Factors Affecting the Evaluation of Collagen Deposition and Fibrosis In Vitro

Immune responses to biomedical implants, wound healing, and diseased tissues often involve collagen deposition by fibroblasts and other stromal cells. Dysregulated collagen deposition can lead to complications, such as biomaterial fibrosis, cardiac fibrosis, desmoplasia, liver fibrosis, and pulmonary fibrosis, which can ultimately result in losses of organ function or failure of biomedical implants. Current in vitro methods to induce collagen deposition include growing the cells under macromolecular crowding conditions or on fibronectin-coated surfaces. However, the majority of these methods have been demonstrated with a single cell line, and the combined impacts of culture conditions and postculture processing on collagen deposition have not been explored in detail. In this work, the effects of macromolecular crowding versus fibronectin coating, fixation with methanol versus fixation with paraformaldehyde, and use of plastic substrates versus glass substrates were evaluated using the WI-38 human lung fibroblast cell line. Fibronectin coating was found to provide enhanced collagen deposition under macromolecular crowding conditions, while a higher plating density led to improved collagen I deposition compared with macromolecular crowding. Collagen deposition was found to be more apparent on plastic substrates than on glass substrates. The effects of primary cells versus cell lines, and mouse cells versus human cells, were evaluated using WI-38 cells, primary human lung fibroblasts, primary human dermal fibroblasts, primary mouse lung fibroblasts, primary mouse dermal fibroblasts, and the L929 mouse fibroblast cell line. Cell lines exhibited enhanced collagen I deposition compared with primary cells. Furthermore, collagen deposition was quantified with picrosirius red staining, and plate-based drug screening through picrosirius red staining of decellularized extracellular matrices was demonstrated. The results of this study provide detailed conditions under which collagen deposition can be induced in vitro in multiple cell types, with applications including material development, development of potential antifibrotic therapies, and mechanistic investigation of disease pathways. Impact Statement This study demonstrated the effects of cell type, biological conditions, fixative, culture substrate, and staining method on in vitro collagen deposition and visualization. Further the utility of plate-based picrosirius red staining of decellularized extracellular matrices for drug screening through collagen quantification was demonstrated. These results should provide clarity and a path forward for researchers who aim to conduct in vitro experiments on collagen deposition.

Pro-regenerative biomaterials recruit immunoregulatory dendritic cells after traumatic injury

During wound healing and surgical implantation, the body establishes a delicate balance between immune activation to fight off infection and clear debris and immune tolerance to control reactivity against self-tissue. Nonetheless, how such a balance is achieved is not well understood. Here we describe that pro-regenerative biomaterials for muscle injury treatment promote the proliferation of a BATF3-dependent CD103+XCR1+CD206+CD301b+ dendritic cell population associated with cross-presentation and self-tolerance. Upregulation of E-cadherin, the ligand for CD103, and XCL-1 in injured tissue suggests a mechanism for cell recruitment to trauma. Muscle injury recruited natural killer cells that produced Xcl1 when stimulated with fragmented extracellular matrix. Without cross-presenting cells, T-cell activation increases, pro-regenerative macrophage polarization decreases and there are alterations in myogenesis, adipogenesis, fibrosis and increased muscle calcification. These results, previously observed in cancer progression, suggest a fundamental mechanism of immune regulation in trauma and material implantation with implications for both short- and long-term injury recovery.

