Effect of hydrophilic and hydrophobic microdomains on mode of interaction between block polymer and blood platelets

Bioactive engineered scaffolds based on PCL-PEG-PCL and tumor cell-derived exosomes to minimize the foreign body reaction

Long-term presence of M1 macrophages causes serious foreign body reaction (FBR), which is the main reason for the failure of biological scaffold integration. Inducing M2 polarization of macrophages near scaffolds to reduce foreign body response has been widely researched. In this work, inspired by the special capability of tumor exosomes in macrophages M2 polarization, we integrate tumor-derived exosomes into biological scaffolds to minimize the FBR. In brief, breast cancer cell-derived exosomes are loaded into polycaprolactone-b-polyethylene glycol-b-polycaprolactone (PCL-PEG-PCL) fiber scaffold through physical adsorption and entrapment to constructed bioactive engineered scaffold. In cellular experiments, we demonstrate bioactive engineered scaffold based on PCL-PEG-PCL and exosomes can promote the transformation of macrophages from M1 to M2 through the PI3K/Akt signaling pathway. In addition, the exosomes release gradually from scaffolds and act on the macrophages around the scaffolds to reduce FBR in a subcutaneous implant mouse model. Compared with PCL-PEG-PCL scaffolds without exosomes, bioactive engineered scaffolds reduce significantly inflammation and fibrosis of tissues around the scaffolds. Therefore, cancer cell-derived exosomes show the potential for constructing engineered scaffolds in inhibiting the excessive inflammation and facilitating tissue formation.

Fluorine-containing bio-inert polymers: Roles of intermediate water

Fluorine-containing polymers are used not only in industrial processes but also in medical applications, because they exhibit excellent heat, weather, and chemical resistance. As these polymers are not easily degraded in our body, it is difficult to use them in applications that require antithrombotic properties, such as artificial blood vessels. The material used for medical applications should not only be stable in vivo, but it should also be inert to biomolecules such as proteins or cells. In this review, this property is defined as "bio-inert," and previous studies in this field are summarized. Bio-inert materials are less recognized as foreign substances by proteins or cells in the living body, and they must be covered at interfaces designed with the concept of intermediate water (IW). On the basis of this concept, we present here the current understanding of bio-inertness and unusual blood compatibility found in fluoropolymers used in biomedical applications. IW is the water that interacts with materials with moderate strength and has been quantified by a variety of analytical methods and simulations. For example, by using differential scanning calorimetry (DSC) measurements, IW was defined as water frozen at around -40°C. To consider the role of the IW, quantification methods of the hydration state of polymers are also summarized. These investigations have been conducted independently because of the conflict between hydrophobic fluorine and bio-inert properties that require hydrophilicity. In recent years, not many materials have been developed that incorporate the good points of both aspects, and their properties have seldom been linked to the hydration state. This has been critically performed now. Furthermore, fluorine-containing polymers in medical use are reviewed. Finally, this review also describes the molecular design of the recently reported fluorine-containing bio-inert polymers for controlling their hydration state. STATEMENT OF SIGNIFICANCE: A material covered with a hydration layer known as intermediate water that interacts moderately with other objects is difficult to be recognized as a foreign substance and exhibits bio-inert properties. Fluoropolymers show high durability, but conflict with bio-inert characteristics requiring hydrophilicity as these research studies have been conducted independently. On the other hand, materials that combine the advantages of both hydrophobic and hydrophilic features have been developed recently. Here, we summarize the molecular architecture and analysis methods that control intermediate water and provide a guideline for designing novel fluorine-containing bio-inert materials.

