Biomedical Engineering Reference
In-Depth Information
the inner layer and a nonwovenmat of randomfibers in the outer layer (Figure 9.4f)
[82]. Since a mat made of random fibers has a larger porosity comparing to the
aligned counterpart, the multilayered conduits would support better nutrient
transport and cell outgrowth without compromising contact guidance. Recently,
a biomimetic scaffold was fabricated by rolling electrospun nanofiber matrices in
a concentric manner with an open central cavity to replicate bone marrow cavity
as well as the lamellar structure of bone [85]. In this case, a rectangular strip of
electrospun nanofibers was rolled around a 1-mm thick Teflon rod to produce the
concentric structure. The compressive modulus of the scaffold was found to be in
the mid-range of human trabecular bone. The porous structure also encouraged
osteoblast infiltration and ECM secretion by mimicking the native structure of the
bone.
9.5
Applications in Regenerative Medicine
9.5.1
Nerve Injury Repair
The recovery of injuries to both peripheral and central nervous systems (CNS)
can greatly benefit from the neural tissue engineering strategy that uses a scaffold
or conduit to facilitate the re-growth of nerves [86]. The most severe injury to a
peripheral nervous system (PNS) is the complete transection of the nerve fiber.
After the injury, protease activity increases at the site of injury, giving rise to a
series of degradation events at the distal ends of the injured nerve fiber [87]. In the
CNS, the initial neurological damage provokes a series of cellular and biochemical
responses, resulting in a secondary injury. The secondary injury prohibits nerve
regeneration and causes more cell death, creating a cavity at the injury site and glial
scar around the lesion [88]. Since the environment at the injured site discourages
the elongation and re-innervation of axonal re-growth, CNS nerve repairs are more
challenging than PNS nerve repairs.
The extension of a regenerating axon requires positive cues to be built within the
scaffold. The growth cone at the tip of the axon cylindrically extends into the ECM
searching for cues and retracts when inhibitory molecules are encountered or if
no positive cues are found. It then transduces the guidance cues into intracellular
signals for neurite extension and orientation. Conventional hydrogel scaffolds are
isotropic, and hence they cannot provide any directional cues [89]. Microchannels,
microridges, microgrooves, and stripes can provide topographical cues to direct
neurite extension, but the dimension of these microstructures are on the same
scale as the diameter of axons or cells and thus they are unable to guide sub-cellular
events [82]. Electrospun nanofibers, on the other hand, are more physiologically
relevant to the fibrous structures of native ECM of neural tissues and can thus
interact intimately with the growth cones to provide contact guidance for directed
neurite extension.
Search WWH ::
Custom Search