In vitro biocompatibility assessment of sulfonated polyrotaxane-immobilized polyurethane surfaces

Synthesis of cyclodextrin-based polyrotaxanes and polycatenanes for supramolecular pharmaceutical sciences

Cyclodextrins (CDs) are essential in the pharmaceutical industry and have long been used as food and pharmaceutical additives. CD-based interlocked molecules, such as rotaxanes, polyrotaxanes, catenanes, and polycatenanes, have been synthesized and have attracted considerable attention in supramolecular chemistry. Among them, CD polyrotaxanes have been employed as slide-ring materials and biomaterials. CD polycatenanes are new materials; therefore, to date, no examples of applied research on CD polycatenanes have been reported. Consequently, we expect that applied research on CD polycatenanes will accelerate in the future. This review article summarizes the syntheses and structural analyses of CD polyrotaxanes and polycatenanes to facilitate their applications in the pharmaceutical industry. We believe that this review will promote further research on CD-based interlocked molecules.

Polyrotaxane-based biointerfaces with dynamic biomaterial functions

The molecular mobility of cyclic molecules (e.g.α-cyclodextrins) threaded along a linear polymer chain (e.g. poly(ethylene glycol)) in polyrotaxanes is a unique feature for biomaterials with dynamic functionality. Surfaces with molecular mobility can be obtained by introducing polyrotaxanes. The molecular mobility of polyrotaxane-based surfaces can be modulated by changing the number of threaded cyclic molecules and modifying their functional groups. Biological ligands modified with α-cyclodextrins exhibit increased multivalent interactions with their receptors due to the molecular mobility of the latter. Furthermore, polyrotaxane-based surfaces not only improve the initial response of cells via multivalent interactions, but also affect cytoskeleton formation and the inherent quality of cells, including differentiation. Such polyrotaxane surfaces can emerge as new biointerfaces that can adapt to the dynamic biological nature.

Polyrotaxane Brushes Dynamically Formed at a Water/Elastomer Interface

Dense polymer brushes with closely packed rotaxane structures were formed at the interface of water and a styrene-butadiene elastomer by spontaneous segregation of an amphiphilic polyrotaxane (PR), a mechanically interlocked polymer consisting of hydrophobic polybutadiene threading through multiple hydrophilic γ-cyclodextrin (γ-CD) derivatives. Segregation of PR at the water/elastomer interface was suggested by X-ray photoelectron spectroscopy. The polymer brush structure at the water interface was investigated using neutron reflectometry. Brush structures were found to depend on the number of CDs on the PRs; the PR with a small number of CDs formed a thinner and homogeneous brush, whereas the PR with a higher number of CDs formed a thicker and less-ordered brush. These PR-brushes showed protein repulsion, resulting from the surface-hydrated brush layer preventing direct contact of proteins.

Review: physico-chemical modification as a versatile strategy for the biocompatibility enhancement of biomaterials

Physico-chemical modification induced improvement in biocompatibility of materials.

Supramolecular polymers based on cyclodextrins for drug and gene delivery

Supramolecular polymers based on cyclodextrins (CDs) have inspired interesting and rapid developments as novel biomaterials in a broad range of drug and gene delivery applications, due to their low cytotoxicity, controllable size, and unique architecture. This review will summarize the potential applications of polyrotaxanes in the field of drug delivery and gene delivery. Generally, cyclodextrin-based biodegradable polypseudorotaxane hydrogels could be used as a promising injectable drug delivery system for sustained and controlled drug release. Temperature-responsive, pH-sensitive, and controllable hydrolyzable polyrotaxane hydrogels have attracted much attention because of their controllable properties, and the self-assembly micelles formed by amphiphilic copolymer threaded with CDs could be used as a carrier for controlled and sustained drug release. Polyrotaxanes with drug or ligand conjugated CDs threaded on a polymer chain with a biodegradable end group could be useful for controlled and multivalent targeted delivery. In the field of gene delivery, cationic polyrotaxanes consisting of multiple OEI-grafted CDs threaded on a block copolymer chain are attractive non-viral gene carries due to the strong DNA-binding ability, low cytotoxicity, and high gene delivery capability. Furthermore, cytocleavable end-caps were introduced in the polyrotaxane systems in order to ensure efficient endosomal escape for intracellular trafficking of DNA. The development of the supramolecular approach using CD-containing polyrotaxanes is expected to provide a new paradigm for biomaterials.

