Compliant vascular models 3D printed with the Stratasys J750: a direct characterization of model distensibility using intravascular ultrasound

Purpose The purpose of this study is to evaluate biomechanical accuracy of 3D printed anatomical vessels using a material jetting printer (J750, Stratasys, Rehovot, Israel) by measuring distensibility via intravascular ultrasound. Materials and methods The test samples are 3D printed tubes to simulate arterial vessels (aorta, carotid artery, and coronary artery). Each vessel type is defined by design geometry of the vessel inner diameter and wall thickness. Vessel inner diameters are aorta = 30mm, carotid = 7mm, and coronary = 3mm. Vessel wall thickness are aorta = 3mm, carotid = 1.5mm, and coronary = 1mm. Each vessel type was printed in 3 different material options. Material options are user-selected from the J750 printer software graphical user interface as blood vessel wall anatomy elements in ‘compliant’, ‘slightly compliant’, and ‘rigid’ options. Three replicates of each vessel type were printed in each of the three selected material options, for a total of 27 models. The vessels were connected to a flow loop system where pressure was monitored via a pressure wire and cross-sectional area was measured with intravascular ultrasound (IVUS). Distensibility was calculated by comparing the % difference in cross-sectional area vs. pulse pressure to clinical literature values. Target clinical ranges for normal and diseased population distensibility are 10.3-44 % for the aorta, 5.1-10.1 % for carotid artery, and 0.5-6 % for coronary artery. Results Aorta test vessels had the most clinically representative distensibility when printed in user-selected ‘compliant’ and ‘slightly compliant’ material. All aorta test vessels of ‘compliant’ material (n = 3) and 2 of 3 ‘slightly compliant’ vessels evaluated were within target range. Carotid vessels were most clinically represented in distensibility when printed in ‘compliant’ and ‘slightly compliant’ material. For carotid test vessels, 2 of 3 ‘compliant’ material samples and 1 of 3 ‘slightly compliant’ material samples were within target range. Coronary arteries were most clinically represented in distensibility when printed in ‘slightly compliant’ and ‘rigid’ material. For coronary test vessels, 1 of 3 ‘slightly compliant’ materials and 3 of 3 ‘rigid’ material samples fell within target range. Conclusions This study suggests that advancements in materials and 3D printing technology introduced with the J750 Digital Anatomy 3D Printer can enable anatomical models with clinically relevant distensibility.

Design, Modeling and Control of an Enhanced Soft Pneumatic Network Actuator

Inspired by nature, soft-bodied pneumatic network actuators (PNAs) composed of compliant materials have been successfully applied in the fields of industry and daily life because of large-amplitude motion and long life span. However, compliant materials simultaneously limit the output force, challenge the dynamic modeling and impede corresponding control. In this paper, we investigate the design, modeling and control of an enhanced PNA. First, an enhanced structure is proposed to improve the output force of PNAs with features of simplification of fabrication, lightweight and compliant material retentivity. Second, a dynamic model of the enhanced PNA is constructed based on the Euler–Lagrange (EL) method. Finally, an adaptive robust controller is addressed for PNAs in presence of system uncertainties without knowledge of its bounds in prior. Experiment results show that the output force of the enhanced PNA is four times greater than the actuator without enhanced structures, which affords to theoretical estimation. Moreover, the proposed controller is utilized and compared with previous works in humanoid finger experiments to illustrate the effectiveness.

When Compliance Checks are Just the Start of the Journey: an Aviation Case

Compliance with standards is assessed through internal and external audits, the findings of which are viewed as imperfections to be quickly repaired. A zero-findings mentality underlies companies that want to excel before the eyes of the authorities, customers, insurance companies and competitors. However, scholars and professionals over the last decades agree that compliance is a necessary but not sufficient condition for optimum system performance. The current study was initiated by a Ground Service Provider that in 2017 underwent an IATA Safety Audit for Ground Operations and revealed several findings, especially in the documentation, such as missing parts, non-compliant material and lack of detail. Their goal was to pass the next audit without any findings within the documented procedures of six operational departments. To assess the audit documentation criteria, the researchers visited the operational departments, analysed 186 procedures, and conducted six semi-structured interviews with managers/supervisors and nine interviews with operational personnel. The analysis showed that all documents were properly controlled, but four departments had duplicated generic guidance material from 6% to 83% of the text checked. The interviewees claimed that understandability was not optimum due to language barriers and the non-tailoring of the content to their needs, leading to some staff disregarding manuals and consulting their supervisor instead. Other remarks included the long length of the documents, lack of knowledge of how to access online material, ignorance of the existence of documentation access points, and low technical accuracy. Overall, the results suggested room for improvement. Most importantly, through this research, the specific Ground Service Provider gained a better understanding behind non-compliance and had the opportunity to improve the quality and communication of its procedures. This study showed that even when compliance is the target, substantial improvement moves beyond box-ticking and engages employees in the revelation and mitigation of system imperfections.

