Biomaterials

- Definitions- Classification and Applications- Biomimetics

General Reading - References

• B. D. Ratner, A. S. Hoffman, F. J. Schoen, J. E. Lemons (Editors) 2004: Biomaterials Science: An Introduction to Materials in Medicine, Academic Press, New York.

• F.H. Silver 1994: Biomaterials Medical Devices and Tissue Engineering an Integrated Approach to Chapman and Hall

• L. L. Hench, 1998: Bioceramics J. Am. Ceram. Soc. 81, 1705–1728.

• L. L. Hench, J. M. Polak, 2002: Third-Generation Biomedical Materials, Science 295, 1014–1017.

• D.F. Williams 1992: Medical and Dental Materials vol 14, Science and Technology of Materials VCH.

• S. Hollister, 2005: Porous scaffold design for tissue engineering Nature Materials 4, 518 - 524

• K. Rezwan, Q. Z. Chen, J. J. Blaker, A. R. Boccaccini, 2006: Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering Biomaterials 27, 3413-31.

Definitions of Biomaterials: Different definitions proposed

• “A biomaterial is a systemically or pharmacologically inert substance designed for implantation within or incorporation with living systems” (Clemson Advisory Board for Biomaterials US Govemment Legal Definition)

• Biomaterials are materials of natural or man made origin that are used to direct supplement or replace the functions of living tissue” (J. Black)

• “A non viable material used in medical devices intended to interact with biological systems” (D.F. Willams)

1.Generation: Inert biomaterials

2. Generation: Biochemical active materials

3. Generation: Genetic active biomaterialien

1960s-1980s

1990s …

BIOMATERIALS

Synthetic biomaterials used in medical applications (I).

Materials Group Examples

Rather stable:Polyethylene, Polypropylene, Polydimethyl-siloxane, Polyurethane, Polyte-trafluorethylene, Polyvinylchloride, Poly-amides, Polymethylmethacrylate, Polycarbo-nate, Polyethyleneterephtalate

Degradable:Polyesters (Polyglycolacid, Polylactideacid, Polyhydroxybutyrate, Poly-caprolactone, Polydioxanone)

No specific shape:Hydrogels(Homopoly-mer, Copolymer, Multipolymer, Interpenetra-ting Polymers)

Polymers

Stainless steel (Fe-Cr-Ni-Mo)Co-Cr alloys(Co-Cr-Mo, Co-Cr-W-Ni, Co-Ni-Cr-Mo-Ti)

Ti-alloys (Ti, Ti-6Al-4V, Ti-Ni shape memory)

Amalgames (Hg-Ag,Sn,Cu)

Noblemetals (Au, Ag)

Synthetic biomaterials used in medical applications (II).

Metals

Bioinert: Silicates (porcelain, enstatite),

Oxides (Al2O3, ZrO2, TiO2), C (PyC, diamond)

Bioactive: Phosphates (Ca5(PO4)3/OH, Ca3(PO4)2, Bioglass(45SiO2-6P2O5-20CaO-25NaO), Glass Ceramics (SiO2-CaO-P2O5-Na2O-TiO2)

Bioresorbable: Ca3(PO4)2

Synthetic biomaterials used in medical applications (III).

Ceramics

Composites

Natural biomaterials

Examples of biomaterials used for implants in medicine.

Typical BiomedicalApplications of Polymers

Poly(methylmethacylate)

UHMWPE(Ultra High MolecularWeight Polyethylene)PET (Polyethylene terephthalate)PolyurethanesPolythema(Polyhydroxyethylmethacrylate)

SiliconesPoly(propylene)

Poly(glycolide)

Hard Contact Lenses Intraocular LensesBone Cements, Denture Base

Bearing Surfaces in Artificial Joint

Artificial ArteriesCatheters

Soft Contact Lenses, Wound DressingsDrug Release MatricesBreast ImplantsSutures, Heart Valves, Finger Joints

