NANOMATERIALS FOR IMPROVED ORTHOPEDIC AND BONE TISSUE ENGINEERING APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 206

mechanical properties similar to those of physiological bone but also cytocompat-
ible surface properties in order to more successfully promote cell adhesion and
tissue integration [21 - 23] ,

7.2.2.2 Osteolysis. As a late-appearing complication, osteolysis induced
by wear particles of implant materials has been regarded as one of the most com-
mon complications and the leading reasons for revision surgery after primary
replacement [26-29]. It can cause severe bone loss which eventually results in
implant instability and failure. Metals, ceramics and polymers (such as polyethyl-
ene, a material used for acetabular components in hip replacements) are widely
accepted as a source of prosthetic particles and serve as a major contributor to
bone resorption. These wear particles appear most commonly at the bearing sur-
face, but are also at host-implant or implant-implant interfaces. Figure 7.2 shows
the osteolysis process caused by biomaterial wear debris.

Particles

Particles bigger than
10 micrometers

Particles smaller than
10 micrometers

Giant cells

Cytokines

Macrophage

Cytokines

PGE2
cytokines

Fibroblast

Fibrous tissue

Preosteoblast

Osteoblasts

Osteoclast

Collagen

Bone resorption

Bone

Figure 7.2. Schematic of biomaterial wear debris activating macrophages and inducing
osteolysis. Particulate debris is generated from wear of arthroplasty components, metal
corrosion or polymer degradation. Particles

10 μ m are engulfed directly by macrophages
but can not be digested easily. Consequently, macrophages begin to release interleukins
(IL-1, IL-6), prostaglandin E 2 (PGE 2 ), and tumor necrosis factors (TNF) which then mediates bone
resorption via osteoclasts [29]. On the other hand, macrophages form giant cells to phagocytose
large particles (

<

10 μ m) and then secrete cytokines to signal fi broblasts to synthesize collagen
to result in a fi brous tissue capsule around the implant. Redrawn from [24,25]. It remains to
be seen what happens when particles are less than 100 nm (in non agglomerated form).

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