Endothelium-Mimicking Materials: A "Rising Star" for Antithrombosis

The advancement of antithrombotic materials has significantly mitigated the thrombosis issue in clinical applications involving various medical implants. Extensive research has been dedicated over the past few decades to developing blood-contacting materials with complete resistance to thrombosis. However, despite these advancements, the risk of thrombosis and other complications persists when these materials are implanted in the human body. Consequently, the modification and enhancement of antithrombotic materials remain pivotal in 21st-century hemocompatibility studies. Previous research indicates that the healthy endothelial cells (ECs) layer is uniquely compatible with blood. Inspired by bionics, scientists have initiated the development of materials that emulate the hemocompatible properties of ECs by replicating their diverse antithrombotic mechanisms. This review elucidates the antithrombotic mechanisms of ECs and examines the endothelium-mimicking materials developed through single, dual-functional and multifunctional strategies, focusing on nitric oxide release, fibrinolytic function, glycosaminoglycan modification, and surface topography modification. These materials have demonstrated outstanding antithrombotic performance. Finally, the review outlines potential future research directions in this dynamic field, aiming to advance the development of antithrombotic materials.

Integrating Metabolic Oligosaccharide Engineering and SPAAC Click Chemistry for Constructing Fibrinolytic Cell Surfaces

To effectively solve the problem of significant loss of transplanted cells caused by thrombosis during cell transplantation, this study simulates the human fibrinolytic system and combines metabolic oligosaccharide engineering with strain-promoted azide-alkyne cycloaddition (SPAAC) click chemistry to construct a cell surface with fibrinolytic activity. First, a copolymer (POL) of oligoethylene glycol methacrylate (OEGMA) and 6-amino-2-(2-methylamido)hexanoic acid (Lys) was synthesized by reversible addition-fragmentation chain transfer (RAFT) copolymerization, and the dibenzocyclooctyne (DBCO) functional group was introduced into the side chain of the copolymer through an active ester reaction, resulting in a functionalized copolymer DBCO-PEG4-POL with ε-lysine ligands. Then, azide functional groups were introduced onto the surface of HeLa model cells through metabolic oligosaccharide engineering, and DBCO-PEG4-POL was further specifically modified onto the surface of HeLa cells via the SPAAC "click" reaction. In vitro investigations revealed that compared with unmodified HeLa cells, modified cells not only resist the adsorption of nonspecific proteins such as fibrinogen and human serum albumin but also selectively bind to plasminogen in plasma while maintaining good cell viability and proliferative activity. More importantly, upon the activation of adsorbed plasminogen into plasmin, the modified cells exhibited remarkable fibrinolytic activity and were capable of promptly dissolving the primary thrombus formed on their surfaces. This research not only provides a novel approach for constructing transplantable cells with fibrinolytic activity but also offers a new perspective for effectively addressing the significant loss of transplanted cells caused by thrombosis.

Surface Engineering of Central Venous Catheters via Combination of Antibacterial Endothelium-Mimicking Function and Fibrinolytic Activity for Combating Blood Stream Infection and Thrombosis

Long-term blood-contacting devices (e.g., central venous catheters, CVCs) still face the highest incidence of blood stream infection and thrombosis in clinical application. To effectively address these complications, this work reports a dual-functional surface engineering strategy for CVCs by organic integration of endothelium-mimicking and fibrinolytic functions. In this proposal, a lysine (Lys)/Cu2+ -incorporated zwitterionic polymer coating (defined as PDA/Lys/Cu-SB) is designed and robustly fabricated onto commercial CVCs using a facile two-step process. Initially, adhesive ene-functionalized dopamine is covalently reacted with Lys and simultaneously coordinated with bactericidal Cu2+ ions, leading to the deposition of a PDA/Lys/Cu coating on CVCs through mussel foot protein inspired surface chemistry. Next, zwitterionic poly(sulfobetaine methacrylate) (pSB) brushes are grafted onto the PDA/Lys/Cu coating to endow lubricant and antifouling properties. In the final PDA/Lys/Cu-SB coating, endothelium-mimicking function is achieved by combining the catalytic generation of nitric oxide from the chelated Cu2+ with antifouling pSB brushes, which led to significant prevention of thrombosis, and bacterial infection in vivo. Furthermore, the immobilized Lys with fibrinolytic activity show remarkably enhanced long-term anti-thrombogenic properties as evidenced in vivo by demonstrating the capability to lyse nascent clots. Therefore, this developed strategy provides a promising solution for long-term blood-contacting devices to combat thrombosis and infection.

