Lubricin-Inspired Loop Zwitterionic Peptide for Fabrication of Superior Antifouling Surfaces

Engineered Antifouling Peptides with Sarcosine Branches for Robust Electrochemical Detection of the HER2 Biomarker in Real Biological Samples

In complex biological matrices, the nonspecific adsorption phenomena occurring on the surfaces of electrochemical biosensors represent a considerable challenge for the precise detection of targets in heterogeneous biological samples. Furthermore, the presence of protein hydrolases in biofluids also affects the stability of biosensing devices utilizing natural proteins or peptides. It is therefore imperative to develop sensing devices capable of effectively minimizing such effects in real biological samples. Herein, we engineered a sarcosine branch-chain peptide (SBCP) with a strong antifouling capability to avoid biofouling and enhanced stability to resist hydrolysis by proteases. The peptide is composed of three sections: an anchoring sequence (CPPPP), an antifouling sequence (EK(Sar)EK(Sar)EK(Sar)EK(Sar)), and a recognition sequence (HLTVSPWY). An electrochemical biosensor was developed through the electrodeposition of poly(3,4-ethylenedioxythiophene) (PEDOT) incorporated with poly(norepinephrine) (PNE) on an electrode surface, followed by the electrodeposition of gold nanoparticles and the self-assembly of SBCP. The biosensor constructed using the SBCP containing a specific recognizing peptide sequence for the cancer biomarker human epidermal growth factor receptor 2 (HER2) was capable of sensitively detecting target HER2, within the concentration range of 1.0 pg mL-1 to 1.0 μg mL-1 and with a limit of detection of 0.37 pg mL-1. Moreover, the biosensor demonstrated antifouling ability and the capacity to accurately detect the target in human serum, exhibiting a high degree of concordance with the assaying results of ELISA kits. These findings suggest that the biosensor based on the engineered peptides possesses promising potential for practical applications.

A generic model for pH-sensitive collapse of hydrophobic polymers

The hydrophobic effect is an important contributor to the stability of proteins and may be influenced by many factors including the pH of the solution. To simplify the study of pH effects on proteins, we parameterize biologically motivated titratable monomers which we insert into the sequence of a hydrophobic polymer and study via constant pH molecular dynamics (MD) simulations. We calculate the potential of mean force of the polymer as a function of its radius of gyration at different pH values and observe that the collapsed state of the polymer is destabilized when the titratable monomer is more charged (high pH for an acid and low pH for a base). Further, the extent of the destabilization is influenced by the position of the titratable monomer along the polymer sequence. The pKa value of the titratable monomer is also observed to be sensitive to polymer conformation, in agreement with protein studies. We further study a zwitterionic polymer with an acidic and a basic monomer in the same sequence which presents a pH-dependent hairpin formation. Our model provides a simplified yet powerful framework to study pH effects on the hydrophobic effect, providing insights into mechanisms governing the behavior of intrinsically disordered proteins (IDPs) and pH-sensitive drug delivery, among other applications.

Atomistic Insights into the Ionic Response and Mechanism of Antifouling Zwitterionic Polymer Brushes

Zwitterionic polymer brushes are not a practical choice since their ionic response mechanisms are unclear, despite their great potential for surface antifouling modification. Therefore, atomic force microscopy and molecular dynamics simulations investigated the ionic response of the surface electrical properties, hydration properties, and protein adhesion of three types of zwitterionic brushes. The surface of PMPC (poly(2-methacryloyloxyethyl phosphorylcholine)) and PSBMA (poly(sulfobetaine methacrylate)) zwitterionic polymer brushes in salt solution exhibits a significant accumulation of cations, which results in a positive shift in the surface potential. In contrast, the surface of PSBMA polymer brushes demonstrates no notable change in potential. Furthermore, divalent Ca2+ enhances protein adhesion to polymer brushes by Ca2+ bridges. Conversely, monovalent Na+ diminishes the number of salt bridges between PSBMA and PCBMA (poly(carboxybetaine methacrylate)) zwitterionic polymer brushes and proteins via a competitive adsorption mechanism, thereby reducing protein adhesion. A summary of polymer brush material selection and design concepts in a salt solution environment is provided based on the salt response law of protein adhesion resistance of various zwitterionic materials. This work closes a research gap on the response mechanism of zwitterionic polymer brushes' antifouling performance in a salt solution environment, significantly advancing the practical use of these brushes.

