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CEB > 2.Metallic biomaterials > Flashcards

2.Metallic biomaterials Flashcards

1
Q

physical properties of metals

A
  • heat and eletrical conductivity
  • ductile and malleable
  • high density
  • high melting point
  • excellent mechanical properties
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2
Q

chemical properties

A

high reactivity
resist to corrosion (metal alloys used in the body e.g., stainless steel, titanium and Cr-Co)
high wear resistance

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3
Q

forces experienced by metallic biomaterials during application

A

tension
compression
shearing
torsion
bending

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4
Q

[mechanical properties of metals and alloys] yield strength

A

the stress at which plastic
strain occurs (“elastic to plastic transition”)

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5
Q

[mechanical properties of metals and alloys] Breaking strength

A

point where the material
breaks

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6
Q

ductility [mechanical properties of metals and alloys]

A

the value of plastic strain required to break the material

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7
Q

Resilience [mechanical properties of metals and alloys]

A

elastic energy that can be stored in a unit volume of stressed material

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8
Q

Toughness [mechanical properties of metals and alloys]

A

energy required to deform a unit volume of material to its breaking point

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9
Q

[mechanical properties of metals and alloys] Ultimate tensile strength

A

maximum nominal stress versus nominal strain plot

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10
Q

Aseptic loosening

A

failure of joint prostheses (~10–20 years postsurgery) often associated to osteolysis (bone resorption) and inflammatory cellular response within the joint.

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11
Q

What are the key requirements that metals should exhibit for such applications?

A
  • Biocompatibility, nontoxicity, not allergenicity;
  • Corrosion resistance;
  • Adequate mechanical properties;
  • Wear resistance.
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12
Q

Lanzutti and co-workers analyzed the failure of a metallic hip prosthesis in a
patient. In your opinion, what are the most common causes of implant
failure?

A

The most probably cause(s) of the failure can be attributed to:
a) Poor integration and bonding with the adjacent tissue.
b) Stress shielding effect.
c) Corrosion mediated failure.
d) Manufacturing and quality control issues

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13
Q

Why metals corrode in the presence of biological fluids?

A
  • Metal atoms react spontaneously with oxygen, hydrogen protons and ionic salts
    over timeàmetal oxides;
  • ~96% of the body weight consists of oxygen, carbon, hydrogen, and nitrogen
    (building blocks of water and proteins);
    Release of metal ions from the materials into the surrounding tissue, which
    can concentrate locally or diffuse systemically (biocompatibility)
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14
Q

Impact of corrosion for:
* Patient

A

Localized pain
Inflammation
Accumulation of metallic ions in the body

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15
Q

Impact of corrosion for:
Implant

A

Fracture and failure
Loss of function

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16
Q

Why most of the metals are used in combination with other metals or
nonmetal elements?

A

Increase the strength
Confer higher corrosion resistance
Improve specific properties
Alloys: mixture of two or more metals or nonmetal elements

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17
Q

Alloys

A

Alloys: mixture of two or more metals or nonmetal elements

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18
Q

Polarization resistance

A

resistance of the specimen to oxidation during the application of an external
potential.

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19
Q

How to minimize corrosion of metallic biomaterials?

A
  • Addition of metal elements with high stability – high resistance to
    corrosion, such as Zr, Ti, Nb, Ta, Pt, Ag, and Au;
  • Surface finishing
  • Avoid to use dissimilar metals in the same implant
20
Q

Major application of stainless steel

A

surgical instrumentation
Screws, rods, and plates for bone fixation and in spinal fusion devices

21
Q

CoCrMo alloys caracteristics

A
  • Higher resistance to fatigue or fracture than stainless steel or titanium;
  • Good resistance to corrosion
  • Higher Mo content to compensate the reduction on Cr and maintain the
    corrosion resistance
  • High resistance
  • Cr=high resistance to corrosion;
    Co=high mechanical properties
22
Q

Titanium and its alloys

A

*Light weight, excellent corrosion resistance, and enhanced biocompatibility
* Excellent mechanical properties
* Density of Ti«stainless steel<cobalt chromium alloy
* good resistance to corrosion
* low wear resistance
* high chemical reactivity at high temperatures in the presence of oxygen

23
Q

Vandium can be

A

carcinogenic

24
Q

Aluminium can cause

A

nerological side effects
and
genetoxicity

25
Q

Which problems/consideration should we take into account when considering porous metallic biomaterials?

