Surface modification with an antithrombin-heparin complex for anticoagulation: studies on a model surface with gold as substrate

Functionalization of Polydimethylsiloxane with Diazirine-Based Linkers for Covalent Protein Immobilization

Biomolecule attachment to solid supports is critical for biomedical devices, such as biosensors and implants. Polydimethylsiloxane (PDMS) is commonly used for these applications due to its advantageous properties. To enhance the biomolecule immobilization on PDMS, a novel technique is demonstrated using newly synthesized diazirine molecules for the surface modification of PDMS. This nondestructive process involves a reaction between diazirine molecules and PDMS through C-H insertion with thermal or ultraviolet activation. The success of the PDMS modification is confirmed by various surface characterization techniques. Bovine serum albumin (BSA) and immunoglobulin G (IgG) are strongly attached to the modified PDMS surfaces, and the amount of protein is quantified using iodine-125 radiolabeling. The results demonstrate that PDMS is rapidly functionalized, and the stability of the immobilized proteins is significantly improved with multiple types of diazirine molecules and activation methods. Confocal microscopy provides three-dimensional images of the distribution of immobilized IgG on the surfaces and the penetration of diazirine-based linkers through the PDMS substrate during the coating process. Overall, this study presents a promising new approach for functionalizing PDMS surfaces to enhance biomolecule immobilization, and its potential applications can extend to multimaterial modifications for various diagnostic and medical applications such as microfluidic devices and immunoassays with relevant bioactive proteins.

Blood biocompatibility enhancement of biomaterials by heparin immobilization: a review

Blood contacting materials are concerned with biocompatibility including thrombus formation, decrease blood coagulation time, hematology, activation of complement system, platelet aggression. Interestingly, recent research suggests that biocompatibility is increasing by incorporating various materials including heparin using different methods. Basic of heparin including uses and complications was mentioned, in which burst release of heparin is major issue. To minimize the problem of biocompatibility and unpredictable heparin release, present review article potentially reviews the reported work and investigates the various immobilization methods of heparin onto biomaterials, such as polymers, metals, and alloys. Detailed explanation of different immobilization methods through different intermediates, activation, incubation method, plasma treatment, irradiations and other methods are also discussed, in which immobilization through intermediates is the most exploitable method. In addition to biocompatibility, other required properties of biomaterials like mechanical and corrosion resistance properties that increase by attachment of heparin are reviewed and discussed in this article.

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.

Mixed monolayer decorated SPR sensing surface for thrombin detection

The development of surface plasmon resonance (SPR) based immunosensor for thrombin detection was aimed. For this purpose, 3,3' Dithiodipropionic acid di (N-hydroxysuccinimide ester) (DSP):6-mercapto-1-hexanol (MCH) mixed self-assembled monolayers (mSAMs) were formed on gold surfaces for immobilization of anti-thrombin antibody. The performance of the immunosensor was determined against the target protein thrombin at various concentrations using flow cell coupled SPR. The linear detection range of the immunosensor was 30.0-100.0 nM with an R² value of 0,992. Limit of Detection (LOD) and Limit of Quantification (LOQ) were determined to be 6.0 nM and 30.0 nM, respectively. The selectivity of the immunosensor was tested against a non-target model protein, human serum albumin (HSA) and the obtained ΔRU value was found to be below the ΔRU value corresponding to the LOQ concentration for thrombin. The immunosensor's capability to detect thrombin in diluted complex serum matrix was also tested and the obtained ΔRU value (159 ± 16) was compared with ΔRU value obtained for thrombin detection in PBS solution (137 ± 19). Based on the results, it was shown that DSP:MCH interface is a promising immobilization platform for binding biological recognition elements for the development of biosensors.

Historical Perspective and Future Direction of Blood Vessel Developments

Over the past 40 years, remarkable advances have been made in our understanding of successful blood vessel regeneration, starting with the failures of early tissue-engineered vascular grafts designed using isolated components or molecules, such as collagen gels. The vascular tissue engineers are today better educated and have steered ongoing research developments toward clinical developments of more complete vascular grafts that replicate the multitude of specialized arterial aspects required for function.

