John H. Slater

Three‐Dimensional Biomimetic Patterning in Hydrogels to Guide Cellular Organization

An image-guided micropatterning method is demonstrated for generating biomimetic hydrogel scaffolds with two-photon laser scanning photolithography. This process utilizes computational methods to directly translate three-dimensional cytoarchitectural features from labeled tissues into material structures. We use this method to pattern hydrogels that guide cellular organization by structurally and biochemically recapitulating complex vascular niche microenvironments with high pattern fidelity at the microscale.

Antibody-conjugated gold-gold sulfide nanoparticles as multifunctional agents for imaging and therapy of breast cancer

The goal of this study was to develop near-infrared (NIR) resonant gold-gold sulfide nanoparticles (GGS-NPs) as dual contrast and therapeutic agents for cancer management via multiphoton microscopy followed by higher intensity photoablation. We demonstrate that GGS-NPs exposed to a pulsed, NIR laser exhibit two-photon induced photoluminescence that can be utilized to visualize cancerous cells in vitro. When conjugated with anti-HER2 antibodies, these nanoparticles specifically bind SK-BR-3 breast carcinoma cells that over-express the HER2 receptor, enabling the cells to be imaged via multiphoton microscopy with an incident laser power of 1 mW. Higher excitation power (50 mW) could be employed to induce thermal damage to the cancerous cells, producing extensive membrane blebbing within seconds leading to cell death. GGS-NPs are ideal multifunctional agents for cancer management because they offer the ability to pinpoint precise treatment sites and perform subsequent thermal ablation in a single setting.

Fabrication of 3D Biomimetic Microfluidic Networks in Hydrogels.

A laser-based hydrogel degradation technique is developed that allows for local control over hydrogel porosity, fabrication of 3D vascular-derived, biomimetic, hydrogel-embedded microfluidic networks, and generation of two intertwining, yet independent, microfluidic networks in a single construct.

Recapitulation and Modulation of the Cellular Architecture of a User-Chosen Cell of Interest Using Cell-Derived, Biomimetic Patterning.

Heterogeneity of cell populations can confound population-averaged measurements and obscure important findings or foster inaccurate conclusions. The ability to generate a homogeneous cell population, at least with respect to a chosen trait, could significantly aid basic biological research and development of high-throughput assays. Accordingly, we developed a high-resolution, image-based patterning strategy to produce arrays of single-cell patterns derived from the morphology or adhesion site arrangement of user-chosen cells of interest (COIs). Cells cultured on both cell-derived patterns displayed a cellular architecture defined by their morphology, adhesive state, cytoskeletal organization, and nuclear properties that quantitatively recapitulated the COIs that defined the patterns. Furthermore, slight modifications to pattern design allowed for suppression of specific actin stress fibers and direct modulation of adhesion site dynamics. This approach to patterning provides a strategy to produce a more homogeneous cell population, decouple the influences of cytoskeletal structure, adhesion dynamics, and intracellular tension on mechanotransduction-mediated processes, and a platform for high-throughput cellular assays.

Modulation of Endothelial Cell Migration via Manipulation of Adhesion Site Growth Using Nanopatterned Surfaces

Orthogonally functionalized nanopatterend surfaces presenting discrete domains of fibronectin ranging from 92 to 405 nm were implemented to investigate the influence of limiting adhesion site growth on cell migration. We demonstrate that limiting adhesion site growth to small, immature adhesions using sub-100 nm patterns induced cells to form a significantly increased number of smaller, more densely packed adhesions that displayed few interactions with actin stress fibers. Human umbilical vein endothelial cells exhibiting these traits displayed highly dynamic fluctuations in spreading and a 4.8-fold increase in speed compared to cells on nonpatterned controls. As adhesions were allowed to mature in size in cells cultured on larger nanopatterns, 222 to 405 nm, the dynamic fluctuations in spread area and migration began to slow, yet cells still displayed a 2.1-fold increase in speed compared to controls. As all restrictions on adhesion site growth were lifted using nonpatterned controls, cells formed significantly fewer, less densely packed, larger, mature adhesions that acted as terminating sites for actin stress fibers and significantly slower migration. The results revealed an exponential decay in cell speed with increased adhesion site size, indicating that preventing the formation of large mature adhesions may disrupt cell stability thereby inducing highly migratory behavior.

Progeny Clustering: A Method to Identify Biological Phenotypes

Estimating the optimal number of clusters is a major challenge in applying cluster analysis to any type of dataset, especially to biomedical datasets, which are high-dimensional and complex. Here, we introduce an improved method, Progeny Clustering, which is stability-based and exceptionally efficient in computing, to find the ideal number of clusters. The algorithm employs a novel Progeny Sampling method to reconstruct cluster identity, a co-occurrence probability matrix to assess the clustering stability, and a set of reference datasets to overcome inherent biases in the algorithm and data space. Our method was shown successful and robust when applied to two synthetic datasets (datasets of two-dimensions and ten-dimensions containing eight dimensions of pure noise), two standard biological datasets (the Iris dataset and Rat CNS dataset) and two biological datasets (a cell phenotype dataset and an acute myeloid leukemia (AML) reverse phase protein array (RPPA) dataset). Progeny Clustering outperformed some popular clustering evaluation methods in the ten-dimensional synthetic dataset as well as in the cell phenotype dataset, and it was the only method that successfully discovered clinically meaningful patient groupings in the AML RPPA dataset.