Enhanced Anti-Interference Photoelectrochemical DNA Bioassay: Grafting a Peptide-Conjugated Hairpin DNA Probe on a COF-Based Photocathode

Precise and sensitive analysis of specific DNA in actual human bodily fluids is crucial for the early diagnosis of major diseases and for a deeper understanding of DNA functions. Herein, by grafting a peptide-conjugated hairpin DNA probe to a covalent organic framework (COF)-based photocathode, a robust anti-interference photoelectrochemical (PEC) DNA bioassay was explored, which could specifically resist potential interference from nonspecific proteins and reducing species. Human immunodeficiency virus (HIV) DNA was used as the target DNA (tDNA) for the PEC DNA bioassay. The vinyl-functionalized COF (COF-V) was modified with meso-tetra(4-carboxyphenyl)-porphine (TCPP) and polydopamine (PDA) to fabricate a PDA/TCPP/COF-V photocathode, which served as the photocurrent signal transducer. Toward the unconventional recognition element, a hairpin DNA probe (hDNA) was efficiently linked with a linear zwitterionic peptide (LZP) to form the LZP-hDNA bioconjugate, which was then grafted onto the COF-based photocathode. The grafting of the LZP generated a sturdy anti-interference interface on the signal transducer. For tDNA probing, AgInS2 (AIS) quantum dots acted as signal quenchers, marked on signaling DNA (sDNA) to obtain AIS-sDNA labeling, and a striking drop in the photocurrent signal was achieved through λ-exonuclease (λ-Exo)-aided target recycling. This novel peptide-conjugated hairpin DNA probe endowed the PEC DNA bioassay with an impressive anti-interference property without requiring tedious steps. By combining the excellent photoelectric properties of the COF-based photocathode with an effective signaling strategy, accurate and sensitive results for tDNA probing were achieved.

A Y-Shaped Peptide-Based Antifouling Electrochemical Aptasensor for Sensitive Aflatoxin B1 Detection in Food

Conquering surface fouling of sensors caused by nonspecific adsorption and accumulation of foulants in a food matrix is of significance in accurate food safety analysis. Herein, an antifouling electrochemical aptasensor based on a Y-shaped peptide and nanoporous gold (NPG) for aflatoxin B1 detection in milk, tofu, and rice flour was proposed. The self-designed Y-shaped peptide involves an anchoring segment (-C), a support structure (-PPPP-), and an antifouling domain with two branches (-EK(KSRE)DER-) inspired by two bioactive peptides. NPG offers not only good electroconductibility but also anchor sites for peptides and aptamers. The antifouling surface can effectively resist fouling from single protein and carbohydrate solutions and even real food. The proposed aptasensor achieves sensitive detection with a low limit of detection of 0.26 pg mL-1 (linear range: 0.001-10 ng mL-1) and accurate analysis with minimal sample pretreatment (recoveries: 91.0-110.8%), offering a potential sensing platform to lower matrix interference.

Construction of Loop Polyzwitterion Brushes on PET Sheets via the Chain-End Closure Strategy To Improve Antifouling and Hemocompatible Properties

Steric stabilization and lubrication give loop polymer brushes enhanced antifouling properties. In the study, linear zwitterionic poly(NMASMCMS) brushes were first constructed on a poly(ethylene terephthalate) (PET) surface through surface-initiated reversible addition-fragmentation chain-transfer (SI-RAFT) polymerization. The tethered linear brushes on sheets were then thiolated with ethanolamine, followed by oxidation to form loop brushes. The chain-end closure strategy to form loop brushes is facile, with a high transformation rate. The physical and chemical structures were characterized by the water contact angle (WCA), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Loop brush grafted sheets (PET-L) exhibited better lubricity than linear brush grafted sheets (PET-B) due to the rigidity of loop brush structures. The two brushes exhibited good antifouling and hemocompatible properties on low protein adsorption, bacteria adhesion, platelet adhesion, and hemolysis. In comparison, loop brushes performed with antifouling properties superior to those of linear brushes.

