Biomedical subjects

Aline F Miller

Publications and source records attributed to Aline F Miller.

4 recordsLinked to original sources

PubMed2006

Thermoreversible protein hydrogel as cell scaffold.

A thermoreversible fibrillar hydrogel has been formed from an aqueous lysozyme solution in the presence of dithiothreitol (DTT). Its physical properties and potential as a tissue engineering scaffold have been explored. Hydrogels were prepared by dissolving 3 mM protein in a 20 mM DTT/water mixture, heating to 85 degrees C and cooling at room temperature. No gel was observed for the equivalent sample without DTT. The elastic nature of the gel formed was confirmed by rheology, and the storage modulus of our gel was found to be of the same order of magnitude as for other cross-linked biopolymers. Micro differential scanning calorimetry (microDSC) experiments confirmed that the hydrogel was thermally reversible and that gelation and melting occurs through a solid-liquid-like first-order transition. Infrared spectroscopy of the hydrogel and transmission electron microscopy studies of very dilute samples revealed the presence of beta-sheet-rich fibrils that were approximately 4-6 nm in diameter and 1 mum in length. These fibrils are thought to self-assemble along their long axes to form larger fibers that become physically entangled to form the three-dimensional network observed in both cryo-scanning electron microscopy (cryo-SEM) and small-angle neutron scattering (SANS) studies. The hydrogel was subsequently cultured with 3T3 fibroblasts and cells spread extensively after 7 days and stretched actin filaments formed that were roughly parallel to each other, indicating the development of organized actin filaments in the form of stress fibers in cells.

Animals↗

PubMed2004

The formation of spherulites by amyloid fibrils of bovine insulin.

Bovine insulin has long been known to self-assemble in vitro into amyloid fibrils. We have observed a further higher-order self-association of the protein into spherical structures, with diameters typically around 50 microm but ranging from 10 to 150 microm. In a polarizing light microscope, these structures exhibit a "Maltese-cross" extinction pattern typical of spherulites. Spherical structures of a similar size distribution can be observed in the environmental scanning electron microscope, which also reveals the presence of significant amounts of water in the structures. The spherulites contain a large quantity of well defined amyloid fibrils, suggesting that they are formed at least in part as a consequence of the self-assembly of preformed fibrils. Similar structures also have been observed in the tissues of patients suffering from amyloid disorders. The ability of amyloid fibrils to form such higher-order assemblies supports the hypothesis that they represent a generic form of polypeptide structure with properties that are analogous to those of classical synthetic polymers.

Amyloid↗

PubMed2004

Neutron reflectivity and external reflection FTIR studies of DL-aspartic acid crystallization beneath nylon 6 spread films.

The crystallization of DL-aspartic acid beneath nylon 6 spread films has been studied for 150% supersaturated systems using neutron reflectivity and external reflection FTIR. The neutron reflectivity data showed the gradual incorporation of DL-aspartic acid within a nylon 6 spread film layer over a period of 6-8 h, culminating in over 50 vol % of the "film" layer comprising DL-aspartic acid. Accumulation of further DL-aspartic acid material to produce microscopic/macroscopic surface crystals occurred, but on a more limited scale, resulting in approximately 1-5% surface coverage of crystals over the same period. External reflection FTIR studies revealed very weak bands attributable to DL-aspartic acid in surface regions devoid of visible crystals, in agreement with the neutron reflectivity studies. In regions with visible crystals, much larger and sharper DL-aspartic acid bands were seen. Changes in the intensity of the nylon 6 NH stretch band were often observed during the visible crystallization and dissolution of DL-aspartic acid and were consistent with the reversible accumulation of nylon 6 around the growing crystals.

Aspartic Acid↗

PubMedDate not supplied

Imaging of anisotropic cellulose suspensions using environmental scanning electron microscopy.

The effect of concentration on anisotropic phase behavior of acid-hydrolyzed cellulose suspensions has been examined using conventional polarizing microscopy and the novel technique of environmental scanning electron microscopy (ESEM). Microcrystalline cellulose dispersed in water formed biphasic suspensions in a narrow concentration range, 4-12 wt % for a suspension pH of 4, where the upper and lower phases were isotropic and anisotropic (chiral nematic), respectively. It is known from previous work that within the biphasic regime total suspension concentration affects only the volume fractions of the two phases, not phase concentration or interfacial packing. As the total suspension concentration surpassed the upper critical limit (c), however, a single anisotropic phase of increasing concentration was observed. It was evident from polarizing microscopy that the chiral nematic pitch of the anisotropic phase decreased with increasing concentration, which has been attributed to a reduction in the electrostatic double layer thickness of the individual rods, thus increasing intermolecular interactions. Chiral nematic textures were also visible using ESEM. This technique has the advantage of studying individual rod orientation within the liquid crystalline phase as it permits the high resolution of electron microscopy to be applied to hydrated samples in their natural state. To our knowledge this is the first time such lyotropic systems have been observed using electron microscopy.

Anisotropy↗