Biomedical Engineering Reference
In-Depth Information
(A)
(B)
(C)
FIGURE 4.7
Fluorescent silica nanoparticles. (A) Transmission electron microscopy (TEM) and (B) scanning electron
microscopy (SEM) of 50 nm silica nanoparticles. The particles were incorporated with rhodamine B to allow
cellular tracking. (C) MC3T3 preosteoblasts efficiently take up the particles and the cytoplasm becomes
saturated. Note that the particles are excluded from the nucleus (dark circle).
nanoscale and various synthesis and surface modifications have only begun to be explored in
dentistry. Recent studies have begun testing the effects of altering size and surface properties on
the functional properties of silica-based nanomaterials in composite resins.
Using the sol
gel process, Kim et al.
[54]
synthesized spherical silica nanoparticles having dif-
ferent sizes (from 5 to 450 nm) that were tested for dispersion in, and adhesion to, a resin matrix of
70 wt% bisphenol-
-glycidyl methacrylate (bis-GMA) and 30 wt% triethyleneglycol dimethacrylate
(TEGDMA). This study determined that particles with
α
-MPS-modified surface were more adhe-
sive and had better dispersion than nontreated particles regardless of size. A similar study used
silica nanoparticles with a size range of 20
γ
50 nm and filler mass fractions of 20%, 30%, 40%,
and 50%
[53]
. These composites were compared to a conventional composite containing 10
m
silica particles. The use of nanosized silica resulted in increased mechanical properties with mass
fractions up to 40% producing an increase in fracture toughness, flexural strength, and hardness in
comparison to control. A third study recently tested similar spherical nanosilica fillers with a size
range of 10
40
μ
20 nm for dispersion, surface roughness, and flexural strength
[60]
. Two filler ratios
were tested, 30 and 35 wt%. The surface modification of
-MPS was determined important for use
in the resin matrix and the higher filler ratio decreased surface roughness but decreased flexural
strength relative to the lower filler ratio.
Spherical particle may not be the only shape that can be used to enhance composite resins,
as other silica-based nanomaterials are now being tested. Tian et al.
[56]
used fibrillar silicate
(diameter in tens of nm and length in
γ
μ
m) in small mass fractions (1% and 2.5%) and determined
that uniform impregnation of fibrillar silicate into dental resins significantly improved mechanical
properties such as flexural strength, elastic modulus, and work to fracture. MSNs have also recently
been explored for enhanced properties in dental composites. The particles were synthesized using
the nonsurfactant templating method in the 500 nm range and the composites prepared using
combinations of MSNs and nonporous fillers
[61]
. The authors concluded that including porous
fillers increased mechanical properties potentially due to the interconnecting pores. These studies
