Rossana M. S. M. Thiré

High resolution imaging of the microstructure of maize starch films

Glycerol-plasticised and non-plasticised cast films were prepared from maize starch suspensions that had been heated under reflux for different periods of time. Light microscopy (LM) and atomic force microscopy (AFM) have been used to observe the morphology of the starch films. In general, LM and AFM topographic images of corresponding non-plasticised films were similar. AFM topographic images of plasticised films revealed differences associated with the retarding effect of glycerol on the gelatinisation process. Relatively high B-type crystallinity indices were determined for plasticised films, independently of the heating conditions to which the suspensions had been submitted. AFM topographic images of plasticised films at higher magnifications revealed smooth and rough domains, that were detailed by phase contrast imaging.

Morphology and thermal properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/attapulgite nanocomposites

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) - PHBV is a biodegradable polyester which has been studied as an option for the production of disposable goods. Attapulgite is a fibrous clay mineral. The aim of this work was to produce and characterize renewable resource derived-nanocomposites based on PHBV and organophilic attapulgite (MAT). The nanocomposites were characterized by XRD, SEM and thermal analysis. It was observed reduction in degree of crystallinity, in melting and glass transition temperatures and in thermal stability of polymer due to the addition of clay to PHBV matrix. The best results were obtained for PHBV films containing 3 and 5% MAT. These films presented a slight increase in processing window and decrease in crystalline temperature and in degree of crystallinity as compared to pure PHBV.

Effect of process parameters on the properties of selective laser sintered Poly(3-hydroxybutyrate) scaffolds for bone tissue engineering

Porous scaffolds are biocompatible and bioactive temporary substrates. They should present appropriated microstructure, mechanical properties and surface properties for guiding bone tissue regeneration. In this work, scaffolds of Poly(3-hydroxybutyrate) (PHB) were printed by Selective Laser Sintering (SLS). The effect of scan spacing (SS) and powder layer thickness (PLT) on the morphology, mechanical properties and dimensional deviations related to the digital model of sintered scaffolds was evaluated. Curling was observed in the first built layers of scaffolds, mainly for scaffolds printed with the lowest PLT. Besides designed pores, the scaffolds also presented micropores derived from the incomplete sinterisation of PHB particles. This morphology can be advantageous for bone regeneration. The variation of PLT caused a higher difference between the values of scaffold mechanical properties than the variation of SS. The scaffolds, except the one printed with the highest PLT or SS, showed mechanical properties within the lower range of human trabecular bone.

Mechanical properties and in vitro characterization of polyvinyl alcohol- nano-silver hydrogel wound dressings

Polyvinyl alcohol (PVA) hydrogels are materials for potential use in burn healing. Silver nanoparticles can be synthesized within PVA hydrogels giving antimicrobial hydrogels. Hydrogels have to be swollen prior to their application, and the common medium available for that in hospitals is saline solution, but the hydrogel could also take up some of the wounds fluid. This work developed gamma-irradiated PVA/nano-Ag hydrogels for potential use in burn dressing applications. Silver nitrate (AgNO3) was used as nano-Ag precursor agent. Saline solution, phosphate-buffered solution (PBS) pH 7.4 and solution pH 4.0 were used as swelling media. Microstructural evaluation revealed an effect of the nanoparticles on PVA crystallization. The swelling of the PVA-Ag samples in solution pH 4.0 was low, as was their silver delivery, compared with the equivalent samples swollen in the other media. The highest swelling and silver delivery were related to samples prepared with 0.50% AgNO3, and they also presented lower strength in PBS pH 7.4 and solution pH 4.0. Both PVA-Ag samples were also non-toxic and presented antimicrobial activity, confirming that 0.25% AgNO3 concentration is sufficient to establish an antimicrobial effect. Both PVA-Ag samples presented suitable mechanical and swelling properties in all media, representative of potential burn site conditions.

Redução da hidrofilicidade de filmes biodegradáveis à base de amido por meio de polimerização por plasma

Due to low cost and excellent biodegradability, the use of starch as a raw material for bioplastic production is growing in interest. However, the properties of starch-based materials are affected by relative humidity during their use and storage due to their hydrophilic character. In this work, thermoplastic cornstarch films were coated by cold plasma technology with a protective thin layer in order to reduce water sensitivity. 1-Butene and 1,3-butadiene were used as monomers for plasma polymerization. Coated films presented a reduction of water absorption up to 80% an increase in contact angle related to water. These results indicated that the coating process reduced significantly the hydrophilic nature of the starch-based materials.