Experimental and computational techniques to investigate the protein resistance of zwitterionic polymers

Most surfaces undergo non-specific protein adsorption upon direct contact with protein-containing environments, resulting in the formation of a protein corona, and the nature and composition of the corona affect the properties of the material. Zwitterionic polymers have oppositely charged groups in their repeating units, which facilitate the formation of a hydration layer on the surface through electrostatic interactions. The hydration layer possesses a strong water-binding ability and can prevent protein adsorption. Therefore, the hydration effect of zwitterionic polymers has become a research focus, and many researchers have investigated this mechanism using experimental and computational methods. This paper reviews the experimental techniques and simulation methods to study the hydration effect of zwitterionic polymers and the advantages and disadvantages of different techniques are discussed.

Zwitterionic Peptides: From Mechanism, Design Strategies to Applications

Zwitterionic peptides, as a type of peptide composed of charged residues, are electrically neutral, which combine the advantages of zwitterionic materials and biological peptides, exhibiting hydrophilicity and programmable properties. As attractive candidates for resisting nonspecific adsorption of biomacromolecules and microorganisms, zwitterionic peptides have been applied in materials science, biomedicine, and biochemistry over the past decade. In this review, the development of zwitterionic peptides has been systematically outlined and analyzed, including their mechanisms, structure-function relationships, and design strategies. Furthermore, this review emphasizes and discusses their recent applications for developing functional coatings, biosensors, drug delivery systems, and engineering proteins. Finally, future research perspectives and challenges of zwitterionic peptides are also prospected and discussed. This review is intended to provide clarity and insight into the design and applications of zwitterionic peptides.

Unveiling the spatiotemporal dynamics of membrane fouling: A focused review on dynamic fouling characterization techniques and future perspectives

Membrane technology has emerged as a crucial method for obtaining clean water from unconventional sources in the face of water scarcity. It finds wide applications in wastewater treatment, advanced treatment, and desalination of seawater and brackish water. However, membrane fouling poses a huge challenge that limits the development of membrane-based water treatment technologies. Characterizing the dynamics of membrane fouling is crucial for understanding its development, mechanisms, and effective mitigation. Instrumental techniques that enable in situ or real-time characterization of the dynamics of membrane fouling provide insights into the temporal and spatial evolution of fouling, which play a crucial role in understanding the fouling mechanism and the formulation of membrane control strategies. This review consolidates existing knowledge about the principal advanced instrumental analysis technologies employed to characterize the dynamics of membrane fouling, in terms of membrane structure, morphology, and intermolecular forces. Working principles, applications, and limitations of each technique are discussed, enabling researchers to select appropriate methods for their specific studies. Furthermore, prospects for the future development of dynamic characterization techniques for membrane fouling are discussed, underscoring the need for continued research and innovation in this field to overcome the challenges posed by membrane fouling.

Fabrication of an Antifouling Surface Plasmon Resonance Sensor with Stratified Zwitterionic Peptides for Highly Efficient Detection of Peanut Allergens in Biscuits

Peanut allergen monitoring is currently an effective strategy to avoid allergic diseases, while food matrix interference is a critical challenge during detection. Here, we developed an antifouling surface plasmon resonance sensor (SPR) with stratified zwitterionic peptides, which provides both excellent antifouling and sensing properties. The antifouling performance was measured by the SPR, which showed that stratified peptide coatings showed much better protein resistance, reaching ultralow adsorption levels (<5 ng/cm2). Atomic force microscopy was used to further analyze the antifouling mechanism from a mechanical perspective, which demonstrated lower adsorption forces on hybrid peptide coatings, confirming the better antifouling performance of stratified surfaces. Moreover, the recognition of peanut allergens in biscuits was performed using an SPR with high efficiency and appropriate recovery results (98.2-112%), which verified the feasibility of this assay. Therefore, the fabrication of antifouling sensors with stratified zwitterionic peptides provides an efficient strategy for food safety inspection.

