Biomedical Engineering Reference
In-Depth Information
long history of use in the dental and orthopaedic fields. Examples include
hydroxyapatite [HA; Ca
10
(PO
4
)
6
(OH)
2
] and tricalcium phosphate [TCP;
Ca
3
(PO
4
)
2
]. These have both been combined with PCL with the aim of im-
proving the bioactivity of the scaffolds. Schantz et al.
28
performed in vitro
studies on PCL-HA (75 : 25 wt%) scaffolds, using fibrin glue as the cell de-
livery matrix, to control and improve the cell seeding process and assist
attachment and proliferation. Fibrin glue is a mixture of the plasma glyco-
protein fibrinogen and the enzyme thrombin (both in solution); thrombin
converts the soluble fibrinogen into insoluble fibrin strands. This is how a
blood clot forms and it is a useful way to immobilise cells within a hydrogel
that is initially injectable. PCL-HA composite scaffolds degraded three to
four times faster than PCL-only scaffolds.
28
Histological and biochemical
analyses have shown that both PCL-only and PCL-HA scaffolds seeded with
bone marrow-derived mesenchymal stromal cells (MSCs) led to proliferation
within the scaffold pores and differentiation of cells down the osteogenic
lineage. The PCL-based scaffolds provided a physically stable framework for
bone formation, while the fibrin glue acted as an effective cell delivery
vehicle suitable for cell proliferation and differentiation.
28
Shor et al.
29
indicated that both PCL-only and PCL-HA (75 : 25 wt%)
scaffolds cultured for 21 days with primary foetal bovine osteoblasts sup-
ported cell growth and proliferation. Between the two groups, PCL-HA
scaffolds produced more mineralised matrix and improved osteoblast dif-
ferentiation compared to PCL-only scaffolds, which was confirmed both by
SEM images and alkaline phosphatase activity assays.
29
In a contrasting study, Chim et al.
30
demonstrated no significant differ-
ence between PCL only and PCL-HA (85 : 15 wt%) composite scaffolds when
seeded with human calvarial osteoblasts. In vitro studies spanning 3 weeks
showed that PCL and PCL-HA scaffolds had a constant rate of cell pro-
liferation and increasing tissue growth throughout the depth of the im-
plants, confirmed through light and confocal imaging microscopy.
30
Subsequent in vivo studies involved seeding the scaffolds with human cal-
varial osteoblasts and 21 days of culture days prior to subcutaneous im-
plantation into balb C nude mice.
30
At 14 weeks, explanted PCL and PCL-HA
constructs showed excellent mechanical strength and evidence of mineral-
isation identified using X-ray imaging. There were no significant differences
detected between PCL and PCL-HA scaffolds. The ratio of HA to PCL in the
composites (15 wt%) was relatively low, which may be the reason no sig-
nificant differences were seen observed.
30
d
n
3
r
4
n
g
|
1
.
9.4.2 Polycaprolactone with Tricalcium Phosphate
PCL-TCP and PCL-HA composites have demonstrated favourable mechan-
ical and biochemical properties as well as favourable degradation and re-
sorption kinetics in comparison to PCL alone. Lam et al.
31
have undertaken
extensive studies on the degradation of FDM fabricated PCL and PCL-TCP
scaffolds. Studies have shown that the addition of TCP particles within the
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