A functionalized poly(ethylene glycol)-based bioassay surface chemistry that facilitates bio-immobilization and inhibits non-specific protein, bacterial, and mammalian cell adhesion

Reusable glycan microarrays using a microwave assisted wet-erase (MAWE) process

Modern studies on binding of proteins to glycans commonly involve the use of synthetic glycans and their derivatives in which a small amount of the material is covalently printed onto a functionalized slide in a glycan microarray format. While incredibly useful to explore binding interactions with many types of samples, the common techniques involve drying the slides, which leads to irreversible association of the protein to the spots on slides to which they bound, thus limiting a microarray to a single use. We have developed a new technique which we term Microwave Assisted Wet-Erase (MAWE) glycan microarrays. In this approach we image the slides under wet conditions to acquire the data, after which the slides are cleaned of binding proteins by treatment with a denaturing SDS solution along with microwave treatment. Slides cleaned in this way can be reused multiple times, and an example here shows the reuse of a single array 15 times. We also demonstrate that this method can be used for a single-array per slide or multi-array per slide platforms. Importantly, the results obtained using this technique for a variety of lectins sequentially applied to a single array, are concordant to those obtained via the classical dry approaches on multiple slides. We also demonstrate that MAWE can be used for different types of samples, such as serum for antibody binding, and whole cells, such as yeast. This technique will greatly conserve precious glycans and prolong the use of existing and new glycan microarrays.

Polyethylene Glycol-Based Polymer-Drug Conjugates: Novel Design and Synthesis Strategies for Enhanced Therapeutic Efficacy and Targeted Drug Delivery

Due to their potential to enhance therapeutic results and enable targeted drug administration, polymer-drug conjugates that use polyethylene glycol (PEG) as both the polymer and the linker for drug conjugation have attracted much research. This study seeks to investigate recent developments in the design and synthesis of PEG-based polymer-drug conjugates, emphasizing fresh ideas that fill in existing knowledge gaps and satisfy the increasing need for more potent drug delivery methods. Through an extensive review of the existing literature, this study identifies key challenges and proposes innovative strategies for future investigations. The paper presents a comprehensive framework for designing and synthesizing PEG-based polymer-drug conjugates, including rational molecular design, linker selection, conjugation methods, and characterization techniques. To further emphasize the importance and adaptability of PEG-based polymer-drug conjugates, prospective applications are highlighted, including cancer treatment, infectious disorders, and chronic ailments.

Anti-Coagulant and Antimicrobial Recombinant Heparin-Binding Major Ampullate Spidroin 2 (MaSp2) Silk Protein

Governed by established structure–property relationships, peptide motifs comprising major ampullate spider silk confer a balance of strength and extensibility. Other biologically inspired small peptide motifs correlated to specific functionalities can be combined within these units to create designer silk materials with new hybrid properties. In this study, a small basic peptide, (ARKKAAKA) known to both bind heparin and mimic an antimicrobial peptide, was genetically linked to a protease-resistant, mechanically robust silk-like peptide, MaSp2. Purified fusion proteins (four silk domains and four heparin-binding peptide repeats) were expressed in E. coli. Successful fusion of a MaSp2 spider silk peptide with the heparin-binding motif was shown using a variety of analytical assays. The ability of the fusion peptide to bind heparin was assessed with ELISA and was further tested for its anticoagulant property using aPTT assay. Its intrinsic property to inhibit bacterial growth was evaluated using zone of inhibition and crystal violet (CV) assays. Using this strategy, we were able to link the two types of genetic motifs to create a designer silk-like protein with improved hemocompatibility and antimicrobial properties.

Effect of upstream priming on transient downstream platelet-substrate interactions

Upstream exposure of platelets to activating proteins 'primes' platelets for increased downstream adhesion, though the mechanics of platelet translocation before permanently arresting are not well understood. To investigate platelet translocation on platelet-binding proteins, primed platelets' transient contacts with immobilized proteins were recorded and analyzed. Using a microfluidic channel, representative of a vascular graft, platelet-activating proteins were covalently attached to the upstream priming, center, and downstream capture positions. Image sequences of platelet interactions with the center protein were captured as platelet-rich plasma (PRP) was perfused through the channel. There was an increase in both platelet pause events and net platelet adhesion on von Willebrand factor, collagen, or fibrinogen following upstream exposure to the same protein. Upstream priming also caused a decrease in average platelet velocity. The duration of transient platelet arrests on the protein-coated surface and the distance that platelets travel between pause events depended on the protein with which they were interacting. The most significant increase in platelet pause events frequency and decrease in average velocity occurred on immobilized von Willebrand factor, compared to the control with no upstream priming. These results demonstrate that platelet priming increases downstream platelet-protein interactions prior to permanent adhesion.

A convenient approach for antibacterial polypeptoids featuring sulfonium and oligo(ethylene glycol) subunits

Bioinspired polypeptoids show great potential in many applications. Here, we report a convenient approach to synthesize a novel type of polypeptoid containing both sulfonium and oligo(ethylene glycol) (OEG) moieties by ring-opening polymerization (ROP) and a post-modification strategy. Three types of epoxides with (OEG)n (n = 1-3) groups are involved to offer various functionalities. The obtained polypeptoid sulfonium salts show positive ζ potential, irrespective of the solution pH and the degree of polymerization (DP). We demonstrate that the polypeptoids exhibit excellent antibacterial activity against Staphylococcus aureus (S. aureus) with MIC (minimal inhibitory concentration) in the range of 3.9-7.8 μg mL-1. In addition, the polypeptoids have a low hemolysis property and good in vitro biocompatibility. Remarkably, the as-prepared polypeptoids show rapid and potent antibacterial activity within 5 min. These features suggest that the obtained polypeptoids offer great potential for antimicrobial agents.

