Biomedical Engineering Reference
In-Depth Information
the tissue engineered construct and a local nanoscale environment for cell
attachment and remolding.
Electrospinning produces an ultrafine meshwork with micron to nanometer
scale fibers by manipulating electrostatic and intermolecular forces. During
electrospinning a high voltage source charges a solvated polymer. This charged
solution accelerates towards a collector of opposite polarity. The repulsive
electrostatic forces between the charged polymer molecules and the attractive
force between the solution and the collector transform the rounded solution±air
interface into a pointed cone. A stream of polymer solution from the cone to the
collector forms once the electrostatic forces of the system overcome the surface
tension of the liquid. The solvent evaporates as the polymer accelerates towards
the collector, leaving a dry polymer mesh on the surface of the collector. The
size of the polymer fibers can be manipulated by altering the applied voltage,
distance between the capillary and the collector, the polymer concentration, and
the solution conductivity. Increasing the distance between the capillary and the
collector, increasing the solution conductivity and decreasing the polymer
concentration in solution can produce smaller fiber diameter meshes (Sill and
von Recum, 2008). Although the harsh fabrication conditions should limit
inclusion of the bioactive molecules in electrospun scaffolds, the use of a
second spinning channel containing aqueous biological agents can be used to
produce a final scaffold seeded with active biological molecules (Zhang et al.,
2007).
10.5.6 Computational techniques
Computer-aided design (CAD) has entered the field of tissue engineering. The
distinct benefit of CAD techniques is that the designer has full control over the
topography of the construct. Consequently, CAD matrix fabrication can
address one of the downfalls of the techniques previously mentioned. In the
case of a more random matrix fabrication, creating a porous construct does not
insure that those pores are interconnected, facilitating diffusion and ingrowth
of nutrients and cells throughout the matrix. However, with the use of
computer design, the location, interconnectivity and size of pores can all be
controlled. This is especially important because two of the primary design
considerations for matrices are mechanical strength and creating a hospitable
environment for cellular growth. Porosity adversely affects mechanical
strength, but aids in cellular ingrowth (Yang et al., 2001). By directly
controlling the architecture of the matrix channels, the benefits of internal
features can be maximized while minimizing the detrimental side effect of
decreased mechanical strength.
One method of converting a computer design into a physical polymer based
matrix for tissue engineering is solid free-form fabrication (SFF). SFF is a
computer-aided scaffold construction method that builds a three-dimensional
