Biomedical Engineering Reference
In-Depth Information
TABLE 1.15
Functional Group Abbreviations, Chemical Formulae, and Silane Precursors
for Silane-Modifi ed Surfaces [235]
Functional Group
Formula
Precursor
NH
2
COOH
OH
C
6
H
5
CH
3
-
(CH
2
)
3
NH
+
-
COO
−
-
CH
2
CH
2
OH
-
C
6
H
5
-
CH
3
3-Aminopropyltrimethoxysilane
Trichlorovinylsilane
a
Trichlorovinylsilane
a
Phenyltrichlorosilane
Dimethyldichlorosilane
a
The COOH and OH surfaces were produced by a postsilanization modifi cation of the vinyl surfaces.
produces well-defi ned and organized substrates with different surface chemistries and energies
[225-228,235,236]. Table 1.15 presents the typical silane precursors for silane-modifi ed surfaces.
1.5.3 T
OPOGRAPHY
(R
OUGHNESS
) M
ODIFICATION
The cell adhesion on ceramic substrates can be enhanced by modifying the surface roughness (e.g.,
by sandblasting, heat treatment, acid etching, etc.). Increased surface wettability or hydrophilicity
has been associated with enhanced protein adsorption and, consequently, cell adhesion on bioma-
terials [237]. There has been, however, only limited work on developing techniques to modify the
surface topography of 3-D ceramic or composite scaffolds [238-240], these techniques being devel-
oped especially for metallic implant for orthopedics.
Another strategy consists of immersing the ceramic substrate in an SBF to mimic the fi rst stage
of bone tissue integration on the
in vivo
implants. The integration of bone tissue on the bioactive
ceramic or composite surfaces takes place by biomineralization of a thin layer of calcium phos-
phate at the interface between the implant and the bone tissue. Therefore, by soaking the bioactive
biomaterial in SBF, a uniform thick-fi lm composed of nanocrystallites of biologically active cal-
cium phosphate is produced [241]. During this biomimetic process, the topography of the ceramic
implant is modifi ed by the precipitation of nanocrystals of calcium phosphate on its surface. The
new nanoscaled texture of the bioactive ceramic implant can improve the cellular adhesion.
1.5.4 P
OLYMER
C
OATINGS
Another strategy to improve the cell-scaffold interaction is coating the substrate with an organic
phase, usually a biodegradable polymer [177]. Moreover, the strong interfacial adhesion between
the ceramic biomaterial and the organic polymer is a key parameter in generating composites with
good mechanical properties. A wide variety of polymers have been investigated for this application,
including PLA, PGA, PLGA, PDLLA, PHA, and PCL [173,177,223,242-244]. It has been antici-
pated that the combination of ceramic scaffolds and appropriate biodegradable polymer coatings
can enhance the interfacial adhesion of proteins.
1.6 CONCLUSIONS
Signifi cant developments have been achieved in the design and fabrication of a variety of bioceramic
and composite scaffolds, which have demonstrated outstanding properties for applications in bone
tissue engineering. However, there are several challenges ahead for material scientists and tissue engi-
neers, associated with, in particular, the improvement of biological functions and mechanical integrity
of synthetic scaffolds. Vascularization is the single most important issue to be addressed prior to