A
  • decreased moduli
  • bone fixation via bone ingrowth
  • resistance to corrosion and fatigue
  • entrapped powder
26
Q

Titanium alloys limitations

A
  • Relatively poor wear resistance in an articulating situation, compared to cobalt
    alloys:
  • Due to their high reactivity in the presence of oxygen during the hightemperature
    processing an inert atmosphere or vacuum is required;
  • High cost – high reactivity and poor machinability;
27
Q

Titanium alloys mojor applications

A
  • Dental implants
  • total joint replacements
  • Good performance at interfacing with the biological system
  • Bone ingrowth into porous titanium surfaces, known as biological fixation, is a
    primary means by which orthopedic implants affix to bone directly
28
Q

Shape memory alloys

A

Titanium–nickel alloys (Nitinol)
Relatively stable cyclic performance (stable memory), good workability, and good resistance to corrosion and fatigue

29
Q

Shape-memory alloys deformation

A

Plastically deformed at a low temperature (martensitic phase)
Return back to their original predeformed
shape when exposed to a high temperature (austenite phase)

30
Q

Definition of biodegradable metals

A

“Corrode gradually in vivo, with an appropriate host response elicited by released
corrosion products, which can pass through or be metabolized or assimilated by cells and/or
tissue, and then dissolve completely upon fulfilling the mission to assist with tissue healing with no implant residues.”

31
Q

Absorbable

A

biodegradation products are metabolized or assimilated by cells/tissue

32
Q

Biodegradable

A

The material/device itseld undergoes biodegradation process

33
Q

Which base metals can be used for biodegradable implants?

A

Ferro
Zinco
Magnesio

34
Q

Characteristics of using magnesium as a base material for biodegradable implants

A

low density
young modulus similar to the bone
fast degradation => mechanical integraty (????)
corrosion produces H2(g)

35
Q

Wolff’s Law

A

living bones will remodel in adaptation to
the external loads they experience

36
Q

How the level of internal strain experienced within the bone affects biological processes?

A

Net mineral loss
Mineral homeostasis
Net mineral gain
Damage formation.

37
Q

stress-shielding

A

Stress shielding is the reduction in bone density (osteopenia) as a result of removal of typical stress from the bone by an implant (for instance, the femoral component of a hip prosthesis). This is because by Wolff’s law, bone in a healthy person or animal remodels in response to the loads it is placed under.

38
Q

Pros of Iron (Fe) based metallic biomaterials

A
  • good corrosion resistance and fatigue resistance in short term applications
  • low cost
  • easy to be machined
39
Q

Cons of Iron (Fe) based metallic biomaterials

A
  • corrosion in long term applications
  • high modulus => The higher the modulus, the stiffer the material (+ rígido)
    *stress shielding effect
40
Q

Applications of Iron (Fe) based metallic biomaterials

A

instruments
temporary devices
permanent implants (stem of hip prostetics)

41
Q

Pros of Cobalt (Co) based metallic biomaterials

A
  • long term corrosion resistance
  • best fatigue and wear resistance
  • biocompatibility
42
Q

Cons of Cobalt (Co) based metallic biomaterials

A
  • difficult to machine = expensive to process
  • high modulus
  • stress-shielding effect
  • Co allergy
43
Q

Application of Cobalt (Co) based metallic biomaterials

A

Permanent joint implants

44
Q

Pros of Titanium (Ti) based metallic biomaterials

A
  • light
  • greatest corrosion resistance
  • best biocompatibility
  • free of metal-related allergy
  • low young’s mudulus (indicates a material that undergoes large (elastic) deformation under a relatively low load. Such materials stretch easily. )
45
Q

Cons of Titanium (Ti) based metallic biomaterials

A
  • lower shear strength
  • low wear resistance
  • still have. though to a lesser degree, stress-shielding effect
46
Q

Applications of Titanium (Ti) based metallic biomaterials

A
  • permanent implant
  • stem of hip prostheses
  • dental screws
  • temporary device
47
Q

How is it possible to reduce the stress-shielding effect?

A
  • Biomaterial selection
  • Implant design
  • Topology optimization

CEB (7 decks)

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