The role of medical equipment in the spread of nosocomial infections: a cross-sectional study in four tertiary public health facilities in Uganda.

BACKGROUND: With many medical equipment in hospitals coming in direct contact with healthcare workers, patients, technicians, cleaners and sometimes care givers, it is important to pay close attention to their capacity in harboring potentially harmful pathogens. The goal of this study was to assess the role that medical equipment may potentially play in hospital acquired infections in four public health facilities in Uganda. METHODS: A cross-sectional study was conducted from December 2017 to January 2018 in four public health facilities in Uganda. Each piece of equipment from the neonatal department, imaging department or operating theatre were swabbed at three distinct points: a location in contact with the patient, a location in contact with the user, and a remote location unlikely to be contacted by either the patient or the user. The swabs were analyzed for bacterial growth using standard microbiological methods. Seventeen bacterial isolates were randomly selected and tested for susceptibility/resistance to common antibiotics. The data collected analyzed in STATA version 14. RESULTS: A total of 192 locations on 65 equipment were swabbed, with 60.4% of these locations testing positive (116/192). Nearly nine of ten equipment (57/65) tested positive for contamination in at least one location, and two out of three equipment (67.7%) tested positive in two or more locations. Of the 116 contaminated locations 52.6% were positive for Bacillus Species, 14.7% were positive for coagulase negative staphylococcus, 12.9% (15/116) were positive for E. coli, while all other bacterial species had a pooled prevalence of 19.8%. Interestingly, 55% of the remote locations were contaminated compared to 66% of the user contacted locations and 60% of the patient contacted locations. Further, 5/17 samples were resistant to at least three of the classes of antibiotics tested including penicillin, glycylcycline, tetracycline, trimethoprim sulfamethoxazole and urinary anti-infectives. CONCLUSION: These results provides strong support for strengthening overall disinfection/sterilization practices around medical equipment use in public health facilities in Uganda. There's also need for further research to make a direct link to the bacterial isolates identified and cases of infections recorded among patients in similar settings.

Silica-dispersed glucose oxidase for glucose sensing: in vitro testing in serum and blood and the effect of condensation pH.

The objectives of this study were to examine the feasibility of using glucose oxidase (GOx) dispersed in a silica matrix for glucose monitoring in whole blood, and then to assess whether the flexibility of silica sol-gel chemistry could be exploited to enhance glucose sensor performance and stability. Silica-dispersed GOx was deployed on platinized platinum (Pt) wire to form a Clark-type amperometric glucose sensor. Sensors were calibrated using buffered glucose standard solutions, and then tested against glucose spiked human serum and whole blood. All serum and whole blood measurements met the minimum FDA requirement of falling within the "A+B region" of a Clark Error Grid. To our knowledge this is the first report of using silica-dispersed GOx to measure glucose in whole blood. The effect of condensation pH on sensor performance was assessed by dispersing GOx in silica condensed at pH 3, 7 and 12, and then testing the sensor response against glucose calibration standards. The pH 12 silica sensors had statistically faster response time, and higher sensor sensitivity compared to pH 7, pH 3 silica and glutaraldehyde crosslinked sensors. Membranes of the pH 12 silica had statistically higher glucose diffusion coefficient than did the pH 7 and 3 sensors. GOx dispersed in pH 12 silica also had the longest half life. We hypothesize that the gel-like pH 12 silica gels provided reduced barriers to glucose diffusion, and the more aqueous microenvironment provided greater stability for the enzyme.

Modeling the relative impact of capsular tissue effects on implanted glucose sensor time lag and signal attenuation.

