Biomembrane surfaces as models for polymer design: the potential for haemocompatibility

Surface modification of neurovascular stents: from bench to patient

Flow-diverting stents (FDs) for the treatment of cerebrovascular aneurysms are revolutionary. However, these devices require systemic dual antiplatelet therapy (DAPT) to reduce thromboembolic complications. Given the risk of ischemic complications as well as morbidity and contraindications associated with DAPT, demonstrating safety and efficacy for FDs either without DAPT or reducing the duration of DAPT is a priority. The former may be achieved by surface modifications that decrease device thrombogenicity, and the latter by using coatings that expedite endothelial growth. Biomimetics, commonly achieved by grafting hydrophilic and non-interacting polymers to surfaces, can mask the device surface with nature-derived coatings from circulating factors that normally activate coagulation and inflammation. One strategy is to mimic the surfaces of innocuous circulatory system components. Phosphorylcholine and glycan coatings are naturally inspired and present on the surface of all eukaryotic cell membranes. Another strategy involves linking synthetic biocompatible polymer brushes to the surface of a device that disrupts normal interaction with circulating proteins and cells. Finally, drug immobilization can also impart antithrombotic effects that counteract normal foreign body reactions in the circulatory system without systemic effects. Heparin coatings have been explored since the 1960s and used on a variety of blood contacting surfaces. This concept is now being explored for neurovascular devices. Coatings that improve endothelialization are not as clinically mature as anti-thrombogenic coatings. Coronary stents have used an anti-CD34 antibody coating to capture circulating endothelial progenitor cells on the surface, potentially accelerating endothelial integration. Similarly, coatings with CD31 analogs are being explored for neurovascular implants.

In vitro biocompatibility analysis of protein-resistant amphiphilic polysulfobetaines as coatings for surgical implants in contact with complex body fluids

The fouling resistance of zwitterionic coatings is conventionally explained by the strong hydrophilicity of such polymers. Here, the in vitro biocompatibility of a set of systematically varied amphiphilic, zwitterionic copolymers is investigated. Photocrosslinkable, amphiphilic copolymers containing hydrophilic sulfobetaine methacrylate (SPe) and butyl methacrylate (BMA) were systematically synthesized in different ratios (50:50, 70:30, and 90:10) with a fixed content of photo-crosslinker by free radical copolymerization. The copolymers were spin-coated onto substrates and subsequently photocured by UV irradiation. Pure pBMA and pSPe as well as the prepared amphiphilic copolymers showed BMA content-dependent wettability in the dry state, but overall hydrophilic properties a fortiori in aqueous conditions. All polysulfobetaine-containing copolymers showed high resistance against non-specific adsorption (NSA) of proteins, platelet adhesion, thrombocyte activation, and bacterial accumulation. In some cases, the amphiphilic coatings even outperformed the purely hydrophilic pSPe coatings.

Device updates in pediatric and neonatal ECMO

Since the early use of extracorporeal life support (ECLS), new innovations and technological advancements have augmented the ability to use this technology in children and neonates. Cannulae have been re-designed to maintain structure and allow for single cannula venovenous (VV) ECLS in smaller patients. Circuit technology, including pumps and tubing, has evolved to permit smaller priming volumes and lower flow rates with fewer thrombotic or hemolytic complications. New oxygenator developments also improve efficiency of gas exchange. This paper serves as an overview of recent device developments in ECLS delivery to pediatric and neonatal patients.

Red blood cell membrane-functionalized Nanofibrous tubes for small-diameter vascular grafts

The off-the-shelf small-diameter vascular grafts (SDVGs) have inferior clinical efficacy. Red blood cell membrane (Rm) has easy availability and multiple bioactive components (such as phospholipids, proteins, and glycoproteins), which can improve the clinic's availability and patency of SDVGs. Here we developed a facile approach to preparing an Rm-functionalized poly-ε-caprolactone/poly-d-lysine (Rm@PCL/PDL) tube by co-incubation and single-step rolling. The integrity, stability, and bioactivity of Rm on Rm@PCL/PDL were evaluated. The revascularization of Rm@PCL/PDL tubes was studied by implantation in the carotid artery of rabbits. Rm@PCL/PDL can be quickly prepared and showed excellent bioactivity with good hemocompatibility and great anti-inflammatory. Rm@PCL/PDL tubes as the substitute for the carotid artery of rabbits had good patency and quick remodeling within 21 days. Rm, as a "self" biomaterial with high biosafety, provides a new and facile approach to developing personalized or universal SDVGs for the clinic, which is of great significance in cardiovascular regenerative medicine and organ chip.

Therapeutic contact lenses for the treatment of corneal and ocular surface diseases: advances in extended and targeted drug delivery

The eye is one of the most important organs in the human body providing critical information on the environment. Many corneal diseases can lead to vision loss affecting the lives of people around the world. Ophthalmic drug delivery has always been a major challenge in the medical sciences. Since traditional methods are less efficient (∼ 5%) at delivering drugs to ocular tissues, contact lenses have generated growing interest in ocular drug delivery due to their potential to enhance drug bioavailability in ocular tissues. The main techniques used to achieve sustained release are discussed in this review, including soaking in drug solutions, incorporating drug into multilayered contact lenses, use of vitamin E barriers, molecular imprinting, nanoparticles, micelles and liposomes. The most clinically relevant results on different eye pathologies are presented. In addition, this review summarizes the benefits of contact lenses over eye drops, strategies for incorporating drugs into lenses to achieve sustained release, results of in vitro and in vivo studies, and the recent advances in the commercialization of therapeutic contact lenses for allergic conjunctivitis.

