Person:

Weaver, James

Plant hydro-actuated systems provide a rich source of inspiration for designing autonomously morphing devices. One such example, the pentagonal ice plant seed capsule, achieves complex mechanical actuation which is critically dependent on its hierarchical organization. The functional core of this actuation system involves the controlled expansion of a highly swellable cellulosic layer, which is surrounded by a non-swellable honeycomb framework. In this work, we extract the design principles behind the unfolding of the ice plant seed capsules, and use two different approaches to develop autonomously deforming honeycomb devices as a proof of concept. By combining swelling experiments with analytical and finite element modelling, we elucidate the role of each design parameter on the actuation of the prototypes. Through these approaches, we demonstrate potential pathways to design/develop/construct autonomously morphing systems by tailoring and amplifying the initial material’s response to external stimuli through simple geometric design of the system at two different length scales.

Geometrical frustration arises when a local order cannot propagate throughout the space because of geometrical constraints. This phenomenon plays a major role in many systems leading to disordered ground-state configurations. Here, we report a theoretical and experimental study on the behavior of buckling-induced geometrically frustrated triangular cellular structures. To our surprise, we find that buckling induces complex ordered patterns which can be tuned by controlling the porosity of the structures. Our analysis reveals that the connected geometry of the cellular structure plays a crucial role in the generation of ordered states in this frustrated system.

Ocean acidification is predicted to impact ecosystems reliant on calcifying organisms, potentially reducing the socioeconomic benefits these habitats provide. Here we investigate the acclimation potential of stony corals living along a pH gradient caused by a Mediterranean CO2 vent that serves as a natural long-term experimental setting. We show that in response to reduced skeletal mineralization at lower pH, corals increase their skeletal macroporosity (features >10 μm) in order to maintain constant linear extension rate, an important criterion for reproductive output. At the nanoscale, the coral skeleton's structural features are not altered. However, higher skeletal porosity, and reduced bulk density and stiffness may contribute to reduce population density and increase damage susceptibility under low pH conditions. Based on these observations, the almost universally employed measure of coral biomineralization, the rate of linear extension, might not be a reliable metric for assessing coral health and resilience in a warming and acidifying ocean.

In this study, we report a novel periodic material with negative Poisson’s ratio (also called auxetic materials) fabricated by denting spherical dimples in an elastic flat sheet. While previously reported auxetic materials are either porous or comprise at least two phases, the material proposed here is non-porous and made of a homogeneous elastic sheet. Importantly, the auxetic behavior is induced by a novel mechanism which exploits the out-of-plane deformation of the spherical dimples. Through a combination of experiments and numerical analyses, we demonstrate the robustness of the proposed concept, paving the way for developing a new class of auxetic materials that significantly expand their design space and possible applications.

Here we describe development of a human ‘lung small airway-on-a-chip’ containing a differentiated, mucociliary, bronchiolar epithelium and an underlying microvascular endothelium that experiences fluid flow, which enables analysis of organ-level lung pathophysiology in vitro. Exposure of the epithelium to IL-13 reconstitutes the goblet cell hyperplasia, cytokine hypersecretion and decreased ciliary function of asthmatics. Small airway chips lined by epithelial cells from chronic obstructive pulmonary disease patients recapitulate features of the disease including selective cytokine hypersecretion, increased neutrophil recruitment, and clinical exacerbations by exposure to viral and bacterial infections. Using this robust in vitro method for modeling human lung inflammatory disorders, it is possible to detect synergistic effects of lung endothelium and epithelium on cytokine secretion, identify new biomarkers of disease exacerbation, and measure therapeutic responses to anti-inflammatory compounds that inhibit cytokine-induced recruitment of circulating neutrophils under flow.

Current in vitro hematopoiesis models fail to demonstrate the cellular diversity and complex functions of living bone marrow; hence, most translational studies relevant to the hematologic system are conducted in live animals. Here we describe a method for fabricating 'bone marrow–on–a–chip' that permits culture of living marrow with a functional hematopoietic niche in vitro by first engineering new bone in vivo, removing it whole and perfusing it with culture medium in a microfluidic device. The engineered bone marrow (eBM) retains hematopoietic stem and progenitor cells in normal in vivo–like proportions for at least 1 week in culture. eBM models organ-level marrow toxicity responses and protective effects of radiation countermeasure drugs, whereas conventional bone marrow culture methods do not. This biomimetic microdevice offers a new approach for analysis of drug responses and toxicities in bone marrow as well as for study of hematopoiesis and hematologic diseases in vitro.

