Biomedical Engineering Reference
In-Depth Information
These nanoscale agents may provide more effective and convenient routes of administration,
lower toxicity, allow targeted delivery and controlled release, and lead to reduced healthcare
costs [37]. Nanoparticle imaging contrast agents have also been shown to have improved
sensitivity and specificity [37].
Nanoparticle-based therapeutic agents have already been introduced in the world of
medicine, and numerous products are currently under clinical investigation. Among these
products, liposomal drugs and polymer-drug conjugates are two dominant classes,
accounting for more than 80% of the total amount (see Table 21.1).
Nanofibers
Nanofibers can be assembled to form porous scaffolds that aid in the process of tissue
engineering. These can be synthesized artificially or naturally. They can be prepared by
electrospinning, phase separation, or self-assembly [38]. Electrospinning is a simple and cost-
effective method for producing nanofibers that involves applying a high voltage to extruded
polymer solution [38]. Drugs and growth factors can also be encapsulated in the form of
nanoparticles, as an embedded layer, or incorporated within the polymer solution itself [39-42].
The phase-separation technique is based on thermodynamic demixing of a homogeneous
polymer-solvent solution into a polymer-rich and a polymer-poor phase, usually by either
exposure of the solution to another immiscible solvent or cooling the solution to a point
below the bimodal solubility curve [43]. One limitation of nanofibrous materials generated
using the phase-separation technique is the lack of interconnected pores, which are critical
for cell seeding, vascularization, and tissue organization [43]. Phase-separation techniques
are often used in combination with other scaffold fabrication techniques, such as porogen
leaching, to overcome this problem. The combined technique provides better control over
the porous architecture of the nanofibers [44].
Nanofibers stimulate cell colonization, successfully mimic the natural ECM because of
their large surface area, and aid in efficient exchange of nutrients and metabolic waste
between the scaffold and its environment [45]. In a recent study, a spatial distribution of the
different cells with a three-dimensional scaffold culture system resulted in better structural
organization as compared with two-dimensional culture systems [45]. In addition, nanofi-
bers can be tailored to have controlled drug release properties.
N
aNobaNdage
Wound injury, due to burns and trauma is a serious health condition which
if left untreated can lead to major infection and eventually death of the patient [46]. With
around 10 million people suffering from major burn and chronic wounds worldwide,
researchers have investigated various natural and synthetic materials such as collagen, gel-
atin, chitin, poly(lactic acid), poly(urethane) and poly (ethyleneimine), to develop gauze and
bandages for a fast and effective treatment of such injuries [46, 47]. In most cases of major
injuries the primary focus is to stop heavy bleeding of the site and the current commercially
available options of bandages such as fibrin dressings and glue, either have short shelf-life or
bring about adverse immune response at the site of the injury. Furthermore, they are not
suitable for applications on many parts of the body such as the neck.
In an effort to develop a product to rapidly seal and promote healing of major wounds
and injuries, specifically those caused on battlefields, researchers at Massachusetts Institute
of Technology (MIT), USA, designed thrombin-coated nanobandages [48, 49]. These were
prepared using thrombin, a natural clotting agent, in solution together with tannic acid
sprayed on gauge sponges using a nanosprayer. The use of nanospray allowed for very high
effective area of absorption of the sponge as well as the area of action of thrombin [48].
Conventionally, gelatin sponges are used in hospitals to halt bleeding. However, such
