Protein adsorption and platelet attachment and activation, on TiN, TiC, and DLC coatings on titanium for cardiovascular applications

Emergence of graphene as a novel nanomaterial for cardiovascular applications

Cardiovascular diseases (CDs) are the foremost cause of death worldwide. Several promising therapeutic methods have been developed for this approach, including pharmacological, surgical intervention, cell therapy, or biomaterial implantation since heart tissue is incapable of regenerating and healing on its own. The best treatment for heart failure to date is heart transplantation and invasive surgical intervention, despite their invasiveness, donor limitations, and the possibility of being rejected by the patient's immune system. To address these challenges, research is being conducted on less invasive and efficient methods. Consequently, graphene-based materials (GBMs) have attracted a great deal of interest in the last decade because of their exceptional mechanical, electrical, chemical, antibacterial, and biocompatibility properties. An overview of GBMs' applications in the cardiovascular system has been presented in this article. Following a brief explanation of graphene and its derivatives' properties, the potential of GBMs to improve and restore cardiovascular system function by using them as cardiac tissue engineering, stents, vascular bypass grafts,and heart valve has been discussed.

Synthesis of Ag-Doped Tetrahedral Amorphous Carbon Coatings and Their Antibiofilm Efficacy for Medical Implant Application

Tetrahedral amorphous carbon (taC) is a hydrogen-free carbon with extensive properties such as hardness, optical transparency, and chemical inertness. taC coatings have attracted much attention in recent times, as have coatings doped with a noble metal. A known antimicrobial metal agent, silver (Ag), has been used as a dopant in taC, with different Ag concentrations on the Ti64 coupons using a hybrid filtered cathodic vacuum arc (FCVA) and magnetron sputtering system. The physiochemical properties of the coated surface were investigated using spectroscopic and electron microscopy techniques. A doping effect of Ag-taC on biofilm formation was investigated and found to have a significant effect on the bacterial-biofilm-forming bacteria Staphylococcus aureus and Pseudomonas aeruginosa depending on the concentration of Ag. Further, the effect of coated and uncoated Ag-taC films on a pathogenic bacterium was examined using SEM. The result revealed that the Ag-taC coatings inhibited the biofilm formation of S. aureus. Therefore, this study demonstrated the possible use of Ag-taC coatings against biofilm-related complications on medical devices and infections from pathogenic bacteria.

Unravelling Surface Modification Strategies for Preventing Medical Device-Induced Thrombosis

The use of biomaterials in implanted medical devices remains hampered by platelet adhesion and blood coagulation. Thrombus formation is a prevalent cause of failure of these blood-contacting devices. Although systemic anticoagulant can be used to support materials and devices with poor blood compatibility, its negative effects such as an increased chance of bleeding, make materials with superior hemocompatibility extremely attractive, especially for long-term applications. This review examines blood-surface interactions, the pathogenesis of clotting on blood-contacting medical devices, popular surface modification techniques, mechanisms of action of anticoagulant coatings, and discusses future directions in biomaterial research for preventing thrombosis. In addition, this paper comprehensively reviews several novel methods that either entirely prevent interaction between material surfaces and blood components or regulate the reaction of the coagulation cascade, thrombocytes, and leukocytes.

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.

Comprehensive hemocompatibility analysis on the application of diamond-like carbon to ePTFE artificial vascular prosthesis

The aim of this study was to obtain comprehensive data regarding the hemocompatibility of diamond-like carbon (DLC)-coated expanded polytetrafluoroethylene (ePTFE). DLC increased the hydrophilicity and smoothened the surface and fibrillar structure, respectively, of the ePTFE. DLC-coated ePTFE had more albumin and fibrinogen adsorption and less platelet adhesion than uncoated ePTFE. There were scarce red cell attachments in in vitro human and in vivo animal (rat and swine) whole blood contact tests in both DLC-coated and uncoated ePTFE. DLC-coated ePTFE had a similar but marginally thicker band movement than uncoated-ePTFE with SDS-PAGE after human whole blood contact test. In addition, survival studies of aortic graft replacement in rats (1.5 mm graft) and arteriovenous shunt in goats (4 mm graft) were performed to compare the patency and clot formation between DLC-coated and uncoated ePTFE grafts. Comparable patency was observed in both animal models. However, clots were observed in the luminal surface of the patent 1.5 mm DLC-coated ePTFE grafts, but not in that of uncoated ePTFE grafts. In conclusions, hemocompatibility of DLC-coated ePTFE was high and comparable to that of uncoated ePTFE. However, it failed to improve the hemocompatibility of 1.5 mm ePTFE graft probably because increased fibrinogen adsorption canceled the other beneficial effects of DLC.

Surface modification techniques of titanium and titanium alloys for biomedical orthopaedics applications: A review

Biomedical alloys have an important share in orthopedic applications. Among them, titanium and its titanium alloys are widely used as implant materials because of their excellent mechanical properties and non-cytotoxicity. However, its disadvantages such as its biological inertness and poor antibacterial properties inhibit its further development. Therefore, the surface properties of titanium are crucial in the implantation process and determine the success of the implant. The main purpose of this review is to provide a comprehensive and detailed description of the modification techniques used for the surface modification of titanium implants. In this paper, the corresponding technical methods are introduced systematically from four aspects: mechanical method, physical surface modification, chemical surface modification and electrochemical technique to understand the experimental mechanism of each modification technique, and the above methods can indeed improve the various properties of titanium and its alloys. With the increasing demand for implants in the future, the requirements for surface properties will also increase. Therefore, the development of new coating materials with higher performance by combining various advantages of existing modification technologies is the main trend of future research on surface modification of titanium alloys.

