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1. Open-source pneumatic pressure pump for drop-based microfluidic flow controls

   https://doi.org/10.1088/2631-8695/ace299  

   Sanchez, Humberto S; Chang, Connie B (July 2023, Engineering Research Express)

   Abstract An open-source pneumatic pressure pump is engineered for driving fluid flow in a microfluidic device. It is designed to be a cost-effective and customizable alternative to commercial systems. The pneumatic pressure pump utilizes a single open-source microcontroller to control four dual-valve pressure regulators. The control scheme is written in the Arduino development environment and the user interface is written in Python. The pump was used to pressurize water and a fluorinated oil that have similar viscosities. The pump can accurately control pressures to a resolution of less than 0.02 psig with rapid response times of less than one second, overshoot of desired pressures by less than 30%, and setting response times of less than two seconds. The pump was also validated in its ability to produce water-in-oil drops using a drop-making microfluidic device. The resultant drop size scaled as expected with the pressures applied to the emulsion phases. The pump is the first custom-made dual-valve regulator that is used to precisely control fluid flow in a microfluidic device. The presented design is an advancement towards making more fully open-source pneumatic pressure pumps for controlling flow in microfluidic devices. 

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2. Computational Fluid Dynamics Modeling of Material Transport Through Triply Periodic Minimal Surface Scaffolds for Bone Tissue Engineering

   https://doi.org/10.1115/1.4067575  

   Coburn, Brandon; Salary, Roozbeh “Ross” (March 2025, Journal of Biomechanical Engineering)

   Nguyen, Thao Vicky; Ethier, C Ross (Ed.)

   Abstract Cell-laden, scaffold-based tissue engineering methods have been successfully utilized for the treatment of bone fractures and diseases, caused by factors such as trauma, tumors, congenital anomalies, and aging. In such methods, the rate of scaffold biodegradation, transport of nutrients and growth factors, as well as removal of cell metabolic wastes at the site of injury are critical fluid-dynamics factors, affecting cell proliferation and ultimately tissue regeneration. Therefore, there is a critical need to identify the underlying material transport mechanisms and factors associated with cell-seeded, scaffold-based bone tissue engineering. The overarching goal of this study is to contribute to patient-specific, clinical treatment of bone pathology. The overall objective of the work is to establish computational fluid dynamics (CFD) models: (i) to identify the consequential mechanisms behind internal and external material transport through/over porous bone scaffolds designed based on the principles of triply periodic minimal surfaces (TPMS) and (ii) to identify TPMS designs with optimal geometry and flow characteristics for the treatment of bone fractures in clinical practice. In this study, advanced CFD models were established based on ten TPMS scaffold designs for (i) single-unit internal flow analysis, (ii) single-unit external flow analysis, and (iii) cubic, full-scaffold external flow analysis, where the geometry of each design was parametrically created. The influence of several design parameters, such as surface representation iteration, wall thickness, and pore size on geometry accuracy as well as computation time, was investigated in order to obtain computationally efficient and accurate CFD models. The fluid properties (such as density and dynamic viscosity) as well as the boundary conditions (such as no-slip condition, inlet flow velocity, and pressure outlet) of the CFD models were set based on clinical/research values reported in the literature, according to the fundamentals of internal and external Newtonian flow modeling. The main fluid characteristics influential in bone regeneration, including flow velocity, flow pressure, and wall shear stress (WSS), were analyzed to observe material transport internally through and externally over the TPMS scaffold designs. Regarding the single-unit internal flow analysis, it was observed that P.W. Hybrid and Neovius designs had the highest level of not only flow pressure but also WSS. This can be attributed to their relatively flat surfaces when compared to the rest of the TPMS designs. Schwarz primitive (P) appeared to have the lowest level of flow pressure and WSS (desirable for development of bone tissues) due to its relatively open channels allowing for more effortless fluid transport. An analysis of streamline velocity exhibited an increase in velocity togther with a depiction of potential turbulent motion along the curved sections of the TPMS designs. Regarding the single-unit external flow analysis, it was observed that Neovius and Diamond yielded the highest level of flow pressure and WSS, respectively, while Schwarz primitive (P) similarly had a relatively low level of flow pressure and WSS suitable for bone regeneration. Besides, pressure buildup was observed within the inner channels of almost all the TPMS designs due to flow resistance and the intrinsic interaction between the fluid flow and the scaffold walls. Regarding the cubic (full-scaffold) external flow analysis, the Diamond and Schwarz gyroid (G) designs appeared to have a relatively high level of both flow pressure and WSS, while Schwarz primitive (P) similarly yielded a low level of flow pressure and WSS. Overall, the outcomes of this study pave the way for optimal design and fabrication of complex, bone-like tissues with desired material transport properties for cell-laden, scaffold-based treatment of bone fractures. 