Dynamics of SARS-CoV-2 Seroprevalence in a Large US population Over a Period of 12 Months

Due to a combination of asymptomatic or undiagnosed infections, the proportion of the United States population infected with SARS-CoV-2 was unclear from the beginning of the pandemic. We previously established a platform to screen for SARS-CoV-2 positivity across a representative proportion of the US population, from which we reported that almost 17 million Americans were estimated to have had undocumented infections in the Spring of 2020. Since then, vaccine rollout and prevalence of different SARS-CoV-2 variants have further altered seropositivity trends within the United States population. To explore the longitudinal impacts of the pandemic and vaccine responses on seropositivity, we re-enrolled participants from our baseline study in a 6- and 12- month follow-up study to develop a longitudinal antibody profile capable of representing seropositivity within the United States during a critical period just prior to and during the initiation of vaccine rollout. Initial measurements showed that, since July 2020, seropositivity elevated within this population from 4.8% at baseline to 36.2% and 89.3% at 6 and 12 months, respectively. We also evaluated nucleocapsid seropositivity and compared to spike seropositivity to identify trends in infection versus vaccination relative to baseline. These data serve as a window into a critical timeframe within the COVID-19 pandemic response and serve as a resource that could be used in subsequent respiratory illness outbreaks.

In Situ Surface-Directed Assembly of 2D Metal Nanoplatelets for Drug-Free Treatment of Antibiotic-Resistant Bacteria

The development of antibiotic resistance among bacterial strains is a major global public health concern. To address this, drug-free antibacterial approaches are needed. Copper surfaces have long been known for their antibacterial properties. In this work, a one-step surface modification technique is used to assemble 2D copper chloride nanoplatelets directly onto copper surfaces such as copper tape, transmission electron microscopy (TEM) grids, electrodes, and granules. The nanoplatelets are formed using copper ions from the copper surfaces, enabling their direct assembly onto these surfaces in a one-step process that does not require separate nanoparticle synthesis. The synthesis of the nanoplatelets is confirmed with TEM, scanning electron microscopy, energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). Antibacterial properties of the Cu nanoplatelets are demonstrated in multidrug-resistant (MDR) Escherichia coli, MDR Acinetobacter baumannii, MDR Staphylococcus aureus, E. coli, and Streptococcus mutans. Nanoplatelets lead to a marked improvement in antibacterial properties compared to the copper surfaces alone, affecting bacterial cell morphology, preventing bacterial cell division, reducing their viability, damaging bacterial DNA, and altering protein expression. This work presents a robust method to directly assemble copper nanoplatelets onto any copper surface to imbue it with improved antibacterial properties.

Fabrication and Use of a Pumpless Microfluidic Lymphatic Vessel Chip

Pumpless microfluidic systems are easy-to-use devices that can be used to culture cells that are sensitive to mechanical shear, such as lymphatic endothelial cells. However, previously developed pumpless systems either provide unidirectional shear where the cell culture medium is discarded, or bidirectional shear that produces endothelial cell cultures with disease characteristics. Here, we describe a PDMS-based system that produces cyclically rising and falling shear that is unidirectional, similar to what has been reported in lymphatic vessels. The system can recirculate cell culture medium, making it possible for proteins and growth factors produced by the cell culture to remain in circulation. In addition, we describe the custom-made rotating platform that we used to create this unique flow pattern. Using this rotating platform, the microfluidic device can be used to grow confluent layers of lymphatic endothelial cells under physiologically relevant growth conditions.

Rational Design of Surface-State Controlled Multicolor Cross-Linked Carbon Dots with Distinct Photoluminescence and Cellular Uptake Properties

We disclose for the first time a facile synthetic methodology for the preparation of multicolor carbon dots (CDs) from a single source barring any chromatographic separations. This was achieved via sequential intraparticle cross-linking of surface abundant carboxylic acid groups on the CDs synthesized from a precursor to control their photoluminescence (PL) spectra as well as affect their degree of cellular internalization in cancer cells. The change in PL spectra with sequential cross-linking was projected by theoretical density functional theory (DFT) studies and validated by multiple characterization tools such as X-ray photoelectron spectroscopy (XPS), PL spectroscopy, ninhydrin assay, etc. The variation in cellular internalization of these cross-linked CDs was demonstrated using inhibitor assays, confocal microscopy, and flow cytometry. We supplemented our findings with high-resolution dark-field imaging to visualize and confirm the colocalization of these CDs into distinct intracellular compartments. Finally, to prove the surface-state controlled PL mechanisms of these cross-linked CDs, we fabricated a triple-channel sensor array for the identification of different analytes including metal ions and biologically relevant proteins.

