Poly(ethylene oxide)-modified carboxylated polystyrene latices--immobilization chemistry and protein adsorption

Plasma functionalization of polycarbonaturethane to improve endothelialization—Effect of shear stress as a critical factor for biocompatibility control

Medical devices made of polycarbonaturethane (PCU) combine excellent mechanical properties and little biological degradation, but restricted hemocompatibility. Modifications of PCU might reduce platelet adhesion and promote stable endothelialization. PCU was modified using gas plasma treatment, binding of hydrogels, and coupling of cell-active molecules (modified heparin, anti-thrombin III (ATIII), argatroban, fibronectin, laminin-nonapeptide, peptides with integrin-binding arginine-glycine-aspartic acid (RGD) motif). Biocompatibility was verified with static and dynamic cell culture techniques. Blinded analysis focused on improvement in endothelial cell (EC) adhesion/proliferation, anti-thrombogenicity, reproducible manufacturing process, and shear stress tolerance of ECs. EC adhesion and antithrombogenicity were achieved with 9/35 modifications. Additionally, 6/9 stimulated EC proliferation and 3/6 modification processes were highly reproducible for endothelialization. The latter modifications comprised immobilization of ATIII (A), polyethyleneglycole-diamine-hydrogel (E) and polyethylenimine-hydrogel connected with modified heparin (IH). Under sheer stress, only the IH modification improved EC adhesion within the graft. However, ECs did not arrange in flow direction and cell anchorage was restricted. Despite large variation in surface modification chemistry and improved EC adhesion under static culture conditions, additional introduction of shear stress foiled promising preliminary data. Therefore, biocompatibility testing required not only static tests but also usage of physiological conditions such as shear stress in the case of vascular grafts.

High contrast upconversion luminescence targeted imaging in vivo using peptide-labeled nanophosphors

Fluorescence targeted imaging in vivo has proven useful in tumor recognition and drug delivery. In the process of in vivo imaging, however, a high autofluorescence background could mask the signals from the fluorescent probes. Herein, a high contrast upconversion luminescence (UCL) imaging protocol was developed for targeted imaging of tumors based on RGD-labeled upconversion nanophosphors (UCNPs) as luminescent labels. Confocal Z-scan imaging of tissue slices revealed that UCL imaging showed no autofluorescence signal even at high penetration depth (approximately 600 microm). More importantly, region of interest (ROI) analysis of the UCL signal in vivo showed that UCL imaging achieved a high signal-to-noise ratio (approximately 24) between the tumor and the background. These results demonstrate that the UCL imaging technique appears particularly suited for applications in tracking and labeling components of complex biological systems.

Polyethylene glycol-grafted polystyrene particles

Densely pegylated particles that can serve as a model system for artificial cells were prepared by covalently grafting amino polyethylene glycol (PEG, molecular weight 3400 or 5000) onto carboxyl polystyrene particles (PS-COOH) using carbodiimide chemistry. PEG-modified particles (PS-PEG) were characterized by determination of the PEG surface concentration, zeta-potential, size, and morphology. Under optimized grafting conditions, a dense "brush-like" PEG layer was formed. A PEG surface concentration of approximately 60 pmol/cm2, corresponding with an average distance between grafted PEG chains of approximately 17 A can be realized. It was shown that grafting of PEG onto PS-COOH reduced the adsorption of proteins from human plasma (85 vol %) in phosphate-buffered saline up to 90%.

Minimization of protein adsorption on poly(vinylidene fluoride)

Surfaces covered with polyethylene glycol (PEG) have been shown to be biocompatible because PEG yields nonimmunogenicity, nonantigenicity and protein rejection. To produce a biocompatible surface coating, we have developed a method for grafting PEG onto modified poly(vinylidene fluoride) (PVDF) films. The first step was to create carboxy groups on the PVDF surface following covalente coupling of polyethylenimine (PEI) to achieve high density of amino groups. These surface amines were reacted with formyl-terminated PEG's with various molecular weight. The modified PVDF surface was characterized by means of static contact angle measurements, infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The influence of the chain length on lysozyme repellence was investigated by means of surface-MALDI-Tof mass spectrometry (Surface-MALDI-Tof-MS). Lysozyme adsorption was significantly suppressed on the PEG 5000 modified PVDF surface.

