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Colin Grant

Publications and source records attributed to Colin Grant.

5 recordsLinked to original sources
PubMed2006

Orientation of a monoclonal antibody adsorbed at the solid/solution interface: a combined study using atomic force microscopy and neutron reflectivity.

Conformational orientations of a mouse monoclonal antibody to the beta unit of human chorionic gonadotrophin (anti-beta-hCG) at the hydrophilic silicon oxide/water interface were investigated using atomic force microscopy (AFM) and neutron reflectivity (NR). The surface structural characterization was conducted with the antibody concentration in solution ranging from 2 to 50 mg.L(-1) with the ionic strength kept at 20 mM and pH = 7.0. It was found that the antibody adopted a predominantly "flat-on" orientation, with the Fc and two Fab fragments lying flat on the surface. The AFM measurement revealed a thickness of 30-33 A of the layer formed in contact with 2 mg.L(-1) antibody in water, but, interestingly, the flat-on antibody molecules formed small nonuniform clusters equivalent to 2-15 antibody molecules. Parallel AFM scanning in air revealed even larger surface clusters, suggesting that surface drying induced further aggregation. The AFM study thus demonstrated that the interaction between protein and the hydrophilic surface is weak and indicated that surface aggregation can be driven by the attraction between neighboring protein molecules. NR measurements at the solid/water interface confirmed the flat-on layer orientation of adsorbed molecules over the entire concentration range studied. Thus, at 2 mg.L(-1), the adsorbed antibody layer was well represented by a uniform layer with a thickness of 40 A. This value is thicker than the 30-33 A observed from AFM, suggesting possible layer compression caused by the tip tapping. An increase in the antibody concentration to 10 mg.L(-1) led to increasing surface adsorption. The corresponding layer structure was well represented by a three-layer model consisting of an inner sublayer of 10 A, a middle sublayer of 30 A, and an outer sublayer of 25 A, with the protein volume fractions in each sublayer being 0.22, 0.42, and 0.10, respectively. The structural transition can be interpreted as a twisting and tilting of segments of the adsorbed molecules, driven by an electrostatic repulsion between them that increases with the surface packing density. Hindrance of antigen access to antibody binding sites, resulting from the change in surface packing, can account for the decrease in antigen binding capacity (AgBC) with increasing surface density of the antibody that is observed.

Animals↗
PubMed2005

Biphasic surface amorphous layer lubrication of articular cartilage.

The biphasic nature of articular cartilage has been acknowledged for some time and is known to play an important role in many of the biomechanical functions performed by this unique tissue. From the lubrication point of view however, a simple biphasic model is unable to account for the extremely low friction coefficients that have been recorded experimentally, particularly during start-up. In addition, research over the last decade has indicated the presence of a surface amorphous layer on top of articular cartilage. Here, we present results from a finite element model of articular cartilage that includes a thin, soft, biphasic surface amorphous layer (BSAL). The results of this study show that a thin BSAL, with lower elastic modulus, dramatically altered the load sharing between the solid and liquid phases of articular cartilage, particularly in the near-surface regions of the underlying bulk cartilage and within the surface amorphous layer itself where the fluid load support exceeded 85%. By transferring the load from the solid phase to the fluid phase, the biphasic surface layer improves lubrication and reduces friction, whilst also protecting the underlying cartilage surface by 'shielding' the solid phase from elevated stresses. The increase in lubrication effectiveness is shown to be greatest during short duration loading scenarios, such as shock loads.

Biomechanical Phenomena↗
PubMed2005

Reversal of laser in situ keratomileusis-induced ectasia with intraocular pressure reduction.

A 40 year-old woman had laser in situ keratomileusis for --7.75 --0.75 x 20 in the right eye. Preoperative examinations, including topography, pachymetry, and intraocular pressures (IOPs), were normal, and best spectacle-corrected visual acuity (BSCVA) was 20/20 in each eye. By 4 months postoperatively, the uncorrected visual acuity and BSCVA in the right eye had decreased to 20/40. Corneal topography of that eye was consistent with ectasia. One drop per day of timolol 0.5% (Timoptic XE) was prescribed. Five months postoperatively, the IOP had decreased and BSCVA and topography had improved. At 11 months, BSCVA returned to 20/20 and corneal topography normalized. Topographic difference maps were used to monitor corneal shape changes. In this case, early reduction in IOP completely reversed the ectasia.

Adult↗
PubMedDate not supplied

Poly(vinyl alcohol) hydrogel as a biocompatible viscoelastic mimetic for articular cartilage.

The prevalence of suboptimal outcome for surgical interventions in the treatment of full-thickness articular cartilage damage suggests that there is scope for a materials-based strategy to deliver a more durable repair. Given that the superficial layer of articular cartilage creates and sustains the tribological function of synovial joints, it is logical that candidate materials should have surface viscoelastic properties that mimic native articular cartilage. The present paper describes force spectroscopy analysis by nano-indentation to measure the elastic modulus of the surface of a novel poly(vinyl alcohol) hydrogel with therapeutic potential as a joint implant. More than 1 order of magnitude decrease in the elastic modulus was detected after adsorption of a hyaluronic acid layer onto the hydrogel, bringing it very close to previously reported values for articular cartilage. Covalent derivatization of the hydrogel surface with fibronectin facilitated the adhesion and growth of cultured rat tibial condyle chondrocytes as evidenced morphologically and by the observance of metachromatic staining with toluidine blue dye. The present results indicate that hydrogel materials with potential therapeutic benefit for injured and diseased joints can be engineered with surfaces with biomechanical properties similar to those of native tissue and are accepted as such by their constituent cell type.

Animals↗