Blood compatibility of photografted hydrogel coatings

An in situ grown ultrathin and robust protein nanocoating for mitigating thromboembolic issues associated with cardiovascular medical devices

Thromboembolism, arising from the utilization of cardiovascular medical devices, remains a prevalent issue entailing substantial morbidity and mortality. Despite the proposal of various surface modification strategies, each approach possesses inherent limitations and drawbacks. Herein, we propose a novel approach for the in situ growth of nanocoatings on various material surfaces through the cooperative assembly of silk fibroin (SF) and lysozyme. The intrinsic in situ growth characteristic enables the nanocoatings to achieve stable and uniform adherence to diverse substrate surfaces, including the inner surface of intravascular catheters, to redefine the surface properties of the material. The features of the hydrophilic and negatively charged nanocoating contribute to its antithrombotic properties, as evidenced by the reduced likelihood of platelet adhesion upon modification of the ultrathin and mechanically robust coating. In vitro assessment confirms a significant reduction in blood clot formation along with the promotion of anticoagulation. Such a SF/Ly nanocoating holds substantial promise as a surface modification strategy to enhance the hemocompatibility of medical devices and other materials that come into contact with blood, particularly in situations where medical-grade materials are temporarily unavailable, thus providing a feasible alternative.

A sustained release lubrication method of agarose-sodium hyaluronate hydrogels for artificial joint

The artificial joint prosthesis's surface is subjected to wear due to the destruction of the joint lubrication environment after surgery. In this study, an agarose-sodium hyaluronate hydrogel was used as lubricant additive in order to supply and preserve the lubricating fluid of artificial joint prostheses. A ball on disc experiment was conducted using this hydrogel to evaluate the lubrication efficiency and release rate under various frequencies. The results showed that this hydrogel could release lubricant under pressure and then absorb the released fluid after decompression. Furthermore, the agarose-sodium hyaluronate hydrogel acted as an effective transport mechanism to release sodium hyaluronate lubricant into the metal-on-polymer friction interface. Compared with pure water lubrication, the friction coefficient and wear volume were reduced by up to 62.9%, and 86.9% respectively. Moreover, the proposed lubrication method provided a long-term lubrication on artificial hip joints.

An Injectable Integration of Autologous Bioactive Concentrated Growth Factor and Gelatin Methacrylate Hydrogel with Efficient Growth Factor Release and 3D Spatial Structure for Accelerated Wound Healing

Growth factors are essential for wound healing owing to their multiple reparative effects. Concentrated growth factor (CGF) is a third-generation platelet extract containing various endogenous growth factors. Here, a CGF extract solution is combined with gelatin methacrylate (GM) by physical blending to produce GM@CGF hydrogels for wound repair. The GM@CGF hydrogels show no immune rejection during autologous transplantation. Compared to CGF, GM@CGF hydrogels not only exhibit excellent plasticity and adhesivity but also prevent rapid release and degradation of growth factors. The GM@CGF hydrogels display good injectability, self-healing, swelling, and degradability along with outstanding cytocompatibility, angiogenic functions, chemotactic functions, and cell migration-promoting capabilities in vitro. The GM@CGF hydrogel can release various effective molecules to rapidly initiate wound repair, stimulate the expressions of type I collagen, transform growth factor β1, epidermal growth factor, and vascular endothelial growth factor, promote the production of granulation tissues, vascular regeneration and reconstruction, collagen deposition, and epidermal cell migration, as well as prevent excessive scar formation. In conclusion, the injectable GM@CGF hydrogel can release various growth factors and provide a 3D spatial structure to accelerate wound repair, thereby providing a foundation for the clinical application and translation of CGF.