Diamond-like carbon films prepared by a low temperature periodic process for application in ventricular assist devices

Due to the poor tribological properties of titanium (Ti) and its alloy Ti6Al4V (commonly used for ventricular assist devices manufacturing), diamond-like carbon (DLC) films with excellent anti-wear properties are pursued to improve the wear resistance of Ti and its alloys. Considering the effect of temperature on magnets inside pump impellers and workpiece deformation, DLC films are preferred to be prepared under low temperature. In this study, DLC films were prepared on Ti6Al4V alloys by periodic and continuous processes, and the corresponding maximum deposition temperature was 85 and 154°C, respectively. The periodic DLC films exhibited the feature of columnar structure, and the surface hillocks were less uniform than that of continuous DLC films. The periodic DLC films possessed more sp³ -bonded structures, and the accessorial sp³ -bonding mainly existed in the form of CH. Compared to continuous DLC films, the periodic DLC films had lower residual stress and better adhesion with Ti6Al4V substrates. Both DLC films could effectively reduce the friction coefficient and wear rate of Ti6Al4V alloys both in air and fetal bovine serum (FBS), and the periodic DLC films exhibited superior anti-wear properties to that of continuous DLC films in FBS. Haemocompatibility evaluation revealed that both DLC films presented similar levels of more human platelet adhesion and activation as compared with that of bare Ti6Al4V. However, both DLC films significantly prolonged plasma clotting time in comparison to bare Ti6Al4V. This study demonstrates the potential of low-temperature DLC films as wear-resistant surface modification for VADs.

How Crystallographic Orientation-Induced Fibrinogen Conformation Affects Platelet Adhesion and Activation on TiO2

Control of protein adsorption is essential for successful integration of healthcare materials into the body. Human plasma fibrinogen (HPF), especially its conformation is a key upstream regulator for platelet behavior and thus pathological clot formation at the blood-biomaterial interface. A previous study by the authors revealed that the conformation of adsorbed HPF can be controlled by rutile surface crystallographic orientation. Therefore, it is hypothesized that pre-adsorbed HPF on specific rutile orientation can regulate platelets adhesion and activation. Here, it is shown that platelets exposed to the four low index (110), (100), (101), (001) facets of TiO2 (rutile) exhibit surface-specific behavior. Scanning electron microscopy (SEM) observations of platelets morphology and P-selectin expression measurement revealed that on (110) facets, platelets adhesion and activation are suppressed. In contrast, extensive surface coverage by fully activated platelets is observed on (001) facets. Platelets' behavior has been linked to the HPF conformation and thereby availability of platelet-binding sequences. Atomic force microscopy (AFM) imaging supported by immunochemical analysis shows that on (110) facets, HPF is adsorbed in trinodular conformation rendering the γ400-411 platelet-binding sequence inaccessible. This research has potential implications on the bioactivity of different materials crystal facets, reducing the risk of pathological clot formation and thromboembolic complications.

Advancements in left ventricular assist devices to prevent pump thrombosis and blood coagulopathy

Mechanical circulatory support (MCS) devices, such as left ventricular assist devices (LVADs) are very useful in improving outcomes in patients with advanced-stage heart failure. Despite recent advances in LVAD development, pump thrombosis is one of the most severe adverse events caused by LVADs. The contact of blood with artificial materials of LVAD pumps and cannulas triggers the coagulation cascade. Heat spots, for example, produced by mechanical bearings are often subjected to thrombus build-up when low-flow situations impair washout and thus the necessary cooling does not happen. The formation of thrombus in an LVAD may compromise its function, causing a drop in flow and pumping power leading to failure of the LVAD, if left unattended. If a clot becomes dislodged and circulates in the bloodstream, it may disturb the flow or occlude the blood vessels in vital organs and cause internal damage that could be fatal, for example, ischemic stroke. That is why patients with LVADs are on anti-coagulant medication. However, the anti-coagulants can cause a set of issues for the patient-an example of gastrointestinal (GI) bleeding is given in illustration. On account of this, these devices are only used as a last resort in clinical practice. It is, therefore, necessary to develop devices with better mechanics of blood flow, performance and hemocompatibility. This paper discusses the development of LVADs through landmark clinical trials in detail and describes the evolution of device design to reduce the risk of pump thrombosis and achieve better hemocompatibility. Whilst driveline infection, right heart failure and arrhythmias have been recognised as LVAD-related complications, this paper focuses on complications related to pump thrombosis, especially blood coagulopathy in detail and potential strategies to mitigate this complication. Furthermore, it also discusses the LVAD implantation techniques and their anatomical challenges.

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Comparative assessment of different versions of axial and centrifugal LVADs: A review

Continuous-flow left ventricular assist devices (LVADs) have gained tremendous acceptance for the treatment of end-stage heart failure patients. Among different versions, axial flow and centrifugal flow LVADs have shown remarkable potential for clinical implants. It is also very crucial to know which device serves its purpose better to treat heart failure patients. A thorough comparison of axial and centrifugal LVADs, which may guide doctors in deciding before the implant, still lacks in the literature. In this work, an assessment of axial and centrifugal LVADs has been made to suggest a better device by comparing their engineering, clinical, and technological development of design aspects. Hydrodynamic and hemodynamic aspects for both types of pumps are discussed along with their biocompatibility, bearing types, and sizes. It has been observed numerically that centrifugal LVADs perform better over axial LVADs in every engineering aspect like higher hydraulic efficiency, better characteristics curve, lesser power intake, and also lesser blood damage. However, the clinical outcomes suggest that centrifugal LVADs experience higher events of infections, renal, and respiratory dysfunction. In contrast, axial LVADs encountered higher bleeding and cardiac arrhythmia. Moreover, recent technological developments suggested that magnetic type bearings along with biocompatible coating improve the life of LVADs.

