Biomedical Engineering Reference
In-Depth Information
The purified collagen materials obtained from either molecu-
lar technology or fibrillar technology are subjected to additional
processing to fabricate the materials into useful scaffold types for
specific tissue-engineered organs. Collagen can be processed into
several types such as membrane (film and sheet), porous material
(sponge, felt, and fiber), gel, solution, filamentous material, tubu-
lar material (membrane and sponge), and composite matrix for
the application of tissue repair, patches, bone and cartilage repair,
nerve regeneration, and vascular and skin repair with/without
cells.
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Physicochemical properties of collagen can be improved by
a variety of homogeneous and heterogeneous composites. Homo-
geneous composites can be formed between ions, peptides, pro-
teins, and polysaccharides into a collagen matrix by means of
ionic and covalent bonding, entrapment, entanglement, and copre-
cipitation. Heterogeneous composites like collagen/synthetic poly-
mers, collagen/biological polymers, and collagen/ceramic hybrids
(collagen/nano-hydroxyapatite and collagen/calcium phosphate)
have been investigated to achieve distinct properties for tissue-
engineered products.
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1.2.4.3 Alginate
Alginate originating from seaweed is composed of two repeating
monosaccharides, L-guluronic acid and D-mannuronic acid. Repeat-
ingstrandsofthesemonosaccharidescanformlinear,water-soluble
polysaccharides. Gelation occurs by interaction of divalent cations
(e.g., Ca
2
+
,Mg
2
+
) with blocks of guluronic acid from different
polysaccharide chains, as shown in Fig. 1.6. From this good gela-
tion property, the encapsulation of calcium alginate beads impreg-
nated with various pharmaceutics, cytokines, or cultured cells has
been extensively investigated. Varying the preparation condition of
gelation can control the structure and physicochemical properties.
Calcium alginate scaffolds did not degrade by hydrolytic reaction,
whereas they can be degraded by a chelating agent such as ethyl-
eneaminetetraaceticacid (EDTA) or by enzymes. Also, the diffusion
of calcium ions from an alginate gel can cause dissociation between
alginate chains, resulting in a decrease of mechanical strength over
time. One of the disadvantages of the alginate matrix is a potential
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