Microfluidic assay of antiplatelet agents for inhibition of shear-induced platelet adhesion and activation

We have developed a microfluidic system to perfuse whole blood through a flow channel with an upstream stenotic region and a downstream protein capture region. This flow-based system was used to assay how effectively antiplatelet agents suppress shear-induced platelet adhesion and activation downstream of the stenotic region. Microcontact printing was used to covalently attach one of three platelet binding proteins [fibrinogen, collagen, or von Willebrand factor (vWf)] to the surface of the downstream capture region. Whole blood with an antiplatelet agent was transiently exposed to an upstream high wall shear rate (either 4860 s-1 or 11 560 s-1), and subsequently flowed over the downstream capture region where the platelet adhesion was measured. Several antiplatelet agents (acetylsalicylic acid, tirofiban, eptifibatide, anti-vWf, and anti-GPIbα) were evaluated for their efficacy in attenuating downstream adhesion. Following antibody blocking of vWf or GPIbα, downstream platelet activation was also assessed in perfused blood by flow cytometry using two activation markers (active GPIIb/IIIa and P-selectin). Acetylsalicylic acid demonstrated its inability to diminish shear-induced platelet adhesion to all three binding proteins. GPIIb/IIIa inhibitors (tirofiban and eptifibatide) significantly reduced platelet adhesion to fibrinogen. Antibody blocking of vWf or GPIbα effectively diminished platelet adhesion to all three capture proteins as well as platelet activation in perfused blood, indicating an essential role of vWf-GPIbα interaction in mediating shear-induced platelet aggregation.

Plasma Processing of Low Vapor Pressure Liquids to Generate Functional Surfaces

The concept of depositing solid films on low-vapor pressure liquids is introduced and developed into a top-down approach to functionalize surfaces by attaching liquid polyethylene glycol (PEG). Solid-liquid gradients were formed by low-pressure plasma treatment yielding cross-linking and/or deposition of a plasma polymer film subsequently bound to a flexible polydimethylsiloxane (PDMS) backing. The analysis via optical transmission spectroscopy (OTS), optical, confocal laser scanning (CLSM) and scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) as well as by water contact angle (WCA) measurements revealed correlations between optical appearance, chemical composition and surface properties of the resulting water absorbing, covalently bound PEG-functionalized surfaces. Requirements for plasma polymer film deposition on low-vapor pressure liquids and effective surface functionalization are defined. Namely, the thickness of the liquid PEG substrate was a crucial parameter for successful film growth and covalent attachment of PEG. The presented method is a practicable approach for the production of functional surfaces featuring long-lasting strong hydrophilic properties, making them predestined for non-fouling or low-friction applications.

Preparation of phospholipid-based polycarbonate urethanes for potential applications of blood-contacting implants

Polyurethanes are widely used in interventional devices due to the excellent physicochemical property. However, non-specific adhesion and severe inflammatory response of ordinary polyurethanes may lead to severe complications of intravenous devices. Herein, a novel phospholipid-based polycarbonate urethanes (PCUs) were developed via two-step solution polymerization by direct synthesis based on functional raw materials. Furthermore, PCUs were coated on biomedical metal sheets to construct biomimetic anti-fouling surface. The results of stress–strain curves exhibited excellent tensile properties of PCUs films. Differential scanning calorimetry results indicated that the microphase separation of such PCUs polymers could be well regulated by adjusting the formulation of chain extender, leading to different biological response. In vitro blood compatibility tests including bovine serum albumin adsorption, fibrinogen adsorption and denaturation, platelet adhesion and whole-blood experiment showed superior performance in inhibition non-specific adhesion of PCUs samples. Endothelial cells and smooth muscle cells culture tests further revealed a good anti-cell adhesion ability. Finally, animal experiments including ex vivo blood circulation and subcutaneous inflammation animal experiments indicated a strong ability in anti-thrombosis and histocompatibility. These results high light the strong anti-adhesion property of phospholipid-based PCUs films, which may be applied to the blood-contacting implants such as intravenous catheter or antithrombotic surface in the future.

Photografting and Patterning of Poly(ethylene glycol) Methacrylate Hydrogel on Glass for Biochip Applications

An efficient procedure for chemical initiator-free, in situ synthesis of a functional polyethylene glycol methacrylate (PEG MA) hydrogel on regular glass substrates is reported. It is demonstrated that self-initiated photografting and photopolymerization driven by UV irradiation can yield tens of nanometer-thick coatings of carboxy-functionalized PEG MA on the aldehyde-terminated borosilicate glass surface. The most efficient formulation for hydrogel synthesis contained methyl methacrylic acid (MAA), 2-hydroxyethyl methacrylate (HEMA), and PEG methacrylate (PEG₁₀MA) monomers (1:1:1). The resulting HEMA/PEG₁₀MA/MAA (HPMAA) coatings had a defined thickness in the range from 11 to 50 nm. The physicochemical properties of the synthesized HPMAA coatings were analyzed by combining water contact angle measurements, stylus profilometry, imaging null ellipsometry, and atomic force microscopy (AFM). The latter technique was employed in the quantitative imaging mode not only for direct probing of the surface topography but also for swelling behavior characterization in the pH range from 4.5 to 8.0. The estimated high swelling ratios of the HPMAA hydrogel (up to 3.2) together with its good stability and resistance to nonspecific protein binding were advantageous in extracellular matrix mimetics via patterning of fibronectin (FN) at a resolution close to 200 nm. It was shown that the fabricated FN micropatterns on HPMAA were equally suitable for single-cell arraying, as well as controlled cell culture lasting at least for 96 h.

