Bioinert and Lubricious Surfaces by Macromolecular Design

Exploring Scent Distinction with Polymer Brush Arrays

The ability to distinguish scents, volatile organic compounds (VOCs), and their mixtures is critical in agriculture, food safety, and public health. This study introduces a proof-of-concept approach for VOC and scent distinction, leveraging polymer brush arrays with diverse chemical compositions designed to interact with various VOCs and scents. When VOCs or scents are exposed to the brush array, they produce distinct mass absorption patterns for different polymer brushes, effectively creating "fingerprints". Scents can be recognized without having to know the absorption of their individual components. This allows for a scent distinction technique, mimicking scent recognition within a mammalian olfactory system. To demonstrate the scent distinction, we synthesized different polymer brushes, zwitterionic, hydrophobic, and hydrophilic, using surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization with eosin Y and triethanolamine as catalysts. The polymer brushes were then exposed to vapors of different single-compound VOCs and complex scents consisting of many VOCs, such as the water-ethanol mixture, rosemary oil, lavender oil, and whiskey scents. Quartz crystal microbalance measurements with dissipation monitoring (QCM-D) show a clear difference in brush absorption for these diverse VOC vapors such that distinct fingerprints can be identified. Our proof-of-concept study aims to pave the way for universal electronic nose sensors that distinguish scents by combining mass absorption patterns from polymer brush-coated surfaces.

Detachable Cyclic Poly(ethylene glycol)-Embedded Choline Phosphate Liposome Used for Long-Acting and Accurate Cancer Chemo-Immunotherapy with High Security

Liposomes have attracted attention in biomedicine and pharmacy for their benefits including reduced toxicity, extended pharmacokinetics, and biocompatibility. However, their limitations include susceptibility to blood clearance, rapid disintegration, and lack of functionality, restricting their further applications. To address these challenges, inspired by the unique topological features of cyclic polymers and the specific binding property of the choline phosphate (CP) lipid, dipole-dipole interactions between CP molecules are utilized to create a detachable cyclic PEG-embedded CP liposome (d-cycPEG-lipo). In comparison to linear PEG-embedded liposomes (d-linPEG-lipo) and PEGylated liposomes (linPEG-lipo), d-cycPEG-lipo demonstrates enhanced resistance to proteins and macrophages in the bloodstream due to its higher compactness and smoother interface. The packing behavior and lubrication property of cyclic PEG also result in reduced accumulation in organs, leading to an extended pharmacokinetic half-life of 13.6 h. At the tumor site, the PEG embedded in d-cycPEG-lipo detached and facilitated a 3.3-fold higher cell uptake than linPEG-lipo. Notably, d-cycPEG-lipo induces lower inflammation and triggers a stronger immune response than d-linPEG-lipo. In the treatment of breast cancer, d-cycPEG-lipo exhibits a significantly high efficacy of 98.5%. Hence, the reversible combination of cyclic PEG with CP liposomes holds tremendous promise for enhancing drug and antibody delivery in clinical tumor therapy.

On the Road to Circular Polymer Brushes: Challenges and Prospects

Polymer brushes are unique surface coatings that have been of high interest in research for the past decades due to their covalent tethering to surfaces and the broad spectrum of polymers that can be grafted to or grafted from various surfaces. Modification of surfaces with brushes may provide lubricious and/or antifouling properties, and they can also potentially be used in many application fields due to their high responsiveness toward certain stimuli. Generally, polymer brushes are long-lasting coatings, while their end-of-life has to date largely been neglected. Therefore, it is important to consider additional design methodologies to produce circular brushes, which will degrade after a certain period of time such that surfaces can be reused, and the potentially obtained monomers may be used again to synthesize new brushes. In this Perspective, we aim to tackle and understand the challenges to translate the knowledge on degradation and chemical recycling of bulk polymers toward circular polymer brushes. We summarized the recent developments on (bio)degradable polymer brushes and the challenges that are to be tackled toward their potential implementation as circular coatings.

Polymer brushes for friction control: Contributions of molecular simulations

When polymer chains are grafted to solid surfaces at sufficiently high density, they form brushes that can modify the surface properties. In particular, polymer brushes are increasingly being used to reduce friction in water-lubricated systems close to the very low levels found in natural systems, such as synovial joints. New types of polymer brush are continually being developed to improve with lower friction and adhesion, as well as higher load-bearing capacities. To complement experimental studies, molecular simulations are increasingly being used to help to understand how polymer brushes reduce friction. In this paper, we review how molecular simulations of polymer brush friction have progressed from very simple coarse-grained models toward more detailed models that can capture the effects of brush topology and chemistry as well as electrostatic interactions for polyelectrolyte brushes. We pay particular attention to studies that have attempted to match experimental friction data of polymer brush bilayers to results obtained using molecular simulations. We also critically look at the remaining challenges and key limitations to overcome and propose future modifications that could potentially improve agreement with experimental studies, thus enabling molecular simulations to be used predictively to modify the brush structure for optimal friction reduction.

