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Introduction: Directing mesenchymal stem cell (MSC) chondrogenesis by bioreactor cultivation provides fundamental insight towards engineering healthy, robust articular cartilage (AC). The mechanical environment is represented by compression, fluid shear stress, hydrostatic pressure, and tension which collectively contribute to the distinct spatial organization of AC. Mimicking this cell niche is necessary for dictating cell growth, fate, and role. Researchers have shown that different mechanical stimulus types improve MSC chondrogenic commitment demonstrated by increases in key chondrogenic gene and protein markers. However, challenges remain in manufacturing spatially, anisotropic AC consisting of defined regions such as native tissue. Our strategy towards furthering this effort involves exposing MSC-laden alginate scaffolds in a multi-chambered, perfusion bioreactor with controlled fluid shear stress magnitudes to better mimic the native AC microenvironment leading to defined regions throughout the scaffold marked by varied cellular phenotypes. Validations made from assessing biochemical content, mRNA expression, western blot analysis, and cell viability will provide meaningful insight towards regulating MSC chondrogenesis. Methods: MSCs grown up to passage 4 were expanded to confluency in a T-175 flask then released from the surface using trypsin. Cells were stored in -80 ℃ freezer until experimentation. Our bioreactor system was sterilized by UV radiation for 4 hours then perfused with 70% ethanol overnight. Cell-laden scaffolds were prepared by first dissolving 1.5% alginate into deionized water. The polymeric solution was sterilely filtered and stored until usage. Cryopreserved MSCs were thawed and suspended in α-MEM medium containing essential supplements. Cells were counted and resuspended in alginate at a density of 106 cells/mL. The mixture was transferred to our multi-chambered bioreactor where they were allowed to crosslink in CaCl2 solution for 45 min. Separate scaffolds (N = 3) were molded within an identical reactor system and removed to serve as a control to compare effects of fluid shear stress on MSC differentiation. All, structures were washed with PBS then supplied with DMEM/F-12 medium containing 10% FBS, 1% penicillin/streptomycin , 1% L-glutamine, 100 nM dexamethasone, 50 µg/mL L-ascorbic acid, and10 ng/mL TGF-β3. The flowrate for the bioreactor was adjusted to 20 mL/min which provided desired fluid shear ranges of 2-87 mPa to stimulate the cells . Cell cultures were grown for 7 days, and medium changed every 3 days. Sectioned samples were analyzed for biochemical content, mRNA expression, and western blot to understand the impact of fluid shear stress magnitudes on MSC differentiation. Results: Directed fluid shear stress across a cell-laden alginate scaffold contained within an individual chamber in our bioreactor indicates varied cellular behavior within the superficial and deep regions of the construct marked by spatially secreted biochemical content as well as mRNA expression. This observation is supported by superficial MSCs stimulated by high and medium mechanical stimulation which indicates a 1.3 and 1.2-fold increase in total collagen production, respectively, when directly compared to cells deep in the construct. A similar effect is supported by total GAG secretion where high and medium shear stress across the fluid hydrogel interface yielded 1.2 and 1.3-fold upregulation of protein secretion, respectively, when observed under similar conditions. Perfused MSCs show upregulation to 3 and 20-fold for Sox9 and aggrecan, respectively, compared to a static culture. Shear ranges distributed throughout our cell-laden alginate scaffold correlates to differential chondrogenic commitment shown by variance of Sox9 expression when assessed by location and depth. Additional information on COL10A1 expression demonstrates mechanical stimulation that reduces hypertrophic cell differentiation contrary to a static culture. Discussion: In this investigation we emphasize that cells respond differently to mechanical stimulation when located in either the superficial or deep region of an alginate scaffold. This observation is supported by enhanced matrix production of chondrogenic protein for cells near the perfused fluid and hydrogel interface compared to deeper areas when stimulated by high and medium fluid shear loading regimes. Most importantly, maintenance of a healthy fluid shear gradient in our TBR provides evidence of promoting MSC chondrogenesis by spatially upregulating anabolic cartilage-like markers in addition to diminishing the onset of cell hypertrophy. Our efforts in monitoring mRNA expression of our samples reveals enhancement of chondrogenic cell differentiation for a perfused sample marked by increases in Sox9 and aggrecan genes; whereas a static sample stimulated only by TGF-β3 leads to undesirable expression of COL10A1. Key takeaways from our study support the contributions from previous researchers in recreating the native AC mechanical environment to encourage MSC differentiation. The development of our TBR system for controlled delivery of fluid shear stresses to MSCs furthers efforts in spatially guiding MSC chondrogenesis which is critical for engineering zonally differentiated AC. 