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3. Investigation of Material Transport Through Triply Periodic Minimal Surface (TPMS) Bone Scaffolds Using Computational Fluid Dynamics (CFD)

   https://doi.org/10.1115/MSEC2024-123878  

   Coburn, Brandon; Salary, Roozbeh “Ross” (June 2024, American Society of Mechanical Engineers (ASME))

   Abstract Cell-laden, scaffold-based tissue engineering methods have been successfully utilized for the treatment of bone fractures and diseases, caused by factors such as trauma, tumors, congenital anomalies, and aging. In such methods, the rate of scaffold biodegradation, transport of nutrients and growth factors, as well as removal of cell metabolic wastes at the site of injury are critical fluid-dynamics factors, affecting cell proliferation and ultimately tissue regeneration. Therefore, there is a critical need to identify the underlying material transport mechanisms and factors associated with cell-seeded, scaffold-based bone tissue engineering. The overarching goal of this study is to contribute to patient-specific, clinical treatment of bone pathology. The overall objective of the work is to establish computational fluid dynamics (CFD) models to identify: (i) the consequential mechanisms behind internal and external material transport through/over porous bone scaffolds and (ii) optimal triply periodic minimal surface (TPMS) scaffold designs toward cell-laden bone fracture treatment. In this study, 10 internal-flow and 10 external-flow CFD models were established using ANSYS, correspondingly based on 10 single-unit TPMS bone scaffold designs, where the geometry of each design was parametrically created using Rhinoceros 3D software. The influence of several design parameters, such as surface representation iteration, merged toggle iso value, and wall thickness, on geometry accuracy as well as computational time, was investigated in order to obtain computationally efficient and accurate CFD models. The fluid properties (such as density and dynamic viscosity) as well as the boundary conditions (such as no-slip condition, inlet flow velocity, and pressure outlet) of the CFD models were set based on clinical/research values reported in the literature as well as according to the fundamentals of internal/external Newtonian flow modeling. Several fluid characteristics, including flow velocity, flow pressure, and wall shear stress, were analyzed to observe material transport internally through and externally over the TPMS scaffold designs. Regarding the internal flow CFD modeling, it was observed that “P.W. Hybrid” (i.e., Design #7) had the highest-pressure output, with “Neovius” (i.e., Design #1) following second to it. These two designs have a relatively flatter surface area. In addition, “Schwarz P” (i.e., Design #2) was the lowest pressure output of all 10 TPMS designs. “Neovius” and “Schwarz P” had the highest and lowest values of wall shear stress. Besides, the velocity streamlines analysis showed an increase in velocity along the curved sections of the scaffolds’ geometry. Regarding the external flow CFD modeling, it was observed that “Neovius” yielded the highest-pressure output within the inlet section, which contains the area of the highest-pressure location. Furthermore, “Diamond” (i.e., Design #8) displayed having the highest values of wall shear stress due to the results of fluid interaction that accrues with complex curved structures. Also, when we look at designs like “Schwarz G”, the depiction of turbulent motion can be seen along the internal curved sections of the structure. As the external velocity streamlines decrease within the inner channels of the designs, this will lead to an increased pressure buildup due to the intrinsic interactions between the fluid with the walls. Overall, the outcomes of this study pave the way for optimal design and fabrication of complex, bone-like tissues with desired material transport properties for cell-laden, scaffold-based treatment of bone fractures. 