Structure of Self-Initiated Photopolymerized Films: A Comparison of Models

Self-initiated photografting and photopolymerization (SI-PGP) uses UV illumination to graft polymers to surfaces without additional photoinitiators using the monomers as initiators, "inimers". A wider use of this method is obstructed by a lack of understanding of the resulting, presumably heterogeneous, polymer structure and of the parallel degradation under continuous UV illumination. We have used neutron reflectometry to investigate the structure of hydrated SI-PGP-prepared poly(HEMA-co-PEG₁₀MA) (poly(2-hydroxyethyl methacrylate-co-(ethylene glycol)₁₀ methacrylate)) films and compared parabolic, sigmoidal, and Gaussian models for the polymer volume fraction distributions. Results from fitting these models to the data suggest that either model can be used to approximate the volume fraction profile to similar accuracy. In addition, a second layer of deuterated poly(methacrylic acid) (poly(dMAA)) was grafted over the existing poly(HEMA-co-PEG₁₀MA) layer, and the resulting double-grafted films were also studied by neutron reflectometry to shed light on the UV-polymerization process and the inevitable UV-induced degradation which competes with the grafting.

Self-Assembly Anchored Cationic Copolymer Interfaces for Applying the Control of Counterion-Induced Bacteria Killing/Release Procedure

In recent years, daily hygiene and disease control issues have received increasing attention, especially the raging epidemics caused by the spread of deadly viruses. The construction of the interface of new polymer materials is focused on, which can provide a cyclic operation process for the killing and releasing of bacteria, and perform repeated regeneration, which is of great significance for the development of advanced medical biomaterials. In order to explore the basic physical phenomena of bacterial attachment and detachment on the polymer material interface by different amine groups, this study plans to synthesize four different butyl methacrylate (BMA)-based cationic copolymers with primary, ternary, and quaternary amine groups, and compare their effects on bactericidal efficiency. Since BMA can generate strong hydrophobic interactions with the benzene ring structure, this study used a polystyrene substrate to realize a self-assembled cationic copolymer interface for controlling the counterion-induced bacterial killing/release process. Furthermore, negatively charged ions are introduced to induce changes in the hydration capability of water molecules and control the subsequent bacterial detachment function. In this study, possible directions to answer and clarify the above concepts are proposed, and there is a basic reference principle that can lead to research work in macromolecular bioscience fields.

Advancements in modification of membrane materials over membrane separation for biomedical applications-Review

A comprehensive overview of various modifications carried out on polymeric membranes for biomedical applications has been presented in this review paper. In particular, different methods of carrying out these modifications have been discussed. The uniqueness of the review lies in the sense that it discusses the surface modification techniques traversing the timeline from traditionally well-established technologies to emerging new techniques, thus giving an intuitive understanding of the evolution of surface modification techniques over time. A critical comparison of the advantages and pitfalls of commonly used traditional and emerging surface modification techniques have been discussed. The paper also highlights the tuning of specific properties of polymeric membranes that are critical for their increased applications in the biomedical industry specifically in drug delivery, along with current challenges faced and where the future potential of research in the field of surface modification of membranes.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

Renatured hydrogel painting

Hydrogel coatings pave an avenue for improving the lubricity, biocompatibility, and flexibility of solid surfaces. From the viewpoint of practical applications, this work establishes a scalable method to firmly adhere hydrogel layers to diverse solid surfaces. The strategy, termed as renatured hydrogel painting (RHP), refers to adhering dehydrated xerogel to a surface with appropriate glues, followed by the formation of a hydrogel layer after rehydration of the xerogel. With the benefits of simplicity and generality, this strategy can be readily applied to different hydrogel systems, no matter what the substrate is. Hydrogel adhesion is demonstrated by its tolerance against mechanical impact with hydrodynamic shearing at 14 m/s. This method affords powerful supplements to renew the surface chemistry and physical properties of solid substrates. In addition, we show that the RHP technique can be applied to living tissue, with potential for clinical applications such as the protection of bone tissue.

Ultrathin and Robust Hydrogel Coatings on Cardiovascular Medical Devices to Mitigate Thromboembolic and Infectious Complications

Thromboembolic and infectious complications stemming from the use of cardiovascular medical devices are still common and result in significant morbidity and mortality. There is no strategy to date that effectively addresses both challenges at the same time. Various surface modification strategies (e.g., silver, heparin, and liquid-impregnated surfaces) are proposed yet each has several limitations and shortcomings. Here, it is shown that the incorporation of an ultrathin and mechanically robust hydrogel layer reduces bacterial adhesion to medical-grade tubing by 95%. It is additionally demonstrated, through a combination of in vitro and in vivo tests, that the hydrogel layer significantly reduces the formation and adhesion of blood clots to the tubing without affecting the blood's intrinsic clotting ability. The adhesion of clots to the tubing walls is reduced by over 90% (in vitro model), which results in an ≈60% increase in the device occlusion time (time before closure due to clot formation) in an in vivo porcine model. The advantageous properties of this passive coating make it a promising surface material candidate for medical devices interfacing with blood.