FTIR analysis and quantification of phenols and flavonoids of five commercially available plants extracts used in wound healing

Natural products are used in wound healing in order to prevent infection. Propolis is a well known antimicrobial with phenolic compounds and flavonoid content which vary according to the propolis origin. Besides propolis (from both Brazilian and UK sources), pomegranate, dragons blood and sage are possible antimicrobials to be used in biomaterials. The goal of this work was to analyze the amount of phenols and flavonoid compounds in these natural products, their antioxidant activities and the bonds present by FTIR. The FTIR analysis revealed the presence of active compounds in all drug samples. The phenols quantification showed that Brazilian propolis was rich in phenols compared to the other drugs, followed by pomegranate and UK propolis. UK propolis was the most rich in flavonoids, which is expected on account of its origin. Pomegranate, UK propolis and Dragons blood presented the highest antioxidant activity. All samples presented antioxidant activity > 82%.

Adsorção de fibronectina a arcabouços de polihidroxibutirato aplicáveis à engenharia óssea

Human plasma fibronectin (FN) was adsorbed onto the surface of polyhydroxybutyrate (PHB) scaffolds with aim of improving adhesion of human osteoblasts (HOB). PHB scaffolds were modified via reaction with ethylenediamine in order to create sites for FN immobilization. Morphological and chemical composition changes were observed for treated scaffolds which led to an increase in the concentration of FN adsorbed onto scaffold surfaces. AFM images showed that FN molecules assumed distinct conformation according to the surface to which they were adsorbed. It is believed that the FN molecules added to non-treated scaffolds assumed an unfolded conformational owing to the exposure of their RGD domains, thus promoting an increased HOB adhesion. On the other hand, FN molecules which were added to the surface of previously treated scaffolds are believed to have assumed a folded conformation, hiding some RGD domains and inhibiting HOB adhesion.

Evaluation of metronidazole-loaded poly(3-hydroxybutyrate) membranes to potential application in periodontitis treatment

Guided tissue regeneration is a technique used for periodontium reconstruction. This technique uses barrier membranes, which prevent epithelial growth in the wound site and may also be used to release antibiotics, to protect the wound against opportunistic infections. Periodontal poly(3-hydroxybutyrate) membranes containing metronidazole (a drug used to help in infection control) were produced and characterized. The kinetic mechanism of the metronidazole delivery of leached and nonleached membrane as well as its cytotoxicity and structural integrity were evaluated. Poly(3-hydroxybutyrate) membranes containing 0.5-2 wt % of the drug and 20 wt % of the plasticizer were manufactured via compression molding. Based on morphological analysis, membranes loaded with 2% metronidazole were considered for detailed studies. The results revealed that metronidazole delivery by the leached membranes seemed to follow the Ficks law. Membranes were noncytotoxic. The amount of metronidazole delivered was in the range of the minimal inhibitory concentration for Porphyromonas gingivalis, and the membranes inhibited the proliferation of these bacteria. Besides, they maintained their mechanical resistance after 30 days of immersion in phosphate buffer at pH 7.4.

Effect of aging on the microstructure of plasticized cornstarch films

Aging of cornstarch films prepared by casting was investigated. Water and glycerol-plasticized cornstarch films were stored at 50% relative humidity over a period of 330 days. Aging was followed by X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD spectra indicated development of B-type crystallinity even for fresh films and that the crystallinity index increased from 0.06 to 0.28 as a function of storage time. AFM images of 270-day-old films revealed that the general morphology and the overall roughness have not changed due to aging. AFM phase contrast images at higher magnification showed an increasing number of ordered domains at the surface of these films, which may be attributed to recrystallization of amylose. No morphological change was observed at least at the surface of the granular region, which is enriched in amylopectin.

Processamento de amido de milho em câmara de mistura

Corn starch/water mixtures at compositions of 70:30, 80:20 and 90:10 (w/w %) were submitted to processing at 90oC and different rates (20, 40, 80 and 100rpm) in an internal mixer (Rheomix 600), equipped with counter-rotating roller type rotors. The effect of the water content and of the rotation rate on the starch processing was investigated by torque and temperature curves given by the in-line Rheocord 9000 torque rheometer. Viscosity measurements, carried out in a Rapid Visco Analyser (RVA), and optical microscopy analysis were performed on the processed samples to complement the rheometry data. The results indicated that the water content and the rotation rate had a significant effect on the characteristics of the processed starch samples. For compositions with 10 and 20% (w/w) water contents and processed at 80 and 100rpm, degradation was observed at a larger extent. For compositions in which water had been added at a 30% (w/w) content, its plastifying property contributed to minimize degradation caused by mechanical and thermal inputs. In these cases, the granular structure of starch was largely preserved.