Medical applications of silicone rubber

Silicone materials revel 60 years of use in medical applications. Rapidly after their marketable accessibility in 1946, methylchlorosilanes were defined to treat glassware to avert blood from coagulation. Silicones are also used in many pharmaceutical applications from process supports like tubing used to manufacture pharmaceuticals, to excipients in topical formulations or adhesives to affix transdermal drug delivery systems. They also have found use as energetic pharmaceutical ingredients in products such as antacid and ant flatulent formulations.

Following are some uses of silicone rubber products:

1. Polydimethylsiloxanes and Biocompatibility

In medical devices and pharmaceutical applications, silicones are used because of their biocompatibility in a wide variety of physical forms. These forms range from unstable and low oligomers to high molecular weight polymers with viscosities from 0.65 to 20x106 to viscoelastic compounds and cross-linked elastomers.

2. Medical Devices and Pharmaceuticals

Apart from their dominant biocompatibility, other properties contribute to the use of silicones in medical and pharmaceutical applications:

• Because of their low liquid surface tension around 20.4 N and slightly higher critical surface tension of wetting of 24 N, PDMS polymers spread easily to form films over substrates like skin but also spread over their own absorbed film.
• Because of their viscoelastic conduct, resin-reinforced silicones or partly crosslinked elastomers (e.g. gels) have pressure delicate properties. Their soft, rubbery performance makes such silicones very suitable materials for contacting biological tissues by lessening the risk of trauma at the interface (e.g., low skin stripping force, gentle removability, no adhesion to wound bed). This permits their use in transdermal drug delivery and wound management applications to secure patches or dressings to the skin with minimum impact on the contacting area.
• Because of their high permeability, silicones allow the diffusion of many substances such as gases (i.e., oxygen, carbon dioxide, water vapour) but also the diffusion of various actives (i.e., plant extract, drug, or even protein). This explains their use in personal care, skin topical applications or wound dressings (no occlusive properties, no maceration). It also explains their use as adhesives or elastomers in controlled drug delivery systems.

3. Pharmaceutical devices

Silicone elastomers are used in drug-loaded pharmaceutical devices for the discharge of several APIs such as levonorgestrel in a subcutaneous contraceptive implant or 17 beta-estradiol in a vaginal ring for the treatment of urinary problems associated with menopause. In these reservoir devices, the release of the API is controlled by the permeability of the PDMS crosslinked network. In all the above applications, silicones have been considered because of their contribution to biocompatibility (medical devices), ease of use (pharmaceutical process aids) or progress of comfort and/or treatment, allowing lower and native dose forms with fewer side effects or making wound dressings easier to apply for potentially improved passivity.

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