Platelet adhesion onto segmented polyurethane surfaces modified by carboxybetaine

Functional Zwitterionic Polyurethanes: State-of-the-Art Review

Recent advancements in bioengineering and medical devices have been greatly influenced and dominated by synthetic polymers, particularly polyurethanes (PUs). PUs offer customizable mechanical properties and long-term stability, but their inherent hydrophobic nature poses challenges in practically biological application processes, such as interface high friction, strong protein adsorption, and thrombosis. To address these issues, surface modifications of PUs for generating functionally hydrophilic layers have received widespread attention, but the durability of generated surface functionality is poor due to irreversible mechanical wear or biodegradation. As a result, numerous researchers have investigated bulk modification techniques to incorporate zwitterionic polymers or groups onto the main or side chains of PUs, thereby improving their hydrophilicity and biocompatibility. This comprehensive review presents an extensive overview of notable zwitterionic PUs (ZPUs), including those based on phosphorylcholine, sulfobetaine, and carboxybetaine. The review explores their wide range of biomedical applications, from blood-contacting devices to antibacterial coatings, fouling-resistant marine coatings, separation membranes, lubricated surfaces, and shape memory and self-healing materials. Lastly, the review summarizes the challenges and future prospects of ZPUs in biological applications.

Tannic Acid-Assisted Immobilization of Copper(II), Carboxybetaine, and Argatroban on Poly(ethylene terephthalate) Mats for Synergistic Improvement of Blood Compatibility and Endothelialization

Due to thrombosis and intimal hyperplasia, small-diameter vascular grafts have poor long-term patency. A combination strategy based on nitric oxide (NO) and anticoagulants has the potential to address those issues. In this study, poly(ethylene terephthalate) (PET) mats were prepared by electrospinning and coated with tannic acid (TA)/copper ion complexes. The chelated copper ions endowed the mats with sustained NO generation by catalytic decomposition of endogenous S-nitrosothiol. Subsequently, zwitterionic carboxybetaine acrylate (CBA) and argatroban (AG) were immobilized on the mats. The introduced AG and CBA had synergistic effects on the improvement of blood compatibility, resulting in reduced platelet adhesion and prolonged blood clotting time. The biocomposite mats selectively promoted the proliferation and migration of human umbilical vein endothelial cells while inhibiting the proliferation and migration of human umbilical arterial smooth muscle cells under physiological conditions. In addition, the prepared mats exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus. Collectively, the prepared mats hold great promise as artificial small-diameter vascular grafts.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Bio-inspired hemocompatible surface modifications for biomedical applications

When blood first encounters the artificial surface of a medical device, a complex series of biochemical reactions is triggered, potentially resulting in clinical complications such as embolism/occlusion, inflammation, or device failure. Preventing thrombus formation on the surface of blood-contacting devices is crucial for maintaining device functionality and patient safety. As the number of patients reliant on blood-contacting devices continues to grow, minimizing the risk associated with these devices is vital towards lowering healthcare-associated morbidity and mortality. The current standard clinical practice primarily requires the systemic administration of anticoagulants such as heparin, which can result in serious complications such as post-operative bleeding and heparin-induced thrombocytopenia (HIT). Due to these complications, the administration of antithrombotic agents remains one of the leading causes of clinical drug-related deaths. To reduce the side effects spurred by systemic anticoagulation, researchers have been inspired by the hemocompatibility exhibited by natural phenomena, and thus have begun developing medical-grade surfaces which aim to exhibit total hemocompatibility via biomimicry. This review paper aims to address different bio-inspired surface modifications that increase hemocompatibility, discuss the limitations of each method, and explore the future direction for hemocompatible surface research.

Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices

This review summarizes recent research on the design of polymer material systems based on biomimetic concepts and reports on the medical devices that implement these systems. Biomolecules such as proteins, nucleic acids, and phospholipids, present in living organisms, play important roles in biological activities. These molecules are characterized by heterogenic nature with hydrophilicity and hydrophobicity, and a balance of positive and negative charges, which provide unique reaction fields, interfaces, and functionality. Incorporating these molecules into artificial systems is expected to advance material science considerably. This approach to material design is exceptionally practical for medical devices that are in contact with living organisms. Here, it is focused on zwitterionic polymers with intramolecularly balanced charges and introduce examples of their applications in medical devices. Their unique properties make these polymers potential surface modification materials to enhance the performance and safety of conventional medical devices. This review discusses these devices; moreover, new surface technologies have been summarized for developing human-friendly medical devices using zwitterionic polymers in the cardiovascular, cerebrovascular, orthopedic, and ophthalmology fields.

2-methoxyethylacrylate modified polyurethane membrane and its blood compatibility

Hydrophilic material 2-methoxyethylacrylate (MEA) was grafted onto polyurethane (PU) membrane via Michael addition reaction. Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscopy (XPS) characterizations of the modified membrane proved that MEA was successfully grafted onto PU membrane surface. The water contact angle of the modified PU membrane decreased from 86° to 48° compared with unmodified PU membrane, which means that the hydrophilicity of the modified membrane was greatly improved. A series of blood compatibility tests including bovine serum protein adsorption, platelet adhesion, hemolysis assay, plasma recalacification time, prothrombin time (PT), partial thromboplastin time (APTT) and thrombin time (TT) were carried out on PU membrane and the modified PU membrane with highest grafted density of MEA. The combined results indicate that MEA plays an important role in improving the blood compatibility of PU membrane.

Hemocompatibility and anti-biofouling property improvement of poly(ethylene terephthalate) via self-polymerization of dopamine and covalent graft of zwitterionic cysteine

Inspired by the composition of adhesive proteins in mussels, we used self-polymerized dopamine to form a thin and surface-adherent polydopamine layer onto poly(ethylene terephthalate) (PET) sheet, followed by covalent grafting cysteine (Cys) to improve hemocompatibility and anti-biofouling property. The obtained surfaces were characterized by water contact angle measurements (WCA), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) analysis. The results of platelet adhesion and protein adsorption tests showed that cysteine immobilized PET was endowed with improved resistance to nonspecific protein adsorption and platelet adhesion. The results of hemolysis rate test showed cysteine grafted PET (PET-g-Cys) had low hemolytic ability. Cell assay results showed that PET-g-Cys surface could greatly inhibit HeLa cell adhesion. These works provide an ideal hemocompatible and antifouling surface for biomedical applications.

Design and characterization of sulfobetaine-containing terpolymer biomaterials

A methacrylic terpolymer system with non-fouling interfacial properties was synthesized by the random copolymerization of hexyl methacrylate, methyl methacrylate and sulfobetaine methacrylate (a monomer bearing a zwitterionic pendant group). Polymers were synthesized from feeds containing 0-15 mol.% of the zwitterion-containing methacrylate. Proton nuclear magnetic resonance verified the incorporation of sulfobetaine methacrylate into the polymer structure. Water absorption studies illustrate that the hydrophilicity of the material increases with increasing zwitterion concentration. The biological properties of the polymer were probed by fibrinogen adsorption, human umbilical vein endothelial cell adhesion and growth, and platelet adhesion. Strong resistance to protein adsorption and cell and platelet attachment was observed on materials synthesized from 15 mol.% sulfobetaine methacrylate. Results were compared to the non-fouling behavior of a PEGylated terpolymer formulation and it was observed that the poly(ethylene glycol)-containing materials were slightly more effective at resisting human umbilical vein endothelial cell adhesion and growth over a 7 day incubation period, but the zwitterion-containing materials were equally effective at resisting fibrinogen adsorption and platelet adhesion. The zwitterion-containing materials were electrospun into three-dimensional random fiber scaffolds. Materials synthesized from 15 mol.% of the zwitterion-containing monomer retained their non-fouling character after fabrication into scaffolds.