Reactive Polymer Targeting dsRNA as Universal Virus Detection Platform with Enhanced Sensitivity

Reactive poly(pentafluorophenyl acrylate) (PPFPA)-grafted surfaces offer a versatile platform to immobilize biomolecules. Here, we utilize PPFPA-grafted surface and double-stranded RNA (dsRNA) recognizing J2 antibody to construct a universal virus detection platform with enhanced sensitivity. PPFPA on silicon substrates is prepared, and surface hydrophilicity is modulated by partial substitution of the pentafluorophenyl units with poly(ethylene glycol). Following dsRNA antibody immobilization, the prepared surfaces can distinguish long dsRNAs from single-stranded RNAs of the same length and short dsRNAs. As long dsRNAs are common byproducts of viral transcription/replication, these surfaces can detect the presence of different kinds of viruses without prior knowledge of their genomic sequences. To increase dsRNA detection sensitivity, a two-step method is devised where the captured dsRNAs are visualized with multiple fluorophore-tagged J2 antibodies. We show that the developed platform can differentiate foreign long dsRNAs from cellular dsRNAs and other biomolecules present in the cell lysate. Moreover, when tested against cells infected with hepatitis A or C viruses, both viruses are successfully detected using a single platform. Our study shows that the developed PPFPA platform immobilized with J2 antibody can serve as a primary diagnostic tool to determine the infection status for a wide range of viruses.

OPENchip: an on-chip in situ molecular profiling platform for gene expression analysis and oncogenic mutation detection in single circulating tumour cells

Liquid biopsy holds promise towards practical implementation of personalized theranostics of cancer. In particular, circulating tumour cells (CTCs) can provide clinically actionable information that can be directly linked to prognosis or therapy decisions. In this study, gene expression patterns and genetic mutations in single CTCs are simultaneously analysed by strategically combining microfluidic technology and in situ molecular profiling technique. Towards this, the development and demonstration of the OPENchip (On-chip Post-processing ENabling chip) platform for single CTC analysis by epithelial CTC enrichment and subsequent in situ molecular profiling is reported. For in situ molecular profiling, padlock probes that identify specific desired targets to examine biomarkers of clinical relevance in cancer diagnostics were designed and used to create libraries of rolling circle amplification products. We characterize the OPENchip in terms of its capture efficiency and capture purity, and validate the probe design using different cell lines. By integrating the obtained results, molecular analyses of CTCs from metastatic breast cancer (HER2 (ERBB2) gene expression and PIK3CA mutations) and metastatic pancreatic cancer (KRAS gene mutations) patients were demonstrated without any off-chip processes. The results substantiate the potential implementation of early molecular detection of cancer through sequencing-free liquid biopsy.

Polyethylene glycol-conjugated alkylamines - A novel class of surfactants for the saturation of immunoassay solid phase surfaces

All solid-phase immunoassay techniques depend on so-called blocking reagents to suppress the background that is caused by unwanted adhesion of assay system components to the solid support. Commonly used blocking reagents based on biological materials bear severe inherent drawbacks such as heterogeneity and cross-reactivity, while synthetic alternatives often show insufficient background prevention. In this study, polyethylene glycol-conjugated alkylamines were synthesized via a versatile building block approach and were studied as novel blocking reagent candidates in immunoassays. The newly developed substances outperformed commonly used blocking reagents in two different ELISA setups, enabling both, excellent prevention of non-specific binding and particularly high assay sensitivity. This class of surfactants therefore may contribute significantly to the field of assay technology.

Downstream platelet adhesion and activation under highly elevated upstream shear forces