Little is known mechanistically about why implanted glucose sensors lag behind blood glucose levels in both the time to peak sensor response and the magnitude of peak sensor response. A mathematical model of glucose transport from capillaries through surrounding tissue to the sensor surface was constructed to address how different aspects of the tissue affect glucose transport to an implanted sensor. Physiologically relevant values of capsule diffusion coefficient, capsule porosity, cellular glucose consumption, capsule thickness, and subcutaneous vessel density were used as inputs to create simulated sensor traces that mimic experimental instances of time lag and concentration attenuation relative to a given blood glucose profile. Using logarithmic sensitivity analysis, each parameter was analyzed to study the effect of these variables on both lag and attenuation. Results identify capsule thickness as the strongest determinant of sensor time lag, while subcutaneous vessel density and capsule porosity had the largest effects on attenuation of glucose that reaches the sensor surface. These findings provide mechanistic insight for the rational design of sensor modifications that may alleviate the deleterious consequences of tissue effects on implanted sensor performance.

Collagen-Mimetic Proteins with Tunable Integrin Binding Sites for Vascular Graft Coatings.

Achieving graft endothelialization following implantation continues to be a challenge in the development of "off-the-shelf," small-caliber, arterial prostheses. Coating grafts with biomolecules to support the retention, migration, and differentiation of adherent endothelial precursor cells (EPCs) is a promising approach toward improving graft endothelialization. Designer Collagen Scl2-2 with 1 integrin binding site per strand (DC2-1X) is a Streptococcus pyogenes-derived, collagen-like protein that has previously been evaluated as a graft coating due to its ability to resist platelet aggregation and to promote attachment and migration of "late outgrowth" EPCs (EOCs). However, these prior assessments were performed in the absence of physiological shear. In addition, although DC2-1X coatings supported increased migration rates relative to native collagen coatings, EOC attachment and spreading remained inferior to collagen controls at all DC2-1X concentrations assayed. Thus, the objectives of the present work were the following: (1) to improve EOC attachment on DC2 coatings by modulating the number and spacing of DC2 integrin binding sites (IBS) and (2) to evaluate the retention, migration, and differentiation of adherent EOCs under physiological shear stress. Using single point mutations, three novel DC2 variants were generated containing either two IBS (DC2-2X) or three IBS (DC2-3X1 and DC2-3X2) per strand. After initial evaluation of the potential of each DC2 variant to support increased EOC attachment relative to DC2-1X, DC2-2X and DC2-3X1 coatings were further assessed under physiological shear for their capacity to promote EOC retention, migration, and differentiation relative to DC2-1X and collagen controls. An increase in the number of IBS from 1 to 3 significantly improved EOC retention on DC2 coatings while also supporting increased average migration rates. Moreover, EOCs on DC2-3X1 coatings showed increased gene-level expression of intermediate endothelial cell differentiation markers relative to collagen. Overall, the current results suggest that DC2-3X1 warrants further investigation as a vascular graft coating.

In vitro, in vivo and post explantation testing of glucose-detecting biosensors: current methods and recommendations.

To date, there have been a number of cases where glucose sensors have performed well over long periods of implantation; however, it remains difficult to predict whether a given sensor will perform reliably, will exhibit gradual degradation of performance, or will fail outright soon after implantation. Typically, the literature emphasizes the sensor that performed well, while only briefly (if at all) mentioning the failed devices. This leaves open the question of whether current sensor designs are adequate for the hostile in vivo environment, and whether these sensors have been assessed by the proper regimen of testing protocols. This paper reviews the current in vitro and in vivo testing procedures used to evaluate the functionality and biocompatibility of implantable glucose sensors. An overview of the standards and regulatory bodies that govern biomaterials and end product device testing precedes a discussion of up-to-date invasive and non-invasive technologies for diabetes management. Analysis of current in vitro, in vivo, and then post explantation testing is presented. Given the underlying assumption that the success of the sensor in vitro foreshadows the long-term reliability of the sensor in the human body, the relative merits of these testing methods are evaluated with respect to how representative they are of human models.

Adult adipose-derived stem cell attachment to biomaterials.