Photografting and Patterning of Poly(ethylene glycol) Methacrylate Hydrogel on Glass for Biochip Applications

An efficient procedure for chemical initiator-free, in situ synthesis of a functional polyethylene glycol methacrylate (PEG MA) hydrogel on regular glass substrates is reported. It is demonstrated that self-initiated photografting and photopolymerization driven by UV irradiation can yield tens of nanometer-thick coatings of carboxy-functionalized PEG MA on the aldehyde-terminated borosilicate glass surface. The most efficient formulation for hydrogel synthesis contained methyl methacrylic acid (MAA), 2-hydroxyethyl methacrylate (HEMA), and PEG methacrylate (PEG₁₀MA) monomers (1:1:1). The resulting HEMA/PEG₁₀MA/MAA (HPMAA) coatings had a defined thickness in the range from 11 to 50 nm. The physicochemical properties of the synthesized HPMAA coatings were analyzed by combining water contact angle measurements, stylus profilometry, imaging null ellipsometry, and atomic force microscopy (AFM). The latter technique was employed in the quantitative imaging mode not only for direct probing of the surface topography but also for swelling behavior characterization in the pH range from 4.5 to 8.0. The estimated high swelling ratios of the HPMAA hydrogel (up to 3.2) together with its good stability and resistance to nonspecific protein binding were advantageous in extracellular matrix mimetics via patterning of fibronectin (FN) at a resolution close to 200 nm. It was shown that the fabricated FN micropatterns on HPMAA were equally suitable for single-cell arraying, as well as controlled cell culture lasting at least for 96 h.

Hydrogel Paint

For a hydrogel coating on a substrate to be stable, covalent bonds polymerize monomer units into polymer chains, crosslink the polymer chains into a polymer network, and interlink the polymer network to the substrate. The three processes-polymerization, crosslinking, and interlinking-usually concur. This concurrency hinders widespread applications of hydrogel coatings. Here a principle is described to create hydrogel paints that decouple polymerization from crosslinking and interlinking. Like a common paint, a hydrogel paint divides the labor between the paint maker and the paint user. The paint maker formulates the hydrogel paint by copolymerizing monomer units and coupling agents into polymer chains, but does not crosslink them. The paint user applies the paint on various materials (elastomer, plastic, glass, ceramic, or metal), and by various operations (brush, cast, dip, spin, or spray). During cure, the coupling agents crosslink the polymer chains into a network and interlink the polymer network to the substrate. As an example, hydrogels with thickness in the range of 2-20 µm are dip coated on medical nitinol wires. The coated wires reduce friction by eightfold, and remain stable over 50 test cycles. Also demonstrated are several proof-of-concept applications, including stimuli-responsive structures and antifouling model boats.

Anticoagulant Polyethylene Terephthalate Surface by Plasma-Mediated Fucoidan Immobilization

Biomaterial-based blood clot formation is one of the biggest drawbacks of blood-contacting devices. To avoid blood clot formation, their surface must be tailored to increase hemocompatibility. Most synthetic polymeric biomaterials are inert and lack bonding sites for chemical agents to bond or tailor to the surface. In this study, polyethylene terephthalate was subjected to direct current air plasma treatment to enhance its surface energy and to bring oxidative functional binding sites. Marine-sourced anticoagulant sulphated polysaccharide fucoidan from Fucus vesiculosus was then immobilized onto the treated polyethylene terephthalate (PET) surface at different pH values to optimize chemical bonding behavior and therefore anticoagulant performance. Surface properties of samples were monitored using the water contact angle; chemical analyses were performed by FTIR and X-ray photoelectron spectroscopy (XPS) and their anticoagulant activity was tested by means of prothrombin time, activated partial thromboplastin time and thrombin time. On each of the fucoidan-immobilized surfaces, anticoagulation activity was performed by extending the thrombin time threshold and their pH 5 counterpart performed the best result compared to others.

