Biomedical Engineering Reference
In-Depth Information
Numerous materials have been used to electrospin scaffolds for cartilage tissue engineering that
include chitosan [47], chitosan/PEO (90/10) [15], PLGA and PLA-PEG [25], PCL [48,49], collagen
type II [12], and hyaluronic acid [50].
Sheilds et al.
[12] produced cross-linked and uncross-linked electrospun collagen type II scaf-
folds. The average fi ber diameters were 1.46 µm and 496 nm, respectively. Because of the impor-
tance of scaffolds withstanding stresses, the average tangent modulus, ultimate tensile strength, and
ultimate strain of the uncross-linked samples were measured. Cellular adhesion and proliferation
collagen II electrospun scaffolds was evaluated with SEM, showing that chondrocytes infi ltrated
the interiors of 3-D nanofi brous scaffolds. However, as collagen II scaffolds have limited mechani-
cal properties without severe cross-linking (which decreases cell and tissue compatibility), it is
questionable if it offers without reinforcement with a synthetic polymer a foundation for articular
cartilage regeneration.
Subramanian
et al.
[51] generated electrospun chitosan/PEO (90:10) submicron scaffolds that
were aligned with slight cross-linking between the parent fi bers. The elastic modulus of the elec-
trospun mats was signifi cantly greater than cast fi lms (2.25 MPa compared with 1.19 MPa). These
authors assessed the cell compatibility of chitosan/PEO electrospun scaffolds by comparing chon-
drocyte adhesion, proliferation, and cellular viability with a cast fi lm. After 3 days, the viability of
the cells on electrospun mats was 69% to that of the tissue culture plastic (TCP) control, but slightly
better than on cast fi lms (63%). Though the chondrocytes grew slowly on the electrospun mats in the
fi rst week, the growth rate subsequently increased. By 10 days, the cell number on the electrospun
chitosan was almost 82% to that of the TCP, and 56% to that of the cast fi lms.
Li et al.
[48] cultured MSCs on randomly orientated PCL electrospun nanofi bers (
d
700 nm)
to examine the capacity for chondrogenesis on these scaffolds. They claim that chondrogenesis was
greater when MSCs were seeded onto electrospun scaffolds than for a high-density cell pellet (CP)
protocol, suggesting that electrospun scaffolds seeded with MSCs are candidates for cartilage tissue
engineering. The signifi cance of this fi nding was that the CP protocol is currently a system that is
widely used to study the chondrogenesis of MSCs, which shows that when the cells are seeded at
high density they undergo chondrogenesis, and form tissue that
is morphologically and biochemi-
cally similar to native cartilage.
=
5.4.3 V
ASCULAR
T
ISSUE
E
NGINEERING
The primary function of the vascular system is to deliver oxygen and nutrients to the tissue and
organs, remove CO
2
and other metabolites, and to distribute messenger molecules. Arteriosclerosis
results in a thickening of large to medium size arterial walls and is characterized by endothelial dys-
function, infl ammation, and eventually calcium and cholesterol plaques. The end result is chronic
luminal obstruction leading to a decreased or absent circulation and hence impaired oxygenation of
end organs. Coronary artery grafts, using mammary arteries or saphenous veins to bypass these
occlusions, is the mainstay of treatments. However, there is frequently a lack of adequate arteries
or veins that are suitable for bypass conduits. Furthermore, compliance mismatch between grafts
might contribute to myointimal hyperplasia.
Based on the above clinical background, investigations into vascular tissue engineering have
been directed at searching for suitable vascular graft substitutes [52]. The challenge is that engi-
neered vascular replacements must withstand pulsation and the high pressure and fl ow rate of the
blood stream. Compliance matching also presents a major challenge and has been addressed by
modifying various aspects of graft design such as materials, structure, and fabrication method,
without compromising the capacity for cells to form strong attachments and complete monolayer
covering of the graft to reduce thrombus. A major reason for grafts failure is the incomplete cover-
ing of the graft surface by endothelial cells and the resultant myointimal hyperplasia.
Electrospinning offers the potential of control over composition, mechanical properties and
structure of a graft while making it theoretically possible to match the compliance of the synthetic
