Alloplasts
Alloplast = synthetic - manufactured from nonhuman, nonanimal, and hence,
nonorganic sources.
Indications
1. reconstruction of soft tissue and bone defect
2. augmentation of soft tissue and bone
3. stabilization of fractures.
Advantages
1. no autogenous donor site
2. unlimited supply
3. lessen operating time
4. no immunologic rejection, transmission of viral diseases
Contraindications
1. history of radiotherapy
2. marginal blood supply of the surrounding tissue,
3. tenuous soft tissue coverage over the implant.
4. infection
Ideal Alloplast
 Biocompatible
o acceptable interaction between the host and the implanted material.
o
 Chemically inert
 Non-Inflammatory
 Non-Carcinogenic
o Oppenheimer Effect– solid state carcinogenesis in animals
 Non-Mutagenic
 Non-Allogenic
 Non-Toxic
 Mechanically stable
 Capable of fabrication to desired form
 Sterilisable
 Readily available – ‘off the shelf’
 Affordable
 Radiolucent
 In some cases, these are desirable
o Integration via soft tissue or bone ingrowth.
o Absorbable
Tissue response
 End-stage healing response to most biomaterials is the formation of an enveloping
fibroconnective tissue scar or fibrous encapsulation.
 This is initiated with the surgical implantation procedure, which generates an acute
inflammatory response due to the induced tissue damage and is followed by a
cascade of events including chronic inflammation, granulation tissue
development, foreign body reaction, and ultimately an enveloping fibrosis.
 This fibrous capsule represents the body's reparative response to separate the
body from the foreign material
 Although most alloplastic materials will develop fibrous encapsulation, numerous
features of an implant have been shown to influence the degree and composition of
this capsule, most notably the form and characteristics of the implant surface.
Considerations
 Tissue bed and implant considereations
Classification
The basic classification of implant materials most commonly used includes metals,
calcium ceramics, polymers, and biologic materials.
1.
2.
3.
4.
Metals
Textiles/polymers
Ceramics
Biosynthetic
Metals
 Characteristics of a desirable metal implant include biocompatibility, strength,
resistance to corrosion, and imaging transparency.
 Biocompatibility of metal implants are primarily determined by their surface
properties and corrosion resistance (electrochemical conversion of a metal to its
base compounds)
 After implantation, an oxide layer quickly forms on the metal's surface, which
determines its resistance to corrosion and the amount of leaching of metals or
oxides to the adjacent tissues.
Stainless steel – iron, chromium, nickel alloys
a. have a higher corrosion potential and a greater amount of metal ion
release and are more likely to require secondary removal
b. nickel content also contributes to an increased incidence of allergic reactions.
Vitallium – cobalt-chromium-molybdenum alloy
a. non-corrosive
b. 2-3 x stronger than steel  low profile miniplates
c. As a result of radiographic imaging and artifact scatter concerns, vitallium has
lost favor for most craniofacial indications due to the increased popularity of
titanium metal
Gold
a. non-corrosive - does not develop a layer of oxide on its surface after
implantation. As a result, it is exceptionally well tolerated in the body
b. expensive
c. malleable
d. one surgical use-as an upper eyelid implant for the treatment of acquired ptosis
in facial nerve palsies
Titanium
a. pure or alloy (+ 6% Al, 4% vanadium)
b. forms a titanium oxide surface layer that is very adherent and highly resistant to
corrosion, and even if the oxide layer is damaged, it reforms in milliseconds.
c. 10 x strength bone, pliable but rigid
d. no reports of titanium allergy, toxicity, or tumorigenesis
e. low density of the metal allows it to have minimal x-ray attenuation and hence
a lack of artifact on computed tomographic or magnetic imaging
f. permits osseointegration - defined as a direct contact between metal and bone,
without a fibrous interface, at the light microscopic level
Textiles/Polymers
The structure of polymers consists of long chains of repeating basic units that can
reach high molecular weights. Commonly used polymer biomaterials include silicone,
polyurethane, polymethylmethacrylate, polyesters, nylon, polyethylene, polypropylene,
cyanoacrylates, and polytetrafluoroethylene.
Silicones – Poly-Dimethylsiloxane
 Synthetic polymers containing a non-carbon chain Si-O backbone with organic
group (mostly methyl) attached to the silicon atom
 extremely resistant to degradation in the body because of the very strong and stable
silicon-oxygen bonds
 viscosity depends on amount of cross linking between between different strands of
polydimethylsiloxane (liquid to rubber)
 Solid silicone
o offers the advantages of easy sterilization by steam autoclaving or irradiation
without degradation of the implant (sterilizing with ethylene oxide requires
significant aeration afterward because of its solubility in silicone), easy
intraoperative modification by scalpel or scissors, retained flexibility through
a wide range of temperature, stabilization by suture or screw fixation through
the implant, and a fairly economical price.
