Biomimetic nanocomposite based on hydroxyapatite mineralization over chemically modified cellulose nanowhiskers: An active platform for osteoblast proliferation.

Functionalized-cellulose nanowhiskers (CNWs) were obtained and used to improve hydroxyapatite (HAp) growth by the biomimetic method. CNWs were obtained through HCl hydrolysis and then submitted to chemical functionalization with carboxylate or amine groups that can induce selective HAp mineralization efficiently. Functionalized-CNWs were tested against HAp growth through the biomimetic method using a simulated body fluid (SBF) as a medium during 14 and 28 days of mineralization. Both chemical surface nature (bearing carboxylate or amine reactive groups) and contact time with SBF influenced the nucleation and growth of HAp crystals over CNWs surface. Nanocomposites immersed for 28 days showed a higher amount of HAp crystals compared to bare CNWs or the ones immersed for 14 days. Biocompatibility of the nanomaterials immersed for 14 days in SBF was evaluated through cell viability test using pre-osteoblasts (MC3T3-E1). In general, functionalized-CNWs containing HAp crystals deposited through biomimetic method showed promising results, with CNWs bearing amine groups showing a slightly larger biocompatibility compared to the ones bearing carboxylate groups during an incubation period of 24 h.

Antibacterial Performance of a PCL-PDMAEMA Blend Nanofiber-Based Scaffold Enhanced with Immobilized Silver Nanoparticles.

In the present study, nanofiber meshes (NFs), composed of polycaprolactone and poly[(2-dimethylamino)ethyl methacrylate] at 80/20 and 50/50 PCL/PDMAEMA blend ratios, were obtained through electrospinning. Silver nanoparticles (AgNPs) formed in situ were then immobilized on NF surfaces through adsorption processes at different pHs. It was possible to observe that the amount of NF-AgNPs can be tuned by changing the pH of AgNPs immobilization and the PCL/PDMAEMA ratio in the blend. The neat NF and NF-AgNPs were characterized with respect to their morphology and mechanical properties. The effects of AgNPs on the antibacterial activities and cytotoxicity of meshes were also evaluated. The antibacterial performance of such NF was improved by the presence of AgNPs. The NF-AgNPs presented good antibacterial effect against S. aureus and partial toxicity against E. coli and P. aeruginosa. Also, compared with neat PCL/PDMAEMA the NF-AgNPs presented lower cytotoxicity against VERO cells, showing their potential for applications in tissue engineering for different types of cell growth.

Hybrid materials for bone tissue engineering from biomimetic growth of hydroxiapatite on cellulose nanowhiskers.

Cellulose nanowhiskers (CNWs) with different surface composition were used to generate the biomimetic growth hydroxyapatite (HAp). Hybrids materials primarily consist of CNWs with HAp content below 24%. CNWs were produced by different inorganic acid hydrolyses to generate cellulose particles with surface groups to induce HAp mineralization. In the present study, we evaluate the use of CNWs prepared from hydrochloric acid, sulfuric acid and phosphoric acid. HAp growth was obtained from the biomimetic method using a simulated body fluid concentration of 1.5M (SBF). The sulfonate and phosphonate groups on the CNW surface have a direct impact on the nucleation and growth of HAp. HAp/CNW were also compared with the physical mixture method using HAp nanoparticles prepared by chemical precipitation. The bioactivity and biocompatibility of the hybrid materials were assessed by cell viability studies using fibroblast cells (L929). The materials obtained from the biomimetic method have superior biocompatibility/bioactivity compared to the material synthesized by the wet chemical precipitation method with an incubation period of 24h.

Covalently-layers of PVA and PAA and in situ formed Ag nanoparticles as versatile antimicrobial surfaces.

The in situ synthesis of silver nanoparticles (AgNPs) within covalently-modified poly(ethylene terephthalate) (PET) films possessing ultra-thin layer of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) is successfully demonstrated. The resulting polymeric films are shown to exhibit antimicrobial activities toward Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and fungus (Candida albicans). To make the films, first PET surfaces were subject to photo-oxidation and subsequent solid-state grafting to attach a PVA layer, followed by a PAA layer. To synthesize the AgNPs inside the films, the PVA and PAA-modified PET was soaked in AgNO3 solution and the polymeric film was modified with the Ag(+) ions via Ag(+)-carboxylate interaction, and then the Ag(+) ions-containing polymer film was subject to either photo-reduction or thermal reduction processes. The PVA and PAA thin layers attached by covalent bonds to the PET surface uniquely promoted not only the in situ synthesis but also the stabilization of AgNPs. The formation of the AgNPs was confirmed by UV-vis spectroscopy or by monitoring the surface plasmon resonance (SPR) peak associated with AgNPs. The resulting PVA and PAA ultrathin layers modified and AgNPs containing PET served as bactericide and fungicide, inhibiting the growth of bacteria and fungi on the surfaces. Given PET's versatility and common use in many commercial processes, the method can be used for producing plastic surfaces with versatile antimicrobial and antibacterial properties.