Polyrotaxanes for applications in life science and biotechnology

Due to their low cytotoxicity, controllable size, and unique architecture, cyclodextrin (CD)-based polyrotaxanes and polypseudorotaxanes have inspired interesting exploitation as novel biomaterials. This review will update the recent progress in the studies on the structures of polyrotaxanes and polypseudorotaxanes based on different CDs and polymers, followed by summarizing their potential applications in life science and biotechnology, such as drug delivery, gene delivery, and tissue engineering. CD-based biodegradable polypseudorotaxane hydrogels could be used as promising injectable drug delivery systems for sustained and controlled drug release. Polyrotaxanes with drug or ligand-conjugated CDs threaded on polymer chain with biodegradable end group could be useful for controlled and multivalent targeting delivery. Cationic polyrotaxanes consisting of multiple oligoethylenimine-grafted CDs threaded on a block copolymer chain were attractive non-viral gene carries due to the strong DNA-binding ability, low cytotoxicity, and high gene transfection efficiency. Cytocleavable end caps were also introduced in the polyrotaxane systems in order to ensure efficient endosomal escape for intracellular trafficking of DNA. Finally, hydrolyzable polyrotaxane hydrogels with cross-linked α-CDs could be a desirable scaffold for cartilage and bone tissue engineering.

Cyclodextrin-based supramolecular architectures: syntheses, structures, and applications for drug and gene delivery

The supramolecular structures formed between cyclodextrins (CDs) and polymers have inspired interesting developments of novel supramolecular biomaterials. This review will update the recent progress in studies on supramolecular structures based on CDs and block copolymers, followed by the design and synthesis of CD-based supramolecular hydrogels and biodegradable polyrotaxanes for potential controlled drug delivery, and CD-containing cationic polymers and cationic polyrotaxanes for gene delivery. Supramolecular hydrogels based on the self-assembly of the inclusion complexes between CDs with biodegradable block copolymers could be used as promising injectable drug delivery systems for sustained controlled release of macromolecular drugs. Biodegradable polyrotaxanes with drug-conjugated CDs threaded on a polymer chain with degradable end-caps could be interesting supramolecular prodrugs for controlled and targeting delivery of drugs. CD-containing cationic polymers as gene carriers showed reduced cytotoxicity than non-CD-containing polymer counterparts. More importantly, the polyplexes of CD-containing cationic polymers with DNA could be pegylated through a supramolecular process using inclusion complexation between the CD moieties and a modified PEO. Finally, new cationic polyrotaxanes composed of multiple oligoethylenimine-grafted CDs threaded and end-capped on a block copolymer chain were designed and synthesized as a new class of polymeric gene delivery vectors, where the chain-interlocked cationic cyclic units formed an integrated supramolecular entity to function as a macromolecular gene vector. The development of the supramolecular biomaterials through inclusion complexation has opened up a new approach for designing novel drug and gene delivery systems, which may have many advantages over the systems based on the conventional polymeric materials.

Surface-attached PEO in the form of activated pluronic with immobilized factor H reduces both coagulation and complement activation in a whole-blood model

In the present work we have bound Pluronic, a class of triblock copolymers consisting of a block of polypropylene oxide (PPO) surrounded on each side by polyethylene oxide (PEO) blocks, to polystyrene surfaces and investigated the thrombogenicity and complement activation of this construct upon exposure to whole blood. The surface was highly inert towards coagulation, unfortunately at the expense of increased complement activation. We, therefore, as an alternative approach, used End-Group Activated Pluronic to conjugate factor H, a regulator of complement activation (RCA), to the surface. The bound factor H did not detach from the surface upon incubation with human serum. Furthermore, factor H bound in a physiological conformation could to a significant degree attenuate complement activation at the Pluronic surface. Thus, we have created a hybrid surface in which the coagulation-inert properties of the original Pluronic are supplemented with a specific complement-inhibitory effect. Medical device technology includes numerous potential applications for crosslinkers that are capable of specifically binding biomolecules to surfaces with retained activity. These applications include coupling of functional biomolecules to biomedical devices such as stents and grafts. The biomolecule may be an RCA, antibody, or other beneficial ligand.

