Biomedical Engineering Reference
In-Depth Information
other molecules to create scaffolds that stimulate the secretion of cartilage matrix. One such study
cross-linked chondroitin sulfate with chitosan to form a scaffold that promoted the chondrocytic
phenotype [
328
]. Chitosan and chitosan composites can also influence cell attachment and growth
in culture. Endothelial and smooth muscle cells seeded onto a dextran sulfate-chitosan composite,
heparin-chitosan composite, or chitosan material alone all showed positive effects on cell attach-
ment and proliferation. However, a GAG-chitosan composite actually inhibited attachment and
growth [
329
]. The modification of chitosan scaffolds with proteoglycans can dramatically change
the overall characteristics of the scaffold. This flexibility is an attractive attribute that could make
chitosan a beneficial material for articular cartilage engineering.
Silk is a naturally occurring polymer that is extruded from insects or worms and has been in-
creasingly used in biomedical applications. The material has good biocompatibility, slow degradation
rates, strong mechanical strength, and can be processed into many different forms useful for tissue
engineering [
330
]. Recent studies investigating silk scaffolds for cartilage engineering have shown
good results for chondrogenesis in seeded stem cells. In comparison to collagen-based scaffolds, silk
constructs had higher type II collagen and GAG deposition, as well as better chondrocytic gene
expressions in seeded mesenchymal stem cells [
331
].
Fibrin glue is another naturally-derived biomaterial that has been used in tissue regeneration
therapies. It is made by mixing fibrinogen with thrombin, which acts to solidify the material either in a
defect site or in another scaffold material. Fibrin glue is popular because it is completely biodegradable
and can be injected before it becomes solid. Unfortunately, the mechanical strength of fibrin glue is
weak, so its use as a primary scaffold in articular cartilage engineering is limited. Because of this, fibrin
is often combined with other materials to help retain its structure. Chondrocytes have been seeded in
pure fibrin glue [
332
], as well as in mixtures with alginate [
333
,
334
] or collagen [
335
]. Biochemical
results did not show major differences from other scaffold materials. However, genipin cross-linked
fibrin scaffolds showed accumulation of collagen type II and aggrecan with a corresponding increase
in compressive and shear moduli [
336
].
Hyaluronan (HA) or hyaluronic acid is a polysaccharide that has been used to create bio-
compatible scaffolds for cartilage engineering applications. HA is a non-sulfated glycosaminoglycan
that helps in lubrication of the joint. It can be cross-linked to form a scaffold capable of supporting
chondrocytes. Similar to fibrin glue, HA is injectable and performs well as a minimally invasive ap-
proach to filling irregularly shaped defects. However, hyaluronan has also been investigated for use
as a solid, porous scaffold. Scaffolds made of an HA-derivative that were implanted
in vivo
showed
good histological results for cartilage matrix deposition [
337
]. Other researchers have found that
cross-linked HA sponges produced better histological results than benzylated HA, which was, in
turn, better than untreated defects [
338
]. Integration with the host tissue improved in conjunction
with histological findings.
A current hypothesis in the field of tissue engineering is to use scaffold materials made
from the same molecules as that of the tissue being repaired [
339
]. One method to achieve this is
through reconstituted matrices. Early instances of using homogenized tissue samples to stimulate
