Design Optimization of a Pneumatic Soft Robotic Actuator Using Model-Based Optimization and Deep Reinforcement Learning

We present two frameworks for design optimization of a multi-chamber pneumatic-driven soft actuator to optimize its mechanical performance. The design goal is to achieve maximal horizontal motion of the top surface of the actuator with a minimum effect on its vertical motion. The parametric shape and layout of air chambers are optimized individually with the firefly algorithm and a deep reinforcement learning approach using both a model-based formulation and finite element analysis. The presented modeling approach extends the analytical formulations for tapered and thickened cantilever beams connected in a structure with virtual spring elements. The deep reinforcement learning-based approach is combined with both the model- and finite element-based environments to fully explore the design space and for comparison and cross-validation purposes. The two-chamber soft actuator was specifically designed to be integrated as a modular element into a soft robotic pad system used for pressure injury prevention, where local control of planar displacements can be advantageous to mitigate the risk of pressure injuries and blisters by minimizing shear forces at the skin-pad contact. A comparison of the results shows that designs achieved using the deep reinforcement based approach best decouples the horizontal and vertical motions, while producing the necessary displacement for the intended application. The results from optimizations were compared computationally and experimentally to the empirically obtained design in the existing literature to validate the optimized design and methodology

Out-of-plane load-bearing and mechanical energy absorption properties of flexible density-graded TPU honeycombs

Honeycomb structures are widely used in applications that require excellent strain energy mitigation at low structural weights. The load-bearing and energy absorption capacity of honeycomb structures strongly depend on their cell wall thickness to edge ratios. This work studies the mechanical response and strain energy absorption characteristics of hexagonal honeycomb structures with various cell wall thicknesses in response to out-of-plane loading conditions. Honeycomb structures with various nominal densities are first additively manufactured from flexible thermoplastic polyurethane (TPU). A comprehensive experimental study characterized the mechanical strength, energy absorption performance, and the strain recoverability of the structures. Density-graded structures are then fabricated by stacking multiple density layers of the honeycombs. Mechanical characterization of the density-graded structures points to their superior load-bearing response at large deformation conditions. From a strain energy absorption perspective, density graded structures are shown to outperform their uniform density counterparts at small deformation conditions. The results obtained in this work highlight the significance of density gradation as a practical means for the development of honeycomb structures with highly tailorable, application-specific mechanical properties

Flexible planar metamaterials with tunable Poisson’s ratios

This research reports on the design, fabrication, and multiscale mechanical characterization of flexible, planar mechanical metamaterials with tailorable mechanical properties. The tunable mechanical behavior of the structures is realized through the introduction of orthogonal perforations with different geometric features. Various configurations of the perforations lead to a wide range of Poisson’s ratios (from −0.8 to 0.4), load-bearing properties, and energy absorption capacities. The correlations between the configuration of the perforations and the auxetic response of the structures are highlighted through computational and experimental characterizations performed at multiple length scales. It is demonstrated that the local in-plane rotation of the solid ligaments in a uniaxially loaded structure is the primary factor that contributes to its strain-dependent auxetic behavior at macroscopic scales. Confinement of these local rotations is then used as a practical strategy to activate a self-strengthening mechanism in the auxetic structures. It is further shown that the fabrication of planar flexible structures with controllable Poisson’s ratios is feasible through spatial adjustment of perforations in the structure. Finally, discussions are provided regarding the practical applications of these structures for a new generation of highly energy-absorbing protective equipment

Flexible planar metamaterials with tunable Poisson\u27s ratios

This research reports on the design, fabrication, and multiscale mechanical characterization of flexible, planar mechanical metamaterials with tailorable mechanical properties. The tunable mechanical behavior of the structures is realized through the introduction of orthogonal perforations with different geometric features. Various configurations of the perforations lead to a wide range of Poisson\u27s ratios (from −0.8 to 0.4), load-bearing properties, and energy absorption capacities. The correlations between the configuration of the perforations and the auxetic response of the structures are highlighted through computational and experimental characterizations performed at multiple length scales. It is demonstrated that the local in-plane rotation of the solid ligaments in a uniaxially loaded structure is the primary factor that contributes to its strain-dependent auxetic behavior at macroscopic scales. Confinement of these local rotations is then used as a practical strategy to activate a self-strengthening mechanism in the auxetic structures. It is further shown that the fabrication of planar flexible structures with controllable Poisson\u27s ratios is feasible through spatial adjustment of perforations in the structure. Finally, discussions are provided regarding the practical applications of these structures for a new generation of highly energy-absorbing protective equipment

Firearm possession and use among youth : reanalysis of findings from a survey of incarcerated juveniles in South Carolina

This paper examines firearms possession and use among teenagers. A survey was taken of juveniles who had used firearms in the commission of crimes. A 92-item questionnaire was developed for use with participants. The results of the survey are reported here along with pertinent statistics

