Silicone- Implants in Plastic Surgery (Silastic)

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(Last Updated On: June 15, 2018)

Silicone implants- Plarecon- header image

Silicone– Polydimethylsiloxane (PDMS)

Silicone (Silastic) is one of the most maligned and hence, most studied biomaterial used in medicine today. It’s a synthetic non-resorbable polymer consisting of repeating ‘Siloxane monomers (Silicon, oxygen, and a saturated hydrocarbon side group). Polydimethyl siloxane [-(CH3)2Si-O-]n where methyl forms the side chain is used in most medical applications.

Depending on the length (n) and degree of cross-linking of the PDMA chains, the mechanical properties of silicone can change to fluid (short, straight chains- <30 monomers), gel (lightly cross-linked chains), or rubber (greater degree of cross-linking– > 3000 monomers).

Advantages of Silicone

  1. Highly biocompatible- inert, nontoxic, nonallergic
  2. Resistant to resorption
  3. Easily to sterilize
  4. Safe- has no proven association with systemic diseases like autoimmune connective tissue disease, neurologic disease, or breast cancer- anaplastic large cell lymphoma (ALCL).

Disadvantages of Silicone

  1. Nonporous- hence, not incorporated–> hard fibrous encapsulation– sometimes painful and disfiguring.
  2. Smoothness- prone to extrusion, displacement– leads to removal.
  3. Silicone rubber has a low tensile strength and may tear easily- eg. in finger joint implants. 💡 
  4. Silicone gel in silicone rubber shell can diffuse out (gel bleed- thus altering its physical property), or rupture out- implant failure– which may be difficult to remove from soft tissue (Inflammatory reaction- not proven). Hence the shell is made of fully polymerized
    silicone with an amorphous (noncrystalline) silica filler added for strength.
  5. Fluid silicone (low molecular weight) as injectable soft-tissue filler led to severe tissue
    reaction and migration of the silicone and hence not used.
  6. Implants and expanders are Expensive.

Uses of Silicone

1. Tissue expansion 

Silicone expanders- Plarecon
Silicone Tissue Expanders (Various shapes)

2. Breast augmentation

Most breast implants are Silicon gel encased in a ‘silicone elastomer shell– they can be classified based on:

   a. Surface– Smooth or Textured (less capsule formation, less mobile).

Breast implants- Smooth, Textured- Plarecon
Breast implants- Smooth, Textured

   b. Shape– Round or Teardrop (more natural shape).

Shape of Breast Implant- Round vs Teardrop- Plarecon
Shape of Breast Implant- Round-Teardrop

   c. Projection/Profile– low, moderate, moderate plus, high, ultra high.

Breast implants- Profiles- Plastic Surgery India
Breast implants- various Profiles-Projections

3. Chin, nasal, malar augmentation

Silicone Implants- Malar, Nasal, Chin - Plarecon
Malar, Nasal, Chin Silicone Implants

4. Penile and Testicular implants

Silicone Penile, Testicular implants- Plarecon
Silicone Penile and Testicular implant

5. Ear, Finger, other Facial Prostheses

These prostheses can be either osseointegrated or tightly fitting which are custom-made, shaped and colored to match the anatomy of the structure it’s replacing, as closely as possible. They mainly supplement aesthetically, but can also have a minimal function.

Silicone Ear, Finger, Facial Prosthesis- Plarecon- aesthetic
Silicone Ear, Finger, Facial Prosthesis- cosmetic

6. Hypertrophic scar treatment, Orbital floor reconstruction

Silicone Gel Sheets (SGS) are used for the above. The mechanism by which it works for a hypertrophic scar is mentioned below.

Silicone Gel Sheet- Plarecon
Silicone Gel Sheet

7. Hand surgery

  • Small joint arthroplasty
  • Flexor tendon replacement (Hunter’s tendon rod)
  • Bone block spacers
Hunter's Silicone Rod for Tendon Reconstruction- Plarecon- plastic surgery
Hunter’s Silicone Rod for Flexor Tendon Reconstruction

Mechanism of action in Hypertrophic Scar

The mechanism of action of Silicon Gel Sheet (SGS) in the treatment of hypertrophic scar is not well understood and the following have been proposed:

  1. The therapeutic effect is not due to pressure, but rather due to wound hydration by decreasing the water vapor transmission rate to nearly half that of normal skin, causing a buildup of moisture on the skin surface under the silicone sheet. Hydration is most likely responsible for the decreased capillary activity, reduced hyperemia, and reduced collagen deposition.
  2. Altered hydration is thought to cause electrostatic changes that influence collagen deposition and remodeling within the scar.
  3. The static electricity generated by friction has also been proposed as a plausible reason for silicone’s anti-scarring effect.

Problems with SGS in scar management

  1. Skin maceration under the sheet
  2. Persistent pruritus
  3. Skin breakdown, skin rash under the SGS and the adhesive tape used to hold the SGS
  4. Foul smell from the gel
  5. Poor durability of the Silicone sheet
  6. A poor response of the scar to treatment
  7. Poor patient compliance

Bibliography

  1. Neligan’s Plastic Surgery- Vol 1- Principles- 4Ed (2017)
  2. Textbook of Plastic, Recon, Aesthetic Surgery- Vol 1- Principles and Advances in Plastic Surgery- Agrawal, Bhattacharya- 1Ed (2017)
Silicone- Implants in Plastic Surgery (Silastic)
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