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4. Numerical Design, Fabrication, and Characterization of Porous Tissue Scaffolds for Bone Regeneration

   Coburn, Brandon (July 2024, Marshall Digital Scholar (https://mds.marshall.edu/etd/1910))

   With the recent advancements within biomedical engineering of bone tissue scaffolds, there is still a need to develop mechanically robust and biocompatible with low immunogenicity for bone regeneration. Additionally, the evaluation of the fluid dynamics of the porous Triply Periodic Minimal Surfaces (TPMS) bone scaffold also shows the need for investigation due to the complex fluid interaction of hemodynamics that occurs with the scaffold internal and external domains. To aid in the development of treating bone fractures, defects, and diseases. Furthermore, with the induction of a wide variety of TPMS architecture that yields different topologies, the Convolutional Neural Network (CNN) model will aid in predicting the TPMS scaffold characteristic to help develop critical design parameters. Thus, this research has observed biocompatible and mechanically strong materials with bone regeneration applications by evaluating polyamide, polyolefin, and cellulose fibers (PAPC) and SimuBone biomaterial. The TPMS scaffolds are fabricated by fused deposition modeling (FDM) additive manufacturing. Furthermore, the evaluation of fluid dynamics of internal and external effects using the computational fluid dynamics (CFD) method is used to observe the fluid interaction of the TPMS scaffold. Therefore, ANSYS (Fluent with Fluent Meshing) software captures the pressure, wall shear stress, and velocity streamline characteristics. As for the bone scaffold topology prediction, machine learning CNN is used and developed within Python to observe these properties. Accuracy, loss, validation accuracy, validation loss, and F-Score will be recorded to aid in developing the hyperparameters with the CNN platform. Therefore, the findings show that PAPC compression modulus performance observed that Neovius and Schwarz-Diamond designs have higher levels of compression strength than that of Schwarz-Primitive and Schwarz-Gyroid designs. As for SimuBone biomaterial, it was observed to be a suitable bone tissue engineering material due to its robust mechanical performance. Additionally, it is observed that the vertical orientations of P.W. Hybrid showed optimal performance with the compression analysis out of 10 different TPMS designs. It also has suitable mechanical mimicry of human trabecular bone yield strength. The evaluation of the CFD analysis of the internal and external performance of 10 TPMS scaffold designs showed that Schwarz Primitive yielded superior fluid properties. The wall shear stress was the lowest for analysis, with the external cubic evaluation showing Schwarz Primitive has a wall shear stress value of 3.4 mPa. In addition, its fluid pressure performance was suitable for improving cell viability and survival. Furthermore, the CNN evaluations displayed the optima hyperparameter for batch size, convolutional layers, dense layers, layer size, and Epoch training as 16, 6, 3, 32, and 25, respectively. A trend can be discerned within accuracy, loss, validation accuracy, validation loss, and F-Score performance, all yielding improved and consistent performance with the 5-replication analysis. Thus, this research has observed the fluid dynamics, mechanical performance, and topology evaluation of the TPMS bone scaffold. This study will aid in designing and experimenting with bone tissue engineering scaffold development. 

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5. Microfluidic Pumps with Laser Streaming from Tips of Optical Fibers and Sewing Needles

   https://doi.org/10.1002/adom.202201534  

   Tong, Tian; Yue, Shuai; Li, Runjia; Lin, Feng; Chen, Di; Xing, Xinxin; Chu, Wei‐Kan; Song, Gangbing; Liu, Dong; Wang, Zhiming; et al (October 2022, Advanced Optical Materials)

   Abstract The discovery of photoacoustic laser streaming has opened up a new avenue to manipulate and drive fluids with light, but the necessity of an in situ “launch pad” has limited its utility in real‐world microfluidic applications due to both the size constraint and the complexity of fabrication. Here, it is demonstrated that 1) a versatile microfluidic pump can be materialized by using laser streaming from an optical fiber, and 2) laser streaming can be generated from a flat metal surface without any fabrication process. In the latter case, by focusing laser on the tip of a sewing needle tip, the needle can be turned into a micropump with controllable flow direction. Additionally, high‐speed imaging of the fluid motion and computational fluid dynamics simulations to confirm the photoacoustic principle of laser streaming are employed, and it is revealed that the streaming direction is determined by the direction of strongest intensity in the divergent ultrasound wavefront. Finally, the potential of laser streaming for microfluidic and optofluidic applications is demonstrated by successfully driving fluid inside a capillary tube. 

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