Anticoagulant sodium alginate sulfates and their mussel-inspired heparin-mimetic coatings

We synthesized novel sodium alginate sulfates (SASs) with different sulfation degrees. All the SASs, DA-g-SASs, and coated substrates had good anticoagulant properties and biocompatibilit.

Osteogenic Surface Modification Based on Functionalized Poly-P-Xylylene Coating

The biotechnology to immobilize biomolecules on material surfaces has been developed vigorously due to its high potentials in medical applications. In this study, a simple and effective method was designed to immobilize biomolecules via amine-N-hydroxysuccinimide (NHS) ester conjugation reaction using functionalized poly-p-xylylene coating on material surfaces. The NHS ester functionalized coating is synthesized via chemical vapor deposition, a facile and solvent-less method, creating a surface which is ready to perform a one-step conjugation reaction. Bone morphogenetic protein 2 (BMP-2) is immobilized onto material surfaces by this coating method, forming an osteogenic environment. The immobilization process is controlled at a low temperature which does not damage proteins. This modified surface induces differentiation of preosteoblast into osteoblast, manifested by alkaline phosphatase (ALP) activity assay, Alizarin Red S (ARS) staining and the expression of osteogenic gene markers, Alpl and Bglap3. With this coating technology, immobilization of growth factors onto material surface can be achieved more simply and more effectively.

Surface modification of poly(dimethylsiloxane) with a covalent antithrombin-heparin complex for the prevention of thrombosis: use of polydopamine as bonding agent

A modified poly(dimethyl siloxane) (PDMS) material is under development for use in an extracorporeal microfluidic blood oxygenator designed as an artificial placenta to treat newborn infants suffering from severe respiratory insufficiency. To prevent thrombosis triggered by blood-material contact, an antithrombin-heparin (ATH) covalent complex was coated on PDMS surface using polydopamine (PDA) as a "bioglue". Experiments using radiolabelled ATH showed that the ATH coating on PDA-modified PDMS remained substantially intact after incubation in plasma, 2% SDS solution, or whole blood over a three day period. The anticoagulant activity of the ATH-modified surfaces was also demonstrated: in contact with plasma the ATH-coated PDMS was shown to bind antithrombin (AT) selectively from plasma and to inhibit clotting factor Xa. It is concluded that modification of PDMS with polydopamine and ATH shows promise as a means of improving the blood compatibility of PDMS and hence of the oxygenator device.

Blood compatible materials: state of the art

Devices that function in contact with blood are ubiquitous in clinical medicine and biotechnology. These devices include vascular grafts, coronary stents, heart valves, catheters, hemodialysers, heart-lung bypass systems and many others. Blood contact generally leads to thrombosis (among other adverse outcomes), and no material has yet been developed which remains thrombus-free indefinitely and in all situations: extracorporeally, in the venous circulation and in the arterial circulation. In this article knowledge on blood-material interactions and "thromboresistant" materials is reviewed. Current approaches to the development of thromboresistant materials are discussed including surface passivation; incorporation and/or release of anticoagulants, antiplatelet agents and thrombolytic agents; and mimicry of the vascular endothelium.

Surface modification of polydimethylsiloxane with a covalent antithrombin-heparin complex to prevent thrombosis

To prevent coagulation in contact with blood, polydimethylsiloxane (PDMS) was modified with an antithrombin-heparin (ATH) covalent complex using polyethylene glycol (PEG) as a linker/spacer. Using NHS chemistry, ATH was attached covalently to the distal chain end of the immobilized PEG linker. Surfaces were characterized by contact angle and X-ray photoelectron spectroscopy; attachment was confirmed by decrease in contact angles and an increase in nitrogen content as determined by X-ray photoelectron spectroscopy. Protein interactions in plasma were investigated using radiolabeled proteins added to plasma as tracers, and by immunoblotting of eluted proteins. Modification of PDMS with PEG alone was effective in reducing non-specific protein adsorption; attachment of ATH at the distal end of the PEG chains did not significantly affect protein resistance. It was shown that surfaces modified with ATH bound antithrombin selectively from plasma through the pentasaccharide sequence on the heparin moiety of ATH, indicating the ability of the ATH-modified surfaces to inhibit coagulation. Using thromboelastography, the effect of ATH modification on plasma coagulation was evaluated directly. It was found that initiation of coagulation was delayed and the time to clot was prolonged on PDMS modified with ATH/PEG compared to controls. For comparison, surfaces modified in a similar way with heparin were prepared and investigated using the same methods. The data suggest that the ATH-modified surfaces have superior anticoagulant properties compared to those modified with heparin.

