Blood-compatible poly(2-methoxyethyl acrylate) for the adhesion and proliferation of endothelial and smooth muscle cells

Poly(2-methoxyethyl acrylate) (PMEA) improves the thromboresistance of FRED flow diverters: a thrombogenic evaluation of flow diverters with human blood under flow conditions

BACKGROUND

Surface modification of flow-diverting stents has been explored to reduce thrombus-related complications that may arise under clinical use. This study investigated the thromboresistant properties of the flow redirection endoluminal device (FRED) X, a flow diverter treated with a copolymer of poly(2-methoxyethyl acrylate) (PMEA; X Technology).

METHODS

The performance of FRED, FRED X, and Pipeline Flex with Shield Technology (sPED) was evaluated in an in vitro blood loop model. Blood activation level was assessed by the concentration of thrombin-antithrombin complex (TAT), β-thromboglobulin (β-TG), and platelet count, and qualitatively by scanning electron microscopy (SEM). Cellular adhesion characteristics were measured using human aortic endothelial cells that were seeded on flat sheets mimicking the surface of FRED, FRED X, and sPED, and evaluated with fluorescence microscopy. Statistical comparisons were conducted using one-way analysis of variance (ANOVA) with Tukey post hoc tests.

RESULTS

FRED X, sPED, and control blood loops showed significantly reduced blood activation levels (TAT and β-TG) compared with FRED (p<0.01). Consequently, FRED showed a significant decrease in platelet count compared with FRED X, sPED, and control loops (p<0.01). SEM imaging showed the lowest accumulation of blood cell-like deposits on FRED X compared with sPED and FRED, while FRED had the highest accumulation. Endothelial cells adhered and were widely spread on X Technology-treated sheets, while minimal cell adhesion was observed on phosphorylcholine-treated sheets.

CONCLUSION

The X Technology surface modification of FRED X demonstrated superior thromboresistant properties over untreated FRED while maintaining comparable cellular adhesion. Taken together, these properties may help mitigate material-related thromboembolic complications.

Biological properties of self-assembled nanofibers of elastin-like block polypeptides for tissue-engineered vascular grafts: platelet inhibition, endothelial cell activation and smooth muscle cell maintenance

Strategic materials design is essential for the development of small-diameter, tissue-engineered vascular grafts. Self-assembled nanofibers of elastin-like polypeptides represent promising vascular graft components as they replicate the organized elastin structure of native blood vessels. Further, the bioactivity of nanofibers can be modified by the addition of functional peptide motifs. In the present study, we describe the development of a novel nanofiber-forming elastin-like polypeptide (ELP) with an arginine-glutamic acid-aspartic acid-valine (REDV) sequence. The biological characteristics of the REDV-modified ELP nanofibers relevant to applications in vascular grafting were compared to ELP without ligands for integrin, ELP with arginine-glycine-aspartic acid (RGD) sequence, collagen and cell culture glass. Among them, REDV-modified ELP nanofibers met the preferred biological properties for vascular graft materials, i.e. (i) inhibition of platelet adhesion and activation, (ii) endothelial cell adhesion and proliferation and (iii) maintenance of smooth muscle cells in a contractile phenotype to prevent cell overgrowth. The results indicate that REDV-modified ELP nanofibers represent promising candidates for the further development of small-diameter vascular grafts.

Cell Adhesion Strength Indicates the Antithrombogenicity of Poly(2-Methoxyethyl Acrylate) (PMEA): Potential Candidate for Artificial Small-Diameter Blood Vessel

Poly (2-methoxyethyl acrylate) (PMEA) is a US FDA-approved biocompatible polymer, although there is insufficient work on human umbilical vein endothelial cells (HUVECs) and platelet interaction analysis on PMEA-analogous polymers. In this study, we extensively investigated HUVEC–polymer and platelet–polymer interaction behavior by measuring the adhesion strength using single-cell force spectroscopy. Furthermore, the hydration layer of the polymer interface was observed using frequency-modulation atomic force microscopy. We found that endothelial cells can attach and spread on the PMEA surface with strong adhesion strength compared to other analogous polymers. We found that the hydration layers on the PMEA-analogous polymers were closely related to their weak platelet adhesion behavior. Based on our results, it can be concluded that PMEA is a promising candidate for the construction of artificial small-diameter blood vessels owing to the presence of IW and a hydration layer on the interface.

