Whole blood coagulation on protein adsorption-resistant PEG and peptide functionalised PEG-coated titanium surfaces

Surface Engineering for Endothelium-Mimicking Functions to Combat Infection and Thrombosis in Extracorporeal Life Support Technologies

Blood-contacting medical devices routinely fail from the cascading effects of biofouling toward infection and thrombosis. Nitric oxide (NO) is an integral part of endothelial homeostasis, maintaining platelet quiescence and facilitating oxidative/nitrosative stress against pathogens. Recently, it is shown that the surface evolution of NO can mediate cell-surface interactions. However, this technique alone cannot prevent the biofouling inherent in device failure with dynamic blood-contacting applications. This work proposes an endothelium-mimicking surface design pairing controlled NO release with an inherently antifouling polyethylene glycol interface (NO+PEG). This simple, robust, and scalable platform develops surface-localized NO availability with surface hydration, leading to a significant reduction in protein adsorption as well as bacteria/platelet adhesion. Further in vivo thrombogenicity studies show a decrease in thrombus formation on NO+PEG interfaces, with preservation of circulating platelet and white blood cell counts, maintenance of activated clotting time, and reduced coagulation cascade activation. It is anticipated that this bio-inspired surface design will enable a facile alternative to existing surface technologies to address clinical manifestations of infection and thrombosis in dynamic blood-contacting environments.

Steps Toward Recapitulating Endothelium: A Perspective on the Next Generation of Hemocompatible Coatings

Endothelium, the lining in this blood vessel, orchestrates three main critical functions such as protecting blood components, modulating of hemostasis by secreting various inhibitors, and directing clot digestion (fibrinolysis) by activating tissue plasminogen activator. No other surface can perform these tasks; thus, the contact of blood and blood-contacting medical devices inevitably leads to the activation of coagulation, often causing device failure, and thromboembolic complications. This perspective, first, discusses the biological mechanisms of activation of coagulation and highlights the efforts of advanced coatings to recapitulate one characteristic of endothelium, hereafter single functions of endothelium and noting necessity of the synergistic integration of its three main functions. Subsequently, it is emphasized that to overcome the challenges of blood compatibility an endothelium-mimicking system is needed, proposing a synergy of bottom-up synthetic biology, particularly synthetic cells, with passive- and bioactive surface coatings. Such integration holds promise for developing advanced biomaterials capable of recapitulating endothelial functions, thereby enhancing the hemocompatibility and performance of blood-contacting medical devices.

Green Solvent-Based Antifouling Polymer Brushes Demonstrate Excellent Hemocompatibility

Medical devices are crucial for patient care, yet even the best biomaterials lead to infections and unwanted activation of blood coagulation, potentially being life-threatening. While hydrophilic polymer brushes are the best coatings to mitigate these issues, their reliance on fossil raw materials underscores the urgency of bio-based alternatives. In this work, we introduce polymer brushes of a green solvent-based monomer, prohibiting protein adsorption, bacterial colonization, and blood clot formation at the same level as fossil-based polymer brushes. The polymer brushes are composed of N,N-dimethyl lactamide acrylate (DMLA), can be polymerized in a controlled manner, and show strong hydrophilicity as determined by thermodynamic analysis of the surface tension components. The contact of various challenging protein solutions results in repellency on the poly(DMLA) brushes. Furthermore, the poly(DMLA) brushes completely prevent the adhesion and colonization of Escherichia coli. Remarkably, upon blood contact, the poly(DMLA) brushes successfully prevent the formation of a fibrin network and leukocyte adhesion on the surface. While showcasing excellent antifouling properties similar to those of N-hydroxypropyl methacrylamide (HPMA) polymer brushes as one of the best antifouling coatings, the absence of hydroxyl groups prevents activation of the complement system in blood. We envision the polymer brushes to contribute to the future of hemocompatible coatings.

The Surface of a PMP Hollow Fiber Membrane Was Modified with a Diamond-like Carbon Film to Enhance the Blood Compatibility of an Artificial Lung Membrane

The contact between the blood and the surface of medical materials causes a series of rejection reactions. In this process, the plasma protein is adsorbed to the surface of materials within seconds and binds to glycoprotein receptors on platelets, causing platelet activation, coagulation cascade, and complement activation to form thrombus, which greatly limits the application of medical materials. In our work, the surface of poly(4-methyl-1-pentene) hollow fiber membranes (PMP HFMs) was coated with a diamond-like carbon (DLC) film by the ion plating method. The blood compatibility of the DLC coating was evaluated by protein adsorption, platelet adhesion, clotting time, red blood cell (RBCs) hemolysis, dynamic coagulation, and extracorporeal blood circulation tests. Compared with the unmodified PMP membrane, the DLC film could effectively reduce protein adsorption and platelet adhesion and prolong the coagulation time. The DLC coating showed BSA adsorption of as low as 0.53 μg/cm2 as well as a long activated partial thromboplastin time (APTT) value of 71.84 s. Furthermore, the PMP membrane modified with the DLC coating was used for extracorporeal blood circulation without thrombosis forming within 28 days. The DLC coating is one of the most promising medical coatings as an artificial lung membrane in extracorporeal membrane oxygenation (ECMO) equipment.

Mesenchymal Migration on Adhesive-Nonadhesive Alternate Surfaces in Macrophages

Mesenchymal migration usually happens on adhesive substrates, while cells adopt amoeboid migration on low/nonadhesive surfaces. Protein-repelling reagents, e.g., poly(ethylene) glycol (PEG), are routinely employed to resist cell adhering and migrating. Contrary to these perceptions, this work discovers a unique locomotion of macrophages on adhesive-nonadhesive alternate substrates in vitro that they can overcome nonadhesive PEG gaps to reach adhesive regions in the mesenchymal mode. Adhering to extracellular matrix regions is a prerequisite for macrophages to perform further locomotion on the PEG regions. Podosomes are found highly enriched on the PEG region in macrophages and support their migration across the nonadhesive regions. Increasing podosome density through myosin IIA inhibition facilitates cell motility on adhesive-nonadhesive alternate substrates. Moreover, a developed cellular Potts model reproduces this mesenchymal migration. These findings together uncover a new migratory behavior on adhesive-nonadhesive alternate substrates in macrophages.

