Biological Responses and Biocompatibility

1
Biological Responses and Biocompatibility

• BioE/ME C117
• March 13, 2006

2
What happens when a foreign object enters the
body?
3
Scenario A Hunting Accident
4
chronic inflammation
normal tissue healing
seconds-minutes
months-years
foreign body removed/ dissolved/ digested
weeks
fibrous encapsulation
5
What determines the outcome?

• Whether the foreign body can be digested or
  degraded
• Foreign body size
• Can it be phagocytosed?
• Surface chemistry
• Different materials preferentially adsorb
  different proteins, or none at all (non-fouling)
• Presence of bioactive molecules (bacterial cell
  wall, tissue engineering scaffold)

6
Fibrous encapsulation
granulation tissue formation
collagen fiber deposition
1-5 days
weeks
4-6 weeks
lt 1 day
scar tissue remodeling
angiogenesis
7
Example Birdshot Left in the Body
Not digestible or degradable, so pellet stays in
tissue Too large to phagocytose, so no frustrated
phagocytosis Birdshot is walled off from the body
by fibrous tissue
8
Chronic Inflammation
granuloma - mass of macrophages and FBGCs
months-years
days-months
lt 1 day
foreign body giant cells form from merged
macrophages and monocytes
macrophages cannot clear material - frustrated
phagocytosis
9
Example Wear-Mediated Osteolysis
osteolysis
disrupted balance between osteoclasts/PMNs and
osteoblasts osteoclasts ?, osteoblasts ?
wear particles
osteoclast/ foreign body giant cell
opsonization
phagocytosis
http//academic.brooklyn.cuny.edu/biology/bio4fv/p
age/aviruses/cellular-immune.html Archibeck, MJ
Jacobs, JJ Roebuck, KA Glant, TT. Journal of
Bone Joint Surg, 2000
10
Biocompatibility
The ability of a material to perform with an
appropriate host response in a specific
application
Ratner, Biomaterials Science, 2004
11
FDA Guidelines for Biocompatibility Testing of
Permanent Implant Devices
http//www.fda.gov/cdrh/bbtable1.html
12
Further Reading

• Reader, pages 41-84
• Ratner et al, Biomaterials Science, 2nd ed. 2004,
  chapters 3-4