Superlubricity of pH-responsive hydrogels in extreme environments

Poly(acrylamide-co-acrylic acid) (P(AAm-co-AA)) hydrogels are highly tunable and pH-responsive materials frequently used in biomedical applications. The swelling behavior and mechanical properties of these gels have been extensively characterized and are thought to be controlled by the protonation state of the acrylic acid (AA) through the regulation of solution pH. However, their tribological properties have been underexplored. Here, we hypothesized that electrostatics and the protonation state of AA would drive the tribological properties of these polyelectrolyte gels. P(AAm-co-AA) hydrogels were prepared with constant acrylamide (AAm) concentration (33 wt%) and varying AA concentration to control the amount of ionizable groups in the gel. The monomer:crosslinker molar ratio (200:1) was kept constant. Hydrogel swelling, stiffness, and friction behavior were studied by systematically varying the acrylic acid (AA) concentration from 0-12 wt% and controlling solution pH (0.35, 7, 13.8) and ionic strength (I = 0 or 0.25 M). The stiffness and friction coefficient of bulk hydrogels were evaluated using a microtribometer and borosilicate glass probes as countersurfaces. The swelling behavior and elastic modulus of these polyelectrolyte hydrogels were highly sensitive to solution pH and poorly predicted the friction coefficient (µ), which decreased with increasing AA concentration. P(AAm-co-AA) hydrogels with the greatest AA concentrations (12 wt%) exhibited superlubricity (µ = 0.005 ± 0.001) when swollen in unbuffered, deionized water (pH = 7, I = 0 M) and 0.5 M NaOH (pH = 13.8, I = 0.25 M) (µ = 0.005 ± 0.002). Friction coefficients generally decreased with increasing AA and increasing solution pH. We postulate that tunable lubricity in P(AAm-co-AA) gels arises from changes in the protonation state of acrylic acid and electrostatic interactions between the probe and hydrogel surface.

Zwitterionic Poly(carboxybetaine) Brush/Albumin Conjugate Films: Structure and Lubricity

Artificial cartilages build up a highly lubricious system with the harmony of biomacromolecules and water. Bioconjugate thin films composed of a zwitterionic poly(carboxybetaine methacrylate) (PCB) brush platform and bovine serum albumin (BSA) were designed. BSA conjugation to the PCB brush chains was achieved by carbodiimide chemistry to give PCB brush/BSA conjugate films. The PCB brush/BSA conjugate films exhibited adaptable interfacial properties due to the amphiphilic nature of BSA. Neutron reflectivity showed that BSAs were localized at the liquid side of the conjugate films in PBS and the BSA conjugation slightly reduced the water content of the top layer, while the swollen state of the carpet PCB brush layer remained unchanged. The PCB brush/BSA conjugate films showed improved lubricity in the boundary lubrication mode but slightly worse fluid lubrication induction properties. This conjugate film could be a model system for the investigation of zwitterion/protein composite interfaces and is worth developing biomaterials that require lubrication in vivo.

Structure and pH-Induced Swelling of Polymer Films Prepared from Sequentially Grafted Polyelectrolytes

We have prepared a series of ampholytic polymer films, using a self-initiated photografting and photopolymerization (SI-PGP) method to sequentially polymerize first anionic (deuterated methacrylic acid (dMAA)) and thereafter cationic (2-aminoethyl methacrylate (AEMA)) monomers to investigate the SI-PGP grafting process. Dry films were investigated by ellipsometry, X-ray, and neutron reflectometry, and their swelling was followed over a pH range from 4.5 to 10.5 with spectroscopic ellipsometry. The deuterated monomer allows us to separate the distributions of the two components by neutron reflectometry. Growth of both polymers proceeds via grafting of solution-polymerized fragments to the surface, and also the second layer is primarily grafted to the substrate and not as a continuation of the existing chains. The polymer films are stratified, with one layer of near 1:1 composition and the other layer enriched in one component and located either above or below the former layer. The ellipsometry results show swelling transitions at low and high pH but with no systematic variation in the pH values where these transitions occur. The results suggest that grafting density in SI-PGP-prepared homopolymers could be increased via repeated polymerization steps, but that this process does not necessarily increase the average chain length.

