Biomedical Engineering Reference
In-Depth Information
2.1
INTRODUCTION: WHY USE NANOPARTICLES?
Nanotechnology is the production of functional materials and structures in the nanoscale using vari-
ous physical and chemical methods
[1]
. Today, the revolutionary development of nanotechnology has
become a highly energized discipline of science and technology. The US National Nanotechnology
Initiative defines nanotechnology in terms of three requirements:
1.
Technology development at the atomic, molecular, or macromolecular levels, in the length scale
of 1-100 nm range.
2.
Creating and using structures, devices and systems that have novel properties and functions
because of their small and/or intermediate size.
3.
Ability to control or manipulate on the atomic/molecular scale.
Thus, the term nanotechnology should imply a high degree of control and planning. The intense
interest in using nanomaterials stems from the idea that they may be employed to manipulate the
structure of materials to provide dramatic improvements in chemical, mechanical, and optical prop-
erties. During the last decade, the use of nanoparticles has become very popular in the design and
development of many dental materials, since they can provide a unique combination of properties.
By far, the largest application has been in dental composites, although several unique adhesive sys-
tems containing nanoparticles have also been commercialized. Every property has a critical length
scale, and by using building blocks smaller than the critical length scale—such as nanoparticles—
one can capitalize on the manifestation of physics at small sizes. An example of this is in light
scattering. Since nanoparticles have dimensions well below the wavelength of visible light (400-
800 nm), they cannot scatter that particular light resulting in inability to detect the particles by naked
eye. This has tremendous implications for controlling the optical properties of materials containing
these particles.
Another important parameter to consider while using nanoparticles is that due to their extremely
small size they have a high surface area to volume ratio. Thus, the precise control of the chemical
composition of the surface of nanoparticles becomes a prerequisite to the reliability and reproduc-
ibility of the nanoparticles. This factor is of crucial importance since a key element in nanotech-
nology is the ability to deliberately control and manipulate the assembly of the nanoparticles to
provide the desirable properties of the nanomaterial and the ultimate performance of the materials
into which they are incorporated. The section in this chapter on the design of true nanofill compos-
ites will amplify this point. The other related factor is that the size of individual nanoparticles often
approaches that of the host matrix materials and hence there can be a molecular scale interaction
between these nanoparticles and the materials comprising the matrix. This factor has been utilized in
providing unique characteristics to dental adhesives such as adhesion strength and radiopacity with-
out adversely affecting other properties. Further details will be provided in the section on adhesives.
2.2
SYNTHESIS OF NANOPARTICLES
There are two approaches to nanotechnology and these are termed bottom-up and top-down
approaches. The bottom-up approach involves synthesis of nanostructures from atomic level or
molecular level whereas the top-down approach involves depositing, for example thin films, and