Synthesis and Antiplatelet Adhesion Behavior of a Poly(L-lactide-co-glycolide)-Poly(1,5-dioxepan-2-one) Multiblock Copolymer

Platelet adhesion and denaturation on artificial medical implants induce thrombus formation. In this study, bioabsorbable copolymers composed of poly(l-lactide-co-glycolide) (PLGA) and poly(1,5-dioxepan-2-one) (PDXO) were synthesized and evaluated for their antiplatelet adhesive properties. The PLGA-PXO multiblock copolymer (PLGA-PDXO MBC) and its random copolymer (PLGA-PDXO RC) showed effective antiplatelet adhesive properties, and the number of adhered platelets was similar to those adhered on poly(2-methoxyethylacrylate), a known antiplatelet adhesive polymer, although a large number of denatured platelets were observed on a PLGA-poly(ε-caprolactone) multiblock copolymer (PLGA-PCL MBC). Using monoclonal antifibrinogen IgG antibodies, we also found that both αC and γ-chains, the binding sites of fibrinogen for platelets, were less exposed on the PLGA-PDXO MBC surface compared to PLGA-PCL MBC. Furthermore, free-standing films of PLGA-PDXO MBC were prepared by casting the polymer solution on glass plates and showed good tensile properties and slow hydrolytic degradation in phosphate-buffered saline (pH = 7.4). We expect that the unique properties of PLGA-PDXO MBC, i.e., antiplatelet adhesive behavior, good tensile strength, and hydrolytic degradation, will pave the way for the development of new bioabsorbable implanting materials suitable for application at blood-contacting sites.

Non-coating method for non-adherent cell culture using high molecular weight dextran sulfate and bovine serum albumin

Non-adherent cell culture surface has been widely used for producing cell spheroids and cell aggregates. The purpose of this study was to formulate a new method for non-adherent cell culture without coating or surface-modification that has been needed. We found that high-molecular-weight dextran sulfate (DS) and bovine serum albumin (BSA) synergistically prevented cell adhesion in media supplemented with no or low serum. This method worked on tissue culture-treated polystyrene surfaces as well as on commercially available low-attachment- and untreated polystyrene surfaces. Further investigation revealed that BSA may mediate the adsorption of DS to the surface. In addition, as the adsorption of fluorescently labeled fibronectin was inhibited by BSA alone, it appears that protein adsorption and cell adhesion do not always correlate. Finally, we demonstrated the successful formation of HepG2 spheroids and cardiomyocyte aggregates using this method. In conclusion, cell adhesion can be effectively suppressed by simply adding DS and BSA to the culture medium without coating or surface modification, and it may be useful for generating cell spheroids and aggregates.

Molecular Dynamics Study on the Water Mobility and Side-Chain Flexibility of Hydrated Poly(ω-methoxyalkyl acrylate)s

Intermediate water (IW) is known to play an important role in the antifouling property of biocompatible polymers. However, how IW prevents protein adsorption is still unclear. To understand the role of IW in the antifouling mechanism, molecular dynamics simulation was used to investigate the dynamic properties of water and side-chains for hydrated poly(ω-methoxyalkyl acrylate)s (PMCxA, where x indicates the number of methylene carbons) with x = 1-6 and poly(n-butyl acrylate) (PBA) in this study. Since the polymers uptake more water than their equilibrium water content (EWC) at the polymer/water interface, we analyzed the hydrated polymers at a water content higher than that of EWC. It was found that the water molecules interacting with one polymer oxygen atom (BW1), of which most are IW molecules, in PMC2A exhibit the lowest mobility, while those in PBA and PMC1A show a higher mobility. The result was consistent with the expectation that the biocompatible polymer with a long-resident hydration layer possesses good antifouling property. Through the detailed analysis of side-chain binding with three different types of BW1 molecules, we found that the amount of side-chains simultaneously interacting with two BW1 molecules, which exhibit the highest flexibility among the three kinds of side-chains, is the lowest for PMC1A. The high mobility of BW1 is thus suggested as the main factor for the poor protein adsorption resistance of PMC1A even though it possesses enough IW content and relatively flexible side-chains. Contrarily, a maximum amount of side-chains simultaneously interacting with two BW1 molecules was found in the hydrated PMC3A. The moderate side-chain length of PMC3A allows side-chains to simultaneously interact with two BW1 molecules and minimizes the hydrophobic part attractively interacting with a protein at the polymer/water interface. The unique structure of PMC3A may be the reason causing the best protein adsorption resistance among the PMCxAs.

