Antifouling Poly(β-peptoid)s

Advance in the Polymerization Strategy for the Synthesis of β-Peptides and β-Peptoids

Peptide mimics, possessing excellent biocompatibility and protease stability, have attracted broad attention and research in the biomedical field. β-Peptides and β-peptoids, as two types of vital peptide mimics, have demonstrated great potential in the field of foldamers, antimicrobials and protein binding, etc. Currently, the main synthetic strategies for β-peptides and β-peptoids include solid-phase synthesis and polymerization. Among them, polymerization in one-pot can minimize the repeated separation and purification used in solid-phase synthesis, and has the advantages of high efficiency and low cost, and can synthesize β-peptides and β-peptoids with high molecular weight. This review summarizes the polymerization methods for β-peptides and β-peptoids. Moreover, future developments of the polymerization method for the synthesis of β-peptides and β-peptoids will be discussed.

A Review on the Synthesis of Polypeptoids

Polyeptoids are a promising class of polypeptide mimetic biopolymers based on N-substituted glycine backbones. Because of the high designability of their side chains, polypeptoids have a wide range of applications in surface antifouling, biosensing, drug delivery, and stimuli-responsive materials. To better control the structures and properties of polypeptoids, it is necessary to understand different methods for polypeptoid synthesis. This review paper summarized and discussed the main synthesis methods of polypeptoids: the solid-phase submonomer synthesis method, ring-opening polymerization method and Ugi reaction method.

Biorecognition antifouling coatings in complex biological fluids: a review of functionalization aspects

Recent progress in biointerface research has highlighted the role of antifouling functionalizable coatings in the development of advanced biosensors for point-of-care bioanalytical and biomedical applications dealing with real-world complex samples. The resistance to nonspecific adsorption promotes the biorecognition performance and overall increases the reliability and specificity of the analysis. However, the process of modification with biorecognition elements (so-called functionalization) may influence the resulting antifouling properties. The extent of these effects concerning both functionalization procedures potentially changing the surface architecture and properties, and the physicochemical properties of anchored biorecognition elements, remains unclear and has not been summarized in the literature yet. This critical review summarizes these key functionalization aspects with respect to diverse antifouling architectures showing low or ultra-low fouling quantitative characteristics in complex biological media such as bodily fluids or raw food samples. The subsequent discussion focuses on the impact of functionalization on fouling resistance. Furthermore, this review discusses some of the drawbacks of available surface sensitive characterization methods and highlights the importance of suitable assessment of the resistance to fouling.

Nanocoating Is a New Way for Biofouling Prevention

Biofouling is a major concern to the maritime industry. Biofouling increases fuel consumption, accelerates corrosion, clogs membranes and pipes, and reduces the buoyancy of marine installations, such as ships, platforms, and nets. While traditionally marine installations are protected by toxic biocidal coatings, due to recent environmental concerns and legislation, novel nanomaterial-based anti-fouling coatings are being developed. Hybrid nanocomposites of organic-inorganic materials give a possibility to combine the characteristics of both groups of material generating opportunities to prevent biofouling. The development of bio-inspired surface designs, progress in polymer science and advances in nanotechnology is significantly contributing to the development of eco-friendly marine coatings containing photocatalytic nanomaterials. The review mainly discusses photocatalysis, antifouling activity, and formulation of coatings using metal and metal oxide nanomaterials (nanoparticles, nanowires, nanorods). Additionally, applications of nanocomposite coatings for inhibition of micro- and macro-fouling in marine environments are reviewed.

An Ultrasoft Self-Fused Supramolecular Polymer Hydrogel for Completely Preventing Postoperative Tissue Adhesion

The intermolecular H-bonding density heavily influences the gelation and rheological behavior of hydrogen-bonded supramolecular polymer hydrogels, thus offering a delicate pathway to tailor their physicochemical properties for meeting a specific biomedical application. Herein, one methylene spacer between two amides in the side chain of N-acryloyl glycinamide (NAGA) is introduced to generate a variant monomer, N-acryloyl alaninamide (NAAA). Polymerization of NAAA in aqueous solution affords an unprecedented ultrasoft and highly swollen supramolecular polymer hydrogel due to weakened H-bonds caused by an extra methylene spacer, which is verified by variable-temperature Fourier transform infrared (FTIR) spectroscopy and simulation calculation. Intriguingly, poly(N-acryloyl alaninamide) (PNAAA) hydrogel can be tuned to form a transient network with a self-fused and excellent antifouling capability that results from the weakened dual amide H-bonding interactions and enhanced water-amide H-bonding interactions. This self-fused PNAAA hydrogel can completely inhibit postoperative abdominal adhesion and recurrent adhesion after adhesiolysis in vivo. This transient hydrogel network allows for its disintegration and excretion from the body. The molecular mechanism studies reveal the signal pathway of PNAAA hydrogel in inhibiting inflammatory response and regulating fibrinolytic system balance. This self-fused, antifouling ultrasoft supramolecular hydrogel is promising as a barrier biomaterial for completely preventing postoperative tissue adhesion.

