Nonthrombogenic, biodegradable elastomeric polyurethanes with variable sulfobetaine content

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.

Water-Triggered Segment Orientation of Long-Lasting Anti-Biofouling Polyurethane Coatings on Biomedical Catheters via Solvent Exchange Strategy

The formation of biofilm and thrombus on medical catheters poses a significant life-threatening concern. Hydrophilic anti-biofouling coatings upon catheter surfaces with complex shapes and narrow lumens are demonstrated to have the potential in reducing complications. However, their effectiveness is constrained by poor mechanical stability and weak substrate adhesion. Herein, a novel zwitterionic polyurethane (SUPU) with strong mechanical stability and long-term anti-biofouling is developed by controlling the ratio of sulfobetaine-diol and ureido-pyrimidinone. Once immersed in water, as-synthesized zwitterionic coating (SUPU3 SE) would undergo a water-driven segment reorientation to obtain much higher durability than its direct drying one, even under various extreme treatments, including acidic solution, abrasion, ultrasonication, flushing, and shearing, in PBS at 37 °C for 14 days. Moreover, SUPU3 SE coating could achieve a 97.1% of exceptional reducing protein fouling, complete prevention of cell adhesion, and long-lasting anti-biofilm performance even after 30 days. Finally, the good anti-thrombogenic formations of SUPU3 SE coating with bacterial treatment are validated in blood circulation through an ex vivo rabbit arteriovenous shunt model. This work provides a facile approach to fabricating stable hydrophilic coating through a simple solvent exchange to reduce thrombosis and infection of biomedical catheters.

Assessment of the Anti-Thrombogenic Activity of Polyurethane Starch Composites

The increasing morbidity and mortality of patients due to post-surgery complications of coronary artery bypass grafts (CABPG) are related to blood–material interactions. Thus, the characterization of the thrombogenicity of the biomaterial for cardiovascular devices is of particular interest. This research evaluated the anti-thrombogenic activity of polyurethanes–starch composites. We previously synthesized polyurethane matrices that were obtained from polycaprolactone diol (PCL), polyethylene glycol (PEG), pentaerythritol (PE), and isophorone diisocyanate (IPDI). In addition, potato starch (AL-N) and zwitterionic starch (AL-Z) were added as fillers. The anti-thrombogenic property was characterized by the clot formation time, platelet adhesion, protein absorption, TAT complex levels, and hemolysis. Additionally, we evaluated the cell viability of the endothelial and smooth muscle cells. Statically significant differences among the polyurethane matrices (P1, P2, and P3) were found for protein absorption and the blood clotting time without fillers. The polyurethanes composites with AL-Z presented an improvement in the anti-thrombogenic property. On the other hand, the composites with AL-Z reduced the viability of the endothelial cells and did not significantly affect the AoSCM (except for P1, which increased). These results classify these biomaterials as inert; therefore, they can be used for cardiovascular 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.

A critical review of fibrous polyurethane-based vascular tissue engineering scaffolds

Certain polymeric materials such as polyurethanes (PUs) are the most prevalent class of used biomaterials in regenerative medicine and have been widely explored as vascular substitutes in several animal models. It is thought that PU-based biomaterials possess suitable hemo-compatibility with comparable performance related to the normal blood vessels. Despite these advantages, the possibility of thrombus formation and restenosis limits their application as artificial functional vessels. In this regard, various surface modification approaches have been developed to enhance both hemo-compatibility and prolong patency. While critically reviewing the recent advances in vascular tissue engineering, mainly PU grafts, this paper summarizes the application of preferred cell sources to vascular regeneration, physicochemical properties, and some possible degradation mechanisms of PU to provide a more extensive perspective for future research.

Recent Advances in Polyurethane/POSS Hybrids for Biomedical Applications

Advanced organic-inorganic materials-composites, nanocomposites, and hybrids with various compositions offer unique properties required for biomedical applications. One of the most promising inorganic (nano)additives are polyhedral oligomeric silsesquioxanes (POSS); their biocompatibility, non-toxicity, and phase separation ability that modifies the material porosity are fundamental properties required in modern biomedical applications. When incorporated, chemically or physically, into polyurethane matrices, they substantially change polymer properties, including mechanical properties, surface characteristics, and bioactivity. Hence, this review is dedicated to POSS-PU composites that have recently been developed for applications in the biomedical field. First, different modes of POSS incorporation into PU structure have been presented, then recent developments of PU/POSS hybrids as bio-active composites for scaffolds, cardiovascular stents, valves, and membranes, as well as in bio-imaging and cancer treatment, have been described. Finally, characterization and methods of modification routes of polyurethane-based materials with silsesquioxanes were presented.

