Metallic Biomaterials 2

Question 1

Properties of commercially pure titanium and titanium alloys?

Answer 1

Low specific gravity and good chemical and mech properties

Better specific strength than other metal implants

Lower modulus than SS or Co-Cr, so less stress shielding of adjacent bone

Question 2

What is the phase of commercially pure titanium (CpTi)? What are the properties and applications?

Answer 2

98-99.6 percent Ti
Single phase HCP (alpha)
Higher impurity content (especially O) reduces ductility and increases strength
Lower strength than other Ti alloys
Commonly used in dental implants due to stable oxide layer

Question 3

What is the structure of titanium alloys (Ti-6Al-4V)? What do Al and V do? What are their applications?

Answer 3

Exists as alpha (HCP) and beta (BCC) structures - can change composition to change mech properties

Al and V stabilize alpha and beta elements, respectively

Used for joint replacements due to better mech properties than CP Ti

Notch sensitive, implant design matters

Used less in articulating surfaces due being less hard & undergo more wear

Question 4

Processing of Ti based implants

Answer 4

Often machined (hard to cast)
Carefully selected hot working temp (depends on alloy composition)
Excessive O, H, and N during annealing must be avoided
Harder to machine that austenitic SS due to low Young’s modulus (sticks to machining tools)
Need sharp tools, abundant coolant, slow speeds, and more

Question 5

What is replaced in new titanium alloys? What are the properties of new Ti alloys?

Answer 5

Replace toxic vanadium with niobium (Nb) or iron (Fe)

Lower modulus and better fatigue strength reported

Mo can be added to stabilize beta Ti phase at low temp

Question 6

Osseointegration

Answer 6

Direct contact between viable remodelled bone and implant without an intervening soft tissue

Allows greater force transfer across biomaterial bone interface, reduces slip across interface, and the soft tissues can be more stable

Question 7

Surface properties of Ti implants

Answer 7

Titanium implant surface consists of: thin oxide layer and bio fluid of water, ions and proteins
Chemical nature influences protein bonding
Physical nature causes different contact areas with proteins and cells
These influence properties, function, and conformation
We know oxide layer resists corrosion, but we don’t know its role in biological response

Question 8

What is the purpose of surface treatment of metallic implants? What are some surface treatment types?

Answer 8

Improve implant fixation and control device performance
Roughness affects bine apposition and pull out strength
Sandblasting can produce surface roughness
Macro or micro porous coating for greater adhesion

Question 9

Morphological fixation

Answer 9

Dense, nonporous inert materials attach by fibrous tissue growth into surface irregularities by press fitting into a defect

Question 10

Biological fixation

Answer 10

From porous inert implants, bone ingrowth occurs that mechanically attaches the bone to the materials

Question 11

Bioactive fixation

Answer 11

Nonporous surface reactive ceramics, glasses, and glass ceramics
Attach directly by chemical bonding with bone

Question 12

Resorbable ceramics

Answer 12

Nonporous or porous reservable ceramics which are designed to slowly be replaced by bone

Question 13

Press-fit fixation of porous coated hip stems

Answer 13

May create bone ingrowth within porous coating, and biological or bioactive fixation
Slow process
More open to revision surgery

Question 14

Cemented fixation of porous coated hip stems

Answer 14

Methacrylate monomer injected as liquid undergoes polymerization to a polymethyl methacrylate bone cement
Patient can exert load on implant

Question 15

Compare the interfacial biomaterial-tissue strength of a material with a porous coating to an uncoated material?

Answer 15

Regardless of implantation time, HA (porous) coating produced greater biomaterial-tissue strength compared to an uncoated material

Question 16

Sintering surface treatment

Answer 16

For beads and meshes
Where only specific regions of implant are coated
Heating creates neck through diffusive mechanisms

Question 17

Plasma or flame spraying surface treatment

Answer 17

Hot plasma charged with metal or ceramic powder directed at surface
Molten powder solidifies on impacts, forming rough surface coating

Question 18

Problems encountered with sintering of porous coating

Answer 18

Sintering, which is carried out at T>0.6 Tm, causes annealing, resulting in reduction of strength and fatigue properties of coating
Necking regions are stress concentrators. reducing strength

Question 19

Other surface treatments of materials

Answer 19

Calcium phosphates (e.g. HA) 
Ion implantation - gives better surface properties
Nitriding - Adding nitrogen atoms on surface and interstitial sites (twice the hardening effect than C or O)

All designed to either improve surface bioactivity, hardness, corrosion or wear properties.

Question 20

Mechanical properties of tantalum based porous implants?

Answer 20

High specific gravity and relatively poor mech strength
Combine high porosity, low modulus, and good erosion corrosion resistance
Has characteristics similar to cancellous bone

Question 21

Biomaterial tissue interaction of porous Ta?

Answer 21

Biological fixation (bone ingrowth mechanically attaches bone through pores)
Microtextured on struts promotes rapid tissue ingrowth and strong fixation

Question 22

Is porous tantalum inert, bioactive, or bioresorable?

Answer 22

Inert in the body

Question 23

Applications of porous Ta?

Answer 23

Can be used as an implant itself, or as an ingrowth material on a substrate such as in THR
Load bearing application such as spinal fusion, hip and knee joint parts, and bone grafts

Question 24

How many grades of CP Ti exist? How do they differ?

Answer 24

4 grades

Vary in composition of Nitrogen, Carbon, Hydrogen, Iron, Oxygen, and Titanium

Question 25

What are the corrosion and wear properties of Ti-based implants?

Answer 25

Titanium forms an oxide layer (10nm) upon exposure to air or water which is good to resist corrosion
Corrosion properties of Ti are better than stainless steel or Co-Cr
Micromotion at implant tissue interface results in wear which can trigger cell responses