The impact of antifouling layers in fabricating bioactive surfaces

Bioactive surfaces modified with functional peptides are critical for both fundamental research and practical application of implant materials and tissue repair. However, when bioactive molecules are tethered on biomaterial surfaces, their functions can be compromised due to unwanted fouling (mainly nonspecific protein adsorption and cell adhesion). In recent years, researchers have continuously studied antifouling strategies to obtain low background noise and effectively present the function of bioactive molecules. In this review, we describe several commonly used antifouling strategies and analyzed their advantages and drawbacks. Among these strategies, antifouling molecules are widely used to construct the antifouling layer of various bioactive surfaces. Subsequently, we summarize various structures of antifouling molecules and their surface grafting methods and characteristics. Application of these functionalized surfaces in microarray, biosensors, and implants are also introduced. Finally, we discuss the primary challenges associated with antifouling layers in fabricating bioactive surfaces and provide prospects for the future development of this field. STATEMENT OF SIGNIFICANCE: The nonspecific protein adsorption and cell adhesion will cause unwanted background "noise" on the surface of biological materials and detecting devices and compromise the performance of functional molecules and, therefore, impair the performance of materials and the sensitivity of devices. In addition, the selection of antifouling surfaces with proper chain length and high grafting density is also of great importance and requires further studies. Otherwise, the surface-tethered bioactive molecules may not function in their optimal status or even fail to display their functions. Based on these two critical issues, we summarize antifouling molecules with different structures, variable grafting methods, and diverse applications in biomaterials and biomedical devices reported in literature. Overall, we expect to shed some light on choosing the appropriate antifouling molecules in fabricating bioactive surfaces.

Ugi four-component polymerization of amino acid derivatives: a combinatorial tool for the design of polypeptoids

The combinatorial Ugi-4C polymerization of amino acid derivatives is attractive for the future development of polypeptoids and resulting applications.

Oligo(β-peptoid)s with Backbone Chirality from Aspartic Acid Derivatives: Synthesis and Property Investigation

Poly(β-peptoid)s (N-substituted poly-β-alanines) are an intriguing class of pseudopeptidic materials for biomedical applications, but the polymers prepared by solution polymerization have restricted diversity and functionality due to synthetic difficulty. Synthesis of structurally diverse poly(β-peptoid)s is highly desirable yet challenging. Herein, we report a new approach to synthesize skeletal chiral β-peptoid polymers from readily available aspartic acid derivatives. Two types of N-substituted β³-homoalanine monomers, i.e., N-(methyl propionate)-Asp-OMe ( ^N MeP-Asp-OMe) and N-(tert-butyl propionate)-Asp-OMe ( ^N tBuP-Asp-OMe), were synthesized in high yield via an aza-Michael addition reaction between l-aspartic acid-1-methyl ester (l-Asp-OMe) and acrylate species. Both N-substituted β³-homoalanines can be readily converted into polymerizable N-substituted β³-homoalanine N-carboxyanhydrides (β-NNCAs). Subsequent ring-opening polymerization (ROP) of these β-NNCA monomers provides access to oligo(β-peptoid)s and mPEG-poly(β-peptoid) diblocks with backbone chirality. Their conformations were preliminarily studied by circular dichroism (CD) spectra and Fourier transform infrared spectroscopy (FT-IR). The synthetic strategy would significantly facilitate the development of novel poly(β-peptoid)s with well-defined and diverse structures.