Sustainable Synthesis of Cyclic Carbonates from Terminal Epoxides by a Highly Efficient CaI2/1,3-Bis[tris(hydroxymethyl)-methylamino]-propane Catalyst

The nonstopping increment of atmospheric carbon dioxide (CO₂) concentration keeps harming the environment and human life. The traditional concept of carbon capture and storage (CCS) is no longer sufficient and has already been corrected to carbon capture, utilization, and storage (CCUS). CCUS involves significant CO₂ utilization, such as cyclic carbonate formation, for its cost effectiveness, less toxicity, and abundant C1 synthon in organic synthesis. However, the high thermodynamic and kinetic stability of CO₂ limits its applications. Herein, we report a mild, efficient, and practical catalyst based on abundant, nontoxic CaI₂ in conjunction with biocompatible ligand 1,3-bis[tris(hydroxymethyl)-methylamino]-propane (BTP) for CO₂ fixation under atmospheric pressure with terminal epoxides to give the cyclic carbonates. The Job plot detected the 1:1 Ca²⁺/BTP binding stoichiometry. Furthermore, formation of a single crystal of the 1:1 Ca²⁺/BTP complex was confirmed by single-crystal X-ray crystallography. The bis(cyclic carbonate) products exhibit potentials for components in the non-isocyanate polyurethanes (NIPUs) process. Notably, this protocol shows attractive recyclability and reusability.

A Zwitterionic Polyurethane Nanoporous Device with Low Foreign-Body Response for Islet Encapsulation

Encapsulation of insulin-producing cells is a promising strategy for treatment of type 1 diabetes. However, engineering an encapsulation device that is both safe (i.e., no cell escape and no breakage) and functional (i.e., low foreign-body response (FBR) and high mass transfer) remains a challenge. Here, a family of zwitterionic polyurethanes (ZPU) with sulfobetaine groups in the polymer backbone is developed, which are fabricated into encapsulation devices with tunable nanoporous structures via electrospinning. The ZPU encapsulation device is hydrophilic and fouling-resistant, exhibits robust mechanical properties, and prevents cell escape while still allowing efficient mass transfer. The ZPU device also induces a much lower FBR or cellular overgrowth upon intraperitoneal implantation in C57BL/6 mice for up to 6 months compared to devices made of similar polyurethane without the zwitterionic modification. The therapeutic potential of the ZPU device is shown for islet encapsulation and diabetes correction in mice for ≈3 months is demonstrated. As a proof of concept, the scalability and retrievability of the ZPU device in pigs and dogs are further demonstrated. Collectively, these attributes make ZPU devices attractive candidates for cell encapsulation therapies.

Thermoplastic polyurethane with controllable degradation and critical anti-fouling properties

Bioresorbable polymers, including polyesters and polypeptides, are being widely used in the medical field. However, these materials still suffer from some long-standing challenges, such as material-induced blood coagulation, foreign body response, non-adjustable degradation rate, and absence of elastic properties. In this work, we explored a new approach to address these challenges by incorporating critical anti-fouling, improved mechanical and controllable degradation properties into the existing bioresorbable polymers. We synthesized a set of zwitterionic thermoplastic polyurethanes, which consist of degradable polycaprolactone diols as soft segments and faster hydrolyzable carboxybetaine (CB) diols as chain extenders. Differential scanning calorimetry and temperature sweep rheology revealed thermal transition performance and thermoplastic behavior of the polymers. The calorimetric study observed that CB-based chain extender played a critical role in the crystallization process by affecting the structure and crystallization temperature. Cell attachment study demonstrated that the degradable zwitterionic polyurethane surfaces highly resist cell attachment even after being submerged in 100% fetal bovine serum for two weeks. The gold standard PEG-based degradable polyurethane showed the initial resistance to the cell attachment for one day and then failed after three days. This work clearly shows that the adaption of existing materials with slightly better anti-fouling properties is unlikely to solve these long-lasting challenges. Our design approach and the material platform with critical anti-fouling properties and other desired tunable properties show the potential to address these complications associated with existing bioresorbable polymers. This method can be adapted to design customized bioresorbable polymers for a wide range of applications, including implantable biomedical devices and drug delivery.

Covalent grafting of PEG and heparin improves biological performance of electrospun vascular grafts for carotid artery replacement

Rapid endothelialization of small-diameter vascular grafts remains a significant challenge in clinical practice. In addition, compliance mismatch causes intimal hyperplasia and finally leads to graft failure. To achieve compliance match and rapid endothelialization, we synthesized low-initial-modulus poly(ester-urethane)urea (PEUU) elastomer and prepared it into electrospun tubular grafts and then functionalized the grafts with poly(ethylene glycol) (PEG) and heparin via covalent grafting. The PEG- and heparin-functionalized PEUU (PEUU@PEG-Hep) graft had comparable mechanical properties with the native blood vessel. In vitro data demonstrated that the grafts are of good cytocompatibility and blood compatibility. Covalent grafting of PEG and heparin significantly promoted the adhesion, spreading, and proliferation of human umbilical vein endothelial cells (HUVECs) and upregulated the expression of vascular endothelial cell-related genes, as well as increased the capability of grafts in preventing platelet deposition. In vivo assessments indicated good biocompatibility of the PEUU@PEG-Hep graft as it did not induce severe immune responses. Replacement of resected carotid artery with the PEUU@PEG-Hep graft in a rabbit model showed that the graft was capable of rapid endothelialization, initiated vascular remodeling, and maintained patency. This study demonstrates the PEUU@PEG-Hep vascular graft with compliance match and efficacious antithrombosis might find opportunities for bioactive blood vessel substitutes.

