Biomaterials (Week 1-2)

Question 1

Biomaterial definition

Answer 1

“is used to make devices to replace/repair a function of the body in a safe, reliable, economic, and physiologically acceptable manner” “is any substance (other than a drug), natural or synthetic, that treats, augments, or replaces any tissue, organ, and body function”.

Question 2

Biomaterials and medical devices comprised of them are commonly used as:

Answer 2

prosthesis in cardiovascular, orthopedic, dental ophthalmological, and reconstructive surgery interventions: surgical sutures, bio-adhesives, controlled drug release devices and particles

Question 3

Biomaterials science addresses both:

Answer 3

therapeutics and diagnosis.

Question 4

The path to create new biomaterials

Answer 4

1) Identification of a problem or a need. 2) Research on biomaterials (chemistry, physics of materials science biology) 3) Engineering to develop a medical device 4) Preclinical and clinical testing 5) Regulatory approval 6) Commercialization and clinical application

Question 5

The success of a biomaterial or implant is highly dependent on three major factors:

Answer 5

1) the properties (mechanical, chemical and tribological) of the biomaterial in question 2) biocompatibility of the implant and 3) the health condition of the recipient and the competency of the surgeon.

Question 6

Biocompatibility

Answer 6

is the ability of a material to perform with an appropriate host response in a specific application

Question 7

Desirable biocompatibility

Answer 7

Noncarcinogenic, nonpyrogenic, nontoxic, nonallergenic, blood compatible, non-inflammatory.

Question 8

Desirable attributes of Biomaterials (4)

Answer 8

1) biocompatibility
2) Sterilizability (Not destroyed by typical sterilizing techniques such as autoclaving, dry heat, radiation, ethylene oxide)
3) Physical characteristics (Strength, elasticity, durability)
4) Manufacturability (Machinable, moldable, extrudable)

Question 9

Requirements for an implant by examining the characteristics that a bone plate must satisfy for stabilizing a fractured femur after an accident:

Answer 9

1. Acceptance of the plate to the tissue surface (biocompatibility). 2. Pharmacological acceptability (non-toxic, non-allergenic, non- immunogenic, non-carcinogenic, etc.). 3. Chemical inert and stable (no time-dependent degradation). 4. Adequate mechanical strength. 5. Adequate fatigue life. 6. Sound engineering design. 7. Proper weight and density. 8. Relatively inexpensive, reproducible, and easy to fabricate and process for large-scale production.

Question 10

Generations of Biomaterials

Answer 10

1. 1st generation: Goal: bioinertness (minimal reaction/interaction)
2. 2nd generation: Goal: bioactivity (resorbable biomaterial; controlled reaction with the physiological environment (e.g. bone bonding, drug release)
3. 3rd generation: Goal: regenerate functional tissue (biointeractive, integrative, resorb able; stimulate specific cell responses at the molecular level (e.g. proliferation, differentiation, ECM, production and organization)

Question 11

Materials used in each generation

Answer 11

1. 1st generation: silicone-rubber (elastomeric polymers), pyrolitic carbon (used today to coat mechanical components of heart valves).
2. 2nd generation: PLA (Polylactic acid) and other biopolymers used to deliver drugs, calcium phosphate, hydroxyapatite-containing bone fillers, nano particles for drug delivery.
3. 3rd generation: regeneration of functional tissue = tissue engineering – true replacement within living tissue.

Question 12

Early biomaterials:

Answer 12

1. Gold: Malleable, inert metal (does not oxidize); used in dentistry by Chinese, Aztecs and Romans - dates 2000 years.
2. Iron, brass: High strength metals; rejoin fractured femur (1775).
3. Glass: Hard ceramic; used to replace eye (purely cosmetic).
4. Wood: Natural composite; high strength to weight; used for limb prostheses and artificial teeth.
5. Bone: Natural composite; uses: needles, decorative piercings.
6. Sausage casing: cellulose membrane used for early dialysis (W Kolff).
7. Other: Ant pincers. Central American Indians used to suture wounds

Question 13

Most biomaterials and medical devices perform satisfactorily in-vivo, so what can go wrong?

Answer 13

1) No manmade construct is perfect. All man- factored devices have a failure rate.
2) Also, all humans are different with differing genetics, gender, body chemistries, living environment, and degrees of physical activity.
3) physicians implant or use these devices with varying degrees of skill.

Question 14

Dental restoration materials:

Answer 14

materials employed for the restoration of teeth include metal alloys (amalgams, gold, stainless steel, and cobalt-chrome) and ceramics (porcelain or alumina). Other uses of restorative materials include polymers as sealants for surface lamination.

Question 15

Intraocular lenses (fabricated from ….)