Interaction Forces on Polyampholytic Hydrogel Gradient Surfaces

Rational design and informed development of nontoxic antifouling coatings requires a thorough understanding of the interactions between surfaces and fouling species. With more complex antifouling materials, such as composites or zwitterionic polymers, there follows also a need for better characterization of the materials as such. To further the understanding of the antifouling properties of charge-balanced polymers, we explore the properties of layered polyelectrolytes and their interactions with charged surfaces. These polymers were prepared via self-initiated photografting and photopolymerization (SIPGP); on top of a uniform bottom layer of anionic poly(methacrylic acid) (PMAA), a cationic poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) thickness gradient was formed. Infrared microscopy and imaging spectroscopic ellipsometry were used to characterize chemical composition and swelling of the combined layer. Direct force measurements by colloidal probe atomic force microscopy were performed to investigate the forces between the polymer gradients and charged probes. The swelling of PMAA and PDMAEMA are very different, with steric and electrostatic forces varying in a nontrivial manner along the gradient. The gradients can be tuned to form a protein-resistant charge-neutral region, and we demonstrate that this region, where both electrostatic and steric forces are small, is highly compressed and the origin of the protein resistance of this region is most likely an effect of strong hydration of charged residues at the surface, rather than swelling or bulk hydration of the polymer. In the highly swollen regions far from charge-neutrality, steric forces dominate the interactions between the probe and the polymer. In these regions, the SIPGP polymer has qualitative similarities with brushes, but we were unable to quantitatively describe the polymer as a brush, supporting previous data suggesting that these polymers are cross-linked.

BloodSurf 2017: News from the blood-biomaterial frontier

From stents and large-diameter vascular grafts, to mechanical heart valves and blood pumps, blood-contacting devices are enjoying significant clinical success owing to the application of systemic antiplatelet and anticoagulation therapies. On the contrary, research into material and device hemocompatibility aimed at alleviating the need for systemic therapies has suffered a decline. This research area is undergoing a renaissance fueled by recent fundamental insights into coagulation and inflammation that are offering new avenues of investigation, the growing recognition of the limitations facing existing therapeutic approaches, and the severity of the cardiovascular disorders epidemic. This Opinion article discusses clinical needs for hemocompatible materials and the emerging research directions for fulfilling those needs. Based on the 2017 BloodSurf conference that brought together clinicians, scientists, and engineers from academia, industry, and regulatory bodies, its purpose is to draw the attention of the wider clinical and scientific community to stimulate further growth. STATEMENT OF SIGNIFICANCE: The article highlights recent fundamental insights into coagulation, inflammation, and blood-biomaterial interactions that are fueling a renaissance in the field of material hemocompatibility. It will be useful for clinicians, scientists, engineers, representatives of industry and regulatory bodies working on the problem of developing hemocompatible materials and devices for treating cardiovascular disorders.

Swelling of Thin Poly(ethylene glycol)-Containing Hydrogel Films in Water Vapor-A Neutron Reflectivity Study

Hydrogels are widely used in biomedicine and for bioanalytical purposes, normally under wet conditions. For certain applications, processing steps, or process monitoring, hydrogel films are used or treated under ambient conditions, and because they are hygroscopic, it is of interest to investigate how they respond to changes in atmospheric humidity. We have used neutron reflectometry to follow the swelling of thin UV-polymerized hydrogel films in air under different relative humidities (RHs). These polymers were prepared to similar thicknesses on silica and gold substrates, and the chemical similarity between them was verified by infrared spectroscopy. The swelling in response to variations in RH was different for the layers on the two substrate types, reflecting structural changes induced by differences in the UV exposure required to achieve a given polymer thickness, as demonstrated also by differences in the Flory-Huggins interaction parameter, obtained by fitting a Flory-Huggins-type sorption model to the swelling data. Wetting studies show small changes in contact angles with surrounding humidity variations, indicating that structural reorganization at the interface in response to humidity changes is limited.