Surface characterization and biological assessment of corrosion-resistant a-C:H:SiOx PACVD coating for Ti-6Al-4V alloy

The paper focuses on the SiO_x-doped amorphous hydrocarbon (a-C:H:SiO_x) coating on the titanium (Ti-6Al-4V) alloy substrate obtained by plasma-assisted chemical vapor deposition (PACVD) in a mixture of argon gas and polyphenylmethylsiloxane vapor using a bipolar substrate bias. It is shown that the a-C:H:SiO_x coating deposition results in the formation of a negative surface potential important for application of this coating for medical implants. The a-C:H:SiO_x coatings improve the corrosion resistance of Ti alloy to 0.5 M NaCl solution and phosphate-buffered saline. In particular, the corrosion current density of the a-C:H:SiO_x-coated sample in a 0.5 M NaCl solution at 22 °C decreases from 1∙10^-8 to 1.7∙10^-10 A/cm², that reduces the corrosion rate from 9∙10^-5 to 15∙10^-7 mm/year. The a-C:H:SiO_x coating facilitates the surface endothelization of an implant located in the thoracic aorta of a mini pig, and reduces the risk of thrombosis and implant failure. This effect can be explained by the ability of the a-C:H:SiO_x coating ability to reduce in vitro a 24-hour secretion of pro-inflammatory interleukins (IL-6, IL-12(p70), IL-15, and IL-17) and cytokines (IFN-g and TNF-a) by blood mononuclear cells (MNCs) and elevates the concentration of anti-inflammatory interleukin IL-1Ra. In vitro analysis shows no cytotoxicity of the a-C:H:SiO_x coating for the human blood MNCs, suggesting a promising PACVD on Ti alloys for cardiovascular implants, including pumps for mechanical heart support systems.

Enhanced Hemocompatibility of a Direct Chemical Vapor Deposition-Derived Graphene Film

A wide range of biomedical devices are being used to treat cardiovascular diseases, and thus they routinely come into contact with blood. Insufficient hemocompatibility has been found to impair the functionality and safety of these devices through the activation of blood coagulation and the immune system. Numerous attempts have been made to develop surface modification approaches of the cardiovascular devices to improve their hemocompatibility. However, there are still no ideal "blood-friendly" coating materials, which possess the desired hemocompatibility, tissue compatibility, and mechanical properties. As a novel multifunctional material, graphene has been proposed for a wide range of biomedical applications. The chemical inertness, atomic smoothness, and high durability make graphene an ideal candidate as a surface coating material for implantable devices. Here, we evaluated the hemocompatibility of a graphene film prepared on quartz glasses (Gra-glasses) from a direct chemical vapor deposition process. We found that the graphene coating, which is free of transfer-mediating polymer contamination, significantly suppressed platelet adhesion and activation, prolonged coagulation time, and reduced ex vivo thrombosis formation. We attribute the excellent antithrombogenic properties of the Gra-glasses to the low surface roughness, low surface energy (especially the low polar component of the surface energy), and the negative surface charge of the graphene film. Given these excellent hemocompatible properties, along with its chemical inertness, high durability, and molecular impermeability, a graphene film holds great promise as an antithrombogenic coating for next-generation cardiovascular devices.

Biomaterials in Valvular Heart Diseases

Valvular heart disease (VHD) occurs as the result of valvular malfunction, which can greatly reduce patient's quality of life and if left untreated may lead to death. Different treatment regiments are available for management of this defect, which can be helpful in reducing the symptoms. The global commitment to reduce VHD-related mortality rates has enhanced the need for new therapeutic approaches. During the past decade, development of innovative pharmacological and surgical approaches have dramatically improved the quality of life for VHD patients, yet the search for low cost, more effective, and less invasive approaches is ongoing. The gold standard approach for VHD management is to replace or repair the injured valvular tissue with natural or synthetic biomaterials. Application of these biomaterials for cardiac valve regeneration and repair holds a great promise for treatment of this type of heart disease. The focus of the present review is the current use of different types of biomaterials in treatment of valvular heart diseases.

Argon and oxygen plasma treatment increases hydrophilicity and reduces adhesion of silicon-incorporated diamond-like coatings

In this study, the structure, adhesion, and cell viability characteristics of silicon-incorporated diamond-like carbon (Si-DLC) coatings on fused silica substrates were investigated. The effects of argon and oxygen postprocessing plasma treatments on the Si-DLC coatings were also studied. The contact angle results showed that the Si-DLC coatings were more hydrophilic than the uncoated surfaces, and postprocessing plasma treatment increased the hydrophilicity of the Si-DLC coatings. Atomic force microscopy and profilometry confirmed that postprocessing plasma treatment increased the thickness and roughness of the Si-DLC coatings. The results of microscratch testing indicated that the plasma treatments reduced the adhesion of the coatings. The x-ray photoelectron spectroscopy (XPS) showed the presence of carbon, oxygen, and silicon in the Si-DLC coatings before and after the plasma treatments. These results show that the postprocessing plasma treatment significantly reduced the atomic percentage of the carbon in the Si-DLC coatings. XPS also confirmed the presence of carbon in the form of sp³(C-C), sp²(C=C), C-O, and C=O bonds in the Si-DLC coatings; it showed that postprocessing treatments significantly increased the percentage of oxygen in the Si-DLC coatings. Fourier transform infrared spectroscopy (FTIR) analysis showed features associated with C-OH stretching, C-H bending, as well as Si-CH₂ and C-H bending in the Si-DLC coating. The XPS and FTIR results confirmed that the plasma treatment caused dissociation of the sp² and sp³ bonds and formation of C-OH bonds. The contact angle data indicated that postprocessing treatment increased the hydrophilicity of the Si-DLC coating. Similar to the uncoated substrates, L929 cells showed no change in cell viability when cultured on Si-DLC coatings. These results of the study indicate the suitability of Si-DLC coatings as inert coatings for medical and biotechnology applications.