Juvenile and young adult firearm use in South Carolina : an update and reanalysis of data

This project is a follow-up to and an expansion of, an earlier report, Juvenile and Young Adult Firearm Use in South Carolina. There were two sets of objectives for the original project. The first involved determining the extent to which firearms are involved in violent crimes committed by children and young adults, identifying key characteristics of those arrested for committing these crimes, identifying who was being victimized by these crimes, and discovering under what circumstances these crimes were being committed. The second set of objectives involved learning more about what motivates children to possess firearms in the first place, how they manage to acquire firearms, and what factors are associated with the decision to use or possess firearms. The purpose of this report is to expand upon the first set of objectives and to reanalyze the findings of the second set, with the goal of achieving a higher degree of confidence in the self-reported data

The Role of Proteasome Beta Subunits in Gastrin-Mediated Transcription of Plasminogen Activator Inhibitor-2 and Regenerating Protein1

The hormone gastrin physiologically regulates gastric acid secretion and also contributes to maintaining gastric epithelial architecture by regulating expression of genes such as plasminogen activator inhibitor 2 (PAI-2) and regenerating protein 1(Reg1). Here we examine the role of proteasome subunit PSMB1 in the transcriptional regulation of PAI-2 and Reg1 by gastrin, and its subcellular distribution during gastrin stimulation. We used the gastric cancer cell line AGS, permanently transfected with the CCK2 receptor (AGS-GR) to study gastrin stimulated expression of PAI-2 and Reg1 reporter constructs when PSMB1 was knocked down by siRNA. Binding of PSMB1 to the PAI-2 and Reg1 promoters was assessed by chromatin immunoprecipitation (ChIP) assay. Subcellular distribution of PSMB1 was determined by immunocytochemistry and Western Blot. Gastrin robustly increased expression of PAI-2 and Reg1 in AGS-GR cells, but when PSMB1 was knocked down the responses were dramatically reduced. In ChIP assays, following immunoprecipitation of chromatin with a PSMB1 antibody there was a substantial enrichment of DNA from the gastrin responsive regions of the PAI-2 and Reg1 promoters compared with chromatin precipitated with control IgG. In AGS-GR cells stimulated with gastrin there was a significant increase in the ratio of nuclear:cytoplasmic PSMB1 over the same timescale as recruitment of PSMB1 to the PAI-2 and Reg1 promoters seen in ChIP assays. We conclude that PSMB1 is part of the transcriptional machinery required for gastrin stimulated expression of PAI-2 and Reg1, and that its change in subcellular distribution in response to gastrin is consistent with this role

School-Based Programs to Reduce Bullying and Victimization

School bullying has serious short-term and long-term effects on children’s physical and mental health. Various anti-bullying programs have been implemented world wide and, more rarely, evaluated. Previous narrative reviews, summarizing the work done on bullying prevention, as well as previous meta-analyses of anti-bullying programs, are limited. The definition of school bullying includes several key elements: physical, verbal, or psychological attack or intimidation that is intended to cause fear, distress, or harm to the victim; an imbalance of power (psychological or physical), with a more powerful child (or children) oppressing less powerful ones; and repeated incidents between the same children over a prolonged period. School bullying can occur in school or on the way to or from school. It is not bullying when two persons of the same strength (physical, psychological, or verbal) victimize each other. This report presents a systematic review and meta-analysis of the effectiveness of programs designed to reduce school bullying perpetration and victimization (i.e. being bullied). The authors indicate the pitfalls of previous reviews and explain in detail how the present systematic review and meta-analysis addresses the gaps in the existing literature on bullying prevention

DESIGN AND CONTROL OF MODULAR SOFT ROBOTIC ACTUATORS WITH ARCHITECTED STRUCTURES

Soft robotic systems composed of highly compliant materials offer unparalleled advantages compared to rigid-body systems in applications such as fragile material handling and human-machine interactions. Often, their motions are prescribed by structural anisotropy and reinforcement materials to directionally limit motion. The continuum motion and non-linear material response intrinsic to soft robotics makes their design, modeling, and control a formidable challenge for engineers. Leveraging the deformation driven response of soft robotic actuators, highly versatile compliant architected structures whose local deformations dictate global material response can be integrated into soft robotic actuators for tunable mechanical responses. In this thesis, flexible center-symmetric perforated structures with strain-dependent Poisson\u27s ratios are investigated for their feasibility in soft robotics. This thesis aims to contribute to the existing literature by developing a novel cell-density graded structure with a near-zero incremental Poisson\u27s ratio, presenting a treatise on the fundamental mechanics and multiscale response of flexible rotating polygon structures, and developing and characterizing novel soft robotic actuators with the aforementioned center-symmetric perforated structures. The results of this thesis demonstrate the feasibility of such architected structures for soft robotics and provides a framework for the development of modular soft robotic actuators with tunable mechanical responses

Role of gastrin in gastric epithelial organisation and maturation

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