The synthesis of polyurethane with mechanical properties that are responsive to water retention states

Water-retention-state-responsive polyurethane was designed and synthesized via introducing zwitterionic sulfobetaine onto its polymer chains.

A biostable, anti-fouling zwitterionic polyurethane-urea based on PDMS for use in blood-contacting medical devices

Polydimethylsiloxane (PDMS) is commonly used in medical devices because it is non-toxic and stable against oxidative stress. Relatively high blood platelet adhesion and the need for chemical crosslinking through curing, however, limit its utility. In this research, a biostable PDMS-based polyurethane-urea bearing zwitterion sulfobetaine (PDMS-SB-UU) was synthesized for potential use in the fabrication or coating of blood-contacting devices, such as a conduits, artificial lungs, and microfluidic devices. The chemical structure and physical properties of synthesized PDMS-SB-UU were confirmed by 1H-nuclear magnetic resonance (1H-NMR), X-ray diffraction (XRD), and uniaxial stress-strain curve. In vitro stability of PDMS-SB-UU was confirmed against lipase and 30% H2O2 for 8 weeks, and PDMS-SB-UU demonstrated significantly higher resistance to fibrinogen adsorption and platelet deposition compared to control PDMS. Moreover, PDMS-SB-UU showed a lack of hemolysis and cytotoxicity with whole ovine blood and rat vascular smooth muscle cells (rSMCs), respectively. The PDMS-SB-UU was successfully processed into small-diameter (0.80 ± 0.05 mm) conduits by electrospinning and coated onto PDMS- and polypropylene-based blood-contacting biomaterials due to its unique physicochemical characteristics from its soft- and hard- segments.

Impact of Additives on Mechanical Properties of Supramolecular Electrospun Scaffolds

The mechanical properties of scaffolds used for mechanically challenging applications such as cardiovascular implants are unequivocally important. Here, the effect of supramolecular additive functionalization on mechanical behavior of electrospun scaffolds was investigated for one bisurea-based model additive and two previously developed antifouling additives. The model additive has no effect on the mechanical properties of the bulk material, whereas the stiffness of electrospun scaffolds was slightly decreased compared to pristine PCL-BU following the addition of the three different additives. These results show the robustness of supramolecular additives used in biomedical applications, in which mechanical properties are important, such as vascular grafts and heart valve constructs.

Biodegradable Polymeric Micro/Nano-Structures with Intrinsic Antifouling/Antimicrobial Properties: Relevance in Damaged Skin and Other Biomedical Applications

Bacterial colonization of implanted biomedical devices is the main cause of healthcare-associated infections, estimated to be 8.8 million per year in Europe. Many infections originate from damaged skin, which lets microorganisms exploit injuries and surgical accesses as passageways to reach the implant site and inner organs. Therefore, an effective treatment of skin damage is highly desirable for the success of many biomaterial-related surgical procedures. Due to gained resistance to antibiotics, new antibacterial treatments are becoming vital to control nosocomial infections arising as surgical and post-surgical complications. Surface coatings can avoid biofouling and bacterial colonization thanks to biomaterial inherent properties (e.g., super hydrophobicity), specifically without using drugs, which may cause bacterial resistance. The focus of this review is to highlight the emerging role of degradable polymeric micro- and nano-structures that show intrinsic antifouling and antimicrobial properties, with a special outlook towards biomedical applications dealing with skin and skin damage. The intrinsic properties owned by the biomaterials encompass three main categories: (1) physical–mechanical, (2) chemical, and (3) electrostatic. Clinical relevance in ear prostheses and breast implants is reported. Collecting and discussing the updated outcomes in this field would help the development of better performing biomaterial-based antimicrobial strategies, which are useful to prevent infections.

Why Polyurethanes Have Been Used in the Manufacture and Design of Cardiovascular Devices: A Systematic Review

We conducted a systematic review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement to ascertain why polyurethanes (PUs) have been used in the manufacture and design of cardiovascular devices. A complete database search was performed with PubMed, Scopus, and Web of Science as the information sources. The search period ranged from 1 January 2005 to 31 December 2019. We recovered 1552 articles in the first stage. After the duplicate selection and extraction procedures, a total of 21 papers were included in the analysis. We concluded that polyurethanes are being applied in medical devices because they have the capability to tolerate contractile forces that originate during the cardiac cycle without undergoing plastic deformation or failure, and the capability to imitate the behaviors of different tissues. Studies have reported that polyurethanes cause severe problems when applied in blood-contacting devices that are implanted for long periods. However, the chemical compositions and surface characteristics of polyurethanes can be modified to improve their mechanical properties, blood compatibility, and endothelial cell adhesion, and to reduce their protein adhesion. These modifications enable the use of polyurethanes in the manufacture and design of cardiovascular devices.

