Minimized platelet interaction with poly(2-hydroxyethyl methacrylate-block-4-bis(trimethylsilyl)methylstyrene) hydrogel showing anomalously high free water content

Stealth and pseudo-stealth nanocarriers

The stealth effect plays a central role on capacitating nanomaterials for drug delivery applications through improving the pharmacokinetics such as blood circulation, biodistribution, and tissue targeting. Here based on a practical analysis of stealth efficiency and a theoretical discussion of relevant factors, we provide an integrated material and biological perspective in terms of engineering stealth nanomaterials. The analysis surprisingly shows that more than 85% of the reported stealth nanomaterials encounter a rapid drop of blood concentration to half of the administered dose within 1 h post administration although a relatively long β-phase is observed. A term, pseudo-stealth effect, is used to delineate this common pharmacokinetics behavior of nanomaterials, that is, dose-dependent nonlinear pharmacokinetics because of saturating or depressing bio-clearance of RES. We further propose structural holism can be a watershed to improve the stealth effect; that is, the whole surface structure and geometry play important roles, rather than solely relying on a single factor such as maximizing repulsion force through polymer-based steric stabilization (e.g., PEGylation) or inhibiting immune attack through a bio-inspired component. Consequently, engineering delicate structural hierarchies to minimize attractive binding sites, that is, minimal charges/dipole and hydrophobic domain, becomes crucial. In parallel, the pragmatic implementation of the pseudo-stealth effect and dynamic modulation of the stealth effect are discussed for future development.

Effect of methoxyethyl and methyl ester groups on platelet compatibility of polymers

Poly(2-methoxyethyl acrylate) is known to exhibit good blood compatibility. This study was designed to understand the effect of methoxyethyl ester groups on the platelet compatibility of polymers. Polymers bearing either methoxyethyl ester or methyl ester groups, such as poly(acrylate)s, poly(methacrylate)s, and poly(vinyl benzoate)s, were prepared and a comparative study of the ester groups was performed. Polymers bearing methoxyethyl ester groups and poly(methyl acrylate) exhibited good and approximately equal platelet compatibility, regardless of their chemical structure, as estimated using flow cytometry and scanning electron microscopy. To understand these results, the static properties (namely, surface wettability by contact angle and water structure by differential scanning calorimetry) and a dynamic property (13C-NMR relaxation time of the functional groups) were analyzed. The results showed that platelet compatibility could be interpreted from the water structure and dynamic property.

Effect of end segment on physicochemical properties and platelet compatibility of poly(propylene glycol)-initiated poly(methyl methacrylate)

It is well known that polyether-based copolymers have good blood compatibility, although many mechanisms have been proposed to explain their favorable performance. Our objective in carrying out the present study was to obtain a better understanding of the effect of the (poly)ether segment on blood compatibility. Therefore, we synthesized poly(propylene glycol) (PPG)-based initiators for atom transfer polymerization, where the number of propylene glycol (PG) units in the PPG (Pn(PG) was varied from 1 to 94. Methyl methacrylate (MMA) was polymerized using the initiators, resulting in the formation of polyMMAs with a PG-based ether part at the polymer terminal. We mainly investigated the effects of Pn(PG) on the surface properties and platelet compatibility of the PPG-polyMMA. X-ray photoelectron spectroscopy and surface contact angle (CA) analysis revealed the exposure of the PG units at the surface of the polymer. The platelet compatibility of the polymers was improved compared with a commercial polyMMA, even when Pn(PG) = 1. These results suggest that PG units have an important influence on favorable blood compatibility, regardless of the Pn(PG) value. We also investigated protein adsorption behavior in terms of the amount and deformation of fibrinogen adsorbed on the polymer surface.

