Biomedical Engineering Reference
In-Depth Information
Along with natural materials, synthetic polymers have been widely used for tissue
engineering. Recently, Patist et al. demonstrated that the implantation of a macro porous
PLA tubular scaffold in the transected rat spinal cord elicited a modest axonal regeneration
response. These particular scaffolds were prepared by a thermally induced polymer-solvent
phase separation process and contained longitudinally oriented macropores connected to
each other by a network of micropores (Patist et al., 2004).
Moore et al. described multiple-channel, biodegradable scaffolds that serve as the basis for a
model to investigate simultaneously the effects of scaffold architecture, transplanted cells,
and locally delivered molecular agents on axon regeneration. PLGA with copolymer ratio
85:15 was used for their experiments. Primary neonatal Schwann cells were distributed in
the channels of the scaffold and remained viable in tissue culture for at least 48 h. Scaffolds
containing SCs implanted into transected adult rat spinal cords contained regenerating
axons at 1 month post-operation. Axon regeneration was demonstrated by three-
dimensional reconstruction of serial histological sections (Moore et al., 2006).
Also it is showed that PGS which have similar
in vitro
and
in vivo
biocompatibility to PLGA,
had no harmful effect on Schwann cell metabolic activity, attachment, or proliferation, and
did not induce apoptosis (Manzanedo, 2005; Sundback et al., 2005).
PHB has been previously used as a wrap-around implant to guide axonal growth after
peripheral nerve injury ( Ljungberg et al., 1999). Novikova et al. prepared a biodegradable
conduit made of PHB fibers which compressed together and running in parallel directions
in two perpendicular layers to form a sheet. Implantation of these PHB conduits coated with
alginate hydrogel and fibronectin and seeded with SCs has been found to reduce spinal cord
cavitation as well as retrograde degeneration of injured spinal tract neurons (Novikov et al.,
2002).
PCL is interesting for the preparation of long term implantable devices, owing to its
degradation, which is even slower than that of polylactide. Schnell et al. designed
biodegradable, aligned poly-e-capro- lactone (PCL) and collagen/PCL (C/PCL) nanofibers
as guidance structures were produced by electrospinning and tested in cell culture assays.
They compared fibers of 100% PCL with fibers consisting of a 25:75% C/PCL blend. Both
types of electrospun fibers supported oriented neurite outgrowth and glial migration from
dorsal root ganglia (DRG) explants. SC migration, neurite orientation, and process
formation of SCs, fibroblasts and olfactory ensheathing cells were improved on C/PCL
fibers, when compared to pure PCL fibers ( Schnell et al., 2007 ).
About PEG, it was showed that focal continuous application of this polymer has minimal
toxicity (Cole and Shi, 2005). Duerstock et al. used three-dimensional computer reconstructions
of PEG treated and spinal cords to determine whether the pathological character of a 1-month-
old injury is ameliorated by application of PEG. In PEG-treated animals, the lesion was more
focal and less diffuse throughout the damaged segment of the spinal cord, so that control
cords showed a significantly extended lesion surface area (Duerstock and Borgens, 2002).
Furthermore, a pHEMA scaffold could be easily incorporated into the nerve guidance tubes.
Flynn et al. developed a method to create longitude in ally oriented channels within
(pHEMA) hydrogels for neural tissue engineering applications. They found that these
scaffolds have the potential to enhance nerve regeneration after section injuries of the spinal
cord by increasing the available surface area and providing guidance to extending axons
and invading cells (Flynn et al., 2003).
Several techniques have been developed to process synthetic and natural scaffold materials
into porous structures as H.
Tabesh et al.
reviewed. Among these techniques, creating tissue
