Polycaprolactone-based Scaffolds Fabricated Using Fused Deposition Modelling or Melt Extrusion Techniques for Bone Tissue Engineering - Biointerfaces: Where Material Meets Biology - page 235

attachment (especially at the central core of scaffold) and improved water-
absorption ability compared to PCL-TCP-only scaffolds. 40 The same group
also showed that electrospun PCL fibres embedded within PCL-TCP (60 : 40
wt%) scaffolds and subsequently coated with a mixture of collagen and
hydroxyapatite improved cell viability and accelerated osteoblastic differ-
entiation and mineralisation compared to uncoated scaffolds. 41 Long-term
studies are still required to validate the findings.
Fibrin glue is still a popular choice for cell delivery. Rai et al. 42 fabricated
scaffolds from PCL-TCP (80 : 20 wt%) (raster angle: 0/60/1201)andusedthese
scaffolds as a cell transportation vehicle. Human mesenchymal stem cells with
fibrin as the cell delivery matrix were assessed in vivo in critical-sized femoral
defects in nude rats. The scaffolds were able to support cell proliferation
and osteogenic differentiation. Fluorescently labelled human mesenchymal
stem cells survived in the defect site up to 3 weeks after implantation. How-
ever, only 50% of the implants showed significant new bone formation. 42
Much the same as standard PCL, PCL-TCP composite scaffolds can be
easily fabricated in any shape or size using FDM techniques. The production
of anatomically relevant constructs was explored by Lim et al. 43 PCL-TCP
scaffold wedges were fabricated and used in a pig osteotomy model, wherein
empty defects served as a control. Computerised tomography scans and
bone mineral density analysis revealed that after 6 months, scaffold groups
had a higher BMD compared to the control group. However, augmentation
with a PCL-TCP scaffold wedge had no additional beneficial effects on bone
consolidation when compared to the control group (empty defect). 43 This
was an unexpected result, most likely due to specific nuances of the model
such as defect location, scaffold composition or scaffold structure.
The results from all these studies have indicated that PCL or PCL-TCP
scaffolds can act as transportation vehicles for cells into defect sites, and the
use of fibrin glue or collagen as cell delivery matrices can effectively enhance
the cell attachment and subsequent cell proliferation, differentiation
and ECM secretion required to form appropriate bone microstructure. Fur-
thermore, Zhang et al. 44,45 have shown that the use of a bioreactor to culture
cell-scaffold constructs may also increase cell viability, proliferation, dif-
ferentiation and secretion of mineralised bone matrix. This approach also
significantly increases new bone formation and neovascularisation, when
implanted into ectopic or femoral defects in a rat model.
In the absence of cells, PCL or PCL-TCP scaffolds alone may not be suf-
ficiently bioactive in nature to promote bone regeneration, as indicated by
Reichert et al. 21 Cylindrical PCL-TCP and PLDLLA-TCP-PCL scaffolds were
implanted into a 2 cm tibial segmental defect sheep model. Groups with
empty defects or autologous bone grafts (which are classed as the gold
standard of clinical treatment) served as negative and positive controls.
At 3 months, both scaffolds showed good biocompatibility and sucient
mechanical strength. The extent of healing was not comparable, however, to
the positive control group which showed the highest amount of new bone
formation (47%). 21

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