A Self-defense Hierarchical Antibacterial Surface with Inherent Antifouling and Bacteria-activated Bactericidal Properties for Infection Resistance

Biomedical device-associated infection (BAI) is one of the main reasons for the function failure of implants in clinic practices. Development of high-efficiency antibacterial materials is of great significance to reduce...

Mussel-Inspired Multiloop Polyethers for Antifouling Surfaces

Despite the widespread use of polymers for antifouling coatings, the effect of the polymeric topology on the antifouling property has been largely underexplored. Unlike conventional brush polymers, a loop conformation often leads to strong steric stabilization of surfaces and antifouling and lubricating behavior owing to the large excluded volume and reduced chain ends. Herein, we present highly antifouling multiloop polyethers functionalized with a mussel-inspired catechol moiety with varying loop dimensions. Specifically, a series of polyethers with varying catechol contents were synthesized via anionic ring-opening polymerization by using triethylene glycol glycidyl ether (TEG) and catechol-acetonide glycidyl ether (CAG) to afford poly(TEG-co-CAG)_n. The versatile adsorption and antifouling effects of multiloop polyethers were evaluated using atomic force microscopy and a quartz crystal microbalance with dissipation. Furthermore, the crucial role of the loop dimension in the antifouling properties was analyzed via a surface force apparatus and a cell attachment assay. This study provides a new platform for the development of versatile antifouling polymers with varying topologies.

Nonbiofouling Coatings Using Bottlebrushes with Concentrated Polymer Brush Architecture

Concentrated polymer brushes (CPBs) are known to suppress biofouling phenomena, such as protein adsorption and cell adhesion. However, a cumbersome process is needed for their synthesis. Here, we report a simple and versatile method for fabricating nonbiofouling coatings that uses well-defined bottlebrushes instead of CPBs. First, a macroinitiator, poly[2-(2-bromoisobutyryloxy)ethyl methacrylate] (PBIEM), was synthesized by reversible addition-fragmentation chain transfer polymerization. Then, poly[poly(ethylene glycol) methyl ether methacrylate] was grafted from PBIEM through atom transfer radical polymerization to form well-defined bottlebrushes. By controlling the graft chain length, two types of bottlebrushes could be prepared, namely those with a semi-dilute polymer brush (SDPB) structure or a CPB structure on the surface of the outermost layer. Crosslinked films of the bottlebrushes were prepared on silicon wafers by spin-coating and subsequent radical coupling. Importantly, the CPB-type bottlebrush films showed significantly better nonbiofouling characteristics than those of the SDPB-type bottlebrush films.

Surface science of cosmetic substrates, cleansing actives and formulations

The development of shampoo and cleansing formulations in cosmetics is at a crossroads due to consumer demands for better performing, more natural products and also the strong commitment of cosmetic companies to improve the sustainability of cosmetic products. In order to go beyond traditional formulations, it is of great importance to clearly establish the science behind cleansing technologies and appreciate the specificity of cleansing biological surfaces such as hair and skin. In this review, we present recent advances in our knowledge of the physicochemical properties of the hair surface from both an experimental and a theoretical point of view. We discuss the opportunities and challenges that newer, sustainable formulations bring compared to petroleum-based ingredients. The inevitable evolution towards more bio-based, eco-friendly ingredients and sustainable formulations requires a complete rethink of many well-known physicochemical principles. The pivotal role of digital sciences and modelling in the understanding and conception of new ingredients and formulations is discussed. We describe recent numerical approaches that take into account the specificities of the hair surface in terms of structuration, different methods that study the adsorption of formulation ingredients and finally the success of new data-driven approaches. We conclude with practical examples on current formulation efforts incorporating bio-surfactants, controlling foaming and searching for new rheological properties.

Mucin Biopolymers and Their Barrier Function at Airway Surfaces

In the lung, the airway epithelium produces secreted and tethered mucin biopolymers to form a mucus hydrogel layer and a surface-attached polymer brush layer. These layers work in concert to facilitate the cilia-mediated transport of mucus for the capture and clearance of inhaled materials to prevent lung damage. The mechanisms by which mucin biopolymers protect the lung from injury have been an intense area of study in airway biology for the past several decades. In this feature article, we will discuss how airway mucins achieve these protective barrier functions. We will present the key findings, rooted in polymer and surface science, that have aided in understanding mucin barrier function. In addition, we will describe how this work may influence the design of nanoparticles to overcome the mucus barrier to effective drug delivery.

