GITAM DENTAL COLLEGE & HOSPITAL

VISAKHAPATNAM - 45

DEPARTMENT OF

ORAL & MAXILLOFACIAL SURGERY

SEMINAR ON

BIOMATERIALS IN ORAL AND MAXILLOFACIAL SURGERY

Presented by

Dr. M.PRUDHVI RAJ

III MDS

TABLE OF CONTENTS

INTRODUCTION

AIM & OBJECTIVE

MATERIALS

APPLICATIONS

CONCLUSION

BIBLIOGRAPHY

INTRODUCTION

Biomaterial is used to make devices to replace a part or a function of the body in

a safe, reliable, economic, and physiologically acceptable manner.

A variety of devices and materials presently used in the treatment of disease or

injury include such common place items as sutures, needles, catheters, plates,

tooth fillings, etc.

The use of biomaterials did not become practical until the advent of an aseptic

surgical technique developed by Dr. J. Lister in the 1860s. Earlier surgical

procedures, whether they involved biomaterials or not, were generally

unsuccessful as a result of infection. Problems of infection tend to be

exacerbated in the presence of biomaterials, since the implant can provide a

region inaccessible to the body’s immunologically competent cells. The earliest

successful implants, as well as a large fraction of modern ones, were in the

skeletal system.

Definitions of biomaterials :

1) A Biomaterial can be simply defined as a synthetic material used to

replace part of a living system or to function in intimate contact with living

tissue.

2) The Clemson University Advisory Board for Biomaterials has formally

defined a biomaterial to be “a systemically and pharmacologically inert

substance designed for implantation within or incorporation with living

systems.”

3) Black (1992) defined biomaterials as “a nonviable material used in a

medical device, intended to interact with biological systems”.

4) Bruck (1980) defined biomaterials as “materials of synthetic as well as of

natural origin in contact with tissue, blood, and biological fluids, and

intended for use for prosthetic, diagnostic, therapeutic, and storage

applications without adversely affecting the living organism and its

components”.

5) Williams (1987) defined the biomaterials as “any substance (other than

drugs) or combination of substances, synthetic or natural in origin, which

can be used for any period of time, as a whole or as a part of a system

which treats, augments, or replaces any tissue, organ, or function of the

body”.

Selection of Biomedical Materials

The process of material selection should ideally be for a logical sequence

involving:

1. Analysis of the problem;

2. Consideration of requirement;

3. Consideration of available material and their properties leading to:

4. Choice of material.

The choice of a specific biomedical material is now determined by consideration

of the following:

1. A proper specification of the desired function for the material;

2. An accurate characterization of the environment in which it must function,

and the effects that environment will have on the properties of the

material;

3. A delineation of the length of time the material must function;

4. A clear understanding of what is meant by safe for human use.

As the number of available materials increases, it becomes more and more

important to be protected from unsuitable products or materials, which haven't

been thoroughly evaluated. Most manufacturers of materials operate an

extensive quality assurance program and materials are thoroughly tested before

being released to the general practitioner.

1. Standard Specifications: Many standard specification tests of both national

and international standards organizations (ISO) are now available, which

effectively maintain quality levels. Such specifications normally give details

for:

(a) the testing of certain products,

(b) the method of calculating the results

(c) the minimum permissible result, which is acceptable.

2. Laboratory Evaluation: Laboratory tests, some of which are used in

standard specification, can be used to indicate the suitability of certain

materials. It is important that methods used to evaluate materials in

laboratory give results, which can be correlated with clinical experience.

3. Clinical Trials: Although laboratory tests can provide many important and

useful data on materials, the ultimate test is the controlled clinical trial and

verdict of practitioners after a period of use in general practice. Many

materials produce good results in the laboratory, only to be found lacking

when subjected to clinical use. The majority of manufacturers carry out

extensive clinical trials of new materials, normally in cooperation with a

university or hospital department, prior to releasing a product for use by

general practitioners.

TYPES OF BIOMATERIALS

The most common classes of materials used as biomedical materials are:

1. polymers,

2. metals

3. ceramics.

These three classes are used singly and in combination to form most of the

implantation devices available today.

