A pulsatile flow system to engineer aneurysm and atherosclerosis mimetic extracellular matrix

Alterations of blood flow patterns strongly correlate with arterial wall diseases such as atherosclerosis and aneurysm. Here, a simple, pumpless, close-loop, easy-to-replicate, and miniaturized flow device is introduced to concurrently expose 3D engineered vascular smooth muscle tissues to high-velocity pulsatile flow versus low-velocity disturbed flow conditions. Two flow regimes are distinguished, one that promotes elastin and impairs collagen I assembly, while the other impairs elastin and promotes collagen assembly. This latter extracellular matrix (ECM) composition shares characteristics with aneurysmal or atherosclerotic tissue phenotypes, thus recapitulating crucial hallmarks of flow-induced tissue morphogenesis in vessel walls. It is shown that the mRNA levels of ECM of collagens and elastin are not affected by the differential flow conditions. Instead, the differential gene expression of matrix metalloproteinase (MMP) and their inhibitors (TIMPs) is flow-dependent, and thus drives the alterations in ECM composition. In further support, treatment with doxycycline, an MMP inhibitor and a clinically used drug to treat vascular diseases, halts the effect of low-velocity flow on the ECM remodeling. This illustrates how the platform can be exploited for drug efficacy studies by providing crucial mechanistic insights into how different therapeutic interventions may affect tissue growth and ECM assembly

Scalable magnetically enhanced transport mechanisms of living microrobots for cancer therapy

Despite advances in nanomedicine and immunotherapy that have led to substantial improvements in cancer therapy, effective drug delivery remains a major hurdle for successful long-term treatment. Cell-based delivery systems that exhibit tumor tropism like bacteria have been proposed as therapeutic agents capable of addressing persisting challenges such as off-target effects and insufficient drug distribution inside the tumor. The benefits offered by the intrinsic properties of these living therapeutics can be further enhanced by application of external forces. The human body is transparent to magnetic fields, making this external source of energy an especially promising means for remote manipulation of the cell-based systems in vivo. Intrinsically magnetically responsive bacteria, also referred as magnetotactic bacteria (MTB), present a unique opportunity for combining both innate and external tumor targeting strategies within a single drug delivery platform. This thesis investigates magnetically assisted transport mechanisms to improve tumor drug delivery by using MTB as a model organism. Rotating magnetic fields (RMF) are chosen as the primary stimulus for magnetic actuation due to the scalability of magnetic torque-based techniques for clinical applications. Starting with remote micro manipulation of bacteria, ferrohydrodynamic phenomena associated with dense suspensions of MTB are studied experimentally and computationally, conceptualizing them as a living ferrofluid. Benchmarking against a synthetic ferrofluid composed of a suspension of iron oxide nanoparticles (IONPs) revealed that the MTB suspensions exhibit an increase of more than two orders of magnitude in flow generated per gram of magnetic material. Detailed comparison of the MTB and IONPs further support the use of bacteria as efficient flow mediators, converting the magnetic energy into a more homogeneous torque-driven fluid motion. After identifying MTB as promising torque actuators, the torque-driven transport mechanisms behind their capacity to overcome biological barriers are elucidated through the establishment of computational and in vitro models. Enhanced surface exploration is shown to increase the likelihood of translocation in the presence of dynamic gaps observed in physiological barriers. Microfluidic devices incorporating collagen gels and endothelialized channels were fabricated as physiologically relevant models for identifying suitable actuation parameters. In agreement with the results of these test platforms, a subsequent in vivo study demonstrates enhanced delivery of MTB through actuation with RMF. As a crucial step towards targeted actuation at larger scales, a scheme for spatially selective manipulation of MTB is identified based on application of a static gating field to suppress the magnetic torque in off-target areas. The application of a selection field at small scales is shown to localize the influence of actuation to the target, leaving off-target areas nearly unaffected. Lastly, the scalability of this actuation scheme is demonstrated by steps taken to design and build a mouse scale setup for in vivo studies. The multi-component setup can generate an RMF of up to 20 mT and a field free region (FFR) with an average 1 cm resolution that can be moved in space by addition of the offset fields. The thesis concludes with a summary and remarks on future in vivo studies enabled by the development of a mouse scale setup. Potential extensions of the findings to other magnetically responsive cell-based systems are also discussed

