Biomedical Engineering Reference
In-Depth Information
PEG can be photo-polymerized under mild conditions in the presence of cells to create a
hydrogel that is biocompatible and non-toxic. Bioactive molecules such as cell adhesion
ligands, growth factors and proteolytic degradation sites have been previously incorporated
into PEG hydrogels and shown to influence adhesion, proliferation, migration, and
extracellular matrix production of vascular smooth muscle cells.
-
Poly (glycerol sebacic acid)
Poly glycerol sebacic acid (PGS), also called bio-rubber, is a tough, biodegradable elastomer
made from biocompatible monomers. Its main features are good mechanical properties,
rubber like elasticity and surface erosion biodegradation. PGS was proved to have similar
in
vitro
and
in vivo
biocompatibility to PLGA, a widely used biodegradable polymer.
(Manzanedo, 2005; Sundback et al., 2005).
-
Poly (2-hydroxyethyl methacrylate)
Hydroxyethyl methacrylate (HEMA) is a hydro-soluble monomer, which can be
polymerized (under various circumstances) at low temperatures (from -20°C to +10°C). It
can be used to prepare various hydrogels and to immobilize proteins or cells. It is widely
used in medicine as an appropriate biomaterial
.
Poly (2-hydroxyethyl methacrylate)
(pHEMA) is particularly attractive for biomedical engineering applications. Because of its
physical properties and high biocompatibility, this polymer can be easily manipulated
through formulated chemistry has been extensively used in medical applications, e.g.
contact lenses, kerato prostheses and orbital implants. Furthermore, a pHEMA scaffold
could be easily incorporated into the nerve guidance tubes (Flynn et al., 2003).
2.3
Methods used for scaffolds design
Several techniques have been developed to process synthetic and natural scaffold materials
into porous structures. These conventional scaffold fabrication techniques are considered as
processes that create scaffolds having a continuous, uninterrupted pore structure. An
overview of such different techniques is as follows: Electrospinning, Solvent-casting,
particulate-leaching, Gas foaming, Fiber meshes/fiber bonding, Phase separation, Melt
molding, Emulsion freeze drying, Solution casting and Freeze drying (Mikos& Temenoff,
2003; Sachlos & Czernuszka, 2003).
2.3.1
Electrospinning
Electrospinning is a technique for nano-fibrous scaffold fabrication. Various synthetic or
natural polymers can be spun to nano fibers with diameters in nano - to micrometer range.
They are characterized by a high surface to volume ratio and thus offer sample substrate for
cell attachment.
In this technique, polymers are dissolved into a proper solvent or melted before being
subjected to a very high voltage to overcome the surface tension and viscoelastic forces as
well as forming different fibers (50 nm -
30 µm)
diameters, which feature a morphologic
similarity to the extracellular matrix of natural tissue and effective mechanical properties.
These nanofibrous scaffolds can be utilized to provide a better environment for cell
attachment, migration, proliferation and differentiation when compared with traditional
scaffolds
(Martins et al., 2007).
In general, the process of electrospinning is mainly affected by (i) system parameters, such as
polymer molecular weight, molecular weight distribution and solution properties (e.g.
viscosity, surface tension, conductivity); and (ii) process parameters, such as flow rate, electric
potential, distance between capillary and collector, motion of collector, etc (Yang et al., 2005).
