Advances in Collagen-based Tissue Engineering - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 208

for instant use. Moreover, coaxial electrospinning can be carried out using a solution
of mixed collagen-based polymers (Thomas et al., 2007; Zhou et al., 2010).
Ultrasonic Fiber splitting
The alternative method of preparing parallel--oriented nano-diameter fibrils is using
ultrasonic splitting of collagen micro-diameter fibers (Zhao and Feng, 2007). This
technique has not been proposed before for use in tissue engineering, but if successful,
it has advantages over electrospinning. Purified collagen fibers, dispersed in an aque-
ous medium are treated with powerful ultrasonic, which split the fibers into constitu-
ent, nano-diameter fibrils. The fibrils are parallel oriented by extruding the aqueous
dispersion of the fibrils through a long, narrow tube onto a drying drum. An important
advantage of this technique over electrospinning is that it avoids the process of dissolv-
ing collagen in an organic solvent. The mechanical and surface properties of the fibrils
should be better and there will be no need for laborious removal of the last traces of
an organic cytotoxic solvent. Although the technique is simple in principle, it requires
considerable effort to develop. The technique can be used for producing scaffolds with
modified rate of biodegradation and/or mechanical properties. This would be done by
preparing nanofibrils from two or more biopolymers, extruding a dispersion of mixed
nanofibrils, forming mixed fibril mats and cross-linking by chemoradiation reactions.
hyBrid sCaFFolds resemBliNG struCture aNd ProPerties oF
Natural tissues
In order to perform its function well, after implantation a scaffold must have the best
achievable biocompatibility, it should also have a microstructure resembling that of
natural tissue (for cell seeding, ingrowth and proliferation), adequate mechanical
strength and biodegradability matching the time-scale of tissue regeneration.
Restitution of skin loss is the oldest and still not totally resolved problems in
the field of surgery. In severely burned patients, the prompt closure of full thickness
wounds is critical for survival. Many different materials including collagen sponges
and cellulose have been used to stimulate granulation tissue in wound base after deep
burns and traumatic injures. Since spontaneous healing of the dermal defects does not
occur, the scar formation for full thickness skin loss is inevitable, unless some skin
substitutes are used. Recently, promising results have been obtained utilizing electros-
pun collagen scaffolds as skin substitutes in athymic mice (Powell et al., 2008). Elec-
trospun collagen scaffolds have been shown to produce skin substitutes with similar
cellular organization, proliferation and maturation to the current, clinically utilized
model, and were shown to reduce wound contraction, which may lead to reduced
morbidity in patient outcomes. The 3D biodegradable porous scaffolds that combined
the advantages of natural Type I collagen and synthetic PLGA knitted mesh have been
also developed for cartilage engineering tissue (Dai et al., 2010).
Collagen hydrogels as substitutes of dura mater
Other problem exists in the case of dura mater. Injury of dura mater may result from
many causes, including cranio-cerebral trauma, destruction by tumor, surgical remov-
al, and various congenital malformations. For almost 100 years various artificial