No abstract

This paper describes the influence of the composition of poly(dimethylsiloxane) (PDMS) on the attachment and growth of several different types of mammalian cells: primary human umbilical artery endothelial cells (HUAECs), transformed 3T3 fibroblasts (3T3s), transformed osteoblast-like MC3T3-E1 cells, and HeLa (transformed epithelial) cells. Cells grew on PDMS having different ratios of base to curing agent: 10:1 (normal PDMS, PDMSN), 10:3 (PDMSCA), and 10:0.5 (PDMSB). They were also grown on "extracted PDMS" (normal PDMS that has reduced quantities of low molecular-weight oligomers, PDMSN,EX) and normal PDMS that had been extracted and then oxidized (PDMSN,EX,OX); all surfaces were exposed to a solution of fibronectin prior to cell attachment. Generally, fibronectin-coated PDMS is a suitable substrate for culturing mammalian cells. Compatibility of cells on some surfaces, however, was dependent on the cell type: PDMSN,EX,OX caused cell detachment of 3T3 fibroblasts and MC3T3-E1 cells, and PDMSCA caused detachment of HUAECs and HeLa cells. Growth of cells on PDMSN, PDMSN,EX, and PDMSB was comparable to growth on tissue culture-treated polystyrene for most of the cell types. All cells grew at similar rates on PDMS substrates regardless of the stiffness of the substrate, for substrates having Young's moduli ranging from E=0.60 +/- 0.04 to 2.6 +/- 0.2 MPa (for PDMSB and PDMSN,EX, respectively).

It is difficult to harness the power generated by biological motors to carry out mechanical work in systems outside the cell. Efforts to capture the mechanical energy of nanomotors ex vivo require in vitro reconstitution of motor proteins and, often, protein engineering. This study presents a method for harnessing the power produced by biological motors that uses intact cells. The unicellular, biflagellated algae Chlamydomonas reinhardtii serve as ''microoxen.'' This method uses surface chemistry to attach loads (1-to 6-m-diameter polystyrene beads) to cells, phototaxis to steer swimming cells, and photochemistry to release loads. These motile microorganisms can transport microscale loads (3-m-diameter beads) at velocities of Ϸ100 -200 m⅐sec ؊1 and over distances as large as 20 cm.biological motors ͉ Chlamydomonas ͉ phototaxis ͉ microfluidics ͉ microspheres T his study demonstrates the biological propulsion of microscale loads by the unicellular photosynthetic algae Chlamydomonas reinhardtii (CR). We exploit the chemistry of the algal cell wall to attach single 1-to 6-m polymer beads to CR. Cells with these ''loads'' attached swim at velocities as high as 100-200 m⅐sec Ϫ1 , approximately the velocity of unmodified cells. CR is phototactic and can be guided by using visible light ( Ϸ 500 nm); we have used this phototaxis to control the transport of microscale loads. A photocleavable linker between the surface of the bead and the cell wall allows us to release loads from the surface of the cell photochemically. We have combined these processes to pick up, transport, guide, and drop off beads by using motile cells.There are many examples of nanometer-scale motors in nature. Within the cell, linear motors, including DNA and RNA polymerase, dyneins, kinesins, and myosin, play a critical role in transcription, mitosis, meiosis, muscle contraction, and transporting organelles and synaptic vesicles (1-5). In eukaryotic mitochondria, a rotary motor, ATP synthase, produces ATP by harnessing the flow of protons down an electrochemical proton gradient (6, 7). Outside of the cell, ciliary dyneins drive the beating of eukaryotic flagella and cilia. In bacteria, a complex of Ϸ20 proteins makes up the remarkable rotary motor that powers the motion of flagella (8).Interest in biological motors is based on both their transduction of energy and their small size and hence their possible relevance to micro͞nanotechnology; the remarkable work of Walker, Vale, Kinosita, Hirokawa, Yanagida and others (9-17) has transformed our understanding of molecular motors. One outcome has been the design and fabrication of new synthetic motors composed entirely of biological molecules (18, 19); another outcome has been the integration of components onto recombinant biological motors (20)(21)(22).Here, we use biological motors intact in cells that use flagella (23). An advantage of this strategy over that using isolated and reconstituted motors is its simplicity. It (i) avoids purification and reconstitution of individual motor proteins, (ii) takes...

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