Investigation of heparin-loaded poly(ethylene glycol)-based hydrogels as anti-thrombogenic surface coatings for extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO), a critical life-sustaining tool, faces significant challenges for the maintenance of normal haemostasis due to the large volume of circulating blood continuously in contact with artificial surfaces, hyperoxia and excessive shear stresses of the extracorporeal circuit. From a biomaterials perspective, it has been hypothesised that drug eluting coatings composed of haemocompatible hydrogels loaded with an anticoagulant drug could potentially enhance the haemocompatibility of the circuit. Poly(ethylene glycol) (PEG) has been well established as a biocompatible and anti-fouling material with wide biomedical application. Unfractionated heparin is the most commonly used anticoagulant for ECMO. In the present study, the feasibility of using heparin-loaded PEG-based hydrogels as anti-thrombogenic surface coatings for ECMO was investigated. The hydrogels were synthesised by photopolymerisation using poly(ethylene glycol) diacrylate (PEGDA) as the crosslinking monomer and poly(ethylene glycol) methacrylate (PEGMA) as the hydrophilic monomer, with heparin loaded into the pre-gel solution. Factors which could affect the release of heparin were investigated, including the ratio of PEGDA/PEGMA, water content, loading level of heparin and the flow of fluid past the hydrogel. Our results showed that increased crosslinker content and decreased water content led to slower heparin release. The hydrogels with water contents of 60 wt% and 70 wt% could achieve a sustained heparin release by adjusting the ratio of PEGDA/PEGMA. The anticoagulation efficacy of the released heparin was evaluated by measuring the activated clotting time of whole blood. The hydrogels with desirable heparin release profiles were prepared onto poly(4-methyl-1-pentene) (PMP) films with the same chemical composition as the PMP ECMO membranes. The coatings showed sustained heparin release with a cumulative release of 70-80% after 7 days. Haemocompatibility tests demonstrated that PEG hydrogel coatings significantly reduced platelet adhesion and prolonged plasma recalcification time. These results suggest that heparin-loaded PEG hydrogels are potential anti-thrombogenic coatings for ECMO.

Bioinspired ultra-low fouling coatings on medical devices to prevent device-associated infections and thrombosis

Addressing thrombosis and biofouling of indwelling medical devices within healthcare institutions is an ongoing problem. In this work, two types of ultra-low fouling surfaces (i.e., superhydrophobic and lubricant-infused slippery surfaces) were fabricated to enhance the biocompatibility of commercial medical grade silicone rubber (SR) tubes that are widely used in clinical care. The superhydrophobic (SH) coatings on the tubing substrates were successfully created by dip-coating in superhydrophobic paints consisting of polydimethylsiloxane (PDMS), perfluorosilane-coated hydrophobic zinc oxide (ZnO) and copper (Cu) nanoparticles (NPs) in tetrahydrofuran (THF). The SH surfaces were converted to lubricant-infused slippery (LIS) surfaces through the infusion of silicone oil. The anti-biofouling properties of the coatings were investigated by adsorption of platelets, whole blood coagulation, and biofilm formation in vitro. The results revealed that the LIS tubes possess superior resistance to clot formation and platelet adhesion than uncoated and SH tubes. In addition, bacterial adhesion was investigated over 7 days in a drip-flow bioreactor, where the SH-ZnO-Cu tube and its slippery counterpart significantly reduced bacterial adhesion and biofilm formation of Escherichia coli relative to control tubes (>5 log10 and >3 log10 reduction, respectively). The coatings also demonstrated good compatibility with fibroblast cells. Therefore, the proposed coatings may find potential applications in high-efficiency on-demand prevention of biofilm and thrombosis formation on medical devices to improve their biocompatibility and reduce the risk of complications from medical devices.

Switchable β-lactoglobulin (BLG) adsorption on protein resistant oligo (ethylene glycol) (OEG) self-assembled monolayers (SAMs)

HYPOTHESIS

Although protein adsorption at an interface is very common and important in biology and biotechnology, it is still not fully understood - mainly due to the intricate balance of forces that ultimately control it. In food processing (and medicine), controlling and manipulating protein adsorption, as well as avoiding protein adsorption (biofilm formation or membrane fouling) by the production of protein-resistant surfaces is of substantial interest. A major factor conferring resistance towards protein adsorption to a surface is the presence of tightly bound water molecules, as is the case in oligo ethylene glycol (OEG)-terminated self-assembled monolayers (SAMs). Due to strong attractive protein-protein and protein-surface interactions observed in systems containing trivalent salt ions, we hypothesize that these conditions may lead to a breakdown of protein resistance in OEG SAMs.

EXPERIMENTS

We studied the adsorption behavior of BLG in the presence of a lanthanum(III) chloride (LaCl₃) at concentrations of 0, 0.1, 0.8 and 5.0 mM on normally protein resistant triethylene glycol-termianted (EG3) SAMs on a gold surface. We used quartz-crystal microbalance with dissipation (QCM-D) and neutron reflectivity (NR) to characterize the morphology of the interfacial region of the SAM.

FINDINGS

We demonstrate that the protein resistance of the EG3 SAM breaks down beyond a threshold salt concentration c^∗ and mirrors the bulk behaviour of this system, showing reduced adsorption beyond a second critical salt concentration c^∗∗. These results demonstrate for the first time the controlled switching of the protein-resistant properties of this type of SAM by the addition of trivalent salt.