I) Metallic biomaterials

Metals are used as biomaterials due to their excellent electrical and thermal

conductivity and mechanical properties. Since some electrons are independent in

metals, they can quickly transfer an electric charge and thermal energy. The

mobile free electrons act as the binding force to hold the positive metal ions

together. This attraction is strong, as evidenced by the closely packed atomic

arrangement resulting in high specific gravity and high melting points of most

metals. Since the metallic bond is essentially nondirectional, the position of the

metal ions can be altered without destroying the crystal structure resulting in a

plastically deformable solid.

The first metal alloy developed specifically for human use was the “vanadium

steel” which was used to manufacture bone fracture plates (Sherman plates) and

screws. Most metals such as iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni),

titanium (Ti), tantalum (Ta), niobium (Nb), molybdenum (Mo), and tungsten (W)

that were used to make alloys for manufacturing implants can only be tolerated

by the body in minute amounts. Sometimes those metallic elements, in naturally

occurring forms, are essential in red blood cell functions (Fe) or synthesis of a

vitamin B 12 (Co), but cannot be tolerated in large amounts in the body [Black,

1992].The metallic systems most frequently used in the body are:

(a) Iron-base alloys of the 316L stainless steel

(b) Titanium and titanium-base alloys, such as

(i)Ti-6% Al-4%V, and commercially pure ≥ 98.9%

(ii) Ti-Ni (55% Ni and 45% Ti)

(c) Cobalt base alloys of four types

(i) Cr (27-30%), Mo (5-7%), Ni (2-5%)

(ii) Cr (19-21%), Ni (9-11%), W (14-16%)

(iii) Cr (18-22%), Fe (4-6%), Ni (15-25%), W (3-4%)

(iv)Cr (19-20%), Mo (9-10%), Ni (33-37%)

1) Stainless steel :

The first stainless steel utilized for implant fabrication was the 18-8 (type 302 in

modern classification), which is stronger and more resistant to corrosion than the

vanadium steel.

Later 18-8s Mo stainless steel was introduced which contains a small percentage

of molybdenum to improve the corrosion resistance in chloride solution (salt

water). This alloy became known as type 316 stainless steel.

In the 1950s the carbon content of 316 stainless steel was reduced from 0.08 to a

maximum amount of 0.03% (all are weight percent unless specified) for better

corrosion resistance to chloride solution and to minimize the sensitization, and

hence became known as type 316L stainless steel.

The minimum effective concentration of chromium is 11% to impart corrosion

resistance in stainless steels. The chromium is a reactive element, but it and its

alloys can be passivated by 30% nitric acid to give excellent corrosion resistance.

The austenitic stainless steels, especially types 316 and 316L , are most widely

used for implant fabrication. These cannot be hardened by heat treatment but

can be hardened by cold-working. This group of stainless steels is nonmagnetic

and possesses better corrosion resistance than any others. The inclusion of

molybdenum enhances resistance to pitting corrosion in salt water.

Compositions of 316L Stainless Steel

(American Society for Testing and Materials)

Element Composition (%)

Carbon 0.03 max

Manganese 2.00 max

Phosphorus 0.03 max

Sulfur 0.03 max

Silicon 0.75 max

Chromium 17.00–20.00

Nickel 12.00–14.00

Molybdenum 2.00–4.00

2) Cobalt chromium ( Co Cr) alloys :

There are basically two types of cobalt-chromium alloys:

1) The castable CoCrMo alloy

2) The CoNiCrMo alloy which is usually Wrought by (hot) forging .

The castable CoCrMo alloy has been used for many decades in dentistry and,

relatively recently, in making artificial joints.

The wrought CoNiCrMo alloy is relatively new, now used for making the stems of

prosthesis for heavily loaded joints such as the knee and hip.

The ASTM lists four types of CoCr alloys which are recommended for surgical

implant applications:

1) cast CoCrMo alloy (F75)

2) wrought CoCrWNi alloy (F90)

3) wrought CoNiCrMo alloy (F562),

4) wrought CoNiCrMoWFe alloy (F563).

At the present time only two of the four alloys are used extensively in implant

fabrications, the castable CoCrMo and the wrought CoNiCrMo alloy.

