Alexandra A.P. Mansur

Chitosan and carboxymethyl-chitosan capping ligands: Effects on the nucleation and growth of hydroxyapatite nanoparticles for producing biocomposite membranes.

Synthetic biomaterials based on calcium phosphates (CaP) have been widely studied for bone tissue reconstruction therapies, but no definitive solution that fulfills all of the required properties has been identified. Thus, this study reports the synthesis of composite membranes based on nanohydroxyapatite particles (nHA) embedded in chitosan (CHI) and O-carboxymethyl chitosan (CMC) matrices produced using a one-step co-precipitation method in water media. Biopolymers were used as capping ligands for simultaneously controlling the nucleation and growth of the nHA particles during the precipitation process and also to form the polymeric network of the biocomposites. The bionanocomposites were extensively characterized using light microscopy (LM), scanning and transmission electron microscopy (SEM/TEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray micro-CT analysis (μCT), andMTT (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazoliumbromide) cell proliferation assays for cell cytotoxicity. The results demonstrated that the ligands used during the synthesis highly affected the composites produced, primarily due the changes in the mechanisms and kinetics of nucleation and growth of the HA particles at the nanoscale level. The SEMimages revealed that the use of carboxyl-functionalized chitosan (CMC) ligands significantly reduced the average size of theHA nanoparticles and caused the formation of a narrower size distribution (90±20nm) compared to theHAnanoparticles producedwith chitosan ligands (220±50nm). The same trend was verified by the AFM analysis,where the nHA particles were formed evenly dispersed in the polymer matrix. However, the CMC-based composites were more homogeneously distributed, which was endorsed by the images collected via X-ray micro-CT. The FTIR spectra and the XRD analysis indicated that nanosized hydroxyapatite was the predominant calcium phosphate phase produced during the co-precipitation aqueous process for both the chitosan and CMC biocomposites. These novel hybrid systems based on chitosan and chitosan-derivatives with nHA composites were non-cytotoxic to a human osteoblast-like model cell line (SAOS) according to MTT in vitro assays. Moreover, the CMC-nHA biocomposites revealed a striking improvement in the cell viability response compared to the CHI-nHA biocomposite, which was attributed to the much higher surface area caused by the refinement of the nanoparticles size. Thus, the results of this study demonstrate that these novel bionanocomposite membranes offer promising perspectives as biomaterials for potential repair and replacement of cartilage and bone tissues.

Enzyme-polymers conjugated to quantum-dots for sensing applications.

In the present research, the concept of developing a novel system based on polymer-enzyme macromolecules was tested by coupling carboxylic acid functionalized poly(vinyl alcohol) (PVA-COOH) to glucose oxidase (GOx) followed by the bioconjugation with CdS quantum-dots (QD). The resulting organic-inorganic nanohybrids were characterized by UV-visible spectroscopy, infrared spectroscopy, Photoluminescence spectroscopy (PL) and transmission electron microscopy (TEM). The spectroscopy results have clearly shown that the polymer-enzyme macromolecules (PVA-COOH/GOx) were synthesized by the proposed zero-length linker route. Moreover, they have performed as successful capping agents for the nucleation and constrained growth of CdS quantum-dots via aqueous colloidal chemistry. The TEM images associated with the optical absorption results have indicated the formation of CdS nanocrystals with estimated diameters of about 3.0 nm. The “blue-shift” in the visible absorption spectra and the PL values have provided strong evidence that the fluorescent CdS nanoparticles were produced in the quantum-size confinement regime. Finally, the hybrid system was biochemically assayed by injecting the glucose substrate and detecting the formation of peroxide with the enzyme horseradish peroxidase (HRP). Thus, the polymer-enzyme-QD hybrid has behaved as a nanostructured sensor for glucose detecting.

Chemical functionalization of ceramic tile surfaces by silane coupling agents: polymer modified mortar adhesion mechanism implications

Adhesion between tiles and mortars are crucial to the stability of ceramic tile systems. From the chemical point of view, weak forces such as van der Waals forces and hydrophilic interactions are expected to be developed preferably at the tiles and polymer modified Portland cement mortar interface. The main goal of this paper was to use organosilanes as primers to modify ceramic tile hydrophilic properties to improve adhesion between ceramic tiles and polymer modified mortars. Glass tile surfaces were treated with several silane derivatives bearing specific functionalities. Contact angle measurements and Fourier Transform Infrared Spectroscopy (FTIR) were used for evaluating the chemical changes on the tile surface. In addition, pull-off tests were conducted to assess the effect on adhesion properties between tile and poly(ethylene-co-vinyl acetate), EVA, modified mortar. The bond strength results have clearly shown the improvement of adherence at the tile-polymer modified mortar interface, reflecting the overall balance of silane, cement and polymer interactions.