Analysis of enterovirus infection is difficult in animals because they express different virus receptors than humans, and static cell culture systems do not reproduce the physical complexity of the human intestinal epithelium. Here, using coxsackievirus B1 (CVB1) as a prototype enterovirus strain, we demonstrate that human enterovirus infection, replication and infectious virus production can be analyzed in vitro in a human Gut-on-a-Chip microfluidic device that supports culture of highly differentiated human villus intestinal epithelium under conditions of fluid flow and peristalsis-like motions. When CVB1 was introduced into the epithelium-lined intestinal lumen of the device, virions entered the epithelium, replicated inside the cells producing detectable cytopathic effects (CPEs), and both infectious virions and inflammatory cytokines were released in a polarized manner from the cell apex, as they could be detected in the effluent from the epithelial microchannel. When the virus was introduced via a basal route of infection (by inoculating virus into fluid flowing through a parallel lower ‘vascular’ channel separated from the epithelial channel by a porous membrane), significantly lower viral titers, decreased CPEs, and delayed caspase-3 activation were observed; however, cytokines continued to be secreted apically. The presence of continuous fluid flow through the epithelial lumen also resulted in production of a gradient of CPEs consistent with the flow direction. Thus, the human Gut-on-a-Chip may provide a suitable in vitro model for enteric virus infection and for investigating mechanisms of enterovirus pathogenesis.

Inspired by the long-term effectiveness of living antifouling materials, we have developed a method for the self-replenishment of synthetic biofouling-release surfaces. These surfaces are created by either molding or directly embedding 3D vascular systems into polydimethylsiloxane (PDMS) and filling them with a silicone oil to generate a nontoxic oil-infused material. When replenished with silicone oil from an outside source, these materials are capable of self-lubrication and continuous renewal of the interfacial fouling-release layer. Under accelerated lubricant loss conditions, fully infused vascularized samples retained significantly more lubricant than equivalent nonvascularized controls. Tests of lubricant-infused PDMS in static cultures of the infectious bacteria Staphylococcus aureus and Escherichia coli as well as the green microalgae Botryococcus braunii, Chlamydomonas reinhardtii, Dunaliella salina, and Nannochloropsis oculata showed a significant reduction in biofilm adhesion compared to PDMS and glass controls containing no lubricant. Further experiments on vascularized versus nonvascularized samples that had been subjected to accelerated lubricant evaporation conditions for up to 48 h showed significantly less biofilm adherence on the vascularized surfaces. These results demonstrate the ability of an embedded lubricant-filled vascular network to improve the longevity of fouling-release surfaces.

Reconfigurable devices, whose shape can be drastically altered, are central to expandable shelters, deployable space structures, reversible encapsulation systems and medical tools and robots. All these applications require structures whose shape can be actively controlled, both for deployment and to conform to the surrounding environment. While most current reconfigurable designs are application specific, here we present a mechanical metamaterial with tunable shape, volume and stiffness. Our approach exploits a simple modular origami-like design consisting of rigid faces and hinges, which are connected to form a periodic structure consisting of extruded cubes. We show both analytically and experimentally that the transformable metamaterial has three degrees of freedom, which can be actively deformed into numerous specific shapes through embedded actuation. The proposed metamaterial can be used to realize transformable structures with arbitrary architectures, highlighting a robust strategy for the design of reconfigurable devices over a wide range of length scales.

Studies of cellular mechanotransduction have converged upon the idea that cells sense extracellular matrix (ECM) elasticity by gauging resistance to the traction forces they exert on the ECM. However, these studies typically utilize purely elastic materials as substrates, whereas physiological ECMs are viscoelastic, and exhibit stress relaxation, so that cellular traction forces exerted by cells remodel the ECM. Here we investigate the influence of ECM stress relaxation on cell behaviour through computational modelling and cellular experiments. Surprisingly, both our computational model and experiments find that spreading for cells cultured on soft substrates that exhibit stress relaxation is greater than cells spreading on elastic substrates of the same modulus, but similar to that of cells spreading on stiffer elastic substrates. These findings challenge the current view of how cells sense and respond to the ECM.