Extent of shielding by counterions determines the bactericidal activity of N,N,N-trimethyl chitosan salts.

In this study, we show that the bactericidal activity of quaternized chitosans (TMCs) with sulfate, acetate, and halide counterions against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) correlates with the "availability" of N-quaternized groups [-(+)N(CH3)3] in the TMCs backbones. N,N,N-trimethyl chitosan sulfate (TMCS) and N,N,N-trimethyl chitosan acetate (TMCAc) displayed the highest activities, probably due to their delocalized π system. Among TMCs with halide counterions, activity was higher for N,N,N-trimethyl chitosan chloride (TMCCl), whereas N,N,N-trimethyl chitosan iodide (TMCI) and N,N,N-trimethyl chitosan bromide (TMCBr) exhibited lower, similar values to each other. This is consistent with the shielding of -(+)N(CH3)3 groups inferred from chemical shifts for halide counterions in (1)HNMR spectra. We also demonstrate that TMCs with distinct bactericidal activities can be classified according to their vibrational spectra using principal component analysis. Taken together, these physicochemical characterization approaches represent a predictive tool for the bactericidal activity of chitosan derivatives.

Covalent TiO(2)/pectin microspheres with Fe(3)O(4) nanoparticles for magnetic field-modulated drug delivery.

Covalent TiO(2)-co-pectin microspheres containing Fe(3)O(4) nanoparticles were developed through an ultrasound-induced crosslinking/polymerization reaction between the glycidyl methacrylate from vinyl groups in TiO(2) and in pectin. ζ-potentials became less negative in the nanostructured microspheres, caused by the presence of both inorganic particles in the negatively charged pectin. The nanostructured pectin microspheres showed an amoxicillin release rate slower than that of pure pectin microspheres. The proposed microspheres were found to be a sustained release system of amoxicillin in the acid medium. Furthermore, the antibiotic release may be modulated by exposition of the microspheres to a remote magnetic field. In practical terms, the nanostructured microspheres could deliver a larger proportion of their initial load to specific site of action. The cytotoxic concentrations for 50% of VERO cells (CC(50)), calculated as the concentration required to reduce cell viability by 50% after 72h of incubation, for pectin-only microspheres and nanostructured pectin microspheres were 217.7±6.5 and 121.5±4.9µgmL(-1), respectively. The obtained CC(50) values indicated acceptable cytotoxic levels for an incubation period of 72h, showing that the pectin microspheres have a great pharmacological potential for uses in biological environments, even after the introduction of both Fe(3)O(4) and TiO(2).

Covalent albumin microparticles as an adjuvant for production of mucosal vaccines against hepatitis B.

Covalently modified albumin (BSA) microparticles were developed for potential use as an adjuvant in mucosal vaccines against hepatitis B. To synthesize consistent protein particles, a covalent approach was proposed to modify BSA. Our strategy was to bond maleic anhydride (MA) molecules to BSA structure by nucleophilic reaction for further radical cross-linking/polymerization reaction with N',N'-dimethylacrylamide (DMAAm). The presence of poly(N',N'-dimethylacrylamide) in the protein network enables the microparticles to show well-defined, homogeneous forms. Cytotoxicity tests showed that the cytotoxic concentration for 50% of VERO cells (CC50) was 216.25 ± 5.30 µg mL(-1) in 72 h of incubation. The obtained CC50 value is relatively low for an incubation time of 72 h, suggesting an acceptable biocompatibility. Assay of total protein showed that the encapsulation efficiency of the microparticles with hepatitis B surface antigen (HBsAg) was 77.7 ± 0.2%. For the reference sample, which was incubated without HBsAg, the quantity of protein was below the limit of detection.

Synthesis of a thermosensitive surface by construction of a thin layer of poly (N-isopropylacrylamide) on maleimide-immobilized polypropylene.

Thermosensitive surfaces were developed by the grafting of a thin layer of PNIPAAm through an UV-induced photopolymerization reaction of vinyl monomers with a free radical-activated polypropylene (PP) surface. PNIPAAm layer covering the PP surface corrected, to some extension, both depressions and fissures of the previously modified PP surfaces. The layered surfaces have morphological characteristic different from those of the non-layered surfaces, and their thickness was dependent on irradiation time. Water contact angles of the layered surfaces revealed a transition at approximately 33.5-36.5 °C as a result of a response to the variation of temperature. There was an increase in the values of the contact angles with an increase in temperature from 26 °C to 44 °C, revealing the nature both hydrophilic and hydrophobic of the surfaces due to a conformational rearrangement of PNIPAAm exposing its isopropyl groups to the liquid drop. This work offers a chemically stable thermosensitive surface (because it is covalently structured) with great potential for use as sensors and actuators.