Selective albumin-binding surfaces modified with a thrombin-inhibiting peptide

Blood-contacting medical devices have been associated with severe clinical complications, such as thrombus formation, triggered by the activation of the coagulation cascade due to the adsorption of certain plasma proteins on the surface of biomaterials. Hence, the coating of such surfaces with antithrombotic agents has been used to increase biomaterial haemocompatibility. Biomaterial-induced clotting may also be decreased by albumin adsorption from blood plasma in a selective and reversible way, since this protein is not involved in the coagulation cascade. In this context, this paper reports that the immobilization of the thrombin inhibitor D-Phe-Pro-D-Arg-D-Thr-CONH2 (fPrt) onto nanostructured surfaces induces selective and reversible adsorption of albumin, delaying the clotting time when compared to peptide-free surfaces. fPrt, synthesized with two glycine residues attached to the N-terminus (GGfPrt), was covalently immobilized onto self-assembled monolayers (SAMs) having different ratios of carboxylate-hexa(ethylene glycol)- and tri(ethylene glycol)-terminated thiols (EG6-COOH/EG3) that were specifically designed to control GGfPrt orientation, exposure and density at the molecular level. In solution, GGfPrt was able to inactivate the enzymatic activity of thrombin and to delay plasma clotting time in a concentration-dependent way. After surface immobilization, and independently of its concentration, GGfPrt lost its selectivity to thrombin and its capacity to inhibit thrombin enzymatic activity against the chromogenic substrate n-p-tosyl-Gly-Pro-Arg-p-nitroanilide. Nevertheless, surfaces with low concentrations of GGfPrt could delay the capacity of adsorbed thrombin to cleave fibrinogen. In contrast, GGfPrt immobilized in high concentrations was found to induce the procoagulant activity of the adsorbed thrombin. However, all surfaces containing GGfPrt have a plasma clotting time similar to the negative control (empty polystyrene wells), showing resistance to coagulation, which is explained by its capacity to adsorb albumin in a selective and reversible way. This work opens new perspectives to the improvement of the haemocompatibility of blood-contacting medical devices.

Bioengineered surfaces to improve the blood compatibility of biomaterials through direct thrombin inactivation

Thrombus formation, due to thrombin generation, is a major problem affecting blood-contacting medical devices. This work aimed to develop a new strategy to improve the hemocompatibility of such devices by the immobilization of a naturally occurring thrombin inhibitor into a nanostructured surface. Boophilin, a direct thrombin inhibitor from the cattle tick Rhipicephalus microplus, was produced as a recombinant protein in Pichia pastoris. Boophilin was biotinylated and immobilized on biotin-terminated self-assembled monolayers (SAM) via neutravidin. In order to maintain its proteinase inhibitory capacity after surface immobilization, boophilin was biotinylated after the formation of a boophilin-thrombin complex to minimize the biotinylation of the residues involved in thrombin-boophilin interaction. The extent of boophilin biotinylation was determined using matrix-assisted laser desorption/ionization-time of flight/time of flight mass spectrometry. Boophilin immobilization and thrombin adsorption were quantified using quartz crystal microbalance with dissipation. Thrombin competitive adsorption from human serum was assessed using ¹²⁵I-thrombin. Thrombin inhibition and plasma clotting time were determined using spectrophotometric techniques. Boophilin-coated SAM were able to promote thrombin adsorption in a selective way, inhibiting most of its activity and delaying plasma coagulation in comparison with boophilin-free surfaces, demonstrating boophilin's potential to improve the hemocompatibility of biomaterials used in the production of blood-contacting devices.