o high degree of chemical inertness and is hydrophobic and extremely resistant to
degradation, and no significant clinical toxicity or allergic reactions seem to
exist
o Tissue ingrowth or attachment to the implant does not occur, and it acts as a
relatively inert filler with a predictable surrounding fibrous encapsulation,
which may change very little, if at all, over a long period of implantation
o where the implant is exposed to mechanical loading, fragmentation of the
material and a synovitis may occur as a result of this substance's poor
mechanical properties
 Liquid silicone
o Unlike its solid counterpart, silicone liquid or gel may not be as inert in
human tissue.
o It is associated with an increased fibroplastic response with a tendency for
migration of the material.
o can be broken down into smaller particles, which may result in macrophage
phagocytosis.
o can potentially lead to a chronic inflammatory response and granuloma
formation at the local site, similar to a foreign-body reaction.
o cellular response also creates the possibility for protein binding and a haptenlike incomplete antigen, which has been shown experimentally, but no adverse
immunologic response in humans has yet to be clinically demonstrated
o thus - silicone liquids or gels should never be intentionally injected into
human tissues
Polyethylene (Medpor- High Density Porous PE)
 Solid and porous forms. Used extensively in cranioplasty. Allows bone and soft
tissue ingrowth. Medpor available as sheets or blocks
 nonresorbable and highly biocompatible with no tendency for chronic inflammatory
reactions
 currently available commercially in three major grades: low- and high-density and
ultrahigh molecular weight polyethylene
 ultrahigh molecular weight grade is used for load-bearing orthopedic implant
fabrications because of its superior mechanical properties with little propensity for
creep.
 high-density variation is used in plastic surgery because of its higher tensile
strength over low-density grades.
 Unlike PTFE, polyethylene has a much firmer consistency that resists material
compression but permits a degree of flexibility
 intramaterial porosity with a pore size between 125 and 250 μm, which permits
extensive fibrovascular ingrowth throughout the implant
 Limited bone ingrowth may occur in select clinical circumstances, but the material
should not be considered truly osteoconductive.
 Forms:
o Medpor- high-density, porous polyethylene implant that is widely used in facial
reconstruction.
o Marlex mesh
o Polypropylene (Prolene) mesh, - made by substituting one methyl group for a
hydrogen atom in each polyethylene unit of the polymer chain, has become
more widely used because of its ability to be autoclaved

Polypropylene (Marlex)
Surgical mesh. Highly porous; autoclavable
Polytetrafluoroethylene (Gortex, Teflon) ie PTFE
 inert and highly biocompatible
 carbon-ethylene backbone to which are attached four fluorine molecules
 bonding of highly reactive fluorine to carbon creates an extremely stable
biomaterial that is not biodegradable in the body because of the absence of any
known human enzyme to disrupt the fluorine-carbon bonds
 surface is very nonadherent with significant antifrictional properties. Due to the
lack of cross-linking in its molecular structure, it is very flexible with a low tensile
strength
 available as sutures, patch or augmentation implants
 The main application for patches has been in the reconstruction of orbital floor
defects and abdominal fascial reconstruction
 Also a variety of blocks, preformed implants, and strips and strands are available for
facial augmentation from subperiosteal to subdermal placement
 Strips are composed of fine expanded polytetrafluoroethylene fibrils that are
oriented and held together by solid pieces of the same material. The fibrillar
composition results in noninter-connected surface openings with pore sizes between
10 to 30 μm. This allows for some soft-tissue ingrowth, less fibrous encapsulation,
and little tendency for migration
Polyester
 comprise a diverse group of surgical devices that have a wide range of forms (e.g.,
suture, mesh, vascular conduits, plates, and screws)
 Nonbiodegradable aromatic polyester vs biodegradable aliphatic polyesters
 Aromatic Polyester
o Polyethylene terephthalate (Dacron) is a biocompatible, flexible,
nonabsorbable polymer that is used as a suture material, as a prosthetic
material for arterial replacement, and as a mesh (Mersilene mesh). It is a
suitable implant for applications that require both tensile strength and
stability, and has been used for abdominal and chest wall reconstruction, as
well as for chin and nasal augmentation
 Aliphatic Polyesters
o resorption of these devices is a two-phase process beginning with a
physicochemical process of absorption of water (hydrolysis), which separates
the ester linkages, followed by metabolic cellular response through
fibrovascular ingrowth, which permits macrophages to clear the monomeric
debris
o As a general rule, molecular weight reduction by means of hydrolysis
precedes strength loss, which precedes mass loss. Thus, a resorbable implant
will have lost its mechanical strength long before the polymer material is
resorbed
o Dexon suture (pure polyglycolic acid)
o Vicryl (90% polyglycolic/10% polylactic)
o Monocryl (polyglecaprone)
o Lactosorb plate (82% polylactic and 18% polyglycolic acid)
Acrylic
 derived from polymerized esters of either acrylic or methylacrylic acids.
 polymethylmethacrylate resin is used in plastic surgery in cranioplasty procedures
for filling full-thickness cranial defects or in secondary forehead contouring
 fabricated intraoperatively (cold-curing) by mixing a liquid monomer with a
powdered polymer
 exothermic reaction results (temperatures can be as high as 80°C) creating a rigid,
nearly translucent plastic
 the monomer is extremely allergenic and cytotoxic, the mixing and initial
polymerization process occurs outside of the body,
 In contouring procedures, metal or resorbable screws can be placed initially before
application of the material for anchorage and fixation of the final implant.
