8 research outputs found
Extreme thermodynamics with polymer gel tori:Harnessing thermodynamic instabilities to induce large-scale deformations
When a swollen, thermoresponsive polymer gel is heated in a solvent bath, it
expels solvent and deswells. When this heating is slow, deswelling proceeds
homogeneously, as observed in a toroid-shaped gel that changes volume whilst
maintaining its toroidal shape. By contrast, if the gel is heated quickly, an
impermeable layer of collapsed polymer forms and traps solvent within the gel,
arresting the volume change. The ensuing evolution of the gel then happens at
fixed volume, leading to phase-separation and the development of inhomogeneous
stress that deforms the toroidal shape. We observe that this stress can cause
the torus to buckle out of the plane, via a mechanism analogous to the bending
of bimetallic strips upon heating. Our results demonstrate that thermodynamic
instabilities, i.e., phase transitions, can be used to actuate mechanical
deformation in an extreme thermodynamics of materials.Comment: 5 pages, 4 figures. To appear in Physical Review E (2018
Self-Propelled Microswimmer Actuated by Stimuli-Sensitive Bilayered Hydrogel
Using computational modeling, we
design a microscopic swimmer made
of a bilayered responsive hydrogel capable of swimming in a viscous
fluid when actuated by a periodically applied stimulus. The gel has
an X-shaped geometry and two bonded layers, one of which is responsive
to environmental changes and the other which is passive. When the
stimulus is turned on, the responsive layer swells and causes the
swimmer to deform. We demonstrate that when such stimulus-induced
deformations occur periodically the gel swimmer effectively propels
forward through the fluid. We show that the swimming speed depends
on the relative stiffness of the two gel layers composing the swimmer,
and we determine the optimal stiffness ratio that maximizes the swimming
speed
A MATHEMATICAL MODEL OF BLOOD FLOW IN AN INTRACRANIAL ANEURYSM: ANALYTICAL AND NUMERICAL STUDY
Bimorph Silk Microsheets with Programmable Actuating Behavior: Experimental Analysis and Computer Simulations
Microscaled self-rolling
construct sheets from silk protein material have been fabricated,
containing a silk bimorph composed of silk ionomers as an active layer
and cross-linked silk β-sheet as the passive layer. The programmable
morphology was experimentally explored along with a computational
simulation to understand the mechanism of shape reconfiguration. The
neutron reflectivity shows that the active silk ionomers layer undergoes
remarkable swelling (eight times increase in thickness) after deprotonation
while the passive silk β-sheet retains constant volume under
the same conditions and supports the bimorph construct. This selective
swelling within the silk-on-silk bimorph microsheets generates strong
interfacial stress between
layers and out-of-plane forces, which trigger autonomous self-rolling
into various 3D constructs such as cylindrical and helical tubules.
The experimental observations and computational modeling confirmed
the role of interfacial stresses and allow programming the morphology
of the 3D constructs with particular design. We demonstrated that
the biaxial stress distribution over the 2D planar films depends upon
the lateral dimensions, thickness and the aspect ratio of the microsheets.
The results allow the fine-tuning of autonomous shape transformations
for the further design of complex micro-origami constructs and the
silk based rolling/unrolling structures provide a promising platform
for polymer-based biomimetic devices for implant applications
International Conference on Mathematical Methods and Models in Biosciences (Biomath) 2011
CERAPP : Collaborative Estrogen Receptor Activity Prediction Project
BACKGROUND: Humans are exposed to thousands of man-made chemicals in the environment. Some chemicals mimic natural endocrine hormones and, thus, have the potential to be endocrine disruptors. Most of these chemicals have never been tested for their ability to interact with the estrogen receptor (ER). Risk assessors need tools to prioritize chemicals for evaluation in costly in vivo tests, for instance, within the U.S. EPA Endocrine Disruptor Screening Program. OBJECTIVES: We describe a large-scale modeling project called CERAPP (Collaborative Estrogen Receptor Activity Prediction Project) and demonstrate the efficacy of using predictive computational models trained on high-throughput screening data to evaluate thousands of chemicals for ER-related activity and prioritize them for further testing. METHODS: CERAPP combined multiple models developed in collaboration with 17 groups in the United States and Europe to predict ER activity of a common set of 32,464 chemical structures. Quantitative structure-activity relationship models and docking approaches were employed, mostly using a common training set of 1,677 chemical structures provided by the U.S. EPA, to build a total of 40 categorical and 8 continuous models for binding, agonist, and antagonist ER activity. All predictions were evaluated on a set of 7,522 chemicals curated from the literature. To overcome the limitations of single models, a consensus was built by weighting models on scores based on their evaluated accuracies. RESULTS: Individual model scores ranged from 0.69 to 0.85, showing high prediction reliabilities. Out of the 32,464 chemicals, the consensus model predicted 4,001 chemicals (12.3%) as high priority actives and 6,742 potential actives (20.8%) to be considered for further testing.CONCLUSION: This project demonstrated the possibility to screen large libraries of chemicals using a consensus of different in silico approaches. This concept will be applied in future projects related to other end points