Robust, Anti-biofouling 2D Nanogel Films from Poly(N-vinyl caprolactam-co-vinylimidazole) Polymers

In analogy with adsorbed protein films, we have fabricated a family of 2D nanofilms composed of poly(N-vinyl caprolactam-co-vinylimidazole) (PNVCL) nanogels. NVCL was copolymerized with 1-vinylimidazole (VIM), then cross-linked with α,ω-dibromoalkanes...

A hemocompatible polyurethane surface having dual fibrinolytic and nitric oxide generating functions

Thrombus formation remains a serious problem in developing blood compatible materials. Despite continuous, intensive efforts over many years to prepare surfaces that prevent clotting, such surfaces have not been achieved; indeed it seems that surface-induced clotting is inevitable. An alternative approach is to accept that clotting will occur and to design surfaces so that small, nascent clots will be lysed before they can cause harm. The generation of plasmin, as in the fibrinolytic system, may be adopted for this purpose. The vascular endothelium (the inner surface of intact blood vessels) releases nitric oxide (NO) on a continuous basis. NO protects against platelet activation and aggregation, and also has an anti-proliferative effect on smooth muscle cells (SMCs). Based on these two important functions of the vascular system, the approach of constructing a fibrinolytic surface that generates NO is developed in the present work. Poly(oligo(ethylene glycol) methyl ether methacrylate-co-6-amino-2-(2-methacylamido)-hexanoic acid) (poly(OEGMA-co-LysMA)) was attached to a vinyl-functionalized polyurethane (PU) surface by graft polymerization giving a surface (PU-POL) with protein-resistant properties (via poly(OEGMA)) and clot lysing properties (via poly(LysMA)). Selenocystamine, which catalyzes S-nitrosothiol decomposition to generate NO in the vasculature, was then immobilized on the PU-POL surface via covalent attachment. A dual functioning surface with fibrinolytic activity (lysis of nascent clots) and NO releasing ability (inhibition of platelet adhesion and SMC adhesion as well as proliferation) was thereby constructed.

Substrate-independent, Schiff base interactions to fabricate lysine-functionalized surfaces with fibrinolytic activity

We demonstrated a simple, substrate-independent approach for the fabrication of lysine-ligand functionalized surfaces with fibrinolytic activity under physiological conditions.

Medicated Janus fibers fabricated using a Teflon-coated side-by-side spinneret

A family of medicated Janus fibers that provides highly tunable biphasic drug release was fabricated using a side-by-side electrospinning process employing a Teflon-coated parallel spinneret. The coated spinneret facilitated the formation of a Janus Taylor cone and in turn high quality integrated Janus structures, which could not be reliably obtained without the Teflon coating. The fibers prepared had one side consisting of polyvinylpyrrolidone (PVP) K60 and ketoprofen, and the other of ethyl cellulose (EC) and ketoprofen. To modulate and tune drug release, PVP K10 was doped into the EC side in some cases. The fibers were linear and had flat morphologies with an indent in the center. They provide biphasic drug release, with the PVP K60 side dissolving very rapidly to deliver a loading dose of the active ingredient, and the EC side resulting in sustained release of the remaining ketoprofen. The addition of PVP K10 to the EC side was able to accelerate the second stage of release; variation in the dopant amount permitted the release rate and extent this phase to be precisely tuned. These results offer the potential to rationally design systems with highly controllable drug release profiles, which can complement natural biological rhythms and deliver maximum therapeutic effects.