Mobilizing Endogenous Repair Through Understanding Immune Reaction With Biomaterials

With few exceptions, humans are incapable of fully recovering from severe physical trauma. Due to these limitations, the field of regenerative medicine seeks to find clinically viable ways to repair permanently damaged tissue. There are two main approaches to regenerative medicine: promoting endogenous repair of the wound, or transplanting a material to replace the injured tissue. In recent years, these two methods have fused with the development of biomaterials that act as a scaffold and mobilize the body's natural healing capabilities. This process involves not only promoting stem cell behavior, but by also inducing activity of the immune system. Through understanding the immune interactions with biomaterials, we can understand how the immune system participates in regeneration and wound healing. In this review, we will focus on biomaterials that promote endogenous tissue repair, with discussion on their interactions with the immune system.

Critical Considerations for the Design of Multi-Organ Microphysiological Systems (MPS)

Identification and approval of new drugs for use in patients requires extensive preclinical studies and clinical trials. Preclinical studies rely on in vitro experiments and animal models of human diseases. The transferability of drug toxicity and efficacy estimates to humans from animal models is being called into question. Subsequent clinical studies often reveal lower than expected efficacy and higher drug toxicity in humans than that seen in animal models. Microphysiological systems (MPS), sometimes called organ or human-on-chip models, present a potential alternative to animal-based models used for drug toxicity screening. This review discusses multi-organ MPS that can be used to model diseases and test the efficacy and safety of drug candidates. The translation of an in vivo environment to an in vitro system requires physiologically relevant organ scaling, vascular dimensions, and appropriate flow rates. Even small changes in those parameters can alter the outcome of experiments conducted with MPS. With many MPS devices being developed, we have outlined some established standards for designing MPS devices and described techniques to validate the devices. A physiologically realistic mimic of the human body can help determine the dose response and toxicity effects of a new drug candidate with higher predictive power.

Near-infrared emitting dual-stimuli-responsive carbon dots from endogenous bile pigments

Carbon dots are biocompatible nanoparticles suitable for a variety of biomedical applications. Careful selection of carbon dot precursors and surface modification techniques has allowed for the development of carbon dots with strong near-infrared fluorescence emission. However, carbon dots that provide strong fluorescence contrast would prove even more useful if they were also responsive to stimuli. In this work, endogenous bile pigments bilirubin (BR) and biliverdin (BV) were used for the first time to synthesize stimuli-responsive carbon dots (BR-CDots and BV-CDots respectively). The precursor choice lends these carbon dots spectroscopic characteristics that are enzyme-responsive and pH-responsive without the need for surface modifications post-synthesis. Both BV- and BR-CDots are water-dispersible and provide fluorescence contrast, while retaining the stimuli-responsive behaviors intrinsic to their precursors. Nanoparticle Tracking Analysis revealed that the hydrodynamic size of the BR-CDots and BV-CDots decreased with exposure to bilirubin oxidase and biliverdin reductase, respectively, indicating potential enzyme-responsive degradation of the carbon dots. Fluorescence spectroscopic data demonstrate that both BR-CDots and BV-CDots exhibit changes in their fluorescence spectra in response to changes in pH, indicating that these carbon dots have potential applications in pH sensing. In addition, BR-CDots are biocompatible and provide near-infrared fluorescence emission when excited with light at wavelengths of 600 nm or higher. This work demonstrates the use of rationally selected carbon sources for obtaining near-infrared fluorescence and stimuli-responsive behavior in carbon dots that also provide strong fluorescence contrast.