Characterization of Hydration Water Bound to Choline Phosphate-Containing Polymers

Zwitterionic methacrylate polymers with either choline phosphate (CP) (poly(MCP)) or phosphorylcholine (PC) (poly(MPC)) side groups were analyzed to characterize the bound hydration water molecules as nonfreezing water (NFW), intermediate water (IW), or free water (FW). This characterization was carried out by differential scanning calorimetry (DSC) of polymer/water systems, and the enthalpy changes of cold crystallization and melting were determined. The electron pair orientation of CP is opposite to that of PC, and the former binds the alkyl terminal groups at the phosphate esters. The numbers of NFW and IW molecules per monomer unit of poly(MCP) with an isopropyl terminal group were estimated to be 10.7 and 11.3 mol/mol, respectively, which were slightly greater than those of the poly(MCP) bearing an ethyl terminal group. More NFW and IW molecules hydrated the phosphobetaine polyzwitterions, poly(MCP) and poly(MPC), compared with carboxybetaine and sulfobetaine polymers. Moreover, the hydration states of polyelectrolytes were compared with the zwitterionic polymers. Finally, we discuss the relationship between the amount of hydration water and bio-inert properties.

Poly(2-Methoxyethyl Acrylate) (PMEA)-Coated Anti-Platelet Adhesive Surfaces to Mimic Native Blood Vessels through HUVECs Attachment, Migration, and Monolayer Formation

Confluent monolayers of human umbilical vein endothelial cells (HUVECs) on a poly(2-methoxyethyl acrylate) (PMEA) antithrombogenic surface play a major role in mimicking the inner surface of native blood vessels. In this study, we extensively investigated the behavior of cell–polymer and cell–cell interactions by measuring adhesion strength using single-cell force spectroscopy. In addition, the attachment and migration of HUVECs on PMEA-analogous substrates were detected, and the migration rate was estimated. Moreover, the bilateral migration of HUVECs between two adjacent surfaces was observed. Furthermore, the outer surface of HUVEC was examined using frequency-modulation atomic force microscopy (FM-AFM). Hydration was found to be an indication of a healthy glycocalyx layer. The results were compared with the hydration states of individual PMEA-analogous polymers to understand the adhesion mechanism between the cells and substrates in the interface region. HUVECs could attach and spread on the PMEA surface with stronger adhesion strength than self-adhesion strength, and migration occurred over the surface of analogue polymers. We confirmed that platelets could not adhere to HUVEC monolayers cultured on the PMEA surface. FM-AFM images revealed a hydration layer on the HUVEC surfaces, indicating the presence of components of the glycocalyx layer in the presence of intermediate water. Our findings show that PMEA can mimic original blood vessels through an antithrombogenic HUVEC monolayer and is thus suitable for the construction of artificial small-diameter blood vessels.

Molecular weight tuning optimizes poly(2-methoxyethyl acrylate) dispersion to enhance the aging resistance and anti-fouling behavior of denture base resin

Poly(methyl methacrylate) (PMMA)-based denture base resins easily develop oral bacterial and fungal biofilms, which may constitute a significant health risk. Conventional bacterial-resistant additives and coatings often cause undesirable changes in the resin. Reduced bacterial resistance over time in the harsh oral environment is a major challenge in resin development. Poly(2-methoxyethyl acrylate) (PMEA) has anti-fouling properties; however, due to the oily/rubbery state of this polymer, and its surface aggregation tendency in a resin mixture, its direct use as a resin additive is limited. This study aimed to optimize the use of PMEA in dental resins. Acrylic resins containing a series of PMEA polymers with various molecular weights (MWs) at different concentrations were prepared, and the mechanical properties, surface gloss, direct transmittance, and cytotoxicity were evaluated, along with the distribution of PMEA in the resin. Resins with low-MW PMEA (2000 g mol^-1) (PMEA-1) at low concentrations satisfied the clinical requirements for denture resins, and the PMEA was homogeneously distributed. The anti-fouling performance of the resin was evaluated for protein adsorption, bacterial and fungal attachment, and saliva-derived biofilm formation. The PMEA-1 resin most effectively inhibited biofilm formation (∼50% reduction in biofilm mass and thickness compared to those of the control). Post-aged resins maintained their mechanical properties and anti-fouling activity, and polished surfaces had the same anti-biofilm behavior. Based on wettability and tribological results, we propose that the PMEA additive creates a non-stick surface to inhibit biofilm formation. This study demonstrated that PMEA additives can provide a stable and biocompatible anti-fouling surface, without sacrificing the mechanical properties and aesthetics of denture resins.

