Grafting of Bioactive Polymers with Various Architectures: A Versatile Tool for Preparing Antibacterial Infection and Biocompatible Surfaces.

The aim of this Research Article is to present three different techniques of poly(sodium styrene sulfonate) (polyNaSS) covalent grafting onto titanium (Ti) surfaces and study the influence of their architecture on biological response. Two of them are "grafting from" techniques requiring an activation step either by thermal or UV irradiation. The third method is a "grafting to" technique involving an anchorage molecule onto which polyNaSS synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization is clicked. The advantage of the "grafting to" technique when compared to the "grafting from" technique is the ability to control the architecture and length of the grafted polymers on the Ti surface and their influence on the biological responses. This investigation compares the effect of the three different grafting processes on the in vitro biological responses of bacteria and osteoblasts. Overall outcomes of this investigation confirmed the significance of the sulfonate functional groups on the biological responses, regardless of the grafting method. In addition, results showed that the architecture and distribution of grafted polyNaSS on Ti surfaces alter the intensity of the bacteria response mediated by fibronectin.

Grafting of architecture controlled poly(styrene sodium sulfonate) onto titanium surfaces using bio-adhesive molecules: Surface characterization and biological properties.

This contribution reports on grafting of bioactive polymers such as poly(sodium styrene sulfonate) (polyNaSS) onto titanium (Ti) surfaces. This grafting process uses a modified dopamine as an anchor molecule to link polyNaSS to the Ti surface. The grafting process combines reversible addition-fragmentation chain transfer polymerization, postpolymerization modification, and thiol-ene chemistry. The first step in the process is to synthetize architecture controlled polyNaSS with a thiol end group. The second step is the adhesion of the dopamine acrylamide (DA) anchor onto the Ti surfaces. The last step is grafting polyNaSS to the DA-modified Ti surfaces. The modified dopamine anchor group with its bioadhesive properties is essential to link bioactive polymers to the Ti surface. The polymers are characterized by conventional methods (nuclear magnetic resonance, size exclusion chromatography, and attenuated total reflection-Fourier-transformed infrared), and the grafting is characterized by x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and quartz crystal microbalance with dissipation monitoring. To illustrate the biocompatibility of the grafted Ti-DA-polyNaSS surfaces, their interactions with proteins (albumin and fibronectin) and cells are investigated. Both albumin and fibronectin are readily adsorbed onto Ti-DA-polyNaSS surfaces. The biocompatibility of modified Ti-DA-polyNaSS and control ungrafted Ti surfaces is tested using human bone cells (Saos-2) in cell culture for cell adhesion, proliferation, differentiation, and mineralization. This study presents a new, simple way to graft bioactive polymers onto Ti surfaces using a catechol intermediary with the aim of demonstrating the biocompatibility of these size controlled polyNaSS grafted surfaces.

Gadolinium-DTPA amphiphile nanoassemblies: agents for magnetic resonance imaging and neutron capture therapy.

Engineering biocompatible and physiologically stable nanoscaled therapeutics and imaging agents with the ability to target tumor tissue is a key challenge for the advancement of cancer therapeutics and diagnostic imaging. Here, we present chelating amphiphiles with the capacity to form nanoassembled colloidal particles containing high payloads of gadolinium (Gd) ions. We present the in situ synthesis and complexation of Gd with colloidal nanoassemblies (NAs) based on diethylenetriamine pentaacetic acid (DTPA) amphiphiles. This method allows for facile simultaneous incorporation of several metal ions for applications in multimodal imaging and therapeutics. The diverse internally nanostructured NAs made from sole precursor amphiphiles and their Gd-complexes were investigated by synchrotron small angle X-ray scattering (SAXS) and cryo-TEM. Depending on the molecular structure of the amphiphiles, the structures of NAs range from micelles to liposomes, to colloidal particles of inverse hexagonal (hexosomes) and inverse bicontinuous cubic phases (cubosomes), to multilayered nanospheres. The in vitro contrast activity of these NAs exhibited high relaxivity values as T1-weighted magnetic resonance imaging (MRI) contrast enhancement agents. Further, an α-Flag antibody fragment (Fab') was bioconjugated to the surface of the Gd-complexed NAs. The binding ability of these targeted NAs to a FLAG-tagged protein was confirmed by SDS-PAGE. The in vitro cytotoxicity against two cell lines showed that except for the negatively charged micellar Gd-DTPA amphiphile, liposomal and higher order internally nanostructured NAs had low cell toxicity. The efficient cellular uptake of Gd-NAs by melanoma cancer cells was also investigated.

Polymer coatings that display specific biological signals while preventing nonspecific interactions.