Optimization of a Novel Preferential Covered Stent through Bench Experiments and in Vitro Platelet Activation Studies

Bare metal stenting (BMS) does not adequately address the atheroembolic characteristic of carotid artery stenosis. While simple covered stents (CS) may prevent dislodged fragments of the atherosclerotic plaque from entering the blood stream, they also block blood flow into the major branches of the artery alongside the lesion, which is not desirable. Preferential covered stents (PCS) behave as a covered stent in a tubular part of a vessel but maintain side-branch flow over the bifurcation region by means of slits in the membrane. Stent design, membrane material, and slits configuration are the three main components contributing to stent performance. Optimization of PCS designs was conducted and tested.

METHODS

A newly designed BMS was developed and compared to a commercially available peripheral stent. Two materials (expanded poly(tetrafluoroethylene)) and silicone polyurethane co-polymers (Elast-eon E2A) were used as stent coverings with slits applied using various cutting methods to form the PCS. These PCS samples were tested for physical resilience, flexibility, ability to preserve side-branch flow, slit edge roughness, and platelet activation.

RESULTS

Fabrication of E2A-coated stents required pretreatment of the stent with poly(ethylene glycol) to achieve firm attachment. The newly designed BMS with nine crowns design and larger cell size showed higher flexibility than commercially available stents. A combination of a larger stent cell size, E2A membrane coating, and three slits per stent cell unit configuration resulted in preserved side-branch flow similar to physiological conditions in the flow experiment. Slit edge roughness changed with different cutting methods and laser machine cutting parameters. In vitro studies showed platelet activation was minimal with lower slit edge roughness samples.

CONCLUSION

An optimized PCS prototype was developed consisting of a newly designed stent, E2A membrane, and a three-slit pattern created by specific femtosecond laser cutting.

Co-immobilization of ACH11 antithrombotic peptide and CAG cell-adhesive peptide onto vascular grafts for improved hemocompatibility and endothelialization

Surface modification by conjugating biomolecules has been widely proved to enhance biocompatibility of small-caliber artificial vascular grafts. In this study, we aimed at developing a multifunctional vascular graft that provides not only good hemocompatibility but also in situ rapid endothelialization. Herein, a vascular graft (inner diameter ∼2 mm) was fabricated by electrospinning with poly(lactic acid-co-caprolactone) and gelatin, and then biofunctionalized with antithrombotic peptide with sequence LTFPRIVFVLG (ACH₁₁) and cell adhesion peptide with sequence CAG through adhesive poly(dopamine) coating. We developed this graft with the synergistic properties of low thrombogenicity and rapid endothelialization. The successful grafting of both CAG and ACH₁₁ peptides was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface micromorphology of the modified surfaces was observed by field emission scanning electron microscopy. Our results demonstrated that the multifunctional surface suppressed the denaturation of absorbed fibrinogen, hindered coagulation factor Xa activation, and inhibited platelet adhesion and aggregation. Importantly, this modified surface could selectively enhance endothelial cells adhesion, proliferation and release of nitric oxide. Upon in vivo implantation of 6 weeks, the multifunctional vascular graft showed improved patency and superior vascular endothelialization. Overall, the results effectively demonstrated that the co-immobilization of ACH₁₁ and CAG provided a promising method for the improvement of hemocompatibility and endothelialization of vascular grafts. STATEMENT OF SIGNIFICANCE: Electrospun small-caliber vascular grafts are increasingly used to treat cardiovascular diseases. Despite their success related to their good biodegradation and mechanical strength, they have some drawbacks, such as low hemocompatibility and endothelialization. The single-function ligands are insufficient to modify surface with both good hemocompatibility and rapid endothelialization simultaneously. Therefore, we functionalized electrospun vascular graft by novel antithrombotic peptide and cell-adhesive peptide to construct superior anticoagulation and ECs-selective adhesion surface in present study. The multifunctional vascular grafts benefit for high long-term patency and rapid endothelialization.

Micropatterning of a 2-methacryloyloxyethyl phosphorylcholine polymer surface by hydrogenated amorphous carbon thin films for endothelialization and antithrombogenicity

The existing first-generation drug-eluting stent (DES) has caused late and very late stent thrombosis related to incomplete stent endothelialization. Hence, biomaterials that possess sufficient anti-thrombogenicity and endothelialization with the controlled drug release system have been highly required. In this work, we have developed a newly designed drug-release platform composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, a non-thrombogenic polymer, and micropatterned hydrogenated amorphous carbon (a-C:H), a cell-compatible thin film. The platelet adhesion and the endothelial cell adhesion behavior on the micropatterned substrates were investigated in vitro. The results indicated that the micropatterned a-C:H/MPC polymer substrates effectively supported the human umbilical vein endothelial cell (HUVEC) proliferation, while suppressing the platelet adhesion. Interestingly, the HUVEC exhibited different shape and behavior by changing the island size of the micropatterned a-C:H. By introducing both a non-thrombogenic polymer and cell-compatible thin films through a simple patterning method, we demonstrated that the platform had the potential to be utilized as a base material for DES with cell controllability. STATEMENT OF SIGNIFICANCE: The current first-generation drug-eluting stents (DES) would cause late and very late stent thrombosis due to the incomplete endothelialization of the metal stent material. In this work, we have developed a new DES platform composed of a 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer micropatterned by hydrogenated amorphous carbon (a-C:H). Two types of differently micropatterned a-C:H stent surface were made. Our studies revealed that the micropatterned a-C:H/MPC polymer substrates could effectively enhance the endothelial cell (EC) proliferation, simultaneously suppressing the platelet adhesion, becoming a highly biocompatible material especially for indwelling devices including a drug-release device. The new drug-release platform could be utilized as a base material for cell-controllable coating on DES.