Rational Design of Functional Peptide-Gold Hybrid Nanomaterials for Molecular Interactions

Gold nanoparticles (AuNPs) have been extensively used for decades in biosensing-related development due to outstanding optical properties. Peptides, as newly realized functional biomolecules, are promising candidates of replacing antibodies, receptors, and substrates for specific molecular interactions. Both peptides and AuNPs are robust and easily synthesized at relatively low cost. Hence, peptide-AuNP-based bio-nano-technological approaches have drawn increasing interest, especially in the field of molecular targeting, cell imaging, drug delivery, and therapy. Many excellent works in these areas have been reported: demonstrating novel ideas, exploring new targets, and facilitating advanced diagnostic and therapeutic technologies. Importantly, some of them also have been employed to address real practical problems, especially in remote and less privileged areas. This contribution focuses on the application of peptide-gold hybrid nanomaterials for various molecular interactions, especially in biosensing/diagnostics and cell targeting/imaging, as well as for the development of highly active antimicrobial/antifouling coating strategies. Rationally designed peptide-gold nanomaterials with functional properties are discussed along with future challenges and opportunities.

Laboratory Diagnosis of Paratyphoid Fever: Opportunity of Surface Plasmon Resonance

Paratyphoid fever is caused by the bacterium Salmonellaenterica serovar Paratyphi (A, B and C), and contributes significantly to global disease burden. One of the major challenges in the diagnosis of paratyphoid fever is the lack of a proper gold standard. Given the absence of a licensed vaccine against S. Paratyphi, this diagnostic gap leads to inappropriate antibiotics use, thus, enhancing antimicrobial resistance. In addition, the symptoms of paratyphoid overlap with other infections, including the closely related typhoid fever. Since the development and utilization of a standard, sensitive, and accurate diagnostic method is essential in controlling any disease, this review discusses a new promising approach to aid the diagnosis of paratyphoid fever. This advocated approach is based on the use of surface plasmon resonance (SPR) biosensor and DNA probes to detect specific nucleic acid sequences of S. Paratyphi. We believe that this SPR-based genoassay can be a potent alternative to the current conventional diagnostic methods, and could become a rapid diagnostic tool for paratyphoid fever.

Low-Fouling Substrates for Plasmonic Sensing of Circulating Biomarkers in Biological Fluids

The monitoring of biomarkers in body fluids provides valuable prognostic information regarding disease onset and progression. Most biosensing approaches use noninvasive screening tools and are conducted in order to improve early clinical diagnosis. However, biofouling of the sensing surface may disturb the quantification of circulating biomarkers in complex biological fluids. Thus, there is a great need for antifouling interfaces to be designed in order to reduce nonspecific adsorption and prevent inactivation of biological receptors and loss of sensitivity. To address these limitations and enable their application in clinical practice, a variety of plasmonic platforms have been recently developed for biomarker analysis in easily accessible biological fluids. This review presents an overview of the latest advances in the design of antifouling strategies for the detection of clinically relevant biomarkers on the basis of the characteristics of biological samples. The impact of nanoplasmonic biosensors as point-of-care devices has been examined for a wide range of biomarkers associated with cancer, inflammatory, infectious and neurodegenerative diseases. Clinical applications in readily obtainable biofluids such as blood, saliva, urine, tears and cerebrospinal and synovial fluids, covering almost the whole range of plasmonic applications, from surface plasmon resonance (SPR) to surface-enhanced Raman scattering (SERS), are also discussed.

Interactions between Lubricin and Hyaluronic Acid Synergistically Enhance Antiadhesive Properties

Preventing the unwanted adsorption of proteins and cells at articular cartilage surfaces plays a critical role in maintaining healthy joints and avoiding degenerative diseases such as osteoarthritis. Immobilized at the surface of healthy articular cartilage is a thin, interfacial layer of macromolecules consisting mainly of hyaluronic acid (HA) and lubricin (LUB; a.k.a. PRG4) that is believed to form a co-adsorbed, composite film now known to exhibit synergistic tribological properties. Bioinspired by the composition of cartilage surfaces, composite layers of HA and LUB were grafted to Au surfaces and the antiadhesive properties were assessed using surface plasmon resonance and quartz crystal microbalance. A clear synergistic enhancement in antiadhesive properties was observed in the composite films relative to grafted HA and LUB layers alone. Atomic force microscopy (AFM) normal force measurements provide insight into the architecture of the HA/LUB composite layer and implicate a strong contribution of hydrophobic interactions in the binding of LUB end-domains directly to HA chains. These AFM force measurements indicate that the adhesion of LUB to HA is strong and indicate that the hydrophobic coupling of LUB to HA shields the hydrophobic domains in these molecules from interactions with other proteins or molecules.

