Biomedical Engineering Reference
In-Depth Information
directional contact guidance have made nonwoven mats of electrospun nanofibers
a new class of promising dural substitutes.
The regeneration rate of the injury site is a key factor in evaluating the efficacy
of a dural substitute. Several prior studies have shown that cells cultured on
scaffolds of uniaxially aligned nanofibers tend to migrate along the nanofibers
[99]. Based on this observation, we developed nanofibers with radial alignment
to specifically target dura mater repair and other applications involving wound
closure. In a typical dural defect, the injured site is still surrounded by healthy,
intact tissue. By accelerating the migration of dura fibroblasts from the periphery,
it is possible to achieve fast closure for the dural defect. We have demonstrated
that dural fibroblasts were able to cover the entire surface of a scaffold made of
radially aligned fibers within four days, while a void still existed on a control based
on random nanofibers, indicating a faster migration rate for the cells on radially
aligned nanofibers (Figure 9.6a,b) [68]. An enlarged view of the center regions
are shown Figure 9.6c,d, where a void of cells can be clearly seen on the random
scaffold.
Synthetic materials possess a range of advantages over collagen matrices: they
are cost effective, mechanically strong, and less prone to diseases transfer. The
ability to generate radially aligned topography distinguishes electrospinning from
other techniques in the fabrication of dural substitutes. A current limitation of
electrospun dural substitutes is that they are not suitable for small dural defects
where on-lay transplantation (without suturing) is needed. Further research should
include efforts to alter the surface chemistry of the electrospun nanofibers so that
they can be used for both on-lay and in-lay purposes.
9.5.3
Tendon/Ligament Repair
Tendon (connecting muscle and bone) and ligament (connecting bone to bone)
tissues are compositionally, structurally, and mechanically similar. Both tissues
are loaded primarily in one direction and their ECM (mostly type I collagen) has
a uniaxially aligned structure, leading to highly anisotropic mechanical properties
[100]. Tendon/ligament has a low propensity for regeneration due to its high
ECM density, collagen organization, and low vascularity [101]. The scar-mediated
healing response of tendon/ligament and its inability to regenerate has led to the
investigation of tissue engineering approaches to replace the damaged or diseased
tissue.
Braided and knitted fabrics have been used as scaffolds for tendon/ligament
repair. The major drawbacks of these constructs are the poor performance in mass
transport, cell attachment, and cell infiltration [102]. Scaffolds based on electrospun
nanofibers have started to gain popularity in the field of tendon/ligament repair not
only because of the high porosity and high cell infiltration rate, but also due to the
ease of generating uniaxial alignment to mimic the anisotropic structure of native
tissues. Fibroblasts and bone mesenchymal stem cells (BMSCs) are often cultured
on aligned nanofibers to generate a cell-seeded scaffold. Ouyang and co-workers
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