Alloplastic Materials : Metallic, Ceramic, Polymeric

Alloplastic Materials

Alloplastic Materials are chemically constructed from a wide array of biomaterials with diverse physical structures and properties. Alloplastic materials can be:

• Metallic implants
• Ceramic implants
• Polymeric implants

We will read about each in detail. 

Metallic Alloplastic Materials

These can be metals and metal alloys. The important characteristics that are required are -

• Mechanical strength or tensile strength
• Comparable weight and density to surrounding tissue
• Resistance to corrosion
  • Corrosion can occur due to the electrochemical activity of unstable metal ions and electrons in physiological salt solutions. This can lead to pain, inflammation, allergic reactions, and device loosening.
  • Iron, chromium, and nickel are common metals or metal alloys. Vitallium, an alloy of cobalt, chromium, and molybdenum, has good tensile strength.
  • Titanium can be used. It is a metal commonly used in plates for reconstructing craniofacial skeletons or cranioplasties.
  • Gold can be used as it does not rust but has low tensile strength and cannot bear the load. It can be used in the reconstruction of lagophthalmos in Bell's palsy.
  • Platinum - inert metal is used in patients who have sensitivity to gold.

Polymers

These are large-chain, high-molecular-weight macromolecules made up of repeated units. They are widely used as they offer ease of fabrication and low cost. They can be processed into tubes, fibers, fabric, mesh, films, and foams.

They can vary with chemical composition, degree of polymerization, and crosslinking between chains. They can also vary due to the presence of chemical additives like plasticizers to increase flexibility or resins, which aid in polymerization.

Polytetrafluoroethylene

Fluoro carbon-carbon ethylene backbone with attached fluorine molecules. These are Non-biodegradable and lack the human enzyme that can break the carbon-fluorine bond.

Polytetrafluoroethylenes have a Low coefficient of friction. They are Non-reactive, Flexible, and Stable at temperatures of 325 degrees F. They can be easily removed in cases of infection and are Anchored to surrounding tissues. They have Low tensile strength.

These were used 1st used in plastic surgery for facial skeletal augmentation.

• Proplast 1 – a composite of PTFE and graphite
• Proplast 2 – a composite of PTFE and aluminum oxide
• Proplast HA – PTFE + hydroxyapatite

Goretex

They are in the form of Sheets, blocks, or performed shapes. Goretex is Soft but strong. It is a type of vascular prosthesis. It is used in Facial augmentation for the chin and malar region, Subcutaneous augmentation, and Subdermal lip implants.

Polyethylene/Polythene

Polyethylene/ Polythene are simple carbon chains with the absence of fluorination. There are 3 grades of polythene:

• Low density
• High density
• Ultra-high density – load-bearing orthopedic implants (hip implants)

High-density Polyethylene/ Polythene is used in plastic surgery because:

• High tensile strength
• Flexibility
• Firm consistency

Medpor

Medpor is High-density porous polyethylene. The Porosity allows tissue ingrowth, which helps stabilize and incorporate implants into the body. This is difficult to remove, while silicone implants are easy to remove. They augment the facial skeleton—jaw, chin, and malar implants. In the case of Microtia, it is placed beneath the temporoparietal fascia. Medpor has difficult intraoperative shaping.

Polyester

Polyester is Widely used in biomaterial. Large polymers with ester linkages between carbon bonds. Meshes, sutures, and vascular prostheses are made with polyester. A very good example is Dacron. It has high-density fibers of polyethylene tetra phthalate are used. Mersilene mesh is used in genioplasty procedures only for chin implants. Bone fixation devices like plates and screws are made up of polylactic acid and polyglycolic acid.

Polyurethane

Polyurethane is an organic polymer of polyol. It is a foam-coated implant filled with silicone gel. Polyurethane remains in position better, thus reducing capsular contracture. It has a spongy appearance that reduces capsular contracture. It has good abrasion resistance. The other polymer used is Polypropylene, which is most commonly used as mesh. Composite mesh can also sometimes be used.

Acrylic Resin

A very commonly used Acrylic lesion is PMMA – Polymethylmethacrylate. It is Impervious/non-biodegradable. It is formed by mixing liquid methyl methacrylate (liquid monomer) with PMMA powder (powdered polymer). This reaction is a Significant exothermic reaction (40-50 C). So, before mixing, ensure sufficient cooling/cool irrigation of the surrounding

Tissue. It is available as a paste or preformed implant. Intraoperative fabrication and adaptation are possible. The body response is in the form of the fibrous capsule formation. The uses of Acrylic Resin are:

• Used in cranioplasty for filling full-thickness cranial defects
• Used for fabrication of gentamycin-impregnated beads
• Secondary forehead contouring

Also Read: Liposuction  Uses , Contraindications And Complications

Silicone

Silicone is Polydimethylsiloxane. It is a Polymer formed from silicone and oxygen backbone. Only non-carbon chain polymers are used in medical practice. The Length of the chain and amount of cross-linking lead to various physical forms of silicone. 

• Short chains are in Liquid form.
• Long chains are in the form of Gel
• Short chains are cross-linked and are in the form of Highly corrosive gel.

Silicone is excellently resistant to high temperatures and UV. It has Poor abrasion resistance and tensile strength. Liquid silicone is not preferred because it is not very inert. It can have an Intense fibroblastic response with a tendency to migrate. It also has a Chronic inflammatory response with granuloma formation. So silicone liquid is not injected into human tissues. Textured silicon has a low tendency for capsular contraction.

Ceramics

Ceremics are non–metallic inorganic substances like Calcium phosphate. Caremics are available as Tricalcium phosphate, apatite and hydroxyapatite. They are Bioactive substances capable of osteoconduction. They Develop actual tissue ingrowth and slowly integrate into the

recipient site. These are Used for bone repair and bony regeneration. They provides a substrate into which new bone from the adjacent surface is deposited. They are Inert, well tolerated and have no inflammatory response. Caremics have Good bioavailability, Low friction coefficient and high wear resistance and stability. The Uses of ceramics are:

• Reconstructing bony defects
• Facial skeleton augmentation (jaw, malar, chin)
• Bone graft augmentation
• Calavarial remodeling

· The drawback of ceramics is that they are brittle.

Complications of alloplastic materials

• Migration
• Extrusion
• Infection (most common)
• Initial phase
• Physicochemical interaction between bacteria and surface
• Managed by mechanical washing and irrigation
• Irreversible cellular phase – cellular interaction between material and bacteria
• Purulent infection – drainage of pus and removal of the implant
• Re-implantation only after 3-6 months after resolution of infection
• Organisms involved can vary with the chemical composition.”
  • Polymeric implants – Staph epidermidis
  • Metal implants – Staph aureus
  • Surface roughness/hydrophobicity/configuration

Also Read: Skin Resurfacing, Chemical Peeling And Dermabrasion 

Frequently Asked Questions:

Q: What is the most important complication of alloplastic material?

Answer: Infection

Q: Grafts derived from animals are known as?

Answer: Xenograft

Q: What density of polythene is used in hip implants?

Answer: Ultra High-Density Polyethylene

Hope you found this blog helpful for your NEET SS Surgery Skin and Subcutaneous preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.