Toward highly blood compatible hemodialysis membranes via blending with heparin-mimicking polyurethane: Study in vitro and in vivo

Polyurethanes and Their Biomedical Applications

The tunable mechanical properties of polyurethanes (PUs), due to their extensive structural diversity and biocompatibility, have made them promising materials for biomedical applications. Scientists can address PUs' issues with platelet absorption and thrombus formation owing to their modifiable surface. In recent years, PUs have been extensively utilized in biomedical applications because of their chemical stability, biocompatibility, and minimal cytotoxicity. Moreover, addressing challenges related to degradation and recycling has led to a growing focus on the development of biobased polyurethanes as a current focal point. PUs are widely implemented in cardiovascular fields and as implantable materials for internal organs due to their favorable biocompatibility and physicochemical properties. Additionally, they show great potential in bone tissue engineering as injectable grafts or implantable scaffolds. This paper reviews the synthesis methods, physicochemical properties, and degradation pathways of PUs and summarizes recent progress in applying different types of polyurethanes in various biomedical applications, from wound repair to hip replacement. Finally, we discuss the challenges and future directions for the translation of novel polyurethane materials into biomedical applications.

Citric Acid: A Nexus Between Cellular Mechanisms and Biomaterial Innovations

Citrate-based biodegradable polymers have emerged as a distinctive biomaterial platform with tremendous potential for diverse medical applications. By harnessing their versatile chemistry, these polymers exhibit a wide range of material and bioactive properties, enabling them to regulate cell metabolism and stem cell differentiation through energy metabolism, metabonegenesis, angiogenesis, and immunomodulation. Moreover, the recent US Food and Drug Administration (FDA) clearance of the biodegradable poly(octamethylene citrate) (POC)/hydroxyapatite-based orthopedic fixation devices represents a translational research milestone for biomaterial science. POC joins a short list of biodegradable synthetic polymers that have ever been authorized by the FDA for use in humans. The clinical success of POC has sparked enthusiasm and accelerated the development of next-generation citrate-based biomaterials. This review presents a comprehensive, forward-thinking discussion on the pivotal role of citrate chemistry and metabolism in various tissue regeneration and on the development of functional citrate-based metabotissugenic biomaterials for regenerative engineering applications.

Advances in Enhancing Hemocompatibility of Hemodialysis Hollow-Fiber Membranes

Hemodialysis, the most common modality of renal replacement therapy, is critically required to remove uremic toxins from the blood of patients with end-stage kidney disease. However, the chronic inflammation, oxidative stress as well as thrombosis induced by the long-term contact of hemoincompatible hollow-fiber membranes (HFMs) contribute to the increase in cardiovascular diseases and mortality in this patient population. This review first retrospectively analyzes the current clinical and laboratory research progress in improving the hemocompatibility of HFMs. Details on different HFMs currently in clinical use and their design are described. Subsequently, we elaborate on the adverse interactions between blood and HFMs, involving protein adsorption, platelet adhesion and activation, and the activation of immune and coagulation systems, and the focus is on how to improve the hemocompatibility of HFMs in these aspects. Finally, challenges and future perspectives for improving the hemocompatibility of HFMs are also discussed to promote the development and clinical application of new hemocompatible HFMs.

Graphical Abstract

Recent advancement challenges with synthesis of biocompatible hemodialysis membranes

The focus of this study is to enhance the protein fouling resistance, hydrophilicity, biocompatibility, hemocompatibility and ability of the membranes and to reduce health complications like chronic pulmonary disease, peripheral vascular disease, cerebrovascular disease, and cardiovascular disease after dialysis, which are the great challenges in HD applications. In the current study, the PSF-based dialysis membranes are studied broadly. Significant consideration has also been provided to membrane characteristics (e.g., flowrate coefficient, solute clearance characteristic) and also on commercially available polysulfone HD membranes. PSF has gained a significant share in the development of HD membranes, and continuous improvements are being made in the process to make high flux PSF-based dialysis membranes with enhanced biocompatibility and improved protein resistance ability as the major issue in the development of membranes for HD application is biocompatibility. There has been a great increase in the demand for novel biocompatible membranes that offer the best performances during HD therapy, for example, low oxidative stress and low change ability of blood pressure.