Recombinant manufacturing of multispecies biolubricants

Lubricin, a lubricating glycoprotein abundant in synovial fluid, forms a low-friction brush polymer interface in tissues exposed to sliding motion including joints, tendon sheaths, and the surface of the eye. Despite its therapeutic potential in diseases such as osteoarthritis and dry eye disease, there are few sources available. Through rational design, we developed a series of recombinant lubricin analogs that utilize the species-specific tissue-binding domains at the N- and C-termini to increase biocompatibility while replacing the central mucin domain with an engineered variant that retains the lubricating properties of native lubricin. In this study, we demonstrate the tissue binding capacity of our engineered lubricin product and its retention in the joint space of rats. Next, we present a new bioprocess chain that utilizes a human-derived cell line to produce O-glycosylation consistent with that of native lubricin and a purification strategy that capitalizes on the positively charged, hydrophobic N- and C-terminal domains. The bioprocess chain is demonstrated at 10 L scale in industry-standard equipment utilizing commonly available ion exchange, hydrophobic interaction and size exclusion chromatography resins. Finally, we confirmed the purity and lubricating properties of the recombinant biolubricant. The biomolecular engineering and bioprocessing strategies presented here are an effective means of lubricin production and could have broad applications to the study of mucins in general.

Study of Hydration Repulsion of Zwitterionic Polymer Brushes Resistant to Protein Adhesion through Molecular Simulations

The fabrication of antifouling zwitterionic polymer brushes represents a leading approach to mitigate nonspecific adhesion on the surfaces of medical devices. This investigation seeks to elucidate the correlation between the material composition and structural attributes of these polymer brushes in preventing protein adhesion. To achieve this goal, we modeled three different zwitterionic brushes, namely, carboxybetaine methacrylate (CBMA), sulfobetaine methacrylate (SBMA), and (2-(methacryloyloxy)ethyl)-phosphorylcholine (MPC). The simulations revealed that elevating the grafting density enhances the structural stability, hydration strength, and resistance to protein adhesion exhibited by the polymer brushes. PCBMA manifests a more robust hydration layer, while PMPC demonstrates the slightest interaction with proteins. In a comprehensive evaluation, PSBMA polymer brushes emerged as the best choice with superior stability, enhanced protein repulsion, and minimally induced protein deformation, resulting in effective resistance to nonspecific adhesion. The high-density SBMA polymer brushes significantly reduce the level of protein adhesion in AFM testing. In addition, we have pioneered the quantitative characterization of hydration repulsion in polymer brushes by analyzing the hydration repulsion characteristics at different materials and graft densities. In summary, our study provides a nuanced understanding of the material and structural determinants influencing the capacity of zwitterionic polymer brushes to thwart protein adhesion. Additionally, it presents a quantitative elucidation of hydration repulsion, contributing to the advancement and application of antifouling polymer brushes.

Design, preparation, and characterization of lubricating polymer brushes for biomedical applications

The lubrication modification of biomedical devices significantly enhances the functionality of implanted interventional medical devices, thereby providing additional benefits for patients. Polymer brush coating provides a convenient and efficient method for surface modification while ensuring the preservation of the substrate's original properties. The current research has focused on a "trial and error" method to finding polymer brushes with superior lubricity qualities, which is time-consuming and expensive, as obtaining effective and long-lasting lubricity properties for polymer brushes is difficult. This review summarizes recent research advances in the biomedical field in the design, material selection, preparation, and characterization of lubricating and antifouling polymer brushes, which follow the polymer brush development process. This review begins by examining various approaches to polymer brush design, including molecular dynamics simulation and machine learning, from the fundamentals of polymer brush lubrication. Recent advancements in polymer brush design are then synthesized and potential avenues for future research are explored. Emphasis is placed on the burgeoning field of zwitterionic polymer brushes, and highlighting the broad prospects of supramolecular polymer brushes based on host-guest interactions in the field of self-repairing polymer brush applications. The review culminates by providing a summary of methodologies for characterizing the structural and functional attributes of polymer brushes. It is believed that a development approach for polymer brushes based on "design-material selection-preparation-characterization" can be created, easing the challenge of creating polymer brushes with high-performance lubricating qualities and enabling the on-demand creation of coatings. STATEMENT OF SIGNIFICANCE: Biomedical devices have severe lubrication modification needs, and surface lubrication modification by polymer brush coating is currently the most promising means. However, the design and preparation of polymer brushes often involves "iterative testing" to find polymer brushes with excellent lubrication properties, which is both time-consuming and expensive. This review proposes a polymer brush development process based on the "design-material selection-preparation-characterization" strategy and summarizes recent research advances and trends in the design, material selection, preparation, and characterization of polymer brushes. This review will help polymer brush researchers by alleviating the challenges of creating polymer brushes with high-performance lubricity and promises to enable the on-demand construction of polymer brush lubrication coatings.

