Functional ferrocene polymer multilayer coatings for implantable medical devices: Biocompatible, antifouling, and ROS-sensitive controlled release of therapeutic drugs

Bacterial infections and the formation of biofilms on the surface of implantable medical devices are critical issues that cause device failure. Implantable medical devices, such as drug delivery technologies, offer promising benefits for targeted and prolonged drug release, but a number of common disadvantages arise that include inadequate release and side effects. Organic film coatings for antifouling and drug delivery are expected to overcome these challenges. Ferrocene polymer-based multifunctional multilayer films were prepared to control the reactive oxygen species (ROS)-responsive release of therapeutic agents while maintaining an antifouling effect and improving biocompatibility. Polymers based on ferrocene and polyethylene glycol were prepared by controlling the molar ratio of carboxylate and amine groups. Layer-by-layer deposition was optimized to achieve the linear growth and self-assembly of dense and stable films. Outstanding anti-biofilm activity (~91% decrease) could be achieved and the films were found to be blood compatible. Importantly, the films effectively incorporated hydrophobic drugs and exhibited dual-responsive drug release at low pH and under ROS conditions at physiological pH. Drug delivery to MCF-7 breast cancer cells was achieved using a Paclitaxel loaded film, which exhibited an anticancer efficacy of 62%. STATEMENT OF SIGNIFICANCE: Healthcare associated infection is caused by the formation of a biofilm by bacteria on the surface of a medical device. In order to solve this, extensive research has been conducted on many coating technologies. Also, a method of chemical treatment by releasing the drug when it enters the body by loading the drug into the coating film is being studied. However, there is still a lack of technology that can achieve both functions of preventing biofilm production and drug delivery. Therefore, in this study, a multilayer thin film that supports drug and inhibits biofilm formation was prepared through Layer-by-Layer coating of a polymer containing PEG to prevent adsorption. As such, it helps the design of multifunctional coatings for implantable medical devices.

New cross-linkable poly[bis(octafluoropentoxy) phosphazene] biomaterials: Synthesis, surface characterization, bacterial adhesion, and plasma coagulation responses

Biomaterial-associated microbial infection and thrombosis represent major issues to the success of long-term use of implantable blood-contacting medical devices. The development of new poly[bis(octafluoropentoxy) phosphazene (OFP) biomaterials provides new routes for combatting microbial infection and thrombosis. However, the limited mechanical properties of OFP to date render them unsuitable for application in medical devices and inhibit any attempts at subsequent surface topography modification. In this study, we synthesized cross-linkable OFPs (X-OFPs) with the different degrees of cross-linking in an effort to improve the mechanical properties. The results showed that the surface chemistry and surface topography of X-OFPs do not change significantly, but the surface mechanical stiffness increased after cross-linking. Atomic force microscopic phase images showed that the polymer phase separation structures changed due to cross-linking. Experiments with three bacterial strains: Staphylococcal epidermidis, Staphylococcal aureus, and Pseudomonas aeruginosa showed that bacterial adhesion was significantly decreased on the OFP and X-OFPs for both the pre-cross-linked and cross-linked as compared to polyurethane biomaterials. Furthermore, bacterial adhesions were lower on X-OFP surfaces than on pre-cross-linked materials, suggesting that mechanical stiffness is an important parameter influencing bacterial adhesion. Blood plasma coagulation responses revealed longer coagulation times for OFP and X-OFP materials than on polyurethanes, indicating that the new cross-linked OFPs are resistant to plasma coagulation compared to currently used polyurethane biomaterials.

Quantifying single-platelet biomechanics: An outsider's guide to biophysical methods and recent advances

Platelets are the key cellular components of blood primarily contributing to formation of stable hemostatic plugs at the site of vascular injury, thus preventing excessive blood loss. On the other hand, excessive platelet activation can contribute to thrombosis. Platelets respond to many stimuli that can be of biochemical, cellular, or physical origin. This drives platelet activation kinetics and plays a vital role in physiological and pathological situations. Currently used bulk assays are inadequate for comprehensive biomechanical assessment of single platelets. Individual platelets interact and respond differentially while modulating their biomechanical behavior depending on dynamic changes that occur in surrounding microenvironments. Quantitative description of such a phenomenon at single-platelet regime and up to nanometer resolution requires methodological approaches that can manipulate individual platelets at submicron scales. This review focusses on principles, specific examples, and limitations of several relevant biophysical methods applied to single-platelet analysis such as micropipette aspiration, atomic force microscopy, scanning ion conductance microscopy and traction force microscopy. Additionally, we are introducing a promising single-cell approach, real-time deformability cytometry, as an emerging biophysical method for high-throughput biomechanical characterization of single platelets. This review serves as an introductory guide for clinician scientists and beginners interested in exploring one or more of the above-mentioned biophysical methods to address outstanding questions in single-platelet biomechanics.

