Design for a lithographically patterned bioartificial endocrine pancreas.

Cell encapsulation provides a means to transplant therapeutic cells for a variety of diseases including diabetes. However, due to the large numbers of cells, approximately on the order of a billion, that need to be transplanted for human diabetes therapy, adequate mass transport of nutrients such as oxygen presents a major challenge. Proof-of-concept for the design of a bioartificial endocrine pancreas (BAEP) that is optimized to minimize hypoxia in a scalable and precise architecture is demonstrated using a combination of simulations and experiments. The BAEP is composed of an array of porous, lithographically patterned polyhedral capsules arrayed on a rolled-up alginate sheet. All the important structural variables such as the capsule dimensions, pore characteristics, and spacing can be precisely engineered and tuned. Further, all cells are encapsulated within a single device with a volume not much greater than the total volume of the encapsulated cells, and no cell within the device is located more than 200 µm from the surrounding medium that facilitates efficient mass transport with the surroundings. Compared with gel-based encapsulation methods, our approach offers unprecedented precision and tunability of structural parameters as well as the volume of the encapsulated cells and consequently the amount of secreted insulin. Our work highlights the utility of lithography and self-assembly in the fabrication of micro- and nanostructured three-dimensional structures that simulate the function of natural endocrine organs.

Self-folding devices and materials for biomedical applications.

Because the native cellular environment is 3D, there is a need to extend planar, micro- and nanostructured biomedical devices to the third dimension. Self-folding methods can extend the precision of planar lithographic patterning into the third dimension and create reconfigurable structures that fold or unfold in response to specific environmental cues. Here, we review the use of hinge-based self-folding methods in the creation of functional 3D biomedical devices including precisely patterned nano- to centimeter scale polyhedral containers, scaffolds for cell culture and reconfigurable surgical tools such as grippers that respond autonomously to specific chemicals.

Self-folding immunoprotective cell encapsulation devices.

Cell encapsulation therapy (CET) provides an attractive means to transplant cells without the need for immunosuppression. The cells are immunoisolated by surrounding them with a synthetic, semipermeable nanoporous membrane that allows selective permeation of nutrients and therapeutics while isolating the cells from hostile immune components. This communication describes the fabrication and in vitro characterization of lithographically structured and self-folded containers for immunoprotective cell encapsulation. Lithographic patterning ensured identical shapes, sizes, tunable porosity, and precise volumetric control, whereas self-folding enabled transformation of two-dimensional porous membranes into cubes, ensuring that pores were present in all three dimensions for adequate diffusion of O(2) and other nutrients to encapsulated cells. We fabricated containers with varying pore sizes and observed that pores sizes of approximately 78 nm were sufficient to significantly inhibit diffusion of IgG (the smallest antibody) and permit adequate diffusion of insulin, highlighting the possibility to utilize these containers to develop a lithographically structured bioartificial pancreas. FROM THE CLINICAL EDITOR: In this paper, a novel immunoisolation technique is presented to enable cell transplant survival by surrounding them with a synthetic, semipermeable nanoporous membrane that allows selective permeation of nutrients and therapeutics while isolating the cells from hostile immune components. This method may pave the way to effective pancreatic islet cell transplantation.

Three-dimensional microwell arrays for cell culture.

We propose the concept of three-dimensional (3D) microwell arrays for cell culture applications and highlight the importance of oxygen diffusion through pores in all three dimensions to enhance cell viability.

Directed growth of fibroblasts into three dimensional micropatterned geometries via self-assembling scaffolds.

We describe the use of conventional photolithography to construct three dimensional (3D) thin film scaffolds and direct the growth of fibroblasts into three distinct and anatomically relevant geometries: cylinders, spirals and bi-directionally folded sheets. The scaffolds were micropatterned as two dimensional sheets which then spontaneously assembled into specific geometries upon release from the underlying substrate. The viability of fibroblasts cultured on these self-assembling scaffolds was verified using fluorescence microscopy; cell morphology and spreading were studied using scanning electron microscopy. We demonstrate control over scaffold size, radius of curvature and folding pitch, thereby enabling an attractive approach for investigating the effects of these 3D geometric factors on cell behaviour.

Tetherless thermobiochemically actuated microgrippers.

We demonstrate mass-producible, tetherless microgrippers that can be remotely triggered by temperature and chemicals under biologically relevant conditions. The microgrippers use a self-contained actuation response, obviating the need for external tethers in operation. The grippers can be actuated en masse, even while spatially separated. We used the microgrippers to perform diverse functions, such as picking up a bead on a substrate and the removal of cells from tissue embedded at the end of a capillary (an in vitro biopsy).

Size selective sampling using mobile, 3D nanoporous membranes.

We describe the fabrication of 3D membranes with precisely patterned surface nanoporosity and their utilization in size selective sampling. The membranes were self-assembled as porous cubes from lithographically fabricated 2D templates (Leong et al., Langmuir 23:8747-8751, 2007) with face dimensions of 200 microm, volumes of 8 nL, and monodisperse pores ranging in size from approximately 10 microm to 100 nm. As opposed to conventional sampling and filtration schemes where fluid is moved across a static membrane, we demonstrate sampling by instead moving the 3D nanoporous membrane through the fluid. This new scheme allows for straightforward sampling in small volumes, with little to no loss. Membranes with five porous faces and one open face were moved through fluids to sample and retain nanoscale beads and cells based on pore size. Additionally, cells retained within the membranes were subsequently cultured and multiplied using standard cell culture protocols upon retrieval.

Self-loading lithographically structured microcontainers: 3D patterned, mobile microwells.

We demonstrate mass-producible, mobile, self-loading microcontainers that can be used to encapsulate both non-living and living objects, thus forming three-dimensionally patterned, mobile microwells.

3D lithographically fabricated nanoliter containers for drug delivery.

Lithographic patterning offers the possibility for precise structuring of drug delivery devices. The fabrication process can also facilitate the incorporation of advanced functionality for imaging, sensing, telemetry and actuation. However, a major limitation of present day lithographic fabrication is the inherent two-dimensionality of the patterning process. We review a new approach to construct three dimensional (3D) patterned containers by lithographically patterning two dimensional (2D) templates with liquefiable hinges that spontaneously fold upon heating into hollow polyhedral containers. The containers have finite encapsulation volumes, can be made small enough to pass through a hypodermic needle, and the 3D profile of the containers facilitates enhanced diffusion with the surrounding medium as compared to reservoir systems fabricated in planar substrates. We compare the features of the containers to those of present day drug delivery systems. These features include ease of manufacture, versatility in size and shape, monodisperse porosity, ability for spatial manipulation and remote triggering to release drugs on-demand, the incorporation of electronic modules, cell encapsulation, biocompatibility and stability. We also review possible applications in drug delivery and cell encapsulation therapy (CET). The results summarized in this review suggest a new strategy to enable construction of "smart", three dimensional drug delivery systems using lithography.