Classes of Biomaterials Used in the Body
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Transcript of Classes of Biomaterials Used in the Body
Classes of Biomaterials Used in the Body
Advantages Disadvantages
Metals Corrosion
Density
Processing
Ceramics Brittle – fractures easily in tension
Polymers Not strong
Not rigid
Time-dependent deformation (creep; stress relaxation)
Degradation
(Source: Park; p. 3)
Example
Metals Joint replacement
Dental roots
Orthopedic fixation
Stents
Ceramics Dental implants
Orthopedic implants (some)
Polymers Sutures
Blood vessels (e.g. vascular grafts)
Joint socket (knee, shoulder)
Ear, nose
Soft tissues in general
Biomaterials for Biological Tissue Replacements
Density
(g/cm3)
Elastic modulus
(GPa)
Yield strength
(MPa)
Tensile Strength (MPa)
% Elongation at break
Stainless Steels
SS 316L
Annealed
7.9 172 485 40%
SS 316L
30% Cold Worked
7.9 690 860 12%
Cobalt-Based Alloys
Haynes-Stellite 21 or ASTM F75
Cast Co-Cr-Mo
8.3 450 655 8%
Haynes-Stellite 25 or ASTM F90
Wrought Co-Cr-W-Ni;
Annealed
9.2 445 970 62%
Haynes-Stellite 25 or ASTM F90
Wrought Co-Cr-W-Ni:
44% Cold-worked
9.2 1610 1900 10%
ASTM-F562 or MP35N
Wrought Co-Ni-Cr-Mo-Ti
Hot forged
~9.2 965 1210 50%
ASTM-F562 or MP35N
Wrought Co-Ni-Cr-Mo-Ti
Cold worked
~9.2 1500 1800 8%
Density
(g/cm3)
Elastic modulus
(GPa)
Yield strength
(MPa)
Tensile Strength (MPa)
% Elongation at break
cp-Titanium and Titanium Alloys
cp-Ti (Grade 4) or ASTM F6730 % Cold Worked
4.5 485 760 15%
Ti-6Al-4V or ASTM F136annealed
4.5 830 900 14%
Tantalum
Tantalum
Annealed
16.6 138 345 20-30%
Tantalum
30% Cold Worked
16.6 207 517 2%
Types of Tissues:1. Epithelial tissue: • covers the body surface and forms the lining for most internal cavities. • skin is an organ made up of epithelial tissue.• Function: protect2. Connective tissue:• Bone, cartilage, dense fibrous tissue, loose connective tissue, fat• Function: support, protection, binds tissues together 3. Muscle Tissue:• Skeletal: voluntary; contraction of skeletal parts; attached to bone via tendons• Smooth: involuntary; walls of internal organs and blood vessels• Cardiac: involuntary; walls of the heart4. Nerve Tissue:• Consists of nerve cell or neurons located in the brain, spinal cord, and nerves• Produces and conducts nervous impulses to and from all parts of the body.
Organ: _______________________________________________
skin, bone, heart, lung, brain, eye, stomach, spleen, pancreas, kidneys, liver,intestines, uterus, and bladder.
Tissue: _______________________________________________
Soft Tissues: - Connect, support, or surround other structures and organs of the body- Muscles: support/moves bone- Tendons: connect muscles to bone- Ligaments: connect bone to bone- Synovial tissue: makes up joint capsule- Fascia: sheet or band of fibrous connective tissue enveloping, separating, or binding together muscles, organs, and other soft structures of the body. - Also: nerves, blood vessels, fat
Hard Tissues:- Tissues that _______________________________- Cartilage and bone
Tissues
Biological Tissues: Mechanical Properties
Tissue
Modulus (MPa)
Tensile Strength (MPa)
Strain at Break(%)
Soft Tissues Smooth Muscle, relaxed 0.006 - 300
Smooth Muscle, contracted 0.01 - 300
Carotid Artery 0.084 ± 0.22 - -
Cerebral Artery 15.69 4.34 50
Cerebral Vein 6.85 2.82 83
Pericardium 20.4 ± 1.9 - 34.9 ± 1.1
Patellar Tendon (29-50 yrs. Old) 660 ± 266 64.7±15 14 ± 6
ACL Ligament (21-30 yrs. Old) 345 ± 22.4 36.4 ± 2.5 15 ± 0.8
Hard TissuesModulus
(GPa)Tensile Strength
(MPa)Strain at Break
(%)
Cortical Bone 17 - 24 90 -130 1-3
Cancellous Bone 0.1 - 4.5 10 - 20 5-7
Cartilage 0.001 - 0.01 10 - 40 15-20
Elastic Modulus“Mechanical Mismatch Issues”: A biomaterial that replaces or repairs a tissue but has, for instance, higher stiffness may be problematic (e.g. may cause “stress shielding” or neointimal hyperplasia). Similarly, if it lacks rigidity, it may also be problematic (e.g. recoil of coronary stents, plastic deformation under physiological conditions).