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.

Cell-membrane-inspired polymers for constructing biointerfaces with efficient molecular recognition

Fabrication of devices that accurately recognize, detect, and separate target molecules from mixtures is a crucial aspect of biotechnology for applications in medical, pharmaceutical, and food sciences. This technology has also been recently applied in solving environmental and energy-related problems. In molecular recognition, biomolecules are typically complexed with a substrate, and specific molecules from a mixture are recognized, captured, and reacted. To increase sensitivity and efficiency, the activity of the biomolecules used for capture should be maintained, and non-specific reactions on the surface should be prevented. This review summarizes polymeric materials that are used for constructing biointerfaces. Precise molecular recognition occurring at the surface of cell membranes is fundamental to sustaining life; therefore, materials that mimic the structure and properties of this particular surface are emphasized in this article. The requirements for biointerfaces to eliminate nonspecific interactions of biomolecules are described. In particular, the major issue of protein adsorption on biointerfaces is discussed by focusing on the structure of water near the interface from a thermodynamic viewpoint; moreover, the structure of polymer molecules that control the water structure is considered. Methodologies enabling stable formation of these interfaces on material surfaces are also presented.

Squid inspired elastomer marine coating with efficient antifouling strategies: Hydrophilized defensive surface and lower modulus

In antifouling applications for the marine industry, low surface energy coatings entail turbulent water flow to release marine biofouling, which presents a substantial challenge for antifouling in the static situation. The traditional solution is to add environmentally friendly antifouling agents, but it has the problem of exhaustion. Therefore, the low surface energy elastic antifouling coating without antifoulants has high research value. Herein, inspired by soft body and epidermal mucus of squid, the stable polyvinylpyrrolidone (PVP) hydrophilic segments were introduced to modify the polydimethylsiloxane-based polyurethane (PDMS-PU), realizing low surface energy elastomer coatings with hydrophilized defensive surface and reduced elastic modulus (<1.1 MPa). In an aqueous environment, the tailored surface exposed sufficient stable hydrophilic segments, exerting excellent antifouling performance, which improved the anti-adsorption effect on biological proteins, bacteria (antibacterial rate 95.24%) and algae (cover rate <3%). The coating exhibited excellent marine antifouling performance within 150 days and also gave a new impetus to developing an eco-friendly and sustainable solution for no-antifoulant marine antifouling applications.

2D Black Phosphorus-Based Cytomembrane Mimics with Stimuli-Responsive Antibacterial Action Inspired by Endotoxin-Associated Toxic Behavior

Biomimetic membrane materials have been widely explored and developed for drug loading and tissue engineering applications due to their excellent biocompatibility and abundant reaction sites. However, novel cytomembrane mimics have been lacking for a long time. In this study, black phosphorus (BP) was used as the foundation for a new generation of promising cytomembrane mimics due to its multiple similarities to cytomembranes. Inspired by the dual function of endotoxins on membranes, we prepared a BP-based cytomembrane mimic with controllable antibacterial ability via electrostatic interaction between BP and [1-pentyl-1-quaternary ammonium-3-vinyl-imidazole]Br ([PQVI]Br). The release of PQVI could be manipulated in different conditions by adjusting the electrostatic force, thereby achieving controllable antibacterial ability. This report confirms the possibility of using BP as a new material to mimic cytomembranes and provides a new concept of controllable antibacterial action based on endotoxins.

Poly(tertiary amide acrylate) Copolymers Inspired by Poly(2-oxazoline)s: Their Blood Compatibility and Hydration States

Modifying the side chain of poly(meth)acrylate with moieties originating from biocompatible polymers can be an effective method for developing novel blood-compatible polymers. Inspired by biocompatible poly(2-methyl-2-oxazoline) (PMeOx) and poly(2-ethyl-2-oxazoline) (PEtOx), four water-soluble poly(tertiary amide acylate) analogues bearing a pendant tertiary amide were synthesized. The results of hemolysis and cell viability tests showed that all the poly(tertiary amide acylate) analogues were compatible with red blood cells, HeLa cells, and normal human dermal fibroblasts as PMeOx or PEtOx. Among the four poly(tertiary amide acylate) analogues, poly[2-(N-methylpropionamido)ethyl acrylate] (PPEA) and poly[2-(N-ethylacetamido)ethyl acrylate] (PEAE) showed thermosensitivity in aqueous solution; especially, PPEA (10 mg mL^-1) exhibited a lower critical solution temperature of 37 °C. Water-insoluble copolymers were prepared to investigate the possibility of applying these synthesized polymers as blood-compatible coatings. The poly[n-butyl methacrylate₇₀-co-2-(N-methylacetamido)ethyl methacrylate₃₀] (coPAEM) coatings significantly suppressed plasma protein adsorption, denaturation degree of adsorbed fibrinogen, and platelet adhesion. Intermediate water (IW), whose content can generally indicate the blood compatibility of polymers, was found in all hydrated homopolymers and copolymers by differential scanning calorimetry. The present work demonstrated that the tertiary amide moiety in the side chain of poly(meth)acrylate was an effective contributor to blood compatibility and IW.