The two basic elements of the CoCr alloys form a solid solution of up to 65% Co.

The molybdenum is added to produce finer grains which results in higher

strengths after casting or forging. The chromium enhances corrosion resistance

as well as solid solution strengthening of the alloy.

The CoNiCrMo alloy originally called MP35N (Standard Pressed Steel Co.) contains

approximately 35% Co and Ni each. The alloy is highly corrosion resistant to

seawater (containing chloride ions) under stress. However, there is a

considerable difficulty of cold working on this alloy, especially when making large

devices such as hip joint stems. Only hot-forging can be used to fabricate a large

implant with the alloy.

3) Titanium Alloys :

A) Pure Titanium and Ti6Al4V :

Titanium used for implant fabrication since 1930s.

Titanium’s lightness (4.5 g/cm3) and good mechanochemical properties

are salient features for implant application.

There are four grades of unalloyed commercially pure (cp) titanium for surgical

implant applications.

The impurity contents separate them; oxygen, iron, and nitrogen should be

controlled carefully. Oxygen in particular has a great influence on the ductility

and strength.

The main alloying elements of the alloy are aluminum (5.5~6.5%) and vanadium

(3.5~4.5%).

Titanium is an allotropic material, which exists as a hexagonal close packed

structure up to 882°C and body-centered cubic structure above that

temperature. Titanium alloys can be strengthened and mechanical properties

varied by controlled composition and thermomechanical processing techniques.

The addition of alloying elements to titanium enables it to have a wide range of

properties:

(1) Aluminum tends to stabilize the alpha-phase, that is increase the

transformation temperature from alpha to beta -phase

(2) vanadium stabilizes the beta-phase by lowering the temperature of the

transformation from alpha to beta phase.

The alpha-alloy has a single-phase microstructure which promotes good

weldability. The stabilizing effect of the high aluminum content of these groups

of alloys makes excellent strength characteristics and oxidation resistance at high

temperature (300~600°C). These alloys cannot be heat treated for precipitation

hardening since they are single-phased.

The addition of controlled amounts of beta-stabilizers causes the higher strength

beta-phase to persist below the transformation temperature which results in the

two-phase system. The precipitates of beta-phase will appear by heat treatment

in the solid solution temperature and subsequent quenching, followed by aging

at a somewhat lower temperature.

The aging cycle causes the coherent precipitation of some fine alpha particles

from the metastable beta particles;

Imparting alpha structure may produce local strain field capable of absorbing

deformation energy. Cracks are stopped or deterred at the alpha particles, so

that the hardness is higher than for the solid solution.

The higher percentage of beta-stabilizing elements (13%V in Ti13V11Cr3Al alloy)

results in a microstructure that is substantially beta which can be strengthened

by heat treatment. Another Ti alloy (Ti13Nb13Zr) with 13% Nb and 13% Zr

showed martensite structure after being water quenched and aged, which

showed high corrosion resistance with low modulus (E = 79 MPa).

Formation of plates of martensite induces considerable elastic distortion in the

parent crystal structure and increases strength.

B) TiNi Alloys

The titanium–nickel alloys show unusual properties i.e., after it is deformed the

material can snap back to its previous shape following heating of the material.

This phenomenon is called shape memory effect (SME). The SME of TiNi alloy

was first observed by Buehler and Wiley at the U.S. Naval Ordnance Laboratory

[Buehler et al., 1963].

The equiatomic TiNi or NiTi alloy (Nitinol) exhibits an exceptional SME near room

temperature: if it is plastically deformed below the transformation temperature,

it reverts back to its original shape as the temperature is raised. The SME can be

generally related to a diffusionless martensitic phase transformation which is also

thermoelastic in nature, the thermoelasticity being attributed to the ordering in

the parent and martensitic phases [Wayman and Shimizu, 1972].

Another unusual property is the superelasticity. As can be seen, the stress does

not increase with increased strain after the initial elastic stress region and upon

release of the stress or strain the metal springs back to its original shape in

contrast to other metals such as stainless steel. The superlastic property is

utilized in orthodontic archwires since the conventional stainless steel wires are

too stiff and harsh for the tooth. In addition, the shape memory effect can also be

utilized.

