Broader Research Goals:
Poly(alkoxy ether)s as platforms for stimuli-responsive materials. Our group uses living anionic polymerization to synthesize poly(glycidyl ether) derivatives that afford multi-stimuli-responsive hydrogels. These materials physically change in response to external stimuli such as temperature, pressure, and light. We develop and interrogate structure property relationships of our materials by using synthetic chemistry and supramolecular chemistry to design polymers that we primarily characterize using rheology (among other characterization techniques).
Living materials and their analogs. Living materials are composites of living cells residing within a polymeric matrix, and a unique feature of these materials is that the cells are metabolically active. Our group develops stimuli-responsive hydrogels for fabricating living materials via 3D printing.
Actuating hydrogels. We use direct-write printing to create stimuli-responsive 3D printed hydrogels, which can fold in response to an external stimulus. 3D printing enables rapid iteration to achieve optimized designs for actuating hydrogels.
Recent Research Interests:
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 (∼90% 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.
Chemical Modification and Printability of Shear-Thinning Hydrogel Inks for Direct-Write 3D Printing
Shear-thinning hydrogels are often employed in direct-write 3D printing, however, the viscoelastic behaviors that define a printable hydrogel have not been fully established. Herein, we demonstrate a library of hydrogel inks based on the incorporation of water-soluble reactive meth(acrylate) monomers into F127-dimethacrylate hydrogels. This strategy afforded printed hydrogels with a broad range of chemical functionalities and mechanical properties. A systematic investigation was also performed to correlate the printability and mechanical properties to the viscoelastic properties of the hydrogel ink formulations. The materials with a high dynamic yield stress afforded extruded filaments that correlated well with the inner diameter of the printing nozzle. The static yield stress of the material was correlated to the extrusion pressure and print speed required for optimal printing. Thus, this study provides a guide for the future development of hydrogel inks for direct-write 3D printing along with a new set of functional hydrogel inks.
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
photo-curing, 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 ‘melted’ 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 multi-walled carbon nanotubes (MWCNTs) were successfully printed. The printed composites with MWCNTs afforded photo- thermally active objects, which have utility as stimuli-responsive actuators.
Cross-Linkable Multi-Stimuli Responsive Hydrogel Inks for Direct-Write 3D Printing
Triple stimuli-responsive ABA triblock copolymer hydrogels composed of poly(allyl glycidyl ether)-stat-poly(alkyl glycidyl ether)-block-poly(ethylene glycol)-block-poly(allyl glycidyl ether)-stat-poly(alkyl glycidyl ether) were synthesized using controlled ring-opening polymerization of glycidyl ethers. These polymers form triple stimuli-responsive hydrogels that respond to temperature, pressure (shear-thinning), and UV light. The stimuli-responsive behaviors of the gels were dependent upon the composition and the molecular weight of the ‘A’ blocks of the triblock copolymers. The hydrogels were analyzed rheometrically to characterize their stimuli-responsive properties. The optimized compositions were 3D printed using a direct-write 3D printer to afford robust 3D objects. We anticipate these materials creating new opportunities in the biomedical and biotechnological fields, by enabling the simple and rapid fabrication of 3D hydrogels.