Modulation of Biological Responses of Tumor Cells Adhered to Poly(2-methoxyethyl acrylate) with Increasing Cell Viability under Serum-Free Conditions

Circulating tumor cells in body fluids are important biomarkers in cancer diagnosis. The culture of tumor cells isolated from body fluids can provide intrinsic information about tumors and can be used to screen for the best anticancer drugs. However, the culture of primary tumor cells has been hindered by their low viability and difficulties in recapitulating the phenotype of primary tumors in in vitro culture. The culture of tumor cells under serum-free conditions is one of the methodologies to maintain the phenotype and genotype of primary tumors. Poly(2-methoxyethyl acrylate) (PMEA)-coated substrates have been investigated to prolong the proliferation of tumor cells under serum-free conditions. In this study, we investigated the detailed behavior and the mechanism of the increase in tumor cell viability after adherence to PMEA substrates. The blebbing formation of tumor cells on PMEA was attributed not to apoptosis but to the low adhesion strength of cells on PMEA. Moreover, blebbing tumor cells showed amoeboid movement and formed clusters with other cells via N-cadherin, leading to an increase in tumor cell viability. Furthermore, the behaviors of tumor cells adhered to PMEA under serum-free conditions were involved in the activation of the PI3K and Rho-associated protein kinase pathways. Thus, we propose that PMEA would be suitable for the development of devices to cultivate primary tumor cells under serum-free conditions for the label-free diagnosis of cancer.

Simultaneous control of the mechanical properties and adhesion of human umbilical vein endothelial cells to suppress platelet adhesion on a supramolecular substrate

The demand for artificial blood vessels to treat vascular disease will continue to increase in the future. To expand the application of blood-compatible poly(2-methoxyethyl acrylate) (pMEA) to artificial blood vessels, control of the mechanical properties of pMEA is established using supramolecular cross-links based on inclusion complexation of acetylated cyclodextrin. The mechanical properties, such as Young's modulus and toughness, of these pMEA-based elastomers change with the amount of cross-links, maintaining tissue-like behavior (J-shaped stress–strain curve). Regardless of the cross-links, the pMEA-based elastomers exhibit low platelet adhesion properties (approximately 3% platelet adherence) compared with those of poly(ethylene terephthalate), which is one of the commercialized materials for artificial blood vessels. Contact angle measurements imply a shift of supramolecular cross-links in response to the surrounding environment. When immersed in water, hydrophobic supramolecular cross-links are buried within the interior of the materials, thereby exposing pMEA chains to the aqueous environment; this is why supramolecular cross-links do not affect the platelet adhesion properties. In addition, the elastomers exhibit stable adhesion to human umbilical vein endothelial cells. This report shows the potential of combining supramolecular cross-links and pMEA.

Supramolecular cross-links in poly(2-methoxyethyl acrylate) enhanced mechanical properties of the polymers maintaining high blood compatibility. The high blood compatibility suggests a potential for artificial blood vessel.

Role of interfacial water in determining the interactions of proteins and cells with hydrated materials

Water molecules play a crucial role in biointerfacial interactions, including protein adsorption and desorption. To understand the role of water in the interaction of proteins and cells at biological interfaces, it is important to compare particular states of hydration water with various physicochemical properties of hydrated biomaterials. In this review, we discuss the fundamental concepts for determining the interactions of proteins and cells with hydrated materials along with selected examples corresponding to our recent studies, including poly(2-methoxyethyl acrylate) (PMEA), PMEA derivatives, and other biomaterials. The states of water were analyzed by differential scanning calorimetry, in situ attenuated total reflection infrared spectroscopy, and surface force measurements. We found that intermediate water which is loosely bound to a biomaterial, is a useful indicator of the bioinertness of material surfaces. This finding on intermediate water provides novel insights and helps develop novel experimental models for understanding protein adsorption in a wide range of materials, such as those used in biomedical applications.

