Simulation Optimization for Computer Models With Multivariate Output

This paper explores the potential of Gaussian process based Metamodels for simulation optimization with multivariate outputs. Specifically we focus on Multivariate Gaussian process models established through separable and non-separable covariance structures. We discuss the advantages and drawbacks of each approach and their potential applicability in manufacturing systems. The advantageous features of the Multivariate Gaussian process models are then demonstrated in a case study for the optimization of manufacturing performance metrics.

A Methodology for Quantifying Cell Density and Distribution in Multidimensional Bioprinted Gelatin-Alginate Constructs

Bioprinted tissue constructs are enabled by microextrusion-based co-printing of cells and hydrogel materials. In this paper, a gelatin-alginate hydrogel material formulation is implemented as the bio-ink towards a 3D cell-laden tissue construct. However, of fundamental importance during the printing process is the interplay between the various parameters that yield the final cell distribution and cell density at different dimensional scales. To investigate these effects, this study advances a multidimensional analytical framework to determine the spatial variations and temporal evolution of cell distribution and cell density within a bioprinted cell-laden construct. In the one dimensional (1D) analysis, the cell distribution and cross-sectional shape for a single printed fiber are observed to be dependent on the process temperature and material concentration parameters. This is illustrated by the reliable fabrication and image line profile analysis of the fiber prints. Round fiber prints with a measured width of 809.5±52.3 μm maintain dispersive cells with a degree of dispersion (Dd) at 96.8 % that can be achieved at high relative material viscosities under low temperature conditions (21 °C) or high material concentrations (10 % w/v gelatin). On the other hand, flat fiber prints with a measured width of 1102.2±63.6 μm coalesce cells towards the fiber midline with Dd = 76.3% that can be fabricated at low relative material viscosities under high temperature (24 °C) or low material concentrations (7.5 % w/v gelatin). In the 2D analysis, a printed grid structure yields differential cell distribution whereby differences in localized cell densities are observed between the strut and cross regions within the printed structure. At low relative viscosities, cells aggregate at the cross regions where two overlapping filaments fuse together, yielding a cell density ratio of 2.06±0.44 between the cross region and strut region. However, at high relative viscosities, the cell density ratio decreases to 0.96±0.03. In the 3D analysis, the cell density attributed to the different layers is studied as a function of printing time elapsed from the initial bio-ink formulation. Due to identifiable gravity and extrusion process-induced effects, the cell distribution within the original bio-ink cartridge or material reservoir is altered over time to yield initial quantitative increases in the cell density over the first several printed layers, followed by quantitative decreases in the subsequent printed layers. Finally, in the time-dependent analysis, the evolution of cell density and the emergence of material degradation effects is studied over a time course study. Variable initial cell densities (0.6 × 106 cells/ml, 1.0 × 106 cells/ml, and acellular control group) printed and cross-linked into cell-laden constructs for the 48 hr time course study exhibit a time-dependent increase in cell density owing to proliferation within the constructs that are presumed to accelerate the degradation rate.

Effect of Needle Diameter on Scaffold Morphology and Strength in E-Jetted Polycaprolactone Scaffolds

