Biomedical Engineering Reference
In-Depth Information
1
Introduction
Tissue engineering is a rapidly growing interdisciplinary field of research
focused on the development of vital autologous tissue, through the use of
a combination of biomaterials, cells, and bioactive molecules, for the purposes
of repairing damaged or diseased tissue and organs. One of its fundamental
concepts is the generation of new functional tissue based on a biodegradable
scaffold in the shape of the organ to be replaced. In vitro tissue engineering
strategies usually involve seeding the scaffold with autologous cells before im-
plantation. As the cells invade the scaffold and produce extracellular matrix
(ECM), thus increasingly lending structure and stability to the tissue, the scaf-
fold is gradually absorbed in vivo. Once absorption is complete, only the newly
created functioning tissue remains [1].
Another strategy is in vivo tissue engineering, which can be accomplished
by implanting an unseeded scaffold into the damaged region to allow the inva-
sion of new blood vessels, innervation, and deposition of ECM, thereby creating
a cell-friendly environment prior to injection of autologous cells into the scaf-
fold [2]. The ultimate in vivo strategy might be guided tissue regeneration,
stimulated by biomolecule-loaded unseeded scaffolds that support and control
the invasion of (stem) cells from the blood stream and surrounding tissues.
Matrix polymers for tissue engineering must possess certain fundamental
properties. A biocompatible material is required that has appropriate me-
chanical properties, has a suitable surface for supporting cell adhesion and
proliferation, that can guide and organize cell growth in the required direc-
tion, that can enable tissue to invade and nutrients to be exchanged, and that
degrades to nontoxic by-products within desirable periods of time [3].
Biodegradable polymers derived from synthetic aliphatic polyesters, such
as poly(glycolide) (PGA), poly(d,l-lactide) (PDLLA), poly(l-lactide) (PLLA),
and their copolymers, are widely used as biomaterials in surgical prac-
tice [4-7]. At present, bioabsorbable sutures are the predominant medical
product made from degradable polyesters. Additionally, suture anchors, or-
thopedic fixation devices, and various other products made from degradable
polyesters are in clinical use. An increasing demand for degradable polyesters
in medical use can be expected in the future, with applications in tissue en-
gineering being especially prominent [8-11].
In recent years, biopolyesters from the group of polyhydroxyalkanoates
(PHAs) have emerged as promising materials for a variety of medical applica-
tions. Potential uses of PHAs can be expected in wound management applica-
tions (sutures, skin substitutes, nerve cuffs, surgical meshes, staples, swabs),
vascular system applications (heart valves, cardiovascular fabrics, pericar-
dial patches, vascular grafts), orthopedics (scaffolds for cartilage engineering,
spinal cages, bone graft substitutes, meniscus regeneration, internal fixation
devices), and drug delivery applications [12-17].