Some possible applications of shape memory alloys are orthodontic dental

archwire, intracranial aneurysm clip, vena cava filters , contractile artificial

muscles for an artificial heart, vascular stent, catheter guide wire, and orthopedic

staple [Duerig et al., 1990]

4) Dental metals :

A. Dental amalgam

B. Gold and gold alloys

5) Other metals :

A. Tantalum

B. Platinum group metals (PGM) such as Pt, Pd, Rh, Ir, Ru, and Os

II) CERAMIC BIOMATERIALS

The most frequently used ceramic implant materials include aluminum oxides,

calcium phosphates, and apatites and graphite. Glasses have also been developed

for medical applications.

The use of ceramics was motivated by:

(i) their inertness in the body,

(ii) their formability into a variety of shapes and porosities,

(iii) their high compressive strength, and

(iv) some cases their excellent wear characteristics.

Applications of ceramics are in some cases limited by their generally poor

mechanical properties:

(a) in tension;

(b) load bearing, implant devices that are to be subjected to significant

tensile stresses must be designed and manufactured with great care if

ceramics are to be safely used.

Ceramics are used for the repair and restoration of diseased or damaged parts

of the musculo-skeletal system.

1) Nonabsorbable or Relatively Bioinert Bioceramics

A. Pyrolitic carbon-coated devices

B. Dense and nonporous aluminum oxides

C. Porous aluminum oxides

D. Zirconia ceramics

E. Dense hydroxyapatites

2) Biodegradable or Resorbable Ceramics

A. Aluminum–calcium–phosphorous oxides

B. Glass fibers and their composites

C. Corals

D. Calcium sulfates, including plaster of Paris

E. Ferric–calcium–phosphorous oxides

F. Hydroxyapatites

G. Tricalcium phosphate

H. Zinc–calcium–phosphorous oxides

I. Zinc–sulfate–calcium–phosphorous oxides

3) Bioactive or Surface-Reactive Ceramics

A. Bioglass and Ceravital

B. Dense and nonporous glasses

C. Hydroxyapatite

III) Polymeric Biomaterials

Polymers have assumed an important role in medical applications. In most

of these applications, polymers have little or no competition from other types of

materials. Their unique properties are:

1- Flexibility;

2- Resistance to biochemical attack;

3- Good biocompatibility;

4- Light weight;

5- Available in a wide variety of compositions with adequate physical and

mechanical properties;

6- Can be easily manufactured into products with the desired shape.

There are a large number of polymeric materials that have been used as implants

or part of implant systems. The polymeric systems include acrylics, polyamides,

polyesters, polyethylene, polysiloxanes, polyurethane, and a number of

reprocessed biological materials.

Some of the applications include the use of membranes of ethylene-vinyl-acetate

(EVA) copolymer for controlled release and the use of poly-glycolic acid for use as

a resorbable suture material.. As bioengineers search for designs of ever

increasing capabilities to meet the needs of medical practice, polymeric materials

alone and in combination with metals and ceramics are becoming increasingly

incorporated into devices used in the body.

1) Polyvinylchloride (PVC)

2) Polyethylene (PE)

3) Polypropylene (PP)

4) Polymethylmetacrylate (PMMA)

5) Polystyrene (PS)

6) Polyethylenterephthalate (PET)

7) Polytetrafluoroethylene (PTFE)

8) Polyurethane (PU)

9) Polyamide (nylon)

(PTFE) Polytetrafluoroethylene is a fluorocarbon–based polymer.

Commercially, the material is best known as Teflon. It is made by free-radical

polymerization of tetrafluoroethylene and has a carbon backbone chain, where

each carbon has two fluorine atoms attached to it.

Properties of PTFE

1-Hydrophobic (Water hating)

2- Biologically inert*

3- Non-biodegradable

4- Has low friction characteristics

5- Excellent "Slipperiness"

6- Relatively lower wear resistance.

7- Highly crystalline (94%)

8- Very high density (2.2 kg.m-3)

9- Low modulus of elasticity (0.5MPa)

10- Low tensile strength (14MPa)

PTFE has many medical uses, including:

1- Arterial grafts (artificial vascular graft);

2- Catheters;

3- Sutures;

4- Uses in reconstructive and cosmetic facial surgery.

