Biomedical Engineering Reference
In-Depth Information
Table 1 Chemical bond forces, energies and corresponding adhesion forces
Bond forces
Dipole
(Keesom
force)
Induction
(Debye
force)
Dispersion
(London
force)
Hydrogen
Covalent
Ionic
Metallic
Energies
[kJ/mol]
\30
\10
\10
\50
60-800
600-1,000
100-800
&10
2
&10
2
&10
2
&10
2
-10
3
&10
4
-10
5
&10
4
-10
5
&10
4
-10
5
Adhesion
[N/mm
2
]
the last decade has been performed on the incorporation of adhesion-promoting
oligopeptides into biomaterial surfaces [
106
,
127
-
132
]. In this way, engineered
microenvironments have been designed for controlled SC differentiation including
biomimetics and controlled release [
120
].
Recent studies on biomimetic materials include the following: bioceramic
implants with drug and protein controlled delivery capability [
133
]; surface
modification with fibrin/hyaluronic acid hydrogel on solid freeform-based scaf-
folds followed by bone morphogenic protein-2 (BMP-2) loading to enhance bone
regeneration [
134
]; synergistic effects of the dual release of stromal cell-derived
factor-1 and BMP-2 from hydrogels on bone regeneration [
135
]; spatial control of
gene expression within a scaffold by localized inducer release [
136
]; bio-activation
via glycosaminoglycans as regulators for SC differentiation [
137
]; and biomimetic
properties of an injectable chitosan/nano-HA/collagen composite [
138
]. In vivo
studies demonstrated that chondrogenic differentiation of MSCs is induced by
collagen-based hydrogels [
139
].
So it is possible to individually control the release of several agents by bio-
material drug release systems. Nevertheless, the appropriate combination of bio-
active factors needed at different time points during tissue regeneration has still to
be studied in more detail. Furthermore, the therapeutic application of growth
factors can be accompanied by undesirable side effects due to the difficulty in
controlling the release in an appropriate dose-dependent manner. Bioactive factors
have been extensively investigated for their effects on angiogenesis, cell growth or
SC differentiation [
140
]. Both native and artificial receptor ligands, i.e., extra-
cellular nucleotides, are known to induce SC differentiation or growth, e.g., BMPs
and transforming growth factor-b used in bone and cartilage regeneration. BMPs
have been shown to recruit MSCs from bone marrow and periosteum to the site of
repair and to support proliferation and differentiation of these cells. Furthermore,
they have been shown to induce vascularization, bone formation, remodeling, and
marrow differentiation. In vitro studies have shown that in articular cartilage,
transforming growth factor- b (TGF-b) induces MSC differentiation to chondro-
cytes and promotes cell proliferation [
72
].
Wei and Ma studied poly(lactides)/apatite composite scaffolds prepared by a
biomimetic approach. The poly(lactide) scaffolds were prepared by conventional
phase separation in dioxane. Nanofibrous scaffolds were prepared by sugar tem-
plate leaching and phase separation in tetrahydrofuran. Nanosphere drug release
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