Protein Removal from Hydrogels through Repetitive Surface Degradation

Suppression of protein adsorption is a necessary property for materials used in the living body. In this study, thermoresponsive and degradable hydrogels were prepared by the radical polymerization of 2-methylene-1,3-dioxepane, 2-hydroxyethyl acrylate (HEA), and poly(ethylene glycol) monomethacrylate (PEGMA). The prepared hydrogels re-exposed PEG-grafted chains to the interface through surface degradation, which was confirmed by the maintenance of the chemical composition of the hydrogel surfaces after hydrolysis. Notably, adsorbed proteins can be removed from the hydrogel surfaces through hydrogel surface degradation at least thrice.

Surface modification strategies to improve titanium hemocompatibility: a comprehensive review

Titanium and its alloys are widely used in different biomaterial applications due to their remarkable mechanical properties and bio-inertness. However, titanium-based materials still face some challenges, with an emphasis on hemocompatibility. Blood-contacting devices such as stents, heart valves, and circulatory devices are prone to thrombus formation, restenosis, and inflammation due to inappropriate blood-implant surface interactions. After implantation, when blood encounters these implant surfaces, a series of reactions takes place, such as protein adsorption, platelet adhesion and activation, and white blood cell complex formation as a defense mechanism. Currently, patients are prescribed anticoagulant drugs to prevent blood clotting, but these drugs can weaken their immune system and cause profound bleeding during injury. Extensive research has been done to modify the surface properties of titanium to enhance its hemocompatibility. Results have shown that the modification of surface morphology, roughness, and chemistry has been effective in reducing thrombus formation. The main focus of this review is to analyze and understand the different modification techniques on titanium-based surfaces to enhance hemocompatibility and, consequently, recognize the unresolved challenges and propose scopes for future research.

A rechargeable anti-thrombotic coating for blood-contacting devices

Despite the potential of anti-thrombogenic coatings, including heparinized surfaces, to improve the performance of blood-contacting devices, the inevitable deterioration of bioactivity remains an important factor in device failure and related thrombotic complications. As a consequence, the ability to restore the bioactivity of a surface coating after implantation of a blood-contacting device provides a potentially important strategy to enhance its clinical performance. Here, we report the regeneration of a multicomponent anti-thrombogenic coating through use of an evolved sortase A to mediate reversible transpeptidation. Both recombinant thrombomodulin and a chemoenzymatically synthesized ultra-low molecular weight heparin were repeatedly and selectively immobilized or removed in a sequential, alternating, or simultaneous manner. The generation of activated protein C (aPC) and inhibition of activated factor X (FXa) was consistent with the molecular composition of the surface. The fabrication of a rechargeable anti-thrombogenic surface was demonstrated on an expanded polytetrafluoroethylene (ePTFE) vascular graft with reconstitution of the surface bound coating 4 weeks after in vivo implantation in a rat model.

Zwitterionic PMCP-functionalized titanium surface resists protein adsorption, promotes cell adhesion, and enhances osteogenic activity

Titanium (Ti) has excellent biocompatibility and corrosion resistance and is widely used as a biomedical material for orthopedic implants. However, the bare Ti surface limits cell adhesion without biological activity and promotes unnecessary protein adsorption, which can activate the coagulation pathway with blood-contacting devices. To improve the antifouling and biological activity of Ti, zwitterionic poly[2-(methacryloyloxy)ethyl choline phosphate] (PMCP) was used to modify the Ti surface via surface-initiated atom transfer radical polymerization. The Ti-PMCP surface reduced bovine serum albumin and fibrinogen adsorption owing to the zwitterionic antifouling property. Ti-PMCP is involved in the unique interaction between PMCP on the Ti surface and phosphate choline on cell membranes, and therefore, the Ti-PMCP surface can promote the adhesion and proliferation of MC3T3-e1 cells and bone marrow mesenchymal cells (BMSCs). In addition, the Ti-PMCP surface was effective in promoting the osteogenic differentiation of MC3T3-e1 cells and BMSCs because the phosphate group in MCP can stimulate osteogenic signaling pathways. Therefore, the PMCP-modified Ti surface can resist protein adsorption and promote the adhesion, proliferation, and differentiation of osteoblast-related cells and has great potential in bone tissue engineering.

Endothelial Cells Differentiated from Porcine Epiblast Stem Cells

Pluripotent stem cells (PSCs) have the ability of self-renewal that can retain the characteristics of the mother cell, and of pluripotency that can differentiate into several body types. PSCs typically include embryonic stem cells (ESCs) derived from the inner cell mass of the preimplantation embryo, and epiblast stem cells (EpiSCs) derived from the epiblast of postimplantation embryo. Although PSCs are able to be used by differentiation into endothelial cells as a potential treatment for vascular diseases, human ESCs and induced PSCs (iPSCs) are followed by ethical and safety issues. Pigs are anatomically and physiologically similar to humans. Therefore, the goal of this study was to establish an efficient protocol that differentiates porcine EpiSCs (pEpiSCs) into the endothelial cells for applying the treatment of human vascular diseases. As a result, alkaline phosphatase (AP)-negative (-) pEpiSCs cultured in endothelial cell growth basal medium-2 (EBM-2) differentiation medium in association with 50 ng/mL of vascular endothelial growth factor (VEGF) for 8 days were changed morphologically like the feature of endothelial cells, and expression of pluripotency-associated markers (OCT-3/4, NANOG, SOX2, and C-MYC) in porcine differentiated cells was significantly decreased (p < 0.05). Additionally, when pEpiSCs were cultured in EBM-2 + 50 ng/mL of VEGF, porcine differentiated cells represented a common endothelial cell marker positive (CD31+) but monocytes and lymphocytes marker negative (CD45-). Therefore, these results indicated that pEpiSCs cultured in EBM-2 + 50 ng/mL of VEGF culture condition were efficiently differentiated into endothelial cells for the treatment of blood vessel diseases.

