Biomedical Engineering Reference
In-Depth Information
bead instead of fi ber formation occurred. A preliminary
in vitro
study was performed using MG63
cell line.
HA and bone morphogenetic protein has also been successfully incorporated in electrospun
nanofi bers of silk fi broin. Li et al.
[43] produced aqueous solutions of silk fi broin and electrospun
in combination with PEO to increase the viscosity and surface tension thus preventing bead for-
mation. The silk fi broin scaffolds (average fi ber diameter of 500-600 nm) allowed attachment of
human MSCs and promoted to a certain extent differentiation toward osteogenic lineage. The aque-
ous electrospinning process allowed the combination of silk fi broin, HAP, and BMP. Hence, this
process prevented denaturing of the BMP and it was envisaged that this process could also be used
for the delivery of other proteins. Tuzlakoglu et al.
[44] investigated electrospun starch-based mate-
rials for bone tissue engineering. Nanofi bers of starch/PCL blends (30:70), produced by electros-
pinning, were incorporated between microfi bers (produced via a fi ber bonding process) of the
same material forming “nano-bridges” (average diameter of fi bers was 400 nm). The authors state
that larger microfi bers were incorporated into the structure to increase the pore size and therefore
improve cell migration. However, the authors failed to report pore size and size of pore interconnec-
tions, which are important parameters. Interestingly, human osteoblast-like osteosarcoma and rat
bone marrow stromal cells bridged the microfi bers and increased metabolic activity, growth rates,
and ALP activity were reported. However, starch is not a biomaterial of fi rst choice and based on its
compromised properties, it is least likely to be applied clinically.
Electrospun scaffolds are also currently being investigated for use as membranes to facilitate
guided bone regeneration (GBR). GBR membranes prevent epithelial tissue in-growth from the mucosa
and ideally should also promote bone growth. However, nondegradable membranes require a second
surgical procedure for removal and therefore research has focused on degradable constructs [45].
Fujihara et al. [46] electrospun polycaprolactone/CaCO
3
composite nanofi bers for GBR. Two
compositions of PCL:CaCO
3
were produced; 75:25 (900
±
450 nm average diameter) and 25:75
(760
190 nm average diameter). Incorporation of CaCO
3
signifi cantly reduced the tensile strength
of the membranes, however, this was limited by incorporation of a second electrospun PCL mem-
brane in the construct. The electrospun meshes were surface treated using air plasma to increase
the surface hydrophilicity (surface energy not quantifi ed). Human osteoblasts were cultured on the
membranes and showed good cell attachment and proliferation and were proportional to the amount
of PCL. However, the study had a number of biological limitations and among many other assays,
which are needed to prove that the membrane is suitable for GBR, ALP, and osteocalcin expressions
were not studied. Electrospun silk fi broin membranes (150-300 nm average fi ber diameter) are also
currently being investigated for GBR.
In vitro
biocompatibility studies using an osteoprogenitor
(MC3T3-E1) showed good cell proliferation with well-defi ned F-actin stress fi bers attached to the
nanofi bers. Osteocalcin production, which was monitored throughout the 14-day culture, increased,
indicating osteoblastic differentiation and calcium phosphate deposition.
In vivo
studies indicated
that the membranes induced new bone formation in rabbit calvarial defects.
±
5.4.2 C
ARTILAGE
T
ISSUE
E
NGINEERING
The articular cartilage of joints provides a smooth, near frictionless surface, whilst also mediating
load transfer between the joint and the underlying subchondral bone. Cartilage defects typically
result from aging, joint injury, and developmental disorder, and can result in pain and immobility.
Because it has a very limited capacity to regenerate, there is a requirement to replace or repair the
damaged cartilages so as to maintain joint functions. Tissue engineering offers the potential to
develop conduits for cell-based replacement and regeneration of articular cartilage. This involves
the isolation of articular chondrocytes or MSCs (precursor cells), which are then seeded onto a scaf-
fold before implantation into a damaged joint. The architecture of the scaffold is critical, as it should
simulate the ECM of cartilage, thus promoting cellular adhesion, proliferation, differentiation, and
migration, whilst also providing resistance to tensile, compressive, and shear stresses.
