Biology subjects

Williams, J. R.

Publications and source records attributed to Williams, J. R..

3 recordsLinked to original sources

bioRxiv2024

OpenExo: An Open-Source Modular Exoskeleton to Augment Human Function

While the field of wearable robotic exoskeletons is rapidly expanding, there are several barriers to entry that discourage many from pursuing research in this area, ultimately hindering growth. Chief among these are the lengthy and costly development time to get an exoskeleton from conception to implementation and the necessity for a broad set of expertise. Additionally, many exoskeletons are designed for a specific utility (e.g., ankle plantarflexor assistance) and are confined to the laboratory environment, limiting the flexibility of the designed system to adapt to answer new questions and explore new domains. To address these barriers, we present OpenExo, an open-source modular untethered exoskeleton framework that provides access to all aspects of the design process including (1) software, (2) electronics, (3) hardware, and (4) control schemes. To demonstrate the utility of this exoskeleton framework, we performed benchtop and experimental validation testing with the system across multiple configurations including (1) hip-only incline assistance, (2) ankle-only indoor and outdoor assistance, (3) hip-and-ankle load-carriage assistance, and (4) elbow-only weightlifting assistance. All aspects of the software architecture, electrical components, hip and Bowden-cable transmission designs, and control schemes are freely available for other researchers to access, use, and modify when looking to address research questions in the field of wearable exoskeletons. Our hope is that OpenExo will rapidly accelerate the development and testing of new exoskeleton designs and control schemes, while simultaneously encouraging others, including those who would have been turned away from entering the field, to explore new and unique research questions. One-Sentence SummaryWe present an open-source, open-hardware exoskeleton to aid in accelerating the growth of robotic exoskeleton research.

bioengineering↗

bioRxiv2024

A Hierarchical Model for eDNA Fate and Transport Dynamics Accommodating Low Concentration Samples

Environmental DNA (eDNA) sampling is an increasingly important tool for answering ecological questions and informing aquatic species management; however, several factors currently limit the reliability of ecological inference from eDNA sampling. Two particular challenges are 1) determining species source location(s) and 2) accurately and precisely measuring low concentration eDNA samples in the presence of multiple sources of ecological and measurement variability. The recently introduced eDNA Integrating Transport and Hydrology (eDITH) model provides a framework for relating eDNA measurements to source locations in riverine networks, but little empirical work has been done to test and refine model assumptions or accommodate low concentration samples, that can be systematically undermeasured. To better understand eDNA fate and transport dynamics and our ability to reliably quantify low concentration samples, we developed a hierarchical model and used it to evaluate a fate and transport experiment. Our model addresses several low concentration challenges by modeling the number of copies in each PCR replicate as a latent variable with a count distribution and conditioning detection and quantification on replicate copy number. We provide evidence that the eDNA removal rate declined through time, estimating that over 80% of eDNA was removed over the first 10 meters, traversed in 41 seconds. After this initial period of rapid decay, eDNA decayed slowly with consistent detection through our farthest site 1km from the release location, traversed in 250 seconds. Our model further allowed us to detect extra-Poisson variation in the allocation of copies to replicates. We extended our hierarchical model to accommodate a continuous effect of inhibitors and used our model to provide evidence for the inhibitor hypothesis and explore the potential implications. While our model is not a panacea for all challenges faced when quantifying low-concentration eDNA samples, it provides a framework for a more complete accounting of uncertainty.

ecology↗

bioRxiv2024

Cooperation between Nodal and FGF signals regulates zebrafish cardiac cell migration and heart morphogenesis

Asymmetric development of the vertebrate heart is driven by a complex sequence of morphogenetic cell movements, coordinated through precise interpretation of signaling cues by the heart primordia. Here, we show that Nodal signaling functions synergistically with FGF to stimulate the migration of cardiac progenitor cells (CPCs) during cardiac jogging--the first morphological asymmetry observed in zebrafish heart development. While Nodal directs the asymmetric migration of CPCs, we find FGF signaling to be dispensable for this asymmetry, suggesting that FGF plays a permissive rather than instructive role. We further demonstrate that Nodal signaling induces asymmetries in actin cytoskeletal dynamics that correlate with the directional migration of CPCs, while FGF does not influence this actin asymmetry. In addition to influencing jogging, FGF and Nodal synergize to ensure proper heart looping. We also provide evidence that FGF contributes to heart looping by promoting the differentiation of the second heart field. Together, these findings offer insight into how the spatiotemporal dynamics of signaling pathways regulate the cellular behaviors driving organ morphogenesis. Summary statementThis study explores the synergistic and independent roles of Nodal and FGF signaling in generating heart asymmetry.

developmental biology↗