Biomedical Engineering Reference
In-Depth Information
Macropores can be introduced through the incorporation of a leachable
porogen, and the resulting scaffolds exhibit excellent mechanical proper-
ties compared to other candidate scaffold materials. Nanofi brous scaffolds
exhibit higher bioactivity, and are capable of increasing osteogenic activity
compared to smooth-walled scaffolds.
4.5
Overall Trends in Biomimetic Scaffold Design
Tissue engineering scaffolds have made great strides over the past two
decades. Initially seem as a passive support that at best would not impede
healing, scaffolds are now seen as a key means of controlling cellular
behavior and accelerating the healing process. While the primary use of
scaffolds is still for providing physical support and controlled drug or
growth factor delivery, scaffold morphology and surface texture using
various synthetic nanofi brous materials has been demonstrated to induce
cellular behaviors that previously required growth factors or the use of
biologically-sourced materials. Three major methods for production of
these new types of scaffolds are self-assembly, electrospinning, and ther-
mally induced phase separation.
The incorporation of nanofi brous materials as scaffolding systems for
use in bone tissue engineering applications is still in its infancy, but initial
results are very promising. In general, a nanofi brous surface, made from a
wide variety of materials, allows for increased protein interaction with the
surface, and hence increased cellular interaction and adhesion. Through
unknown means this induces and accelerates osteogenic behavior, even
leading to ectopic bone formation in an acellular porous poly(lactic
acid) scaffold used to repair a mouse calvarial defect. It appears that this
enhanced cellular attachment mimics what a cell senses on a biological
surface, and responds more naturally than when on a traditional synthetic
material. Further studies are needed to better understand this relationship
between surface binding and cellular differentiation, osteogenesis, and
the overall healing process.
Current nanofi brous scaffold fabrication techniques still possess
important limitations in their mechanical and structural properties. Self-
assembling scaffolds remain gel-like rather than a consolidated material,
limiting cellular infi ltration and mechanical properties. Electrospun scaf-
folds are easily customized in terms of nanofi ber size and alignment, but
suffer from very small pore sizes (on the same scale as the nano- or micro-
fi bers themselves), which again limit cellular infi ltration. Electrospinning
tends to form mats or sheets of fi bers as well, rather than a bulk material
more suitable for large bone-grafting applications. Thermally induced
phase separation techniques can provide excellent control over pore size
and connectivity and more suitable mechanical integrity, but limitations
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