Sulfobetaine Methacrylate Polymers of Unconventional Polyzwitterion Architecture and Their Antifouling Properties

Combining high hydrophilicity with charge neutrality, polyzwitterions are intensely explored for their high biocompatibility and low-fouling properties. Recent reports indicated that in addition to charge neutrality, the zwitterion's segmental dipole orientation is an important factor for interacting with the environment. Accordingly, a series of polysulfobetaines with a novel architecture was designed, in which the cationic and anionic groups of the zwitterionic moiety are placed at equal distances from the backbone. They were investigated by in vitro biofouling assays, covering proteins of different charges and model marine organisms. All polyzwitterion coatings reduced the fouling effectively compared to model polymer surfaces of poly(butyl methacrylate), with a nearly equally good performance as the reference polybetaine poly(3-(N-(2-(methacryloyloxy)ethyl)-N,N-dimethylammonio)propanesulfonate). The specific fouling resistance depended on the detailed chemical structure of the polyzwitterions. Still, while clearly affecting the performance, the precise dipole orientation of the sulfobetaine group in the polyzwitterions seems overall to be only of secondary importance for their antifouling behavior.

In vitro investigation of an intracranial flow diverter with a fibrin-based, hemostasis mimicking, nanocoating

Flow diversion aims at treatment of intracranial aneurysms via vessel remodeling mechanisms, avoiding the implantation of foreign materials into the aneurysm sack. However, complex implantation procedure, high metal surface and hemodynamic disturbance still pose a risk for thromboembolic complications in the clinical praxis. A novel fibrin and heparin based nano coating considered as a hemocompatible scaffold for neointimal formation was investigated regarding thrombogenicity and endothelialization. The fibrin-heparin coating was compared to a bare metal as well as fibrin- or heparin-coated flow diverters. The implants were tested separately in regard to inflammation and coagulation markers in two different in vitro hemocompatibility models conducted with human whole blood (n = 5). Endothelialization was investigated through a novel dynamic in vitro cell seeding model containing primary human cells with subsequent viability assay. It was demonstrated that platelet loss and platelet activation triggered by presence of a bare metal stent could be significantly reduced by applying the fibrin-heparin, fibrin and heparin coating. Viability of endothelial cells after proliferation was similar in fibrin-heparin compared to bare metal implants, with a slight, non-significant improvement observed in the fibrin-heparin group. The results suggest that the presented nanocoating has the potential to reduce thromboembolic complications in a clinical setting. Though the new model allowed for endothelial cell proliferation under flow conditions, a higher number of samples is required to assess a possible effect of the coating.

Antifibrotic strategies for medical devices

A broad range of medical devices initiate an immune reaction known as the foreign body response (FBR) upon implantation. Here, collagen deposition at the surface of the implant occurs as a result of the FBR, ultimately leading to fibrous encapsulation and, in many cases, reduced function or failure of the device. Despite significant efforts, the prevention of fibrotic encapsulation has not been realized at this point in time. However, many next-generation medical technologies including cellular therapies, sensors and devices depend on the ability to modulate and control the FBR. For these technologies to become viable, significant advances must be made in understanding the underlying mechanism of this response as well as in the methods modulating this response. In this review, we highlight recent advances in the development of materials and coatings providing a reduced FBR and emphasize key characteristics of high-performing approaches. We also provide a detailed overview of the state-of-the-art in strategies relying on controlled drug release, the surface display of bioactive signals, materials-based approaches, and combinations of these approaches. Finally, we offer perspectives on future directions in this field.

Amphiphilic Dicyclopentenyl/Carboxybetaine-Containing Copolymers for Marine Fouling-Release Applications

Zwitterionic materials received great attention in recent studies due to their high antifouling potential, though their application in practical coatings is still challenging. Amphiphilic polymers have been proven to be an effective method to combat fouling in the marine environment. This study reports the incorporation of small amounts of zwitterionic carboxybetaine methacrylate (CBMA) into hydrophobic ethylene glycol dicyclopentenyl ether acrylate (DCPEA). A new set of copolymers with varying amphiphilicities was synthesized and coated on chemically modified glass substrates. The antifouling capabilities were assessed against the diatom Navicula perminuta and multiple species in the field. Unsurprisingly, high diatom densities were observed on the hydrophobic control coatings. The integration of small zwitterionic contents of only ∼5 wt % was already sufficient to rapidly form a hydrophilic interface that led to a strong reduction of fouling. Ultralow fouling was also observed for the pure zwitterionic coatings in laboratory experiments, but it failed when tested in the real ocean environment. We noticed that the ability to absorb large amounts of water and the diffuse nature of the interphase correlate with the adsorption of silt, which can mask the hydrophilic chemistries and facilitate the settlement of organisms. The amphiphilic coatings showed low fouling in dynamic short-term field exposures, which could be explained by the reduced tendency of the coatings for sediment adsorption.

