Biomedical Engineering Reference
In-Depth Information
ized as a Skeletal Repair System (SRS®, Norian
Corporation, Cupertino, CA). The product is
used mostly in orthopedic and trauma applica-
tions. The material is said to allow normal frac-
ture healing by resorption via normal cellular
remodeling and to maintain strength during
the remodeling process. Norian SRS is deliv-
ered to the surgery room as a mixture of calcium
phosphate and carbonate. After being mixed
with a sodium phosphate solution, it forms
an injectable paste that hardens in about
cell-material interaction and osteoblastic
activity. The addition of coated ABM particles
promoted cell adhesion, enhanced osteoblastic
activity, and increased matrix mineralization
[
].
An in vitro study of the morphology of
nucleus pulposus cells seeded onto gelatin,
demineralized bone matrix (DBM), and poly-
lactide scaffolds showed that cells attached to
gelatin microcarriers and DBM fragments
assumed an elongated, fi broblast-like morphol-
ogy, retained metabolic activity, and expressed
genes for major ECM components. Both the
gelatin and DBM are said to have potential for
use in injectable composites for intervertebral
disc tissue engineering [
77
10
minutes, with a compressive strength of about
10
MPa that then increases to about
55
MPa in
12
hours. Tensile and shear strengths, however,
are much lower, attaining a maximum of the
order of
]. Norian has also
been used in craniofacial surgery [
2
to
3
MPa [
19
,
58
].
To provide preventive antibiotic therapy in
vivo, tetracycline, at concentrations up to
12
].
A variety of water-soluble gelling agents have
been employed to produce a fully injectable
calcium phosphate cement. A necessary condi-
tion for their use is that they do not substan-
tially affect the setting properties of the cement.
Aqueous solutions of glycerine, derivatives of
cellulose, and salts of alginic acid were exam-
ined as modifi ers for an apatitic calcium phos-
phate cement [
67
%
wt, was added to an injectable calcium phos-
phate cement that contained silicone (
7
% by
weight). The combination of tetracycline and
silicone caused setting time to increase and
mechanical properties to diminish [
2
].
All injectable materials to be used in bone
repair must be sterilizable. Injectable calcium
phosphate cements are often sterilized by
gamma radiation, which does not affect chemi-
cal reactivity [
84
]. The addition of glycerine or
cellulose derivatives resulted in sticky pastes
that did not set properly, nor was there satisfac-
tory conversion of the ingredients to hydroxy-
apatite. The addition of salts of alginic acid
imparted satisfactory fl ow properties to the
cement and did not affect the setting reaction
drastically, even though the phase conversion
was retarded somewhat. A
56
]. The natural and synthetic
polymer gels and solutions used for modifi ca-
tion of the viscoelastic properties of the IBSs,
however, undergo changes because polymers
tend to be subject to scission and/or cross
linking under hydrolytic conditions. Polymers
used in these applications must therefore be
tested after sterilization with gamma radiation,
steam, or ultrafi ltration [
103
% w/w ratio of the
gelling agent permitted smooth fl ow through
an
2
-gauge needle and resulted in a setting
time of
18
103
].
20
minutes and a mean compressive
strength of
MPa, a value comparable to
that of trabecular bone. X-ray diffraction and
Fourier transform infrared analyses indicated
that the cement had been converted to a
hydroxyapatite structure that was similar to
vertebrate bone [
11
to
12
7.4 Hydrogel-Based
Injectable Scaffolds
].
The utilization of aqueous solutions of
natural polymers to modify the rheological
properties of ceramic-based scaffolds has also
led to the introduction of bioactive ingredients
in ceramic bone scaffolds [
56
Hydrogels have proven to be effective as thera-
peutic delivery devices of cells and growth
factors for soft-tissue engineering applications.
From a biological viewpoint, aqueous gels make
ideal porous scaffolds when load-bearing
support is either unnecessary or otherwise
available. These scaffolds possess the cohesive
properties of soft solids and permit diffuse
liquid transport. As viscoelastic solids, they
have low static and dynamic moduli because of
high water content and high permeability for
9
,
12
,
56
,
64
,
77
,
80
,
84
].
Anorganic bone mineral (ABM) particles
coated with the cell-binding domain of type I
collagen (P-
,
103
peptide) and suspended in inject-
able hyaluronate hydrogels were tested in vitro
by using human osteosarcoma cells to evaluate
15
