Biomedical Engineering Reference
In-Depth Information
cells to the injured site, exhibited mechanical properties similar to those of native
cartilage, and contained higher concentrations of type II collagen and aggrecan.
In addition, the microchannels in the scaffold functioned as conduits for cell
homing, diffusion, histogenesis, and angiogenesis, thereby promoting tissue
regeneration. In this study, it was proposed that some of the endogenous cells were
recruited from the synovium, bone marrow, adipose tissue, and vasculature. The
porous surface of the proximal end of the implanted scaffold and the presence of
the microchannels may enable access to synovium stem cells and bone marrow
progenitor cells, while providing a conduit for the migration of these cells.
Therefore, this study demonstrated the possibility of utilizing a cell homing
strategy to regenerate the entire articular cartilage surface, beyond focal defect
healing, with the aid of growth-factor-loaded scaffolds.
6.2 Hydrogels
For cartilage tissue engineering, hydrogels are the most extensively investigated
class of scaffold materials, as they provide a variety of advantages, including high
water content and elastic properties that mimic native cartilage tissue, technical
capacity for cell encapsulation, and effective transport of water and nutrients
owing to their high equilibrium swelling [
103
]. Hydrogels may be tuned to mimic
the function and architecture of native cartilage, which is composed of chondro-
cytes and ECM proteins [
104
,
105
]. Therefore, success criteria for a functional
hydrogel material for the delivery of cells and growth factors for cartilage
regeneration include (1) biocompatibility, (2) an ability to encapsulate cells and
support their viability and proliferation, (3) a capacity for sufficient hydration to
provide effective diffusion of molecules in physiological conditions, (4) suitable
mechanical properties, and (5) possible degradation to provide space for neotissue
regeneration and remodeling. Naturally derived polymers such as alginate [
106
],
fibrin [
58
,
107
], silk [
108
,
109
], chitosan [
110
,
111
], and blends of these com-
ponents [
112
,
113
] as well as ECM components in native cartilage, including
collagen, HA [
56
,
114
], and CS [
115
], have been used to fabricate functional
hydrogels for cartilage regeneration [
116
]. Although hydrogels comprising natu-
rally derived materials generally exhibit excellent cytocompatibility and cell
adhesion, synthetic polymers have the potential to overcome some of the limita-
tions of naturally derived hydrogel materials, especially the general lack of tun-
ability and insufficient mechanical strength. Synthetic polymers have been utilized
in the fabrication of functional hydrogel systems owing, in large part, to their
ability to modulate key physical properties of the hydrogels, such as the
mechanical properties (e.g., elasticity and injectability), as well as the degradation
kinetics. Surface properties of synthetically derived polymeric biomaterials can
also be modulated to increase hydrophilicity, mobilize ECM-derived proteins, and
fabricate micropatterned and nanopatterned surfaces [
117
]. In addition, it is also
possible to fabricate hybrid composite gels by combining natural and synthetic
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