A novel waterborne polyurethane with biodegradability and high flexibility for 3D printing

Three-dimensional (3D) printing provides a new approach of fabricating implantable products because it permits a flexible manner to extrude complex and customized shapes of the tissue scaffolds. Compared with other printable biomaterials, the polyurethane elastomer has several merits, including excellent mechanical properties and good biocompatibility. However, some intrinsic behavior, especially its high melting point and slow rate of degradation, hampered its application in 3D printed tissue engineering. Herein, we developed a 3D printable amino acid modified biodegradable waterborne polyurethane (WBPU) using a water-based green chemistry process. The flexibility of this material endows better compliance with tissue during implantation and prevents high modulus transplants from scratching surrounding tissues. The histocompatibility experiments show that the WBPU induces no apparent acute rejection or inflammation in vivo. We successfully fabricated a highly flexible WBPU scaffold by deposition 3D printing technology at a low temperature (50°C ~ 70 °C), and the printed products could support the adhesion and proliferation of chondrocytes and fibroblasts. The printed blocks possessed controllable degradability due to the different amounts of hydrophilic chain extender and did not cause accumulation of acidic products. In addition, we demonstrated that our WBPU is highly applicable for implantable tissue engineering because there is no cytotoxicity during its degradation. Taken together, we envision that this printable WBPU can be used as an alternative biomaterial for tissue engineering with low temperature printing, biodegradability, and compatibility.

Winning the fight against biofilms: the first six-month study showing no biofilm formation on zwitterionic polyurethanes

Biofilms have been a long-standing challenge for healthcare, water transport, and many other industries. They lead to bacterial growth and infections in animals, food products, and humans, cause premature removal of the implanted materials or devices from patients, and facilitate fouling and corrosion of metals. Despite some published and patented methods on minimizing the effects of biofilms for a short period (less than two weeks), there exists no successful means to mitigate or prevent the long-term formation of biofilms. It is even more challenging to integrate critical anti-fouling properties with other needed physical and chemical properties for a range of applications. In this study, we developed a novel approach for combining incompatible, highly polar anti-fouling groups with less polar, mechanically modifying groups into one material. A multifunctional carboxybetaine precursor was designed and introduced into polyurethane. The carboxybetaine precursors undergo rapid, self-catalyzed hydrolysis at the water/material interface and provide critical anti-fouling properties that lead to undetectable bacterial attachment and zero biofilm formation after six months of constant exposure to Pseudomonas aeruginosa and Staphylococcus epidermidis under the static condition in a nutrient-rich medium. This zwitterionic polyurethane is the first material to demonstrate both critical anti-biofilm properties and tunable mechanical properties and directly validates the unproven anti-fouling strategy and hypothesis for biofilm formation prevention. This approach of designing 'multitasking materials' will be useful for the development of next generation anti-fouling materials for a variety of applications.

Fabrication of a polypropylene immunoassay platform by photografting reaction

The technology of an immunoassay detection platform is critical to clinical disease diagnoses, especially for developing a medical diagnostic system. A polymer-based immunoassay platform was fabricated on nonwoven fabric polypropylene (PP) using a photografting reaction to graft 2-hydroxyethyl methacrylate (HEMA) and sulfobetaine (SBMA). The antifouling properties of PP-g-P(HEMA-co-SBMA) were investigated by fibrinogen adsorption and platelet adhesion. Carbonyldiimidazole was employed to activate the pendant hydroxyl groups in HEMA moieties and covalently coupled antibody molecules. The detection of the limit of the immunoassay platform was as low as 10 pg/mL. Antibody amount and bioactivity affected the availability of antibody and the sensitivity of immunoassay. The immune efficiency was dependent on the strategies of antibody immobilization. The immune efficiency of Au-g-P(SBMA-co-HEMA) and Au-SH surfaces measured by QCM-D was 165% and 35.7%, respectively. The covalently binding antibody via hydrophilic polymer chains as spacers could retain fragment antigen-binding up orientation, maintain the bioactivity of antibody, and mainly improve the accessibility of antibody molecules via adjusting the conformations of polymer chains when the antibodies recognized the antigens. Therefore, grafting hydrophilic polymers, such as zwitterionic PSBMA and reactive PHEMA onto nonwoven fabric PP, and binding antibody by covalent strategy had the potential to be developed as a commercial immunoassay platform.

State of the Art of Small-Diameter Vessel-Polyurethane Substitutes

Cardiovascular diseases are a severe threat to human health. Implantation of small-diameter vascular substitutes is a promising therapy in clinical operations. Polyurethane (PU) is considered one of the most suitable materials for this substitution due to its good mechanical properties, controlled biostability, and proper biocompatibility. According to biodegradability and biostability, in this review, PU small-diameter vascular substitutes are divided into two groups: biodegradable scaffolds and biostable prostheses, which are applied to the body for short- and long-term, respectively. Following this category, the degradation principles and mechanisms of different kinds of PUs are first discussed; then the chemical and physical methods for adjusting the properties and the research advances are summarized. On the basis of these discussions, the problems remaining at present are addressed, and the contour of future research and development of PU-based small-diameter vascular substitutes toward clinical applications is outlined.