PTFE can be fabricated in many forms, such as:

1- Can be woven into a porous fabric like mesh. When implanted in the

body, this mesh allows tissue to grow into its pores, making it ideal for

medical devices, such as vascular grafts;

2- Pastes;

3- Tubes;

4- Strands;

5- Sheets.

Disadvantages of PTFE

PTFE has relatively low wear resistance. Under compression or in

solutions where rubbing or abrasion can occur, it can produce wear particles.

These can result in a chronic inflammatory reaction, an undesirable outcome.

Polyethylene, (PE)

It is chemically the simplest of all polymers and as a homochain polymer.

It is essentially:

1- Stable and suitable for long-time implantation under many

circumstances;

2- Relatively inexpensive;

3- Has good general mechanical properties.

So that it has become a versatile biomedical polymer with applications

ranging from catheters to joint-replacement.

Polypropylene, (PP)

Polypropylene is widely used in medical devices ranging from sutures to

finger joints and oxygenerators.

Poly (methyl methacrylate), PMMA

It is a hard brittle polymer that appears to be unsuitable for most clinical

applications, but it does have several important characteristics.

(a) It can be prepared under ambient conditions so that it can be

manipulated in the operating theater or dental clinic, explaining its

use in dentures and bone cement.

(b) The relative success of many joint prostheses is dependent on the

performance of the PMMA cement, which is prepared intraoperatively

by mixing powdered polymer with monomeric

methylmethacrylate, which forms a dough that can be placed in

the bone, where it then sets.

The disadvantages of PMMA

(a) The exotherm of polymerization;

(b) The toxicity of the volatile methylmethacrylate;

(c) The poor fracture toughness.

(But no better material has been developed to date)

Polyesters

Polyurathanes

MATERIALS IN MAXILLOFACIAL PROSTHETICS

Despite improvements in surgical and restorative techniques, the materials

used in maxillofacial prosthetics are far from ideal. An ideal material should be

inexpensive, biocompatible, strong, and stable. In addition, the material should

be skin-like in color and texture. Maxillofacial materials must exhibit resistance

to tearing and should be able to withstand moderate thermal and chemical

challenges. Currently, no material fulfills all of these requirements. A brief

description of maxillofacial materials is included in the following paragraphs:

LATEXES

Latexes are soft, inexpensive materials that may be used to create lifelike

prostheses. Unfortunately, these materials are weak, degenerate rapidly, exhibit

color instability and can cause allergic reactions. A recently developed synthetic

latex is a tripolymer of butylacrylate, methyl methacrylate, and methyl

metharylamide. This material is nearly transparent, but has limited applications.

VINYL PLASTISOLS

They are plasticized vinyl resin sometimes are used in maxillofacial applications.

Plastsols are thick liquids comprising small vinyl particles dispersed in a plasticizer.

Colorants are added to these materials to match individual skin tones.

Unfortunately, vinyl plastisols harden with age because plasticizer loss. Ultraviolet

light also has an adverse effect on these materials. For these reasons, the use of

vinyl is limited.

SILICONE RUBBERS

Both heat-vulcanizing and room temperature vulcanizing silicones are in use

today and both exhibit advantages and disadvantages. Room temperature

vulcanizing silicones are supplied as single- paste systems. These silicones are not

as strong as the heat-vulcanized silicones and generally are monochromatic.

Heat-vulcanizing silicone is supplied as a semi-solid material that requires milling,

packing under pressure, and 30-minute heat treatment application cycle at

180oC. Heat vulcanizing silicone displays better strength and color than room

temperature vulcanizing silicone.

POLYURETHANE POLYMERS

Polyurethane is the most recent of the materials used in maxillofacial prosthetics.

Fabrication of a polyurethane prosthesis requires accurate proportioning of three

materials. The material is placed in a stone or metal mold and allowed to

polymerize at room temperature. Although a polyurethane prosthesis has a

natural feel and appearance, it is susceptible to rapid deterioration. The loss of

natural teeth, through disease or trauma, has for many years been compensated

by the provision of artificial teeth in the form of bridges and dentures. These

essentially provide an aesthetic replacement of crown of the tooth but do nothing

to replace the root and its attachment to the bone of the jaw.

