Biomedical Engineering Reference
In-Depth Information
ymers (e.g. Pus) [30]. PCL has been approved by the FDA for specific applications, such as a
drug delivery devices, sutures, or adhesion barriers. It has been widely used as a scaffold
material for tissue engineering with mismatched mechanical properties and slow degrada‐
tion rate [171,172]. In rats the
in vivo
degradation of PCL is about 3 years [173].
Various categories of drugs have been encapsulated in PCL, in microsphere, nanosphere or
bulk states, for targeted drug delivery and for controlled drug release [174-176]. For exam‐
ple, a PCL scaffold modified by grafting nerve growth factor (NGF) and Tirofiban (TF) has
been used as nerve conduits to promote the regeneration of sciatic nerves [177]. Low molec‐
ular weight PCL pieces can be ingested and digested ultimately by phagocyte and giant cell
without any cumulate vice-products (Figure 8) [178-180].
Figure 8.
Micrographs illustrating extracellular degradation of biomaterials by macrophage fused multinuclear giant
cells. (A) A foreign body giant cell (FBGC) engulfed a fragment of poly(epsilon-caprolactone), PCL polymer
in vivo
. Nu,
nuclei of FBGC. The PCL polymer was dissolved during sample preparation. Transmission electron microscopy (TEM),
bar = 2
μ
m. (B)
In situ
cross-section of the interface between a multinuclear giant cell (MnGC) and PLGA film. Note the
pseudopodia of the MnGC penetrated deep inside the surface of PLGA film and formed sealed compartments. PLGA
polymers are eroded within the compartments. Focused ion beam (FIB) microscopy, bar = 5
μ
m. (C)
In situ
cross-sec‐
tion of the interface between an osteoclasts-like cell (OC) and calcium phosphate cement. Note the typical ruffled
board of OC and vesicles (V) secreting from OC to the sealed extracellular space. FIB microscopy, bar = 2
μ
m [162].
12. Polyurethane (PU)
PU is a series of biomaterials that contains urethane radical and offers the greatest versatility
in compositions and properties of any family of polymers. Especially, a few specific elasto‐
meric PU compositions have demonstrated a combination of toughness, durability, biocom‐
patibility and biostability for being used as implantable medical devices, which is not
Search WWH ::
Custom Search