Fluorescent nanohybrids: quantum dots coupled to polymer recombinant protein conjugates for the recognition of biological hazards

The present research introduces the concept of developing a novel nanohybrid system based on fluorescent quantum dots coupled to polymer–protein bioconjugates for the detection of potential biological hazards. The organic–inorganic hybrids were constructed by the chemical conjugation of carboxylic functionalized poly(vinyl alcohol) with the designed synthetic recombinant protein specific to bovine herpesvirus (rHBoV5), followed by coupling to II–VI semiconductor quantum dots (QDs). These nanostructures were characterized by UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). The results clearly showed that the polymer–protein bioconjugates (PVA–COOH/rHBoV5) were synthesized via the proposed zero-length linker route. Moreover, these bioconjugates proved to be successful capping agents for producing CdS and CdSe quantum dots using aqueous colloidal chemistry. The TEM images associated with the optical absorption results indicated the formation of nanocrystals with estimated diameters in the range of 4.0–5.0 nm. The “blue-shift”, in the visible absorption spectra, and the PL values present strong evidence that the CdS and CdSe QDs behaved as fluorophores in the quantum-size confinement regime. Finally, the hybrid system was validated by immunochemical assay of bovine herpesvirus utilized as the model for detecting biological hazards. This research opens a window of opportunity of using a new class of hybrid nanomaterials for the rapid detection of potentially threatening biological species.

One-step biofunctionalization of quantum dots with chitosan and N-palmitoyl chitosan for potential biomedical applications.

Carbohydrates and derivatives (such as glycolipids, glycoproteins) are of critical importance for cell structure, metabolism and functions. The effects of carbohydrate and lipid metabolic imbalances most often cause health disorders and diseases. In this study, new carbohydrate-based nanobioconjugates were designed and synthesized at room temperature using a single-step aqueous route combining chitosan and acyl-modified chitosan with fluorescent inorganic nanoparticles. N-palmitoyl chitosan (C-Pal) was prepared aiming at altering the lipophilic behavior of chitosan (CHI), but also retaining its reasonable water solubility for potential biomedical applications. CHI and C-Pal were used for producing biofunctionalized CdS quantum dots (QDs) as colloidal water dispersions. Fourier transform infrared spectroscopy (FTIR), thermal analysis (TG/DSC), surface contact angle (SCA), and degree of swelling (DS) in phosphate buffer were used to characterize the carbohydrates. Additionally, UV-Visible spectroscopy (UV-Vis), photoluminescence spectroscopy (PL), dynamic light scattering (DLS), scanning and transmission electron microscopy (SEM/TEM) were used to evaluate the precursors and nanobioconjugates produced. The FTIR spectra associated with the thermal analysis results have undoubtedly indicated the presence of N-palmitoyl groups “grafted” to the chitosan chain (C-Pal) which significantly altered its behavior towards water swelling and surface contact angle as compared to the unmodified chitosan. Furthermore, the results have evidenced that both CHI and C-Pal performed as capping ligands on nucleating and stabilizing colloidal CdS QDs with estimated average size below 3.5 nm and fluorescent activity in the visible range of the spectra. Therefore, an innovative “one-step” process was developed via room temperature aqueous colloidal chemistry for producing biofunctionalized quantum dots using water soluble carbohydrates tailored with amphiphilic behavior offering potential applications as fluorescent biomarkers in the investigation of glycoconjugates for the nutrition, biology, pharmaceutical, and medicine fields.

Beyond biocompatibility: an approach for the synthesis of ZnS quantum dot-chitosan nano-immunoconjugates for cancer diagnosis

In this study, we designed and developed novel biocompatible ZnS quantum dot (QD) nano-immunoconjugates to detect cancer cells strictly via an environmentally-friendly chemistry process. ZnS QDs were capped by chitosan-based ligands that were chemically conjugated at room temperature with an antibody-specific cancer biomarker for non-Hodgkin lymphoma using a one-pot aqueous colloidal route. The nano-immunoconjugates were extensively characterised by several spectroscopic and morphological approaches and biological assays. The results demonstrated that ultra-small colloidal ZnS nanocrystals with an average diameter of 3.7 nm were produced and stabilised by the chitosan-antibody conjugates. In addition, they exhibited intense fluorescence activity and were effective for specific targeting, labelling, and bioimaging of cancerous lymphocyte B-cells. Moreover, the results of in vitro cell viability assays using fibroblast cell line indicated that the ZnS-nanoconjugates were cytocompatible. These may be used in numerous applications in oncology diagnosis and nanomedicine.