Phospholipid Bilayer Integrated with Multifunctional Peptide for Ultralow-Fouling Electrochemical Detection of HER2 in Human Serum

Electrochemical biosensing devices face challenges of severe nonspecific adsorption in complex biological matrices for the detection of biomarkers, and thus, there is a significant need for sensitive and antifouling biosensors. Herein, a sensitive electrochemical biosensor with antifouling and antiprotease hydrolysis ability was constructed for the detection of human epidermal growth factor receptor 2 (HER2) by integrating multifunctional branched peptides with distearoylphosphatidylethanolamine-poly(ethylene glycol) (DSPE-PEG) self-assembled bilayer. The peptide was designed to possess antifouling, antiprotease hydrolysis, and HER2 recognizing capabilities. Molecular dynamics simulations demonstrated that the DSPE was able to effectively self-assemble into a bilayer, and the water contact angle and electrochemical experiments verified that the combination of peptide with the DSPE-PEG bilayer was conducive to enhancing the hydrophilicity and antifouling performance of the modified surface. The constructed HER2 biosensor exhibited excellent antifouling and antiprotease hydrolysis capabilities, and it possessed a linear range of 1.0 pg mL-1 to 1.0 μg mL-1, and a limit of detection of 0.24 pg mL-1. In addition, the biosensor was able to detect HER2 in real human serum samples without significant biofouling, and the assaying results were highly consistent with those measured by the enzyme-linked immunosorbent assay (ELISA), indicating the promising potential of the antifouling biosensor for clinical diagnosis.

Designed Polyhydroxyproline Helical Peptide with Ultrarobust Antifouling Capability for Electrochemical Sensing in Diverse Complex Biological Fluids

Developing a generalized strategy for the nonfouling detection of biomarkers in diverse biological fluids presents a significant challenge. Herein, a polyhydroxyproline helical peptide (PHHP) was designed and adopted to fabricate electrochemical microsensors capable of detecting targets in various biological media. The PHHP possessed unique properties such as strong hydrophilicity, rigid structure, and lack of ionizable side-chain groups. Compared with common zwitterionic peptides (ZIPs), the PHHP exhibited similar antifouling capability but exceptional stability, allowing its antifouling performance to be unaffected by environmental alteration. The PHHP can prevent biofouling even in fluctuating pH conditions, high ionic strength environments, and the presence of high-valence ions and resist the protease hydrolysis. The PHHP-modified carbon fiber microelectrode was further immobilized with an aptamer to construct an antifouling microsensor for cortisol detection across diverse biofluids, and the microsensor exhibited acceptable accuracy and higher sensitivity than the ELISA method. In addition, different biological samples of mice were collected in situ using a microsensing device, and cortisol levels were analyzed in each specifically tailored region. This nonfouling sensing strategy based on PHHP allows a comprehensive assessment of biomarkers in both spatial and temporal dimensions in diverse biological environments, holding promising potential for early disease diagnosis and real-time health monitoring.