UV-trained and metal-enhanced fluorescence of biliverdin and biliverdin nanoparticles

Increasing the fluorescence quantum yield of fluorophores is of great interest for in vitro and in vivo biomedical imaging applications. At the same time, photobleaching and photodegradation resulting from continuous exposure to light are major considerations in the translation of fluorophores from research applications to industrial or healthcare applications. A number of tetrapyrrolic compounds, such as heme and its derivatives, are known to provide fluorescence contrast. In this work, we found that biliverdin (BV), a naturally-occurring tetrapyrrolic fluorophore, exhibits an increase in fluorescence quantum yield, without exhibiting photobleaching or degradation, in response to continuous ultraviolet (UV) irradiation. We attribute this increased fluorescence quantum yield to photoisomerization and conformational changes in BV in response to UV irradiation. This enhanced fluorescence can be further altered by chelating BV with metals. UV irradiation of BV led to an approximately 10-fold increase in its 365 nm fluorescence quantum yield, and the most favorable combination of UV irradiation and metal chelation led to an approximately 18.5-fold increase in its 365 nm fluorescence quantum yield. We also evaluated these stimuli-responsive behaviors in biliverdin nanoparticles (BVNPs) at the bulk-state and single-particle level. We determined that UV irradiation led to an approximately 2.4-fold increase in BVNP 365 nm quantum yield, and the combination of UV irradiation and metal chelation led to up to a 6.75-fold increase in BVNP 365 nm quantum yield. Altogether, these findings suggest that UV irradiation and metal chelation can be utilized alone or in combination to tailor the fluorescence behavior of imaging probes such as BV and BVNPs at selected wavelengths.

Current trends in pyrrole and porphyrin-derived nanoscale materials for biomedical applications

This article is written to provide an up-to-date review of pyrrole-based biomedical materials. Porphyrins and other tetrapyrrolic molecules possess unique magnetic, optical and other photophysical properties that make them useful for bioimaging and therapy. This review touches briefly on some of the synthetic strategies to obtain porphyrin- and tetrapyrrole-based nanoparticles, as well as the variety of applications in which crosslinked, self-assembled, porphyrin-coated and other nanoparticles are utilized. We explore examples of these nanoparticles' applications in photothermal therapy, drug delivery, photodynamic therapy, stimuli response, fluorescence imaging, photoacoustic imaging, magnetic resonance imaging, computed tomography and positron emission tomography. We anticipate that this review will provide a comprehensive summary of pyrrole-derived nanoparticles and provide a guideline for their further development.

Nanoparticle delivery in vivo: A fresh look from intravital imaging

Nanomedicine has proven promising in preclinical studies. However, only few formulations have been successfully translated to clinical use. A thorough understanding of how nanoparticles interact with cells in vivo is essential to accelerate the clinical translation of nanomedicine. Intravital imaging is a crucial tool to reveal the mechanisms of nanoparticle transport in vivo, allowing for the development of new strategies for nanomaterial design. Here, we first review the most recent progress in using intravital imaging to answer fundamental questions about nanoparticle delivery in vivo. We then elaborate on how nanoparticles interact with different cell types and how such interactions determine the fate of nanoparticles in vivo. Lastly, we discuss ways in which the use of intravital imaging can be expanded in the future to facilitate the clinical translation of nanomedicine.

Biodegradable MRI Visible Drug Eluting Stent Reinforced by Metal Organic Frameworks

Metal-organic frameworks (MOFs) have applications in numerous fields. However, the development of MOF-based "theranostic" macroscale devices is not achieved. Here, heparin-coated biocompatible MOF/poly(ε-caprolactone) (PCL) "theranostic" stents are developed, where NH₂ -Materials of Institute Lavoisier (MIL)-101(Fe) encapsulates and releases rapamycin (an immunosuppressive drug). These stents also act as a remarkable source of contrast in ex vivo magnetic resonance imaging (MRI) compared to the invisible polymeric stent. The in vitro release patterns of heparin and rapamycin respectively can ensure a type of programmed model to prevent blood coagulation immediately after stent placement in the artery and stenosis over a longer term. Due to the presence of hydrolysable functionalities in MOFs, the stents are shown to be highly biodegradable in degradation tests under various conditions. Furthermore, there is no compromise of mechanical strength or flexibility with MOF compositing. The system described here promises many biomedical applications in macroscale theranostic devices. The use of MOF@PCL can render a medical device MRI-visible while simultaneously acting as a carrier for therapeutic agents.