A Novel Joint Design for Robotic Hands With Humanlike Nonlinear Compliance

Robotic hands are typically too rigid to react against unexpected impacts and disturbances in order to prevent damage. Human hands have great versatility and robustness due, in part, to the passive compliance at the hand joints. In this paper, we present a novel design for joint with passive compliance that is inspired by biomechanical properties of the human hands. The design consists of a compliant material and a set of pulleys that rotate and stretch the material as the joint rotates. We created six different compliant materials, and we optimized the joint design to match the desired humanlike compliance. We present two design features that allow for the tuning of the joint torque profile, namely, a pretension mechanism to increase pretension of the compliant material, and a design of varying pulley configuration. We built a prototype for the new joint by using additive manufacturing to fabricate the design components and built a test-bed with a force sensor and a servo motor. Experimental results show that the joint exhibits a nonlinear, double exponential joint compliance with all six compliant materials. The design feature involving variable pulley configurations is effective in adjusting the slope of joint torque during the joint rotation while the pretension mechanism showed only a limited effect on increasing the torque amplitude. Overall, with its small size, light weight, low friction, and humanlike joint compliance, the presented joint design is ready for implementation in robotic hands.

Regional Responses of Rat Brain to Impactor Parameters

The closed head impact (CHI) rat models are commonly used for studying the traumatic brain injury. Although various impact parameters (e.g., impact depth, velocity, and position) have been investigated by a number of researchers, little is known about the effects of the impactor shape, diameter, and material on the internal responses of the rat brain. In this work, numerical CHI experiments were conducted to investigate the sensitivities of intracranial responses to the impactor details such as impactor shape, diameter, and material. A 3D finite element rat head model with anatomical details was subjected to impact loadings. Results revealed that the impactor shape can affect the intracranial responses significantly. The effect of impactor diameter on the intracranial responses in different brain regions was uniform. In addition, careful attention should be paid when using an extremely compliant material for the impactor, since the actual impact depth might be compensated by the impactor deformation.

Biomechanical Analysis of Embryonic Atrioventricular Valvulogenesis

Heart valve development is directed by a complex interaction of molecular and mechanical cues[1]. Both molecular and mechanical based approaches are needed to clarify these relationships. Many technologies exist for the former, but the short length scale and super-compliant material properties of embryonic valve tissue make conventional mechanical testing techniques ineffective. The pipette aspiration technique has been a useful tool in cell mechanics[2] and has recently been applied to adult valve leaflets[3]. Geometric effects of thin, planar tissues however compromise the utility of aspiration based measurements. Herein, we utilize pipette aspiration and a novel uni-axial micro-tensile testing apparatus to quantify the biomechanical evolution of avian embryonic heart valves. We then relate biomechanical stiffening to changes in underlying structural composition.

Surface detection in nanoindentation of soft polymers

In this work, we performed nanoindentation studies on polymers with different moduli in the range of several millipascals up to several gigapascals. The focus was on the initial contact identification during indentation testing. Surface-detection methods using quasi-static loading as well as methods employing the dynamic forces associated with the continuous stiffness measurement technique were compared regarding their practicability and accuracy for the testing of polymeric materials. For the most compliant material with a modulus of 1 MPa, where contact identification is most critical, we used load-displacement curves obtained from finite element modeling analysis as a reference for the evaluation of experimental techniques. The results show how crucial the precise surface detection is for achieving accurate indentation results, especially for compliant materials. Further, we found that surface detection by means of dynamic testing provides mechanical-property values of higher accuracy for all polymers used in this study. This was due to smaller errors in surface detection, thus avoiding a significant underestimation of the contact area.

Processing of Non-Oxide Ceramic Matrix Composites: An Overview

Ceramic matrix composites (CMCs) comprise a fiber reinforcement embedded in a ceramic matrix, the two main constituents being bonded through an interphase, which is a thin layer of a compliant material with a low shear stress, arresting and deflecting the matrix microcracks formed under load. Non-oxide CMCs, such as C/C ; C/SiC or SiC/SiC, are fabricated from a suitable precursor of the matrix, following a gaseous (CVI-process), a liquid (PIP and RMI processes) or a slurry (SI-HPS) routes. Each of these routes is briefly depicted focusing on fundamental aspects and its advantages and drawbacks discussed. Possible extensions of the processes to new composites are suggested. Finally, a comparison of these techniques, in terms of processability and composites properties is presented.