Nature exhibits phenomenally intricate architecture in various organisms and it is through these structures that researchers in the fi eld of materials science derive inspiration in creating new biomaterials. [ 1 ] One such organism that has drawn attention due to its architecture is the diatom, a unicellular algae, which has a characteristic ornate siliceous cell wall (known as a "frustule") that current engineering practices cannot fabricate. The proposed applications for diatoms in catalysis, [ 2 ] separation science, [ 3 ] and optics [ 4 ] are heavily dependent on the architecture of the diatom. There has been an interest in altering the chemistry of the frustule, and replication of the frustule in order to expand on possible applications frustule. [ 5 ] Inorganic replicas have predominated: (i) MgO, [ 5a ] TiO 2 , [ 5b ] and ZrO 2[ 5c ] replicas via gas/solid displacement reactions, and (ii) gold replicas by electroless deposition. [ 5d ] There has been a paucity of reports describing the generation of organic replicas. [ 6 ] Herein, we report on the successful grafting of a unique three-dimensional poly 2-(dimethylamino) ethyl methacrylate-co -ethylene glycol dimethacrylate (polyDMAEMAco -EGDMA) polymer from the centric diatom Thalassiosira weissfl ogii via deactivation enhanced atom transfer radical polymerization (DE-ATRP). The DE-ATRP method, fi rst reported for the synthesis of hyperbranched copolymers by Wang and colleagues , [ 7 ] is advantageous for introducing Drug Delivery
A bioactive platform for the quantitative observation of cell migration is presented by 1) presenting migration factors in a well-defined manner on 2-D substrates, and 2) enabling continuous cell tracking. Well-defined substrate presentation is achieved by correctly orienting immobilized proteins (chemokines and cell adhesion molecules), such that the active site is accessible to cell surface receptors. A thiol-terminated self-assembled monolayer on a silica slide was used as a base substrate for subsequent chemistry. The thiol-terminated surface was converted to an immobilized metal ion surface using a maleimido-nitrilotriacetic acid (NTA) cross-linker that bound Histidine-tagged recombinant proteins on the surface with uniform distribution and specific orientation. This platform was used to study the influence of surface-immobilized chemokine SDF-1α and cell adhesion molecule ICAM-1 on murine splenic B lymphocyte migration. While soluble SDF-1α induced trans-migration in a Boyden Chamber type chemotaxis assay, immobilized SDF-1α alone did not elicit significant surface-migration on our test-platform surface. Surface-immobilized cell adhesion protein, ICAM-1, in conjunction with activation enabled migration of this cell type on our surface. Controlled exposure to UV light was used to produce stable linear gradients of His-tagged recombinant SDF-1α co-immobilized with ICAM-1 following our surface chemistry approach. XPS and antibody staining showed defined gradients of outwardly oriented SDF-1α active sites. This test platform can be especially valuable for investigators interested in studying the influence of surface-immobilized factors on cell behavior and may also be used as a cell migration enabling platform for testing the effects of various diffusible agents.
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