Surface charge-bias impact of amine-contained pseudozwitterionic biointerfaces on the human blood compatibility

This work discusses the impact of the charge bias and the hydrophilicity on the human blood compatibility of pseudozwitterionic biomaterial gels. Four series of hydrogels were prepared, all containing negatively-charged 3-sulfopropyl methacrylate (SA), and either acrylamide, N-isopropylacrylamide, 2-dimethylaminoethyl methacrylate (DMAEMA) or [2-(methacryloyloxy)ethyl]trimethylammonium (TMA), to form S_nA_m, S_nN_m, S_nD_m or S_nT_m hydrogels, respectively. An XPS analysis proved that the polymerization was well controlled from the initial monomer ratios. All gels present high surface hydrophilicity, but varying bulk hydration, depending on the nature/content of the comonomer, and on the immersion medium. The most negative interfaces (pure SA, S7A3, S5A5) showed significant fibrinogen adsorption, ascribed to the interactions of the αC domains of the protein with the gels, then correlated to considerable platelet adhesion; but low leukocyte/erythrocyte attachments were measured. Positive gels (excess of DMAEMA or TMA) are not hemocompatible. They mediate protein adsorption and the adhesion of human blood cells, through electrostatic attractive interactions. The neutral interfaces (zeta potential between -10mV and +10mV) are blood-inert only if they present a high surface and bulk hydrophilicity. Overall, this study presents a map of the hemocompatible behavior of hydrogels as a function of their surface charge-bias, essential to the design of blood-contacting devices.

Crosslinking Polymer Brushes with Ethylene Glycol-Containing Segments: Influence on Physicochemical and Antifouling Properties

The introduction of different types and concentrations of crosslinks within poly(hydroxyethyl methacrylate) (PHEMA) brushes influences their interfacial, physicochemical properties, ultimately governing their adsorption of proteins. PHEMA brushes and brush-hydrogels were synthesized by surface-initiated, atom-transfer radical polymerization (SI-ATRP) from HEMA, with and without the addition of di(ethylene glycol) dimethacrylate (DEGDMA) or tetra(ethylene glycol) dimethacrylate (TEGDMA) as crosslinkers. Linear (pure PHEMA) brushes show high hydration and low modulus and additionally provide an efficient barrier against nonspecific protein adsorption. In contrast, brush-hydrogels are stiffer and less hydrated, and the presence of crosslinks affects the entropy-driven, conformational barrier that hinders the surface interaction of biomolecules with brushes. This leads to the physisorption of proteins at low concentrations of short crosslinks. At higher contents of DEGDMA or in the presence of longer TEGDMA-based crosslinks, brush-hydrogels recover their antifouling properties due to the increase in interfacial water association by the higher concentration of ethylene glycol (EG) units.

Ultra-low fouling and high antibody loading zwitterionic hydrogel coatings for sensing and detection in complex media

For surface-based diagnostic devices to achieve reliable biomarker detection in complex media such as blood, preventing nonspecific protein adsorption and incorporating high loading of biorecognition elements are paramount. In this work, a novel method to produce nonfouling zwitterionic hydrogel coatings was developed to achieve these goals. Poly(carboxybetaine acrylamide) (pCBAA) hydrogel thin films (CBHTFs) prepared with a carboxybetaine diacrylamide crosslinker (CBAAX) were coated on gold and silicon dioxide surfaces via a simple spin coating process. The thickness of CBHTFs could be precisely controlled between 15 and 150nm by varying the crosslinker concentration, and the films demonstrated excellent long-term stability. Protein adsorption from undiluted human blood serum onto the CBHTFs was measured with surface plasmon resonance (SPR). Hydrogel thin films greater than 20nm exhibited ultra-low fouling (<5ng/cm(2)). In addition, the CBHTFs were capable of high antibody functionalization for specific biomarker detection without compromising their nonfouling performance. This strategy provides a facile method to modify SPR biosensor chips with an advanced nonfouling material, and can be potentially expanded to a variety of implantable medical devices and diagnostic biosensors.