Low Fouling Protein Detection in Complex Biological Media Supported by a Designed Multifunctional Peptide

The construction of sensitive and selective biosensors capable of detecting specific targets in complex biological samples remains a challenge highly relevant to a range of sensor/diagnostic applications. Herein, we have utilized a multifunctional peptide to present an interface that supports the very specific recruitment of targets from serum. The novel peptide sequence designed contains an anchoring domain (CPPPP-), an antifouling domain (-NQNQNQNQDHWRGWVA), and a human immunoglobulin G (IgG) recognition domain (-HWRGWVA), and the whole peptide was designed to be antifouling. These were integrated into polyaniline nanowire arrays in supporting the quantification of IgG (with a limit of detection of 0.26 ng mL^-1) in neat serum and real clinical samples. The strategy of utilizing multisegment peptide films to underpin highly selective target recruitment is, of course, readily extended to a broad range of targets for which an affinity sequence can be generated.

Smart functional polymer coatings for paper with anti-fouling properties

Preparation of functionalized cellulose films on SiO₂ to introduce protein repellent properties evaluated by spectroscopic in situ ellipsometry.

PEGylated Polyaniline Nanofibers: Antifouling and Conducting Biomaterial for Electrochemical DNA Sensing

Biofouling arising from nonspecific adsorption is a substantial outstanding challenge in diagnostics and disease monitoring, and antifouling sensing interfaces capable of reducing the nonspecific adsorption of proteins from biological complex samples are highly desirable. We present herein the preparation of novel composite nanofibers through the grafting of polyethylene glycol (PEG) polymer onto polyaniline (PANI) nanofibers and their application in the development of antifouling electrochemical biosensors. The PEGylated PANI (PANI/PEG) nanofibers possessed large surface area and remained conductive and at the same time demonstrated excellent antifouling performances in single protein solutions as well as complex human serum samples. Sensitive and low fouling electrochemical biosensors for the breast cancer susceptibility gene (BRCA1) can be easily fabricated through the attachment of DNA probes to the PANI/PEG nanofibers. The biosensor showed a very high sensitivity to target BRCA1 with a linear range from 0.01 pM to 1 nM and was also efficient enough to detect DNA mismatches with satisfactory selectivity. Moreover, the DNA biosensor based on the PEGylated PANI nanofibers supported the quantification of BRCA1 in complex human serum, indicating great potential of this novel biomaterial for application in biosensors and bioelectronics.

Ultra-low fouling methylimidazolium modified surfaces for the detection of HER2 in breast cancer cell lysates

We synthesized novel ultra-low fouling ionic liquids and demonstrated their use with surface plasmon resonance (SPR) sensing for the analysis of HER2 in breast cancer cell lysates.

The pathology of the foreign body reaction against biomaterials

The healing process after implantation of biomaterials involves the interaction of many contributing factors. Besides their in vivo functionality, biomaterials also require characteristics that allow their integration into the designated tissue without eliciting an overshooting foreign body reaction (FBR). The targeted design of biomaterials with these features, thus, needs understanding of the molecular mechanisms of the FBR. Much effort has been put into research on the interaction of engineered materials and the host tissue. This elucidated many aspects of the five FBR phases, that is protein adsorption, acute inflammation, chronic inflammation, foreign body giant cell formation, and fibrous capsule formation. However, in practice, it is still difficult to predict the response against a newly designed biomaterial purely based on the knowledge of its physical-chemical surface features. This insufficient knowledge leads to a high number of factors potentially influencing the FBR, which have to be analyzed in complex animal experiments including appropriate data-based sample sizes. This review is focused on the current knowledge on the general mechanisms of the FBR against biomaterials and the influence of biomaterial surface topography and chemical and physical features on the quality and quantity of the reaction. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 927-940, 2017.

Ugi Reaction of Natural Amino Acids: A General Route toward Facile Synthesis of Polypeptoids for Bioapplications

Polypeptoids represent a significant class of synthetic analogues of natural polypeptides with potential biomimetic applications in materials, catalysis, and pharmaceuticals, but their simple and general synthesis still remains a key challenge. Herein, we demonstrate that Ugi reaction of natural amino acids leads to structurally diverse polypeptoids, including γ- and δ-, as well as poly(ε-peptoid)s, under mild conditions (open to air, room temperature, and catalyst free). Moreover, this strategy also offers manifold opportunities to introduce functional groups such as fluorescent and clickable alkenes groups into polypeptoids. Such poly(ε-peptoid)s not only exhibit good biocompatibility and antibacterial activity, but perform very effectively as a drug-delivery system. The bacterial inhibition rate of poly(ε-peptoid) was up to 88.8% at concentration of 20 μg mL^-1 in comparison to 61.8% of the poly(ε-lysine) control. Overall, this study offers us a general methodology toward facile preparation of polypeptoids for bioapplications.