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

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

Improved hemocompatibility of polysulfone hemodialyzers with Endexo® surface modifying molecules

Anticoagulation therapy is widely used to reduce clotting during hemodialysis (HD), but may cause adverse effects in end-stage kidney disease patients. A new hemodialyzer with a membrane modified by surface modifying molecule was developed to improve hemocompatibility that aimed to reduce the need for anticoagulation during dialysis treatments. We compared membrane surface characteristics and in vitro hemocompatibility of the new hemodialyzer to the standard polysulfone (PSF) hemodialyzer membrane. Scanning electron microscopy, contact angle measurement (68° ± 3° test vs. 41.6° ± 6° control), and X-ray photoelectron spectrometry measurement for fluorine atomic % (7.4% ± 0.4% test vs. not detectable control), showed that the membrane surface was modified with surface modifying macromolecule (SMM1) but maintained membrane structure and surface hydrophilicity. Zeta potential of the blood-contacting surface showed that the absolute surface charge was reduced at neutral pH (-3.3 mV ± 1.1 mV test vs. -15.6 mV ± 1.0 mV control). Platelet count reduction was significantly less for the SMM1-modified dialyzer (40.88% ± 21.89%) compared to the standard PSF dialyzer (62.62% ± 34.13%), along with Platelet Factor 4 (1824.10 ng/ml ± 436.26 ng/ml test vs. 2479.00 ng/ml ± 852.96 ng/ml control). These studies demonstrate the successful incorporation of SMM1 into the new hemodialyzer with the expected results. Our in vitro experiments indicate that the SMM1-modified hemodialyzers could improve hemocompatibility compared to standard PSF hemodialyzers and have the potential to minimize the patient's anticoagulant requirements during HD. Additional research with SMM1 additives incorporated into the entire dialysis circuit and use in a clinical settings are required to confirm these promising findings.

Recent advances in heparinization of polymeric membranes for enhanced continuous blood purification

Continuous blood purification technology such as hemodiafiltration has been used worldwide for saving patients suffering from severe diseases or organ function failure, especially in the intensive care unit and emergency setting. The filters as core devices are commonly made of polymer materials as hollow fiber membranes. However, the membrane is often inductively blocked by blood clot formation due to its interactions with blood components. Heparin is the anticoagulant often used in clinical practice for anti-coagulation. Recently, heparin is also employed to modify the hollow fiber membranes either chemically or physically to improve the filtration performance. This review summarizes recent advances in methodology for surface heparinization of such hollow fiber membranes, and their filtration performance improvement. The review also provides expert opinions for further research in this rapidly expanding field.

A chitosan modified asymmetric small-diameter vascular graft with anti-thrombotic and anti-bacterial functions for vascular tissue engineering

Rapid endothelialization and prevention of restenosis are two vital challenges for the preparation of a small-diameter vascular graft (SDVG), while postoperative infection after implantation is often neglected.

Development of Poor Cell Adhesive Immersion Precipitation Membranes Based on Supramolecular Bis-Urea Polymers

A variety of biomedical applications requires tailored membranes; fabrication through a mix-and-match approach is simple and desired. Polymers based on supramolecular bis-urea (BU) moieties are capable of modular integration through directed non-covalent stacking. Here, it is proposed that non-cell adhesive properties can be introduced in polycaprolactone-BU-based membranes by the addition of poly(ethylene glycol) (PEG)-BU during immersion precipitation membrane fabrication, while unmodified PEG is not retained in the membrane. PEG-BU addition results in denser membranes with a similar pore size compared to pristine membranes, while PEG addition induces defect formation. Infrared spectroscopy and surface hydrophobicity measurements indicate that PEG-BU is retained during membrane processing. Additionally, PEG-BU incorporation successfully leads to poor cell adhesive surfaces. No evidence is observed to indicate PEG retention. The results obtained indicate that the BU system enables intimate mixing of BU-modified polymers after processing. Collectively, the results provide the first steps toward BU-based immersion precipitated supramolecular membranes for biomedical applications.

