Polycaprolactone-based Scaffolds Fabricated Using Fused Deposition Modelling or Melt Extrusion Techniques for Bone Tissue Engineering - Biointerfaces: Where Material Meets Biology - page 238

concluded that delivering of tissue-relevant heparan sulfate instead of hep-
arin might prove to be more stimulatory for osteogenesis as heparan sulfates
are known to control stem/progenitor cells by virtue of their effects on de-
velopmental signalling cascades. 52

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9.5.3 Collagen-mimetic Peptide: The Peptide Sequence
GFOGER
The effect of biological substances on cell attachment is generally a result of
specific polypeptide integrins interacting with cells. Rather than using an
undefined ECM mixture it may be advantageous for ecacy and regulatory
reasons or cost to consider pure forms of the integrins of interest. Fibro-
nectin is a common protein used as an attachment factor, of which some-
times simply the RGD sequence motif is used. In the same way, the
attachment integrins for collagen are DGEA and GFOGER. Wojtowicz et al. 53
coated PCL scaffolds with a triple helical peptide containing the hexapeptide
sequence GFOGER (PCL-GFOGER) and subsequently used the scaffold in a
critical-sized rat femoral defect model. The GFOGER was passively adsorbed
onto the PCL scaffolds and the effectiveness of PCL-GFOGER scaffolds in
promoting bone repair was examined and compared to uncoated PCL scaf-
folds and empty defects. Histological, m-CT, and X-ray analysis on implants
retrieved at 4, 8 and 12 weeks revealed that PCL-GFOGER scaffolds promoted
significantly faster and greater bone formation, mineralisation and defect
bridging compared to PCL scaffolds without the peptide addition. 53 Fur-
thermore, the extent of new bone formation was found to be dependent on
the PCL-GFOGER scaffold surface area available for host tissue interaction,
wherein scaffolds with greater surface area to volume ratio showed higher
bone volume compared to scaffolds with lower surface area to volume
ratio. 53

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9.5.4 Plasma Modification and Fibronectin Coating
Plasma modification allows the creation of micro-scale roughness and/or
formation of controllable chemical functional groups on the material
surfaces homogeneously, without changing the bulk properties of the
biosubstrate; thereby enhancing cell-material interaction. 54 Fibronectin is
an adhesive glycoprotein present in ECM that has been widely incorporated
as a bioactive ligand onto scaffold surfaces to improve the binding strength
of cells. A study carried out by Yildirim et al. 55 investigated subjecting PCL
scaffolds to oxygen-plasma modification, fibronectin coating or a com-
bination of both. Atomic force microscopy analysis revealed that plasma
modification significantly increased the scaffold surface roughness com-
pared to unmodified and fibronectin coated PCL scaffolds. Scaffolds in this
study were also seeded with 7F2 mouse osteoblasts cells and cultured for 21
days. Among all groups (unmodified, plasma modified, fibronectin coated