POLYMERIC IMPLANTS

Biodegradable suture

Intraocular Lens

Wound dressing

Contact Lens

Some Commonly Used Polymers

Material Applications Silicone rubber Catheters, tubing Dacron Vascular grafts Cellulose Dialysis membranes Poly(methyl methacrylate) Intraocular lenses, bone cement Polyurethanes Catheters, pacemaker leads Hydogels Opthalmological devices, Drug DeliveryCollagen (reprocessed) Opthalmologic applications, wound

dressings

Polymer Devices

Advantages: Disadvantages:

Examples:Some joint replacement articulating surfacesSpinal cagesBiodegradable bone plates for low load regionsBiodegradable sutures

Hip joint Spinal cage for spine fusion Bone plates

Mechanical Properties: Why is important to study for all biomaterials?

Toe implant

polymermetal

polymer

______________ hydrogel ____________

Determines how well it will work (or not work) for a given device.

One major factor is the modulus of the material.

Polymers• Terminology:

– copolymer: polymers of two mer types• random · · ·-B-A-B-A-B-B-A-· · ·• alternating· · ·-A-B-A-B-A-B-A-· · · • block · · ·-A-A-A-A-B-B-B-· · ·

– heteropolymer: polymers of many mer types

COPOLYMER

Polymers Structure

Linear

Branched

Crosslinked

Synthetic Polymers

Biodegradable Synthetic Polymers• Poly(alkylene ester)s

• PLA, PCL, PLGA

• Poly(aromatic/aliphatic ester)s

• Poly(amide-ester)s

• Poly(ester-urethane)s

• Polyanhydrides

• Polyphosphazenes

Biostable Polymers• Polyamides• Polyurethanes• Polyethylene• Poly(vinylchloride)• Poly(hydroxyethylmethacrylate)• Poly(methylmethacrylate)• Poly(tetrafluoroethylene)• Poly(dimethyl siloxane)• Poly(vinylalcohol)• Poly(ethylenglycol)

Stimuli Responsive Poly(ethylene oxide-co-propilene oxide) Poly(methylvinylether) Poly(N-alkyl acrylamide)s Poly(phosphazone)s

PolymersBioinertBiodegradable

PolymersNaturalSynthetic

Synthetic Biomaterials

• POLYMERS: Silicones, Gore-tex (ePTFE), Polyethylenes (LDPE,HDPE,UHMWPE,) Polyurethanes, Polymethylmethacrylate, Polysulfone, Delrin

• Uses: Orthopedics, artificial tendons, catheters, vascular grafts, facial and soft tissue reconstruction

• COMPOSITES: CFRC, self reinforced, hybrids • Uses: Orthopedics, scaffolds• HYDROGELS: Cellulose, Acrylic co-polymers• Uses: Drug delivery, vitreous implants, wound healing• RESORBABLES: Polyglycolic Acid, Polylactic acid, polyesters• Uses: sutures, drug delivery, in-growth, tissue engineering

Polymers: Biomedical Applications

• Polyethylene (PE)– five density grades: ultrahigh, high, low, linear low and

very low density

– UHMWPE and HDPE more crystalline– UHMWPE has better mechanical properties, stability

and lower cost– UHMWPE can be sterilized

(C2H4)nH2

Polymers: Biomedical Applications

• UHMWPE: Acetabular caps in hip implants and patellar surface of knee joints.

• HDPE used as pharmaceutical bottles, fabrics.

• Others used as bags, pouches, tubes etc.

Artificial Hip Joints (UHMWPE)

http://www.totaljoints.info/Hip.jpg

Polymers: Biomedical Applications

• Polymethylmethacrylate (PMMA, lucite, acrylic, plexiglas)

• (C5O2H8)n

– acrylics

– transparency

– tough

– biocompatible

• Used in dental restorations, membrane for dialysis, ocular lenses, contact lenses, bone cements

Intraocular Lens3 basic materials - PMMA, acrylic, silicone

Polymers: Biomedical Applications

• Polyamides (PA, nylon)• PA 6 : [NH−(CH2)5−CO]n made from ε-Caprolactam

– high degree of crystallinity

– interchain hydrogen bonds provide superior mechanical strength (Kevlar fibers stronger than metals)

– plasticized by water, not good in physiological environment

• Used as sutures

Polymers: Biomedical Applications

• Polyvinylchloride (PVC) (monomer residue must be very low)