The goal of the greater project is to provide students with hands-on learning experiences while removing cost as a barrier to participation. Our Low-Cost Desktop Learning Modules (or LCDLMs) help students visualize and experience engineering concepts where books prove less than adequate and provide class members with the opportunity to learn as a group and collaborate with one another. LCDLMs have been found to improve motivation and attention while providing direct and vicarious learning opportunities, encouraging information retention in a learning environment. The goal of this paper is to introduce the latest LCDLM in development, for glucose analysis, which will mark the first LCDLM to feature a chemical reaction. In this paper we will also go over future work to be done to make the glucose analyzer viable for classroom use. The new module will feature a glucose solution meant for analysis, a set of reagents to convert the solution from transparent to a red-violet color of intensity correlated to the glucose concentration, and a simple apparatus students can use to read the concentration of the sample. The apparatus is meant to be used to teach students multiple engineering concepts through visual demonstration. In this LCDLM concept, chemicals from a set of reservoirs flow through a transparent microfluidics mixing chamber, which leads to a colorimetric reaction based on the amount of glucose present, teaching students about kinetics and, to a lesser extent, microfluidics. Dissolved oxygen is a limiting reagent, which will demonstrate to students the relevance of stoichiometry and mass transfer in a closed system. The mixture then collects in a chamber with two transparent sides. Green light passes through the red solution and into the lens of a smartphone camera to measure the intensity of the light. This is meant to demonstrate Beer’s law and complimentary colors. The more light that can pass through, the lower the glucose concentration. Students will need to measure a series of solutions with varied but known concentrations, construct a calibration curve, and then find an unknown solution concentration based on where an absorbance reading falls on the curve, modeling a routine wet lab test but without the need for expensive instrumentation. Prototyping is needed before a definitive version can be implemented in the classroom. The final design for the analyzer, how it will be assembled, parts to be used, etc., is being determined, and up-to-date results will be presented. The geometry of the mixing chamber with attached reservoirs for adding reagents must be optimized for small samples. The plan is to design a 3D model in SolidWorks and then cut out a prototype from an acrylic sheet with a laser cutter. The prototype will then be tested for leaks. The module itself will consist of the channel sheet glued between two other sheets, making assembly straightforward. 

Evaporative cooling, used in many industrial and residential applications, is a complex coupled heat and mass transfer process where fluid cooling occurs due to water vaporization and the conversion of sensible to latent heat. In this paper, the development, testing, and implementation of a small, highly visual, Low-Cost Desktop Learning Module (LCDLM) for demonstration of evaporative cooling phenomena in the undergraduate classroom will be presented. The newly developed cross-flow direct evaporative cooler module is constructed from inexpensive expanded aluminum packing media, an off-the-shelf, battery-powered computer fan, a simple water distribution system with a battery-powered pump, and clear acrylic housing. The LCDLM is operated in a non-steady-state recycle mode where a small volume of water is circulated and, depending on the water temperature, either heats or cools incoming air. Preliminary data for simple experiments that can be repeated in the classroom are presented showing the effect of varying the initial water temperature, water flow rate, and air velocity on the cooling rate and temperature profiles in the module. These variables can be easily controlled in the classroom so that students can quickly observe their effect on the performance of the evaporative cooler. Finally, we outline worksheet and conceptual assessment questions to accompany classroom activities and present conceptual assessment results from a spring 2022 pilot classroom implementation of the evaporative cooler LCDLM in a Fluid Mechanics and Heat Transfer course. Significant student learning gains were observed after implementation, suggesting a positive influence of the LCDLM on understanding. 

In this paper we report on the development and testing of hands-on desktop learning modules for transport courses in the Chemical and Mechanical Engineering disciplines. Two modules were developed to demonstrate fluid mechanics-related concepts, while two other modules were created for energy transport in heat exchangers. These devices are small, inexpensive, and made of see-through polycarbonate plastics using injection molding. These desktop learning modules are particularly suitable for use in undergraduate classrooms in conjunction with lectures to illustrate the working mechanism of devices seen in an industrial setting. Experiments are performed to understand the flow behavior and heat transfer performance on these modules. Our results show an excellent agreement for hydraulic head loss, volumetric flow rates, and overall heat transfer coefficients between experimental data and the corresponding theory, justifying the design and use of these devices in the classroom. Furthermore, we have measured student learning gains through pre-and posttests for each module based on in-class implementations at different universities. Assessment of student learning outcomes shows significant improvement in conceptual understanding when these modules are used in the undergraduate class. 

Our team has developed Low-Cost Desktop Learning Modules (LCDLMS) as tools to study transport phenomena aimed at providing hands-on learning experiences. With an implementation design embedded in the community of inquiry framework, we disseminate units to professors across the country and train them on how to facilitate teacher presence in the classroom with the LC-DLMs. Professors are briefed on how create a homogenous learning environment for students based on best-practices using the LC-DLMs. By collecting student cognitive gain data using pre/posttests before and after students encounter the LC-DLMs, we aim to isolate the variable of the professor on the implementation with LC-DLMs. Because of the onset of COVID-19, we have modalities for both hands-on and virtual implementation data. An ANOVA whereby modality was grouped and professor effect was the independent variable had significance on the score difference in pre/posttest scores (p<0.0001) and on posttest score only (p=0.0004). When we divide out modality between hands-on and virtual, an ANOVA with an F- test using modality as the independent variable and professor effect as the nesting variable also show significance on the score difference between pre and posttests (p-value=0.0236 for hands- on, and p-value=0.0004 for virtual) and on the posttest score only (p-value=0.0314 for hands-on, and p-value<0.0001 for virtual). These results indicate that in all modalities professor had an effect on student cognitive gains with respect to differences in pre/posttest score and posttest score only. Future will focus on qualitative analysis of features of classrooms yield high cognitive gains in undergraduate engineering students. 

As this NSF LCDLM dissemination, development, and assessment project matures going into our fourth year of support we are moving forward in parallel on several fronts. We are developing and testing an injection-molded shell-and-tube heat exchanger for heat transfer concepts, an evaporative cooler to expand to another industrial-based heat exchange system, and a bead separation module to demonstrate principles of fluid mechanics in blood cell separations applications. We are also comparing experimental data for our miniaturized hydraulic loss and venturi meter LCDLMs to predicted values based on standard industrial correlations. As we develop these new learning components, we are assessing differential gains based on gender and ethnicity, as well as how students learn with existing LCDLMs in a virtual mode with online videos compared to an in-person hands-on mode of instruction.