Synthesis of Thermoplastic Poly(2-methoxyethyl acrylate)-Based Polyurethane by RAFT and Condensation Polymerization

Thermoplastic solid poly(2-methoxyethyl acrylate) (PMEA)-based polyurethane (PU) is synthesized through the reversible addition-fragmentation chain transfer (RAFT) polymerization and the condensation polymerization, using hydroxyl-terminated RAFT reagents and diisocyanate, respectively. Neat PMEA is a promising antithrombogenic liquid used in the medical fields. The thermoplastic property of the solid PMEA-based PU due to hydrogen bonding is confirmed by the dynamic mechanical analysis (DMA) at temperature below 72 °C. The antithrombogenic property of PMEA-based PU is also analyzed by the platelet adhesion test. The number of platelets on PMEA-based PU is 17 cells per unit area, which is smaller than that on the fluorinated diamond-like carbon (F-DLC), a well-known highly antithrombogenic material. It is concluded that a newly synthesized PMEA-based PU exhibits thermoplastic characteristics with excellent antithrombogenicity.

Biocompatibility and adhesive strength properties of poly(methyl acrylate-co-acrylic acid) as a function of acrylic acid content

Metals and metal alloys are widely used in medical devices that contact blood and/or tissue, and various coating materials for the metal parts have been proposed to improve surface properties such as biocompatibility. This study aims to understand the performance of new coating materials, copolymers of methyl acrylate and acrylic acid, in terms of their biocompatibility and adhesive strength to a metal surface. Blood compatibility was investigated through platelet and coagulation system responses. Cytocompatibility was studied in three cell-line types (endothelium, smooth muscle, and fibroblasts) in terms of cell viability and morphology; these tests showed that compatibility depended on the cell types and acrylic acid content of the copolymers. Because of their blood compatibility and adhesion strength, the methyl acrylate and acrylic acid copolymers containing 10–24 mol% acrylic acid were found to be excellent candidates as potential coating materials for devices contacting blood.

In vitro measurement of platelet adhesion to intact endothelial cells under low shear conditions

BACKGROUND

Prediction of thrombus formation at intact arterial walls under low shear flow conditions is clinically important particularly for better prognoses of embolisation in cerebral aneurysms. Although a new mathematical model for this purpose is necessary, little quantitative information has been known about platelet adhesion to intact endothelial cells.

OBJECTIVE

The objective of this study is to measure the number of platelets adhering to intact endothelial cells with a focus upon the influence of the shear rate.

METHODS

Endothelial cells disseminated in μ-slides were exposed to swine whole blood at different shear rates. Adenosine diphosphate (ADP) was used as an agonist. Adherent platelets were counted by means of scanning electron microscopy.

RESULTS

At an ADP concentration of 1 µM, 20.8 ± 3.1 platelets per 900 µm2 were observed after 30-minute perfusion at a shear rate of 0.8 s-1 whereas only 3.0 ± 1.4 per 900 µm2 at 16.8 s-1.

CONCLUSIONS

The number of adherent platelets is determined by a balance between the shear and the degree of stimulation by the agonist. At an ADP concentration of 1 µM, a limit to the shear rate at which platelets can adhere to intact endothelial cells is considered to be slightly higher than 16.8 s-1.

Monoether-Tagged Biodegradable Polycarbonate Preventing Platelet Adhesion and Demonstrating Vascular Cell Adhesion: A Promising Material for Resorbable Vascular Grafts and Stents

We developed a biodegradable polycarbonate that demonstrates antithrombogenicity and vascular cell adhesion via organocatalytic ring-opening polymerization of a trimethylene carbonate (TMC) analogue bearing a methoxy group. The monoether-tagged polycarbonate demonstrates a platelet adhesion property that is 93 and 89% lower than those of poly(ethylene terephthalate) and polyTMC, respectively. In contrast, vascular cell adhesion properties of the polycarbonate are comparable to those controls, indicating a potential for selective cell adhesion properties. This difference in the cell adhesion property is well associated with surface hydration, which affects protein adsorption and denaturation. Fibrinogen is slightly denatured on the monoether-tagged polycarbonate, whereas fibronectin is highly activated to expose the RGD motif for favorable vascular cell adhesion. The surface hydration, mainly induced by the methoxy side chain, also contributes to slowing the enzymatic degradation. Consequently, the polycarbonate exhibits decent blood compatibility, vascular cell adhesion properties, and biodegradability, which is promising for applications in resorbable vascular grafts and stents.