Biomedical Engineering Reference
In-Depth Information
molecules that stimulate the regeneration of
bone and cartilage in a biomimetic fashion.
Silica-based ceramics, calcium- and phosphate-
based solids, natural and synthetic polymers,
and composites containing one or more of
these materials have been fabricated as aqueous
solutions, pastes, and gels that can be injected
directly into an injured site and then solidifi ed
chemically, thermoreversibly, or by other
means. In all cases, bone morphogenetic
protein (BMP), basic fi broblast growth factor
(
fi ed, including biocompatibility, biological
character, sterilizability, and viscous and vis-
coelastic properties.
7.2.1 Biocompatibility
As with all biomaterials used in the human
body, the components of an injectable scaffold
must be biocompatible.
This means that the
material must not elicit an unresolved infl am-
matory
response
or
demonstrate
extreme
), cells to generate tissue forma-
tion, and a variety of other additives can be
included in the scaffold mixture to enhance
bioactivity. Reviews of materials for tissue
replacement have been published [
β
-FGF/FGF-
2
immunogenicity or cytotoxicity
[
]. A biode-
gradable material is preferred in most cases.
The degradation products of the scaffold must
also be biocompatible so that they can be elimi-
nated from the body in an appropriate period
of time. A generally accepted defi nition of bio-
compatibility for tissue-engineered products
is as follows: “The biocompatibility of a
scaffold or matrix for a tissue-engineering
product refers to the ability to perform as a
substrate that will support the appropriate
cellular activity, including the facilitation of
molecular and mechanical signalling systems,
in order to optimize tissue regeneration,
without eliciting any undesirable effects in
those cells, or inducing any undesirable local
or systemic responses in the eventual host.
They actively participate in the signalling
process, usually with the requirement of
safe degradation as part of the process.” [
96
11
,
14
,
32
,
37
,
58
].
The term “injectable scaffold” requires clari-
fi cation, since not all such materials proposed
in the literature are injectable in a noninvasive
sense. For example, many of the injectable
ceramic/polymer composites are mixtures of a
particulate calcium phosphate compound dis-
persed in a moldable polymer matrix. The
design of a one- or two-syringe/needle device
for dispensing such a product is determined by
the nature of the application, the size, shape,
and concentration of the particles, and the vis-
coelastic response and chemical reactivity of
the composite. The diameter of the needle
required, for example, will certainly be limited
by these factors. In addition, the manner in
which the scaffold accomplishes the specifi c
interaction between the biomaterial and the
local and systemic tissues requires specifi ca-
tion. The only offi cially accepted defi nition of
a scaffold is (ASTM: F
,
66
, 68,
69
,
85
,
88
,
96
100,
101
].
7.2.2 Biological Character
Although the scaffold matrix itself need not be
bioactive, it should provide a positive environ-
ment for cell activity, including enhanced cell
adhesion, migration, and function, as well as
vascularization (where appropriate) and free
space for bone or other tissue growth. A
primary objective should be that the scaffold
creates a biomimetic system that resembles as
closely as possible that of the host.
A]“the
s
upport,
delivery vehicle, or matrix for facilitating the
migration, binding, or transport of cells or bio-
active molecules used to replace, repair, or
regenerate tissues.”
2150
) [
2
7.2 Necessary Properties of
an Injectable Scaffold
7.2.3 Sterilizability
In order to develop an acceptable injectable
scaffold for orthopedic applications in which
the regeneration of bone and cartilage is stimu-
lated by active cells within the scaffold, a
number of fundamental biological, mechanical
and morphological conditions must be satis-
As with all implanted materials, an injectable
scaffold material must be easily sterilized to
prevent infection when implanted. The method
of sterilization must not negatively affect
chemical composition, biocompatibility, or
bioactivity [
96
].