– Cl side chains

– amorphous, hard and brittle due to Cl

– metallic additives prevent thermal degradation

• Used as blood and solution bags, packaging, IV sets, dialysis devices, catheter, bottles, cannulae

Polymers: Biomedical Applications

• Polypropylene (PP) (C3H6)n

– properties similar to HDPE

– good fatigue resistance

• Used as syringes, oxygenator membranes, sutures, fabrics, vascular grafts

• Polyesters (polymers which contain the ester functional group in their main chain)

• PET (C10H8O4)n

– hydrophobic (beverage container PET)

– molded into complex shapes

• Used as vascular grafts, sutures, heart valves, catheter housings

Polymers: Biomedical Applications

• Polytetrafluoroethylene (PTFE, teflon) (C2F4)n

– low coefficient of friction (low interfacial forces between its surface and another material)

– very low surface energy

– high crystallinity

– low modulus and strength

– difficult to process

• catheters, artificial vascular grafts

Polymers: Biomedical Applications

• Polyurethanes

– block copolymer structure

– good mechanical properties

– good biocompatibility

• tubing, vascular grafts, pacemaker lead insulation, heart

assist balloon pumps

PolyurethanesA urethane has an ester group and amide group bonded to the same carbon. Urethanes can be prepare by treating an isocyanate with an alcohol.

RN C O ROH RNH C

O

OR+

an isocyanate an alcohol a urethane

Polyurethanes are polymers that contain urethane groups.

O C NCH3

N C O

toluene-2,6-diisocyanate

+ HOCH2CH2OHethylene glycol

C

O

NHCH3

NH C

O

OCH2CH2O C

O

NH NH C

O

OCH2CH2O C

OCH3

n

a polyurethane

Synthetic vascular grafts from W.L.Gore

Useful Definitions

BiodegradableUndergoes degradation in the body

- Degradation: _____________________________

- Degradation products are harmless and can be secreted naturally

PLLA bone plates

waterLactic acid

Polymers: Biomedical Applications

• Rubbers

– latex, silicone

– good biocompatibility

• Used as maxillofacial prosthetics

Biomedical polymerBiomedical polymer ApplicationApplicationPoly(ethylene) (PE)Poly(ethylene) (PE) Low density (LDPE)Low density (LDPE) High density (HDPE)High density (HDPE) Ultra high molecular weightUltra high molecular weight (UHMWPE) (UHMWPE)

Bags, tubingBags, tubingNonwoven fabric, catheterNonwoven fabric, catheter  Orthopedic and facial implants Orthopedic and facial implants

Poly(methyl methacrylate) (PMMA) Poly(methyl methacrylate) (PMMA) Intraocular lens, dentures, bone cementIntraocular lens, dentures, bone cement

Poly(vinyl chloride) (PVC) Poly(vinyl chloride) (PVC) Blood bags, catheters, cannulae Blood bags, catheters, cannulae

Poly(ethylene terephthalate) (PET)Poly(ethylene terephthalate) (PET) Artificial vascular graft, sutures,Artificial vascular graft, sutures, heart valves heart valves

Poly(esters)Poly(esters) Bioresorbable sutures, surgicalBioresorbable sutures, surgical products, controlled drug releaseproducts, controlled drug release

Poly(amides) (Nylons)Poly(amides) (Nylons) Catheters, suturesCatheters, sutures

Poly(urethanes) (PU) Poly(urethanes) (PU) Coat implants, film, tubing Coat implants, film, tubing

Table The clinical uses of some of the most common biomedical polymers relate to their chemical structure and physical properties.

Hydrogels• Water-swollen, crosslinked polymeric structure

produced by reactions of monomers or by hydrogen bonding

• Hydrophilic polymers that can absorb up to thousands of times their dry weight in H2O

• Three-dimensional insoluble polymer networks

Applications of Hydrogels

• Soft contact lenses• Pills/capsules• Bioadhesive carriers• Implant coatings• Transdermal drug delivery• Electrophoresis gels• Wound healing• Chromatographic packaging material

Types of Hydrogels

• Classification – Method of preparation

• Homo-polymer, Copolymer, Multi-polymer, Interpenetrating polymeric

– Ionic charge• Neutral, Catatonic, Anionic, Ampholytic

– Physical structure• Amorphous, Semi-crystalline, Hydrogen-bonded

Types of Gelation•Physical , Chemical

ژله اي شدن فيزيكي: زنجيرهاي پليمر از طريق واكنش هاي يوني،

پيوند هيدروژني، درهم گره خوردن مولكولي يا از راه طبيعت

آب گريزي ماده اتصال مي يابند. ژله اي شدن شيميايي: زنجيرهاي هيدروژل با پيوند كوواالنت به يكديگر متصل شده اند. در اين فرآيند، روش هايي نظير تابش،

افزودن اتصال دهنده هاي عرضي شيميايي و تركيبات واكنش گر چند

منظوره به كار مي روند.

