Wander L. Vasconcelos

Synthesis and characterization of poly (vinyl alcohol) hydrogels and hybrids for rMPB70 protein adsorption

Polyvinyl alcohol (PVA), PVA crosslinked with glutaraldehyde hydrogels (PVA/GA), PVA with tetraethylorthosilicate (PVA/TEOS) and PVA/GA/TEOS hybrids with recombinant MPB70 protein (rMPB70) incorporated were chemically characterized by Fourier transform infrared spectroscopy (FTIR). FTIR spectra of PVA hydrogel samples showed the absorption regions of the specific chemical groups associated with poly(vinyl alcohol) (-OH, -CO, -CH2) and PVA/GA confirming the formation of crosslinked hydrogel (duplet -CH). It was observed C-H broad alkyl stretching band (n = 2850-3000 cm-1) and typical strong hydroxyl bands for free alcohol (nonbonded -OH stretching band at n = 3600-3650 cm-1), and hydrogen bonded band (n = 3200-3570 cm-1). The most important vibration bands related to silane alcoxides have been verified on FTIR spectra of PVA/TEOS and PVA/GA/TEOS hybrids (Si-O-Si, n = 1080 and n = 450 cm-1; Si-OH, n = 950 cm-1). FTIR spectra of f PVA hydrogel with rMPB70 incorporated have indicated the specific groups usually found in protein structures, such as amides I, II and III, at 1680-1620 cm-1, 1580-1480 cm-1 and 1246 cm-1, respectively. These results have given strong evidence that recombinant protein rMPB70 was successfully adsorbed in the hydrogels and hybrids networks. These PVA based hydrogels and hybrids were further used in immunological assays (Enzyme-Linked Immunosorbent Assay - ELISA). Tests were performed to detect antibodies against rMPB70 protein in serum samples from bovines that were positive in the tuberculin test. Corresponding tests were carried out without PVA samples in microtiter plates as control. Similar results were found for commercially available microplates and PVA based hydrogels and hybrids developed in the present work regarding to immunoassay sensitivity and specificity response.

Corrosion resistance of stainless steel coated with sol-gel silica

Abstract Sol–gel silica films were deposited on AISI 304 stainless steel using tetraethyl ortosilicate (TEOS) as chemical precursor. The coated steels were heat-treated from room temperature to 600°C. The structural evaluation of the coated steel samples was made by scanning electron microscopy, infrared absorption spectroscopy, and chemical deep profiles of Si, O, and Fe obtained by Rutherford backscattering spectroscopy. Corrosion experiments were carried out on samples with and without coatings, in 1 N H2SO4 and 3.5% NaCl solutions to measure corrosion potential, current density and pitting potential. The obtained sol–gel silica coatings were homogeneous, free of cracks and had thickness from 50 to 120 nm. Polarization curves of the coated samples indicated improvement of the corrosion resistance. For tests carried out in a 1 N H2SO4 solution, the corrosion potential increased from −341 mV (stainless steel) to +383 mV for coated sample heat-treated at 80°C, and up to +508 mV for coated sample heat-treated at 200°C. The corrosion current density decreased from 3.65 μA / cm 2 to 0.027 μA / cm 2 and 0.021 μA / cm 2 , for the 80°C and 200°C heat-treated silica coatings, respectively. For the corrosion experiment carried out in a 3.5% NaCl solution, the coated sample (heat-treated at 80°C) increased the corrosion potential c.a. 230 mV and increased by one order of magnitude the pitting potential.

Preparation of silica by sol-gel method using formamide

In this work we obtained microporous and mesoporous silica gels by sol-gel processing. Tetraethylortosilicate (TEOS) was used as precursor. Nitric acid and hydrofluoric acid were used as catalysts. In order to study the affect of formamide as drying additive, we used a molar ratio alkoxide/formamide of 1/1. The performance of formamide in obtaining crack-free gels was evaluated through monolithicity measurements. The structural evolution occurring in the interconnected network of the gels during thermal treatment was monitored by Fourier transform infrared spectroscopy (FTIR), shrinkage and density measurements and nitrogen gas sorption. We noted that in the presence of formamide, the Si-O-Si bonds are stronger and belong to a more cross-linked structure. The samples obtained in the presence of formamide have larger pore volume and its pore structure is in the range of mesoporosity. The samples obtained without additive are microporous. Formamide allowed the preparation of crack-free silica gels stabilized at high temperatures.

