Publications

An understanding of protein adsorption process is crucial for designing biomaterial surfaces. In this work, with the use of a quartz-crystal microbalance with dissipation monitoring, we researched the following: (a) the kinetics of adsorption on TiO2 surfaces of three extensively described proteins that are relevant for metallic implant integration [i.e., albumin (BSA), fibrinogen (Fbg), and fibronectin (Fn)]; and (b) the competition of those proteins for adsorbing on TiO2 in a two-step experiment consisted of sequentially exposing the surfaces to different monoprotein solutions. Each protein showed a different process of adsorption and properties of the adlayer-calculated using the Voigt model. The competition experiments showed that BSA displaced larger proteins such as Fn and Fbg when BSA was introduced as the second protein in the system, whereas the larger proteins laid on top of BSA forming an adsorbed protein bi-layer when those were introduced secondly in the system.

JTD Keywords: QCM, Human plasma fibronectin, Induced conformational-changes, Von-willebrand-factor, BSA, Protein adsortion, Polymer surfaces, Solid-surfaces, Viscoelastic properties, Globular-proteins

Collagen IV (Col IV) and laminin (Lam) are the main structural components of the basement membrane where they form two overlapping polymeric networks. We studied the adsorption pattern of these proteins on five model surfaces with tailored density of -OH groups obtained by copolymerization of different ratios ethyl acrylate (EA) and hydroxyl EA (HEA): X(OH) = 0, X(OH) = 0.3, X(OH) = 0.5, X(OH) = 0.7, and X(OH) = 1 (where X refers the ratio of HEA). Atomic force microscopy revealed substratum-specific adsorption patterns of Col IV and Lam, ranging from single molecules deposition on more hydrophilic substrata to the formation of complex networks on hydrophobic ones. Human umbilical endothelial cells were used to study the biological performance of adsorbed proteins, following the overall cell morphology, the quantities for cell adhesion and spreading, and the development of focal adhesion complexes and actin cytoskeleton. Surprisingly, two optima in the cellular interaction were observed-one on the most hydrophilic X(OH) = 1 and other on the relatively hydrophobic X(OH) = 0.3 substrate-valid for both Col IV and Lam. When the proteins were adsorbed consecutively, a hydrophobic shift to X(OH) = 0 substratum was obtained. Collectively, these data suggest that varying with the density of -OH groups one can tailor the conformation and the functional activity of adsorbed basement membrane proteins.

JTD Keywords: Atomic-force microscopy, Fibronectin adsorption, Basement-membranes, Polymer surfaces, Cell-adhesion, Biomaterials, Wettability, Fibrinogen

Fibronectin (FN) fibrillogenesis is a cell-mediated process involving integrin activation that results in conformational changes of FN molecules and the organization of actin cytoskeleton. A similar process can be induced by some chemistries in the absence of cells, e.g., poly(ethyl acrylate) (PEA), which enhance FN-FN interactions leading to the formation of a biologically active network. Atomic force microscopy images of single FN molecules, at the early stages of adsorption on plane PEA, allow one to rationalize the process. Further, the role of the spatial organization of the FN network on the cellular response is investigated through its adsorption on electrospun fibers. Randomly oriented and aligned PEA fibers were prepared to mimic the three-dimensional organization of the extracellular matrix. The formation of the FN network on the PEA fibers but not on the supporting coverglass was confirmed. Fibroblasts aligned with oriented fibers, displayed extended morphology, developed linearly organized focal adhesion complexes, and matured actin filaments. Conversely, on random PEA fibers, cells acquired polygonal morphology with altered actin cytoskeleton but well-developed focal adhesions. Late FN matrix formation was also influenced: spatially organized FN matrix fibrils along the oriented PEA fibers and an altered arrangement on random ones.

JTD Keywords: AFM, Cell-adhesion, Dependent conformations, Hydrophobic surfaces, Extracellular-matrix, Bound fibronectin, Polymer surfaces, Integrin binding, Biocompatibility, Adsorption