Elevated shear force caused by an anastomotic stenosis is a common complication at the blood vessel-vascular implant interface. Although elevated shear forces were found to cause platelet aggregation around a stenotic region, transient platelet exposure to elevated shear forces and subsequent downstream events occurring under lower shear force were not extensively studied. We hypothesize that effects of elevated shear forces on pre-activation of platelets for downstream adhesion and activation are relevant in understanding the increased thrombotic risk associated with blood-contacting devices. We designed a microfluidic flow system to mimic the hemodynamic environment of vasculature with an upstream anastomotic stenosis with five wall shear strain rates ranging from 1620 s^-1 to 11560 s^-1. Under shear flow conditions, transient exposure of whole blood to elevated shear forces resulted in higher downstream platelet adhesion onto three different immobilized platelet agonists: fibrinogen, collagen, or von Willebrand factor. Platelet expression of four activation markers (P-selectin, GPIIb/IIIa, lysosomal glycoprotein, and phosphatidylserine) significantly increased after transient exposure to higher upstream wall shear strain rates of 2975-11560 s^-1. A significant lysis was observed when platelets were primed by upstream wall shear strain rate of 11560 s^-1. These experimental results could be helpful to understand how altered hemodynamics around an anastomotic stenosis promotes thrombus formation downstream. STATEMENT OF SIGNIFICANCE: Studying the downstream response of platelets following transient exposure to an upstream agonist is important because of significant clinical implications to the implantation of vascular devices. Due to intimal fibrous hyperplasia, vascular biomaterials such as synthetic small-diameter vascular grafts sometimes become stenotic (narrow), leading to transient platelet exposure to elevated shear forces. In this study, a microfluidic flow system was developed to mimic a stenosed vascular graft and to investigate how highly elevated, transient upstream shear forces, typically found in severe stenosis, results in the pre-activation of platelets for downstream adhesion and activation. The findings of the present study have implications for optimizing the design of blood-contacting biomaterials in order to minimize thrombotic risk associated with transiently elevated shear forces. The findings also provide additional insights into the mechanisms of thrombus formation at the post-stenotic regions of vascular implants.

Low-Fouling Characteristics of Ultrathin Zwitterionic Cysteine SAMs

Surface fouling remains an exigent issue for many biological implants. Unwanted solutes adsorb to reduce device efficiency and hasten degradation while increasing the risks of microbial colonization and adverse inflammatory response. To address unwanted fouling in modern implants in vivo, surface modification with antifouling polymers has become indispensable. Recently, zwitterionic self-assembled monolayers, which contain two or more charged functional groups but are electrostatically neutral and form highly hydrated surfaces, have been the focus of many antifouling coatings. Reports using various compositions of zwitterionic polymer brushes have demonstrated ultralow fouling in the ng/cm² range. These coatings, however, are thick and can hinder the target application of biological devices. Here, we report an ultrathin (8.52 Å) antifouling self-assembled monolayer composed of cysteine that is amenable to facile fabrication. The antifouling characteristics of the zwitterionic surfaces were evaluated against bovine serum albumin, fibrinogen, and human blood in real time using quartz crystal microbalance and surface plasmon resonance imaging. Compared to untreated gold surfaces, the ultrathin cysteine coating reduced the adsorption of bovine serum albumin by 95% (43 ng/cm² adsorbed) after 3 h and 90% reduction after 24 h. Similarly, the cysteine self-assembled monolayer reduced the adsorption of fibrinogen as well as human blood by >90%. The surfaces were further characterized using scanning electron microscopy: protein-enhanced adsorption and cellular adsorption in human blood was found on untreated surfaces but not on the cysteine SAM-protected surfaces. These findings suggest that surfaces can be functionalized with an ultrathin layer of cysteine to resist the adsorption of key proteins, with performance comparable to zwitterionic polymer brushes. As such, cysteine surface coatings are a promising methodology to improve the long-term utility of biological devices.

Programmable hydrogels

Programmable hydrogels are defined as hydrogels that are able to change their properties and functions periodically, reversibly and/or sequentially on demand. They are different from those responsive hydrogels whose changes are passive or cannot be stopped or reversed once started and vice versa. The purpose of this review is to summarize major progress in developing programmable hydrogels from the viewpoints of principles, functions and biomedical applications. The principles are first introduced in three categories including biological, chemical and physical stimulation. With the stimulation, programmable hydrogels can undergo functional changes in dimension, mechanical support, cell attachment and molecular sequestration, which are introduced in the middle of this review. The last section is focused on the introduction and discussion of four biomedical applications including mechanistic studies in mechanobiology, tissue engineering, cell separation and protein delivery.

Electron Beam Immobilization of Novel Antimicrobial, Short Peptide Motifs Leads to Membrane Surfaces with Promising Antibacterial Properties

In this study, the efficacy of electron beam irradiation versus chemical coupling for yielding polyethersulfone (PES) membranes with antibacterial properties was investigated. For the surface coating, a recently discovered lead compound, IL-KKA, comprising a short peptide sequence functionalized with imidazolium groups, was used. For better integration within the membrane, several novel variants of IL-KKA were generated. Membrane immobilization was achieved using different doses of electron beam irradiation and NHS/EDC chemical coupling. Physicochemical characterization of the coated membranes was performed by water contact angle measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy. Our results show that electron beam irradiation is as effective and gentle as chemical coupling using the NHS/EDC method. Moreover, it was demonstrated that the obtained membranes exhibit promising antibacterial activity against B. subtilis. In summary, the technique presented herein might be promising as a template for developing future anti-biofilm devices.

Tuning Bacterial Attachment and Detachment via the Thickness and Dispersity of a pH-Responsive Polymer Brush

We investigated the effect of two brush parameters, thickness and dispersity in the molecular weight distribution, on the adhesion of bacteria to pH-responsive poly(acrylic acid) (PAA) brushes synthesized using surface-initiated atom transfer radical polymerization. The attachment and detachment of Staphylococcus epidermidis to PAA brushes at pH 4 and pH 9, respectively, were examined with confocal microscopy. An optimal range of brush thickness, 13-18 nm, was identified for minimizing bacterial adhesion on PAA brushes at pH 4, and bacterial attachment did not depend on the brush dispersity. Increasing either the brush thickness or dispersity detached bacteria from the brushes when the pH was increased from 4 to 9. Bacterial detachment likely arose from an enhanced actuation effect in thick or high-dispersity brushes, as PAA brushes change conformation from collapsed to extended states when the pH is increased from 4 to 9. These results suggest that manipulating the molecular weight distribution provides a route to separately tune the attachment and detachment of bacteria.

