Alvaro Antonio Alencar de Queiroz

Hydrophilic hybrid IPNs of segmented polyurethanes and copolymers of vinylpyrrolidone for applications in medicine

The preparation and biocompatibility properties of thermoplastic apparent interpenetrating polymer networks (T-IPNs) of a segmented polyurethaneurea, Biospan (BS), and vinylpyrrolidone-dimethylacrylamide (VP-DMAm) copolymers, are described. The biological interaction between the obtained materials and blood was studied by in vitro methods. The addition of the VP-DMAm copolymers to form T-IPNs with BS substantially increased the equilibrium water uptake and water diffusion coefficients. Investigation of the proteins adsorption, platelet adhesion, thrombus formation and factor XII activation is presented. Investigations of the proteins adsorption of the BS/VP-DMAm T-IPNs surfaces show that the segmented polyurethane (BS) containing VP-DMAm copolymers with higher VP content adsorb more albumin than fibrinogen and gamma-globulin. The platelets adhesion, thrombus formation and factor XII activation are effectively suppressed with respect to the segmented polyurethane when VP-DMAm copolymers with high VP contents are incorporated into BS as T-IPNs.

Immobilization of a nonsteroidal antiinflammatory drug onto commercial segmented polyurethane surface to improve haemocompatibility properties.

A method has been developed in which a layer of p-aminosalicylic acid (4-amino-2-hydroxybenzoic acid) (PAS), a water soluble pharmaceutical compound of the nonsteroidal anti-inflammatory drug (NSAID) class with antiaggregant platelet activity, is covalently immobilized onto a segmented polyurethane, Biospan (SPU) surface. Thus, SPU surfaces were modified by grafting of hexamethylenediisocyanate. and the free isocyanate remaining on the SPU surface were then coupled through a condensation reaction to amine groups of p-aminosalicylic acid. The bonding of PAS from aqueous solution onto SPU surface was studied by ATR-FTIR. UV and fluorescence spectroscopy. Plateau levels of coupled PAS were reached within 1.2 microg/cm2 using PAS solution concentrations of 1mg/ ml. The surface wettability of the polymeric films measured by contact angle indicate that the introduction of the PAS turns the surface more hydrophilic (theta(water) = 43.1 +/- 2.1) relatively to the original SPU films (theta(water) = 70.3 +/- 1.9). The in vitro albumin (BSA) adsorption shows that the PAS-SPU films adsorb more BSA (250/microgmm2) than the original SPU (112 microg mm2). Thrombogenicity was assessed by measuring the thrombus formation and platelet adhesion of the SPU containing PAS relatively to nonmodified SPU surfaces. The polymeric surfaces with immobilized PAS had better nonthrombogenic characteristics as indicated by the low platelet adhesion, high adsorption of albumin relatively to fibrinogen and low thrombus formation, making them potentially good candidates for biomedical applications.

SURFACE STUDIES OF ALBUMIN IMMOBILIZED ONTO PE AND PVC FILMS

The aim of this study is to evaluate the thrombogenic behaviour of the low density polyethylene and poly(vinyl chloride) modified by radiation-grafting technique. After copolymerization with acrylic acid by gamma-rays from a 60Co source, BSA was immobilized onto functionalized graft copolymers. The biological interaction between these materials and blood was studies by in vitro methods. The BSA immobilization effectively suppressed the adhesion and activation of platelets when it contacted whole blood.

Resistive‐type humidity sensors based on PVP–Co and PVP–I2 complexes

Poly(vinylpyrrolidone) films containing cobalt chloride or iodine were investigated to obtain information on their possible use as a humidity sensor element. FTIR and UV-VIS spectroscopies were used to characterize the PVP-I 2 and PVP-Co complexes. Infrared spectroscopy revealed a structural change of both shape and intensity of the carbonyl and lactam bands, indicating the formation of an ion-coordination polymer. The J-E curves for pure PVP, PVP-I 2 , and PVP-Co films obey ohms law at low voltages, deviate from the linear response at higher voltages, and finally display breakdown behavior. An increase in current density of the PVP matrix with iodine or cobalt doping is attributed to the formation of charge transfer complexes. The observed hysteresis of the I-V characteristics implies that there was some standing voltage in the film, which could be attributed to a disorientation of polar side groups of PVP. The electrical conductivities of the polymeric complexes were very sensitive to environmental humidity. An explanation of the humidity-sensing behavior of the PVP-I 2 and PVP-Co complexes is presented.

Invertase immobilization onto radiation-induced graft copolymerized polyethylene pellets

Abstract The graft copolymer poly(ethylene-g-acrylic acid) (LDPE-g-AA) was prepared by radiation-induced graft copolymerization of acrylic acid onto low density polyethylene (LDPE) pellets, and characterized by infrared photoacoustic spectroscopy and scanning electron microscopy (SEM). The presence of the grafted poly(acrylic acid) (PAA) was established. Invertase was immobilized onto the graft polymer and the thermodynamic parameters of the soluble and immobilized enzyme were determined. The Michaelis constant, K m , and the maximum reaction velocity, V max , were determined for the free and the immobilized invertase. The Michaelis constant, K m was larger for the immobilized invertase than for the free enzyme, whereas V max was smaller for the immobilized invertase. The thermal stability of the immobilized invertase was higher than that of the free enzyme.