Biodegradable Zwitterionic Polymer Coatings for Magnesium Alloy Stents

Degradable metallic stents, most commonly composed of Mg-based alloys, are of interest as an alternative to traditional metallic stents for application in cardiac and peripheral vasculature. Two major design challenges with such stents are control of the corrosion rate and acute presentation of a nonthrombogenic surface to passing blood. In this study, several types of sulfobetaine (SB)-bearing biodegradable polyurethanes were developed and assessed as physical, chemical, and combination-type coatings for a model degradable Mg alloy, AZ31. For physical coatings, poly(ester sulfobetaine)urethane ureas, PESBUUs were synthesized using variable monomers that allowed the incorporation of a varying extent of carboxyl groups. Introduction of the carboxyl groups was associated with faster polymer degradation time. Simple physical coating of PESBUUs reduced macro- and microscopic thrombogenic deposition together with good stability of the coating attachment compared to a control coating of polylactic- co-glycolic acid. For PESBUUs incorporating carboxyl groups (PESBUUs-COOH), these groups could be converted to siloxane groups (PESBUUs-Si), thus creating polymers that could be surface reacted with the oxidized or phytic acid treated AZ31 surface. Chemical (silanization) attachment of these polymers reduced underlying alloy corrosion rates, but following the salination reaction with physical coating most reduced corrosion rates and protected the surface better from the consequences of oxidation occurring under the coating, such as blistering. The application of a multilayered coating approach using a sulfobetaine-based biodegradable elastomer thus offers options for degradable metallic stent design where thromboresistance is desired in combination with a means to control both polymeric coating degradation rates and underlying alloy corrosion rates.

Active wrinkles to drive self-cleaning: A strategy for anti-thrombotic surfaces for vascular grafts

The inner surfaces of arteries and veins are naturally anti-thrombogenic, whereas synthetic materials placed in blood contact commonly experience thrombotic deposition that can lead to device failure or clinical complications. Presented here is a bioinspired strategy for self-cleaning anti-thrombotic surfaces using actuating surface topography. As a first test, wrinkled polydimethylsiloxane planar surfaces are constructed that can repeatedly transition between smooth and wrinkled states. When placed in contact with blood, these surfaces display markedly less platelet deposition than control samples. Second, for the specific application of prosthetic vascular grafts, the potential of using pulse pressure, i.e. the continual variation of blood pressure between systole and diastole, to drive topographic actuation was investigated. Soft cylindrical tubes with a luminal surface that transitioned between smooth and wrinkled states were constructed. Upon exposure to blood under continual pressure pulsation, these cylindrical tubes also showed reduced platelet deposition versus control samples under the same fluctuating pressure conditions. In both planar and cylindrical cases, significant reductions in thrombotic deposition were observed, even when the wrinkles had wavelengths of several tens of μm, far larger than individual platelets. We speculate that the observed thrombo-resistance behavior is attributable to a biofilm delamination process in which the bending energy within the biofilm overcomes interfacial adhesion. This novel strategy to reduce thrombotic deposition may be applicable to several types of medical devices placed into the circulatory system, particularly vascular grafts.

Enhancing anti-thrombogenicity of biodegradable polyurethanes through drug molecule incorporation

Sufficient and sustained anti-thrombogenicity is essential for blood-contacting materials, because blood coagulation and thrombosis caused by platelet adhesion and activation on material surfaces may lead to functional failure and even fatal outcomes. Covalently conjugating antithrombogenic moieties into polymer, instead of surface modifying or blending, can maintain the anti-thrombogenicity of polymer at a high level over a time range. In this study, series of randomly crosslinked, elastic, biodegradable polyurethanes (PU-DPA) were synthesized through a one-pot and one-step method from polycaprolactone (PCL) diol, hexamethylene diisocyanate (HDI) and anti-thrombogenic drug, dipyridamole (DPA). The mechanical properties, hydrophilicity, in vitro degradation, and anti-thrombogenicity of the resultant PU-DPA polymers can be tuned by altering the incorporated DPA amount. The surface and bulk hydrophilicity of the polyurethanes decreased with increasing hydrophobic DPA amount. All PU-DPA polymers exhibited strong mechanical properties and good elasticity. The degradation rates of the PU-DPAs decreased with increasing DPA content in both PBS and lipase/PBS solutions. Covalently incorporating DPA into the polyurethane significantly reduced the platelet adhesion and activation compared to the polyurethane without DPA, and also can achieve sustained anti-thrombogenicity. The PU-DPA films also supported the growth of human umbilical vein endothelial cells. The attractive mechanical properties, blood compatibility, and cell compatibility of this anti-thrombogenic biodegradable polyurethane indicate that it has a great potential to be utilized for blood-contacting devices, and cardiovascular tissue repair and regeneration.

