Our ability to create precise, pre-designed, spatially patterned biochemical and physical microenvironments inside polymer scaffolds could provide a powerful tool in studying progenitor cell behavior and differentiation under biomimetic, three-dimensional (3D) culture conditions. We have developed a simple and fast, layer-by-layer microstereolithography system consisting of an ultra-violet light source, a digital micro-mirror masking device, and a conventional computer projector, that allows fabrication of complex internal features along with precise spatial distribution of biological factors inside a single scaffold. Photo-crosslinkable poly(ethylene glycol) diacrylates were used as the scaffold material, and murine bone marrow-derived cells were successfully encapsulated or seeded on fibronectin-functionalized scaffolds. Fluorescently-labeled polystyrene microparticles were used to show the capability of this system to create scaffolds with complex internal architectures and spatial patterns. We demonstrate that precisely controlled pore size and shapes can be easily fabricated using a simple, computer-aided process. Our results further indicate that multi-layered scaffolds with spatially distributed factors in the same layer or across different layers can be efficiently manufactured using this technique. These microfabricated scaffolds are conducive for osteogenic differentiation of marrow-derived stem cells, as indicated by efficient matrix mineralization.

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Understanding cell behavior inside complex, three-dimensional (3D) microenvironments with controlled spatiotemporal patterning of physical and biochemical factors would provide significant insights into the basic biology of organ development and tissue functions. One of the fundamental limitations in studying such behavior has been the inability to create patterned microenvironments within 3D scaffold structures. Here a simple, layer-by-layer stereolithography (SL) method that can precisely pattern ligands, extracellular-matrix (ECM) components, and growth factors, as well as controlled release particles inside a single scaffold, has been developed. The process also allows fabrication of predesigned internal architectures and porosities. Photocrosslinkable poly(ethylene glycol) dimethacrylate (PEGDMA) was used as the basic structural component of these microfabricated scaffolds. PEG acrylates, covalently modified with the cell adhesive peptide arginine-glycine-aspartic acid (RGD) or the ECM component heparan sulfate, was incorporated within the scaffolds to facilitate cell attachment and to allow spatial sequestration of heparan-binding growth factors. Fluorescently labeled polymer microparticles and basic fibroblast growth factor (FGF-2) were chosen to illustrate the capability of SL to spatiotemporally pattern scaffolds. The results demonstrate that a precise, predesigned distribution of single or multiple factors within a single 3D structure can be created, and specific internal architectures can be fabricated. Functionalization of these scaffolds with RGD is demonstrated, and heparan sulfate allows efficient cell attachment and spatial localization of growth factors. Such patterned scaffolds might provide effective systems to study cell behavior in complex microenvironments and could eventually lead to engineering of complex, hybrid tissue structures through predesigned, multilineage differentiation of a single stem-cell population.

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A direct-current current-voltage (DCIV) measurement technique of interface and oxide traps on oxidized silicon is demonstrated. It uses the gate-controlled parasitic bipolar junction transistor of a metal-oxide-silicon field-effect transistor in a pln junction isolation well to monitor the change of the oxide and interface trap density. The dc base and collector currents are the monitors, hence, this technique is more sensitive and reliable than the traditional ac methods for determination of fundamental kinetic rates and transistor degradation mechanisms, such as charge pumping.