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Biomaterials in Bone Tissue Engineering

Miqin ZhangMiqin ZhangProfessor of Dept of Materials Science and EngineeringProfessor of Dept of Materials Science and Engineering

Adjunct Prof. of Neurological Surgery, Radiology, and OrthopaediAdjunct Prof. of Neurological Surgery, Radiology, and Orthopaedics cs & Sports Medicine& Sports Medicine

University of WashingtonUniversity of Washington

Outline

Background in tissue engineeringStructure and function of boneMotivation and background in bone tissueengineering Biomaterials in bone tissue engineering

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History of Tissue Engineering

4~ 25 years4Yannnas et al: artificial

skin from collagen and glycosaminoglycan (1980) Cima et al: chondrocytes

from PLGA (1991)4Langer and Vacanti

(1993) defined “tissue engineering”

L. Bonassar, CA Vacanti, Journal of Cellular Biochemistry Supplements, 30/31:297-303 (1998)

Possible Tissue-Engineered Devices

3

Host Response

Material Response

ParticulatesSwelling

and leaching

Corrosion Deformationand failure

4

Material/device-Living System Interaction

Integrin

RGDRGD RGDAdhesion Protein

Cytoskeletal connection

α β

Material/device

Material/device Material/device

(1) Proteinadsorption

(2) Cell

adhesion

Material/device

+ Biological System

Integrin

Cell membrane

RGDRGD RGDAdhesion Protein

Cytoskeletal connection

α β

Material/device

Material/device Material/device

(1) Proteinadsorption

(2) Cell

adhesion

Material/device

+ Biological System

Effects of Surface Properties on Living Systems

SurfaceCrystallinity

SurfaceComposition

Surface topo-graphy

Hydrophilic/hydrophobic Character

Surface Roughness

CellCell

Protein

OH

CO

OH

PEG

5

Most implants

Biofunctional

Biointerfaces

Bioinert

Tissue engineering

Resist non-specificprotein adsorption

Promote protein adsorption

Outline

Background in tissue engineeringStructure and function of boneMotivation and background Biomaterials in bone tissue engineering

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Function of Bone

SupportProtection

Storage and productionLeverage

Composition of Bone

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The Structure of Bone4 Bone organic composition: 95% type I collagen,

and 5% of proteoglycans and noncollagenousproteins

4Bone: cortical (compact) and cancellous (spongy)

Collagen fibers

Bone apatite

The Types and Locations of Bone Cells

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Bone Remodeling

Outline

Background in tissue engineeringStructure and function of boneMotivation and background in bone tissueengineering Biomaterials in bone tissue engineering

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Trauma, tumors, aging, osteoporosis ….

Causes of Bone Defects

Osteoposis: 15% of those 50-59; 70% of those over 89

Spine disorders: 80% of population

Bone Defects – Affect Everyone

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Data from AAOS, NIH, NOF and http://www.usbjd.org

1 out of 7 Americans have musculoskeletal impairments.36.9 million Americans incur injuries every year.1 out of 2 women and 1 out of4 men over 50 suffer an osteoporosis-related fracture $300 billion every year

Musculoskeletal Conditions are Worsening!!!

Treatments of Bone Defects

Autograft Allograft Xenograft Tissue engineering

Material substitutes

1. Patient pain

2. Infection3. High cost

Metalspolymers

bioceramicsdo not

have goodproperties

1. Immunerejection2. Pathogens

1. Donor shortage

2. Infection3. Pathogens4 Immune

Rejection

Patient Otherpatient

Animal Biomaterial Promisingtherapy

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Bone Tissue Engineering

Scaffolds gradually degraded and eventually eliminatedPatient-derived bone cells onto a macroporous man-made scaffolds to create completely natural new tissuesCommon cells: osteoblast, mesenchymal stem cells

Scaffold Cultivated cells

Cells on scaffold

Scaffold with cells implanted in bone

Criteria for Scaffold Materials

Excellent mechanical strengthCancerous bone (compressive stress 0.5-10 MPa) Three dimensional (3D) interconnected macroporous microstructures Controllable biodegradation and bioresorptionSuitable surface chemistryMalleableGood biocompatibility and biofunctionality

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Biocompatibility of Porous Materials for Bone Tissue Engineering

Bioactive: form bond between tissues and materialsOsteoconduction: stimulate cell attachment and migration Osteoinduction: stimulate proliferation and differentiation of stem cellsOsteogenesis: produce bone independently

Resist non-specific protein adsorption

Biofunctional

Bioinert

Outline

Background in tissue engineeringStructure and function of boneMotivation and background in bone tissueengineering Biomaterials in bone tissue engineering• Porous ceramic scaffolds for load bearing bone• Polymeric materials for non-load bearing bone

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I. Porous Scaffolds for load-bearingBone Tissue Engineering (hard tissue)Tissue Engineering (hard tissue)

Background:Background: Existing Porous Scaffolds Existing Porous Scaffolds

High mechanical strength ~ 14 MPalimited resources, expensiveuncontrollable microstructures

Can be converted intoHA

Coral

High mechanical strength Not bioactive and osteoconductiveneed surface coatings

Stainless SteelTitanium

Metals

Composition similar to boneβ-TCP > HA in degradationbioactive, osteoconductive~ 2MPa

HA & β-TCPCeramics

Hydroxyapatite (HA), tricalcium phosphate (TCP)

14

100 µm 15 KV

C

CP

P

100µm 15KV

Compressive yield stress: 5 MPaCompressive elastic modulus: 7 GPa

HA Scaffolds by a GelHA Scaffolds by a Gel--Polymer MethodPolymer Method

H. Ramay and M. Zhang, Biomaterials 24 (19), 2003

β-TCP and HA Nanofiber Nanocomposite Scaffolds

100 μm

200 μm

(a)

(b)

80 nm

Compressive stress 9.8 MPa – Human cancellous bone 2-10MPaH. Ramay and M. Zhang, Biomaterials, 25 (21), 5171-5180 (2004). Filed US patent.

