Biomedical Engineering Reference
In-Depth Information
These involved the incorporation of nanostructures with polymer through one of
four ways.
127
Solvent casting involves dissolution of polymers inadequate solvent
with nanoscale particles and evaporation of solvent or precipitation. In the melt-
mixing process, the melted polymer is directly mixed with the nanoparticle. In
situ polymerization is performed in the presence of the nanoparticles that are first
dispersed in the liquid monomer or monomer solution. In template synthesis, the
nanoparticles are synthesized from precursor solution using polymers as template.
In solvent casting, a solvent in which the polymer is soluble is used for flex-
ible low-cost and short-term fabrication process of the polymeric nanocompos-
ite film.
127
This is widely used for the fabrication process where the different
solvents used represent a key point in the film production that needs to be eluci-
dated. In this methodology, the choice of solvent influences the film properties,
heterogeneity of the surface structure, reorientation or mobility of the surface
crystal segment, swelling, and deformation.
284-286
The polymer solubility cor-
related with the surface structure of the nanocomposite film; however, more
studies needs to focus on the specific properties of solvent (i.e. electron-pair
donation, solvochromic parameter, hydrogen bond formation, and dielectric
constant) that can support an effective dispersion of nanostructures in the sol-
vent and in the resulting polymer matrix.
Composites made from HA particles and biodegradable polymers in various
forms have been used clinically due to the good osteoconductivity and osteoin-
ductivity of HA with the biodegradability of polymer matrix in the composites.
In PLA/HA blending system, only physical adsorption is achieved between HA
particles and the PLA matrix leading to poor mechanical properties that result in
limited load-bearing applications. Thus, it appears that the interface adhesion of
HA particles and polymer matrix plays a major factor affecting the properties of
the PLA/HA composites. To increase the PLA/HA interfacial strength, various
methods have been applied.
233,234,235,287
Improvements in the bonding between
HA particles and poly(L-lactide) (PLLA) that increases the mechanical proper-
ties of the PLLA/HA composite were accomplished by using surface-grafted
hydroxyapatite (g-HA) nanoparticles with the polymer that further blended with
the PLLA.
288
This process produced uniform nanocomposites with improved
tensile strength, bending strength, bending modulus, and impact energy at 4%
particle by weight (compared with PLLA/HA composites). Improved cell com-
patibility of the PLLA/g-HA composites that is attributed to the good biocom-
patibility of the HA nanoparticles and a more uniform distribution of the g-HA
nanoparticles on the film surface were demonstrated.
233-235,287,288
Carbon nanostructures and biodegradable polymer-based nanocomposite
films showed enhanced mechanical, thermal, and electrical properties. These
were shown in nanocomposite based on PLLA and SWCNTs and carboxylated
SWCNTs at 1% weight.
127,289
Different PLLA crystallites were formed and an
interface polymer was organized around the nanotube sidewalls with good inter-
facial adhesion and a good homogeneous dispersion that can be leveraged to
achieve the full potential of SWCNT reinforcing material.
271,290-292