The impact of antifouling layers in fabricating bioactive surfaces

Bioactive surfaces modified with functional peptides are critical for both fundamental research and practical application of implant materials and tissue repair. However, when bioactive molecules are tethered on biomaterial surfaces, their functions can be compromised due to unwanted fouling (mainly nonspecific protein adsorption and cell adhesion). In recent years, researchers have continuously studied antifouling strategies to obtain low background noise and effectively present the function of bioactive molecules. In this review, we describe several commonly used antifouling strategies and analyzed their advantages and drawbacks. Among these strategies, antifouling molecules are widely used to construct the antifouling layer of various bioactive surfaces. Subsequently, we summarize various structures of antifouling molecules and their surface grafting methods and characteristics. Application of these functionalized surfaces in microarray, biosensors, and implants are also introduced. Finally, we discuss the primary challenges associated with antifouling layers in fabricating bioactive surfaces and provide prospects for the future development of this field. STATEMENT OF SIGNIFICANCE: The nonspecific protein adsorption and cell adhesion will cause unwanted background "noise" on the surface of biological materials and detecting devices and compromise the performance of functional molecules and, therefore, impair the performance of materials and the sensitivity of devices. In addition, the selection of antifouling surfaces with proper chain length and high grafting density is also of great importance and requires further studies. Otherwise, the surface-tethered bioactive molecules may not function in their optimal status or even fail to display their functions. Based on these two critical issues, we summarize antifouling molecules with different structures, variable grafting methods, and diverse applications in biomaterials and biomedical devices reported in literature. Overall, we expect to shed some light on choosing the appropriate antifouling molecules in fabricating bioactive surfaces.

Polysiloxane Nanofilaments Infused with Silicone Oil Prevent Bacterial Adhesion and Suppress Thrombosis on Intranasal Splints

Like all biofluid-contacting medical devices, intranasal splints are highly prone to bacterial adhesion and clot formation. Despite their widespread use and the numerous complications associated with infected splints, limited success has been achieved in advancing their safety and surface biocompatibility, and, to date, no surface-coating strategy has been proposed to simultaneously enhance the antithrombogenicity and bacterial repellency of intranasal splints. Herein, we report an efficient, highly stable lubricant-infused coating for intranasal splints to render their surfaces antithrombogenic and repellent toward bacterial cells. Lubricant-infused intranasal splints were prepared by creating superhydrophobic polysiloxane nanofilament (PSnF) coatings using surface-initiated polymerization of n-propyltrichlorosilane (n-PTCS) and further infiltrating them with a silicone oil lubricant. Compared with commercially available intranasal splints, lubricant-infused, PSnF-coated splints significantly attenuated plasma and blood clot formation and prevented bacterial adhesion and biofilm formation for up to 7 days, the typical duration for which intranasal splints are kept. We further demonstrated that the performance of our engineered biointerface is independent of the underlying substrate and could be used to enhance the hemocompatibility and repellency properties of other medical implants such as medical-grade catheters.

Hierarchical Structures, with Submillimeter Patterns, Micrometer Wrinkles, and Nanoscale Decorations, Suppress Biofouling and Enable Rapid Droplet Digitization

Liquid repellant surfaces have been shown to play a vital role for eliminating thrombosis on medical devices, minimizing blood contamination on common surfaces as well as preventing non-specific adhesion. Herein, an all solution-based, easily scalable method for producing liquid repellant flexible films, fabricated through nanoparticle deposition and heat-induced thin film wrinkling that suppress blood adhesion, and clot formation is reported. Furthermore, superhydrophobic and hydrophilic surfaces are combined onto the same substrate using a facile streamlined process. The patterned superhydrophobic/hydrophilic surfaces show selective digitization of droplets from various solutions with a single solution dipping step, which provides a route for rapid compartmentalization of solutions into virtual wells needed for high-throughput assays. This rapid solution digitization approach is demonstrated for detection of Interleukin 6. The developed liquid repellant surfaces are expected to find a wide range of applications in high-throughput assays and blood contacting medical devices.

Single and multi-functional coating strategies for enhancing the biocompatibility and tissue integration of blood-contacting medical implants

Device-associated clot formation and poor tissue integration are ongoing problems with permanent and temporary implantable medical devices. These complications lead to increased rates of mortality and morbidity and impose a burden on healthcare systems. In this review, we outline the current approaches for developing single and multi-functional surface coating techniques that aim to circumvent the limitations associated with existing blood-contacting medical devices. We focus on surface coatings that possess dual hemocompatibility and biofunctionality features and discuss their advantages and shortcomings to providing a biocompatible and biodynamic interface between the medical implant and blood. Lastly, we outline the newly developed surface modification techniques that use lubricant-infused coatings and discuss their unique potential and limitations in mitigating medical device-associated complications.

Polyethylene Glycol Pulsed Electrodeposition for the Development of Antifouling Coatings on Titanium

Titanium dental implants are widely used for the replacement of damaged teeth. However, bacterial infections at the interface between soft tissues and the implant can impair the functionality of the device and lead to failure. In this work, the preparation of an antifouling coating of polyethylene glycol (PEG) on titanium by pulsed electrodeposition was investigated in order to reduce Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) adhesion while maintaining human fibroblast adhesion. Different pulsed conditions were prepared and characterized by contact angle, Focused Ion Beam (FIB), Fourier Transformed Infrared Spectroscopy in the Attenuated Total Reflectance mode (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). XPS tested fibronectin adsorption. S. aureus, E. coli and human fibroblast adhesion was tested in vitro in both mono and co-culture settings. Physicochemical characterization proved useful for confirming the presence of PEG and evaluating the efficiency of the coating methods. Fibronectin adsorption decreased for all of the conditions, but an adsorption of 20% when compared to titanium was maintained, which supported fibroblast adhesion on the surfaces. In contrast, S. aureus and E. coli attachment on coated surfaces decreased up to 90% vs. control titanium. Co-culture studies with the two bacterial strains and human fibroblasts showed the efficacy of the coatings to allow for eukaryotic cell adhesion, even in the presence of pre-adhered bacteria.