Relationship between water structure and properties of poly(methyl methacrylate-b-2-hydroxyethyl methacrylate) by solid-state NMR

We previously reported that the platelet compatibility of methyl methacrylate (MMA)-2-hydroxyethyl methacrylate (HEMA) diblock copolymers is related to the characteristic water structure in the copolymer, as the copolymer has an excess amount of nonfreezing water when compared with that estimated from the amounts of water in HEMA and MMA homopolymers. Thus, in this study, the relationship between water structure and polymer structure, including the heterogeneity and mobility of the copolymer, was investigated using differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spectroscopy. The prepared copolymers were classified into two groups: copolymers with a short, constant polyMMA segment length (Mn = ~2900) and copolymers with a constant polyHEMA segment length (Mn = ~9500), whereas the lengths of the counter segments varied. DSC analysis showed that when the polyMMA and polyHEMA segment lengths are similar, the amount of nonfreezing water increases, regardless of the total molecular weight of the copolymer. NMR analysis showed that heterogeneity of the copolymer is enhanced and the mobility of the copolymer decreases when the segment lengths are similar. These findings suggested that the excess amount of nonfreezing water is formed when the properties of water near the HEMA unit change from freezing to nonfreezing owing to interactions with the MMA unit. In addition, it is suggested that the heterogeneity of the copolymer structure or the mobility of the polymer are involved in the generation of excess nonfreezing water.

Novel hemocompatible nanocomposite hydrogels crosslinked with methacrylated gelatin

Methacrylated gelatin is developed as a macromolecular crosslinker to prepare a novel hemocompatible nanocomposite hydrogel based on polyacrylamide and LAPONITE®.

Gelatin Effects on the Physicochemical and Hemocompatible Properties of Gelatin/PAAm/Laponite Nanocomposite Hydrogels

In recent years, inorganic nanoparticles such as Laponite have frequently been incorporated into polymer matrixes to obtain nanocomposite hydrogels with hierarchical structures, ultrastrong tensibilities, and high transparencies. Despite their unique physical and chemical properties, only a few reports have evaluated Laponite-based nanocomposite hydrogels for biomedical applications. This article presents the synthesis and characterization of a novel, hemocompatible nanocomposite hydrogels by in situ polymerization of acrylamide (AAm) in a mixed suspension containing Laponite and gelatin. The compatibility, structure, thermal stability, and mechanical properties of the resulting NC gels with varied gel compositions were investigated. Our results show that the prepared nanocomposite hydrogels exhibit good thermal stability and mechanical properties. The introduction of a biocompatible polymer, gelatin, into the polymer matrix did not change the transparency and homogeneity of the resulting nanocomposite hydrogels, but it significantly decreased the hydrogel's pH-responsive properties. More importantly, gelatins that were incorporated into the PAAm network resisted nonspecific protein adsorption, improved the degree of hemolysis, and eventually prolonged the clotting time, indicating that the in vitro hemocompatibility of the resulting nanocomposite hydrogels had been substantially enhanced. Therefore, these nanocomposite hydrogels provide opportunities for potential use in various biomedical applications.

Vitamin E triggers poly(2-hydroxyethyl methacrylate) (PHEMA) embolic potential: a proposed application for endovascular surgery

Poly(2-hydroxyethyl methacrylate) (PHEMA) is a biocompatible polymer used as embolizing agent for endovascular surgery. Blending of PHEMA with a hydrophobic and anti-oxidant agent, Vitamin E (Vit.E, 0.1-10%, w/v), modified PHEMA's haemocombatibility, evaluated measuring wettability, plasma protein adsorption along with whole blood coagulation time. The presence of Vit.E increases PHEMA's hydrophobicity and plasma protein adsorption (in particular albumin and Immunoglobulin G), while it also accelerates blood clot formation. These effects are developed due to a combination of issues such as surface hydrophobicity and plasma protein adsorption induced by the presence of Vit.E, suggesting that Vit.E blending could improve the use of PHEMA as embolizing agent.

Study on blood compatibility with poly(2-methoxyethylacrylate)—relationship between surface structure, water structure, and platelet compatibility in 2-methoxyethylacrylate/2-hydroxyethylmethacrylate diblock copolymer

