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A laser-based hydrogel degradation technique was developed that allowed 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.

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Despite the key role of the capillaries in neurovascular function, a thorough characterization of cerebral capillary network properties is currently lacking. Here, we define a range of metrics (geometrical, topological, flow, mass transfer, and robustness) for quantification of structural differences between brain areas, organs, species, or patient populations and, in parallel, digitally generate synthetic networks that replicate the key organizational features of anatomical networks (isotropy, connectedness, space-filling nature, convexity of tissue domains, characteristic size). To reach these objectives, we first construct a database of the defined metrics for healthy capillary networks obtained from imaging of mouse and human brains. Results show that anatomical networks are topologically equivalent between the two species and that geometrical metrics only differ in scaling. Based on these results, we then devise a method which employs constrained Voronoi diagrams to generate 3D model synthetic cerebral capillary networks that are locally randomized but homogeneous at the network-scale. With appropriate choice of scaling, these networks have equivalent properties to the anatomical data, demonstrated by comparison of the defined metrics. The ability to synthetically replicate cerebral capillary networks opens a broad range of applications, ranging from systematic computational studies of structure-function relationships in healthy capillary networks to detailed analysis of pathological structural degeneration, or even to the development of templates for fabrication of 3D biomimetic vascular networks embedded in tissue-engineered constructs.

Metastatic recurrence is a major hurdle to overcome for successful control of cancer-associated death. Residual tumor cells in the primary site, or disseminated tumor cells in secondary sites, can lie in a dormant state for long time periods, years to decades, before being reactivated into a proliferative growth state. The microenvironmental signals and biological mechanisms that mediate the fate of disseminated cancer cells with respect to cell death, single cell dormancy, tumor mass dormancy and metastatic growth, as well as the factors that induce reactivation, are discussed in this review. Emphasis is placed on engineered, in vitro, biomaterial-based approaches to model tumor dormancy and subsequent reactivation, with a focus on the roles of extracellular matrix, secondary cell types, biochemical signaling and drug treatment. A brief perspective of molecular targets and treatment approaches for dormant tumors is also presented. Advances in tissue-engineered platforms to induce, model, and monitor tumor dormancy and reactivation may provide much needed insight into the regulation of these processes and serve as drug discovery and testing platforms.

The cell and tissue engineering fields have profited immensely through the implementation of highly-structured biomaterials. The development and implementation of advanced biofabrication techniques has established new avenues for generating biomimetic scaffolds for a multitude of cell and tissue engineering applications. Among these, laser-based degradation of biomaterials has been 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 influence 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.

Investigating stages of maturation of cellular adhesions to the extracellular matrix from the initial binding events to the formation of small focal complexes has been challenging because of the difficulty in fabricating the necessary nanopatterned substrates with controlled biochemical functionality. We present the fabrication and characterization of surfaces presenting fibronectin nanopatterns of controlled size and pitch that provide well-defined cellular adhesion sites against a nonadhesive polyethylene glycol background. The nanopatterned surfaces allow us to control the number of fibronectin proteins within each adhesion site from 9 to 250, thereby limiting the number of integrins involved in each cell-substrate adhesion. We demonstrate the presence of fibronectin on the nanoislands, while no protein was observed on the passivated background. We show that the cell adheres to the nanopatterns with adhesions that are much smaller and more evenly distributed than on a glass control. The nanopattern influences cellular proliferation only at longer times, but influences spreading at both early and later times, indicating adhesion size and adhesion density play a role in controlling cell adhesion and signaling. However, the overall density of fibronectin on all patterns is far lower than on homogeneously coated control surfaces, showing that the local density of adhesion ligands, not the average density, is the important parameter for cell proliferation and spreading.

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.