Multifunctional, Low Friction, Antimicrobial Approach for Biomaterial Surface Enhancement

Poly(vinyl chloride) (PVC) biomaterials perform a host of life-saving and life-enhancing roles when employed as medical devices within the body. High frictional forces between the device surface and interfacing tissue can, however, lead to a host of complications including tissue damage, inflammation, pain, and infection. We herein describe a versatile surface modification method using multifunctional hydrogel formulations to increase lubricity and prevent common device-related complications. In a clinically relevant model of the urinary tract, simulating the mechanical and biological environments encountered in vivo, coated candidate catheter surfaces demonstrated significantly lower frictional resistance than uncoated PVC, with reductions in coefficient of friction values of more than 300-fold due to hydration of the surface-localized polymer network. Furthermore, this significant lubrication capacity was retained following hydration periods of up to 28 days in artificial urine at pH 6 and pH 9, representing the pH of physiologically normal and infected urine, respectively, and during 200 repeated cycles of applied frictional force. Importantly, the modified surfaces also displayed excellent antibacterial activity, which could be facilely tuned to achieve reductions of 99.8% in adherence of common hospital-acquired pathogens, Staphylococcus aureus and Proteus mirabilis, relative to their uncoated counterparts through incorporation of chlorhexidine in the coating matrix as a model antiseptic. The remarkable, and pH-independent, tribological performance of these lubricious, antibacterial, and highly durable surfaces offers exciting promise for use of this PVC functionalization approach in facilitating smooth and atraumatic insertion and removal of a wide range of medical implants, ultimately maintaining user health and dignity.

Analysis of Interaction Between Interfacial Structure and Fibrinogen at Blood-Compatible Polymer/Water Interface

The correlation between the interfacial structure and protein adsorption at a polymer/water interface was investigated. Poly(2-methoxyethyl acrylate)(PMEA), which is one of the best blood compatible polymers available, was employed. Nanometer-scale structures generated through the phase separation of polymer and water were observed at the PMEA/phosphate buffered saline interface. The interaction between the interfacial structures and fibrinogen (FNG) was measured using atomic force microscopy. Attraction was observed in the polymer-rich domains as well as in the non-blood compatible polymer. In contrast, no attractive interactions were observed, and only a repulsion occurred in the water-rich domains. The non-adsorption of FNG into the water rich domains was also clarified through topographic and phase image analyses. Furthermore, the FNG molecules adsorbed on the surface of PMEA were easily desorbed, even in the polymer-rich domains. Water molecules in the water-rich domains are anticipated to be the dominant factor in preventing FNG adsorption and thrombogenesis on a PMEA interface.

Voltaglue Bioadhesives Energized with Interdigitated 3D-Graphene Electrodes

Soft tissue fixation of implant and bioelectrodes relies on mechanical means (e.g., sutures, staples, and screws), with associated complications of tissue perforation, scarring, and interfacial stress concentrations. Adhesive bioelectrodes address these shortcomings with voltage cured carbene-based bioadhesives, locally energized through graphene interdigitated electrodes. Electrorheometry and adhesion structure activity relationships are explored with respect to voltage and electrolyte on bioelectrodes synthesized from graphene 3D-printed onto resorbable polyester substrates. Adhesive leachates effects on in vitro metabolism and human-derived platelet-rich plasma response serves to qualitatively assess biological response. The voltage activated bioadhesives are found to have gelation times of 60 s or less with maximum shear storage modulus (G') of 3 kPa. Shear modulus mimics reported values for human soft tissues (0.1-10 kPa). The maximum adhesion strength achieved for the ≈50 mg bioelectrode films is 170 g cm^-2 (17 kPa), which exceeds the force required for tethering of electrodes on dynamic soft tissues. The method provides the groundwork for implantable bio/electrodes that may be permanently incorporated into soft tissues, vis-à-vis graphene backscattering wireless electronics since all components are bioresorbable.