Electro-hydrodynamic Jetting or E-Jetting is a process in which a polymer, dissolved in a solvent and extruded through a needle onto a substrate. A potential difference is applied between the needle and the substrate to facilitate the homogeneous extrusion of the fiber. This process is used to fabricate two dimensional scaffolds with porous mesh surfaces which act as a template for cell growth. As cells are very minute and are required to attach to the surface of the scaffold, it is essential to for the scaffold to have an adequate pore size that allows for nutrient transfer while preventing the penetration of cells through the scaffold. The fiber dimensions of the scaffold may be modified by varying the diameter of the needle through which the fiber is extruded. The change in fiber diameter subsequently results in the change in the bulk mechanical characteristics of the scaffold. It also causes a change in the net porosity of the scaffold. This paper aims to study the effect of the needle diameter on the bulk mechanical properties of the scaffold such as Young’s modulus, Tensile strength and Breaking Strength as well as morphological properties (porosity and pore size) of the Scaffolds are dependent on the cell type, as each type of cell has a different set of requirements depending on the functionality. Bone cells are smaller than soft tissue cells, hence a common scaffold design may not be suit either of the applications. Thus, a one size fits all approach is not suitable for the scaffold [9]. As seen in Figure 1, the Red Blood Cells are a fraction of the size of the fibroblasts and bone marrow stem cells [20–22]. Similarly, the stiffness of the cells is also different. Electro Hydrodynamic Jetting (E-jetting) is a process that is used to fabricate such 2D scaffolds by extruding a polymer solution through a needle and forming a fiber by applying a scaffold. For this study, twelve scaffolds belonging to three study groups were synthesized using e-jetting. By studying the effect of needle diameter on scaffold morphology and strength, we aim to develop a co-relation between the scaffold parameters, which will ultimately help in the creation of a knowledge database. The purpose of creating this database is to choose a select needle for a selected biomedical application.

An Experimental Method of Needle Deflection and Prostate Movement Using the Anatomically Accurate Prostate Simulator and the Electromagnetic Tracking System

This study develops an experimental method to measure the needle deflection and prostate movement using an anatomically accurate prostate simulator with the electromagnetic tracking (EMT) system. Accurate needle insertion is crucial for prostate biopsy to acquire the tissue samples from cancer sites identified by magnetic resonance imaging. False negatives or inability to diagnose are the clinical challenges in the biopsy procedure. The main cause is that the needle tip missed the targeted cancer sites due to needle deflection and prostate movement. An anatomically accurate prostate simulator was developed to quantitatively and experimentally measure the deviation of needle tip from the ideal path and the movement of a target point in the prostate. The EMT system was utilized to simultaneously track the needle tip and target point positions in 3D space. Results show that the maximal needle deflection occurred at the first 60-mm insertion with 6.7 and 0.7 mm in and perpendicular to the needle insertion plane, respectively. The corresponding target point movements were 6.5 mm and 2.4 mm in and perpendicular to the needle insertion plane, respectively. Differences between multiple insertions through the same path have also been quantified. This method can be utilized to study clinical prostate biopsy techniques, evaluate the accuracy of needle devices, and train clinicians for accurate prostate needle biopsy.

Flexible Job-Shop Scheduling for Reduced Manufacturing Carbon Footprint

In order to help manufacturing companies quantify and reduce product carbon footprints in a mixed model manufacturing system, a product carbon footprint oriented multi-objective flexible job-shop scheduling optimization model is proposed. The production portion of the product carbon footprint, based on the mapping relations between products and the carbon emissions within the manufacturing system, is proposed to calculate the product carbon footprint in the mixed model manufacturing system. Non-Dominated Sorting Genetic Algorithm-II (NSGA-II) is adopted to solve the proposed model. In order to help decision makers to choose the most suitable solution from the Pareto set as its execution solution, a method based on grades of product carbon footprints is proposed. Finally, the efficacy of the proposed model and algorithm are examined via a case study.

A Desktop Application for Sustainability Performance Assessment of Composed Unit-Based Manufacturing Systems

Life cycle assessment software packages such as SimaPro, GaBi, and Umberto have become well-established tools for conducting environmental impact analysis. However, applications for broader sustainability assessment are limited. Recent research has developed an information modeling framework to compose models of unit manufacturing processes for sustainability assessment and has led to the definition of unit manufacturing process information modeling concepts. An engineer can use the framework to conduct manufacturing system-level sustainability assessments by composing models of unit manufacturing processes. Assessment results can aid engineers in selecting the superior manufacturing process flow for a given product. To demonstrate usefulness of the information framework, a prototype desktop application has been developed. The application was implemented in Windows Project Foundation (WPF) using C# as the coding language to create a graphical user interface. Mathworks MATLAB serves as the calculation engine. Unit manufacturing process models follow the framework and are read by the application, which produces a sustainability assessment for the manufacturing process flow. A manufacturing process flow for an automobile-like metal product acts is used to demonstrate the software application.