Attachment of adipose-derived stem cells (ASCs) to biomaterials prior to implantation is a possible strategy for mediating inflammation and wound healing. In this study, the ASC percent coverage was measured on common medical grade biosensor materials subjected to different surface treatments. Cell coverage on silicone elastomer (poly-dimethylsiloxane) was below 20% for all surface treatments. Polyimide (Kapton), polyurethane (Pellethane) and tissue culture polystyrene all exhibited >50% coverage for surfaces treated with fibronectin (Fn), fibronectin plus avidin/biotin (dual ligand), and oxygen plasma plus fibronectin treatments (FnO2). The fibronectin treatment performed as well or better on polyimide, polyurethane, and tissue culture polystyrene compared to the dual ligand and fibronectin oxygen plasma-treated surfaces. Cell detachment with increasing shear stresses was <25% for each attachment method on both polyimide and polyurethane. The effects of attachment methods on the basic cell functions of proliferation, metabolism, ATP concentration, and caspase-3 activity were analyzed yielding proliferation profiles that were very similar among all of the materials. No significant differences in metabolism, intracellular ATP, or intracellular caspase-3 activity were observed for any of the attachment methods on either polyimide or polyurethane.

The effect of covalently immobilized rhIL-1ra-ELP fusion protein on the inflammatory profile of LPS-stimulated human monocytes.

The objective of this research was to investigate whether immobilized anti-inflammatory cytokines will signal changes in the inflammatory profile of cultured monocytes. A fusion protein of recombinant human IL-1 receptor antagonist and elastin-like peptide (IL-1ra-ELP) was expressed in Escherichia coli. THP-1 human monocytes were cultured on either carboxyl-terminated self-assembled monolayers (SAMs), or SAMs with either covalently immobilized or soluble IL-1ra-ELP. LPS-stimulated monocytes exposed to either soluble or immobilized IL-1ra-ELP were prevented from cell differentiation, showed attenuated expression of pro-inflammatory cytokines, and had increased production of anti-inflammatory and pro-wound healing cytokines. These results suggest that immobilized anti-inflammatory cytokines have the potential to be immunomodulatory biomaterials.

The use of mild trypsinization conditions in the detachment of endothelial cells to promote subsequent endothelialization on synthetic surfaces.

A necessary condition for endothelialization of small diameter grafts is rapid and firm adhesion of endothelial cells upon exposure to flow. To retain integrins on the cell surface, we assessed the effects of trypsin concentration, the duration of trypsin incubation, and trypsin neutralization methods on endothelial cell adhesion. Human umbilical vein endothelial cells which were detached using 0.025% trypsin for 5 min and seeded onto glass pretreated with fibronectin had close to 100% cell retention when shear stresses as high as 200 dyn/cm2 were applied for 2 min. An equivalent level of cell retention was observed on fibronectin coated Teflon-AF for shear stresses up to 60 dyn/cm2 applied for 4h. Using 0.025% trypsin, initial cell spreading and cell surface alpha5beta1 integrins were increased relative to cells treated with 0.5% trypsin. After 1h of attachment, focal adhesions formed when low trypsin concentrations were used but were less evident with high trypsin concentrations. These results showed that low trypsin concentrations produced faster spreading, a higher number of intact integrins, and rapid focal adhesion formation.

Response of monocytes exposed to phagocytosable particles and discs of comparable surface roughness.

This in vitro study characterized the temporal cytokine expression profile from human monocytes exposed to phagocytosable Ti particles (0.78+/-0.12 microm) and to Ti discs of comparable surface roughness. Human THP-1 monocytes were cultured in six well tissue culture polystyrene (TCPS) plates. Each well was either bare, contained Ti particles (the particles were clearly engulfed by the monocytes), or contained a Ti disc. Half of the wells were treated with 1 microg/mL lipopolysaccharide (LPS), while the other half were left unstimulated. Unstimulated and LPS-stimulated cells in bare wells were the negative and positive controls, respectively. Supernatant was sampled from each well at 1, 6, 24, 48, and 72 h and assayed for the expression of nine different cytokines using a Luminex system. Three cytokines (IL-1beta, GM-CSF and IL-13) gave little to no response under all conditions, while six cytokines (TNF-alpha, IL-6, MIP-1alpha, MCP-1, VEGF, and IL-1ra) were clearly detectable. Expression levels generally increased with culture time, particle concentration, and LPS stimulation. Most significantly, it was found that cells treated by Ti discs produced in many instances a higher cytokine expression than did particles.

