Biomedical Engineering Reference
In-Depth Information
images of NACP: (A) Example of small NACP, (B) example of NACP clusters. In (A), arrows
indicate individual ACP particles that overlapped a larger ACP particle. In (B), arrows indicate
individual ACP particles and a cluster. The cluster appeared to contain numerous small particles,
which likely had stuck to form the cluster in the spray-drying chamber before they were completely
dried. Measurement of 100 random particles yielded an average size of 37 nm for individual
NACP, and an average size of 225 nm for NACP clusters
[50]
.
Two types of co-fillers were used for reinforcement: barium boroaluminosilicate glass particles
of a mean diameter of 1.4
m (Caulk/Dentsply, Milford, DE) and nanosized silica glass (Aerosil-
OX50, Degussa, Ridgefield, NJ) with a mean diameter of 40 nm. Each glass was silanized with 4%
3-methacryloxypropyltrimethoxysilane and 2% n-propylamine (all by mass, unless otherwise
noted). A resin of bisphenol glycerolate dimethacrylate (BisGMA) and triethylene glycol dimetha-
crylate (TEGDMA) at 1:1 mass ratio was rendered light-curable with 0.2% camphorquinone and
0.8% ethyl 4-N,N-dimethylaminobenzoate (referred to as BisGMA
µ
TEGDMA resin). The NACP
mass fraction in the resin was 30%, and the glass mass fraction was 35%, following a previous
study
[33]
. The resin filled with 30% NACP without any glass fillers is referred to as “resin with
30% NACP without glass.” The composite filled with 30% NACP
1
35% nanosilica is referred to
as “NACP
1
nano silica composite.” The composite filled with 30% NACP
1
35% barium boroalu-
minosilicate glass is referred to as “NACP composite.”
The synthesis of bis(2-methacryloyloxyethyl) dimethylammonium bromide, termed ionic
dimethacrylate-1 (IDMA-1), was described recently
[20]
. IDMA-1 was selected as the quaternary
ammonium dimethacrylate (QADM) to incorporate into the nanocomposites in the present study.
Its synthesis was carried out using a modified Menschutkin reaction, where a tertiary amine group
was reacted with an organo-halide. A benefit of this reaction is that the reaction products are gener-
ated at virtually quantitative amounts and require minimal purification
[20,21]
. Briefly, 10 mmol of
2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA; Sigma-Aldrich, St. Louis, MO) and
10 mmol of 2-bromoethyl methacrylate (BEMA; Monomer-Polymer and Dajec Labs, Trevose, PA)
were combined with 3 g of ethanol in a 20 mL scintillation vial. A magnetic stir bar was added,
and the vial was stirred at 60
C for 24 h. The solvent was removed via evaporation, forming a
clear, colorless, and viscous liquid. The QADM thus obtained was then mixed with the photo-
activated BisGMA
TEGDMA resin at a QADM mass fraction of 20%. This resin is referred to as
the BisGMA
QADM resin. A previous study showed that 20% QADM greatly
reduced bacterial growth on the polymer surfaces
[20]
. The BisGMA
TEGDMA
QADM resin
was then filled with 30% NACP and 35% barium boroaluminosilicate glass, and this composite is
referred to as “NACP
TEGDMA
QADM.” Hence, the QADM mass fraction in the final composite was
1
20%
7%.
Silver 2-ethylhexanoate powder (Strem Chemicals, New Buryport, MA) at 0.08 g was dissolved
into 1 g of 2-(tert-butylamino)ethyl methacrylate (TBAEMA; Sigma) by stirring, and then 1% of
this solution was added to the resin. The mass fraction of Ag salt in the resin was 0.08%, according
to a recent study
[51]
. TBAEMA improves the solubility by forming Ag
35%
3
5
N coordination bonds
with Ag ions, thereby facilitating the Ag salt to dissolve in the resin solution. TBAEMA was
selected since it contains reactive methacrylate groups and can be chemically incorporated into the
polymer network upon photopolymerization
[51]
. The nanoparticles of silver (NAg) had particle
sizes of 2.7
a
0.6 nm, as shown in
Figure 6.1C
. The particles appeared to be well dispersed in the
resin, without noticeable clustered particles or agglomerates
[21]
.
6
