubing, by sealing both ends with silicone (medical-grade) adhesive to encapsulate either levonorgestrel crystals alone (generation I) or a solid dispersion of levonorgestrel in silicone elastomer matrix (generation II). It is designed to attain a continuous release of levonorgestrel, at a daily dosage rate of 30 mg, to each subject (following the subcutaneous implantation of either 6 units of I or 2 units of II); for up to 7 years.^(35–38)

Compudose^® implant

This controlled-release subdermal implant is fabricated by dispersing micronized estradiol crystals in a viscous mixture of silicone elastomer and catalyst and then coating the estradiol-polymer dispersion around a rigid (drug-free) silicone rod by an extrusion technique to form a cylinder-shaped implant (Fig.4). This implant is designed for subcutaneous implantation in the steer’s ear flap for duration of 200 or 400 days, during which a controlled quantity of estradiol is released daily for growth promotion.⁽³⁹⁾

Figure 4: Compudose^® implant, controlled-release subdermal implant

In these devices, the active drug release is controlled by its diffusion through the silicone network which is possible thanks to the very high permeability of silicones to various actives, particularly when these are lipophilic and of low to medium molecular weight. Implants are particularly attractive when a low dose of the active is to be administered over a long period of time, that is when the drug is active at low concentrations and the need is chronic. Compared to oral dosages, the degradation in the GI tract or by the liver is avoided with such controlled release devices. They also allow for better treatment compliance and more comfort to the patient. Silicones are preferred in such applications, not only because of the simplicity to shape them by extrusion, injection or moulding and their crosslinking at low temperatures without by-products but also because of their stability and their outstanding biocompatibility.

Silicone Adhesives

Silicone adhesives are made of high-molecular-weight poly-dimethyl siloxane (silicone gum) and silicate resin, which consists of (CH₃)₃SiO and SiO₂ units. The ratio of silicone gum to silicate resin is 100/50 to 100/150 by weight. The advantage of silicone adhesives is their chemical inertness and high drug permeability. However, drug solubility in the adhesive is quite low. These properties suggest that silicone adhesives are more suitable for reservoir-type TDS than for drug-in-adhesive-type TDS.

Silicone pressure sensitive adhesives are also used in reservoir devices like the Transdermal-Nitro® releasing nitroglycerine transdermally at a rate of 0.5 (mg/cm2)/day for a daily relief of angina.^{(41, 42)} Here, the silicone contributes with the ethylenevinylacetate copolymer membrane to the control of the active drug release whilst also providing adhesion of the patch to the skin. A silicone adhesive is used here because of its very high permeability to the active drug. Silicone PSA’s are also used in matrix devices where the PSA acts as both the matrix for the active drug and as the patch adhesive. Silicone PSA’s are used for 1-day patches but longer wearing times are possible (2 or more days).

Figure 5: Transderm-Nitro^®, controlled-release transdermal therapeutic system

Contrary to organic adhesives, silicone PSA’s are formulated without anti-oxidant and without organic tackifying resins. Silicone PSA’s have been extensively tested on humans: they induce neither skin irritation nor allergenicity, they are non-toxic, and they are used in prolonged therapies using successive patches and can be removed easily. ⁽⁴⁰⁾

Silicones in Various Health Care Applications

Dental Care

With their excellent stability, tear strength and non-reactive qualities, silicones are a key component in impression molds used for bridge and crown reconstruction that require an accurate replication of teeth and gum lines. Now a days teeth whitening preparation called zoom whitening made from silicone extensively used. These zoom whitening is totally safe.

Infant Care

Silicones help make baby feeding bottles and baby care products including baby bottle nipples, baby feeding bottles, baby care accessories like silicon nipples, polycarbonate feeding bottles, smooth neck polypropylene feeding bottles, breast pumps, spill proof valves and pacifiers sturdy but flexible.

Prosthetics

Silicones can most closely approximate the consistency of skin and offer exceptional cushion and comfort. Silicone-based prosthetics can be molded to a cushioning shape and have the durability to retain the shape. Silicones also resist bacterial growth and help reduce the risk of infections.

Respirators

Health care professionals use silicone-based respirators because of comfort, flexibility and ease of cleaning. Just as important, silicone is hypoallergenic. Transparent silicone material provides excellent respirator bag re-expansion and is resistant to extreme temperatures.

Hearing aids:

Silicone is a common material for use in molds for behind-the-ear style hearing aids. It has excellent sealing properties, making it an ideal choice for patients with profound hearing losses who need high-powered hearing aids.

Women care products

• Menstrual cup is a type of cup or barrier worn inside the vagina during menstruation to collect menstrual fluid, made from durable medical-grade silicone, is a comfortable, secure alternative to disposable menstrual products.

Unlike more common methods, such as tampons and pads, the cup neither absorbs the flow nor catches it outside the body. It resembles the contraceptive diaphragm (although it is not a contraceptive device). Current brands include “Mooncup” (manufactured in the UK and USA), “DivaCup” (manufactured in Canada), “Keeper” (manufactured in the USA), “LadyCup” (manufactured in the Czech Republic, “Lunette” (manufactured in Finland), “FemmeCup” (manufactured in the UK).

• Pink Silicone Lubricant: Highly concentrated, long-lasting silicone lubricant formulated especially for women. Give Maximum comfort for women. It is hypoallergenic; condom-safe contains vitamin E and aloe vera. It can easy to wash off after application.
• Silicone breast implants: Controversy developed in the 1980s and 1990s around claims that the silicone gel in breast implants was responsible for a number of systemic health problems, including autoimmune diseases and cancer. However, multiple studies and expert review panels performed worldwide since then have consistently concluded that women with silicone breast implants are no more likely to develop systemic illness than women without breast implants. In 2006 both Health Canada and the US FDA adopted positions similar to other countries in permitting the use of silicone implants for cosmetic breast augmentation in their respective countries.

Silicone Tubing

Tubing made from various polymeric materials and in particular, silicone polymers are largely used in pharmaceutical manufacturing operations for the transfer between reactors e.g. for the production of vaccines, in peristaltic pumps, or in filling equipment lines. Both peroxide and Pt cured tubings are used but the Pt cured tubings are recommended as the peroxide cured tubings contain peroxide by-products, including PCB’s, susceptible to be released to contaminate the transferred product. Other criteria to consider when selecting silicone tubings are: compatibility (chemical resistance, lack of absorption and contamination), preparation (cleaning and sterilisation), pressure resistance, resilience (pump life), kinking resistance, and regulatory status (compliance to Pharmacopoeia and supplier’s quality system: product traceability, extrusion conditions and manufacturing site registration). In most cases, the users prefer to limit the usage of these tubings to a single operation rather than to validate difficult cleaning procedures for multiple re-use operations. Silicone tubings are preferred in these applications because of their purity (no plasticisers), flexibility, and ease of use and essentially burst resistance.

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About Authors:

D’souza J. I., More H. N., Sow T. K., Yadav S. B.

D souza J.I
Department of Pharmaceutics, Bharati Vidyapeeth College of Pharmacy, Near Chitranagari, Kolhapur 416013, M.S., India
Email: johnsir4u@gmail.com

More H. N
Department of Pharmaceutics, Bharati Vidyapeeth College of Pharmacy,
Near Chitranagari, Kolhapur 416013, M.S., India

Sow T. K.
Department of Pharmaceutics, Bharati Vidyapeeth College of Pharmacy,
Near Chitranagari, Kolhapur 416013, M.S., India

Yadav S. B.
Department of Pharmaceutics, Bharati Vidyapeeth College of Pharmacy,
Near Chitranagari, Kolhapur 416013, M.S., India