NATURAL POLYMERS

Natural polymers, or polymers, derived from living creatures, are of great

interest in the biomaterials field. In the area of tissue-engineering, for example,

scientists and engineers look for scaffold on which one may successfully grow

cells to replace damaged tissue.

Typically, it is desirable for these scaffolds to be:

(1) Biodegradable;

(2) Non-toxic/ non-inflammatory;

(3) Mechanically similar to the tissue to be replaced;

(4) Highly porous;

(5) Encouraging of cell attachments and growth;

(6) Easy and cheap to manufacture;

(7) Capable of attachment with other molecules ( to potentially increase

scaffold interaction with normal tissue)

Normal polymers often easily fulfill these expectations, as they are naturally

engineered to work well within the living beings from which they come. Three

examples of natural polymers that have been previously studied for use as

biomaterials are: collagen, chitosan, and alginate.

IV) COMPOSITE BIOMATERIALS

Composite materials have been extensively used in dentistry and prosthesis

designers are now incorporating these materials into other applications. Typically,

a matrix of ultrahigh-molecular-weight polyethylene (UHMWPE) is reinforced

with carbon fibers. These carbon fibers are made by pyrolizing acrylic fibers to

obtain oriented graphitic structure of high tensile strength and high modulus of

elasticity. The carbon fibers are 6-15mm in diameter, and they are randomly

oriented in the matrix. In order for the high modulus property of the reinforcing

fibers to strengthen the matrix, a sufficient interfacial bond between the fiber and

matrix must be achieved during the manufacturing process. Since the mechanical

properties of these composites with the proportion of carbon fibers in the

composites, it is possible to modify the material design flexibility to suit the

ultimate design of prostheses. Composites have unique properties and are usually

stronger than any of the single materials from which they are made. Workers in

this field have taken advantages of this fact and applied it to some difficult

problems where tissue in-growth is necessary.

- Deposited Al2O3 onto carbon;

- Carbon / PTFE;

- Al2O3 / PTFE;

- PLA-coated Carbon fibers.

Some applications of composites in biomaterial applications are:

(1) dental filling composites

(2) reinforced methyl methacrylate bone cement and ultra-high-molecular-

weight polyethylene

(3) orthopedic implants with porous surfaces.

V) BIODEGRADABLE POLYMERIC BIOMATERIALS

Another class of materials that is receiving increased attention is biodegradable

materials. Generally, when a material degrades in the body its properties change

from their original values leading to altered and less desirable performance. It is

possible, however, to design into an implant's performance the controlled

degradation of a material, such that natural tissue replaces the prosthesis and its

function.

Suture material that hold a wound together but resorb in the body as the wound

heals and gains strength. Another application of these materials occurs when they

are used to encourage natural tissue to grow. Certain wound dressings and

ceramic bone augmentation materials encourage tissue to grow into them by

providing a "scaffold". The scaffold material may or may not resorb over a period

of time but in each case, natural tissue has grown into the space, then by

restoring natural function. One final application of biodegradable materials is in

drug therapy, where it is possible to chemically bond certain drugs to the

biodegradable material, when these materials are placed within the body the

drug is released as the material degrades, thereby providing a localized, sustained

release of drugs over a predictable period of time.

1) Glycolide/Lactide-Based Biodegradable Linear Aliphatic polyesters

A. Glycolide-Based Biodegradable Homopolymer Polyesters

B. Glycolide-Based Biodegradable Copolyesters Having Aliphatic

Polyester-Based Co-Monomers

C. Glycolide-Based Biodegradable Copolyesters with Non-Aliphatic Polyester-

Based Co-Monomers

D. Glycolide-Derived Biodegradable Polymers Having Ether Linkage

E. Lactide Biodegradable Homopolymers and Copolymers

2) Non-Glycolide/Lactide-Based Linear Aliphatic Polyesters

3) Non-Aliphatic Polyesters Type Biodegradable Polymers

A. Aliphatic and Aromatic Polycarbonates

B. Poly(alkylene oxalates) and Copolymers

VI) BIOLOGIC BIOMATERIALS

1) Tissue-Derived Biomaterials (Collagen)

