Abstract: The response of biomaterial surfaces when exposed to blood is in part dependent upon the nature and composition of the adsorbed layer of proteins. Surfaces passivated with albumin have been shown to reduce platelet adhesion and activation. In an attempt to develop surfaces that can selectively and specifically bind albumin, silicon-based surfaces were functionalized with linear peptides and chemical ligands that displayed an affinity for albumin. Peptide functionalized surfaces were observed to preferentially bind albumin when compared to human immunoglobulin and human fibrinogen, which possess low densities of surface adsorbed platelets. The platelet morphology was noted to be discoid on the peptide modified surface. Both the unmodified control and SCL functionalized surfaces had high densities of surface adhered platelets with spread out morphology. The peptide and SCL functionalized surfaces were noted to have no impact on PTT and PT clotting times, indicating that the extrinsic and intrinsic pathways were unperturbed by the surfaces generated.
Abstract: Both pulsed- and square-wave, low-intensity ultrasound (US) signals have been reported to impact chondrocyte function and biosynthetic activity. In this study, a low-intensity diffuse ultrasound (LIDUS) signal at 5.0 MHz (0.14 mW/cm(2)) was employed to stimulate bovine chondrocytes seeded in three-dimensional (3D) chitosan-based matrices. While the duration of application was constant at 51 s, US was applied once, twice, four times and eight times/day, and the impacts of US on the biosynthetic activity of chondrocytes and the expression of chondrocyte-specific genes were evaluated. When stimulated with continuous US for predetermined time intervals, chondrocytes had higher levels of type II collagen, aggrecan, L-Sox5 and Sox9 mRNA expression when compared to controls; however, under the same conditions, the expression of MMP-3 was downregulated. Interestingly, both Sox5 and Sox9 genes coordinately responded to changes in US stimulation and generally mirrored the response of collagen type II transcript to changes in US stimulation. RT-PCR analysis revealed that US stimulation increased the gene expression of cell-surface integrins α5 and β1. The expression of integrins α2 was downregulated by US treatment, suggesting that multiple integrin subunits may be involved in the regulation of chondrocytic function in response to US stimuli. The enhancement in the abundance of the mRNA transcripts upon US stimulation was observed to correlate with the protein expression of collagen type I, collagen type II, and integrins α5 and β1. In conclusion, the US stimulation regimen employed was shown to modulate the proliferative capacity, biosynthetic activity and integrin mRNA expression of articular chondrocytes maintained in 3D matrices.
Abstract: Surface modification strategies that take advantage of the passivation effects of albumin are important in the development of biomaterial surfaces. In this study, linear peptides (LP1, LP2) and a small chemical ligand (SCL) with albumin binding affinities were grafted onto silane functionalized silicon substrates. Surfaces were characterized with contact angle and ellipsometric measurements, and densities of immobilized ligands were assessed spectroscopically. Ellipsometrically measured thickness correlated with the predicted molecular lengths of grafted moieties. Contact angle analysis indicated that the LP1 and LP2 functionalized surfaces were hydrophilic compared to SCL functionalized and control surfaces. Adsorption of albumin from human serum was evaluated and quantified via specific enzyme-linked immunosorbent assays and 2D gel electrophoresis. The following trend was noted for surface adsorbed albumin: LP1 > LP2 > SCL > C, with LP1 derivatized surfaces having ~2.450 μg/cm(2) of bound albumin. LP1 derivatized surfaces possessed the least number of adsorbed platelets with rounded platelet morphology when compared to control surface.