Types of Hydrogels • Natural Polymers

– Dextran, Chitosan, Collagen, Alginate, Dextran Sulfate, . . .

– Advantages• Generally have high biocompatibility• Intrinsic cellular interactions• Biodegradable• Cell controlled degradability• Low toxicity byproducts

– Disadvantages• Mechanical Strength• Batch variation• Animal derived materials may pass on viruses

Types of Hydrogels • Synthetic Polymers

– PEG-PLA-PEG, Poly (vinyl alcohol)

– Advantages• Precise control and mass produced• Can be tailored to give a wide range of properties (can be

designed to meet specific needs)• Low immunogenecity • Minimize risk of biological pathogens or contaminants

– Disadvantages• Low biodegradability• Can include toxic substances

• Combination of natural and synthetic– Collagen-acrylate, P (PEG-co-peptides)

Properties of Hydrogels

• Swelling properties influenced by changes in the environment – pH, temperature, ionic strength, solvent

composition, pressure, and electrical potential

• Can be biodegradable, bioerodible, and bioabsorbable

• Can degrade in controlled fashion

Properties of Hydrogels• Pore Size

• Fabrication techniques

• Shape and surface/volume ratio

• H2O content

• Strength

• Swelling activation

Advantages of Hydrogels• Environment can protect cells and other substances (i.e.

drugs, proteins, and peptides)

• Timed release of growth factors and other nutrients to ensure proper tissue growth

• Good transport properties

• Biocompatible

• Can be injected

• Easy to modify

Disadvantages of Hydrogels

• Low mechanical strength

• Hard to handle

• Difficult to load

• Sterilization

Why Hydrogels ?: Tissue Engineering

• Biocompatible• H2O content • Sterilizibilty• Ease of use• High mechanical

Strength • Surface to volume ratio• Good cell adhesion • High nutrient transport

Why Hydrogels?: Cell Culture Systems

• Biocompatible substrate – Non-toxic and have no immunological

responses• Cytoarchitecture which favors cell growth

– Flexibility for cells to rearrange in 3-D orientation

– Seeded with appropriate growth and adhesion factors

– Porosity (i.e. channels for nutrients to be delivered)

Why Hydrogels?: Cell Culture Systems

• Mimic cytomechanical situations– 3-D space provides balanced cytoskeleton

forces– Dynamic loading to promote cell growth

• Flexibility– Provide scaffold for various cells

• Consistent, reproducible and easy to construct

Why Hydrogels?: Drug Delivery

• Safe degradation products• Biocompatible • High loading with ensured molecule efficacy • High encapsulation• Variable release profile • Stable • Inexpensive • High quality

• Hydrogels are network polymers that swell through a variety of mechanisms in an aqueous environment

• Environment controls mechanisms of swelling:– pH, ionic strength, solvent composition, pressure

and even electric fields• Applications in medicine, engineering, and

biology

Chitosan• Chitosan (2-amino-2deoxy-

(1→4)-β-D-glucopyranan), a polyaminosaccharide,

• obtained by alkaline deacetylation of chitin (the principal component of living organisms such as fungi and crustacea).

Chitosan’s key properties:

• 1) biocompatibility • 2) nonantigenicity • 3) nontoxicity (its degradation products are

known natural metabolites) • 4) the ability to improve wound healing/or clot

blood • 5) the ability to absorb liquids and to form

protective films and coatings, and • 6) selective binding of acidic liquids, thereby

lowering serum cholesterol levels.

Alginate

Mannuronic acid Guluronic acid

These products are produced from naturally occurring calcium and sodium salts of alginic acid found in a family of brown seaweed.

Alginates are rich in either mannuronic acid or guluronic acid, the relative amount of each influence the amount of exudate absorbed and the shape the dressing will retain.

کتاب زیستمواد، اندامهای 11 و 10فصل •مصنوعی و مهندسی بافت