engineered grafts, etc. [107]. The hydrolytically (synthetic in most cases) degradable polymers are usually preferred as implants compared to enzymatically
(natural) degradable polymers due to their minimal site-to-site and patient-topatient variations [108]. Polymers of glycolic acid and lactic acid have been
using in the medical industry since the 1960s, beginning with biodegradable sutures
[109]. Other materials, such as poly(dioxanone), poly(trimethylene carbonate)
copolymers, and E-caprolactone homo- and copolymers have also been used as
medical devices [82, 110, 111]. Functional groups that are easy to hydrolyze, such
as ester, phosphazene, anhydride, carbonate, amide, and urethane [112], are
logically the most important for the synthetic biodegradable polymers [polyesters,
polyphosphazenes, polyanhydrites, polyurethanes, and poly(amino acids)] currently used in biomedical science.
Synthetic biomaterials are generally biologically inert and have more predictable properties than natural polymers. Thus, for biological applications these
materials requires a certain level of biological activity. However, strategies have
only been developed to incorporate biological motifs (e.g., HAp for bone tissue
regeneration) onto synthetic polymers to generate hybrid materials. However, only
a few novel procedures are currently being introduced [113].
6.2.2 Natural Degradable Polymers
Polysaccharides
Polysaccharides contain monosaccharide units joined together by glycosidic
linkages. Polysaccharides display unique biological functions ranging from cell
signaling to immune recognition. Combined with new synthetic routes currently
available for synthesis or modification of polysaccharides, their biodegradability
and ability to form specific interactions make them one of the most important and
extensively investigated groups of natural biomaterials.
Chitin and Chitosan
Chitosan (CTS) is a natural copolymer derived from chitin, which is a homopolymer comprising 2-acetamido-2-deoxy-β-D-glucopyranose units. The deacetylated
form, namely 2-amino-2-deoxy-β-D-glucopyranose, is the major composition of
CTS chains. With a minimum 50% deacetylation of chitin, it becomes soluble in
dilute acids and is referred to as CTS. The main sources exploited are two marine
crustaceans, shrimp and crab [114–119]. The structures of chitin and CTS are
shown in Fig. 8. Recently CTS has attracted much attention due to its wide range
of applications in medicine, drug delivery, waste-water treatment, biomembranes,
and hydrogel development [114, 120–122]. CTS is also a potential candidate for
pharmaceutical and cosmetic applications due to its biodegradability, biocompatibility, high charge density, nontoxicity, and absorption [123]. Furthermore, the
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(natural) degradable polymers due to their minimal site-to-site and patient-topatient variations [108]. Polymers of glycolic acid and lactic acid have been
using in the medical industry since the 1960s, beginning with biodegradable sutures
[109]. Other materials, such as poly(dioxanone), poly(trimethylene carbonate)
copolymers, and E-caprolactone homo- and copolymers have also been used as
medical devices [82, 110, 111]. Functional groups that are easy to hydrolyze, such
as ester, phosphazene, anhydride, carbonate, amide, and urethane [112], are
logically the most important for the synthetic biodegradable polymers [polyesters,
polyphosphazenes, polyanhydrites, polyurethanes, and poly(amino acids)] currently used in biomedical science.
Synthetic biomaterials are generally biologically inert and have more predictable properties than natural polymers. Thus, for biological applications these
materials requires a certain level of biological activity. However, strategies have
only been developed to incorporate biological motifs (e.g., HAp for bone tissue
regeneration) onto synthetic polymers to generate hybrid materials. However, only
a few novel procedures are currently being introduced [113].
6.2.2 Natural Degradable Polymers
Polysaccharides
Polysaccharides contain monosaccharide units joined together by glycosidic
linkages. Polysaccharides display unique biological functions ranging from cell
signaling to immune recognition. Combined with new synthetic routes currently
available for synthesis or modification of polysaccharides, their biodegradability
and ability to form specific interactions make them one of the most important and
extensively investigated groups of natural biomaterials.
Chitin and Chitosan
Chitosan (CTS) is a natural copolymer derived from chitin, which is a homopolymer comprising 2-acetamido-2-deoxy-β-D-glucopyranose units. The deacetylated
form, namely 2-amino-2-deoxy-β-D-glucopyranose, is the major composition of
CTS chains. With a minimum 50% deacetylation of chitin, it becomes soluble in
dilute acids and is referred to as CTS. The main sources exploited are two marine
crustaceans, shrimp and crab [114–119]. The structures of chitin and CTS are
shown in Fig. 8. Recently CTS has attracted much attention due to its wide range
of applications in medicine, drug delivery, waste-water treatment, biomembranes,
and hydrogel development [114, 120–122]. CTS is also a potential candidate for
pharmaceutical and cosmetic applications due to its biodegradability, biocompatibility, high charge density, nontoxicity, and absorption [123]. Furthermore, the
156
A. Bhowmick et al.