Molecular mechanisms of improved adhesion and growth of an endothelial cell line cultured on polystyrene implanted with fluorine ions

Endothelial cells derived from the bovine pulmonary artery (line CPAE, CCL 209, American Tissue Culture Collection, Rockville, MD, USA) were cultured on pristine or fluorine ion-irradiated polystyrene (5 x 10(12) or 5 x 10(14) F ions/cm2, 150 keV). At 24-h post-seeding interval, the number of cells which adhered to the ion-modified polystyrene was significantly higher than on the unmodified material (+20 and +58% in cultures with the polystyrene irradiated by lower and higher ion doses, respectively). On day 7, the populations cultured on the irradiated substrates grew to higher densities, exceeding the controls at the lower and higher ion doses by 69 and 180%, respectively. The cells on ion-implanted samples were also larger (+70-95% and +90-99% at the lower and higher ion doses, respectively) and contained more protein (+16% at both ion doses). As was shown by ELISA, the polystyrene irradiated by the higher ion dose enhanced the expression of a cytoskeletal protein, vimentin (+65%) and protein of focal adhesion plaques, talin (+15%). The content of integrin alpha5beta1 (VLA-5), receptor for fibronectin, was increased at both lower and higher ion doses (+22 and +57%). In contrast to this, the content of ICAM-1 and vinculin was similar in cells grown on both pristine and ion-irradiated growth substrates. Moreover, the expression of VCAM-1 and ELAM-1 was lower by 11-14% in both ion dose groups. The present study has shown that ion implantation of polymers improves the adhesion and growth of endothelial cells without elevating the expression of immunoglobulin and selectin types of adhesion molecules. This surface modification should promote colonization of an artificial vascular prosthesis by endothelial cells and make it less vulnerable by immune system cells of the recipient.

Quantitative determination of the peptide retention of polymeric substrates using matrix-assisted laser desorption/ionization mass spectrometry

Polymer surface-peptide binding interactions have been shown previously to lead to reductions in peptide matrix assisted laser desorption/ionization (MALDI) ion signals. In previous studies, increases in surface-peptide binding were characterized by the increases in both the initially adsorbed and retained quantities of 125I-radiolabeled peptides. The present studies establish a specific correlation between the peptide retention properties of the polymer surface and the reduction in the peptide MALDI ion signal. This correlation is demonstrated by obtaining MALDI mass spectra of angiotensin I applied to various polymer surfaces having a range of peptide adsorption and retention properties. In addition, the use of a MALDI based method of standard additions is shown to allow the quantitation of the polymer surface-peptide retention affinity for angiotensin I and porcine insulin. The MALDI standard additions method for measurement of surface-peptide retention affinities offers a number of significant advantages over conventional radiolabeled peptide binding methods and promises to be a valuable tool for the determination of this important biomaterial characteristic.

Migration resistant, blood-compatible plasticized polyvinyl chloride for medical and related applications

Plasticized polyvinyl chloride (PVC), although not a blood-compatible polymer, is the material of choice for the manufacture of blood bags and hemodialysis tubing throughout the world. PVC is usually plasticized with di-(2-ethylhexyl phthalate) (DEHP) to impart flexibility and low temperature properties to the final product. DEHP belongs to a class of agents called hypolipidemic hepatocarcinogens, and it migrates in small quantities into the storage medium such as blood, plasma, or serum, resulting in a number of toxic effects. It has been shown that the migration resistance and blood compatibility of flexible PVC could be significantly improved by grafting polyethylene glycol (PEG), the most blood-compatible polymer known today, onto the surface of flexible PVC by the classical Williamson ether synthesis reaction. The technique is simple and versatile enough to produce blood-compatible, migration resistant PVC surfaces for many medical applications. The method may also find use for preventing plasticizer migration from PVC cling films and polyvinylidene chloride films used extensively in food packaging.