Material E (GPa)
Silicone Elastomer (Rubber) ~0.002
UHMWPE 0.69
PMMA 2.2-3.2
Soft tissue See previous table
Cortical Bone 17-24
Cancellous Bone 0.1 – 4.5
Glass 73
Gold 77
Ti-6Al-4V 114
Stainless Steel 316L 190
Tantalum 190
Haynes-Stellite 21 (Cast Co-Cr-Mo) 210
Aluminum oxide 380
Diamond 700-1200
f04_01_pg6
Elastic Modulus
DensityA biomaterial that replaces an equivalent volume of tissue may have different weight as a result of the differences in density. In some applications, this can be problematic.
Material Density (g/cm3)
Fat 0.94
UHMWPE 0.94
Water 1.0
Soft tissue 1.01-1.06
Silicone Elastomer (Rubber) 0.99-1.50
PMMA 1.19
Cortical Bone 1.8-2.1
Cancellous Bone ~1
Glass 2.4-2.8
Diamond 3.5
Aluminum oxide 3.98
Ti-6Al-4V 4.5
Stainless Steel 316L 7.9
Haynes-Stellite 21 (Cast Co-Cr-Mo) 8.3
Tantalum 16.6
Gold 19.3
Source: J. Park & R.S. Lakes, Biomaterials: An Introduction (3 rd Ed), p. 93 ISBN 978-0-387-3789-4
f03_01_pg6
Density
Metallic Biomaterials
Device Annual # of Devices in USA
Intraocular Lenses (2003) 2,500,000
Vascular Grafts 300,000
Breast prostheses 250,000
**Heart Valves (rings, cages) 100,000 (some)
**Pacemakers 400,000
*Coronary Stents 1,500,000
*Hip Prostheses (2002) 250,000
*Knee Prostheses (2002) 250,000
*Dental Implants 910,000
- Source: Ratner, B.D. et al. “Biomaterials Science: An Introduction to Materials in Medicine, 2nd Edition, Elsevier Academic Press, San Diego, CA, 2004.- In 2004 (unless otherwise stated)- *indicates all or predominantly metal- **indicates metal-containing
Categories of Metallic Biomaterials
1. Stainless Steel2. Cobalt-based Alloys3. Titanium Alloys4. Specialty Metallic Alloys
Steel
• A steel alloy that is highly resistant to corrosion• Fe is combined/alloyed with at least 11 wt% chromium (Cr)
1. Stainless Steel (SS)
• An Fe & C alloy- cp-Fe: <0.008 wt% C- steels: 0.008-2.14 wt% C- cast irons: 2.14-6.7 wt% C
• “ferrous alloy”: Fe is main constituent (FYI: Fig. 11.1)• May contain appreciable amounts of other alloying elements
Stainless Steel
Stainless Steel 316L (SS 316L)
• ASTM F138, F139
•Composition:- Fe: 60-65 wt%- Cr: 17-19 wt%- Ni: 12-14 wt%- C: 0.03 wt% max- Minor: Mn, P, Si, Mo
Cr[O2] Cr2O3 (chromium oxide at surface = protective water-barrier)
Low [C] (<0.03 wt%):
Higher [C] (> 0.03 wt%):
Cr + C[O2] Cr23C6 (chromium carbides)
whichppt @ grain boundaries
Depletes Cr at adjacent grain boundariesCr2O3
@ surfacewater penetration
ASTM = American Society for Testing and Materials
• Name:- 316: Contains Mo- L: Low C content
• Rationale for Composition: (1) Corrosion Resistance:
Sensitized SS = SS where carbides have formed
(2) Mechanical Properties of SS 316L
SS316L is “austenitic”• -Fe, FCC• Stabilized by Ni• non-magnetic, generally stronger
“Ferritic” SS • -Fe, BCC• Stabilized by Mo, Si
FYI: Table 11.4
E (GPa) y (Mpa) TS (MPa)
%EL
Cold Worked
190 690 860 12%
Annealed 190 172 485 40%