Nanocomposites of Poly(Vinyl Alcohol)/Functionalized-Multiwall Carbon Nanotubes Conjugated With Glucose Oxidase for Potential Application as Scaffolds in Skin Wound Healing

A novel nanocomposite scaffold based on poly(vinyl alcohol) (PVA) and multiwalled carbon nanotubes (MWNT) were synthesized and characterized regarding to morphological, physical, and mechanical properties and also the preliminary biocompatibility was assessed by MTT assay. Additionally, the concept of developing hybrid systems was tested by bioconjugating functionalized MWNT to glucose oxidase and dispersed in the PVA matrix. The nanocomposites have presented mechanical properties, degree of swelling, and cytocompatibility comparable to the skin tissues. Moreover, the bionanocomposite with enzyme showed bioactivity toward injecting glucose with simultaneous antimicrobial behavior against bacterial pathogens due to the generation hydrogen peroxide.

Engineered hybrid scaffolds of poly(vinyl alcohol)/bioactive glass for potential bone engineering applications: synthesis, characterization, cytocompatibility, and degradation

The synthesis, characterization, preliminary cytocompatibility, and degradation behavior of the hybrids based on 70% Poly(vinyl alcohol) and 30% bioactive glass (58SiO2-33CaO-9P2O5, BaG) with macroporous tridimensional structure is reported for the first time. The effect of glutaraldehyde covalent crosslinker in the organic-inorganic nanostructures produced and, as a consequence, tailoring the hybrids properties was investigated. The PVA/BaG hybrids scaffolds are characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray Microcomputed tomography analysis (µCT). Cytotoxicity assessment is performed by the MTT method with VERO cell culture. Additionally, the hybrid in vitro degradation assay is conducted by measuring the mass loss by soaking in deionized water at 37°C for up to 21 days. The results have clearly shown that it is possible to modify the PVA/BaG hybrids properties and degradation behavior by engineering the structure using different concentrations of the chemical crosslinker. Moreover, these hybrid crosslinked nanostructures have presented 3D hierarchical pore size architecture varying within 10-450 µm and a suitable cytocompatibility for potential use in bone tissue engineering applications.

Characterization and Accelerated Ageing of UHMWPE Used in Orthopedic Prosthesis by Peroxide

Ultra-high molecular weight polyethylene (UHMWPE) has been the most commonly used bearing material in total joint arthroplasty. Wear and oxidation fatigue resistance of UHMWPE are regarded as two important mechanical properties to extend the longevity of knee prostheses. Though accelerated in vitro protocols have been developed to test the relative oxidation resistance of various types of UHMWPE, its mechanism is not accurately understood yet. Thus, in the present study an accelerated ageing of UHMWPE in hydrogen peroxide solution was performed and relative oxidation was extensively characterized by Fourier Transformed Infrared Spectroscopy (FTIR) spectroscopy and the morphological changes were analyzed by Scanning Electron Microscopy (SEM). Different chemical groups of UHMWPE associated with the degradation reaction were monitored for over 120 days in order to evaluate the possible oxidation mechanism(s) which may have occurred. The results have provided strong evidence that the oxidation mechanism is rather complex, and two stages with their own particular first-order kinetics reaction patterns have been clearly identified. Furthermore, hydrogen peroxide has proven to be an efficient oxidative medium to accelerate ageing of UHMWPE.

Niobium-Doped Hydroxyapatite Bioceramics: Synthesis, Characterization and In Vitro Cytocompatibility

Doping calcium phosphates with ionic species can play an important role in biological responses promoting alkaline phosphatase activity, and, therefore inducing the generation of new bone. Thus, in this study, the synthesis of niobium-doped hydroxyapatite (Nb-HA) nanosize particles obtained by the precipitation process in aqueous media followed by thermal treatment is presented. The bioceramics were extensively characterized by X-ray diffraction, wavelength dispersive X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy analysis, transmission electron microscopy, atomic force microscopy and thermal analysis regarding their chemical composition, structure and morphology. The results showed that the precipitate dried at 110 °C was composed of amorphous calcium phosphate and HA, with polidisperse particles ranging from micro to nano dimensions. After the thermal treatment at 900 °C, the bioceramic system evolved predominantly to HA crystalline phase, with evident features of particle sintering and reduction of surface area. Moreover, the addition of 10 mol% of niobium salt precursor during the synthesis indicated the complete incorporation of the Nb(V) species in the HA crystals with detectable changes in the original lattice parameters. Furthermore, the incorporation of Nb ions caused a significant refinement on the average particle size of HA. Finally, the preliminary cytocompatibility response of the biomaterials was accessed by human osteoblast cell culture using MTT and resazurin assays, which demonstrated no cytotoxicity of the Nb-alloyed hydroxyapatite. Thus, these findings seem promising for developing innovative Nb-doped calcium phosphates as artificial biomaterials for potential use in bone replacements and repair.