STATEMENT OF SIGNIFICANCE

In this work, we developed an approach to realize ultra-low fouling and high ligand loading with a highly-crosslinked, purely zwitterionic, carboxybetaine thin film hydrogel (CBHTF) coating platform. The CBHTF on a hydrophilic surface demonstrated long-term stability. By varying the crosslinker content in the spin-coated hydrogel solution, the thickness of CBHTFs could be precisely controlled. Optimized CBHTFs exhibited ultra-low nonspecific protein adsorption below 5ng/cm(2) measured by a surface plasmon resonance (SPR) sensor, and their 3D architecture allowed antibody loading to reach 693ng/cm(2). This strategy provides a facile method to modify SPR biosensor chips with an advanced nonfouling material, and can be potentially expanded to a variety of implantable medical devices and diagnostic biosensors.

A New Route of Fucoidan Immobilization on Low Density Polyethylene and Its Blood Compatibility and Anticoagulation Activity

Beside biomaterials’ bulk properties, their surface properties are equally important to control interfacial biocompatibility. However, due to the inadequate interaction with tissue, they may cause foreign body reaction. Moreover, surface induced thrombosis can occur when biomaterials are used for blood containing applications. Surface modification of the biomaterials can bring enhanced surface properties in biomedical applications. Sulfated polysaccharide coatings can be used to avoid surface induced thrombosis which may cause vascular occlusion (blocking the blood flow by blood clot), which results in serious health problems. Naturally occurring heparin is one of the sulfated polysaccharides most commonly used as an anticoagulant, but its long term usage causes hemorrhage. Marine sourced sulfated polysaccharide fucoidan is an alternative anticoagulant without the hemorrhage drawback. Heparin and fucoidan immobilization onto a low density polyethylene surface after functionalization by plasma has been studied. Surface energy was demonstrated by water contact angle test and chemical characterizations were carried out by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Surface morphology was monitored by scanning electron microscope and atomic force microscope. Finally, their anticoagulation activity was examined for prothrombin time (PT), activated partial thromboplastin time (aPTT), and thrombin time (TT).

In vitro hemocompatibility on thin ceramic and hydrogel films deposited on polymer substrate performed in arterial flow conditions

Hydrogel coatings were stabilized by titanium carbonitride a-C:H:Ti:N buffer layers deposited directly onto the polyurethane (PU) substrate beneath a final hydrogel coating. Coatings of a-C:H:Ti:N were deposited using a hybrid method of pulsed laser deposition (PLD) and magnetron sputtering (MS) under high vacuum conditions. The influence of the buffer a-C:H:Ti:N layer on the hydrogel coating was analysed by means of a multi-scale microstructure study. Mechanical tests were performed at an indentation load of 5 mN using Berkovich indenter geometry. Haemocompatible analyses were performed in vitro using a blood flow simulator. The blood-material interaction was analysed under dynamic conditions. The coating fabrication procedure improved the coating stability due to the deposition of the amorphous titanium carbonitride buffer layer.

Photopolymerized poly(2-hydroxyethyl methacrylate)/poly(ε-caprolactone)/poly(ethylene glycol) system as a potential wound dressing material

Polymeric hydrogel systems based on poly(2-hydroxyethyl methacrylate), poly(ε-caprolactone), and poly(ethylene glycol) were prepared by photopolymerization using 2,4,6-trimethyl benzoyl diphenyl phosphine oxide as the photoinitiator. The structural details, morphology, and crystallinity were evaluated by Fourier transform infrared, scanning electron microscope, and X-ray diffraction analysis. The fluid uptake of the hydrogels was measured using swelling analysis. Based on a hemolysis assay, the prepared hydrogels were non-hemolytic. No attachment of fibroblasts to the hydrogel systems was observed. Stress–strain results indicated that the poly(2-hydroxyethyl methacrylate), poly(ε-caprolactone), and poly(ethylene glycol) hydrogel system (85:10:5) possessed better mechanical properties. Cytotoxic assessment by direct contact method of 85:10:5 systems found that the hydrogel was non-cytotoxic to L929 fibroblasts. This hydrophilic polymer system has a potential for wound dressing applications.