Evaluation of late outgrowth endothelial progenitor cell and umbilical vein endothelial cell responses to thromboresistant collagen-mimetic hydrogels.

Bioactive coatings which support the adhesion of late-outgrowth peripheral blood endothelial progenitor cells (EOCs) are actively being investigated as a means to promote rapid endothelialization of "off-the-shelf," small-caliber arterial graft prostheses following implantation. In the present work, we evaluated the behavior of EOCs on thromboresistant graft coatings based on the collagen-mimetic protein Scl2-2 and poly(ethylene glycol) (PEG) diacrylate. Specifically, the attachment, proliferation, migration, and phenotype of EOCs on PEG-Scl2-2 hydrogels were evaluated as a function of Scl2-2 concentration (4, 8, and 12 mg/mL) relative to human umbilical vein endothelial cells (HUVECs). Results demonstrate the ability of each PEG-Scl2-2 hydrogel formulation to support EOC and HUVEC adhesion, proliferation, and spreading. However, only the 8 and 12 mg/mL PEG-Scl2-2 hydrogels were able to support stable EOC and HUVEC confluence. These PEG-Scl2-2 formulations were, therefore, selected for evaluation of their impact on EOC and HUVEC phenotype relative to PEG-collagen hydrogels. Cumulatively, both gene and protein level data indicated that 8 mg/mL PEG-Scl2-2 hydrogels supported similar or improved levels of EOC maturation relative to PEG-collagen controls based on evaluation of CD34, VEGFR2, PECAM-1, and VE-Cadherin. The 8 mg/mL PEG-Scl2-2 hydrogels also appeared to support similar or improved levels of EOC homeostatic marker expression relative to PEG-collagen hydrogels based on von Willebrand factor, collagen IV, NOS3, thrombomodulin, and E-selectin assessment. Combined, the present results indicate that PEG-Scl2-2 hydrogels warrant further investigation as "off-the-shelf" graft coatings. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1712-1724, 2017.

Porous, Dexamethasone-loaded polyurethane coatings extend performance window of implantable glucose sensors in vivo.

Continuous glucose sensors offer the promise of tight glycemic control for insulin dependent diabetics; however, utilization of such systems has been hindered by issues of tissue compatibility. Here we report on the in vivo performance of implanted glucose sensors coated with Dexamethasone-loaded (Dex-loaded) porous coatings employed to mediate the tissue-sensor interface. Two animal studies were conducted to (1) characterize the tissue modifying effects of the porous Dex-loaded coatings deployed on sensor surrogate implants and (2) investigate the effects of the same coatings on the in vivo performance of Medtronic MiniMed SOF-SENSOR™ glucose sensors. The tissue response to implants was evaluated by quantifying macrophage infiltration, blood vessel formation, and collagen density around implants. Sensor function was assessed by measuring changes in sensor sensitivity and time lag, calculating the Mean Absolute Relative Difference (MARD) for each sensor treatment, and performing functional glucose challenge test at relevant time points. Implants treated with porous Dex-loaded coatings diminished inflammation and enhanced vascularization of the tissue surrounding the implants. Functional sensors with Dex-loaded porous coatings showed enhanced sensor sensitivity over a 21-day period when compared to controls. Enhanced sensor sensitivity was accompanied with an increase in sensor signal lag and MARD score. These results indicate that Dex-loaded porous coatings were able to elicit an attenuated tissue response, and that such tissue microenvironment could be conducive towards extending the performance window of glucose sensors in vivo. STATEMENT OF SIGNIFICANCE: In the present article, a coating to extend the functionality of implantable glucose sensors in vivo was developed. Our study showed that the delivery of an anti-inflammatory agent with the presentation of micro-sized topographical cues from coatings may lead to improved long-term glucose sensor function in vivo. We believe that improved function of sensors treated with the novel coatings was a result of the observed decreases in inflammatory cell density and increases in vessel density of the tissue adjacent to the devices. Furthermore, extending the in vivo functionality of implantable glucose sensors may lead to greater adoption of these devices by diabetic patients.