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Mechanisms for Increased Toughness

Wavy fracture surface– Area of crack surface

is increased

Clinching at crack tip– Clinching reduces the

applied stress intensity factor 10 μm

II. Porous polymeric scaffolds for non-load bearing bone

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Polyglycolic acid (PGA)

Polylactic acid (PLA)

Poly- lactic-co-glycolic(PLGA)

Synthetic polymers

• Hydrophobic• Acidic

degradation products

More biocompatibleMinimal foreign body reactionHydrophilicSuitable surface chemistry

Chitosan

Natural polymer

Polymeric Porous Scaffolds

WeakSwelling

Soluble in strong acidDifficult to incorporate

drug

StrongStrong ironic bondingNo swellingNeutral pH: easy to incorporate drugs

Chitosan+ Alginate

Natural polymer

Why Chitosan-alginate Scaffolds?

Chitosan

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Mechanical and Swelling Properties

3~4 times increase in mechanical strength and compressive modulus

C

Chitosan hybrid Chitosan

Chitosan composite scaffolds• Do not swell in PBS solution• Stable in neutral solution• Incorporation of proteins

without denaturization

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Yiel

d S

treng

th (M

pa)

Chitosan Composite

0

2

4

6

8

10

You

ng's

Mod

ules

(MP

a)

Chitosan Composite

3 days 7 days

In vitro Study of Bone Mineralization

A large amount of minerals was formed on chitosan-alginate scaffold

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In vivo Ectopic Animal Model

Z. Li, H. Ramay, K. Hauch, D. Xiao, and M. Zhang, Biomaterials, 26 (18), 3919-3928 (2005).

Compatibility of Chitosan-alginate Scaffolds

No fibroticlayer

Blood vesselformation

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In vivo Study of Mineral Formation

4 weeks 8 weeks

Black stain indicates bone formation

In vivo Orthotopic Animal Model: Digit Bone In vivo Orthotopic Animal Model: Digit Bone Defect RepairDefect Repair

Chris Allan (MD, UW Orthopedics) (bone)Buddy Ratner (UW Bioengineering)Miqin Zhang (UW Materials Science and Engineering)

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Richard Hopper (MD, Children Hospital) Miqin Zhang (UW Materials Science and Engineering)

In vivo Orthotopic Animal Model: In vivo Orthotopic Animal Model: Cranial defectsCranial defects

Micro CT results Micro CT results

All samples show defect closureThe CA scaffolds with BMP-2 have the best result on bone formation

4 weeks 16 weeks

ControlNo scaffolds

CA scaffolds+ MSC

CA scaffolds+Bone marrow

CA scaffolds+ BMP

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III. Other novel biomaterialsfor bone tissue engineeringtissue engineering

Biomimic Extracellular Matrix

Extracellular matrix: proteoglycans and fibrous proteins with fiber diameters in the range of 50 to 150 nm

motor

Rotation Controller

motor

Transverse motor

High voltage

Polymer jets

15 kV20–50 kV

1 2 3 4

motormotor

Rotation Controller

motor

Transverse motor

High voltage

Polymer jets

15 kV20–50 kV

1 2 3 4

Chitosan40-500nm

Electronspinning

100 nm 100 nm 50 μm 500 nm100 nm100 nm100 nm 100 nm100 nm100 nm 50 μm50 μm50 μm 500 nm500 nm500 nm

DDD

N. Bhattarai, D. Edmondson, O. Veiseh, F. A. Matsen, and M. Zhang, Biomaterials,

26 (31), 6176-6184 (2005) 2006.

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Various Electronspun Nanofibers

Gelatin

100 µm

TEM image of PLLA/Iron oxide nanoparticle

1 µm

50 75 1000

15

30

Diameter (nm)

N. Bhattarai, C. Li, D. Edmondson, M. Zhang, Advanced Material, 2006

0

2

4

6

8

10

CaCl2 treated fibers

Tens

ile M

odul

us (M

Pa)

As spun fiberAlginate

Polycaprolactone

10 µm

Silk fibroin2 µm

Polylactide(PLLA)

2 µm

Thermoreversible Hydrogel

<100C 370C

Gel + nanoparticlesprolonged drug releasefor months

0 500 1000 1500 2000 2500 30000

1

2

3

4

5

6

7

At 10°C

Time (second)

Vis

cosi

ty (P

a.S

)

At 37°C

Vis

cosi

ty (P

a.S

)

Time (second)

G2 G1 G3 G4

3000 2500 2000 1500 1000 500 0

0

1

2

3

4

5

6

7

G2 G1 G3 G4

N. Bhattarai, F. A. Matsen, and M. Zhang*, Macromolecular Bioscience, 5, 107-111 (2005).

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Thermoreversible Hydrogel for Controlled Drug release

N. Bhattarai, H. R. Ramay, J. Gunn, F. A. Matsen, and M. Zhang, Journal of Controlled Release, 103,

609-624 (2005).

0 10 20 30 400

20

40

60

80

100

Cum

uliti

ve R

elea

se (%

)

Time (days)

1000 µg/ml 800 µg/ml 600 µg/ml 400 µg/ml 200 µg/ml

0 10 20 30 40 500

20

40

60

80

100

Cum

mul

ativ

e re

leas

e (%

)

Time (h)

A B C

Treatment of osteoporosis