Sol-Gel Transition and Structural Evolution on Multicomponent Gels Derived from the Alumina-Silica System

The capacity of the sol-gel process of producing highly pure, homogeneous alumina-silica based materials had been demonstrated in the last few years. However, a full understanding on the mechanisms associated to sol formation and sol to gel transition has not yet been achieved and is required for the development of a new generation of nano-structurally tailored materials that will significantly enhance the technological importance of the sol-gel process. In this work, tetraethyl orthosilicate (TEOS) and aluminum isopropoxide were used to prepare materials within the entire silica-alumina system. Process parameters, such as gelation time, were correlated to variables of the initial stage of the process, such as pH, temperature of hydrolysis and water/alkoxide ratio. The obtained gels were dried at 105°C and subsequently heat treated at 500 and 1100°C for 3 hours. X-ray diffraction and infrared spectroscopy were used to characterize the materials and phase transformations. Structural information obtained from phase characterization and phase transformations was correlated to the effects of the process variables on sol formation and gelation, providing insights related to the mechanisms involved. The influence of temperature of aluminum isopropoxide hydrolysis on peptization and gelation of the mixtures was noted. The different behavior of mixtures hydrolyzed at low and high temperatures was suggested to be caused by different mechanisms of surface charge formation on the structurally different aluminum hydroxides. Monophasic and diphasic mullite xerogels were produced by changing temperature of aluminum isopropoxide hydrolysis, and led to formation of mullite and Al−Si spinel phases respectively, when treated at 1100°C.

Sol-gel silica based networks with controlled chemical properties

Abstract In this work, different chemical functionalities, both organic and inorganic, were inserted in a silica glass based sol–gel derived network to create specific chemical activities. Modified silica glass networks were prepared by reacting alkoxysilanes with different chemical functionalities, such as tetraethoxysilane (TEOS), aminopropyl triethoxysilane (APS) and mercaptopropyl triethoxysilane (MPTS), among others. The obtained gels were evaluated by using infrared spectroscopy, mercury picnometry and electron microscopy. The chemical activity of the created multifunctional surfaces was evaluated by the ability of the incorporated proteins to remain adsorbed onto the different gels. Porcine insulin (PI) and bovine serum albumin (BSA) were impregnated into modified networks and desorption of those proteins was monitored. Results showed that gels with multifunctionalities regularly dispersed can be successfully produced by optimizing some of the processing parameters of the gels, such as pH and concentration of reactants. Results also revealed that the type and concentration of chemical functionalities within the gels regulate the ability of incorporated proteins to remain adsorbed on them, suggesting that chemically patterned surfaces and interfaces can be prepared which regulate protein–substrate interactions.

Structural Evolution of Silica Sols Modified with Formamide

In this work we investigated the influence of formamide on the acid-catalyzed sol-gel process by Fourier transform infrared spectroscopy (FTIR). Three silica sols were studied: Sol catalyzed with nitric acid without formamide, sol catalyzed with nitric acid containing formamide and sol catalyzed with a mixture of nitric acid and hydrofluoric acid and modified with formamide. Following the time evolution of both the Si-(OH) stretching vibration at around 950 cm-1 and the Si-O-(Si) vibration between 1040 cm-1 and 1200 cm-1 we were able to describe the structural evolution of each sol. The curve of evolution of Si-(OH) stretching vibration corresponding to sol A has a simple asymptotic evolution. In the case of formamide containing sol, we observed a two-step structural evolution indicating that for the system containing formamide the polymerization goes through a temporary stabilization of oligomers, which can explain the non-variation of the Si-O(H) bond wavenumber for a certain time. Gelation times were of several days for gels without formamide and few hours for gels containing additive. The presence of additive resulted in a highly interconnected gel.

Novel multicomponent silicate–poly(vinyl alcohol) hybrids with controlled reactivity

Abstract By a combination of inorganic and organic species at a molecular level, a new series of biomaterials having optimal controllable properties can be fabricated. The goal of this work is to determine how the reactivity of the composites (inorganic–organic hybrids) can be controlled by altering the nanostructure of the materials. Hybrids were synthesized by reacting poly(vinyl alcohol) (PVA) in acidic solution with either tetraethoxy silane (TEOS) or tetramethoxy silane (TMOS). The inorganic phase was also modified by incorporating calcium and phosphate compounds. The properties of the hybrids were determined by swelling experiments, infrared spectroscopy, and scanning electron microscopy/microprobe analysis. Transparent PVA–silicate hybrid free-standing films, having a range of compositions within the system, were produced by allowing the rate of hydrolysis of the alkoxide to be compatible with the kinetics of the dissolution processes of both the polymer and calcium-phosphate compounds. Results obtained from swelling experiments and infrared spectroscopy showed that the crosslink density can be increased when hybrids are prepared with larger concentrations of the inorganic component. Moreover, hybrids prepared at temperatures as high as 60°C have, among other properties, greater crosslink densities and inorganic phases with larger amounts of S–O–Si bridging bonds. Swelling experiments also showed that the obtained hybrids varied in their reactivities ranging from fast dissolution to hydrogel properties. We also demonstrate that the degree of reactivity can be controlled by manipulating structural factors of the hybrids such as the crosslink density, proportion of the phases and composition of the inorganic phase, among others.