Answer 15

fabricated from a variety of transparent materials including poly(methyl methacrylate), silicone elastomers, soft acrylic polymers, and hydrogels.

Question 16

Dental implants today are fabricated from …..

Answer 16

Pure titanium (cpTi)

Question 17

Cardiovascular stents:

1) design
2) materials (3 types)

Answer 17

1) Tubular scaffolds,
2) made from either 316L stainless steel, nitinol (NiTi alloy) or CoCr based alloys.

Question 18

Total-hip replacement prostheses: fabricated from (5 types) ……

Answer 18

titanium alloys (Ti6Al4V), CoCr, CoCrMo, UHMWPE, ceramics.

1. Femoral stem: titanium alloy
2. Femoral head: alumina-zirconia ceramic
3. Acetabular cup: UHMWPE infused with vitamin E antioxidant.

Question 19

Total US biomaterials expenditures (2009)

Answer 19

$2.5 trillion per year

Question 20

Heart valve prostheses: fabricated from ……….

Answer 20

from carbons, metals, elastomers, plastics, fabrics, and animal or human tissues chemically pretreated.

Question 21

Cardiovascular assist devices: in devices such as pacemakers the cardiac pacing leads have to ……..

Biomaterials used in the design of the leads should be……..

Answer 21

…… have to survive in the harsh endocardial environment.

………………stable, flexible, possess adequate conductive and resistive properties, and provide endocardial contact with the heart.

Question 22

Tissue engineering is:

Answer 22

cell seeding and and tissue implantation

Question 23

How materials are structure (2 structures)?

Answer 23

1. Surface structure: interface with biological environment (Interactive forces)
2. Bulk structure: dictates mechanical performance such as how strong, ductil and elastic a material is (attractive forces)

Question 24

1. 4 Atrractive forces in the universe are:
   
   1. 3 aren’t important an 1 is important

Answer 24

1. Gravitational, Weak nuclear, Strong nuclear, Electromagnetic
2. Gravitational, Weak nuclear, Strong nuclear: Not high enough in magnitude to hold atoms together

Question 25

2 Types of electromagnetic forces

Answer 25

1. Weak electromagnetic leading to liquids 2. Strong electromagnetic leading to solids

Question 26

2 Forces athe the surface (interface) of materials

Answer 26

1. Intermolecular 2. Intramolecular

Question 27

The bond-energy curve provides several important macroscopic material properties. Specifically, one can estimate: 1. the ____ \_\_\_\_\_\_\_\_\_ 2. the __________ \_\_\_\_\_ \_\_\_\_\_\_\_\_ 3. the __________ \_\_\_\_\_\_\_\_\_\_ 4. the _________ \_\_ ________ \_\_\_\_\_\_\_\_\_\_

Answer 27

1. bond energy, 2. average bond length 3. elastic modulus 4. coefficient of thermal expansion

Question 28

Electrostatic forces that hold atoms together (5)

Answer 28

1. Van der Waals interactions 2. Ionic 3. Hydrogen (H) bonding 4. Metalic 5. Covalent

Question 29

Van der Waals interactions

Answer 29

Once a random dipole is formed in one atom, an induced dipole is formed in the adjacent atom. Relative strength: Weak

Question 30

Ionic forces

Answer 30

Atoms with a permanent positive (+) charge attract atoms with a permanent negative (-) charge. Relative strength: Very strong

Question 31

Hydrogen (H) bonding

Answer 31

The interaction of a covalently bound hydrogen with an electronegative atom, such as oxygen or fluorine. Relative strength: Medium

Question 32

Metallic interatomic force

Answer 32

The attractive force between a "sea" of positively charged atoms and delocalized electrons.

Question 33

Covalent Force

Answer 33

A sharing of electrons between two atoms. Relative strength: strong

Question 34

Strong intermolecular forces arise from \_\_\_\_

Answer 34

the sharing of electrons between two or more atoms

Question 35

Characteristics of Covalent and metallic bonds:

Answer 35

1. Valency 2. Directionality 3. Short range (1 -2 Å) 4. Relatively strong (100 - 300 kT/bond)

Question 36

Simple bonding models assume that the total bonding results from the sum of two forces: ## Footnote The repulsive force dominates at \_\_\_\_\_\_ \_\_\_\_\_\_\_\_and the attractive force dominates at _______ \_\_\_\_\_\_\_\_\_ At equilibrium they are ____ \_\_\_\_\_\_\_\_

Answer 36

an attractive force (FA ) and a repulsive (FR). FN =FA+FR small distances, larger distances. just equal.