Modification of polyurethane surface with an antithrombin-heparin complex for blood contact: influence of molecular weight of polyethylene oxide used as a linker/spacer

Polyurethane (PU) was modified using isocyanate chemistry to graft polyethylene oxide (PEO) of various molecular weights (range 300-4600). An antithrombin-heparin (ATH) covalent complex was subsequently attached to the free PEO chain ends, which had been functionalized with N-hydroxysuccinimide (NHS) groups. Surfaces were characterized by water contact angle and X-ray photoelectron spectroscopy (XPS) to confirm the modifications. Adsorption of fibrinogen from buffer was found to decrease by ~80% for the PEO-modified surfaces compared to the unmodified PU. The surfaces with ATH attached to the distal chain end of the grafted PEO were equally protein resistant, and when the data were normalized to the ATH surface density, PEO in the lower MW range showed greater protein resistance. Western blots of proteins eluted from the surfaces after plasma contact confirmed these trends. The uptake of ATH on the PEO-modified surfaces was greatest for the PEO of lower MW (300 and 600), and antithrombin binding from plasma (an indicator of heparin anticoagulant activity) was highest for these same surfaces. The PEO-ATH- and PEO-modified surfaces also showed low platelet adhesion from flowing whole blood. It is concluded that for the PEO-ATH surfaces, PEO in the low MW range, specifically MW 600, may be optimal for achieving an appropriate balance between resistance to nonspecific protein adsorption and the ability to take up ATH and bind antithrombin in subsequent blood contact.

Immobilization of an antithrombin-heparin complex on gold: anticoagulant properties and platelet interactions

The anticoagulant properties and platelet interactions of gold surfaces modified with an antithrombin-heparin (ATH) complex are reported. ATH was attached to gold through either a short disulfide (linker) or a thiol-terminated polyethylene oxide (PEO) (linker, spacer). Analogous surfaces were prepared with uncomplexed heparin. Antithrombin (AT) uptake was measured before and after selectively destroying the active pentasaccharide sequence of the heparin moiety, and was found to be predominantly through the active sequence on all of the surfaces. AT binding was higher on the ATH surfaces than on the corresponding heparin surfaces. Heparin activity was assessed by an anti-factor Xa assay. The ratio of active heparin density (from the anti-FXa assay) to total heparin density was taken as a measure of heparin bioactivity. The ratio was greater on the ATH- than on the heparin-modified surfaces, i.e. the PEO-ATH surfaces showed the greater proportion of active heparin. Platelet adhesion from flowing whole blood was found to be reduced on PEO- and ATH-modified surfaces compared to bare gold. The PEO-ATH modified surfaces, but not the heparinized surfaces, were shown to prolong the clotting time of recalcified plasma.

Anti-fouling bioactive surfaces

Bioactive surfaces refer to surfaces with immobilized bioactive molecules aimed specifically at promoting or supporting particular interactions. Such surfaces are of great importance for various biomedical and biomaterials applications. In the past few years, considerable effort has been made to create bioactive surfaces by forming specific biomolecule-modified surfaces on a non-biofouling "base" or "background". Hydrophilic and bioinert polymers have been widely used as anti-fouling layers that resist non-specific protein interactions. They can also serve as "spacers" to effectively move the immobilized biomolecule away from the surface, thus enhancing its bioactivity. In this review we summarize several successful approaches for the design and preparation of bioactive surfaces based on different types of anti-fouling/spacer materials. Some perspectives on future research in this area are also presented.

Nanoscale surface modifications of medically relevant metals: state-of-the art and perspectives

Evidence that nanoscale surface properties stimulate and guide various molecular and biological processes at the implant/tissue interface is fostering a new trend in designing implantable metals. Cutting-edge expertise and techniques drawn from widely separated fields, such as nanotechnology, materials engineering and biology, have been advantageously exploited to nanoengineer surfaces in ways that control and direct these processes in predictable manners. In this review, we present and discuss the state-of-the-art of nanotechnology-based approaches currently adopted to modify the surface of metals used for orthopedic and dental applications, and also briefly consider their use in the cardiovascular field. The effects of nanoengineered surfaces on various in vitro molecular and cellular events are firstly discussed. This review also provides an overview of in vivo and clinical studies with nanostructured metallic implants, and addresses the potential influence of nanotopography on biomechanical events at interfaces. Ultimately, the objective of this work is to give the readership a comprehensive picture of the current advances, future developments and challenges in the application of the infinitesimally small to biomedical surface science. We believe that an integrated understanding of the in vitro and particularly of the in vivo behavior is mandatory for the proper exploitation of nanostructured implantable metals and, indeed, of all biomaterials.