Biomedical Engineering Reference
In-Depth Information
and solvent [105, 121]. The characteristic features of these hydrogels have
been creatively utilized for various biomedical and pharmaceutical applica-
tions [123, 124]. For example, hydrogels have been tailored to produce smart
sensors that can detect small levels of blood-glucose [125], and as in situ
insulin pumps to control glucose levels [126]. In addition, smart polymeric
gels have also been considered as model biomimetic materials since they
demonstrate several attributes of biomolecules such as sensitivity, selectivity,
mobility, shape memory, self-organization, and healing [115, 127-130].
Recent years have witnessed a surge of interest in using bio-mimicking
hydrogels as tissue engineering scaffolds. This increased interest in hydro-
gels for tissue engineering applications is attributed to their water content,
viscoelasticity akin to the native tissues, biocompatibility, and their ability
to permit diffusion of nutrients and bioactive molecules. In addition to the
structural stability, the mechanical and biological properties of hydrogels can
also be easily molecularly tailored to incorporate suitable biological signals
that can stimulate cell proliferation and differentiation. The porosity of hy-
drogel can be easily tailored via controlling the crosslink density, monomer
concentration, and molecular weight of the precursor. Hydrogels are consid-
ered as good candidates for in vivo applications because of their hydrophilic
nature which resists protein and cell adhesion to the implant surface. More-
over, the soft viscoelastic nature of hydrogels minimizes irritation to the
surrounding tissues as well as prevents stress shielding [95, 131, 132]. An-
chorage independent cells like chondrocytes exhibit good cell viability within
hydrophilic scaffolds like hydrogels [133]. Moreover, many investigators have
shown that the hydrophilicity of the scaffold facilitates the re-differentiation
of de-differentiated human nasal chondrocytes [134].
Another attractive feature of hydrogels is that they can be delivered in
a minimally invasive manner as mentioned earlier. This is a very import-
ant aspect in tissue engineering approaches (for clinical applications) which
has received a lot of attention recently, since hydrogel-cell systems can be in-
jected into the body in a noninvasive manner for arthroscopic surgery. In our
laboratory, we use this approach extensively for musculoskeletal tissue engin-
eering applications. A detailed discussion on the minimal invasive application
of polymers in the biomedical field is provided later in Sect. 6. Hydrogels
can be broadly divided into two categories—natural and synthetic hydrogels,
based on their source.
4.1
Natural Hydrogels
Natural hydrogels are water-liking networks that are made out of naturally de-
rived polymers, and are widely used in tissue engineering. For example, extra
cellular matrix components (ECM) such as hyaluronic acid (HA), chondroitin
sulfate (CS), matrigel, and collagen-based hydrogels are used as scaffolds for