Control over cell-material surface interactions is the key to many new and improved biomedical devices. It can only be achieved if interactions that are mediated by nonspecifically adsorbed serum proteins are minimized and if cells instead respond to specific ligand molecules presented on the surface. Here, we present a simple yet effective surface modification method that allows for the covalent coupling and presentation of specific biological signals on coatings which have significantly reduced nonspecific biointerfacial interactions. To achieve this we synthesized bottle brush type copolymers consisting of poly(ethylene glycol) methyl ether methacrylate and (meth)acrylates providing activated NHS ester groups as well as different spacer lengths between the NHS groups and the polymer backbone. Copolymers containing different molar ratios of these monomers were grafted to amine functionalized polystyrene cell culture substrates, followed by the covalent immobilization of the cyclic peptides cRGDfK and cRADfK using residual NHS groups. Polymers were characterized by GPC and NMR and surface modification steps were analyzed using XPS. The cellular response was evaluated using HeLa cell attachment experiments. The results showed strong correlations between the effectiveness of the control over biointerfacial interactions and the polymer architecture. They also demonstrate that optimized fully synthetic copolymer coatings, which can be applied to a wide range of substrate materials, provide excellent control over biointerfacial interactions.

Evaluation of in situ curable biodegradable polyurethanes containing zwitterion components.

Porous polyurethane networks containing covalently attached zwitterionic compounds dihydroxypolycaprolactone phosphorylcholine and 1,2-dihydroxy-N,N-dimethylamino-propane sulfonate have been prepared and characterised. Three polymers were prepared by reacting methyl 2,6-diisocyanato hexanoate functionalised D: -glucose as prepolymer A with either polycaprolactone triol alone or with addition of 10 mol% zwitterion as prepolymer B. All polymer compositions were mixed with 10 wt% hydrated gelatin beads. The cured polymers with the gelatin beads showed compression strengths that were still suitable for use in articular cartilage repair. The incorporation of zwitterions yielded more hydrophilic polymers that showed increased water absorption and increased porosity. After four months degradation in phosphate buffered saline, the polymers containing zwitterions had approximately 50% mass loss compared with 30% mass loss for that with polycaprolactone triol alone. All polymers were non-toxic in chondrocyte-based assays. Subcutaneous implantation of these polymers into rats confirmed that the polymers degraded slowly. Only a very mild inflammatory response was observed and the polymers were able to support new, well vascularised tissue formation.

Effects of base material, plasma proteins and FGF2 on endothelial cell adhesion and growth.

Blood-contacting materials rapidly acquire a coating of plasma proteins which can lead to local platelet activation and thrombus formation. This phenomenon seriously limits the usefulness of small diameter synthetic vascular grafts. One solution to this problem is to pre-seed or encourage in situ colonisation of the material with endothelial cells to maintain a non-thrombogenic surface. We have investigated the effect of contact with plasma and serum on the subsequent ability of human endothelial cells to adhere to model hydrophobic and hydrophylic plastic surfaces, and the effect of surface bound fibroblast growth factor 2 (FGF2) on endothelial cell proliferation. Cell adhesion was mainly dependent on adsorbed fibrinogen or vitronectin, depending on the polymer surface, and correlated with antibody binding to these molecules rather than quantitative surface concentrations. Cell proliferation was directly correlated with surface bound FGF2. Surface binding of the latter was controlled both by the chemical nature of the polymer surface and by the presence of FGF-binding molecules adsorbed on the surface. FGF2 bound specifically to surface-adsorbed fibrinogen, fibronectin and vitronectin as well as to pre-coated heparan sulphate proteoglycan, perlecan. Binding was significantly inhibited by plasma and serum which contained high levels of FGF2 binding proteins. To be effective in supporting endothelialisation of vascular grafts in vivo, surface-bound FGF2 would need to be protected from surface dissociation into the circulating blood.

Rate of endothelial expansion is controlled by cell:cell adhesion.

Procedures used to alleviate blood vessel occlusion result in varying degrees of damage to the vascular wall and endothelial denudation. The presence of intact, functioning endothelium is thought to be important in controlling smooth muscle cell growth, and limiting the intimal thickening which results from damage to the vessel wall. Recovery of the endothelium is commonly slow and incomplete, due in part to endothelial lateral cell:cell adhesion, which limits cell migration and proliferation. We have investigated the effect of fibroblast growth factor 2 and vascular/endothelial growth factor on the relationship between the temporal distribution of the junctional adhesion proteins, platelet/endothelial cell adhesion molecule, vascular/endothelial cadherin and plakoglobin, and cellular migration and proliferation in an in vitro model of endothelial expansion. We found that whereas cell:cell junctions were initially disturbed to similar extents by single applications of the growth factors, outward cell migration and proliferation rates were inversely correlated with the speed at which cell:cell junctions were re-established. This occurred very rapidly with vascular/endothelial growth factor treatment and more slowly with fibroblast growth factor-2, resulting in more extensive outward migration and proliferation in response to the latter. Platelet/endothelial cell adhesion molecule and vascular/endothelial cadherin appeared to be associated with cell:cell junctional control of migration and proliferation, while plakoglobin did not contribute. It was concluded that the rate of endothelial expansion in response to growth factors, is limited by the rate of re-association of junctional complexes following initial disruption.