Directing cell migration and organization via nanocrater-patterned cell-repellent interfaces.

Although adhesive interactions between cells and nanostructured interfaces have been studied extensively, there is a paucity of data on how nanostructured interfaces repel cells by directing cell migration and cell-colony organization. Here, by using multiphoton ablation lithography to pattern surfaces with nanoscale craters of various aspect ratios and pitches, we show that the surfaces altered the cells focal-adhesion size and distribution, thus affecting cell morphology, migration and ultimately localization. We also show that nanocrater pitch can disrupt the formation of mature focal adhesions to favour the migration of cells towards higher-pitched regions, which present increased planar area for the formation of stable focal adhesions. Moreover, by designing surfaces with variable pitch but constant nanocrater dimensions, we were able to create circular and striped cellular patterns. Our surface-patterning approach, which does not involve chemical treatments and can be applied to various materials, represents a simple method to control cell behaviour on surfaces

Natural functionally-graded composites in hard-to-soft tissue (bone- tendon) junctions

Composite materials are often functionally engineered to imbue desired mechanical properties in materials for structural applications. Nature has long engaged in such composite engineering of biological organisms, which has evolved in both flora and fauna in response to specific mechanical demands. Incorporation of phenolic compounds (like lignin) in stiffening cell assemblies in plant basts, or of silica in plant leaves to resist chomping insect incursions, are good examples in the plant world. Skeletal bone in vertebrates is the classic example in the animal kingdom, a composite of flexible fibrous polymerized organic protein and platy-crystalline inorganic mineral that results in a mechanically strong, hard, tough tissue. The musculo-skeletal system of vertebrates in fact comprises a variety of both hard and soft tissue types (bone, cartilage, tendon, ligament), generative cell types (osteoblasts, chondrocytes, tenocytes, fibroblasts, all of which can derive from multipotent mesenchymal stem cell precursors), and fibrous connective-tissue proteins (chiefly collagen, types I and II) that are susceptible to varying degrees of mineralization. In the case of bone, mineralization is extensive and forms a bi-continuous composite of mineral (chiefly partially-carbonated hydroxyapatite [Ca10(PO4,CO3)6(OH)2] and precursors) and collagen (a triple a-helix polypeptide) that self-assembles into protein fibrils (mostly type I collagen). Bone continually remodels itself and also re-forms as a consequence of injury or around implanted prostheses (such as knee and hip prostheses). High-resolution analytical TEM reveals [1] a mineralization mechanism which entails initial creation, at the mitochondria of bone-forming cells (osteoblasts), of pre-packaged vesicles that fill with a calcium-phosphate hydrogel and thereafter migrate through the cell wall. The vesicle contents subsequently crystallize [2] in the extra-cellular space with the dissolution of the vesicle containment wall, shortly before self-assembling collagen is expressed from the osteoblasts, providing a “just-in-time” ready source of Ca and P for mineralization of collagen fibrils with close to (though not identical with) the Ca/P ratio of hydroxyapatite found in the mature bone composite. The critical connective junctions between different tissue types in the musculo-skeletal system (bone, cartilage, tendon, muscle, ligament) involve several hard-tissue/soft-tissue interfaces, characterized by gradients in mineralization, cell type, cell morphology, and collagen self-assembly modes. For example, standard procedure for re-attachment of ruptured tendons—by surgically re-locating the tendon proximally to bone—re-establishes the important bone-tendon junction (enthesis) in a period of about one year. The process proceeds through growth, contiguous to the (fully mineralized) bone surface, of a partially-mineralized fibrocartilage layer (comprising collagen, expressed by chondrocyte cells, that self-assembles into principally Type II and Type X collagens). TEM [3] of ovine models shows that mineralization of this cartilaginous layer appears to occur via the identical mechanism established [1,2] for bone mineralization but initiated instead by chondrocyte cells. SEM [3] reveals that the cell-type in the remaining unmineralized cartilage portion gradually morphs into tenocytes, which form more elastic tendon fibers comprising, again, mostly Type I collagen (but also Types III, IV, V and IX self-assembly motifs). The resulting hard-tissue/soft-tissue enthesis junction is thus seen [3] to be a multiply graded interface involving three different cell types, several different collagen self-assembly motifs, and the functional gradation of a composite material paradigm spanning fully-hard tissue (bone) to fully-soft tissue (tendon). [1] S. Boonrungsiman, E. Gentleman, R. Carzaniga, N.D. Evans, D.W. McComb, A. E. Porter and M.M. Stevens, PNAS 109 (2012) 141. [2] V. Benezra, L. W. Hobbs and M. Spector, Biomaterials 23 (2001) 725; A. E. Porter, L. W. Hobbs, V. Benezra and M. Spector, Biomaterials 23 (2001) 921. [3] L. W. Hobbs, H. Wang, W. M. Reese, B. M. Tomerline, T. Y. C. Lim, A. E. Porter, M. Walton and M. J. Cotton, Microscopy & Microanalysis 19 (2013) 182