Creation of antifouling microarrays by photopolymerization of zwitterionic compounds for protein assay and cell patterning

Nonspecific binding or adsorption of biomolecules presents as a major obstacle to higher sensitivity, specificity and reproducibility in microarray technology. We report herein a method to fabricate antifouling microarray via photopolymerization of biomimetic betaine compounds. In brief, carboxybetaine methacrylate was polymerized as arrays for protein sensing, while sulfobetaine methacrylate was polymerized as background. With the abundant carboxyl groups on array surfaces and zwitterionic polymers on the entire surfaces, this microarray allows biomolecular immobilization and recognition with low nonspecific interactions due to its antifouling property. Therefore, low concentration of target molecules can be captured and detected by this microarray. It was proved that a concentration of 10ngmL^-1 bovine serum albumin in the sample matrix of bovine serum can be detected by the microarray derivatized with anti-bovine serum albumin. Moreover, with proper hydrophilic-hydrophobic designs, this approach can be applied to fabricate surface-tension droplet arrays, which allows surface-directed cell adhesion and growth. These light controllable approaches constitute a clear improvement in the design of antifouling interfaces, which may lead to greater flexibility in the development of interfacial architectures and wider application in blood contact microdevices.

InP Nanowire Biosensor with Tailored Biofunctionalization: Ultrasensitive and Highly Selective Disease Biomarker Detection

Electrically active field-effect transistors (FET) based biosensors are of paramount importance in life science applications, as they offer direct, fast, and highly sensitive label-free detection capabilities of several biomolecules of specific interest. In this work, we report a detailed investigation on surface functionalization and covalent immobilization of biomarkers using biocompatible ethanolamine and poly(ethylene glycol) derivate coatings, as compared to the conventional approaches using silica monoliths, in order to substantially increase both the sensitivity and molecular selectivity of nanowire-based FET biosensor platforms. Quantitative fluorescence, atomic and Kelvin probe force microscopy allowed detailed investigation of the homogeneity and density of immobilized biomarkers on different biofunctionalized surfaces. Significantly enhanced binding specificity, biomarker density, and target biomolecule capture efficiency were thus achieved for DNA as well as for proteins from pathogens. This optimized functionalization methodology was applied to InP nanowires that due to their low surface recombination rates were used as new active transducers for biosensors. The developed devices provide ultrahigh label-free detection sensitivities ∼1 fM for specific DNA sequences, measured via the net change in device electrical resistance. Similar levels of ultrasensitive detection of ∼6 fM were achieved for a Chagas Disease protein marker (IBMP8-1). The developed InP nanowire biosensor provides thus a qualified tool for detection of the chronic infection stage of this disease, leading to improved diagnosis and control of spread. These methodological developments are expected to substantially enhance the chemical robustness, diagnostic reliability, detection sensitivity, and biomarker selectivity for current and future biosensing devices.

Chemical Functionalization of Plasmonic Surface Biosensors: A Tutorial Review on Issues, Strategies, and Costs

In an ideal plasmonic surface sensor, the bioactive area, where analytes are recognized by specific biomolecules, is surrounded by an area that is generally composed of a different material. The latter, often the surface of the supporting chip, is generally hard to be selectively functionalized, with respect to the active area. As a result, cross talks between the active area and the surrounding one may occur. In designing a plasmonic sensor, various issues must be addressed: the specificity of analyte recognition, the orientation of the immobilized biomolecule that acts as the analyte receptor, and the selectivity of surface coverage. The objective of this tutorial review is to introduce the main rational tools required for a correct and complete approach to chemically functionalize plasmonic surface biosensors. After a short introduction, the review discusses, in detail, the most common strategies for achieving effective surface functionalization. The most important issues, such as the orientation of active molecules and spatial and chemical selectivity, are considered. A list of well-defined protocols is suggested for the most common practical situations. Importantly, for the reported protocols, we also present direct comparisons in term of costs, labor demand, and risk vs benefit balance. In addition, a survey of the most used characterization techniques necessary to validate the chemical protocols is reported.

Binary agonist surface patterns prime platelets for downstream adhesion in flowing whole blood

As platelets encounter damaged vessels or biomaterials, they interact with a complex milieu of surface-bound agonists, from exposed subendothelium to adsorbed plasma proteins. It has been shown that an upstream, surface-immobilized agonist is capable of priming platelets for enhanced adhesion downstream. In this study, binary agonists were integrated into the upstream position of flow cells and the platelet priming response was measured by downstream adhesion in flowing whole blood. A nonadditive response was observed in which platelets transiently exposed to two agonists exhibited greater activation and downstream adhesion than that from the sum of either agonist alone. Antibody blocking of one of the two upstream agonists eliminated nonadditive activation and downstream adhesion. Crosstalk between platelet activation pathways likely led to a synergistic effect which created an enhanced activation response in the platelet population. The existence of synergy between platelet priming pathways is a concept that has broad implications for the field of biomaterials hemocompatibility and platelet activity testing.