Hemodialysis performance and anticoagulant activities of PVP-k25 and carboxylic-multiwall nanotube composite blended Polyethersulfone membrane

Non-covalent electrostatic interaction between amide nitrogen and carbonyl carbon of shorter chain length of polyvinylpyrrolidone (PVP-k25) was developed with in-house carboxylic oxidized multiwall carbon nanotubes (O-MWCNT) and then blended with Polyethersulfone (PES) polymer. FTIR analysis was utilized to confirm bonding nature of nano-composites (NCs) of O-MWCNT/PVP-k25 and casting membranes. Non-solvent induces phase separation process developed regular finger-like channels in composite membranes whereas pristine PES exhibited spongy entities as studied by cross sectional analysis report of FESEM. Further, FESEM instrument was also utilized to observe the dispersion of O-MWCNT/PVP based nanocomposite (NCs) with PES and membranes leaching phenomena analysis. Contact angle experiments described 24% improvement of hydrophilic behaviour, leaching ratio of additives was reduced to 1.89%, whereas water flux enhanced up to 6 times. Bovine serum albumin (BSA) and lysozyme based antifouling analysis shown up to 25% improvement, whereas 84% of water flux was regained after protein fouling than pristine PES. Anticoagulant activity was reported by estimating prothrombin, thrombin, plasma re-calcification times and production of fibrinogen cluster with platelets-adhesions photographs and hemolysis experiments. Composite membranes exhibited 3.4 and 3 times better dialysis clearance ratios of urea and creatinine solutes as compared to the raw PES membrane.

Mussel-Inspired Catechol-Functionalized Hydrogels and Their Medical Applications

Mussel adhesive proteins (MAPs) have a unique ability to firmly adhere to different surfaces in aqueous environments via the special amino acid, 3,4-dihydroxyphenylalanine (DOPA). The catechol groups in DOPA are a key group for adhesive proteins, which is highly informative for the biomedical domain. By simulating MAPs, medical products can be developed for tissue adhesion, drug delivery, and wound healing. Hydrogel is a common formulation that is highly adaptable to numerous medical applications. Based on a discussion of the adhesion mechanism of MAPs, this paper reviews the formation and adhesion mechanism of catechol-functionalized hydrogels, types of hydrogels and main factors affecting adhesion, and medical applications of hydrogels, and future the development of catechol-functionalized hydrogels.

Heparin-based and heparin-inspired hydrogels: size-effect, gelation and biomedical applications

Heparin is the highest negatively charged biomolecule, which is a polysaccharide belonging to the glycosaminoglycan family, and its role as a regulator of various proteins, cells and tissues in the human body makes it an indispensable macromolecule. Heparin-based hydrogels are widely investigated in various applications including implantation, tissue engineering, biosensors, and drug-controlled release due to the 3D-constructs of hydrogels. However, heparin has supply and safety problems because it is usually derived from animal sources, and has the clinical limitations of bleeding and thrombocytopenia. Therefore, analogous heparin-mimicking polymers and hydrogels derived from non-animal and/or totally synthetic sources have been widely studied in recent years. In this review, the progress and potential biomedical applications of heparin-based and heparin-inspired hydrogels are highlighted. We classify the forms of these hydrogels by their size including macro-hydrogels, injectable hydrogels, and nano-hydrogels. Then, we summarize the various fabrication strategies for these hydrogels including chemical covalent bonding, physical conjugation, and the combination of chemical and physical interactions. Covalent bonding includes free radical polymerization of vinyl-containing components, amide bond formation reaction, Michael-type addition reaction, click-chemistry, divinyl sulfone crosslinking, and mussel-inspired coating. Hydrogels physically conjugated via host-guest interaction, electrostatic interaction, hydrogen bonding, and hydrophobic interaction are also discussed. Finally, we conclude with the challenges and future directions for the fabrication and the industrialization of heparin-based and heparin-inspired hydrogels. We believe that this review will attract more attention toward the design of heparin-based and heparin-inspired hydrogels, leading to future advancements in this emerging research field.