Hydration and chain entanglement determines the optimum thickness of poly(HEMA-co-PEG₁₀MA) brushes for effective resistance to settlement and adhesion of marine fouling organisms

Understanding how surface physicochemical properties influence the settlement and adhesion of marine fouling organisms is important for the development of effective and environmentally benign marine antifouling coatings. We demonstrate that the thickness of random poly(HEMA-co-PEG10MA) copolymer brushes affect antifouling behavior. Films of thicknesses ranging from 50 to 1000 Å were prepared via surface-initiated atom-transfer radical polymerization and characterized using infrared spectroscopy, ellipsometry, atomic force microscopy and contact angle measurements. The fouling resistance of these films was investigated by protein adsorption, attachment of the marine bacterium Cobetia marina, settlement and strength of attachment tests of zoospores of the marine alga Ulva linza and static immersion field tests. These assays show that the polymer film thickness influenced the antifouling performance, in that there is an optimum thickness range, 200-400 Å (dry thickness), where fouling of all types, as well as algal spore adhesion, was lower. Field test results also showed lower fouling within the same thickness range after 2 weeks of immersion. Studies by quartz crystal microbalance with dissipation and underwater captive bubble contact angle measurements show a strong correlation between lower fouling and higher hydration, viscosity and surface energy of the poly(HEMA-co-PEG10MA) brushes at thicknesses around 200-400 Å. We hypothesize that the reduced antifouling performance is caused by a lower hydration capacity of the polymer for thinner films, and that entanglement and crowding in the film reduces the conformational freedom, hydration capacity and fouling resistance for thicker films.

Polypeptoid brushes by surface-initiated polymerization of N-substituted glycine N-carboxyanhydrides

Polypeptoid brushes were synthesized by surface-initiated polymerization of N-substituted glycine N-carboxyanhydrides on self-assembled amine monolayers. Using the presented grafting-from approach, polypeptoid brush thicknesses of approximately 40 nm could be obtained as compared to previously reported brush thicknesses of 4 nm. Moreover, hydrophilic, hydrophobic and amphiphilic polymer brushes were realized which are expected to have valuable applications as nonfouling surfaces and as model or references systems for surface grafted polypeptides.

Influence of the molecular structure of surface-attached poly(N-alkyl acrylamide) coatings on the interaction of surfaces with proteins, cells and blood platelets

Blood protein adsorption and blood platelet adhesion onto surface-attached poly(alkylacrylamide) networks that exhibit small and systematic variations in chemical composition are investigated. The polymer coatings are generated by depositing a thin layer of benzophenone-group-containing copolymer onto a solid substrate, followed by photo crosslinking and simultaneous surface-attachment. The correlation of the swelling of the obtained surface-attached networks with the adsorption of blood proteins and cellular adhesion is studied. The swollen surface-attached layers are inert to blood proteins and platelet cells. These results suggest that the hydrogel-coated materials are promising candidates for the generation of hemocompatible surfaces.

NCO-sP(EO-stat-PO) coatings on gold sensors--a QCM study of hemocompatibility

The reliability of implantable blood sensors is often hampered by unspecific adsorption of plasma proteins and blood cells. This not only leads to a loss of sensor signal over time, but can also result in undesired host vs. graft reactions. Within this study we evaluated the hemocompatibility of isocyanate conjugated star shaped polytheylene oxide-polypropylene oxide co-polymers NCO-sP(EO-stat-PO) when applied to gold surfaces as an auspicious coating material for gold sputtered blood contacting sensors. Quartz crystal microbalance (QCM) sensors were coated with ultrathin NCO-sP(EO-stat-PO) films and compared with uncoated gold sensors. Protein resistance was assessed by QCM measurements with fibrinogen solution and platelet poor plasma (PPP), followed by quantification of fibrinogen adsorption. Hemocompatibility was tested by incubation with human platelet rich plasma (PRP). Thrombin antithrombin-III complex (TAT), β-thromboglobulin (β-TG) and platelet factor 4 (PF4) were used as coagulation activation markers. Furthermore, scanning electron microscopy (SEM) was used to visualize platelet adhesion to the sensor surfaces. Compared to uncoated gold sensors, NCO-sP(EO-stat-PO) coated sensors revealed significant better resistance against protein adsorption, lower TAT generation and a lower amount of adherent platelets. Moreover, coating with ultrathin NCO-sP(EO-stat-PO) films creates a cell resistant hemocompatible surface on gold that increases the chance of prolonged sensor functionality and can easily be modified with specific receptor molecules.