Hierarchical Surface Architecture of Hemodialysis Membranes for Eliminating Homocysteine Based on the Multifunctional Role of Pyridoxal 5'-phosphate

Patients with end-stage renal disease are prone to developing a complication of hyperhomocysteinemia, manifesting as an elevation of the homocysteine (Hcy) concentration in human plasma. However, Hcy as a protein-bound toxin is barely removed by conventional hemodialysis membranes. Here, we report a novel hemodialysis membrane by preparing a bioactive coating of pyridoxal 5'-phosphate (PLP) and adding biocompatible hyperbranched polyglycerol (HPG) brushes to achieve Hcy removal. The dip-applied PLP coating, a coenzyme with a role in Hcy metabolism, dramatically promoted a decrease in the Hcy concentration in human plasma. Moreover, the aldehyde group of PLP had an intrinsic chemical reactivity toward the terminal amino group to immobilize the HPG brushes on the hemodialysis membrane surface. The hierarchical PLP-HPG layer-functionalized membranes had a high efficacy for eliminating Hcy, with a concentration from the initial stage of 150 μmol/L reduced to a nearly normal level of 20 μmol/L in simulated dialysis. By analyzing the impact of HPG brushes with various chain lengths, we found that HPG brushes with a medium length enabled the PLP coating with the bioactive function of Hcy conversion to additionally protect Hcy-attacked target cells by providing excellent hydrophilicity and a dense enough chain volume overlap of the hyperbranched architecture. Simultaneously, the densely packed HPG brushes generated a maximal steric and hydration barrier that significantly improved biofouling resistance against blood proteins. The optimally functionalized membranes showed a clearance of 83.1% urea and 49.6% lysozyme and a rejection of 96.0% bovine serum albumin. The diversely functionalized PLP-HPG layers demonstrate a potential route for a more integrated hemodialysis membrane that can cope with the urgent issue of hyperhomocysteinemia in clinical hemodialysis therapy.

Interfacial Energy Measurement on the Reconstructive Polymer Surface: Dynamic Polymer Brush by Segregation of Amphiphilic Block Copolymers

Herein, the interfacial energy of a reconstructive polymer surface formed by segregation is analyzed by measuring the change in the size of elastomer thin films floating on water. When a system in which amphiphilic diblock copolymers are mixed with the hydrophobic elastomer is in contact with water, surface reconstruction is triggered by the segregation of copolymers with a gain in the hydration energy of the hydrophilic blocks. The hydrophilic brush layer spontaneously formed at the elastomer-water interface is named the dynamic polymer brush. Although it is anticipated that the interfacial energy will significantly decrease in the dynamic polymer brush system, a direct measurement of the interfacial energy of the reconstructive interface is a challenge. We propose a novel method to measure the interfacial energy of a reconstructive polymer surface by measuring the deformation of elastomer thin films floating on water and apply it to the dynamic polymer brush system. The interfacial energy of the dynamic polymer brush formed by the segregation of amphiphilic diblock copolymers with longer hydrophilic chains drastically decreased to zero due to the high hydration energy of hydrophilic chains. Based on the neutron reflectometry results, the graft density and thickness of the dynamic polymer brush system floating on water were found to be lower than those of the system fixed onto solid substrates. This indicates that the floating system can respond to an external environment with a high degree of freedom (graft density, brush thickness, and interface area).

Recent Developments in the Design of Non-Biofouling Coatings for Nanoparticles and Surfaces

Biofouling is a major issue in the field of nanomedicine and consists of the spontaneous and unwanted adsorption of biomolecules on engineered surfaces. In a biological context and referring to nanoparticles (NPs) acting as nanomedicines, the adsorption of biomolecules found in blood (mostly proteins) is known as protein corona. On the one hand, the protein corona, as it covers the NPs' surface, can be considered the biological identity of engineered NPs, because the corona is what cells will "see" instead of the underlying NPs. As such, the protein corona will influence the fate, integrity, and performance of NPs in vivo. On the other hand, the physicochemical properties of the engineered NPs, such as their size, shape, charge, or hydrophobicity, will influence the identity of the proteins attracted to their surface. In this context, the design of coatings for NPs and surfaces that avoid biofouling is an active field of research. The gold standard in the field is the use of polyethylene glycol (PEG) molecules, although zwitterions have also proved to be efficient in preventing protein adhesion and fluorinated molecules are emerging as coatings with interesting properties. Hence, in this review, we will focus on recent examples of anti-biofouling coatings in three main areas, that is, PEGylated, zwitterionic, and fluorinated coatings.