Thermo-economic analysis of transcritical CO2 cycles with bounded and unbounded reheats in low-temperature heat recovery applications

Performance of transcritical CO2 Rankine cycles with and without reheat process is investigated thermo-economically in low-grade waste heat recovery applications. Two reheating scenarios are proposed to evaluate the effect of bounded and unbounded reheats on the cycle. In the first method, the constant available heat flow is distributed between the evaporator and the reheater via an optimized ratio, while in the second, the required energy for the reheat process is provided with optimized additional fuel consumption. The proposed cycles are modeled and optimized for source temperatures ranging from 150 to 300 degrees C at fixed flow rate of 1000 kg/s. The results obtained from thermodynamic optimization indicate that reheat cycle with burning additional fuel leads to the largest power generations ranging from 14 to 57 MW depending on the source temperature, while the reheat cycle with heat stream division shows the weakest performance by producing 8-37 MW. In the thermo-economic optimization, the ratio of power output to the cycle total bare module cost has been maximized. Under these conditions, the reheat cycle with burners still shows the highest rate of power production, while economic indicators limit the power generation and introduce the simple Rankine cycle as the best option. (C) 2017 Elsevier Ltd. All rights reserved

Engineering Cell-Based Systems for Smart Cancer Therapy

Due to the difficulty of targeting systemically delivered therapeutics for cancer, interest has grown in exploiting biological agents to enhance tumor accumulation and mediate localized drug delivery. Equipped with onboard sensing and active motility, some cells respond to specific cues of the tumor microenvironment, making them ideal candidates for smart cancer therapy. Herein, recent progress and developments are presented on the use of four of the most promising cell-based systems for tumor targeting and drug delivery-immune cells, stem cells, platelets, and bacteria. Strategies to further enhance specificity at the tissue and cell level are discussed, including genetic engineering, chemical cell surface modification, and the use of external physical stimuli. With crucial ongoing efforts addressing the safety and efficacy of living intelligent therapeutics, a new era of cancer medicine is on the horizon.ISSN:2640-456

A theoretical examination of localized nanoscale induction by single domain magnetic particles

Single domain magnetic nanoparticles are increasingly investigated as actuators of biological and chemical processes that respond to externally applied magnetic fields. Although their localized effects have often been attributed to nanoscale heating, recent experimental evidence suggests the need to consider alternative hypotheses. Here, using the stochastic Landau-Lifshitz-Gilbert equation and finite element modeling, we investigate and critically examine an alternative hypothesis that localized effects may instead involve the induced electric fields arising from the dynamical behavior of individual single domain magnetic particles. We model the magnetization dynamics and resulting induced electric fields for two relevant and distinct cases of magnetic nanoparticles in alternating magnetic fields: (1) magnetogenetic stimulation of channel proteins associated with ferritin and (2) catalytic enhancement of electrochemical hydrolysis. For the first case, while the local electric fields that ferritin generates are shown to be insufficient to perturb the transmembrane potential, fields on the surface of its mineral core on the order of 10 2-10 3 V/m may play a more plausible role in mass transport of iron ions that indirectly lead to stimulation. For the second case, our model indicates that the highest interfacial electric field strengths, on the order of 10 2 V/m, are expected during reversal events. Thus, nanoparticles well suited for hysteresis heating can also act as intermittent sources of localized induced electric fields in response to an alternating applied field. Finally, we compare the magnitude and timescale of these electric fields to technologically relevant phenomena, showing that they are generally weaker and faster.ISSN:0021-8979ISSN:1089-755

Spatially selective delivery of living magnetic microrobots through torque-focusing

Rotating magnetic fields enable biomedical microrobots to overcome physiological barriers and promote extravasation and accumulation in tumors. Nevertheless, targeting deeply situated tumors requires suppression of off-target actuation in healthy tissue. Here, we investigate a control strategy for applying spatially selective torque density to microrobots by combining rotating fields with magnetostatic selection fields. Taking magnetotactic bacteria as diffuse torque-based actuators, we numerically model off-target torque suppression, indicating the feasibility of centimeter to millimeter resolution for human applications. We study focal torque application in vitro, observing off-target suppression of actuation-dependent effects such as colonization of bacteria in tumor spheroids. We then design and construct a mouse-scale torque-focusing apparatus capable of maneuvering the focal point. Applying this system to a mouse tumor model increased accumulation of intravenously injected bacteria within tumors receiving focused actuation compared to non-actuated or globally actuated groups. This control scheme combines the advantages of torque-based actuation with spatial targeting.ISSN:2041-172