Amino Acid-Based Zwitterionic Polymer Surfaces Highly Resist Long-Term Bacterial Adhesion

The surfaces or coatings that can effectively suppress bacterial adhesion in the long term are of critical importance for biomedical applications. Herein, a group of amino acid-based zwitterionic polymers (pAAZ) were investigated for their long-term resistance to bacterial adhesion. The polymers were derived from natural amino acids including serine, ornithine, lysine, aspartic acid, and glutamic acid. The pAAZ brushes were grafted on gold via the surface-initiated photoiniferter-mediated polymerization (SI-PIMP). Results show that the pAAZ coatings highly suppressed adsorption from the undiluted human serum and plasma. Long-term bacterial adhesion on these surfaces was investigated, using two kinds of representative bacteria [Gram-positive Staphylococcus epidermidis and Gram-negative Pseudomonas aeruginosa] as the model species. Results demonstrate that the pAAZ surfaces were highly resistant to bacterial adhesion after culturing for 1, 5, 9, or even 14 days, representing at least 95% reduction at all time points compared to the control unmodified surfaces. The bacterial accumulation on the pAAZ surfaces after 9 or 14 days was even lower than on the surfaces grafted with poly[poly(ethyl glycol) methyl ether methacrylate] (pPEGMA), one of the most common antifouling materials known to date. The pAAZ brushes also exhibited excellent structural stability in phosphate-buffered saline after incubation for 4 weeks. The bacterial resistance and stability of pAAZ polymers suggest they have good potential to be used for those applications where long-term suppression to bacterial attachment is desired.

Design and mechanisms of antifouling materials for surface plasmon resonance sensors

Surface plasmon resonance (SPR) biosensors have many possible applications, but are limited by sensor chip surface fouling, which blocks immobilization and specific binding by the recognizer elements. Therefore, there is a pressing need for the development of antifouling surfaces. In this paper, the mechanisms of antifouling materials were firstly discussed, including both theories (hydration and steric hindrance) and factors influencing antifouling effects (molecular structures and self-assembled monolayer (SAM) architectures, surface charges, molecular hydrophilicity, and grafting thickness and density). Then, the most recent advances in antifouling materials applied on SPR biosensors were systematically reviewed, together with the grafting strategies, antifouling capacity, as well as their merits and demerits. These materials included, but not limited to, zwitterionic compounds, polyethylene glycol-based, and polysaccharide-based materials. Finally, the prospective research directions in the development of SPR antifouling materials were discussed.

STATEMENT OF SIGNIFICANCE

Surface plasmon resonance (SPR) is a powerful tool in monitoring biomolecular interactions. The principle of SPR biosensors is the conversion of refractive index change caused by molecular binding into resonant spectral shifts. However, the fouling on the surface of SPR gold chips is ubiquitous and troublesome. It limits the application of SPR biosensors by blocking recognition element immobilization and specific binding. Hence, we write this paper to review the antifouling mechanisms and the recent advances of the design of antifouling materials that can improve the accuracy and sensitivity of SPR biosensors. To our knowledge, this is the first review focusing on the antifouling materials that were applied or had potential to be applied on SPR biosensors.

Bio-inspired strategies for designing antifouling biomaterials

Contamination of biomedical devices in a biological medium, biofouling, is a major cause of infection and is entirely avoidable. This mini-review will coherently present the broad range of antifouling strategies, germicidal, preventive and cleaning using one or more of biological, chemical and physical techniques. These techniques will be discussed from the point of view of their ability to inhibit protein adsorption, usually the first step that eventually leads to fouling. Many of these approaches draw their inspiration from nature, such as emulating the nitric oxide production in endothelium, use of peptoids that mimic protein repellant peptides, zwitterionic functionalities found in membrane structures, and catechol functionalities used by mussel to immobilize poly(ethylene glycol) (PEG). More intriguing are the physical modifications, creation of micropatterns on the surface to control the hydration layer, making them either superhydrophobic or superhydrophilic. This has led to technologies that emulate the texture of shark skin, and the superhyprophobicity of self-cleaning textures found in lotus leaves. The mechanism of antifouling in each of these methods is described, and implementation of these ideas is illustrated with examples in a way that could be adapted to prevent infection in medical devices.