Diblock copolymers composed of 2-methoxyethylacrylate (MEA) and 2-hydroxyethylmethacrylate (HEMA) were firstly prepared (the composition ratio = 90/10, 79/21, 66/34, and 48/52 mol/mol) by anion living polymerization. ESCA analysis of their surface structures (dry state) revealed that PMEA segment was segregated to the top surface in all of the polymers, whereas the results of contact angle of water (wet state) showed that the surfaces were covered with PHEMA segment. In vitro platelet adhesion test showed that these polymers had the excellent compatibility with platelet compared to PHEMA homopolymer. Water structure in the hydrated copolymers was investigated by DSC and freezing bound water was observed for all the polymers like PMEA homopolymer, whereas it was not found in PHEMA homopolymer. Further investigation of water structure based on the results of DSC and EWCMS (equilibrium water content by moisture sorption) suggested that freezing bound water existed in PHEMA segment in addition to PMEA segment. We have proposed that the water plays a key role in the appearance of good blood compatibility of the copolymer, according to our previous works (Tanaka et al. Biomacromolecules 2002;3:36-41, Tanaka et al. J Biomed Mater Res A 2004;68:684-695).

Effect of water structure on blood compatibility? thermal analysis of water in poly(meth)acrylate

The purpose of this study is to clarify the main factor causing excellent blood compatibility of poly(2-methoxyethyl acrylate)(PMEA) by the comparison between PMEA and seven PMEA analogous polymers. The polymers have a typical functional group as ester side chains such as methoxyethyl, hydroxyethyl, phenoxyethyl, and alkyl groups. The properties of the polymers relating to water were investigated in terms of contact angle, equilibrium water content (EWC), and thermal analysis by differential scanning calorimetry. The water in PMEA could be classified into three types: nonfreezing water, freezing bound water, and free water while the water in the analogous polymers was classified into just two types: free and nonfreezing waters, regardless of the chemical structure of the side chain. The surface property represented by the contact angle of water corresponded to the content of the bound water (nonfreezing water + freezing bound water). The platelet compatibility in vitro did not depend on the contents of these waters, or on the contact angle. On the basis of the results of this work and the previous work on the platelet compatibility of poly(MEA-co-HEMA) (Tanaka et al. Biomacromolecules 2002;3;36-41), the main factor causing the excellent compatibility of PMEA is discussed.

Cell adhesion on poly(propylene fumarate-co-ethylene glycol) hydrogels

We synthesized poly(propylene fumarate-co-ethylene glycol) block copolymers [P(PF-co-EG)] that were crosslinked to form hydrogels and investigated the effect of copolymer composition on cell adhesion to the hydrogels. These copolymers were water soluble when the molar ratio of ethylene glycol repeating unit to propylene fumarate repeating unit was higher than 4.4. The water content of swollen hydrogels increased from 29 to 63% and the water contact angle decreased from 38 to 21 degrees as the molar ratio increased from 0.6 to 4.4. No significant change in either property was observed for ratios higher than 4.4. In a cell adhesion assay under serum-free conditions, the number of adherent platelets and smooth muscle cells decreased from 21 to 2% and from 78 to 20% of the initial seeding density, respectively, as the molar ratio increased from 0.6 to 7.8. Adherent smooth muscle cells did not spread on the hydrogels of the compositions tested. Adherent platelets did not show any filopodia. These results suggest that the hydrophilicity of P(PF-co-EG) hydrogels is one of the factors affecting cell adhesion, and that copolymer modification may be required for enhancing cell adhesion for an application involving the copolymers as in situ crosslinkable cell carriers.

Study of blood compatibility with poly(2-methoxyethyl acrylate). Relationship between water structure and platelet compatibility in poly(2-methoxyethylacrylate-co-2-hydroxyethylmethacrylate)

Previously, we reported that poly(2-methoxyethylacrylate) (PMEA) showed excellent blood compatibility and implied that the water structure in PMEA contributed to the blood compatibility. In this study, the relationship between the water structure and the blood compatibility is clarified by studying the influence of the monomer composition of poly(MEA-co-HEMA) on the water structure and the blood compatibility of the copolymers. The water in the polymer was classified into three types: free water, freezing bound water, and nonfreezing water. The polymers with 0-30 mol % of HEMA content had a significant amount of freezing bound water, and the amount decreases greatly when the composition of HEMA exceeded 30 mol %. On the other hand, the amount of other water increased simply with an increase of HEMA content. The evaluation of the platelet compatibility of poly(MEA-co-HEMA) revealed that the adhesion number and the morphological change of platelet on the copolymer surface were least when the HEMA content was 0-20 mol %. These two results strongly suggest that the freezing bound water relates to the platelet compatibility of the polymers.