A t-PA/nanoparticle conjugate with fully retained enzymatic activity and prolonged circulation time

A major issue in the therapeutic use of tissue plasminogen activator (t-PA) for the treatment of thrombotic diseases is its very short half-life in the circulation due to the effects of inhibitors. The present study aims to resolve the issue using a t-PA/gold nanoparticle (t-PA/AuNP) conjugate prepared via bio-affinity ligation under physiological conditions. The ligation is based on the specific interactions between t-PA and ε-lysine (a ligand that has affinity to a specific domain in t-PA) immobilized on the AuNP surface through polyvinyl pyrrolidone (PVP) as a spacer. The conjugate can not only retain almost full enzymatic activity and clot dissolving efficiency, but also protect t-PA from inhibition by PAI-1 to some extent as compared with free t-PA in vitro. Moreover, the conjugate showed prolonged circulation time in vivo.

Surfaces having dual affinity for plasminogen and tissue plasminogen activator: in situ plasmin generation and clot lysis

In situ activation of a surface-integrated zymogen was achieved by introducing affinity ligands for both the zymogen and its activator.

Surface immobilization of a protease through an inhibitor-derived affinity ligand: a bioactive surface with defensive properties against an inhibitor

Surface immobilization of a protease through its inhibitor-derived peptide was shown to be advantageous in retaining the enzymatic activity of the protease and protecting the protease from being inhibited by its inhibitor.

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.

Thermoresponsive copolymer decorated surface enables controlling the adsorption of a target protein in plasma

The control of protein/surface interactions by external stimuli is often required in bioapplications such as bioseparation and biosensors. Although regulation of protein adsorption has been achieved on the surfaces modified with stimuli-responsive polymers, controlled protein adsorption is still challenging for a target protein in a multiprotein system. The present study developed a concept of surface design for the controlled adsorption of a specific protein from plasma by combining a thermoresponsive polymer with an affinity ligand on the surface. In this regard, a polyurethane (PU) surface was modified with the copolymer of N-isopropylacrylamide (NIPAAm) and a ε-lysine-containing monomer (LysMA). ε-Lysine is a specific ligand for plasminogen that was used as the model "target protein" in this study. The PU-P(NIPAAm-co-Lys) surfaces exhibited distinct thermoresponsivity of plasminogen adsorption from plasma with a larger quantity adsorbed at 37 °C than at 23 °C. By contrast, the surfaces showed a low level of adsorption for other plasma proteins at both temperatures. In addition, plasminogen adsorbed on a PU-P(NIPAAm-co-Lys) surface could be partly desorbed by lowering the temperature, and the activity of plasminogen adsorbed was well preserved. We believe that the concept developed in this study can be extended to other proteins by combining PNIPAAm and specific ligands with affinities for the proteins of interest.

125I-radiolabeling, surface plasmon resonance, and quartz crystal microbalance with dissipation: three tools to compare protein adsorption on surfaces of different wettability

The extent of protein adsorption is an important consideration in the biocompatibility of biomaterials. Various experimental methods can be used to determine the quantity of protein adsorbed, but the results usually differ. In the present work, self-assembled monolayers (SAMs) were used to prepare a series of model gold surfaces varying systematically in water wettability, from hydrophilic to hydrophobic. Three commonly used methods, namely, surface plasmon resonance (SPR), quartz crystal microbalance with dissipation (QCM-D), and (125)I-radiolabeling, were employed to quantify fibrinogen (Fg) adsorption on these surfaces. This approach allows a direct comparison of the mass of Fg adsorbed using these three techniques. The results from all three methods showed that protein adsorption increases with increasing surface hydrophobicity. The increase in the mass of Fg adsorbed with increasing surface hydrophobicity in the SPR data was parallel to that from (125)I-radiolabeling, but the absolute values were different and there does not seem to be a "universally congruent" relationship between the two methods for surfaces with varying wettability. For QCM-D, the variation in protein adsorption with wettability was different from that for SPR and radiolabeling. On the more hydrophobic surfaces, QCM-D gave an adsorbed mass much higher than from the two other methods, possibly because QCM-D measures both the adsorbed Fg and its associated water. However, on the more hydrophilic surfaces, the adsorbed mass from QCM-D was slightly greater than that from SPR, and both were smaller than from (125)I-radiolabeling; this was true no matter whether the Sauerbrey equation or the Voigt model was used to convert QCM-D data to adsorbed mass.