Response of brain tissue to chronically implanted neural electrodes.

Chronically implanted recording electrode arrays linked to prosthetics have the potential to make positive impacts on patients suffering from full or partial paralysis. Such arrays are implanted into the patient's cortical tissue and record extracellular potentials from nearby neurons, allowing the information encoded by the neuronal discharges to control external devices. While such systems perform well during acute recordings, they often fail to function reliably in clinically relevant chronic settings. Available evidence suggests that a major failure mode of electrode arrays is the brain tissue reaction against these implants, making the biocompatibility of implanted electrodes a primary concern in device design. This review presents the biological components and time course of the acute and chronic tissue reaction in brain tissue, analyses the brain tissue response of current electrode systems, and comments on the various material science and bioactive strategies undertaken by electrode designers to enhance electrode performance.

In vivo performance of dual ligand augmented endothelialized expanded polytetrafluoroethylene vascular grafts.

In this study, we examined combinations of three approaches to improve the adhesion of endothelial cells (EC) onto expanded polytetrafluoroethylene (ePTFE) vascular grafts placed at the femoral artery of rats: (1) high-affinity receptor-ligand binding of RGD-streptavidin (SA) and biotin to supplement integrin-mediated EC adhesion; (2) cell sodding to pressurize the seeded EC into the interstices of the ePTFE grafts; and (3) longer postseeding attachment time from 1 to 24 h prior to implantation. An in vitro system, which accounts for cell loss due to both graft handling and shear stress, was designed to optimize conditions for in vivo experiments. Results suggest that longer in vitro attachment time enabled the adherent EC to endure mechanical stresses by forming strong adhesions to the underlying extracellular matrix substrates; cell sodding helped to retain the adherent EC by physically docking the cells against the graft interstices; and the SA-biotin interaction enhanced the early attachment of EC but did not lead to better cell retention or reduced surface coverage of blood clot in the current study. Mechanical manipulation of cells during implantation is a limiting factor in maintaining a confluent EC layer on synthetic vascular grafts.

Modeling the Physiological Factors Affecting Glucose Sensor Function in Vivo.

For implantable sensors to become a more viable option for continuous glucose monitoring strategies, they must be able to persist in vivo for periods longer than the 3- to 7-day window that is the current industry standard. Recent studies have attributed such limited performance to tissue reactions resulting from implantation. While in vivo biocompatibility studies have provided much in the way of understanding histology surrounding an implanted sensor, little is known about how each constituent of the foreign body response affects sensor function. Due to the ordered composition and geometry of implant-associated tissue reactions, their effects on sensor function may be computationally modeled and analyzed in a way that would be prohibitive using in vivo studies. This review both explains how physiologically accurate computational models of implant-associated tissue reaction can be designed and shows how they have been utilized thus far. Going forward, these in silico models of implanted sensor behavior may soon complement in vivo studies to provide valuable information for improved sensor designs.

Extended fatigue life of a catalyst free self-healing acrylic bone cement using microencapsulated 2-octyl cyanoacrylate.

The tissue adhesive 2-octyl cyanoacrylate (OCA) was encapsulated in polyurethane microshells and incorporated into bone cement to form a catalyst free, self-healing bone cement comprised of all clinically approved components. The bending strength, modulus, and fatigue lifetime were investigated in accordance with ASTM and ISO standards for the testing of PMMA bone cement. The bending strength of bone cement specimens decreased with increasing wt % capsules content for capsules without or with OCA, with specimens of <5 wt % capsule content showing minimal effect. In contrast, bone cement bending modulus was insensitive to capsule content. Load controlled fatigue testing was performed in air at room temperature on capsule free bone cement (0 wt %), bone cement with 5 wt % OCA-free capsules (5 wt % No OCA), and 5 wt % OCA-containing capsules (5 wt % OCA). Specimens were tested at a frequency of 5 Hz at maximum stresses of 90%, 80%, 70%, and 50% of each specimen's bending strength until failure. The 5 wt % OCA exhibited significant self-healing at 70% and 50% of its reference strength (p < 0.05). Fatigue testing of all three specimen types in air at 22 MPa (50% of reference strength of the 5 wt % OCA specimens) showed that the cycles to failure of OCA-containing specimens was increased by two-fold compared with the OCA-free and capsule-free specimens. This study represents the first demonstration of dynamic, catalyst free self-healing in a biomaterial formulation.

