Biomedical Engineering Reference
In-Depth Information
became a semisolid at body temperature. When
the semisolid hydrogel was cross-linked with
genipin in situ, protein was released for up to
40
blasts, epithelial cells, keratinocytes, and hepa-
tocytes was observed [
]. Silk threads from
Bombyx mori
have a fi brous core of fi broin, a
biocompatible structural protein that favors
cell adhesion and activation [
98
,
99
days. The hydrogel can be prepared in solu-
tions at a physiological pH, allowing incorpo-
ration of a wide range of bioactive molecules
used in tissue-engineering applications [
]. When
dissolved in water, regenerated fi broin mole-
cules act as hydrophilic-hydrophobic-hydro-
philic polymers that form an emulsion of
irregularly sized micelles by chain folding and
hydrophobic interactions [
2
,
70
,
98
].
Hyaluronic acid (HA) is an important con-
stituent of the ECM. It is a polyanionic glycos-
aminoglycan (GAG) that is required for cell
proliferation and differentiation and to regu-
late cell adhesion [
7
]. The intervention
of hydrophilic blocks within the hydrophobic
sequences prevents
52
91
]. Although HA is widely
-sheet crystallization and,
as the concentration of micelles increases,
results in the formation of a skeletal arrange-
ment of micelles “cross-linked” by hydrogen
bonding and hydrophobic interactions [
β
used medically [
], its use as an
injectable scaffold has been limited. Sodium
hyaluronate has been evaluated as a matrix to
deliver
5
,
60
,
65
,
76
β
-FGF/FGF-
2
in the course of bone
].
Regenerated fi broin is prepared by degumming
B. mori
cocoons in aqueous Na
2
CO
3
solutions,
dissolving the nearly pure fi broin in lithium
bromide solution, and then dialyzing against
distilled water to obtain aqueous solutions of
the order of
52
repair [
]. A single injection of the gel into a
fresh rabbit fi bula fracture caused an increase
of bone and callus formation and restored the
mechanical strength at the site [
37
].
Recent work on the development of an inject-
able, cross-linkable hydrogel of HA with
3
37
% weight/unit volume. An
injectable hydrogel is formed directly from solu-
tion at a pH below the isoelectric point [
2
% to
5
-thiopropanoyl hydrazide-poly(ethylene glycol-
diacrylate) (HA-DTPH/PEGDA) at a
molar
ratio indicated potential utility for tissue-
engineering uses [
2
:
1
25
,
73
].
human osteoblast cell-line bioactivity
was examined on pure fi broin-based injectable
hydrogels prepared by different methods. In
vitro biocompatibility was evaluated by mea-
suring lactic dehydrogenase release, cell pro-
liferation (WST
MG
63
91
]. A PEGDA solution seeded
with T
human tracheal scar fi broblasts was
added to an HA-DTPH solution containing
newborn calf serum, L-glutamine, and an
antibiotic-antimycotic to form a cross-linkable
hydrogel with
31
, water-soluble tetrazolium
salt), differentiation (ALP, alkaline phospha-
tase and OC, Osteocalcin) and synthetic activ-
ity (collagen I, TGF-
1
% water content.
The hydrogel was used to determine in vitro
cell viability and proliferation and in vivo
fi brous tissue generation. This was done by
bilaterally transplanting the hydrogel into sur-
gically prepared subcutaneous pockets on the
backs of
97
.
5
% to
98
.
8
β
1
, transforming growth
factor
]. In vitro tests
also confi rmed that the fi broin hydrogels were
not cytotoxic [
β
1
and interleukin-
6
) [
28
]. In a series of in vivo tests, it
was found that a
73
fi bro-
blast viability was demonstrated by an almost
10
4
- to
6
-week-old nude mice. T
31
wt% fi broin hydrogel had
the capacity to regenerate bone in critical-size
holes drilled into the femoral condyle of rabbits,
without the addition of cells, growth factors, or
other components known for their bioactivity
[
2
.
5
28
days of culture in vitro. The in vivo measure-
ments were made at
-fold increase in the number of cells after
weeks after
implantation. There was no evidence of necro-
sis or damage to the tissues, and the cells
retained their initial phenotype and were
actively secreting new ECM.
Regenerated silk fi broin has been used for the
fabrication of fi lms, nets, regenerated fi bers,
foams, creams, and hydrogels [
2
,
4
, and
8
]. The in vivo studies were performed at the
Rizzoli Orthopaedic Institute of Bologna [
28
28
]
by implanting
% fi broin hydrogels, brought
to their isoelectric points by the addition of
citric acid, into bilateral confi ned cancellous
defects (
2
.
5
10
-mm depth and
6
-mm diameter) in
53
,
72
,
73
,
74
,
86
,
the femoral condyle of
adult New Zealand
white disease-free rabbits. Four control speci-
mens were used. The cancellous defects in two
rabbits were left untreated; in two other rabbits
a commercial scaffold of poly(D,L-glycolide)
copolymer (ratio
10
87
]. Injectable fi broin hydrogels and their
composites have also been evaluated for their
effectiveness in bone regeneration [
,
98, 99
].
Human cell lines and primary cells isolated
from biopsies were seeded on fi broin-based
materials. Proliferation of fi broblasts, osteo-
25
,
28
mol%) dispersed in an
aqueous solution of PEG and
50
:
50
15
% dextran
