Antithrombogenic polymer alloy composed of 2-methacryloyloxyethyl phosphorylcholine polymer and segmented polyurethane

Thrombogenicity assessment of perfusable tissue engineered constructs: a systematic review

Vascular surgery faces a critical demand for novel vascular grafts that are biocompatible and thromboresistant. This urgency particularly applies to bypass operations involving small caliber vessels. In the realm of tissue engineering, the development of fully vascularized organs holds great promise as a solution to organ shortage for transplantation. To achieve this, it is imperative to (re-)construct a biocompatible and non-thrombogenic vascular network within these organs. In this systematic review, we identify, classify and discuss basic principles and methods used to perform in vitro/ex vivo dynamic thrombogenicity testing of perfusable tissue engineered organs and tissues. We conducted a pre-registered systematic review of studies published in the last 23 years according to PRISMA-P Guidelines, comprising a systematic data extraction, in-depth analysis and risk of bias assessment of 116 included studies. We identified shaking (n=28), flow loop (n=17), ex vivo (arterio-venous shunt, n=33) and dynamic in vitro models (n=38) as main approaches for thrombogenicity assessment. This comprehensive review unveils a prevalent lack of standardization and serves as a valuable guide in the design of standardized experimental setups.

Facile preparation of medical segmented poly(ester-urethane) containing uniformly sized hard segments and phosphorylcholine groups for improved hemocompatibility

In order to improve the hemocompatibility of durable medical-grade polyurethane, a novel series of segmented poly(ester-urethane)s containing uniformly sized hard segments and phosphorylcholine (PC) groups on the side chains (SPU-PCs) was prepared by a facile method. The 2-methacryloyloxyethyl phosphorylcholine (MPC) was first reacted with α-thioglycerol by Michael addition to give a diol compound (MPC-diol), then the SPU-PCs with various PC content were prepared by a one-step chain extension of the mixture of MPC-diol and poly(ε-caprolactone) diol (PCL-diol) with aliphatic diurethane diisocyanates (HBH). The chemical structures of MPC-diol and SPU-PCs were confirmed by ¹H NMR and FT-IR, and the influences of PC content on the physicochemical properties of the SPU-PC films were studied. The introduction of PC groups enhanced the degree of micro-phase separation and improved the hydrolytic degradation of the films. Due to the denser hydrogen bonds formed in the uniformly sized hard segments, the films exhibited favorable tensile properties and a slow hydrolytic degradation rate. The results of water contact angle and XPS analysis indicated that the PC groups on the flexible side chains were concentrated on the surface after contact with water. The surface hemocompatibility of the films was evaluated by testing the protein adsorption and platelet adhesion, and the results revealed that the films surfaces could dramatically suppress the protein adsorption and platelet adhesion. The PC-containing polyurethane films possessed outstanding tensile properties, low degradation rate and good surface hemocompatibility, implying their great potential for use as long-term implant or blood-contacting devices.

Antithrombotic Protein Filter Composed of Hybrid Tissue-Fabric Material has a Long Lifetime

There are recent reports of hybrid tissue-fabric materials with good performance-high biocompatibility and high mechanical strength. In this study, we demonstrate the capability of a hybrid material as a long-term filter for blood proteins. Polyester fabrics were implanted into rats to fabricate hybrid tissue-fabric material sheets. The hybrid materials comprised biological tissue grown on the fabric. The materials were extracted from the rat's body, approximately 100 days post-implantation. The tissues were decellularized to prevent immunological rejection. An antithrombogenicity test was performed by dropping blood onto the hybrid material surface. The hybrid material showed lesser blood coagulation than polysulfone and cellulose. Blood plasma was filtered using the hybrid material to evaluate the protein removal percentage and the lifetime of the hybrid material in vitro. The hybrid material showed a comparable performance to conventional filters for protein removal. Moreover, the hybrid material could work as a protein filter for 1 month, which is six times the lifetime of polysulfone.

Bioactive technologies for hemocompatibility

The contact of any biomaterial with blood gives rise to multiple pathophysiologic defensive mechanisms such as activation of the coagulation cascade, platelet adhesion and activation of the complement system and leukocytes. The reduction of these events is of crucial importance for the successful clinical performance of a cardiovascular device. This can be achieved by improving the hemocompatibility of the device materials or by pharmacologic inhibition of the key enzymes responsible for the activation of the cascade reactions, or a combination of both. Different strategies have been developed during the last 20 years, and this article attempts to review the most significant, by dividing them into three main categories: bioinert or biopassive, biomimetic and bioactive strategies. With regard to bioactive strategies, particular attention is given to heparin immobilization and recent related technologies. References from both scientific literature and commercial sites are provided. Future development and studies are suggested.

