Biomedical Engineering Reference
In-Depth Information
in size [27]. In tissue engineering, biomaterials replace the native ECM found in the body to
allow cells to create a highly ordered assembly of tissue formation. Hence, ideally, the
artificial matrix should support cell growth and maintenance by providing the appropriate
mechanical, chemical, and biological characteristics of the native ECM [28]. On this basis
three-dimensional nanomaterials appear to be the most suitable scaffold to influence stem-
cell behavior for tissue engineering.
Nanomaterials for Organ Regeneration
An appropriate three-dimensional scaffold should facilitate normal cellular organization
and behavior, define and maintain the desired tissue volume, and at the same time promote
host integration and implant vascularization [29]. Ultimately, the scaffold should undergo
nontoxic degradation as it is replaced by the healthy host tissue. Hence, a biodegradable
scaffold is ideally used in tissue engineering. Geometric variables of the scaffold such as
porosity, pore size, and pore morphology are also important. A porous scaffold provides a
large surface area for neovascularization, nutrient and waste exchange, cell migration, and
matrix deposition [29]. Understanding of the cell-biomaterial interface is important in the
choice of scaffold due to a direct impact on cell adhesion, an important step in the survival
of anchorage-dependent cells [29]. Both cell proliferation and differentiation can be
controlled by functionalization of the biomaterial surface. Multiple studies have shown that
the interactions between cells and biomaterials occur at the nanoscale [30-32]. With the
advent of nanotechnology, nanoparticles are being merged to synthetic scaffolds to develop
nanostructured biomaterials and enhance interaction of proteins that control cell adhesion
and, thus, tissue formation. Nanocomposites can be defined as multiphase solid materials
where one of the phases has a dimension of less than 100 nm [33]. Nanomaterials have been
developed as promising cell-carrier scaffolds due to their ability to mimic the nanoscale
properties of the ECM [28]. Nanofibrous composite scaffolds are found to decrease
immunogenicity, improve the capacity for cell interaction [34], and to harbor increased
concentrations of fibronectin and vitronectin; the adsorption proteins that reduce apoptosis
of transplanted cells [35]. For example collagen is a self-assembled triple helical bundle of
nanofibers of 300 nm in length and 1.5 nm in diameter. Scaffolds manufactured from nano-
fibers, nanotubes, and nanoparticles have all shown to be useful in tissue engineering of
organs.
Nanofibers are the most highly documented nanoscaffolds, including polylactic acid
(PLA) and polycaprolactone (PCL). They have emerged as an important nanomaterial due
to their high surface area and highly interconnected pores [26]. These properties would allow
efficient cell nutrient and metabolic waste between the scaffold and environment [26]. In this
chapter, we will now explore the use of nanomaterials as scaffolds for tissue-engineering
strategies, which have reached clinical application or are undergoing current clinical trials.
Clinical Application of Nanopolymers
Nanoparticles
The use of nanomaterials in medicine provides unique freedom to modify essential properties
such as solubility, diffusivity, drug half-life and release properties, and immunogenicity [36].
In the past few decades, a number of nanoparticle-based diagnostic and therapeutic
agents have been developed for the treatment of cancer, asthma, endocrine and neurological
conditions, pain, infections, and for tissue-engineering applications [36, 37].
