4 research outputs found
Sticky Ends in a Self-Assembling ABA Triblock Copolymer: The Role of Ureas in Stimuli-Responsive Hydrogels
Directing polymer self-assembly through noncovalent interactions is a powerful way to control the structure and function of nanoengineered materials. Dynamic hydrogen bonds are particularly useful for materials with structures that change over time or in response to specific stimuli. In the present work, we use the supramolecular association of urea moieties to manipulate the morphology, thermal response, and mechanical properties of soft polymeric hydrogels. Urea-terminated poly(isopropyl glycidyl ether)-b-poly(ethylene oxide)-b-poly(isopropyl glycidyl ether) ABA triblock copolymers were synthesized using controlled, anionic ring-opening polymerization and subsequent chain-end functionalization. Triblock copolymers with hydroxy end-groups were incapable of hydrogelation, while polymers terminated with meta-bis-urea motifs formed robust gels at room temperature. Rheometric analysis of the bulk gels, variable-temperature infrared spectroscopy (VT-IR), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) confirmed the formation of structured hydrogels via association of the meta-bis-urea end-groups. Monourea end-groups did not result in the same regular structure as the meta-bis-urea. In future, the reported hydrogels could be useful for elastomeric, shape-morphing 3D-printed constructs, or as biomimetic scaffolds with precisely tailored porosity and mechanical properties
Catalytically Initiated Gel-in-Gel Printing of Composite Hydrogels
Herein, we describe a method to 3D
print robust hydrogels and hydrogel composites via gel-in-gel 3D printing
with catalytically activated polymerization to induce cross-linking.
A polymerizable shear-thinning hydrogel ink with tetramethylethylenediamine
as catalyst was directly extruded into a shear-thinning hydrogel support
bath with ammonium persulfate as initiator in a pattern-wise manner.
When the two gels came into contact, the free radicals generated by
the catalyst initiated the free-radical polymerization of the hydrogel
ink. Unlike photocuring, a catalyst-initiated polymerization is suitable
for printing hydrogel composites of varying opacity, since it does
not depend upon light penetration through the sample. The hydrogel
support bath also exhibited a temperature-responsive behavior in which
the gel âmeltedâ upon cooling below 16 °C. Therefore,
the printed object was easily removed by cooling the gel to a liquid
state. Hydrogel composites with graphene oxide and multiwalled carbon
nanotubes (MWCNTs) were successfully printed. The printed composites
with MWCNTs afforded photothermally active objects, which have utility
as stimuli-responsive actuators
Additive Manufacturing of Bovine Serum Albumin-Based Hydrogels and Bioplastics
Bio-sourced and biodegradable polymers for additive manufacturing could
enable the rapid fabrication of parts for a broad spectrum of applications
ranging from healthcare to aerospace. However, a limited number of these
materials are suitable for vat photopolymerization processes. Herein, we report a two-step additive
manufacturing process to fabricate robust protein-based constructs using a
commercially available laser-based SLA printer. Methacrylated bovine serum
albumin (MA-BSA) was synthesized and formulated into aqueous resins that were used
to print complex 3D objects with a resolution comparable to a commercially
available resin. The MA-BSA resins were characterized by rheometry to determine
the viscosity and the cure rate, as both of these parameters can ultimately be
used to predict the printability of the resin. In the first step of patterning
these materials, the MA-BSA resin was 3D printed, and in the second step, the
printed construct was thermally cured to denature the globular protein and
increase the intermolecular noncovalent interactions. Thus, the final 3D
printed part was comprised of both chemical and physical cross-links. Compression
studies of hydrated and dehydrated constructs demonstrated a broad range of
compressive strengths and Youngâs moduli that could be further modulated by
adjusting the type and amount of co-monomer. The printed hydrogel constructs
demonstrated good cell viability (> 95%) after a 21-day culture period. These
MA-BSA resins are expected to be compatible with other vat photopolymerization
techniques including digital light projection (DLP) and continuous liquid
interface production (CLIP)
Additive Manufacturing of Catalytically Active Living Materials
Living
materials, which are composites of living cells residing in a polymeric
matrix, are designed to utilize the innate functionalities of the
cells to address a broad range of applications such as fermentation
and biosensing. Herein, we demonstrate the additive manufacturing
of catalytically active living materials (AMCALM) for continuous fermentation.
A multi-stimuli-responsive yeast-laden hydrogel ink, based on F127-dimethacrylate,
was developed and printed using a direct-write 3D printer. The reversible
stimuli-responsive behaviors of the polymer hydrogel inks to temperature
and pressure are critical, as they enabled the facile incorporation
of yeast cells and subsequent fabrication of 3D lattice constructs.
Subsequent photo-cross-linking of the printed polymer hydrogel afforded
a robust elastic material. These yeast-laden living materials were
metabolically active in the fermentation of glucose into ethanol for
2 weeks in a continuous batch process without significant reduction
in efficiency (âŒ90% yield of ethanol). This cell immobilization
platform may potentially be applicable toward other genetically modified
yeast strains to produce other high-value chemicals in a continuous
biofermentation process