Effect of streptavidin affinity mutants on the integrin-independent adhesion of biotinylated endothelial cells.

We have previously shown that the high-affinity streptavidin (SA)-biotin interaction enhanced the initial integrin-mediated adhesion of biotinylated endothelial cells to SA-coated surface by serving as an extrinsic bond to stabilize and enhance the intrinsic fibronectin-integrin binding between the cell and surface. However, the SA-biotin interaction produced considerable detachment by cohesive failure of the membrane. In this study, we examined the hypothesis that reducing the SA-biotin bond affinity could reduce cohesive failure without reducing overall cell detachment. Two mutants of SA, W120F and W120A in which the tryptophan residue at position 120 of the SA molecule was substituted by phenylalanine and alanine, respectively, were characterized and tested in cell adhesion experiments. The binding affinity (K(A)) of SA to adsorbed biotin-labeled bovine serum albumin (b-BSA) ranged from 5.2+/-0.1 x 10(10)M(-1) for wild-type to 3.3+/-0.2 x 10(9)M(-1) for W120F and 4.1+/-1.0 x 10(6)M(-1) for W120A. One hour after cell attachment, the critical shear stress was 26.8+/-2.9 dyn/cm(2) for WT, 26.6+/-3.0 dyn/cm(2) for W120F, and 15.4+/-3.0 dyn/cm(2) for W120A. The focal contact areas of adherent cells were greater for the WT and W120F than the lower affinity mutant, W120A. When shear flow was applied to detach adherent cells, adhesive failure (ligand bond breakage) was favored over cohesive failure (membrane rupture), as the SA binding affinity decreased. Thus, cell adhesion augmented by SA-biotin linkages is dependent on the affinity constants of the SA-biotin bonds, but the reduction in cohesive failure was offset by a reduced strength of adhesion.

Effect of streptavidin-biotin on endothelial vasoregulation and leukocyte adhesion.

The current study examines whether the adhesion promoting arginine-glycine-aspartate-streptavidin mutant (RGD-SA) also affects two important endothelial cell (EC) functions in vitro: vasoregulation and leukocyte adhesion. EC adherent to surfaces via fibronectin (Fn) or Fn plus RGD-SA were subjected to laminar shear flow and media samples were collected over a period of 4h to measure the concentration of nitric oxide (NO), prostacyclin (PGI(2)), and endothelin-1 (ET-1). Western blot analysis was used to quantify the levels of endothelial-derived nitric oxide synthase (eNOS) and cyclooxygenase II (COX II). In a separate set of experiments, fluorescent polymorphonuclear leukocyte (PMN) adhesion to EC was quantified for EC with and without exposure to flow preconditioning. When cell adhesion was supplemented with the SA-biotin system, flow-induced production of NO and PGI(2) increased significantly relative to cells adherent on Fn alone. Previous exposure of EC to shear flow also significantly decreased PMN attachment to SA-biotin supplemented EC, but only after 2h of exposure to shear flow. The observed decrease in PMN-EC adhesion was negated by NG-nitro-L-arginine methyl ester (L-NAME), an antagonist of NO synthesis, but not by indomethacin, an inhibitor to PGI(2) synthesis, indicating the induced effect of PMN-EC interaction is primarily NO-dependent. Results from this study suggest that the use of SA-biotin to supplement EC adhesion encourages vasodilation and PMN adhesion in vitro under physiological shear-stress conditions. We postulate that the presence of SA-biotin more efficiently transmits the shear-stress signal and amplifies the downstream events including the NO and PGI(2) release and leukocyte-EC inhibition. These results may have ramifications for reducing thrombus-induced vascular graft failure.