Diblock Polymer Brush (PHEAA- b-PFMA): Microphase Separation Behavior and Anti-Protein Adsorption Performance

In this paper, a series of amphiphilic diblock polymers of poly(hydroxyethylacrylamide)- b-poly(1H,1H-pentafluoropropyl methacrylate) (PHEAA- b-PFMA) were grafted from silicon wafer via surface-initiated atom transfer radical polymerization (SI-ATRP). Surface wettability and chemical compositions of the modified surfaces were characterized by contact angle goniometer and X-ray photoelectron spectroscopy (XPS) respectively. Molecular weight and polydispersity of each block were measured using gel permeation chromatography (GPC). The topography and the microphase separation behavior of PHEAA- b-PFMA surfaces were investigated by atomic force microscope (AFM). The results show that only when the grafting density (σ) and thickness of PHEAA brush were in the range of 0.9-1.3 (chain/nm²) and 6.6-15.1 nm, respectively, and the ratio of PFMA/PHEAA varied from 89/42 to 89/94, could the diblock copolymer phase separate into nanostructures. Further, the antiprotein adsorption performance of the modified surfaces against BSA, fibrinogen, and lysozyme was studied. The results indicated the modified surfaces could reduce the protein adsorption compared to the pristine silicon wafer. For Fibrinogen, the antiadsorption effect of PHEAA- b-PFMA-modified surfaces with microphase segregation was better than that of corresponding PHEAA modified surfaces. The results provide further evidence that surface composition and microphase segregation of fluorinated moieties of block copolymer brushes significantly impact protein adsorption behaviors.

Surface Characterization and Platelet Adhesion on Thin Hydrogel Films of Poly(vinyl ether)

Poly(vinyl ether), with short oxyethylene side chains which possess a simple and relatively polar structure, should be a unique candidate for a bioinert material thanks to its solubility in water. On the basis of living cationic copolymerization and subsequent ultraviolet light irradiation, thin films of poly(2-methoxyethyl vinyl ether) with different cross-linking densities were prepared on solid substrates. The films were thickened in water, and the extent was dependent on the cross-linking density. Although the surface chemistry and aggregation states were almost identical to one another, the stiffness, or the softness, of the outermost region in the film was strongly dependent on the cross-linking density. That is, the interface between polymer and water became thicker, or more diffused, with decreasing cross-linking density. The blood compatibility based on the platelet adhesion on to the hydrogel films was better for a more diffused interface.

Effect of local chain dynamics on a bioinert interface

Although many kinds of synthetic polymers have been investigated to construct blood-compatible materials, only a few have achieved success. To establish molecular designs for blood-compatible polymers, the chain structure and dynamics at the water interface must be understood using solid evidence as the first bench mark. Here we show that polymer dynamics at the water interface impacts on structure of the interfacial water, resulting in a change in protein adsorption and of platelet adhesion. As a particular material, a blend composed of poly(2-methoxyethyl acrylate) (PMEA) and poly(methyl methacrylate) was used. PMEA was segregated to the water interface. While the local conformation of PMEA at the water interface was insensitive to its molecular weight, the local dynamics became faster with decreasing molecular weight, resulting in a disturbance of the network structure of waters at the interface. This leads to the extreme suppression of protein adsorption and platelet adhesion.

Anti-biofouling surface with sub-20 nm heterogeneous nanopatterns

We have developed a nanometer-sized heterogeneous pattern with an excellent anti-biofouling property to control protein–surface/cell–surface interactions at the molecular level.

