Biomedical Engineering Reference
In-Depth Information
engineering scaffolds in nano-scale may bring unpredictable new properties to the material-
such as mechanical (stronger), physical (lighter), more porous (tunable),optical (color
emission), chemical reactivity (more active and less corrosive), electronic properties (more
electrically conductive),and magnetic properties (super paramagnetic which are very
important in nerve regeneration). Such scaffolds may come up with new functionalities as
well-which are unavailable at micro or macro scales (Tabesh et al., 2009).
The process of electrospinning is used for nano-fibrous scaffold fabrication. Electrospinning
can even be used to create biocompatible thin films with useful coating designs and surface
structures that can be deposited on implantable devices inorder to facilitate the integration
of these devices with the body. Silk-like polymers with fibronectin have been electrospun to
make biocompatible films used on prosthetic devices aimed to be implanted in the central
nervous system (Buchko et al., 1999).
Moreover, an elegant way to produce nanofibrous scaffold using PLLA by a liquid-liquid
phase separation method quite similar to natural extracellular matrix (ECM) was developed
by a group of scientists. They showed its efficacy in supporting the neural stem cell (NSC)
differentiation and neurite outgrowth (Yang et al., 2004).
In addition, a new and facile method for the creation of longitudinally oriented channels in
pHEMA gels using a fiber templating technique was described. Biodegradable
polycaprolactone (PCL) fibers were extruded and embedded in transparent pHEMA gels,
leading to the creation of a pHEMA-PCL composite.
4. Conclusion
In this chapter, efficacious biomaterials (natural and synthetic) for scaffolds in tissue
engineering and cell seeding were discussed and also techniques to their fabrication were
reviewed. Considering results using such materials and the mentioned criteria for an
appropriate scaffold, it is proved that the selection of materials and method of fabrication
depend on the cells and their characteristics. The reasons are: scaffold candidates should
mimic the structure and biological activity of the native ECM proteins which provide
adequate mechanical support and regulate cellular activates. In addition, scaffolds must
support and define the three-dimensional structure of the tissue engineered space and
maintain the normal state of differentiation within the cellular compartment.
Furthermore the structure of scaffold, pore size and porosity, may affect the mass transfer,
shear rate and pressure drop. Mass transfer is the major hindrance in tissue engineering.
Although surface area to volume ratios of a scaffold can decrease mass transfer limitations,
it is still one of the greatest challenge in tissue engineering. It has been observed that the
pore size and shape influence the shear stress level and distribution, while the porosity
affects only the distribution. Therefore the wall shear stress is an important parameter in cell
adhesion processes.
Two case studies, blood and nerve systems, with regard to their challenges have been
investigated. First, for blood system, a scaffold must have the function of native blood and
must provide appropriate mechanical, endothelialization and antithrombogenic properties.
Therefore choosing a proper biomaterial which provides these characters is prominent. With
respect to multilayered construction of blood vessels, the combined structure is particularly
attractive for vascular tissue engineering applications. For a better simulation, various types
of materials and cells have been used to form different layers of this tissue.