Antifouling Surfaces Based on Polyzwitterion Loop Brushes

Antifouling surfaces have attracted increasing interest in recent years due to their potential application in various fields. In this work, we report a loop polyzwitterionic coating that exhibits excellent resistance to protein adsorption. Triblock and diblock copolymers of 2-[(2-hydroxyethyl)disulfanyl]ethyl methacrylate) (HSEMA) and 2-(dimethylamino)ethyl methacrylate) (DMAEMA) were synthesized by atom-transferred radical polymerization, followed by betainization of the DMAEMA block with 1,3-propane sultone and reduction of the disulfide bond in HSEMA to yield a triblock copolymer comprising a zwitterionic poly(sulfobetaine methacrylate) (PSBMA) midblock and poly(2-sulfanylethyl methacrylate) (PSEMA) terminal blocks as well as its diblock analogue that was of the same composition as the former and half the chain length. Both copolymers adsorbed to the gold substrate via the thiol groups in the terminal PSEMA block(s), creating loop and linear PSBMA brush coatings of comparable thickness, as revealed by X-ray photoelectron spectroscopy and ellipsometry. Adsorption of bovine serum albumin and fibrinogen as model proteins from solution to these surfaces was investigated by a quartz crystal microbalance with dissipation and confocal laser scanning microscopy (CLSM), and platelet and bacterial adhesions were assessed by scanning electron microscopy and CLSM. The results demonstrate that both linear and loop polyzwitterion brushes are excellent in resisting the adsorption of the foulants, and the loop brushes are superior to the linear analogues.

Chemical antifouling strategies in sensors for food analysis: A review

Surface biofouling induced by the undesired nonspecific adsorption of foulants (e.g., coexisting proteins and cells) in food matrices is a major issue of sensors for food analysis, hindering their reliability and accuracy of sensing. This issue can be addressed by developing antifouling strategies to prevent or alleviate nonspecific binding. Chemical antifouling strategies involve the use of chemical modifiers (i.e., antifouling materials) to strongly hydrate the surface and reduce surface biofouling. Through appropriate immobilization approaches, antifouling materials can be tethered onto sensors to form antifouling surfaces with well-ordered structures, balanced surface charges, and appropriate surface density and thickness. A rational antifouling surface can reduce the matrix effect, simplify sample pretreatment, and improve analytical performance. This review summarizes recent developments in chemical antifouling strategies in sensing. Surface antifouling mechanisms and common antifouling materials are described, and factors that may influence the antifouling effects of antifouling surfaces and approaches incorporating antifouling materials onto sensing surfaces are highlighted. Moreover, the specific applications of antifouling sensors in food analysis are introduced. Finally, we provide an outlook on future developments in antifouling sensors for food analysis.

Surface modification of commercial intraocular lens by zwitterionic and antibiotic-loaded coating for preventing postoperative endophthalmitis

After cataract surgery, to prevent possible postoperative endophthalmitis (POE) caused by attached pathogenic bacteria onto the surface of implanted intraocular lens (IOL), various antibiotic-loaded IOLs have been proposed and widely studied to inhibit bacterial infection. However, most of these developed antibiotic-loaded IOLs still suffer from shortcomings such as insufficient drug loading, short release time, poor biocompatibility, and risk of secondary infection. Herein, we propose a zwitterionic and high-drug loading coating for surface modification of commercial hydrophobic IOL with both antifouling and antibacterial properties to effectively prevent POE. In this strategy, zwitterionic poly(carboxylbetaine-co-dopamine methacrylamide) copolymers (pCBDA) and dopamine (DA) were first robustly co-deposited onto IOL surface via facile mussel-inspired chemistry, resulting in a hydrophilic coating (defined as PCB) without sacrificing the high light transmittance of the native IOL. Subsequently, amikacin (AMK), an amine-rich antibiotic was reversibly conjugated onto the coating through the acid-sensitive Schiff base bonds formed by the reaction between amino and catechol groups, with high-drug payload over ∼35.5 μg per IOL and 30 days of sustained drug release under weak acid environment. Benefiting from the antifouling property of zwitterionic pCBDA copolymers, the intraocularly implanted PCB/AMK-coated IOL could effectively resist the adhesion and proliferation of residual LECs to inhibit the development of posterior capsule opacification (PCO) without affecting the normal ocular tissues, demonstrating excellent in vivo biocompatibility. Moreover, the synergy of zwitterionic pCBDA and conjugated AMK with acidic-dependent release behavior endowed this PCB/AMK-coated IOL strong antibacterial activity against both in vitro biofilm formation and in vivo postoperative Staphylococcus aureus infection, suggesting its promising application in preventing POE.

