Lecture 1 - Biomaterials

8/10/2019 Lecture 1 - Biomaterials

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Medical Biomaterials:From Polymer Implants to Engineered Tissues

Sujata K. BhatiaHarvard University


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Why get involved with medical biomaterials? The incidence of major chronic diseases, including

diabetes, heart disease, and cancer, is rising

The United States has a graying population: in 2030,

over 20% of the U.S. population will be over age 65

(battling degenerative diseases - arthritis, Alzheimers)

These diseases will require innovative medical device

solutions; drugs and lifestyle changes are not enough

Medical devices are extremely beneficial - every $1spent on healthcare returns $3 worth of health gains

Medical devices are valuable a $150 billion industry


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OK, but why shouldI get involved?

Medical biomaterials is a fascinating field,integrating principles of engineering,

biology, chemistry, and medicine

Working in this field allows you to improve

the practice of medicine, and directlyimpact peoples lives

We can be heroesWe can be heroeswhat dwhat dyou say?you say?--David Bowie, 1977David Bowie, 1977


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A person is,A person is,

among all else,among all else,

a material thing,a material thing,easily torn,easily torn,

not easily mended.not easily mended.

--Ian McEwan,Ian McEwan,AtonementAtonement, 2001, 2001

The ParalyticJean-Baptiste Greuze, 1763


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What is a biomaterial anyway?

A biomaterial is a nonviable material usedin a medical device, intended to interact

with biological systems

An essential characteristic of biomaterials is

biocompatibility, the ability of the materialto perform its function without causing an

adverse effect


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Requirements of Biomaterials

Mechanical performance

Mechanical engineering

Desired characteristics of stability or degradability

Chemistry and biochemistry

Biocompatibility and non-toxicity

Molecular biology

Producible at a large scale

Chemical engineering

Clinically beneficial and cost-effective

Medicine


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Clinical Applications ofBiomaterials Orthopedics

Cardiology and Vascular Medicine

Ophthalmology

Dentistry Neurology

General Surgery

Organ Replacement


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Orthopedic Biomaterials Hip replacements

Titanium, polyethylene, ceramic

Knee replacements Titanium, polyethylene

Bone plates (fracture fixation)

Stainless steel Bone cement

Poly(methyl methacrylate)

Bony defect repair Hydroxyapatite

Artificial tendons & ligaments

Dacron, Teflon


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Cardiovascular Biomaterials Blood vessel prostheses

Dacron, Teflon, polyurethane

Heart valves Reprocessed tissue, stainless steel

Intravascular catheters

Polyurethane, Teflon, silicone Pacemakers

Platinum electrodes,

polyurethane, silicone


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Ophthalmic Biomaterials Intra-ocular lens

Poly(methyl methacrylate)

Contact lens Silicone-acrylate, hydrogel

Corneal bandage

Collagen, hydrogel


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Dental Biomaterials Dental implants (tooth fixation)

Titanium, alumina, calcium

phosphate Dental fillings

Ceramic, composites of powdered

glass and plastic resins


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Biomaterials in Neurology Cochlear implants

Platinum electrode

Deep brain stimulation Pacemaker for the brain

Platinum leads


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Biomaterials in General Surgery Skin repair template

Silicone-collagen composite

Surgical sutures Silk, nylon, poly(glycolide-co-

lactide)

Adhesives and sealants Cyanoacrylate, fibrin

Hernia mesh

Polypropylene


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Organ Replacement Biomaterials Heart-lung machine

Silicone rubber

Artificial kidney(hemodialyzer)

Cellulose, polyacrylonitrile

Artificial heart Polyurethane

Hollow-fiber

dialyzer


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Shortcomings of CurrentBiomaterials

Infection Thrombosis (clotting)

Inflammation

Poor healing, leading toencapsulation

Limited durability

Limited adaptability toenvironment

Limited biological activity

Chronic inflammation around wear

debris of polyethylene elbow

prosthesis (top) and knee prosthesis

(bottom)


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The Next Generation ofBiomaterials Surface-modified biomaterials

Dr. Buddy Ratner (University of Washington)

Smart biomaterials

Dr. Nick Peppas (University of Texas, Austin) Bioactive biomaterials

Dr. Elazer Edelman (Harvard/MIT)

Tissue engineered materials

Dr. Robert Langer (MIT)


