Materials

Question 1

Biocompatibility

Answer 1

applicable materials must not lead to any adverse secondary effects; material must be stable; material must not be harmful

Question 2

Types of biomaterials

Answer 2

Metals, ceramics, polymers

Question 3

Metals

Answer 3

Stainless steel, titanium, cobalt chromium

Question 4

Stainless steels

Answer 4

316, 316LS; min 10.5% Cr; high stiffness, strength, very good corrosion resistance

Question 5

Titanium alloy

Answer 5

Grades 5 and 23; lightweight, stiff, strong, good corrosion resistance; 6% Al, 4% V; high compatibility with the human body

Question 6

Cobalt Chromium (CoCrMo)

Answer 6

Vitalium (65% Co, 30% Cr, 5% Mo)

Question 7

Advantages of metals

Answer 7

High impact tensile strength, resistance to wear, strain energy absorption

Question 8

Disadvantages of metals

Answer 8

Low biocompatibility, corrosion in physical environments, mismatch of mechanical properties with bio-tissues, high density (heavy)

Question 9

Metal applications

Answer 9

Screws, pins, wires, rods, implants

Question 10

Ceramics

Answer 10

Aluminum oxides, calcium oxides, titanium oxides

Question 11

Advantages of ceramics

Answer 11

good bio-compatibility; good corrosion resistance

Question 12

Disadvantages of ceramics

Answer 12

Low impact tensile strength, difficult to fabricate, low mechanical reliability, lack of resistance, high density

Question 13

Applications of ceramics

Answer 13

Hip prostheses, teeth implants for phalanges

Question 14

Polymers

Answer 14

Nylon, PMMA, Teflon, PP, PE, UHMWPE, Silastic rubber, PEEK, Copoly

Question 15

Nylon

Answer 15

Absorbs water (0.1-13.5%) and irritates tissue; loses tensile strength

Question 16

PMMA

Answer 16

In cement form: high generation of heat during polymerization; in rigid form: susceptible to crazing, abrasion, loss of strength by heating

Question 17

Teflon

Answer 17

Very high resilience

Question 18

PP

Answer 18

up to 5400 psi UTS, 0.01-1% water absorption

Question 19

PE

Answer 19

very low water absorption (0.05-0.5%); UHMWPE up to 7740 psi UTS compared to 4100 psi

Question 20

Advantages of polymers

Answer 20

very good resilience; easy to fabricate, low density

Question 21

Disadvantages of polymers

Answer 21

Low impact tensile strength, time degradation polymers are viscoelastic

Question 22

Applications of polymers

Answer 22

Artificial arteries, veins, small joints, wear surfaces

Question 23

Typical properties

Answer 23

Young’s modulus: 10MPa to 4GPa for polymers, 50MPa to 400GPa for metals; UTS: 10MPa to 100MPa for polymers, 100MPa to 10GPa for metals; elongation: 1000% for polymers, <100% for metals

Question 24

Plastic polymer modeling

Answer 24

Plastic polymers are highly nonlinear; use the secant modulus, plastic yield stress, Poisson ratio (0.4-0.45); can use nonlinear Mooney-Rivlin model; can use curve fitting process

Question 25

Secant modulus (Es)

Answer 25

obtained at a predetermined value of strain by finding the slope of a line (typically 0.2% strain is used); often described in a percentage of E