The role of adsorbed fibrinogen in platelet adhesion to polyurethane surfaces: A comparison of surface hydrophobicity, protein adsorption, monoclonal antibody binding, and platelet adhesion

Ten specially synthesized polyurethanes (PUs) were used to investigate the effects of surface properties on platelet adhesion. Surface composition and hydrophilicity, fibrinogen (Fg) and von Willebrand's factor (vWf) adsorption, monoclonal anti-Fg binding, and platelet adhesion were measured. PUs preadsorbed with afibrinogenemic plasma or serum exhibited very low platelet adhesion, while adhesion after preadsorption with vWf deficient plasma was not reduced, showing that Fg is the key plasma protein mediating platelet adhesion under static conditions. Platelet adhesion to the ten PUs after plasma preadsorption varied greatly, but was only partially consistent with Fg adsorption. Thus, while very hydrophilic PU copolymers containing PEG that had ultralow Fg adsorption also had very low platelet adhesion, some of the more hydrophobic PUs had relatively high Fg adsorption but still exhibited lower platelet adhesion. To examine why some PUs with high Fg adsorption had lower platelet adhesion, three monoclonal antibodies (mAbs) that bind to sites in Fg thought to mediate platelet adhesion were used. The antibodies were: M1, specific to gamma-chain C-terminal; and R1 and R2, specific to RGD containing regions in the alpha-chain N- and C-terminal, respectively. Platelet adhesion was well correlated with M1 binding, but not with R1 or R2 binding. When these mAbs were incubated with plasma preadsorbed surfaces, they blocked adhesion to variable degrees. The ability of the R1 and R2 mAbs to partially block adhesion to adsorbed Fg suggests that RGD sites in the alpha chain may also be involved in mediating platelet adhesion and act synergistically with the C-terminal of the gamma-chain.

Protein resistant polyurethane surfaces by chemical grafting of PEO: amino-terminated PEO as grafting reagent

The objective of this work was to gain a better understanding of the mechanism of resistance to protein adsorption of surfaces grafted with poly(ethylene oxide) (PEO). A polyurethane-urea was used as a substrate to which PEO was grafted. Grafting was carried out by introducing isocyanate groups into the surface followed by reaction with amino-terminated PEO. Surfaces grafted with PEO of various chain lengths (PUU-NPEO) were prepared and characterized by water contact angle and X-ray photoelectron spectroscopy (XPS). XPS data indicated higher graft densities on the PUU-NPEO surfaces than on analogous surfaces prepared using hydroxy-PEO (PUU-OPEO) as reported previously [J.G. Archambault, J.L. Brash, Colloids Surf. B: Biointerf. 33 (2004) 111-120]. Protein adsorption experiments using radiolabeled myoglobin, concanavalin A, albumin, fibrinogen and ferritin as single proteins in buffer showed that adsorption was reduced on the PEO-grafted surfaces by up to 95% compared to the control. Adsorption decreased with increasing PEO chain length and reached a minimum at a PEO MW of 2000. Adsorption levels on surfaces with 5000 and 2000 MW grafts were similar. There was no clear effect of protein size on resistance to protein adsorption. Adsorption on the PUU-NPEO surfaces was significantly lower than on the corresponding PUU-OPEO surfaces, again suggesting higher graft densities on the former. Adsorption of fibrinogen from plasma was also greatly reduced on the grafted surfaces. From analysis (SDS-PAGE, immunoblotting) of the proteins eluted after plasma exposure, it was found that the grafted surfaces and the unmodified substrate adsorbed the same proteins in roughly the same proportions, suggesting that adsorption to the PEO surfaces occurs on patches of bare substrate. The PEO grafts did not apparently cause differential access to the substrate based on protein size.