Zwitterionic Polyurethanes with Tunable Surface and Bulk Properties

To address the lack of blood compatibility and antifouling properties of polyurethanes (PUs), a novel zwitterionic poly(carboxybetaine urethane) (PCBHU) platform with excellent antifouling and tunable mechanical properties is presented. PCBHU was synthesized via the condensation polymerization of diisocyanate with carboxybetaine (CB)-based triols. Postpolymerization hydrolysis of triol segments at the interface generates zwitterionic CB functional groups that provide superior antifouling properties via the enhanced hydration capacities of CB groups. Thermogravimetric analysis and differential scanning calorimetry measurement show the high thermal stability of PCBHU with up to 305 °C degradation temperature. Tunable mechanical properties and water uptakes can be finely tuned by controlling the structure and ratio of CB-based triol cross-linkers. This study presents a new strategy to incorporate CB functional groups into PU without significantly changing the synthetic methods and conditions of PU. It also provides a deeper understanding on structure-property relationships of zwitterionic PUs. Because of its superior antifouling properties than existing PUs and similar cost, mechanical properties, stability, and processability, PCBHU has the great potential to replace current PUs and may open a new avenue to PUs for more challenging biomedical applications in which the existing PUs are limited by calcification and poor antifouling properties.

Introducing multiple bio-functional groups on the poly(ether sulfone) membrane substrate to fabricate an effective antithrombotic bio-interface

It has been widely recognized that functional groups on biomaterial surfaces play important roles in blood compatibility. To construct an effective antithrombotic bio-interface onto the poly(ether sulfone) (PES) membrane surface, bio-functional groups of sodium carboxylic (-COONa), sodium sulfonic (-SO₃Na) and amino (-NH₂) groups were introduced onto the PES membrane surface in three steps: the synthesis of PES with carboxylic (-COOH) groups (CPES) and water-soluble PES with sodium sulfonic (-SO₃Na) groups and amino (-NH₂) groups (SNPES); the introduction of carboxylic groups onto the PES membrane by blending CPES with PES; and the grafting of SNPES onto CPES/PES membranes via the coupling of amino groups and carboxyl groups. The physical/chemical properties and bioactivities were dependent on the proportions of the additives. After introducing bio-functional groups, the excellent hemocompatibility of the modified membranes was confirmed by the inhibited platelet adhesion and activation, prolonged clotting times, suppressed blood-related complement and leukocyte-related complement receptor activations. Furthermore, cell tests indicated that the modified membranes showed better cytocompatibility in endothelial cell proliferation than the pristine PES membrane due to the synergistic promotion of the functional groups. To sum up, these results suggested that modified membranes present great potential in fields using blood-contacting materials, such as hemodialysis and surface endothelialization.

Decellularized matrices in regenerative medicine

Of all biologic matrices, decellularized extracellular matrix (dECM) has emerged as a promising tool used either alone or when combined with other biologics in the fields of tissue engineering or regenerative medicine - both preclinically and clinically. dECM provides a native cellular environment that combines its unique composition and architecture. It can be widely obtained from native organs of different species after being decellularized and is entitled to provide necessary cues to cells homing. In this review, the superiority of the macro- and micro-architecture of dECM is described as are methods by which these unique characteristics are being harnessed to aid in the repair and regeneration of organs and tissues. Finally, an overview of the state of research regarding the clinical use of different matrices and the common challenges faced in using dECM are provided, with possible solutions to help translate naturally derived dECM matrices into more robust clinical use.

STATEMENT OF SIGNIFICANCE

Ideal scaffolds mimic nature and provide an environment recognized by cells as proper. Biologically derived matrices can provide biological cues, such as sites for cell adhesion, in addition to the mechanical support provided by synthetic matrices. Decellularized extracellular matrix is the closest scaffold to nature, combining unique micro- and macro-architectural characteristics with an equally unique complex composition. The decellularization process preserves structural integrity, ensuring an intact vasculature. As this multifunctional structure can also induce cell differentiation and maturation, it could become the gold standard for scaffolds.

Current and Emerging Approaches to Engineer Antibacterial and Antifouling Electrospun Nanofibers

From ship hulls to bandages, biological fouling is a ubiquitous problem that impacts a wide range of industries and requires complex engineered solutions. Eliciting materials to have antibacterial or antifouling properties describes two main approaches to delay biofouling by killing or repelling bacteria, respectively. In this review article, we discuss how electrospun nanofiber mats are blank canvases that can be tailored to have controlled interactions with biologics, which would improve the design of intelligent conformal coatings or freestanding meshes that deliver targeted antimicrobials or cause bacteria to slip off surfaces. Firstly, we will briefly discuss the established and emerging technologies for addressing biofouling through antibacterial and antifouling surface engineering, and then highlight the recent advances in incorporating these strategies into electrospun nanofibers. These strategies highlight the potential for engineering electrospun nanofibers to solicit specific microbial responses for human health and environmental applications.

