Diet selection at three spatial scales: Implications for conservation of an endangered Hawaiian tree snail

Several recent studies suggest local adaptation in multiple taxa across Hawaii’s steep environmental gradients. Restoration efforts in devastated tropical island ecosystems may be deficient if we lack an understanding of the interactions and dependencies in communities that occur along these gradients. Endangered Hawaiian tree snails are part of a snail epiphyte plant system where they graze fungi and other microbes on the leaf surface, a process difficult to observe using conventional techniques. Tree snails have undergone catastrophic decline due to introduced predators, removal by shell collectors, and human-influenced habitat degradation. Prior to this study, little was known about the relationship among tree-snails, their host plants, and the epiphytic microbes on which they feed. In this study, we identified scale-dependent selection of substrates in Achatinella sowerbyana and Achatinella lila across the species’ ranges. We assessed: (1) within-plant diet selection using high-throughput DNA sequencing (micro-scale); (2) among-plant selection of tree host species (smallscale); (3) and the influence of climate on this system (macro-scale). Selection of substrates occurred at two scales: fungal communities in fecal samples differed in composition from those available on leaf surfaces; and at all sites, snail occurrence on Metrosideros polymorpha, a foundational forest plant, was significantly higher than expected based on availability. Habitat restoration efforts should focus on outplanting of M. polymorpha, the preferred snail host tree, in degraded habitat. Fungal differences across sites suggest relocation efforts to predator-free enclosures may be hindered by microbial shifts associated with geographic distance or differing environments

Bioinspired fibrillar adhesives: a review of analytical models and experimental evidence for adhesion enhancement by surface patterns

Fibrillar structures are found on the attachment pads of insects and small reptiles. These structures enable exquisite conformation to rough surfaces, increase the number of van der Waals interactions between the structure and the target surface, and thus enhance adhesion. Biomimetic adhesives replicate this effect by patterning polymer films with micron- or sub-micron-sized protrusions. Numerical contact-mechanics models as well as experimental adhesion measurements have been reported for a variety of protrusion shapes including flat, rounded, mushroom and spatula geometries. Although superior adhesion has been reported for the mushroom and spatula tip geometries, straight, flat-tipped pillars offer the potential for much simpler mass production such as by injection moulding and are thus the focus of this review. Existing models for straight, flat-tipped pillar arrays do not fully agree with reported experimental results. Analytical models are generally limited to elastic materials, and inherently assume that neighbouring pillars behave independently. For elastic pillars in close proximity, however, pillars do in fact interact mechanically, affecting adhesion. Moreover, visco- and hyper-elastic materials are often used in practice, yet dissipative effects receive little attention in analytical models. We find that no study has conclusively investigated the limit of adhesive strength achievable by fibrillar adhesives. It also remains unclear what happens to the adhesive strength as the areal density of contacting regions approaches 100%.Accepted versio

Acoustic fields and microfluidic patterning around embedded micro-structures subject to surface acoustic waves

Recent research has shown that interactions between acoustic waves and microfluidic channels can generate microscale interference patterns with the application of a traveling surface acoustic wave (SAW), effectively creating standing wave patterns with a traveling wave. Forces arising from this interference can be utilized for precise manipulation of micron-sized particles and biological cells. The patterns that have been produced with this method, however, have been limited to straight lines and grids from flat channel walls, and where the spacing resulting from this interference has not previously been comprehensively explored. In this work we examine the interaction between both straight and curved channel interfaces with a SAW to derive geometrically deduced analytical models. These models predict the acoustic force-field periodicity near a channel interface as a function of its orientation to an underlying SAW, and are validated with experimental and simulation results. Notably, the spacing is larger for flat walls than for curved ones and is dependent on the ratio of sound speeds in the substrate and fluid. Generating these force-field gradients with only travelling waves has wide applications in acoustofluidic systems, where channel interfaces can potentially support a range of patterning, concentration, focusing and separation activities by creating locally defined acoustic forces

A deep learning approach for designed diffraction-based acoustic patterning in microchannels