Improvement of interfacial adhesion of biodegradable polymers coated on metal surface by nanocoupling

A method of securing the adhesion of biodegradable polymer coating was investigated for drug-eluting metal stents, using surface-initiated ring-opening polymerization (SI-ROP) of L-lactide. Introduction of oligolactide on the stainless steel (SS) surface was successful and the thickness of the oligolactide grafts remained on the nanometer scale, as determined by ellipsometry. The presence of an oligolactide graft was also identified using attenuated total reflection-Fourier transform infrared (ATR-FTIR) and electron spectroscopy for chemical analysis (ESCA). On top of the grafts, poly(D,L-lactide-co-glycolide) (PLGA) coating was carried out on different substrates such as SS control, plasma-treated SS, and lactide-grafted (referred to as a nanocoupled) SS using electrospraying. When the adhesion forces were measured with a scratch tester, the nanocoupled SS showed the strongest interfacial adhesion between polymer coating layer and metal substrate. The outcome of the peel-off test was also consistent with the result of the scratch test. When degradation behavior of the polymer coating in vitro was examined for up to 4 weeks in a continuous fluid flow, the SEM images demonstrated that polymer degradation was obvious due to hydration and swelling of the polymer matrix. Although the matrix completely disappeared after 4 weeks for SS control and plasma-treated substrates, the nanocoupled SS was persistent with some polymer matrix. In addition, the release profiles of SRL-loaded PLGA coating appeared slightly different between control and nanocoupled groups. This work suggested that the concept of nanocoupling remarkably improved the interfacial adhesion stability between metal surface and polymer layer and controlled drug release, and showed the feasibility of drug-eluting stents.

In situ forming, metal-adhesive heparin hydrogel surfaces for blood-compatible coating

Durable and blood-compatible coating of metallic biomaterials remains a major issue in biomedical fields despite its long history of development. In this study, in situ forming, metal-adhesive heparin hydrogels were developed to coat metallic substrates to enhance blood compatibility. The hydrogels are composed of metal-adhesive and enzyme-reactive amphiphilic block copolymer (Tetronic-tyramine/dopamine; TTD) and enzyme-reactive heparin derivatives (heparin-tyramine or heparin-polyethylene glycol-tyramine), which are cross-linkable in situ via an enzyme reaction. The combinations of heparin and Tetronic formed hydrogels with relatively high mechanical strengths of 300-5000 Pa within several tens of seconds; this was also confirmed by observing a dried porous structure as coated on a metal surface. The introduction of dopamine to the hydrogel network enhanced the durability of the hydrogel layers coated on metal, such that more than 60% heparin remained for 7 days. Compared to bare metal surfaces, hydrogel-coated metal surfaces exhibited significantly enhanced blood compatibility. Reduced fibrinogen adsorption and platelet adhesion showed that blood compatibility was 3-5-fold-enhanced on coated hydrogel layers than on the bare metal surface. In conclusion, hydrogels containing heparin and dopamine prepared by enzyme reaction have the potential to be an alternative coating method for enhancing blood compatibility of metallic biomaterials.

Patterned polymer carpets

For the development of polymer carpets as active devices for micro- and nanotechnology, a control of the polymer carpet morphology and especially control of the stimulus responsive polymer brush is needed. Here, we report on the first example for the fabrication of patterned polymer carpets. On a two-dimensional framework of fully crosslinked and chemically patterned nanosheets, polymer brushes of styrene and 4-vinyl pyridine were grafted by self-initiated surface photopolymerization and photografting (SIPGP). It was found that polymer grafting by SIPGP occurred over the entire nanosheets but with a preferred grafting on the amino functionalized nanosheet areas. This results in continuous polymer carpets with an intact nanosheet framework but with amplification of the chemical patterning into a three dimensional topography of the grafted polymer brush. In the case of negative patterned nanosheets, the patterned carpet could be prepared as freestanding ultrathin membranes. Furthermore, swelling experiments with poly(4-vinyl pyridine) carpets showed that the patterns induces a directional buckling of the flexible polymer carpet. This may open the possibility of the development of micro- or nanoactuator devices with anisotropic responds upon environmental changes.