Photothermal Off-Resonance Tapping for Rapid and Gentle Atomic Force Imaging of Live Cells

Imaging living cells by atomic force microscopy (AFM) promises not only high-resolution topographical data, but additionally, mechanical contrast, both of which are not obtainable with other microscopy techniques. Such imaging is however challenging, as cells need to be measured with low interaction forces to prevent either deformation or detachment from the surface. Off-resonance modes which periodically probe the surface have been shown to be advantageous, as they provide excellent force control combined with large amplitudes, which help reduce lateral force interactions. However, the low actuation frequency in traditional off-resonance techniques limits the imaging speed significantly. Using photothermal actuation, we probe the surface by directly actuating the cantilever. Due to the much smaller mass that needs to be actuated, the achievable measurement frequency is increased by two orders of magnitude. Additionally, photothermal off-resonance tapping (PORT) retains the precise force control of conventional off-resonance modes and is therefore well suited to gentle imaging. Here, we show how photothermal off-resonance tapping can be used to study live cells by AFM. As an example of imaging mammalian cells, the initial attachment, as well as long-term detachment, of human thrombocytes is presented. The membrane disrupting effect of the antimicrobial peptide CM-15 is shown on the cell wall of Escherichia coli. Finally, the dissolution of the cell wall of Bacillus subtilis by lysozyme is shown. Taken together, these evolutionarily disparate forms of life exemplify the usefulness of PORT for live cell imaging in a multitude of biological disciplines.

Surface Nanostructuring of Parylene-C Coatings for Blood Contacting Implants

This paper investigates the effects on the blood compatibility of surface nanostructuring of Parylene-C coating. The proposed technique, based on the consecutive use of O₂ and SF₆ plasma, alters the surface roughness and enhances the intrinsic hydrophobicity of Parylene-C. The degree of hydrophobicity of the prepared surface can be precisely controlled by opportunely adjusting the plasma exposure times. Static contact angle measurements, performed on treated Parylene-C, showed a maximum contact angle of 158°. The nanostructured Parylene-C retained its hydrophobicity up to 45 days, when stored in a dry environment. Storing the samples in a body-mimicking solution caused the contact angle to progressively decrease. However, at the end of the measurement, the plasma treated surfaces still exhibited a higher hydrophobicity than the untreated counterparts. The proposed treatment improved the performance of the polymer as a water diffusion barrier in a body simulating environment. Modifying the nanotopography of the polymer influences the adsorption of different blood plasma proteins. The adsorption of albumin—a platelet adhesion inhibitor—and of fibrinogen—a platelet adhesion promoter—was studied by fluorescence microscopy. The adsorption capacity increased monotonically with increasing hydrophobicity for both studied proteins. The effect on albumin adsorption was considerably higher than on fibrinogen. Study of the proteins simultaneous adsorption showed that the albumin to fibrinogen adsorbed ratio increases with substrate hydrophobicity, suggesting lower thrombogenicity of the nanostructured surfaces. Animal experiments proved that the treated surfaces did not trigger any blood clot or thrombus formation when directly exposed to the arterial blood flow. The findings above, together with the exceptional mechanical and insulation properties of Parylene-C, support its use for packaging implants chronically exposed to the blood flow.

Refractory plasmonics: orientation-dependent plasmonic coupling in TiN and ZrN nanocubes

Transition metal nitrides have recently been considered as potential replacements for noble metals as plasmonic materials. In particular, the localized surface plasmon resonance (LSPR) of refractory transition metal nitrides, such as TiN and ZrN, is an interesting option for plasmonic-based devices. Using FDTD simulations, the extinction, absorption and scattering cross sections were calculated for a pair of 42 nm TiN nanocubes, along with the electric field intensity "modes" for several separation distances. The face-to-face and edge-to-edge orientations were investigated and a plasmon ruler equation was derived from the exponential fitting for both orientations. It was found that the smaller the separation distance, the more the coupling achieved. The results of different combinations of materials for nanocube pairs, such as TiN, ZrN, Ag and Au combinations, were also obtained. The (Ag-Ag) showed the highest electric field intensity, (Au-Au) was the second and (ZrN-ZrN) was quite close to gold. Upon decreasing the separation distance, a red-shift in the wavelength of the plasmon peak was observed. The separation distance at which the TiN nanocube pair showed an LSPR wavelength equivalent to that of an isolated nanocube was identified. The "hot spot" region between the nanocubes was also identified, which is very important for many applications such as cancer therapeutics, imaging, sensing, photovoltaic solar cells, surface enhanced Raman scattering, near field scanning optical microscopy, water splitting and nanoscale optical devices.

Electroconductive nanoscale topography for enhanced neuronal differentiation and electrophysiological maturation of human neural stem cells

Biophysical cues, such as topography, and electrical cues can provide external stimulation for the promotion of stem cell neurogenesis. Here, we demonstrate an electroconductive surface nanotopography for enhancing neuronal differentiation and the functional maturation of human neural stem cells (hNSCs). The electroconductive nanopatterned substrates were prepared by depositing a thin layer of titanium (Ti) with nanograting topographies (150 to 300 nm groove/ridge, the thickness of the groove - 150 μm) onto polymer surfaces. The Ti-coated nanopatterned substrate (TNS) induced cellular alignment along the groove pattern via contact guidance and promoted focal adhesion and cytoskeletal reorganization, which ultimately led to enhanced neuronal differentiation and maturation of hNSCs as indicated by significantly elevated neurite extension and the upregulated expression of the neuronal markers Tuj1 and NeuN compared with the Ti-coated flat substrate (TFS) and the nanopatterned substrate (NS) without Ti coating. Mechanosensitive cellular events, such as β1-integrin binding/clustering and myosin-actin interaction, and the Rho-associated protein kinase (ROCK) and mitogen-activated protein kinase/extracellular signal regulated kinase (MEK-ERK) pathways, were found to be associated with enhanced focal adhesion and neuronal differentiation of hNSCs by the TNS. Among the neuronal subtypes, differentiation into dopaminergic and glutamatergic neurons was promoted on the TNS. Importantly, the TNS increased the induction rate of neuron-like cells exhibiting electrophysiological properties from hNSCs. Finally, the application of pulsed electrical stimulation to the TNS further enhanced neuronal differentiation of hNSCs due probably to calcium channel activation, indicating a combined effect of topographical and electrical cues on stem cell neurogenesis, which postulates the novelty of our current study. The present work suggests that an electroconductive nanopatterned substrate can serve as an effective culture platform for deriving highly mature, functional neuronal lineage cells from stem cells.