Computed tomography-guided additive manufacturing of Personalized Absorbable Gastrointestinal Stents for intestinal fistulae and perforations

Small bowel perforations and obstructions are relatively frequent surgical emergencies, are potentially life-threatening, and have multiple etiologies. In general, treatment requires urgent surgical repair or resection and at times can lead to further complications. Stents may be used to help with healing intestinal perforations but use is limited as currently available stents are non-absorbable, are manufactured in a narrow size range, and/or are limited to usage in locations that are accessible for endoscopic removal post-healing. The use of 3D-printed bioresorbable polymeric stents will provide patients with a stent that can prevent leakage, is tailored specifically to their geometry, and will be usable within the small bowel, which is not amenable to endoscopic stent placement. This work focused on the rapid manufacturing of gastrointestinal stents composed of a polycaprolactone-polydioxanone (PCL-PDO) composite. Dynamic Mechanical Analysis (DMA) tests were conducted to separately analyze the effects of composition, the filament formation process, and physiological temperature on the PCL-PDO material properties. The proposed stent design was then modeled using computer-aided design, and Finite Element Analysis (FEA) was used to simulate the effects of physiologically relevant forces on stent integrity. The presence of hydrolysable ester bonds was confirmed using FT-IR spectroscopy. In vitro studies were used to evaluate the biocompatibility of the polymer composite. Further analyses were conducted through stent placement in ex vivo pig intestines. PCL-PDO stents were then 3D-printed and placed in vivo in a pig model.

Pumpless microfluidic devices for generating healthy and diseased endothelia

We have developed a pumpless cell culture chip that can recirculate small amounts of cell culture medium (400 μL) in a unidirectional flow pattern. When operated with the accompanying custom rotating platform, the device produces an average wall shear stress of up to 0.588 Pa ± 0.006 Pa without the use of a pump. It can be used to culture cells that are sensitive to the direction of flow-induced mechanical shear such as human umbilical vein endothelial cells (HUVECs) in a format that allows for large-scale parallel screening of drugs. Using the device we demonstrate that HUVECs produce pro-inflammatory indicators (interleukin 6, interleukin 8) under both unidirectional and bidirectional flow conditions, but that the secretion was significantly lower under unidirectional flow. Our results show that pumpless devices can simulate the endothelium under healthy and activated conditions. The developed devices can be integrated with pumpless tissues-on-chips, allowing for the addition of barrier tissues such as endothelial linings.

Biodegradable Biliverdin Nanoparticles for Efficient Photoacoustic Imaging

Photoacoustic imaging has emerged as a promising imaging platform with a high tissue penetration depth. However, biodegradable nanoparticles, especially those for photoacoustic imaging, are rare and limited to a few polymeric agents. The development of such nanoparticles holds great promise for clinically translatable diagnostic imaging with high biocompatibility. Metabolically digestible and inherently photoacoustic imaging probes can be developed from nanoprecipitation of biliverdin, a naturally occurring heme-based pigment. The synthesis of nanoparticles composed of a biliverdin network, cross-linked with a bifunctional amine linker, is achieved where spectral tuning relies on the choice of reaction media. Nanoparticles synthesized in water or water containing sodium chloride exhibit higher absorbance and lower fluorescence compared to nanoparticles synthesized in 2-(N-morpholino)ethanesulfonic acid buffer. All nanoparticles display high absorbance at 365 and 680 nm. Excitation at near-infrared wavelengths leads to a strong photoacoustic signal, while excitation with ultraviolet wavelengths results in fluorescence emission. In vivo photoacoustic imaging experiments in mice demonstrated that the nanoparticles accumulate in lymph nodes, highlighting their potential utility as photoacoustic agents for sentinel lymph node detection. The biotransformation of these agents was studied using mass spectroscopy, and they were found to be completely biodegraded in the presence of biliverdin reductase, a ubiquitous enzyme found in the body. Degradation of these particles was also confirmed in vivo. Thus, the nanoparticles developed here are a promising platform for biocompatible biological imaging due to their inherent photoacoustic and fluorescent properties as well as their complete metabolic digestion.