Biodegradable Sutures

Typical BiomedicalApplications of Ceramics

AluminaPartially StabilisedZirconia

Calcium PhosphatesBioactive glassesCarbonsPorcelain

Femoral Heads, Dental Ceramics

Femoral Heads

Bone Substitutes, TE scaffoldsBone Substitutes, TE scaffolds

Heart ValvesDental Crowns

Biomedical Applications of Metals

TitaniumTi6Al4V AlloyCo-Cr Alloys316 Stainless SteelShape MemoryMetals (Nitanol)Amalgam

Heart Pacemaker HousingsHip ProsthesesHip ProsthesesFracture Fixation Plates

Stents, Orthodontic WireDental Fillings

Biomedical Applicationsof Natural Materials

CollagenFibrin GlueCoralGelatin

Artifical Ligaments Bone GlueMicroporous Bone Substitute

Artificial Heart Valves

Other biomaterials are composite and hybrid biomaterials combining polymers, ceramics and/or metals as well as of natural materials (or even living cells) incorporated in a synthetic matrix(Tissue engineering and regenerative medicine).

Examples of biomedical composite materials(Ratner et al., Biomaterials Science, 2004).

Examples of applications of biomaterials.

Tissue Engineering

In vitro - Cell culture

Implant

Signaling molecules

Scaffold

Cells

Langer & Vacanti, 1991

““...the science of persuading the body to regenerate or repair ...the science of persuading the body to regenerate or repair tissues that fail to regenerate or heal spontaneously.tissues that fail to regenerate or heal spontaneously.””

((AgrawalAgrawal and Ray, 2001)and Ray, 2001)

Scaffolds made of composite materials (for bone and cartilage tissue engineering)

Bioactive material(e.g. hydroxyapatite,

bioactive glasses)

Composites for tissue engineering scaffolds

Resorbable polymers(natural or synthetic, e.g.

PLA, PGA etc.)

A bioactive phase will improve osteoconductivity of a polymer scaffold enabling the formation of hydroxycarbonate apatite (HCA) on the surface and a site for bone re-growth.

Moreover, the bioactive phase can be used to control the degradation rate of the polymer and to enhance mechanical properties.

A. R. Boccaccini, et al, Ceram. Eng. Sci. Proc. (2002).

HA Pre-clinical studyPetite et al., Nat Biotechnol 18;959:2000.

Bone Tissue Engineering

Human skeletal stem cells from patient⇓

Cell culture (expansion)⇓

Attachment to scaffold⇓

Transplantation

Microstructure of biomaterials

Bulk and Interface/Surface dominated properties

Biomimetics

• Nature produces designs using materials valuable knowledge understanding of biomaterials in general

• and the performance of biomaterials when they are replacing human tissue.

Biological Materials

• In order to design and produce successful biomaterials we need to appreciate and understand the biological materials and systems we are replacing.

• Properties of natural materials such as bone, tooth and cartilage should be understood.

• Natural materials have a complex architecture/microstructure exhibiting hierachical organisation from molecular structure through to microstructure and macrostructure.

Biomimetics• Increasing emphasis on biomimetics or the mimicking of

the way nature synthesises and produces materials both for the development of novel biomedical materials and for industrial materials synthesis.

• Nature is outstanding, achieving the best possible properties from a material by accurate control of both macrostructure and microstructure (nanostructure).

• Biological materials have very complex architecture with organisation and they exhibit unique properties that are hard to reproduce with synthetic (man-made) materials and devices

The abalone shell is a microlaminate composite of calcium carbonate crystals and proteins, with a fracture-toughness 3,000-times greater than that of the crystals alone (upper). Although the proteins comprise only a few percent of the mass of the composite, they are responsible for the tremendous enhancement of strength of the material and the precise control of its unique nanostructure

Natural biomaterials

Biological Materials are Smart

• Organisms respond to the external environment materials/tissues also respond.

• Biological materials such as bone:• Change shape during growth.• Self repairing capability.

• Adapt to external stimuli (e.g. applied loads).

Hierarchical structure of natural biomaterials: bone

Wolff‘s Law

• Functional adaptation of bone Wolff‘s Law. (Julius Wolff)

• The form of bone being given the bone elements place or displace themselves in the direction of the functional pressure and decrease their mass to reflect the amount of functional pressure (Julius Wolff 1982)