Scanning electron microscopy observations of the enthesis in an ovine model

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, June 2010."May 2009." Page 47 blank. Cataloged from PDF version of thesis.Includes bibliographical references (pages 28-29).The present study investigates the naturally occurring interface between bone and tendon using scanning electron microscopy. The micrographs revealed a cartilaginous layer, 100 to 400 [mu]m thick apposing bone, that contained cells varying in size and shape as a function of their location in this cartilaginous layer. Further investigation is required to conclude whether these cells are undergoing further differentiation during development of this graded layer. This study found the interface between bone and the cartilaginous layer to be interdigitated, which may explain why injuries at the bone-tendon interface are comparatively rare. Also, the cartilaginous layer was revealed to be substantially mineralized. A somewhat higher concentration of calcium and phosphorus was observed near the interface with the apposing bone that gradually diminished into the cartilaginous layer. These findings support the four zone description of the bone-tendon interface established by others using histological methods. However, further research is suggested to resolve other questions about the observed sub-micrometer morphologies of the bone-tendon interface.by Willie Mae Reese.S.B

Surface Modifications for Cell Culture Systems

This dissertation focuses on methods to understand and improve surface modifications for 2D and 3D cell culture platforms. In this work, novel methods are investigated for their ability to alter cell adhesion and block small molecule absorption, events that have the ability to alter cell behavior and phenotype.Chapter 1 is an introduction to surface modification techniques, the mechanisms within the cell that are currently understood to probe these alterations of surface chemistry, topography, and other attributes, and the application of these methods. This chapter serves to tie together the investigations done in this dissertation.Chapter 2 presents an investigation on the effects of change of topography using multi-photon ablation lithography to fabricate arrays of nanoscale craters in quartz substrates with a variety of geometries and spacing (i.e. pitch). This direct-write patterning method developed by a collaborator induced directed NIH 3T3 cell migration. In this work, I focused on understanding the mechanism of action for this phenomena. Briefly, the direct write patterning produced sub-micron sized pits in quartz that could be arranged in any number of spacial patterns. I investigated both isometrically spaced pits (2-8µm) as well as gradient spaced patterns, where pits were spaced at 1µm spacings toward the center of the pattern up to 10µm toward the perimeter of the pattern. Immunofluorescent labeling of intracellular focal adhesion Vinculin was used to quantify focal adhesion size and revealed significant differences based on pattern spacing. In isometric patterns, 2 and 4 µm patterns showed significantly smaller focal adhesion size distributions leading to the conclusion that the nanocraters restricted focal adhesion size and also maturity leading to higher turnover of these adhesion. Higher turnover in regions where the pits were densely arranged led to an observation of cells migrating away. With motion tracking on gradient patterns, cells were seen to migrate areas where the nanopits were spaced closer together along directions of the highest rate of increase in surface area, confirming that the pits were restricting the area available for cells to form larger stable focal adhesions. Other researchers have shown that area is a critical attribute for focal adhesion formation that can be overcome by intercellular adhesion protein activation. To investigate this, NIH3t3 cells were transfected with a plasmid containing the DNA for the first 405 amino acids of the Talin-1 protein, which has shown to perform as the full Talin molecule in intracellular signaling. After transfection, cells showed no significant difference on any of focal adhesion size on any of the isometric patterns and also lost their directed migration function on gradient patterns. This data supports our hypothesis that the physical restriction of area for adhesion causes cells to statistically migrate from regions of high pit density (low pitch) to regions where more area is available, but with intracellular signaling of talin this can be overcome by the cell. This study helps to elucidate the mechanism through which cells probe their substrate topography and if employed on more biologically relevant surfaces can be used as a way to decrease cell adhesion.Chapter 3 presents a novel method using a macrocylic polyphenol coating to block drug absorption in Poly(dimethysilane) (PDMS) based microfluidic Microphysiological Systems (MPS). MPS can be used to combine genetically relevant cell lines in micro-environments that recapitulate not only genetically relevant organ specific structure, but also organ system relationships to access on and off-target toxicities and efficacies. Most MPSs are easily manufactured via soft lithography techniques using poly-dimethylsiloxane (PDMS), which has shown to be biologically compatible and amenable to many standard cell culture techniques due to its high transparency, high oxygen permeability, and low auto-fluorescence. Although PDMS has several positive attributes, many have shown that due to its hydrophobicity, small lipophilic molecules can be absorbed into PDMS creating unpredictable drug concentrations in MPSs.To address this limitation, we designed and developed a novel macrocyclic polyphenol, which is able to reduce the absorbance of the model drug compounds rhodamine B, C1-BODIPY-C12, Brilliant Green, and Metanil Yellow into PDMS by 87, 96, 93, and 95 percent, respectively. This outperforms established polyphenol coatings such as polydopamine or pyrogallol. Initial experiments have shown low cytotoxicity allowing for the culture of iPSC-derived cardiomyocytes for at least one month. Preliminary experiments also show good coating stability not only on PDMS but also on other biologically relevant polymeric materials such as tissue culture polystyrene, polycarbonate, and Teflon. This coating is also advantageous over other solutions of drug absorption such as Sol-Gel methods or other glass like coatings, due to its ease of use, low cost, and high oxygen permeability.Chapter 4 gives an overall conclusion and details future directions for investiga- tions in Chapter 2 and 3

Proof of concept of the μOrgano system.

