Accelerated Sonochemical Extraction of Cellulose Nanowhiskers.

Studies on sonochemical hydrolysis of cellulose have been suggested as an alternative route to obtaining cellulose nanoparticles. In this work, the potential use of acid hydrolysis assisted by sonication to obtain cellulose whiskers was studied. Parameters such as acid concentration, hydrolysis time and temperature were investigated to evaluate their effect on the morphological properties of the nanowhiskers, as compared to the conventional extraction process by acid hydrolysis with mechanical stirring. Morphology and degree of crystallinity of the nanowhiskers were studied by atomic force microscopy (AFM) and X-ray diffraction (XRD). Results indicated that the extraction time was reduced from about 45 min to less than 3 min using the same acid concentration and temperature used in conventional acid hydrolysis treatment. Likewise, it was possible, within the range of 30 min, to extract whiskers at room temperature or using half the concentration of acid by raising the temperature to about 80 degrees C. These are promising results towards a more economically viable and ecologically friendly extraction procedure used to obtain cellulose nanowhiskers, since both extraction time and acid concentration, used in nanowhisker extraction, were significantly reduced by replacing mechanical with sonochemical stirring.

Controlled Release of Linalool Using Nanofibrous Membranes of Poly(lactic acid) Obtained by Electrospinning and Solution Blow Spinning: A Comparative Study.

The controlled-release of natural plant oils such as linalool is of interest in therapeutics, cosmetics, and antimicrobial and larvicidal products. The present study reports the release characteristics of linalool encapsulated at three concentrations (10, 15 and 20 wt.%) in poly(lactic acid) nanofibrous membranes produced by electrospinning and solution blow spinning (SBS) as well as the effect of linalool on fiber morphology and structural properties. PLA nanofibrous membranes were characterized by Scanning Electron Microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and contact angle measurements. The average diameters of the electrospun and solution blow spun nanofibers were similar, ranging from 176 to 240 nm. Linalool behaved as a plasticizer to PLA decreasing the glass transition temperature (Tg), melting point (Tm) and crystallization temperature (TC) of PLA. Curves of the release of linalool at 35 °C were non-linear, showing a clear biphasic pattern consistent with one or more Fickian release components. The time required to release 50% of linalool (t1/2) decreased with increasing linalool concentration. The range in t1/2 values for SBS nanofibers was higher (291-1645s) than the t1/2 values for electrospun fibers (76-575s).

Controlled release and antiviral activity of acyclovir-loaded PLA/PEG nanofibers produced by solution blow spinning.

Herpetic dermatitis and oral recurrent herpes (ORH) are among the most common human infections. Antiviral drugs such as acyclovir (ACV) are used in the standard treatment for ORH. Despite its therapeutic efficacy, ACV is continuously and repetitively administered in high doses. In this sense, the development of controlled release drug delivery systems such as core-shell fibers have a great potential in the treatment of ORH. In this work, poly(lactic acid)/poly(ethylene glycol) (PLA/PEG) fibers were produced by solution blow spinning (SBS) for the controlled release of ACV encapsulated in the core. PLA/PEG nanofibers containing four different blend ratios (100:0, 90:10, 80:20 and 70:30 wt%) without or with 10 wt% ACV were characterized by scanning electron microscopy (SEM), thermogravimetry (TG) and differential scanning calorimetry (DSC). The ACV release profile for 21 days was accessed by UV-Vis spectroscopy. Static water contact angles of the spun fiber mats were measured by the sessile drop method to evaluate fiber wettability upon contact with skin for transdermal release. Cytotoxicity and antiviral efficacy against Herpes simplex viruses (HSV-1) were evaluated using Vero cells. ACV addition did not impact on morphology, but slightly improved thermal stability of the fibers. Addition of hydrophilic PEG in PLA/PEG blends, however, increased drug release as confirmed by contact angle measurements and release profile. The in vitro tests showed the effectiveness of the drug delivery systems developed in reducing HSV-1 viral titer, which is related to the judicious combination of polymers used in the fibrous mats, in addition to not being cytotoxic to Vero cells. These results show the great potential of PLA/PEG solution blow-spun fibers in the controlled release of ACV to develop practical devices for the treatment of cold sores, while favoring the aesthetic appearance by covering them with a soft tissue patch (fibrous mats).

Advances in Functional Polymer Nanofibers: From Spinning Fabrication Techniques to Recent Biomedical Applications.

