Engineering Fibrous Tissues and Their Interfaces with Bone - Structural Interfaces and Attachments in Biology - page 325

of canine ligament fibroblast was measured via gel filtration chromatography [ 107 ].
After 24 hours, cells cultured with a 1 1 resulted in

significantly higher proteoglycan synthesis than the growth factor-free control
[ 107 ]. In vivo studies have also been performed to evaluate the effects of growth
factors on healing of an injured ACL [ 108 ]. TGF-

g/mL solution of TGF-

m b

1 was administered to rabbits at
the site of an overstretched injury in the right ACL. After 12 weeks, results revealed
that the application of 4 ng of TGF-

b

1 significantly enhanced the healing in the
injured site, as seen through increased stiffness of the tissue and increased maxi-
mum load values [ 108 ]. It is suggested that this is the result of increased collagen
type I production in the matrix network.

b

PDGF :An in vitro study with a canine model was performed to examine the effects
of single and combined growth factors on cell proliferation and collagen produc-
tion. Fibroblasts isolated from the intrasynovial flexor tendon were cultured in
media containing 10 ng/mL of PDGF and/or 10 ng/mL bFGF. After cell culture
for 24 houes, cell proliferation, determined via thymidine incorporation, in the
presence of PDGF increased 13-fold when compared to the no-growth factor
control [ 73 ]. When PDGF and bFGF were combined, both cell proliferation and
collagen synthesis, measured by 3H-proline incorporation, increased in a dose-
dependent manner from 5 to 40 ng/mL [ 73 ].
It has been shown that PDGF increases mechanical properties of ligament tissue
in vivo [ 109 ]. This study used a rabbit model to introduce PDGF at concentrations
of 400 ng and 20 g into the ruptured right medial collateral ligament. After 6

weeks, results demonstrated that both doses of PDGF caused a significant increase
in cross sectional area when compared to the negative-growth factor control [ 109 ].
Stiffness and ultimate elongation values were significantly higher than the control
values for 20

m

g dose of PDGF, suggesting that the growth factor enhanced
structural properties during healing [ 109 ].
bFGF : As evidenced in the study described above, bFGF can stimulate cell
proliferation [ 73 ]. In addition, bFGF increases migration of rat tendon fibroblasts
in an in vitro wound model at dosages ranging from 0-50 m g/L. At 10 m g/L, bFGF
“wound” closure was most accelerated. Through measurement of 5-bromo-2-
deoxyuridine incorporation, the mechanism for this process was identified as cell
proliferation [ 110 ].

m

IGF-1 : IGF-1 acts to promote matrix synthesis and cell proliferation [ 111 - 113 ].
IGF-1 mRNA and protein levels have been shown to increase at injury sites in soft
tissues. This upregulation can help the healing process because IGF-1 increases
proliferation activity that is associated with the inflammatory and proliferation
stages of healing [ 104 ].

Growth factors also play a role in MSC maintenance and differentiation. The
previously mentioned growth factors have all shown to increase MSC growth and
tendon/ligament ECM production [ 114 - 116 ]. In addition, growth and differentia-
tion factors (GDF) 5, 6 and 7, classified in the bone morphogenetic protein (BMP)
family, play a major role in tendon and ligament differentiation.