1.7 Biomaterials
Be able to define what constitutes a biomaterial
Be able to define what constitutes a biomaterial
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Lernkarten
What is biomaterial?
materials of a natural or man-made origin that are used to direct, supplement or replace the functions of living tissue
Explain the term biofunctional.
means that the material must perform in a mechanically satisfactory way
What is the primary factor that is related to changes in the mechanical properties of bone?
Changes in the mechanical properties of bone, whilst related to a number of factors, are primarily related to age.
What are the two "phases" of bone?
Biomechanically, bone tissue may be regarded as a two-phases (biphasic) comosite material, with the mineral as one phase and the collagen and ground substance as the other
Which of the following has the lowest elastic modulus?
What is the term used to descibe a material that exhibits different mechanical properties when loaded along different axes?
anisotropy
What is Wolff's law?
"Bones that is not stressed is lost"
Alteration in the internal architecture as well as the external form of bones, occur, as a consequence of primary changes in the shape and stressing of bones
What is osteopenia, and when is it more likely to occour?
Osteopenia =
- Too little stress
- Too much stress
What is the most important mechanical property of collagen fibres?
The most important mechnical property of collagen fibres is their tensile strength. (Zugfestigkeit)
What are the two primary functions of articular cartilage in diarthrodial joints?
- distribute joint loads over a wide area
- allow relative movement of the opposing joint surface with minimal friction and wear
Give three reasons why metals are very popular materials for use in a wide variety of orthopeadic application.
- have relatively high elastic moduli and reasonable yield points
- are ductile (dehnbar) enough
- have relatively high fatigue strength
What is the first step in alloy fabrication?
Extraction of metal ores from mineral deposits
Give another name for investment casting
lost wax casting
What is the difference between forging and working?
forging: forming of components
working: pre-processing of alloys before final forming
Name three finishing processes of metals and briefly describe each one
Machining (drehen, fräsen, schleifen)
Forging (schmieden)
Grinding (schleifen)
What are implant grade stainless steels mainly used for in orthopaedics today?
This has been largely abandoned since early casting alloys displayed inadequate yield and fatigue strengths, resulting in unnacceptable incidences of hip stem bending and comonent fatigue fracture
Which is the most corrosion resistant of all the implant metals?
Titanium-base Alloys
- Titanium
- Aluminium
- Vanadium
Which is the most commonly used cobalt chrome alloy for the manufacture of joint replacement components?
F75
is used for knee femoral components, femoral augmentation blocks and tibial wedges
What are the spaces between the beads on porous coated structures called?
interstices
What are the two main constituents of HA (Hydroxyapatite) and what is it used for?
- 50% amorphous
- 50% crystalline
- 150 microns thick
act as an osteo-inductive material providing more extensive and rapid bone ingrowth
What are the three steps in the production of UHMWPE?
- polymerisation
- consolidation
- machining
The two methods for converting the UHMWPE poser to a solid are ...(1)... and ... (2)...
- ram extrusion
- compression moulding
What is often added to UHMWPE to improve handling during manufacture, and what is the disadvantage of doing this?
- adding = Calcium Stearate
- disadvantage = Fusion defect
Which type of UHMWPE is currently used at DePuy?
GUR1020
Lower molecular weight, without calcium stearate
Name the three most common types of wear reported to affect UHMWPE components?
- Adhesive wear
- Abrasive wear
- Fatigue wear
Briefly explain cross-linking and chain scission.
Cross-linking occours when carbon free radicals from two separate chains join to produce on longer chain
Chain scission means that oxygen reacts with a free radical that breaks the long polyethylende chain and reates another free radical that can undergo further reactions
Why do we package our UHMWPE in vacuum-foil?
result in a significant increase in polymer chain cross-linging and a marked reduction in the number of free radicals available for oxidising reactioins.
The Marathon process is used to:
The Marathon process is a:
The radiation dose used in the Marathon process is
Gamma and electron beam irradiation of polyethylene produces
The second Marathon stage involves:
Heating irradiated polyethylene to its-melt-point for 20 hours creates:
Annealing is used to:
Marathon polyethylene is sterilised by:
What was acrylic cement first used for?
Dentistry
What is the purpose of bone cement in total joint replacement?
conveniaent gap filler between the bone and prosthesis (and adherence)
Basic ceramics are produced from
Advanced ceramics are produced from:
Ceramics can be worked by