Nanoplasmonic Sensing at the Carbon-Bio Interface: Study of Protein Adsorption at Graphitic and Hydrogenated Carbon Surfaces

Various forms of carbon are known to perform well as biomaterials in a variety of applications and an improved understanding of their interactions with biomolecules, cells, and tissues is of interest for improving and tailoring their performance. Nanoplasmonic sensing (NPS) has emerged as a powerful technique for studying the thermodynamics and kinetics of interfacial reactions. In this work, the in situ adsorption of two proteins, bovine serum albumin and fibrinogen, were studied at carbon surfaces with differing chemical and optical properties using nanoplasmonic sensors. The carbon material was deposited as a thin film onto NPS surfaces consisting of 100 nm Au nanodisks with a localized plasmon absorption peak in the visible region. Carbon films were fully characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and spectroscopic ellipsometry. Two types of material were investigated: amorphous carbon (a-C), with high graphitic content and high optical absorptivity, and hydrogenated amorphous carbon (a-C:H), with low graphitic content and high optical transparency. The optical response of the Au/carbon NPS elements was modeled using the finite difference time domain (FDTD) method, yielding simulated analytical sensitivities that compare well with those observed experimentally at the two carbon surfaces. Protein adsorption was investigated on a-C and a-C:H, and the protein layer thicknesses were obtained from FDTD simulations of the expected response, yielding values in the 1.8-3.3 nm range. A comparison of the results at a-C and a-C:H indicates that in both cases fibrinogen layers are thicker than those formed by albumin by up to 80%.

Investigation of silicon carbon nitride nanocomposite films as a wear resistant layer in vitro and in vivo for joint replacement applications

Silicon-contained CN_x nanocomposite films were prepared using the ion beam assisted magnetron sputtering under different nitrogen gas pressure. With increase of the nitrogen pressure, silicon and nitrogen content of the CN_x films drastically increase, and is saturated as the P_N2 reach about 40%. Surface roughness and the contact angle are increase, while the friction coefficient decreased. The CN_x film with 5.7at.% Si content possess the lowest friction coefficient of only 0.07, and exhibited the best tribological properties. The impact of CN_x films with different silicon content on the growth and the activation of osteoblasts were compared to that of Ti6Al4V. The incorporation of silicon in the CN_x film also showed an increase cell adhesion. Bonding structure and surface energy were determined to be the factors contributing to the improved biocompatibility. Macrophages attached to 5.7at.% Si contained CN_x films down regulated their production of cytokines and chemokines. Moreover, employed with Si contained CN_x coated joint replacements, which were implanted subcutaneously into Sprague-Dawley mice for up to 36days, the tissue reaction and capsule formation was significantly decreased compared to that of Ti6Al4V. A mouse implantation study demonstrated the excellent in vivo biocompatibility and functional reliability of wear resist layer for joint replacements with a Si doped a-CN_x coating for 36days.

Diamond coated artificial cardiovascular devices

Ultrananocrystalline diamond (UNCD), an extremely smooth, low cost diamond coating was successfully developed herein for antithrombogenic application which requires high biocompatibility, low wear, low friction, and chemical inertness. The substrate materials utilized in the Jarvik 2000 ventricular assist device (VAD), silicon carbide and titanium alloy, provide an excellent substrate match for UNCD integration. The paper addresses the development of medical-quality UNCD films to significantly improve the knowledge base regarding the defect mechanisms of UNCD films, to reduce or eliminate known wear-inducing imperfections in the film, and to thoroughly characterize and test the films as well as assembled UNCD-coated VADs. After the defect reduction and seeding experiments to improve film adhesion and coating quality, the best candidate deposition method has been down-selected for coating and assembly of VAD parts from Jarvik Heart. The coated and assembled devices have been tested with mechanical and blood-simulating fluid hydrodynamic testing at Jarvik Heart for full verification of the new coating technology. UNCD interface takes advantage of combining unmatched durability and antithrombogenicity.

Evaluation of Subretinal Implants Coated with Amorphous Aluminum Oxide and Diamond-like Carbon

Retinal prostheses may be used to support patients suffering from age-related macular degeneration (AMD) or retinitis pigmentosa (RP). A hermetic encapsulation of the poly(imide) (PI)-based prosthesis is important in order to prevent the leakage of water and ions into the electric circuitry embedded in the poly(imide) matrix. The deposition of amorphous aluminum oxide (by sputtering) and diamond like carbon (by pulsed laser ablation) were made for applications in retinal prostheses. The thin films obtained were characterized for composition, thickness, adhesion and smoothness by scanning electron microscopy-energy dispersive spectroscopy, atomic force microscopy, profilometry and light microscopy. Biocompatibility was tested in vivo by implanting coated specimen subretinally in the eye of Yucatan pigs. While amorphous aluminum oxide is more readily deposited with sufficient adhesion quality, superior biocompatibility behavior was shown by diamond-like carbon. Amorphous aluminum oxide had more adverse effects and caused more severe damage to the retinal tissue.

