4 research outputs found
Evaluation of Sulfonium Borate Initiators for Cationic Photopolymerization and Their Application in Hot Lithography
Sulfonium hexafluorophosphates
and perfluorinated tetraphenylborates
are well established initiators in the field of cationic photopolymerization
and have already been applied in 3D-printing at elevated temperatures,
named hot lithography. The cyanide-ligated borane-based photoinitiator B2 shows lower molecular weight compared to state-of-the-art
borates and is less expensive to synthesize from commercial starting
materials. By comparing reactivity in the epoxy monomer BADGE, B2 outperforms commercial initiators in a broad range of temperatures
with outstanding epoxy group conversions of up to 99%. Besides B2’s excellent performance as a cationic initiator,
formulations containing B2 are thermally and storage
stable and can be sensitized by anthracene derivatives. Hot lithography
of B2 was carried out successfully at 90 °C and
compared to existing sulfonium initiators. Layer quality and coloration
of the fabricated and postcured parts are superior for B2. Overall, the cyanide-ligated sulfonium salt B2 represents
an excellent initiator for cationic photopolymerization and application
in hot lithography
Laser Photofabrication of Cell-Containing Hydrogel Constructs
The two-photon polymerization (2PP)
of photosensitive gelatin in
the presence of living cells is reported. The 2PP technique is based
on the localized cross-linking of photopolymers induced by femtosecond
laser pulses. The availability of water-soluble photoinitiators (PI)
suitable for 2PP is crucial for applying this method to cell-containing
materials. Novel PIs developed by our group allow 2PP of formulations
with up to 80% cell culture medium. The cytocompatibility of these
PIs was evaluated by an MTT assay. The results of cell encapsulation
by 2PP show the occurrence of cell damage within the laser-exposed
regions. However, some cells located in the immediate vicinity and
even within the 2PP-produced structures remain viable and can further
proliferate. The control experiments demonstrate that the laser radiation
itself does not damage the cells at the parameters used for 2PP. On
the basis of these findings and the reports by other groups, we conclude
that such localized cell damage is of a chemical origin and can be
attributed to reactive species generated during 2PP. The viable cells
trapped within the 2PP structures but not exposed to laser radiation
continued to proliferate. The live/dead staining after 3 weeks revealed
viable cells occupying most of the space available within the 3D hydrogel
constructs. While some of the questions raised by this study remain
open, the presented results indicate the general practicability of
2PP for 3D processing of cell-containing materials. The potential
applications of this highly versatile approach span from precise engineering
of 3D tissue models to the fabrication of cellular microarrays
A Straightforward Synthesis and Structure–Activity Relationship of Highly Efficient Initiators for Two-Photon Polymerization
The development of practical two-photon absorption photoinitiators
(TPA PIs) has been slow due to their complicated syntheses often reliant
on expensive catalysts. These shortcomings have been a critical obstruction
for further advances in the promising field of two-photon-induced
photopolymerization (TPIP) technology. This paper describes a series
of linear and cyclic benzylidene ketone-based two-photon initiators
containing double bonds and dialkylamino groups synthesized in one
step via classical aldol condensation reactions. Systematic investigations
of structure–activity relationships were conducted via quantum-chemical
calculations and experimental tests. These results showed that the
size of the central ring significantly affected the excited state
energetics and emission quantum yields as well as the two-photon initiation
efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator
displayed much broader ideal processing windows than its counterparts
with a central five-membered ring and previously described highly
active TPA PIs. Surprisingly, a writing speed as high as 80 mm/s was
obtained for the microfabrication of complex 3D structures employing
acrylate-based formulations. These highly active TPA PIs also exhibit
excellent thermal stability and remain inert to one-photon excitation.
Straightforward synthesis combined with high TPA initiation efficiency
makes these novel initiators promising candidates for commercialization
A Straightforward Synthesis and Structure–Activity Relationship of Highly Efficient Initiators for Two-Photon Polymerization
The development of practical two-photon absorption photoinitiators
(TPA PIs) has been slow due to their complicated syntheses often reliant
on expensive catalysts. These shortcomings have been a critical obstruction
for further advances in the promising field of two-photon-induced
photopolymerization (TPIP) technology. This paper describes a series
of linear and cyclic benzylidene ketone-based two-photon initiators
containing double bonds and dialkylamino groups synthesized in one
step via classical aldol condensation reactions. Systematic investigations
of structure–activity relationships were conducted via quantum-chemical
calculations and experimental tests. These results showed that the
size of the central ring significantly affected the excited state
energetics and emission quantum yields as well as the two-photon initiation
efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator
displayed much broader ideal processing windows than its counterparts
with a central five-membered ring and previously described highly
active TPA PIs. Surprisingly, a writing speed as high as 80 mm/s was
obtained for the microfabrication of complex 3D structures employing
acrylate-based formulations. These highly active TPA PIs also exhibit
excellent thermal stability and remain inert to one-photon excitation.
Straightforward synthesis combined with high TPA initiation efficiency
makes these novel initiators promising candidates for commercialization