Antifouling Polymer Brushes Displaying Antithrombogenic Surface Properties.

The contact of blood with artificial materials generally leads to immediate protein adsorption (fouling), which mediates subsequent biological processes such as platelet adhesion and activation leading to thrombosis. Recent progress in the preparation of surfaces able to prevent protein fouling offers a potential avenue to mitigate this undesirable effect. In the present contribution, we have prepared several types of state-of-the-art antifouling polymer brushes on polycarbonate plastic substrate, and investigated their ability to prevent platelet adhesion and thrombus formation under dynamic flow conditions using human blood. Moreover, we compared the ability of such brushes--grafted on quartz via an adlayer analogous to that used on polycarbonate--to prevent protein adsorption from human blood plasma, assessed for the first time by means of an ultrahigh frequency acoustic wave sensor. Results show that the prevention of such a phenomenon constitutes one promising route toward enhanced resistance to thrombus formation, and suggest that antifouling polymer brushes could be of service in biomedical applications requiring extensive blood-material surface contact.

A survey of state-of-the-art surface chemistries to minimize fouling from human and animal biofluids.

Upon contact with bodily fluids, synthetic materials spontaneously acquire a layer of various species (most notably proteins) on their surface. The concern with respect to biomedical equipment, implants or devices resides in the possibility for biological processes with potentially harmful effects to ensue. In biosensor technology, the issue with this natural fouling phenomenon is that of non-specific adsorption to sensing platforms, which generates an often overwhelming interference signal that prevents the detection, not to mention the quantification, of target analytes present at considerably lower concentration. To alleviate this ubiquitous, recurrent problem - this genuine biotechnological plague - considerable research efforts have been devoted over the last few decades to engineer antifouling coatings. Extensive literature now exists that describes stealth organic adlayers capable of reducing fouling surface coverage Γ down to a few ng cm(-2)- however from biotechnologically irrelevant buffered solutions free or nearly depleted of any potentially interfering species. Regrettably indeed, few coatings are known to display/retain such level of performance when exposed to otherwise more complex, real-life biosamples (even diluted). Herein, we comprehensively review the state-of-the-art surface chemistries developed to date (January 2015) to minimize fouling from 8 such uncomparatively more challenging biological media (blood plasma, blood serum, cell lysate, cerebrospinal fluid, egg, milk, saliva, and urine) - whether of human or animal origin. Literature search for another 25 biological milieux generated no (exploitable) hit. Also discussed in this Review are the identification of the species responsible for fouling, and the dependence of antifouling properties on biosample source variability.

Ultrathin Surface Chemistry to Delay Anion Fouling.

The unwanted fouling of surfaces by ionic adsorption has received little research attention. In this context, ultrathin organic adlayer surface chemistry-featuring monoethylene glycol based molecular residues-is described that is capable of noticeably decreasing the rate of anion depletion from solution. The strategy is exemplified with glass as the substrate material and fluoride as the anion foulant.

Prevention of surface-induced thrombogenesis on poly(vinyl chloride).

Much biomedical equipment consisting of or containing plastic polymer(s) must come into contact with blood - an interaction that, at the molecular level, may unfortunately prompt biological processes with potentially deleterious, short- or long-term effects such as thrombosis. In the present investigation, this problem is alleviated for poly(vinyl chloride) (PVC) through chemical surface modification with an ultrathin, monoethylene glycol-based coating - a transformation that is characterized using X-ray photoelectron spectroscopy (XPS) supplemented by contact angle goniometry (CAG). Antithrombogenic properties are assessed through calculation (for the first 10 min, and after 60 min) of the surface coverage percentage due to platelet adhesion, aggregation and thrombus formation upon continuous exposure to fluorescently-labelled whole human blood. At all shear rates investigated (300, 900, and 1500 s-1), surface coverage decreases by >99% with respect to bare PVC (10 min, short-term contact with blood). Most importantly, antithrombogenic performance is retained for longer-term exposure experiments (60 min), regardless of applied shear rate as well.

On the hydration of subnanometric antifouling organosilane adlayers: a molecular dynamics simulation.

The connection between antifouling and surface hydration is a fascinating but daunting question to answer. Herein, we use molecular dynamics (MD) computer simulations to gain further insight into the role of surface functionalities in the molecular-level structuration of water (surface kosmotropicity)--within and atop subnanometric organosilane adlayers that were shown in previous experimental work to display varied antifouling behavior. Our simulations support the hypothesized intimate link between surface hydration and antifouling, in particular the importance of both internal and interfacial hydrophilicity and kosmotropicity. The antifouling mechanism is also discussed in terms of surface dehydration energy and water dynamicity (lability and mobility), notably the crucial requirement for clustered water molecules to remain tightly bound for extensive periods of time--i.e. exhibit slow exchange dynamics. A substrate effect on surface hydration, which would also participate in endowing antifouling adlayers with hydrogel-like characteristics, is also proposed. In contrast, the role of adlayer flexibility, if any, is assigned a secondary role in these ultrathin structures made of short building blocks. The conclusions from this work are well in line with those previously drawn in the literature.

A true theranostic approach to medicine: towards tandem sensor detection and removal of endotoxin in blood.