Mechanical behavior and blood compatibility of copper-containing films as potential biomaterials

Surface modification is one approach to enhance the biocompatibility of implanted cardiovascular devices. In this work, a copper-containing film used to blood contacted biomaterials was prepared by vacuum arc deposition. The phase composition of the films was investigated via X-ray diffraction, and the adherence strength of the films was evaluated with conventional deformation tests. Blood compatibility of the films was characterized by hemolysis ratio, clotting time and platelet adhesion etc. The surface of inferior vena cava filters were smooth and uniform, no cracks or delaminations were observed on the deformed surface. These results indicate that the mechanical behavior of the films is suitable for withstanding deformation stresses as operation in clinic. Good blood compatibility of the copper-containing films was identified through experiment in vitro, the activated partial thromboplastin times (APTTs) of Cu/Ti films were similar to that of the uncoated substrate, and Cu/Ti films were also found to inhibit platelet adhesion comparing to the nitinol substrate. However, with increasing ratio of Cu/Ti, the hemolysis ratio increased, resulting in platelet damage. These results indicate that the copper-containing film has potential application on blood contacted devices.

Surface modification of titanium substrate with a novel covalently-bound copolymer thin film for improving its platelet compatibility

Despite of its widely uses in various clinical applications, the titanium-based material still faces different challenges, such as hemocompatibility and anti-biofouling characteristics required in various situations. The objective of this investigation was to develop a novel surface modification strategy for titanium-based material to improve the platelet compatibility that is important in rigorous blood-contacting cardiovascular applications. In this work, a series of copolymers, which composed of novel 6-acryloyloxy hexyl phosphonic acid (AcrHPA) and sulfobetaine methacrylate (SBMA) was synthesized. The phosphonic acid group in these copolymers can impart covalent binding to the titanium substrate while the zwitterionic sulfobetaine functionality is considered being able to reduce the platelet adhesion and activation on the modified titanium substrate. NMR analyses suggested that copolymerization reaction is likely not an ideal statistical reaction but to add the monomers in a random order. Studies have shown that the composition of the monomers affected the surface characteristics and platelet compatibility of these covalent-bound AcrHPA-SBMA copolymers on titanium substrate. Contact angle analysis has shown the addition of SBMA can increase surface hydrophilicity of the spun-coated copolymers. In addition, AFM analyses have revealed that the surface roughness of the spun-coated copolymer layer were varied with the ratio of AcrHPA and SBMA. The most platelet compatible surface was noted on the one modified by the highest amount of SBMA added (i.e. 70 mol%) in copolymerization. In summary, the surface modification scheme presented here would be of potential as well as manufacturing process applicable for future development in blood-contacting titanium-based biomedical devices.

Development of clinically relevant implantable pressure sensors: perspectives and challenges

This review describes different aspects to consider when developing implantable pressure sensor systems. Measurement of pressure is in general highly important in clinical practice and medical research. Due to the small size, light weight and low energy consumption Micro Electro Mechanical Systems (MEMS) technology represents new possibilities for monitoring of physiological parameters inside the human body. Development of clinical relevant sensors requires close collaboration between technological experts and medical clinicians.  Site of operation, size restrictions, patient safety, and required measurement range and resolution, are only some conditions that must be taken into account. An implantable device has to operate under very hostile conditions. Long-term in vivo pressure measurements are particularly demanding because the pressure sensitive part of the sensor must be in direct or indirect physical contact with the medium for which we want to detect the pressure. New sensor packaging concepts are demanded and must be developed through combined effort between scientists in MEMS technology, material science, and biology. Before launching a new medical device on the market, clinical studies must be performed. Regulatory documents and international standards set the premises for how such studies shall be conducted and reported.

Directing vascular cell selectivity and hemocompatibility on patterned platforms featuring variable topographic geometry and size

It is great challenge to generate multifunctionality of vascular grafts and stents to enable vascular cell selectivity and improve hemocompatibility. Micro/nanopatterning of vascular implant surfaces for such multifunctionality is a direction to be explored. We developed a novel patterned platform featuring two typical geometries (groove and pillar) and six pattern sizes (0.5-50 μm) in a single substrate to evaluate the response of vascular cells and platelets. Our results indicate that targeted multifunctionality can be indeed instructed by rationally designed surface topography. The pillars nonselectively inhibited the growth of endothelial and smooth muscle cells. By contrast, the grooves displayed selective effects: in a size-dependent manner, the grooves enhanced endothelialization but inhibited the growth of smooth muscle cells. Moreover, our studies suggest that topographic cues can affect response of vascular cells by regulating focal adhesion and stress fiber development, which define cytoskeleton organization and cell shape. Notably, both the grooves and the pillars at 1 μm size drastically reduced platelet adhesion and activation. Taken together, these findings suggest that the topographic pattern featuring 1 μm grooves may be the optimal design of surface multifunctionality that favors vascular cell selectivity and improves hemocompatibility.

MRI-compatible Nb-60Ta-2Zr alloy used for vascular stents: haemocompatibility and its correlation with protein adsorption

Nb-60Ta-2Zr is a newly developed MRI-compatible alloy used for vascular stents. In this work, its haemocompatibility was investigated, including platelet adhesion (lactate dehydrogenase activity), platelet activation (P-selectin expression), coagulation and haemolysis. For comparison, parallel assessments for these factors were performed for the niobium, tantalum, 316L stainless steel (316L SS) and L605 Co-Cr alloy (L605). In addition, albumin and fibrinogen were selected to examine the correlation of protein adsorption with platelet adhesion and metal surface properties. The propensity for platelet adhesion and activation on the Nb-60Ta-2Zr alloy was at nearly the same level as that for Nb and Ta but was slightly less than those of 316L SS and L605. The mitigated platelet adhesion and activation of the Nb-60Ta-2Zr alloy is associated with its decreased adsorption of fibrinogen. The Nb-60Ta-2Zr alloy has a longer clotting time and exhibits significantly superior thromboresistance than 316L SS and L605. Moreover, the haemolysis rate of the Nb-60Ta-2Zr alloy satisfies the bio-safety requirement of the ISO 10993-4 standard. The favourable haemocompatiblity of the Nb-60Ta-2Zr alloy provides evidence of its good biocompatibility and of its suitability as a candidate stent material.

