Page 178 - Biodegradable Polyesters

156 7 Electrospun Scaffolds of Biodegradable Polyesters: Manufacturing and Biomedical Application

engineering [6]. However, these materials have significant drawbacks, such as the
fact that they are not biodegradable, they are not easy to process, and they do
not provide a biomimetic matrix for cell growth and tissue formation. In contrast
to metal and ceramics, polymers are unique because they have great processing
flexibility and their biodegradability can be imparted through molecular design
or modification of their chemical and physical surface properties. Therefore,
polymers are a dominant scaffolding material for use in tissue engineering [7].
A variety of techniques are employed for the production of scaffolds. The
processing technique should be chosen according to the needs of the tissue to
be repaired and the characteristics of the scaffolds produced by each technique.
Electrospinning is one the most common methods for producing biomedical
scaffolds. Electrospinning is an adaptable and rapid method that can produce
polymeric scaffolds formed by continuous fibers with diameters ranging from
a few nanometers to micrometers with high surface-to-volume ratio and high
porosity. The electrospun fiber scaffolds are able to reproduce in dimension
and structure the collagen fibers of the native ECM, providing a biomimetic
microenvironment for cell development. In addition, these scaffolds exhibit
interconnected pores in their structure, which facilitates cellular migration,
transport of nutrients and metabolic waste, and permits in vitro creation of
tissue [8, 9]. The electrospun scaffolds can be produced from natural or synthetic
polymers. Polymers prepared from natural sources have the potential advantage
of biological recognition and cell adhesion, but problems associated with complex
structural composition, purification, and immunogenicity have stimulated the
development of new or modified synthetic polymers for use as scaffolding materi-
als. Synthetic polymers are more easily processed by electrospinning than natural
polymers and have been extensively used to produce fiber scaffolds. Among these
synthetic polymers, the polyesters make up an extensively investigated class of
polymers for use in medical products such as sutures, bone screws and, currently,
in the production of biomedical scaffolds [10].
The polyester class of polymers show immense diversity, synthetic versatility,
a controllable degradation profile, good biocompatibility, and make the control
of electrospun fiber morphology possible [11, 12]. The biodegradable polyesters
used for the production of electrospun scaffolds are mainly derived from glycol-
ide (GA), lactide (LA), ε-caprolactone (ε-CL), 1,5-dioxepan-2-one (DXO), and
trimethyl carbonate (TMC) [10, 13]. The different structures of the polyesters
provide them with a number of properties, offering a great number of options
to choose the polymer according to the needs of the tissue that requires regen-
eration. Because of these characteristics, the polyesters demonstrate potential
suitability for use as scaffolds in tissue engineering applications; however, the
bioactivity of these polymers is limited. Generally, polyesters are hydrophobic
and do not have active natural cell binding sites or functional groups along their
backbones [14, 15].
The scaffolds should be able to promote cell adhesion, spreading, and prolif-
eration. The success or failure in a particular application depends quite often on
special surface properties of the material with regard to chemical composition,