This paper shows how to create a hydrogel that has many zones, each of which has different mechanical properties. The gel above has four zones, which stretch to different extents. The modulus of the stiffest zone is 100 times the modulus of the softest zone. Our approach could be used to build realistic mimics of the spinal discs present between our vertebrae, which have a soft core and a stiff shell.
This paper shows how to endow a capsule with a ‘hermetic’ seal, i.e., one that is perfectly leak-proof. This is done by making the capsule shell out of a wax with a defined melting temperature. Above this temperature, the shell melts and the contents are released in a burst. The ability to hold on to contents for long times and then release them on-demand makes these capsules useful in a variety of applications.
Making gels by 3D printing requires an expensive ‘printer’ and special UV-sensitive ‘inks’. This paper shows an alternative way to create 3D gels of the biopolymer alginate. The key is to induce gelation by an electric field, i.e., by a process called ‘electroformation’. It can be easily done in any lab at low cost, and it yields robust gels in precise shapes and patterns. Living cells can be readily embedded in these gels.
Many molecules (‘gelators’) self-assemble into long fibers, which entangle to form molecular gels. Such gelation occurs in some organic solvents, but not in others. But is it possible to predict if gelation would occur beforehand? This paper provided a framework to predict molecular gelation using thermodynamic parameters of the various solvents. The same framework has now been used by many researchers.
This paper showed for the first time how one could easily create a ‘photorheological fluid‘ in the lab, i.e., a fluid whose viscosity could be dramatically altered by shining light. The fluid contained molecules that self-assembled into long chains initially. Irradiation with UV light altered the geometry of the molecules, which made them re-assemble into tiny spheres. This caused a 10,000-fold drop in viscosity.
This paper reported the first example of a nanoparticle-based fluid whose viscosity could be significantly transformed by shining light. The fluid was initially a flowing suspension (sol) of clay nanoparticles. When subjected to UV light, molecules in the sol became photolyzed to form acid. The acid induced the nanoparticles to form a 3-D network, and thereby the sol turned into a gel.
Kerry defended her Ph.D. in Chemistry in Aug 2018, after which she joined Gelest Inc. in Philadelphia. In her Ph.D. work, she created polymer capsules with ‘emergent‘ properties as a result of internal chemical reactions. Her paper on inflating and exploding capsules was recently published in Langmuir.
The architecture of life is based on cells (microscale containers), which have organelles, i.e., smaller containers inside them. We are trying to mimic this by creating microscale capsules that have smaller capsules inside them. These multicompartment capsules (MCCs) can contain nanoparticles, enzymes, or bacteria in specific inner compartments (see paper in Chemical Science, 2017). We are collaborating with Prof. Bill Bentley (BioE) in this research.