Daniel Morales
| PhD, Chemical Engineering, 2015 North Carolina State University M.S., Chemical Engineering, 2012 North Carolina State University B.S., Chemical Engineering, 2010 Florida State University, Tallahassee |  |
Research Focus: Utilizing electric fields to manipulate the ionic equilibria of polyelectrolyte hydrogels
Polyelectrolyte-based ionic hydrogels are three-dimensional networks which facilitate the transport of ions, particles and other molecules while maintaining their structure during swelling, shrinking and/or bending. Due to their biocompatibility and vigorous response to various external stimuli, hydrogels hold large promise as elements of stimuli-sensitive systems. My research focuses on tuning the ionic equilibria of hydrogels using electric fields to enable their application as soft matter actuators, sensors and robotic components. I am currently studying two systems wherein the first utilizes electric fields in solution to mobilize counter ions and induce an osmotic pressure gradient and the second uses electric fields in contact with the hydrogel network to locally control ion binding.
Engineering new classes of soft matter actuators from polyelectrolyte hydrogels
We focus on mimicking the locomotion of miniature walking species, such as inchworms, by applying an electric field to manipulate gel ion distribution in solution. We have characterized the response of the hydrogel networks as a function fixed charge density and salt concentration in the external media. By adhering cationic and anionic networks together, prototype walkers with functionalized moving “legs” for an asymmetric response mechanism were developed.
Figure 1: Actuation mechanism of the gel walker. (a) Illustrations depicting the two modes of actuation depending on the direction of the applied electric field. Fc and Fa are the friction force of the cationic leg (dark blue) and anionic leg (light grey) respectively. (b) Photographs of a gel walker in 0.01 M NaCl composed of 50% NaAc and 30% DMAEMA-Q legs with an applied field of 5 V/cm. Scale bar = 5 mm.
A new way to pattern, structure and actuate hydrogels by current-induced ion binding
We also developed a method for patterning ions on hydrated gels utilizing metal ion complexation by an electric field. Termed ‘ionoprinting’ this technique has the capability to topographically structure and actuate gels in 2D and 3D by patterning ions from electrodes in contact with hydrogels. These ionic patterns are stable for months and the ionoprinting process is fully reversible since patterns erase when immersed in a chelator. The ionic binding changes the local mechanical properties of the gel to induce 2D relief patterns and in some cases evokes localized stresses large enough to cause folding. These prepatterned hydrogels exhibit programmable temporal and spatial shape memory behaviour and serve as basis of a new class of soft actuators able to gently manipulate objects both in air and in liquid.
Figure 2: Reversible two and three dimensional patterning by ionoprinting. a, An ionoprinted pNaAc (poly sodium acrylate) gel using a penny as the anode (15 s at 15 V). Features are replicated with high definition and can be scaled down by a factor of 5 after gel dehydration. Scale bar = 100 µm; b, Stresses induced by the lines ionoprinted with a (slightly tilted) copper wire anode are used to fold a 3D gel coil. This 3D shape is conserved when the gel is dehydrated. Scale bar = 5 mm. c, A 3 mm deep 5 mm diameter circular pattern, ionoprinted on a pNaAc gel, is erased by immersion in EDTA (Ethylenediaminetetra acetic acid) for 4 h. The pattern disappears due to the chelation and the gel shrinks due to osmotic equilibrium in 0.1 M EDTA. The hydrogel sample was extracted from solution to take the corresponding photos.
Awards
Student Leader at Council for Chemical Research Annual Meeting (2014)
NC Space Grant Recipient (2014)
Milliken Graduate Research Symposium Lecturer (2014)
NC State Dept. of Chemical and Biomolecular Engineering Vivian T. Stannett Fellow (2014)
Publications