Collagen is the most widely found protein in mammals (25% of our protein

mass) and is the major provider of strength to tissue. A typical collagen

molecule consists of three interwined protein chains that form a helical structure

similar to a typical staircase). These molecules polymerize together to form

collagen fibers of varying length, thickness and interweaving pattern (some

collagen molecules will form ropelike structures, while others will form meshes

or networks). There are actually at least 15 different types of collagen, differing

in their structure, function, location, and other characteristics. The predominant

form used in biomedical applications, however, is type I collagen, which is a

"rope-forming" collagen and can be found almost everywhere in the body,

including skin and bone.

Collagen can be resorbed into the body, is non-toxic produces only a

minimal immune response, and is excellent for attachment and biological

interaction with cell. Collagen may also be processed into a variety of formats,

including porous sponges, gels and sheets, and can be cross-linked with

chemicals to make it stronger or to alter its degradation rate. The number of

biomedical applications in which collagen has been utilized is too high to count

here, it not only explored for use in various types of surgery, cosmetics, and

drug delivery, but in bio-prosthetic implants and tissue-engineering of multiple

organs as well. Cells grown in collagen often come close to behaving as they do

within the body, which is why collagen is so promising when one is trying to

duplicate natural tissue function and healing.

However, some disadvantages to using collagen as a cell substrate do

exist. Depending on how it is processed, collagen can potentially cause

alteration of cell behavior (e.g. changes in growth or movement), have

inappropriate mechanical properties, or undergo contraction (shrinkage).

Because cells interact so easily with collagen, cells can actually pull and

reorganize collagen fibers, causing scaffolds to lose their shape if they are not

properly stabilized by cross-linking or mixing with another less "vulnerable

material". Fortunately, collagen can be easily combined with other biological or

synthetic materials, to improve its mechanical properties or change the way cells

behave when grown upon it.

CHITOSAN

It is derived from chitin, a type of polysaccharide (sugar) that is present in

the hard exoskeletons of shellfish like shrimp and crab. Chitin has sparked

interest in the tissue-engineering field due to several desirable properties:

1- Minimal foreign body reaction;

2- Mild processing conditions (synthetic polymers often need to be

dissolved in harsh chemicals; chitosan will dissolve in water based on pH);

3- Controllable mechanical/biodegradation properties (such as scaffold

porosity);

4- Availability of chemical side groups for attachment to other molecules.

Chitosan has already been investigated for use in the engineering of

cartilage, nerve and liver tissues. Chitosan has also been studied for use in

wound healing and drug delivery. Current difficulties with using chitosan as a

polymer scaffold in tissue-engineering, however, include low strength and

inconsistent behavior with seeded cells. Fortunately, chitosan may be easily

combined with other materials in order to increase its strength and

cellattachment potential. Mixtures with synthetic polymers such as poly (vinyl

alcohol) and poly (ethylene glycol) or natural polymers such as collagen have

already been produced.

ALGINATE

It is a polysaccharide derived from brown seaweed. Like chitosan,

alginate can be processed easily in water and has been found to be fairly nontoxic

and non-inflammatory enough, so that it has been approved in some

countries for wound dressing and for use in food products. Alginate is

biodegradable, has controllable porosity, and may be linked to other biologically

active molecules. Interestingly, encapsulation of certain cell types into alginate

beads may actually enhance cell survival and growth. In addition, alginate has

been explored for use in liver, nerve, heart, and cartilage tissue-engineering.

Unfortunately, some drawbacks of alginate include mechanical weakness and

poor cell adhesion. Again, to overcome these limitations, the strength and cell

behavior of alginate have been enhanced by mixing with other materials,

including the natural polymers agarose and chitosan.

CONCLUSION

In the future, the practice of oral and maxillofacial surgery will be shaped by these

tools. The emerging fields of tissue engineering and biomaterials are truly

exciting. Products of the future, including those from genetically engineered

proteins all the way to tissue-engineered organs, are and will be in clinical trials in

the very near future. Our specialty will benefit from the development of many of

these biomaterials, and our future will be shaped by their use.