Blood coagulation response and bacterial adhesion to biomimetic polyurethane biomaterials prepared with surface texturing and nitric oxide release

A dual functional polyurethane (PU) film that mimics aspects of blood vessel inner surfaces by combining surface texturing and nitric oxide (NO) release was fabricated through a soft lithography two-stage replication process. The fabrication of submicron textures on the polymer surface was followed by solvent impregnation with the NO donor, S-nitroso-N-acetylpenicillamine (SNAP). An in vitro plasma coagulation assay showed that the biomimetic surface significantly increased the plasma coagulation time and also exhibited reduced platelet adhesion and activation, thereby reducing the risk of blood coagulation and thrombosis. A contact activation assay for coagulation factor XII (FXII) demonstrated that both NO release and surface texturing also reduced FXII contact activation, which contributes to the inhibition of plasma coagulation. The biomimetic surface was also evaluated for bacterial adhesion in plasma and results demonstrate that this combined strategy enables a synergistic effect to reduce bacterial adhesion of Staphylococcus epidermidis, Staphylococcus aureus, and Pseudomonas aeruginosa microorganisms. The results strongly suggest that the biomimetic modification with surface texturing and NO release provides an effective approach to improve the biocompatibility of polymeric materials in combating thrombosis and microbial infection. STATEMENT OF SIGNIFICANCE: (1) Developed a dual functional polyurethane (PU) film that mimics blood vessel inner surface by combining surface texturing and nitric oxide (NO) release for combatting biomaterial associated thrombosis and microbial infection. (2) Studied the blood coagulation response and bacterial adhesion to such biomimetic PU surfaces, and demonstrated that the combination of surface texturing and NO release synergistically reduced the platelet adhesion and bacterial adhesion in plasma, providing an effective approach to improve the biocompatibility of biomaterials used in blood-contacting medical devices. (3) The NO releasing surface significantly inhibits the plasma coagulation via the reduction of contact activation of FXII, indicating the multifunctional roles of NO in improving the biocompatibility of biomaterials in blood-contacting medical devices.

Octadecyl Chains Immobilized onto Hyaluronic Acid Coatings by Thiol-ene "Click Chemistry" Increase the Surface Antimicrobial Properties and Prevent Platelet Adhesion and Activation to Polyurethane

Infection and thrombus formation are still the biggest challenges for the success of blood contact medical devices. This work aims the development of an antimicrobial and hemocompatible biomaterial coating through which selective binding of albumin (passivant protein) from the bloodstream is promoted and, thus, adsorption of other proteins responsible for bacterial adhesion and thrombus formation can be prevented. Polyurethane (PU) films were coated with hyaluronic acid, an antifouling agent, that was previously modified with thiol groups (HA-SH), using polydopamine as the binding agent. Octadecyl acrylate (C18) was used to attract albumin since it resembles the circulating free fatty acids and albumin is a fatty acid transporter. Thiol-ene "click chemistry" was explored for C18 immobilization on HA-SH through a covalent bond between the thiol groups from the HA and the alkene groups from the C18 chains. Surfaces were prepared with different C18 concentrations (0, 5, 10, and 20%) and successful immobilization was demonstrated by scanning electron microscopy (SEM), water contact angle determinations, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The ability of surfaces to bind albumin selectively was determined by quartz crystal microbalance with dissipation (QCM-D). Albumin adsorption increased in response to the hydrophobic nature of the surfaces, which augmented with C18 saturation. HA-SH coating reduced albumin adsorption to PU. C18 immobilized onto HA-SH at 5% promoted selective binding of albumin, decreased Staphylococcus aureus adhesion and prevented platelet adhesion and activation to PU in the presence of human plasma. C18/HA-SH coating was established as an innovative and promising strategy to improve the antimicrobial properties and hemocompatibility of any blood contact medical device.

Surface modification strategies for combating catheter-related complications: recent advances and challenges

This review summarizes the progress made in addressing bacterial colonization and other surface-related complications arising from catheter use.

Protein adsorption, platelet adhesion, and bacterial adhesion to polyethylene-glycol-textured polyurethane biomaterial surfaces

Traditional strategies for surface modification to enhance the biocompatibility of biomaterials often focus on a single route utilizing either chemical or physical approaches. This study combines the chemical and physical treatments as applied to poly(urethane urea) (PUU) biomaterials to enhance biocompatibility at the interface for inhibiting platelet-related thrombosis or bacterial adhesion-induced microbial infections. PUU films were first textured with submicron patterns by a soft lithography two-stage replication process, and then were grafted with polyethylene glycol (PEG). A series of biological response experiments including protein adsorption, platelet adhesion/activation, and bacterial adhesion/biofilm formation showed that PEG-grafted submicron textured biomaterial surfaces were resistant to protein adsorption, and greatly increased the efficiency in reducing both platelet adhesion/activation and bacterial adhesion/biofilm formation due to the additive effects of physical topography and grafted PEG. Results suggest that a combination of chemical modification and surface texturing will be more efficient in preventing biomaterial-associated thrombosis and infection of biomaterials. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 668-678, 2017.