© 2020, The Author(s). Acoustic waves can be used to accurately position cells and particles and are appropriate for this activity owing to their biocompatibility and ability to generate microscale force gradients. Such fields, however, typically take the form of only periodic one or two-dimensional grids, limiting the scope of patterning activities that can be performed. Recent work has demonstrated that the interaction between microfluidic channel walls and travelling surface acoustic waves can generate spatially variable acoustic fields, opening the possibility that the channel geometry can be used to control the pressure field that develops. In this work we utilize this approach to create novel acoustic fields. Designing the channel that results in a desired acoustic field, however, is a non-trivial task. To rapidly generate designed acoustic fields from microchannel elements we utilize a deep learning approach based on a deep neural network (DNN) that is trained on images of pre-solved acoustic fields. We use then this trained DNN to create novel microchannel architectures for designed microparticle patterning

Self-Aligned Acoustofluidic Particle Focusing and Patterning in Microfluidic Channels from Channel-Based Acoustic Waveguides

Acoustic fields have been widely used for manipulation of particles and cells within microfluidic systems. In this Letter, we explore a novel acoustofluidic phenomenon for particle patterning and focusing, where a periodic acoustic pressure field is produced parallel to internal channel boundaries with the imposition of either a traveling or standing surface acoustic wave (SAW). This effect results from the propagation and intersection of edge waves from the channel walls according to the Huygens-Fresnel principle and classical wave fronts from the substrate-fluid interface. We demonstrate versatile control over this effect to produce both one- and two-dimensional acoustic patterning from one-dimensional SAW fields and its utility for continuous particle focusing. Uniquely, this channel-guided acoustic focusing permits the generation of robust acoustic fields without channel resonance conditions and particle focusing positions that are difficult or impossible to produce otherwise

Addressing Unmet Clinical Needs with UV Bioadhesives

The invasive practice of suturing for wound closure has persisted for millennia; with the rate of medical development, it is staggering that there are few viable alternatives to invasive mechanical fasteners. Biocompatible and biodegradable polymers are attractive candidates for versatile bioadhesives and could revolutionize surgical procedures. Bioadhesives can be broadly placed into two groups: activated and instant. Almost all commercially available bioadhesives are instant, which cross-link by mixing two components or on contact with moisture. Activated bioadhesives, on the other hand, allow control of when and where a bioadhesive cross-links and, in some cases, the extent of cross-linking. Despite significant progress, there has been little translation of activated bioadhesives to clinical use. This review discusses recent developments in UV-activated bioadhesives toward addressing unmet clinical needs.MOE (Min. of Education, S’pore)Published versio

Rapid cell separation with minimal manipulation for autologous cell therapies

The ability to isolate specific, viable cell populations from mixed ensembles with minimal manipulation and within intra-operative time would provide significant advantages for autologous, cell-based therapies in regenerative medicine. Current cell-enrichment technologies are either slow, lack specificity and/or require labelling. Thus a rapid, label-free separation technology that does not affect cell functionality, viability or phenotype is highly desirable. Here, we demonstrate separation of viable from non-viable human stromal cells using remote dielectrophoresis, in which an electric field is coupled into a microfluidic channel using shear-horizontal surface acoustic waves, producing an array of virtual electrodes within the channel. This allows high-throughput dielectrophoretic cell separation in high conductivity, physiological-like fluids, overcoming the limitations of conventional dielectrophoresis. We demonstrate viable/non-viable separation efficacy of >98% in pre-purified mesenchymal stromal cells, extracted from human dental pulp, with no adverse effects on cell viability, or on their subsequent osteogenic capabilities.Published versio

Mitogenomic diversity in Sacred Ibis mummies sheds light on early Egyptian practices

The ancient catacombs of Egypt harbor millions of well-preserved mummified Sacred Ibis (Threskiornis aethiopicus) dating from ~600BC. Although it is known that a very large number of these ‘votive’ mummies were sacrificed to the Egyptian God Thoth, how the ancient Egyptians obtained millions of these birds for mummification remains unresolved. Ancient Egyptian textual evidences suggest they may have been raised in dedicated large-scale farms. To investigate the most likely method used by the priests to secure birds for mummification, we report the first study of complete mitochondrial genomes of 14 Sacred Ibis mummies interred ~2500 years ago. We analysed and compared the mitogenomic diversity among Sacred Ibis mummies to that found in modern Sacred Ibis populations from throughout Africa. The ancient birds show a high level of genetic variation comparable to that identified in modern African populations, contrary to the suggestion in ancient hieroglyphics (or ancient writings) of centralized industrial scale farming of sacrificial birds. This suggests a sustained short-term taming of the wild migratory Sacred Ibis for the ritual yearly demand