Zwitterionic Modifications for Enhancing the Antifouling Properties of Poly(vinylidene fluoride) Membranes

The development of effective antibiofouling membranes is critical for many scientific interests and industrial applications. However, the existing available membranes often suffer from the lack of efficient, stable, and scalable antifouling modification strategy. Herein, we designed, synthesized, and characterized alternate copolymers of p(MAO-DMEA) (obtained by reaction between poly(maleic anhydride-alt-1-octadecene) and N,N-dimethylenediamine) and p(MAO-DMPA) (obtained by reaction between poly(maleic anhydride-alt-1-octadecene) and 3-(dimethylamino)-1-propylamine) of different carbon space length (CSL) using a ring-opening zwitterionization. We coated these copolymers on poly(vinylidene fluoride) (PVDF) membranes using a self-assembled anchoring method. Two important design parameters-the CSL of polymers and the coating density of polymers on membrane-were extensively examined for their effects on the antifouling performance of the modified membranes using a series of protein, cell, and bacterial assays. Both zwitterionic-modified membranes with different coating densities showed improved membrane hydrophilicity, increased resistance to protein, bacteria, blood cells, and platelet adsorption. However, while p(MAO-DMEA) with two CSLs and p(MAO-DMPA) with three CSLs only differ by one single carbon between the amino and ammonium groups, such subtle structural difference between the two polymers led to the fact that the membranes self-assembled with MAO-DMEA outperformed those modified with MAO-DMPA in all aspects of surface hydration, protein and bacteria resistance, and blood biocompatibility. This work provides an important structural-based design principle: a subtle change in the CSL of polymers affects the surface and antifouling properties of the membranes. It can help to achieve the design of more effective antifouling membranes for blood contacting applications.

Controllable Nonspecific Protein Adsorption by Charged Hyperbranched Polyglycerol Thin Films

Antifouling thin films derived from charged hyperbranched polyglycerol (hbPG) layers were fabricated and evaluated. The anionic hbPG (a-hbPG) monolayers and cationic hbPG/anionic hbPG (c/a-hbPG) bilayers were adsorbed on the underlying self-assembled monolayers (SAMs) of cysteamine and 3-mercaptopropionic acid (3-MPA) by electrostatic interaction, respectively, and their procession was monitored by surface plasmon resonance spectroscopy (SPR). The adsorption of bovine serum albumin (BSA) and fibrinogen on the premade a-hbPG and c/a-hbPG thin films was measured and the capability of these thin films to resist nonspecific protein adsorption was evaluated by SPR as well. It is observed that the c/a-hbPG bilayer films possessed good antifouling properties. With c/a-hbPG bilayers consisting of higher molecular weight a-hbPG, the adsorption of BSA and fibrinogen were as low as 0.015 ng/mm(-2) and 0.0076 ng/mm(-2), respectively, comparable to the traditionally ultralow antifouling surfaces (<0.05 ng/mm(-2) of nonspecific protein adsorption). This work proved that the charged hbPG thin films can strongly reduce the nonspecific protein adsorption and have the promise for the antifouling coatings with improved performance.

Sequence Programmable Peptoid Polymers for Diverse Materials Applications

Polymer sequence programmability is required for the diverse structures and complex properties that are achieved by native biological polymers, but efforts towards controlling the sequence of synthetic polymers are, by comparison, still in their infancy. Traditional polymers provide robust and chemically diverse materials, but synthetic control over their monomer sequences is limited. The modular and step-wise synthesis of peptoid polymers, on the other hand, allows for precise control over the monomer sequences, affording opportunities for these chains to fold into well-defined nanostructures. Hundreds of different side chains have been incorporated into peptoid polymers using efficient reaction chemistry, allowing for a seemingly infinite variety of possible synthetically accessible polymer sequences. Combinatorial discovery techniques have allowed the identification of functional polymers within large libraries of peptoids, and newly developed theoretical modeling tools specifically adapted for peptoids enable the future design of polymers with desired functions. Work towards controlling the three-dimensional structure of peptoids, from the conformation of the amide bond to the formation of protein-like tertiary structure, has and will continue to enable the construction of tunable and innovative nanomaterials that bridge the gap between natural and synthetic polymers.