Substrate-independent and widely applicable deposition of antibacterial coatings

Antibacterial coatings are regarded as a necessary tool to prevent implant-related infections. Substrate-independent and widely applicable coating techniques are gaining significant interest to synthesize different types of antibacterial films, which can be relevant from a fundamental and application-oriented perspective. Plasma polymer- and polydopamine-based antibacterial coatings represent the most widely studied and versatile approaches among these coating techniques. Both single- and dual-functional antibacterial coatings can be fabricated with these approaches and a variety of dual-functional antibacterial coating strategies can still be explored in future work. These coatings can potentially be used for a wide range of different implants (material, shape, and size). However, for most implants, significantly more fundamental knowledge needs to be gained before these coatings can find real-life use.

Mitigation of Cellular and Bacterial Adhesion on Laser Modified Poly (2-Methacryloyloxyethyl Phosphorylcholine)/Polydimethylsiloxane Surface

Nowadays, using polymers with specific characteristics to coat the surface of a device to prevent undesired biological responses can represent an optimal strategy for developing new and more efficient implants for biomedical applications. Among them, zwitterionic phosphorylcholine-based polymers are of interest due to their properties to resist cell and bacterial adhesion. In this work, the Matrix-Assisted Laser Evaporation (MAPLE) technique was investigated as a new approach for functionalising Polydimethylsiloxane (PDMS) surfaces with zwitterionic poly(2-Methacryloyloxyethyl-Phosphorylcholine) (pMPC) polymer. Evaluation of the physical-chemical properties of the new coatings revealed that the technique proposed has the advantage of achieving uniform and homogeneous stable moderate hydrophilic pMPC thin layers onto hydrophobic PDMS without any pre-treatment, therefore avoiding the major disadvantage of hydrophobicity recovery. The capacity of modified PDMS surfaces to reduce bacterial adhesion and biofilm formation was tested for Gram-positive bacteria, Staphylococcus aureus (S. aureus), and Gram-negative bacteria, Escherichia coli (E. coli). Cell adhesion, proliferation and morphology of human THP-1 differentiated macrophages and human normal CCD-1070Sk fibroblasts on the different surfaces were also assessed. Biological in vitro investigation revealed a significantly reduced adherence on PDMS-pMPC of both E. coli (from 29 × 10 ⁶ to 3 × 10² CFU/mL) and S. aureus (from 29 × 10⁶ to 3 × 10² CFU/mL) bacterial strains. Additionally, coated surfaces induced a significant inhibition of biofilm formation, an effect observed mainly for E. coli. Moreover, the pMPC coatings improved the capacity of PDMS to reduce the adhesion and proliferation of human macrophages by 50% and of human fibroblast by 40% compared to unmodified scaffold, circumventing undesired cell responses such as inflammation and fibrosis. All these highlighted the potential for the new PDMS-pMPC interfaces obtained by MAPLE to be used in the biomedical field to design new PDMS-based implants exhibiting long-term hydrophilic profile stability and better mitigating foreign body response and microbial infection.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Conformation-dominated surface antifouling and aqueous lubrication

Antifouling and aqueous lubrication are important properties for biomaterials, especially for those with implantation purposes. In order to better understand the polymer conformation dependence of the surface antifouling and lubrication properties, poly(ethylene glycol) (PEG) polymers with mono-functional and difunctional catechol anchors were designed and anchored on surface to adopt tail and loop conformations. Diblock and triblock copolymers with poly(dopamine methacrylamide) (PDMA) block as anchors and PEG block as the main body were synthesized and anchored on silicon surfaces by a "grafting to" strategy. The chemical composition, film thickness, and surface roughness of both coatings were controlled to be similar to give a direct comparison of looped brushes and tailed analogues. Then, the antifouling and surface friction behaviors were detected to verify the topological conformation effect of PEG polymer brushes. Results showed that PEG triblock copolymer modified surface exhibited an obviously better antifouling property and a lower friction coefficient of ∼0.011 than that of PEG diblock copolymer modified surface. Additionally, calculation and simulation results demonstrated that triblock copolymer had higher adsorption energy and anchored on surface with looped conformation. It is indicated that the strongly anchored PEG loops are effective for excellent antifouling and lubricating properties due to its strong hydration and steric hindrance. The conformation-dominated enhanced antifouling and reduced interfacial friction is an effective method for the development of excellent antifouling surfaces.