Lubricant-Infused PET Grafts with Built-In Biofunctional Nanoprobes Attenuate Thrombin Generation and Promote Targeted Binding of Cells

New surface coatings that enhance hemocompatibility and biofunctionality of synthetic vascular grafts such as expanded poly(tetrafluoroethylene) (ePTFE) and poly(ethylene terephthalate) (PET) are urgently needed. Lubricant-infused surfaces prevent nontargeted adhesion and enhance the biocompatibility of blood-contacting surfaces. However, limited success has been made in incorporating biofunctionality onto these surfaces and generating biofunctional lubricant-infused coatings that both prevent nonspecific adhesion and enhance targeted binding of biomolecules remains a challenge. Here, a new generation of fluorosilanized lubricant-infused PET surfaces with built-in biofunctional nanoprobes is reported. These surfaces are synthesized by starting with a self-assembled monolayer of fluorosilane that is partially etched using plasma modification technique, thereby creating a hydroxyl-terminated fluorosilanized PET surface. Simultaneously, silanized nanoprobes are produced by amino-silanizing anti-CD34 antibody in solution and directly coupling the anti-CD34-aminosilane nanoprobes onto the hydroxyl terminated, fluorosilanized PET surface. The PET surfaces are then lubricated, creating fluorosilanized biofunctional lubricant-infused PET substrates. Compared with unmodified PET surfaces, the designed biofunctional lubricant-infused PET surfaces significantly attenuate thrombin generation and blood clot formation and promote targeted binding of endothelial cells from human whole blood.

The blood compatibility challenge. Part 2: Protein adsorption phenomena governing blood reactivity

The adsorption of proteins is the initiating event in the processes occurring when blood contacts a "foreign" surface in a medical device, leading inevitably to thrombus formation. Knowledge of protein adsorption in this context has accumulated over many years but remains fragmentary and incomplete. Moreover, the significance and relevance of the information for blood compatibility are not entirely agreed upon in the biomaterials research community. In this review, protein adsorption from blood is discussed under the headings "agreed upon" and "not agreed upon or not known" with respect to: protein layer composition, effects on coagulation and complement activation, effects on platelet adhesion and activation, protein conformational change and denaturation, prevention of nonspecific protein adsorption, and controlling/tailoring the protein layer composition. STATEMENT OF SIGNIFICANCE: This paper is part 2 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

Nitric oxide-releasing vascular grafts: A therapeutic strategy to promote angiogenic activity and endothelium regeneration

Small-diameter vascular grafts (SDVGs) are associated with a high incidence of failure due to infection and obstruction. Although several vascular grafts are commercially available, specific anatomical differences of defect sites require patient-based design and fabrication. Design and fabrication of such custom-tailored grafts are possible with 3d-printing technology. The aim of this study is to develop 3d-printed SDVGs with a nitric oxide (NO)-releasing coating to improve the success rate of implantation. The SDVGs were printed from polylactic acid and coated with blending of 10 wt% S-nitroso-N-acetyl-D-penicillamine into the polymeric substrate consisting of poly (ethylene glycol) and polycaprolactone. Our results show that NO is released in the physiological range (0.5-4 × 10^-10 mol·cm^-2·min^-1) for 14 days and NO-releasing coating showed significant antibacterial potential against Gram-positive and Gram-negative strains. It was shown that both NO-releasing and control grafts are biocompatible in-vitro and in-vivo. Interestingly, the NO-releasing SDVGs dramatically enhanced ECs proliferation and significantly enhanced ECs migration in-vitro compared to control grafts. In addition, the NO-releasing SDVGs showed angiogenic potential in-vivo which can further prove the results of our in-vitro study. These findings are expected to facilitate tissue regeneration and integration of custom-made vascular implants with enhanced clinical success. STATEMENT OF SIGNIFICANCE: A series of 3d-printed small-diameter vascular grafts (SDVGs, <6 mm) with controlled release of nitric oxide (NO) were prepared to combine the advantages of 3D printing technology and NO-releasing systems. The resulting NO-releasing grafts were promisingly showing sustained NO release in the physiological range over a two weeks period. In addition to the evaluation of endothelial cell migration in-vitro, we implanted for the first time the NO-releasing vascular grafts in a chick chorioallantoic membrane (CAM) to investigate the effect of the prepared grafts on the angiogenesis in-vivo. The fabricated grafts also exhibited bactericidal properties which prevent the formation of a biofilm layer and can thereby enhance the chance of endothelialization on the surface. Taken together, the innovative combination of rapid and highly accurate 3d-printing technology as a patient-specific fabrication method with NO-releasing coating represents a promising approach to develop bactericidal SDVGs with improved endothelialization.

An Albumin Biopassive Polyallylamine Film with Improved Blood Compatibility for Metal Devices

Nowadays, a variety of materials are employed to make numerous medical devices, including metals, polymers, ceramics, and others. Blood-contact devices are one of the major classes of these medical devices, and they have been widely applied in clinical settings. Blood-contact devices usually need to have good mechanical properties to maintain clinical performance. Metal materials are one desirable candidate to fabricate blood-contact devices due to their excellent mechanical properties and machinability, although the blood compatibility of existing blood-contact devices is better than other medical devices, such as artificial joints and artificial crystals. However, blood coagulation still occurs when these devices are used in clinical settings. Therefore, it is necessary to develop a new generation of blood-contact devices with fewer complications, and the key factor is to develop novel biomaterials with good blood compatibility. In this work, one albumin biopassive polyallylamine film was successfully established onto the 316L stainless steel (SS) surface. The polyallylamine film was prepared by plasma polymerization in the vacuum chamber, and then polyallylamine film was annealed at 150 °C for 1 h. The chemical compositions of the plasma polymerized polyallylamine film (PPAa) and the annealed polyallylamine film (HT-PPAa) were characterized by Fourier transform infrared spectrum (FTIR). Then, the wettability, surface topography, and thickness of the PPAa and HT-PPAa were also evaluated. HT-PPAa showed increased stability when compared with PPAa film. The major amino groups remained on the surface of HT-PPAa after annealing, indicating that this could be a good platform for numerous molecules' immobilization. Subsequently, the bovine serum albumin (BSA) was immobilized onto the HT-PPAa surface. The successful introduction of the BSA was confirmed by the FTIR and XPS detections. The blood compatibility of these modified films was evaluated by platelets adhesion and activation assays. The number of the platelets that adhered on BSA-modified HT-PPAa film was significantly decreased, and the activation degree of the adhered platelets was also decreased. These data revealed that the blood compatibility of the polyallylamine film was improved after BSA immobilized. This work provides a facile and effective approach to develop novel surface treatment for new-generation blood-contact devices with improved hemocompatibility.