FTIR and UV‒vis study of chemically engineered biomaterial surfaces for protein immobilization

The biomaterials research field has broadened in the last 3 decades, including replacement of diseased or damaged parts, assist in healing, correct and improve functional abnormality, drug delivery systems, immunological kits and biosensors. Proteins play crucial role in almost every biological system. They are involved in enzymatic catalysis, transport and storage, coordinated motion, mechanical support, immune protection, control of growth and cell differentiation among many others. The immobilization of proteins onto surface functionalized substrates has been one of the most promising areas in bioengineering field. It is important to note that the term immobilization can refer either to a temporary or to a permanent localization of the biomolecule on or within a support. Proteins have very particular chain configurations and conformations that promote high levels of specificity during chemical interactions. In the present work, we aimed to study the phenomenon of protein immobilization onto biomaterial with chemically engineered surface. We have tailored the surface of the porous gels of SiO2 with 5 different silane surface modifying agents: tetraethoxysilane (TEOS), 3‒mercaptopropyltrimethoxysilane (MPTMS) and 3‒aminopropyltriethoxysilane (APTES), 3‒glycidoxypropyltrimethoxysilane (GPTMS) and 3‒isocyanatopropyltriethoxysilane (ICPES). Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the presence of all specific chemical groups in the materials. The surface functionalized gels were then immersed in porcine insulin (PI) solutions for protein immobilization. The incorporation of protein within the gels was also monitored by FTIR spectroscopy. The kinetics of protein adsorption and desorption from the gel matrix in vitro tests were monitored by UV‒visible spectroscopy. We could not observe any evidence of denaturation of insulin after its desorption from gel matrices using UV‒visible spectroscopy technique. In vivo tests with adult male rats were used to verify the immobilized insulin bioactivity after implantation of different biomaterial with functionalized surfaces. Plasma glucose levels were obtained by using the Glucose GOD‒ANA Colorimetric Assay. All surface modified materials have presented acute hypoglycemic peak response associated with the insulin bioactivity.

Surface-modified 3D scaffolds for tissue engineering

The aim of this work was to use sol–gel processing to develop bioactive materials to serve as scaffolds for tissue engineering that will allow the incorporation and release of proteins to stimulate cell function and tissue growth. We obtained organofunctionalized silica with large content of amine and mercaptan groups (up to 25%). The developed method can allow the incorporation and delivery of proteins at a controlled rate. We also produced bioactive foams with binary SiO2–CaO and ternary SiO2–CaO–P2O5 compositions. In order to enhance peptide–material surface properties, the bioactive foams were modified with amine and mercaptan groups. These materials exhibit a highly interconnected macroporous network and high surface area. These textural features together with the incorporation of organic functionally groups may enable them to be used as scaffolds for the engineering of soft tissue.

Preparation of hybrid biomaterials for bone tissue engineering

Tissue engineering has evolved from the use of biomaterials for bone substitution that fulfill the clinical demands of biocompatibility, biodegradability, non-immunogeneity, structural strength and porosity. Porous scaffolds have been developed in many forms and materials, but few reached the need of adequate physical, biological and mechanical properties. In the present paper we report the preparation of hybrid porous polyvinyl alcohol (PVA)/bioactive glass through the sol-gel route, using partially and fully hydrolyzed polyvinyl alcohol, and perform structural characterization. Hybrids containing PVA and bioactive glass with composition 58SiO2-33CaO-9P2O5 were synthesized by foaming a mixture of polymer solution and bioactive glass sol-gel precursor solution. Sol-gel solution was prepared from mixing tetraethoxysilane (TEOS), triethylphosphate (TEP), and calcium chloride as chemical precursors. The hybrid composites obtained after aging and drying at low temperature were chemically and morphologically characterized through infrared spectroscopy and scanning electron microscopy. The degree of hydrolysis of PVA, concentration of PVA solution and different PVA-bioglass composition ratios affect the synthesis procedure. Synthesis parameters must be very well combined in order to allow foaming and gelation. The hybrid scaffolds obtained exhibited macroporous structure with pore size varying from 50 to 600 µm.