Key parameters in blood-surface interactions of 3D bioinspired ceramic materials

Direct contact of materials with blood components may trigger numerous processes which ultimately lead to hemolysis, clot formation and recruitment of inflammatory cells. In this study, the blood-surface interactions for two inert bioinspired ceramic scaffolds obtained from natural resources; biomorphic carbon and silicon carbides (bioSiC) from different origins have been studied. The response of the blood in contact with carbon is well known, however little has been identified on the influence of their 3D porous structure. Moreover, to our knowledge, there is no reference in the literature about the hemocompatibility of biomorphic silicon carbide as a porous scaffold. The experimental results showed the surface energy to be crucial to evaluate the hemocompatibility of a material however the surface topography and material porosity are also parameters to be considered. Surface roughness modifies clot formation whereas for protein adsorption total sample porosity seems to be the key parameter to be considered for hydrophilic materials (biomorphic silicon carbides), while the size of the pores determines the hemolytic response.

Multi-layer haemocompatible diamond-like carbon coatings obtained by combined radio frequency plasma enhanced chemical vapor deposition and magnetron sputtering

Radio-frequency Plasma Enhanced Chemical Vapour Deposition (in different methane dilutions) was used to synthesize adherent and haemocompatible diamond-like carbon (DLC) films on medical grade titanium substrates. The improvement of the adherence has been achieved by interposing a functional buffer layer with graded composition TixTiC1-x (x = 0-1) synthesized by magnetron co-sputtering. Bonding strength values of up to ~67 MPa have been measured by pull-out tests. Films with different sp(3)/sp(2) ratio have been obtained by changing the methane concentration in the deposition chamber. Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed for the physical-chemical characterization of the samples. The highest concentration of sp(3)-C (~87 %), corresponding to a lower DLC surface energy (28.7 mJ/m(2) ), was deposited in a pure methane atmosphere. The biological response of the DLC films was assayed by a state-of-the-art biological analysis method (surface enhanced laser desorption/ionization-time of flight mass spectroscopy), in conjunction with other dedicated testing techniques: Western blot and partial thromboplastin time. The data support a cause-effect relationship between sp(3)-C content, surface energy and coagulation time, as well as between platelet-surface adherence properties and protein adsorption profiles.

Facets of protein assembly on nanostructured titanium oxide surfaces

One key for the successful integration of implants into the human body is the control of protein adsorption by adjusting the surface properties at different length scales. This is particularly important for titanium oxide, one of the most common biomedical interfaces. As for titania (TiO(2)) the interface is largely defined by its crystal surface structure, it is crucial to understand how the surface crystallinity affects the structure, properties and function of protein layers mediating subsequent biological reactions. For rutile TiO(2) we demonstrate that the conformation and relative amount of human plasma fibrinogen (HPF) and the structure of adsorbed HPF layers depend on the crystal surface nanostructure by employing thermally etched multi-faceted TiO(2) surfaces. Thermal etching of polycrystalline TiO(2) facilitates a nanoscale crystal faceting and, thus, the creation of different surface nanostructures on a single specimen surface. Atomic force microscopy shows that HPF arranges into networks and thin globular layers on flat and irregular crystal grain surfaces, respectively. On a third, faceted category we observed an alternating conformation of HPF on neighboring facets. The bulk grain orientation obtained from electron backscatter diffraction and thermodynamic mechanisms of surface reconstruction during thermal etching suggest that the grain and facet surface-specific arrangement and relative amount of adsorbed proteins depend on the associated free crystal surface energy. The implications for potentially favorable TiO(2) crystal facets regarding the inflammatory response and hemostasis are discussed with a view to the advanced surface design of future implants.

Chemico-physical characterisation and in vivo biocompatibility assessment of DLC-coated coronary stents

The vast majority of stent thrombosis occurs in the acute and sub-acute phases and is more common in patients with acute coronary syndromes, due to the thrombotic milieu where stent struts are positioned. Stent thrombosis is likely due to incomplete tissue coverage of metallic stents as the contact between metallic stents and blood elements may lead to platelet adhesion and trigger vessel thrombosis. If a stent is covered after 7 days, the risk that it will be found uncovered at later stages is very low (<1%). In this article, we demonstrate that diamond-like carbon (DLC) coatings, deposited by physical vapour deposition, promote rapid endothelisation of coronary stent devices, with very low platelets activation, reducing thrombotic clots. We relate these behaviours to the surface and bulk material properties of the DLC films, subjected to a comprehensive chemico-physical characterisation using several techniques (X-ray photoelectron spectroscopy, atomic force microscopy, field-emission scanning electron microscope, transmission electron microscopy combined with electron energy loss spectroscopy, Raman and dispersive X-ray spectroscopy). In vivo studies, conducted on 24 pigs, have shown complete endothelisation after 7 days, with no fibrin mesh and with only rare monocytes scattered on the endothelial layer while 30 and 180 days tests have shown reduced inflammatory activation and a complete stabilisation of the vessel healing, with a minimal neointimal proliferation. The integral and permanent DLC film coating improves haemo- and bio-compatibility and leads to an excellent early vessel healing of the stent whilst the extremely thin strut thickness reduces the amount of late neointima and consequently the risk of late restenosis. These data should translate into a reduced acute and sub-acute stent thrombosis.