Functional polymeric micro-/nanofibers have emerged as promising materials for the construction of structures potentially useful in biomedical fields. Among all kinds of technologies to produce polymer fibers, spinning methods have gained considerable attention. Herein, we provide a recent review on advances in the design of micro- and nanofibrous platforms via spinning techniques for biomedical applications. Specifically, we emphasize electrospinning, solution blow spinning, centrifugal spinning, and microfluidic spinning approaches. We first introduce the fundamentals of these spinning methods and then highlight the potential biomedical applications of such micro- and nanostructured fibers for drug delivery, tissue engineering, regenerative medicine, disease modeling, and sensing/biosensing. Finally, we outline the current challenges and future perspectives of spinning techniques for the practical applications of polymer fibers in the biomedical field.

Improved mechanical performance of self-adhesive resin cement filled with hybrid nanofibers-embedded with niobium pentoxide.

OBJECTIVES: In this study hybrid nanofibers embedded with niobium pentoxide (Nb2O5) were synthesized, incorporated in self-adhesive resin cement, and their influence on physical-properties was evaluated. METHODS: Poly(D,L-lactide), PDLLA cotton-wool-like nanofibers with and without silica-based sol-gel precursors were formulated and spun into submicron fibers via solution blow spinning, a rapid fiber forming technology. The morphology, chemical composition and thermal properties of the spun fibers were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC), respectively. Produced fibers were combined with a self-adhesive resin cement (RelyX U200, 3M ESPE) in four formulations: (1) U200 resin cement (control); (2) U200+1wt.% PDLLA fibers; (3) U200+1wt.% Nb2O5-filled PDLLA composite fibers and (4) U200+1wt.% Nb2O5/SiO2-filled PDLLA inorganic-organic hybrid fibers. Physical properties were assessed in flexure by 3-point bending (n=10), Knoop microhardness (n=5) and degree of conversion (n=3). Data were analyzed with One-way ANOVA and Tukey's HSD (α=5%). RESULTS: Composite fibers formed of PDLLA-Nb2O5 exhibited an average diameter of ∼250nm, and hybrid PDLLA+Nb2O5/SiO2 fibers were slightly larger, ∼300nm in diameter. There were significant differences among formulations for hardness and flexural strength (p<0.05). Degree of conversion of resin cement was not affected for all groups, except for Group 4 (p<0.05). SIGNIFICANCE: Hybrid reinforcement nanofibers are promising as fillers for dental materials. The self-adhesive resin cement with PDLLA+Nb2O5 and PDLLA+Nb2O5/SiO2 presented superior mechanical performance than the control group.

In vitro antimicrobial activity of solution blow spun poly(lactic acid)/polyvinylpyrrolidone nanofibers loaded with Copaiba (Copaifera sp.) oil.

In this study poly(lactic acid) (PLA) and polyvinylpyrrolidone (PVP) micro- and nanofiber mats loaded with Copaiba (Copaifera sp.) oil were produced by solution blow spinning (SBS). The Copaiba (Copaifera sp.) oil was characterized by gas chromatography (GC). Neat PLA and four PLA/PVP blends containing 20% (wt.%) oil were spun and characterized by scanning electron microscopy (SEM) and by studying the surface contact angle, in vitro release rate, and antimicrobial activity. All compositions evaluated were able to produce continuous and smooth fibers by SBS. The addition of PVP increased fiber diameter, and decreased the surface contact angle. GC analysis demonstrated that the main component of the Copaiba oil was ß-caryophyllene, a known antimicrobial agent. In vitro release tests of Copaiba oil volatiles demonstrated a higher release rate in fibers containing PVP. Fiber mats made from blends containing higher amounts of PVP had greater antimicrobial action against Staphylococcus aureus. The results confirm the potential of the fiber mats for use in controlled drug release and could lead to promising applications in the biomedical field.

Effect of fiber treatments on tensile and thermal properties of starch/ethylene vinyl alcohol copolymers/coir biocomposites.

Coir fibers received three treatments, namely washing with water, alkali treatment (mercerization) and bleaching. Treated fibers were incorporated in starch/ethylene vinyl alcohol copolymers (EVOH) blends. Mechanical and thermal properties of starch/EVOH/coir biocomposites were evaluated. Fiber morphology and the fiber/matrix interface were further characterized by scanning electron microscopy (SEM). All treatments produced surface modifications and improved the thermal stability of the fibers and consequently of the composites. The best results were obtained for mercerized fibers where the tensile strength was increased by about 53% as compared to the composites with untreated fibers, and about 33.3% as compared to the composites without fibers. The mercerization improved fiber-matrix adhesion, allowing an efficient stress transfer from the matrix to the fibers. The increased adhesion between fiber and matrix was also observed by SEM. Treatment with water also improved values of Young's modulus which were increased by about 75% as compared to the blends without the fibers. Thus, starch/EVOH blends reinforced with the treated fibers exhibited superior properties than neat starch/EVOH.