3D magnetically controlled spatiotemporal probing and actuation of collagen networks from a single cell perspective

Cells continuously sense and react to mechanical cues from their surrounding matrix, which consists of a fibrous network of biopolymers that influences their fate and behavior. Several powerful methods employing magnetic control have been developed to assess the micromechanical properties within extracellular matrix (ECM) models hosting cells. However, many of these are limited to in-plane sensing and actuation, which does not allow the matrix to be probed within its full 3D context. Moreover, little attention has been given to factors specific to the model ECM systems that can profoundly influence the cells contained there. Here we present methods to spatiotemporally probe and manipulate extracellular matrix networks at the scale relevant to cells using magnetic microprobes (mu Rods). Our techniques leverage 3D magnetic field generation, physical modeling, and image analysis to examine and apply mechanical stimuli to fibrous collagen matrices. We determined shear moduli ranging between hundreds of Pa to tens of kPa and modeled the effects of proximity to rigid surfaces and local fiber densification. We analyzed the spatial extent and dynamics of matrix deformation produced in response to magnetic torques on the order of 10 pNm, deflecting fibers over an area spanning tens of micrometers. Finally, we demonstrate 3D actuation and pose extraction of fluorescently labelled mu Rods.ISSN:1473-0197ISSN:1473-018

Engineering Living Immunotherapeutic Agents for Improved Cancer Treatment

Bacteria-based agents are emerging as promising tools for cancer therapy due to their ability to actively target tumors, trigger localized inflammation, and induce tumor regression. There has been growing interest in using bacteria that are responsive to external cues, such as magnetic fields, to facilitate the formation of robust colonies in tumors and achieve the threshold for clinical efficacy. Several studies have demonstrated the potential of innately magnetically responsive bacteria, known as magnetotactic bacteria (MTB), as steerable agents. However, their immunostimulatory properties, which play a central role in their function as therapeutic agents, have not yet been adequately studied. Here, key aspects of human immune cell response to MTB strain Magnetospirillum magneticum AMB-1 in physiological environments are characterized. The ability of MTB to maintain magnetic properties, remain viable in whole blood, elicit cytokine production by macrophages, and stimulate uptake of cancer cell material by dendritic cells is examined. This study also investigates the use of MTB-liposome complexes for effective delivery of therapeutic payloads in vitro and explores response to the agent in vivo. Overall, this work establishes the potential of MTB as a versatile, combined delivery platform for immune-mediated cancer therapy.ISSN:2366-398

A Pulsatile Flow System to Engineer Aneurysm and Atherosclerosis Mimetic Extracellular Matrix

Alterations of blood flow patterns strongly correlate with arterial wall diseases such as atherosclerosis and aneurysm. Here, a simple, pumpless, close‐loop, easy‐to‐replicate, and miniaturized flow device is introduced to concurrently expose 3D engineered vascular smooth muscle tissues to high‐velocity pulsatile flow versus low‐velocity disturbed flow conditions. Two flow regimes are distinguished, one that promotes elastin and impairs collagen I assembly, while the other impairs elastin and promotes collagen assembly. This latter extracellular matrix (ECM) composition shares characteristics with aneurysmal or atherosclerotic tissue phenotypes, thus recapitulating crucial hallmarks of flow‐induced tissue morphogenesis in vessel walls. It is shown that the mRNA levels of ECM of collagens and elastin are not affected by the differential flow conditions. Instead, the differential gene expression of matrix metalloproteinase (MMP) and their inhibitors (TIMPs) is flow‐dependent, and thus drives the alterations in ECM composition. In further support, treatment with doxycycline, an MMP inhibitor and a clinically used drug to treat vascular diseases, halts the effect of low‐velocity flow on the ECM remodeling. This illustrates how the platform can be exploited for drug efficacy studies by providing crucial mechanistic insights into how different therapeutic interventions may affect tissue growth and ECM assembly.ISSN:2198-384