Cell adhesion on phase-separated surface of block copolymer composed of poly(2-methacryloyloxyethyl phosphorylcholine) and poly(dimethylsiloxane)

We investigated the morphological effect of phase-separated block copolymer surfaces composed of poly(2-methacryloyloxyethyl phosphorylcholine (MPC)) (PMPC) and poly(dimethylsiloxane) (PDMS) on protein adsorption and cell adhesion behavior. We observed three different types of phase-separated surface morphologies by TEM and AFM. The elemental composition of phosphorus on the surface increases with the PMPC composition. Furthermore, the polymer surface formed by a block copolymer-containing a higher MPC unit composition shows a slightly lower static water contact angle. This result indicates that the elemental surface ratio of the surface depends on the MPC composition in the block copolymer. Protein adsorption tests revealed that only hydrophobic PDMS domains showed selective protein adsorption. Cell adhesion tests revealed that the number of adhered cells increased with increasing hydrophobic PDMS domain size of block copolymers in serum-containing media. In contrast, no cells adhered onto block copolymer surfaces in serum-free media, whereas a large amount of adhered cells were observed on the hydrophobic PDMS surface. This result indicates that segregated hydrophobic domains on a biocompatible PMPC surface strongly affect serum protein adsorption, thereby promoting considerable cell adhesion, although the surface is hydrophilic. Thus, both the composition of MPC units and the segregated hydrophobic surface morphology are important considerations in biomaterial surface design.

A small diameter, fibrous vascular conduit generated from a poly(ester urethane)urea and phospholipid polymer blend

The thrombotic and hyperplastic limitations associated with synthetic small diameter vascular grafts have generated sustained interest in finding a tissue engineering solution for autologous vascular segment generation in situ. One approach is to place a biodegradable scaffold at the site that would provide acute mechanical support while vascular tissue develops. To generate a scaffold that possessed both non-thrombogenic character and mechanical properties appropriate for vascular tissue, a biodegradable poly(ester urethane)urea (PEUU) and non-thrombogenic bioinspired phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-methacryloyloxyethyl butylurethane) (PMBU) were blended at PMBU weight fractions of 0-15% and electrospun to create fibrous scaffolds. The composite scaffolds were flexible with breaking strains exceeding 300%, tensile strengths of 7-10MPa and compliances of 2.9-4.4 x 10(-4) mmHg(-1). In vitro platelet deposition on the scaffold surfaces significantly decreased with increasing PMBU content. Rat smooth muscle cell proliferation was also inhibited on PEUU/PMBU blended scaffolds with greater inhibition at higher PMBU content. Fibrous vascular conduits (1.3mm inner diameter) implanted in the rat abdominal aorta for 8 weeks showed greater patency for grafts with 15% PMBU blending versus PEUU without PMBU (67% versus 40%). A thin neo-intimal layer with endothelial coverage and good anastomotic tissue integration was seen for the PEUU/PMBU vascular grafts. These results are encouraging for further evaluation of this technique in larger diameter applications for longer implant periods.

The surface modification of silver nanoparticles by phosphoryl disulfides for improved biocompatibility and intracellular uptake

In order to enhance the biocompatibility and cell affinity of metal nanoparticles for biosensing and drug delivering applications, we prepared the phospholipid derivatives containing disulfide groups to modify silver nanoparticle surfaces. By adding sodium borohydride to reduce both disulfide bonds of the derivatives and silver ions simultaneously, the generated thiol groups can be reacted with newborn silver atoms immediately to generate nanoclusters. The assemblies consisted of either phosphorylcholine (PC) or phosphorylethanolamine (PE) head groups, which made the silver clusters biocompatibile. Transmission electron microscope (TEM) and optical absorption spectra assisted in modulating reaction conditions, demonstrating that a surfactant/Ag ratio of 0.4 led to the formation of uniform, well-dispersed spherical particles about 3.8 nm in diameter. X-ray photoelectron spectra and infrared spectra also illustrated the elemental and molecular structures of nanoparticles. The insertion of rhodamine dye into the surfactant layer enabled the nanoparticles to be used as a fluorescent probe. In cell culture tests, the nanoparticles were internalized into platelet or fibroblast cells in a short period of incubation without harming the cells.