Manufacturing and Computational Fluid Dynamics Modeling of a Patient-Specific Fistula Model

Arteriovenous fistula is the joining of an artery to a vein to create vascular access for dialysis. The failure or maturation of fistula is affected by the vessel wall shear stress (WSS), which is difficult to measure in clinic. A computational fluid dynamics (CFD) model was built to estimate WSS of a patient-specific fistula model. To validate this model, a silicone phantom was manufactured and used to carry out a particle imaging velocimetry (PIV) experiment. The flow field from the PIV experiment shows a good agreement with the CFD model. From the CFD model, the highest WSS (40 Pa) happens near the anastomosis. WSS in the vein is larger than that in the artery. WSS on the outer venous wall is larger than that on the inner wall. The combined technique of additive manufacturing, silicone molding, and CFD is an effective tool to understand the maturation mechanism of a fistula.

Nonlinear Parameter Estimation in a Typical Industrial Air Handler Unit

The energy usage inside of a manufacturing plant is mainly from two sources: energy demand from the production lines to support manufacturing processes, and the plant building temperature control to maintain a comfortable working environment. It is reported that in the US, 14% of the primary energy and 32% of electricity is used by the industry and commercial building heating, ventilation and air conditioning (HVAC) system. As an important part of the HVAC system, the air handler unit (AHU) is a comprehensive air control system consisting of multiple sub-units. Accurate modeling of the supply air temperature of AHU is important for later controller design and fault detection, but it is also challenging because of the application of variable frequency drive (VFD) systems, overall degradation, and limited sensor information and meter data. Parameter estimation of the industry AHU is therefore worth studying. In this study, the authors intend to establish a deterministic physical model of AHU system, identify the unknown parameters based on the limited meter inputs, and compare the nonlinear parameter estimation results with the design parameters, in order to achieve the goal of improving the modeling accuracy without installing expensive metering systems.

Patterned Microstructure Array Fabrication by Using a Novel Standing Surface Acoustic Wave Device

This paper develops a novel standing surface acoustic wave (SAW) device with three-pair of interdigital transducers (IDTs) to fabricate the patterned microstructure arrays with the assistance of ultraviolet (UV) polymerization. The working principle, structural design, and fabrication of the SAW device are presented. Then experimental setup was conducted to investigate the fabrication process and method of the patterned microstructure arrays on a thin liquid polymer surface. By adjusting the input wavelength and working voltage and selecting the pairs of IDTs, several types of patterned microstructure arrays, such as linear undulate and latticed undulate with different surface morphologies, could be fabricated. Results also demonstrated that the developed SAW device with the assistance of UV polymerization is an effective method to fabricate the patterned microstructure arrays, which may have great potential in the application of biomedical and microelectronic fields.

Bingham Fluid-Assisted Fabrication of 3D Vascular-Like Constructs of Interpenetrating Network Hydrogel

Organ printing, which utilizes advanced manufacturing technologies to fabricate three-dimensional (3D) functional organs based on layer-by-layer mechanism, is emerging as a promising solution to solve the organ donor shortage problem affecting all over the world. One of the biggest challenges for fabrication of functional and effective thick tissues/organs is the engineering of vascular networks. This paper introduces a Bingham fluid (Carbopol gel) to assist fabrication of 3D vascular-like constructs of interpenetrating network (IPN) hydrogels. Carbopol gel as a Bingham fluid exhibits a characteristic yield stress behavior. As the nozzle moves inside Carbopol, the shear stress is larger than the yield stress and the Carbopol gel behaves like a viscous fluid with a specific viscosity. After the nozzle moves away, the shear stress decreases below the yield stress and the Carbopol gel rapidly solidifies behaving like a solid. This unique rheological property is utilized to support and maintain the shape of the fabricated 3D structures, although the fluid printed is not crosslinked. Finally, the fabricated structures are subject to a two-step gelation process to successfully form 3D vascular-like constructs of IPN hydrogels. This novel approach enables effective and efficient fabrication of complex vascular network of IPN hydrogels.