<p><b>a</b>) General procedure for biological experiments with the μOrgano system. <b>b</b>) Combined culture of two devices with 3T3 fibroblasts: Live (green) /dead (red) staining in both devices after 1 day of individual and 2 days of combined culture show that viability can be maintained. <b>c</b>) In-series culture of two heart-on-a-chip devices: tracings of the beating motion of cardiac tissue formed by hiPSC-cardiomyocytes—i) optical microscopy image—in two connected MPSs (ii) MPS 1; iii) MPS 2). The analysis using computational motion tracking reveals that a physiological phenotype is retained and individual cardiac devices beat with distinct frequencies. (scale bars = 200 μm).</p

Characterization of μOrgano building blocks.

<p><b>a</b>) Transition time of the interface of a liquid advancing through a system of two MPSs and a linear connector. The time necessary to advance from the cell chamber in MPS 1 to the cell chamber in MPS 2 is plotted versus the inner diameters of the glass capillaries in the respective systems. Insets show pictures of the respective glass capillaries (scale bars = 2 mm). <b>b</b>) Scatter plot of the transition times for ten independent systems connected by the same type of connectors featuring 50 μm ID capillaries. <b>c</b>) Time series of microscopy images from a channel section in the proximity of the inlet of the second MPS initially filled with clear water. The continuous transition occurring after connection to a MPS filled with coloured water using a food dye reveals the bubble less connection ability of the system (scale bar = 100 μm). <b>d</b>) Time series of pictures showing two MPSs connected by a linear connector whereby MPS 1 is prefilled with red dyed water, and MPS 2 and the connector with blue dyed water. Pumping red dyed water into MPS 1 leads to the replacement of the blue dyed water in both the connector and MPS 2 without the occurrence of leakage. <b>e</b>) Volume flown through MPS 2 (left; in flow direction) and MPS 3 (right) plotted as percentage of the total volume after connection to MPS 1 via a bifurcation connector.</p

Challenges and solution for multi-organ-systems.

<p><b>a</b>) General requirements for multi-organ-chips: i) initial separate loading of the respective cells; ii) individual culture for differentiation, formation, equilibration, and maturation of the tissues; and, iii) combined culture for drug screening purposes. <b>b</b>) Underlying concept of the μOrgano system: Schematics depicting the basic μOrgano components: the master-organ-chip and exemplary plug & play connectors. Conceptual idea of the usage principle of the μOrgano system for the connection of two MPSs in series via a simple linear channel connector with a close-up of the connected system highlighting the resulting media flow.</p

Fabrication of μOrgano building blocks.

<p>Schematic protocol for the fabrication of connectors (and MPSs) with precise in- and outlet positions via multi step UV-lithography: i) microscopic channel structures are patterned in photoresist using UV lithography; ii) macroscopic in- and outlets are patterned as pillars on top of the microscopic channel structures using a second UV lithography step; iii) microfluidic PDMS devices are fabricated with predefined in- and outlets via exclusion molding; iv) PDMS connectors are cut and bonded to pre-cut microscope slides; and, v) glass capillaries are inserted and bonded into the in- and outlets of the connectors.</p

μOrgano: A Lego^®-Like Plug & Play System for Modular Multi-Organ-Chips

<div><p>Human organ-on-a-chip systems for drug screening have evolved as feasible alternatives to animal models, which are unreliable, expensive, and at times erroneous. While chips featuring single organs can be of great use for both pharmaceutical testing and basic organ-level studies, the huge potential of the organ-on-a-chip technology is revealed by connecting multiple organs on one chip to create a single integrated system for sophisticated fundamental biological studies and devising therapies for disease. Furthermore, since most organ-on-a-chip systems require special protocols with organ-specific media for the differentiation and maturation of the tissues, multi-organ systems will need to be temporally customizable and flexible in terms of the time point of connection of the individual organ units. We present a customizable Lego^®-like plug & play system, μOrgano, which enables initial individual culture of single organ-on-a-chip systems and subsequent connection to create integrated multi-organ microphysiological systems. As a proof of concept, the μOrgano system was used to connect multiple heart chips in series with excellent cell viability and spontaneously physiological beat rates.</p></div