Bulk-state and single-particle imaging are central to understanding carbon dot photo-physics and elucidating the effects of precursor composition and reaction temperature

Carbon dots have garnered attention for their strong multi-color luminescence properties and unprecedented biocompatibility. Despite significant progress in the recent past, a fundamental understanding of their photoluminescence and structure-properties relationships, especially at the bulk vs. single-particle level, has not been well established. Here we present a comparative study of bulk- and single-particle properties as a function of precursor composition and reaction temperature. The synthesis and characterization of multicolored inherently functionalized carbon dots were achieved from a variety of carbon sources, and at synthesis temperatures of 150 °C and 200 °C. Solvothermal synthesis at 200 °C led to quantum yields as high as 86%, smaller particle sizes, and a narrowed fluorescence emission, while synthesis at 150 °C resulted in a greater UV-visible absorbance, increase in nanoparticle stability, red-shifted fluorescence, and a greater resistance to bulk photobleaching. These results suggest the potential for synthesis temperature to be utilized as a simple tool for modulating carbon dot photophysical properties. Single-particle imaging resolved that particle brightness was determined by both the instantaneous intensity and the on-time duty cycle. Increasing the synthesis temperature caused an enhancement in blinking frequency, which led to an increase in on-time duty cycle in three out of four precursors.

Impact of Clinically Relevant Elliptical Deformations on the Damage Patterns of Sagging and Stretched Leaflets in a Bioprosthetic Heart Valve

After implantation of a transcatheter bioprosthetic heart valve its original circular circumference may become distorted, which can lead to changes in leaflet coaptation and leaflets that are stretched or sagging. This may lead to early structural deterioration of the valve as seen in some explanted transcatheter heart valves. Our in vitro study evaluates the effect of leaflet deformations seen in elliptical configurations on the damage patterns of the leaflets, with circular valve deformation as the control. Bovine pericardial tissue heart valves were subjected to accelerated wear testing under both circular (N = 2) and elliptical (N = 4) configurations. The elliptical configurations were created by placing the valve inside custom-made elliptical holders, which caused the leaflets to sag or stretch. The hydrodynamic performance of the valves was monitored and high resolution images were acquired to evaluate leaflet damage patterns over time. In the elliptically deformed valves, sagging leaflets experienced more damage from wear compared to stretched leaflets; the undistorted leaflets of the circular valves experienced the least leaflet damage. Free-edge thinning and tearing were the primary modes of damage in the sagging leaflets. Belly region thinning was seen in the undistorted and stretched leaflets. Leaflet and fabric tears at the commissures were seen in all valve configurations. Free-edge tearing and commissure tears were the leading cause of valve hydrodynamic incompetence. Our study shows that mechanical wear affects heart valve pericardial leaflets differently based on whether they are undistorted, stretched, or sagging in a valve configuration. Sagging leaflets are more likely to be subjected to free-edge tear than stretched or undistorted leaflets. Reducing leaflet stress at the free edge of non-circular valve configurations should be an important factor to consider in the design and/or deployment of transcatheter bioprosthetic heart valves to improve their long-term performance.