Cell mimetic lateral stabilization of outer cell mimetic bilayer on polymer surfaces by peptide bonding and their blood compatibility

The biological lipid bilayer membranes are stabilized laterally with the help of integral proteins. We have simulated this with an optimized ternary phospholipid/glycolipid/cholesterol system, and stabilized laterally on functionalized poly methyl methacrylate (PMMA) surfaces, using albumin, heparin, and polyethylene glycol as anchors. We have earlier demonstrated the differences due to orientation and packing of the ternary phospholipid monolayers in relation to blood compatibility (Kaladhar and Sharma, Langmuir 2004;20:11115-11122). The structure of albumin is changed here to expose its interior hydrophobic core by treating with organic solvent. The interaction between the hydrophobic core of the albumin molecule and the hydrophobic core of the lipid molecules is confirmed by incorporating the molecule into bilayer membranes. The secondary structure of the membrane incorporated albumin is studied by CD spectral analysis. The structure of the altered albumin molecule contains more beta-sheet as compared to the native albumin. This conformation is also retained in membranes. The partitioning of the different anchors based on its polarity and ionic interactions in the monolayer is studied from the pressure-area (pi-A) isotherm of the lipid monolayers at the air/water interface using Langmuir-Blodgett (LB) trough facility. Such two monolayers are deposited onto the functionalized PMMA surface using LB trough and crosslinked by carbodiimide chemistry. The structure of the deposited bilayer is studied by depth analysis using contact mode AFM in dry conditions. The stabilized bilayer shows stability up to 1 month by contact angle studies. Preliminary blood compatibility studies reveal that the calcification, protein adsorption, as well as blood-cell adhesion is significantly reduced after the surface modification. The reduced adsorption of ions, proteins, and cells to the modified surfaces may be due to the fluidity of the microenvironment along with the contribution of the mobile PEG groups at the surface and the phosphorylcholine groups of the phospholipids. The stability of the anchored bilayer under low shear stress conditions promises that the laterally stabilized supported bilayer system can be used for low shear applications like small diameter vascular graft and modification of biosensors, and so forth.

Segmented polyurethane modified by photopolymerization and cross-linking with 2-methacryloyloxyethyl phosphorylcholine polymer for blood-contacting surfaces of ventricular assist devices

To improve the biocompatibility of pulsatile ventricular assist devices (VADs), the blood-contacting surface of the segmented polyurethane (SPU) diaphragm employed in an electromechanical VAD was modified by introducing 2-methacryloyloxyethyl phosphorylcholine (MPC) units into its surface and forming an interpenetrating polymer network (IPN) structure, which contained independently cross-linked MPC polymer and SPU. The SPU diaphragm modified with an IPN structure was then assembled into a target test pump and underwent continuous pump operation at 37 degrees C for 2 weeks in a simulated systemic circulation using a mock circulatory loop. The surface characteristics of the pump diaphragm after 2 weeks of pump operation were then analyzed with an X-ray photoelectron spectroscope (XPS) and gold-colloid-labeled immunoassay. The XPS surface analysis of the IPN-modified SPU indicated the firm anchoring of MPC units even after 2 weeks of pump operation (the phosphor : carbon ratio was reduced by only 0.09%). The IPN-modified diaphragm prevented protein adsorption as well as cell adhesion in comparison to the unmodified SPU surface. This result thus validated that (1) the IPN structure could firmly secure MPC units to the SPU surface even in a high-mechanical-stress and high-shear environment, (2) the antithrombogenic power of MPC units remained unchanged after 2 weeks of continuous exposure to a high-shear environment, and (3) the IPN modified SPU cross-linked with MPC could be a powerful antithrombogenic surface for blood pumps used for chronic circulatory support of cardiac patients.