Biomimetic Surface Patterning Promotes Mesenchymal Stem Cell Differentiation

Both chemical and mechanical stimuli can dramatically influence cell behavior. By optimizing the signals cells experience, it may be possible to control the behavior of therapeutic cell populations. In this work, biomimetic geometries of adhesive ligands, which recapitulate the morphology of mature cells, are used to direct human mesenchymal stem cell (HMSC) differentiation toward a desired lineage. Specifically, adipocytes cultured in 2D are imaged and used to develop biomimetic virtual masks used in laser scanning lithography to form patterned fibronectin surfaces. The impact of adipocyte-derived pattern geometry on HMSC differentiation is compared to the behavior of HMSCs cultured on square and circle geometries, as well as adipocyte-derived patterns modified to include high stress regions. HMSCs on adipocyte mimetic geometries demonstrate greater adipogenesis than HMSCs on the other patterns. Greater than 45% of all HMSCs cultured on adipocyte mimetic patterns underwent adipogenesis as compared to approximately 19% of cells on modified adipocyte patterns with higher stress regions. These results are attributed to variations in cytoskeletal tension experienced by cells on the different protein micropatterns. The effects of geometry on adipogenesis are mitigated by the incorporation of a cytoskeletal protein inhibitor; exposure to this inhibitor leads to increased adipogenesis on all patterns examined.

Microcontact printing for co-patterning cells and viruses for spatially controlled substrate-mediated gene delivery

Spatial organization of gene expression is a crucial element in the development of complex native tissues, and the capacity to achieve spatially controlled gene expression profiles in a tissue engineering construct is still a considerable challenge. To give tissue engineers the ability to design specific, spatially organized gene expression profiles in an engineered construct, we have investigated the use of microcontact printing to pattern recombinant adeno-associated virus (AAV) vectors on a two dimensional surface as a first proof-of-concept study. AAV is a highly safe, versatile, stable, and easy-to-use gene delivery vector, making it an ideal choice for this application. We tested the suitability of four chemical surfaces (–CH3, –COOH, –NH2, and –OH) to mediate localized substrate-mediated gene delivery. First, polydimethylsiloxane stamps were used to create microscale patterns of various self-assembled monolayers on gold-coated glass substrates. Next, AAV particles carrying genes of interest and human fibronectin (HFN) were immobilized on the patterned substrates, creating a spatially organized arrangement of gene delivery vectors. Immunostaining studies reveal that –CH3 and –NH2 surfaces result in the most successful adsorption of both AAV and HFN. Lastly, HeLa cells were used to analyze viral transduction and spatial localization of gene expression. We find that –CH3, –COOH, and –NH2 surfaces support complete uniform cell coverage with high gene expression. Notably, we observe a synergistic effect between HFN and AAV for substrate-mediated gene delivery. Our flexible platform should allow for the specific patterning of various gene and shRNA cassettes, resulting in spatially defined gene expression profiles that may enable the generation of highly functional tissue.

Fundamentals of Laser-Based Hydrogel Degradation and Applications in Cell and Tissue Engineering

The cell and tissue engineering fields have profited immensely through the implementation of highly structured biomaterials. The development and implementation of advanced biofabrication techniques have established new avenues for generating biomimetic scaffolds for a multitude of cell and tissue engineering applications. Among these, laser-based degradation of biomaterials is implemented to achieve user-directed features and functionalities within biomimetic scaffolds. This review offers an overview of the physical mechanisms that govern laser-material interactions and specifically, laser-hydrogel interactions. The influences of both laser and material properties on efficient, high-resolution hydrogel degradation are discussed and the current application space in cell and tissue engineering is reviewed. This review aims to acquaint readers with the capability and uses of laser-based degradation of biomaterials, so that it may be easily and widely adopted.

Biomimetic Surfaces for Cell Engineering

Cell behavior, in particular, migration, proliferation, differentiation, apoptosis, and activation, is mediated by a multitude of environmental factors: (i) extracellular matrix (ECM) properties including molecular composition, ligand density, ligand gradients, stiffness, topography, and degradability; (ii) soluble factors including type, concentration, and gradients; (iii) cell–cell interactions; and (iv) external forces such as shear stress, material strain, osmotic pressure, and temperature changes. The coordinated influence of these environmental cues regulate embryonic development, tissue function, homeostasis, and wound healing as well as other crucial events in vivo. From a fundamental biology perspective, it is of great interest to understand how these environmental factors regulate cell fate and ultimately cell and tissue function. From an engineering perspective, it is of interest to determine how to present these factors in a well-controlled manner to elicit a desired cell output for cell and tissue engineering applications. Both biophysical and biochemical factors mediate intracellular signaling cascades that influence gene expression and ultimately cell behavior, making it difficult to unravel the hierarchy of cell fate stimuli. Accordingly, much effort has focused on the fabrication of biomimetic surfaces that recapitulate a single or many aspects of the in vivo microenvironment including topography, elasticity, and ligand presentation, and by structured materials that allow for control over cell shape, spreading, and cytoskeletal tension. Controlled presentation of these properties to develop a desired microenvironment can be harnessed to guide cell fate decisions toward chosen paths and has provided a wealth of knowledge concerning which cues regulate apoptosis, proliferation, migration, lineage-specific stem cell differentiation, and immune cell activation to name a few. This chapter focuses on the implementation of biomimetic surfaces that recapitulate and control one or more aspects of the cellular microenvironment to induce a desired cell response. More specifically, biomimetic surfaces that mimic in vivo ECM composition, density, gradients, stiffness, or topography; those that allow for control over cell shape, spreading, or cytoskeletal tension; and those that mimic cell surfaces are discussed.