Bacterial Inhibition and Osteoblast Adhesion on Ti Alloy Surfaces Modified by Poly(PEGMA- r-Phosmer) Coating

We have synthesized and immobilized PEGMA₅₀₀-Phosmer to Ti6Al4V surfaces by a simple procedure to reduce bacteria-associated infection without degrading the cell response. Adhered bacteria coverage was lessened to 1% on polymer-coated surfaces when exposed to Escherichia coli, Staphylococcus epidermidis, and Streptococcus mutans. Moreover, PEGMA₅₀₀-Phosmer and homoPhosmer coatings presented better responses to MC3T3-E1 preosteoblast cells when compared with the results for PEGMA₂₀₀₀-Phosmer-coated and raw Ti alloy surfaces. The behavior of balancing bacterial inhibition and cell attraction of the PEGMA₅₀₀-Phosmer coating was explained by the grafted phosphate groups, with an appropriate PEG brush length facilitating greater levels of calcium deposition and further fibronectin adsorption when compared with that of the raw Ti alloy surface.

Electropolymerized hydrophilic coating on stainless steel for biomedical applications

Current metal implants (e.g. stents) covered with drug-eluting coatings are not robust for long-term usage. Other types and methods of coatings are needed, especially ones that are not prone to activity loss in vivo. In this paper, the method of stainless steel (SS) coating with poly(ethylene glycol) dimethacrylate (PEGDMA) with the use of electropolymerization (EP) is presented. The application of a specific and simple reaction mixture enabled the production of SS-PEGDMA materials that possessed a homogenous surface. The polymer coating was durable for 28 days of constant washing. The resulting materials were non-toxic and haemolysis did not occur after incubation with blood. Moreover, because the coating filled up scratches present on bare SS and hydrophilized the SS surface, it reduced fibrinogen adsorption five times in comparison to SS and, unlike on SS, no platelet activation was detected. The presented method is a very promising candidate for scale up due to its simplicity and low cost.

Regulation of macrophage polarization and promotion of endothelialization by NO generating and PEG-YIGSR modified vascular graft

As an effective clinic treatment for cardiovascular disease, vascular transplantation gains much acceptance recently. However, due to the acute thrombosis and intimal hyperplasia, long-term failure of synthetic grafts after implanted in small diameter blood vessel decelerates its commercial use. The continued acute inflammation and delayed endothelialization have been considered as fundamental reasons. To enhance the adhesion and organization of endothelial cells (ECs) and improve the vascular remodeling process, we have constructed a vascular graft based on electrospun polycaprolactone (PCL) matrix, on which organoselenium-immobilized polyethyleneimine (SePEI) for in situ nitric oxide (NO) generation and hyaluronic acid (HA) grafted with poly (ethylene glycol) (PEG) modified Tyr-Ile-Gly-Ser-Arg (YIGSR) for antifouling and EC adhesion were deposited through electrostatic layer-by-layer assembly. The in vitro results showed that SePEI deposited on the grafts could catalyze stable generation of NO. After in situ implantation in rats for 4 and 8weeks, the graft promoted the transformation of macrophages into an anti-inflammatory phenotype (M2), which helped endothelium remodeling. YIGSR on the outmost layer facilitated more rapid and organized EC adhesion compared to PCL and non-modified grafts. PEG polymer chain on the outmost layer mitigated nonspecific adsorption of undesirable blood components. In our study, we first demonstrated the regulation of macrophage polarization by an NO-generating vascular graft. The results indicated that the approach of anti-inflammatory macrophage polarization and enhanced endothelialization through NO generation and PEG-modified YIGSR in our study may provide a new perspective for the clinic application of cell-free small-diameter vascular grafts.

Blood Compatibility of ZrO₂ Particle Reinforced PEEK Coatings on Ti6Al4V Substrates

Titanium (Ti) and its alloys are widely used in biomedical devices. As biomaterials, the blood compatibility of Ti and its alloys is important and needs to be further improved to provide better functionality. In this work, we studied the suitability of zirconia (ZrO₂) particle reinforced poly-ether-ether-ketone (PEEK) coatings on Ti6Al4V substrates for blood-contacting implants. The wettability, surface roughness and elastic modulus of the coatings were examined. Blood compatibility tests were conducted by erythrocytes observation, hemolysis assay and clotting time of recalcified human plasma, to find out correlations between the microstructure of the ZrO₂-filled PEEK composite coatings and their blood compatibilities. The results suggested that adding ZrO₂ nanoparticles increased the surface roughness and improved the wettability and Derjaguin-Muller-Toporov (DMT) elastic modulus of PEEK coating. The PEEK composite matrix coated Ti6Al4V specimens did not cause any aggregation of erythrocytes, showing morphological normal shapes. The hemolysis rate (HR) values of the tested specimens were much less than 5% according to ISO 10993-4 standard. The values of plasma recalcification time (PRT) of the tested specimens varied with the increasing amount of ZrO₂ nanoparticles. Based on the results obtained, 10 wt % ZrO₂ particle reinforced PEEK coating has demonstrated an optimum blood compatibility, and can be considered as a candidate to improve the performance of existing PEEK based coatings on titanium substrates.