Self-assembled biomimetic monolayers using phospholipid-containing disulfides

Several phospholipid-based disulfide molecules were synthesized and attached onto the gold-coated silicon wafer using the self-assembling method. The syntheses of these surface-modifying agents were conducted by introducing bromoethylphosphorate (PBr), phosphorylcholine (PC) or phosphorylethanolamine (PE) groups on the terminals of a dialkyl disulfide. After disulfides adsorption onto gold substrate surfaces, the composition, the film thickness, and the conformational order of self-assembled monolayer surfaces were explored and discussed in detail based on reflection-absorption infrared spectroscopy, contact angle measurement, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and so on. The monolayer having the PBr end group could also be converted to a PC surface by treating with trimethylamine. The model functional surfaces of Au-SC11-PC, -PE, -PBr, -OH or corresponding mixed layers were used to mimic biomembrane surfaces. The monolayer having PC groups was found to reduce fibrinogen adsorption as evaluated from protein adsorption experiments using quartz crystal microbalance. It also showed relatively low platelet adherence compare to the glass, PBr and PE surfaces. The cell viability test also revealed that the PC surface displayed lower cytotoxicity than other surfaces.

Synthetic studies on nonthrombogenic biomaterials 14: synthesis and characterization of poly(ether-urethane) bearing a Zwitterionic structure of phosphorylcholine on the surface

A new Zwitterionic compound of the phosphorylcholine analogue, 4-hydroxylbutyl phosphorylcholine (HBPC), was synthesized and characterized. HBPC was chemically tethered onto the surface of poly(ether-urethane) (PEU) films with hexamethylene diisocyanate (HDI) as a coupling agent. The existence of a phosphorylcholine structure on the PEU surface was demomstrated by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. The nonthrombogenicity of the modified films was evaluated by platelet-rich plasma (PRP) assay. The results showed that films grafted with HBPC have excellent platelet adhesion resistance.

Enhanced blood compatibility of polymers grafted by sulfonated PEO via a negative cilia concept

In our laboratory sulfonated PEO (PEO-SO(3)) was designed as a "negative cilia model" to investigate a synergistic effect of PEO and negatively charged SO(3) groups. PEO-SO(3) itself exhibited a heparin-like anticoagulant activity of 14% of free heparin. Polyurethane grafted with PEO-SO(3) (PU-PEO-SO(3)) increased the albumin adsorption to a great extent but suppressed other proteins, while PU-PEO decreased the adsorption of all the proteins. The platelet adhesion was decreased on PU-PEO but least on PU-PEO-SO(3) to demonstrate an additional effect of SO(3) groups. The enhanced blood compatibility of PU-PEO-SO(3) in the ex vivo rabbit and in vivo canine implanting tests was confirmed. Furthermore, PU-PEO-SO(3) exhibited an improved biostability and suppressed calcification in addition to the enhanced antithrombogenicity. The in vivo antithrombogenicity and biostability were improved in the order of PU<PU-PEO<PU-PEO-SO(3). The calcium amounts deposited was decreased in the order of PU>PU-PEO>PU-PEO-SO(3) in spite of the possible attraction between negative SO(3) groups and positive calcium ions. The bioprosthetic tissue (BT) was grafted with H(2)N-PEO-SO(3) via glutaraldehyde (GA) residues after conventional GA fixation. BT-PEO-SO(3) also displayed the decreased calcification by in vivo animal models. The application of PEO-SO(3) was extended by designing amphiphilic copolymers containing PEO-SO(3) moiety and hydrophobic long alkyl groups as anchors. The superior effect of PEO-SO(3) groups on thromboresistance compared to PEO was confirmed also in the case of copolymers coated or blended with other polymers and the systems coupled by UV irradiation, photoreaction or gold/sulfur or silane coupling technology, and therefore it might be very useful for the medical devices.

Physical properties and blood compatibility of surface-modified segmented polyurethane by semi-interpenetrating polymer networks with a phospholipid polymer

Segmented polyurethanes, (SPU)s, are widely used in the biomedical fields because of their excellent mechanical property. However, when blood is in contact with the SPU, non-specific biofouling on the SPU occurs which reduces its mechanical property. To obtain novel blood compatible elastomers, the surface of the SPU was modified with 2-methacryloyloxyethyl phosphorylcholine (MPC) by forming a semi-interpenetrating polymer network (semi-IPN). The SPU film modified by MPC polymer with the semi-IPN (MS-IPN film) was prepared by visible light irradiation of the SPU film in which the monomers were diffused. X-ray photoelectron spectroscopy confirmed that the MPC units were exposed on the MS-IPN film surface. The mechanical properties of the MS-IPN film characterized by tensile testing were similar to those of the SPU film. Platelet adhesion on MS-IPN films was also investigated before and after stress loading to determine the effects of the surface modification on the blood compatibility. Many platelets did adhere on the SPU film before and after stress loading. On the other hand, the MS-IPN film prevented platelet adhesion even after repeated stress loading.