Superior Antifouling Performance of a Zwitterionic Peptide Compared to an Amphiphilic, Non-Ionic Peptide

The aim of this study was to explore the influence of amphiphilic and zwitterionic structures on the resistance of protein adsorption to peptide self-assembled monolayers (SAMs) and gain insight into the associated antifouling mechanism. Two kinds of cysteine-terminated heptapeptides were studied. One peptide had alternating hydrophobic and hydrophilic residues with an amphiphilic sequence of CYSYSYS. The other peptide (CRERERE) was zwitterionic. Both peptides were covalently attached onto gold substrates via gold-thiol bond formation. Surface plasmon resonance analysis results showed that both peptide SAMs had ultralow or low protein adsorption amounts of 1.97-11.78 ng/cm2 in the presence of single proteins. The zwitterionic peptide showed relatively higher antifouling ability with single proteins and natural complex protein media. We performed molecular dynamics simulations to understand their respective antifouling behaviors. The results indicated that strong surface hydration of peptide SAMs contributes to fouling resistance by impeding interactions with proteins. Compared to the CYSYSYS peptide, more water molecules were predicted to form hydrogen-bonding interactions with the zwitterionic CRERERE peptide, which is in agreement with the antifouling test results. These findings reveal a clear relation between peptide structures and resistance to protein adsorption, facilitating the development of novel peptide-containing antifouling materials.

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

Fouling of artificial surfaces by biofluids is a plague Biotechnology deeply suffers from. Herein, we inventory the state-of-the-art surface chemistries developed to minimize this effect from both human and animal biosamples.

Synthesis, characterization and self-assembly behavior of zwitterionic amphiphilic triblock copolymers bearing pendant amino acid residues

Zwitterionic amphiphilic triblock copolymers bearing pendant amino acid residues PAGE/cys-b-PCL-b-PEG were synthesized and characterized. The self-assembly behavior of the copolymers was studied.

Antifouling gold surfaces grafted with aspartic acid and glutamic acid based zwitterionic polymer brushes

We report two new amino acid based antifouling zwitterionic polymers, poly(N(4)-(2-methacrylamidoethyl)asparagine) (pAspAA) and poly(N(5)-(2-methacrylamidoethyl)glutamine) (pGluAA). The vinyl monomers were developed from aspartic acid and glutamic acid. Surface-initiated photoiniferter-mediated polymerization was employed to graft polymer brushes from gold surfaces. Different thickness of polymer brushes was controlled by varying UV irradiation time. The nonspecific adsorption from undiluted human blood serum and plasma was studied by surface plasmon resonance (SPR). With the polymer film as thin as 11-12 nm, the adsorption on pAspAA from serum and plasma was as low as 0.75 and 5.18 ng/cm(2), respectively, and 1.88 and 10.15 ng/cm(2), respectively, for pGluAA. The adsorption amount is comparable to or even better than other amino acid based zwitterionic polymers such as poly(serine methacrylate), poly(lysine methacrylamide), and poly(ornithine methacrylamide) and other widely used antifouling polymers such as poly(sulfobetaine methacrylate), even under thinner polymer film thickness. The pAspAA and pGluAA grafted surfaces also showed strong resistance to endothelial cell attachment. The possession of both zwitterionic structure and hydrophilic amide groups, biomimetic property, and multifunctionality make pAspAA and pGluAA promising candidates for biocompatible antifouling functionalizable materials.

Grafting hyaluronic acid onto gold surface to achieve low protein fouling in surface plasmon resonance biosensors

Antifouling surfaces capable of reducing nonspecific protein adsorption from natural complex media are highly desirable in surface plasmon resonance (SPR) biosensors. A new protein-resistant surface made through the chemical grafting of easily available hyaluronic acid (HA) onto gold (Au) substrate demonstrates excellent antifouling performance against protein adsorption. AFM images showed the uniform HA layer with a thickness of ∼10.5 nm on the Au surface. The water contact angles of Au surfaces decreased from 103° to 12° with the covalent attachment of a carboxylated HA matrix, indicating its high hydrophilicity mainly resulted from carboxyl and amide groups in the HA chains. Using SPR spectroscopy to investigate nonspecific adsorption from single protein solutions (bovine serum albumin (BSA), lysozyme) and complex media (soybean milk, cow milk, orange juice) to an HA matrix, it was found that ultralow or low protein adsorptions of 0.6-16.1 ng/cm(2) (e.g., soybean milk: 0.6 ng/cm(2)) were achieved on HA-Au surfaces. Moreover, anti-BSA was chosen as a model recognition molecule to characterize the immobilization capacity and the antifouling performance of anti-BSA/HA surfaces. The results showed that anti-BSA/HA sensor surfaces have a high anti-BSA loading of 780 ng/cm(2), together with achieving the ultralow (<3 ng/cm(2) for lysozyme and soybean milk) or low (<17 ng/cm(2) for cow milk and 10% blood serum) protein adsorptions. Additionally, the sensor chips also exhibited a high sensitivity to BSA over a wide range of concentrations from 15 to 700 nM. Our results demonstrate a promising antifouling surface using extremely hydrophilic HA as matrix to resist nonspecific adsorption from complex media in SPR biosensors.