In vitro and in vivo anticoagulant activity of heparin-like biomacromolecules and the mechanism analysis for heparin-mimicking activity

Heparin-like biomacromolecules (HepLBm), exhibiting similar chemical structure and biological properties to heparin, can be obtained by modifying either synthetic biopolymers or natural biomacromolecules with physical or chemical methods. In this work, a low-cost and biocompatible sodium alginate was chosen as a model biomacromolecule to design anticoagulant HepLBm with a similar sulfation degree to heparin. FTIR, ¹H NMR, and element analysis data were used to confirm the chemical structure of HepLBm. Hemolysis tests, clotting time, complement activation, and contact activation tests were carried out to determine the in vitro anticoagulant activity of HepLBm. In addition, systematic studies of blood cell count, coagulation function, and histopathology were performed to demonstrate the in vivo anticoagulant activity and toxicity of HepLBm with SD rat experiments. Furthermore, a series of linear molecules containing carboxyl groups, sulfonic groups, and hydroxyl groups were selected and their clotting time was tested to provide a mechanism analysis for the excellent anticoagulant activity of HepLBm. With the excellent in vitro/in vivo anticoagulant activity, good biocompatibility, and low cost, the HepLBm synthesized in this work would have great potential for substitution of heparin in many application fields, such as the surface modification of biomedical devices, extracorporeal anticoagulants, and other clinical fields.

Synthesis and characterisation of composite sulphonated polyurethane/polyethersulphone membrane for blood purification application

Polyurethane (PU) with three different functional groups: carboxyl, hydroxyl and sulphonyl group on its molecular structure were synthesised in this work. The synthesised material suppresses blood clotting and exhibits anticoagulant characteristics due to the presence of the important anionic groups. The synthesised PU was blended with polyethersulphone (PES) and fabricated into flat-sheet membrane to study the physico-chemical and biocompatibility properties of the PES membrane for blood purification application. PES-PU flat-sheet membranes were fabricated via the dry-wet phase separation technique. Different loading of PU (0, 1, 2, 3, 4, and 5%) blended with PES was studied and compared. Based on the in-vitro biocompatibility analysis of the membrane, it can be suggested that the membrane incorporated with PU has better anticoagulant properties compared to the pristine PES membrane. PU incorporation prolonged the clotting time, decreased the formation of thrombin, decreased soluble complement component 3a (C3a) generation and suppressed platelet adhesion and aggregation. The anionic groups on the membrane surface might bind to coagulation factors (antithrombin) and the calcium ions, Ca²⁺ and thus improve anticoagulant ability. Based on both physico-chemical and in-vitro studied, 4% loading of PU is the optimum loading for incorporation with PES membrane. These results suggested that the blended PES-PU membranes with good haemocompatibility allowed practical application in the field of blood purification.

Graphene-based advanced nanoplatforms and biocomposites from environmentally friendly and biomimetic approaches

Environmentally friendly and biomimetic approaches to fabricate graphene-based advanced nanoplatforms and biocomposites for biomedical applications are summarized in this review.

Introduction of Nature's Complexity in Engineered Blood-compatible Biomaterials

Biomaterials with excellent blood-compatibility are needed for applications in vascular replacement therapies, such as vascular grafts, heart valves and stents, and in extracorporeal devices such as hemodialysis machines and blood-storage bags. The modification of materials that are being used for blood-contacting devices has advanced from passive surface modifications to the design of more complex, smart biomaterials that respond to relevant stimuli from blood to counteract coagulation. Logically, the main source of inspiration for the design of new biomaterials has been the endogenous endothelium. Endothelial regulation of hemostasis is complex and involves a delicate interplay of structural components and feedback mechanisms. Thus, challenges to develop new strategies for blood-compatible biomaterials now lie in incorporating true feedback controlled mechanisms that can regulate blood compatibility in a dynamic way. Here, supramolecular material systems are highlighted as they provide a promising platform to introduce dynamic reciprocity, due to their inherent dynamic nature.

Low-fouling PES membranes fabricated via in situ copolymerization mediated surface zwitterionicalization

PEGylated and zwitterionic PES membranes were fabricated during membrane formation, showing superior antifouling and anticoagulant properties.

Pengaruh Agen Pencangkok Heparin terhadap Kemampuan Transpor Kreatinin dan Urea Membran Turunan Kitosan

Immersi heparin dilakukan pada membran kitosan untuk menambah sisi aktif membran, pada proses transpor urea. Dari data analisis didapatkan terjadi peningkatan persentase transpor urea dari 17,57 % menjadi 27,09 % dengan adanya penambahan heparin.