Polymer brushes based on PLLA-b-PEO colloids for the preparation of protein resistant PLA surfaces

Deposition of PLLA-b-PEO colloidal nanoparticles from selective solvents onto a polylactide surface resulting in an anti-fouling and cell repulsive surface.

Importance of zwitterionic incorporation into polymethacrylate-based hydrogels for simultaneously improving optical transparency, oxygen permeability, and antifouling properties

The introduction of zwitterionic SBMA into HEMA hydrogels enables to improve optical transparency, oxygen permeability, and antifouling property for contact lenses-based ophthalmic applications.

Microbes at Surface-Air Interfaces: The Metabolic Harnessing of Relative Humidity, Surface Hygroscopicity, and Oligotrophy for Resilience

The human environment is predominantly not aqueous, and microbes are ubiquitous at the surface-air interfaces with which we interact. Yet microbial studies at surface-air interfaces are largely survival-oriented, whilst microbial metabolism has overwhelmingly been investigated from the perspective of liquid saturation. This study explored microbial survival and metabolism under desiccation, particularly the influence of relative humidity (RH), surface hygroscopicity, and nutrient availability on the interchange between these two phenomena. The combination of a hygroscopic matrix (i.e., clay or 4,000 MW polyethylene glycol) and high RH resulted in persistent measurable microbial metabolism during desiccation. In contrast, no microbial metabolism was detected at (a) hygroscopic interfaces at low RH, and (b) less hygroscopic interfaces (i.e., sand and plastic/glass) at high or low RH. Cell survival was conversely inhibited at high RH and promoted at low RH, irrespective of surface hygroscopicity. Based on this demonstration of metabolic persistence and survival inhibition at high RH, it was proposed that biofilm metabolic rates might inversely influence whole-biofilm resilience, with ‘resilience’ defined in this study as a biofilm’s capacity to recover from desiccation. The concept of whole-biofilm resilience being promoted by oligotrophy was supported in desiccation-tolerant Arthrobacter spp. biofilms, but not in desiccation-sensitive Pseudomonas aeruginosa biofilms. The ability of microbes to interact with surfaces to harness water vapor during desiccation was demonstrated, and potentially to harness oligotrophy (the most ubiquitous natural condition facing microbes) for adaptation to desiccation.

Functional assay of antiplatelet drugs based on margination of platelets in flowing blood

A novel functional assay of antiplatelet drug efficacy was designed by utilizing the phenomena of platelet margination in flowing blood and transient platelet contacts with surface-immobilized platelet agonists. Flow margination enhances transient contacts of platelets with the walls of flow chambers covered with surface-immobilized proteins. Depending on the type and the surface density of the immobilized agonists, such transient interactions could "prime" the marginated platelet subpopulation for enhanced activation and adhesion downstream. By creating an upstream surface patch with an immobilized platelet agonist, platelet flow margination was used to test how effective antiplatelet drugs are in suppressing downstream platelet activation and adhesion. The platelet adhesion downstream was measured by a so-called "capture" patch region close to the distal end of the flow chamber. Platelet adhesion downstream was found to be dose-dependent on the upstream surface coverage of the "priming" patch, with immobilized fibrinogen acting as a platelet agonist. Several antiplatelet agents (acetylsalicylic acid, eptifibatide, and tirofiban) were evaluated for their efficacy in attenuating downstream adhesion after upstream platelet priming. The activation of the platelet population was found to be dependent on both the extent of the upstream agonist stimulus and the antiplatelet drug concentration. Such a relationship provides an opportunity to measure the efficacy of specific antiplatelet agents against the type and concentration of upstream platelet agonists.

Real-time monitoring of specific oxygen uptake rates of embryonic stem cells in a microfluidic cell culture device

Oxygen plays a key role in stem cell biology as a signaling molecule and as an indicator of cell energy metabolism. Quantification of cellular oxygen kinetics, i.e. the determination of specific oxygen uptake rates (sOURs), is routinely used to understand metabolic shifts. However current methods to determine sOUR in adherent cell cultures rely on cell sampling, which impacts on cellular phenotype. We present real‐time monitoring of cell growth from phase contrast microscopy images, and of respiration using optical sensors for dissolved oxygen. Time‐course data for bulk and peri‐cellular oxygen concentrations obtained for Chinese hamster ovary (CHO) and mouse embryonic stem cell (mESCs) cultures successfully demonstrated this non‐invasive and label‐free approach. Additionally, we confirmed non‐invasive detection of cellular responses to rapidly changing culture conditions by exposing the cells to mitochondrial inhibiting and uncoupling agents. For the CHO and mESCs, sOUR values between 8 and 60 amol cell⁻¹ s⁻¹, and 5 and 35 amol cell⁻¹ s⁻¹ were obtained, respectively. These values compare favorably with literature data. The capability to monitor oxygen tensions, cell growth, and sOUR, of adherent stem cell cultures, non‐invasively and in real time, will be of significant benefit for future studies in stem cell biology and stem cell‐based therapies.

