Biomedical subjects

Kristen Bremmell

Publications and source records attributed to Kristen Bremmell.

4 recordsLinked to original sources

PubMed2006

The influence of polymer structure and morphology on talc wettability.

Advancing water contact angles were measured on freshly cleaved talc faces as well as on talc particles. The intrinsic hydrophobicity of talc was shown to be due to the dominance of the apolar components of the work of adhesion. Polyacrylamides and polysaccharides adsorb onto the surface of talc, displaying strikingly different morphologies. Adsorbed amount, apparent layer thickness, and polymer structure control talc wettability.

Journal Article↗

PubMed2005

Improved dewatering behavior of clay minerals dispersions via interfacial chemistry and particle interactions optimization.

Orthokinetic flocculation of clay dispersions at pH 7.5 and 22 degrees C has been investigated to determine the influence of interfacial chemistry and shear on dewatering and particle interactions behavior. Modification of pulp chemistry and behavior was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and anionic polyacrylamide copolymer (PAM A) and non-ionic polyacrylamide homopolymer (PAM N) as flocculants. The pivotal role of shear, provided by a two-blade paddle impeller, was probed as a function of agitation rate (100-500 rpm) and time (15/60 s). Particle zeta potential and adsorption isotherms were measured to quantify the interfacial chemistry, whilst rheology and cryogenic SEM were used to investigate particle interactions and floc structure and aggregate network, respectively. Osmotic swelling, accompanied by the formation of "honeycomb" particle network structure and high yield stress, was produced by the Na-exchanged smectite, but not kaolinite, dispersions. Dispersion of the clay particles in 0.05 M Ca(II) or Mn(II) solution led to a marked reduction in particle zeta potential, complete suppression of swelling, honeycomb network structure collapse and a concomitant reduction in shear yield stress of smectite pulps. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs comprised (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time, and (iv) anionic rather than non-ionic PAM. The optimum dewatering rates were significantly higher than those produced by standard, manual-mixing flocculation techniques (plunging and cylinder inversion) commonly used in industry for flocculant trials. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20-22 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5-7 wt% solid. Higher shear yield stresses and greater settling rates were displayed by PAM A based than PAM N based pulps and this is attributed to the former's more expanded interfacial conformation and greater clay particles bridging ability. It appears that the intrinsic clay particles' physico-chemical properties and interactions limit compact pulp consolidation.

Journal Article↗

PubMed2005

Morphology of adsorbed polymers and solid surface wettability.

The adsorption of a polyacrylamide (MW 14600) and two polysaccharides (MW 9260 and 706 x 10(3)) onto model silica surfaces of different hydrophobicities was investigated. In all cases, adsorption adhered to the Freundlich isotherm, reflecting the heterogeneous character of the solid substrates. The latter strongly influenced the character of the adsorbed polymer, with morphologies from chainlike structures to thin films and patches being observed. Surface roughness, polymer type, and molecular weight also play roles in controlling adsorbed polymer morphology. Surface wettability is strongly influenced by the thickness of the adsorbed layer.

Journal Article↗

PubMed2004

Vitronectin adsorption on surfaces visualized by tapping mode atomic force microscopy.

Vitronectin (Vn) is an abundant glycoprotein present in plasma and the extracellular matrix of most tissue and is an important medium required for bone cells to attach and spread on biomaterial surfaces. Hence, Vn adsorption is an initial and key step in implantation. In this study, adsorption of Vn molecules on mica and oxidized titanium substrates in Milli-Q water (pH 5.6) and in simulated body fluid (SBF, pH 7.4) has been investigated using tapping mode atomic force microscopy. Conformation of the adsorbed proteins was determined from the images. The effect of adsorption time was investigated on mica surfaces. The protein first attaches to the surface, then immediately spreads out with different lateral dimensions of adsorbed protein and becomes aggregated. After 15 min of adsorption, globular Vn molecules form clusters of aggregates in extended chains on the mica surface. Globular Vn molecules appear flatter (i.e., oblate ellipsoids) and coalesce on the ridges of the uneven oxidized titanium surface. From cross-sectional analyses of the Vn images, it was found that the contact areas of Vn molecules associated with Ti surfaces are larger than those with mica surfaces. This suggests that the different surface properties of substrates contribute to this different conformation of adsorbed Vn molecules. The larger contact areas of Vn associated with Ti substrates indicates higher affinity for the biomaterial oxidized titanium surface than for mica. In SBF, Vn interacted weakly with the mica surfaces and Vn molecules were easily desorbed during the imaging process. On oxidized titanium substrates, after 3 h of incubation time in Vn-SBF solution, images can be obtained showing adsorbed Vn aggregates on the oxidized titanium surface. In this case, the protein colloids are strongly adherent, with increased lateral dimensions compared with the adsorption on mica.

Adsorption↗