Antimicrobial Peptide-Polymer Conjugates with High Activity: Influence of Polymer Molecular Weight and Peptide Sequence on Antimicrobial Activity, Proteolysis, and Biocompatibility

We report the synthesis, characterization, activity, and biocompatibility of a novel series of antimicrobial peptide-polymer conjugates. Using parent peptide aurein 2.2, we designed a peptide array (∼100 peptides) with single and multiple W and R mutations and identified antimicrobial peptides (AMPs) with potent activity against Staphylococcus aureus (S. aureus). These novel AMPs were conjugated to hyperbranched polyglycerols (HPGs) of different molecular weights and number of peptides to improve their antimicrobial activity and toxicity. The cell and blood compatibility studies of these conjugates demonstrated better properties than those of the AMP alone. However, conjugates showed lower antimicrobial activity in comparison to that of peptides, as determined from minimal inhibition concentrations (MICs) against S. aureus, but considerably better than that of the available polymer-AMP conjugates in the literature. In addition to measuring MICs and characterizing the biocompatibility, circular dichroism spectroscopy was used to investigate the interaction of the novel conjugates with model bacterial biomembranes. Moreover, the novel conjugates were exposed to trypsin to evaluate their stability. It was found that the conjugates resist proteolysis in comparison with unprotected peptides. The peptide conjugates were active in serum and whole blood. Overall, the results show that combining a highly active AMP and low-molecular-weight HPG yields bioconjugates with excellent biocompatibility, MICs below 100 μg/mL, and proteolytic stability, which could potentially improve its utility for in vivo applications.

An omniphobic lubricant-infused coating produced by chemical vapor deposition of hydrophobic organosilanes attenuates clotting on catheter surfaces

Catheter associated thrombosis is an ongoing problem. Omniphobic coatings based on tethering biocompatible liquid lubricants on self-assembled monolayers of hydrophobic organosilanes attenuate clotting on surfaces. Herein we report an efficient, non-invasive and robust process for coating catheters with an antithrombotic, omniphobic lubricant-infused coating produced using chemical vapor deposition (CVD) of hydrophobic fluorine-based organosilanes. Compared with uncoated catheters, CVD coated catheters significantly attenuated thrombosis via the contact pathway of coagulation. When compared with the commonly used technique of liquid phase deposition (LPD) of fluorine-based organosilanes, the CVD method was more efficient and reproducible, resulted in less disruption of the outer polymeric layer of the catheters and produced greater antithrombotic activity. Therefore, omniphobic coating of catheters using the CVD method is a simple, straightforward and non-invasive procedure. This method has the potential to not only prevent catheter thrombosis, but also to prevent thrombosis on other blood-contacting medical devices.

The impact of cell surface PEGylation and short-course immunotherapy on islet graft survival in an allogeneic murine model

Islet transplantation is a promising therapy for Type 1 diabetes mellitus; however, host inflammatory and immune responses lead to islet dysfunction and destruction, despite potent systemic immunosuppression. Grafting of poly(ethylene glycol) (PEG) to the periphery of cells or tissues can mitigate inflammation and immune recognition via generation of a steric barrier. Herein, we sought to evaluate the complementary impact of islet PEGylation with a short-course immunotherapy on the survival of fully-MHC mismatched islet allografts (DBA/2 islets into diabetic C57BL/6J recipients). Anti-Lymphocyte Function-associated Antigen 1 (LFA-1) antibody was selected as a complementary, transient, systemic immune monotherapy. Islets were PEGylated via an optimized protocol, with resulting islets exhibiting robust cell viability and function. Following transplantation, a significant subset of diabetic animals receiving PEGylated islets (60%) or anti-LFA-1 antibody (50%) exhibited long-term (>100d) normoglycemia. The combinatorial approach proved synergistic, with 78% of the grafts exhibiting euglycemia long-term. Additional studies examining graft cellular infiltrates at early time points characterized the local impact of the transplant protocol on graft survival. Results illustrate the capacity of a simple polymer grafting approach to impart significant immunoprotective effects via modulation of the local transplant environment, while short-term immunotherapy serves to complement this effect.

STATEMENT OF SIGNIFICANCE

We believe this study is important and of interest to the biomaterials and transplant community for several reasons: 1) it provides an optimized protocol for the PEGylation of islets, with minimal impact on the coated islets, which can be easily translated for clinical applications; 2) this optimized protocol demonstrates the benefits of islet PEGylation in providing modest immunosuppression in a murine model; 3) this work demonstrates the combinatory impact of PEGylation with short-course immunotherapy (via LFA-1 blockage), illustrating the capacity of PEGylation to complement existing immunotherapy; and 4) it suggests macrophage phenotype shifting as the potential mechanism for this observed benefit.

Platelet Immobilization on Supported Phospholipid Bilayers for Single Platelet Studies

The worldwide cardiovascular disease (CVD) epidemic is of grave concern. A major role in the etiology of CVDs is played by the platelets (thrombocytes). Platelets are anuclear cell fragments circulating in the blood. Their primary function is to catalyze clot formation, limiting traumatic blood loss in the case of injury. The same process leads to thrombosis in the case of CVDs, which are commonly managed with antiplatelet therapy. Platelets also have other, nonhemostatic functions in wound healing, inflammation, and tissue regeneration. They play a role in the early stages of atherosclerosis and the spread of cancer through metastases. Much remains to be learned about the regulation of these diverse platelet functions under physiological and pathological conditions. Breakthroughs in this regard are expected to come from single platelet studies and systems approaches. The immobilization of platelets at surfaces is advantageous for developing such approaches, but platelets are activated when they come in contact with foreign surfaces. In this work, we develop and validate a protocol for immobilizing platelets on supported lipid bilayers without activation due to immobilization. Our protocol can therefore be used for studying platelets with a wide variety of surface-sensitive techniques.

Stirred, shaken, or stagnant: What goes on at the blood-biomaterial interface

There is a widely recognized need to improve the performance of vascular implants and external medical devices that come into contact with blood by reducing adverse reactions they cause, such as thrombosis and inflammation. These reactions lead to major adverse cardiovascular events such as heart attacks and strokes. Currently, they are managed therapeutically. This need remains unmet by the biomaterials research community. Recognized stagnation of the blood-biomaterial interface research translates into waning interest from clinicians, funding agencies, and practitioners of adjacent fields. The purpose of this contribution is to stir things up. It follows the 2014 BloodSurf meeting (74th International IUVSTA Workshop on Blood-Biomaterial Interactions), offers reflections on the situation in the field, and a three-pronged strategy integrating different perspectives on the biological mechanisms underlying blood-biomaterial interactions. The success of this strategy depends on reengaging clinicians and on the renewed cooperation of the funding agencies to support long-term efforts.