Two amino acid-based superlow fouling polymers: poly(lysine methacrylamide) and poly(ornithine methacrylamide)

We developed and investigated two new antifouling zwitterionic polymers, poly(lysine methacrylamide) (pLysAA) and poly(ornithine methacrylamide) (pOrnAA), both derived from natural amino acids - lysine and ornithine, respectively. The pLysAA and pOrnAA brushes were grafted on gold via the surface-initiated photoiniferter-mediated polymerization, with the polymer film thickness controlled by the UV-irradiation time. Nonspecific adsorption from human blood serum and plasma was investigated by surface plasmon resonance. Results show that the adsorption level decreased with the increasing film thickness. With the thin films of ∼14.5 nm, the minimal adsorption on pLysAA was 3.9 ng cm(-2) from serum and 5.4 ng cm(-2) from plasma, whereas the lowest adsorption on pOrnAA was 1.8 and 3.2 ng cm(-2), from serum and plasma, respectively. Such protein resistance is comparable to other widely reported antifouling surfaces such as poly(sulfobetaine methacrylate) and polyacrylamide, with a much thinner polymer film thickness. Both pLysAA and pOrnAA showed better protein resistance than the previously reported serine-based poly(serine methacrylate), whereas the pOrnAA is the best among three. The pLysAA- and pOrnAA-grafted surfaces also highly resisted the endothelial cell attachment and Escherichia coli K12 bacterial adhesion. Nanogels made of pLysAA and pOrnAA were found to be ultrastable in undiluted serum, with no aggregation observed after culturing for 24h. Dextran labeled with fluorescein isothiocyanate (FITC-dextran) was encapsulated in nanogels as a model drug. The encapsulated FITC-dextran exhibited controlled release from the pOrnAA nanogels. The superlow fouling, biomimetic and multifunctional properties of pLysAA and pOrnAA make them promising materials for a wide range of applications, such as implant coating, drug delivery and biosensing.

Preparation and characterizations of poly(2-methyl-2-oxazoline) based antifouling coating by thermally induced immobilization

Poly[(2-methyl-2-oxazoline)-random-glycidylmethacrylate] was immobilized on a silicon/glass surface via a simple annealing procedure to obtain a covalent and cross-linked antifouling coating.

Peptoids for biomaterials science

Reports of peptoid structures and interfaces highlighting their potential as synthetically convenient, multifunctional, modular and precisely tunable biomaterials are reviewed.

Antifouling glycocalyx-mimetic peptoids

The glycocalyx of the cell is composed of highly hydrated saccharidic groups conjugated to protein and lipid cores. Although components of the glycocalyx are important in cell-cell interactions and other specific biological recognition events, a fundamental role of the glycocalyx is the inhibition of nonspecific interactions at the cell surface. Inspired by glycoproteins present in the glycocalyx, we describe a new class of synthetic antifouling polymer composed of saccharide containing N-substituted polypeptide (glycopeptoid). Grafting of glycopeptoids to a solid surface resulted in a biomimetic shielding layer that dramatically reduced nonspecific protein, fibroblast, and bacterial cell attachment. All-atom molecular dynamics simulation of grafted glycopeptoids revealed an aqueous interface enriched in highly hydrated saccharide residues. In comparison to saccharide-free peptoids, the interfacial saccharide residues of glycopeptoids formed a higher number of hydrogen bonds with water molecules. Moreover, these hydrogen bonds displayed a longer persistence time, which we believe contributed to fouling resistance by impeding interactions with biomolecules. Our findings suggest that the fouling resistance of glycopeptoids can be explained by the presence of both a 'water barrier' effect associated with the hydrated saccharide residues as well as steric hindrance from the polymer backbone.