Biomedical Engineering Reference
In-Depth Information
Proliferation
differentiation
Nucleus
ERK/MAPK
P
RhoA/Rock
Stem cell
αα
β
α
β
β
Integrins
Proteins
e,g., fibronectin, vitronectin etc.
Nanomaterial scaffold
Figure 14.2
Schematic pathways involved in the interaction of stem cells and nanostructured
matrices. When integrins on the cell membranes bind to nanostructured ECM components, cascades
of signal transduction occur for translating physical contact with nanostructures into biological
responses, such as cell morphological change, proliferation, and differentiation. Reprinted from [2]
with permission from Elsevier.
Nature manages to make structures with the minimum amount of essential chemicals.
The natural ECM includes less than 1% solid materials, yet they are mechanically strong
and have various functionality. Nature regulates the mechanical characteristics of biological
tissue by fine adjustments of its composition with an alteration of its nanoscale structure
from molecular level up to macroscopic scale [18]. Therefore, investigators have tried to
engineer artificial matrices that resemble the nanoscale features of the natural ECM and
current literature strongly supports nanostructured matrices due to their greater cell attach-
ment and phenotypic activity than macroscopic matrices [19]. The matrices with nanoscale
features can be categorized into nanofibers, nanocomposites, and nanostructured surfaces.
Nanofibers
Nanofibers, with diameters ranging from 1 to 1000 nm, are the most popular nanostruc-
tured biomaterials that have been widely used in tissue engineering, due to the similarity of
diameter size scales between nanofiber structures and ECM fibers and large surface area,
which is favorable for cell adhesion and bioactive factor encapsulation.
There are three commonly used methods to produce nanofibers: electrospinning,
self-assembly and phase separation [20], and the fiber composition, alignment, diameter,
degradation, and mechanical characteristics can be controlled for different types of tissue
regeneration. Fibers have been fabricated for stem-cell expansion using self-assembly pep-
tides and a range of polymers such as poly(ε-caprolactone) (PCL), poly(
l
-lactic acid)
(PLLA), poly(
d
,
l
-lactide-co-glycolide) (PLGA), and other synthetic or natural polymers
and also their blends or copolymers (Table 14.1).
Poly(
ε
-Caprolactone)
Poly(ε-caprolactone) is widely chosen as a Food and Drugs Administartion approved model
polymer due to its low toxicity, low cost, and ease of fabrication. Disadvantages of unmodified
PCL are slow degradation rates (weeks to months), weak mechanical properties, nonreactivity,