Question 37

r = r₀

Answer 37

Equilibrium separation distance

Question 38

Equilibrium separtion distance:

Answer 38

r = r_{0 Ions occupy finite amount of space so this is the closest separation ===> bond length}

Question 39

Equilibrium separtion distance: Ions ____ finite ________ \_\_ _____ so this is the closest ______ ===\> _______ length

Answer 39

r = r_{0 Ions occupy finite amount of space so this is the closest separation ===> bond length}

Question 40

Equilibrium separtion distance: Ions occupy ________ amount __ \_\_\_\_\_ so this is the ______ separation ===\> bond \_\_\_\_\_\_\_

Answer 40

r = r_{0 Ions occupy finite amount of space so this is the closest separation ===> bond length}

Question 41

At equilibrium when r = r₀ F_net = U_net =

Answer 41

Fnet = 0 Unet = 0

Question 42

F_a =

Answer 42

attractive forces (Coulombic force)

Question 43

Ionic bond: Once charge transfer has occurred a ______ \_\_ \_\_\_\_\_\_\_\_ occurs between ions \_\_\_

Answer 43

force of atraction F_a

Question 44

F_a =

Answer 44

€₀ = permittivity of vacuum €₀ = 8.85 x 10^-12 C²/Nm²

Question 45

Repulsive force equation

Answer 45

F_r = - B / (r^m) B and m are constants 9

Question 46

Force of attraction and Force of repulsion

Answer 46

F_a = A / r² ----\> A = q₁q₂ /(4π€₀) F_r = - B / (r^m) B and m are constants 9 \< m \< 12 F_r is dominant at small r values F_a is dominant at larger r values

Question 47

Net force at the equilibrium separation distance is: Bond-Force curve: it gives ___ \_\_\_\_\_ _______ by ___ \_\_\_\_ as a _________ of \_\_

Answer 47

F_net = F_a + F_r F_net = 0 the force experienced by the ions as a function of r

Question 48

The bond-force curve will provide us with the information about __________ \_\_ \_\_\_\_\_\_\_\_\_\_\_ or \_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_\_\_

Answer 48

The bond-force curve will provide us with the information **_modulus of elasticity_** or **_Young's modulus (E)_**

Question 49

The slope of the bond-force curve is ______ and it is the measure of ___ \_\_\_\_\_ (\_\_) required to _______ \_\_\_\_\_ from ____ \_\_\_\_\_\_\_\_\_ ______ ( )

Answer 49

dF/dr it is the measure of _the force 9F)_ required to _displace atoms_ from _their equilibrium position (r₀)_

Question 50

Near r₀ we have: F α

Answer 50

F α Δr F / Δr = aE Force is proporcional to separation distance by a factor E E = Young's modulus a = geometric factor

Question 51

Young's modulus:

Answer 51

is the a measure of the resistance of the material to relative atomic separation (stiffness)

Question 52

Different classes of Materials will exhibit _________ \_\_\_\_\_\_\_\_\_\_\_\_ and thus __________ \_\_\_\_\_\_\_\_\_\_\_ Compare the curves for materiasl A and B (slopes and E values):

Answer 52

will exhibit _different curves_ and thus _different slopes:_ _The steeper the slope,_ the greater the force required to move atoms from their equilibrium position, _the higher the value of E_

Question 53

F_a does work as it ______ \_\_\_\_\_\_ \_\_\_\_\_\_\_ from an ________ \_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_ Energy = \_\_\_\_\_\_ = U(a) =

Answer 53

Fa does work as it _draws ions together_ from an _infinite separation distance._ Energy = work = U(a) = U(a) = integral ∞ to r (Fa δr) = -A/r A = (Q1Q2) / 4Πε₀ U(a) = integral ∞ to r (Fa δr) = - (Q1Q2) / 4Πε₀r

Question 54

Repulsion Energy (U_r)

Answer 54

U(r) = integral r to ∞ (Fa δr) = C/rⁿ n = m-1 C = B/n

Question 55

U(net) = F(net) at the bottom of the _energy well =_

Answer 55

U(net) = U(a) + U(r) F(net) = 0 There is _not thermal energy_ and _not vibration_.

Question 56

bond length

Answer 56

equilibrium separation distance

Question 57

What happends to bond length when thermal energy increases?

Answer 57

desparation distance increases ---\> this give ions mobility (vibration)

Question 58

What does the depht of the well means (on the energy-bond curve)?

Answer 58

Measure of inherent bond strength

Question 59

Coefficient of thermal expansion: Definition: Equation:

Answer 59

Ast temperature increases, atoms gain energy and move up the sides of the energy well. (r_e - r_o) / r_o = α_th (T – T_o) r_e = equilibrium separation at temperature T r_o = equilibrium separation at T_o α_th = coefficient of linear expansion