Thermoresponsive polymers and their biomedical application in tissue engineering - a review

Thermoresponsive polymers hold great potential in the biomedical field, since they enable the fabrication of cell sheets, in situ drug delivery and 3D-printing under physiological conditions. In this review we provide an overview of several thermoresponsive polymers and their application, with focus on poly(N-isopropylacrylamide)-surfaces for cell sheet engineering. Basic knowledge of important processes like protein adsorption on surfaces and cell adhesion is provided. For different thermoresponsive polymers, namely PNIPAm, Pluronics, elastin-like polypeptides (ELP) and poly(N-vinylcaprolactam) (PNVCL), synthesis and basic chemical and physical properties have been described and the mechanism of their thermoresponsive behavior highlighted. Fabrication methods of thermoresponsive surfaces have been discussed, focusing on PNIPAm, and describing several methods in detail. The latter part of this review is dedicated to the application of the thermoresponsive polymers and with regard to cell sheet engineering, the process of temperature-dependent cell sheet detachment is explained. We provide insight into several applications of PNIPAm surfaces in cell sheet engineering. For Pluronics, ELP and PNVCL we show their application in the field of drug delivery and tissue engineering. We conclude, that research of thermoresponsive polymers has made big progress in recent years, especially for PNIPAm since the 1990s. However, manifold research possibilities, e.g. in surface fabrication and 3D-printing and further translational applications are conceivable in near future.

Photopolymerized microdomains in both lipid leaflets establish diffusive transport pathways across biomimetic membranes

Controlled transport within a network of aqueous subcompartments provides a foundation for the construction of biologically-inspired materials. These materials are commonly assembled using the droplet interface bilayer (DIB) technique, adhering droplets together into a network of lipid membranes. DIB structures may be functionalized to generate conductive pathways by enhancing the permeability of pre-selected membranes, a strategy inspired by nature. Traditionally these pathways are generated by dissolving pore-forming toxins (PFTs) in the aqueous phase. A downside of this approach when working with larger DIB networks is that transport is enabled in all membranes bordering the droplets containing the PFT, instead of occurring exclusively between selected droplets. To rectify this limitation, photopolymerizable phospholipids (23:2 DiynePC) are incorporated within the aqueous phase of the DIB platform, forming conductive pathways in the lipid membranes post-exposure to UV-C light. Notably these pathways are only formed in the membrane if both adhered droplets contain the photo-responsive lipids. Patterned DIB networks can then be generated by controlling the lipid composition within select droplets which creates conductive routes one droplet thick. We propose that the incorporation of photo-polymerizable phospholipids within the aqueous phase of DIB networks will improve the resolution of the patterned conductive pathways and reduce diffusive loss within the synthetic biological network.

Preparation, Physicochemical Properties, and Hemocompatibility of the Composites Based on Biodegradable Poly(Ether-Ester-Urethane) and Phosphorylcholine-Containing Copolymer

To improve the hemocompatibility of the biodegradable medical poly(ether-ester-urethane) (PEEU), containing uniform-size aliphatic hard segments that was prepared in our lab, a copolymer containing phosphorylcholine (PC) groups was blended with the PEEU. The PC-copolymer of poly(MPC-co-EHMA) (PMEH) was first obtained by copolymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-ethylhexyl methacrylate (EHMA), and then dissolved in mixed solvent of ethanol/chloroform to obtain a homogeneous solution. The composite films (PMPU) with varying PMEH content were prepared by solvent evaporation method. The physicochemical properties of the composite films with varying PMEH content were researched. The PMPU films exhibited higher thermal stability than that of the pure PEEU film. With the PMEH content increasing from 5 to 20 wt%, the PMPU films also possessed satisfied tensile properties with ultimate stress of 22.9-15.8 MPa and strain at break of 925-820%. The surface and bulk hydrophilicity of the films were improved after incorporation of PMEH. In vitro degradation studies indicated that the degradation rate increased with PMEH content, and it took 12-24 days for composite films to become fragments. The protein adsorption and platelet-rich plasma contact tests were adapted to evaluate the surface hemocompatibility of the composite films. It was found that the amount of adsorbed protein and adherent platelet on the surface decreased significantly, and almost no activated platelets were observed when PMEH content was above 5 wt%, which manifested good surface hemocompatibility. Due to the biodegradability, acceptable tensile properties and good surface hemocompatibility, the composites can be expected to be applied in blood-contacting implant materials.

Self-Association Behavior of Cell Membrane-Inspired Amphiphilic Random Copolymers in Water

Water-soluble and amphiphilic random copolymers (P(MPC/DMA_x)) composed of hydrophilic 2-methacryloyloxyethyl phosphorylcholine (MPC) and hydrophobic n-dodecyl methacrylate (DMA) were prepared via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. The compositions of DMA unit (x) in the copolymer were in the range of 0 to 38 unit mol %. The degree of polymerization of P(MPC/DMA_x) was adjusted to about 200. Since the monomer reactivity ratios of MPC and DMA are 1.01 and 1.00, respectively, ideal free radical copolymerization occurred. In aqueous solutions, interpolymer aggregation occurred due to the hydrophobic pendant n-dodecyl groups. The aggregation number (N_agg) increased with an increasing x. The mobilities of the DMA and MPC pendant groups in aqueous solutions were restricted, as confirmed by ¹H NMR relaxation time measurements, because a part of the MPC units were trapped in the hydrophobic microdomain formed from the pendant n-dodecyl groups. The polarity of the hydrophobic microdomain formed from P(MPC/DMA₃₈) in water was similar to that of ethyl acetate according to fluorescence probe experiments. No specific interactions were found in water between P(MPC/DMA_x) and bovine serum albumin because the surface of the interpolymer aggregates contained only hydrophilic MPC units.