Staphylococcus aureus Fibronectin-Binding Protein A Mediates Cell-Cell Adhesion through Low-Affinity Homophilic Bonds

Staphylococcus aureus is an important opportunistic pathogen which is a leading cause of biofilm-associated infections on indwelling medical devices. The cell surface-located fibronectin-binding protein A (FnBPA) plays an important role in the accumulation phase of biofilm formation by methicillin-resistant S. aureus (MRSA), but the underlying molecular interactions are not yet established. Here, we use single-cell and single-molecule atomic force microscopy to unravel the mechanism by which FnBPA mediates intercellular adhesion. We show that FnBPA is responsible for specific cell-cell interactions that involve the FnBPA A domain and cause microscale cell aggregation. We demonstrate that the strength of FnBPA-mediated adhesion originates from multiple low-affinity homophilic interactions between FnBPA A domains on neighboring cells. Low-affinity binding by means of FnBPA may be important for biofilm dynamics. These results provide a molecular basis for the ability of FnBPA to promote cell accumulation during S. aureus biofilm formation. We speculate that homophilic interactions may represent a generic strategy among staphylococcal cell surface proteins for guiding intercellular adhesion. As biofilm formation by MRSA strains depends on proteins rather than polysaccharides, our approach offers exciting prospects for the design of drugs or vaccines to inhibit protein-dependent intercellular interactions in MRSA biofilms.

IMPORTANCE

Staphylococcus aureus is a human pathogen that forms biofilms on indwelling medical devices, such as central venous catheters and prosthetic joints. This leads to biofilm infections that are difficult to treat with antibiotics because many cells within the biofilm matrix are dormant. The fibronectin-binding proteins (FnBPs) FnBPA and FnBPB promote biofilm formation by clinically relevant methicillin-resistant S. aureus (MRSA) strains, but the molecular mechanisms involved remain poorly understood. We used atomic force microscopy techniques to demonstrate that FnBPA mediates cell-cell adhesion via multiple, low-affinity homophilic bonds between FnBPA A domains on adjacent cells. Therefore, FnBP-mediated homophilic interactions represent an interesting target to prevent MRSA biofilms. We propose that such homophilic mechanisms may be widespread among staphylococcal cell surface proteins, providing a means to guide intercellular adhesion and biofilm accumulation.

Staphylococcus epidermidis Affinity for Fibrinogen-Coated Surfaces Correlates with the Abundance of the SdrG Adhesin on the Cell Surface

Staphylococcus epidermidis is a world-leading pathogen in healthcare facilities, mainly causing medical device-associated infections. These nosocomial diseases often result in complications such as bacteremia, fibrosis, or peritonitis. The virulence of S. epidermidis relies on its ability to colonize surfaces and develop thereupon in the form of biofilms. Bacterial adherence on biomaterials, usually covered with plasma proteins after implantation, is a critical step leading to biofilm infections. The cell surface protein SdrG mediates adhesion of S. epidermidis to fibrinogen (Fg) through a specific "dock, lock, and latch" mechanism, which results in greatly stabilized protein-ligand complexes. Here, we combine single-molecule, single-cell, and whole population assays to investigate the extent to which the surface density of SdrG determines the ability of S. epidermidis clinical strains HB, ATCC 35984, and ATCC 12228 to bind to Fg-coated surfaces. Strains that showed enhanced adhesion on Fg-coated polydimethylsiloxane (PDMS) were characterized by increased amounts of SdrG proteins on the cell surface, as observed by single-molecule analysis. Consistent with previous reports showing increased expression of SdrG following in vivo exposure, this work provides direct evidence that abundance of SdrG on the cell surface of S. epidermidis strains dramatically improves their ability to bind to Fg-coated implanted medical devices.

The role of plasma, albumin, and fibronectin in Staphylococcus epidermidis adhesion to polystyrene surface

The influence of soluble and immobilized plasma, albumin, and fibronectin (Fn) on the adhesion of three Staphylococcus epidermidis strains to polystyrene was investigated. Both soluble and immobilized plasma and albumin cause to 7-fold reduction of the amounts of adhered cells, regardless of the strain used. The soluble Fn exhibited the adhesion for one strain and did not affect the bacterial sorption for remaining strains, whereas on Fn-coated polystyrene two of the three strains showed about 1.5-fold increase in the number of adsorbed bacteria. The plasma- and albumin-coated surfaces became much more hydrophilic as the contact angle changed from 78 ± 2° for control to 18 ± 2° for plasma and 21 ± 3° for albumin. The ligand-receptor specific interactions strains S. epidermidis with Fn-coated surfaces were proved by measuring the adhesion forces between cell surface and Fn-coated AFM tip. The surface roughness measured using AFM after the plasma and proteins immobilization was changed within 10 nm and not correlate with changes in bacterial adhesion.