Hydrophobic Antifouling Electrospun Mats from Zwitterionic Amphiphilic Copolymers

A porous material that is both hydrophobic and fouling-resistant is needed in many applications, such as water purification by membrane distillation. In this work, we take a novel approach to fabricating such membranes. Using the zwitterionic amphiphilic copolymer poly(trifluoroethyl methacrylate- random-sulfobetaine methacrylate), we electrospin nonwoven, porous membranes that combine high hydrophobicity with resistance to protein adsorption. By changing the electrospinning parameters and the solution composition, membranes can be prepared with a wide range of fiber morphologies including beaded, bead-free, wrinkly, and ribbonlike fibers, with diameters ranging between ∼150 nm and 1.5 μm. The addition of LiCl to the spinning solution not only helps control the fiber morphology but also increases the segregation of zwitterionic groups on the membrane surface. The resultant electrospun membranes are highly porous and very hydrophobic, yet resist the adsorption of proteins and retain a high contact angle (∼140°) even after exposure to a protein solution. This makes these materials promising candidates for the membrane distillation of contaminated wastewater streams and as self-cleaning materials.

Surface modification and endothelialization of polyurethane for vascular tissue engineering applications: a review

Cardiovascular implants, especially vascular grafts made of synthetic polymers, find wide clinical applications in the treatment of cardiovascular diseases. However, cases of failure still exist, notably caused by restenosis and thrombus formation. Aiming to solve these problems, various approaches to surface modification of synthetic vascular grafts have been used to improve both the hemocompatibility and long-term patency of artificial vascular grafts. Surface modification using hydrophilic molecules can enhance hemocompatibility, but this may limit the initial vascular endothelial cell adhesion. Therefore, the improvement of endothelialization on these grafts with specific peptides and biomolecules is now an exciting field of research. In this review, several techniques to improve surface modification and endothelialization on vascular grafts, mainly polyurethane (PU) grafts, are summarized, together with the recent development and evolution of the different strategies: from the use of PEG, zwitterions, and polysaccharides to peptides and other biomolecules and genes; from in vitro endothelialization to in vivo endothelialization; and from bio-inert and bio-active to bio-mimetic approaches.

Biocompatible, degradable thermoplastic polyurethane based on polycaprolactone-block-polytetrahydrofuran-block-polycaprolactone copolymers for soft tissue engineering

Biodegradable synthetic polymers have been widely used as tissue engineering scaffold materials. Even though they have shown excellent biocompatibility, they have failed to resemble the low stiffness and high elasticity of soft tissues because of the presence of massive rigid ester bonds. Herein, we synthesized a new thermoplastic polyurethane elastomer (CTC-PU(BET)) using poly ester ether triblock copolymer (polycaprolactone-block-polytetrahydrofuran-block-polycaprolactone triblock copolymer, PCTC) as the soft segment, aliphatic diisocyanate (hexamethylene diisocyanate, HDI) as the hard segment, and degradable diol (bis(2-hydroxyethyl) terephthalate, BET) as the chain extender. PCTC inhibited crystallization and reduced the melting temperature of CTC-PU(BET), and BET dramatically enhanced the thermal decomposition and hydrolytic degradation rate when compared with conventional polyester-based biodegradable TPUs. The CTC-PU(BET) synthesized in this study possessed a low tensile modulus and tensile strength of 2.2 MPa and 1.3 MPa, respectively, and an elongation-at-break over 700%. Meanwhile, it maintained a 95.3% recovery rate and 90% resilience over ten cycles of loading and unloading. In addition, the TPU could be electrospun into both random and aligned fibrous scaffolds consisting of major microfibers and nanobranches. 3T3 fibroblast cell culture confirmed that these scaffolds outperformed the conventional biodegradable TPU scaffolds in terms of substrate-cellular interactions and cell proliferation. Considering the advantages of this TPU, such as ease of synthesis, low cost, low stiffness, high elasticity, controllable degradation rate, ease of processability, and excellent biocompatibility, it has great prospects to be used as a tissue engineering scaffold material for soft tissue regeneration.

Biomimetic Principles to Develop Blood Compatible Surfaces

Functionalized biomaterial surface patterns capable of resisting nonspecific adsorption while retaining their bioactivity are crucial in the advancement of biomedical technologies, but currently available biomaterials intended for use in whole blood frequently suffer from nonspecific adsorption of proteins and cells, leading to a loss of activity over time. In this review, we address two concepts for the design and modification of blood compatible biomaterial surfaces, zwitterionic modification and surface functionalization with glycans – both of which are inspired by the membrane structure of mammalian cells – and discuss their potential for biomedical applications.