Sepsis is one of the leading causes of death around the world. The condition occurs when a local infection overcomes the host natural defense mechanism and suddenly spreads into the circulatory system, triggering a vigorous, self-injurious inflammatory host response. The pathogenesis of sepsis is relatively well known, one of the most potent immuno-activator being bacterial lipopolysaccharide (LPS) - also known as 'endotoxin'. Tests exist to detect endotoxin in bodily fluids, but are expensive, not necessarily user-friendly and require reporter molecules. In addition, the situation for safe and effective anti-endotoxin therapy is problematical. At the present time, endotoxin removal through cartridge hemoperfusion is one of the better alternatives to combat sepsis. The capability to both measure endotoxemia levels and offer an adapted response treatment in a timely manner is crucial for better management and improved prognosis, but is currently unavailable. In this context, we describe herein preliminary research towards the development of an alternative LPS biosensor and an innovative LPS neutralization cartridge to be eventually combined in an all-integrated configuration for the theranostic, personalized treatment of blood endotoxemia/sepsis. LPS detection is performed in a real-time and label-free manner in full human blood plasma, using ultra-high frequency acoustic wave sensing in combination with ultrathin, oligoethylene glycol-based mixed surface chemistry imposed on piezoelectric quartz discs. Biosensing platforms are functionalized with polymyxin B (PMB), a cyclic peptide antibiotic with high affinity for LPS. Analogous surface modification is used on glass beads for the therapeutic cartridge component of the combined strategy. Incubation of LPS-spiked whole blood with PMB-bead chemistry resulted in a significant decrease in the production of pro-inflammatory TNF-α cytokine. LPS neutralization is discussed in relation to the perturbation of its supramolecular chemistry in solution.

Prevention of thrombogenesis from whole human blood on plastic polymer by ultrathin monoethylene glycol silane adlayer.

In contemporary society, a large percentage of medical equipment coming in contact with blood is manufactured from plastic polymers. Unfortunately, exposure may result in undesirable protein-material interactions that can potentially trigger deleterious biological processes such as thrombosis. To address this problem, we have developed an ultrathin antithrombogenic coating based on monoethylene glycol silane surface chemistry. The strategy is exemplified with polycarbonate--a plastic polymer increasingly employed in the biomedical industry. The various straightforward steps of surface modification were characterized with X-ray photoelectron spectroscopy supplemented by contact angle goniometry. Antithrombogenicity was assessed after 5 min exposure to whole human blood dispensed at a shear rate of 1000 s(-1). Remarkably, platelet adhesion, aggregation, and thrombus formation on the coated surface was greatly inhibited (>97% decrease in surface coverage) compared to the bare substrate and, most importantly, nearly nonexistent.

Probing the hydration of ultrathin antifouling organosilane adlayers using neutron reflectometry.

Neutron reflectometry data and modeling support the existence of a relatively thick, continuous phase of water stemming from within an antifouling monoethylene glycol silane adlayer prepared on oxidized silicon wafers. In contrast, this physically distinct (from bulk) interphase is much thinner and only interfacial in nature for the less effective adlayer lacking internal ether oxygen atoms. These results provide further insight into the link between antifouling and surface hydration.

Critical role of surface hydration on the dynamics of serum adsorption studied with monoethylene glycol adlayers on gold.

The dynamics of serum adsorption on bare and monoethylene glycol adlayer-modified gold surfaces is investigated using acoustic wave physics. Hydration experiments support the pivotal role ascribed to water in the antifouling of surfaces. Behavioural discrepancy is interpreted in terms of difference in water structuring properties (surface kosmotropicity).

Surface chemistry to minimize fouling from blood-based fluids.

Upon contact with bodily fluids/tissues, exogenous materials spontaneously develop a layer of proteins on their surface. In the case of biomedical implants and equipment, biological processes with deleterious effects may ensue. For biosensing platforms, it is synonymous with an overwhelming background signal that prevents the detection/quantification of target analytes present in considerably lower concentrations. To address this ubiquitous problem, tremendous efforts have been dedicated over the years to engineer protein-resistant coatings. There is now extensive literature available on stealth organic adlayers able to minimize fouling down to a few ng cm(-2), however from technologically irrelevant single-protein buffered solutions. Unfortunately, few coatings have been reported to present such level of performance when exposed to highly complex proteinaceous, real-world media such as blood serum and plasma, even diluted. Herein, we concisely review the surface chemistry developed to date to minimize fouling from these considerably more challenging blood-based fluids. Adsorption dynamics is also discussed.

New functionalizable alkyltrichlorosilane surface modifiers for biosensor and biomedical applications.

We report herein three unprecedented alkyltrichlorosilane surface modifiers bearing pentafluorophenyl ester (PFP), benzothiosulfonate (BTS), or novel ß-propiolactone (BPL) functionalizable terminal groups. Evidence is provided that these molecules can be prepared in very high purity (as assessed by NMR) through a last synthetic step of Pt-catalyzed alkene hydrosilylation then directly employed, without further purification, for the surface modification of quartz and medical grade stainless steel. Subsequent on-surface functionalizations with amine and thiol model molecules demonstrate the potential of these molecular adlayers to be important platforms for future applications in the bioanalytical and biomedical fields.

Single ether group in a glycol-based ultra-thin layer prevents surface fouling from undiluted serum.

Through systematic structural modification, it is shown that the internal, single oxygen atom of simple monoethylene glycol-based organic films is essential for radically altering the fouling behaviour of quartz against undiluted serum, as characterized by the electromagnetic piezoelectric acoustic sensor. The synergy is strongest with distal hydroxyls.

Label-free detection of HIV-2 antibodies in serum with an ultra-high frequency acoustic wave sensor.

Herein is described a label-free immunosensor dedicated to the detection of HIV-2. The biosensor platform is constructed as a mixed self-assembled monolayer-coated quartz wafer onto which HIV-2 immunodominant epitopes are immobilized. The biosensing properties, in terms of specific vs. non-specific antigen-antibody interactions, are evaluated with the electromagnetic piezoelectric acoustic sensor (EMPAS) using equimolar serum solutions of HIV-2 or HIV-1 monoclonal antibodies, respectively. This immunosensor constitutes the first real-world application of the EMPAS technology in the bioanalytical field.