Highly stable polyglutamate derivatives/siRNA polyplex efficiently down-relegate survivin expression and augment the efficacy of cisplatin

RNA interfere (RNAi)-based technology holds great promise in cancer treatment. The use of small interfering RNA (siRNA), however, is hampered by its low delivery efficiency in vivo when they are diluted in blood biofluids and in the presence of serum and salt. In this study, we developed the polyglutamate derivative polymer brush, poly(ethyleneglycol) monomethyl ether-b-polyglutamate-g-spermine (mPEG-b-PG-g-spermine, PPGS), which could efficiently deliver survivin-siRNA under ultra-high dilution and in the presence of salt (NaCl 150mM) and serum (10% FBS), most likely due to its PEG-shelled polymer brush structure. On the contrary, aggregation occurred when PEI/siRNA polyplex dispersed in saline and serum-containing media and PEI polyplex dissociated after making a 256-fold dilution. PPGS/si-survivin polyplex exhibited high cellular uptake efficiency and efficiently down-regulated the expression of survivin mRNA in the cisplatin-resistance of non-small cell human lung adenocarcinoma (A549/DDP) cells in the presence of serum. However, either PEI polyplex or Lipofectmine 2000 complex was unstable in serum and salt-containing media and at high dilution rates, which resulted in their dramatical decrease of cellular uptake and gene-silencing efficiency in these conditions. The PPGS/si-survivin polyplex also exhibited synergistic effects of killing the cancer cells by combination treatment with cisplatin. Therefore, the PPGS gene carrier showed great potential in systemic siRNA delivery, and its combination with chemotherapeutic drug is promising in treating drug resistant cancers.

Fabrication of Semiordered Nanopatterned Diamond-like Carbon and Titania Films for Blood Contacting Applications

Biomaterials with the ability to interface with, but not activate, blood components are essential for a multitude of medical devices. Diamond-like carbon (DLC) and titania (TiO2) have shown promise for these applications; however, both support platelet adhesion and activation. This study explored the fabrication of nanostructured DLC and TiO2 thin film coatings using a block copolymer deposition technique that produced semiordered nanopatterns with low surface roughness (5-8 nm Rrms). These surfaces supported fibrinogen and plasma protein adsorption that predominantly adsorbed between the nanofeatures and reduced the overall surface roughness. The conformation of the adsorbed fibrinogen was altered on the nanopatterned surfaces as compared with the planar surfaces to reveal higher levels of the platelet binding region. Planar DLC and TiO2 coatings supported less platelet adhesion than nanopatterned DLC and TiO2. However, platelets on the nanopatterned DLC coatings were less spread indicating a lower level of platelet activation on the nanostructured DLC coatings compared with the planar DLC coatings. These data indicated that nanostructured DLC coatings may find application in blood contacting medical devices in the future.

Delayed hepatic uptake of multi-phosphonic acid poly(ethylene glycol) coated iron oxide measured by real-time magnetic resonance imaging

We report on the synthesis, characterization, stability and pharmacokinetics of novel iron based contrast agents for magnetic resonance imaging (MRI).

Co-grafting of antiadhesive and antimicrobial agents onto UV-micropatterned copper surfaces

Adhesion of proteins and bacteria was reduced by a factor close to one order of magnitude, and adhered bacteria were dramatically damaged on copper surfaces by grafting a PEG-modified PMMA-based (polymethyl methacrylate) copolymer together with an antimicrobial peptide. To obtain PEG and a peptide grafted together on the surface, a UV sensitive copolymer (containing PMMA, PEG and a UV sensitive reagent) was primary synthesized and deposited. After selective UV irradiation of this copolymer layer, an antimicrobial peptide, Magainin I, was grafted onto freed-polymer coated-copper surface via a spacer molecule (a mercapto carboxylic acid). The functionalization was characterized at each step by Polarization Modulation Reflection Absorption Infrared Spectroscopy (PM-RAIRS). The antiadhesive properties of the copolymer layer and antibacterial activity of the anchored Magainin I, were individually tested toward adsorption of bovine serum albumin (BSA) proteins, and against Gram positive bacteria, Listeria ivanovii, respectively. The results revealed that adhesion of both proteins and bacteria has been considerably reduced; moreover, the peptide still displays some antimicrobial activity after grafting. This work gives new ideas and perspectives to elaborate complex surface coatings where several agents are needed like for anti-biofilm or sensing applications.

Review: physico-chemical modification as a versatile strategy for the biocompatibility enhancement of biomaterials

Physico-chemical modification induced improvement in biocompatibility of materials.

A survey of state-of-the-art surface chemistries to minimize fouling from human and animal biofluids

Fouling of artificial surfaces by biofluids is a plague Biotechnology deeply suffers from. Herein, we inventory the state-of-the-art surface chemistries developed to minimize this effect from both human and animal biosamples.

Monte Carlo simulation of protein adsorption on energetically heterogeneous surfaces

The modified triangular-well potential model was applied to incorporate the effect of surface energy on the adsorption of particles or proteins on energetically heterogeneous surfaces. The method is convenient in simulating the adsorption on heterogeneous surface of which different region possesses different free energy. Spherical particles with attractive forces were added on the surface and underwent surface diffusion before they were quenched in place. It was seen that the ratio of surface energies of two regions had to be greater than 10 in order to simulate the adsorption in which the particles were selectively adsorbed on a favorable area. At a fixed ratio of surface energies, the obtained structures were similar. If the ratio was less than 10, the probability of adsorption on any site on the surface was not much different so the adsorption would be homogeneous adsorption. The method, thus, could be applied widely to simulate the adsorption of various conditions.