Biomedical Engineering Reference
In-Depth Information
A series of functionally graded HA coatings incorporated with
various percentages of silver were deposited on titanium substrates
usingionbeam-assisteddeposition.Theanalysisofthecoating'scross-
section revealed a decreased crystallinity as well as a distribution of
nano-sized (10-50 nm) silver particles from the coating/substrate
interface to top surface [1110]. A functionally graded HA/PMMA
biocomposite was developed based on sedimentary HA distributions
in a PMMA viscous fluid, using a centrifuge to avoid stress convergence
on the interface. The stress-strain curves of this biocomposite
showed a sufficient strength for biomedical applications along with
the relaxation of brittleness and fragility [543]. A compositionally
graded collagen/nanodimensional HA biocomposite scaffold might
be prepared by an
diffusion method [1111]. Chemical and
microstructural analysis revealed a gradient of the Ca to P ratio
across the width of the scaffold template, resulting in the formation
of a Ca-rich side and a Ca-depleted side of scaffold. The Ca-rich side
featured low porosity and agglomerates of the nanodimensional HA
crystallites, while the Ca-depleted side featured higher porosity and
nanodimensional HA crystallites integrated with collagen fibrils to
form a porous network structure [1111]. A three-layered graded
biocomposite membrane, with one face of 8% nanodimensional
carbonateapatite/collagen/PLGA porous membrane, the opposite
face of pure PLGA non-porous membrane and the middle layer
of 4% nanodimensional carbonateapatite/collagen/PLGA as the
transition was prepared through the layer-by-layer casting method
[611]. Functionally graded non-woven meshes of PCL incorporated
by nano-sized particles of β-TCP were prepared using a hybrid twin-
screw extrusion/electrospinning process [1112]. A functionally
graded HA/silk fibroin biocomposite was prepared by pulse electric
current sintering [1113]. HA/glass FGM layers were coated on
titanium alloy (Ti - 6Al - 4V) substrates. The design of these layers
and the use of the glass were for achieving a strong bonding between
the FGM layered coatings and the substrates [1114, 1115].
Functionally graded β-TCP/FA biocomposites combine the
biostability of FA with the bioresorbable properties of β-TCP [1116].
An interesting multilayered (each layer of 1 mm thick) structure
consisting of β-TCP/FA biocomposites with different molar ratios
has been prepared, giving rise to formation of a FGM (Fig. 4.11).
in situ
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