Electrospinning of Hyperbranched Poly-L-Lysine/Polyaniline Nanofibers for Application in Cardiac Tissue Engineering

Electrospun polyaniline nanofibers are one of the most promising materials for cardiac tissue engineering due to their tunable electroactive properties. Moreover, the biocompatibility of polyaniline nanofibes can be improved by grafting of adhesive peptides during the synthesis. In this paper, we describe the biocompatible properties and cardiomyocytes proliferation on polyaniline electrospun nanofibers modified by hyperbranched poly-L-lysine dendrimers (HPLys). The microstructure characterization of the HPLys/polyaniline nanofibers was carried out by scanning electron microscopy (SEM). It was observed that the application of electrical current stimulates the differentiation of cardiac cells cultured on the nanofiber scaffolds. Both electroactivity and biocompatibility of the HPLys based nanofibers suggest the use this material for culture of cardiac cells and opens the possibility of using this material as a biocompatible electroactive 3-D matrix in cardiac tissue engineering.

Physicochemical and antimicrobial properties of boron-complexed polyglycerol–chitosan dendrimers

A polyglycerol with dendritic structure (PGLD) was synthesized by ring-opening polymerization of deprotonated glycidol using a polyglycerol as core functionality in a step-growth process. Then, PGLD reacted with O-carboxymethylated chitosan to obtain PGLD-chitosan dendrimer (PGLD-Ch). After the reaction of PGLD-Ch with boric acid, there was a marked increase in the bulk viscosity evidencing physically that boron can initiate a charge transfer complex formation, (PGLD-Ch)B. Gel permeation chromatography analysis was used to characterize the molecular weight and the polydispersivity of the synthesized PGLD-Ch. A dendritic structure with a molecular mass of 16.7 kDa and a narrow polydispersity (M w/M n = 1.05) was obtained. 1H-NMR and 13C-NMR measurements were employed to assess the degree of branching in PGLD. The obtained value of 0.85 indicates the tendency toward a dentritic structure for PGLD. The glass transition temperature values of (PGLD-Ch)B membranes containing 10% and 30% PGLD were −19°C and −26°C, respectively, which favor its potential use as surface coating of several polymers. The in vitro cytotoxicity was evaluated using the minimum essential medium elution test assay. Extracts of boroncomplexed PGLD exhibited lower cytotoxicity than the controls, suggesting that the material has an improved biocompatibility. Antibacterial studies of (PGLD-Ch)B against Staphylococcus aureus and Pseudomonas aeruginosa showed a significant activity. Our study confirms and supports the effectiveness of (PGLD-Ch)B as an antimicrobial coating due to its capacity in suppressing the bacterial proliferation. The best in vivo response was found for (PGLD-Ch)B-30 membranes, which exhibited higher synthesis of collagen fibers than PGLD-ChB-10.

Adsorption of plasma proteins to DMAA hydrogels obtained by ionizing radiation and its relationship with blood compatibility

The interaction of plasma proteins such as albumin, gamma-globulin, and fibrinogen with the surface of graft copolymers DMAA-G-PTFE, DMAA-G-PETFE, and DMAA-G-PE obtained by radiation graft polymerization was studied. The adsorption of serum proteins was affected by the hydrophilicity of the graft copolymers. Increased albumin adsorption and decreased fibrinogen and gamma-globulin adsorption with increasing grafting levels was shown. A certain range of degrees of grafting showed an improved blood compatibility of the polymeric surfaces due to the existence of a hydrophilic/hydrophobic balance on the polymers. The results suggest that the DMAA-G-PTFE, DMAA-G-PETFE, and DMAA-G-PE graft copolymers can be used as biomaterials for long-term use in cardiovascular systems.

Hemocompatible properties of polymeric derivative of paracetamol

Copolymerization of N,N-dimethylacrylamide (DMAA) and p-acryloyloxiacetanilide (AOA) was carried out at different mole ratios of the monomers to obtain copolymers of varying compositions. DMAA contents were very near to the corresponding monomer feed and varied between 0.20 and 0.80. Investigation of the protein adsorption of these polymer surfaces showed that copolymers with higher DMAA content adsorbed more albumin than fibrinogen. The scanning electron micrographs of the polymer-coated coverslips after contact with blood showed an antithrombogenic behaviour of these surfaces.

Dendronized polyaniline nanotubes for cardiac tissue engineering.

Today, nanobiomaterials represent a very important class of biomaterials because they differ dramatically in their bulk precursors. The properties of these materials are determined by the size and morphology, thus creating a fascinating line in their physicochemical properties. Polyaniline nanotubes (PANINTs) are one of the most promising nanobiomaterials for cardiac tissue engineering applications due to their electroactive properties. The biocompatibility and low hydrophilic properties of PANINTs can be improved by their functionalization with the highly hydrophilic polyglycerol dendrimers (PGLDs). Hydrophilicity plays a fundamental role in tissue regeneration and fundamental forces that govern the process of cell adhesion and proliferation. In this work, the biocompatible properties and cardiomyocyte proliferation onto PANINTs modified by PGLD are described. PGLDs were immobilized onto PANINTs via surface-initiated anionic ring-opening polymerization of glycidol. The microstructure and morphology of PGLD-PANINTs was determined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. The cardiac cell growth on the PGLD-PANINTs was investigated. The PGLD-coated PANINTs showed noncytotoxic effects to Chinese hamster ovary cells. It was observed that the application of microcurrent stimulates the differentiation of cardiac cells cultured on PGLD-PANINTs scaffolds. The electroactive and biocompatible results of PGLD-PANINTs observed in this work demonstrate the potential of this nanobiomaterial for the culture of cardiac cells and open the possibility of using this material as a biocompatible electroactive three-dimensional matrix in cardiac tissue engineering.