Molecular Understanding and Structural-Based Design of Polyacrylamides and Polyacrylates as Antifouling Materials

Design and synthesis of highly bioinert and biocompatible antifouling materials are crucial for a broad range of biomedical and engineering applications. Among antifouling materials, polyacrylamides and polyacrylates have proved so promising because of cheap raw materials, ease of synthesis and applicability, and abundant functional groups. The strong surface hydration and the high surface packing density of polyacrylamides and polyacrylates are considered to be the key contributors to their antifouling property. In this article, we review our studies on the design and synthesis of a series of polyacrylamides and polyacrylates with different molecular structures. These polymers can be fabricated into different architectural forms (brushes, nanoparticles, nanogels, and hydrogels), all of which are highly resistant to the attachment of proteins, cells, and bacteria. We find that small structural changes in the polymers can lead to large enhancement in surface hydration and antifouling performance, both showing a positive correlation. This reveals a general design rule for effective antifouling materials. Furthermore, polyacrylamides and polyacrylates are readily functionalized with other bioactive compounds to achieve different new multifunctionalities.

Macrophage phagocytic activity toward adhering staphylococci on cationic and patterned hydrogel coatings versus common biomaterials

Biomaterial-associated-infection causes failure of biomaterial implants. Many new biomaterials have been evaluated for their ability to inhibit bacterial colonization and stimulate tissue-cell-integration, but neglect the role of immune cells. This paper compares macrophage phagocytosis of adhering Staphylococcus aureus on cationic-coatings and patterned poly(ethylene)glycol-hydrogels versus common biomaterials and stainless steel in order to identify surface conditions that promote clearance of adhering bacteria. Staphylococci were allowed to adhere and grow on the materials in a parallel-plate-flow-chamber, after which murine macrophages were introduced. From the decrease in the number of adhering staphylococci, phagocytosis-rates were calculated, and total macrophage displacements during an experiment determined. Hydrophilic surfaces had the lowest phagocytosis-rates, while common biomaterials had intermediate phagocytosis-rates. Patterning of poly(ethylene)glycol-hydrogel coatings increased phagocytosis-rates to the level of common biomaterials, while on cationic-coatings phagocytosis-rates remained relatively low. Likely, phagocytosis-rates on cationic coatings are hampered relative to common biomaterials through strong electrostatic binding of negatively-charged macrophages and staphylococci. On polymeric biomaterials and glass, phagocytosis-rates increased with macrophage displacement, while both parameters increased with biomaterial surface hydrophobicity. Thus hydrophobicity is a necessary surface condition for effective phagocytosis. Concluding, next-generation biomaterials should account for surface effects on phagocytosis in order to enhance the ability of these materials to resist biomaterial-associated-infection.

Synthesis of ultrastable copper sulfide nanoclusters via trapping the reaction intermediate: potential anticancer and antibacterial applications

Copper-based nanomaterials have broad applications in electronics, catalysts, solar energy conversion, antibiotics, tissue imaging, and photothermal cancer therapy. However, it is challenging to prepare ultrasmall and ultrastable CuS nanoclusters (NCs) at room temperature. In this article, a simple method to synthesize water-soluble, monodispersed CuS NCs is reported based on the strategy of trapping the reaction intermediate using thiol-terminated, alkyl-containing short-chain poly(ethylene glycol)s (HS-(CH2)11-(OCH2CH2)6-OH, abbreviated as MUH). The MUH-coated CuS NCs have superior stability in solutions with varied pH values and are stable in pure water for at least 10 months. The as-prepared CuS NCs were highly toxic to A549 cancer cells at a concentration of higher than 100 μM (9.6 μg/mL), making them be potentially applicable as anticancer drugs via intravenous administration by liposomal encapsulation or by direct intratumoral injection. Besides, for the first time, CuS NCs were used for antibacterial application, and 800 μM (76.8 μg/mL) CuS NCs could completely kill the E. coli cells through damaging the cell walls. Moreover, the NCs synthesized here have strong near-infrared (NIR) absorption and can be used as a candidate reagent for photothermal therapy and photoacoustic imaging. The method of trapping the reaction intermediate for simple and controlled synthesis of nanoclusters is generally applicable and can be widely used to synthesize many metal-based (such as Pt, Pd, Au, and Ag) nanoclusters and nanocrystals.

Chimeric peptides as implant functionalization agents for titanium alloy implants with antimicrobial properties

Implant-associated infections can have severe effects on the longevity of implant devices and they also represent a major cause of implant failures. Treating these infections associated with implants by antibiotics is not always an effective strategy due to poor penetration rates of antibiotics into biofilms. Additionally, emerging antibiotic resistance poses serious concerns. There is an urge to develop effective antibacterial surfaces that prevent bacterial adhesion and proliferation. A novel class of bacterial therapeutic agents, known as antimicrobial peptides (AMP's), are receiving increasing attention as an unconventional option to treat septic infection, partly due to their capacity to stimulate innate immune responses and for the difficulty of microorganisms to develop resistance towards them. While host- and bacterial- cells compete in determining the ultimate fate of the implant, functionalization of implant surfaces with antimicrobial peptides can shift the balance and prevent implant infections. In the present study, we developed a novel chimeric peptide to functionalize the implant material surface. The chimeric peptide simultaneously presents two functionalities, with one domain binding to a titanium alloy implant surface through a titanium-binding domain while the other domain displays an antimicrobial property. This approach gains strength through control over the bio-material interfaces, a property built upon molecular recognition and self-assembly through a titanium alloy binding domain in the chimeric peptide. The efficiency of chimeric peptide both in-solution and absorbed onto titanium alloy surface was evaluated in vitro against three common human host infectious bacteria, S. mutans, S. epidermidis, and E. coli. In biological interactions such as occurs on implants, it is the surface and the interface that dictate the ultimate outcome. Controlling the implant surface by creating an interface composed chimeric peptides may therefore open up new possibilities to cover the implant site and tailor it to a desirable bioactivity.