Codeposition of Polydopamine and Zwitterionic Polymer on Membrane Surface with Enhanced Stability and Antibiofouling Property

Although abundant works have been developed in mussel-inspired antifouling coatings, most of them suffer from poor chemical stability, especially in a strongly alkaline environment. Herein, we report a robust one-step mussel-inspired method to construct a highly chemical stable and excellent antibiofouling membrane surface coating with a highly efficient codeposition of polydopamine (PDA) with zwitterionic polymer. In the study, PDA and polyethylenimine-quaternized derivative (PEI-S) are codeposited on the surface of poly(ether sulfone) (PES) ultrafiltration membrane in water at room temperature. In contrast to individual PDA coating, the obtained PDA/PEI-S coating exhibits excellent chemical stability even in a strongly alkaline environment owing to the cross-linking and unexpected cation-π interaction between the PEI-S and PDA. Thanks to the introduction of PEI-S, systematic protein adsorption tests and bacteria adhesion experiments demonstrated that the surfaces could prevent bovine serum fibrinogen and lysozyme adsorption and could reduce Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli adhesion. Benefiting from the versatile functionality of PDA, the proposed strategy is not limited to PES membrane surface but also others such as poly(ethylene terephthalate) sheets and commercial polypropylene microfiltration membranes. Overall, this work enriches the exploration of a remarkable coating with enhanced stability and excellent antifouling property via a facile, robust, and material-independent approach to modifying the membrane surface.

Blood-Compatible Surfaces with Phosphorylcholine-Based Polymers for Cardiovascular Medical Devices

For the acquisition of blood-compatible materials, various hydrophilic polymers for surface modification have been examined. Among them, polymers with a representative phospholipid polar group, the phosphorylcholine (PC) group, are a successful example. These polymers were designed from inspiration of the cell membrane surface and provide protein adsorption resistance even following contact with plasma. This important property is based on the unique hydration state of water molecules surrounding hydrated polymer; in other words, water molecules weakly interact with the polymers and maintain their favorable cluster structure through hydrogen bonding. These polymers are not only hydrophilic, but also electrically neutral, important characteristics which make hydrogen bonding with water molecules less likely to occur and avoid hydrophobic interactions. Phosphorylcholine groups and other zwitterionic structures are significant as hydrophilic functional groups meeting these important requirements. In this review, blood compatibility of a polymer having a PC group is introduced in relation to its hydration structure, followed by a description of the applications of this polymer to cardiovascular medical devices.

Romantic Surfaces: A Systematic Overview of Stable, Biospecific, and Antifouling Zwitterionic Surfaces

This Feature Article focuses on recent advances in the bioconjugation of surface-bound zwitterionic polymers for biospecific antifouling surfaces. Various approaches for the functionalization of antifouling zwitterionic polymers are systematically investigated, such as chain-end and side-chain functionalization. Side-chain functionalization methods can be further classified as those that are achieved through homopolymerization of custom-synthesized zwitterionic monomers equipped with reactive groups, or those that are achieved via synthesis of random or block copolymers combining different monomers with antifouling functionality and others with reactive groups. Several of the pros and cons of these approaches are outlined and discussed. Finally, some perspective and future directions of research are presented toward long-term stable, generically repelling surfaces that strongly and specifically adhere to a single component in a complex mixture.

Nanotechnology in cell replacement therapies for type 1 diabetes

Islet transplantation is a promising long-term, compliance-free, complication-preventing treatment for type 1 diabetes. However, islet transplantation is currently limited to a narrow set of patients due to the shortage of donor islets and side effects from immunosuppression. Encapsulating cells in an immunoisolating membrane can allow for their transplantation without the need for immunosuppression. Alternatively, "open" systems may improve islet health and function by allowing vascular ingrowth at clinically attractive sites. Many processes that enable graft success in both approaches occur at the nanoscale level-in this review we thus consider nanotechnology in cell replacement therapies for type 1 diabetes. A variety of biomaterial-based strategies at the nanometer range have emerged to promote immune-isolation or modulation, proangiogenic, or insulinotropic effects. Additionally, coating islets with nano-thin polymer films has burgeoned as an islet protection modality. Materials approaches that utilize nanoscale features manipulate biology at the molecular scale, offering unique solutions to the enduring challenges of islet transplantation.

Novel Surfaces in Extracorporeal Membrane Oxygenation Circuits

The balance between systemic anticoagulation and clotting is challenging. In normal hemostasis, the endothelium regulates the balance between anticoagulant and prothrombotic systems. It becomes particularly more challenging to maintain this physiologic hemostasis when we are faced with extracorporeal life support therapies, where blood is continuously in contact with a foreign extracorporeal circuit surface predisposing a prothrombotic state. The blood-surface interaction during extracorporeal life support therapies requires the use of systemic anticoagulation to decrease the risk of clotting. Unfractionated heparin is the most common anticoagulant agent widely used in this setting. New trends include the use of direct thrombin inhibitor agents for systemic anticoagulation; and surface modifications that aim to overcome the blood-biomaterial surface interaction by modifying the hydrophilicity or hydrophobicity of the polymer surface; and coating the circuit with substances that will mimic the endothelium or anti-thrombotic agents. To improve hemocompatibility in an extracorporeal circuit, replication of the anti-thrombotic and anti-inflammatory properties of the endothelium is ideal. Surface modifications can be classified into three major groups: biomimetic surfaces (heparin, nitric oxide, and direct thrombin inhibitors); biopassive surfaces [phosphorylcholine, albumin, and poly- 2-methoxyethylacrylate]; and endothelialization of blood contacting surface. The focus of this paper will be to review both present and future novel surface modifications that can obviate the need for systemic anticoagulation during extracorporeal life support therapies.

