Biomedical Engineering Reference
In-Depth Information
crustacean shells, may provide unlimited mate-
rials for making 3D scaffolds.
Despite the advances made with these mate-
rials, the majority of them cannot match the
performance of autografts. Natural polymer-
based 3D scaffolds have shown good tissue
biocompatibility and produce safe degradation
products but are mechanically weak, have fast
and uncontrollable degradation rates, require
immunosuppressive drugs, and retain batch-
to-batch variation of physico-chemical proper-
ties. Synthetic materials typically have the
advantage of being readily available, eliciting
a limited immune response, and being pro-
duced with highly specific degradation rates.
However, they lack cell-recognition signaling
and release acidic by-products during degra-
dation, leading to local inflammation
[32]
.
Hybrid biomaterials that combine the favora-
ble biological properties of natural polymers
and mechanical properties of synthetic poly-
mers represent a potential approach to enhance
the properties of tissue engineering scaffolds
[33-36]
.
Control of pore size and pore interconnectiv-
ity in a 3D scaffold are important considera-
tions also. Although specific means to control
porosity are mentioned in Section
7.2
for each
fabrication technique, in general porosity is
controlled through varying processing param-
eters. Pores allow effective transport of nutri-
ents to regions throughout the bioscaffold as
well as removal of waste from various regions
of the bioscaffold. However, the porosity and
mechanical strength of the material must be
optimized to ensure that the bioscaffold is nei-
ther too brittle nor too dense. Optimal pore
diameters are also needed to ensure that desired
cellular behavior is achieved. Cells must main-
tain communication with one another and infil-
trate the bioscaffold to its core, a necessary
event for proper tissue formation.
The last issue to consider is the topographi-
cal features of the bioscaffold. Nanoscale
features located uniformly on a bioscaffold will
aid in proactively directing cellular arrange-
ment
[14, 37]
. Biomechanical cues can be trans-
mitted to cells via micro- or nanoscale substrate
topography. Morphological and functional
changes have been observed for various types
of cells, including mesenchymal stem cells
(MSCs), when cultured on substrates with
micro- or nanoscale topographical features
such as fibers, pillars, grooves, or pits
[38-42]
.
A variety of techniques can achieve nanoscale
surface roughness, such as embedding nanofib-
ers into a solid matrix, electrospraying onto a
scaffold, and physically and chemically etching
[43-45]
.
This chapter focuses on the fabrication and
use of nanostructured materials as 3D biomi-
metic scaffolds for tissue regeneration. We
also mention various techniques used to create
micro/nanoporous
structures
for
tissue
regeneration.
7.2 FABRICATION OF 3D
BIOSCAFFOLDS
In living tissues, cells reside in a 3D, cushioned
ECM network and are protected from external
mechanical stress
[46, 47]
. The ECM also pro-
motes cellular functions such as cell adhesion,
migration, proliferation, and differentiation due
to molecular interactions between specific cell
membrane receptors and signaling cues from
the ECM
[14, 40, 48]
. Therefore, as previously
mentioned, the architecture of scaffolds should
mimic the natural ECM and instruct cellular
behavior while adequately housing the cells.
Although enormous progress has been made in
designing tissue engineering scaffolds using a
variety of materials and various processing con-
ditions, more research remains to be done.
Table
7.1
summarizes some of the commonly used 3D
scaffold fabrication techniques. In the follow-
ing section, we discuss several representative