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Surface-Modified Biomaterials

Attack on a

biomaterial beginswith deposition of

proteins or cells on

the outer surface of

the biomaterial

Maybe attack can be prevented if biomaterialsurfaces are modified to create stealth

surfaces that resist protein & cell adsorption


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Surface-Modified Biomaterials Surface modification can be achieved by

coating with hydrophilic polymer (PEG) Surface-modified biomaterials should be

resistant to clotting, bacterial colonization,

and the foreign body responseU. Washington

Engineered

Biomaterials


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Smart Biomaterials Smart biomaterials

are materials thatrespond to changes

in pH, temperature,

electrical stimuli, orchemical stimuli

These materials can

be made using pH-sensitive or thermo-

sensitive polymers


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Smart Biomaterials Hydrogels with pH-responsive swelling

behavior are made from ionic networks Poly(methacrylic acid) grafted with

poly(ethylene glycol)

Temperature-responsive hydrogels exist also Poly(N-isopropylacrylamide)

Smart biomaterials may have powerfulapplications in drug delivery

An insulin pill that encapsulates drug at pH 2

in the stomach, and swells to release drug at pH 7


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Bioactive Biomaterials Several bioactive biomaterials are already on

the market, with a dramatic clinical impact: Drug-eluting stents for minimally invasive

treatment of coronary artery disease

Chemotherapeutic(BCNU)-eluting wafersfor local treatment of brain cancer

Lupron-releasing implants for local

treatment of prostate cancer Bone-morphogenic protein (BMP)-

releasing implants for spinal surgery and

fracture repair


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Tissue Engineering

Tissue engineering is an

approach to organregeneration in which live

cells are seeded onto a

degradable polymer scaffold

Following implantation,

the polymer constructgradually degrades, and

the live cells grow into

organized tissue


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Tissue Engineering

Tissue engineering has been investigated for

virtually every organ system: Dermal fibroblasts + collagen matrix Skin (in clinical use)

Vascular endothelial cells + tubular scaffold Blood vessels

Vascular endothelial cells + leaflet scaffold

Heart valves Urothelial cells + tubular or flat scaffold Ureters, Bladder

Chondrocytes + molded scaffold Cartilage

Periosteal cells + polymer mesh Bone

Hepatocytes + polymer mesh Liver Enterocytes + tubular scaffold Intestine

Neurons + electrically conducting polymerNerves


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We can rebuild him. WeWe can rebuild him. Wehave the technology. Wehave the technology. We

have the capability to makehave the capability to make

the worldthe worlds first bionic man.s first bionic man.

Steve Austin will be thatSteve Austin will be that

man. Better than he wasman. Better than he wasbefore.before.

BetterBetterstrongerstronger faster.faster.


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Summary Biomaterials have improved

millions of lives by providingmaterial solutions to biomedical

problems

Traditional biomaterials have beenmade from polymers, ceramics, and

metals

The next generation of biomaterials

will incorporate biomolecules,

therapeutic drugs, and living cells

The Agnew Clinic

Thomas Eakins, 1889


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So, do biomaterials make a difference?

50 years ago certain death

25 years ago open bypass surgery

Involves cracking open the chest cavity

Infection, graft clotting, graft failure

15 years agoballoon angioplasty

Vascular injury by balloon; incomplete opening 10 years agobare-metal stent

Risk of re-closure of artery within a few years

Today drug-eluting stent

Combination of drug and device provides lasting solution

Supposeyourdad has a heart attack:


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For More Information Biomedical Engineering Society - www.bmes.org

Society for Biomaterials - www. biomaterials.org

Advanced Medical Technology - www.advamed.org

Science Careers - nextwave.sciencemag.org

Langer, R. and Peppas, N.A. Advances in biomaterials,

drug delivery, and bionanotechnology, AIChE J. 2003;49:2990-3006.

Langer, R. and Tirrell, D.A. Designing materials forbiology and medicine, Nature 2004 Apr 1; 428:487-492.

Bhatia, S.K. and Bhatia, S.R. Biomaterials,Encyclopedia of Chemical Processsing 2005.

Bhatia, S.K. and Bhatia, S.R. Bioactive Devices,Encyclopedia of Chemical Processsing 2009.

Documents

Lecture 1 - Biomaterials