Design and biocompatibility of endovascular aneurysm filling devices

The rupture of an intracranial aneurysm, which can result in severe mental disabilities or death, affects approximately 30,000 people in the United States annually. The traditional surgical method of treating these arterial malformations involves a full craniotomy procedure, wherein a clip is placed around the aneurysm neck. In recent decades, research and device development have focused on new endovascular treatment methods to occlude the aneurysm void space. These methods, some of which are currently in clinical use, utilize metal, polymeric, or hybrid devices delivered via catheter to the aneurysm site. In this review, we present several such devices, including those that have been approved for clinical use, and some that are currently in development. We present several design requirements for a successful aneurysm filling device and discuss the success or failure of current and past technologies. We also present novel polymeric-based aneurysm filling methods that are currently being tested in animal models that could result in superior healing.

In vitro investigation of antioxidant, anti-Inflammatory, and antiplatelet adhesion properties of genistein-modified poly(ethersulfone)/poly(vinylpyrrolidone) hemodialysis membranes

Hemocompatibility of genistein-modified poly(ethersulfone)/poly(vinylpyrrolidone) (PES/PVP) hemodialysis (HD) membranes has been investigated in vitro with emphasis on evaluation of cell viability, antioxidant, anti-inflammatory, and antiplatelet adhesion properties. Genistein modified PES/PVP membranes reveal significant reduction of the reactive oxygen species and also considerable suppression of interleukin-1β and tumor necrosis factor-α levels in whole blood, but to a lesser extent ininterleukin-6. The incorporation of PVP into the HD membrane reduces platelet adhesion by virtue of its hydrophilicity. Of particular importance is that platelet adhesion of the genistein modified membranes declines noticeably at low concentrations of genistein for about 5-10%, beyond which it raises the number of adhered platelets. The initial decline in the platelet adhesion is attributable to genistein's ability to inhibit intercellular and/or vascular cell adhesion, whereas the reversal of this adhesion trend with further increase of genistein loading is ascribed to the inherent hydrophobicity of the genistein modified HD membrane.

Currently available biomaterials for use in cardiopulmonary bypass

Cardiopulmonary bypass (CPB) represents one of the most important technical innovations in healthcare history, yet the systemic responses to CPB remain a fundamentally unresolved problem. Study of the blood-biomaterial interaction and development of biocompatible materials is intimately related to efforts to optimize patient outcome following CPB. This article reviews the design innovations in biomaterial surfaces that have been introduced into clinical practice in an attempt to ameliorate the detrimental consequences of CPB, contrasting the actual clinical improvements and patient benefits achieved against those predicted on the basis of theory and in vitro testing. Some discussion of the underlying mechanisms of action as presently understood is provided and the current limitations of biomaterial-dependent strategies to improve outcome following CPB are addressed.

A review of block copolymer-based biomaterials that control protein and cell interactions

Block copolymers posses the ability to phase separate into micro and nanoscale patterns resulting in nonhomogeneous surfaces and solids. This nonhomogeneity has been harnessed to improve mechanical properties, control degradation, and add functionality to biomaterials. The ability of block copolymers to generate a wide variety of surface chemistries and morphologies can also be harnessed to control protein adsorption, protein conformation, and cell adhesion. Proteins and cells will respond to periodically structured surfaces, so block copolymers have a great deal of potential as biomaterials. This review will explore the ability of block copolymers to control specific biological responses such as cell adhesion, protein adsorption and conformation, parameters that govern the overall host response to a material. In addition, some of the specific applications of block copolymer, antithrombogenic materials and their ability to pattern proteins, will be discussed.

Creation of a blood-compatible surface: a novel strategy for suppressing blood activation and coagulation using a nitroxide radical-containing polymer with reactive oxygen species scavenging activity