Facile modification of electrospun fibrous structures with antifouling zwitterionic hydrogels

Electrospinning technology can easily produce different shaped fibrous structures, making them highly valuable to various biomedical applications. However, surface contamination of biomolecules, cells, or blood has emerged as a significant challenge to the success of electrospun devices, especially artificial blood vessels, catheters and wound dressings etc. Many efforts have been made to resist the surface non-specific biomolecules or cells adsorption, but most of them require complex pre-treatment processes, hard-to-remove metal catalysts or rigorous reaction conditions. In addition, the stability of antifouling coatings, especially in complex conditions, is still a major concern. In this work, inspired by the interpenetrating polymer network and reinforced concrete structure, an efficient and facile strategy for modifying hydrophobic electrospun meshes and tubes with antifouling zwitterionic hydrogels has been introduced. The resulting products could efficiently resist the adhesion of proteins, cells, or even fresh whole blood. Meanwhile, they could maintain the shapes and mechanical strength of the original electrospun structures. Furthermore, the hydrogel structures could retain stable in a physiological condition for at least 3 months. This paper provided a general antifouling and hydrophilicity surface modification strategy for various fibrous structures, and could be of great value for many biomedical applications where antifouling properties are critical.

Hemocompatibility of hyaluronan enhanced linear low density polyethylene for blood contacting applications

Despite their overall success, different blood-contacting medical devices such as heart valves, stents, and so forth, are still plagued with hemocompatibility issues which often result in the need for subsequent replacement and/or life-long anticoagulation therapy. Consequently, there is a significant interest in developing biomaterials that can address these issues. Polymeric-based materials have been proposed for use in many applications due to their ability to be finely tuned through manufacturing and surface modification to enhance hemocompatibility. In this study, we have developed a novel, hydrophilic biomaterial comprised of an interpenetrating polymer network (IPN) of hyaluronan (HA) and linear low density polyethylene (LLDPE). HA is a highly lubricous, anionic polysaccharide ubiquitously found in the human body. It is currently being investigated for a vast array of biomedical applications including cardiovascular therapies such as hydrogel-based regenerative cell therapies for myocardial infarction, HA-coated stents, and surface modifications of polyurethane and metals for use in blood-contacting implants. The aim of this study was to assess the in vitro thrombogenic response of the hydrophilic polymer surface, HA-LLDPE for future potential use as flexible heart valve leaflets. The results indicate that HA-LLDPE is non-toxic and reduces thromobogenicity as compared to LLDPE surfaces, asserting its feasibility for use as a blood-contacting biomaterial. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1964-1975, 2018.

A review of the recent advances in antimicrobial coatings for urinary catheters

More than 75% of hospital-acquired or nosocomial urinary tract infections are initiated by urinary catheters, which are used during the treatment of 15-25% of hospitalized patients. Among other purposes, urinary catheters are primarily used for draining urine after surgeries and for urinary incontinence. During catheter-associated urinary tract infections, bacteria travel up to the bladder and cause infection. A major cause of catheter-associated urinary tract infection is attributed to the use of non-ideal materials in the fabrication of urinary catheters. Such materials allow for the colonization of microorganisms, leading to bacteriuria and infection, depending on the severity of symptoms. The ideal urinary catheter is made out of materials that are biocompatible, antimicrobial, and antifouling. Although an abundance of research has been conducted over the last forty-five years on the subject, the ideal biomaterial, especially for long-term catheterization of more than a month, has yet to be developed. The aim of this review is to highlight the recent advances (over the past 10years) in developing antimicrobial materials for urinary catheters and to outline future requirements and prospects that guide catheter materials selection and design.

STATEMENT OF SIGNIFICANCE

This review article intends to provide an expansive insight into the various antimicrobial agents currently being researched for urinary catheter coatings. According to CDC, approximately 75% of urinary tract infections are caused by urinary catheters and 15-25% of hospitalized patients undergo catheterization. In addition to these alarming statistics, the increasing cost and health related complications associated with catheter associated UTIs make the research for antimicrobial urinary catheter coatings even more pertinent. This review provides a comprehensive summary of the history, the latest progress in development of the coatings and a brief conjecture on what the future entails for each of the antimicrobial agents discussed.

Nonspecific Binding Domains in Lipid Membranes Induced by Phospholipase A2

Phospholipase A2 (PLA2) is a peripheral membrane protein that can hydrolyze phospholipids to produce lysolipids and fatty acids. It has been found to play crucial roles in various cellular processes and is thought as a potential candidate for triggering drug release from liposomes for medical treatment. Here, we directly observed that PLA2 hydrolysis reaction can induce the formation of PLA2-binding domains at lipid bilayer interface and found that the formation was significantly influenced by the fluidity of the lipid bilayer. We prepared supported lipid bilayers (SLBs) with various molar ratios of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) to adjust the reactivity and fluidity of the lipid bilayers. A significant amount of the PLA2-induced domains was observed in mixtures of DPPC and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) but not in either pure DPPC or pure DOPC bilayer, which might be the reason that previous studies rarely observed these domains in lipid bilayer systems. The fluorescently labeled PLA2 experiment showed that newly formed domains acted as binding templates for PLA2. The AFM result showed that the induced domain has stepwise plateau structure, suggesting that PLA2 hydrolysis products may align as bilayers and accumulate layer by layer on the support, and the hydrophobic acyl chains at the side of the layer structure may be exposed to the outside aqueous environment. The introduced hydrophobic region could have hydrophobic interactions with proteins and therefore can attract the binding of not only PLA2 but also other types of proteins such as proteoglycans and streptavidin. The results suggest that the formation of PLA2-induced domains may convert part of a zwitterionic nonsticky lipid membrane to a site where biomolecules can nonspecifically bind.