Varying RGD concentration and cell phenotype alters the expression of extracellular matrix genes in vocal fold fibroblasts

The impact of RGD integrin binding-peptide concentration and cell phenotype on directing extracellular matrix (ECM) gene expression in vocal fold fibroblasts is little understood. Less is known about cell response to RGD concentration on a biomaterial when fibroblasts are in a scar-like environment compared to a healthy environment. We investigated the effects of varying RGD integrin-binding peptide surface concentration on ECM gene expression of elastin, collagen type 3 alpha 1, decorin, fibronectin, hyaluronan synthase 2, and collagen type 1 alpha 2 in scarred and unscarred immortalized human vocal fold fibroblasts (I-HVFFs). Phenotype and RGD concentration affected ECM gene expression. Phenotype change from healthy to myofibroblast-like resulted in ECM gene up-regulation for all genes tested, except for decorin. Systematically altering RGD concentration affected the expression of elastin and collagen type 3 alpha 1 in a myofibroblast phenotype. Specifically greater up-regulation in gene expression was observed with higher RGD concentrations. This research demonstrates that controlling RGD concentration may influence ECM gene expression levels in fibroblasts. Such knowledge is critical in developing the next generation of bioactive materials that, when implanted into sites of tissue damage and scarring, will direct cells to regenerate healthy tissues with normal ECM ratios and morphologies.

Protease-degradable PEG-maleimide coating with on-demand release of IL-1Ra to improve tissue response to neural electrodes

Neural electrodes are an important part of brain-machine interface devices that can restore functionality to patients with sensory and movement disorders. Chronically implanted neural electrodes induce an unfavorable tissue response which includes inflammation, scar formation, and neuronal cell death, eventually causing loss of electrode function. We developed a poly(ethylene glycol) hydrogel coating for neural electrodes with non-fouling characteristics, incorporated an anti-inflammatory agent, and engineered a stimulus-responsive degradable portion for on-demand release of the anti-inflammatory agent in response to inflammatory stimuli. This coating reduces in vitro glial cell adhesion, cell spreading, and cytokine release compared to uncoated controls. We also analyzed the in vivo tissue response using immunohistochemistry and microarray qRT-PCR. Although no differences were observed among coated and uncoated electrodes for inflammatory cell markers, lower IgG penetration into the tissue around PEG+IL-1Ra coated electrodes indicates an improvement in blood-brain barrier integrity. Gene expression analysis showed higher expression of IL-6 and MMP-2 around PEG+IL-1Ra samples, as well as an increase in CNTF expression, an important marker for neuronal survival. Importantly, increased neuronal survival around coated electrodes compared to uncoated controls was observed. Collectively, these results indicate promising findings for an engineered coating to increase neuronal survival and improve tissue response around implanted neural electrodes.

Protein-resistance performance of amphiphilic copolymer brushes consisting of fluorinated polymers and polyacrylamide grafted from silicon surfaces

A series of random copolymer brushes of acrylamide (AM) and 2-(perfluorinated hexyl)ethyl methacrylate (FMA) were grafted from initiator-functionalized silicon wafers by surface-initiated atom transfer radical polymerization.

Nonfouling property of zwitterionic cysteine surface

Applications of implantable bioelectronics for analytical and curative purposes are currently limited by their poor long-term biofunctionality in physiological media and nonspecific interactions with biomolecules. In an attempt to prolong in vivo functionality, recent advances in surface modifications have demonstrated that zwitterionic coatings can rival the performance of conventional poly(ethylene glycol) polymers in reducing nonspecific protein fouling. Herein, we report the fabrication of a very thin layer of nonfouling zwitterionic cysteine surface capable of protecting implantable bioelectronics from nonspecific adsorption of plasma proteins. This work is the first of its kind to fabricate, through solution chemistry, a cysteine surface exhibiting zwitterionic state as high as 88% and to demonstrate antibiofouling under the exposure of bovine serum albumin (BSA) and human serum. The fabricated surface utilized a minimal amount of gold substrate, approximately 10 nm, and an extremely thin antifouling layer at 1.14 nm verified by ellipsometry. X-ray photoelectron spectroscopy assessment of the nitrogen (N1s) and carbon (C1s) spectra conclude that 87.8% of the fabricated cysteine surface is zwitterionic, 2.5% is positively charged, and 9.6% is noncharged. Antibiofouling performance of the cysteine surface is quantitatively determined by bicinchoninic acid (BCA) protein assay as well as qualitatively confirmed using scanning electron spectroscopy. Cysteine surfaces demonstrated a BSA fouling of 3.9 ± 4.84% μg/cm(2), which is 93.6% and 98.5% lower than stainless steel and gold surfaces, respectively. Surface plasmon resonance imaging analysis returned similar results and suggest that a thinner cysteine coating will enhance performance. Scanning electron microscopy confirmed the results of BCA assay and suggested that the cysteine surface demonstrated a 69% reduction to serum fouling. The results reported in this paper demonstrate that it is possible to achieve a highly zwitterionic surface through solution chemistry on a macroscopic level that is capable of improving biocompatibility of long-term implantable bioelectronics.