Effect of streptavidin RGD mutant on the adhesion of endothelial cells.

Adhesion of endothelial cells (EC) to surfaces can be enhanced by supplementing the integrin-mediated adhesion with high-affinity streptavidin (SA) that links a biotinylated EC to a biotinylated surface. Biotin pullout from the EC membrane limits the effectiveness of this treatment, leading to a predominance of EC detachment by cohesive failure. In this study we investigated whether a RGD-SA mutant that links SA to EC integrin receptors, and eliminates EC biotinylation, improves EC adhesion. Suspended EC were incubated with the RGD-SA mutant prior to cell seeding, primarily via attachment to the RGD binding site on alpha(v)beta(3) integrin. RGD-SA-incubated EC were subsequently seeded onto a surface preadsorbed with a mixture of fibronectin (Fn) and biotinylated bovine serum albumin (b-BSA). Results showed EC adhesion supplemented with the RGD-SA-biotin system significantly increased cell retention under flow, critical shear stresses for detachment, focal contact area, and force per bond relative to SA used with biotinylated EC. These increases were accompanied by significant reductions in membrane fragments left behind following EC detachment, which suggested cohesive failure via cell membrane rupture was significantly reduced, and enhanced phosphorylation of focal adhesion kinase, which suggested activation and clustering of integrin receptors. Together, these results show that the integrin-independent augmentation of EC adhesion using SA-biotin can be further improved through use of an RGD-SA mutant.

Synergistic effect of high-affinity binding and flow preconditioning on endothelial cell adhesion.

The current study examined whether the combined introduction of high-affinity avidin-biotin bonds and fibronectin-integrin bonds (i.e., dual ligand treatment) would further augment the adhesion of flow-preconditioned endothelial cells to model substrates via contributions to the actin cytoskeleton and the formation of focal contacts. Human umbilical vein endothelial cells (HUVEC) were grown under static conditions or exposed to a flow-preconditioning regimen for 24 h. Cell retention was determined by exposure to 75 dynes/cm(2). The combination of flow preconditioning and the dual ligand treatment yielded higher cell retention under flow compared to the cells adherent via fibronectin-integrin bonds only. This increase in adhesion strength correlated with a greater focal contact area. Elongation of the HUVEC occurred after exposure to flow preconditioning; however, orientation of dual ligand adherent cells was restricted due to the presence of the high-affinity ligand. Flow-preconditioned cells showed increased stress fiber formation compared to nonconditioned cells although the stress fibers per cell for flow-preconditioned cells were the same on both the ligand systems employed. The results indicate that enhanced adhesion strength is due to a combination of increased focal contact area, stress fiber formation, and cell alignment.

High-affinity augmentation of endothelial cell attachment: long-term effects on focal contact and actin filament formation.

Coadsorption of high-affinity avidin with lower affinity cell adhesion protein fibronectin has been shown to significantly augment short-term (1 h) adhesion and spreading of endothelial cells; however, the longer term persistence of avidin binding and its effect on endothelial cell adhesion have not been addressed. In this study, the presence of avidin-biotin bonds 24 h after cell adhesion to the dual ligand surfaces was verified by laser confocal microscopy of a fluorescent avidin analog, streptavidin. Total internal reflection microscopy showed that the focal contact area, focal contact density, and cell spreading all increased significantly at 24 h compared to fibronectin-treated control surfaces. Focal contact area was identical when measured with cells that were labeled with either the fluorescent streptavidin or a carbocyanine dye incorporated in the cell membrane. Confocal images of stress fibers formed in cells adherent to dual ligand surfaces after 24 h were thicker and more numerous compared to cells adherent to fibronectin controls. The results indicate that 24 h after initial attachment avidin-biotin is localized to focal contacts on the basal surface and affects cell spreading, actin filament organization, and focal contact density.