Various polymeric materials have been used in medical devices, including blood-contacting artificial organs. Contact between blood and foreign materials causes blood cell activation and adhesion, followed by blood coagulation. Concurrently, the activated blood cells release inflammatory cytokines together with reactive oxygen species (ROS). We have hypothesized that the suppression of ROS generation plays a crucial role in blood activation and coagulation. To confirm this hypothesis, surface-coated polymers containing nitroxide radical compounds (nitroxide radical-containing polymers (NRP)) were designed and developed. The NRP was composed of a hydrophobic poly(chloromethylstyrene) (PCMS) chain to which 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) moieties were conjugated via condensation reaction of the chloromethyl groups in PCMS with the sodium alcoholate group of 4-hydroxy-TEMPO. Blood compatibility was investigated by placing NRP-coated beads in contact with rat whole blood. The amount of ROS generated on PCMS-coated beads used as a control increased significantly with time, while NRP-coated beads suppressed ROS generation. It is interesting to note that the suppression of inflammatory cytokine generation by NRP-coated beads was shown to be significantly higher than that by PCMS-coated beads. Both platelet and leukocyte adhesion to the beads were suppressed with increasing TEMPO incorporation in the polymer. These results confirm that the suppression of ROS by NRP prevents inflammatory cytokine generation, which in turn results in the suppression of blood activation and coagulation on the beads.

Synthesis of biomimetic segmented polyurethanes as antifouling biomaterials

Controlling the non-specific adsorption of proteins, cells and bacteria onto biomaterial surfaces is of crucial importance for the development of medical devices with specific levels of performance. Among the strategies pursued to control the interactions between material surfaces and biological tissues, the immobilization of non-fouling polymers on biomaterial surfaces as well as the synthesis of the so-called biomimetic polymers are considered promising approaches to elicit specific cellular responses. In this study, in order to obtain materials able to prevent infectious and thrombotic complications related to the use of blood-contacting medical devices, heparin-mimetic segmented polyurethanes were synthesized and fully characterized. Specifically, sulfate or sulfamate groups, known to be responsible for the biological activity of heparin, were introduced into the side chain of a carboxylated polyurethane. Due to the introduction of these groups, the obtained polymers possessed a higher hard/soft phase segregation (lower glass transition temperatures) and a greater hydrophilicity than the pristine polymer. In addition, the synthesized polymers were able to significantly delay the activated partial thromboplastin time, this increased hemocompatibility being related both to polymer hydrophilicity and to the presence of the -SO3H groups. This last feature was also responsible for the ability of these biomimetic polymers to prevent the adhesion of a strain of Staphylococcus epidermidis.

Effect of microphase separation on the protein resistance of a polymeric surface

Segmented polyurethanes (PUs) containing poly(ethylene glycol) (PEG), poly(propylene glycol), or poly(dimethylsiloxane) soft segments have been prepared by two-step condensation polymerization. Atom force microscopy observation in air and solution indicates that the segmented PU forms a microphase separation on the surface. By use of quartz crystal microbalance with dissipation and surface plasmon resonance, we have investigated the adsorption of fibrinogen, bovine serum albumin, and lysozyme on a surface constructed by such a PU in aqueous solution in real time. Our results reveal that the protein resistance of the PUs arises from the hydrated PEG segments instead of microphase separation.

Polymeric membrane materials for artificial organs

Many polymeric materials have already been used in the field of artificial organs. However, the materials used in artificial organs are not necessarily created with the best material selectivity and materials design; therefore, the development of synthesized polymeric membrane materials for artificial organs based on well-defined designs is required. The approaches to the development of biocompatible polymeric materials fall into three categories: (1) control of physicochemical characteristics on material surfaces, (2) modification of material surfaces using biomolecules, and (3) construction of biomimetic membrane surfaces. This review will describe current issues regarding polymeric membrane materials for use in artificial organs.

Developments of the spin labelling study of polymers at interfaces

The spin labelling method has been used in a large variety of situations, in the broad field of polymers at solid interfaces. The relevance of the method is confirmed on linear neutral chains of poly (ethylene oxide) (PEO) in well defined situations and compared with the simple theoretical calculations of a mean field theory or some scaling arguments. Both theories have their own strengths and weaknesses. Then the fact, that polymers at solid liquid interfaces are three components systems, is considered and successively the effect of varying the polymer architecture, the solid surface and the solvent is studied. In all these cases specific results are obtained by Electron Paramagnetic Resonance (EPR) showing the usefulness and the versatility of the method.