 Advantages:
1. very low cost
2. intraoperative fabrication and adaptation (contourable with a handpiece and
burr after curing)
3. can be loaded with antibiotics by mixing antibiotic powder in the acrylic resin,
4. is very durable
5. can be heated or autoclaved without change in its physical form.
 Disadvantages
1. very profound and offensive odor when mixed that has caused allergic
reactions through its fumes in operative personnel in the same room
2. high cure temperatures require cool irrigation after placement until set to
prevent thermal damage to adjacent tissues
3. material has a very high bacterial adhesion property that makes it poorly
tolerated in the body once infected or in close proximity to the oral cavity, airfilled sinuses, or in tissues with recent infection.
4. thinning of the overlying skin, implant exposure, and infection can occur
with long-term implantation in pediatric cranioplasties.
 Also available as a preformed (heat-cured) craniofacial implant that is custommanufactured to the patient's defect from a computed tomographic scan - useful as a
replacement for large, full-thickness defects involving the cranial, frontal, and
orbital regions where sufficient autologous material may not be available
 Cyanoacrylate
o
quick-setting, biodegradable, polymeric tissue adhesives that have become
useful tissue-bonding agents
o
polymerize by an exothermic reaction in the presence of water and
hydroxyl groups on the wound surface,
o
Histoacryl degrade more slowly than the methyl and ethyl cyanoacrylates,
and therefore cause less tissue toxicity since the host tissues are able to
clear the toxic metabolites more readily. Histoacryl is the safest of the
cyanoacrylate tissue adhesives
o
Experimental and clinical applications of cyanoacrylates include
sutureless skin closure, fixation of bone and cartilage grafts, fixation of
craniofacial fractures, tendon repair, tarsorrhaphy, and repair of retinal
detachments and corneal perforations.
Polyamide
 organopolymer derivatives of nylon, chemically related to the polyester family of
materials, and are best known clinically as a mesh material (Supramid).
 very hydroscopic, are structurally unstable in vivo, and undergo hydrolytic
degradation.
 once used for nasal contouring and augmentation genioplasty, clinical experience
ultimately confirmed the animal work with fibrosis and resorption of the material
over time. Now historical
Ceramics
 Note – demineralised bone matrix allografts contains human bone matrix proteins
that are osteoinductive. Some contain particles of whole bone, which are
osteoconductive.
Calcium Phosphate
 bioactive (capable of osteoconduction) and have the potential to develop actual
tissue ingrowth and integration into the recipient site after placement.
 not osteoinductive
 Extremely biocompatible
 very well tolerated with essentially no inflammatory response, minimal fibrous
encapsulation, and no negative effects on local bone mineralization
 manufactured as hydroxyapatite [Ca10(PO4)6(OH)2], which is the principal inorganic
component of bone, accounting for up to 70 percent of the calcified skeleton. I
 manufactured as either ceramic or nonceramic apatites
1. Ceramic hydroxyapatite – available as granules or blocks
 Dense vs porous forms

Porous forms (50 to 200 μm) permits fibrovascular and osseous
ingrowth and the potential for cell-mediated resorption and osseous
replacement
2. Nonceramic hydroxyapatite - powder and liquid mixtures
 mixed intraoperatively, filled or contoured into the bony defect
 because of its limited shear resistance, its use is limited to nonstress
bearing craniofacial regions
 BoneSource – bone cement mixed with sodium phosphate solution to
accelerate set time. Isothermic
 Other brands – SRS(Norian), alpha BSM.
Tricalcium phosphate Ca3(PO4)2
 Unlike hydroxyapatite, tricalcium phosphate is resorbable, with resorption rates
ranging from 30% to 85% by 6 months, depending on the porosity and implantation
conditions.
 Sobio is a ceramic bone substitute composed of hydroxyapatite and tricalcium
phosphate – tricalcium dissolves to leave hydroxyapatite framework for
osseoconduction.
Calcium Sulfate (Osteoset)
 Highly purified plaster of paris
 Rapidly resorbed and no inherent structural strength.
 No effect on bone healing found in 1 randomised study on tibia
 In an attempt to increase the amount of bone ingrowth within the implant., Calcium
phosphate ceramics have been combined with
o bone growth factor-2 (BMP)
o TGF-B1
o bFGF in hyaluronic acid
o bovine collagen
o chitosan (a biopolymer extracted from crustacean shells)
Biosynthetic materials (collagen, fibril)
See:
skin substitutes
soft tissue fillers