Tyrosinase-Mediated Surface Coimmobilization of Heparin and Silver Nanoparticles for Antithrombotic and Antimicrobial Activities

Thrombus and infections are the most common causes for the failure of medical devices, leading to higher hospitalization costs and, in some cases, patient morbidity. It is, therefore, necessary to develop novel strategies to prevent thrombosis and infection caused by medical devices. Herein, we report a simple and a highly efficient strategy to impart antithrombotic and antimicrobial properties to substrates, by simultaneously immobilizing heparin and in situ-synthesized silver nanoparticles (Ag NPs) via a tyrosinase-catalyzed reaction. This consists of tyrosinase-oxidized phenolic groups of a heparin derivative (heparin-grafted tyramine, HT) to catechol groups, followed by immobilizing heparin and inducing the in situ Ag NP formation onto poly(urethane) (PU) substrates. The successful immobilization of both heparin and in situ Ag NPs on the substrates was confirmed by analyses of water contact angles, XPS, SEM, and AFM. The sustained silver release and the surface stability were observed for 30 days. Importantly, the antithrombotic potential of the immobilized surfaces was demonstrated by a reduction in fibrinogen absorption, platelet adhesion, and prolonged blood clotting time. Additionally, the modified PU substrates also exhibited remarkable antibacterial properties against both Gram-positive and Gram-negative bacteria. The results of this work suggest a useful, effective, and time-saving method to improve simultaneous antithrombotic and antibacterial performances of a variety of substrate materials for medical devices.

Mussel-inspired post-heparinization of a stretchable hollow hydrogel tube and its potential application as an artificial blood vessel

We report the fabrication and post-functionalization of a highly stretchable hydrogel tube and its potential application as an artificial blood vessel.

Bioinspired Polyethersulfone Membrane Design via Blending with Functional Polyurethane

Polyurethanes (PUs) are currently considered to be biocompatible materials but limited by a low resistance to thrombus. We therefore design a heparin-like PU (HLPU) to modify polyethersulfone (PES) membranes approaching integrated antifouling and antithrombotic properties by bioinspiration of heparin structure. Poly(vinyl pyrrolidone)-HLPU (PVP-HLPU) was synthesized via reversible addition-fragmentation chain transfer polymerization of VP using PU as a macroinitiator and then sulfonated by concentrated H2SO4. FTIR and NMR results demonstrated the successful synthesis of PVP-HLPU. By incorporation of PVP-HLPU, the cross-sectional structure of PES composite membranes altered from finger-like structure to sponge-like structure resulting in tunable permeability. The increased hydrophilicity verified by water contact angles benefited both the permeability and antifouling property. As a consequence, the composite membranes showed good blood compatibility, including decreased protein adsorption, suppressed platelet adhesion, lowered thrombin-antithrombin III generation, reduced complement activation, and prolonged clotting times. Interestingly, the PVP-capped HLPU showed better blood compatibility compared to polyethyleneglycol-capped and citric acid-capped HLPUs. The results demonstrated the enhanced antifouling and antithrombotic properties of PES hemodialysis membranes by the introduction of functional HLPUs. Also, the proposed method may forward the fabrication of hemocompatible membranes via bioinspired surface design.

Heparin-Mimicking Polymers: Synthesis and Biological Applications

Heparin is a naturally occurring, highly sulfated polysaccharide that plays a critical role in a range of different biological processes. Therapeutically, it is mostly commonly used as an injectable solution as an anticoagulant for a variety of indications, although it has also been employed in other forms such as coatings on various biomedical devices. Due to the diverse functions of this polysaccharide in the body, including anticoagulation, tissue regeneration, anti-inflammation, and protein stabilization, and drawbacks of its use, analogous heparin-mimicking materials are also widely studied for therapeutic applications. This review focuses on one type of these materials, namely, synthetic heparin-mimicking polymers. Utilization of these polymers provides significant benefits compared to heparin, including enhancing therapeutic efficacy and reducing side effects as a result of fine-tuning heparin-binding motifs and other molecular characteristics. The major types of the various polymers are summarized, as well as their applications. Because development of a broader range of heparin-mimicking materials would further expand the impact of these polymers in the treatment of various diseases, future directions are also discussed.