Zeolite-loaded alginate-chitosan hydrogel beads as a topical hemostat

Hemorrhage is the leading cause of preventable death after a traumatic injury, and the largest contributor to loss of productive years of life. Hemostatic agents accelerate hemostasis and help control hemorrhage by concentrating coagulation factors, acting as procoagulants and/or interacting with erythrocytes and platelets. Hydrogel composites offer a platform for targeting both mechanical and biological hemostatic mechanisms. The goal of this work was to develop hydrogel particles composed of chitosan, alginate, and zeolite, and to assess their potential to promote blood coagulation via multiple mechanisms: erythrocyte adhesion, factor concentration, and the ability to serve as a mechanical barrier to blood loss. Several particle compositions were synthesized and characterized. Hydrogel bead composition was optimized to achieve the highest swelling capacity, greatest erythrocyte adhesion, and minimal in vitro cytotoxicity. These results suggest a polymer hydrogel-aluminosilicate composite material may serve as a platform for an effective hemostatic agent that incorporates multiple mechanisms of action. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1662-1671, 2018.

Copper-Catalyzed Syntheses of Pyrene-Pyrazole Pharmacophores and Structure Activity Studies for Tubulin Polymerization

Tubulin polymerization is critical in mitosis process, which regulates uncontrolled cell divisions. Here, we report a new class of pyrene-pyrazole pharmacophore (PPP) for targeting microtubules. Syntheses of seven pyrenyl-substituted pyrazoles with side-chain modification at N-1 and C-3 positions of the pyrazole ring were accomplished from alkenyl hydrazones via C-N dehydrogenative cross-coupling using copper catalyst under aerobic condition. Tubulin polymerization with PPPs was investigated using docking and biological tools to reveal that these ligands are capable of influencing microtubule polymerization and their interaction with α-, β-tubulin active binding sites, which are substituent specific. Furthermore, cytotoxicity response of these PPPs was tested on cancer cells of different origin, such as MCF-7, MDA-MB231, and C32, and also noncancerous normal cells, such as MCF-10A. All newly synthesized PPPs showed excellent anticancer activities. The anticancer activities and half-maximal inhibitory concentration (IC₅₀) values of all PPPs across different cancer cell lines (MCF-7, MDA-MB231, and C32) have been demonstrated. 1,3-Diphenyl-5-(pyren-1-yl)-1H-pyrazole was found to be best among all other PPPs in killing significant population of all of the cancerous cell with IC₅₀ values 1 ± 0.5, 0.5 ± 0.2, and 5.0 ± 2.0 μM in MCF-7, MDA-MB231, and C32 cells, respectively.

Crack Propagation and Its Shear Mechanisms in the Bovine Descending Aorta

Aortic dissection and rupture may involve circumferential shear stress in the circumferential-longitudinal plane. Inflation of bovine descending aortic ring specimens provides evidence of such shear from the non-uniform circumferential distortion of radial lines drawn on the circumferential-radial ring face. Delamination without tensile peeling induces cracks that propagate nearly circumferentially in the circumferential-longitudinal plane from the root of a radial cut representing rupture initiation in a ring. Translational shear deformation tests of small rectangular aortic wall blocks in the circumferential and longitudinal direction measure the consequences of such shear on substructures in the aortic wall, in particular the collagen fibers. The two directions of shear deformation produce no statistical difference in the shear stress response of the wall. Possibly, the interfiber connections between collagen fibers are put into tension by either translational shear deformation so that the stress measured reflects the tensile response of these connections. Wall rupture may involve failure of these connections; such failure is supported by the voids parallel to the collagen fibers observed in a histological study after translational shear. Further, interstitial fluid is redistributed by shear as evidenced by the measured weight loss of a set of specimens during the translational shear of blocks. Because the mass changes, mathematical modeling of aortic tissue in vitro as incompressible is an approximation. These observations suggest that no simple modification of classical rupture theories, whether based on energy functions, stress or strain, suffices to predict the rupture of hydrated soft biological tissue that has complex substructures.