Antifouling Electrospun Nanofiber Mats Functionalized with Polymer Zwitterions

In this study, we exploit the excellent fouling resistance of polymer zwitterions and present electrospun nanofiber mats surface functionalized with poly(2-methacryloyloxyethyl phosphorylcholine) (polyMPC). This zwitterionic polymer coating maximizes the accessibility of the zwitterion to effectively limit biofouling on nanofiber membranes. Two facile, scalable methods yielded a coating on cellulose nanofibers: (i) a two-step sequential deposition featuring dopamine polymerization followed by the physioadsorption of polyMPC, and (ii) a one-step codeposition of polydopamine (PDA) with polyMPC. While the sequential and codeposited nanofiber mat assemblies have an equivalent average fiber diameter, hydrophilic contact angle, surface chemistry, and stability, the topography of nanofibers prepared by codeposition were smoother. Protein and microbial antifouling performance of the zwitterion modified nanofiber mats along with two controls, cellulose (unmodified) and PDA coated nanofiber mats were evaluated by dynamic protein fouling and prolonged bacterial exposure. Following 21 days of exposure to bovine serum albumin, the sequential nanofiber mats significantly resisted protein fouling, as indicated by their 95% flux recovery ratio in a water flux experiment, a 300% improvement over the cellulose nanofiber mats. When challenged with two model microbes Escherichia coli and Staphylococcus aureus for 24 h, both zwitterion modifications demonstrated superior fouling resistance by statistically reducing microbial attachment over the two controls. This study demonstrates that, by decorating the surfaces of chemically and mechanically robust cellulose nanofiber mats with polyMPC, we can generate high performance, free-standing nanofiber mats that hold potential in applications where antifouling materials are imperative, such as tissue engineering scaffolds and water purification technologies.

Pilot Mouse Study of 1 mm Inner Diameter (ID) Vascular Graft Using Electrospun Poly(ester urea) Nanofibers

An off-the-shelf, small diameter tissue engineered vascular graft (TEVG) would be transformative to surgeons in multiple subspecialties. Herein, the results of a small diameter (ID ≈ 1 mm) vascular graft constructed from resorbable, amino acid-based poly(ester urea) (PEU) are reported. Electrospun PEU grafts of two different wall thicknesses (type A: 250 μm; type B: 350 μm) are implanted as abdominal infra-renal aortic grafts in a severe combined immune deficient/beige mouse model and evaluated for vessel remodeling over one year. Significantly, the small diameter TEVG does not rupture or lead to acute thrombogenic events during the intervals tested. The pilot TEVG in vivo shows long-term patency and extensive tissue remodeling with type A grafts. Extensive tissue remodeling in type A grafts leads to the development of well-circumscribed neovessels with an endothelial inner lining, a neointima containing smooth muscle cells. However, due to slow degradation of the PEU scaffold materials in vivo, the grafts remain after one year. The type B grafts, which have 350 μm thick walls, experience occlusion over the one year interval due to intimal hyperplasia. This study affords significant findings that will guide the design of future generations of small diameter vascular grafts.

Low-fouling electrospun PLLA films modified with zwitterionic poly(sulfobetaine methacrylate)-catechol conjugates

In this work, we modified a hydrophobic electrospun poly (l-lactic) acid (PLLA) film with poly (sulfobetaine methacrylate) (pSBMA)-catechol conjugates of different molecular weights to improve the biocompatibility of the film. These conjugates were synthesized via atom transfer radical polymerization. They consist of an ultra-low fouling pSBMA zwitterionic polymer with a surface-adhesive catechol moiety. X-ray photoelectron spectroscopy, contact angle and scanning electron microscopy experiments were performed to characterize films before and after modification with pSBMA-catechol conjugates. Enzyme-linked immunosorbent and fluorescently-labeled bovine serum albumin were used to study the interactions of proteins with these films. Results showed that low molecular weight zwitterionic pSBMA-catechol conjugates greatly discouraged protein adsorption as shown by use of single protein solutions on PLLA films when the modification was performed in ethanolic Tris-HCl solution. This work offers a convenient and effective method to modify electrospun PLLA films for biomedical applications.

STATEMENT OF SIGNIFICANCE

In this work, we report a convenient and effective method to modify electrospun PLLA films using pSBMA-catechol conjugates via "graft-to" for biomedical applications. After pSBMA modification, the PLLA surface becomes hydrophilic with low contact angle and protein adsorption. Results showed that lower molecular weight zwitterionic pSBMA-catechol conjugate led to lower contact angles and better nonfouling properties on PLLA films when the coating was performed in a solution containing ethanol.

Preparation and application of novel biodegradable polyurethane copolymer

Polyurethanes and polylactides are widely used due to their excellent mechanical properties, biocompatibility, and flexible construction options and their degradable, hydrolyzable and biocompatible characteristics, respectively.

A porous elastomeric polyurethane monolith synthesized by concentrated emulsion templating and its pressure-sensitive conductive property

The spontaneous distribution of acid-treated MWCNTs in the concentrated emulsion leads to the press-sensitive conductivity of the porous PU.

Layer by layer assembly of sulfonic poly(ether sulfone) as heparin-mimicking coatings: scalable fabrication of super-hemocompatible and antibacterial membranes

In this study, super-hemocompatible and antibacterial polymeric membranes with surface coated nanofilms were fabricated by LBL assembly of water-soluble heparin-mimicking polymer and quaternized chitosan.