The Quest for Nonthrombotic Surface Modifications to Achieve Hemocompatibility of Implantable Devices

The use of blood-contacting implantable devices is limited by surface-induced thrombosis, which has led to the development of thromboresistant surfaces. Multidisciplinary efforts have promoted the development of surface modifications to minimize thrombosis by targeting surface-induced coagulation. To this date, no material has been identified that remains irrevocably hemocompatible with time but many options are now available with their own limitations. Essential to this review is the understanding of some of the challenges in this field and newer opportunities for hemocompatibility research. This report will also briefly review many of the achievements in the development of hemocompatible biomaterial coating, including surface modifications against protein adsorption and platelet adhesion, biomimetism, and endothelialization.

Catch bond interaction allows cells to attach to strongly hydrated interfaces

Hyaluronans are a class of glycosaminoglycans that are widespread in the mammalian body and serve a variety of functions. Their most striking characteristic is their pronounced hydrophilicity and their capability to inhibit unspecific adhesion when present at interfaces. Catch-bond interactions are used by the CD44 receptor to interact with this inert material and to roll on the surfaces coated with hyaluronans. In this minireview, the authors discuss the general properties of hyaluronans and the occurrence and relevance of the CD44 catch-bond interaction in the context of hematopoiesis, cancer development, and leukemia.

Heterogeneous surfaces to repel proteins

The nonspecific adsorption of proteins is usually undesirable on solid surfaces as it induces adverse responses, such as platelet adhesion on medical devices, negative signals of biosensors and contamination blockage of filtration membranes. Thus, an important scheme in material science is to design and fabricate protein-repulsive surfaces. Early approaches in this field focused on homogeneous surfaces comprised of single type functionality. Yet, recent researches have demonstrated that surfaces with heterogeneities (chemistry and topography) show promising performance against protein adsorption. In this review, we will summarize the recent achievements and discuss the new perspectives in the research of developing and characterizing heterogeneous surfaces to repel proteins. The protein repulsion mechanisms of different heterogeneous surfaces will also be discussed in details, followed by the perspective and challenge of this emerging field.

Non-covalent hydrophilization of reduced graphene oxide used as a paclitaxel vehicle

Phosphorylcholine oligomer grafted perylene (Perylene-PCn) was synthesized. By π–π stacking interaction of reduced graphene oxide (RGO) and perylene moiety, water dispersible RGO/Perylene-PCn composites were prepared and used as paclitaxel vehicle.

Surface modification strategies on mesoporous silica nanoparticles for anti-biofouling zwitterionic film grafting

In the past decade, zwitterionic-based anti-biofouling layers had gained much focus as a serious alternative to traditional polyhydrophilic films such as PEG. In the area of assembling silica nanoparticles with stealth properties, the incorporation of zwitterionic surface film remains fairly new but considering that silica nanoparticles had been widely demonstrated as useful biointerfacing nanodevice, zwitterionic film grafting on silica nanoparticle holds much potential in the future. This review will discuss on the conceivable functional chemistry approaches, some of which are potentially suitable for the assembly of such stealth systems.

Surface nanostructures for fluorescence probing of supported lipid bilayers on reflective substrates

The fluorescence interference contrast (FLIC) effect prevents the use of fluorescence techniques to probe the continuity and fluidity of supported lipid bilayers on reflective materials due to a lack of detectable fluorescence. Here we show that adding nanostructures onto reflective surfaces to locally confer a certain distance between the deposited fluorophores and the reflecting surface enables fluorescence detection on the nanostuctures. The nanostructures consist of either deposited nanoparticles or epitaxial nanowires directly grown on the substrate and are designed such that they can support a lipid bilayer. This simple method increases the fluorescence signal sufficiently to enable bilayer fluorescence detection and to observe the recovery of fluorescence after photobleaching in order to assess lipid bilayer formation on any reflective surface.

Structural Features of Micelles of Zwitterionic Dodecyl-phosphocholine (C₁₂PC) Surfactants Studied by Small-Angle Neutron Scattering