Fabrication of permeable tubular constructs from chemically modified chitosan with enhanced antithrombogenic property

The failure of artificial vascular grafts in small diameter vessel replacement is mainly due to the early formation of thrombosis. To prevent the occurrence of thrombosis, much effort has been focused on developing an anti-thrombogenic coating of synthetic vascular prostheses or artificial conduits with improved anti-thrombogenic properties. Because surface coatings may be unstable for long-term applications, a bulk material with anti-thrombogenic property is desirable for the fabrication of vascular grafts or conduits. To this end, we have chemically modified chitosan by phthalization to derive an anti-thrombogenic material for the fabrication of vascular grafts. The chemical structure of phthalized chitosan was characterized with infrared spectroscopy. The hydrophilicity was examined with contact angle measurement, and the molecular weight distribution was measured using gel permeation chromatography (GPC). Protein adsorption, hemolysis, and platelet adhesion assays were used to confirm the enhanced anti-thrombogenic properties of this phthalized chitosan. Cytotoxicity and proliferation assays were performed to test its high biocompatibility. With its improved solubility and processibility, this phthalized chitosan was fabricated into selective permeable tubular constructs of varying sizes and morphology through a wet phase-inversion process. With improved anti-thrombogenic property, biocompatibility, and great processibility, phthalized chitosan has great potential as the material for the fabrication of small diameter vascular grafts.

A lubricious formulation exhibiting reduced thrombogenicity, cell proliferation, and protein adsorption

The adhesion of human platelets, erythrocytes, and leukocytes, the adsorption of protein, and the proliferation of human umbilical vein endothelial cells (HUVEC) on the surface of electropolished stainless steel and the lumen of polyurethane tubing coated with Hydromer's lubricious Duality T8B formulation was evaluated. Following exposure to a platelet-enriched suspension from citrated human whole blood, stainless steel coated with this formulation exhibited significantly reduced adhesion of platelets, erythrocytes, and granulocytes. This reduction in adhesion was confirmed using an immunohistochemical method utilizing antibodies to CD41, CD235, and CD15, respectively. The proliferation of HUVEC cells were significantly reduced when cultured on coated stainless steel. This formulation was also able to significantly reduce the adsorption of plasma proteins and the major protein in tear fluid (lysozyme) to the surface of stainless steel. The nonthrombogenic properties of Duality T8B after application to the lumen of polyurethane tubing were also examined. Following a short-term (3 h) static exposure to citrated human whole blood, microscopic examination revealed that the adhesion of platelets and erythrocytes was reduced significantly, a finding confirmed using anti-CD41 and anti-CD235 antibodies in the immunohistochemical method. A long-term (12 day) study yielded essentially identical results indicating a significant reduction in the adhesion of blood components on the luminal surface of coated polyurethane tubing. In summary, these data indicate that the application of Duality T8B onto surfaces of medical devices, such as catheters, extracorporeal circuitry, and coronary stents, could aid in reducing or preventing not only thrombus formation but also the process of restenosis.

Platelet adhesive resistance of polyurethane surface grafted with zwitterions of sulfobetaine

A possible approach to improve the blood compatibility of poly(etherurethane)s (PU) involves the covalent attachment of key molecular on its surface. Recently, polymer tailed with zwitterions was found having good blood compatibility. The purpose of present study was to design and synthesis a novel nonthrombogenic biomaterial by modifying the surface of poly(etherurethane) with zwitterions of sulfobetaine via HDI spacer. The films of polyurethane were grafted with sulfobetaine by a three-step procedure. In the first step, the film surfaces were treated with hexamethylene diisocyanate (HDI) in toluene at 50 degrees C in the presence of di-n-butyl tin dilaurate(DBTDL) as a catalyst. The extent of the reaction was measured by ATR-IR spectra; a maximum number of free NCO group was obtained after a reaction time of 2.5 h. In the second step, the primary amine group of N,N-diethylethylenediamine (DEA) or N,N-dimethylethylenediamine (DMA) was allowed to react in toluene with isocyanate groups bound on surface. In the third step, two kinds of sulfobetaines were formed in the surface through the ring-opening reaction between tertiary amine of DMA or DEA and 1,3- propanesultone (PS). The reaction process was monitored with ATR-IR spectra and XPS spectra. The wettability of films was investigated by water contact angle measurement. A platelet adhesion experiment was conducted as a preliminary test to confirm the improved blood compatibility of PU. The number of platelets adhering to PU decreased greatly compared to original after 1 h and 3 h of contact with human plate-rich plasma.