Small-angle neutron scattering (SANS) was used to investigate the size and shape of zwitterionic dodecyl phosphocholine (C12PC) micelles formed at various concentrations above its critical micelle concentration (CMC = 0.91 mM). The predominant spherical shape of micelles is revealed by SANS while the average micellar size was found to be broadly consistent with the hydrodynamic diameters determined by dynamic light scattering (DLS). Cryogenic tunneling electron microscopy (cryo-TEM) shows a uniform distribution of structures, proposing micelle monodispersity ( Supporting Information ). H/D substitution was utilized to selectively label the chain, head, or entire surfactant so that structural distributions within the micellar assembly could be investigated using fully protonated, head-deuterated, and tail-deuterated PC surfactants in D2O and fully deuterated surfactants in H2O. Using the analysis software we have developed, the four C12PC contrasts at a given concentration were simultaneously analyzed using various core-shell models consisting of a hydrophobic core and a shell representing hydrated polar headgroups. Results show that at 10 mM, C12PC micelles can be well represented by a spherical core-shell model with a core radius and shell thicknesses of 16.9 ± 0.5 and 10.2 ± 2.0 Å (total radius 27.1 ± 2.0 Å), respectively, with a surfactant aggregation number of 57 ± 5. As the concentration was increased, the SANS data revealed an increase in core-shell mixing, characterized by the emergence of an intermediate mixing region at the spherical core-shell interface. C12PC micelles at 100 mM were found to have a core radius and shell thicknesses of 19.6 ± 0.5 and 7.8 ± 2.0 Å, with an intermediate mixing region of 3.0 ± 0.5 Å. Further reduction in the shell thickness with concentration was also observed, coupled with an increased mixing of the core and shell regions and a reduction in miceller hydration, suggesting that concentration has a significant influence on surfactant packing and aggregation within micelles.

Effect of a Novel Stent on Re-Endothelialization, Platelet Adhesion, and Neointimal Formation

AIM

Vascular endothelial-cadherin (VE-cadherin) is specifically expressed by outgrowth endothelial cells (OECs). Zwitterionic stent showed high antifouling and excellent blood compatibility. Therefore, we hypothesized that anti-VE-cadherin antibody-coated zwitterionic stents (VE-cad-Z stents) would promote re-endothelialization, reduce neointimal formation, and resist thrombus.

METHODS

VE-cad-Z stents were examined using platelet adhesion test, platelet activation, and OEC capture ability in vitro. In vivo effect of VE-cad-Z stents on re-endothelialization, thrombus-resistance, and neointima hyperplasia was investigated in left common carotid arteries of rabbits (n=15).

RESULTS

In vitro, VE-cad-Z stents showed better platelet-resistance and OEC-capture ability (DNA concentration: 297.23±22.71 versus 67.49±15.26 ng/µL, P＜0.01). In vivo, VE-cad-Z stents exhibited better patency rate than bare metal stents (BMS) (15/15 versus 12/15), and it significantly reduced platelet adhesion and neointima formation (neointima area: 1.13±0.05 versus 1.00±0.05mm(2), P＜0.01 and 3.04±0.11versus 1.05±0.06mm(2), P＜0.01, at 3 and 30 days, respectively; % stenosis: 20.99±0.98 versus 18.72±0.97, P＜0.01 and 56.46±2.20 versus 19.45±1.24, P＜0.01, at 3 and 30 days, respectively).

CONCLUSION

These data suggested that VE-cad-Z stents could specifically capture OECs, consequently promote endothelial healing, and also reduce platelet adhesion and neointima formation.

Anti-fouling Coatings of Poly(dimethylsiloxane) Devices for Biological and Biomedical Applications

Fouling initiated by nonspecific protein adsorption is a great challenge in biomedical applications, including biosensors, bioanalytical devices, and implants. Poly(dimethylsiloxane) (PDMS), a popular material with many attractive properties for device fabrication in the biomedical field, suffers serious fouling problems from protein adsorption due to its hydrophobic nature, which limits the practical use of PDMS-based devices. Effort has been made to develop biocompatible materials for anti-fouling coatings of PDMS. In this review, typical nonfouling materials for PDMS coatings are introduced and the associated basic anti-fouling mechanisms, including the steric repulsion mechanism and the hydration layer mechanism, are described. Understanding the relationships between the characteristics of coating materials and the accompanying anti-fouling mechanisms is critical for preparing PDMS coatings with desirable anti-fouling properties.

Nanoprecipitation of polymeric nanoparticle micelles based on 2-methacryloyloxyethyl phosphorylcholine (MPC) with 2-(diisopropylamino)ethyl methacrylate (DPA), for intracellular delivery applications

Biodistribution of nanoparticle-based intracellular delivery systems is mediated primarily by particle size and physicochemical properties. As such, overcoming the rapid removal of these by the reticuloendothelial system remains a significant challenge. To date, a number of copolymer nanoparticle systems based on 2-methacryloyloxyethyl phosphorylcholine (MPC) with 2-(diisopropylamino)ethyl methacrylate (DPA), displaying biomimetic and pH responsive properties, have been published, however these have been predominately polymersome based, whilst micelle systems have remained relatively unexplored. This study utilised nanoprecipitation to investigate the effects of solvent and buffer choice upon micelle size and polydispersity, and found using methanol produced monodisperse micelles of circa 70 nm diameter, whilst ethanol produced polydisperse systems with nanoparticles of circa 128 nm diameter. The choice of aqueous buffer, dialysis of the systems, extended storage, and exposure to a wide temperature range (5-70 °C) had no significant effect on micelle size, and the systems were highly resistant to dilution, indicating excellent colloidal stability. Optimisation of the nanoprecipitation process, post precipitation, was investigated, and model drugs successfully loaded whilst maintaining system stability. Subsequent in vitro studies suggested that the micelles were of negligible cellular toxicity, and an apparent cellular uptake was observed via confocal laser scanning microscopy. This paper presents the first report of an optimised nanoprecipitation methodology for the formation of MPC-DPA nanoparticle micelles, and in doing so achieved monodisperse systems with the size and physicochemical characteristics seen as desirable for long circulating therapeutic delivery vehicles.